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.
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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)