miRNA-221 is elevated in cystic fibrosis airway epithelial cells and regulates expression of ATF6. OglesbyIrene K. AgrawalRaman MallMarcus A. McElvaneyNoel G. GreeneCatherine M. 2019 <h4>Background</h4> <h4>MicroRNA (miRNA) and messenger RNA (mRNA) expression differs in cystic fibrosis (CF) versus non-CF bronchial epithelium. Here, the role of miRNA in basal regulation of the transcription factor ATF6 was investigated in bronchial epithelial cells <em>in vitro</em> and <em>in vivo</em>.</h4> <h4>Methods</h4> <p>Using <em>in silico</em> analysis, miRNAs predicted to target the 3′untranslated region (3′UTR) of the human ATF6 mRNA were identified.</p> <h4>Results</h4> <p>Three of these miRNAs, miR-145, miR-221 and miR-494, were upregulated in F508del-CFTR homozygous CFBE41o- versus non-CF 16HBE14o- bronchial epithelial cells and also in F508del-CFTR homozygous or heterozygous CF (<em>n</em> = 8) versus non-CF (<em>n</em> = 9) bronchial brushings. ATF6 was experimentally validated as a molecular target of these miRNAs through the use of a luciferase reporter vector containing the full-length 3′UTR of ATF6. Expression of ATF6 was observed to be decreased in CF both <em>in vivo</em> and <em>in vitro</em>. miR-221 was also predicted to regulate murine ATF6, and its expression was significantly increased in native airway tissues of 6-week-old βENaC-overexpressing transgenic mice with CF-like lung disease versus wild-type littermates.</p> <h4>Conclusions</h4> <p>These results implicate miR-145, miR-221 and miR-494 in the regulation of ATF6 in CF bronchial epithelium, with miR-221 demonstrating structural and functional conservation between humans and mice. The altered miRNA expression evident in CF bronchial epithelial cells can affect expression of transcriptional regulators such as ATF6.</p>