Prostaglandin E1 and forskolin antagonize C-kinase activation in the human platelet

Abstract

In human platelets, prostaglandin E1 and forskolin inhibit 5-hydroxytryptamine-induced phospholipase C, C-kinase and myosin light-chain kinase activity in a concentration-dependent way. Phospholipase C activation, however, was only partly inhibited, and this at higher concentrations than the protein kinases. Direct activation of the C kinase either by exogenous synthetic diacylglycerol or by 12-O-tetradecanoylphorbol 13-acetate was antagonized by prostaglandin E1 and forskolin. Since C-kinase activation is one of the key events in excitatory signal transduction in the platelets, we suggest that the inhibitory effect of agents that increase platelet cyclic AMP on platelet secretion and aggregation might reside in their capacity to antagonize C-kinase activity.

Increased protein synthesis response to insulin in fibroblasts treated with the diacylglycerol kinase inhibitor R59022

“…Inhibition of DAG kinase has been shown in both platelets and neutrophils to lead to increased DAG levels after stimulation by agonists which are thought to act through phospholipase C [20,21]. The present results show that in the presence of such a kinase inhibitor insulin causes an increase in the incorporation of radioactive glycerol into 1,2-DAG in 3T3 ceils.…”

“…Diacylglycerol synthesis can be assessed qualitatively but not in absolute terms by measuring the amount of radioactivity in DAG after prelabelling of cells with [3H]glycerol [19]. Using such methods R59022 alone was found to have no effect on DAG synthesis (as also found in [19,20]); in seven experiments the mean stimulation was 3 + 9% (SE). However, in the presence of the inhibitor a marked stimulation (mean stimulation of 90 + 16°70 using five separate cell preparations) of DAG labelling was detected in response to 1 mU/ml insulin (table 2).…”

The synergistic effect of serotonin and epinephrine on the human platelet at the level of signal transduction

“…500&i [32P]orthophosphate/ml. Phospholipid extraction, phospholipid analysis and phosphoprotein analysis were performed exactly as described in [24,25].…”

Purification, cDNA‐cloning and expression of human diacylglycerol kinase

“…Among the compounds which have been described to inhibit DG kinase [31,32], the compound R59022 [32] is indeed a potent inhibitor of the human WBC enzyme, but 1-monooleoylglycerol and 1,2-dioctanoylethylene glycol are not (data not shown). Furthermore, the enzyme is also inhibited by .,v '-ethylmaleimide and …”