Abstract
Abstract Introduction and Objective: Renal cell carcinoma (RCC) is the third leading cause of death among urological tumors. Wnt/beta-catenin signaling, which plays an important role in cancer, includes beta-catenin dependent and beta-catenin independent pathways. The functional significance of several wnt antagonists have been reported in renal cancer. However the functional significance of Wnt antagonist DICKKOPF-4 (DKK4) has not been investigated in RCC. Recently DKK4 function has been reported to have two opposing functions (oncogenic or tumor suppressor) in colon cancer. As far as we know, there have been no reports regarding DKK4 and renal cancer. Therefore we focused on the role of DKK4 in renal cancer. Methods: We analyzed the expression of DKK4 in renal cancer tissues and adjacent normal kidney tissues by immunohistochemistry. To assess the function of DKK4, we established stable DKK4 transfected A-498 cells and performed functional analyses including TCF/LEF reporter assay, cell viability, colony formation, apoptosis, cell cycle, invasive capability, wound healing capability and in vivo tumor growth. Results: DKK4 expression was significantly higher in cancer compared to adjacent normal kidney tissues. The relative TCF/LEF activity was significantly lower in DKK4 transfected cells compared to empty vector, and nuclear beta-catenin expression was decreased in DKK4 transfectants. Also beta-catenin downstream effector proteins, cyclinD1 and c-Myc, showed decreased expression in DKK4 transfectants. This result suggests that DKK4 may be involved in the beta-catenin dependent pathway and that DKK4 is a beta-catenin dependent pathway inhibitor. However, higher invasiveness and migration was observed in stably transfected DKK4 cells and DKK4 promoted tumor growth in vitro and in vivo. To investigate the oncogenic function in DKK4 transfectants, we focused on the Wnt non-canonical/JNK signaling pathway and phosphorylation of JNK. We found that expression and phosphorylation of c-Jun were increased in DKK4 transfected A-498 cells. MMP-2 expression was also significantly increased in DKK4 stable trasnfectants. These results suggest that DKK4 promotes the non-canonical pathway by activating JNK, resulting in up-regulation of c-Jun expression and phosphorylation, and increasing MMP-2 expression. Conclusions: This is the first report documenting that DKK4 expression is higher in renal cancer tissues compared to matched normal kidney tissues. We examined the role of DKK4 in the canonical and non-canonical Wnt pathways and found that DKK4 inhibited the canonical pathway. Though DKK4 did not induce apoptosis it promoted renal cancer cell proliferation, invasion, and migration via the non-canonical JNK pathway, which also increased MMP-2 expression. Thus the current findings contribute important information about the role of DKK4 in renal cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5173. doi:10.1158/1538-7445.AM2011-5173
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