Heat shock protein 27 protects L929 cells from cisplatin-lnduced apoptosis by enhancing Akt activation and abating suppression of thioredoxin reductase activity

Abstract

Purpose: Heat shock protein 27 (Hsp27) is up-regulated in multiple malignancies and implicated in cisplatin resistance. It is attempted to know how Hsp27 endues cell with cisplatin resistance by interfering with upstream of both apoptosis signal - regulating kinase 1 (ASK1)/p38 mitogen-activated protein kinase - activated apoptotic signaling and serine/threonine kinase Akt-dependent survival signaling. Experimental Design: The mouse L929 cells stably transfected with human Hsp27 or its dominant-negative mutant and the human cervical cancer HeLa cells transfected with Hsp27 si RNA were used. The cisplatin-induced apoptosis and activation of ASK1, p38, and Akt were compared in control cells, cells overexpressing Hsp27, and cells with their endogenous Hsp27 knocked down. Results: Hsp27 effectively protected the cells from cisplatin-induced DNA fragmentation. The p38 inhibitors obviously decreased whereas Akt inhibitors markedly increased the apoptotic fraction in cisplatin-treated cells. Overexpression of Hsp27 doubly enhanced the drug-induced Akt activation while substantially depressing the drug-induced activation of ASK1 and p38. Knockdown of the endogenous Hsp27 in HeLa cells resulted in the effects opposite to that observed in the Hsp27-overexpressing cells. Enhancement of Akt activation is associated with complex formation between Akt and Hsp27, whereas depression of ASK1/p38 activation is attributed to a reversion of the drug-induced inhibition of thioredoxin reductase activity and subsequent oxidation of thioredoxin. Conclusions: Hsp27 endues cells with cisplatin resistance via depression of the drug-induced ASK1/p38 activation and enhancement of the drug-induced Akt activation. This study revealed the intervention of Hsp27 in upstream of both ASK1/p38 apoptotic signaling and phosphatidylinositol 3-kinase/Akt survival signaling.Therefore, the inhibition of Hsp27 may be a novel strategy of cancer chemotherapy. © 2007 American Association for Cancer Research.