Ovarian cancer metastasis is characterized by the spread of cancer cells from the ovarian surface and their implantation onto the peritoneum, a layer of cells that surrounds the abdominal organs. We conducted a proteomic study investigating the interaction between peritoneal and ovarian cancer cells and identified annexin A2 to be upregulated in the conditioned media of co-cultured ovarian cancer (OVCAR-5) and peritoneal (LP-9) cells. Annexin A2, a calcium dependent phospholipid-binding protein, has been shown to be over expressed in many cancers but its role has not been investigated previously in ovarian cancer.
Our study characterized the expression of annexin A2 in human ovarian cancer tissues and cell lines. Western blot and real time-PCR showed annexin A2 was expressed in ovarian cancer cell lines (OVCAR-3, OVCAR-5, OV-90 and SKOV-3). Immunohistochemistry demonstrated annexin A2 expression in epithelial cancer cells, the cancer associated stromal cells and peritoneal mesothelial cells. Stromal annexin A2 levels were significantly increased in ovarian cancer tissues compared to the stromal surrounding non-invasive borderline ovarian tumours and benign ovarian tumors. Increased annexin A2 expression was also observed in ovarian cancer cells adjacent to peritoneal cells.
We also investigated the role of annexin A2 in ovarian cancer invasion. In vitro functional assays showed that neutralizing antibodies against annexin A2 could inhibit OVCAR-5 and OV-90 cell motility, invasion and adhesion to peritoneal cells. Moreover, knockdown of annexin A2 expression using siRNA decreased OVCAR-3, OVCAR-5, OV-90 and SKOV-3 cancer cell motility and invasion in vitro. We assessed ovarian cancer invasion in vivo using a matrigel graft in a chick embryo chorioallantoic membrane (CAM) model. Treatment of chick embryos with neutralizing antibodies against annexin A2 significantly blocked OV-90 ovarian cancer cells invasion (p=0.004, Mann-Whitney U test).
Our findings indicate that annexin A2, which is increased as a result of ovarian cancer-peritoneal cell interactions, plays an important role in promoting ovarian cancer metastasis.