Leukocyte elastase negatively regulates Stromal cell-derived factor-1 (SDF-1)/CXCR4 binding and functions by
Agustín Valenzuela-Fernández1, Thierry Planchenault, Françoise Baleux
1Unité d'Immunologie Virale, INSERM U485 de l'Institut Pasteur, 28 Rue du Dr. Roux, 75724 Paris Cedex 15, France.
Insights
Leukocyte elastase cleaves stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4, inactivating their functions. This proteolysis impacts HIV entry and may regulate immune responses.
Area of Science:
- Immunology
- Molecular Biology
- Biochemistry
Background:
- Stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 are crucial for immune cell trafficking and HIV entry.
- Activation requires interaction of the amino-terminal domains of SDF-1 and CXCR4.
Purpose of the Study:
- To investigate the role of leukocyte-derived proteinases in the functional regulation of SDF-1 and CXCR4.
- To identify the specific enzymes involved in the proteolysis of SDF-1 and CXCR4.
Main Methods:
- Mass spectrometry to characterize SDF-1 fragments.
- Flow cytometry and immunoprecipitation to assess CXCR4 proteolysis.
- Use of a leukocyte elastase inhibitor and purified leukocyte elastase.
Main Results:
- Leukocyte proteinases generate an SDF-1 fragment lacking amino-terminal residues, rendering it functionally inactive.
- Proteolysis of SDF-1 by leukocyte enzymes prevents its agonistic functions and blocks inhibition of CXCR4-tropic HIV fusion.
- Leukocyte proteinases also cleave the extracellular amino-terminal domain of CXCR4.
- Leukocyte elastase was identified as the primary enzyme responsible for SDF-1 and CXCR4 inactivation.
Conclusions:
- Elastase-mediated proteolysis of SDF-1 and CXCR4 serves as a regulatory mechanism for their biological functions.
- This pathway may play a role in both homeostatic immune processes and pathological conditions, including HIV pathogenesis.
Abstract:
Activation of CXCR4 by the CXC chemokine stromal cell-derived factor-1 (SDF-1) requires interaction of the amino-terminal domains of both molecules. We report that proteinases released from either mononucleated blood cells or polymorphonuclear neutrophils degranulated by inflammatory stimuli generate an SDF-1 fragment that is deleted from amino-terminal residues Lys(1)-Pro(2)-Val(3), as characterized by mass spectrometry analysis. The proteolyzed chemokine fails to induce agonistic functions and is unable to prevent the fusogenic capacity of CXCR4-tropic human immunodeficiency viruses. Furthermore, we observed that exposure of CXCR4-expressing cells to leukocyte proteinases results in the proteolysis of the extracellular amino-terminal domain of the receptor, as assessed by flow cytometry analysis and electrophoretic separation of immunoprecipitated CXCR4. Blockade of SDF-1 and CXCR4 proteolysis by the specific leukocyte elastase inhibitor, N-methoxysuccinyl-alanine-alanine-proline-valine-chloromethyl ketone, identified elastase as the major enzyme among leukocyte-secreted proteinases that accounts for inactivation of both SDF-1 and CXCR4. Indeed, purified leukocyte elastase generated in either SDF-1 or CXCR4 a pattern of cleavage indistinguishable from that observed with leukocyte-secreted proteinases. Our findings suggest that elastase-mediated proteolysis of SDF-1/CXCR4 is part of a mechanism regulating their biological functions in both homeostatic and pathologic processes.
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