Activins and activin antagonists in hepatocellular carcinoma

Table 1 Overview of described alterations of activins and activin antagonists in HCC and HCC-derived cell lines

Activin subunits and activin antagonists	Proposed function in activin signaling	Alterations observed in HCC and hepatoma cells
Activin βA subunit	Activates activin receptors	Increased activin A in circulation of HCC patients[6061]
		Decreased expression in rat and human liver tumors[62]
		Loss of expression in hepatoma cells[74114]
Activin βE subunit	Induces apoptosis by as yet undefined mechanisms	Decreased expression in rat and human liver tumors[6285]
Follistatin	Binds activins and blocks their interaction with receptors	Increased in circulation of HCC patients[60]
		Increased expression in human mouse and rat liver tumors[62112]
		Expressed in hepatoma cells[112114]
FLRG	Binds activins and blocks their interaction with receptors	Increased in rat but decreased in human liver tumors[62]
BAMBI	Binds TGFβ-family type II receptors and blocks typeIreceptor activation	Increased in HCC and colon cancer[135]
Cripto	Blocks interaction of activins (and TGFβ) with their receptors	Overexpressed in hepatoma cells[132]
Smad 7	Inhibits activation of Smads by activin (and TGFβ) receptors	Increased expression in HCC[146147]