Abstract
Bisphenol A (BPA) is a plasticizer wildly used in polycarbonate (PC) and epoxy plastic products, dental sealants and inner coating of cans. BPA is an endocrine disrupt compounds (EDCs) able to compete with estrogen for estrogen receptor (ER) binding to affect cell function. Endometrial hyperplasia is one of the risk factors to lead to endometrial cancer. Our previous study found endometrial hyperplasia patients have higher serum BPA levels than normal women, and BPA exposure induces inflammatory response and increases gene expression of cell proliferation in human endometrial cancer RL95-2 cells. Aberrant microRNAs (miRNAs) regulation has been identified in endometrial cancer (EC) patients. Therefore, this study assumed BPA exposure disrupted miRNA regulation and its gene expression in human endometrial cells corresponding to EC carcinogenesis. The purposes of this study were (1) to investigate whether BPA exposure affected miRNAs and their target genes in human endometrial cells; (2) to assess whether BPA exposure affected gene functions relevant to EC; and (3) to figure out whether BPA exposure dysregulated miRNA-mediated pathways to lead to endometrial carcinogenesis. This study used Phalanx Human miRNA OneArray® v4 chip and Phalanx Human mRNA OneArray® v5 chip to respectively determine differentially expressed miRNAs and mRNAs (DEGs) in human endometrial cancer RL95-2 cells exposure to 10, 103 and 105 nM BPA. In addition, this study performed a literature survey to explore miRNAs relevant to human EC progression. The differentially expressed miRNAs both presented in the miRNA chip of BPA exposure and in the literature survey were selected to further predict the potential target genes using miRDB website. These potential target genes corresponded to DEGs in the mRNA chip of BPA exposure were the candidate DEGs regarding to BPA exposure and EC progression. The candidate DEGs were analyzed for ontology and gene network construction using KEGG (Kyoto Encyclopedia of Genes and Genomes database) and Cytoscape software. According to the analysis of KEGG pathway and Cytoscape gene network, this study identified that BPA exposure reduced miR-149 expression to down-regulate miR-149-mediated DNA repair gene ARF6 (ADP-ribosylation factor 6), TP53 (tumor protein p53) and up-regulate CCNE2 (cyclin E2) to interrupt cell cycle. BPA induced miR-141 and miR-205 to down-regulate their target genes PRC1 (polycomb repressor complex1) and SMAD2 (SMAD family member 2) in tumor suppression. BPA also increased miR-107 and suppressed hedgehog signaling regulatory factors SUFU (suppressor of fused homolog) and GLI3 (GLI family zinc finger 3) to activate hedgehog signaling for the carcinogenesis. Furthermore, this study transfected miR-149 mimic and miR-107 inhibitor to confirm the effect of BPA exposure on miRNA regulation and gene expression. After miR-149 mimic transfection in RL95-2 cells, the gene expression of ARF6, TP53 and CCNE2 displayed no significant differences between BPA exposure and control. After miR-107 inhibitor transfection in RL95-2 cells, the gene expression of SUFU and GLI3 were mildly reduced in BPA exposure. This study discovered that BPA exposure affected miR-141, -107, -205 and miR-149 to disrupt cell cycle arrest, suppress DNA repair system, and activate hedgehog signaling, which has been reported to participate in cancer development and metastasis. These findings provided an insight into the potential epigenetic mechanism of BPA exposure on the risk of endometrial carcinogenesis.