Heat shock protein 70-2 (HSP70-2) a novel cancer testis antigen that promotes growth of ovarian cancer

Abstract

Heat shock protein 70-2 (HSP70-2) is known to be involved in tumor progression. However, its molecular role and mechanism in epithelial ovarian cancer (EOC) remains unknown. In the present investigation, we examined the role of HSP70-2 in cell cycle, apoptosis and epithelial mesenchymal transition pathways in EOC cells in in vitro and in-vivo xenograft mouse model. To investigate the role of HSP70-2 in ovarian cancer, plasmid driven short hairpin RNA approach was used to examine HSP70-2 gene and protein expression in ovarian cancer cell line A-10 (origin: serous papillary cystadenocarcinoma), Caov-3 (origin: adenocarcinoma) and SKOV3 (origin: adenocarcinoma; derived from metastatic site: ascites) by RT-PCR, quantitative-PCR, immunohistochemistry and Western blotting. Light microscopy, scanning electron microscopy, viability tests, and flow cytometry were used to study the cellular proliferation, onset of senescence, colony forming ability and morphological features of cancer cells. Cell migration and invasion ability was evaluated by wound healing and Boyden chamber assays. Further, we studied the effect of HSP70-2 protein ablation on human ovarian xenograft mice model. At molecular level, various molecules involved in apoptosis, cell cycle and epithelial-mesenchymal-transition were also examined both in in-vitro and in-vivo xenograft mouse model. The knockdown of HSP70-2 expression by gene silencing resulted in the onset of apoptosis, senescence, reduced cellular growth and colony forming ability of EOC cells. Interestingly, the migration, invasion and wound healing abilities of cells were also significantly inhibited. In addition, the ablation of HSP70-2 resulted in the upregulation of cytochrome-C, caspase 3, caspase 7, caspase 9, APAF1, BAX, BIM, BAK, BAD, BID, PUMA, NOXA, p16, p21, Rb, E-cadherin, cytokeratin 18, EMA in these cells as well as in the xenograft tumor specimens. However, there was downregulation of PARP1, BCL-2, Bcl-xL, MCL-1, Survivin, XIAP, cIAP2, CDK1, CDK2, CDK4, CDK6, cyclin D1, cyclin E, cyclin A2, cyclin B1, p-Rb, N-cadherin, SNAIL, SLUG, VIMENTIN, SMA, MMP2, MMP3, MMP9 and TWIST in these samples. Furthermore, the xenograft studies showed significant reduction in the tumor growth. Our results suggest that HSP70-2 can promote cellular growth and invasion of EOC cells and therefore may be a potential therapeutic target in EOC.