An investigation into the biochemical, molecular and epigenetic effects of fumonisin B1 in liver (HEPG2) cells.
Year: 2014
Type: dissertation
Abstract: Fumonisins are carcinogenic mycotoxins that occur world wide in maize and maizebased \nproducts intended for human consumption. Consumption of fumonisincontaminated \nmaize as a staple diet has been associated with oesophageal and liver \ncancer in South Africa and China. Fumonisin B1 (FB1) inhibits sphingolipid \nbiosynthesis and has been implicated in cancer promoting activity in animals and \nhumans. FB1 disrupts DNA methylation and induces chromatin modifications in \nhuman hepatoma (HepG2) cells. In this study FB1 (IC50=200μM) altered liver enzyme \nexpression of DNA methyltransferases and demethylases. DNA methyltransferase \nactivities of DNMT1, 3a and 3b were significantly decreased, whilst both DNA \nmethylase (MBD2) activity and expression was significantly up-regulated resulting in \nglobal DNA hypomethylation. In addition the histone demethylases, KDM5B and \nKDM5C, expression was increased. FACS data confirmed FB1 significantly increased \nglobal DNA hypomethylation – a process that causes chromatin instability. Next the \neffect of FB1 on miRNA expression was evaluated; FB1 significantly down-regulated \n(11 fold) expression of miR-27b. MiR-27b modulates expression of human \ncytochrome P450 (CYP1B1) that catalyzes the metabolic activation of many \nprocarcinogens. In order to directly assess the effect of miR-27b on CYP1B1 mRNA \nlevels, liver cells were transfected with the mimic to miR-27b. CYP1B1 mRNA and \nprotein expression was significantly up-regulated by 1.8- fold and 2.6- fold \nrespectively. CYP1B1 is post-transcriptionally regulated by miR-27b suggesting that \nFB1- induced modulation of miR-27b in hepatic cells may be an additional mode of \nhepatic neoplastic transformation. Finally, the effect of FB1 on the apoptotic pathway \nin HepG2 cells was investigated using an mRNA expression array panel of pro- and \nanti- apoptotic molecules. FB1 significantly increased an AIP family member - BIRC 8/ILP-2 (8-fold) in an apoptosis array. In addition, ILP2 protein expression was \nincreased (2.3-fold) with a corresponding decrease in Smac/DIABLO protein levels \n(1.7-fold). Further analysis showed an FB1 (0μM, 50μM, 100μM, 200μM) dosedependent \nincrease in BIRC-8/ILP-2 mRNA and protein expression in HepG2 cells. \nThis data suggests that FB1 modulates apoptosis in a complex dose-dependent \nregulation of pro- and anti-apoptotic molecules – and it is not a matter of simply \nswitching on or off. \nIn conclusion, the data shows that FB1 possess epigenetic properties by inducing \nglobal DNA hypomethylation, modulating miRNA expression, and increasing \nexpression of the AIP protein family (BIRC8/ILP-2) that may lead to liver \ntumourigenesis.
Author: Anil A. Chuturgoon
Language: English
Subfield: Plant Science
Domain: Life Sciences
Open Access status: green
Funder: National Research Foundation
OpenAlex ID: W1717227644