Genome-wide screening identifies novel genes implicated in cellular sensitivity to BRAF^V600E expression

The V600E mutation of BRAF (BRAF^V600E), which constitutively activates the ERK/MAPK signaling pathway, is frequently found in melanoma and other cancers. Like most other oncogenes, BRAF^V600E causes oncogenic stress to normal cells, leading to growth arrest (senescence) or apoptosis. Through genome-wide screening, we identified genes implicated in sensitivity of human skin melanocytes and fibroblasts to BRAF^V600E overexpression. Among the identified genes shared by the two cell types are proto-oncogenes ERK2, a component of the ERK/MAPK pathway, and VAV1, a guanine nucleotide exchange factor for Rho family GTPases that also activates the ERK/MAPK pathway. CDKN1A, which has been known to promote senescence of fibroblasts but not melanocytes, is implicated in sensitivity of the fibroblasts but not the melanocytes to BRAF^V600E overexpression. Disruptions of GPR4, a pH-sensing G-protein coupled receptor, and DBT, a subunit of the branched chain α-keto acid dehydrogenase that is required for the second and rate-limiting step of branched amino acid catabolism and implicated in maple syrup urine disease, are the most highly selected in the melanocytes upon BRAF^V600E overexpression. Disruption of DBT severely attenuates ERK/MAPK signaling, p53 activation, and apoptosis in melanocytes, at least in part due to accumulation of branched chain α-keto acids. The expression level of BRAF positively correlates with that of DBT in all cancer types and with that of GPR4 in most cancer types. Overexpression of DBT kills all four melanoma cell lines tested regardless of the presence of BRAF^V600E mutation. Our findings shed new lights on regulations of oncogenic stress signaling and may be informative for development of novel cancer treatment strategies.