Cyclooxygenase-2 (COX-2) is directly involved but not decisive in proliferation of human hepatocellular carcinoma cells

Expression of cyclooxygenase-2 (COX-2) is involved in the chronic inflammation-related development of hepatocellular carcinoma (HCC), and the use of selective COX-2 inhibitors might provide new chemoprevention strategies for HCC. However, the role of the COX-2 in hepatocarcinogenesis remains obscure, particularly as it has been primarily studied with selective COX-2 inhibitors that may affect other cellular proteins involved in cell proliferation. Therefore, we investigated the effects of the inhibition of COX-2 by the selective COX-2 inhibitor NS-398 as well as by COX-2 specific small interfering RNA (siRNA) in the human HCC cell lines Hep3B and SNU-387. These cell lines expressed COX-2, and NS-398 induced apoptosis of these cells. NS-398 inhibited more than 60% of prostaglandin E-2 (PGE2) production and cell proliferation in a concentration-dependent manner in these cells. The inhibition of proliferation was almost restored with PGE2 supplement, suggesting that NS-398 may inhibit cell growth partially through inhibition of COX-2 and PGE2 production in human HCC cells. However, treatment with NS-398 led to increased expression of COX-2 in Hep3B and SNU-387 cells. To examine the effect of COX-2 depletion on these cells, we electroporated COX-2-specific siRNAs into SNU-387 cells. We observed significant, sequence-specific reductions in COX-2 expression, PGE2 production, and cell proliferation, though the reduction in cell proliferation was less than that induced by NS-398. In conclusion, these data suggest that COX-2 itself is directly involved, though not decisively, in proliferation of human HCC cells. RNA interference may provide a useful tool for manipulating COX-2-related hepatocarcinogenesis in research and therapeutic settings.