Abstract 4486: Redox regulation of the biosynthesis of mitronic tsmiR miR6855 in the basal like breast cancer cells

Abstract

Abstract Radiation and chemotherapeutic agents eradicate tumors by inducing irreparable DNA damage. However, cancer cells often develop resistance to therapy by manipulating the DNA repair machinery. Conversely, a dividing cell constantly exposed to environmental and endogenous DNA damaging agents can transform into a tumor due to incorrect repair. Therefore the expression level of DNA repair proteins is critical both for cancer therapy and tumorigenesis. Our preliminary studies implied a unique mechanism involving an miRNA miR-6855-3p that promotes the biosynthesis of the transcriptional regulator protein SPRDX5 which enhances the expression of the tumor suppressor protein BRCA2 leading to the genotoxin and radiation-resistance of aggressive SLUG-high basal-like breast cancer (BLBC) cells. The miRNA miR-6855-3p thus acts as a tumor suppressor miRNA (tsmiR). Interestingly, the gene for the miRNA miR-6855-3p is mitronic and is nested within the intron#13 of the USP20 gene which is a deubiquitinase. Thus, the transcription of miR-6855-3p gene is regulated through the USP20 gene promoter. We present evidence here that USP20 and miR-6855 gene transcriptions are up regulated by oxidative stress. Tert-butylhydroperoxide was used for oxidative stress. Under the oxidative stress conditions tested, NRF2 level and the levels of several NRF2-regulated proteins are increased, indicating activation of NRF2 in the stressed BLBC cells. Under the stress conditions the levels of USP20 and miR-6855-3p are increased significantly. Knockdown of NRF2 prevented stress-induced elevation of USP20 and miR-6855-3p RNA level in the BLBC cells indicating the involvement of NRF2 in this process. The binding of NRF2 to the USP20 gene promoter and its function were characterized by ChIP analysis, site-directed mutagenesis and using the promoter-luciferase reporter constructs. We conclude that the biosynthesis of the tsmiR miR-6855-3p in the BLBC cells is regulated by oxidative stress and involves NRF2. Since oxidative stress is a hallmark in the etiology and progression of metastatic breast cancer, understanding the redox regulation of a tsmiR that positively influences BRCA2 gene expression in the BLBC cells could be clinically significant. Supported in part by DOD-CDMRP IDEA Expansion Grant# BC103645 and NIH/NCI grant 1R21CA181920-01 to GC and 1U54RR026140 to SM. Citation Format: Smita Misra, Gautam Chaudhuri. Redox regulation of the biosynthesis of mitronic tsmiR miR6855 in the basal like breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4486. doi:10.1158/1538-7445.AM2017-4486