Sphingolipid metabolites such as sphingosine-1-phosphate (S1P) and ceramide modulate apoptosis during development and in response to stress. In general, ceramide promotes apoptosis, whereas S1P stimulates cell proliferation and protects against apoptosis. S1P is irreversibly degraded by the enzyme S1P lyase (SPL). In this study, we show a crucial role for SPL in mediating cellular responses to stress. SPL expression in HEK293 cells potentiated apoptosis in response to stressful stimuli including DNA damage. This effect seemed to be independent of ceramide generation but required SPL enzymatic activity and the actions of p38 MAP kinase, p53, p53-inducible death domain protein (PIDD), and caspase-2 as shown by molecular and chemical inhibition of each of these targets. Further, SPL expression led to constitutive activation of p38. Endogenous SPL expression was induced by DNA damage in WT cells, whereas SPL knockdown diminished apoptotic responses. Importantly, SPL expression was significantly downregulated in human colon cancer tissues in comparison with normal adjacent tissues, as determined by quantitative real-time PCR (Q-PCR) and immunohistochemical analysis. Down-regulation of S1P phosphatases was also observed, suggesting that colon cancer cells manifest a block in S1P catabolism. In addition, SPL expression and activity were down-regulated in adenomatous lesions of the Min mouse model of intestinal tumorigenesis. Taken together, these results indicate that endogenous SPL may play a physiological role in stress-induced apoptosis and provide an example of altered SPL expression in a human tumor. Our findings suggest that genetic or epigenetic changes affecting intestinal S1P metabolism may correlate with and potentially contribute to carcinogenesis.intestinal tumorigenesis ͉ Min mouse ͉ sphingolipid ͉ etoposide S phingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite and the final common product of complex sphingolipid metabolism. S1P acts through its cognate G proteincoupled receptors to inhibit apoptosis, regulate lymphocyte trafficking and to promote DNA synthesis, cell proliferation, cell migration, and angiogenesis (1, 2). The SPHK1 gene, which encodes the major sphingosine kinase responsible for S1P synthesis, can act as an oncogene in model systems (3). Further, parenteral administration of S1P-specific antibodies markedly slows human cancer xenograft progression and angiogenesis (4). S1P signaling has been implicated in the development of the drug resistant phenotype in cancer cells (5). Together, these findings strongly support a role for S1P signaling in promoting tumorigenesis and cancer progression. Despite these observations, evidence of genetic changes in human cancer tissues that would directly implicate S1P signaling in these processes is lacking. S1P is irreversibly degraded by the pyridoxal 5Ј-phosphatedependent enzyme, S1P lyase (SPL). SPL is highly conserved throughout evolution, is required for maintenance of physiological levels of S1P and other sphingolipid intermediates an...

In most eukaryotes, sphingolipids (SLs) are critical membrane components and signaling molecules. However, mutants of the trypanosomatid protozoan Leishmania lacking serine palmitoyltransferase (spt2 À ) and SLs grow well, although they are defective in stationary phase differentiation and virulence. Similar phenotypes were observed in sphingolipid (SL) mutant lacking the degradatory enzyme sphingosine 1-phosphate lyase (spl À ). This epistatic interaction suggested that a metabolite downstream of SLs was responsible. Here we show that unlike other organisms, the Leishmania SL pathway has evolved to be the major route for ethanolamine (EtN) synthesis, as EtN supplementation completely reversed the viability and differentiation defects of both mutants. Thus Leishmania has undergone two major metabolic shifts: first in deemphasizing the metabolic roles of SLs themselves in growth, signaling, and maintenance of membrane microdomains, which may arise from the unique combination of abundant parasite lipids; Second, freed of typical SL functional constraints and a lack of alternative routes to produce EtN, Leishmania redirected SL metabolism toward bulk EtN synthesis. Our results thus reveal a striking example of remodeling of the SL metabolic pathway in Leishmania.

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FTY720 is a novel immunomodulatory agent that inhibits lymphocyte trafficking and prevents allograft rejection. FTY720 is phosphorylated in vivo, and the phosphorylated drug acts as agonist for a family of G protein-coupled receptors that recognize sphingosine 1-phosphate. Evidence suggests that FTY720-phosphate-induced activation of S1P 1 is responsible for its mechanism of action. FTY720 was rationally designed by modification of myriocin, a naturally occurring sphingoid base analog that causes immunosuppression by interrupting sphingolipid metabolism. In this study, we examined interactions between FTY720, FTY720-phosphate, and sphingosine-1-phosphate lyase, the enzyme responsible for irreversible sphingosine 1-phosphate degradation. FTY720-phosphate was stable in the presence of active sphingosine-1-phosphate lyase, demonstrating that the lyase does not contribute to FTY720 catabolism. Conversely, FTY720 inhibited sphingosine-1-phosphate lyase activity in vitro. Treatment of mice with FTY720 inhibited tissue sphingosine-1-phosphate lyase activity within 12 h, whereas lyase gene and protein expression were not significantly affected. Tissue sphingosine 1-phosphate levels remained stable or increased throughout treatment. These studies raise the possibility that disruption of sphingosine 1-phosphate metabolism may account for some effects of FTY720 on immune function and that sphingosine-1-phosphate lyase may be a potential target for immunomodulatory therapy.FTY720 is a novel immunosuppressive agent that modulates lymphocyte trafficking and prevents allograft rejection (1, 2). FTY720 treatment stimulates lymphocyte homing to peripheral lymph nodes and Peyer's patches, resulting in prolonged survival of allograft tissues and both prevention and treatment of various autoimmune diseases in animal models (3). FTY720 induces numerous effects on the immune system including inhibited egress of both naïve and activated CD4 ϩ , CD8 ϩ , and B lymphocytes from peripheral lymphoid organs and thymus, cysteinyl leukotriene-dependent T cell chemotaxis to lymph nodes, peripheral blood lymphopenia, egress of lymphocytes from the spleen, displacement of B cells from the marginal zone of the spleen, decreased ␤1 integrin expression on marginal zone B cells, homing of hematopoietic progenitor cells to the bone marrow, and decreased vascular permeability (4 -12). Importantly, while FTY720 prevents the migration of lymphocytes to allogeneic graft tissue and other sites of inflammation, it does not diminish the activation, proliferation, or effector functions of B and T lymphocytes in response to antigen stimulation (13). Toxicities associated with FTY720 are limited and distinct from those of other immunosuppressive drugs, which makes FTY720 an ideal candidate for combination immunosuppressive transplantation regimens.FTY720 was rationally designed based on chemical modifications of myriocin, a naturally occurring sphingoid base analog that causes immunosuppression by interrupting sphingolipid metabolism (14). FTY720 is phosphoryl...