F2R and breast carcinoma: To test whether KLK4S207A,L185D inhibits cleavage of the full-length wild-type PAR1 transmembrane receptor by KLK4WT (i.e., whether KLK4S207A,L185D serves as a potential PAR1 antagonist) in an in-vitro cellular system, we used the breast cancer MCF7 and melanoma WM3682 cell lines as model systems.