The Thrombospondin Receptor Integrin-associated Protein (CD47) Functionally Couples to Heterotrimeric Gi*


Integrin-associated protein (IAP; CD47) is a thrombospondin receptor that forms a signaling complex with β3 integrins resulting in enhanced αvβ3-dependent cell spreading and chemotaxis and, in platelets, αIIbβ3-dependent spreading and aggregation. These actions of CD47 are all specifically abrogated by pertussis toxin treatment of cells. Here we report that CD47, its β3 integrin partner, and Gi proteins form a stable, detergent-soluble complex that can be recovered by immunoprecipitation and affinity chromatography. G is released from this complex by treatment with GTP or AlF4. GTP and AlF4 also reduce the binding of CD47 to its agonist peptide (4N1K) derived from thrombospondin, indicating a direct association of CD47 with Gi. 4N1K peptide causes a rapid decrease in intraplatelet cyclic AMP levels, a Gi-dependent event necessary for aggregation. Finally, 4N1K stimulates the binding of GTPγ35S to membranes from cells expressing IAP and αvβ3. This functional coupling of CD47 to heterotrimeric G proteins provides a mechanistic explanation for the biological effects of CD47 in a wide variety of systems.


  • * This work was supported by National Institutes of Health Grants GM51466 (to M. E. L.), GM54390, and CA65872 (to W. A. F.), GM38330 (to E. J. B.), and grants from Monsanto/Searle (to W. A. F., F. P. L., and E. J. B.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

  • To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biophysics, Box 8231, Washington University School of Medicine, St. Louis, MO 63110. Tel.: 314-362-3348; Fax: 314-362-7183; E-mail: frazier{at}

  • Abbreviations:
    integrin-associated protein
    monoclonal antibody
    polyacrylamide gel electrophoresis
    nitrilotriacetic acid
    seven-transmembrane segment
    guanyl-5′-yl thiophosphate
    guanosine 5′-3-O-(thio)triphosphate
    • Received December 21, 1998.
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