α<sub>2A</sub>‐Adrenergic receptors activate protein kinase C in human platelets via a pertussis toxin‐sensitive G‐protein

Nieuwiand, Rienk; Wijburg, Odilia L. C.; Willigen, Gijsbert van; Akkerman, Jan-Willem Ν.

doi:10.1016/0014-5793(94)80389-7

Cited by 15 publications

(5 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Indeed, Erk1/2 phosphorylation may be mediated by either Gq or Gi/o and be dependent on PKC or Ras activation 2040 As α 2 adrenoceptors stimulate PKC via a Gi dependent pathway in OK cells or in human platelets,41 42 and as they increase phospholipase C activity and intracellular Ca ++ in HEL or transfected CHO cells,43 we investigated if the effect of UK14304 involved PKC activation. Short term exposure of Caco2-3B cells to the PKC activator PMA resulted in an increase in Erk phosphorylation.…”

Section: Discussionmentioning

confidence: 99%

Alpha2 adrenoceptors regulate proliferation of human intestinal epithelial cells

Schaak

Cussac

Cayla

et al. 2000

Gut

View full text Add to dashboard Cite

Background and aims-Previous studies on rodents have suggested that catecholamines stimulate proliferation of the intestinal epithelium through activation of 2 adrenoceptors located on crypt cells. The occurrence of this eVect awaits demonstration in humans and the molecular mechanisms involved have not yet been elucidated. Here, we examined the eVect of 2 agonists on a clone of Caco2 cells expressing the human 2A adrenoceptor. Methods-Cells were transfected with a bicistronic plasmid containing the 2C10 and neomycin phosphotransferase genes. G418 resistant clones were assayed for receptor expression using radioligand binding. Receptor functionality was assessed by testing its ability to couple Gi proteins and to inhibit cAMP production. Mitogen activated protein kinase (MAPK) phosphorylation was followed by western blot, and cell proliferation was estimated by measuring protein and DNA content. Results-Permanent transfection of Caco2 cells allowed us to obtain a clone (Caco2-3B) expressing 2A adrenoceptors at a density similar to that found in normal human intestinal epithelium. Caco2-3B retained morphological features and brush border enzyme expression characteristic of enterocytic diVerentiation. The receptor was coupled to Gi2/Gi3 proteins and its stimulation caused marked diminution of forskolin induced cAMP production. Treatment of Caco2-3B with UK14304 ( 2 agonist) induced a rapid increase in the phosphorylation state of MAPK, extracellular regulated protein kinase 1 (Erk1), and 2 (Erk2). This event was totally abolished in pertussis toxin treated cells and in the presence of kinase inhibitors (genistein or PD98059). It was unaVected by protein kinase C downregulation but correlated with a transient increase in Shc tyrosine phosphorylation. Finally, sustained exposure of Caco2-3B to UK14304 resulted in modest but significant acceleration of cell proliferation. None of these eVects was observed in the parental cell line Caco2. Conclusion-The results obtained in the present study support a regulatory role for 2 adrenoceptors in intestinal cell proliferation. (Gut 2000;47:242-250)

show abstract

Section: Discussionmentioning

confidence: 99%

Alpha2 adrenoceptors regulate proliferation of human intestinal epithelial cells

Schaak

Cussac

Cayla

et al. 2000

Gut

View full text Add to dashboard Cite

show abstract

“…The purpose of this study was to investigate the effects of cAMP enhancing drugs on platelet aggregation, in experimental conditions that provide the concomitant activation of G i and G q , and to assess whether the inhibitory action is exerted directly at the level of ␣IIb␤3 and not merely due to the lack of ADP release. For this purpose we studied the effects of high concentrations of iloprost on platelet aggregation and fibrinogen binding evoked by the simultaneous activation of G q (by means of U46619) and G i (by means of epinephrine) (16) proteins. In a recent work we have shown that the activation of an enzyme downstream of Gq, such as phospholipase C (PLC) or protein kinase C (PKC), was able to cause the conformational changes in the integrin ␣IIb␤3 provided a G i protein coupled receptor was activated (17).…”

