Dissociation of endogenous cellular ceramide from NF-kappa B activation

Ceramide: an endogenous regulator of apoptosis and growth suppression

The action of several cytokines is mediated via activation of the sphingomyelin cycle of signal transduction. Ceramide, the product of this pathway, is emerging as an intracellular messenger that mediates effects on terminal differentiation, apoptosis and cell-cycle arrest. Here, Marina Pushkareva, Lina Obeid and Yusuf Hannun discuss the regulation and mechanism of action of this stress-activated pathway.

Ceramide: a stress signal and mediator of growth suppression and apoptosis

A novel pathway termed the sphingomyelin cycle has been identified whereby membrane sphingomyelin is hydrolyzed in response to multiple extracellular stimuli (such as tumor necrosis factor alpha) which cause activation of regulated sphingomyelinases. The product, ceramide, has emerged as a second messenger that mediates many of the cellular effects of these extracellular stimuli. An intriguing relation exists between activation of the sphingomyelin cycle and the action of multiple stress stimuli that induce growth arrest and programmed cell death. Exogenously administered ceramide mimics these growth-suppressing effects, including the induction of apoptosis. This review will highlight the role of the sphingomyelin cycle in signal transduction and will focus on the role and function of ceramide in the regulation of cell growth in general and apoptosis specifically.

A neutral galactocerebroside sulfate sulfatidase from mouse brain

We have described an enzyme in brain that catabolizes galactocerebroside sulfatide with a pH optimum of 7.2. To our knowledge, this is the first description of a catabolic enzyme for sulfatide at a neutral pH. Activity at a neutral pH implies a non-lysosomal location for this sulfatidase. Galactocerebroside sulfate sulfatidase (n-sulfatidase) activity was not apparent in crude microsomal extracts and was detected following partial purification of the enzyme. This enzyme, n-sulfatidase, differs from other arylsulfatases in its M(r), inability to bind to concanavalin A, and substrate specificity; n-sulfatidase was unable to hydrolyze p-nitrocatechol sulfate or estrone sulfate. The molecular mass of n-sulfatidase obtained by Sephacryl S-200 chromatography was 72 kDa, and the active fraction from this procedure was purified > 600-fold by isoelectric focusing. Following SDS-polyacrylamide gel electrophoresis, two bands were obtained with apparent molecular masses of 58 and 66 kDa. Enzyme activity was regenerated from both of these bands, with the 66-kDa band showing greater activity. The Km of the sulfatidase was determined as 5.8 x 10(-5) M. The pI of n-sulfatidase was 7.7 in contrast to the pI of 4.9 for the sulfotransferase. No requirement was found for Mg2+ or ATP for sulfatidase activity; vitamin K1 enhanced sulfatidase activity approximately 3.3-fold. Therefore, this enzyme may have a role in the pathogenesis of metachromatic leukodystrophy in which sulfatides accumulate in the nervous and other tissues and in myelination since sulfatides are an important component of myelin.