In our studies the EC values for

In our studies, the EC50 values for long-chain unsaturated fatty acids added to the short form of human GPR120 receptor (BC101175), were higher than the EC50 values previously reported (Hirasawa et al., 2005) for the long form of GPR120 (NM_181745), which was co-expressed with Gα16 protein.(Table 2). The difference in EC50 values could be caused by enhanced signaling from the extra Gα16 protein added to the “long” form human GPR120 receptor (NM_181745). It is also possible that the extra exon in the NM_181745 form of human GPR120 causes a difference in the protein folding after the fatty Streptozocin binds, consequently changing the amount of calcium signaling that occurs following binding only when the Gα16 is added. In contrast, the medium and long-chain saturated fatty acids had similar EC50's at the cynomolgus monkey and both human GPR120 receptor forms. (Table 2). Further studies will address the significance of this potential differential signaling between the human splice variants. The small molecule GPR40/GPR120 agonist GW9508 had similar EC50 values for both cynomolgus monkey GPR120 receptor and cells stably expressing human GPR120 (BC101175). These values compare well with the data reported by Briscoe in cells expressing the long form human GPR120 receptor (NM_181745) (Briscoe et al., 2006). (Table 2).
Introduction G-protein-coupled receptors (GPCRs) comprise a family of seven transmembrane domain receptors that mediate a variety of cellular functions [1], [2], [3]. Among GPCRs, free fatty acids (FFAs) receptors have been identified, including GPCR 120 (GPR120) and GPR40. GPR120 and GPR40 are activated by the binding of long and medium chain FFAs [4], [5]. GPR120 regulates the secretion of glucagon-like peptide-1 and indicates insulin-sensitizing and anti-inflammatory effects [6], [7]. On the other hand, GPR40 promotes the insulin secretion stimulated by glucose in pancreatic islet cells [8]. Therefore, GPR120 and GPR40 are considered as target molecules for obesity, diabetes and inflammatory disorders [9]. Ethionine is an ethyl analog of methionine and has a variety of biological actions through an antagonistic effect to methionine in animals, such as growth inhibition, fatty liver and pancreatic acinar necrosis [10]. In addition, ethionine has potent liver carcinogenic potency in rats. The prolonged ethionine feeding at 0.25% level for 8months induced liver tumors in rats [11]. Ethionine interferes with the methionine metabolism, leading to depletion of the primary methyl donor, S-adenosylmethionine. The hepatocarcinogenic effects of ethionine were prevented by the extra supplemented administration of methionine in rats [10]. In our recent study, we indicated that ethionine regulated cell motile activity through lysophosphatidic acid (LPA) signaling in rat liver epithelial WB-F344 cells [12]. LPA is a physiological lipid mediator which exhibits a wide range of cellular responses through G-protein-coupled LPA receptors [13], [14]. In the present study, to assess the roles of GPR120 and GPR40 in cell motile activity induced by ethionine, we measured the expression levels of the Gpr120 and Gpr40 genes and the cell motile activity in WB-F344 cells treated with ethionine.
Materials and methods
Results
Discussion Recently we reported that the induction of LPA receptor-3 (LPA3) was involved in the cell motile activity stimulated by ethionine in WB-F344 cells [12]. Moreover, LPA3 enhanced the cell motile activities of WB-F344 cells treated with 12-O-tetradecanoylphorbol-13-acetate, 17β-estradiol and ethinyl estradiol [18], [19]. In contrast, diethylstilbestrol suppressed the cell motile activity of WB-F344 cells, correlating with the induction of LPA1 expression [19]. Since GPR120 and GPR40 belong to GPCRs as well as LPA receptors, we assessed the roles of GPR120 and GPR40 in cell motile activity induced by ethionine in WB-F344 cells. The present study indicated that ethionine increased the expression levels of the Gpr120 and Gpr40 genes in WB-F344 cells and simultaneously elevated the cell motile activity. The increased cell motile activity by ethionine was significantly suppressed by GPR120 knockdown. GW9508 is used as the agonist of GPR120 and GPR40 [17]. While the cell motile activity was enhanced by GW9508 in WB-F344 cells treated with ethionine, GW9508 inhibited the cell motile activity of GPR120 knockdown cells. In addition, the GPR40 antagonist GW1100 elevated the cell motile activity by ethionine [17]. Therefore, these results demonstrate that GPR120 enhanced and GPR40 suppressed the cell motile activity, suggesting that opposite effects of GPR120 and GPR40 are involved in the cell motile activity stimulated by ethionine in WB-F344 cells, similar to the case for LPA1 and LPA3[12], [18], [19].