Roles of lysophosphatidic acid (LPA) receptor-2 (LPA2) in the regulation of cellular responses induced by X-ray irradiation and hydrogen peroxide in pancreatic cancer cells

Involvement of lysophosphatidic acid (LPA) receptor-mediated signaling in breast cancer cell functions by long-term tamoxifen treatment under hypoxic and estrogen-deprived conditions

BACKGROUND

Tamoxifen (TAM) is a selective estrogen receptor modulator and has anti-estrogenic activity. Breast cancer cells acquire drug resistance to TAM as a consequence of long-term treatment. Lysophosphatidic acid (LPA) receptor-mediated signaling contributes to the promotion of tumor progression. This study aimed to evaluate the role of LPA receptors in the modulation of biological functions by long-term TAM treatment in breast cancer MCF-7 cells under hypoxic and estrogen-deprived conditions.

METHODS

Long-term TAM treated (MCF-TAM) cells were generated from MCF-7 cells. Cells were cultured in estrogen-free medium at 1 % O2. LPA receptor expressions were measured by quantitative real-time RT-PCR analysis. Cell motile activity was investigated using Cell Culture Inserts. The CCK-8 kit was used to determine the cell proliferation rate.

RESULTS

LPAR1 and LPAR3 expressions were elevated in MCF-TAM cells. MCF-TAM cell motility was enhanced by culturing at 1 % O2, compared with MCF-7 cells. When cells were cultured in estrogen-deprived medium at 1 % O2, the cell proliferation rate of MCF-TAM cells was significantly higher than that of MCF-7 cells.

CONCLUSION

These results suggest that LPA receptor-mediated signaling plays an important role in the acquisition of malignant properties in long-term TAM treated MCF-7 cells under hypoxic and estrogen-deprived conditions.

Lysophosphatidic acid (LPA) receptor-mediated signaling and cellular responses to anticancer drugs and radiation of cancer cells

Lysophosphatidic acid (LPA) is a simple physiological lipid and structurally consists of a fatty, a phosphate and a glycerol. LPA binds to G protein-coupled LPA receptors (LPA1 to LPA6). LPA receptor-mediated signaling mediates a variety of biological responses, such as cell growth, migration, morphogenesis, differentiation and protection from apoptosis. It is considered that LPA receptor-mediated signaling plays an important role in the pathogenesis of human malignancies. So far, genetic and epigenetic alterations of LPA receptors have been found in several cancer cells as well as abnormal LPA production. In addition, LPA receptor-mediated signaling regulates the promotion of malignant behaviors, including chemo- and/or radiation-resistance. Chemotherapy and radiotherapy are the common approaches to the treatments of cancers. However, resistance to anticancer drugs and irradiation is the most critical limitation for chemotherapy and radiotherapy. In this review, we provide the roles of LPA receptor-mediated signaling in the regulation of cellular responses induced by chemotherapeutic agents and irradiation and its biological utility as a possible molecular target for improving cancer cell responses to chemotherapy and radiotherapy.

Regulation of cellular responses to X-ray irradiation through the activation of lysophosphatidic acid (LPA) receptor-3 (LPA3) and LPA2 in osteosarcoma cells

Lysophosphatidic acid (LPA) binds to its specific G protein-coupled LPA receptors (LPA1 to LPA6), resulting in the activation of various cellular functions. LPA receptor-mediated signaling facilitates tumor progression in human malignancies. In the present study, we investigated whether LPA receptor-mediated signaling contributes to cellular responses to X-ray irradiation in osteosarcoma MG-63 cells. After X-ray irradiation (2, 4 and 8 Gy), LPAR2 and LPAR3 expression levels in MG-63 cells were significantly elevated in a dose-dependent manner, but no change of LPAR1 expression level was observed. The cell growth activities of MG-63 cells irradiated with X-rays (2, 4 and 8 Gy) were reduced by LPA. Conversely, LPA3 agonist (2 S)-OMPT enhanced the cell growth activities of X-ray irradiated MG-63 cells. The cell movement of MG-63 cells exposed to X-ray irradiation (8 Gy) was inhibited by (2 S)OMPT. In cell survival assay, (2 S)-OMPT suppressed the cell survival to cisplatin (CDDP) of MG-63 cells irradiated with X-rays (8 Gy). The cell survival to CDDP of X-ray irradiated cells was elevated by LPA3 knockdown. Moreover, we evaluated the effects of LPA2 on the cell survival to CDDP of MG-63 cells exposed to X-ray irradiation (8 Gy). The cell survival to CDDP of X-ray irradiated cells was increased by LPA2 agonist GRI-977143 and reduced by LPA2 knockdown. These results suggest that LPA receptor-signaling participates in the modulation of cellular functions induced by X-ray irradiation in osteosarcoma cells.

The Emerging Role of LPA as an Oncometabolite

Lysophosphatidic acid (LPA) is a phospholipid that displays potent signalling activities that are regulated in both an autocrine and paracrine manner. It can be found both extra- and intracellularly, where it interacts with different receptors to activate signalling pathways that regulate a plethora of cellular processes, including mitosis, proliferation and migration. LPA metabolism is complex, and its biosynthesis and catabolism are under tight control to ensure proper LPA levels in the body. In cancer patient specimens, LPA levels are frequently higher compared to those of healthy individuals and often correlate with poor responses and more aggressive disease. Accordingly, LPA, through promoting cancer cell migration and invasion, enhances the metastasis and dissemination of tumour cells. In this review, we summarise the role of LPA in the regulation of critical aspects of tumour biology and further discuss the available pre-clinical and clinical evidence regarding the feasibility and efficacy of targeting LPA metabolism for effective anticancer therapy.