Calpain inhibitors reduce the cornified cell envelope formation by inhibiting proteolytic processing of transglutaminase 1

Abstract

Calpain I ( -calpain) and II (m-calpain) are well known calcium-activated neutral cysteine proteases. Many reports have shown that activation of calpain is related to cataract formation, neuronal degeneration, blood clotting, ischemic injuries, muscular dystrophy and cornified cell envelope (CE) formation. Here, we report that insoluble CE formation was reduced after treatment with calpain I inhibitor (N-acetyl-leucylleucyl-norleucinal) on normal human epidermal keratinocytes (NHEK), whereas serine and thiol protease inhibitors had no effect on the reduction of CE. When NHEK cells were confluent, keratinocytes were treated with various concentrations (0.5 M -0.5 mM) of calpain I inhibitor or serine and thiol protease inhibitors under calcium induced differentiation. Insoluble CE formation was reduced about 90 % in the 50 M calpain inhibitor I treated group by day 9 of culture, whereas insoluble CE was reduced only 10 % in the same condition. Interestingly TGase activity was blocked by 90 % in the 0.5 mM calpain inhibitor treated group within 72 h, whereas TGase activity was retained by 80 % in the 0.5 mM serine protease inhibitor treated group at 7 day treatment. Therefore it can be suggested that cysteine protease calpains might be responsible for the activation of the TGase 1 enzyme to complete insoluble CE formation during epidermal differentiation.

Topical Antihistamines Display Potent Anti-Inflammatory Activity Linked in Part to Enhanced Permeability Barrier Function

“…Topical applications of H1r and H2r antagonists enhanced epidermal differentiation, the latter at both the mRNA and protein levels, which could reflect the ability of these agents to mobilize intracellular calcium (Koizumi and Ohkawara, 1999). Enhanced differentiation translated further into a significant increase in the thickness of cornified envelopes, which should yield more robust corneocytes, also a Ca ++ -dependent process (Kim and Bae, 1998, Nemes and Steinert, 1999). The converse certainly proves this point -- effete cornified envelopes occur in several inherited disorders of cornification, including loss-of-function mutations in transglutaminase 1-deficient (lamellar) ichthyosis [rev.…”

Hoxb13 Up-regulates Transglutaminase Activity and Drives Terminal Differentiation in an Epidermal Organotypic Model

“…During terminal differentiation, full-length TGase 1 proteins undergo proteolytic cleavage, leading to ϳ100 to 1000-fold higher specific activity (42,43). Calpain, a Ca 2ϩ -dependent protease, may activate TGase 1 in vivo (44,45), and microarray analyses of Hoxb13 knock-out versus wild-type skin (24) revealed that calpain expression is significantly reduced in the Hoxb13 knock-out (data not shown). Finally, it is interesting to note that another Hox protein, HoxA7, down-regulates TGase 1 expression at the transcriptional level, and inhibits differentiation (46).…”

Cathepsin D—Many functions of one aspartic protease

“…In keratinocytes, most of the newly synthesized TG-1 is attached to membrane and therefore the possible mechanism of its cleavage by lysosomal CD remains ambiguous [102]. Moreover, the role of cytoplasmic caplain in TG-1 processing and cornified envelope formation has also been demonstrated [103].…”