Sphingosine-1-phosphate lyase potentiates apoptosis via p53- and p38-dependent pathways and is down-regulated in colon cancer.
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 down-regulated 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.
Oskouian
Babak
B
Children's Hospital Oakland Research Institute Center for Cancer Research, Oakland, CA 94609-1673, USA.
Sooriyakumaran
Prathap
P
Borowsky
Alexander D
AD
Crans
Angelina
A
Dillard-Telm
Lisa
L
Tam
Yuen Yee
YY
Bandhuvula
Padmavathi
P
Saba
Julie D
JD
D000446:Aldehyde-Lyases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism; D002384:Catalysis; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D004247:DNA / Q000235:genetics; D004249:DNA Damage / Q000235:genetics; D053418:Death Domain Receptor Signaling Adaptor Proteins; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007417:Intestinal Polyps / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
D002352:Carrier Proteins; D053418:Death Domain Receptor Signaling Adaptor Proteins; C485896:PIDD1 protein, human; D016159:Tumor Suppressor Protein p53; D004247:DNA; D048051:p38 Mitogen-Activated Protein Kinases; D000446:Aldehyde-Lyases; C022649:sphingosine 1-phosphate lyase (aldolase)