Induction of p27(KIP1) as a mechanism underlying NS398-Induced growth inhibition in human lung cancer cells

Increased expression of cyclooxygenase-2 (COX-2) causes enhanced production of prostaglandins, which are emerging as important mediators of growth sti mulation of cancer cells. Overexpression of COX-2 has been found in human n on-small cell lung cancer tissues and cell lines. In vitro and in vivo stud ies showed that nonselective cyclooxygenase inhibitors (like aspirin and in domethacin) may suppress growth of lung cancer cells and may prevent lung t umorigenesis induced by the tobacco-specific carcinogens. However, the mole cular mechanisms that mediated the anticancer action of these inhibitors ar e not well defined. In this study, we examined the effect of a specific COX -2 inhibitor, N-(2-cyclohexyloxy-4-nitrophenyl) methanesulfonamide (NS398), on high COX-2-expressing A549 lung cancer cells. Our results indicated tha t NS398 inhibited prostaglandin E-2 synthesis and induced G(1) growth arres t in these cells. NS398 specifically up-regulated cyclin-dependent kinase i nhibitor p27(KIP1), whereas the expressions of G(1)-acting cyclins and cycl in-dependent kinases were not changed. Additionally, NS398 effectively supp ressed cyclin E-associated kinase activity in A549 cells. The molecular mec hanism responsible for the induction of p27(KIP1) by NS398 was characterize d. We found that NS398 did not induce p27(KIP1) through transcriptional act ivation because this drug could not stimulate the p27(KIP1) promoter. Metab olic labeling experiments showed that the synthesis rate of p27(KIP1) prote in was not altered by NS398. Conversely, pulse-chase assays demonstrated th at degradation of p27(KIP1) protein was obviously reduced in NS398-treated cells. We conclude that NS398 enhances p27(KIP1) expression via post-transl ational regulation, and our results provide a new mechanism by which specif ic COX-2 inhibitors suppress proliferation of cancer cells.