Heat Shock Protein 70I Promotes Carcinogen-induced Liver Tumorigenesis by Regulating Hepatic Metabolism and Insulin Sensitivity

Abstract

Hepatocellular carcinoma (HCC) is one of the most lethal and prevalent cancers in the world. The treatment options for HCC, however are very limited. In mice, the carcinogen diethylnitrosamine (DEN) induces HCC, which has been proven to be comparable to human HCC in many key aspects. DEN-induced HCC leads to initial hepatocyte death followed by compensatory proliferation and inflammatory response. The cycles of hepatocyte death and compensatory proliferation eventually lead to genomic mutations and HCC development. The inducible heat shock protein-HSP70 (HSP70i) is overexpressed in a number of malignancies, including liver cancer. Tumor cells have metabolic changes which producing intermediates for cell growth and division. We hypothesize that HSP70i plays a role in HCC development through its control of glucose metabolism. To determine the impact of HSP70i in HCC, we treated a cohort of wild-type and hsp70i-deficient mice using the carcinogen DEN. Tumor development in the liver was examined after 8 months. Results show that the deletion of hsp70i leads to a significant delay in HCC development. DEN-treated hsp70i-/- mice exhibit reduced levels of alanine aminotransferase (ALT) and asparate aminotransferase (AST) in the serum compared to wild-type (WT) mice, suggesting reduced liver damage in hsp70i-/- mice. Furthermore, to investigate the mechanisms underlying HSP70i inhibition of tumorigenesis, we performed TUNEL assays to detect hepatocyte death, and Ki67 immunostaining to detect hepatocyte proliferation. As expected, hsp70i-/- mice exhibit a lower level of cell death and lower levels of cellular proliferations compared to wild-type mice. In addition, hsp70i-/- mice exhibit increased glucose consumption as evident by an increase in key enzymes involved in both glycolysis and TCA cycle. Low net glucose production induces lower lipid accumulation. Finally, treatment of DEN-treated wild-type mice with 2-phenylethynesulfonamid (PES), which is an HSP70i specific inhibitor, also delays HCC development. Overall, the alterations in the metabolic pathways in hsp70i null mice appear to contribute to delayed HCC development. Therefore, we conclude that HSP70i can be a powerful therapeutic target for HCC.