Sphingosine kinase activity counteracts ceramide-mediated cell death in human melanoma cells: role of Bcl-2 expression

Abstract

While most of the pharmacological therapies for melanoma utilize the apoptotic machinery of the cells, the available therapeutic options are limited due to the ability of melanoma cells to resist programmed cell death. Human melanoma cell lines A-375 and M186 are sensitive to ceramide-and Fas-induced cell death, while Mel-2a and M221 are resistant. We have now found that Mel-2a and M221 cells have a significantly higher ceramide/sphingosine-1-phosphate (S1P) ratio than A-375 and M186 cells. As sphingosine kinase (SphK) type 1 plays a critical role in determining the dynamic balance between the proapoptotic sphingolipid metabolite ceramide and the prosurvival S1P, we examined its role in apoptosis of melanoma cells. Increasing SphK1 expression reduced the sensitivity of A-375 melanoma cells to Fas-and ceramide-mediated apoptosis. Conversely, downregulation of SphK1 with small interfering RNA decreased the resistance of Mel-2a cells to apoptosis. Importantly, overexpression of the prosurvival protein Bcl-2 in A-375 cells markedly stimulated SphK1 expression and activity, while downregulation of Bcl-2 reduced SphK1 expression. This link between Bcl-2 and SphK1 might be an additional clue to chemotherapy resistance of malignant melanoma.

Sphingosine kinase 1 and 2 regulate the capacity of mesangial cells to resist apoptotic stimuli in an opposing manner

“…Limaye et al (2005) showed that S1P generated by SK-1 overexpression in endothelial cells exerted a cell protective effect due to activation of PKB and specific upregulation of Bcl-2. On the other hand, it was shown that cellular overexpression of Bcl-2 in A-375 cells markedly stimulated SphK1 expression and activity, whereas downregulation of Bcl-2 decreased SphK1 expression (Bektas et al, 2005). The relationship between Bcl-2 and SK-1 seems to be cell-type-specific, because no significant changes in Bcl-2 mRNA or protein expression were caused by either SK-1 or SK-2 depletion in renal mesangial cells ( Figure 4A) and, importantly, in whole kidney (data not shown).…”

The natural marine anhydrophytosphingosine, Jaspine B, induces apoptosis in melanoma cells by interfering with ceramide metabolism

“…Three main metabolic pathways can modulate ceramide levels to produce nonantiproliferative sphingolipids: (i) biosynthesis of sphingomyelin (SM) through sphingomyelin synthase (SMS), (ii) biosynthesis of cerebrosides through glycosyltransferases and (iii) production of sphingosine and then sphingosine-1-phosphate via ceramidase and sphingosine kinase [6]. In human melanoma cell lines, resistance to stress-induced apoptosis has been associated with low ceramide levels and, conversely, high sphingosine-1-phosphate levels and sphingosine kinase activity [7]. On the contrary, treatment with a ceramidase inhibitor was shown to 4 increase ceramide content and elicit apoptosis [8].…”

Sphingosine kinase-1 mediates BCR/ABL-induced upregulation of Mcl-1 in chronic myeloid leukemia cells

“…expression of Mcl-1 through the activation of RAS/ RAF/MAP kinase pathway (Aichberger et al, 2005). Recently, several reports have shown that SPK1 and S1P signaling is associated with regulating the expression of bcl-2 family genes (Bektas et al, 2005;Limaye et al, 2005). Given the fact that both SPK1-and Mcl-1-mediated suppressive effect of BCR/ABL could induce the survival and proliferation of CML cells, we further checked whether SPK1 is involved in BCR/ABLinduced upregulation of Mcl-1 expression.…”