A role for cathepsin E in the processing of mast-cell carboxypeptidase A.
Mast-cell carboxypeptidase A is stored in the secretory granule and is released, together with a range of other inflammatory mediators, upon mast-cell degranulation. Carboxypeptidase A, like all mast-cell proteases, is stored in the granule as an active enzyme (i.e. with its propeptide removed). Although the processing mechanisms for the other classes of mast-cell proteases (in particular the chymases) have been clarified to some extent, the processing of procarboxypeptidase A is poorly characterized. Here, we show that mast cells from mice lacking the aspartic protease cathepsin E display an accumulation of procarboxypeptidase A, indicating a defect in carboxypeptidase-A processing. By contrast, mast cells lacking cathepsins B, L or D have normal carboxypeptidase-A processing. Furthermore, recombinant cathepsin E was found to process recombinant procarboxypeptidase A in vitro, under conditions resembling those found in mast-cell granules. Immunohistochemical analysis revealed staining for cathepsin E in mast cells from normal mice but not in mast cells from mice lacking heparin, indicating that cathepsin E is bound to heparin proteoglycan within mast-cell granules. In accordance with this notion, affinity chromatography showed that recombinant cathepsin E bound strongly to heparin under acidic conditions (the conditions prevailing in mast-cell granules) but not at neutral pH. Moreover, mast-cell degranulation resulted in the release of cathepsin E. Taken together, our results indicate that cathepsin E is located in mast-cell secretory granules in complex with heparin proteoglycans, and that it has a role in the processing of procarboxypeptidase A into active protease.
Henningsson
Frida
F
Swedish University of Agricultural Sciences, Department of Molecular Biosciences, The Biomedical Centre, Box 575, 751 23 Uppsala, Sweden.
Yamamoto
Kenji
K
Saftig
Paul
P
Reinheckel
Thomas
T
Peters
Christoph
C
Knight
Stefan D
SD
Pejler
Gunnar
G
D000818:Animals; D015153:Blotting, Western; D043422:Carboxypeptidases A / Q000737:chemistry / Q000378:metabolism*; D002401:Cathepsin B / Q000502:physiology; D002402:Cathepsin D / Q000502:physiology; D020059:Cathepsin E / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D056668:Cathepsin L; D002403:Cathepsins / Q000502:physiology; D002460:Cell Line; D002478:Cells, Cultured; D003001:Cloning, Molecular; D003546:Cysteine Endopeptidases / Q000502:physiology; D004789:Enzyme Activation; D005260:Female; D006493:Heparin / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007249:Inflammation; D008407:Mast Cells / Q000201:enzymology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D008958:Models, Molecular; D010447:Peptide Hydrolases / Q000378:metabolism; D011509:Proteoglycans / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry; D022142:Secretory Vesicles / Q000378:metabolism; D013997:Time Factors
D011509:Proteoglycans; D011994:Recombinant Proteins; D006493:Heparin; D002403:Cathepsins; D010447:Peptide Hydrolases; C468648:CPA3 protein, human; D043422:Carboxypeptidases A; C503326:Cpa3 protein, mouse; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; C534281:CTSL protein, human; D056668:Cathepsin L; C534278:Ctsl protein, mouse; D020059:Cathepsin E; D002402:Cathepsin D