Aflatoxin B1 Negatively Regulates Wnt/β-Catenin Signaling Pathway through Activating miR-33a

PLOS ONE, Dec 2019

MicroRNAs are known to play an important role in modulating gene expression in various diseases including cancers and cardiovascular disorders, but only a few of them are associated with the pathology of aflatoxin B1 (AFB1), a potent mycotoxin. Here, we discovered a novel regulatory network between AFB1, miR-33a and β-catenin in human carcinoma cells. The level of miR-33a was up-regulated in hepatocellular carcinoma (HCC) cells treated with AFB1, while in the same cells causing the decrease in β-catenin expression when treated at their IC50 values. miR-33a, specifically miR-33a-5p, was demonstrated to down-regulate the expression of β-catenin, affect the β-catenin pathway, and inhibit cell growth. Also, by employing a luciferase assay, we found that miR-33a down-regulated β-catenin by directly binding to the 3’-UTR of β-catenin. These results suggested that AFB1 might down-regulate β-catenin by up-regulating miR-33a. This understanding opens new lines of thought in the potential role of miR-33a in the clinical therapy of cancer.

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Aflatoxin B1 Negatively Regulates Wnt/β-Catenin Signaling Pathway through Activating miR-33a

et al. (2013) Aflatoxin B1 Negatively Regulates Wnt/-Catenin Signaling Pathway through Activating miR-33a. PLoS ONE 8(8): e73004. doi:10.1371/journal.pone.0073004 Aflatoxin B1 Negatively Regulates Wnt/-Catenin Signaling Pathway through Activating miR-33a Yi Fang 0 Youjun Feng 0 Tongjin Wu 0 Swaminath Srinivas 0 Weiqiang Yang 0 Jue Fan 0 Chi Yang 0 Shihua Wang 0 Masaru Katoh, National Cancer Center, Japan 0 1 The Ministry of Education Key Laboratory of Biopesticide and Chemical Biology and the College of Life Sciences, Fujian Agriculture and Forestry University , Fuzhou , P. R. China , 2 Academy of Integrative Medicine, Fujian University of Traditional Chinese Medicine , Fuzhou , P. R. China , 3 Fujian Key Laboratory of Integrative Medicine on Geriatrics, Fujian University of Traditional Chinese Medicine , Fuzhou , P. R. China , 4 Department of Microbiology, University of Illinois at Urbana-Champaign, Champaign, Illinois, United States of America, 5 Department of Biochemistry, University of Illinois at Urbana-Champaign , Champaign, Illinois , United States of America MicroRNAs are known to play an important role in modulating gene expression in various diseases including cancers and cardiovascular disorders, but only a few of them are associated with the pathology of aflatoxin B1 (AFB1), a potent mycotoxin. Here, we discovered a novel regulatory network between AFB1, miR-33a and -catenin in human carcinoma cells. The level of miR-33a was up-regulated in hepatocellular carcinoma (HCC) cells treated with AFB1, while in the same cells causing the decrease in -catenin expression when treated at their IC50 values. miR-33a, specifically miR-33a-5p, was demonstrated to down-regulate the expression of -catenin, affect the -catenin pathway, and inhibit cell growth. Also, by employing a luciferase assay, we found that miR-33a down-regulated catenin by directly binding to the 3'-UTR of -catenin. These results suggested that AFB1 might down-regulate catenin by up-regulating miR-33a. This understanding opens new lines of thought in the potential role of miR-33a in the clinical therapy of cancer. - Funding: This work was supported by the National Natural Science Foundation of China (No. 31000961 and No. 31172297), and the Natural Science Foundation of Fujian Province (No. 2013J01081). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Aflatoxins are secondary metabolites produced by Aspergillus parasiticus (aflatoxins B1, B2, G1, and G2) and Aspergillus flavus (aflatoxins B1 and B2) with aflatoxin B1 (AFB1) being the most prevalent toxin. These aflatoxins producing by members of Aspergillus commonly contaminate food, especially peanuts and corn. In humans, evidence has shown that acute aflatoxicosis could cause vomiting, disease of the liver and heart, pulmonary edema, coma and even death [1,2]. Being one of the most critical hepatocarcinogenic factors in many animal species [35], AFB1 exposure typically leads to hepatocellular carcinoma (HCC) through prolonged dietary exposure along with other risk factors including the hepatitis B virus (HBV), hepatitis C virus (HCV) or heavy alcohol intake. AFB1 is accumulated and metabolized predominantly in the liver, and its toxicity requires cytochromes P450 (CYPs) like CYP1A2, CYP3A4 and CYP2A6 in the liver for its metabolic activation [68]. These enzymes usually catalyze AFB1 to AFB1-8,9-exo-epoxide (exo-AFBO), which is a putative reactive intermediate and carcinogenic epoxide [9]. Exo-AFBO exhibits toxicity by binding to nucleic acids and proteins [10]. Exposure to aflatoxin B1 leads to accumulation of DNA adducts, p53 gene mutation in hepatocellular carcinoma [11], and overexpression of -catenin [12]. In addition to the accumulation of -catenin, mutations in CTNNB1, the gene encoding -catenin, were reported at a low frequency in HCC in response to high AFB1 exposure [1215]. This suggested that other unidentified biomolecules modulating -catenin stability may be involved in aflatoxin-associated HCC, and that these molecules might either be miRNAs or the products of mutations of another Wnt/ -catenin signaling components [13]. -catenin is a subunit of the cadherin-associated protein complex which constitute the adherens junctions. It has also been implicated to be an essential component in the wellknown Wnt/-catenin signaling pathway. -catenin also plays an important role in cell differentiation, proliferation, apoptosis, metastasis and tumorigenesis [16,17]. In normal cells, catenin is always controlled at a proper level by the phophorylation of GSK-3, while the mutation and accumulation of -catenin always lead to cancer [1821]. catenin not only regulates the basal expression levels of CYPs, but also controls the magnitude of induction and hepatic localization of the response to xenobiotic inducers [22]. microRNAs (miRNAs) are a class of small noncoding RNA molecules, which are expressed endogeno (...truncated)


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Yi Fang, Youjun Feng, Tongjin Wu, Swaminath Srinivas, Weiqiang Yang, Jue Fan, Chi Yang, Shihua Wang. Aflatoxin B1 Negatively Regulates Wnt/β-Catenin Signaling Pathway through Activating miR-33a, PLOS ONE, 2013, 8, DOI: 10.1371/journal.pone.0073004