Search Article Keyword:  

PubMed Submission Abstract PDF Feed Back Count: 5655 Download Count: 1275 

ISSN 1007-9327 CN 14-1219/R  World J Gastroenterol  2008 March 21;14(11): 1699-1709
               TOPIC HIGHLIGHT
Activins and activin antagonists in hepatocellular carcinoma

Alev Deli, Emanuel Kreidl, Stefan Santifaller, Barbara Trotter, Katja Seir, Walter Berger, Rolf Schulte-Hermann,
Chantal Rodgarkia-Dara, Michael Grusch

Alev Deli, Emanuel Kreidl, Stefan Santifaller, Barbara Trotter, Katja Seir, Walter Berger, Rolf Schulte-Hermann, Chantal Rodgarkia-Dara, Michael Grusch, Institute of Cancer Research, Department of Medicine I, Medical University of Vienna, Borschkegasse 8a, Vienna A-1090, Austria

Author contributions: Deli A, Kreidl E, Santifaller S, Trotter B, Seir K, and Grusch M reviewed the literature, wrote the paper, and designed the figure. Berger W, Schulte-Hermann R, and Rodgarkia-Dara C critically revised and improved the manuscript.

Supported by Herzfelder Foundation

Correspondence to: Michael Grusch, Department of Medicine I, Division: Institute of Cancer Research, Medical University of Vienna, Borschkegasse 8a, Vienna A-1090, Austria.

Telephone: +43-1-427765144  Fax: +43-1-42779651

Received: December 4, 2007   Revised: January 1, 2008



In many parts of the world hepatocellular carcinoma (HCC) is among the leading causes of cancer-related mortality but the underlying molecular pathology is still insufficiently understood. There is increasing evidence that activins, which are members of the transforming growth factor b (TGFb) superfamily of growth and differentiation factors, could play important roles in liver carcinogenesis. Activins are disulphide-linked homo- or heterodimers formed from four different b subunits termed bA, bB, bC, and bE, respectively. Activin A, the dimer of two bA subunits, is critically involved in the regulation of cell growth, apoptosis, and tissue architecture in the liver, while the hepatic function of other activins is largely unexplored so far. Negative regulators of activin signals include antagonists in the extracellular space like the binding proteins follistatin and FLRG, and at the cell membrane antagonistic co-receptors like Cripto or BAMBI. Additionally, in the intracellular space inhibitory Smads can modulate and control activin activity. Accumulating data suggest that deregulation of activin signals contributes to pathologic conditions such as chronic inflammation, fibrosis and development of cancer. The current article reviews the alterations in components of the activin signaling pathway that have been observed in HCC and discusses their potential significance for liver tumorigenesis.


© 2008 WJG. All rights reserved.


Key words: Hepatocellular carcinoma; Activin; Follistatin; Transforming growth factor b

Peer reviewer: Hiroshi Yoshida, MD, First Department of Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan


Deli A, Kreidl E, Santifaller S, Trotter B, Seir K, Berger W, Schulte-Hermann R, Rodgarkia-Dara C, Grusch M. Activins and activin antagonists in hepatocellular carcinoma. World J Gastroenterol 2008; 14(11): 1699-1709  Available from: URL:  DOI:



Hepatocellular carcinoma (HCC) is the predominant form of primary malignancy of the liver and accounts for more than half a million deaths per year[1]. In some geographical regions it is the most prevalent form of malignancy and the most common cause of death from cancer[2] making its containment a top priority. Chronic infection with the hepatitis B or C virus (HBV, HCV), dietary exposure to the hepatocarcinogen aflatoxin B1 (AFB1), ethanol abuse, and obesity are among the main risk factors for liver cancer[3]. Despite recent advances, the molecular pathology of the disease is not well understood and the therapeutic possibilities are largely limited to surgical procedures including resection, liver transplantation, or local tumor ablation[4]. A consistent pattern of changes comparable to the sequential mutations in tumor suppressor genes and oncogenes, like the one identified in colon carcinogenesis during adenoma to carcinoma progression[5,6], has not been defined for HCC. Nevertheless, multiple genetic alterations including mutations of p53, inactivation of the Rb pathway, and activation of the Wnt/b-catenin pathway have been linked to HCC development and progression[3,7]. In addition deregulated expression of growth factors and their cognate receptors has been described in HCC for both, positive regulators of hepatocyte growth, such as insulin-like growth factor 2 (IGF-2), hepatocyte growth factor (HGF), and transforming growth factor a (TGFa), as well as for negative regulators like TGFb[8].

In recent years activins, a subgroup of the TGFb family of growth, differentiation, and death factors which share part of their signaling mechanisms with TGFb, have gained attention with respect to their role in tumor development in several organs[9]. Activin subunits, their receptors and several antagonistic proteins are expressed in the normal liver. Deregulation of this balanced expression appears to contribute to hepatic dysfunctions like impaired regeneration, fibrogenesis and tumorigenesis[10]. The current knowledge about the role of activins and activin antagonists in HCC is discussed in this review.



Activins are secreted polypeptides and represent a subgroup of the TGFb superfamily of growth and differentiation factors. Additional members of this superfamily include TGFb1-3, bone morphogenetic proteins (BMPs), growth and differentiation factors (GDFs), myostatin, Muellerian inhibiting substance (MIS), nodal and several others[10,11]. Activins are homo- or heterodimers composed of four different b subunits (bA, bB, bC, bE), each encoded by a single gene. The b subunits can either form activins by dimerization with a second b subunit, or alternatively can form inhibins by dimerizing with a single a subunit encoded in mammalian genomes[12]. Activin terminology is dependent on the dimer configuration with a single letter designating homodimers (activins A, B, C, and E) and two letters designating heterodimers according to their subunit composition (activins AB, AC, AE, BC etc.). With respect to tissue expression, transcripts of the bA and bB subunits were found to be detectable in almost all tissues analyzed with especially high expression in reproductive organs[13,14]. The bC and bE subunits, in contrast, are predominantly expressed in the liver and at lower levels in a limited number of additional organs[14-18].

Activin b subunits are synthesized as precursor molecules with 350-426 amino acids and molecular weights between 38 kDa and 50 kDa[19]. The prodomains are removed in the ER and in the early Golgi by members of the protease family of subtilase-like pro-protein convertases (SPC)[20] to release mature peptides with either 115 (bB, bE) or 116 (bA, bC) amino acids. The amino acid sequences of the mature peptides are approximately 50% conserved among the four human b subunits, whereas the sequence homology in the prodomain is only about 20%. Analysis of the phylogenetic relationship of the mature human peptides groups together bA and bB on the one and bC and bE on the other hand[21].

Like other members of the TGFb family, the activin b subunits contain nine conserved cysteines in the mature peptides. The sixth is used for dimerization, whereas the other eight form intramolecular disulfide bonds which determine the three-dimensional structure of the peptides[22]. While all cysteines in the mature chain of activin bA are necessary for biosynthesis of activin A dimers or for their full biological activity, four additional cysteines in the prodomain are dispensable for dimerization and secretion. Protein folding and dimerization take place in the lumen of the ER and are catalyzed by members of the protein disulfide isomerase (PDI) family[23,24]. Unlike TGFb, which is secreted as a latent complex consisting of the TGFb homodimer, its prodomain (also termed latency-associated propeptide, LAP), and the latent TGFb binding protein (LTBP)[25], activins are secreted as dimers of the mature peptides and need no further processing in the extracellular space to gain bioactivity. Activin A signals are transduced via two types of single-pass transmembrane serine threonine kinase receptors, termed activin receptors typeand type [26]. Activin A first binds to the type receptors which in turn recruit and phosphorylate the typereceptors[27]. Two type receptors for activin A (ActR- (A) or ACVR2 (A) and ActR-B or ACVR2B) have been identified. The main typereceptor for activin A is ALK (Activin Receptor-Like kinase) 4, also designated as ActR-IB or ACVR1B, whereas activins B and AB have a preference for ALK 7 (ACVR1C) as typereceptor[28]. Receptors for activins containing bC or bE subunits have not been identified so far. Activin C, however, did not compete with activin A for receptor binding[29] and a chimeric activin construct in which the receptor binding sequence (amino acids 46-78) of bA was replaced by the corresponding region of bC retained type receptor binding but was unable to recruit the typereceptor ALK 4[30].

Inhibins have been shown to form a complex with type receptors via their b subunits and with betaglycan also known as TGFb type receptor. The a subunit, however, is unable to bind typereceptors and consequently activin receptor signaling is inhibited[31,32]. There is in general a considerable degree of promiscuity in receptor usage by different TGFb superfamily members. In addition to activin A, for instance, myostatin, and several BMPs were shown to signal via ActR-B[33].

