Abstract 1072: Activation of the Ras signaling pathway promotes the over-expression of anti-apoptotic heme oxygenase-1 in human renal cancer

Abstract

Abstract Activation of the proto-oncogene ras may play a critical role in the development and rapid progression of different types of human cancers, including renal cancer. It has been shown that the Ras pathway can mediate pro-survival signals in cancer cells by inhibiting cellular apoptosis. It is established that the cytoprotective enzyme heme oxygenase-1 (HO-1) is over-expressed in several cancers, and may play a significant role in the growth and metastasis of tumors by inducing cell survival pathways. However, it is not known if there is an association between Ras activation and HO-1 over-expression in cancer. We have recently demonstrated that the treatment of human renal cancer cells with the immunosuppressive agent cyclosporine may activate the H-Ras pathway, and promote a rapid progression of the disease. We have also shown that HO-1 is over-expressed in human renal cancer, and plays a key role in the survival of renal cancer cells by inhibiting cellular apoptosis. Here, we wished to analyze if the activation of H-Ras pathway can regulate the expression of HO-1 in two different human renal cancer cell lines 786-0 and Caki-1. In co-transfection assays, using a full-length HO-1 promoter-luciferase construct, we found that the activated form of H-Ras (H-Ras12V) promoted HO-1 transcriptional activation as observed by increased luciferase activity. We also found that the activation of H-Ras increased the mRNA expression of HO-1 as observed by real-time PCR. By using a dominant-inhibitory mutant construct H-Ras17N, we confirmed that the inhibition of H-Ras expression significantly decreased HO-1 promoter activity. We next wanted to determine which effector molecule(s) (Raf, Rho and PI-3K) is functional for H-Ras-mediated HO-1 over-expression. We made use of three different effector domain mutant constructs of H-Ras; Ras(12V,35S) retains full-length Raf-1 binding activity, Ras(12V,37G) retains Rho binding activity, and Ras(12V,40C) retains PI-3K binding activity. In co-transfection assays using these effector domain mutant constructs, we observed that the Ras-induced HO-1 transcriptional activation is mediated primarily through the Raf-1 signaling pathway. Together, our findings suggest that the Ras-Raf signaling pathway might play an important role in the survival of human renal cancer cells through the induction of HO-1 over-expression. Thus, targeting this H-Ras pathway for HO-1 over-expression might act as novel therapeutics to inhibit human renal tumors through the induction of cellular apoptosis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1072. doi:10.1158/1538-7445.AM2011-1072