Functional characterization of lysophosphatidic acid receptor 1 mutants identified in rat cancer tissues

Reduction of LPAR1 Expression in Neuroblastoma Promotes Tumor Cell Migration

Neuroblastoma is the most common extracranial solid tumor in children. Tumor metastasis in high-risk NB patients is an essential problem that impairs the survival of patients. In this study, we aimed to use a comprehensive bioinformatics analysis to identify differentially expressed genes between NB and control cells, and to explore novel prognostic markers or treatment targets in tumors. In this way, FN1, PIK3R5, LPAR6 and LPAR1 were screened out via KEGG, GO and PPI network analysis, and we verified the expression and function of LPAR1 experimentally. Our research verified the decreased expression of LPAR1 in NB cells, and the tumor migration inhibitory effects of LPA on NB cells via LPAR1. Moreover, knockdown of LPAR1 promoted NB cell migration and abolished the migration-inhibitory effects mediated by LPA-LPAR1. The tumor-suppressing effects of the LPA-LPAR1 axis suggest that LPAR1 might be a potential target for future treatment of NB.

Molecular Regulation of Lysophosphatidic Acid Receptor 1 Maturation and Desensitization

Lysophosphatidic acid receptor 1 (LPA1) belongs to the G protein-coupled receptor family. The ligand for LPA1 is LPA, the simplest lysophospholipid. LPA is considered a growth factor and induces cell proliferation, anti-apoptosis, and cell migration. The pro-inflammatory and pro-fibrotic roles of LPA have also been well-demonstrated. Most of the biological functions of LPA are mostly executed through LPA1. The mature form of LPA1 is glycosylated and localized on the plasma membrane. LPA1 is bound to heterotrimetric G proteins and transduces intracellular signaling in response to ligation to LPA. Desensitization of LPA1 negatively regulates LPA1-mediated signaling and the resulting biological functions. Phosphorylation and ubiquitination are well-demonstrated posttranslational modifications of GPCR. In this review, we will discuss our knowledge of LPA1 glycosylation, maturation, and trafficking from the endoplasmic reticulum (ER)/Golgi to the plasma membrane. Moreover, in light of recent findings, we will also discuss molecular regulation of LPA1 internalization and stability.

The Roles of Lpar1 in Central Nervous System Disorders and Diseases

Lysophosphatidic acid receptor 1 (Lpar1), which is found in almost all human tissues but is most abundant in the brain, can couple to G protein-coupled receptors (GPCRs) and participate in regulating cell proliferation, migration, survival, and apoptosis. Endothelial differentiation gene-2 receptor (Edg2), the protein encoded by the Lpar1 gene, is present on various cell types in the central nervous system (CNS), such as neural stem cells (NSCs), oligodendrocytes, neurons, astrocytes, and microglia. Lpar1 deletion causes neurodevelopmental disorders and CNS diseases, such as brain cancer, neuropsychiatric disorders, demyelination diseases, and neuropathic pain. Here, we summarize the possible roles and mechanisms of Lpar1/Edg2 in CNS disorders and diseases and propose that Lpar1/Edg2 might be a potential therapeutic target for CNS disorders and diseases.

Clinical Significance of Lysophosphatidic Acid Receptor-2 (LPA2) and Krüppel-Like Factor 5 (KLF5) Protein Expression Detected by Tissue Microarray in Gastric Adenocarcinoma

Background

The aim of this study was to evaluate lysophosphatidic acid receptor-2 (LPA2) and Krüppel-like factor 5 (KLF5) protein expression in gastric adenocarcinoma and their correlation with patient clinicopathological characteristics and prognosis.

Material/Methods

Fifty-one gastric adenocarcinoma tissue samples, 21 gastric intraepithelial neoplasia (GIN) samples, and 13 normal gastric tissue samples were collected to test for LPA2 and KLF5 expression by tissue microarray and immunohistochemistry assay. LPA2 and KLF5 positive expression rate between gastric adenocarcinoma, GIN, and normal gastric tissue were compared. The relationship between LPA2 expression, KLF5 expression, and patients’ clinicopathological characteristics and prognosis were evaluated.

Results

The positive expression rate of LPA2 and KLF5 were statistical different in gastric adenocarcinoma, GIN, and normal gastric tissue (P<0.05). LPA2 positive expression was associated with tumor invasion depth, Lauren type, vascular invasion, local lymph node metastasis, and clinical stage (P<0.05). There was no correlation between LPA2 expression (hazard ratio [HR]=1.84, 95% confidence interval [CI]: 0.89–3.80, P>0.05), KLF5 expression (HR=1.13, 95% CI: 0.53–2.36, P>0.05), and gastric cancer patients’ overall survival.

Conclusions

LPA2 and KLF5 protein expressions were differently expressed in gastric adenocarcinoma, GIN, and normal gastric tissue, and differences were correlated with patients’ clinical characteristic. However, LPA2 and KLF5 expressions were not correlated with the patients’ prognosis.

Involvement of LPA signaling via LPA receptor-2 in the promotion of malignant properties in osteosarcoma cells

Lysophosphatidic acid (LPA) signaling via G protein-coupled LPA receptors mediates various biological effects in cancer cells. This study aimed to investigate the roles of LPA receptors in the regulation of cellular functions during tumor progression in osteosarcoma cells. Long-term cisplatin (CDDP)-treated MG63-C and MG63-R7-C cells were generated from osteosarcoma MG-63 and highly-migratory MG63-R7 cells, respectively. LPAR2 and LPAR3 expression levels were significantly higher in MG63-C cells than in MG-63 cells, while LPAR1 expression was reduced. MG63-C cells were highly motile, compared with MG-63 cells. MG63-C cell motility was suppressed by LPA₂ knockdown and enhanced by the LPA₁/LPA₃ antagonist, dioctanoylglycerol pyrophosphate. LPAR2 and LPAR3 expression levels were significantly elevated in MG63-R7-C cells in comparison with MG63-R7 cells. MG63-R7-C cells were found to be highly invasive, correlating with metalloproteinase-2 activation. MG63-R7-C cells formed large colonies, whereas colony formation was absent from MG63-R7 cells. Notably, MG63-R7-C cell activities were inhibited by LPA₂ knockdown. These results suggest that LPA signaling via LPA₂ plays an important role in the acquisition of malignant properties during tumor progression in MG-63 cells.