Epigenetic changes to the MDR1 locus in response to chemotherapeutic drugs

Abstract

The mechanism of action of chemotherapeutic drugs and their ability to induce multidrug resistance (MDR) are of relevance to cancer treatment. Overexpression of P-glycoprotein (Pgp) encoded by the MDR1 gene following chemotherapy can severely limit the efficacy of anticancer agents; however, the manner by which cells acquire high levels of Pgp has not been defined. Herein, we demonstrate that chemotherapeutic drugs induce specific epigenetic modifications at the MDR1 locus, concomitant with MDR1 upregulation mediated by transcriptional activation, and a potential post-transcriptional component. We have established that the mechanisms are not mutually exclusive and are dependent on the methylation state of the MDR1 promoter. MDR1 upregulation did not result in further changes to the CpG methylation profile. However, dramatic changes in the temporal and spatial patterning of histone modifications occurred within the 5 0 hypomethylated region of MDR1, directly correlating with MDR1 upregulation. Specifically, drug-induced upregulation of MDR1 was associated with increases in H3 acetylation and induction of methylated H3K4 within discrete regions of the MDR1 locus. Our results demonstrate that chemotherapeutic drugs can actively induce epigenetic changes within the MDR1 promoter, and enhance the MDR phenotype.

The histone deacetylase inhibitor trichostatin A downregulates human MDR1 (ABCB1) gene expression by a transcription-dependent mechanism in a drug-resistant small cell lung carcinoma cell line model

“…Changes in H3 and H4 acetylation were rapid (within 8 h) and directly correlated with ABCB1 induction. Similar data have been reported in NB4 cells incubated with FK228 (Tabe et al, 2006), or in CEM-Bcl2 cells treated with daunorubicin (Baker et al, 2005). In TSA-treated H69VP cells, H4 acetylation exhibited the same kinetics than in drug-sensitive cells, in spite of the repression of the ABCB1 gene induced.…”

“…This decrease in acetylated H3 might be linked to nucleosomes loss instead of H3 deacetylation (Deckert and Struhl, 2001), but this seems rather unlikely as this loss would result in concomitant decrease in acetylated H4 level. H4 by TSA has already been described at the level of mouse mammary tumour virus and c-jun promoters (Thompson et al, 2001;Mulholland et al, 2003), and even ABCB1 promoter in CEMBcl2 cells (Baker et al, 2005). Nevertheless, it should be noted that the H3 acetylation level observed after 24 h TSA in H69VP cells was always above the basal value measured in untreated cells.…”

“…In drug-sensitive cells, several studies have reported an increase in ABCB1 expression by HDAC inhibitors, a phenomenon we also observed in H69WT cells. For instance, ABCB1 gene was overexpressed in SW620 colon carcinoma and CEM-Bcl2 cells exposed to TSA (Jin and Scotto, 1998;Baker et al, 2005), or KU812 and NB4 cells exposed to depsipeptide (Tabe et al, 2006;Yamada et al, 2006). In drug-resistant cells, HDAC inhibition also increased ABCB1 expression in CEM-A7R, Kasumi-1, and Kasumi-6 cell lines (El-Osta et al, 2002;Tabe et al, 2006).…”

The temporal relationship between ABCB1 promoter hypomethylation, ABCB1 expression and acquisition of drug resistance

“…Partial hypomethylation of the ABCB1 promoter in CEM-Bcl2 cells induced ABCB1 transcription and daunorubicin-induced H3 acetylation of the ABCB1 promoter preceded such changes in ABCB1 expression. 12 The effect of Aza treatment, TSA treatment and combined Aza and TSA treatment on epirubicin or paclitaxel sensitivity was assessed using clonogenic assays. Under identical conditions as those, which induced demethylation of the ABCB1 promoter and increased ABCB1 expression in MCF-7 CC cells, addition of 1 mM Aza to cultures for 96 h consistently prevented colony formation in semi-solid medium, even after 14 days post administration.…”

“…Many studies have simply compared drug-sensitive tumor cells with tumor cells selected for resistance to high concentrations of chemotherapy agents. 8,11,12 These and other studies have not examined whether changes in the methylation status of CpG dinucleotides (in any gene) are temporally or causally correlated to acquisition of drug resistance. In addition, most epigenetic studies have assessed changes in ABCB1 promoter methylation in response to selection for resistance to a single chemotherapy drug (primarily doxorubicin).…”