RNAi Screen Identified Novel Long Non-Coding RNAs Involved in Cell Growth Control, Migration, and Invasion
Tse-Chun Kuo1, Hui-Ju Chou2, Sheng-Chieh Hsu1,2, Pei-Shan Li1, Szu-Huei Wu2, Jen-Shin Song2, Hsing-Jien Kung1,3
1Institute of Molecularand Genomic Medicine, National Health Research, Institutes, Miaoli, Taiwan; 2Institute of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Miaoli, Taiwan; 3Department of Biochemistry and Molecular Medicine, University of California Davis School of Medicine, University of California Davis Cancer Center, Sacramento, CA, USA
Triple-negative breast cancer (TNBC) is a highly aggressive form of breast cancer often associated with poor prognosis. Owing to the lack of therapeutic targets, patients with TNBC tend to rely on standard chemotherapy; however, chemo-resistance often develops in TNBC as a result of deregulated cell death control like in many other tumors. Long non-coding RNAs (lncRNAs) are transcripts longer than 200bp and have little or no protein-coding capacity. Although once considered as transcriptional noise, significant numbers of lncRNAs are now known as modulators of protein expression and functions and are implicated in a range of developmental processes and diseases. As many of them influence oncogenes and tumor suppressors in cancer, they represent excellent biomarkers as well as potential targets for therapy. In order to gain more insight on cell death regulation and to seek potential targets for TNBC, we employed an RNAi screen targeting 2231 lncRNAs in MDA-MB-231 TNBC cells. By using changes in cell metabolic activity (MTT assay) as readouts for primary screen and changes in cell number as confirmation, our unbiased screen identified novel lncRNAs that drastically reduced cell proliferation when depleted. One lncRNA hit was pursued further as it is highly expressed in cancerous cells and clinical breast tumors. We found knockdown of this lncRNA in tumor cells led to increased apoptosis, impaired migration/invasion, and diminished tumorigenicity. Interestingly, cell death was preceded by elevated mitochondrial respiration. Given suppression of mitochondria metabolism is frequently observed in cancer cells, our results suggest the lncRNA might regulate metabolic switch between mitochondrial oxidation and glycolysis. We are now trying to delineate the detailed molecular mechanism(s) by which the lncRNA contributes to tumorigenesis.