A K-RAS ONCOGENE INCREASES RESISTANCE TO SULINDAC-INDUCED APOPTOSIS IN RAT ENTEROCYTES

Background & Aims: Mutations of c-K-ras occur commonly in colonic neop lasms. The aim of this study was to determine how c-K-ras mutations al ter the responses to the chemopreventive agent sulindac. Methods: The parental rat intestinal cell line IEC-18 and c-K-ras-transformed deriv atives were treated with sulindac sulfide. Cell cycle distribution was determined by flow-cytometric analysis (fluorescence-activated cell s orter), apoptosis by DNA fragmentation (laddering), flow cytometry, an d microscopy, and changes in gene expression by immunoblotting. Result s: Sulindac sulfide inhibited cell growth and induced apoptosis in a t ime- and dose-dependent manner more rapidly in and at lower concentrat ions in parental cells than ras-transformed cells. Expression of the s ulindac sulfide arrested cells in G0/G1, but cells entered apoptosis t hroughout the cell cycle. Proapoptotic protein Bak was relatively high in untreated parental cells and increased markedly after sulindac sul fide but was low in untreated ras-transformed cells and did not increa se after sulindac sulfide. Expression of other Bcl-2 family members wa s unchanged after sulindac sulfide. However, sulindac sulfide reduced levels of cyclin D1 protein and cyclin E- and cyclin D1-associated kin ase activity. Conclusions: c-K-ras-transformed enterocytes are relativ ely resistant to sulindac sulfide-induced growth inhibition and apopto sis, which may result from specific reduction of bak expression.