OBJECTIVETo investigate the mechanisms of lysophosphatidic acid (LPA) in stimulating invasion and metastatic colonization of ovarian cancer cells.

METHODSThe metastatic ability in vivo of ovarian cancer SK-OV3, HEY, OVCAR3, and IGROV1 cells was determined in tumor-bearing nude mouse models. Matrigel assay was used to detect the changes of response in vitro of ovarian cancer cells to LPA after Rac(-) or Rac(+) adenovirus treatment. LPA-induced Rho GTPase activation was detected by GST-fusion protein binding assay.

RESULTSThe peritoneal metastatic colonization assay showed overt metastatic colonization in mice receiving SK-OV3 and HEY cell inoculation, indicating that they are invasive cells. Metastatic colonization was not detected in animals receiving OVCAR3 and IGROV1 cells, indicating that these cells are non-invasive cells. In the matrigel invasion assay, exposure to LPA led to a notably greater migratory response in metastatic SK-OV3 and HEY cells (Optical density: SK-OV3 cells: 0.594±0.023 vs. 1.697±0.049, P<0.01; HEY cells: 0.804±0.070 vs. 1.851±0.095, P<0.01). But LPA did little in the non-metastatic OVCAR3 and IGROV1 cells (Optical density A: OVCAR3 cells: 0.336±0.017 vs. 0.374±0.007, P>0.05; IGROV1 cells: 0.491±0.036 vs. 0.479±0.061, P>0.05). LPA migratory responses of ovarian cancer cells were closely related to their metastatic colonization capabilities (r = 0.983, P<0.05). Rac(-) blocked the LPA response of invasive SK-OV3 and HEY cells (LPA-induced fold increase of cell migration: SK-OV3 cells: 2.988±0.095 vs. 0.997±0.100,P=0.01; HEY cells: 2.404±0.059 vs. 0.901±0.072, P=0.01). But Rac(+) confered the non-invasive cells with LPA response and invasion capability (LPA-induced fold increase of cell migration: OVCAR3 cells: 1.072±0.080 vs. 1.898±0.078, P<0.01; IGROV1 cells: 1.002±0.044 vs. 2.141±0.057, P<0.05). Among Rho GTPases, only Rac activation was different between ovarian cancer cell lines with different metastatic capability after LPA stimulation: Cdc42 could not be activated in both the invasive and non-invasive cell lines. RhoA could be activated in both the invasive and non-invasive cell lines. Rac could be activated by LPA in the invasive ovarian cancer cell lines. However, Rac could not be activated in the non-invasive cell lines.

CONCLUSIONLysophosphatidic acid stimulates invasion and metastasis of ovarian cancer cells through Rac activation.