Sphingosine kinase expression regulates apoptosis and caspase activation in PC12 cells

Abstract

Sphingosine-1-phosphate (SPP), a bioactive sphingolipid metabolite, suppresses apoptosis of many types of cells, including rat pheochromocytoma PC12 cells. Elucidating the molecular mechanism of action of SPP is complicated by many factors, including uptake and metabolism, as well as activation of speci®c G-protein-coupled SPP receptors, known as the endothelial differentiation gene-1 (EDG-1) family. In this study, we overexpressed type 1 sphingosine kinase (SPHK1), the enzyme that converts sphingosine to SPP, in order to examine more directly the role of intracellularly generated SPP in neuronal survival. Enforced expression of SPHK1 in PC12 cells resulted in signi®cant increases in kinase activity, with corresponding increases in intracellular SPP levels and concomitant decreases in both sphingosine and ceramide, and marked suppression of apoptosis induced by trophic factor withdrawal or by C 2 -ceramide. NGF, which protects PC12 cells from serum withdrawal-induced apoptosis, also stimulated SPHK1 activity. Surprisingly, overexpression of SPHK1 had no effect on activation of two known NGFstimulated survival pathways, extracellular signal regulated kinase ERK 1/2 and Akt. However, trophic withdrawal-induced activation of the stress activated protein kinase, c-Jun amino terminal kinase (SAPK/JNK), and activation of the executionary caspases 2, 3 and 7, were markedly suppressed. Moreover, this abrogation of caspase activation, which was prevented by the SPHK inhibitor N,N-dimethylsphingosine, was not affected by pertussis toxin treatment, indicating that the cytoprotective effect was likely not mediated by binding of SPP to cell surface G i -coupled SPP receptors. In agreement, there was no detectable release of SPP into the culture medium, even after substantially increasing cellular SPP levels by NGF or sphingosine treatment. In contrast to PC12 cells, C6 astroglioma cells secreted SPP, suggesting that SPP might be one of a multitude of known neurotrophic factors produced and secreted by glial cells. Collectively, our results indicate that SPHK/SPP may play an important role in neuronal survival by regulating activation of SAPKs and caspases.

CXCL4‐induced monocyte survival, cytokine expression, and oxygen radical formation is regulated by sphingosine kinase 1

“…3B and 4, or published earlier by our group [3]), indicating that caspase activity is regulated by these kinases in monocytes. Our results support previous findings by Edsall et al [35], who could demonstrate that overexpression of SphK1 in neuronal cells leads to suppression of caspases. Moreover, in 2003 Allan et al described that inhibition of caspase-9 is mediated through phosphorylation by Erk [36].…”

213Bi-induced death of HSC45-M2 gastric cancer cells is characterized by G2 arrest and up-regulation of genes known to prevent apoptosis but induce necrosis and mitotic catastrophe

“…With respect to regulation of proliferation and apoptosis, the CD36 receptor ligand thrombospondin 1 presents both stimulatory and inhibitory effects (25). As observed in PC12 cells, increased expression of SPHK1 resulted in increases of sphingosine-1-phosphate levels and marked suppression of apoptosis (26). This again suggests that 213 Bi-induced cell death is different from apoptosis as already postulated (10).…”

Hypoxia Enhances Sphingosine Kinase 2 Activity and Provokes Sphingosine-1-Phosphate-Mediated Chemoresistance in A549 Lung Cancer Cells

“…Although both SphK enzymes are located intracellularly and first reports on signaling properties of S1P described intracellular effects, the identification of direct S1P targets awaits further clarification (15,27,28). Besides, S1P is exported from the cell by members of the ATP-binding cassette transporter family.…”