title: C-Raf inhibits MAPK activation and transformation by B-Raf(V600E).
abstract: Activating B-Raf mutations that deregulate the MAPK pathway commonly occur in cancer. Whether additional proteins modulate the enzymatic activity of oncogenic B-Raf is unknown. Here we show that the proto-oncogene C-Raf paradoxically inhibits B-Raf(V600E) kinase activity through the formation of B-Raf(V600E)-C-Raf complexes. Although all Raf family members associate with oncogenic B-Raf, this inhibitory effect is specific to C-Raf. Indeed, a B-Raf(V600E) isoform with impaired ability to interact with C-Raf exhibits elevated oncogenic potential. Human melanoma cells expressing B-Raf(V600E) display a reduced C-Raf:B-Raf ratio, and further suppression of C-Raf increases MAPK activation and proliferation. Conversely, ectopic C-Raf expression lowers ERK phosphorylation and proliferation. Moreover, both oncogenic Ras and Sorafenib stabilize B-Raf(V600E)-C-Raf complexes, thereby impairing MAPK activation. This inhibitory function of C-Raf on B-Raf(V600E)-mediated MAPK activation may explain the lack of co-occurrence of B-Raf(V600E) and oncogenic Ras mutations, and influence the successful clinical development of small molecule inhibitors for B-Raf(V600E)-driven cancers.
authors.affiliation: Li Ka Shing Centre, Cambridge Research Institute, Cancer Research UK, Robinson Way, Cambridge CB2 0RE, UK.
authors.forename: Florian A
authors.initials: FA
authors.lastname: Karreth
authors.forename: Gina M
authors.initials: GM
authors.lastname: DeNicola
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Winter
authors.forename: David A
authors.initials: DA
authors.lastname: Tuveson
mesh_terms: D000818:Animals; D001557:Benzenesulfonates / Q000494:pharmacology; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D004789:Enzyme Activation; D006801:Humans; D047468:Immunoprecipitation; D020935:MAP Kinase Signaling System; D008545:Melanoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009154:Mutation; D041681:NIH 3T3 Cells; D009536:Niacinamide / Q000031:analogs & derivatives; D010671:Phenylurea Compounds; D010766:Phosphorylation; D011485:Protein Binding / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D000090063:Proto-Oncogene Mas; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D000077157:Sorafenib; D014162:Transfection; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001557:Benzenesulfonates; C000715470:MAS1 protein, human; D010671:Phenylurea Compounds; D047428:Protein Kinase Inhibitors; D000090063:Proto-Oncogene Mas; D011725:Pyridines; D009536:Niacinamide; D000077157:Sorafenib; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins