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Publication Abstract from PubMed

RAS-MAPK signaling is fundamental for cell proliferation and altered in most human cancers(1-3). However, our mechanistic understanding of how RAS signals through RAF is still incomplete. While studies revealed snapshots for autoinhibited and active RAF-MEK1-14-3-3 complexes(4), the intermediate steps leading to RAF activation remain unclear. The MRAS-SHOC2-PP1c holophosphatase de-phosphorylates RAF on Serine 259 resulting in 14-3-3 partial displacement and RAF-RAS association(3,5,6). MRAS, SHOC2 and PP1C are mutated in Rasopathies, developmental syndromes caused by aberrant MAPK pathway activation(6-14) and SHOC2 itself has emerged as potential target in RTK-RAS driven tumors(15-18). Despite its importance, structural understanding of the SHOC2 holophosphatase is lacking. Here we reveal a 1.95 A X-ray crystal structure of the MRAS-SHOC2-PP1C complex. SHOC2 bridges PP1C and MRAS via its concave surface and enables reciprocal interactions between all three subunits. Biophysical characterization indicates a cooperative assembly driven by the MRAS GTP-bound active state, an observation extendible to other RAS isoforms. Our findings support the concept of a RAS-driven and multi-molecular model for RAF activation in which individual RAS-GTP molecules recruit RAF-14-3-3 and SHOC2-PP1C to produce downstream pathway activation. Importantly, we find that Rasopathy and cancer mutations reside at protein-protein interfaces within the holophosphatase, resulting in enhancing affinities and function. Collectively our findings shed light on a fundamental mechanism of RAS biology and on mechanisms for clinically observed enhanced RAS-MAPK signaling, thus providing the structural basis for therapeutic interventions.

Structure of the MRAS-SHOC2-PP1C phosphatase complex.,Hauseman ZJ, Fodor M, Dhembi A, Viscomi J, Egli D, Bleu M, Katz S, Park E, Jang DM, Porter KA, Meili F, Guo H, Kerr G, Molle S, Velez-Vega C, Beyer KS, Galli GG, Maira SM, Stams T, Clark K, Eck MJ, Tordella L, Thoma CR, King DA Nature. 2022 Jul 13. pii: 10.1038/s41586-022-05086-1. doi:, 10.1038/s41586-022-05086-1. PMID:35830882^[4]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.