Crosstalk between Galpha(i)- and Galpha(q)-coupled receptors is mediated by Gbetagamma exchange.
Activation of Galpha(i)-coupled receptors often causes enhancement of the inositol phosphate signal triggered by Galpha(q)-coupled receptors. To investigate the mechanism of this synergistic receptor crosstalk, we studied the Galpha(i)-coupled adenosine A(1) and alpha(2C) adrenergic receptors and the Galpha(q)-coupled bradykinin B(2) and a UTP-preferring P2Y receptor. Stimulation of either Galpha(i)-coupled receptor expressed in COS cells increased the potency and the efficacy of inositol phosphate production by bradykinin or UTP. Likewise, overexpression of Gbeta(1)gamma(2) resulted in a similar increase in potency and efficacy of bradykinin or UTP. In contrast, these stimuli did not affect the potency of direct activators of Galpha(q); a truncated Gbeta(3) mutant had no effect on the receptor-generated signals whereas signals generated at the G-protein level were still enhanced. This suggests that the Gbetagamma-mediated signal enhancement occurs at the receptor level. Almost all possible combinations of Gbeta(1-3) with Ggamma(2-7) were equally effective in enhancing the signals of the B(2) and a UTP-preferring P2Y receptor, indicating a very broad specificity of this synergism. The enhancement of the bradykinin signal by (i) Galpha(i)-activating receptor ligands or (ii) cotransfection of Gbetagamma was suppressed when the B(2) receptor was replaced by a B(2)Gbeta(2) fusion protein. Gbetagamma enhanced the B(2) receptor-stimulated activation of G-proteins as determined by GTPgammaS-induced decrease in high affinity agonist binding and by B(2) receptor-enhanced [(35)S]GTPgammaS binding. These findings support the concept that Gbetagamma exchange between Galpha(i)- and Galpha(q)-coupled receptors mediates this type of receptor crosstalk.
Quitterer
U
U
Institut für Pharmakologie und Toxikologie der Universität Würzburg, Versbacher Strasse 9, 97078 Würzburg, Germany.
Lohse
M J
MJ
D000818:Animals; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015151:Immunoblotting; D007295:Inositol Phosphates / Q000378:metabolism; D008954:Models, Biological; D016296:Mutagenesis; D020239:Receptor Cross-Talk / Q000502:physiology*; D043782:Receptor, Bradykinin B2; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism; D018002:Receptors, Bradykinin / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism; D014544:Uridine Triphosphate / Q000378:metabolism
D007295:Inositol Phosphates; D043782:Receptor, Bradykinin B2; D018343:Receptors, Adrenergic, beta-2; D018002:Receptors, Bradykinin; D011993:Recombinant Fusion Proteins; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium; D014544:Uridine Triphosphate