Abstract 2401: Oncogenic H-Ras is a key regulator of death receptor-induced apoptosis

Abstract

Abstract Ras oncogenes, including H-Ras, K-Ras and N-Ras, are widely implicated in tumorigenesis. Oncogenic K-Ras mutations are found in about 30% of human tumors rendering constitutive activation of Ras-dependent pathways to promote cell proliferation, survival, and transformation. By contrast, H-Ras mutations are rarely detected; however, its expression levels are often elevated in cancer cells. This study aims to identify the molecular pathways by which H-Ras exerts its oncogenic activity. Our previous data drew a link between H-Ras and apoptosis via death receptors (DRs), particularly DR4 and DR5 that are known to induce apoptosis upon ligation of their cognate ligand namely Tumor Necrosis Factor-related apoptosis inducing ligand (TRAIL). We showed that wild-type H-Ras was overexpressed in several human cancer cell lines that were resistant to TRAIL (Chen et al, Oncotarget, 2014). In this study, we tested H-Ras expression and its relationship with cellular susceptibility to TRAIL in a large panel of human cancer cell lines and xenograft tumor models. This included the use of stable cell lines that were developed via transfection of doxycycline-inducible sh-RNA against H-Ras transcript. These cancer cell lines were used to detect surface expression of DR4 and DR5 as well as TRAIL-induced apoptosis. A xenograft mouse model was developed by injecting the TRAIL-resistant H-Ras mutant cells into athymic mice. The mice were fed with water containing doxycycline, which effectively induced sh-RNA mediated reduction of H-Ras protein in the xenografts, and were subjected to intratumor injection with TRAIL, and immunohistochemistry analysis. Our results show that wild-type H-Ras GTPase is upregulated in TRAIL-resistant cells compared to TRAIL-sensitive cells. The elevated H-Ras expression correlated with a loss of DR4 and DR5 receptor expression on the plasma membrane in TRAIL-resistant cells. Knockdown of H-Ras in TRAIL-resistant cells restored the surface expression of DR4 and DR5, and subsequently increased apoptosis in response to TRAIL treatment. The xenograft mice developed tumors upon injection of the H-Ras mutant cells. Knockdown of H-Ras and TRAIL injection showed an increase of apoptotic markers in the tumor. This study confirms our previous report that high expression levels of H-Ras, while is found in its wild-type state, protect cancer cells from TRAIL induced apoptosis. As a TNF-related cytokine, TRAIL has been implicated in tumor immune surveillance by inducing apoptosis in target cells. H-Ras appears to suppress surface expression of DR4 and DR5, thereby promoting cancer cell survival through evasion from the immune surveillance mechanisms. These data have potential implications in identifying novel therapeutic targets for the development of effective cancer therapy. Citation Format: Su-Ryun Kim, Ancy D. Nalli, Baolin Zhang. Oncogenic H-Ras is a key regulator of death receptor-induced apoptosis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2401.