Analysis of kallikrein-related peptidase 7 (KLK7) autolysis reveals novel protease and cytokine substrates

Kallikrein-related peptidase 7 (KLK7) is one of 15 members of the tissue kallikrein family and is primarily expressed in the skin epidermis. The activity of KLK7 is tightly regulated by multiple stages of maturation and reversible inhibition, similar to several other extracellular proteases. In this work, we used protease-specific inhibitors and active site variants to show that KLK7 undergoes autolysis at two separate sites in the 170 and 99 loops (chymotrypsinogen numbering), resulting in a loss of enzymatic activity. A protein BLAST search using the autolyzed KLK7 loop sequences identified mast cell chymase as a potential KLK7 substrate. Indeed, KLK7 cleaves chymase resulting in a concomitant loss of activity. We further demonstrate that KLK7 can hydrolyze other mast cell proteases as well as several cytokines. These cytokines belong mainly to the interferon and IL-10 families including IFN-α, IFN-β, IFN-γ, IL-28A/IFN-λ2, IL-20, IL-22, and IL-27. This is the first study to identify a possible molecular interaction link between KLK7 and mast cell proteases and cytokines. Although the precise biological implications of these findings are unclear, this study extends our understanding of the delicate balance of proteolytic regulation of enzyme activity that maintains physiological homeostasis, and facilitates further biological investigations.