RESUMO
G2A is a G protein-coupled receptor that is predominantly expressed in lymphoid tissues and macrophages. G2A can be induced by diverse stimuli to cause cell cycle arrest in the G(2)/M phase in pro-B and T cells. G2A is also expressed in macrophages within atherosclerotic lesions, suggesting G2A involvement in atherosclerosis. Recently, G2A was discovered to possess proton-sensing ability. In this paper, we report another function of G2A, that is, as a receptor for 9-hydroxyoctadecadienoic acid (9-HODE) and other oxidized free fatty acids. G2A, expressed in CHO-K1 or HEK293 cells, showed 9-HODE-induced intracellular calcium mobilization, inositol phosphate accumulation, inhibition of cAMP accumulation, [(35)S]guanosine 5'-3-O-(thio)triphosphate binding, and MAP kinase activation. Furthermore, G2A was activated by various oxidized derivatives of linoleic and arachidonic acids, but it was weakly activated by cholesteryl-9-HODE. Oxidized phosphatidylcholine (1-palmitoyl-2-linoleoyl) when hydrolyzed with phospholipase A(2) also evoked intracellular calcium mobilization in G2A-expressing cells. These results indicate that G2A is activated by oxidized free fatty acids produced by oxidation and subsequent hydrolysis of phosphatidylcholine or cholesteryl linoleate. Thus, G2A might have a biological role in diverse pathological conditions including atherosclerosis.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Ácidos Graxos não Esterificados/metabolismo , Ácidos Linoleicos Conjugados/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Animais , Células CHO , Cálcio/metabolismo , Proteínas de Ciclo Celular/genética , Linhagem Celular , Cricetinae , Cricetulus , AMP Cíclico/metabolismo , Embrião de Mamíferos , Ativação Enzimática/efeitos dos fármacos , Citometria de Fluxo , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/fisiologia , Expressão Gênica , Guanosina 5'-O-(3-Tiotrifosfato)/metabolismo , Humanos , Fosfatos de Inositol/metabolismo , Rim , Ácidos Linoleicos Conjugados/química , Ácidos Linoleicos Conjugados/farmacologia , MAP Quinase Quinase 4/metabolismo , Oxirredução , Fosfatidilcolinas/metabolismo , Hidrolisados de Proteína , Receptores Acoplados a Proteínas G/genética , Proteínas Recombinantes , Transdução de Sinais/fisiologia , Relação Estrutura-Atividade , TransfecçãoRESUMO
Lysophosphatidic acid is a multifunctional phospholipid mediator and elicits a variety of biological responses in vitro and in vivo. Evidence is accumulating that lysophosphatidic acid plays important physiological roles in diverse mammalian tissues and cells. In the present study, we first examined whether lysophosphatidic acid is present in human saliva. We found that a significant amount of lysophosphatidic acid is present in the saliva (0.785 nmol/ml). The predominant fatty acyl moiety of lysophosphatidic acid was 18:1n-9 + n-7 followed by 18:0 and 16:0. A small amount of lysoplasmanic acid, an alkyl ether-linked analog of lysophosphatidic acid, was also detected in the saliva (0.104 nmol/ml). We found that physiologically relevant concentrations of lysophosphatidic acid induced accelerated growth of cells of mouth, pharynx, and esophagus origin in vitro. Lysophosphatidic acid also induced rapid increases in the intracellular free Ca2+ concentrations in these cells. We obtained evidence that lysophosphatidic acid receptor mRNAs are actually present in these cells. These results strongly suggest that lysophosphatidic acid is involved in wound healing in the upper digestive organs such as the mouth, pharynx, and esophagus.
Assuntos
Lisofosfolipídeos/metabolismo , Receptores Acoplados a Proteínas G , Saliva/metabolismo , Cálcio/metabolismo , Epitélio/crescimento & desenvolvimento , Epitélio/metabolismo , Esôfago/crescimento & desenvolvimento , Esôfago/metabolismo , Humanos , Lisofosfolipídeos/química , Espectrometria de Massas , RNA Mensageiro/metabolismo , Receptores de Superfície Celular/biossíntese , Receptores de Superfície Celular/genética , Receptores de Ácidos Lisofosfatídicos , Saliva/química , Células Tumorais CultivadasRESUMO
A substantial amount of lysophosphatidic acid (LPA) (15.66 nmol/g tissue) was found to occur in the brain isolated from rats killed in liquid nitrogen. We found that a significant portion of brain LPA was accounted for by the arachidonic acid-containing species (5.4%). We obtained evidence that both 2-arachidonoyl species and 1-arachidonoyl species of LPA are present. The occurrence of 2-arachidonoyl LPA in the brain (0.53 nmol/g tissue) is a notable observation, because of its structural resemblance to 2-arachidonoyl-sn-glycerol (2-AG), an endogenous cannabinoid receptor ligand. We then examined the biological activity of 2-arachidonoyl LPA and compared it with that of 2-AG using neuroblastoma x glioma hybrid NG108-15 cells which express both the LPA receptor and cannabinoid CB1 receptor. We found that 2-arachidonoyl LPA interacts with the LPA receptor(s) to elicit the elevation of intracellular free Ca(2+) concentrations, whereas 2-AG interacts exclusively with the cannabinoid CB1 receptor. Next, we examined the possible metabolic relationship between 2-arachidonoyl LPA and 2-AG and obtained clear evidence that rapid enzymatic conversion of 2-arachidonoyl LPA to 2-AG took place in the brain homogenate. It is noteworthy that two types of endogenous ligands, that interact with different types of receptors, are closely related metabolically and rapidly interconvert.
