A novel double-negative feedback loop between miR-489 and the HER2-SHP2-MAPK signaling axis regulates breast cancer cell proliferation and tumor growth

// Yogin Patel 1, 2, * , Nirav Shah 1, 2, * , Ji Shin Lee 3 , Eleni Markoutsa 4 , Chunfa Jie 5 , Shou Liu 1, 2 , Rachel Botbyl 1, 2 , David Reisman 1, 2 , Peisheng Xu 4 , Hexin Chen 1, 2 1 Department of Biological Science, University of South Carolina, Columbia, SC, USA 2 Center for Colon Cancer Research, University of South Carolina, Columbia, SC, USA 3 Department of Surgery, Chonnam National University, Gwangju, Republic of Korea 4 Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC, USA 5 Master of Science in Biomedical Sciences Program, Des Moines University, Des Moines, IA, USA * These authors have contributed equally to this work Correspondence to: Hexin Chen, e-mail: hchen@biol.sc.edu Keywords: microRNA, miR-489, HER2, breast cancer, tumor suppressor Received: December 2, 2015     Accepted: February 11, 2016     Published: February 22, 2016 ABSTRACT Human epidermal growth factor receptor 2 (HER2 or ErBb2) is a receptor tyrosine kinase overexpressed in 20-30% of breast cancers and associated with poor prognosis and outcome. Dysregulation of several microRNAs (miRNAs) plays a key role in breast cancer progression and metastasis. In this study, we screened and identified miRNAs dysregualted in HER2-positive breast cancer cells. Our molecular study demonstrated that miR-489 was specifically downregulated by the HER2-downstream signaling, especially through the MAPK pathway. Restoration or overexpression of miR-489 in HER2-positive breast cancer cells significantly inhibited cell growth in vitro and decreased the tumorigenecity and tumor growth in xenograft mice. Mechanistically, we found that overexpression of miR-489 led to the decreased levels of HER2 and SHP2 and thus attenuated HER2-downstream signaling. Furthermore, we for the first time demonstrated that HER2 is a direct target of miR-489 and therefore HER2-SHP2-MAPK and miR-489 signaling pathways form a mutually inhibitory loop. Using quantitative real-time PCR analysis and Fluorescent in situ hybridization technique (FISH), we found that miR-489 was expressed at significantly lower level in tumor tissues compared to the adjacent normal tissues. Downregulation of miR-489 in breast cancers was associated with aggressive tumor phenotypes. Overall, our results define a double-negative feedback loop involving miR-489 and the HER2-SHP2-MAPK signaling axis that can regulate breast cancer cell proliferation and tumor progression and might have therapeutic relevance for HER2-positive breast cancer.