Research article

Hes-6, an inhibitor of Hes-1, is regulated by 17β-estradiol and promotes breast cancer cell proliferation

Johan Hartman¹ , Eric W-F Lam² , Jan-Åke Gustafsson^1,3 and Anders Ström³

¹  Department of Biosciences and Nutrition, Karolinska Institutet, Nobels väg 5, Solna Alfred Nobels Allé 8, 141 57 Huddinge, Sweden

²  Cancer Research-UK Labs, Department of Oncology, MRC Cyclotron Building, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK

³  Center for Nuclear Receptors and Cell Signaling, Department of Biology and Biochemistry, University of Houston, 4800 Calhoun Road, Houston, TX 77204, USA

author email corresponding author email

Breast Cancer Research 2009, 11:R79doi:10.1186/bcr2446

Published:	5 November 2009

Abstract

Introduction

Hes-6 is a member of the basic helix-loop-helix (bHLH) family of transcription factors, and its overexpression has been reported in metastatic cancers of different origins. Hes-6 has been described as an inhibitor of Hes-1 during neuronal development, although its function in cancer is not known. In this study, we investigated the function of Hes-6 in breast cancer and tested the hypothesis that Hes-6 enhances breast cancer cell proliferation and is regulated by estrogen.

Methods

To investigate the function of Hes-6, T47D cells stably expressing Hes-6 were generated by lentiviral transduction, and conversely, siRNA also was used to knock down Hes-6 expression in breast cancer cells. The Hes-6-expressing T47D cells were transplanted into immunodeficient mice to study effects on tumor growth.

Results

We found that Hes-6 expression was significantly higher in the high-grade, estrogen receptor (ER)α-negative SKBR3 and MDA-MB-231 cells compared with the ERα-positive, non-metastasizing T47D and MCF-7 breast carcinoma cells. Moreover, the level of Hes-6 mRNA was 28 times higher in breast cancer samples compared with normal breast samples. In Hes-6-expressing T47D cells, Hes-6 ectopic expression was shown to stimulate cell proliferation in vitro as well as breast tumor growth in xenografts. Moreover, expression of Hes-6 resulted in induction of E2F-1, a crucial target gene for the transcriptional repressor Hes-1. Consistently, silencing of Hes-6 by siRNA resulted in downregulation of E2F-1 expression, whereas estrogen treatment caused induction of Hes-6 and downstream targets hASH-1 and E2F-1 in MCF-7 cells.

Conclusions

Together, the data suggest that Hes-6 is a potential oncogene overexpressed in breast cancer, with a tumor-promoting and proliferative function. Furthermore, Hes-6 is a novel estrogen-regulated gene in breast cancer cells. An understanding of the role and regulation of Hes-6 could provide insights into estrogen signaling and endocrine resistance in breast cancer and, hence, could be important for the development of novel anticancer drugs.