Mast cells and neutrophils proteolytically activate chemokine precursor CTAP-III and are subject to counterregulation by PF-4 through inhibition of chymase and cathepsin G.
The CXC chemokines platelet factor 4 (PF-4/CXCL4) and connective tissue-activating peptide III (CTAP-III) are released by activated human platelets in micromolar concentrations. So far, neutrophils have been recognized to cleave the precursor CTAP-III to form the active chemokine neutrophil-activating peptide 2 (NAP-2/CXCL7) through limited proteolysis by membrane-associated cathepsin G. Here we show for the first time that activated human skin mast cells (MCs) convert CTAP-III into biologically active NAP-2 through proteolytic cleavage by released chymase. A direct comparison on a cell number basis revealed that unstimulated MCs exceed the CTAP-III-processing potency of neutrophils about 30-fold, whereas MCs activated by IgE cross-linking exhibit even 1000-fold higher CTAP-III-processing capacity than fMLP-stimulated neutrophils. Intriguingly, PF-4 counteracted MC- as well as neutrophil-mediated NAP-2 generation at physiologically relevant concentrations. Addressing the underlying mechanism, we obtained evidence that PF-4 acts as an inhibitor of the CTAP-III-processing enzymes cathepsin G and chymase without becoming cleaved itself as a competitive substrate. Because cleavage of the CTAP-III-unrelated substrate substance P was also affected by PF-4, our results suggest a regulatory role for PF-4 not only in NAP-2 generation but also in neutrophil- and MC-mediated processing of other physiologically relevant inflammatory mediators.
Schiemann
Florian
F
Department of Immunology and Cell Biology, Forschungszentrum Borstel, Parkallee 22, D-23485 Borstel, Germany. fschie@fz-borstel.de
Grimm
Tobias Alexander
TA
Hoch
Josef
J
Gross
Roland
R
Lindner
Buko
B
Petersen
Frank
F
Bulfone-Paus
Silvia
S
Brandt
Ernst
E
D056649:Cathepsin G; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism; D053818:Chymases; D006801:Humans; D007073:Immunoglobulin E / Q000378:metabolism; D008407:Mast Cells / Q000378:metabolism*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D010455:Peptides / Q000378:metabolism*; D010978:Platelet Factor 4 / Q000502:physiology*; D012697:Serine Endopeptidases / Q000378:metabolism*; D015842:Serine Proteinase Inhibitors; D013373:Substance P / Q000378:metabolism
C104356:NAP1L4 protein, human; D009687:Nuclear Proteins; D010455:Peptides; D015842:Serine Proteinase Inhibitors; D013373:Substance P; D010978:Platelet Factor 4; D007073:Immunoglobulin E; D009240:N-Formylmethionine Leucyl-Phenylalanine; C009862:connective tissue-activating peptide; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G; D053818:Chymases