Protein-protein interaction map is a key gateway into liver regeneration

Table 1 Liver cell types and their functions during liver regeneration

Cell types	Functions
Hepatocytes	Organized in single cell plates; perform metabolic and detoxification function; can secrete HGF, IL-6, proteases and protease inhibitors
Sinusoidal endothelial cells	Involved in endocytosis and metabolism of molecules; can produce TGFβ, HGF, IL-6 and nitric oxide
Biliary epithelial cells	Can promote fibrogenesis by attraction of hepatic stellate cells and can secrete cytokines such as MCP-1 and IL-6
Kupffer cells	Major producers of cytokines such as TNF and IL-6
Hepatic stellate cells	Store vitamin A and secrete laminins, collagens and growth factor: HGF, EGF, TGFβ and cytokines IL-6; also produce MMPs
Oval cells	Can differentiate to biliary and hepatocytes lineage

HGF: Hepatocyte growth factor; IL-6: Interleukin-6; EGF: Epidermal growth factor; TGF: Transforming growth factor; MCP: Monocyte chemotactic protein; MMP: Matrix metalloproteinase; TNF: Tumor necrosis factor.

Table 2 Some protein-protein interaction maps established in recent years

Researcher	Yr	Level	Model organisms	Method	PPI numbers
Bartel et al[26]	1996	Proteome	T7 phage	Y2H	25
Uetz et al[21]	2000	Proteome	Saccharomyces cerevisiae	Y2H	1389
Ito et al[27]	2000	Proteome	Saccharomyces cerevisiae	Y2H	183
Walhout et al[28]	2000	Proteome	Caenorhabditis elegans	Y2H	148
Ito et al[29]	2001	Proteome	Saccharomyces cerevisiae	Y2H	4549
Ho et al[30]	2002	Proteome	Saccharomyces cerevisiae	MS	367
Giot et al[22]	2003	Proteome	Drosophila melanogaster	Y2H	20 240
Colland et al[31]	2004	Pathway	Caenorhabditis elegans	Y2H	755
Stanyon et al[32]	2004	Cell cycle	Drosophila melanogaster	Y2H	20 000
Li et al[6]	2004	Proteome	Caenorhabditis elegans	Y2H	3955
Lehner et al[33]	2004	mRNA	Human	Y2H	247
Formstecher et al[34]	2005	Proteome	Drosophila melanogaster	Y2H	2300
Stelzl et al[24]	2005	Proteome	Human	Y2H	3083
Rual et al[8]	2005	Proteome	Human	Y2H	2529
Ewing et al[35]	2007	Proteome	Human	MS	24 540
Parrish et al[36]	2007	Proteome	Camp. jejuni.	Y2H	11 687
Gao et al[37]	2008	Liver regeneration	Human	Y2H	64
Chen et al[38]	2008	Protein degradation	Human	Y2H	114

Y2H: Yeast two-hybrid; MS: Mass spectrometry; PPI: Protein-protein interaction.