Cyclooxygenase-2 promotes hepatocellular carcinoma cell growth through Akt activation: evidence for Akt inhibition in celecoxib-induced apoptosis.

Cyclooxygenase-2 (COX-2)-controlled prostaglandin (PG) metabolism recently has been implicated in the pathogenesis of hepatocellular carcinoma (HCC). However, the biologic role and molecular mechanism of COX-2-mediated PGs in the control of liver cancer growth have not been established. This study was designed to examine the direct effect of COX-2 and its inhibitor celecoxib on the growth control of liver cancer cells. Human HCC cell lines Hep3B and HepG2 transfected with COX-2 expression vector showed increased cell growth and enhanced phosphorylation of serine/threonine protein kinase B (Akt). The level of COX-2 expression and Akt phosphorylation is correlated positively in cultured HCC cells and human liver cancer tissues. Inhibition of Akt activation by phosphatidylinositol 3-kinase (PI3-kinase) inhibitor LY294002 significantly decreased the viability of Hep3B and HepG2 cells (P <.01). These results reveal a novel role of Akt activation in COX-2-induced HCC cell survival. Furthermore, HCC cells treated with the COX-2 inhibitor celecoxib showed significant reduction of Akt phosphorylation and marked morphologic and biochemical characteristics of apoptosis. Overexpression of COX-2 or addition of exogenous PGE(2) partially prevented celecoxib-induced apoptosis (P <.01). In conclusion, our results suggest the involvement of COX-2-dependent and -independent mechanisms in celecoxib-mediated HCC cell apoptosis.