Butyrate inhibits pro-proliferative miR-92a by diminishing c-Myc-induced miR-17-92a cluster transcription in human colon cancer cells

Abstract

BackgroundCompromised colonic butyrate production resulting from low dietary fiber or altered gut microbiota may promote colon neoplasia. Previous reports indicate these actions are mediated in part by altered levels of miRNAs, including suppressed expression of the oncogenic miR-17-92a cluster. Here, we sought to identify the mechanisms underlying these effects of butyrate in colon cancer.MethodsmiR-92a levels were measured in archived human colon cancer and adjacent normal colon specimens by microarray and quantitative RT-PCR (qPCR). The effects of butyrate and other histone deacetylase inhibitors (suberoylanilide hydroxamic acid (SAHA) and valproic acid) on primary (pri-miR17-92a), precursor and mature miR-92a were analyzed in HCT-116 and HT-29 human colon cancer cells using qPCR. The effects of butyrate, SAHA and valproic acid on protein levels of c-Myc, Drosha and p57 were measured in HCT-116 cells using immunoblotting. Regulation of C13orf25 promoter activity by butyrate was analyzed by luciferase reporter assay using modified pGL3 constructs containing a wild-type or mutated c-Myc binding site. Expression of c-Myc was modulated using siRNA or adenovirus vectors. p57 mRNA and protein were measured before and after transfection with miR-92a-mimic molecules. Following butyrate treatment and miR-92a-mimic transfection, apoptosis was analyzed by TUNEL staining and caspase-3 immunoblotting.ResultsMicroarray, confirmed by qPCR, revealed a seven-fold increase in miR-92a levels in sporadic human colon cancer tissue compared to adjacent normal colon. Treating human colon cancer cells with butyrate reduced the levels of pri-miR17-92a, precursor and mature miR-92a, as well as c-Myc. SAHA and valproic acid had similar effects. Mutation of the c-Myc binding site diminished butyrate’s inhibitory effects on C13orf25 promoter activity. Silencing c-Myc expression reduced miR-92a levels. c-Myc over-expression neutralized butyrate-induced attenuation of pri-miR17-92a. Exogenous miR-92a inhibited butyrate-induced p57 expression and reversed the beneficial actions of butyrate on colon cancer cell proliferation and apoptosis.ConclusionsOur findings identify a novel cellular mechanism whereby butyrate inhibits miR-92a transcription by reducing c-Myc, thus augmenting p57 levels. These actions diminish colon cancer cell proliferation and stimulate apoptosis. This newly described regulation of oncogenic miRNA biogenesis expands our understanding of colon cancer cell biology and identifies novel therapeutic targets.

High‐fat diet‐induced dysbiosis mediates MCP‐1/CCR2 axis‐dependent M2 macrophage polarization and promotes intestinal adenoma‐adenocarcinoma sequence

“…SCFAs mainly include acetate, propionate and butyrate, and have anti‐inflammatory and antineoplastic properties, particularly butyrate, which is the preferred energy source for colonocytes . Related clinical studies revealed that patients with advanced CRC had diminished butyrate‐producing bacteria and lower levels of SCFAs when compared with healthy controls . Our study showed that the abundance of SCFAs‐producing bacteria ( Roseburia , Barnesiella , Lachnospiraceae bacterium‐A4 and Lachnospiraceae bacterium‐COE1 ) was reduced in HFD group.…”

The Role of Bioactive Dietary Components in Modulating miRNA Expression in Colorectal Cancer

“…In addition, the same group of researchers demonstrated that in vivo supplementation of a high red meat diet (300 g/day lean red meat) with butylated resistant starch (40 g/day butylated high amylose maize starch), restored miR-17-92 levels to baseline, thus miR-21 remained unchanged [79]. Recently, a novel mechanism of butyrate able to induce apoptosis and decrease proliferation was described [150]. Along with miR-17-29 down-regulation previously described, Hu et al demonstrated that butyrate decreases c-myc and increases p57 expression in colon cancer cells.…”

Non‐digestible carbohydrates supplementation increases miR‐32 expression in the healthy human colorectal epithelium: A randomized controlled trial

“…miRNAs regulate the expression of thousands of genes by inhibiting their expression and, consequently, have effects on many biological processes including those involved in tumorigenesis . Abnormal expression of miRNAs is implicated in the pathogenesis of CRC, where it is associated with disease progression, treatment response, and prognosis .…”