The CXCR4 agonist ligand stromal derived factor-1 maintains high affinity for receptors in both Galpha(i)-coupled and uncoupled states

Eur J Pharmacol. 2000 Dec 8;409(2):143-54. doi: 10.1016/s0014-2999(00)00846-3.

Abstract

The alpha chemokine receptor CXCR4 and its only characterized chemokine ligand, stromal cell-derived factor-1 (SDF-1), are postulated to be important in the development of the B-cell arm of the immune system. In addition, CXCR4 is a critical coreceptor in support of viral entry by T-cell line tropic strains (X4) of the Human Immunodeficiency Virus Type 1 (HIV-1), viral variants which predominate in some infected individuals in end stage disease. SDF-1 can block X4-tropic HIV-1 infection of CD4+ target cells in vitro, and allelic variants of the human gene encoding SDF-1 in vivo correlate with delayed disease progression. Therefore, CXCR4 may be an appropriate target for therapeutic intervention in acquired immunodeficiency syndrome (AIDS), and knowledge of the pharmacology of SDF-1 binding to its cognate receptor will be important in the interpretation of these experiments. We report here a Kd derived using a competition binding assay of 4.5 nM for CXCR4 endogenously expressed on peripheral blood monocytes and T-cells. This affinity is similar to that which SDF-1 exhibits when binding to endogenous CXCR4 on an established immortal Jurkat T-cell line as well as recombinant CXCR4 transfected into Chinese Hamster Ovary (CHO) cells. We also demonstrate that the determined affinity of SDF-1 for CXCR4 is reflective of its ability to induce a CXCR4-mediated signal transduction in these different cell types. Furthermore, using Bordetella pertussis toxin, we observe that high affinity binding of SDF-1 to CXCR4 is independent of the G-protein coupled state of the receptor, as uncoupling of G-protein did not lead to the appearance of measurable low affinity SDF-1 binding sites. Moreover, binding affinity and receptor number were unaffected by uncoupling for both recombinant and endogenously expressed CXCR4. Thus, SDF-1 is novel among agonist ligands of G protein-coupled receptors in that it appears to have equal affinity for both the G protein-coupled and uncoupled states of CXCR4.

MeSH terms

  • Animals
  • Binding, Competitive / drug effects
  • CHO Cells
  • Chemokine CXCL12
  • Chemokines, CXC / metabolism*
  • Chemokines, CXC / pharmacology
  • Colforsin / pharmacology
  • Cricetinae
  • Cyclic AMP / metabolism
  • Dose-Response Relationship, Drug
  • GTP-Binding Protein alpha Subunits, Gi-Go / metabolism*
  • Gene Expression
  • Guanosine 5'-O-(3-Thiotriphosphate) / pharmacology
  • Humans
  • Jurkat Cells
  • Leukocytes, Mononuclear / cytology
  • Leukocytes, Mononuclear / drug effects
  • Leukocytes, Mononuclear / metabolism
  • Pertussis Toxin
  • Receptors, CXCR4 / agonists
  • Receptors, CXCR4 / genetics
  • Receptors, CXCR4 / metabolism*
  • Signal Transduction / drug effects
  • T-Lymphocytes / cytology
  • T-Lymphocytes / drug effects
  • T-Lymphocytes / metabolism
  • Virulence Factors, Bordetella / pharmacology

Substances

  • CXCL12 protein, human
  • Chemokine CXCL12
  • Chemokines, CXC
  • Receptors, CXCR4
  • Virulence Factors, Bordetella
  • Colforsin
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • Cyclic AMP
  • Pertussis Toxin
  • GTP-Binding Protein alpha Subunits, Gi-Go