Near‐genomewide RNA i screening for regulators of BRAF V 600E ‐induced senescence identifies RASEF , a gene epigenetically silenced in melanoma

Summary The activation of oncogenes in primary cells blocks proliferation by inducing oncogene‐induced senescence ( OIS ), a highly potent in vivo tumor‐suppressing program. A prime example is mutant BRAF , which drives OIS in melanocytic nevi. Progression to melanoma occurs only in the context of additional alteration(s) like the suppression of PTEN , which abrogates OIS . Here, we performed a near‐genomewide short hairpin (sh) RNA screen for novel OIS regulators and identified by next generation sequencing and functional validation seven genes. While all but one were upregulated in OIS , depletion of each of them abrogated BRAF V 600E ‐induced arrest. With genome‐wide DNA methylation analysis, we found one of these genes, RASEF , to be hypermethylated in primary cutaneous melanomas but not nevi. Bypass of OIS by depletion of RASEF was associated with suppression of several senescence biomarkers including senescence‐associated ( SA )‐ β ‐galactosidase activity, interleukins, and tumor suppressor p15 INK 4B . Restoration of RASEF expression inhibited proliferation. These results illustrate the power of sh RNA OIS bypass screens and identify a potential novel melanoma suppressor gene.