SERPINE1 and melanoma: Metastatic melanoma progression is mediated by the activation of the urokinase plasminogen activator receptor (uPAR), the urokinase plasminogen activator (uPA) and its inhibitor PAI-1, as well as the gelatinase system, including the metalloproteinases MMP-2 and MMP-9 and their inhibitors TIMP-1 and TIMP-2 [32].