CDK4 and melanoma: To verify the relationship between cell cycle regulation in melanoma cells by hSulf-1 and the activity of cell signaling pathways, we overexpressed hSulf-1 in the melanoma cell lines M21 and A375 via adenovirus infection and then examined changes in the protein levels of the signaling molecule protein kinase B (AKT) and the cell cycle regulator cyclin-dependent kinase 4 (CDK4).