Dissecting G-Mediated Plasma Membrane Translocation of Sphingosine Kinase-1.

Diverse extracellular signals induce plasma membrane translocation of sphingosine kinase-1 (SphK1), thereby enabling inside-out signaling of sphingosine-1-phosphate. We have shown before that G-coupled receptors and constitutively active Gα specifically induced a rapid and long-lasting SphK1 translocation, independently of canonical G/phospholipase C (PLC) signaling. Here, we further characterized G regulation of SphK1.

Characterization of cholesterol homeostasis in sphingosine-1-phosphate lyase-deficient fibroblasts reveals a Niemann-Pick disease type C-like phenotype with enhanced lysosomal Ca storage.

Sphingosine-1-phosphate (S1P) lyase irreversibly cleaves S1P, thereby catalysing the ultimate step of sphingolipid degradation. We show here that embryonic fibroblasts from S1P lyase-deficient mice (Sgpl1-MEFs), in which S1P and sphingosine accumulate, have features of Niemann-Pick disease type C (NPC) cells. In the presence of serum, overall cholesterol content was elevated in Sgpl1-MEFs, due to upregulation of the LDL receptor and enhanced cholesterol uptake.

Upregulation of ABC transporters contributes to chemoresistance of sphingosine 1-phosphate lyase-deficient fibroblasts.

Sphingosine 1-phosphate (S1P) is an extra- and intracellular mediator that regulates cell growth, survival, migration, and adhesion in many cell types. S1P lyase is the enzyme that irreversibly cleaves S1P and thereby constitutes the ultimate step in sphingolipid catabolism. It has been reported previously that embryonic fibroblasts from S1P lyase-deficient mice (Sgpl1(-/-)-MEFs) are resistant to chemotherapy-induced apoptosis through upregulation of B cell lymphoma 2 (Bcl-2) and Bcl-2-like 1 (Bcl-xL).

Evidence for a link between histone deacetylation and Ca²+ homoeostasis in sphingosine-1-phosphate lyase-deficient fibroblasts.

Embryonic fibroblasts from S1P (sphingosine-1-phosphate) lyase-deficient mice [Sgpl1-/- MEFs (mouse embryonic fibroblasts)] are characterized by intracellular accumulation of S1P, elevated cytosolic [Ca2+]i and enhanced Ca2+ storage. Since S1P, produced by sphingosine kinase 2 in the nucleus of MCF-7 cells, inhibited HDACs (histone deacetylases) [Hait, Allegood, Maceyka, Strub, Harikumar, Singh, Luo, Marmorstein, Kordula, Milstein et al. (2009) Science 325, 1254-1257], in the present study we analysed whether S1P accumulated in the nuclei of S1P lyase-deficient MEFs and caused HDAC inhibition.

Cis-4-methylsphingosine is a sphingosine-1-phosphate receptor modulator.

Sphingosine-1-phosphate (S1P) acts as high affinity agonist at specific G-protein-coupled receptors, S1P(1-5), that play important roles e.g. in the cardiovascular and immune systems.

Enhanced Ca2+ storage in sphingosine-1-phosphate lyase-deficient fibroblasts.

Sphingosine-1-phosphate (S1P) regulates cell growth and survival, migration and adhesion in many cell types. S1P is generated by sphingosine kinases (SphKs), and dephosphorylated by phosphatases or cleaved by S1P lyase. Extracellular S1P activates specific G protein-coupled receptors while intracellular S1P can mobilize Ca2+ from thapsigargin-sensitive stores.