Vol. 58, Issue 6, 1398-1403, December 2000

Induction of p27^KIP1 as a Mechanism Underlying NS398-Induced Growth Inhibition in Human Lung Cancer Cells

Wen-Chun Hung, Hui-Chiu Chang, Mei-Ren Pan, Te-Hsiu Lee, and Lea-Yea Chuang

School of Technology for Medical Sciences (W.-C.H., M.-R.P., T.-H.L.), Department of Physiology (H.-C.C.) and Department of Biochemistry (L.-Y.C.), Kaohsiung Medical University, Kaohsiung, Taiwan, Republic of China

Increased expression of cyclooxygenase-2 (COX-2) causes enhanced production of prostaglandins, which are emerging as important mediators of growth stimulation of cancer cells. Overexpression of COX-2 has been found in human non-small cell lung cancer tissues and cell lines. In vitro and in vivo studies showed that nonselective cyclooxygenase inhibitors (like aspirin and indomethacin) may suppress growth of lung cancer cells and may prevent lung tumorigenesis induced by the tobacco-specific carcinogens. However, the molecular mechanisms that mediated the anticancer action of these inhibitors are 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 that NS398 inhibited prostaglandin E₂ synthesis and induced G₁ growth arrest in these cells. NS398 specifically up-regulated cyclin-dependent kinase inhibitor p27^KIP1, whereas the expressions of G₁-acting cyclins and cyclin-dependent kinases were not changed. Additionally, NS398 effectively suppressed cyclin E-associated kinase activity in A549 cells. The molecular mechanism responsible for the induction of p27^KIP1 by NS398 was characterized. We found that NS398 did not induce p27^KIP1 through transcriptional activation because this drug could not stimulate the p27^KIP1 promoter. Metabolic labeling experiments showed that the synthesis rate of p27^KIP1 protein was not altered by NS398. Conversely, pulse-chase assays demonstrated that degradation of p27^KIP1 protein was obviously reduced in NS398-treated cells. We conclude that NS398 enhances p27^KIP1 expression via post-translational regulation, and our results provide a new mechanism by which specific COX-2 inhibitors suppress proliferation of cancer cells.