Transcriptional regulation of the MDR1 gene by histone acetyltransferase and deacetylase is mediated by NF-Y

LEC1-LIKE paralog transcription factor: how to survive extinction and fit in NF-Y protein complex

Transcription factor function is crucial for eukaryotic systems. The presence of transcription factor families in genomes represents a significant technical challenge for functional studies. To understand their function, we must understand how they evolved and maintained by organisms. Based on genome scale searches for homologs of LEAFY COTYLEDON-LIKE (L1L; AtNF-YB6), NF-YB transcription factor, we report the discovery and annotation of a complete repertoire of thirteen novel genes that belong to the L1L paralogous gene family of Solanum lycopersicum. Gene duplication events within the species resulted in the expansion of the L1L family. Sequence and structure-based phylogenetic analyses revealed two distinct groups of L1Ls in tomato. Natural selection appears to have contributed to the asymmetric evolution of paralogs. Our results point to key differences among SlL1L paralogs in the presence of motifs, structural features, cysteine composition and expression patterns during plant and fruit development. Furthermore, differences in the binding domains of L1L members suggest that some of them evolved new binding specificities. These results reveal dramatic functional diversification of L1L paralogs for their maintenance in tomato genome. Our comprehensive insights on tomato L1L family should provide the basis for further functional and genetic experimentation.

Novel and functional ABCB1 gene variant in sporadic Parkinson's disease

Parkinson's disease (PD) is a common progressive neurodegenerative disease. Most cases of PD are sporadic, which is caused by interaction of genetic and environmental factors. To date, genetic causes for sporadic PD remain largely unknown. ATP-binding cassette sub-family B member 1 (ABCB1) is a membrane-associated protein that acts as an efflux transporter for many substrates, including chemotherapeutic agents, anti-epilepsy medicine, antibiotics and drugs for PD. ABCB1 gene is widely expressed in human tissues, including endothelial cells of capillary blood vessels at blood-brain barrier sites. In PD patients, decreased ABCB1 levels have been reported. We speculated that misregulation of ABCB1 gene expression, caused by DNA sequence variants (DSVs) within its regulatory regions, may be involved in PD development. In this study, we genetically and functionally analyzed the proximal promoter of the human ABCB1 gene, which is required for constitutive expression, in sporadic PD patients and healthy controls. The results showed that a novel and heterozygous DSV g.117077G>A was identified in one PD patient, but in none of the controls. This DSV significantly altered the transcriptional activity of the ABCB1 gene promoter in transiently transfected HEK-293 cells. A heterozygous DSV g.116347T>C was only found in one control. Four single-nucleotide polymorphisms, g.116154T>C (rs28746504), g.117130A>G (rs2188524), g.117356C>G (rs34976462) and g.117372T>C (rs3213619), and one heterozygous deletion DSV g.116039del were found in PD patients and controls with similar frequencies. Therefore, our findings suggest that ABCB1 gene promoter DSVs may contribute to PD development as a rare risk factor.

mRNA levels of related Abcb genes change opposite to each other upon histone deacetylase inhibition in drug-resistant rat hepatoma cells

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.

Epigenetic regulation of MDR1 gene through post-translational histone modifications in prostate cancer

BACKGROUND

Multidrug resistance 1 (MDR1) gene encodes for an ATP binding cassette transporter--P-glycoprotein (P-gp)-- involved in chemoresistance to taxanes. MDR1 promoter methylation is frequent in prostate carcinoma (PCa), suggesting an epigenetic regulation but no functional correlation has been established. We aimed to elucidate the epigenetic mechanisms involved in MDR1 deregulation in PCa.

RESULTS

MDR1 promoter methylation and P-gp expression were assessed in 121 PCa, 39 high-grade prostatic intraepithelial neoplasia (HGPIN), 28 benign prostatic hyperplasia (BPH) and 10 morphologically normal prostate tissue (NPT) samples, using quantitative methylation specific PCR and immunohistochemistry, respectively. PCa cell lines were exposed to a DNA methyltransferases inhibitor 5-aza-2'deoxycytidine (DAC) and histone deacetylases inhibitor trichostatin A (TSA). Methylation and histone posttranscriptional modifications status were characterized and correlated with mRNA and protein expression. MDR1 promoter methylation levels and frequency significantly increased from NPTs, to HGPIN and to PCa. Conversely, decreased or absent P-gp immunoexpression was observed in HGPIN and PCa, inversely correlating with methylation levels. Exposure to DAC alone did not alter significantly methylation levels, although increased expression was apparent. However, P-gp mRNA and protein re-expression were higher in cell lines exposed to TSA alone or combined with DAC. Accordingly, histone active marks H3Ac, H3K4me2, H3K4me3, H3K9Ac, and H4Ac were increased at the MDR1 promoter after exposure to TSA alone or combined with DAC.

CONCLUSION

Our data suggests that, in prostate carcinogenesis, MDR1 downregulation is mainly due to histone post-translational modifications. This occurs concomitantly with aberrant promoter methylation, substantiating the association with P-gp decreased expression.

The network of P-glycoprotein and microRNAs interactions

Overexpression of P-glycoprotein (P-gp) contributes to the multidrug resistance (MDR) phenotype found in many cancer cells. P-gp has been identified as a promising molecular target, although attempts to find successful therapies to counteract its function as a drug efflux pump have largely failed to date. Apart from its role in drug efflux, P-gp may have other cellular functions such as being involved in apoptosis, and is found in various locations in the cell. Its expression is highly regulated, namely by microRNAs (miRNAs or miRs). In addition, P-gp may regulate the expression of miRs in the cell. Furthermore, both P-gp and miRs may be found in microvesicles or exosomes and may be transported to neighboring, drug-sensitive cells. Here, we review this current issue together with recent evidence of this network of interactions between P-gp and miRs.

Identification of a negative feedback loop between cyclic di-GMP-induced levels of IFI16 and p202 cytosolic DNA sensors and STING

A host type I IFN response is induced by cytosolic sensing of the bacterial second messenger cyclic-di-GMP (c-di-GMP) by STING (stimulator of IFN genes). Because the STING, an adaptor protein, links the cytosolic detection of DNA by the cytosolic DNA sensors such as the IFN-inducible human IFI16 and murine p202 proteins to the TBK1/IRF3 axis, we investigated whether c-di-GMP-induced signaling could regulate expression of IFI16 and p202 proteins. Here, we report that activation of c-di-GMP-induced signaling in human and murine cells increased steady-state levels of IFI16 and p202 proteins. The increase was c-di-GMP concentration- and time-dependent. Unexpectedly, treatment of cells with type I IFN decreased levels of the adaptor protein STING. Therefore, we investigated whether the IFI16 or p202 protein could regulate the expression of STING and activation of the TBK1/IRF3 axis. We found that constitutive knockdown of IFI16 or p202 expression in cells increased steady-state levels of STING. Additionally, the knockdown of IFI16 resulted in activation of the TBK1/IRF3 axis. Accordingly, increased levels of the IFI16 or p202 protein in cells decreased STING levels. Together, our observations identify a novel negative feedback loop between c-di-GMP-induced levels of IFI16 and p202 cytosolic DNA sensors and the adaptor protein STING.

