Lipid phosphate phosphatase-1 and Ca2+ control lysophosphatidate signaling through EDG-2 receptors.
The serum-derived phospholipid growth factor, lysophosphatidate (LPA), activates cells through the EDG family of G protein-coupled receptors. The present study investigated mechanisms by which dephosphorylation of exogenous LPA by lipid phosphate phosphatase-1 (LPP-1) controls cell signaling. Overexpressing LPP-1 decreased the net specific cell association of LPA with Rat2 fibroblasts by approximately 50% at 37 degrees C when less than 10% of LPA was dephosphorylated. This attenuated cell activation as indicated by diminished responses, including cAMP, Ca(2+), activation of phospholipase D and ERK, DNA synthesis, and cell division. Conversely, decreasing LPP-1 expression increased net LPA association, ERK stimulation, and DNA synthesis. Whereas changing LPP-1 expression did not alter the apparent K(d) and B(max) for LPA binding at 4 degrees C, increasing Ca(2+) from 0 to 50 micrometer increased the K(d) from 40 to 900 nm. Decreasing extracellular Ca(2+) from 1.8 mm to 10 micrometer increased LPA binding by 20-fold, shifting the threshold for ERK activation to the nanomolar range. Hence the Ca(2+) dependence of the apparent K(d) values explains the long-standing discrepancy of why micromolar LPA is often needed to activate cells at physiological Ca(2+) levels. In addition, the work demonstrates that LPP-1 can regulate specific LPA association with cells without significantly depleting bulk LPA concentrations in the extracellular medium. This identifies a novel mechanism for controlling EDG-2 receptor activation.
Xu
J
J
Departments of Biochemistry (Signal Transduction Laboratories and Lipid Biology Research Group) and Cell Biology, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
Love
L M
LM
Singh
I
I
Zhang
Q X
QX
Dewald
J
J
Wang
D A
DA
Fischer
D J
DJ
Tigyi
G
G
Berthiaume
L G
LG
Waggoner
D W
DW
Brindley
D N
DN
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D005347:Fibroblasts; D049452:Green Fluorescent Proteins; D007700:Kinetics; D008164:Luminescent Proteins / Q000032:analysis; D008246:Lysophospholipids / Q000493:pharmacokinetics / Q000494:pharmacology*; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism*; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D010711:Phosphatidate Phosphatase / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D049368:Receptors, Lysophosphatidic Acid; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D016335:Zinc Fingers
D008164:Luminescent Proteins; D008246:Lysophospholipids; D009687:Nuclear Proteins; D020319:Oligodeoxyribonucleotides, Antisense; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D049368:Receptors, Lysophosphatidic Acid; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D000242:Cyclic AMP; C112948:lipid phosphate phosphatase; D010711:Phosphatidate Phosphatase; D002118:Calcium