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 beta(3) integrins resulting in enhanced alpha(v)beta(3)-dependent cell spreading and chemotaxis and, in platelets, alpha(IIb)beta(3)-dependent spreading and aggregation. These actions of CD47 are all specifically abrogated by pertussis toxin treatment of cells. Here we report that CD47, its beta(3) integrin partner, and G(i) proteins form a stable, detergent-soluble complex that can be recovered by immunoprecipitation and affinity chromatography, G(i alpha) 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 G(i). 4N1K peptide causes a rapid decrease in intraplatelet cyclic AMP levels, a G(i)-dependent event necessary for aggregation. Finally, 4N1K stimulates the binding of GTP gamma(35)S to membranes from cells expressing IAP and alpha(v)beta(3). 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.