Phosphorylated TGFb family receptors recruit intracellular mediators called Smads, which transduce activin signals to the nucleus[26]. Smads can be divided into receptor Smads (Smads 1, 2, 3, 5 and 8), a common mediator Smad (Smad 4) and inhibitory Smads (Smads 6 and 7). Activin A receptors, as well as TGFb receptors, recruit and phosphorylate the receptor Smads 2 and 3, whereas receptor Smads 1, 5, and 8 are recruited by BMP receptors but not activin receptors[34]. Recent evidence suggests that-similar to TGFb-additional Smad-independent signaling pathways may contribute to activin A signaling, as for instance, RhoA, MEKK1, JNK, and p38 were found to be involved in activin-induced cytoskeleton reorganization and cell migration in keratinocytes and in promoter activation of the transcription factor Pit-1 in pituitary lactotrope cells[35,36].

Activin signals are tightly regulated on the one hand by a spatially and temporally restricted production of activin subunits and on the other hand by the expression of several extra- as well as intracellular antagonists of activin signaling. An overview of activin-mediated signaling events and the corresponding interaction points with endogenous activin antagonists is presented in Figure 1.



Activin bA

Activin A, the homodimer of two bA subunits, is by far the most extensively investigated activin. Multiple biological functions of activin A in a variety of cells and tissues have been described. Activin A has been implicated for instance in mesoderm induction[37], stem cell biology[38], reproductive biology[39], erythroid differentiation[40], systemic inflammation[41], cell death induction[42], wound healing[43], and fibrosis[44]. Knock-out mice for bA have severe defects in craniofacial development and die shortly after birth[45]. Concerning the liver, activin A potently inhibits mitogen-induced DNA synthesis and induces apoptosis in hepatocytes in vivo and in vitro[46-48]. Activin bA antisense oligonucleotides stimulated cell proliferation in the human hepatoma cell line HLF suggesting a growth inhibitory function of endogenous activin A[49]. In regenerating liver, activin bA gene expression was reduced at time points when hepatocyte replication took place and was increased at later periods when liver regeneration terminated[50]. Increased expression of bA at earlier time points after partial hepatectomy, however, has also been described[51,52]. Besides the effects on DNA synthesis and cell growth, activin A also regulates restoration of liver architecture after partial hepatectomy by stimulating collagen production in hepatic stellate cells (HSC) and tubulogenesis of sinusoidal endothelial cells[53,54]. Stimulation of HSC may also contribute to liver fibrosis and several investigations have found elevated levels of activin bA in fibrotic and cirrhotic rat livers[55-58]. Elevated levels of circulating activin A were found in patients suffering from chronic viral hepatitis or alcohol induced liver cirrhosis and in HCC patients[59-61]. Reduced expression of activin bA transcripts in contrast, was observed in tumor tissue from chemically-induced rat  liver tumors and in 5 of 11 HCC specimens[62]. In addition to a pro-apoptotic effect on the parenchymal cells and a pro-fibrotic effect on HSC, activin A has also been linked to neoangiogenesis via stimulation of VEGF expression in human hepatoma cells[63].


Activin bB

Like activin bA, the bB subunit is expressed in multiple tissues and organs[13,14]. Despite a considerable overlap in tissue expression and in some biological activities, important differences exist[64]. Knock-out mice for bB are viable but have defects in eyelid development and female reproduction[65]. When the coding region of the mature peptide of the bA subunit gene was replaced with the corresponding region of the bB subunit gene the developmental defects of the bA knock-out mice were only partially rescued[66]. Concerning the liver, the role of the bB subunit is not well characterized. In the normal rat liver the bB subunit was the only activin subunit undetectable by RNAse protection assay[14]. Weak positive immunoreactivity for bB was, however, detected in hepatocytes of normal rat livers and in connective tissue septa in fibrotic livers when analyzed by immunohistochemistry[55]. Activin bB mRNA was induced in stellate cells of CCl4 treated rat livers[55]. Exposure to the peroxisome proliferator di-n-butyl phthalate led to a transient surge of bB mRNA expression
6 h after treatment in rat livers[67]. With respect to biological activities, recombinant activins A and AB but not activin B inhibited EGF induced DNA synthesis in primary rat hepatocytes[68]. In normal human liver the bB transcript is readily detectable by RT-PCR (M.G. unpublished observation), but no data with regard to expression changes of the bB subunit in liver tumors compared to normal liver have been reported yet.


Activin bC

The activin bC subunit was cloned from liver cDNA and demonstrated to be predominantly expressed in hepatocytes by Northern blot analysis and RNAse protection assays[14,18,52,69]. By immunohistochemistry significant activin bC expression has been detected in cells from additional organs including the prostate, ovary, testes, and pituitary gland[15,70]. Formation of homodimeric activin C as well as heterodimeric activins AC, BC, CE, as well as inhibin C has been demonstrated by ectopic expression of the respective subunits in different cell models[14,70,71]. After partial hepatectomy a transient down-regulation of activin bC expression was observed by several studies[50,52,72,73]. A decrease of activin bC expression has also been observed in HepG2 and Hep3B hepatoma cells versus normal liver tissue[74] and in rat hepatocytes during primary culture with and without EGF treatment[52]. In contrast, increased activin bC expression was reported in the rat liver during the development of CCl4 induced cirrhosis[56,75] and in response to treatment with the peroxisome proliferator bi-n-butyl phthalate[67]. The functions of the activin bC subunit are controversial. Activin bC knock-out mice developed normally and liver regeneration after partial hepatectomy proceeded similar in knock-out animals and wild-type littermates[76]. Ectopic expression of activin bC induced apoptosis in human (HepG2, Hep3B) and rat (H4EC3) hepatoma cells and delayed liver regeneration in mice[74,77]. In AML12 cells, an immortalized mouse hepatocyte cell line in contrast, and in primary rat hepatocytes, activin bC increased DNA synthesis[29]. Adenovirus-mediated expression of activin bC accelerated liver regeneration after partial hepatectomy in rats[78]. A specific association of activin bC immunoreactivity with mitotic hepatocytes was observed in regenerating liver after partial hepatectomy[50]. It was shown that activin C does not activate activin A-responsive promoters, and it was suggested that the bC subunit regulates the levels of bioactive activin A via the formation of signaling-incompetent activin AC heterodimers in PC3 human prostate cancer cells[79,80]. Data regarding the expression of the bC subunit in human liver tumors are not available yet.


Activin bE

Similar to activin bC, the bE subunit is predominantly expressed in hepatocytes but has also been detected in human heart, testis, peripheral blood leucocytes, placenta, and skeletal muscle[14,16,21,81]. Formation of homodimeric activin E as well as heterodimeric activins AE and CE has been demonstrated after ectopic co-expression of the respective subunits[14,16]. Activin bE mRNA expression was transiently up-regulated after partial hepatectomy or portal vein branch ligation[73,76] and in response to lipopolysaccharide treatment[81]. Increased bE expression has also been observed in hepatic fibrosis induced by CCl4[75]. Recently, induction of bE expression has been described as a marker for phospholipidosis in HepG2 hepatoma cells[82]. Similar to bC, bE subunit knock-out mice and double knock-outs lacking both bC and bE expression developed normally and had no defects in liver function[76]. When ectopically expressed in HepG2 or Hep3B hepatoma cells or in the murine hepatocyte cell line AML12, activin bE reduced cell number and increased apoptosis rates[74,83]. Transient overexpression of bE by non-viral gene transfer in the mouse liver inhibited regenerative DNA synthesis[77]. These observations suggest that activin E may have a growth-limiting function similar to activin A, however, the two subunits show a reciprocal pattern with respect to diurnal variations of expression[10]. In line with a growth-limiting function of activin E, transgenic mice overexpressing bE in the pancreas showed reduced proliferation of pancreatic exocrine cells[84]. Regarding liver cancer, reduced expression of the bE subunit was found in human HCC specimens as well as in N-nitroso morpholine-induced rat liver tumors[62,85]. Interestingly, activin bE expression was found to be regulated by the tumor suppressor gene RASSF1A[86], a gene frequently inactivated by promoter hypermethylation in HCC[87,88].


Inhibin a

The inhibin a subunit is part of inhibins but not activins and in many biological systems activins and inhibins have antagonistic effects[89]. Historically activins received their name from the fact that they activated follicle stimulating hormone (FSH) secretion from the pituitary, whereas the previously described inhibins represented the long sought-after gonadal feed-back inhibitor of pituitary FSH secretion[12]. Knock-out mice for the inhibin a subunit developed gonadal sex-cord stromal tumors suggesting a tumor suppressive function of the inhibin a subunit[90]. In several human tumor types including some types of ovarian carcinoma and adrenal tumors, in contrast, overexpression of inhibin a has been demonstrated, and inhibins have been used as serum markers for early detection of ovarian germ cell tumors and monitoring of recurrence[9]. With regard to liver cell growth, treatment with inhibin A per se had no effect on DNA synthesis of HepG2 hepatoma cells but antagonized the inhibitory effect of activin A[91]. In normal and fibrotic rat liver absence of inhibin a subunit immunoreactivity has been reported[55]. Immunostaining for inhibin a has been used to distinguish adrenal cortical tumors, which are positive in about 70% of cases, from HCC and renal cell carcinoma, which are mostly negative[92,93].



