Galphas-coupled receptor signaling actively down-regulates alpha4beta1-integrin affinity: a possible mechanism for cell de-adhesion

BMC Immunol. 2008 Jun 5;9:26. doi: 10.1186/1471-2172-9-26.

Abstract

Background: Activation of integrins in response to inside-out signaling serves as a basis for leukocyte arrest on endothelium, and migration of immune cells. Integrin-dependent adhesion is controlled by the conformational state of the molecule (i.e. change in the affinity for the ligand and molecular unbending (extension)), which is regulated by seven-transmembrane Guanine nucleotide binding Protein-Coupled Receptors (GPCRs). alpha4beta1-integrin (CD49d/CD29, Very Late Antigen-4, VLA-4) is expressed on leukocytes, hematopoietic stem cells, hematopoietic cancer cells, and others. Affinity and extension of VLA-4 are both rapidly up-regulated by inside-out signaling through several Galphai-coupled GPCRs. The goal of the current report was to study the effect of Galphas-coupled GPCRs upon integrin activation.

Results: Using real-time fluorescent ligand binding to assess affinity and a FRET based assay to probe alpha4beta1-integrin unbending, we show that two Galphas-coupled GPCRs (H2-histamine receptor and beta2-adrenergic receptor) as well as several cAMP agonists can rapidly down modulate the affinity of VLA-4 activated through two Galphai-coupled receptors (CXCR4 and FPR) in U937 cells and primary human peripheral blood monocytes. This down-modulation can be blocked by receptor-specific antagonists. The Galphas-induced responses were not associated with changes in the expression level of the Galphai-coupled receptors. In contrast, the molecular unbending of VLA-4 was not significantly affected by Galphas-coupled GPCR signaling. In a VLA-4/VCAM-1-specific myeloid cell adhesion system, inhibition of the VLA-4 affinity change by Galphas-coupled GPCR had a statistically significant effect upon cell aggregation.

Conclusion: We conclude that Galphas-coupled GPCRs can rapidly down modulate the affinity state of VLA-4 binding pocket through a cAMP dependent pathway. This plays an essential role in the regulation of cell adhesion. We discuss several possible implications of this described phenomenon.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adrenergic beta-Agonists / pharmacology
  • Cell Adhesion / drug effects
  • Cell Adhesion / immunology*
  • Chemokine CXCL12 / agonists
  • Chemokine CXCL12 / pharmacology
  • Down-Regulation
  • Histamine Agonists / pharmacology
  • Humans
  • Integrin alpha4beta1 / chemistry*
  • Integrin alpha4beta1 / immunology
  • Integrin alpha4beta1 / metabolism*
  • Isoproterenol / pharmacology
  • Leukocytes, Mononuclear
  • Oligopeptides / pharmacology
  • Phenylurea Compounds / pharmacology
  • Protein Binding / drug effects
  • Protein Conformation
  • Receptor Cross-Talk / immunology*
  • Receptors, Adrenergic, beta-2 / immunology
  • Receptors, Adrenergic, beta-2 / metabolism
  • Receptors, CXCR4 / agonists
  • Receptors, Histamine H2 / immunology
  • Receptors, Histamine H2 / metabolism
  • Recombinant Proteins / agonists
  • Signal Transduction*
  • Thiazoles / pharmacology
  • U937 Cells

Substances

  • 4-((N'-2-methylphenyl)ureido)phenylalanyl-leucyl-alpha-aspartyl-valyl-prolyl-alanyl-alanyl-lysine
  • Adrenergic beta-Agonists
  • CXCL12 protein, human
  • CXCR4 protein, human
  • Chemokine CXCL12
  • Histamine Agonists
  • Integrin alpha4beta1
  • Oligopeptides
  • Phenylurea Compounds
  • Receptors, Adrenergic, beta-2
  • Receptors, CXCR4
  • Receptors, Histamine H2
  • Recombinant Proteins
  • Thiazoles
  • amthamine
  • Isoproterenol