Non-steroidal anti-inflammatory drug-induced apoptosis in gastric cancer cells is blocked by protein kinase C activation through inhibition of c-myc

Apoptosis plays a major role in gastrointestinal epithelial cell turnover, ulcerogenesis and tumorigenesis. We have examined apoptosis induction by no n-steroidal anti-inflammatory drugs (NSAIDs) in human gastric (AGS) cancer cells and the role of protein kinase C (PKC) and apoptosis-related oncogene s. After treatment with aspirin or indomethacin, cell growth was quantified by MTT assay, and apoptosis was determined by acridine orange staining, DN A fragmentation and flow cytometry. The mRNA and protein of p53, p21(waf1/c ip1) and c-myc was detected by Northern and Western blotting respectively. The influence of PKC on indomethacin-induced apoptosis was determined by co -incubation of 12-O-tetradecanoylphorbol 13-acetate (TPA). The role of c-my c was determined using its antisense oligonucleotides. The results showed t hat both aspirin and indomethacin inhibited cell growth and induced apoptos is of AGS cells in a dose- and time-dependent manner, without altering the cell cycle. Indomethacin increased c-myc mRNA and protein, whereas p53 and p21(waf1/cip1) were unchanged. Down-regulation of c-myc by its antisense ol igonucleotides reduced apoptosis induction by indomethacin. TPA could inhib it indomethacininduced apoptosis and accumulate cells in G(2)/M. Overexpres sion of c-myc was inhibited by TPA and p21(waf1/cip1) mRNA increased. In co nclusion, NSAIDs induce apoptosis in gastric cancer cells which may be medi ated by up-regulation or c-myc proto-oncogene. PKC activation can abrogate the effects of NSAIDs by decreasing c-myc expression.