Tumor suppressor SCUBE2 inhibits breast-cancer cell migration and invasion through the reversal of epithelial-mesenchymal transition

Signal peptide-CUB-EGF domain-containing protein 2 (SCUBE2) belongs to a secreted and membrane-associated multi-domainSCUBE protein family. We previously demonstrated that SCUBE2 is a novel breast-tumor suppressor and could be a useful prognosticmarker. However, the role of SCUBE2 in breast-cancer cellmigration and invasion and how it is regulated during theepithelial-mesenchymal transition (EMT) remain undefined. In thisstudy, we showed that ectopic SCUBE2 overexpression couldenhance the formation of E-cadherin-containing adherens junctionsby b-catenin-SOX-mediated induction of forkhead box A1 (apositive regulator of E-cadherin) and upregulation of E-cadherin, which in turn led to epithelial transition and inhibited migration and invasion of aggressive MDA-MB-231 breast-carcinoma cells. SCUBE2 expression was repressed together with that of E-cadherinin TGF-b-induced EMT; direct expression of SCUBE2 alone was sufficient to inhibit the TGF-b-induced EMT. Furthermore, quantitative DNA methylation, methylation-specific PCR, and chromatin immunoprecipitation analyses revealed that SCUBE2 expression was inactivated by DNA hypermethylation at the CpG islands by recruiting and binding DNA methyltransferase 1 during TGF-b-induced EMT. Together, our results suggest that SCUBE2 plays a key role in suppressing breast-carcinoma-cell mobility and invasiveness by increasing the formation of the epithelial E-cadherin-containing adherens junctions to promote epithelial differentiation and drive the reversal of EMT.