After confirming that KLK4S207A,L185D had the ability to inhibit melanoma cell migration and invasion (Fig. 5a and c, respectively) by inhibiting PAR1 cleavage by KLK4WT or other endogenous proteases (as shown by the confocal microscopy results in Fig. 3 and Supplementary Fig. S2), we examined the ability of KLK4S207A,L185D to inhibit the activation of MAPK/ERK, which is a major downstream signal produced by PAR1 activation through the KLK4WT-induced cleavage of PAR1's extracellular region17 and an important downstream signaling effector involved in cell motility34,35. This evidence concerns the gene F2R and melanoma.