The pBabe-Puro-BRAF-V600E plasmid (Addgene plasmid #15269) was used for introduced overexpression of BRAF V600E in cells that naturally did not harbor BRAF V600E mutation. The BRAF WT was generated from plasmid carrying the V600E mutation (T1799A) using the QuikChange Lightning Site-Directed Mutagenesis Kit (Stratagene, La Jolla, CA) with primers listed in Supplementary Table 2. Retroviral particles were produced by co-transfecting HEK293T cells with the pBabe-Puro-BRAF-V600E or pBabe-Puro-BRAF-WT plasmid, the packaging plasmid pUMVC, and the envelope plasmid pCMV-VSV-G using Lipofectamine 3000 (Invitrogen). The retroviral supernatant was harvested 48 h after transfection. The WRO cells were infected with a mixture of retrovirus and 8 μg ml−1 polybrene (Millipore) and cell pools with stable transfection were selected by 2 μg ml−1 puromycin (Sigma-Aldrich).