Hes-6, an inhibitor of Hes-1, is regulated by 17beta-estradiol and promotes breast cancer cell proliferation.
BACKGROUND
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)alpha-negative SKBR3 and MDA-MB-231 cells compared with the ERalpha-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.
Hartman
Johan
J
Department of Biosciences and Nutrition, Karolinska Institutet, Nobels väg 5, Solna Alfred Nobels Allé 8, 141 57 Huddinge, Sweden. johan.hartman@ki.se
Lam
Eric W-F
EW
Gustafsson
Jan-Ake
JA
Ström
Anders
A
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D048708:Cell Growth Processes / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D050687:E2F1 Transcription Factor / Q000037:antagonists & inhibitors / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000096:biosynthesis / Q000378:metabolism; D005260:Female; D018398:Homeodomain Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000008:administration & dosage / Q000235:genetics; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000072056:Transcription Factor HES-1; D014162:Transfection; D014183:Transplantation, Heterologous
D051792:Basic Helix-Loop-Helix Proteins; D050687:E2F1 Transcription Factor; D004958:Estradiol; D047628:Estrogen Receptor alpha; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D000072056:Transcription Factor HES-1; C411859:HES6 protein, human; C078493:HES1 protein, human