Requirement of TCF7L2 for TGF-β-dependent Transcriptional Activation of the TMEPAI Gene

Naoko Nakano,Susumu Itoh,Yukihide Watanabe,Kota Maeyama,Fumiko Itoh,Mitsuyasu Kato

doi:10.1074/jbc.m110.132209

Naoko Nakano, Susumu Itoh + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m110.132209

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Abstract

The TGF-β and Wnt pathways are involved in cell fate and tumorigenicity. A recent report indicated that a TGF-β target gene, TMEPAI (transmembrane prostate androgen-induced RNA), is possibly also a downstream target of Wnt signaling. Although TMEPAI was believed to be involved in tumorigenicity because of its blockage of TGF-β signaling, how TGF-β and Wnt signals affect the activation of the TMEPAI gene is not well understood. Herein, we show that the TMEPAI promoter is regulated synergistically by TGF-β/Smad and Wnt/β-catenin/T cell factor (TCF) 7L2. The critical cis-element for dual signals, termed TGF-β-responsive TCF7L2-binding element (TTE), is located in intron 1 of the TMEPAI gene. TCF7L2, but not Smad proteins, bound to TTE, whereas the disruption of TTE by mutagenesis remarkably counteracted both TGF-β and TCF7L2 responses. The introduction of mutations in critical Smad-binding elements blocked the activation of the TMEPAI promoter by TCF7L2. Furthermore, our DNA-protein interaction experiments revealed the indirect binding of TCF7L2 to Smad-binding elements via Smad3 upon TGF-β stimulation as well as its TGF-β-dependent association with TTE. We demonstrate that the Wnt/β-catenin/TCF7L2 pathway is preferentially able to alter the transcriptional regulation of the TGF-β-target gene, TMEPAI.

Highlights

Promotes tumor progression and metastasis by inducing epithelial-mesenchymal transition, invasion, immunesuppression, and blood vessel intravasation by carcinoma cells [2, 6]
Because we principally used HepG2 cells in the following experiments, we investigated whether TMEPAI mRNA in HepG2 cells could be induced by TGF-␤
Because the sequences of the TMEPAI promoter from the transcriptional initiation site (ϩ1) to Ϫ850 are highly homologous in human and mouse, we cloned the fragment from ϩ67 to Ϫ1972 using the mouse BAC clone including the TMEPAI gene and inserted it into the pGL3-basic vector (Ϫ1972TMEPAI-luc) (Fig. 1C)

Summary

Introduction

Promotes tumor progression and metastasis by inducing epithelial-mesenchymal transition, invasion, immunesuppression, and blood vessel intravasation by carcinoma cells [2, 6]. LEF1, a member of the same protein family as TCF7L2, could only marginally activate the promoter of the TMEPAI gene, its expressions were relatively higher than those of TCF7L2 when the same amount of DNA was transfected in cells (Fig. 2C).

Results

Conclusion