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

Abstract

Induced expression of the Abcb1 drug transporter often occurs in tumors in response to chemotherapy. The role that epigenetic modifications within the ABCB1 promoter play in Abcb1 expression remains unclear. We selected MCF-7 cells for survival in increasing doses of chemotherapy drugs, and assessed the methylation status of 66 CpG sites within the ABCB1 promoter preceding, accompanying and following the onset of drug resistance. Increased ABCB1 transcript expression coincident with acquisition of resistance to epirubicin or paclitaxel was temporally associated with hypomethylation of the ABCB1 downstream promoter in the absence of gene amplifications or changes in mRNA stability. Treatment of control MCF-7 cells with demethylating and/or acetylating agents increased ABCB1 transcript expression. In addition to broad promoter hypomethylation, dramatic reductions in the methylation of specific CpG sites within the promoter were observed, suggesting that these sites may play a predominant role in transcriptional activation through promoter hypomethylation. Furthermore, our data suggest that allele-specific reductions in ABCB1 promoter methylation regulate promoter usage within paclitaxel-resistant cells. This study provides strong evidence that changes in ABCB1 promoter methylation, ABCB1 promoter usage and ABCB1 transcript expression can be temporally and causally correlated with the acquisition of drug resistance in breast tumor cells.

Influence of ABCB1 Genotype in Collies on the Pharmacokinetics and Pharmacodynamics of Loperamide in a Dose-Escalation Study

“…P-gp expression is under the control of transcription factors (Chen and Sikic, 2012;Henrique et al, 2013;Kobori et al, 2014) that can be activated by a wide variety of agents (Cascorbi, 2011). Expression is also altered epigenetically through changes in DNA methylation or acetylation (Reed et al, 2010;Chen and Sikic, 2012;Tomiyasu et al, 2014) or changes in ubiquitination (Zhang et al, 2004;Nawa et al, 2012). Changes in P-gp expression can also be influenced by changes in the expression of other transporter genes and prior drug exposure (Xia et al, 2009;Kobori et al, 2014).…”

Sphingolipid abnormalities in cancer multidrug resistance: Chicken or egg?

“…Since many of these transcription factors are altered by stress signals, ABCB1 is highly susceptible to upregulation during a stress response. ABCB1 expression can also be modified by single nucleotide polymorphisms (SNPs) [91, 92], which play a very important role in the context of cancer therapy, as well as by gene rearrangements [93], mutations [82, 94], epigenetic regulation [95, 96] and post-translational mechanisms [97]. …”

Nuclear Receptors in Drug Metabolism, Drug Response and Drug Interactions

“…3) Development stage-dependent CYP2E1 expression is influenced by the methylation status of this gene. 4) Phase II genes including UGT1A1 , GSTP1 , SULT1A1 and genes for efflux transporters like MDR1, BCRP and members of the OATP family of uptake transporters are epigenetically regulated due to DNA methylation [86, 87, 89, 88]. …”