Follistatin is a secreted, monomeric glycoprotein lacking homology to the TGFb superfamily. The biological activities described for follistatin, however, seem to depend entirely on its interaction with activins and other members of the TGFb family. Follistatin is expressed in most of the organs, that also express activin[13,94], and it binds mature secreted activin A with very high affinity (Kd 50-680 pmol/L)[95-97]. Complex formation with follistatin completely abolished receptor binding of activin A, thus blocking activin signaling[96,98]. Two follistatin molecules embrace one activin dimer and bury one-third of its residues and its receptor binding sites[99]. Three major forms of secreted follistatin exist, resulting from alternative splicing and protein processing of a single follistatin gene and containing 288, 303 and 315 amino acids, respectively[95]. All forms of follistatin contain three homologous follistatin domains[100] of which the first two, but not the third, are necessary for activin A binding[97,101]. Follistatin 288 binds to heparan sulfates, whereas this binding is blocked by an acidic tail in follistatin 315[95]. In addition to binding activins A, B, AB, and E, follistatin was also shown to bind and antagonize myostatin as well as BMPs 2, 4, 6 and 7[16,102-105]. Follistatin administration by intraportal infusion or adenovirus-mediated overexpression caused DNA synthesis and liver growth in normal rat livers presumably by antagonizing tonic inhibition of liver growth by activin A[106,107]. Following partial hepatectomy follistatin expression was up-regulated after 24-48 h, the time period in which hepatocyte replication was increased[50]. Under similar conditions administration of follistatin accelerated liver regeneration but led to impaired restoration of normal tissue architecture and compromised liver function[108-110]. Administration of exogenous follistatin in CCl4 treated rats attenuated the formation of liver fibrosis[111]. These results likely reflect the ability of follistatin to antagonize both growth-inhibitory and pro-fibrotic activities of activin A.

In human liver cancer and also in animal models follistatin expression was increased in about 60% of tumor tissues. Increased follistatin levels were also found in the blood of patients with liver cirrhosis and HCC[60,62,112]. Administration of follistatin stimulated DNA synthesis in preneoplastic rat hepatocytes in an ex vivo system, whereas hepatoma cell lines were unresponsive to exogenous follistatin possibly due to autocrine production of follistatin or other activin antagonists[62,112-114].



Follistatin-related protein, encoded by follistatin-related gene (FLRG), also designated as follistatin-like 3 (FSTL-3) has a high similarity to follistatin and shares its ability to bind TGFb family proteins, but contains only two instead of three follistatin domains[115]. Several other proteins, containing 1-10 follistatin domains, like the extracellular matrix-associated proteins SPARC and agrin, on the other hand were not able to bind TGFb family members[100,116]. The FLRG gene was originally identified as a target of chromosomal rearrangement in leukemia[117]. The highest tissue expression of FLRG was found in placenta, whereas highest follistatin expression was found in ovary, testis, and pituitary[115,118]. In HepG2 hepatoma cells, expression of both FLRG and follistatin was induced in response to activin A treatment suggesting that they participate in a feedback loop to restrict activin A signals[119]. FLRG mRNA is up-regulated in rat livers in response to a necrogenic dose of CCl4 (M.G. unpublished observation) but otherwise the role of FLRG in liver regeneration has not been characterized. Elevated expression of FLRG was found in chemically induced rat liver tumors and H4E rat hepatoma cells but not in human liver tumor specimens[62] indicating species-specific differences with respect to FLRG regulation or differences between liver tumors of different etiologies.


Activin receptors

The type activin receptors ActR- (A) and ActR-B and the typeactivin receptors ALK4 and ALK7 are expressed in multiple cell types and tissues including the liver. Adenovirus-mediated overexpression of a dominant-negative type activin receptor caused DNA synthesis and liver growth in normal rat livers[120]. During liver regeneration after partial hepatectomy, no change of ActR was observed while ActRB was transiently decreased[50]. During CCl4 induced rat liver cirrhosis, ActRA was reduced after 5 wk but returned to control levels after 10 wk[56]. Ectopic overexpression of ActR-IB (ALK4) and ActR-B or of ALK7 induced apoptosis in hepatoma cells[121,122]. In HCC tissue specimens, expression of activin receptors (ActR-I, ActR-IB, ActR-, and ActR-B) was demonstrated by immunohistochemistry[63]. Inactivating mutations of activin receptors have been found in microsatellite instable colon cancer, pancreatic cancer and prostate cancer, but have not been investigated in HCC so far[123-126].


Regulators of activin receptor activity

Several membrane-associated proteins exist which regulate activin-induced receptor activation. Cripto/TDGF1 is a member of the EGF-CFC (epidermal growth factor-Cripto/frl/cryptic) family of growth factor-like molecules. This secreted protein can attach to the outer cell membrane via a glycosylphosphatidylinositol anchor and functions as a co-receptor for nodal signaling during embryogenesis. Cripto has been found overexpressed in high percentages of several human malignancies including breast, pancreas, lung, colon and bladder cancer[127]. Cripto inhibits ligand receptor interactions of activins and TGFb[128-130] and this has been suggested to contribute to its pro-tumorigenic activity. However, an additional activin receptor-independent signaling pathway for Cripto involving Glypican-1 and c-Src has also been described[127]. Expression of a shorter Cripto variant was observed in colon cancer including liver metastases, as well as in colon cancer and hepatoma cell lines[131,132]. Expression of this short variant is driven by Wnt signaling which is frequently constitutively activated in colon cancer and HCC. Based on these findings, a more extensive investigation on the role of Cripto in HCC is certainly warranted.

BAMBI (bone morphogenetic protein and activin membrane-bound inhibitor) also known as nma (non metastatic gene A) is a pseudoreceptor related to the type
receptors of the TGFb family. It lacks an intracellular kinase domain and inhibits activin A, TGFb, and BMP signaling by stably associating with TGFb family receptors[133]. A recent study links LPS/Toll-like receptor 4-induced downregulation of BAMBI in hepatic stellate cells to hepatic fibrosis[134]. In contrast, elevated BAMBI expression driven by the Wnt/b-catenin pathway was found in HCC and CRC specimens[135].

ARIPS 1 and 2 (activin receptor-interacting proteins) are PDZ (PSD-95/Discs-large/ZO-1) protein-protein interaction domain-containing proteins that were described to interact with type activin receptors and inhibit or augment activin signaling, depending on the isoforms expressed[136-138]. ARIP 2 was recently shown to be induced by activin A in the mouse hepatoma cell line Hepa1-6 and to decrease activin-mediated collagen expression, suggesting that it participates in a negative feedback regulation of activin-induced liver fibrosis[139]. Data with regard to a role of ARIPS in HCC or other tumor types are missing so far.


Intracellular inhibitors of signal transduction

Downstream from activin receptors, signals are transduced by receptor Smad 2 and Smad 3 and the common mediator Smad 4, the same set of Smad proteins also used by TGFb receptors. Mutations of Smad proteins are frequent in pancreatic and colorectal cancer and have also been detected in HCC[140-142]. Smads 6 and 7 associate with TGFb family receptors but are not phosphorylated and thus inhibit signal transduction[143,144]. Smad7 has been demonstrated to inhibit activin signaling and to protect hepatocytes from activin A-induced growth inhibition[145]. Increased expression of Smad7 has been observed in HCC tissue compared to adjacent tissue[146] and in advanced HCC compared to early HCC or dysplastic nodules[147]. No mutations of either Smad 6 or Smad 7 were found in 52 HCC samples[148].

Smurf-type ubiquitin E3 ligases, Smad anchor for receptor activation (SARA), and transcriptional co-activators and co-repressors such as CBP, p300, c-Ski, and SnoN, control Smad activation by TGFb-family receptors or shuttling of activated Smads into the nucleus as well as transcriptional activity of Smad-containing complexes[42]. Their role in the link between activin signals and liver carcinogenesis has yet to be defined.

In summary, increasing evidence suggests that deregulation of activin signals frequently occurs in and contributes to HCC development and progression. An overview of alterations in activin subunits and activin antagonists described in liver tumors and hepatoma cells is presented in Table 1.



Activin signaling is complex. At least three features of the activin signaling cascade contribute to this complexity. First, four activin b and one inhibin a subunit can give rise to multiple homo and heterodimers with different receptor binding capabilities. Secondly, a number of different extracellular activin-binding and receptor-interacting proteins can modulate ligand receptor interactions not only of activins but also of TGFb, BMPs and GDFs. Thirdly, there is a considerable degree of promiscuity with respect to usage of receptors and intracellular signaling molecules between different members of the TGFb superfamily[149]. For instance, activins and TGFb use different typeand type receptors but rely on the same Smad proteins for intracellular propagation of their signals. This makes it a difficult task to dissect their specific contribution to biological activities, especially in tissues such as the liver, where both activins and TGFb are expressed. In addition, BAMBI, Cripto and Smad7 have all been shown to interfere with signal transduction of activins as well as of TGFb.

