Epigenetic regulation of the ABCB1 gene in drug-sensitive and drug-resistant lymphoid tumour cell lines obtained from canine patients

Multidrug resistance (MDR) is a major obstacle in the treatment of cancer. Overexpression of P-glycoprotein (P-gp), encoded by the ABCB1 (MDR1) gene, is an important factor in determining the MDR phenotype of a tumour. Although recent studies have revealed the epigenetic transcriptional regulation of the human ABCB1 gene, such regulation of this gene has not been examined in dogs. The aim of the current study was to evaluate differences in epigenetic regulation of the ABCB1 gene, between drug-sensitive and drug-resistant canine lymphoid tumour cell lines.In two drug-sensitive cell lines, GL-1 and CLBL-1, ABCB1 mRNA expression was significantly lower than in two drug-resistant cell lines, UL-1 and Ema, using real-time quantitative polymerase chain reaction (QPCR). Bisulphite sequencing and real-time methylation-specific PCR revealed that the CpG island present in the upstream region of exon 2 was hypermethylated in GL-1 and CLBL-1, but hypomethylated in UL-1 and Ema. Chromatin immunoprecipitation and QPCR revealed that histone H3 acetylation in the same CpG island was significantly increased in UL-1 and Ema compared to GL-1 and CLBL-1. Treatment with 5-aza 2'-deoxycytidine or trichostatin A increased ABCB1 mRNA expression in GL-1 and CLBL-1. DNA methylation and histone H3 acetylation were shown to be involved in ABCB1 gene expression and associated with an MDR phenotype in these canine lymphoid tumour cell lines.