Abstract 1074: Epigenetic silencing of DACH1 in triple negative breast cancer contributes to the tumorigenesis
Authors: Chu Qian , Han Na , Dong Yan , Yuan Xun , Guo Mingzhou , Xu Hanxiao , Yu Shiying , Wu Kongming 
Published: August 2015

Abstract
BACKGROUND: Increasing evidence indicates that cell fate determination factor DACH1 functions as a tumor suppressor. Specifically, in estrogen receptor positive (luminal), highly expression of DACH1 predicted longer cancer specific survival and disease free interval, as well as reduced metastasis formation. Our analysis of over 2,000 patients demonstrated increased nuclear DACH1 expression correlated inversely with cellular mitosis and predicted 40 months survival advantage in breast cancer patients. But, endogenous DACH1 was dramatically reduced in breast cancer cell lines with high expression of tumor initiation cell markers and in patient samples of triple negative breast cancer, the most aggressive subtype. We proposed that epigenetically change might contribute to the loss expression of DACH1 in breast cancer. MATERIALS AND METHODS: Clinical samples included 10cases of normal breast tissues, 26 cases of luminal breast cancer(ER+,PR+,HER1-2+), and 32 cases of triple negative breast cancer(ER-,PR-,HER-). Genomic DNA was extracted from formalin-fixed tissue and methylation-specific PCR of DACH1 promoter was performed. DACH1 protein expression was detected in human breast cancer tissue arrays by immunohistochemistry. Human triple negative breast cancer cell lines MDA-MB-231 and sum159 were cultured in DME medium supplied with 10% fetal bovine serum and growth factors. Stable cell lines expressing DACH1 were established in MDA-MB-231 and Sum159 though lentivirus transfection. In vitro cell growth was evaluated by MTT assay and colony formation. In vivo tumor growth was measured in xenograft mice model. RESULTS: There is no methylation of DACH1 promoter region was found in normal breast tissues, but methylation was found in 2 out of 26 (7.7%) in luminal breast cancer and 10 of 32(32%) in triple negative breast cancer. Consisting with previous report, immunohistochemical stain revealed nuclear stain of DACH1 in all normal and majority of luminal type breast cancer tissues, but lost or very weak expression of DACH1 in triple negative cancer tissues. Correspondingly, expression microarrays demonstrated that DACH1 mRNA levels in triple negative breast cancer cell lines were dramatically less than that of normal breast cell line and luminal breast cancer cell lines. Treatment of MDA-MB-231 and Sum159 cells with 5-Aza-2′-deoxyazacytidine induced the expression of DACH1 and decreased cellular proliferation. Ectopic expression of DACH1 inhibited in vitro cell growth and in vivo tumor formation. CONCLUSION: Promoter hypermethylation is a main factor leading to the inactivation of DACH1 in triple negative breast cancer; Re-expression of DACH1by epigenetic modification might provide a novel therapeutic strategy for this aggressive cancer.
Citation Format: Qian Chu, Na Han, Yan Dong, Xun Yuan, Mingzhou Guo, Hanxiao Xu, Shiying Yu, Kongming Wu. Epigenetic silencing of DACH1 in triple negative breast cancer contributes to the tumorigenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1074. doi:10.1158/1538-7445.AM2015-1074