title: Heterologous desensitization of response mediated by selective PKC-dependent phosphorylation of G(i-1) and G(i-2).
abstract: This study examined the ability of protein kinase C (PKC) to induce heterologous desensitization by targeting specific G proteins and limiting their ability to transduce signals in smooth muscle. Activation of PKC by pretreatment of intestinal smooth muscle cells with phorbol 12-myristate 13-acetate, cholecystokinin octapeptide, or the phosphatase 1 and phosphatase 2A inhibitor, calyculin A, selectively phosphorylated Galpha(i-1) and Galpha(i-2), but not Galpha(i-3) or Galpha(o), and blocked inhibition of adenylyl cyclase mediated by somatostatin receptors coupled to G(i-1) and opioid receptors coupled to G(i-2), but not by muscarinic M(2) and adenosine A(1) receptors coupled to G(i-3). Phosphorylation of Galpha(i-1) and Galpha(i-2) and blockade of cyclase inhibition were reversed by calphostin C and bisindolylmaleimide, and additively by selective inhibitors of PKCalpha and PKCepsilon. Blockade of inhibition was prevented by downregulation of PKC. Phosphorylation of Galpha-subunits by PKC also affected responses mediated by betagamma-subunits. Pretreatment of muscle cells with cANP-(4-23), a selective agonist of the natriuretic peptide clearance receptor, NPR-C, which activates phospholipase C (PLC)-beta3 via the betagamma-subunits of G(i-1) and G(i-2), inhibited the PLC-beta response to somatostatin and [D-Pen(2,5)]enkephalin. The inhibition was partly reversed by calphostin C. Short-term activation of PKC had no effect on receptor binding or effector enzyme (adenylyl cyclase or PLC-beta) activity. We conclude that selective phosphorylation of Galpha(i-1) and Galpha(i-2) by PKC partly accounts for heterologous desensitization of responses mediated by the alpha- and betagamma-subunits of both G proteins. The desensitization reflects a decrease in reassociation and thus availability of heterotrimeric G proteins.
authors.affiliation: Departments of Medicine and Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298-0711, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Murthy
authors.forename: J R
authors.initials: JR
authors.lastname: Grider
authors.forename: G M
authors.initials: GM
authors.lastname: Makhlouf
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006728:Hormones / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009281:Naphthalenes / Q000494:pharmacology; D054799:Phospholipase C beta; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D020033:Protein Isoforms / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011817:Rabbits; D015398:Signal Transduction / Q000187:drug effects; D012844:Sincalide / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D004791:Enzyme Inhibitors; D006728:Hormones; D007527:Isoenzymes; D009281:Naphthalenes; D020033:Protein Isoforms; D005576:Colforsin; D020881:Enkephalin, D-Penicillamine (2,5)-; D000242:Cyclic AMP; D011493:Protein Kinase C; D010744:Phosphoric Monoester Hydrolases; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases; C058819:calphostin C; D012844:Sincalide; D013755:Tetradecanoylphorbol Acetate