Autotaxin Regulates Maintenance of Ovarian Cancer Stem Cells through Lysophosphatidic Acid-Mediated Autocrine Mechanism

Abstract

Ovarian cancer shows high mortality due to development of resistance to chemotherapy and relapse. Cancer stem cells (CSCs) have been suggested to be a major contributor in developing drug resistance and relapse in ovarian cancer. In this study, we isolated CSCs through sphere culture of A2780, SKOV3, OVCAR3 epithelial ovarian cancer cells and primary ovarian cancer cells from patients. We identified heat-stable factors secreted from ovarian CSCs stimulated migration and proliferation of CSCs. Mass spectrometry and ELISA analysis revealed that lysophosphatidic acid (LPA) was significantly elevated in CSC culture media compared with non-CSC culture media. Treatment of CSCs with LPA resulted in augmented CSC characteristics such as sphere-forming ability, resistance to anticancer drugs, tumorigenic potential in xenograft transplantation, and high expression of CSC-associated genes, including OCT4, SOX2, and aldehyde dehydrogenase 1. Treatment of CSCs with LPA receptor 1-specific inhibitors or silencing of LPA receptor 1 expression abrogated the LPA-stimulated CSC properties. Autotaxin, an LPAproducing enzyme, is highly secreted from ovarian CSCs, and pharmacological inhibition or knockdown of autotaxin markedly attenuated the LPA-producing, tumorigenic, and drug resistance potentials of CSCs. Clinicopathological analysis showed a significant survival disadvantage of patients with positive staining of autotaxin. In addition, we further identified that AKT1 activity was upregulated in ovarian CSCs through an LPA-dependent mechanism and silencing of AKT1 expression led to suppression of CSC characteristics. These results suggest that autotaxin-LPA-LPA receptor 1-AKT1 signaling axis is critical for maintaining CSC characteristics through an autocrine loop and provide a novel therapeutic target for ovarian CSCs. STEM CELLS 2016;34:551-564 SIGNIFICANCE STATEMENTEpithelial ovarian cancer shows high mortality due to development of resistance to chemotherapy and recurrence of cancer cells. Cancer stem cells have been implicated in drug resistance and relapse of ovarian cancer. Our findings suggested that ATX-LPA-LPAR1-AKT1 signaling axis is critical for maintenance of cancer stem-like characteristics in an ovarian cancer stem cell subpopulation through an autocrine loop. Inhibiting ATX-LPA-LPAR1-AKT1 signaling axis by chemical inhibitor or knockdown of gene expression increased the sensitivity of cancer stem cells to chemotherapeutic reagents. Our findings provide therapeutic opportunities for development of relapse-free treatment of epithelial ovarian cancer.

Hypoxia-NOTCH1-SOX2 signaling is important for maintaining cancer stem cells in ovarian cancer

“…We have recently reported isolation of sphere-forming CSCs from several epithelial ovarian cancer cell lines and primary ovarian cancer cells [27, 28]. In the present study, we isolated sphere-forming cells from three ovarian cancer cell lines, SKOV3, PA-1, and A2780 cells, by culturing cells in CSC culture medium (Figure 1A).…”

Role of autotaxin in cancer stem cells

“…Overexpression of ATX does not induce tumorigenesis, whereas the combination of ATX expression with Ras transformation promotes tumor aggressiveness and metastasis [68], suggesting a pivotal role of ATX in the acquisition of metastatic potential. Consistent with the LPA-stimulated self-renewal of ovarian CSC, ATX has been found to play an important role in the maintenance and proliferation of ovarian cancer stem cells [61]. ATX was demonstrated to be highly expressed in sphereforming CSC-like populations of ovarian cancer cell lines and primary ovarian CSC isolated from patients [61].…”

“…Furthermore, overexpression of LPA1, LPA2, and LPA3 receptors under the control of the mouse mammary tumor virus long terminal repeat promoter results in metastatic mammary carcinomas [60]. In addition, in ovarian cancer cells, LPA treatment stimulates the expression of CSC-associated genes, including OCT4, SOX2, ALDH1 , and drug transporters [61]. Moreover, LPA promotes CSC-like characteristics, such as sphere-forming ability, resistance to anti-cancer drugs, and tumorigenic potential in xenograft transplantation.…”

Advances in Lipidomics for Cancer Biomarkers Discovery

“…The GPLs, including lysophospholipids (LPLs), and SLs are defined as polar lipids. GPLs compose bio-cellular membranes; LPLs act as ligands for numerous signaling pathways [23]. The polar lipids (GPLs, LPLs and SLs) are so involved in critical cell functions and they are the principal lipid class studied in lipidomic research.…”