GTP analogues stimulate inositol trisphosphate formation transiently in Dictyostelium

1987 ◽  
Vol 87 (4) ◽  
pp. 513-518
Author(s):  
G.N. Europe-Finner ◽  
P.C. Newell
Keyword(s):  
Cyclic Amp ◽  
G Proteins ◽  
Inositol Trisphosphate ◽  
Signal Transduction Pathway ◽  
Transduction Pathway ◽  
Permeabilized Cells ◽  
Maximal Stimulation ◽  
Gamma S ◽  
Stimulation Of

Permeabilization of amoebae of Dictyostelium discoideum with saponin was found not to uncouple the chemotactic cell surface cyclic AMP receptors from inositol trisphosphate (IP3) formation, and stimulation of permeabilized amoebae with 50 nM-cyclic AMP produced peaks of IP3 at 5, 15 and 30 s in a manner comparable to that seen previously in non-permeabilized cells. The possible involvement of a GTP-binding protein (G-protein) in this IP3 signal transduction pathway was investigated by studying the effects on such permeabilized amoebae of added GTP and non-hydrolysable GTP analogues. While GDP produced only very minor effects, stimulation of the amoebae (in the absence of added cyclic AMP) with GTP or the non-hydrolysable GTP analogues GTP gamma S (guanosine 5′-O-(3-thio-triphosphate] and Gpp(NH)p (5′-guanylylimidodiphosphate) induced transient formation of IP3 in an oscillatory manner, with peaks similar in magnitude and timing to those elicited by cyclic AMP. A dose-response curve for GTP gamma S indicated a concentration for half-maximal stimulation of approximately 8 microM. When tested at 300 s after addition of GTP gamma S, the basal level of IP3 was found to be twofold elevated with shallow (presumably asynchronous) oscillations still just discernible. The significance of the IP3 oscillations elicited by GTP and its analogues is discussed in relation to the mechanism of signal adaptation and the presumed role of G-proteins.

scholarly journals Adaptation to chemotactic cyclic AMP signals in Dictyostelium involves the G-protein

1987 ◽  
Vol 88 (4) ◽  
pp. 537-545
Author(s):  
N.V. Small ◽  
G.N. Europe-Finner ◽  
P.C. Newell
Keyword(s):  
Cyclic Amp ◽  
G Protein ◽  
Cyclic Gmp ◽  
Transduction Pathway ◽  
Adaptation Mechanism ◽  
Permeabilized Cells ◽  
Inositol 1,4,5 Trisphosphate ◽  
Gamma S ◽  
Stimulation Of

Amoebae of Dictyostelium discoideum show adaptation towards a chemotactic cyclic AMP signal. Within a few seconds of receipt of the signal they are inhibited for a period of 1–2 min from further chemotactic responses to subsequent cyclic AMP signals of similar or smaller magnitude. The site of this adaptation mechanism in the chemotactic transduction pathway was investigated by addition of components of the transduction chain (GTP analogues, myo-inositol-1,4,5-trisphosphate (InsP3) and Ca2+) to permeabilized cells followed by determination of the amount of cyclic GMP formed as a measure of the chemotactic response. This approach was made possible by finding that permeabilization of amoebae with saponin did not uncouple the cell surface cyclic AMP receptors from stimulation of cyclic GMP formation. It was found that InsP3 and Ca2+ were ‘downstream’ from the adaptation mechanism: they could trigger a cyclic GMP response in cyclic AMP-adapted amoebae but could not themselves induce adaptation. In contrast, GTP gamma S was unable to trigger a cyclic GMP response in cyclic AMP-adapted cells, although it could trigger multiple cyclic GMP responses in non-adapted cells. We deduce that the site of adaptation to cyclic AMP stimulation is at the G-protein involved in this signalling pathway. Moreover, as GTP gamma S was found to be unable to induce adaptation, we conclude that the mechanism of adaptation involves an action of the cyclic AMP receptor on the G-protein that is distinct from its commonly reported action of stimulating G-protein binding of GTP.

Effect of flow on prostaglandin E2 and inositol trisphosphate levels in osteoblasts

1991 ◽  
Vol 261 (3) ◽  
pp. C428-C432 ◽  
Author(s):  
K. M. Reich ◽  
J. A. Frangos
Keyword(s):  
Fluid Flow ◽  
Prostaglandin E2 ◽  
Inositol Trisphosphate ◽  
Mechanical Strain ◽  
Signal Transduction Pathway ◽  
Fold Increase ◽  
Prostaglandin Synthesis ◽  
External Signal ◽  
Transduction Pathway ◽  
Stimulation Of

Osteoblasts in culture respond to mechanical strains. Fluid flow has been shown to increase intracellular adenosine 3',5'-cyclic monophosphate levels in cultured osteoblasts, and this response is mediated by prostaglandin synthesis. The signal transduction pathway of these cells exposed to fluid flow is still unknown. In the present study, we have demonstrated a 9- and 20-fold increase in the rate of prostaglandin E2 (PGE2) production in osteoblasts exposed to low (6 dyn/cm2) and high (24 dyn/cm2) steady shear, respectively. We further observed that fluid flow induced increases in the intracellular levels of inositol trisphosphate (IP3), another important second messenger. A shear stress of 24 dyn/cm2 increased IP3 levels dramatically for up to 2 h. Removal of flow resulted in a gradual return of IP3 to basal levels. The stimulation of IP3 levels was partially inhibited by 20 microM ibuprofen and 14 microM indomethacin, indicating that the IP3 response was partly dependent on flow-induced prostaglandin synthesis. The IP3 response was unaffected by daltroban, a specific thromboxane antagonist. These results show that fluid flow induced prostaglandin E2 production and increased intracellular levels of IP3 in osteoblasts. This suggests that flow may be the external signal produced by loading and that these messengers may be involved in the transduction of mechanical strain into a biochemical response.

Signal transduction pathway and physiological role of endothelin in the kidney

1994 ◽  
Vol 1 ◽  
pp. 80
Author(s):  
K. Tomita ◽  
A. Owada ◽  
H. Nonoguchi ◽  
Y. Terada ◽  
F. Marumo
Keyword(s):  
Signal Transduction ◽  
Signal Transduction Pathway ◽  
Physiological Role ◽  
Transduction Pathway

scholarly journals The role of insulin in the modulation of glucagon-dependent control of phenylalanine hydroxylation in isolated liver cells

1987 ◽  
Vol 242 (3) ◽  
pp. 655-660 ◽  
Author(s):  
M J Fisher ◽  
A J Dickson ◽  
C I Pogson
Keyword(s):  
Cyclic Amp ◽  
Insulin Action ◽  
Phenylalanine Hydroxylase ◽  
Liver Cells ◽  
Phosphorylation State ◽  
Isolated Liver Cells ◽  
The Impact ◽  
Isolated Liver ◽  
Stimulation Of

The stimulation of phenylalanine hydroxylation in isolated liver cells by sub-maximally effective concentrations of glucagon (less than 0.1 microM) is antagonized by insulin (0.1 nM-0.1 microM). This phenomenon is a consequence of a decrease in the glucagon-stimulated phosphorylation of phenylalanine hydroxylase from liver cells incubated in the presence of insulin. The impact of insulin on the phosphorylation state and activity of the hydroxylase is mimicked by incubation of liver cells in the presence of orthovanadate (10 microM). A series of cyclic AMP and cyclic GMP analogues enhanced phenylalanine hydroxylation: in each case insulin diminished the stimulation of flux. These results are discussed in the light of the characteristics of insulin action on other metabolic processes.

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