mentioning

confidence: 99%

Evidence for Platelet αIIbβ3 Activation despite Elevated Cytosolic cAMP

2001

View full text Add to dashboard Cite

SummaryCyclic nucleotides, such as cAMP, are known to inhibit the multistep cascade that results in platelet aggregation. In the present study we provide evidence that it is possible to bypass cAMP inhibitory effect on fibrinogen binding site exposure induced by the thromboxane A2 synthetic analogue U46619, the snake venom toxin convulxin, or by the direct PKC activator OAG, by concomitantly activating a Gi-coupled receptor by means of epinephrine or by inducing cytosolic calcium influx by means of ionomycin. In fact, in our study we demonstrate that, in iloprost-treated platelets, the inhibition of both platelet aggregation and fibrinogen binding was overcome by adding epinephrine or ionomycin. To further confirm this, we used the cAMP analogue dibutyryl cAMP and we obtained platelet aggregation in response to U46619, convulxin or OAG plus epinephrine. Moreover, a complete inhibition of platelet aggregation in the presence of high concentrations of cAMP was observed only in the case of U46619, while a small percentage of aggregation persisted when convulxin or OAG were used, due to the small amount of ADP that both convulxin and OAG are able to release.Since PKC inhibition didn’t allow platelet aggregation to occur in response to the concomitant activation of U46619 or convulxin, plus epinephrine or ionomycin, we can conclude that cAMP-induced inhibition of aggregation can be counteracted by the simultaneous activation of PKC in the presence of an activated Gi-coupled receptor or of an induced calcium influx.

show abstract

“…The most likely subtype of G protein mediating this effect is Gi as linkage between a2-adrenoceptors and this G protein has been described in other cell types (Limbird, 1988;Nieuwland et al, 1994). However, the possibility that the action of a2-adrenoceptors is mediated by some other pertussis toxinsensitive G protein cannot be excluded.…”

Section: Discussionmentioning

confidence: 99%

The mechanism of action of α₂‐adrenoceptors in human isolated subcutaneous resistance arteries

Parkinson

Hughes

1995

British J Pharmacology

View full text Add to dashboard Cite

pertussis toxin inhibited responses to azepexole, but had no significant effect on tone induced by KPSS or noradrenaline. ETYA, an inhibitor of phospholipase A2, lipoxygenase and cyclo-oxygenase, had no effect on azepexole-induced contraction in the presence of NW nitro-L-arginine methyl ester. 6 Azepexole, a selective a2-adrenoceptor agonist, contracts human subcutaneous resistance arteries by a mechanism largely dependent on the influx of extracellular Ca2", probably through voltage-operated calcium channels. This action involves a pertussis toxin-sensitive G protein, possibly GQ.

show abstract

α_2A‐Adrenergic receptors activate protein kinase C in human platelets via a pertussis toxin‐sensitive G‐protein

Cited by 15 publications

References 36 publications

Alpha2 adrenoceptors regulate proliferation of human intestinal epithelial cells

Alpha2 adrenoceptors regulate proliferation of human intestinal epithelial cells

Evidence for Platelet αIIbβ3 Activation despite Elevated Cytosolic cAMP

The mechanism of action of α₂‐adrenoceptors in human isolated subcutaneous resistance arteries

Contact Info

Product

Resources

About

α2A‐Adrenergic receptors activate protein kinase C in human platelets via a pertussis toxin‐sensitive G‐protein

Cited by 15 publications

References 36 publications

Alpha2 adrenoceptors regulate proliferation of human intestinal epithelial cells

Alpha2 adrenoceptors regulate proliferation of human intestinal epithelial cells

Evidence for Platelet αIIbβ3 Activation despite Elevated Cytosolic cAMP

The mechanism of action of α2‐adrenoceptors in human isolated subcutaneous resistance arteries

Contact Info

Product

Resources

About

α_2A‐Adrenergic receptors activate protein kinase C in human platelets via a pertussis toxin‐sensitive G‐protein

The mechanism of action of α₂‐adrenoceptors in human isolated subcutaneous resistance arteries