Frazier W A, Gao A G, Dimitry J, Chung J, Brown E J, Lindberg F P, Linder M E
Departments of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
J Biol Chem. 1999 Mar 26;274(13):8554-60. doi: 10.1074/jbc.274.13.8554.
Integrin-associated protein (IAP; CD47) is a thrombospondin receptor that forms a signaling complex with beta3 integrins resulting in enhanced alphavbeta3-dependent cell spreading and chemotaxis and, in platelets, alphaIIbbeta3-dependent spreading and aggregation. These actions of CD47 are all specifically abrogated by pertussis toxin treatment of cells. Here we report that CD47, its beta3 integrin partner, and Gi proteins form a stable, detergent-soluble complex that can be recovered by immunoprecipitation and affinity chromatography. Gialpha 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 GTPgamma35S to membranes from cells expressing IAP and alphavbeta3. 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.
整合素相关蛋白（IAP；CD47）是一种血小板反应蛋白受体，它与β3整合素形成信号复合物，导致依赖αvβ3的细胞铺展和趋化作用增强，在血小板中则导致依赖αIIbβ3的铺展和聚集增强。细胞经百日咳毒素处理后，CD47的这些作用均被特异性消除。在此我们报告，CD47、其β3整合素伴侣和Gi蛋白形成一种稳定的、可溶于去污剂的复合物，该复合物可通过免疫沉淀和亲和层析回收。用GTP或AlF4处理可使Gαi从该复合物中释放出来。GTP和AlF4还可降低CD47与其源自血小板反应蛋白的激动剂肽（4N1K）的结合，表明CD47与Gi直接相关。4N1K肽可使血小板内的环磷酸腺苷水平迅速降低，这是聚集所需的依赖Gi的事件。最后，4N1K刺激GTPγ35S与表达IAP和αvβ3的细胞的膜结合。CD47与异源三聚体G蛋白的这种功能偶联为CD47在多种系统中的生物学效应提供了一种机制解释。
