The Heat Shock Pathway In Cancer Therapy

Human breast tumors always resist to such therapy as hyperthermia due toheat shock protein (Hsps) overexpression. In the present study, we inhibited theexpression of Hsps by blocking the heat shock transcription factor 1 (HSF1)function with its dominant-negative mutant (mHSF1) in Bcap37 cells, athermotolerant breast cancer cell line. We found that retrovirus mediated transferof mHSF1 led to massive cell death of Bcap37 after hyperthermia and failed toestablish thermotolerance in Bcap37 cells. mHSF1 sensitized Bcap37 cells tohyperthermia by promoting apoptosis induced by heat shock. The apoptosis ratiowas correlated with the HSF1 status. We also examined the efficacy of mHSF1gene therapy in nude mouse. mHSF1 transfection led to diminution of tumorgrowth with hyperthermia therapy. We then studied the possible role of the stress induced apoptotic pathway,caspase-3 or c-Jun N-terminal kinase (JNK) signaling pathway, in this abolishingprocess of thermotolerance. Other hyperthermia-induced kinases implicated incell survival and death, such as Akt, ERK and p38, were also investigated. Theresults indicated that mHSF1 abolished acquired or intrinsic thermotolerance inBcap37 cells by enhancing caspase-3 and JNK pathways after hyperthermia, andinterference with either one of them attenuated hyperthermia-induced apoptosis.Furthermore, caspases inhibitors had no effect on mHSF1-mediated JNKactivation, while JNK inhibitor led to caspase-3 activity suppression afterhyperthermia, suggesting that JNK was upstream of the caspase-3 pathway. 中国科学院上海生命科学研究院生物化学与细胞生物学研究所 博士学位论文 4第一部分 HSF1 的显性负突变体可致肿瘤热敏感Conversely, specific inhibitors of Akt, ERK or p38 did not influence the effect ofmHSF1, indicating that these kinases were not implicated in this abolishingprocess. In addition, we found that the development of acquired thermotoleranceof Bcap37 cells was associated with the suppression of JNK activation after mildpreheat treatment and was not reduced by Akt, ERK or p38 inhibition. In contrast,the intrinsic thermotolerance of Bcap37 cells was due to the intrinsic high levelsof Akt and ERK activities since Akt or ERK inhibition resulted in increasedthermosensitivity of Bcap37 cells. Our results suggest that mHSF1 plays avaluable role in the thermotolerance abolishment of Bcap37 cells, which likelycontributes to tumor therapy in combination with hyperthermia.