Upregulation of FasL by LPA on ovarian cancer cell surface leads to apoptosis of activated lymphocytes

Constitutive expression and upregulation of FasL by malignant epithelial cells counterattack infiltrating natural killer (NK) cells and cytotoxic T lymphocytes (CTLs) and induce apoptosis of normal cells within the tumor, which may induce metastasis. As little is known about the mechanisms that regulate expression of Fas ligand and the subsequent release of FasL in epithelial ovarian cancer cells (EOC), we investigated the effects of lysophosphatidic acid (LPA) on FasL expression and associated signaling pathways. We used established EOC cell lines that were incubated with or without LPA and FasL expression was detected by flow cytometry. Cells were additionally lysed and detected for total protein expression. Activated CD4+ T cells, after coculture with or without EOC, were collected for apoptosis staining and analysis by flow cytometry. Flow cytometry showed that LPA strongly upregulated FasL expression on the OVCAR3 cell surface (P < 0.01), yet in Dov13 cells, LPA significantly upregulated FasL expression only in the presence of the general matrix metalloproteinase (MMP) inhibitors GM6001 and MMP inhibitor II (P < 0.01). The MEK/ERK1/2 kinase cascade is required for FasL upregulation, since the MEK inhibitor PD98059 significantly inhibited FasL upregulation induced by LPA (P < 0.01). Type II secretory phospholipase A2 (sPLA2-II), which promotes protein exocytosis from secretory vesicles and gelatinase granules, affects FasL translocation from intracellular to the cell surface. Pretreatment of Dov13 cells with LPA increased activated T cell apoptosis in cocultures. These data suggest that upregulation of FasL by LPA provides EOC immune-privilege and leads to apoptosis of activated T lymphocytes.