Overexpression of Id1 in transgenic mice promotes mammary basal stem cell activity and breast tumorigenesis

// Dong-Hui Shin 1, * , Ji-Hye Park 2, * , Jeong-Yeon Lee 2, * , Hee-Young Won 1 , Ki-Seok Jang 1 , Kyueng-Whan Min 1 , Si-Hyong Jang 1 , Jong-Kyu Woo 3 , Seung Hyun Oh 3 , Gu Kong 1, 2 1 Department of Pathology, College of Medicine, Hanyang University, Seoul, Republic of Korea 2 Institute for Bioengineering and Biopharmaceutical Research (IBBR), Hanyang University, Seoul, Republic of Korea 3 College of Pharmacy, Gachon University, Incheon, Republic of Korea * These authors have contributed equally to this work Correspondence to: Gu Kong, e-mail: gkong@hanyang.ac.kr Keywords: basal-like breast cancer, cancer stem cell, Id1, mammary stem cell, c-Myc Received: January 14, 2015      Accepted: April 06, 2015      Published: April 16, 2015 ABSTRACT Inhibitor of differentiation/DNA binding (Id)1 is a crucial regulator of mammary development and breast cancer progression. However, its effect on stemness and tumorigenesis in mammary epithelial cells remains undefined. Herein, we demonstrate that Id1 induces mammary tumorigenesis by increasing normal and malignant mammary stem cell (MaSC) activities in transgenic mice. MaSC-enriched basal cell expansion and increased self-renewal and in vivo regenerative capacity of MaSCs are observed in the mammary glands of MMTV-Id1 transgenic mice. Furthermore, MMTV-Id1 mice develop ductal hyperplasia and mammary tumors with highly expressed basal markers. Id1 also increases breast cancer stem cell (CSC) population and activity in human breast cancer lines. Moreover, the effects of Id1 on normal and malignant stem cell activities are mediated by the Wnt/c-Myc pathway. Collectively, these findings provide in vivo genetic evidence of Id1 functions as an oncogene in breast cancer and indicate that Id1 regulates mammary basal stem cells by activating the Wnt/c-Myc pathway, thereby contributing to breast tumor development.