scholarly journals Calmodulin binding distinguishes between βγ subunits of activated G proteins and transducin

1992 ◽  
Vol 283 (3) ◽  
pp. 683-690 ◽  
Author(s):  
L A Mangels ◽  
R R Neubig ◽  
H E Hamm ◽  
M E Gnegy
Keyword(s):  
Adenylate Cyclase ◽  
G Protein ◽  
G Proteins ◽  
Bovine Brain ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Dependent Manner ◽  
Protein Activation ◽  
Calmodulin Binding ◽  
Gamma Subunits

The interactions between guanine nucleotide regulatory proteins and the Ca(2+)-binding protein calmodulin were studied using calmodulin-Sepharose affinity chromatography. Purified bovine brain beta gamma subunits bound to calmodulin-Sepharose in a Ca(2+)-dependent manner. On the contrary, beta gamma subunits produced in an activated Go/Gi preparation did not bind to calmodulin-Sepharose. The effect was independent of the type of bovine brain G protein (Go/Gi, Gs), method of activation and the presence of magnesium. To distinguish whether the binding of purified beta gamma subunits to calmodulin was unique to brain beta gamma or to the method of purification, similar experiments were performed using transducin. In contrast to bovine brain G proteins, both purified transducin beta gamma subunits and beta gamma released from rhodopsin-activated transducin bound to calmodulin-Sepharose in a Ca(2+)-dependent manner. To assess the functional significance of the binding of bovine brain beta gamma subunits to calmodulin, the ability of purified beta gamma and of beta gamma in unactivated and activated Go/Gi to inhibit partially purified calmodulin-sensitive adenylate cyclase was determined. Purified beta gamma was highly effective in inhibiting calmodulin-stimulated adenylate cyclase activity. However, unactivated Go/Gi and preactivated Go/Gi inhibited calmodulin-stimulated adenylate cyclase activity to the same extent. This Go/Gi-mediated inhibition also occurred in the presence of a 500-fold molar excess of calmodulin over added G protein. These results demonstrate: (1) that beta gamma subunits may not be completely released upon G protein activation, and (2) that inhibition of calmodulin-stimulated adenylate cyclase by beta gamma subunits does not appear to be mediated by a direct beta gamma-calmodulin interaction. Differences in the binding properties of activated bovine brain G proteins versus those of transducin could be explained by differences in the gamma subunit between the proteins, or by differences in affinities of the alpha and beta gamma subunits for each other and for calmodulin. The different functional properties of purified beta gamma subunits and beta gamma subunits produced in situ by activation of G proteins indicates that extrapolation from the effects of purified subunits to events occurring in membranes should be done with caution.

scholarly journals Enhanced expression of inhibitory guanine nucleotide regulatory protein in spontaneously hypertensive rats. Relationship to adenylate cyclase inhibition

1992 ◽  
Vol 288 (1) ◽  
pp. 79-85 ◽  
Author(s):  
M B Anand-Srivastava
Keyword(s):  
Adenylate Cyclase ◽  
G Protein ◽  
G Proteins ◽  
Spontaneously Hypertensive Rats ◽  
Regulatory Protein ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Heart Sarcolemma

We have previously shown that the stimulatory effects of guanine nucleotides, N-ethylcarboxamide-adenosine and other agonists on adenylate cyclase activity were diminished in aorta and heart sarcolemma of spontaneously hypertensive rats (SHR) [Anand-Srivastava (1988) Biochem. Pharmacol. 37, 3017-3022]. In the present studies, we have examined whether the decreased response of these agonists is due to the defective GTP-binding proteins (G-proteins) which couple the receptors to adenylate cyclase, and have therefore measured the levels of G-proteins in aorta and heart from SHR and their respective Wistar-Kyoto (WKY) controls by using pertussis toxin (PT)- and cholera toxin (CT)-catalysed ADP-ribosylations and immunoblotting techniques using specific antibodies against G-proteins. The labelling with [32P]NAD+ and PT identified a 40/41 kDa protein in heart and aorta from WKY and SHR and was significantly increased in the hearts (approximately 100%) and aorta (approximately 30-40%), from SHR as compared with WKY. Immunoblotting revealed an increase in the levels of the G-protein alpha-subunits Gi alpha-2 and Gi alpha-3 in heart and Gi alpha-2 in aorta, whereas no change in Go alpha was observed in heart from SHR and WKY. On the other hand, no differences were observed in CT labelling or immunoblotting of stimulatory G-protein (Gs) in heart and aorta from WKY and SHR. In addition, CT stimulated the adenylate cyclase activity in heart sarcolemma from WKY and SHR to a similar extent. These results were correlated with adenylate cyclase inhibition and stimulation by various hormones. Angiotensin II (AII), atrial natriuretic factor (ANF) and oxotremorine-mediated inhibition was found to be greater in SHR as compared with WKY, whereas the stimulatory effects of adrenaline, isoprenaline, dopamine and forskolin were diminished in SHR aorta as compared to WKY. These results indicate that regulatory protein G(i) is more expressed in SHR, which may be associated with the decreased responsiveness of stimulatory hormones and increased sensitivity of inhibitory hormones to stimulate/inhibit adenylate cyclase activity. It may thus be suggested that the enhanced G(i) activity may be one of the mechanisms responsible for the diminished vascular tone and impaired myocardial functions in hypertension.