TGF-b1 has a well recognized dual role in carcino-genesis[150]. It acts as a tumor suppressor in early stages of hepatocarcinogenesis by inducing apoptosis and eliminating precursor lesions[151,152]. At a later stage, however, liver tumor cells often become resistant to its proapoptotic effect, and produce large amounts of TGFb themselves[153]. From the available data on both loss of expression in tumor cells and apoptosis induction[74,114,154], one would postulate that activin A, and possibly activin E, may have a similar tumor suppressive function in the liver as TGFb. Whether also activins may shift to a pro-tumorigenic function during tumor progression is little explored. For activin A, a contribution to liver fibrosis, enhanced expression of the angiogenic factor VEGF in hepatoma cells, and stimulation of growth and invasiveness of esophageal squamous cell carcinoma cells has been demonstrated[58,63,155].

Despite all the complexity, however, a general theme in HCC and in other tumor types seems to be the elevated expression of activin antagonistic proteins in the tumor cells, as observed for follistatin, BAMBI, Cripto, and Smad7[62,127,135,146,147]. These may serve to block the growth inhibitory and pro-apoptotic activity of activin A on hepatocytes. Similar observations have been made in additional tumor types, for instance for Cripto in multiple epithelial tumors, BAMBI in colon carcinoma, follistatin in melanoma and FLRG in breast cancer[127,135,156,157].

Consequently, a targeted inhibition of activin antagonists might restore sensitivity to activin-induced growth inhibition and apoptosis, and may thus represent a feasible strategy to inhibit tumor growth. In line with this hypothesis, it has recently been shown that siRNA-mediated silencing of FLRG inhibited breast tumor cell growth in vitro, and that monoclonal antibodies to Cripto inhibited growth of testicular and colon cancer cells in xenograft models[128,156]. Future studies will have to clarify whether such approaches may offer new therapeutic opportunities for combating liver cancer.



1      Parkin DM, Bray F, Ferlay J, Pisani P. Global cancer statistics, 2002. CA Cancer J Clin 2005; 55: 74-108  PubMed

2      Chen JG, Zhu J, Parkin DM, Zhang YH, Lu JH, Zhu YR, Chen TY. Trends in the incidence of cancer in Qidong, China,

        1978-2002. Int J Cancer 2006; 119: 1447-1454  PubMed

3      El-Serag HB, Rudolph KL. Hepatocellular carcinoma: epidemiology and molecular carcinogenesis. Gastroenterology

        2007; 132: 2557-2576  PubMed

4      Befeler AS, Di Bisceglie AM. Hepatocellular carcinoma: diagnosis and treatment. Gastroenterology 2002; 122: 1609-

        1619  PubMed

5      Chung DC. The genetic basis of colorectal cancer: insights into critical pathways of tumorigenesis. Gastroenterology

        2000; 119: 854-865  PubMed

6      Fearon ER, Vogelstein B. A genetic model for colorectal tumorigenesis. Cell 1990; 61: 759-767  PubMed

7      Teufel A, Staib F, Kanzler S, Weinmann A, Schulze-Bergkamen H, Galle PR. Genetics of hepatocellular carcinoma. World

        J Gastroenterol 2007; 13: 2271-2282  PubMed

8      Breuhahn K, Longerich T, Schirmacher P. Dysregulation of growth factor signaling in human hepatocellular carcinoma.

        Oncogene 2006; 25: 3787-3800  PubMed

9      Risbridger GP, Schmitt JF, Robertson DM. Activins and inhibins in endocrine and other tumors. Endocr Rev 2001; 22:

        836-858   PubMed

10    Rodgarkia-Dara C, Vejda S, Erlach N, Losert A, Bursch W, Berger W, Schulte-Hermann R, Grusch M. The activin axis in

        liver biology and disease. Mutat Res 2006; 613: 123-137  PubMed

11    Chang H, Brown CW, Matzuk MM. Genetic analysis of the mammalian transforming growth factor-beta superfamily.

        Endocr Rev 2002; 23: 787-823  PubMed

12    Ling N, Ying SY, Ueno N, Shimasaki S, Esch F, Hotta M, Guillemin R. Pituitary FSH is released by a heterodimer of the

        beta-subunits from the two forms of inhibin. Nature 1986; 321: 779-782  PubMed

13    Tuuri T, Eramaa M, Hilden K, Ritvos O. The tissue distribution of activin beta A- and beta B-subunit and follistatin

        messenger ribonucleic acids suggests multiple sites of action for the activin-follistatin system during human

        development. J Clin Endocrinol Metab 1994; 78: 1521-1524  PubMed

14    Vejda S, Cranfield M, Peter B, Mellor SL, Groome N, Schulte-Hermann R, Rossmanith W. Expression and dimerization of

        the rat activin subunits betaC and betaE: evidence for the ormation of novel activin dimers. J Mol Endocrinol 2002; 28:

        137-148  PubMed

15    Gold EJ, O’Bryan MK, Mellor SL, Cranfield M, Risbridger GP, Groome NP, Fleming JS. Cell-specific expression of betaC-

        activin in the rat reproductive tract, adrenal and liver. Mol Cell Endocrinol 2004; 222: 61-69  PubMed

16    Hashimoto O, Tsuchida K, Ushiro Y, Hosoi Y, Hoshi N, Sugino H, Hasegawa Y. cDNA cloning and expression of human

        activin betaE subunit. Mol Cell Endocrinol 2002; 194: 117-122  PubMed

17    Fang J, Wang SQ, Smiley E, Bonadio J. Genes coding for mouse activin beta C and beta E are closely linked and exhibit a

        liver-specific expression pattern in adult tissues. Biochem Biophys Res Commun 1997; 231: 655-661  PubMed

18    Schmitt J, Hotten G, Jenkins NA, Gilbert DJ, Copeland NG, Pohl J, Schrewe H. Structure, chromosomal localization, and

        expression analysis of the mouse inhibin/activin beta C (Inhbc) gene. Genomics 1996; 32: 358-366  PubMed

19    Grusch M, Rodgarkia-Dara C, Bursch W, Schulte-Hermann R. Activins and the liver-Transforming Growth Factor-b in

        Cancer Therapy. New York: Humana Press, 2007: 1-20 

20    Salvas A, Benjannet S, Reudelhuber TL, Chretien M, Seidah NG. Evidence for proprotein convertase activity in the

        endoplasmic reticulum/early Golgi. FEBS Lett 2005; 579: 5621-5625  PubMed

21    Fang J, Yin W, Smiley E, Wang SQ, Bonadio J. Molecular cloning of the mouse activin beta E subunit gene. Biochem

        Biophys Res Commun 1996; 228: 669-674  PubMed

22    Mason AJ. Functional analysis of the cysteine residues of activin A. Mol Endocrinol 1994; 8: 325-332  PubMed

23    Freedman RB, Hirst TR, Tuite MF. Protein disulphide isomerase: building bridges in protein folding. Trends Biochem Sci

        1994; 19: 331-336   PubMed

24    Ellgaard L, Ruddock LW. The human protein disulphide isomerase family: substrate interactions and functional

        properties. EMBO Rep 2005; 6: 28-32  PubMed 

25    Todorovic V, Jurukovski V, Chen Y, Fontana L, Dabovic B, Rifkin DB. Latent TGF-beta binding proteins. Int J Biochem Cell

        Biol 2005; 37: 38-41  PubMed 

26    Abe Y, Minegishi T, Leung PC. Activin receptor signaling. Growth Factors 2004; 22: 105-110  PubMed

27    Attisano L, Wrana JL, Montalvo E, Massague J. Activation of signalling by the activin receptor complex. Mol Cell Biol

        1996; 16: 1066-1073  PubMed

28    Tsuchida K, Nakatani M, Yamakawa N, Hashimoto O, Hasegawa Y, Sugino H. Activin isoforms signal through type I

        receptor serine/threonine kinase ALK7. Mol Cell Endocrinol 2004; 220: 59-65  PubMed

29    Wada W, Maeshima A, Zhang YQ, Hasegawa Y, Kuwano H, Kojima I. Assessment of the function of the betaC-subunit of

        activin in cultured hepatocytes. Am J Physiol Endocrinol Metab 2004; 287: E247-E254  PubMed

