Lysophosphatidic acid (LPA) exerts a variety of biological responses through specific receptors: three subtypes of the EDG-family receptors, LPA 1 , LPA 2 , and LPA 3 (formerly known as EDG-2, EDG-4, and EDG-7, respectively), and LPA 4 /GPR23, structurally distinct from the EDG-family receptors, have so far been identified. In the present study, we characterized the action mechanisms of 3-(4-[4-([1-(2-chlorophenyl)ethoxy]carbonyl amino)-3-methyl-5-isoxazolyl] benzylsulfanyl) propanoic acid (Ki16425) on the EDG-family LPA receptors. Ki16425 inhibited several responses specific to LPA, depending on the cell types, without any appreciable effect on the responses to other related lipid receptor agonists, including sphingosine 1-phosphate. With the cells overexpressing LPA 1 , LPA 2 , or LPA 3 , we examined the selectivity and mode of inhibition by Ki16425 against the LPA-induced actions and compared them with those of dioctyl glycerol pyrophosphate (DGPP 8:0), a recently identified antagonist for LPA receptors. Ki16425 inhibited the LPA-induced response in the decreasing order of LPA 1 Ն LPA 3 Ͼ Ͼ LPA 2 , whereas DGPP 8:0 preferentially inhibited the LPA 3 -induced actions. Ki16425 inhibited LPA-induced guanosine 5Ј-O-(3-thio)triphosphate binding as well as LPA receptor binding to membrane fractions with a same pharmacological specificity as in intact cells. The difference in the inhibition profile of Ki16425 and DGPP 8:0 was exploited for the evaluation of receptor subtypes involved in responses to LPA in A431 cells. Finally, Ki16425 also inhibited LPA-induced longterm responses, including DNA synthesis and cell migration. In conclusion, Ki16425 selectively inhibits LPA receptor-mediated actions, especially through LPA 1 and LPA 3 ; therefore, it may be useful in evaluating the role of LPA and its receptor subtypes involved in biological actions.Lysophosphatidic acid (LPA) has been shown to elicit diverse biological actions, including Ca 2ϩ mobilization, change in cAMP accumulation, change in cell shape and motility in association with actin rearrangement, and proliferation in a variety of cell types (Moolenaar, 1999;Contos et al., 2000;Ye et al., 2002). Extracellular LPA has also been shown to be involved in certain diseases, such as atherosclerosis and cancer (Xu et al., 1995(Xu et al., , 2001Siess et al., 1999;Maschberger et al., 2000). LPA was first thought to be released from activated platelets; however, a major part of extracellular LPA has been shown to be produced from lysophosphatidylcholine by lysophospholipase D, which was previously called autotaxin (Sano et al., 2002;Tokumura et al., 2002;Umezu-Goto et al., 2002). The concentration of plasma LPA is about 100 nM, and its serum concentration can be as high as 5 M (Sano et al., 2002). LPA increases low-density lipoprotein during its oxidation, activates endothelial cells (Siess et al., This work was supported in part by a research grant grants-in-aid for scientific research from the Japan Society for the Promotion of Science and by research gr...

Cytokines and growth factors in malignant ascites are thought to modulate a variety of cellular activities of cancer cells and normal host cells. The motility of cancer cells is an especially important activity for invasion and metastasis. Here, we examined the components in ascites, which are responsible for cell motility, from patients and cancer cell-injected mice. Ascites remarkably stimulated the migration of pancreatic cancer cells. This response was inhibited or abolished by pertussis toxin, monoglyceride lipase, an enzyme hydrolyzing lysophosphatidic acid (LPA), and Ki16425 and VPC12249, antagonists for LPA receptors (LPA 1 and LPA 3 ), but not by an LPA 3 -selective antagonist. These agents also inhibited the response to LPA but not to the epidermal growth factor. In malignant ascites, LPA is present at a high level, which can explain the migration activity, and the fractionation study of ascites by lipid extraction and subsequent thin-layer chromatography indicated LPA as an active component. A significant level of LPA 1 receptor mRNA is expressed in pancreatic cancer cells with high migration activity to ascites but not in cells with low migration activity. Small interfering RNA against LPA 1 receptors specifically inhibited the receptor mRNA expression and abolished the migration response to ascites. These results suggest that LPA is a critical component of ascites for the motility of pancreatic cancer cells and LPA 1 receptors may mediate this activity. LPA receptor antagonists including Ki16425 are potential therapeutic drugs against the migration and invasion of cancer cells.

