RBM38 is involved in TGF-β-induced epithelial-to-mesenchymal transition by stabilising zonula occludens-1 mRNA in breast cancer

Background: The transforming growth factor-b (TGF-beta) pathway plays a vital role in driving cancer cell epithelial-mesenchymal transition (EMT). Zonula occludens-1 (ZO-1), which is downregulated in response to TGF-beta, is able to control endothelial cell-cell tension, cell migration, and barrier formation. However, the molecular mechanism of how TGF-b regulates ZO-1 expression remains unclear. Methods: Breast cancer cells were treated with TGF-b to induce an EMT progress. Chromatin immunoprecipitation and dualluciferase reporter assay were performed to investigate direct relationship between Snail and RNA binding motif protein 38 (RBM38). The RNA immunoprecipitation combined with RNA electrophoretic mobility shift assay and dual-luciferase reporter assay were conducted to testify direct relationship between RBM38 and ZO-1. The ZO-1 siRNA was transfected to breast cancer cells that overexpress RBM38 and the control, followed by transwell and Matrigel invasion assays to examine cell migratory and invasive ability. Results: Transforming growth factor-b induced a remarkable downregulation of RBM38 in breast cancer that was directly regulated by transcription repressor Snail targeting the E-box elements in promoter region of RBM38 gene. Additionally, RBM38 positively regulated ZO-1 transcript via directly binding to AU/U-rich elements in its mRNA 30-UTR. Moreover, by magnifying RBM38 expression, cell migration and invasion mediated by knockdown of ZO-1 in breast cancer were reversed. Conclusions: All the results clarified a linear regulation relationship among Snail, RBM38, and ZO-1, implicating RBM38 as a pivotal mediator in TGF-beta-induced EMT in breast cancer.