OTUD3 inhibits breast cancer cell metastasis by regulating TGF-β pathway through deubiquitinating SMAD7.

BACKGROUND: Breast cancer (BRCA) is the most common malignant tumor in women, and distant metastasis is an important cause of death. Epithelial mesenchymal transition (EMT) is an important factor in tumor cell metastasis, in which TGF-β signaling pathway plays an important role. SMAD7 can inhibit TGF-β pathway. Previously, we found that ovarian tumor domain-containing protein 3(OTUD3) could maintain the stability of multiple molecules through deubiquitination. In this study, multiple experiments were conducted to verify whether OTUD3 can inhibit TGF-β pathway by deubiquitinating SMAD7. METHODS: Firstly, bioinformatics was used to search the expression of OTUD3 in breast cancer and its correlation with SMAD7 in the TCGA database. The correlation between the protein and mRNA expression levels of OTUD3 and SMAD7 in multiple BRCA cell lines was verified. Also, the OTUD3 and SMAD7 expression in human BRCA samples and its influence on prognosis were verified by immunohistochemical experiments. Then, the CO-IP experiment was performed by transfecting OTUD3 and SMAD7 in HEK293T cells to confirm whether OTUD3 could maintain SMAD7 protein stability through deubiquitination. Furthermore, luciferase reporting assay, in vitro protein interaction, and transwell assay were used to verify whether OTUD3 could inhibit TGF-β pathway by deubiquitinating SMAD7 and affect cell invasion. Western blot and RT-qPCR were used to detect the correlation between OTUD3 and molecules regulated by the TGF-β pathway. Finally, the effect of OTUD3 on tumor cells was determined by 3D matrigel cell culture. RESULTS: The expression of OTUD3 was low in BRCA and positively correlated with SMAD7. Cytological experiments and immunohistochemistry confirmed that OTUD3 was positively correlated with the expression of SMAD7, and the patients with a low expression of OTUD3 had a short recurrence-free survival (RFS). Cell experiments confirmed that OTUD3 could regulate the TGF-β pathway by deubiquitinating SMAD7, which affected EMT and inhibited cell invasion. OTUD3 was found to inhibit the stemness of tumor cells by 3D matrigel cell culture. CONCLUSIONS: Our findings indicated OTUD3 inhibited BRCA metastasis associated with TGF-β signaling by deubiquitination to stabilize SMAD7 protein levels.