Journal of the National Cancer Institute Advance Access published online on November 11, 2008
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djn378
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© The Author 2008. Published by Oxford University Press.
ARTICLES |
Lysophosphatidic Acid Receptors Determine Tumorigenicity and Aggressiveness of Ovarian Cancer Cells
Affiliations of authors: Department of Systems Biology (SY, MMM, YL, SL, HSH, GBM), Department of Pathology (JL), and Department of Veterinary Medicine (LCS), M. D. Anderson Cancer Center, Houston, TX; Department of Biochemistry & Molecular Biology, Virginia Commonwealth University, Richmond, VA (XF)
Correspondence to: Gordon B. Mills, MD, PhD, Department of Systems Biology, Division of Cancer Medicine, PO Box 317, M. D. Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030 (e-mail: gmills{at}mdanderson.org).
Background: Lysophosphatidic acid (LPA) acts through the cell surface G protein–coupled receptors, LPA1, LPA2, or LPA3, to elicit a wide range of cellular responses. It is present at high levels in intraperitoneal effusions of human ovarian cancer increasing cell survival, proliferation, and motility as well as stimulating production of neovascularizing factors. LPA2 and LPA3 and enzymes regulating the production and degradation of LPA are aberrantly expressed by ovarian cancer cells, but the consequences of these expression changes in ovarian cancer cells were unknown.
Methods: Expression of LPA1, LPA2, or LPA3 was inhibited or increased in ovarian cancer cells using small interfering RNAs (siRNAs) and lentivirus constructs, respectively. We measured the effects of changes in LPA receptor expression on cell proliferation (by crystal violet staining), cell motility and invasion (using Boyden chambers), and cytokines (interleukin 6 [IL-6], interleukin 8 [IL-8], and vascular endothelial growth factor [VEGF]) production by enzyme-linked immunosorbent assay. The role of LPA receptors in tumor growth, ascites formation, and cytokine production was assessed in a mouse xenograft model. All statistical tests were two-sided.
Results: SKOV-3 cells with increased expression of LPA receptors showed increased invasiveness, whereas siRNA knockdown inhibited both migration (P < .001, Student t test) and invasion. Knockdown of the LPA2 or LPA3 receptors inhibited the production of IL-6, IL-8, and VEGF in SKOV-3 and OVCAR-3 cells. SKOV-3 xenografts expressing LPA receptors formed primary tumors of increased size and increased ascites volume. Invasive tumors in the peritoneal cavity occurred in 75% (n = 4) of mice injected with LPA1 expressing SKOV-3 and 80% (n = 5) of mice injected with LPA2 or LPA3 expressing SKOV-3 cells. Metastatic tumors expressing LPA1, LPA2, and LPA3 were identified in the liver, kidney, and pancreas; tumors expressing LPA2 and LPA3 were detected in skeletal muscle; and tumors expressing LPA2 were also found in the cervical lymph node and heart. The percent survival of mice with tumors expressing LPA2 or LPA3 was reduced in comparison with animals with tumors expressing β-galactosidase.
Conclusions: Expression of LPA2 or LPA3 during ovarian carcinogenesis contributes to ovarian cancer aggressiveness, suggesting that the targeting of LPA production and action may have potential for the treatment of ovarian cancer.
| CONTEXT AND CAVEATS Prior knowledge Signaling by lysophosphatidic acid (LPA) has effects on survival and proliferation of ovarian cancer cells as well as the production of neovascularizing factors. The extent to which LPA’s effects on ovarian cancer cells are mediated by G protein–coupled receptors LPA1, LPA2, and LPA3, the latter two of which are typically highly expressed in human ovarian cancer cell lines, was unknown. Study design Expression of individual LPA receptors was inhibited or increased using RNA interference or lentivirus constructs, respectively, in ovarian cancer cells. Effects of these expression changes were studied in vitro cell assays and in a mouse xenograft model. Contribution Based on the sensitivity of ovarian cancer cell proliferation and invasiveness and in vivo tumor growth to the levels of individual LPA receptors, this study suggests that signaling by LPA via LPA2 and LPA3 receptors may play a critical role in the progression of ovarian cancer. Implications The identification of individual LPA receptors that mediate LPA action in ovarian cancer raises the possibility that these receptors may be useful therapeutic targets. Limitations The role of LPA signaling in ovarian cancer was studied using cell lines that may not be adequate models for many human cancers. From the Editors
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Manuscript received February 6, 2008; revised August 14, 2008; accepted September 22, 2008.
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J Natl Cancer Inst 2008 100: 1561.