Sphingomyelin-degrading pathways in human cells - Role in cell signalling

The ubiquitous sphingophospholipid sphingomyelin (SM) can be hydrolysed in human cells to ceramide by different sphingomyelinases (SMases). These enzy mes exert a dual role, enabling not only the turnover of membrane SM and th e degradation of exogenous (lipoprotein) SM, but also the signal-induced ge neration of the lipid second messenger ceramide. This review focuses on the function(s) of the different SMases in living cells. While both lysosomal and non-lysosomal pathways that ensure SM hydrolysis in intact cells can be distinguished, the precise contribution of each of these SM-cleaving enzym es to the production of ceramide as a signalling molecule remains to be cla rified. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.