Sphingosine-like stimulatory effects of propranolol on phospholipase D activity in NIH 3T3 fibroblasts

Propranolol and sphingosine exhibit several common biochemical effects, including inhibition of phosphatidic acid phosphohydrolase and protein kinase C (PKC) activities. In NIH 3T3 fibroblasts, sphingosine has also been shown to stimulate phospholipase D (PLD)-mediated hydrolysis of both phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) (Kiss Z and Anderson WB, J Biol Chem 265: 7345-7350, 1990). The present study demonstrates that in [14C]palmitic acid-labeled NIH 3T3 fibroblasts, propranolol (50-100 microM) and sphingosine had similar stimulatory effects on PLD-mediated synthesis of phosphatidylethanol in the presence of ethanol. In [14C]choline- and [14C]-ethanolamine-labeled fibroblasts, both compounds also stimulated the hydrolysis of both [14C]PtdCho and [14C]PtdEtn. However, while sphingosine preferentially stimulated PtdEtn hydrolysis, propranolol had greater effects on PtdCho hydrolysis. At each time point examined (15-45 min), lower concentrations (25-50 microM) of propranolol and 100 nM phorbol 12-myristate 13-acetate (PMA) synergistically enhanced PtdEtn hydrolysis; a higher concentration (100 microM) of propranolol inhibited this PMA effect only when the incubation time was 45 min. On the other hand, propranolol (10-100 microM) had either no effect or it inhibited PMA-induced PtdCho hydrolysis after treatments for 15 or 45 min, respectively. These potentiating and inhibitory actions of propranolol on the hydrolysis of PtdCho and PtdEtn were similarly elicited by sphingosine. The present study identified the PLD system as another common target for the pharmacological actions of sphingosine and propranolol.