Down-regulation of Sox7 is associated with aberrant activation of Wnt/β-catenin signaling in endometrial cancer

Although the mortality rate of endometrial cancer is comparatively low in gynecologic malignancies, a rising trend of this cancer has been observed for the past decade. The understanding of the molecular mechanism will favor for the clinical management of this disease. Aberrant activation of Wnt/β-catenin signaling pathway plays a major role in the pathogenesis of endometrioid adenocarcinoma including this cancer type. In this study, we reported that Sox7, one of Sox transcriptional factors, was frequently underexpressed in endometrial cancer and importantly, it was associated with dysregulation of the Wnt/β-catenin signaling activity. Immunohistochemical and quantitative RT-PCR analyses showed that Sox7 was underexpressed and was associated with high-grade tumor (P=0.021), increased expressions of β-catenin (P=0.038) and its downstream targets; CyclinD1 (P<0.001) and FGF9 (P<0.001). In addition, using HEK293T cell model, we found that Sox7 was able to inhibit TCF/LEF-1-dependent luciferase activity induced by Wnt-1. This was further proved by that Sox7 could significantly suppress the expressions of Wnt targets; Cyclin D1 and C-myc in endometrial cells. Immuno-fluorescent microscopy revealed that Sox7 was co-localizaed with either mutant β-catenin or TCF4 protein in nucleus, while co-immunopreciptation assay demonstrated that Sox7 could physically interact with not only wild-type but also mutant β-catenin, as well as TCF4 proteins. Functionally, enforced expression of Sox7 could significantly inhibit endometrial or endometrioid ovarian cancer cells (OEA) harboring either wild-type or mutant β-catenin. These data suggest Sox7 is a negative regulator of Wnt/β-catenin signaling pathway through impeding the transcriptional machinery of β-catenin/TCF/LEF-1 transcriptional complex, and the loss of expression may be involved in the pathogenesis of endometrial cancer.