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Cancer Biol Ther ; 3(6): 540-8, 2004 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-15034303

RESUMO

Resistance to the cytotoxic actions of antineoplastic drugs, whether intrinsic or acquired, remains a barrier to the establishment of curative chemotherapy regimens for advanced breast cancer. Over-expression of P-glycoprotein (P-gp), encoded by the MDR1 gene and known to mediate resistance to many antineoplastic drugs, may contribute to poor breast cancer treatment outcome. Nonetheless, the precise molecular mechanisms responsible for high or low level P-gp expression in breast cancer cells have not been established. We assessed the role of DNA hypermethylation near the MDR1 transcriptional regulatory region in MDR1 expression in MCF-7 breast cancer cells, which fail to express MDR1 mRNA, and MCF-7/ADR cells, known to express high MDR1 mRNA levels. When compared to MCF-7/ADR cells, MCF-7 cells manifested markedly diminished MDR1 transcription rates by nuclear run-off assay, but equivalent MDR1 promoter trans-activation activity in transient transfection experiments, indicating that cis factors were most likely responsible for the differences in MDR1 transcription between MCF-7/ADR cells and MCF-7 cells. Bisulfite genomic sequencing analyses revealed substantially less extensive MDR1 promoter methylation in MCF-7/ADR cells than in MCF-7 cells, suggesting that CpG dinucleotide methylation might contribute to the observed MDR1 transcription differences. Chromatin immunoprecipitation analyses indicated an inactive MDR1 chromatin conformation in MCF-7 cells, with a paucity of acetylated histones and the presence of 5-mC-binding proteins MeCP2 and MBD2, and an active MDR1 chromatin conformation in MCF-7/ADR cells, with an abundance of acetylated histones and the presence of the transcriptional trans-activator YB-1. Stable MCF-7 sublines which had been treated with the DNA methyltransferase inhibitor 5-azacytidine, exhibited a reduction in MDR1 promoter methylation and a complex MDR1 chromatin configuration, characterized by the simultaneous presence of transcriptional activators and repressors. In this state, MDR1 expression was markedly sensitive to treatment with the histone deacetylase inhibitor trichostatin A.


Assuntos
Membro 1 da Subfamília B de Cassetes de Ligação de ATP/genética , Azacitidina/análogos & derivados , Azacitidina/farmacologia , Neoplasias da Mama/genética , Cromatina/genética , Metilação de DNA , Regiões Promotoras Genéticas/genética , Ativação Transcricional , Membro 1 da Subfamília B de Cassetes de Ligação de ATP/metabolismo , Acetilação , Antibióticos Antineoplásicos/farmacologia , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Cromatina/metabolismo , Imunoprecipitação da Cromatina , Metilases de Modificação do DNA/antagonistas & inibidores , Decitabina , Doxorrubicina/farmacologia , Resistência a Múltiplos Medicamentos , Resistencia a Medicamentos Antineoplásicos , Inibidores Enzimáticos/farmacologia , Feminino , Regulação Neoplásica da Expressão Gênica , Inibidores de Histona Desacetilases , Histonas/metabolismo , Humanos , Ácidos Hidroxâmicos/farmacologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ativação Transcricional/efeitos dos fármacos , Ativação Transcricional/fisiologia , Células Tumorais Cultivadas/efeitos dos fármacos , Células Tumorais Cultivadas/metabolismo
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