30    Muenster U, Harrison CA, Donaldson C, Vale W, Fischer WH. An activin-A/C chimera exhibits activin and myostatin

        antagonistic properties. J Biol Chem 2005; 280: 36626-36632  PubMed

31    Cook RW, Thompson TB, Jardetzky TS, Woodruff TK. Molecular biology of inhibin action. Semin Reprod Med 2004; 22:

        269-276  PubMed

32    Lewis KA, Gray PC, Blount AL, MacConell LA, Wiater E, Bilezikjian LM, Vale W. Betaglycan binds inhibin and can mediate

        functional antagonism of activin signalling. Nature 2000; 404: 411-414  PubMed

33    Rebbapragada A, Benchabane H, Wrana JL, Celeste AJ, Attisano L. Myostatin signals through a transforming growth

        factor beta-like signaling pathway to block adipogenesis. Mol Cell Biol 2003; 23: 7230-7242  PubMed

34    Heldin CH, Miyazono K, ten Dijke P. TGF-beta signalling from cell membrane to nucleus through SMAD proteins. Nature

        1997; 390: 465-471  PubMed 

35    de Guise C, Lacerte A, Rafiei S, Reynaud R, Roy M, Brue T, Lebrun JJ. Activin inhibits the human Pit-1 gene promoter

        through the p38 kinase pathway in a Smad-independent manner. Endocrinology 2006; 147: 4351-4362  PubMed

36    Zhang L, Deng M, Parthasarathy R, Wang L, Mongan M, Molkentin JD, Zheng Y, Xia Y. MEKK1 transduces activin signals

        in keratinocytes to induce actin stress fiber formation and migration. Mol Cell Biol 2005; 25: 60-65  PubMed

37    McDowell N, Gurdon JB. Activin as a morphogen in Xenopus mesoderm induction. Semin Cell Dev Biol 1999; 10: 311-

        317  PubMed

38    Beattie GM, Lopez AD, Bucay N, Hinton A, Firpo MT, King CC, Hayek A. Activin A maintains pluripotency of human

        embryonic stem cells in the absence of feeder layers. Stem Cells 2005; 23: 489-495  PubMed

39    de Kretser DM, Hedger MP, Loveland KL, Phillips DJ. Inhibins, activins and follistatin in reproduction. Hum Reprod

        Update 2002; 8: 529-541  PubMed

40    Maguer-Satta V, Bartholin L, Jeanpierre S, Ffrench M, Martel S, Magaud JP, Rimokh R. Regulation of human

        erythropoiesis by activin A, BMP2, and BMP4, members of the TGFbeta family. Exp Cell Res 2003; 282: 110-120 


41    Jones KL, de Kretser DM, Patella S, Phillips DJ. Activin A and follistatin in systemic inflammation. Mol Cell Endocrinol

        2004; 225: 119-125  PubMed

42   Chen YG, Wang Q, Lin SL, Chang CD, Chuang J, Ying SY. Activin signaling and its role in regulation of cell proliferation,

        apoptosis, and carcinogenesis. Exp Biol Med (Maywood) 2006; 231: 534-544  PubMed

43    Munz B, Smola H, Engelhardt F, Bleuel K, Brauchle M, Lein I, Evans LW, Huylebroeck D, Balling R, Werner S.

        Overexpression of activin A in the skin of transgenic mice reveals new activities of activin in epidermal morphogenesis,

        dermal fibrosis and wound repair. EMBO J 1999; 18: 5205-5215  PubMed

44    Werner S, Alzheimer C. Roles of activin in tissue repair, fibrosis, and inflammatory disease. Cytokine Growth Factor Rev

        2006; 17: 157-171  PubMed 

45    Matzuk MM, Kumar TR, Vassalli A, Bickenbach JR, Roop DR, Jaenisch R, Bradley A. Functional analysis of activins during

        mammalian development. Nature 1995; 374: 354-356  PubMed

46    Hully JR, Chang L, Schwall RH, Widmer HR, Terrell TG, Gillett NA. Induction of apoptosis in the murine liver with

        recombinant human activin A. Hepatology 1994; 20: 854-862  PubMed

47    Schwall RH, Robbins K, Jardieu P, Chang L, Lai C, Terrell TG. Activin induces cell death in hepatocytes in vivo and in

        vitro. Hepatology 1993; 18: 347-356  PubMed

48    Yasuda H, Mine T, Shibata H, Eto Y, Hasegawa Y, Takeuchi T, Asano S, Kojima I. Activin A: an autocrine inhibitor of

        initiation of DNA synthesis in rat hepatocytes. J Clin Invest 1993; 92: 1491-1496  PubMed

49    Takabe K, Lebrun JJ, Nagashima Y, Ichikawa Y, Mitsuhashi M, Momiyama N, Ishikawa T, Shimada H, Vale WW.

        Interruption of activin A autocrine regulation by antisense oligodeoxynucleotides accelerates liver tumor cell proliferation.

        Endocrinology 1999; 140: 3125-3132  PubMed

50    Gold EJ, Zhang X, Wheatley AM, Mellor SL, Cranfield M, Risbridger GP, Groome NP, Fleming JS. betaA- and betaC-

        activin, follistatin, activin receptor mRNA and betaC-activin peptide expression during rat liver regeneration. J Mol

        Endocrinol 2005; 34: 505-515  PubMed

51    Date M, Matsuzaki K, Matsushita M, Tahashi Y, Sakitani K, Inoue K. Differential regulation of activin A for hepatocyte

        growth and fibronectin synthesis in rat liver injury. J Hepatol 2000; 32: 251-260  PubMed

52    Zhang YQ, Shibata H, Schrewe H, Kojima I. Reciprocal expression of mRNA for inhibin betaC and betaA subunits in

        hepatocytes. Endocr J 1997; 44: 759-764  PubMed

53    Wada W, Kuwano H, Hasegawa Y, Kojima I. The dependence of transforming growth factor-beta-induced collagen

        production on autocrine factor activin A in hepatic stellate cells. Endocrinology 2004; 145: 2753-2759  PubMed

54    Endo D, Kogure K, Hasegawa Y, Maku-uchi M, Kojima I. Activin A augments vascular endothelial growth factor activity in

        promoting branching tubulogenesis in hepatic sinusoidal endothelial cells. J Hepatol 2004; 40: 399-404  PubMed

55    De Bleser PJ, Niki T, Xu G, Rogiers V, Geerts A. Localization and cellular sources of activins in normal and fibrotic rat

        liver. Hepatology 1997; 26: 905-912  PubMed

56    Gold EJ, Francis RJ, Zimmermann A, Mellor SL, Cranfield M, Risbridger GP, Groome NP, Wheatley AM, Fleming JS.

        Changes in activin and activin receptor subunit expression in rat liver during the development of CCl4-induced cirrhosis.

        Mol Cell Endocrinol 2003; 201: 143-153  PubMed

57    Huang X, Li DG, Wang ZR, Wei HS, Cheng JL, Zhan YT, Zhou X, Xu QF, Li X, Lu HM. Expression changes of activin A in

        the development of hepatic fibrosis. World J Gastroenterol 2001; 7: 37-41  PubMed

58    Sugiyama M, Ichida T, Sato T, Ishikawa T, Matsuda Y, Asakura H. Expression of activin A is increased in cirrhotic and

        fibrotic rat livers. Gastroenterology 1998; 114: 550-558  PubMed

59    Patella S, Phillips DJ, de Kretser DM, Evans LW, Groome NP, Sievert W. Characterization of serum activin-A and

        follistatin and their relation to virological and histological determinants in chronic viral hepatitis. J Hepatol 2001; 34: 576-

        583  PubMed

60    Yuen MF, Norris S, Evans LW, Langley PG, Hughes RD. Transforming growth factor-beta 1, activin and follistatin in

        patients with hepatocellular carcinoma and patients with alcoholic cirrhosis. Scand J Gastroenterol 2002; 37: 233-238 


61    Pirisi M, Fabris C, Luisi S, Santuz M, Toniutto P, Vitulli D, Federico E, Del Forno M, Mattiuzzo M, Branca B, Petraglia F.

