Abolition of the expression of inhibitory guanine nucleotide regulatory protein Gi activity in diabetes.
Many cell-surface receptors for hormones appear to exert their effects on target cells by interacting with specific guanine nucleotide binding regulatory proteins (G-proteins) which couple receptors to their second-messenger signal generation systems. A common intracellular second messenger, which is used by many hormones, is cyclic AMP. This is produced by adenylate cyclase, whose activity is controlled by two G-proteins, Gs which mediates stimulatory effects and Gi inhibitory effects on adenylate cyclase activity. In liver, the hormone glucagon increases intracellular cAMP concentrations by activating adenylate cyclase by a Gs-mediated process. This effect of glucagon is antagonised by the hormone insulin, although the molecular mechanism by which insulin elicits its actions is obscure. However, insulin receptors exhibit a tyrosyl kinase activity and appear to interact with G-proteins, perhaps by causing phosphorylation of them. In type I diabetes, circulating insulin levels are abnormally low, giving rise to gross perturbations of metabolism as well as to a variety of complications such as ionic disturbances, neuropathies of the nervous system, respiratory and cardiovascular aberrations and predisposition to infection. We show here that experimentally-induced type I diabetes leads to the loss of expression of Gi in rat liver. As it has been suggested that Gi may couple receptors to K+-channels as well as mediating the inhibition of adenylate cyclase, aberrations in the control of expression of this key regulatory protein in type I diabetes may be expected to lead to pleiotropic effects.
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D005934:Glucagon / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D008099:Liver / Q000378:metabolism; D051381:Rats; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D000246:Adenosine Diphosphate Ribose; D006165:Guanylyl Imidodiphosphate; D005934:Glucagon; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases