Sphingolipids as differential regulators of cellular signalling processes

Sphingomyelin is a phospholipid that is preferentially located in the outer leaflet of the plasma membrane of mammalian cells. It can be hydrolysed by three distinct isoforms of a phospholipase C (PLC)-like enzyme, sphingomyelinase, which are distinguished by their pH optima and Mg2+-dependence. Activation of sphingomyelinase occurs in response to stimulation of a number of distinct cell-surface receptors by a variety of biological agonists, such as cytokines and growth factors [l]. Several metabolites of sphingomyelin have been identified as potential second-messenger molecules