Alpha1-adrenergic receptor signaling via Gh is subtype specific and independent of its transglutaminase activity.
Tissue transglutaminase (TGase II) is a Ca2+- and thiol-dependent enzyme that catalyzes the post-translational modification of proteins via the formation of epsilon(gamma-glutamyl) lysine bonds. We have shown previously that the GTP-binding protein, Gh, is a TGase II that mediates intracellular signaling by the alpha1B-adrenergic receptor (AR) (Nakaoka, H., Perez, D. M., Baek, K. J., Das, T., Husain, A., Mison, K., Im, M.-J., and Graham, R. M. (1994) Science 264, 1593-1596). Here, we evaluated the ability of Gh as compared with Gq to mediate receptor-stimulated inositol phosphate turnover by the three alpha1-subtypes (alpha1A, alpha1B, and alpha1D). In addition, we questioned if the transglutaminase function of Gh is involved in its receptor signaling activity. A mutant form of a human TGase II cDNA in which the codon for the active site cysteine (Cys277) was replaced by serine was cloned into the mammalian expression vector pMT2'. Compared with wild-type TGase II, no transglutaminase activity was observed with transient transfection of this Cys-->Ser mutant in COS-1 cells. However, like wild-type TGase, the Cys-->Ser mutant mediated receptor-stimulated inositol phosphate turnover when cotransfected with an alpha1B-AR cDNA. Galphaq supported alpha1-AR-mediated inositol phosphate turnover by all three receptor subtypes. By contrast, although both the wild-type and Cys-->Ser construct mediated receptor signaling by the alpha1B AR and alpha1D AR, the alpha1A-AR was unable to interact with Gh. However, a Gh-dependent signaling phenotype could be rescued by a chimeric alpha1A construct in which the third intracellular loop of the alpha1A-AR was replaced by that of the alpha1B-AR. Thus, the signaling function of Gh is independent of its transglutaminase activity and is alpha1-AR subtype specific. This subtype specificity of the interaction between alpha1 ARs and Gh involves important determinants in their third intracellular loops.
Chen
S
S
Victor Chang Cardiac Research Institute, St. Vincent's Hospital, Darlinghurst, New South Wales 2010, Australia. b.graham@victorchang.unsw.edu.au
Lin
F
F
Iismaa
S
S
Lee
K N
KN
Birckbichler
P J
PJ
Graham
R M
RM
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D004837:Epinephrine / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000502:physiology*; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008969:Molecular Sequence Data; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D015398:Signal Transduction; D014162:Transfection; D011503:Transglutaminases / Q000378:metabolism*
D004963:Estrenes; D007295:Inositol Phosphates; D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D018340:Receptors, Adrenergic, alpha-1; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C074854:U 73343; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D004837:Epinephrine