Lipid Phosphate Phosphatase-1 and Ca2+ Control Lysophosphatidate Signaling through EDG-2 Receptors

• Published in: The Journal of biological chemistry 2000-09, Vol.275 (36), p.27520-27530
• Main Authors: Xu, J, Love, L M, Singh, I, Zhang, Q X, Dewald, J, Wang, D A, Fischer, D J, Tigyi, G, Berthiaume, L G, Waggoner, D W, Brindley, D N
• Format: Article
• Language: English
• Subjects: Animals; Calcium - metabolism; Calcium - pharmacology; Calcium Signaling - physiology; Cell Line; Cyclic AMP - metabolism; Fibroblasts; Green Fluorescent Proteins; Kinetics; Luminescent Proteins - analysis; Lysophospholipids - pharmacokinetics; Lysophospholipids - pharmacology; Models, Biological; Nuclear Proteins - metabolism; Oligodeoxyribonucleotides, Antisense - pharmacology; Phosphatidate Phosphatase - genetics; Phosphatidate Phosphatase - metabolism; Phosphorylation; Rats; Receptors, Cell Surface; Receptors, G-Protein-Coupled; Receptors, Lysophosphatidic Acid; Recombinant Fusion Proteins - metabolism; Signal Transduction - drug effects; Signal Transduction - physiology; Transcription Factors - metabolism; Transfection; Zinc Fingers
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M003211200

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 °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 °C, increasing Ca 2+ from 0 to 50 μ m increased the K d from 40 to 900 n m . Decreasing extracellular Ca 2+ from 1.8 m m to 10 μ m 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.