title: RAF inhibitor-induced KSR1/B-RAF binding and its effects on ERK cascade signaling.
abstract: RAF kinase inhibitors can induce ERK cascade signaling by promoting dimerization of RAF family members in the presence of oncogenic or normally activated RAS. This interaction is mediated by a dimer interface region in the RAF kinase domain that is conserved in members of the ERK cascade scaffold family, kinase suppressor of RAS (KSR). In this study, we find that most RAF inhibitors also induce the binding of KSR1 to wild-type and oncogenic B-RAF proteins, including V600E B-RAF, but promote little complex formation between KSR1 and C-RAF. The inhibitor-induced KSR1/B-RAF interaction requires direct binding of the drug to B-RAF and is dependent on conserved dimer interface residues in each protein, but, unexpectedly, is not dependent on binding of B-RAF to activated RAS. Inhibitor-induced KSR/B-RAF complex formation can occur in the cytosol and is observed in normal mouse fibroblasts, as well as a variety of human cancer cell lines. Strikingly, we find that KSR1 competes with C-RAF for inhibitor-induced binding to B-RAF and, as a result, alters the effect of the inhibitors on ERK cascade signaling.
authors: Laboratory of Cell and Developmental Signaling, Center for Cancer Research, National Cancer Institute-Frederick, Frederick, MD 21702, USA.
authors: Melissa M
authors: MM
authors: McKay
authors: Daniel A
authors: DA
authors: Ritt
authors: Deborah K
authors: DK
authors: Morrison
mesh_terms: D000818:Animals; D002289:Carcinoma, Non-Small-Cell Lung; D045744:Cell Line, Tumor; D019281:Dimerization; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D008545:Melanoma; D051379:Mice; D011485:Protein Binding; D047428:Protein Kinase Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism*; D011725:Pyridines / Q000378:metabolism / Q000494:pharmacology; D048490:raf Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C530671:L-779,450; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D011494:Protein Kinases; C097199:KSR-1 protein kinase; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases