title: Cross-regulation between G-protein-mediated pathways. Stimulation of adenylyl cyclase increases expression of the inhibitory G-protein, Gi alpha 2.
abstract: The hormone-sensitive adenylyl cyclase system is under dual control, receiving both stimulatory and inhibitory inputs. Guanine nucleotide-binding regulatory proteins (G-proteins) transduce signals from cell surface receptors to effectors such as adenylyl cyclase. Hormonal stimulation is propagated via Gs, inhibition by Gi. Persistent (24-h) activation of the stimulatory pathway of adenylyl cyclase by the diterpene forskolin or the beta-adrenergic agonist isoproterenol in S49 mouse lymphoma cells enhanced the effects of somatostatin mediated via the inhibitory pathway of adenylyl cyclase. Stimulating cells with forskolin or isoproterenol for 24 h resulted in a 3-fold increase in the steady-state levels of Gi alpha 2 and a 25% decline in Gs alpha, as quantified by immunoblotting. Within 12 h of stimulation of adenylyl cyclase, Gi alpha 2 mRNA levels increased 4-fold, measured by DNA-excess solution hybridization. Gs alpha mRNA levels, in contrast, increased initially (25%), but then declined to 75% of control. In S49 variants that lack functional protein kinase A (kin-), stimulation by isoproterenol failed to alter Gi alpha 2 expression at either the protein or the mRNA levels. A 3-fold increase in relative synthesis rate and no change in the half-life (approximately 80 h) of Gi alpha 2 was observed in response to forskolin stimulation. Although Gs alpha synthesis increased (70%) modestly in response to forskolin stimulation, the half-life of Gs alpha actually decreased from 55 h in naive cells to 34 h in treated cells. Thus, the two G-protein-mediated pathways controlling adenylyl cyclase display "cross-regulation." Persistent activation of the stimulatory pathway increases Gi alpha 2 mRNA and expression. Transiently elevated Gs alpha mRNA levels are counterbalanced by a reduction in the half-life of the protein.
authors.affiliation: Department of Pharmacology, School of Medicine, State University of New York, Stony Brook 11794-8651.
authors.forename: J R
authors.initials: JR
authors.lastname: Hadcock
authors.forename: M
authors.initials: M
authors.lastname: Ros
authors.forename: D C
authors.initials: DC
authors.lastname: Watkins
authors.forename: C C
authors.initials: CC
authors.lastname: Malbon
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D004273:DNA, Neoplasm / Q000235:genetics; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D015870:Gene Expression; D015151:Immunoblotting; D007700:Kinetics; D008223:Lymphoma; D046911:Macromolecular Substances; D008954:Models, Biological; D009693:Nucleic Acid Hybridization; D015398:Signal Transduction
chemical_list: D004273:DNA, Neoplasm; D046911:Macromolecular Substances; D005576:Colforsin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases