title: RAF inhibitor resistance is mediated by dimerization of aberrantly spliced BRAF(V600E).
abstract: Activated RAS promotes dimerization of members of the RAF kinase family. ATP-competitive RAF inhibitors activate ERK signalling by transactivating RAF dimers. In melanomas with mutant BRAF(V600E), levels of RAS activation are low and these drugs bind to BRAF(V600E) monomers and inhibit their activity. This tumour-specific inhibition of ERK signalling results in a broad therapeutic index and RAF inhibitors have remarkable clinical activity in patients with melanomas that harbour mutant BRAF(V600E). However, resistance invariably develops. Here, we identify a new resistance mechanism. We find that a subset of cells resistant to vemurafenib (PLX4032, RG7204) express a 61-kDa variant form of BRAF(V600E), p61BRAF(V600E), which lacks exons 4-8, a region that encompasses the RAS-binding domain. p61BRAF(V600E) shows enhanced dimerization in cells with low levels of RAS activation, as compared to full-length BRAF(V600E). In cells in which p61BRAF(V600E) is expressed endogenously or ectopically, ERK signalling is resistant to the RAF inhibitor. Moreover, a mutation that abolishes the dimerization of p61BRAF(V600E) restores its sensitivity to vemurafenib. Finally, we identified BRAF(V600E) splicing variants lacking the RAS-binding domain in the tumours of six of nineteen patients with acquired resistance to vemurafenib. These data support the model that inhibition of ERK signalling by RAF inhibitors is dependent on levels of RAS-GTP too low to support RAF dimerization and identify a novel mechanism of acquired resistance in patients: expression of splicing isoforms of BRAF(V600E) that dimerize in a RAS-independent manner.
authors: Department of Molecular Pharmacology and Chemistry, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA.
authors: Poulikos I
authors: PI
authors: Poulikakos
authors: Yogindra
authors: Y
authors: Persaud
authors: Manickam
authors: M
authors: Janakiraman
authors: Xiangju
authors: X
authors: Kong
authors: Charles
authors: C
authors: Ng
authors: Gatien
authors: G
authors: Moriceau
authors: Hubing
authors: H
authors: Shi
authors: Mohammad
authors: M
authors: Atefi
authors: Bjoern
authors: B
authors: Titz
authors: May Tal
authors: MT
authors: Gabay
authors: Maayan
authors: M
authors: Salton
authors: Kimberly B
authors: KB
authors: Dahlman
authors: Madhavi
authors: M
authors: Tadi
authors: Jennifer A
authors: JA
authors: Wargo
authors: Keith T
authors: KT
authors: Flaherty
authors: Mark C
authors: MC
authors: Kelley
authors: Tom
authors: T
authors: Misteli
authors: Paul B
authors: PB
authors: Chapman
authors: Jeffrey A
authors: JA
authors: Sosman
authors: Thomas G
authors: TG
authors: Graeber
authors: Antoni
authors: A
authors: Ribas
authors: Roger S
authors: RS
authors: Lo
authors: Neal
authors: N
authors: Rosen
authors: David B
authors: DB
authors: Solit
mesh_terms: D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics*; D005091:Exons / Q000235:genetics; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008545:Melanoma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D051379:Mice; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D055503:Protein Multimerization / Q000187:drug effects / Q000235:genetics*; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology; D000077484:Vemurafenib
chemical_list: D007211:Indoles; D050505:Mutant Proteins; D020033:Protein Isoforms; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D000077484:Vemurafenib; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D048049:Extracellular Signal-Regulated MAP Kinases