Chromatin neutral sphingomyelinase and its role in hepatic regeneration.

Ceramide acts as a second messenger and modulates many cellular functions. This molecule can be produced by enzymatic digestion of sphingomyelin, a phospholipid which has been shown to be in high concentration in a chromatin phospholipidic fraction. In order to clarify whether chromatin sphingomyelin has a role in this signal transduction pathway, it is necessary to define the sphingomyelin cycle. Neutral sphingomyelinase represents the first step of the cycle. In this paper we demonstrate that sphingomyelinase activity can be detected also in the chromatin of rat hepatocyte nuclei and it increases in relation to the entrance in S phase of hepatocyte after hepatectomy. The enzyme can be distinguished from that present in the nuclear envelope on the basis of optimum pH and Km. The role of the spingomyelin pathway in relation to liver regeneration is discussed.