Abstract 84: Characterization of oncogenic KRAS A59 alleles and their cooperation with the MAPK signaling pathway

Abstract

Abstract The Kirsten rat sarcoma (KRAS) proto-oncogene regulates signaling pathways that control proliferation (e.g. MAPK pathway), metabolism and survival (e.g. AKT pathway), and apoptosis (e.g. Hippo pathway). Mutations in KRAS are found in 40% of colorectal cancers (CRC). However, there are no FDA-approved drugs for CRC that target this oncogene. One reason why developing drugs against KRAS is difficult is because a number of different oncogenic alleles have been identified. Thus, an allele-specific approach to target KRAS is necessary. In turn, this approach requires a detailed understanding of their structure and function to drive cell transformation and tissue dysregulation. Our goal is to characterize the function of KRAS A59T in CRC. These alleles are interesting for a number of reasons. First, A59T discriminates retroviral homologues of mammalian RAS from their cellular counterparts. Second, unlike other oncogenic alleles, the KRAS A59T protein undergoes autophosphorylation, the biological function of which is unknown. Third, patient data show that A59 alleles of KRAS frequently co-occur with other genetic alterations in the MAPK signaling pathway, which is uncommon for other KRAS alleles. We hypothesize that KRAS autophosphorylation promotes CRC in a manner that is independent, but cooperative, with the MAPK signaling pathway. To test this hypothesis, we first characterized the function of KRAS A59T and its phosphomimetic A59E using in silico and biochemical techniques, along with classic assays of cell transformation. Next, we generated a new genetically engineered mouse model, K-Ras+/LSL-A59E, in order to test how KRAS autophosphorylation cooperates with other oncogenic mechanisms of MAPK pathway activation to alter colon homeostasis and model colon tumorigenesis. Consistent with our hypothesis, KRAS autophosphorylation and A59E inhibit KRAS-effector interactions that activate the MAPK, AKT, and Hippo signaling pathways. How this change in function alters the ability of K-RasA59E, versus K-RasG12D, to promote hyperproliferation and tumor development in combination with N-RasQ61K and Apc loss in the mouse colon, is currently underway. Ultimately, these studies bring us closer to discovering allele-specific vulnerabilities of KRAS and provide a means to test less understood aspects of oncogenic KRAS signaling. Citation Format: Christian W. Johnson, Elizabeth M. Terrell, Christin E. Burd, Deborah Morrison, Kevin M. Haigis. Characterization of oncogenic KRAS A59 alleles and their cooperation with the MAPK signaling pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 84.