Cyclooxygenase-2 Promotes Human Cholangiocarcinoma Growth: Evidence for Cyclooxygenase-2-Independent Mechanism in Celecoxib-Mediated Induction of p21 and p27 and Cell Cycle Arrest

The expression of cyclooxygenase-2 (COX-2) is increased in human cholangiocarcinoma. However, the biologic function and molecular mechanisms of COX-2 in the control of cholangiocarcinoma cell growth have not been well established. This study was designed to examine the direct effect of COX-2 and its inhibitor celecoxib on the growth of human intrahepatic cholangiocarcinoma cells. Overexpression of COX-2 or treatment with prostaglandin E2 (PGE2) enhanced human cholangiocarcinoma cell growth, whereas antisense depletion of COX-2 in these cells decreased PGE2 production and inhibited growth. These findings demonstrate a direct role of COX-2-mediated PGE2 in the growth regulation of human cholangiocarcinoma cells. Furthermore, the COX-2 inhibitor celecoxib induced a dose-dependent inhibition of cell growth, cell cycle arrest at the G1-S checkpoint, and induction of cyclin-dependent kinase inhibitors p21 and p27. However, the high concentration of celecoxib (50 M) required for inhibition of growth, the incomplete protection of celecoxib-induced inhibition of cell growth by PGE2 or COX-2 overexpression, and the fact that overexpression or antisense depletion of COX-2 failed to alter the level of p21 and p27 indicate the existence of a COX-2-independent mechanism in celecoxib-induced inhibition of cholangiocarcinoma cell growth.