Published online Mar 14, 2018. doi: 10.3748/wjg.v24.i10.1120
Peer-review started: December 8, 2017
First decision: December 20, 2017
Revised: December 29, 2017
Accepted: January 24, 2018
Article in press: January 24, 2018
Published online: March 14, 2018
Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. Metastasis often occurs in HCC patients, thus leading to a poor prognosis. It is urgent for us to find out molecules that are responsible for HCC metastasis to improve the prognosis of HCC patients.
Proteinase-activated receptor 2 (PAR2) is reported to be responsible for HCC development, but the underlying mechanism is unclear. Figuring out the detailed mechanisms for PAR2-induced metastasis of HCC could give us more options for HCC treatment.
Although the role of PAR2 in HCC has been reported, the underlying mechanism for PAR2-induced metastasis is more important. Therefore, we aimed to find out the downstream signaling for PAR2-induced HCC metastasis. This could help us to find targets for HCC treatment.
PAR2 expression levels were assessed by qRT-PCR and immunohistochemistry in patient tissues. Cell proliferation was investigated by CCK8 and colony formation assays in vitro and tumor xenograft in vivo. HCC cell metastasis was assessed by transwell and wound healing assays in vitro and intrasplenic injection of HCC cells in mice in vivo. Immunoblotting was carried out to monitor the levels of mitogen-activated protein kinases and epithelial-mesenchymal transition (EMT) markers to figure out the underlying mechanisms for PAR2. This is the first time to analyze the correlation between PAR2 expression and HCC clinicopathological characteristics. Also, it is the first for us to investigate the underlying mechanism for PAR2-mediated HCC metastasis. What’s more, we proved the role of PAR2 in HCC proliferation and metastasis using an animal model.
The prognosis of patients with high PAR2 levels was poorer than those with low PAR2 levels. Patients with high PAR2 levels had advanced tumor stage, larger tumor size, and high microvascular invasion rate. The proliferation and metastasis ability of SMMC-7721 and HepG2 cells was increased after PAR2 overexpression, while knockdown of PAR2 decreased the proliferation and metastasis ability of SMMC-7721 and HepG2 cells. Knockdown of PAR2 also inhibited HCC tumor cell growth and liver metastasis in nude mice. Mechanistically, PAR2 increased the proliferation ability of SMMC-7721 and HepG2 cells via ERK activation. Activated ERK further promoted the epithelial-mesenchymal transition of these cells with the help of EGR-1 and Snail, which endowed them with enhanced migration and invasion ability.
In this study, we found that PAR2 was upregulated in HCC tumor tissues and related with poor prognosis in HCC patients. In addition, we proved that PAR2 could not only promote the proliferation and metastasis ability of SMMC-7721 and HepG2 cells in vitro, but also promoted xenograft tumor growth and HCC cell liver metastasis in vivo. These effects were mediated by the activation of ERK, which further induced EMT by EGR-1 and Snail of HCC cells. Therefore, targeting PAR2 may present a favorable anticancer target for treatment.
As we all know, PAR2 is activated via its N-terminal cleavage by several proteases such as serine proteases, but which protease is responsible for PAR2 activation in HCC is still not clear. This is a very interesting direction in the following study. Recently, some growth factors such as HGF were reported to be responsible for EMT in HCC. Whether HGF participates in PAR2-induced EMT could be further investigated based on this study.