Abstract 1956: High-throughput screens identify microRNAs essential for HER2-positive breast cancer cell growth.

Abstract

Abstract MicroRNAs (miRNAs) are small non-coding RNAs regulating gene expression post-transcriptionally. Due to their capability to target multiple genes, often in a same pathway, miRNAs would be ideal candidates for therapeutic targeting. Here, our aim was to characterize the role of miRNAs in the regulation of HER2-signaling in breast cancer. HER2 is a receptor tyrosine kinase amplified in over 20% of human breast cancers and it regulates many important cellular processes, including cell growth and survival. HER2 mediates its signals by activating downstream pathways, such as phosphatidyl-inositol-3 kinase (PI3K)/AKT and the mitogen-activated protein kinases. We performed miRNA gain-of-function assays by screening two HER2-positive cell lines (KPL-4 and JIMT-1) with a miRNA mimic library consisting of 810 human miRNAs. The levels of HER2, phospho-AKT, phospho-ERK1/2, cell proliferation (Ki67) and apoptosis (cleaved PARP) were detected with specific antibodies using protein lysate microarrays. In order to find the miRNAs most efficiently inhibiting HER2 signaling and proliferation as well as inducing apoptosis, we did rank product analyses through the whole data matrix. These analyses resulted in 38 miRNAs (q≤0.05). Among them were miR-491-5p, miR-342-5p and miR-744*, which were significantly (p≤0.05) down-regulated in HER2-positive breast tumors as compared to HER2-negative tumors. miR-342-5p appeared to specifically inhibit HER2-positive cell growth, as it had no effect on the growth of HER2-negative control cell line. Furthermore, higher expression of miR-342-5p was associated with better survival in breast cancer patients. We characterized also miRNAs directly targeting HER2 and identified eight novel miRNAs (miR-552, miR-541, miR-193a-5p, miR-453, miR-134, miR-498, miR-449b, and miR-449a) as direct regulators of the HER2 3’UTR. Taken together, the miRNAs identified here are potent negative regulators of HER2 function and they may also play a role in vivo during breast cancer progression. These results suggest mechanistic insights in HER2 regulation in breast cancer and open potential new strategies towards prevention and therapeutic inhibition of HER2-positive breast cancer. Citation Format: Suvi-Katri Leivonen, Kristine Kleivi Sahlberg, Rami Makela, Olli Kallioniemi, Anne-Lise Borresen-Dale, Merja Perala. High-throughput screens identify microRNAs essential for HER2-positive breast cancer cell growth. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1956. doi:10.1158/1538-7445.AM2013-1956