Activation of JNK by TPA promotes apoptosis via PKC pathway in gastric cancer cells
- 生命科学－已发表论文 
AIM: INK cascade plays an important role in cell proliferation, differentiation and apoptosis. However, the exact function of INK cascade for apoptosis induction remains largely unknown. In this study, the role of INK activation stimulated by TPA in the process of apoptosis induction and its signaling transduction pathway in gastric cancer cells were investigated and determined. METHODS: Expressions of mRNA and protein were detected by Northern blot and Western blot. Transcription activity was measured by transient transfection and CAT assay. Apoptotic cells were displayed through staining the nucleus with DAPI and were observed under fluorescence microscope. The apoptotic index was determined by counting 1000 cells randomly. RESULTS: INK protein was stimulated rapidly by TPA, and reached its highest peak within 3 hr, then decreased in a time-dependent manner, but the expression level of INK protein induced by TPA was always keeping higher than that in untreated cells. Similar pattern was seen in c-jun mRNA level induced by TPA. TPA significantly activated the transcriptional activity of activator protein-1 with a TPA-dose-dependent manner. Furthermore, activation of INK was mediated through PKC pathway. Treatment of cells with PKC specific inhibitor, Wortmannin, led to repression of INK even in the presence of TPA. More importantly, all these effects were associated with induction of apoptosis in gastric cancer cells. TPA inducted apoptosis obviously in gastric cancer cells. The apoptotic cells became smaller and rounded, and their nuclei became condensation and fragmentation with brightly stained chromatin. However, suppression of INK by PKC specific inhibitor, Wortmannin, resulted in the decrease of apoptosis induced by TPA in a time-dependent manner, apoptotic index dramatically decreased from 32.56% to 8.71%. CONCLUSION: TPA stimulates INK cascade, including up-regulation of INK protein expression level and c-jun mRNA expression level, and activation of activator protein-1 transcriptional activity. Activation of INK is mediated through PKC pathway, which has an association with induction of apoptosis by TPA. Thus, activation of INK via PKC pathway may represent one of important mechanisms for TPA to induce apoptosis in gastric cancer cells.