EVIDENCE OF THE EFFECT OF 4-HYDROXYNONENAL ON ADENYLATE CYCLASE ACTIVITY OF PLASMAMEMBRANES VIA THE GUANINE REGULATORY G-PROTEINS.

1991 ◽  
pp. 487-493 ◽  
Author(s):  
Mario U. Dianzani ◽  
Luciana Paradisi ◽  
Clelia Di Mauro ◽  
Antonio Cervo ◽  
Giuseppina Barrera ◽  
...  
Keyword(s):  
Adenylate Cyclase ◽  
G Proteins ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity

Specific coupling of a cation-sensing receptor to G protein alpha-subunits in MDCK cells

1997 ◽  
Vol 273 (1) ◽  
pp. F129-F135 ◽  
Author(s):  
J. M. Arthur ◽  
G. P. Collinsworth ◽  
T. W. Gettys ◽  
L. D. Quarles ◽  
J. R. Raymond
Keyword(s):  
G Protein ◽  
G Proteins ◽  
Plasma Membranes ◽  
Mdck Cells ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Cellular Activation ◽  
Protein Activation ◽  
A Cell ◽  
Cation Sensing

Extracellular cations such as Ca2+ stimulate a G protein-coupled, cation-sensing receptor (CaR). We used microphysiometry to determine whether an extracellular cation-sensing mechanism exists in Madin-Darby canine kidney (MDCK) cells. The CaR agonists Ca2+ and Gd3+ caused cellular activation in a concentration-dependent manner. mRNA for the CaR was identified by reverse transcription and polymerase chain reaction (PCR) using nested CaR-specific primers, identification of an appropriately located restriction site, and sequencing of the subcloned fragment obtained by PCR. G protein activation was evaluated using the GTP photoaffinity label [alpha-32P]GTP azidoanalide (AA-GTP). After stimulation with Gd3+ and cross-linking, plasma membranes were solubilized and immunoprecipitated with antisera specific for Gq/11 alpha and Gi alpha family members. Gd3+ increased incorporation of AA-GTP into Gq/11 alpha precipitates by 146 +/- 48% and into G alpha i-2 and G alpha i-3 to a lesser extent but not into G alpha i-1. Direct effects of Gd3+ on the G proteins were ruled out using partially purified mammalian G proteins expressed in Escherichia coli or Sf9 cells. We conclude that MDCK cells possess a cell-surface CaR that activates Gq/11 alpha, G alpha i-2, and G alpha i-3 but not G alpha i-1.

G-protein Activation Decreases Isoflurane Inhibition of N-type Ba2+Currents

2003 ◽  
Vol 99 (2) ◽  
pp. 392-399 ◽  
Author(s):  
Igor M. Nikonorov ◽  
Thomas J. J. Blanck ◽  
Esperanza Recio-Pinto
Keyword(s):  
Cholera Toxin ◽  
G Protein ◽  
G Proteins ◽  
Pertussis Toxin ◽  
Volatile Anesthetic ◽  
Cell Voltage ◽  
Dependent Manner ◽  
Protein Activation ◽  
G Protein Activation ◽  
Voltage Dependent

Background G-protein activation mediates inhibition of N-type Ca2+ currents. Volatile anesthetics affect G-protein pathways at various levels, and activation of G-proteins has been shown to increase the volatile anesthetic potency for inhibiting the electrical-induced contraction in ileum. The authors investigated whether isoflurane inhibition of N-type Ba2+ currents was mediated by G-protein activation. Methods N-type Ba2+ currents were measured in the human neuronal SH-SY5Y cell line by using the whole cell voltage-clamp method. Results Isoflurane was found to have two effects on N-type Ba2+ currents. First, isoflurane reduced the magnitude of N-type Ba2+ currents to a similar extent (IC50 approximately 0.28 mm) in the absence and presence of GDPbetaS (a nonhydrolyzable GDP analog). Interestingly, GTPgammaS (a nonhydrolyzable GTP analog and G-protein activator) in a dose-dependent manner reduced the isoflurane block; 120 microm GTPgammaS completely eliminated the block of 0.3 mm isoflurane and reduced the apparent isoflurane potency by approximately 2.4 times (IC50 approximately 0.68 mm). Pretreatment with pertussis toxin or cholera toxin did not eliminate the GTPgammaS-induced protection against the isoflurane block. Furthermore, isoflurane reduced the magnitude of voltage-dependent G-protein-mediated inhibition of N-type Ba2+ currents, and this effect was eliminated by pretreatment with pertussis toxin or cholera toxin. Conclusions It was found that activation of G-proteins in a neuronal environment dramatically reduced the isoflurane potency for inhibiting N-type Ba2+ currents and, in turn, isoflurane affected the G-protein regulation of N-type Ba2+ currents.

