Yuuki Koide

Sphingosine 1-Phosphate (S1P) Regulates Vascular Contraction via S1P3 Receptor: Investigation Based on a New S1P3 Receptor Antagonist

Sphingosine 1-phosphate (S1P) induces diverse biological responses in various tissues by activating specific G protein-coupled receptors (S1P1–S1P5 receptors). The biological signaling regulated by S1P3 receptor has not been fully elucidated because of the lack of an S1P3 receptor-specific antagonist or agonist. We developed a novel S1P3 receptor antagonist, 1-(4-chlorophenylhydrazono)-1-(4-chlorophenylamino)-3,3-dimethyl- 2-butanone (TY-52156), and show here that the S1P-induced decrease in coronary flow (CF) is mediated by the S1P3 receptor. In functional studies, TY-52156 showed submicromolar potency and a high degree of selectivity for S1P3 receptor. TY-52156, but not an S1P1 receptor antagonist [(R)-phosphoric acid mono-[2-amino-2-(3-octyl-phenylcarbamoyl)-ethyl] ester; VPC23019] or S1P2 receptor antagonist [1-[1,3-dimethyl-4-(2-methylethyl)-1H-pyrazolo[3,4-b]pyridin-6-yl]-4-(3,5-dichloro-4-pyridinyl)-semicarbazide; JTE013], inhibited the decrease in CF induced by S1P in isolated perfused rat hearts. We further investigated the effect of TY-52156 on both the S1P-induced increase in intracellular calcium ([Ca2+]i) and Rho activation that are responsible for the contraction of human coronary artery smooth muscle cells. TY-52156 inhibited both the S1P-induced increase in [Ca2+]i and Rho activation. In contrast, VPC23019 and JTE013 inhibited only the increase in [Ca2+]i and Rho activation, respectively. We further confirmed that TY-52156 inhibited FTY-720-induced S1P3 receptor-mediated bradycardia in vivo. These results clearly show that TY-52156 is both sensitive and useful as an S1P3 receptor-specific antagonist and reveal that S1P induces vasoconstriction by directly activating S1P3 receptor and through a subsequent increase in [Ca2+]i and Rho activation in vascular smooth muscle cells.

Newly synthetic ceramide-1-phosphate analogs; their uptake, intracellular localization, and roles as an inhibitor of cytosolic phospholipase A2α and inducer of cell toxicity

Ceramide-1-phosphate (C1P) regulates cellular functions including arachidonic acid (AA) metabolism and modulates cell fate. The mechanism by which C1P is taken up is unclear, and the development of lipophilic analogs may be useful for regulating C1Ps actions. We synthesized new mono- and di-methyl-ester (MM and DM, respectively) analogs of C1P with N-acyl chains of different lengths, and examined their effects on AA release and cell toxicity. Short-N-acyl-DM-C1P analogs including C5- and C6-DM-C1P, but not long-N-acyl-DM-C1P analogs, inhibited the release of AA mediated by α type cytosolic phospholipase A(2) (cPLA(2)α) in Chinese hamster ovary (CHO) cells and the enzymatic activity. Short-N-acyl-DM-C1P analogs including C6-DM-C1P caused morphological changes with cell toxicity 24h after the treatment in three cells lines (CHO, L929, and RLC-18 cells), although the role of AA in the toxicity was not clear. Neither long-N-acyl-DM-C1P analogs nor MM-C1P analogs including C6-MM-C1P affected cPLA(2)α activity and cell toxicity. Similar to C6-ceramide having a 4-nitrobenzo-2-oxa-1,3-diazole (NBD) group on a C6-N-acyl chain (NBD-C6-ceramide), NBD-C6-DM-C1P and C6-DM-C1P-NBD (with a C6-N-acyl chain and an NBD-labeled C14-alkyl chain) were accumulated in the Golgi complex, although less C6-DM-C1P-NBD than NBD-C6-DM-C1P was taken up. NBD-C6-ceramide was converted to various metabolites including NBD-C6-sphingomyelin, but both NBD-C6-DM-C1P and C6-DM-C1P-NBD were stable in cells within 2h. The short-N-acyl-DM-C1P analogs acted directly as an inhibitor of cPLA(2)α and an inducer of cell toxicity, and may be useful for the regulation of ceramide/C1P-regulated responses.