1. RAF Inhibitors Activate the MAPK Pathway by Relieving Inhibitory Autophosphorylation
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Tobi Nagel, Frank McCormick, John Tellew, John Chan, Huili Zhai, Darrin Stuart, Marco Wallroth, Stephen F. Hardy, Matthew Holderfield, Laura Tandeske, Mohammad Hekmat-Nejad, and Hanne Merritt
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MAPK/ERK pathway ,Proto-Oncogene Proteins B-raf ,Cancer Research ,endocrine system diseases ,MAP Kinase Signaling System ,medicine.disease_cause ,Adenosine Triphosphate ,Cell Line, Tumor ,medicine ,Humans ,Phosphorylation ,Protein kinase A ,neoplasms ,chemistry.chemical_classification ,Oncogene ,Chemistry ,Autophosphorylation ,Cell Biology ,digestive system diseases ,Proto-Oncogene Proteins c-raf ,Enzyme ,Oncology ,Cell culture ,Cancer research ,raf Kinases ,Carcinogenesis ,V600E - Abstract
ATP competitive inhibitors of the BRAF(V600E) oncogene paradoxically activate downstream signaling in cells bearing wild-type BRAF (BRAF(WT)). In this study, we investigate the biochemical mechanism of wild-type RAF (RAF(WT)) activation by multiple catalytic inhibitors using kinetic analysis of purified BRAF(V600E) and RAF(WT) enzymes. We show that activation of RAF(WT) is ATP dependent and directly linked to RAF kinase activity. These data support a mechanism involving inhibitory autophosphorylation of RAF's phosphate-binding loop that, when disrupted either through pharmacologic or genetic alterations, results in activation of RAF and the mitogen-activated protein kinase (MAPK) pathway. This mechanism accounts not only for compound-mediated activation of the MAPK pathway in BRAF(WT) cells but also offers a biochemical mechanism for BRAF oncogenesis.
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