Siow Deanna L, Anderson Charles D, Berdyshev Evgeny V, Skobeleva Anastasia, Natarajan Viswanathan, Pitson Stuart M, Wattenberg Binks W
Department of Biochemistry and Molecular Biology, School of Medicine, University of Louisville, Louisville, KY 40202, USA.
Adv Enzyme Regul. 2011;51(1):229-44. doi: 10.1016/j.advenzreg.2010.09.004. Epub 2010 Nov 12.
The sphingosine kinases (sphingosine kinase-1 and -2) have been implicated in a variety of physiological functions. Discerning their mechanism of action is complicated because in addition to producing the potent lipid second messenger sphingosine-1-phosphate, sphingosine kinases, both by producing sphingosine-1-phosphate and consuming sphingosine, have profound effects on sphingolipid metabolism. Sphingosine kinase-1 translocates to the plasma membrane upon agonist stimulation and this translocation is essential for the pro-oncogenic properties of this enzyme. Many of the enzymes of sphingolipid metabolism, including the enzymes that degrade sphingosine-1-phosphate, are membrane bound with restricted subcellular distributions. In the work described here we explore how subcellular localization of sphingosine kinase-1 affects the downstream metabolism of sphingosine-1-phosphate and the access of sphingosine kinase to its substrates. We find, surprisingly, that restricting sphingosine kinase to either the plasma membrane or the endoplasmic reticulum has a negligible effect on the rate of degradation of the sphingosine-1-phosphate that is produced. This suggests that sphingosine-1-phosphate is rapidly transported between membranes. However we also find that cytosolic or endoplasmic-reticulum targeted sphingosine kinase expressed at elevated levels produces extremely high levels of dihydrosphingosine-1-phosphate. Dihydrosphingosine is a proximal precursor in ceramide biosynthesis. Our data indicate that sphingosine kinase can divert substrate from the ceramide de novo synthesis pathway. However plasma membrane-restricted sphingosine kinase cannot access the pool of dihydrosphingosine. Therefore whereas sphingosine kinase localization does not affect downstream metabolism of sphingosine-1-phosphate, localization has an important effect on the pools of substrate to which this key signaling enzyme has access.
鞘氨醇激酶（鞘氨醇激酶-1和-2）参与了多种生理功能。辨别它们的作用机制很复杂，因为除了产生强效脂质第二信使鞘氨醇-1-磷酸外，鞘氨醇激酶通过产生鞘氨醇-1-磷酸和消耗鞘氨醇，对鞘脂代谢有深远影响。激动剂刺激后，鞘氨醇激酶-1转位至质膜，这种转位对于该酶的促癌特性至关重要。鞘脂代谢的许多酶，包括降解鞘氨醇-1-磷酸的酶，都与膜结合，亚细胞分布受限。在本文所述的研究中，我们探讨了鞘氨醇激酶-1的亚细胞定位如何影响鞘氨醇-1-磷酸的下游代谢以及鞘氨醇激酶对其底物的接触。令人惊讶的是，我们发现将鞘氨醇激酶限制在质膜或内质网对所产生的鞘氨醇-1-磷酸的降解速率影响可忽略不计。这表明鞘氨醇-1-磷酸在膜之间快速转运。然而，我们还发现，高水平表达的胞质或内质网靶向的鞘氨醇激酶会产生极高水平的二氢鞘氨醇-1-磷酸。二氢鞘氨醇是神经酰胺生物合成中的近端前体。我们的数据表明，鞘氨醇激酶可使底物从神经酰胺从头合成途径中转移。然而，质膜限制的鞘氨醇激酶无法接触二氢鞘氨醇池。因此，尽管鞘氨醇激酶的定位不影响鞘氨醇-1-磷酸的下游代谢，但定位对该关键信号酶可接触的底物池有重要影响。
