Abstract 4360: Altering the regulation of KRAS GTPase cycle via Src and SHP2 creates a potential therapeutic vulnerability for pancreatic cancer

Abstract

Abstract More than 30% of all human cancers have Ras mutations and more than 95% of pancreatic cancers harbor KRAS mutations. However, therapeutically targeting cancers driven by oncogenic Ras mutations is still an ongoing investigation. KRas is a small GTPase found in either a GDP-bound inactive form or a GTP-loaded activated form. The activated form of KRas localizes on the membrane where it binds and activates downstream effector proteins such as Raf kinases. GDP-bound Ras can be activated by nucleotide exchange of GTP for GDP, a reaction that is catalyzed by guanine nucleotide exchange factors (GEFs). Ras is inactivated by hydrolysis of GTP, which is assisted by GTPase activating proteins (GAPs). It was recently reported that Ras can be tyrosyl phosphorylated by Src and dephosphorylated by SHP2 (PNAS 2014;111(36):E3785-94; Nat Commun 2015;6:8859). Here we have characterized the structural and functional alterations of Src-phosphorylated KRas to mechanistically explain the impact of tyrosyl phosphorylation on the GTPase cycle. Our NMR and MS analyses show that Src phosphorylates KRas at Tyr32 and Tyr64, which perturbs the chemical shifts of several residues in each of the two "switch" regions that mediate interactions with effectors and regulators. Using real-time NMR and biolayer interferometry (Octet) assays, we demonstrated the negative impact of KRas phosphorylation on the GTPase cycle as well as BRAF binding. Conversely, the SH2 domain containing inositol 5-phosphatase 2 (SHP2) dephosphorylates KRAS and reverses Src-induced phosphorylation. In vivo, either the pharmacologic inhibition or genetic ablation of SHP2 promotes cell death in several KRAS mutant cancers. Our findings reveal that altering the KRas GTPase cycle regulation via the balance of Src and SHIP2 activities may create a therapeutic vulnerability for pancreatic cancer. Citation Format: Teklab Gebregiworgis, Christopher B. Marshall, Yoshihito Kano, Nikolina Radulovich, Ming-Sound Tsao, Michael Ohh, Mitsuhiko Ikura. Altering the regulation of KRAS GTPase cycle via Src and SHP2 creates a potential therapeutic vulnerability for pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4360.