Expression of activins C and E induces apoptosis in human and rat hepatoma cells

Activins C and E (homodimers of the beta(C) and beta(E) subunits), which are almost exclusively expressed in the liver, are members of the transforming growth factor beta (TGFbeta) superfamily of growth factors. We examined their expression in three different hepatoma cell lines and found that, compared with normal liver or primary hepatocytes, human hepatoblastoma (HepG2), human hepatocellular carcinoma (Hep3B) and rat hepatoma (H4IIEC3) cells have either completely lost or drastically reduced the expression of activins C and E. In order to elucidate the biological function of these proteins we transiently transfected HepG2, Hep3B and H4IIEC3 cell lines with rat activin beta(C) or beta(E) cDNA to study the consequences of restoring activin expression in hepatoma cells. Transfection with activin beta(A), a known inhibitor of hepatic DNA synthesis and inducer of apoptosis, served as a positive control. We found that transfection of the three cell lines with activin beta(C) or beta(E), as well as with activin beta(A), reduced the increase in cell number by up to 40% compared with cells transfected with a control plasmid. Co-culture with a CHO cell clone secreting activin C also inhibited HepG2 cell multiplication. Furthermore, the three hepatoma cell lines studied showed an enhanced rate of apoptosis and elevated levels of active caspases in response to activin transfection. These results indicate that activins C and E share the potential to induce apoptosis in liver derived cell lines with activin A and TGFbeta(1).