Sphingosine-1-phosphate lyase potentiates apoptosis via p53- and p38-dependent pathways and is down-regulated in colon cancer

Abstract

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...

Sphingosine-1-Phosphate Metabolism and Intestinal Tumorigenesis: Lipid Signaling Strikes Again

“…Our results suggested that SPL expression was significantly reduced in colon cancer compared to uninvolved colonic tissue in eight of ten patients. 62 Similarly, we found that S1P phosphatases were downregulated in the cancer samples, indicating that S1P metabolism was likely blocked in colon cancer cells compared to normal colonic epithelium. To further investigate this observation, we turned to a well-characterized murine model of intestinal tumorigenesis, the Min mouse.…”

“…61,62 To determine the mechanism by which SPL expression enhances cell death responses, we dissected tumor suppressor pathways capable of activating stress-induced apoptotic cascades. Using chemical inhibitors and dominant negative constructs, we showed that SPL requires the activities of both p53 and p38 to promote apoptosis.…”

“…Using chemical inhibitors and dominant negative constructs, we showed that SPL requires the activities of both p53 and p38 to promote apoptosis. 62 The fact that cell death required the activation of caspase-2 and also a downstream target of p53 called PIDD led us to formulate the following hypothesis: cellular or genomic stress acting through SPL results in p53-dependent activation of PIDD. Once activated, PIDD forms a tripartite protein complex that activates caspase-2, an initiator caspase known to respond to DNA damage.…”

Lipid signalling in disease

“…An alternative strategy for lowering S1P levels might be the activation of S1P lyase 127 , an ER-localized enzyme, which cleaves S1P to yield ethanolamine phosphate and hexadecanal. Indeed, S1P lyase was reported to promote apoptosis and to be downregulated in colon cancer 128 .…”

The role of sphingosine-1-phosphate in the tumor microenvironment and its clinical implications

“…In addition, SPL expression and activity were down-regulated in adenomatous lesions of the multiple intestinal neoplasia mouse model of intestinal tumorigenesis. 64,65 Taken together, these results indicate that endogenous SPL plays a physiological role in stressinduced apoptosis and provide an example of altered SPL expression in a human tumor affecting the TME.…”