Fludarabine treatment favors the retention of miR-485-3p by prostate cancer cells: implications for survival

Background

Circulating microRNAs (miRNAs) have been found in many body fluids and represent reliable markers of several physio-pathological disorders, including cancer. In some cases, circulating miRNAs have been evaluated as markers of the efficacy of anticancer treatment but it is not yet clear if miRNAs are actively released by tumor cells or derive from dead tumor cells.

Results

We showed that a set of prostate cancer secretory miRNAs (PCS-miRNAs) were spontaneously released in the growth medium by DU-145 prostate cancer cells and that the release was greater after treatment with the cytotoxic drug fludarabine. We also found that the miRNAs were associated with exosomes, implying an active mechanism of miRNA release. It should be noted that in fludarabine treated cells the release of miR-485-3p, as well as its association with exosomes, was reduced suggesting that miR-485-3p was retained by surviving cells. Monitoring the intracellular level of miR-485-3p in these cells, we found that miR-485-3p was stably up regulated for several days after treatment. As a possible mechanism we suggest that fludarabine selected cells that harbor high levels of miR-485-3p, which in turn regulates the transcriptional repressor nuclear factor-Y triggering the transcription of topoisomerase IIα, multidrug resistance gene 1 and cyclin B2 pro-survival genes.

Conclusions

Cytotoxic treatment of DU-145 cells enhanced the release of PCS-miRNAs with the exception of miR-485-3p which was retained by surviving cells. We speculate that the retention of miR-485-3p was a side effect of fludarabine treatment in that the high intracellular level of miR-485-3p plays a role in the sensitivity to fludarabine.

Targeting the Y/CCAAT box in cancer: YB-1 (YBX1) or NF-Y?

The Y box is an important sequence motif found in promoters and enhancers containing a CCAAT box - one of the few elements enriched in promoters of large sets of genes overexpressed in cancer. The search for the transcription factor(s) acting on it led to the biochemical purification of the nuclear factor Y (NF-Y) heterotrimer, and to the cloning - through the screening of expression libraries - of Y box-binding protein 1 (YB-1), an oncogene, overexpressed in aggressive tumors and associated with drug resistance. These two factors have been associated with Y/CCAAT-dependent activation of numerous growth-related genes, notably multidrug resistance protein 1. We review two decades of data indicating that NF-Y ultimately acts on Y/CCAAT in cancer cells, a notion recently confirmed by genome-wide data. Other features of YB-1, such as post-transcriptional control of mRNA biology, render it important in cancer biology.

ORF50-dependent and ORF50-independent activation of the ORF45 gene of Kaposi's sarcoma-associated herpesvirus

The ORF45 gene of Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a multifunctional tegument protein. Here, we characterize the transcriptional control of the ORF45 gene and show that its promoter can be activated by ORF50 protein, a latent-lytic switch transactivator. The ORF45 promoter can also be induced by sodium butyrate (SB), a histone deacetylase inhibitor, in the absence of ORF50 protein. Although SB induces the ORF45 gene independently of ORF50, its full activation may require the presence of ORF50. Deletion and point mutation analyses revealed that two RBP-Jκ-binding sites in the ORF45 promoter confer the ORF50 responsiveness, whereas NF-Y and Sp1-binding sites mediate the response to SB. Direct binding of NF-Y, Sp1, or RBP-Jκ protein to the ORF45 promoter is required for the promoter activation induced by SB or by ORF50. In conclusion, our study demonstrates both ORF50-dependent and ORF50-independent transcriptional mechanisms operated on the activation of the ORF45 gene.

Regulation of the MDR1 promoter by E2F1 and EAPP

Multidrug resistance (MDR), one of the main reasons for diminishing efficacy of prolonged chemotherapy, is frequently caused by the elevated expression of the ABCB1/MDR1 gene encoding PGP (P-glycoprotein). EAPP (E2F Associated PhosphoProtein) is a frequently overexpressed protein in human tumor cells. It inhibits apoptosis in a p21-dependent manner. We show here that EAPP stimulates the MDR1 promoter resulting in higher PGP levels. Independently of EAPP, E2F1 also increases the activity of the MDR1 promoter. Co-expression of pRb inhibits E2F1-, but not EAPP-dependent promoter activation. The upregulation of PGP might contribute to the survival of tumor cells during chemotherapy and worsen the prognosis for the patient.

Functional characterization of genetic variations in the MDR3 promoter

Multidrug resistance 3 (MDR3) is present on the canalicular membrane of the hepatocyte and plays an important role in protecting the liver from bile acids. In this study, we characterized the transcriptional effects of four common haplotypes and four polymorphic variants in the promoter region of MDR3 that were identified in 126 DNA samples from Koreans. We measured the luciferase activities of the four MDR3 promoter haplotypes using in vitro reporter assays. Among them, two haplotypes showed a significant decrease in reporter activity compared to the reference. One of the mechanisms by which these haplotypes might decrease MDR3 transcriptional activity was determined: one of the polymorphisms that are present in haplotype 3, was associated with a significant reduction in the promoter activity of MDR3, and the transcription factor NF-Y was predicted to bind to the promoter in the region of g.-1584C>T. Electrophoretic mobility shift assays showed that the g.-1584C allele exhibited greater binding to NF-Y than did the g.-1584T allele. Through the measurement of promoter activity after the overexpression of NF-Y, we found that NF-Y can act as a transcriptional activator of MDR3. These data suggest that the reduced transcriptional activity of g.-1584C>T results from a reduction in the binding affinity of the activator NF-Y to the MDR3 promoter region. Our study suggests that two common haplotypes of MDR3 can regulate the transcriptional rate of MDR3 and that NF-Y may be one of the transcriptional factors involved in this regulation.

Dual regulation of P-glycoprotein expression by trichostatin A in cancer cell lines

Background

It has been reported that the histone deacetylase inhibitor (iHDAc) trichostatin A (TSA) induces an increase in MDR1 gene transcription (ABCB1). This result would compromise the use of iHDACs in combination with other cytotoxic agents that are substrates of P-glycoprotein (Pgp). It has also been reported the use of alternative promoters by the ABCB1 gene and the existence of a translational control of Pgp protein. Finally, the ABCB1 gene is located in a genetic locus with the nested gene RUNDC3B in the complementary DNA strand, raising the possibility that RUNDC3B expression could interfere with ABCB1 alternative promoter regulation.

Methods

A combination of RT-PCR, real time RT-PCR, Western blot and drug accumulation assays by flow cytometry has been used in this study.

Results

The iHDACs-induced increase in MDR1 mRNA levels is not followed by a subsequent increase in Pgp protein levels or activity in several pancreatic and colon carcinoma cell lines, suggesting a translational control of Pgp in these cell lines. In addition, the MDR1 mRNA produced in these cell lines is shorter in its 5^′ end that the Pgp mRNA produced in cell lines expressing Pgp protein. The different size of the Pgp mRNA is due to the use of alternative promoters. We also demonstrate that these promoters are differentially regulated by TSA. The translational blockade of Pgp mRNA in the pancreatic carcinoma cell lines could be related to alterations in the 5^′ end of the MDR1 mRNA in the Pgp protein expressing cell lines. In addition, we demonstrate that the ABCB1 nested gene RUNDC3B expression although upregulated by TSA is independent of the ABCB1 alternative promoter used.

Conclusions

The results show that the increase in MDR1 mRNA expression after iHDACs treatment is clinically irrelevant since this mRNA does not render an active Pgp protein, at least in colon and pancreatic cancer cell lines. Furthermore, we demonstrate that TSA in fact, regulates differentially both ABCB1 promoters, downregulating the upstream promoter that is responsible for active P-glycoprotein expression. These results suggest that iHDACs such as TSA may in fact potentiate the effects of antitumour drugs that are substrates of Pgp. Finally, we also demonstrate that TSA upregulates RUNDC3B mRNA independently of the ABCB1 promoter in use.

Elevated level of lysine 9-acetylated histone H3 at the MDR1 promoter in multidrug-resistant cells

Failure of chemotherapy in breast cancer presents a major problem and is often due to elevated expression of ATP binding cassette (ABC)-type transporters, such as MDR1 protein. It has been shown that MDR1/ABCB1 gene expression is regulated at the chromatin level by DNA methylation and histone acetylation. However, the modified histone residues have not been identified and the role of various histone acetyl transferases (HATs) is not fully understood. By studying a breast carcinoma model cell line and its MDR1-overexpressing derivative, we show that the histone 3 lysine 9 (H3K9) acetylation level is elevated 100-fold in the promoter and first exon of the MDR1 gene in the drug-resistant cell line compared to the drug-sensitive cell line. The acetylation level of the other examined lysine residues (H3K4, H3K14, H4K8, and H4K12) is weakly or not at all elevated in the MDR1 locus, although their acetylation is generally increased genome-wide in the drug-resistant cell. Downregulation of the expression of HATs PCAF and GCN5 by RNAi effectively reduces the expression of MDR1. Unexpectedly, treatment with a p300-selective inhibitor (HAT inhibitor II) further increases MDR1 expression and drug efflux in the drug-resistant cells. Our data suggest that repeated exposure to chemotherapy may result in deregulated histone acetylation genome-wide and in the MDR1 promoter.

Epigenetic mechanisms in tumorigenesis, tumor cell heterogeneity and drug resistance

Resistance of cancer cells to chemotherapeutics and emerging targeted drugs is a devastating problem in the treatment of cancer patients. Multiple mechanisms contribute to drug resistance such as increased drug efflux, altered drug metabolism, secondary mutations in drug targets, and activation of downstream or parallel signal transduction pathways. The rapid kinetics, the reversibility of acquired drug resistance and the absence of genetic mutations suggest an epigenetic basis for drug insensitivity. Similar to the cellular variance seen in the human body, epigenetic mechanisms, through reversible histone modifications and DNA methylation patterns, generate a variety of transcriptional states resulting in a dynamic heterogeneous tumor cell population. Consequently, epigenomes favoring survival in the presence of a drug by aberrant transcription of drug transporters, DNA-repair enzymes and pro-apoptotic factors render cytotoxic and targeted drugs ineffective and allow selection of rare drug-resistant tumor cells. Recent advances in charting cancer genomes indeed strongly indicate a role for epigenetic regulators in driving cancer, which may result in the acquisition of additional (epi)genetic modifications leading to drug resistance. These observations have important clinical consequences as they provide an opportunity for "epigenetic drugs" to change reversible drug-resistance-associated epigenomes to prevent or reverse non-responsiveness to anti-cancer drugs.

Molecular pathways: regulation and therapeutic implications of multidrug resistance

Multidrug transporters constitute major mechanisms of MDR in human cancers. The ABCB1 (MDR1) gene encodes a well-characterized transmembrane transporter, termed P-glycoprotein (P-gp), which is expressed in many normal human tissues and cancers. P-gp plays a major role in the distribution and excretion of drugs and is involved in intrinsic and acquired drug resistance of cancers. The regulation of ABCB1 expression is complex and has not been well studied in a clinical setting. In this review, we elucidate molecular signaling and epigenetic interactions that govern ABCB1 expression and the development of MDR in cancer. We focus on acquired expression of ABCB1 that is associated with genomic instability of cancer cells, including mutational events that alter chromatin structures, gene rearrangements, and mutations in tumor suppressor proteins (e.g., mutant p53), which guard the integrity of genome. In addition, epigenetic modifications of the ABCB1 proximal and far upstream promoters by either demethylation of DNA or acetylation of histone H3 play a pivotal role in inducing ABCB1 expression. We describe a molecular network that coordinates genetic and epigenetic events leading to the activation of ABCB1. These mechanistic insights provide additional translational targets and potential strategies to deal with clinical MDR.

Activation of Oas1a gene expression by type I IFN requires both STAT1 and STAT2 while only STAT2 is required for Oas1b activation

The murine 2'-5' oligoadenylate synthetase 1a (Oas1a) and Oas1b genes are type 1 IFN responsive genes. Oas1a is an active synthetase with broad antiviral activity mediated through RNase L. Oas1b is inactive but can inhibit Oas1a synthetase activity and mediate a flavivirus-specific antiviral activity through an unknown RNase L-independent mechanism. Analysis of promoter elements regulating gene transcription confirmed that an IFN-stimulated response element (ISRE) is required for IFN beta-activation but neither the overlapping IRF binding site present in both promoters nor the adjacent Oas1b NF-kappa B site is required. Mutation of the overlapping STAT site negatively affected IFN beta-induction of Oas1a but not of Oas1b. Also, IFN beta induction of Oas1a was STAT1- and STAT2-dependent, while induction of Oas1b was STAT1-independent but STAT2-dependent. The two promoters differ at a single nucleotide in the STAT site. The data indicate that these two duplicated genes can be differentially regulated by IFN beta.

Mechanisms of resistance to histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors are a new class of anticancer agents. HDAC inhibitors induce acetylation of histones and nonhistone proteins which are involved in regulation of gene expression and in various cellular pathways including cell growth arrest, differentiation, DNA damage and repair, redox signaling, and apoptosis (Marks, 2010). The U.S. Food and Drug Administration has approved two HDAC inhibitors, vorinostat and romidepsin, for the treatment of cutaneous T-cell lymphoma (Duvic & Vu, 2007; Grant et al., 2010; Marks & Breslow, 2007). Over 20 chemically different HDAC inhibitors are in clinical trials for hematological malignancies and solid tumors. This review considers the mechanisms of resistance to HDAC inhibitors that have been identified which account for the selective effects of these agents in inducing cancer but not normal cell death. These mechanisms, such as functioning Chk1, high levels of thioredoxin, or the prosurvival BCL-2, may also contribute to resistance of cancer cells to HDAC inhibitors.

Establishment and characterization of two 5-fluorouracil-resistant hepatocellular carcinoma cell lines

5-Fluorouracil (5-FU) chemotherapy is the first choice treatment for advanced hepatocellular carcinoma (HCC), and resistance is the major obstacle to successful treatment. Recent studies have reported that epithelial-to-mesenchymal transition (EMT) is associated with chemoresistance in cancers. We speculated that EMT and 5-FU metabolism are related to the mechanism of 5-FU resistance. First, two 5-FU-resistant cell lines, HLF-R4 and HLF-R10, were established from the HLF undifferentiated human HCC cell line. Whereas cell growth was similar in the HLF and HLF-R cell lines, HLF-Rs are about 4- and 10-fold more resistant compared with the HLF cells; thus, we named these cell lines HLF-R4 and HLF-R10, respectively. The terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling assay also showed a dramatically decreased number of apoptotic cells in the HLF-Rs after treatment with 5-FU. We next assessed the characteristics of the HLF, HLF-R4 and HLF-R10 cells. Consistent with our hypothesis, the HLF-Rs had typical morphologic phenotypes of EMT, loss of cell-cell adhesion, spindle-shaped morphology and increased formation of pseudopodia. Real-time quantitative reverse transcriptase polymerase chain reaction data showed downregulated E-cadherin and upregulated Twist-1 and also indicated that EMT changes occurred in the HLF-Rs. We also found decreased ribonucleotide reductase and increased multidrug resistance protein 5 genes in the HLF-R cells. Our results suggested that the metabolism of EMT and 5-FU has important roles in 5-FU chemoresistance in the HLF-R cells, and that the HLF-R cells would be useful in vitro models for understanding the 5-FU-resistant mechanisms in HCC.

Role for Class I histone deacetylases in multidrug resistance

Recent reports have showed that histone deacetylase (HDAC) inhibitor resulted in multidrug resistance (MDR) to other chemotherapeutic agents. However, the molecular mechanisms of Class I HDACs on MDR regulation are poorly understood. In this study, HDAC1 and HDAC2 acted as enhancers to intensify the chemosensitivities of anti-cancer drugs via reducing the expression levels of P-gp, MRP1 and MRP2. Furthermore, the dissociation of HDAC1 and HDAC2 led to transcriptional regulation of P-gp expression via the recruitment of p300, PCAF and NF-Y to the P-gp promoter region, which subsequently increased the level of the active gene marker, hyperacetylated histone H3. In parallel, selective inhibition of HDAC1 and HDAC2 induced the recruitment of p300, PCAF, NF-Y via acetylation of Sp1. Thus, our findings showed HDAC1 and 2 regulated P-gp expression through dynamic changes in chromatin structure and transcription factor association within the promoter region.

The NF-Y/p53 liaison: well beyond repression

NF-Y is a sequence-specific transcription factor - TF - targeting the common CCAAT promoter element. p53 is a master TF controlling the response to stress signals endangering genome integrity, often mutated in human cancers. The NF-Y/p53 - and p63, p73 - interaction results in transcriptional repression of a subset of genes within the vast NF-Y regulome under DNA-damage conditions. Recent data shows that NF-Y is also involved in pro-apoptotic activities, either directly, by mediating p53 transcriptional activation, or indirectly, by being targeted by a non coding RNA, PANDA. The picture is subverted in cells carrying Gain-of-function mutant p53, through interactions with TopBP1, a protein also involved in DNA repair and replication. In summary, the connection between p53 and NF-Y is crucial in determining cell survival or death.

P-glycoproteins and other multidrug resistance transporters in the pharmacology of anthelmintics: Prospects for reversing transport-dependent anthelmintic resistance

Parasitic helminths cause significant disease in animals and humans. In the absence of alternative treatments, anthelmintics remain the principal agents for their control. Resistance extends to the most important class of anthelmintics, the macrocyclic lactone endectocides (MLs), such as ivermectin, and presents serious problems for the livestock industries and threatens to severely limit current parasite control strategies in humans. Understanding drug resistance is important for optimizing and monitoring control, and reducing further selection for resistance. Multidrug resistance (MDR) ABC transporters have been implicated in ML resistance and contribute to resistance to a number of other anthelmintics. MDR transporters, such as P-glycoproteins, are essential for many cellular processes that require the transport of substrates across cell membranes. Being overexpressed in response to chemotherapy in tumour cells and to ML-based treatment in nematodes, they lead to therapy failure by decreasing drug concentration at the target. Several anthelmintics are inhibitors of these efflux pumps and appropriate combinations can result in higher treatment efficacy against parasites and reversal of resistance. However, this needs to be balanced against possible increased toxicity to the host, or the components of the combination selecting on the same genes involved in the resistance. Increased efficacy could result from modifying anthelmintic pharmacokinetics in the host or by blocking parasite transporters involved in resistance. Combination of anthelmintics can be beneficial for delaying selection for resistance. However, it should be based on knowledge of resistance mechanisms and not simply on mode of action classes, and is best started before resistance has been selected to any member of the combination. Increasing knowledge of the MDR transporters involved in anthelmintic resistance in helminths will play an important role in allowing for the identification of markers to monitor the spread of resistance and to evaluate new tools and management practices aimed at delaying its spread.

NF-Y and the transcriptional activation of CCAAT promoters

The CCAAT box promoter element and NF-Y, the transcription factor (TF) that binds to it, were among the first cis-elements and trans-acting factors identified; their interplay is required for transcriptional activation of a sizeable number of eukaryotic genes. NF-Y consists of three evolutionarily conserved subunits: a dimer of NF-YB and NF-YC which closely resembles a histone, and the "innovative" NF-YA. In this review, we will provide an update on the functional and biological features that make NF-Y a fundamental link between chromatin and transcription. The last 25 years have witnessed a spectacular increase in our knowledge of how genes are regulated: from the identification of cis-acting sequences in promoters and enhancers, and the biochemical characterization of the corresponding TFs, to the merging of chromatin studies with the investigation of enzymatic machines that regulate epigenetic states. Originally identified and studied in yeast and mammals, NF-Y - also termed CBF and CP1 - is composed of three subunits, NF-YA, NF-YB and NF-YC. The complex recognizes the CCAAT pentanucleotide and specific flanking nucleotides with high specificity (Dorn et al., 1997; Hatamochi et al., 1988; Hooft van Huijsduijnen et al, 1987; Kim & Sheffery, 1990). A compelling set of bioinformatics studies clarified that the NF-Y preferred binding site is one of the most frequent promoter elements (Suzuki et al., 2001, 2004; Elkon et al., 2003; Mariño-Ramírez et al., 2004; FitzGerald et al., 2004; Linhart et al., 2005; Zhu et al., 2005; Lee et al., 2007; Abnizova et al., 2007; Grskovic et al., 2007; Halperin et al., 2009; Häkkinen et al., 2011). The same consensus, as determined by mutagenesis and SELEX studies (Bi et al., 1997), was also retrieved in ChIP-on-chip analysis (Testa et al., 2005; Ceribelli et al., 2006; Ceribelli et al., 2008; Reed et al., 2008). Additional structural features of the CCAAT box - position, orientation, presence of multiple Transcriptional Start Sites - were previously reviewed (Dolfini et al., 2009) and will not be considered in detail here.

Histone deacetylase inhibitors: emerging mechanisms of resistance

The histone deacetylase inhibitors (HDIs) have shown promise in the treatment of a number of hematologic malignancies, leading to the approval of vorinostat and romidepsin for the treatment of cutaneous T-cell lymphoma and romidepsin for the treatment of peripheral T-cell lymphoma by the U.S. Food and Drug Administration. Despite these promising results, clinical trials with the HDIs in solid tumors have not met with success. Examining mechanisms of resistance to HDIs may lead to strategies that increase their therapeutic potential in solid tumors. However, relatively few examples of drug-selected cell lines exist, and mechanisms of resistance have not been studied in depth. Very few clinical translational studies have evaluated resistance mechanisms. In the current review, we summarize many of the purported mechanisms of action of the HDIs in clinical trials and examine some of the emerging resistance mechanisms.

The short-chain fatty acid butyrate is a substrate of breast cancer resistance protein

Colorectal cancer is one of the most common cancers worldwide. Butyrate (BT) plays a key role in colonic epithelium homeostasis. The aim of this work was to investigate the possibility of BT being transported by P-glycoprotein (MDR1), multidrug resistance proteins (MRPs), or breast cancer resistance protein (BCRP). Uptake and efflux of (14)C-BT and (3)H-folic acid were measured in Caco-2, IEC-6, and MDA-MB-231 cell lines. mRNA expression of BCRP was detected by RT-PCR. Cell viability, proliferation, and differentiation were quantified with the lactate dehydrogenase, sulforhodamine B, and alkaline phosphatase activity assays, respectively. In both IEC-6 cells and Caco-2 cells, no evidence was found for the involvement of either MDR1 or MRPs in (14)C-BT efflux from the cells. In contrast, several lines of evidence support the conclusion that BT is a substrate of both rat and human BCRP. Indeed, BCRP inhibitors reduced (14)C-BT efflux in IEC-6 cells, both BT and BCRP inhibitors significantly decreased the efflux of the known BCRP substrate (3)H-folic acid in IEC-6 cells, and BCRP inhibitors reduced (14)C-BT efflux in the BCRP-expressing MDA-MB-231 cell line. In IEC-6 cells, combination of BT with a BCRP inhibitor significantly potentiated the effect of BT on cell proliferation. The results of this study, showing for the first time that BT is a BCRP substrate, are very important in the context of the high levels of BCRP expression in the human colon and the anticarcinogenic and anti-inflammatory role of BT at that level. So, interaction of BT with BCRP and with other BCRP substrates/inhibitors is clearly of major importance.

UHRF1 inhibits MDR1 gene transcription and sensitizes breast cancer cells to anticancer drugs

Overexpression of MDR1 in breast cancer remains a major cause for the failure of chemotherapy. In the present report, we find UHRF1 plays an important role in inhibiting MDR1 promoter activity by directly binding to the MDR1 promoter. Knockdown of UHRF1 activates MDR1 promoter activity and expression, attenuates the binding of UHRF1 and HDAC1 to the MDR1 promoter.Overexpression of UHRF1 in NCI/ADR-RES cells can induce deacetylation of histones H3 and H4 on the MDR1 promoter, which is facilitated by recruitment of HDAC1 to the MDR1 promoter. Loss of histone acetylation is accompanied by loss of binding of the key transcription factor, MyoD, CBP and p300, locking in marked suppression of MDR1, increasing sensitivity of MDR cancer cells to cytotoxic drugs that are transported by P-glycoprotein(P-gp). The inhibition of MDR1 expression by UHRF1 may provide potential ways to overcome multidrug resistance (MDR) in breast cancer treatment.

Activation of the CMV-IE promoter by hyperthermia in vitro and in vivo: biphasic heat induction of cytosine deaminase suicide gene expression

The cytomegalovirus-immediate early (CMV-IE) promoter is widely used as a strong and constitutively active promoter. Although the CMV-IE promoter does not harbor heat-responsive sequences, we determined its heat inducibility. We analyzed in vitro and in vivo heat responsiveness and possible mechanisms of heat induction of the CMV-IE promoter. We used transfected SW480 human colon carcinoma cells (SW480/CMVCD), expressing CMV-IE promoter-driven bacterial cytosine deaminase (CD) gene. These cells were heated at 42 degrees C. The SW480/CMVCD cells were also used for in vivo studies, in which tumor-bearing animals were treated with hyperthermia at 41.5 degrees C. As controls, SW480 (SW480/HSPCD) cells were used, in which CD expression is driven by the HSP70-promoter. In vitro, we observed a biphasic, up to 25-fold heat induction of CMV-IE-driven CD expression after hyperthermia in SW480/CMVCD cells. In vivo, we found a 2.5-fold induction of CD expression after hyperthermia in SW480/CMVCD tumor-bearing animals. The analysis of the CMV-IE promoter sequence revealed several transcription factor-binding sites, which mediate stress responsiveness. YB-1 and C/EBP-beta might mediate heat responsiveness of the CMV-IE promoter. These data point to limitations in heat-induction gene therapy studies, in which the CMV-IE promoter is used as control system. In addition, the CMV-IE promoter itself could well be used for construction of heat-inducible vectors.

Escape from stress granule sequestration: another way to drug resistance?

Overexpression of P-glycoprotein, encoded by the MDR1 (multidrug resistance 1) gene, is often responsible for multidrug resistance and chemotherapy failure in cancer. We have demonstrated that, in leukaemic cells, P-glycoprotein expression is regulated at the translational level. More recently, we have shown that in cells overexpressing P-glycoprotein, MDR1 mRNA does not aggregate into translationally silent stress granules. Importantly, this is not unique for MDR1, since other transcripts encoding transmembrane proteins, and which are thus translated at the endoplasmic reticulum, follow the same pattern. By using a series of chimaeric transcripts, we have demonstrated that transcript localization at the endoplasmic reticulum bypasses the signals dictating stress granule sequestration. Polysome profile analyses and protein synthesis experiments indicate that, upon stress withdrawal, endoplasmic-reticulum-bound transcripts resume translation faster than those at the cytosol, which have been sequestered into stress granules. This may represent a novel mechanism by which drug-resistant cells respond quickly to stress, helping them to survive the cytotoxic effect of chemotherapeutic drugs.

Histone methyltransferase MLL1 regulates MDR1 transcription and chemoresistance

The multidrug resistance 1 gene (MDR1) encodes P-glycoprotein (Pgp), a member of the ATP-binding cassette (ABC) transporter family that confers tumor drug resistance by actively effluxing a number of antitumor agents. We had previously shown that MDR1 transcription is regulated by epigenetic events such as histone acetylation, and had identified the histone acetylase P/CAF and the transcription factor NF-Y as the factors mediating the enzymatic and DNA-anchoring functions, respectively, at the MDR1 promoter. It has also been shown that MDR1 activation is accompanied by increased methylation on lysine 4 of histone H3 (H3K4). In this study, we further investigated histone methylation in MDR1 regulation and function. We show that the mixed lineage leukemia 1 (MLL1) protein, a histone methyltransferase specific for H3K4, is required for MDR1 promoter methylation, as knockdown of MLL1 resulted in a decrease in MDR1 expression. The regulation of MDR1 by MLL1 has functional consequences in that downregulation of MLL1 led to increased retention of the Pgp-specific substrate DIOC(2)(3), as well as increased cellular sensitivity to several Pgp substrates. Regulation of MDR1 by MLL1 was dependent on the CCAAT box within the proximal MDR1 promoter, similar to what we had shown for MDR1 promoter acetylation, and also requires NF-Y. Finally, overexpression of the most prevalent MLL fusion protein, MLL-AF4, led to increased MDR1 expression. This is the first identification of a histone methyltransferase and its leukemogenic rearrangement that regulates expression of an ABC drug transporter, suggesting a new target for circumvention of tumor multidrug resistance.

Human AP endonuclease (APE1/Ref-1) and its acetylation regulate YB-1-p300 recruitment and RNA polymerase II loading in the drug-induced activation of multidrug resistance gene MDR1

Overexpression of human AP-endonuclease (APE1/Ref-1), a key enzyme in the DNA base excision repair (BER) pathway, is often associated with tumor cell resistance to various anticancer drugs. In this study, we examined the molecular basis of transcriptional regulatory (non repair) function of APE1 in promoting resistance to certain types of drugs. We have recently shown that APE1 stably interacts with Y-box-binding protein 1 (YB-1), and acts as its coactivator for the expression of multidrug resistance gene MDR1, thereby causing drug-resistance. Here we show for the first time that APE1 is stably associated with the basic transcription factor RNA polymerase II (RNA pol II) and the coactivator p300 on the endogenous MDR1 promoter. APE1’s depletion significantly reduces YB-1/p300 recruitment to the promoter, resulting in reduced RNA pol II loading. Drug-induced APE1 acetylation which is mediated by p300 enhances formation of acetylated APE1 (AcAPE1)/YB-1/p300 complex on the MDR1 promoter. Enhanced recruitment of this complex increases MDR1 promoter dependent luciferase activity and its endogenous expression. Using APE1 downregulated cells and cells overexpressing wild type APE1 or its nonacetylable mutant we have demonstrated that the loss of APE1’s acetylation impaired MDR1 activation and sensitizes the cells to cisplatin or etoposide. We have thus established the basis for APE1’s acetylation-dependent regulatory function in inducing MDR1-mediated drug resistance.

Non-peptide macrocyclic histone deacetylase inhibitors derived from tricyclic ketolide skeleton

Inhibition of histone deacetylase (HDAC) function is a validated therapeutic strategy for cancer treatment. Of the several structurally distinct small molecule histone deacetylase inhibitors (HDACi) reported, macrocyclic depsipeptides possess the most complex cap groups and have demonstrated excellent HDAC inhibition potency and isoform selectivity. Unfortunately, the development of macrocyclic depsipeptides has been hampered in part because of development problems characteristic of large peptides and the complex reaction schemes required for their synthesis. Herein we report that tricyclic ketolide TE-802 is an excellent mimetic for the peptide backbone of macrocyclic HDACi. Compounds derived from this template are particularly selective against HDACs 1 and 2 with nanomolar inhibitory activity. Interrogation of the association between a subset of these compounds and key HDAC isoforms, using AutoDock, enables a molecular description of the interaction between the HDAC enzyme's outer rim and the inhibitors' macrocyclic cap group that are responsible for compound affinity and presumably isoform selectivity.

Glucosylceramide synthase upregulates MDR1 expression in the regulation of cancer drug resistance through cSrc and beta-catenin signaling

Background

Drug resistance is the outcome of multiple-gene interactions in cancer cells under stress of anticancer agents. MDR1 overexpression is most commonly detected in drug-resistant cancers and accompanied with other gene alterations including enhanced glucosylceramide synthase (GCS). MDR1 encodes for P-glycoprotein that extrudes anticancer drugs. Polymorphisms of MDR1 disrupt the effects of P-glycoprotein antagonists and limit the success of drug resistance reversal in clinical trials. GCS converts ceramide to glucosylceramide, reducing the impact of ceramide-induced apoptosis and increasing glycosphingolipid (GSL) synthesis. Understanding the molecular mechanisms underlying MDR1 overexpression and how it interacts with GCS may find effective approaches to reverse drug resistance.

Results

MDR1 and GCS were coincidently overexpressed in drug-resistant breast, ovary, cervical and colon cancer cells; silencing GCS using a novel mixed-backbone oligonucleotide (MBO-asGCS) sensitized these four drug-resistant cell lines to doxorubicin. This sensitization was correlated with the decreased MDR1 expression and the increased doxorubicin accumulation. Doxorubicin treatment induced GCS and MDR1 expression in tumors, but MBO-asGCS treatment eliminated "in-vivo" growth of drug-resistant tumor (NCI/ADR-RES). MBO-asGCS suppressed the expression of MDR1 with GCS and sensitized NCI/ADR-RES tumor to doxorubicin. The expression of P-glycoprotein and the function of its drug efflux of tumors were decreased by 4 and 8 times after MBO-asGCS treatment, even though this treatment did not have a significant effect on P-glycoprotein in normal small intestine. GCS transient transfection induced MDR1 overexpression and increased P-glycoprotein efflux in dose-dependent fashion in OVCAR-8 cancer cells. GSL profiling, silencing of globotriaosylceramide synthase and assessment of signaling pathway indicated that GCS transfection significantly increased globo series GSLs (globotriaosylceramide Gb3, globotetraosylceramide Gb4) on GSL-enriched microdomain (GEM), activated cSrc kinase, decreased β-catenin phosphorylation, and increased nuclear β-catenin. These consequently increased MDR1 promoter activation and its expression. Conversely, MBO-asGCS treatments decreased globo series GSLs (Gb3, Gb4), cSrc kinase and nuclear β-catenin, and suppressed MDR-1 expression in dose-dependent pattern.

Conclusion

This study demonstrates, for the first time, that GCS upregulates MDR1 expression modulating drug resistance of cancer. GSLs, in particular globo series GSLs mediate gene expression of MDR1 through cSrc and β-catenin signaling pathway.

Disrupted transforming growth factor-beta signaling in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a late-onset lower motor neuron disease caused by the expansion of a trinucleotide CAG repeat, which encodes a polyglutamine tract in androgen receptor (AR). Although it is commonly held that the pathogenic polyglutamine proteins accumulate in neurons and thereby induce transcriptional dysregulation, the downstream molecular events have remained elusive. Here, we examined whether TGF-beta signaling is dysregulated in SBMA. Nuclear translocation of phosphorylated Smad2/3, a key step in TGF-beta signaling, is suppressed in the spinal motor neurons of male transgenic mice carrying the mutant human AR. A similar finding was also observed in the motor neurons, but not in Purkinje cells, of SBMA patients. The pathogenic AR, the causative protein of SBMA, inhibits the transcription of TGF-beta receptor type II (TbetaRII) via abnormal interactions with NF-Y and p300/CBP-associated factor. Furthermore, overexpression of TbetaRII dampens polyglutamine-induced cytotoxicity in a neuroblastoma cell line expressing the pathogenic AR. The present study thus indicates that disruption of TGF-beta due to the transcriptional dysregulation of TbetaRII is associated with polyglutamine-induced motor neuron damage in SBMA.

