Targeting of Mortalin-Mutant p53 Interactions by Mortalin shRNA Leads to Selective Apoptotic Death of Human Hepatocellular Carcinoma

Abstract

Restoration of deregulated apoptotic pathway is one of the main strategies for cancer therapeutics. Mortalin/mitochondria heat shock protein 70 (mtHSP70) is a stress protein that is overexpressed in cancer cells and tissues, which has been proposed to have a role in human carcinogenesis. It was previously shown that mortalin interacts with wild type tumor suppressor protein p53 resulting in abrogation of its transcriptional activation and control of centrosome duplication functions, both tightly related to cancer development. Normal human fibroblasts were shown to lack mortalin-wild type p53 interactions. It was also identified as a marker for hepatocellular carcinoma (HCC) metastasis and recurrence by proteomics analysis of matched tumor and nontumor tissues. In this study, we examined mortalin expression in 100 HCC patients and found that its upregulation has strong correlation with tumor stage and microsatellite formation. In order to validate the critical role of mortalin in HCC development and progression, we recruited its shRNA in eight HCC-derived cell lines varying in p53 status (loss/mutant p53/wild type). MortalinshRNA caused apoptosis in most, but not all, HCC cell lines. By examination of mortalin-p53 interactions and molecular pathway for apoptosis, we found that induction of apoptosis by mortalinshRNA depended on occurrence of mortalin-mutant p53 interactions; the cell lines that lacked these interactions escaped apoptosis. Most importantly, mortalin-p53 interactions were induced by cellular stress by chemotherapeutic drug (cisplatin) following which the cells were sensitized to mortalin shRNA induced apoptosis. Based on the data, a model for mortalin and p53 interactions in cancer (physiologically a stressed condition) cells and use of mortalin-shRNA for selective killing of cancer cells is documented. Since p53 mutations are found in more than 80% of the tumors, mortalin shRNA is proposed as an effective cancer cell specific therapeutic tool.