Growth suppression by dual BRAF(V600E) and NRAS(Q61) oncogene expression is mediated by SPRY4 in melanoma.

The underlying forces that shape mutational patterns within any type of cancer have been poorly characterized. One of the best preserved exclusionary relationships is that between BRAF(V600E) and NRAS(Q61) in melanomas. To explore possible mechanisms which could explain this phenomenon, we overexpressed NRAS(Q61) in a set of BRAF(V600E) melanoma lines and vice versa. Controlled expression of a second activating oncogene led to growth arrest ("synthetic suppression") in a subset of cells, which was accompanied by cell cycle arrest and senescence in several melanoma cell lines along with apoptosis. Through differential gene expression analysis, we identified SPRY4 as the potential mediator of this synthetic response to dual oncogene suppression. Ectopic introduction of SPRY4 recapitulated the growth arrest phenotype of dual BRAF(V600E)/NRAS(Q61) expression while SPRY4 depletion led to a partial rescue from oncogenic antagonism. This study thus defined SPRY4 as a potential mediator of synthetic suppression, which is likely to contribute to the observed exclusivity between BRAF(V600E) and NRAS(Q61R) mutations in melanoma. Further leverage of the SPRY4 pathway may also hold therapeutic promise for NRAS(Q61) melanomas.