        Evaluation of circulating activin-A as a serum marker of hepatocellular carcinoma. Cancer Detect Prev 2000; 24: 150-

        155  PubMed

62    Grusch M, Drucker C, Peter-Vorosmarty B, Erlach N, Lackner A, Losert A, Macheiner D, Schneider WJ, Hermann M,

        Groome NP, Parzefall W, Berger W, Grasl-Kraupp B, Schulte-Hermann R. Deregulation of the activin/follistatin system in

        hepatocarcinogenesis. J Hepatol 2006; 45: 673-680  PubMed

63    Wagner K, Peters M, Scholz A, Benckert C, Ruderisch HS, Wiedenmann B, Rosewicz S. Activin A stimulates vascular

        endothelial growth factor gene transcription in human hepatocellular carcinoma cells. Gastroenterology 2004; 126:

        1828-1843   PubMed

64   Thompson TB, Cook RW, Chapman SC, Jardetzky TS, Woodruff TK. Beta A versus beta B: is it merely a matter of

        expression? Mol Cell Endocrinol 2004; 225: 9-17  PubMed

65    Vassalli A, Matzuk MM, Gardner HA, Lee KF, Jaenisch R. Activin/inhibin beta B subunit gene disruption leads to defects

        in eyelid development and female reproduction. Genes Dev 1994; 8: 414-427  PubMed

66    Brown CW, Houston-Hawkins DE, Woodruff TK, Matzuk MM. Insertion of Inhbb into the Inhba locus rescues the Inhba-

        null phenotype and reveals new activin functions. Nat Genet 2000; 25: 453-457  PubMed

67    Kobayashi T, Niimi S, Fukuoka M, Hayakawa T. Regulation of inhibin beta chains and follistatin mRNA levels during rat

        hepatocyte growth induced by the peroxisome proliferator di-n-butyl phthalate. Biol Pharm Bull 2002; 25: 1214-1216 


68    Niimi S, Horikawa M, Seki T, Ariga T, Kobayashi T, Hayakawa T. Effect of activins AB and B on DNA synthesis stimulated

        by epidermal growth factor in primary cultured rat hepatocytes. Biol Pharm Bull 2002; 25: 437-440  PubMed 

69    Hotten G, Neidhardt H, Schneider C, Pohl J. Cloning of a new member of the TGF-beta family: a putative new activin

        beta C chain. Biochem Biophys Res Commun 1995; 206: 608-613  PubMed

70    Mellor SL, Cranfield M, Ries R, Pedersen J, Cancilla B, de Kretser D, Groome NP, Mason AJ, Risbridger GP. Localization

        of activin beta(A)-, beta(B)-, and beta(C)-subunits in humanprostate and evidence for formation of new activin

        heterodimers of beta(C)-subunit. J Clin Endocrinol Metab 2000; 85: 4851-4858  PubMed

71    Ushiro Y, Hashimoto O, Seki M, Hachiya A, Shoji H, Hasegawa Y. Analysis of the function of activin betaC subunit using

        recombinant protein. J Reprod Dev 2006; 52: 487-495  PubMed

72    Esquela AF, Zimmers TA, Koniaris LG, Sitzmann JV, Lee SJ. Transient down-regulation of inhibin-betaC expression

        following partial hepatectomy. Biochem Biophys Res Commun 1997; 235: 553-556  PubMed

73    Takamura K, Tsuchida K, Miyake H, Tashiro S, Sugino H. Activin and activin receptor expression changes in liver

        regeneration in rat. J Surg Res 2005; 126: 3-11   PubMed

74    Vejda S, Erlach N, Peter B, Drucker C, Rossmanith W, Pohl J, Schulte-Hermann R, Grusch M. Expression of activins C

        and E induces apoptosis in human and rat hepatoma cells. Carcinogenesis 2003; 24: 1801-1809   PubMed

75    Huang X, Li D, Lu H, Wang Z, Wei H, Wang Y, Zhang J, Xu Q. Expression of activins, follistatin mRNA in the development

        of hepatic fibrosis. Zhonghua Ganzangbing Zazhi 2002; 10: 85-88  PubMed

76    Lau AL, Kumar TR, Nishimori K, Bonadio J, Matzuk MM. Activin betaC and betaE genes are not essential for mouse liver

        growth, differentiation, and regeneration. Mol Cell Biol 2000; 20: 6127-6137  PubMed

77    Chabicovsky M, Herkner K, Rossmanith W. Overexpression of activin beta(C) or activin beta(E) in the mouse liver

        inhibits regenerative deoxyribonucleic acid synthesis of hepatic cells. Endocrinology 2003; 144: 3497-3504  PubMed

78    Wada W, Medina J, Hasegawa Y, Kuwano H, Kojima I. Adenovirus-mediated overexpression of the activin betaC subunit

        accelerates liver regeneration in partially hepatectomized rats. J Hepatol 2005; 43: 823-828  PubMed

79    Mellor SL, Ball EM, O’Connor AE, Ethier JF, Cranfield M, Schmitt JF, Phillips DJ, Groome NP, Risbridger GP. Activin

        betaC-subunit heterodimers provide a new mechanism of regulating activin levels in the prostate. Endocrinology 2003;

        144: 4410-4419  PubMed

80    Butler CM, Gold EJ, Risbridger GP. Should activin betaC be more than a fading snapshot in the activin/TGFbeta family

        album? Cytokine Growth Factor Rev 2005; 16: 377-385  PubMed

81    O’Bryan MK, Sebire KL, Gerdprasert O, Hedger MP, Hearn MT, de Kretser DM. Cloning and regulation of the rat activin

        betaE subunit. J Mol Endocrinol 2000; 24: 409-418  PubMed

82    Atienzar F, Gerets H, Dufrane S, Tilmant K, Cornet M, Dhalluin S, Ruty B, Rose G, Canning M. Determination of

        phospholipidosis potential based on gene expression analysis in HepG2 cells. Toxicol Sci 2007; 96: 101-114  PubMed 

83    Wada W, Medina JJ, Kuwano H, Kojima I. Comparison of the function of the beta(C) and beta(E) subunits of activin in

        AML12 hepatocytes. Endocr J 2005; 52: 169-175  PubMed

84    Hashimoto O, Ushiro Y, Sekiyama K, Yamaguchi O, Yoshioka K, Mutoh K, Hasegawa Y. Impaired growth of pancreatic

        exocrine cells in transgenic mice expressing human activin betaE subunit. Biochem Biophys Res Commun 2006; 341:

        416-424  PubMed

85    Chow C, Wong N, To KF, Lo KW. Activin beta E (INHBE), a RASSF1A target gene is downregulated in hepatocellular

        carcinoma. Proceedings of the 2007 Annual Meeting of the American Association for Cancer Research; 2007, April 14-

        18, Los Angeles, CA. Los Angeles, 2007: 26   

86    Chow LS, Lam CW, Chan SY, Tsao SW, To KF, Tong SF, Hung WK, Dammann R, Huang DP, Lo KW. Identification of

        RASSF1A modulated genes in nasopharyngeal carcinoma. Oncogene 2006; 25: 310-316  PubMed

87    Macheiner D, Heller G, Kappel S, Bichler C, Stattner S, Ziegler B, Kandioler D, Wrba F, Schulte-Hermann R, Zochbauer-

        Muller S, Grasl-Kraupp B. NORE1B, a candidate tumor suppressor, is epigenetically silenced in human hepatocellular         carcinoma. J Hepatol 2006; 45: 81-89  PubMed

88    Schagdarsurengin U, Wilkens L, Steinemann D, Flemming P, Kreipe HH, Pfeifer GP, Schlegelberger B, Dammann R.

         Frequent epigenetic inactivation of the RASSF1A gene in hepatocellular carcinoma. Oncogene 2003; 22: 1866-1871 


89    Welt C, Sidis Y, Keutmann H, Schneyer A. Activins, inhibins, and follistatins: from endocrinology to signaling. A paradigm

        for the new millennium. Exp Biol Med (Maywood) 2002; 227: 724-752  PubMed

90    Matzuk MM, Finegold MJ, Su JG, Hsueh AJ, Bradley A. Alpha-inhibin is a tumour-suppressor gene with gonadal

        specificity in mice. Nature 1992; 360: 313-319  PubMed

91    Xu J, McKeehan K, Matsuzaki K, McKeehan WL. Inhibin antagonizes inhibition of liver cell growth by activin by a

        dominant-negative mechanism. J Biol Chem 1995; 270: 6308-6313  PubMed

92    Renshaw AA, Granter SR. A comparison of A103 and inhibin reactivity in adrenal cortical tumors: distinction from

        hepatocellular carcinoma and renal tumors. Mod Pathol 1998; 11: 1160-1164  PubMed

93    Pan CC, Chen PC, Tsay SH, Ho DM. Differential immuno-profiles of hepatocellular carcinoma, renal cell carcinoma, and

        adrenocortical carcinoma: a systemic immunohistochemical survey using tissue array technique. Appl Immunohistochem

        Mol Morphol 2005; 13: 347-352  PubMed

94    Michel U, Rao A, Findlay JK. Rat follistatin: ontogeny of steady-state mRNA levels in different tissues predicts organ-

        specific functions. Biochem Biophys Res Commun 1991; 180: 223-230  PubMed

95    Sugino K, Kurosawa N, Nakamura T, Takio K, Shimasaki S, Ling N, Titani K, Sugino H. Molecular heterogeneity of

        follistatin, an activin-binding protein. Higher affinity of the carboxyl-terminal truncated forms for heparan sulfate

        proteoglycans on the ovarian granulosa cell. J Biol Chem 1993; 268: 15579-15587  PubMed

96    Schneyer AL, Rzucidlo DA, Sluss PM, Crowley WF Jr. Characterization of unique binding kinetics of follistatin and activin

        or inhibin in serum. Endocrinology 1994; 135: 667-674  PubMed

97    Harrington AE, Morris-Triggs SA, Ruotolo BT, Robinson CV, Ohnuma S, Hyvonen M. Structural basis for the inhibition of

        activin signalling by follistatin. EMBO J 2006; 25: 1035-1045  PubMed

98    de Winter JP, ten Dijke P, de Vries CJ, van Achterberg TA, Sugino H, de Waele P, Huylebroeck D, Verschueren K, van

        den Eijnden-van Raaij AJ. Follistatins neutralize activin bioactivity by inhibition of activin binding to its type II receptors.

