Phosphorylation of the immunomodulator FTY720 inhibits programmed cell death of fibroblasts via the S1P3 receptor subtype and Bcl-2 activation.

BACKGROUND: FTY720, a synthetic compound produced by modification of a metabolite from Isaria sinclairii, is known as a unique immunosuppressive agent that exerts its activity by inhibiting lymphocyte egress from secondary lymphoid tissues. FTY720 is phosphorylated in vivo by sphingosine kinase 2 to FTY720-phosphate (FTY720-P), which acts as a potent sphingosine-1-phosphate (S1P) receptor agonist. Despite its homology to S1P, which exerts antiapoptotic actions in different cells, FTY720 has also been reported to be able to induce apoptosis in a variety of cells. METHODS: Therefore, we investigated the action of both, FTY720 and its phosphorylated version FTY720-P, on apoptosis. Moreover, signalling pathways of apoptosis in response to FTY720 and FTY720-P were examined. RESULTS AND CONCLUSIONS: Although FTY720 acts apoptotic at micromolar concentrations in human fibroblasts the phosphorylated compound FTY720-P possesses a pronounced antiapoptotic effect counteracting FTY720-induced programmed cell death. Interestingly, none of the classical antiapoptotic pathways like MAP kinases, Akt or mTOR play a role in the protective role of FTY720-P. Most important, we identified that the S1P(3) receptor subtype is involved in the antiapoptotic action of FTY720-P leading to an increased phosphorylation of Bcl-2 and changes in the mitochondrial membrane potential.

Glucocorticoids protect renal mesangial cells from apoptosis by increasing cellular sphingosine-1-phosphate.

Neutral ceramidase (NCDase) and sphingosine kinases (SphKs) are key enzymes regulating cellular sphingosine-1-phosphate (S1P) levels. In this study we found that stress factor-induced apoptosis of rat renal mesangial cells was significantly reduced by dexamethasone treatment. Concomitantly, dexamethasone increased cellular S1P levels, suggesting an activation of sphingolipid-metabolizing enzymes. The cell-protective effect of glucocorticoids was reversed by a SphK inhibitor, was completely absent in SphK1-deficient cells, and was associated with upregulated mRNA and protein expression of NCDase and SphK1. Additionally, in vivo experiments in mice showed that dexamethasone also upregulated SphK1 mRNA and activity, and NCDase protein expression in the kidney. Fragments (2285, 1724, and 1126 bp) of the rat NCDase promoter linked to a luciferase reporter were transfected into rat kidney fibroblasts and mesangial cells. There was enhanced NCDase promoter activity upon glucocorticoids treatment that was abolished by the glucocorticoid receptor antagonist RU-486. Single and double mutations of the two putative glucocorticoid response element sites within the promoter reduced the dexamethasone effect, suggesting that both glucocorticoid response elements are functionally active and required for induction. Our study shows that glucocorticoids exert a protective effect on stress-induced mesangial cell apoptosis in vitro and in vivo by upregulating NCDase and SphK1 expression and activity, resulting in enhanced levels of the protective lipid second messenger S1P.

Dexamethasone protects human fibroblasts from apoptosis via an S1P3-receptor subtype dependent activation of PKB/Akt and Bcl XL.

Topical used glucocorticoids (GC) represent an important class of steroid hormones for the treatment of a broad range of acute or chronic inflammatory diseases. Most interestingly, GC exert a pronounced anti-apoptotic effect in primary human fibroblasts whereas in variety of hematopoietic cells a pro-apoptotic effect is visible. Recently, it has been discovered that in human fibroblasts the GC dexamethasone (Dex) exerts its protection from programmed cell death via the formation of the lipid mediator sphingosine 1-phosphate (S1P) followed by an activation of the S1P(3)-receptor subtype. In the present study, the molecular mechanism of Dex to protect human fibroblasts from apoptosis was elucidated. Thereupon, Dex not only mediates its anti-apoptotic effect via activation of phosphoinositide 3-kinase (PI3K)/Akt signalling but also includes an involvement of the Bcl-2 family protein Bcl(XL). Most interestingly, the use of S1P(3)-knockout fibroblasts revealed that the S1P(3)-receptor subtype is crucial for activation of PKB/Akt as well as Bcl(XL) by Dex.

Involvement of the ABC-transporter ABCC1 and the sphingosine 1-phosphate receptor subtype S1P(3) in the cytoprotection of human fibroblasts by the glucocorticoid dexamethasone.

Glucocorticoids (GC) represent the most commonly used drugs for the treatment of acute and chronic inflammatory skin diseases. However, the topical long-term therapy of GC is limited by the occurrence of skin atrophy. Most interestingly, although GC inhibit proliferation of human fibroblasts, they exert a pronounced anti-apoptopic action. In the present study, we further elucidated the molecular mechanism of the GC dexamethasone (Dex) to protect human fibroblasts from programmed cell death. Dex not only significantly alters the expression of the cytosolic isoenzyme sphingosine kinase 1 but also initiated an enhanced intracellular formation of the sphingolipid sphingosine 1-phosphate (S1P). Investigations using S1P (3) ((-/-)) -fibroblasts revealed that this S1P-receptor subtype is essential for the Dex-induced cytoprotection. Moreover, we demonstrate that the ATP-binding cassette (ABC)-transporter ABCC1 is upregulated by Dex and may represent a crucial carrier to transport S1P from the cytosol to the S1P(3)-receptor subtype.