scholarly journals Inhibition of adenylate cyclase activity by galanin in rat insulinoma cells is mediated by the G-protein Gi3

1994 ◽  
Vol 303 (2) ◽  
pp. 369-375 ◽  
Author(s):  
P de Mazancourt ◽  
P K Goldsmith ◽  
L S Weinstein
Keyword(s):  
Adenylate Cyclase ◽  
G Protein ◽  
Pancreatic Beta Cells ◽  
Protein S ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Rinm5f Cells ◽  
Insulinoma Cells ◽  
Galanin Receptors ◽  
Rat Insulinoma

Galanin inhibits adenylate cyclase activity and insulin secretion and modulates ion channels in pancreatic beta-cells through pertussis-toxin-sensitive G-protein(s). Antibodies directed against the C-terminal region of specific G-protein alpha-subunits were used to determine which G-protein(s) couple galanin receptors to inhibition of adenylate cyclase in the rat insulinoma cell line RINm5F. Preincubation of membranes with EC antibody (anti-alpha i3) decreased the inhibition of forskolin-stimulated adenylate cyclase activity by galanin (100 nM) by 45% compared with control IgG (P < 0.05) whereas preincubation with AS (anti-alpha i1, alpha i2) or GO (anti-alpha o) antibodies had no significant effect. To confirm these results, RINm5F cells were exposed intermittently over a 4-day period to phosphorothioate oligodeoxynucleotides that were either sense or antisense to alpha i1, alpha i2, alpha i3 or alpha o. Oligodeoxynucleotides antisense to alpha i2, alpha i3 and alpha o specifically decreased the levels of the targeted alpha-subunit in membranes. alpha i1 was undetectable in these cells. Inhibition of adenylate cyclase activity by galanin was largely abolished in membranes from cells exposed to the oligodeoxynucleotide antisense to alpha i3, whereas all other oligodeoxynucleotides had no significant effect on this pathway. Indirect immunofluorescence and immunoblotting of specific membrane fractions with EC antibody show significant localization of alpha i3 to intracellular membrane compartments. These results suggest that Gi3 is the G protein that couples galanin receptors to inhibition of adenylate cyclase activity in RINm5F cells.

Role of G proteins in shear stress-mediated nitric oxide production by endothelial cells

1994 ◽  
Vol 267 (3) ◽  
pp. C753-C758 ◽  
Author(s):  
M. J. Kuchan ◽  
H. Jo ◽  
J. A. Frangos
Keyword(s):  
Nitric Oxide ◽  
Endothelial Cells ◽  
Shear Stress ◽  
G Protein ◽  
G Proteins ◽  
No Production ◽  
Dependent Manner ◽  
Protein Activation ◽  
Synthase Inhibitor

Exposure of cultured endothelial cells to shear stress resulting from well-defined fluid flow stimulates the production of nitric oxide (NO). We have established that an initial burst in production is followed by sustained steady-state NO production. The signal transduction events leading to this stimulation are not well understood. In the present study, we examined the role of regulatory guanine nucleotide binding proteins (G proteins) in shear stress-mediated NO production. In endothelial cells not exposed to shear stress, AIF4-, a general activator of G proteins, markedly elevated the production of guanosine 3',5'-cyclic monophosphate (cGMP). Pretreatment with NO synthase inhibitor N omega-nitro-L-arginine completely blocked this stimulation. Incubation with guanosine 5'-O-(2-thiodiphosphate) (GDP beta S), a general G protein inhibitor, blocked the flow-mediated burst in cGMP production in a dose-dependent manner. Likewise, GDP beta S inhibited NOx (NO2 + NO3) production for the 1st h. However, inhibition was not detectable between 1 and 3 h. Pertussis toxin (PTx) had no effect on the shear response at any time point. The burst in NO production caused by a change in shear stress appears to be dependent on a PTx-refractory G protein. Sustained shear-mediated production is independent of G protein activation.

Impairment of adenylate cyclase activity and G-proteins in human uterine leiomyoma

2000 ◽  
Vol 32 (5) ◽  
pp. 399-404 ◽  
Author(s):  
A. Bajo ◽  
I. Carrero ◽  
R.L. Hrı̈stov ◽  
P. Valenzuela ◽  
P. Martı́nez ◽  
...  
Keyword(s):  
Adenylate Cyclase ◽  
G Proteins ◽  
Uterine Leiomyoma ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity
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