title: The phosphorylation motif at serine 225 governs the localization and function of sphingosine kinase 1 in resistance arteries.
abstract: OBJECTIVE
  The purpose of this study was to characterize a phosphorylation motif at serine 225 as a molecular switch that regulates the pressure-dependent activation of sphingosine kinase 1 (Sk1) in resistance artery smooth muscle cells.
  
  
  RESULTS
  In isolated hamster gracilis muscle resistance arteries, pressure-dependent activation/translocation of Sk1 by ERK1/2 was critically dependent on its serine 225 phosphorylation site. Specifically, expression of Sk1(S225A) reduced resting and myogenic tone, resting Ca(2+), pressure-induced Ca(2+) elevations, and Ca(2+) sensitivity. The lack of function of the Sk1(S225A) mutant could not be entirely overcome by forced localization to the plasma membrane via a myristoylation/palmitylation motif; the membrane anchor also significantly inhibited the function of the wild-type Sk1 enzyme. In both cases, Ca(2+) sensitivity and myogenic tone were attenuated, whereas Ca(2+) handling was normalized/enhanced. These discrete effects are consistent with cell surface receptor-mediated effects (Ca(2+) sensitivity) and intracellular effects of S1P (Ca(2+) handling). Accordingly, S1P(2) receptor inhibition (1 micromol/L JTE013) attenuated myogenic tone without effect on Ca(2+).
  
  
  CONCLUSIONS
  Translocation and precise subcellular positioning of Sk1 is essential for full Sk1 function; and two distinct S1P pools, proposed to be intra- and extracellular, contribute to the maintenance of vascular tone.
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Darcy
authors.initials: D
authors.lastname: Lidington
authors.forename: Bernhard Friedrich
authors.initials: BF
authors.lastname: Peter
authors.forename: Anja
authors.initials: A
authors.lastname: Meissner
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Kroetsch
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Pitson
authors.forename: Ulrich
authors.initials: U
authors.lastname: Pohl
authors.forename: Steffen-Sebastian
authors.initials: SS
authors.lastname: Bolz
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001158:Arteries / Q000201:enzymology*; D020013:Calcium Signaling / Q000502:physiology; D002463:Cell Membrane Permeability / Q000502:physiology; D002478:Cells, Cultured; D006224:Cricetinae; D009131:Muscle, Smooth, Vascular / Q000098:blood supply* / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011312:Pressure; D011336:Probability; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction; D014655:Vascular Resistance / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology; D000099157:Sphingosine Kinase
chemical_list: D017853:Phosphotransferases (Alcohol Group Acceptor); D012694:Serine; D000099157:Sphingosine Kinase