Aberrant DNA methylation of drug metabolism and transport genes in nodular goiter

The genes encoding drug-metabolizing enzymes and transporters play an important role in transporting various kinds of molecules import or export the cells, which is closely associated with the development of various human diseases, mainly including solute carrier (SLC) superfamily, cytochrome P450 (CYP) superfamily and ATP binding cassette (ABC) superfamily [1]. To date, most of studies focused on investigating SNPs or gene mutation in these genes, however, it is has recently been reported that epigenetic mechanisms were involved in the regulation of these genes [2]. In the present study, we choose 11 drug metabolism and transport genes, including ABCB1, ABCB4, ABCG2, CYP1A1, CYP1B1, CYP24A1, CYP27B1, CYP39A1, SLC1A2, SLC19A3, and SLC26A2, to detect their methylation status of promoter region in a cohort of nodular goiter and normal thyroid tissues using methylation-specific PCR (MSP).Methylation analysis of thyroid tissues was carried out in a series of 27 nodular goiter and 23 normal thyroid paraffin-embedded tissues, which were obtained from the Department of Pathology of the First Affiliated Hospital of Xi'an Jiaotong University School of Medicine. All samples underwent histological examination by a senior pathologist. The genomic DNA was isolated from paraffin-embedded tissues using xylene to remove the paraffin and sodium dodecyl sulfate (SDS) and proteinase K to digest tissues, followed by standard phenol-chloroform extraction and ethanol precipitation of DNA. DNA was subsequently treated with sodium bisulfite to detect the methylation status of these 11 genes using methylation-specific PCR (MSP) as described previously [3]. Normal leukocyte DNA was methylated in vitro with Sss I methylase (New England Biolabs, Beverly, MA) to generate completely methylated DNA as a positive control. The primer sequences and their annealing temperatures were presented in Table 1. To examine the role of DNA methylation in the regulation of gene expression, we treated 3 thyroid