Kyoko Okabe

Differential function of lysophosphatidic acid receptors in cell proliferation and migration of neuroblastoma cells.

Lysophosphatidic acid (LPA) is a bioactive lipid mediator that induces diverse cellular biological effects and interacts with G protein-coupled transmembrane LPA receptors. In the present study, to assess biological roles of LPA receptors in the pathogenesis of tumor cells, each LPA receptor (Lpar1, Lpar2 or Lpar3)-expressing rat neuroblastoma B103 cells (lpa1-1, lpa2-2 or lpa3-3-2 cells, respectively) were used. In cell motility and invasion assay, lpa2-2 and lpa3-3-2 cells showed significant higher intrinsic activity without LPA treatment than LPA receptor-unexpressing AB2-1bf cells. LPA treatment further increased cell motility of these cells, which was suppressed by the pretreatment with inhibitors of Gi, Gq protein, or ROCK. By contrast, lpa1-1 cells markedly decreased intrinsic cell motility and invasion, compared with AB2-1bf cells. Constitutively active mutant Lpar1-expressing cells (lpa1Δ-1) showed significant high motility, comparable with those of lpa2-2 and lpa3-3-2. In soft agar assay, lpa3-3-2 and lpa1Δ-1 cells showed colony formation, but other cells failed. These results suggest that LPA receptors may play different roles in cell proliferation and migration of rat neuroblastoma cells.

Differential expressions and DNA methylation patterns of lysophosphatidic acid receptor genes in human colon cancer cells

Lysophosphatidic acid (LPA), which is a bioactive phospholipid, interacts with specific G protein-coupled transmembrane receptors. Recently, alterations of LPA receptor genes have been reported in some tumor cells. In this study, we examined the expression profiles and DNA methylation status of LPA receptor 1–5 (LPA1–5) genes in human colon cancer cells and also looked for the mutations. Reverse transcription–polymerase chain reaction (PCR) and bisulfite sequencing analyses were carried out. While LPA1, LPA2, and LPA4 genes were expressed in DLD1, SW480, HCT116, CaCo-2, SW48, and LoVo cells, the expressions of LPA3 and LPA5 genes were various. These expression levels were correlated with DNA methylation status in the 5′ upstream regions of the LPA receptor genes. Mutation analysis was also performed using a PCR–single-strand conformation polymorphism method. Although no mutations in LPA1, LPA3 and LPA5 genes were found in all types of cells, LPA2 mutations in DLD1 and SW48 cells, and LPA4 mutation were found in DLD1 cells. On the basis of the present results, we demonstrate that these colon cancer cells will be available to understanding the molecular pathway through LPA receptors in the development of tumor cells, and that LPA receptors may be new molecular targets for therapeutic approaches and chemoprevention.

Lysophosphatidic acid receptor‐3 increases tumorigenicity and aggressiveness of rat hepatoma RH7777 cells

Lysophosphatidic acid (LPA), which interacts with G protein‐coupled transmembrane LPA receptors exhibits several biological effects, such as cell proliferation, migration, and differentiation. Recently, it has been reported that alteration of LPA receptor genes occurs in several cancer cells. In this study, to assess the biological role of LPA receptor‐3 (LPA3) in the pathogenesis of tumor cells, we generated the Lpar3‐expressing cells (RHa3B12 and RHa3G8) from rat hepatoma RH7777 cells, and examined their abilities of cell migration and tumorigenicity, compared with the Lpar3‐unexpressing cells. In cell motility and invasion assays, RHa3B12 and RHa3G8 cells showed significantly higher intrinsic activity without LPA treatment than control RH7777AB cells. LPA treatment further increased cell motility and invasion of these cells. The cell motility of RHa3B12 and RHa3G8 cells stimulated by LPA treatment was significantly suppressed by pretreatment with inhibitors of Gi or Gq proteins. In a soft agar assay, the large sized colonies were formed in RHa3B12 and RHa3G8 cells, but not in RH7777AB cells. The cell survival of RHa3G8 cells treated with cisplatin (CDDP) or doxorubicin (DOX) was higher than that of RH7777AB cells, correlating with the elevated expression levels of multidrug‐resistance related genes, Mdr1a, Mdr1b, and Gstp1. These results suggest that LPA3 may be involved in progression and aggressiveness of rat hepatoma RH7777 cells.

Induction of lysophosphatidic acid receptor-3 by 12-O-tetradecanoylphorbol-13-acetate stimulates cell migration of rat liver cells.

12-O-tetradecanoylphorbol-13-acetate (TPA) which is one of tumor promoting agents stimulates cell migration ability of several tumor cells. In the present study, we investigated whether lysophosphatidic acid (LPA) receptors are involved in cell migration of rat liver cells stimulated by TPA. The rat liver epithelial WB-F344 and hepatoma RH7777 cells were treated by TPA for 48h. The expression levels of LPA receptor genes in those cells were measured by real-time reverse transcription (RT)-polymerase chain reaction (PCR) analysis. The expressions of the LPA receptor-3 (Lpar3) gene were significantly elevated in WB-F344 and RH7777 cells treated by TPA, but not Lpar1 and Lpar2 genes. In cell migration assay, TPA treatment showed markedly high cell migration in both cells. The pretreatment with inhibitors of Gi protein suppressed those migration abilities. We next generated the Lpar3 knockdown cells from WB-F344 cells and investigated the effect on cell migration. Interestingly, the cell migration of the knockdown cells was not stimulated by TPA. These results suggest that TPA-stimulated cell migration of rat liver cells may be mainly dependent on the LPA(3)-mediated effect.

Possible involvement of lysophosphatidic acid receptor-5 gene in the acquisition of growth advantage of rat tumor cells.

Aberrant expressions of lysophosphatidic acid (LPA) receptor genes have been reported in tumor cells. Here, we measured the expression levels of the Lpa5 gene and its DNA methylation status in rat tumor cells, and investigated cell growth effects of LPA in Lpa5 expressed cells. Real‐time reverse transcription (RT)‐polymerase chain reaction (PCR) analysis revealed that increased expressions of the Lpa5 gene were detected in rat liver‐derived hepatoma RH7777 and lung‐derived adenocarcinoma RLCNR cells. For the analysis of methylation status, bisulfite sequencing was performed with RH7777 and RLCNR cells and compared with other tumor cells and liver epithelial cells. The Lpa5 gene in Lpa5 unexpressed cells and liver epithelial cells were highly methylated in the 5′ upstream region. In contrast, the Lpa5 gene in RH7777 and RLCNR cells was unmethylated, correlating with increased expressions of Lpa5. In the assays for cell growth effects of LPA, LPA enhanced cell proliferation and motility in RH7777 and RLCNR cells. LPA also stimulated cell invasion in RLCNR, but not in RH7777 cells. In rat liver and lung tumors induced by nitroso‐compounds, 4 out of 6 hepatocellular carcinomas and 5 out of 6 lung adenocarcinomas indicated increased expressions of Lpa5 with unmethylated status. These results suggest that increased Lpa5 expressions due to aberrant DNA methylation may be involved in the acquisition of growth advantage of rat tumor cells.

Different expressions and DNA methylation patterns of lysophosphatidic acid receptor genes in mouse tumor cells.

Objective: Lysophosphatidic acid (LPA) receptors act as several biological effectors through LPA, which is a bioactive phospholipid. Recently, aberrant expressions of LPA receptor genes due to DNA methylation have been detected in several tumor cells. In this study, we measured expression levels and DNA methylation status of LPA receptor genes in mouse tumor cells, LL/2 lung carcinoma, B16F0 melanoma, FM3A mammary carcinoma and L1210 leukemia cells, compared with normal tissues. Methods: Total RNAs were extracted and RT-PCR analysis was performed. For DNA methylation status, bisulfite sequencing analysis was carried out, comparing outcomes with other tumor cells and normal tissues. Results: The expressions of LPA1 gene were shown in LL/2, but not in B16F0, FM3A and L1210 cells. While the LPA2 gene was expressed in all 4 tumor cells, the LPA3 gene was unexpressed in them. The LPA1 and LPA3 unexpressed cells were highly methylated, although normal tissues were all unmethylated. The DNA methylation status was correlated with gene expression levels in cancer cells. Conclusion: The present results demonstrate that DNA methylation patterns of LPA receptor genes are dependent on cancer cell types, suggesting that LPA receptors may be new molecular targets for therapeutic approaches and chemoprevention.

