Roles and regulation of membrane-associated serine proteases

Area of Science:

• Cell Biology
• Biochemistry
• Protease Signaling

Background:

• Pericellular proteolytic activity influences cellular behavior through extracellular matrix, growth factor, and receptor processing.
• Serine proteases, particularly receptor-bound and transmembrane proteases, possess sensitive regulatory mechanisms in this context.
• The urokinase plasminogen activator (uPA)/uPAR (uPAR receptor) system exemplifies receptor-bound proteases, but initiation mechanisms at the cell surface are unclear.

Purpose of the Study:

• To investigate the role of type II transmembrane serine proteases (TTSPs) in initiating pericellular proteolytic activity.
• To elucidate the mechanisms by which TTSPs regulate the uPA/uPAR system and activate growth factors like HGF.
• To explore the potential of TTSPs as upstream initiators of proteolytic cascades.

Main Methods:

• Investigated the expression of matriptase in leukocytes and its correlation with active uPA.
• Utilized small interfering RNA (siRNA) to demonstrate matriptase's role in activating uPAR-associated pro-uPA.
• Examined the activation of HGF by matriptase and hepsin in purified systems.

Main Results:

• Matriptase expression in leukocytes correlates with active cell surface uPA.
• Matriptase specifically activates uPAR-associated pro-uPA via siRNA-mediated knockdown.
• Contrary to previous implications, HGF activation was not linked to the uPA/uPAR system but was directly mediated by matriptase and hepsin.
• Hepsin demonstrated high efficiency in activating HGF, with HGF's cleavage sequence being an ideal substrate for hepsin.
• Both matriptase and hepsin can undergo autocatalytic activation at the cell surface.

Conclusions:

• Type II transmembrane serine proteases (TTSPs), specifically matriptase, act as key initiators of pericellular proteolytic activity by activating the uPA/uPAR system on leukocytes.
• TTSPs, including matriptase and hepsin, directly activate hepatocyte growth factor (HGF), independent of the uPA/uPAR system.
• Autocatalytic activation of TTSPs at the cell surface positions them as critical upstream regulators with broad downstream effects on cellular behavior.