THE MECHANISM OF SPHINGOSINE ENHANCEMENT OF PHORBOL ESTER-MEDIATED PHOSPHOLIPASE-D ACTIVATION IN LYMPHOCYTES

Tumor-promoting phorbol esters stimulate the production of phosphatidy lethanol (PEt) in bovine lymph node lymphocytes through the activation of Phospholipase D (PLD). Sphingosine enhanced the 12-O-tetradecanoyl phorbol-13-acetate (TPA)-mediated formation of PEt in lymphocytes, whi le it had no effect by itself. Interestingly, the incorporation of lab eled arachidonic acid into phospholipids was increased by sphingosine. Examination of the effect of sphingosine along with TPA on the incorp oration of [1-C-14]labeled-arachidonic acid into individual phospholip ids revealed that they enhanced significantly the specific activity of only PC These observations indicate that sphingosine does not activat e PLD It appears that sphingosine increases the specific radioactivity of the substrate pool for PLD which results in an apparent increase i n PEt when both sphingosine and TPA are present. (C) 1995 Academic Pre ss, Inc.