Due to the important role of the AP-1 complex in human melanoma, the lack of information on FOSL1 function in this tumor type, and the MAPK pathway dependent induction of FOSL1 in melanoma cell lines, we investigated the effect of FOSL1 knockdown on the proliferation of two melanoma cell lines and found a significant inhibition of cells entering the S phase, which was not due to the induction of apoptosis (data not shown). The gene discussed is JUN; the disease is melanoma.