Genetic and Epigenetic Modeling of the Origins of Multidrug-Resistant Cells in a Human Sarcoma Cell Line

Abstract

The origin of drug-resistant cells in human cancers has been a fundamental problem of cancer pharmacology. Two major contrasting hypotheses (genetics versus epigenetics) have been proposed to elucidate the mechanisms of acquired drug resistance. In this study, we answer these fundamental questions through investigation of the genetic and epigenetic pathways that control the origin of ABCB1 (MDR1) gene activation with acquired multidrug resistance in drugsensitive human sarcoma (MES-SA cells). The genetic and epigenetic bases of this selected activation involve the initiation of transcription at a site 112 kb upstream of the ABCB1 proximal promoter (P1) in the drug-resistant cells. This activation was associated with a chromatin-remodeling process characterized by an increase in acetylated histone H3 within a 968-bp region 5V of the ABCB1 upstream promoter. These alterations provide both genetic and epigenetic susceptibility for ABCB1 expression in drug-resistant cells. Complete activation of the ABCB1 gene through the coding region was proposed by interactions of selected trans-alterations or epigenetic changes on the ABCB1 proximal promoter, which occurred during initial drug exposure. Thus, our data provide evidence for a major genomic alteration that changes the chromatin structure of the ABCB1 upstream promoter via acetylation of histone H3 initiating ABCB1 activation, further elucidating the genetic and epigenetic bases that determine chemotherapeutic response in drug-resistant derivatives of MES-SA cells. (Cancer Res 2005; 65(20): 9388-97)

Involvement of CtBP1 in the transcriptional activation of the MDR1 gene in human multidrug resistant cancer cells

“…For instance, it has been shown that the activation of MDR1 expression by chemotherapeutic drugs is correlated with methylation and hyperacetylation of histone H3 as well as methylation status of the MDR1 promoter (21,22,29,30). These histone modifications are brought about by histone-modifying enzymes such as histone acetyltransferase and histone deacetylase, which are known to be required in the transcriptional regulation of the MDR1 gene (21).…”

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

“…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).…”

Facilitation of drug resistance development by γ-irradiation in human cancer cells

“…In addition to gene amplification, there are many ways to induce Pgp/mdr1 overexpression in the drug-resistant cells, e.g. transcription activation (16), epigenetic modification of the mdr1 promoter (17), gene rearrangement (18,19), etc. By Southern blot analysis, the mdr1 gene in all of the Doxselected HepG2 cells is markedly amplified when compared with their respective parental cells (Fig.…”