The Mechanistic Action of DDX3 in Colorectal Tumor Progression

DDX3 has been shown to be associated with tumor progression in hepatocellular carcinoma, breast cancer, and lung cancer. However, conflicting role of DDX3 in human tumorigensis was reported in different cancers. For example, DDX3 plays a tumor suppressor role in hepatocellular and lung tumorigenesis, but as an oncogene in breast tumorigenesis. Recently, DDX3 has been shown as a subunit to bind and activate CK1ε kinase activity, and consequently to promote the development of Xenopus and Caenorhabditis elegans via increased ß-catenin nuclear translocation. It is documented that Wnt/ß-catenin signaling pathway plays a crucial role in colorectal tumorigenesis. Therefore, we hypothesized that DDX3 might promote tumor progression and metastasis via increased ß-catenin nuclear translocation. Importantly, no report mentioned the role of DDX3 in colorectal tumorigenesis up to date. Therefore, in this project, we will aim to explore the mechanistic action of DDX3 in tumor progression and metastasis in cellular and animal model. In the first year, we will explore whether DDX3 could play an oncogenic role to promote invasiveness and drug resistance via upregulation of ZEB1 due to increased β-catenin nuclear translocation in colon cancer cells. The molecular manipulations (knockdown or overexpression) were performed to investigate: (1) Whether DDX3 expression could promote cell growth, invasion, and 5-FU resistance in colon cancer cells? (2) Whether DDX3 could promote invasiveness and drug resistance via upregulation of ZEB1? (3) whether DDX3 could promote tumor progression and metastasis via increased β-catenin nuclear translocation; (4) the underling mechanism of DDX3 in tumor metastasis could be through upregulation of ZEB1 expression will be explored. In the second year, two possible mechanistic actions of DDX3 in promoting β-catenin nuclear translocation will be discovered: (1) Whether phosphorylation of GSKβ at Ser9 by DDX3-mediated AKT activation could suppress β-catenin ubiquilization via phosphorylated β-catenin at Ser33? (2) Whether DDX3 could promote CK1ε-mediated β-catenin phosphorylation at Ser45 to block ubiquilization of β-catenin? In the third year, we will explored (1) Whether DDX3-mediated tumor invasion and drug resistance could partially suppress by AKT inhibitor and CK1ε-knockdown or completely reduced by the inhibitor of β-catenin nuclear translocation – XAV-939 in cells and xenograft tumors in nude mice? (2) Whether the prognostic significance of DDX3 on overall survival and relapse free survival and unfavorable response of DDX3 to 5-FU-based chemotherapy were observed in colorectal cancer patient? The results obtained from this project will be helpful to understand whether DDX3 may play a crucial role in tumor progression and drug resistance in colorectal cancer. These results will be helpful to address feasible therapeutic approach to improve 5-FU-based chemotherapy efficacy and the outcome and life quality in colorectal cancer patients with DDX3 positive tumors.