        Mol Cell Endocrinol 1996; 116: 105-114  PubMed

99    Thompson TB, Lerch TF, Cook RW, Woodruff TK, Jardetzky TS. The structure of the follistatin:activin complex reveals

        antagonism of both type I and type II receptor binding. Dev Cell 2005; 9: 535-543  PubMed

100  Shimasaki S, Koga M, Esch F, Cooksey K, Mercado M, Koba A, Ueno N, Ying SY, Ling N, Guillemin R. Primary structure of

        the human follistatin precursor and its genomic organization. Proc Natl Acad Sci USA 1988; 85: 4218-4222  PubMed

101  Keutmann HT, Schneyer AL, Sidis Y. The role of follistatin domains in follistatin biological action. Mol Endocrinol 2004;

        18: 228-240   PubMed

102  Schneyer A, Schoen A, Quigg A, Sidis Y. Differential binding and neutralization of activins A and B by follistatin and

        follistatin like-3 (FSTL-3/FSRP/FLRG). Endocrinology 2003; 144: 1671-1674  PubMed

103  Iemura S, Yamamoto TS, Takagi C, Uchiyama H, Natsume T, Shimasaki S, Sugino H, Ueno N. Direct binding of follistatin

        to a complex of bone-morphogenetic protein and its receptor inhibits ventral and epidermal cell fates in early Xenopus

        embryo. Proc Natl Acad Sci USA 1998; 95: 9337-9342  PubMed

104  Amthor H, Nicholas G, McKinnell I, Kemp CF, Sharma M, Kambadur R, Patel K. Follistatin complexes Myostatin and

        antagonises Myostatin-mediated inhibition of myogenesis. Dev Biol 2004; 270: 19-30  PubMed 

105  Glister C, Kemp CF, Knight PG. Bone morphogenetic protein (BMP) ligands and receptors in bovine ovarian follicle cells:

        actions of BMP-4, -6 and -7 on granulosa cells and differential modulation of Smad-1 phosphorylation by follistatin.

        Reproduction 2004; 127: 239-254  PubMed

106  Kogure K, Zhang YQ, Maeshima A, Suzuki K, Kuwano H, Kojima I. The role of activin and transforming growth factor-

        beta in the regulation of organ mass in the rat liver. Hepatology 2000; 31: 916-921  PubMed

107  Takabe K, Wang L, Leal AM, Macconell LA, Wiater E, Tomiya T, Ohno A, Verma IM, Vale W. Adenovirus-mediated

        overexpression of follistatin enlarges intact liver of adult rats. Hepatology 2003; 38: 1107-1115  PubMed

108  Kogure K, Omata W, Kanzaki M, Zhang YQ, Yasuda H, Mine T, Kojima I. A single intraportal administration of follistatin

        accelerates liver regeneration in partially hepatectomized rats. Gastroenterology 1995; 108: 1136-1142  PubMed

109  Kogure K, Zhang YQ, Shibata H, Kojima I. Immediate onset of DNA synthesis in remnant rat liver after 90% hepatectomy

        by an administration of follistatin. J Hepatol 1998; 29: 977-984  PubMed

110 Endo D, Maku-Uchi M, Kojima I. Activin or follistatin: which is more beneficial to support liver regeneration after massive

        hepatectomy? Endocr J 2006; 53: 73-78  PubMed

111  Patella S, Phillips DJ, Tchongue J, de Kretser DM, Sievert W. Follistatin attenuates early liver fibrosis: effects on hepatic

        stellate cell activation and hepatocyte apoptosis. Am J Physiol Gastrointest Liver Physiol 2006; 290: G137-G144  PubMed

112  Rossmanith W, Chabicovsky M, Grasl-Kraupp B, Peter B, Schausberger E, Schulte-Hermann R. Follistatin overexpression

        in rodent liver tumors: a possible mechanism to overcome activin growth control. Mol Carcinog 2002; 35: 1-5  PubMed

113  Fuwii M, Ishikawa M, Iuchi M, Tashiro S. Effect of follistatin on rat liver regeneration and tumor growth after portal

        occlusion. Hepatogastroenterology 2005; 52: 833-838  PubMed

114  Mashima H, Kanzaki M, Nobusawa R, Zhang YQ, Suzuki M, Mine T, Kojima I. Derangements in the activin-follistatin

        system in hepatoma cells. Gastroenterology 1995; 108: 834-840   PubMed

115  Tsuchida K, Arai KY, Kuramoto Y, Yamakawa N, Hasegawa Y, Sugino H. Identification and characterization of a novel

        follistatin-like protein as a binding protein for the TGF-beta family. J Biol Chem 2000; 275: 40788-40796  PubMed

116  Ullman CG, Perkins SJ. The Factor I and follistatin domain families: the return of a prodigal son. Biochem J 1997; 326

        (Pt 3): 939-941   PubMed

117  Hayette S, Gadoux M, Martel S, Bertrand S, Tigaud I, Magaud JP, Rimokh R. FLRG (follistatin-related gene), a new

        target of chromosomal rearrangement in malignant blood disorders. Oncogene 1998; 16: 2949-2954  PubMed

118  Tortoriello DV, Sidis Y, Holtzman DA, Holmes WE, Schneyer AL. Human follistatin-related protein: a structural

        homologue of follistatin with nuclear localization. Endocrinology 2001; 142: 3426-3434  PubMed

119  Bartholin L, Maguer-Satta V, Hayette S, Martel S, Gadoux M, Corbo L, Magaud JP, Rimokh R. Transcription activation of

        FLRG and follistatin by activin A, through Smad proteins, participates in a negative feedback loop to modulate activin A

        function. Oncogene 2002; 21: 2227-2235  PubMed

120  Ichikawa T, Zhang YQ, Kogure K, Hasegawa Y, Takagi H, Mori M, Kojima I. Transforming growth factor beta and activin

        tonically inhibit DNA synthesis in the rat liver. Hepatology 2001; 34: 918-925  PubMed

121  Chen W, Woodruff TK, Mayo KE. Activin A-induced HepG2 liver cell apoptosis: involvement of activin receptors and smad

        proteins. Endocrinology 2000; 141: 1263-1272  PubMed

122  Kim BC, van Gelder H, Kim TA, Lee HJ, Baik KG, Chun HH, Lee DA, Choi KS, Kim SJ. Activin receptor-like kinase-7 induces

        apoptosis through activation of MAPKs in a Smad3-dependent mechanism in hepatoma cells. J Biol Chem 2004; 279:

        28458-28465  PubMed

123  Jung B, Doctolero RT, Tajima A, Nguyen AK, Keku T, Sandler RS, Carethers JM. Loss of activin receptor type 2 protein

        expression in microsatellite unstable colon cancers. Gastroenterology 2004; 126: 654-659  PubMed

124  Hempen PM, Zhang L, Bansal RK, Iacobuzio-Donahue CA, Murphy KM, Maitra A, Vogelstein B, Whitehead RH, Markowitz

        SD, Willson JK, Yeo CJ, Hruban RH, Kern SE. Evidence of selection for clones having genetic inactivation of the activin A

        type II receptor (ACVR2) gene in gastrointestinal cancers. Cancer Res 2003; 63: 994-999  PubMed

125  Su GH, Bansal R, Murphy KM, Montgomery E, Yeo CJ, Hruban RH, Kern SE. ACVR1B (ALK4, activin receptor type 1B) gene

        mutations in pancreatic carcinoma. Proc Natl Acad Sci USA 2001; 98: 3254-3257  PubMed

126  Rossi MR, Ionov Y, Bakin AV, Cowell JK. Truncating mutations in the ACVR2 gene attenuates activin signaling in prostate

        cancer cells. Cancer Genet Cytogenet 2005; 163: 123-129  PubMed

127  Bianco C, Strizzi L, Normanno N, Khan N, Salomon DS. Cripto-1: an oncofetal gene with many faces. Curr Top Dev Biol

        2005; 67: 85-133   PubMed

128  Adkins HB, Bianco C, Schiffer SG, Rayhorn P, Zafari M, Cheung AE, Orozco O, Olson D, De Luca A, Chen LL, Miatkowski

        K, Benjamin C, Normanno N, Williams KP, Jarpe M, LePage D, Salomon D, Sanicola M. Antibody blockade of the Cripto

        CFC domain suppresses tumor cell growth in vivo. J Clin Invest 2003; 112: 575-587  PubMed

129  Gray PC, Harrison CA, Vale W. Cripto forms a complex with activin and type II activin receptors and can block activin

        signaling. Proc Natl Acad Sci USA 2003; 100: 5193-5198  PubMed

130  Gray PC, Shani G, Aung K, Kelber J, Vale W. Cripto binds transforming growth factor beta (TGF-beta) and inhibits TGF-

        beta signaling. Mol Cell Biol 2006; 26: 9268-9278  PubMed

131  Baldassarre G, Tucci M, Lembo G, Pacifico FM, Dono R, Lago CT, Barra A, Bianco C, Viglietto G, Salomon D, Persico MG.

        A truncated form of teratocarcinoma-derived growth factor-1 (cripto-1) mRNA expressed in human colon carcinoma cell

        lines and tumors. Tumour Biol 2001; 22: 286-293  PubMed

132  Hamada S, Watanabe K, Hirota M, Bianco C, Strizzi L, Mancino M, Gonzales M, Salomon DS. beta-Catenin/TCF/LEF

        regulate expression of the short form human Cripto-1. Biochem Biophys Res Commun 2007; 355: 240-244  PubMed

133  Onichtchouk D, Chen YG, Dosch R, Gawantka V, Delius H, Massague J, Niehrs C. Silencing of TGF-beta signalling by the

        pseudoreceptor BAMBI. Nature 1999; 401: 480-485  PubMed

134  Seki E, De Minicis S, Osterreicher CH, Kluwe J, Osawa Y, Brenner DA, Schwabe RF. TLR4 enhances TGF-beta signaling

        and hepatic fibrosis. Nat Med 2007; 13: 1324-1332  PubMed

135  Sekiya T, Adachi S, Kohu K, Yamada T, Higuchi O, Furukawa Y, Nakamura Y, Nakamura T, Tashiro K, Kuhara S, Ohwada

        S, Akiyama T. Identification of BMP and activin membrane-bound inhibitor (BAMBI), an inhibitor of transforming growth

        factor-beta signaling, as a target of the beta-catenin pathway in colorectal tumor cells. J Biol Chem 2004; 279: 6840-

        6846   PubMed

136  Shoji H, Tsuchida K, Kishi H, Yamakawa N, Matsuzaki T, Liu Z, Nakamura T, Sugino H. Identification and characterization

        of a PDZ protein that interacts with activin type II receptors. J Biol Chem 2000; 275: 5485-5492  PubMed 

137  Matsuzaki T, Hanai S, Kishi H, Liu Z, Bao Y, Kikuchi A, Tsuchida K, Sugino H. Regulation of endocytosis of activin type II

        receptors by a novel PDZ protein through Ral/Ral-binding protein 1-dependent pathway. J Biol Chem 2002; 277: 19008-

        19018  PubMed

138  Liu ZH, Tsuchida K, Matsuzaki T, Bao YL, Kurisaki A, Sugino H. Characterization of isoforms of activin receptor-interacting

        protein 2 that augment activin signaling. J Endocrinol 2006; 189: 409-421  PubMed

139  Zhang HJ, Tai GX, Zhou J, Ma D, Liu ZH. Regulation of activin receptor-interacting protein 2 expression in mouse

        hepatoma Hepa1-6 cells and its relationship with collagen type IV. World J Gastroenterol 2007; 13: 5501-5505  PubMed

140  Eppert K, Scherer SW, Ozcelik H, Pirone R, Hoodless P, Kim H, Tsui LC, Bapat B, Gallinger S, Andrulis IL, Thomsen GH,

        Wrana JL, Attisano L. MADR2 maps to 18q21 and encodes a TGFbeta-regulated MAD-related protein that is functionally

        mutated in colorectal carcinoma. Cell 1996; 86: 543-552   PubMed

141  Hahn SA, Schutte M, Hoque AT, Moskaluk CA, da Costa LT, Rozenblum E, Weinstein CL, Fischer A, Yeo CJ, Hruban RH,

        Kern SE. DPC4, a candidate tumor suppressor gene at human chromosome 18q21.1. Science 1996; 271: 350-353 


142  Yakicier MC, Irmak MB, Romano A, Kew M, Ozturk M. Smad2 and Smad4 gene mutations in hepatocellular carcinoma.

        Oncogene 1999; 18: 4879-4883  PubMed

143  Imamura T, Takase M, Nishihara A, Oeda E, Hanai J, Kawabata M, Miyazono K. Smad6 inhibits signalling by the TGF-

        beta superfamily. Nature 1997; 389: 622-626  PubMed

144  Nakao A, Afrakhte M, Moren A, Nakayama T, Christian JL, Heuchel R, Itoh S, Kawabata M, Heldin NE, Heldin CH, ten

        Dijke P. Identification of Smad7, a TGFbeta-inducible antagonist of TGF-beta signalling. Nature 1997; 389: 631-635 


145  Kanamaru C, Yasuda H, Takeda M, Ueda N, Suzuki J, Tsuchida T, Mashima H, Ohnishi H, Fujita T. Smad7 is induced by

        norepinephrine and protects rat hepatocytes from activin A-induced growth inhibition. J Biol Chem 2001; 276: 45636-

        45641  PubMed

146  Ji GZ, Wang XH, Miao L, Liu Z, Zhang P, Zhang FM, Yang JB. Role of transforming growth factor-beta1-smad signal

        transduction pathway in patients with hepatocellular carcinoma. World J Gastroenterol 2006; 12: 644-648  PubMed

147  Park YN, Chae KJ, Oh BK, Choi J, Choi KS, Park C. Expression of Smad7 in hepatocellular carcinoma and dysplastic

        nodules: resistance mechanism to transforming growth factor-beta. Hepatogastroenterology 2004; 51: 396-400 


148  Kawate S, Ohwada S, Hamada K, Koyama T, Takenoshita S, Morishita Y, Hagiwara K. Mutational analysis of the Smad6

        and Smad7 genes in hepatocellular carcinoma. Int J Mol Med 2001; 8: 49-52  PubMed

149  Tsuchida K, Nakatani M, Uezumi A, Murakami T, Cui X. Signal Transduction Pathway through Activin Receptors as a

        Therapeutic Target of Musculoskeletal Diseases and Cancer. Endocr J 2007; (Epub ahead of print)  PubMed

150  Piek E, Roberts AB. Suppressor and oncogenic roles of transforming growth factor-beta and its signaling pathways in

        tumorigenesis. Adv Cancer Res 2001; 83: 1-54   PubMed

151  Mullauer L, Grasl-Kraupp B, Bursch W, Schulte-Hermann R. Transforming growth factor beta 1-induced cell death in

        preneoplastic foci of rat liver and sensitization by the antiestrogen tamoxifen. Hepatology 1996; 23: 840-847  PubMed

152  Chabicovsky M, Wastl U, Taper H, Grasl-Kraupp B, Schulte-Hermann R, Bursch W. Induction of apoptosis in mouse liver

        adenoma and carcinoma in vivo by transforming growth factor-beta1. J Cancer Res Clin Oncol 2003; 129: 536-542  


153  Abou-Shady M, Baer HU, Friess H, Berberat P, Zimmermann A, Graber H, Gold LI, Korc M, Buchler MW. Transforming

        growth factor betas and their signaling receptors in human hepatocellular carcinoma. Am J Surg 1999; 177: 209-215 


154  Jeruss JS, Sturgis CD, Rademaker AW, Woodruff TK. Down-regulation of activin, activin receptors, and Smads in high-

        grade breast cancer. Cancer Res 2003; 63: 3783-3790   PubMed

155  Yoshinaga K, Yamashita K, Mimori K, Tanaka F, Inoue H, Mori M. Activin a causes cancer cell aggressiveness in

        esophageal squamous cell carcinoma cells. Ann Surg Oncol 2008; 15: 96-103  PubMed

156  Razanajaona D, Joguet S, Ay AS, Treilleux I, Goddard-Leon S, Bartholin L, Rimokh R. Silencing of FLRG, an antagonist

        of activin, inhibits human breast tumor cell growth. Cancer Res 2007; 67: 7223-7229  PubMed

157  Stove C, Vanrobaeys F, Devreese B, Van Beeumen J, Mareel M, Bracke M. Melanoma cells secrete follistatin, an

        antagonist of activin-mediated growth inhibition. Oncogene 2004; 23: 5330-5339  PubMed


S- Editor  Zhong XY    L- Editor  Alpini GD    E- Editor  Ma WH



Reviews Add

Related Articles:
Recurrence or metastasis of HCC:predictors, early detection and experimental antiangiogenic therapy
Inhibitory effect of IGF- II antisense RNA on malignant phenotype of hepatocellular carcinoma
Analysis of in vivo patterns of caspase 3 gene expression in primary hepatocellular carcinoma and its relationship to p21WAF1 expression and hepatic apoptosis
Hepatocellular carcinoma in central Sydney:a 10-year review of patients seen in a medical oncology department
Characterization of six tumor suppressor genes and microsatellite instability in hepatocellular carcinoma in southern African blacks