Nitric oxide/cGMP pathway signaling actively down-regulates α4β1-integrin affinity: an unexpected mechanism for inducing cell de-adhesion

BMC Immunol. 2011 May 17;12:28. doi: 10.1186/1471-2172-12-28.

Abstract

Background: Integrin activation in response to inside-out signaling serves as the basis for rapid leukocyte arrest on endothelium, migration, and mobilization of immune cells. Integrin-dependent adhesion is controlled by the conformational state of the molecule, which is regulated by seven-transmembrane Guanine nucleotide binding Protein-Coupled Receptors (GPCRs). α4β1-integrin (CD49d/CD29, Very Late Antigen-4, VLA-4) is expressed on leukocytes, hematopoietic progenitors, stem cells, hematopoietic cancer cells, and others. VLA-4 conformation is rapidly up-regulated by inside-out signaling through Gαi-coupled GPCRs and down-regulated by Gαs-coupled GPCRs. However, other signaling pathways, which include nitric oxide-dependent signaling, have been implicated in the regulation of cell adhesion. The goal of the current report was to study the effect of nitric oxide/cGMP signaling pathway on VLA-4 conformational regulation.

Results: Using fluorescent ligand binding to evaluate the integrin activation state on live cells in real-time, we show that several small molecules, which specifically modulate nitric oxide/cGMP signaling pathway, as well as a cell permeable cGMP analog, can rapidly down-modulate binding of a VLA-4 specific ligand on cells pre-activated through three Gαi-coupled receptors: wild type CXCR4, CXCR2 (IL-8RB), and a non-desensitizing mutant of formyl peptide receptor (FPR ΔST). Upon signaling, we detected rapid changes in the ligand dissociation rate. The dissociation rate after inside-out integrin de-activation was similar to the rate for resting cells. In a VLA-4/VCAM-1-specific myeloid cell adhesion system, inhibition of the VLA-4 affinity change by nitric oxide had a statistically significant effect on real-time cell aggregation.

Conclusions: We conclude that nitric oxide/cGMP signaling pathway can rapidly down-modulate the affinity state of the VLA-4 binding pocket, especially under the condition of sustained Gαi-coupled GPCR signaling, generated by a non-desensitizing receptor mutant. This suggests a fundamental role of this pathway in de-activation of integrin-dependent cell adhesion.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Adhesion / immunology
  • Cell Communication / immunology
  • Cell Movement / immunology
  • Cyclic GMP / metabolism*
  • Down-Regulation / immunology
  • Endothelium, Vascular / immunology
  • Fluorescent Dyes
  • Humans
  • Integrin alpha4beta1 / genetics
  • Integrin alpha4beta1 / immunology
  • Integrin alpha4beta1 / metabolism*
  • Monocytes / immunology
  • Monocytes / metabolism*
  • Monocytes / pathology
  • Nitric Oxide / metabolism*
  • Protein Binding / immunology
  • Signal Transduction* / immunology
  • U937 Cells

Substances

  • Fluorescent Dyes
  • Integrin alpha4beta1
  • Nitric Oxide
  • Cyclic GMP