The intermediate-activity (L597V)BRAF mutant acts as an epistatic modifier of oncogenic RAS by enhancing signaling through the RAF/MEK/ERK pathway.
(L597V)BRAF mutations are acquired somatically in human cancer samples and are frequently coincident with RAS mutations. Germline (L597V)BRAF mutations are also found in several autosomal dominant developmental conditions known as RASopathies, raising the important question of how the same mutation can contribute to both pathologies. Using a conditional knock-in mouse model, we show that endogenous expression of (L597V)Braf leads to approximately twofold elevated Braf kinase activity and weak activation of the Mek/Erk pathway. This is associated with induction of RASopathy hallmarks including cardiac abnormalities and facial dysmorphia but is not sufficient for tumor formation. We combined (L597V)Braf with (G12D)Kras and found that (L597V)Braf modified (G12D)Kras oncogenesis such that fibroblast transformation and lung tumor development were more reminiscent of that driven by the high-activity (V600E)Braf mutant. Mek/Erk activation levels were comparable with those driven by (V600E)Braf in the double-mutant cells, and the gene expression signature was more similar to that induced by (V600E)Braf than (G12D)Kras. However, unlike (V600E)Braf, Mek/Erk pathway activation was mediated by both Craf and Braf, and ATP-competitive RAF inhibitors induced paradoxical Mek/Erk pathway activation. Our data show that weak activation of the Mek/Erk pathway underpins RASopathies, but in cancer, (L597V)Braf epistatically modifies the transforming effects of driver oncogenes.
Department of Biochemistry, University of Leicester, Leicester LE1 9HN, United Kingdom.
Catherine
C
Andreadi
Lai-Kay
LK
Cheung
Susan
S
Giblett
Bipin
B
Patel
Hong
H
Jin
Kathryn
K
Mercer
Tamihiro
T
Kamata
Pearl
P
Lee
Alexander
A
Williams
Martin
M
McMahon
Richard
R
Marais
Catrin
C
Pritchard
D000818:Animals; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D004843:Epistasis, Genetic; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D055879:Gene Knock-In Techniques; D006801:Humans; D008168:Lung / Q000473:pathology; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D009154:Mutation; D040081:Protein Array Analysis; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics*; D015398:Signal Transduction; D048008:TNF Receptor-Associated Factor 3; D048490:raf Kinases / Q000378:metabolism*
D047428:Protein Kinase Inhibitors; D048008:TNF Receptor-Associated Factor 3; C482120:Braf protein, mouse; D048493:Proto-Oncogene Proteins B-raf; D048490:raf Kinases; D016283:Proto-Oncogene Proteins p21(ras)