Regulation of Transcription Factor Twist Expression by the DNA Architectural Protein High Mobility Group A2 during Epithelial-to-Mesenchymal Transition

E-Jean Tan,Sylvie Thuault,Laia Caja,Tea Carletti,Carl-Henrik Heldin,Aristidis Moustakas

doi:10.1074/jbc.m111.291385

Abstract

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 β 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.

Highlights

Epithelial-to-mesenchymal transition (EMT) has important biological implications, but mechanisms governing this process are only partially understood
Mammary Epithelial Cells Overexpressing high mobility group A2 (HMGA2) Strongly Up-regulate Twist—We previously reported that when normal mammary epithelial cells were stably transfected with HMGA2, several transcriptional regulators that promote EMT were upregulated, and the cells shifted to a mesenchymal phenotype that lacked key features of the parental epithelial phenotype, such as expression of E-cadherin [14, 15]
Quantitative RT-PCR analysis of the mRNA from the same two cell types confirmed that cells expressing HMGA2 had dramatically higher levels of Twist mRNA compared with parental NMuMG cells, which paralleled the Snail expression profile (Fig. 1A)

Summary

Background

Epithelial-to-mesenchymal transition (EMT) has important biological implications, but mechanisms governing this process are only partially understood. HMGA2 associates with Smad complexes and induces expression of an established regulator of EMT, the zinc finger transcription factor Snail. The large numbers of cellular events that characterize the mesenchymal transition are thought to be collectively regulated by a group of transcription factors that coordinate the transcriptional program of EMT. In vitro studies in immortalized epithelial cells and in carcinoma cell lines, complemented by in vivo studies in transgenic mice, have clearly shown that TGF␤ plays a critical role in the control of EMT of tumor cells [8, 9]. Cancers of mesenchymal origin (e.g. fibrosarcomas) and metastatic cancers overexpress HMGA2 [16], which is compatible with a model of transition of tumor cells (via EMT) to phenotypes that reactivate embryonic transcriptional programs [2]. The new work firmly establishes that the EMT program promoted by TGF␤ signaling involves a stable crosstalk and interplay of multiple embryonic transcription factors

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION