A role for G protein-coupled lysophospholipid receptors in sphingolipid-induced Ca2+ signaling in MC3T3-E1 osteoblastic cells.
Sphingolipids have been proposed to modulate cell function by acting as intracellular second messengers and through binding to plasma membrane receptors. Exposure of MC3T3-E1 osteoblastic cells to sphingosine (SPH), sphingosine-1-phosphate (SPP), or sphingosylphosphorylcholine (SPC) led to the release of Ca2+ from the endoplasmic reticulum (ER) and acute elevations in cytosolic-free Ca2+ ([Ca2+]i). Desensitization studies suggest that SPP and SPC bind plasma membrane endothelial differentiation gene (Edg) receptors for lysophosphatidic acid (LPA). Consistent with the coupling of Edg receptors to G proteins, SPP- and SPC-induced Ca2+ signaling was inhibited by pretreatment of the cells with pertussis toxin (PTx). Of the Edg receptors known to bind SPH derivatives in other cell types, MC3T3-E1 cells were found to express transcripts encoding Edg-1 and Edg-5 but not Edg-3, Edg-6, or Edg-8. In contrast to SPP and SPC, the ability of SPH to elicit [Ca2+]i elevations was affected neither by prior exposure of cells to LPA nor by PTx treatment. However, LPA-induced Ca2+ signaling was blocked in MC3T3-E1 cells previously exposed to SPH. Elevations in [Ca2+]i were not evoked by SPP or SPC in cells treated with 2-aminoethoxydiphenylborate (2-APB), an inhibitor of inositol 1,4,5-trisphosphate (IP3)-gated Ca2+ channels in the ER. No effect of 2-APB was observed on SPH-or LPA-induced [Ca2+]i elevations. The data support a model in which SPP and SPC bind Edg-1 and/or Edg-5 receptors in osteoblasts leading to the release of Ca2+ from the ER through IP3-gated channels.
Lyons
J M
JM
Department of Biological Sciences, University of Delaware, Newark 19716, USA.
Karin
N J
NJ
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D018076:DNA, Complementary / Q000235:genetics; D019204:GTP-Binding Proteins / Q000378:metabolism*; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism; D015640:Ion Channel Gating; D008246:Lysophospholipids / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism*; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D049312:Receptors, Lysophospholipid; D013107:Sphingolipids / Q000494:pharmacology*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology
D018076:DNA, Complementary; D017874:Immediate-Early Proteins; D008246:Lysophospholipids; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D049312:Receptors, Lysophospholipid; D013107:Sphingolipids; C005356:sphingosine phosphorylcholine; D010767:Phosphorylcholine; C060506:sphingosine 1-phosphate; D019204:GTP-Binding Proteins; D013110:Sphingosine