title: Sphingosine kinase localization in the control of sphingolipid metabolism.
abstract: 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.
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Medicine, University of Louisville, Louisville, KY 40202, USA.
authors.forename: Deanna L
authors.initials: DL
authors.lastname: Siow
authors.forename: Charles D
authors.initials: CD
authors.lastname: Anderson
authors.forename: Evgeny V
authors.initials: EV
authors.lastname: Berdyshev
authors.forename: Anastasia
authors.initials: A
authors.lastname: Skobeleva
authors.forename: Viswanathan
authors.initials: V
authors.lastname: Natarajan
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Pitson
authors.forename: Binks W
authors.initials: BW
authors.lastname: Wattenberg
mesh_terms: D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008246:Lysophospholipids / Q000378:metabolism*; D015394:Molecular Structure; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D013107:Sphingolipids / Q000737:chemistry / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism; D000099157:Sphingosine Kinase
chemical_list: D007527:Isoenzymes; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D013107:Sphingolipids; D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate