Troglitazone reverses the multiple drug resistance phenotype in cancer cells

A major problem in treating cancer is the development of drug resistance. We previously demonstrated doxorubicin (DOX) resistance in K562 human leukemia cells that was associated with upregulation of glyoxalase 1 (GLO-1) and histone H3 expression. The thiazolidinedione troglitazone (TRG) downregulated GLO-1 expression and further upregulated histone H3 expression and post-translational modifications in these cells, leading to a regained sensitivity to DOX. Given the pleiotropic effects of epigenetic changes in cancer development, we hypothesized that TRG may downregulate the multiple drug resistance (MDR) phenotype in a variety of cancer cells. To test this, MCF7 human breast cancer cells and K562 cells were cultured in the presence of low-dose DOX to establish DOX-resistant cell lines (K562/DOX and MCF7/DOX). The MDR phenotype was confirmed by Western blot analysis of the 170 kDa P-glycoprotein (Pgp) drug efflux pump multiple drug resistance protein 1 (MDR-1), and the breast cancer resistance protein (BCRP). TRG markedly decreased expression of both MDR-1 and BCRP in these cells, resulting in sensitivity to DOX. Silencing of MDR-1 expression also sensitized MCF7/DOX cells to DOX. Use of the specific and irreversible peroxisome proliferator-activated receptor gamma (PPARγ) inhibitor GW9662 in the nanomolar range not only demonstrated that the action of TRG on MCF/DOX was PPARγ-independent, but indicated that PPARγ may play a role in the MDR phenotype, which is antagonized by TRG. We conclude that TRG is potentially a useful adjunct therapy in chemoresistant cancers

Antagonistic Gcn5-Hda1 interactions revealed by mutations to the Anaphase Promoting Complex in yeast

<p>Abstract</p> <p>Background</p> <p>Histone post-translational modifications are critical for gene expression and cell viability. A broad spectrum of histone lysine residues have been identified in yeast that are targeted by a variety of modifying enzymes. However, the regulation and interaction of these enzymes remains relatively uncharacterized. Previously we demonstrated that deletion of either the histone acetyltransferase (HAT) <it>GCN5 </it>or the histone deacetylase (HDAC) <it>HDA1 </it>exacerbated the temperature sensitive (<it>ts</it>) mutant phenotype of the Anaphase Promoting Complex (APC) <it>apc5^CA</it>allele. Here, the <it>apc5^CA</it>mutant background is used to study a previously uncharacterized functional antagonistic genetic interaction between Gcn5 and Hda1 that is not detected in <it>APC5 </it>cells.</p> <p>Results</p> <p>Using Northerns, Westerns, reverse transcriptase PCR (rtPCR), chromatin immunoprecipitation (ChIP), and mutant phenotype suppression analysis, we observed that Hda1 and Gcn5 appear to compete for recruitment to promoters. We observed that the presence of Hda1 can partially occlude the binding of Gcn5 to the same promoter. Occlusion of Gcn5 recruitment to these promoters involved Hda1 and Tup1. Using sequential ChIP we show that Hda1 and Tup1 likely form complexes at these promoters, and that complex formation can be increased by deleting <it>GCN5</it>.</p> <p>Conclusions</p> <p>Our data suggests large Gcn5 and Hda1 containing complexes may compete for space on promoters that utilize the Ssn6/Tup1 repressor complex. We predict that in <it>apc5^CA</it>cells the accumulation of an APC target may compensate for the loss of both <it>GCN5 </it>and <it>HDA1</it>.</p