Modulation of sphingolipid biosynthesis in primary cultured neurons by long chain bases

Sphingosine-1-phosphate, a novel second messenger involved in cell growth regulation and signal transduction, affects growth and invasiveness of human breast cancer cells

This review will focus on the role of sphingosine and its phosphorylated derivative sphingosine-1-phosphate (SPP) in cell growth regulation and signal transduction. We will show that many of the effects attributed to sphingosine in quiescent Swiss 3T3 fibroblasts are mediated via its conversion to SPP. We propose that SPP has appropriate properties to function as an intracellular second messenger based on the following: it elicits diverse cellular responses; it is rapidly produced from sphingosine by a specific kinase and rapidly degraded by a specific lyase; its concentration is low in quiescent cells but increases rapidly and transiently in response to the growth factors, fetal calf serum (FCS) and platelet derived growth factor (PDGF); it releases Ca2+ from internal sources in an InsP3-independent manner; and finally, it may link sphingolipid signaling pathways to cellular ras-mediated signaling pathways by elevating phosphatidic acid levels. The effects of this novel second messenger on growth, differentiation and invasion of human breast cancer cells will be discussed.

Modulation of the free sphingosine levels in Epstein Barr virus transformed human B lymphocytes by phorbol dibutyrate

The amounts of free sphingosine in Epstein Barr virus transformed B lymphocytes (EBV-B) treated with sphingosine and phorbol-12,13-dibutyrate (PD) has been quantified by high performance liquid chromatography (HPLC). PD treatment did not affect intracellular sphingosine level, while it seems to lessen the removal of this long chain base in sphingosine-treated EBV-B cells. The previous results relative to sphingosine-dependent changes in choline-metabolite levels have to be interpreted on the basis of these results.

Sphingolipid biosynthesis in cultured neurons. Down-regulation of serine palmitoyltransferase by sphingoid bases

Addition of exogenous sphingosine homologues (D-erythro configuration) with different alkyl chain lengths (12 and 18 carbon atoms) to the medium of primary cultured cerebellar cells resulted in a decrease of serine palmitoyltransferase activity in a time- and concentration-dependent manner. This enzyme catalyzes the first committed step in sphingolipid biosynthesis. Half-maximal reduction of enzyme activity occurred after a 4-h treatment with 25 microM sphingoid bases. Maximal decrease (approx. 80%) was obtained after treating the cells for 4-8 h with 50 microM long-chain bases. When a biosynthetically inert sphingoid, azidosphingosine (10-50 microM), was fed to the cells, decrease of 3-ketosphinganine formation was much slower, reaching its maximum (approx. 80%) after 24 h. In contrast to D-erythro-sphingosine, L-threo-C18-sphingosine did not yield any decrease of serine palmitoyltransferase activity when added to the cells under identical experimental conditions. Decrease of serine palmitoyltransferase activity was fully reversible after removal of the long-chain bases from the culture medium. Activities of other enzymes of lipid metabolism, ceramide synthase, long-chain acyl-CoA synthase and choline phosphotransferase, were not affected by the addition of sphingoid bases, indicating that the down regulation of serine palmitoyltransferase is quite specific.