3149

HMGB3

Deciphering molecular mechanisms that control epithelial-to-mesenchymal transition (EMT) contributes to our understanding of how tumor cells become invasive and competent for intravasation. We have established that transforming growth factor beta activates Smad proteins, which induce expression of the embryonic factor high mobility group A2 (HMGA2), which causes mesenchymal transition. HMGA2 associates with Smad complexes and induces expression of an established regulator of EMT, the zinc finger transcription factor Snail. We now show that HMGA2 can also induce expression of a second regulator of EMT, the basic helix-loop-helix transcription factor Twist. Silencing of endogenous Twist demonstrated that this protein acts in a partially redundant manner together with Snail. Double silencing of Snail and Twist reverts mesenchymal HMGA2-expressing cells to a more epithelial phenotype when compared with single silencing of Snail or Twist. Furthermore, HMGA2 can directly associate with A:T-rich sequences and promote transcription from the Twist promoter. The new evidence proposes a model whereby HMGA2 directly induces multiple transcriptional regulators of the EMT program and, thus, is a potential biomarker for carcinomas displaying EMT during progression to more advanced stages of malignancy.

MiR-27b downregulation is significantly associated with tamoxifen resistance in breast cancer cells. However, how it is downregulated in tamoxifen resistant (TamR) breast cancer cells and its downstream regulation were not clear. By performing MSP assay and QRT-PCR analysis with the use of 5-AZA-dC, a DNA methyltransferase inhibitor, we observed that TamR MCF-7 cells had significantly higher levels of methylation in the miR-27b promoter region than tamoxifen sensitive MCF-7 (TamS) cells and demethylation restored miR-27b expression. Re-expression of miR-27b sensitized TamR MCF-7 cells to tamoxifen, inhibited invasion and reversed epithelial-mesenchymal transition (EMT)-like properties. By using bioinformatics analysis and following dual luciferase and western blot analysis, this study confirmed a direct regulation of miR-27b on HMGB3 expression by binding to the 3'UTR. In addition, this study also found that silencing of HMGB3 indeed partially phenocopied the effects of miR-27b in reducing tamoxifen resistance and cell invasion and in reversing EMT-like properties. Therefore, we infer that HMGB3 is a functional target of miR-27b in modulation of tamoxifen resistance and EMT.CI - Copyright (c) 2016 Elsevier Inc. All rights reserved.