Ceramide: a novel second messenger.

Sphingomyelin used to be considered only as a structural molecule of the outer leaflet of the plasma membrane of mammalian cells. However, in the last five years it has become clear that sphingomyelin is rapidly degraded and resynthesized in a pathway that could function in signal transduction. Indeed, it is now known that this pathway plays a role in signal transduction for at least one cytokine, tumour necrosis factor alpha. It seems possible that other cell surface receptors will also utilize this pathway for signalling.