Regulatory Mechanisms and Functional Roles of Hypoxia-Induced Long Non-Coding RNA MTORT1 in Breast Cancer Cells

Yi-Chun Cheng; Li-Yu Su; Li-Han Chen; Tzu-Pin Lu; Eric Y Chuang; Mong-Hsun Tsai; Li-Ling Chuang; Liang-Chuan Lai

doi:10.3389/fonc.2021.663114

Regulatory Mechanisms and Functional Roles of Hypoxia-Induced Long Non-Coding RNA MTORT1 in Breast Cancer Cells

Front Oncol. 2021 Jun 1:11:663114. doi: 10.3389/fonc.2021.663114. eCollection 2021.

Authors

Yi-Chun Cheng¹, Li-Yu Su¹, Li-Han Chen², Tzu-Pin Lu^{3

4}, Eric Y Chuang^{4

5

6}, Mong-Hsun Tsai^{4

7}, Li-Ling Chuang^{8

9}, Liang-Chuan Lai^{1

4}

Affiliations

¹ Institute of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
² Institute of Fisheries Science, College of Life Science, National Taiwan University, Taipei, Taiwan.
³ Institute of Epidemiology and Preventive Medicine, National Taiwan University, Taipei, Taiwan.
⁴ Bioinformatics and Biostatistics Core, Center of Genomic and Precision Medicine, National Taiwan University, Taipei, Taiwan.
⁵ Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan.
⁶ Collage of Biomedical Engineering, China Medical University, Taichung, Taiwan.
⁷ Institute of Biotechnology, National Taiwan University, Taipei, Taiwan.
⁸ School of Physical Therapy and Graduate Institute of Rehabilitation Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
⁹ Department of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital, Taoyuan, Taiwan.

Abstract

Long non-coding RNAs (lncRNAs) have been found to participate in multiple genetic pathways in cancer. Also, mitochondria-associated lncRNAs have been discovered to modulate mitochondrial function and metabolism. Previously, we identified oxygen-responsive lncRNAs in MCF-7 breast cancer cells under different oxygen concentrations. Among them, a novel mitochondria-encoded lncRNA, mitochondrial oxygen-responsive transcript 1 (MTORT1), was chosen for further investigation. Nuclear, cytoplasmic, and mitochondrial fractionation assays were performed to evaluate the endogenous expression levels of MTORT1 in breast cancer cells. In vitro proliferation and migration assays were conducted to investigate the functions of MTORT1 in breast cancer cells by knockdown of MTORT1. RNA immunoprecipitation and luciferase reporter assays were used to examine the physical binding between MTORT1 and microRNAs. Our results showed that MTORT1 had low endogenous expression levels in breast cancer cells and was mainly located in the mitochondria. Knockdown of MTORT1 enhanced cell proliferation and migration, implying a tumor suppressor role of this novel mitochondrial lncRNA. MTORT1 served as sponge of miR-26a-5p to up-regulate its target genes, CREB1 and STK4. Our findings shed some light on the characterization, function, and regulatory mechanism of the novel hypoxia-induced mitochondrial lncRNA MTORT1, which functions as a microRNA sponge and may inhibit breast cancer progression. These data suggest that MTORT1 may be a candidate for therapeutic targeting of breast cancer progression.

Keywords: breast cancer; function; hypoxia; long noncoding RNA; microRNA; mitochondria.