NRAS and melanoma: However, c-FOS protein is stabilized by post-translational modifications, such as phosphorylation at serines 362 and 374,22–24 whose levels are directly related with the activation of the MAPK pathway.38 In view of that, c-FOS levels in the analyzed cell lines, besides being regulated by miR-221&222, are dependent upon the phosphorylation status of ERK1/2, as suggested for the NGF-dependent cell survival in PC12 cells.39 This might explain the low level of c-FOS detectable in primary melanomas (as Mel501 and Me1007) lacking any of the frequent mutations in B-RAF or N-RAS genes.