CHROMATIN NEUTRAL SPHINGOMYELINASE AND ITS ROLE IN HEPATIC REGENERATION

Ceramide acts as a second messenger and modulates many cellular functi ons. This molecule can be produced by enzymatic digestion of sphingomy elin, a phospholipid which has been shown to be in high concentration in a chromatin phospholipidic fraction. In order to clarify whether ch romatin sphingomyelin has a role in this signal transduction pathway, it is necessary to define the sphingomyelin cycle. Neutral sphingomyel inase represents the first step of the cycle. In this paper we demonst rate that sphingomyelinase activity can be detected also in the chroma tin of rat hepatocyte nuclei and it increases in relation to the entra nce in S phase of hepatocyte after hepatectomy. The enzyme can be dist inguished from that present in the nuclear envelope on the basis of op timum pH and Km. The role of the spingomyelin pathway in relation to l iver regeneration is discussed. (C) 1997 Academic Press.