title: Adenylyl cyclase regulates signal onset via the inhibitory GTP-binding protein, Gi.
abstract: Adenylyl cyclase, the enzyme that converts ATP to cAMP, is regulated by its stimulatory and inhibitory GTP-binding proteins, G(s) and G(i), respectively. Recently, we demonstrated that besides catalyzing the synthesis of cAMP, type V adenylyl cyclase (ACV) can act as a GTPase-activating protein for Galpha(s) and also enhance the ability of activated receptors to stimulate GTP-GDP exchange on heterotrimeric G(s) (Scholich, K., Mullenix, J. B., Wittpoth, C., Poppleton, H. M., Pierre, S. C., Lindorfer, M. A., Garrison, J. C., and Patel, T. B. (1999) Science 283, 1328-1331). This latter action of ACV would facilitate the rapid onset of signaling via G(s). Because the C1 region of ACV interacts with the inhibitory GTP-binding protein Galpha(i), we investigated whether the receptor-mediated activation of heterotrimeric G(i) was also regulated by ACV and its subdomains. Our data show that ACV and its C1 domain increased the ability of a muscarinic receptor mimetic peptide (MIII-4) to enhance activation of heterotrimeric G(i) such that the amount of peptide required to stimulate G(i) in steady-state GTPase activity assays was 3-4 orders of magnitude less than without the C1 domain. Additionally, the MIII-4-mediated binding of guanosine 5'-(gamma-thio)triphosphate (GTPgammaS) to G(i) was also markedly increased in the presence of ACV or its C1 domain. In contrast, the C2 domain of ACV was not able to alter either the GTPase activity or the GTPgammaS binding to G(i) in the presence of MIII-4. Furthermore, in adenylyl cyclase assays employing S49 cyc(-) cell membranes, the C1 (but not the C2) domain of ACV enhanced the ability of peptide MIII-4 as well as endogenous somatostatin receptors to activate endogenous G(i) and to inhibit adenylyl cyclase activity. These data demonstrate that adenylyl cyclase and its C1 domain facilitate receptor-mediated activation of G(i).
authors.affiliation: Department of Pharmacology, University of Tennessee, The Health Science Center, Memphis, Tennessee 38163, USA.
authors.forename: C
authors.initials: C
authors.lastname: Wittpoth
authors.forename: K
authors.initials: K
authors.lastname: Scholich
authors.forename: J D
authors.initials: JD
authors.lastname: Bilyeu
authors.forename: T B
authors.initials: TB
authors.lastname: Patel
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D051379:Mice; D018716:Molecular Mimicry; D043588:Receptor, Muscarinic M4; D011976:Receptors, Muscarinic / Q000378:metabolism; D015398:Signal Transduction; D013004:Somatostatin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D043588:Receptor, Muscarinic M4; D011976:Receptors, Muscarinic; D006153:Guanosine Diphosphate; D005576:Colforsin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013004:Somatostatin; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases