Oncogenic BRAF induces whole-genome doubling through suppression of cytokinesis

Melanomas and other solid tumors commonly have increased ploidy, with near-tetraploid karyotypes being most frequently observed. Such karyotypes have been shown to arise through whole-genome doubling events that occur during early stages of tumor progression. The generation of tetraploid cells via whole-genome doubling is proposed to allow nascent tumor cells the ability to sample various pro-tumorigenic genomic configurations while avoiding the negative consequences that chromosomal gains or losses have in diploid cells. Whereas a high prevalence of whole-genome doubling events has been established, the means by which whole-genome doubling arises is unclear. Here, we find that BRAF(V600E), the most common mutation in melanomas, can induce whole-genome doubling via cytokinesis failure in vitro and in a zebrafish melanoma model. Mechanistically, BRAF(V600E) causes decreased activation and localization of RhoA, a critical cytokinesis regulator. BRAF(V600E) activity during G1/S phases of the cell cycle is required to suppress cytokinesis. During G1/S, BRAF(V600E) activity causes inappropriate centriole amplification, which is linked in part to inhibition of RhoA and suppression of cytokinesis. Together these data suggest that common abnormalities of melanomas linked to tumorigenesis – amplified centrosomes and whole-genome doubling events – can be induced by oncogenic BRAF and other mutations that increase RAS/MAPK pathway activity.