Abstract 2981: Regulation of Snail by DDX3 and ATM in response to DNA damage

Epithelial-mesenchymal transition (EMT) is the initial step for cancer invasion and metastasis. The hallmark of EMT is the loss of expression of E-cadherin, a cell-cell adhesion protein, allowing cancer cells to gain mobility leaving the site of primary tumor to invade adjacent tissues. Snail, as a transcription repressor, binds to the E-boxes of E-cadherin and then inhibits E-cadherin expression. Thus, Snail is essential to trigger EMT during tumor progression and it has been implicated in the acquisition of invasive growth phenotype of tumors. There is a strong correlation of Snail over-expression with tumor invasion and metastasis. However, how Snail expression is regulated is not fully known. Here we report that Snail is regulated by DDX3, a DEAD box protein family member which contributes to cancer progression. Knock-down of DDX3 by shRNA reduces the basal level of Snail, and this is associated with reduced cell proliferation and migration. Snail protein and mRNA levels are increased in the presence of the HDAC inhibitors sodium butyrate or trichostatin A, and the increases are attenuated in cells with DDX3 knocked down. Treatment of cells with a DNA damaging agent camptothecin also enhances Snail protein levels in a DDX3 dependent manner. Therefore we conclude that DDX3 is required for the basal level and the increase in Snail induced by HDAC inhibitors or camptothecin, indicating that this action of DDX3 may contribute to its promotion of the progression of some cancers. This conclusion is supported by our clinical investigations that analysis of 31 glioblastoma patient samples has revealed a strong correlation between the levels of DDX3 and Snail. Snail is a phosphor-protein, and kinases responsible for phosphorylation include Pak1 and GSK3-β. We also find Pak-1 and GSK-3 independent Snail phosphorylation in response to DNA damage. Further we find that inhibition of the activity of the ATM kinase, a critical element in DNA damage responses, eliminated DNA damage-induced Snail stabilization. Taken together, these observations have highlighted a comprehensive signaling network regulating Snail in response to DNA damage and indicated a critical role of optimal DNA damage responses in tumor invasion and metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstra