Expression of the Wnt antagonist Dickkopf-3 is associated with prognostic clinicopathologic characteristics and impairs proliferation and invasion in endometrial cancer.

OBJECTIVE: Emerging evidence implicates the Wnt antagonist Dickkopf-3 (Dkk3) as a tumor suppressor and potential biomarker in solid tumors. We investigated whether Dkk3 plays an important role in the carcinogenesis of endometrial cancer (EC).
METHODS: We analyzed Dkk3 mRNA expression via real-time RT-PCR in twenty-seven human primary EC tissues, and six matched normal endometrial controls. Dkk3 levels were correlated with various clinicopathologic characteristics. Additionally, enforced Dkk3 expression was examined in proliferation and tumorigenesis in vitro and in vivo, using MTT, soft agar assay, invasion assay, a xenograft mouse model, and a β-catenin-responsive SuperTopFlash luciferase assay.
RESULTS: Compared with matched normal endometrial cases, Dkk3 was down-regulated in EC (p<0.0001). Among cancer cases, Dkk3 expression was significantly reduced in patients with higher stage (p=0.002), positive pelvic lymph nodes (p=0.0004), non-endometrioid histology (p=0.02), and cytology-positive ECs (p=0.02). Enforced expression of Dkk3 in EC cell lines showed reduced proliferation (p<0.0001), anchorage-independent growth (p=0.005), invasion (p=0.02), and reduced TCF activity (p=0.04), confirming Dkk3 as a negative regulator of the β-catenin/Wnt signaling pathway. Tumor growth in Dkk3-injected mice was not statistically different, though did plateau towards the end, and was associated with increased lymphoid infiltration and tumor necrosis.
CONCLUSION: Dkk3 gene expression is frequently downregulated in endometrial cancer, and is associated with poor prognostic clinicopathologic markers. The results also identify a role for Dkk3 as a tumor suppressor in EC, affecting both proliferation and invasiveness. These findings may prove to be important in the design of novel biomarkers and treatment modalities for advanced EC.