Classical RAS proteins are not essential for paradoxical ERK activation induced by RAF inhibitors

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 119; no. 5
• Main Authors: Lai, Lick Pui, Fer, Nicole, Burgan, William, Wall, Vanessa E, Xu, Bingfang, Soppet, Daniel, Esposito, Dominic, Nissley, Dwight V, McCormick, Frank
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 01.02.2022
• Subjects: Allosteric properties; Animals; Antineoplastic Agents - pharmacology; Biological Sciences; Cell Line, Tumor; Cell proliferation; Cell Proliferation - drug effects; Complexity; Embryo fibroblasts; Extracellular signal-regulated kinase; Fibroblasts; Inhibitors; Intracellular Signaling Peptides and Proteins - drug effects; Intracellular Signaling Peptides and Proteins - metabolism; K-Ras protein; Kinases; Lung cancer; MAP Kinase Signaling System - physiology; Mice; Mouse Embryonic Stem Cells - metabolism; Mutation - drug effects; Phosphorylation; Protein Kinase Inhibitors - pharmacology; Proteins; Proto-Oncogene Proteins B-raf - metabolism; Proto-Oncogene Proteins c-raf - metabolism; raf Kinases - antagonists & inhibitors; raf Kinases - metabolism; Raf protein; ras Proteins - metabolism; ras Proteins - physiology; Signal Transduction - drug effects; Signaling; Transcription; Tumor cell lines; Tumor cells; paradoxical ERK activation; RAS GTPase; MRAS; RAF inhibitors; RAS-related GTPase
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2113491119

RAF inhibitors unexpectedly induce ERK signaling in normal and tumor cells with elevated RAS activity. Paradoxical activation is believed to be RAS dependent. In this study, we showed that LY3009120, a pan-RAF inhibitor, can unexpectedly cause paradoxical ERK activation in KRAS -dependent lung cancer cell lines, when KRAS is inhibited by ARS1620, a KRAS inhibitor. Using H/N/KRAS-less mouse embryonic fibroblasts, we discovered that classical RAS proteins are not essential for RAF inhibitor-induced paradoxical ERK signaling. In their absence, RAF inhibitors can induce ERK phosphorylation, ERK target gene transcription, and cell proliferation. We further showed that the MRAS/SHOC2 complex is required for this process. This study highlights the complexity of the allosteric RAF regulation by RAF inhibitors, and the importance of other RAS-related proteins in this process.