Acidosis has been shown to induce depletion of bone calcium from the body. This calcium release process is thought to be partially cell mediated. In an organ culture of bone, acidic pH has been shown to induce cyclooxygenase-2 (COX-2) induction and prostaglandin E 2 (PGE 2 ) production, resulting in stimulation of bone calcium release. However, the molecular mechanisms whereby osteoblasts sense acidic circumstances and thereby induce COX-2 induction and PGE 2 production remain unknown. In this study, we used a human osteoblastic cell line (NHOst) to characterize cellular activities, including inositol phosphate production, intracellular Ca 2+ concentration ([Ca 2+ ] i ), PGE 2 production, and COX-2 mRNA and protein expression, in response to extracellular acidification. Small interfering RNA (siRNA) specific to the OGR1 receptor and specific inhibitors for intracellular signaling pathways were used to characterize acidification-induced cellular activities. We found that extracellular acidic pH induced a transient increase in [Ca 2+ ] i and inositol phosphate production in the cells. Acidification also induced COX-2 induction, resulting in PGE 2 production. These proton-induced actions were markedly inhibited by siRNA targeted for the OGR1 receptor and the inhibitors for G q/11 protein, phospholipase C, and protein kinase C. We conclude that the OGR1/G q/11 / phospholipase C/protein kinase C pathway regulates osteoblastic COX-2 induction and subsequent PGE 2 production in response to acidic circumstances.

While inflammatory cytokines are well-recognized critical factors for the induction of cyclooxygenase-2 (COX-2) in activated fibroblast-like synovial cells, the roles of biologically active components other than inflammatory cytokines in synovial fluid remain unknown. Herein, we assessed the role of lysophosphatidic acid (LPA), a pleiotropic lipid mediator, in COX-2 induction using synovial fluid of patients with rheumatoid arthritis (RA) in fibroblast-like RA synovial cells. Synovial fluid from RA patients stimulated COX-2 induction, which was associated with prostaglandin E2 production, in RA synovial cells. The synovial fluid-induced actions were inhibited by Gi/o protein inhibitor pertussis toxin and LPA receptor antagonist 3-(4-[4-([1-(2-chlorophenyl)ethoxy]carbonyl amino)-3-methyl-5-isoxazolyl] benzylsulfanyl) propanoic acid (Ki16425). In fact, LPA alone significantly induced COX-2 expression and enhanced IL-1α- or IL-1β-induced enzyme expression in a manner sensitive to pertussis toxin and Ki16425. RA synovial cells abundantly expressed LPA1 receptor compared with other LPA receptor subtypes. Moreover, synovial fluid contains a significant amount of LPA, an LPA-synthesizing enzyme autotaxin, and its substrate lysophosphatidylcholine. In conclusion, LPA existing in synovial fluid plays a critical role in COX-2 induction in collaboration with inflammatory cytokines in RA synovial cells. Ki16425-sensitive LPA receptors may be therapeutic targets for RA.

Cerebrospinal fluid (CSF) induced neurite retraction of differentiated PC12 cells; the action was observed in 15 min (a rapid response) and the activity further increased until 6 h (a long-acting response) during exposure of CSF to the cells. The CSF action was sensitive to monoglyceride lipase and diminished by homologous desensitization with lysophosphatidic acid (LPA) and by pretreatment with an LPA receptor antagonist Ki16425. Although fresh CSF contains LPA to some extent, the LPA content in the medium was increased during culture of PC12 cells with CSF. The rapid response was mimicked by exogenous LPA, and a long-acting response was duplicated by a recombinant autotaxin, lysophospholipase D (lyso-PLD). Although the lyso-PLD substrate lysophosphatidylcholine (LPC) was not detected in CSF, lyso-PLD activity and an 120-kDa autotaxin protein were detected in CSF. On the other hand, LPC but not lyso-PLD activity was detected in the conditioned medium of a PC12 cell culture without CSF. Among neural cells examined, leptomeningeal cells expressed the highest lyso-PLD activity and autotaxin protein. These results suggest that leptomeningeal cells may work as one of the sources for autotaxin, which may play a critical role in LPA production and thereby regulate axonal and neurite morphological change.