The Microbe-Derived Short Chain Fatty Acid Butyrate Targets miRNA-Dependent p21 Gene Expression in Human Colon Cancer

Colonic microbiota ferment non-absorbed dietary fiber to produce prodigious amounts of short chain fatty acids (SCFAs) that benefit the host through a myriad of metabolic, trophic, and chemopreventative effects. The chemopreventative effects of the SCFA butyrate are, in part, mediated through induction of p21 gene expression. In this study, we assessed the role of microRNA(miRNA) in butyrate's induction of p21 expression. The expression profiles of miRNAs in HCT-116 cells and in human sporadic colon cancers were assessed by microarray and quantitative PCR. Regulation of p21 gene expression by miR-106b was assessed by 3′ UTR luciferase reporter assays and transfection of specific miRNA mimics. Butyrate changed the expression of 44 miRNAs in HCT-116 cells, many of which were aberrantly expressed in colon cancer tissues. Members of the miR-106b family were decreased in the former and increased in the latter. Butyrate-induced p21 protein expression was dampened by treatment with a miR-106b mimic. Mutated p21 3′UTR-reporter constructs expressed in HCT-116 cells confirmed direct miR-106b targeting. Butyrate decreased HCT-116 proliferation, an effect reversed with the addition of the miR-106b mimic. We conclude that microbe-derived SCFAs regulate host gene expression involved in intestinal homeostasis as well as carcinogenesis through modulation of miRNAs.结肠菌群发酵未被吸收的膳食纤维，产生大量短链脂肪酸（short chain fatty acids, SCFAs），这类物质可通过多种代谢、营养及化学预防作用使宿主获益。其中短链脂肪酸中的丁酸，其化学预防作用部分通过诱导p21基因表达得以介导。本研究旨在探讨微小RNA（microRNA, miRNA）在丁酸诱导p21基因表达过程中的作用。研究采用微阵列（microarray）与定量聚合酶链反应（quantitative PCR），检测了HCT-116细胞及人类散发性结肠癌组织中miRNA的表达谱。通过3'非翻译区（3' untranslated region, 3'UTR）荧光素酶报告基因实验以及特定miRNA模拟物转染，评估了miR-106b对p21基因表达的调控作用。结果显示，丁酸可改变HCT-116细胞中44种miRNA的表达水平，其中多种miRNA在结肠癌组织中存在异常表达；miR-106b家族成员在前者（HCT-116细胞）中表达下调，在后者（结肠癌组织）中表达上调。经miR-106b模拟物处理后，丁酸诱导的p21蛋白表达受到抑制。在HCT-116细胞中表达的突变型p21 3'UTR报告基因载体实验证实，miR-106b可直接靶向p21基因。丁酸可抑制HCT-116细胞增殖，而加入miR-106b模拟物可逆转这一效应。本研究最终得出结论：微生物来源的短链脂肪酸可通过调控miRNA，调节参与肠道稳态及癌变过程的宿主基因表达。