Matriptase zymogen supports epithelial development, homeostasis and regeneration

Abstract

Background: Matriptase is a membrane serine protease essential for epithelial development, homeostasis, and regeneration, as well as a central orchestrator of pathogenic pericellular signaling in the context of inflammatory and proliferative diseases. Matriptase is an unusual protease in that its zymogen displays measurable enzymatic activity. Results: Here, we used gain and loss of function genetics to investigate the possible biological functions of zymogen matriptase. Unexpectedly, transgenic mice mis-expressing a zymogen-locked version of matriptase in the epidermis displayed pathologies previously reported for transgenic mice mis-expressing wildtype epidermal matriptase. Equally surprising, mice engineered to express only zymogen-locked endogenous matriptase, unlike matriptase null mice, were viable, developed epithelial barrier function, and regenerated the injured epithelium. Compatible with these observations, wildtype and zymogen-locked matriptase were equipotent activators of PAR-2 inflammatory signaling. Conclusion: The study demonstrates that the matriptase zymogen is biologically active and is capable of executing developmental and homeostatic functions of the protease.

Blocking the proteolytic activity of zymogen matriptase with antibody-based inhibitors

“…This result is consistent with the reported zymogenicity factor of 27 for rat matriptase (20). Our findings that zymogen matriptase possesses basal activity are in support of recent studies showing that the R614A (R15A) fulllength WT matriptase variant is capable of performing its physiological catalytic functions required for homeostasis (24,32). Besides being proposed to be at a pinnacle of cascades, matriptase may be transactivating other matriptase zymogens due to the match between the activation motif and the substrate specificity of matriptase itself, a unique feature among serine proteases (21,33).…”

“…S3 and S4). We observed an unchanged V max and an increased K m in the presence of aZ-mAb-6 and aZ-mAb-7, suggesting a competitive mechanism of inhibition (24). For the antibodies aZ-mAb-1, -2, -3, -5, -9, and -10, little change in K m and V max was detected ( Table 2), suggesting that they are noncompetitive or mixed inhibitors.…”

“…It is clear that many cells have zymogen matriptase on the plasma membrane and that this may have enough catalytic activity to control the activation of growth factors, signaling pathways, etc. to sustain survival (24,32). Our working hypothesis is that zymogen matriptase, which is found in low concentrations on the cell surface, is a pinnacle protease in multiple cascades with enough catalytic activity to perform its physiological role.…”

“…Furthermore, we have previously shown that the zymogen form of matriptase reacts with a peptide inhibitor biotin-Arg-Gln-Arg-Arg chloromethyl ketone (CMK) (23). Finally, it was recently shown that a nonactivatable (zymogen-locked) version of mouse matriptase was able to support the natural function of matriptase in a transgenic mouse model system where natural matriptase had been ablated, in strong support of a physiological role of zymogen activity of matriptase (24).…”

Membrane-Anchored Serine Proteases and Protease-Activated Receptor-2–Mediated Signaling: Co-Conspirators in Cancer Progression

“…Matriptase is expressed as a precursor or zymogen form that may be proteolytically processed first within the SEA domain, and then activated by further cleavage at a highly conserved R#VVGG motif by pericellular serine proteases or by autoactivation by matriptase itself (67). Interestingly, the zymogen form of matriptase, unusual among trypsin-like serine proteases, possesses measurable enzymatic activity and was recently shown to be capable of executing the in vivo developmental and homeostatic functions of the proteolytically processed protease (68).…”