Acceleration by ceramide of calcium-dependent translocation of phospholipase A2 from cytosol to membranes in platelets

The effect of ceramide on Ca2+-dependent translocation of cytosolic phospholipase A(2) (cPLA(2)) to membranes was studied. Pretreatment of platelets with sphingomyelinase or C-6-ceramide (N-hexanoylsphingosine) led to apparent enhancement of Ca2+-ionophore A23187-stimulated arachidonic acid release but did not affect the cytosolic phospholipase A(2) (cPLA(2)) activity. Under these conditions, the cPLA(2) proteins in membranes increased significantly, compared with those by A23187 alone. Sphingomyelinase and C-6-ceramide, but not C-6-dihydroceramide, a control analog of C-6-ceramide, also facilitated the Ca2+-dependent increase in the cPLA(2) protein, as well as the activity, in membranes induced by addition of Ca2+ into platelet lysate. Protein kinase C alpha, which possesses a Ca2+-dependent lipid binding domain, was increased in membranes in a Ca2+-dependent manner, but the increase was not accelerated by sphingomyelinase or CB-ceramide. These findings suggest that ceramide in membranes potentiates Ca2+-dependent cPLA(2) translocation from cytosol to membranes, probably through modification of membrane phospholipid organization. (C) 2000 Academic Press.