Ferritin H induction by histone deacetylase inhibitors

Because both iron deficiency and iron excess are deleterious to normal cell function, the intracellular level of iron must be tightly controlled. Ferritin, an iron binding protein, regulates iron balance by storing iron in a bioavailable but nontoxic form. Ferritin protein comprises two subunits: ferritin H, which contains ferroxidase activity, and ferritin L. Here we demonstrate that ferritin H mRNA and protein are induced by histone deacetylase inhibitors (HDAC inhibitors), a promising class of anti-cancer drugs, in cultured human cancer cells. Deletion analysis and EMSA assays reveal that the induction of ferritin H occurs at a transcriptional level via Sp1 and NF-Y binding sites near the transcriptional start site of the human ferritin H promoter. Classically, HDAC inhibitors modulate gene expression by increasing histone acetylation. However, ChIP assays demonstrate that HDAC inhibitors induce ferritin H transcription by increasing NF-Y binding to the ferritin H promoter without changes in histone acetylation. These results identify ferritin H as a new target of HDAC inhibitors, and recruitment of NF-Y as a novel mechanism of action of HDAC inhibitors.

Role of nuclear factor Y in stress-induced activation of the herpes simplex virus type 1 ICP0 promoter

Herpesviruses are characterized by the ability to establish lifelong latent infections and to reactivate periodically, leading to recurrent disease. The herpes simplex virus type 1 (HSV-1) genome is maintained in a quiescent state in sensory neurons during latency, which is characterized by the absence of detectable viral protein synthesis. Cellular factors induced by stress may act directly on promoters within the latent viral genome to induce the transcription of viral genes and trigger reactivation. In order to identify which viral promoters are induced by stress and elucidate the cellular mechanism responsible for the induction, we generated a panel of HSV-1 promoter-luciferase constructs and measured their response to heat shock. Of the promoters tested, those of ICP0 and ICP22 were the most strongly upregulated after heat shock. Microarray analysis of lytically infected cells supported the upregulation of ICP0 and ICP22 promoters by heat shock. Mutagenic analysis of the ICP0 promoter identified two regions necessary for efficient heat-induced promoter activity, both containing predicted nuclear factor Y (NF-Y) sites, at bases -708 and -75 upstream of the transcriptional start site. While gel shift analysis confirmed NF-Y binding to both sites, only the site at -708 was important for efficient heat-induced activity. Reverse transcription-PCR analysis of selected viral transcripts in the presence of dominant-negative NF-Y confirmed the requirement for NF-Y in the induction of the ICP0 but not the ICP22 promoter by heat shock in lytically infected cells. These findings suggest that the immediate-early ICP0 gene may be among the first genes to be induced during the early events in HSV-1 reactivation, that NF-Y is important for this induction, and that other factors induce the ICP22 promoter.

Mechanisms of multidrug resistance in cancer

The development of multidrug resistance (MDR) to chemotherapy remains a major challenge in the treatment of cancer. Resistance exists against every effective anticancer drug and can develop by numerous mechanisms including decreased drug uptake, increased drug efflux, activation of detoxifying systems, activation of DNA repair mechanisms, evasion of drug-induced apoptosis, etc. In the first part of this chapter, we briefly summarize the current knowledge on individual cellular mechanisms responsible for MDR, with a special emphasis on ATP-binding cassette transporters, perhaps the main theme of this textbook. Although extensive work has been done to characterize MDR mechanisms in vitro, the translation of this knowledge to the clinic has not been crowned with success. Therefore, identifying genes and mechanisms critical to the development of MDR in vivo and establishing a reliable method for analyzing clinical samples could help to predict the development of resistance and lead to treatments designed to circumvent it. Our thoughts about translational research needed to achieve significant progress in the understanding of this complex phenomenon are therefore discussed in a third section. The pleotropic response of cancer cells to chemotherapy is summarized in a concluding diagram.

Doxorubicin loaded Polymeric Nanoparticulate Delivery System to overcome drug resistance in osteosarcoma

BACKGROUND

Drug resistance is a primary hindrance for the efficiency of chemotherapy against osteosarcoma. Although chemotherapy has improved the prognosis of osteosarcoma patients dramatically after introduction of neo-adjuvant therapy in the early 1980's, the outcome has since reached plateau at approximately 70% for 5 year survival. The remaining 30% of the patients eventually develop resistance to multiple types of chemotherapy. In order to overcome both the dose-limiting side effects of conventional chemotherapeutic agents and the therapeutic failure incurred from multidrug resistant (MDR) tumor cells, we explored the possibility of loading doxorubicin onto biocompatible, lipid-modified dextran-based polymeric nanoparticles and evaluated the efficacy.

METHODS

Doxorubicin was loaded onto a lipid-modified dextran based polymeric nano-system. The effect of various concentrations of doxorubicin alone or nanoparticle loaded doxorubicin on KHOS, KHOSR2, U-2OS, and U-2OSR2 cells was analyzed. Effects on drug retention, immunofluorescence, Pgp expression, and induction of apoptosis were also analyzed.

RESULTS

Dextran nanoparticles loaded with doxorubicin had a curative effect on multidrug resistant osteosarcoma cell lines by increasing the amount of drug accumulation in the nucleus via Pgp independent pathway. Nanoparticles loaded with doxorubicin also showed increased apoptosis in osteosarcoma cells as compared with doxorubicin alone.

CONCLUSION

Lipid-modified dextran nanoparticles loaded with doxorubicin showed pronounced anti-proliferative effects against osteosarcoma cell lines. These findings may lead to new treatment options for MDR osteosarcoma.

CpG hypomethylation of MDR1 gene in tumor and serum of invasive ductal breast carcinoma patients

OBJECTIVES

Multidrug resistance 1 (MDR1) gene encodes P-glycoprotein (P-gp), a transmembrane calcium-dependent efflux pump, implicated in drug resistance. In this prospective study, methylation status of MDR1 promoter and its correlation with clinicopathological parameters were evaluated in tumor and serum of breast cancer patients.

DESIGN AND METHODS

Methylation-specific PCR was carried out to investigate the promoter methylation status of MDR1 in tumor and serum of 100 patients with invasive ductal carcinomas of breast (IDCs). The effect of promoter methylation on protein expression was evaluated by immunohistochemistry.

RESULTS

MDR1 was hypomethylated in 47% tumors and 44% paired sera of IDC patients and correlated significantly with increased tumor size and advanced tumor stage. Promoter hypomethylation of MDR1 in serum DNA showed 98% specificity and 50% sensitivity.

CONCLUSIONS

Hypomethylation of MDR1 promoter in IDCs accounted for P-gp overexpression and aggressive biologic behavior in a subset of patients. Detection of these epigenetic changes in circulating DNA may not only enhance insight into the biological behavior of the primary tumor of an individual but may also provide valuable information regarding prognosis that can be readily monitored throughout the disease course.

