RESUMO
The multidrug-resistant phenotype of tumor cells is acquired via an increased capability of drug efflux by ABC transporters and causes serious problems in cancer treatment. With the aim to uncover whether changes induced by epigenetic mechanisms in the expression level of drug transporter genes correlates with changes in the drug resistance phenotypes of resistant cells, we studied the expression of drug transporters in rat hepatoma cell lines. We found that of the three major rat ABC transporter genes Abcb1a, Abcb1b and Abcc1 the activity of only Abcb1b increased significantly in colchicine-selected, drug-resistant cells. Increased transporter expression in drug-resistant cells results primarily from transcriptional activation. A change in histone modification at the regulatory regions of the chromosomally adjacent Abcb1a and Abcb1b genes differentially affects the levels of corresponding mRNAs. Transcriptional up- and down-regulation accompany an increase in acetylation levels of histone H3 lysine 9 at the promoter regions of Abcb1b and Abcb1a, respectively. Drug efflux activity, however, does not follow tightly the transcriptional activity of drug transporter genes in hepatoma cells. Our results point out the need for careful analysis of cause-and-effect relationships between changes in histone modification, drug transporter expression and drug resistance phenotypes.
Assuntos
Subfamília B de Transportador de Cassetes de Ligação de ATP/genética , Carcinoma Hepatocelular/genética , Resistencia a Medicamentos Antineoplásicos/genética , Inibidores de Histona Desacetilases/farmacologia , Neoplasias Hepáticas/genética , RNA Mensageiro/genética , Subfamília B de Transportador de Cassetes de Ligação de ATP/metabolismo , Acetilação/efeitos dos fármacos , Animais , Carcinoma Hepatocelular/metabolismo , Linhagem Celular , Ativação Enzimática/efeitos dos fármacos , Amplificação de Genes , Dosagem de Genes , Expressão Gênica , Histonas/metabolismo , Neoplasias Hepáticas/metabolismo , Regiões Promotoras Genéticas , Estabilidade de RNA , Ratos , Ativação TranscricionalRESUMO
Hemin is an extremely versatile molecule that may have cytotoxic or cytoprotective effects on certain cells. We investigated the effect of hemin on the growth of hepatoma cells, including the multidrug-resistant ones. Searching for new tools that interfere with the growth of hepatomas is an important area of clinical research. Cell viability and proliferation of drug-sensitive and multidrug-resistant hepatoma cell lines was determined using the trypan-blue exclusion test XTT/PMS and colony-forming ability assays. Apoptosis was assessed by confocal microscopy and DNA ladder assay. Hemin inhibited the proliferation and induced apoptosis in both drug-sensitive and multidrug-resistant hepatoma cells overexpressing functional P-glycoprotein. zVAD-fmk inhibited the hemin-induced decrease in cell viability, pointing to a role of caspases in hemin-induced apoptosis. The antiproliferative and apoptosis-inducing effects of hemin might be considered in the design of treatment for patients with hepatoma.
