Abstract 3419: N-myc downstream regulated gene 1, NDRG1, modulates Wnt-β-catenin signaling and pleiotropically suppresses metastasis

Abstract

Abstract It is of paramount interest to delineate the underlining molecular pathways of cancer metastasis in order to identify a novel therapeutic target for this devastating disease. Previously, we identified NDRG1 as a tumor metastasis suppressor gene and found that it is negatively involved in metastatic progression of prostate and breast cancer. Herein, we sought to determine how NDRG1 gene exerts its metastasis suppressor function. We used the yeast two-hybrid system to identify proteins interacting with NDRG1, and also the phospho-site profiling system to search for potential signaling pathway involved in NDRG1 function. We found that NDRG1 interacted with Wnt receptor, LRP6, and blocked its phosphorylation. Moreover, NDRG1 induced phosphorylated- activation of GSK3β (Tyr279/216), an essential negative regulator of Wnt pathway, followed by inhibition of β-catenin/TCF transcriptional activity. Further investigations revealed that NDRG1 inhibited the expression of ATF3, a potent metastasis promoter, through Wnt- β-catenin/TCF signaling. Consistently, the results of our immunohisochemical studies revealed an inverse correlation between NDRG1 expression and ATF3 and membrane β-catenin, respectively, while ATF3 expression was significantly correlated with cytoplasm/nuclear expression of β-catenin in prostate cancer patients. When we assessed the possible steps of metastasis cascade that were affected by NDRG1, we found that NDRG1 dramatically inhibited Wnt-induced EMT of tumor cells. Furthermore, NDRG1 not only significantly reduced local invasive ability of tumor cells, but also impaired the later steps of invasion-metastasis cascade including infiltration, initial survival and extravasation in the mice lung parenchyma. To determine whether NDRG1 indeed suppresses metastasis via the inhibition of Wnt pathway in vivo, we isolated tumor cells from a MMTV-Wnt1 mouse and established a series of cell lines with or without NDRG1 expression in combination with a dominant active Wnt signaling. Our results indicate that NDRG1 significantly decreased metastasis while it did not affect the primary tumor growth. However, a dominant active form of β-catenin effectively overcame the metastasis-suppressive effect of NDRG1. Importantly, restoring NDRG1 expression by a small molecule compound significantly suppressed the capability of otherwise highly metastatic tumor cells to thrive in circulation and distant organs in animal models. Finally, using a combined expression status of Wnt and NDRG1 as a signature, we could stratify patients who have significant higher relapse or metastasis incidence than others in clinical databases. Taken together, our results revealed a novel mechanism of metastasis suppression by which NDRG1 suppresses pleiotropic effects of Wnt signaling on metastatic cascade through impeding the upstream activation of Wnt co-receptor LRP6. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3419. doi:1538-7445.AM2012-3419