[Change in the level of sphingosine in rat liver nuclei and cells during oncogene superexpression induced by cycloheximide]. / Izmenenie urovnia sfingozina v iadrakh i kletkakh pecheni krys pri indutsirovannoi superékspressii onkogenov tsiklogeksimidom.

Changes in the sphingosine content in rat liver cells and nuclei have been studied with reference to the level of nuclear oncogene expression, induced by cycloheximide (0.1, 0.5 and 3.0 mg/kg). It has been found that only the sublethal (3 mg/kg) dose of cycloheximide which induces the superexpression of c-fos and c-myc oncogenes can promote sphingosine accumulation in the cell. At the moment of enhanced expression of nuclear oncogenes, the maximum content of free sphingosine exceeds the control level 1.5- and 3-fold in the cell and in the nuclei, respectively. The difference in the sphingosine accumulation patterns in the cell and in the nuclei testifies to the fact that sphingomyelin metabolism is more active in the nuclei than in the cell. Sphingosine accumulation in the nuclei is characterized by coordination of sphingomyelinase activity and changes in the sphingomyelin content. A comparative analysis of activities of enzymes of sphingomyelin (sphingomyelinase) and phosphatidyl inositol (phosphatidyl inositol kinase) cycles indicates that in the nuclei the activation of the sphingomyelin cycle forestalls the cycloheximide-induced activation of the phosphatidyl inositol cycle and the maximal accumulation of nuclear oncogene mRNAs. A model of activation of oncogene expression with participation of sphingosine inhibiting protein kinase C and activating casein kinase II, the key enzymes of the signal transduction system of cell proliferation and differentiation, is proposed.

[The effect of tumor necrosis factor on the free sphingosine level and sphingomyelinase in murine liver cells and nuclei]. / Vliianie faktora nekroza opukholi na uroven'svobodnogo sfingozina i aktivnost' sfingomielinazy v kletkakh i iadrakh pecheni myshei.

The effects of the human recombinant tumour necrosis factor (TNF) (10 and 40 mg/kg of body mass) on sphingomyelinase activity and sphingosine content in mouse (C57bl) liver cells and nuclei have been studied. Whereas sphingomyelinase is known to be a key enzyme of sphingomyelin metabolism, sphingosine, being a product of deep enzymatic hydrolysis of sphingomyelin, controls the activity of various phosphokinases. The primary response of liver cell to TNF consists in the inhibition of sphingomyelinase; its activation occurs at later periods: after 2 hours at 10 mg/kg TNF and after 4 hours at 40 mg/kg TNF. In the nucleus activation of sphingomyelinase is observed within the first 60 min after TNF administration. Sphingosine accumulation in mouse liver cells and nuclei coincides in time with sphingomyelinase stimulation. In the nuclei activation of the sphingomyelin cycle by TNF is far more pronounced than in the cells, being observed at early periods after TNF injection. A signal mechanism of TNF action on mouse liver cells and nuclei involving a TNF-specific receptor and sphingosine which may activate this receptor phosphorylation is discussed.

[Change in the level of endogenous sphingosine in cell nuclei from regenerating rat liver]. / Izmenenie urovnia éndogennogo sfingozina v iadrakh kletok regeneriruiushchei pecheni krys.

High-performance liquid chromatography was used to study the changes in the sphingosine content in regenerating rat liver cell nuclei during RNA and DNA synthesis. It was found that activation of nucleic acid synthesis was accompanied by sphingosine accumulation in cell nuclei in parallel with the induction of the sphingomyelin cycle consisting in the increasing activity of sphingomyelinase and alteration of the sphingomyelin and ceramide content. To clarify the mechanism of sphingosine involvement in replication and transcription, the ability of this product to interact with DNA and modify the activity of RNA-polymerase in vitro was studied. At 10(-4) M sphingosine prevented the interaction of acridine orange with DNA and activated the transcription enzymes. Several alternative mechanisms of sphingosine involvement in the control of nucleic acid synthesis are discussed.