Characterize the Critical Role of Dub3 in Breast Cancer Progression and Metastasis

Snail, a protein that acts as a master switch in the nucleus to suppress E-cadherin expression and induce EMT in the cell, is elevated in breast cancer. High levels of Snail have been linked to metastasis, tumor cell survival, and tumor recurrence and a prediction of a poor clinical outcome for women with breast cancer. However, Snail is highly unstable protein and is rapidly degraded by ubiquitination mediated proteasomes pathway. Then how breast cancer cell counteracts the ubiquitination and degradation of Snail remains elusive. Because the ubiquitination is a reversible process and ubiquitin moieties can be removed from polypeptides by deubiquitylating enzymes (DUBs), we screened cells with a siRNA library of putative DUBs. We finally focus on Dub3. Interestingly, Dub3 is induced by inflammatory cytokines IL-6 in the immediately time. Depletion of Dub3 from breast cancer cells reduces their proliferative potential in vivo. I first found that high Dub3 expression has a significantly higher probability of developing metastasis and of reduced survival. Dub3 correlated with the expression of Snail positively in breast cancer cell lines and metastatic breast cancer specimens. We also demonstrated that expression of Dub3 induces stabilization of Snail and enhances suppression of the E-cadherin promoter mediated by Snail. Furthermore, we found interaction of Snail with Dub3. In addition, we found inflammatory factor IL-6 induced Dub3 expression and Snail stabilization within 2 hr and Dub3 knockdown inhibit IL-6 induced Snail stabilization. Based on my interesting findings, I hypothesize that Dub3 may function as a molecular “sensor” to recognize the tumor microenvironmental signals and thus trigger the Snail-mediated breast cancer metastasis. I propose that Dub3 functions as a deubiquitinating enzyme for Snail and is critical for IL-6 induced EMT and metastasis, while expression of Dub3 in breast cancer induces stabilization of Snail, thus triggering cell migration and metastasis of breast cancer. I will test this hypothesis by determining (1) the molecular mechanism of stabilization of Snail by Dub3; (2) the role of Dub3 in IL-6 induced EMT and metastasis via Snail stabilization; (3) whether drug treatment of Dub3 inhibit breast cancer metastasis, the effect of Dub3 in breast cancer metastasis with mouse model, and the functional regulation of Dub3 in human breast cancer.