Suppression of BRAF^V599E in human melanoma abrogates transformation

Activating mutations in the BRAF serine/threonine kinase are found in >70% of human melanomas, of which >90% are BRAF^V599E. We sought to investigate the role of the BRAF^V599E allele in malignant melanoma. We here report that suppression of BRAF^V599E expression by RNA interference in cultured human melanoma cells inhibits the mitogen-activated protein kinase cascade, causes growth arrest, and promotes apoptosis. Furthermore, knockdown of BRAF^V599E expression completely abrogates the transformed phenotype as assessed by colony formation in soft agar. Similar targeting of BRAF^V599E or wild-type BRAF in human fibrosarcoma cells that lack the BRAF^V599E mutation does not recapitulate these effects. Moreover, these results are specific for BRAF, as targeted interference of CRAF in melanoma cells does not significantly alter their biological properties. Thus, when present, BRAF^V599E appears to be essential for melanoma cell viability and transformation and, therefore, represents an attractive therapeutic target in the majority of melanomas that harbor the mutation.