JNK- and Akt-mediated Puma expression in the apoptosis of cisplatin-resistant ovarian cancer cells

BH3 (Bcl-2 homology domain 3)-only proteins have an important role in the cisplatin resistance of cells. However, the effect of BH3-only proteins on cisplatin-resistant ovarian cancer cells has not been thoroughly elucidated. Our results from the present study indicate that Puma plays a critical role in the apoptosis of chemo-resistant ovarian cancer cells treated with BetA (betulinic acid). The reduction of Puma expression inhibits Bax activation and apoptosis. However, p53 gene silencing has little effect on Puma activation. Further experiments demonstrated that Akt-mediated FoxO3a (forkhead box O3a) nuclear translocation and the JNK (c-Jun N-terminal kinase)/c-Jun pathway only partially trigger Puma induction and apoptosis, whereas dominant-negative c-Jun expression with FoxO3a reduction completely inhibits Puma expression and cell death. Furthermore, our results suggest that JNK regulates the Akt/FoxO3a signalling pathway. Therefore the dual effect of JNK can efficiently trigger Puma activation and apoptosis in chemoresistant cells. Taken together, our results demonstrate the role of Puma in BetA-induced apoptosis and the molecular mechanisms of Puma expression regulated by BetA during ovarian cancer cell apoptosis. Our findings suggest that the JNK-potentiated Akt/FoxO3a and JNK-mediated c-Jun pathways co-operatively trigger Puma expression, which determines the threshold for overcoming chemoresistance in ovarian cancer cells.