Reiss Ulrike, Oskouian Babak, Zhou Jianhui, Gupta Vinita, Sooriyakumaran Prathap, Kelly Samuel, Wang Elaine, Merrill Alfred H, Saba Julie D
Children's Hospital Oakland Research Institute, Oakland, California 94609-1673, USA.
J Biol Chem. 2004 Jan 9;279(2):1281-90. doi: 10.1074/jbc.M309646200. Epub 2003 Oct 21.
Sphingosine-1-phosphate lyase is a widely expressed enzyme that catalyzes the essentially irreversible cleavage of the signaling molecule sphingosine 1-phosphate. To investigate whether sphingosine-1-phosphate lyase influences mammalian cell fate decisions, a recombinant human sphingosine-1-phosphate lyase fused to green fluorescent protein was expressed in HEK293 cells. The recombinant enzyme was active, localized to the endoplasmic reticulum, and reduced baseline sphingosine and sphingosine 1-phosphate levels. Stable overexpression led to diminished viability under stress, which was attributed to an increase in apoptosis and was reversible in a dose-dependent manner by exogenous sphingosine 1-phosphate. In contrast to sphingosine 1-phosphate, the products of the lyase reaction had no effect on apoptosis. Lyase enzymatic activity was required to potentiate apoptosis, because cells expressing a catalytically inactive enzyme behaved like controls. Stress increased the amounts of long- and very long-chain ceramides in HEK293 cells, and this was enhanced in cells overexpressing wild type but not catalytically inactive lyase. The ceramide increases appeared to be required for apoptosis, because inhibition of ceramide synthase with fumonisin B1 decreased apoptosis in lyase-overexpressing cells. Thus, sphingosine-1-phosphate lyase overexpression in HEK293 cells decreases sphingosine and sphingosine 1-phosphate amounts but elevates stress-induced ceramide generation and apoptosis. This identifies sphingosine-1-phosphate lyase as a dual modulator of sphingosine 1-phosphate and ceramide metabolism as well as a regulator of cell fate decisions and, hence, a potential target for diseases with an imbalance in these biomodulators, such as cancer.
鞘氨醇-1-磷酸裂解酶是一种广泛表达的酶，它催化信号分子鞘氨醇1-磷酸的基本不可逆裂解。为了研究鞘氨醇-1-磷酸裂解酶是否影响哺乳动物细胞命运的决定，将与绿色荧光蛋白融合的重组人鞘氨醇-1-磷酸裂解酶在HEK293细胞中表达。重组酶具有活性，定位于内质网，并降低了基线鞘氨醇和鞘氨醇1-磷酸水平。稳定的过表达导致应激状态下细胞活力下降，这归因于细胞凋亡增加，并且外源性鞘氨醇1-磷酸可使其以剂量依赖的方式逆转。与鞘氨醇1-磷酸相反，裂解酶反应的产物对细胞凋亡没有影响。增强细胞凋亡需要裂解酶的酶活性，因为表达催化失活酶的细胞表现得与对照细胞一样。应激增加了HEK293细胞中长链和极长链神经酰胺的含量，在过表达野生型而非催化失活裂解酶的细胞中这种增加更为明显。神经酰胺的增加似乎是细胞凋亡所必需的，因为用伏马菌素B1抑制神经酰胺合酶可减少过表达裂解酶的细胞中的细胞凋亡。因此，HEK293细胞中鞘氨醇-1-磷酸裂解酶的过表达降低了鞘氨醇和鞘氨醇1-磷酸的含量，但增加了应激诱导的神经酰胺生成和细胞凋亡。这确定了鞘氨醇-1-磷酸裂解酶是鞘氨醇1-磷酸和神经酰胺代谢的双重调节剂以及细胞命运决定的调节剂，因此是这些生物调节剂失衡相关疾病（如癌症）的潜在靶点。
