WNT7A regulates tumor growth and progression in ovarian cancer through the WNT/β-catenin pathway

Abnormal activation the WNT/β-catenin signaling pathway has been associated with ovarian carcinomas, but a specific WNT ligand and pertinent downstream mechanisms are not fully understood. In this study, we found abundant WNT7A in the epithelium of serous ovarian carcinomas, but not detected in borderline and benign tumors, normal ovary or endometrioid carcinomas. To characterize the role of WNT7A in ovarian tumor growth and progression, nude mice were injected either intraperitoneally (i.p.) or subcutaneously (s.c.) with WNT7A knocked down SKOV3.ip1 and overexpressed SKOV3 cells. In the i.p. group, mice receiving SKOV3.ip1 cells with reduced WNT7A expression developed significantly fewer tumor lesions. Gross and histological examination revealed greatly reduced invasion of WNT7A knockdown cells into intestinal mesentery and serosa compared to the control cells. Tumor growth was regulated by loss or overexpression of WNT7A in mice receiving s.c. injection as well. In vitro analysis of cell function revealed that cell proliferation, adhesion, and invasion were regulated by WNT7A. The activity of the TCF/LEF reporter was stimulated by overexpression of WNT7A in ovarian cancer cells. Co-transfection with WNT7A and FZD5 receptor further increased activity, and this effect was inhibited by co-transfection with SFRP2, or dominant-negative TCF4. Overexpression of WNT7A stimulated MMP7 promoter, and mutation of TCF binding sites in MMP7 promoter confirmed that activation of MMP7 promoter by WNT7A was mediated by β-catenin/TCF signaling. Collectively, these results suggest that re-expression of WNT7A during malignant transformation of ovarian epithelial cells plays a critical role in ovarian cancer progression mediated by WNT/β-catenin signaling pathway