Different regulation of phospholipase D activity in glioma C6 cells by sphingosine, propranolol, imipramine and phorbol ester.

ABSTRACT

In has been found that sphingosine, propranolol, imipramine and phorbol ester (12-O-tetradecanoylphorbol-13-acetate, TPA) have a stimulatory effect on phospholipase D activity in glioma C6 cells. The cells were prelabelled with [1-(14)C]palmitic acid and phospholipase D-mediated synthesis of [(14)C]phosphatidylethanol was measured. The enhancing effect of TPA was almost completely blocked by a specific protein kinase C inhibitor, GF 109203X. In contrast, GF 109203X failed to inhibit the sphingosine, imipramine and propranolol stimulatory effects, indicating that their stimulation was independent of protein kinase C. The effect of TPA on phospholipase D was also blocked by imipramine and propranolol, whereas sphingosine additively potentiated TPA-mediated phospholipase D activity, both at shorter and longer (2-60 min) times of incubation. These results suggest that in glioma C6 cells, sphingosine is not only involved in a different phospholipase D activation than the TPA regulatory system, but also that it operates in a different compartment of the cell.