Department of Experimental Medicine and Biochemical Sciences, University of Rome 'Tor Vergata', 00133 Rome, Italy. E-mail: tesrob@flashnet.it.
A growing number of cell surface receptors are now being shown to generate signals that trigger the hydrolysis of sphingomyelin to release diffusible ceramides. Ceramides have been implicated as key mediators in signaling pathways, with outcomes as diverse as cellular activation, proliferation, differentiation, growth arrest and apoptosis. The response depends on cell type, whether the signal is integrated with other signals and on the subcellular location of sphingomyelin hydrolysis and ceramide release.