Constitutively active lysophosphatidic acid receptor-1 enhances the induction of matrix metalloproteinase-2

Lysophosphatidic acid (LPA) is a simple phospholipid which interacts with at least six G protein-coupled transmembrane LPA receptors (LPA(1)-LPA(6)). In rat neuroblastoma B103 cells, we have recently reported that each LPA receptor indicates the different cellular functions, including cell motility, invasion and tumorigenicity. Especially, mutated and constitutively active LPA(1) enhanced these cellular effects in B103 cells. In the present study, to better understand a role of mutated LPA(1) underlying progression of cancer cells, we measured the expression and activity levels of matrix metalloproteinases (MMPs) in constitutively active mutant Lpar1-expressing B103 cells (lpa1Δ-1), compared with each wild-type LPA receptor-expressing cells. LPA receptor-unexpressing cells were also used as control. In quantitative real time RT-PCR analysis, the expressions of Mmp-9 were detected at the same levels in all cells. By contrast, Mmp-2 expressions of lpa1Δ-1 were significantly higher than those of other cells. In gelatin zymography, proMmp-9 was observed at the same levels in all cells. Interestingly, markedly high levels of proMmp-2 and Mmp-2 were detected in lpa1Δ-1 cells, whereas no activation was in other cells. The increased expression and activity of Mmp-2 in lpa1Δ-1 cells were suppressed by the pretreatment with a Gq protein inhibitor. These results suggest that mutated LPA(1) may involve in the enhancement of Mmp-2 expression and activation in rat neuroblastoma cells.

Mutations of lysophosphatidic acid receptor genes in human osteosarcoma cells.

Objective: Lysophosphatidic acid (LPA), which is a bioactive phospholipid, interacts with specific G protein-coupled transmembrane receptors. Recently, alterations in LPA receptor genes have been reported in some tumor cells. In this study, to assess an involvement of LPA receptor genes in the development of human cancer cells, we looked for the presence of mutations in LPA receptor 1–6 (LPA1–6) genes in MG63 osteosarcoma, HT1080 fibrosarcoma, A549 lung adenocarcinoma, MCF-7 breast carcinoma, and G-361 melanoma cells. Methods: Genomic DNAs were extracted from each cell and polymerase chain reaction-single-strand conformation polymorphism analysis was performed to identify the mutations. Results: MG63 showed mutations in LPA1 and LPA3 genes, while no mutations in the LPA receptor genes were found in HT1080, A549, MCF-7 and G-361 cells. Sequence analysis revealed a CGC to CGT (Arg to Arg) transition at codon 314 in LPA1, and a GCG to GTG (Ala to Val) transition at codon 247 in LPA3. Conclusion: These results indicated that the mutations in LPA1 and LPA3 genes occur in MG63 cells, suggesting that the alterations in LPA receptor genes may play some role in the pathogenesis in human osteosarcoma cells.

Genetic and Epigenetic Alterations of Lysophosphatidic Acid Receptor Genes in Rodent Tumors by Experimental Models

Lysophosphatidic acid (LPA) is a bioactive mediator and induces several biological effects, including cell proliferation, migration, morphogenesis and differentiation. LPA interacts with at least six G protein-coupled receptors (GPCRs), including LPA receptor-1 (LPA1), LPA2, LPA3, LPA4, LPA5 and LPA6. These receptors show different biological functions through the binding of LPA, depending on the type of cells. In human malignancies, a high level of LPA production was found in plasma and ascites in ovarian cancer cases. Moreover, aberrant expression levels of LPA receptor genes were detected in some cancer cells. Therefore, it is suggested that LPA receptors may be involved in the pathogenesis of tumor cells as well as LPA per se. Recently, we have reported that alterations of LPA receptor genes also occur in rodent tumors. In this review, we summarize the recent evidence in the investigations of LPA receptor alterations in rodent tumors by experimental models.

Alterations of the LKB1 gene in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine in rats.

Objective: Germ line mutations of the LKB1 gene cause the autosomal dominant Peutz-Jeghers syndrome (PJS), and PJS has also been associated with an increased risk of developing cancers, suggesting LKB1 may act as a tumor suppressor in PJS. By contrast, LKB1 mutations are rare events in most sporadic tumors in non-PJS patients, except for lung cancers. To better understand the involvement of LKB1 gene alterations during lung carcinogenesis, we investigated the LKB1 gene mutations and expressions in lung adenocarcinomas induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats. Methods: Male Wistar rats, 6 weeks old, were given 2,000 ppm BHP in their drinking water for 12 weeks and maintained without further treatment until they were sacrificed at 25 weeks. A total of 15 lung adenocarcinomas were obtained, and genomic DNA was extracted for the search of mutations using polymerase chain reaction (PCR)-single strand conformation polymorphism analysis. To assess altered expressions of the LKB1 gene, reverse transcription-PCR analysis was also performed. Results: No mutations were found throughout exons 1–9 in any of the tumors. Aberrant transcripts bearing deletions of nucleotides 216–1459, 289–1302, 268–1261, or 257–1378 were detected in 5 of 15 adenocarcinomas (33.3%). Conclusion: These results suggest that alterations of the LKB1 gene might be involved in the development of lung adenocarcinomas induced by BHP in rats.