Sphingosine 1-phosphate stimulates hydrogen peroxide generation through activation of phospholipase C-Ca2+ system in FRTL-5 thyroid cells: possible involvement of guanosine triphosphate-binding proteins in the lipid signaling.
Exogenous sphingosine 1-phosphate (S1P) stimulated hydrogen peroxide (H2O2) generation in association with an increase in intracellular Ca2+ concentration in FRTL-5 thyroid cells. S1P also induced inositol phosphate production, reflecting activation of phospholipase C (PLC) in the cells. These three S1P-induced events were inhibited partially by pertussis toxin (PTX) and markedly by U73122, a PLC inhibitor, and were conversely potentiated by N6-(L-2-phenylisopropyl)adenosine, an A1-adenosine receptor agonist. In FRTL-5 cell membranes, S1P also activated PLC in the presence of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), but not in its absence. Guanosine 5'-O-(2-thiodiphosphate) inhibited the S1P-induced GTP gamma S-dependent activation of the enzyme. To characterize the signaling pathways, especially receptors and G proteins involved in the S1P-induced responses, cross-desensitization experiments were performed. Under the conditions where homologous desensitization occurred in S1P-, lysophosphatidic acid (LPA)-, and bradykinin-induced induction of Ca2+ mobilization, no detectable cross-desensitization of S1P and bradykinin was observed. This suggests that the primary action of S1P in its activation of the PLC-Ca2+ system was not the activation of G proteins common to S1P and bradykinin, but the activation of a putative S1P receptor. On the other hand, there was a significant cross-desensitization of S1P and LPA; however, a still significant response to S1P (50-80% of the response in the nontreated control cells) was observed depending on the lipid dose employed after a prior LPA challenge. S1P also inhibited cAMP accumulation in a PTX-sensitive manner. We conclude that S1P stimulates H2O2 generation through a PLC-Ca2+ system and also inhibits adenylyl cyclase in FRTL-5 thyroid cells. The S1P-induced responses may be mediated partly through a putative lipid receptor that is coupled to both PTX-sensitive and insensitive G proteins.
Okajima
F
F
Laboratory of Signal Transduction, Gunma University, Maebashi, Japan.
Tomura
H
H
Sho
K
K
Kimura
T
T
Sato
K
K
Im
D S
DS
Akbar
M
M
Kondo
Y
Y
D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000378:metabolism*; D050356:Lipid Metabolism; D008246:Lysophospholipids / Q000494:pharmacology; D051381:Rats; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism*
D000067956:Adenylyl Cyclase Inhibitors; D008246:Lysophospholipids; C060506:sphingosine 1-phosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006861:Hydrogen Peroxide; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D013110:Sphingosine; D001920:Bradykinin; D002118:Calcium