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Original Article |
Vß3 Integrins and Is Required for Go-mediated Signal Transduction
Correspondence to: Laurie Erb, Department of Biochemistry, M121 Medical Science Building, University of Missouri-Columbia, Columbia, MO 65212. Tel:(573) 882-1708 Fax:(573) 884-4597 E-mail:erbl{at}missouri.edu.
The P2Y2 nucleotide receptor (P2Y2R) contains the integrin-binding domain arginine-glycine-aspartic acid (RGD) in its first extracellular loop, raising the possibility that this G proteincoupled receptor interacts directly with an integrin. Binding of a peptide corresponding to the first extracellular loop of the P2Y2R to K562 erythroleukemia cells was inhibited by antibodies against
Vß3/ß5 integrins and the integrin-associated thrombospondin receptor, CD47. Immunofluorescence of cells transfected with epitope-tagged P2Y2Rs indicated that
V integrins colocalized 10-fold better with the wild-type P2Y2R than with a mutant P2Y2R in which the RGD sequence was replaced with RGE. Compared with the wild-type P2Y2R, the RGE mutant required 1,000-fold higher agonist concentrations to phosphorylate focal adhesion kinase, activate extracellular signalregulated kinases, and initiate the PLC-dependent mobilization of intracellular Ca2+. Furthermore, an anti-
V integrin antibody partially inhibited these signaling events mediated by the wild-type P2Y2R. Pertussis toxin, an inhibitor of Gi/o proteins, partially inhibited Ca2+ mobilization mediated by the wild-type P2Y2R, but not by the RGE mutant, suggesting that the RGD sequence is required for P2Y2R-mediated activation of Go, but not Gq. Since CD47 has been shown to associate directly with Gi/o family proteins, these results suggest that interactions between P2Y2Rs, integrins, and CD47 may be important for coupling the P2Y2R to Go.
Key Words: purinergic receptors, cell surface receptors, integrins, GTP-binding proteins, signal transduction
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