期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2012
卷号：109
期号：15
页码：5826-5831
DOI：10.1073/pnas.1118118109
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Human inducible nitric oxide synthase (hiNOS) gene expression is regulated by transcriptional and posttranscriptional mechanisms. The purpose of this study was to determine whether specific microRNA (miRNA) directly regulate hiNOS gene expression. Sequence analysis of the 496-bp hiNOS 3'-untranslated region (3'-UTR) revealed five putative miR-939 binding sites. The hiNOS 3'-UTR conferred significant posttranscriptional blockade of luciferase activity in human A549, HCT8, and HeLa cells. The hiNOS 3'-UTR also exerted basal and cytokine-stimulated posttranscriptional repression in an orientation-dependent manner. Functional studies demonstrated that transfection of miR-939 into primary human hepatocytes (HCs) significantly inhibited cytokine-induced NO synthesis in a dose-dependent manner that was abrogated by a specific miR-939 inhibitor. MiR-939 (but not other miRNAs) abolished cytokine-stimulated hiNOS protein in human HC, but had no effect on hiNOS mRNA levels. Site-directed mutagenesis of miR-939 bindings sites at +99 or +112 bp in the hiNOS 3'-UTR increased reporter gene expression. Furthermore, intact miR-939 binding sites at +99 or +112 positions were required for posttranscriptional suppression by miR-939. Cytokine stimulation directly increased miR-939 levels in human HC. Transfection of miR-939 inhibitor (antisense miR-939) enhanced cytokine-induced hiNOS protein and increased NO synthesis in vitro in human HC. Finally, cytokine or LPS injection in vivo in mice increased hepatic miR-939 levels. Taken together, these data identify that miR-939 directly regulates hiNOS gene expression by binding in the 3'-UTR to produce a translational blockade. These findings suggest dual regulation of iNOS gene expression where cytokines induce iNOS transcription and also increase miR-939, leading to translational inhibition in a check-and-balance system.
