Abstract PR05: Selective contribution of the SHOC2 phosphatase complex to ERK pathway dynamics highlights its potential as a therapeutic target

Abstract

Abstract The ERK signaling pathway is hyperactivated in the majority of human cancers. However, ERK signaling mediates myriad physiologic responses and on-target toxicity has severely limited the clinical efficacy of current ERK pathway inhibitors. Despite the key role of RAF kinases in physiology and disease, we still lack a complete understanding of their regulation. Here we show that dephosphorylation of the conserved ‘S259’ RAF inhibitory site is a key activating step mediated by the SHOC2-MRAS-PP1 complex. Gain-of-function mutations in SHOC2, MRAS, PP1 and CRAF (clustering around S259) found in Noonan syndrome independently validate the important role of the SHOC2 complex in RAF-ERK pathway regulation. We have used CRISPR/cas9 to knock out SHOC2 and the 3 RAF isoforms in colorectal DLD-1 cancer cells. Our data show that SHOC2 is required for EGF-induced dephosphorylation of S365 BRAF, 14-3-3 and MEK dissociation from BRAF and RAF dimerization. However, whereas SHOC2 function is essential for a rapid transient phase of ERK activation in response to EGF stimulation, it is not required for a slow, sustained phase that is instead driven by palmitoylated H/N-RAS proteins and N-region phosphorylation of CRAF. Redundancy makes SHOC2 dispensable for ERK activation and proliferation in 2D whereas KRAS mutant cells rely on SHOC2 for ERK signaling under anchorage-independent/3D conditions, which thus presents a therapeutic opportunity. This study highlights a context-dependent contribution of SHOC2 to ERK pathway dynamics that is preferentially engaged by KRAS oncogenic signaling and provides a biochemical framework for how targeting the SHOC2 regulatory node would allow for selective ERK pathway inhibition, likely to provide improved therapeutic margins in the clinic. This abstract is also being presented as Poster A32. Citation Format: Isabel Boned del Rio, Lucy C. Young, Sibel Sari, Greg G. Jones, Amandeep Bhamra, Silvia Surinova, Pablo Rodriguez-Viciana. Selective contribution of the SHOC2 phosphatase complex to ERK pathway dynamics highlights its potential as a therapeutic target [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr PR05.