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Myeloperoxidase-mediated modulation of chemotactic peptide binding to human neutrophils
Abstract:
Methionine-containing chemotactic peptides, such as formyl-methionyl-leucyl-phenylalanine (FMLP), are inactivated via a neutrophil-derived, myeloperoxidase-mediated oxidation of the methionine residue. We report that extracellular inactivation of FMLP by myeloperoxidase modulates the apparent binding of methionine-containing chemotactic peptides to their surface receptors. Inhibitors of myeloperoxidase enhanced FMLP binding. At subsaturating concentrations of 3H-FMLP (20 nM), 1 mM cyanide (KCN) increased the binding of 3H-FMLP to human neutrophils (PMN) by 51% +/- 12%. Similar increases occurred with 0.1 mM azide and 10 mM aminotriazole (ATZ). KCN had little effect on maximal 3H-FMLP binding to PMN at saturation (control-17,040 +/- 910 receptors/PMN; KCN-16,820 +/- 1,940 receptors/PMN), but decreased the concentration of 3H-FMLP required to half-saturate the PMN receptors (control-39 +/- 3 nM; KCN-17 +/- 1 nM). ATZ gave similar results. The binding to PMN of the non-methionine-containing chemotactic peptide 125I-formyl-norleucyl-leucyl-phenylalanyl-norleucyl-tyrosyl-lysine (125I-FNLPNTL) was unaltered by KCN. Also, the binding of 3H-FMLP to myeloperoxidase-deficient PMN was unaltered by KCN. Both KCN and ATZ decreased the oxidation of FMLP by PMN. Finally, ATZ (but not KCN) enhanced the chemotactic migration of PMN in response to submaximal concentrations of FMLP. These studies show that intact PMN inactivate methionine-containing chemotactic peptides by a pathway that is sensitive to myeloperoxidase inhibitors and is absent in myeloperoxidase-deficient PMN. This action results in an apparent decrease in the affinity of the chemotactic peptide receptor for methionine-containing chemotactic peptides, which may modulate chemotatic events in inflammatory loci.
Insights
Neutrophils inactivate chemotactic peptides like FMLP through myeloperoxidase, affecting their receptor binding. Inhibiting myeloperoxidase boosts FMLP binding and may influence inflammatory responses.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Methionine-containing chemotactic peptides, exemplified by formyl-methionyl-leucyl-phenylalanine (FMLP), are crucial for neutrophil recruitment.
- Neutrophil myeloperoxidase (MPO) is known to oxidize and inactivate these peptides by targeting the methionine residue.
Purpose of the Study:
- To investigate how extracellular inactivation of FMLP by MPO influences the binding of methionine-containing chemotactic peptides to neutrophil surface receptors.
- To determine the role of MPO activity in modulating the apparent affinity of chemotactic peptide receptors.
Main Methods:
- Experiments utilized radiolabeled FMLP (3H-FMLP) and a non-methionine-containing peptide (125I-FNLPNTL) to assess binding to human neutrophils (PMN).
- Myeloperoxidase inhibitors, including cyanide (KCN), azide, and aminotriazole (ATZ), were used to block MPO activity.
- Binding assays were performed at both subsaturating and saturating concentrations of 3H-FMLP, and chemotaxis assays were conducted.
Main Results:
- Inhibitors of myeloperoxidase significantly enhanced the binding of 3H-FMLP to PMN, particularly at subsaturating concentrations, by increasing apparent receptor affinity.
- The binding of a non-methionine-containing peptide (125I-FNLPNTL) and FMLP binding to MPO-deficient PMN were unaffected by MPO inhibitors.
- MPO inhibitors reduced FMLP oxidation by PMN, and ATZ enhanced PMN chemotaxis at submaximal FMLP concentrations.
Conclusions:
- Intact neutrophils inactivate methionine-containing chemotactic peptides via an MPO-dependent pathway, which reduces the apparent affinity of these peptides for their receptors.
- This MPO-mediated inactivation mechanism plays a role in modulating chemotactic signaling during inflammatory processes.
- Targeting MPO activity could represent a strategy to modulate inflammatory cell recruitment.