Editors' ChoiceImmunology

Neutrophils Generate Their Own Activators

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Science Signaling  16 Oct 2012:
Vol. 5, Issue 246, pp. ec268
DOI: 10.1126/scisignal.2003692

Activated neutrophils release proteases that function in neutrophil extracellular traps to mediate bacterial killing and that also function as autocrine regulators of neutrophil function. Previous work had shown that neutrophils deficient in two proteases, cathepsin G and elastase (CG/NE), did not respond to activation by immune complexes in vitro and that the response was restored by exogenous addition of cathepsin G. Woloszynek et al. performed a proteomic proteolysis screen of CG/NE-deficient neutrophils stimulated with immune complexes and then treated with cathepsin G and identified four candidate targets of cathepsin G. Of these, Annexin A1 (AnxA1) and CRAMP (the mouse ortholog of human cathelicidin) had been previously reported as substrates of serine proteases that modulate neutrophil function, and those were selected for further evaluation. Both AnxA1 and CRAMP were substrates of cathepsin G in vitro, with AnxA1 cleaved to the active product and CRAMP only partially cleaved. Comparison of stimulated wild-type and CG/NE-deficient neutrophils showed that the abundance of cell-associated AnxA1 and CRAMP either was unchanged or the reduction was slowed in the CG/NE-deficient neutrophils, suggesting that cleavage and release were compromised by the absence of these two proteases. In an in vivo air pouch assay, compared with wild-type mice, less CRAMP and AnxA1 (full-length and truncated forms) were detected in lavages of the pouch from CG- or CG/NE-deficient mice but not from NE-deficient mice. Addition of the active cleavage products of AnxA1 or CRAMP stimulated release of the chemokine CXCL2 from CG/NE-deficient neutrophils, and release was blocked by the addition of an inhibitor of the formyl peptide receptor (FPR). FPR agonists stimulated CXCL2 release from CG-deficient neutrophils. Addition of cathepsin G alleviated inhibition of FPR by an antagonist in CG/NE-deficient neutrophils, suggesting that the FPR ligands generated by cathepsin G competed for FPR. Thus, cathepsin G released from neutrophils contributes to the production of FPR ligands to generate autocrine signals that promote the inflammatory response.

J. C. Woloszynek, Y. Hu, C. T. N. Pham, Cathepsin G-regulated release of formyl peptide receptor agonists modulate neutrophil effector functions. J. Biol. Chem. 287, 34101–34109 (2012). [Abstract] [Full Text]

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