title: Gα(h)/transglutaminase-2 activity is required for maximal activation of adenylylcyclase 8 in human and rat glioma cells.
abstract: Gα(h) (or transglutaminase-2 (TG2)) is an atypical guanine nucleotide binding-protein that associates with G protein-coupled receptors. TG2 also exerts transglutaminase activity that catalyzes posttranslational protein cross-linking with the formation of ε-(γ-glutamyl) lysine or (γ-glutamyl) polyamine bonds. Here, the role of Gα(h)/TG2 in signal transduction in glial cells was examined in detail. In 1321N1 human astrocytoma cells that lack Gα(h)/TG2, overexpression of Gα(h)/TG2 caused an enhancement of cAMP accumulation stimulated with the β-adrenergic receptor agonist, isoproterenol, or the adenylylcyclase activator, forskolin. This cAMP-enhancement was reversed by the TG2 inhibitor, ERW1069. In rat C6 glioma cells that express endogenous Gα(h)/TG2, cAMP accumulation induced by isoproterenol or forskolin was significantly inhibited by overexpression of Gα(h)/TG2-C277V, a dominant-negative mutant that lacks transglutaminase activity, but was not inhibited by the Gα(h)/TG2-S171E mutant that cannot bind GTP/GDP. These results suggest Gα(h)/TG2 potentiates adenylylcyclase activity by its transglutaminase activity and not by its G-protein activity. Gα(h)/TG2 also increased the activities of the cAMP response element and interleukin-6 promoter, accompanied by an of cAMP in both glioma cells. Since adenylylcyclase 8 plays a major role in cAMP production, we focused on post-translational modification of adenylylcyclase 8 by Gα(h)/TG2. Adenylylcyclase 8 is expressed in both 1321N1 and C6 cells; however, Gα(h)/TG2 affected neither adenylylcyclase 8 expression levels, glycosylation, nor dimerization status. In contrast, pentylamine, a substrate of Gα(h)/TG2, was incorporated into adenylylcyclase 8 in a transglutaminase activity-dependent manner. Taking these results together, Gα(h)/TG2 promotes cAMP production accompanied by a modification of adenylylcyclase 8 in glioma cells.
authors.affiliation: Department of Cellular Signaling, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan. obaray@med.id.yamagata-u.ac.jp
authors.forename: Yutaro
authors.initials: Y
authors.lastname: Obara
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Yanagihata
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Abe
authors.forename: Laila
authors.initials: L
authors.lastname: Dafik
authors.forename: Kuniaki
authors.initials: K
authors.lastname: Ishii
authors.forename: Norimichi
authors.initials: N
authors.lastname: Nakahata
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D019943:Amino Acid Substitution; D000818:Animals; D045744:Cell Line, Tumor; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005910:Glioma / Q000378:metabolism / Q000473:pathology; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D011503:Transglutaminases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D015850:Interleukin-6; C000717609:Tgm2 protein, rat; D005576:Colforsin; D000242:Cyclic AMP; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; C118292:adenylyl cyclase 8; D007545:Isoproterenol