Dual regulation of sphingosine 1-phosphate-induced phospholipase D activity through RhoA and protein kinase C-α in C2C12 myoblasts

Previous studies showed that in C2C12 cells, phospholipase D (PLD) and its known regulators, RhoA and protein kinase C alpha (PKC alpha), were downstream effectors in sphingosine I-phosphate (SPP) signalling. Moreover, the role of PKC for SPP-mediated PLD activation and the requirement of PKC alpha for RhoA translocation were reported. The present results demonstrated that inactivation of RhoA, by overexpression of RhoGDP dissociation inhibitor (RhoGDI) as well as treatment with C3 exotoxin, attenuated SPP-stimulated PLD activity, supporting the involvement of RhoA in the stimulation of PLD activity by the bioactive lipid in C2C12 myoblasts. In addition, the effect of PKC alpha inhibitor Go6976 on the SPP-induced PLD activation in myoblasts, where RhoA function was inactivated, was consistent with a dual regulation of the enzyme through RhoA and PKC alpha. Interestingly, the subcellular distribution of PLD isoforms, RhoA and PKC alpha, in SPP-stimulated cells supported the view that the functional relationship between the two PLD regulators, demonstrated to occur in SPP signalling, represents a novel mechanism of regulation of specifically localized PLD. (C) 2001 Elsevier Science Inc. All rights reserved.