Laboratory correlates for a phase II trial of romidepsin in cutaneous and peripheral T-cell lymphoma

Romidepsin has shown promise in the treatment of T-cell lymphomas, and so we evaluated molecular endpoints gathered from 61 patients enrolled on a phase II trial of romidepsin in cutaneous and peripheral T-cell lymphoma at the National Institutes of Health. The endpoints included histone H3 acetylation and ABCB1 gene expression in peripheral blood mononuclear cells (PBMCs); ABCB1 gene expression in tumour biopsy samples; and blood fetal haemoglobin levels (HbF), all of which were increased following romidepsin treatment. The fold increase in histone acetylation in PBMCs at 24 h was weakly to moderately well correlated with the pharmacokinetic parameters C(max) and area under the curve (AUC)(last) (rho = 0.37, P = 0.03 and rho = 0.36, P = 0.03 respectively) and inversely associated with clearance (rho = -0.44; P = 0.03). Histone acetylation in PBMCs at 24 h was associated with response (P = 0.026) as was the increase in fetal haemoglobin (P = 0.014); this latter association may be due to the longer on-study duration for patients with disease response. Together, these results suggest that pharmacokinetics may be an important determinant of response to histone deacetylase inhibitors (HDIs) - the association with histone acetylation in PBMCs at 24 h is consistent with a hypothesis that potent HDIs are needed for a critical threshold of drug exposure and durable activity.

Anti-leukemia activity of MS-275 histone deacetylase inhibitor implicates 4-1BBL/4-1BB immunomodulatory functions

Histone deacetylase inhibitors (HDACi) have demonstrated promising therapeutic potential in clinical trials for hematological malignancies. HDACi, such as SAHA/Vorinostat, Trichostatin A, and MS-275 were found to induce apoptosis of leukemic blasts through activation of the death receptor pathway and transcriptional induction of the Tumor Necrosis Factor (TNF)-related pro-apoptotic family members, TRAIL and FasL. The impact of HDACi on TNF-related costimulatory molecules such as 4-1BB ligand (4-1BBL/TNFSF9) is however not known. Following exposure to SAHA/Vorinostat, Trichostatin A, and MS-275, transcript levels were determined by real time PCR in Jurkat, Raji and U937 cells. Treatment with HDACi up-regulated TNFSF9 gene expression in the three leukemia cell lines, yet to different extend and with distinct kinetics, which did not require de novo protein synthesis and was not associated with DNAse I hypersensitive chromatin remodeling. Transcriptional activity of TNFSF9 promoter-luciferase constructs was induced up to 12 fold by HDACi, and implication of Sp1/Sp3 transcription factors binding to functional GC-box elements was evidenced by reporter gene assays, site-directed mutagenesis, and electrophoretic mobility shift assays. Functionality of modulated target genes was assessed in allogeneic mixed leukocyte reaction experiments. MS-275- and to a lesser extent Trichostatin A- and SAHA-treated Raji cells significantly up regulated T lymphocytes proliferation which was reduced by about 50% by a 4-1BB blocking recombinant protein, while MS-275- but neither Trichostatin A- nor SAHA-treated cells up-regulated IFNγ secretion by T lymphocytes. Our results identify 4-1BBL/4-1BB as a downstream target of HDACi, especially of MS-275 anti-leukemia action in vitro. Thus, HDACi such as MS-275 displaying dual TNF-dependent proapoptotic and costimulatory activities might be favored for inclusion in HDACi-based anti-cancer therapeutic strategies.

Epigenetic modifiers: basic understanding and clinical development

More than 60 years after the first description of differentiation in cell culture and 40 years after the synthesis of 5-azacytidine, epigenetic therapies have been added to the anticancer armamentarium. DNA methyltransferase (DNMT) inhibitors such as 5-aza-2'-deoxycytidine or 5-azacytidine have been approved in myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML), whereas the histone deacetylase inhibitors (HDIs) including vorinostat, romidepsin, panobinostat, belinostat, and entinostat have been shown to be active in cutaneous and peripheral T-cell lymphoma. Although the range of malignancies in which monotherapy with DNMT inhibitors or HDIs are effective has been limited to date, the possibility remains that a broader spectrum of activity will be identified as combination studies are completed. Meanwhile, basic science has provided a steadily increasing understanding of the complexity of the epigenome, including the histone code and triggers for aberrant methylation, and their contribution to oncogenesis. As our basic understanding of the epigenetics of cancer increases, the number of potential therapeutic targets will also increase, offering more hope in the quest to treat cancer by normalizing the epigenome. This issue of CCR Focus is dedicated to understanding the clinical and translational aspects of epigenetics research.

Histone deacetylase inhibitors induce a very broad, pleiotropic anticancer drug resistance phenotype in acute myeloid leukemia cells by modulation of multiple ABC transporter genes

PURPOSE

Histone deacetylase inhibitors (HDACi) are being studied in clinical trials with the aim to induce cellular differentiation, growth arrest, and apoptosis of tumor cells. Recent reports suggest that the multidrug resistance-1 (MDR1) gene is regulated by epigenetic mechanisms. To investigate whether additional drug transporters are regulated by HDACi and how this affects cytotoxicity, acute myeloid leukemia (AML) cells were examined.

EXPERIMENTAL DESIGN

AML cells were cultured in the presence of phenylbutyrate, valproate, suberoylanilide hydroxamic acid, or trichostatin A and analyzed for drug transporter expression and function as well as sensitivity to anticancer drugs.

RESULTS

MDR1, breast cancer resistance protein (BCRP), and multidrug resistance-associated proteins (MRP) 7 and 8 were induced in a dose- and time-dependent manner as shown by semiquantitative PCR. The pattern of gene induction was cell line specific. Phenylbutyrate induced P-glycoprotein and BCRP expression and the efflux of drugs as determined with labeled substrates. KG-1a cells treated with phenylbutyrate developed resistance to daunorubicin, mitoxantrone, etoposide, vinblastine, paclitaxel, topotecan, gemcitabine, and 5-fluorouracil; as a result drug-induced apoptosis was impaired. Chromatin immunoprecipitation revealed the hyperacetylation of histone proteins in the promoter regions of MDR1, BCRP, and MRP8 on valproate treatment. Furthermore, an alternative MRP8 promoter was induced by HDACi treatment.

CONCLUSIONS

Exposure of AML cells to HDACi induces a drug resistance phenotype broader than the "classic multidrug resistance," which might negatively affect treatment effectiveness.

Histone deacetylase inhibitor induction of P-glycoprotein transcription requires both histone deacetylase 1 dissociation and recruitment of CAAT/enhancer binding protein beta and pCAF to the promoter region

Although histone deacetylase (HDAC) inhibitors are appreciated as a promising class of anticancer drugs, recent reports show that P-glycoprotein (P-gp) is induced by HDAC inhibitor treatment in cancer cells, resulting in multidrug resistance of cancer cells to other chemotherapeutic agents. In this study, we investigated the molecular mechanism of HDAC inhibitor induction of P-gp expression. HDAC inhibitor treatment causes cell type-specific induction of P-gp expression without changes in the CpG methylation status of the promoter region. In addition, our data show that HDAC inhibitor does not alter the DNA binding activity of Sp1 but facilitates both the recruitment of a coactivator complex that includes CAAT/enhancer binding protein beta and pCAF and the dissociation of the repressive complex, HDAC1, to the Sp1 binding region. Subsequently, the hyperacetylated histone H3 becomes enriched in the promoter region, leading to RNA polymerase II recruitment to activate P-gp gene transcription. Furthermore, specific down-regulation of HDAC1, but not HDAC2, by RNA silencing was enough to induce P-gp expression in HeLa cells, strongly supporting the essential role of HDAC1 in HDAC inhibitor induction of P-gp. Concomitantly, cell type-specific induction of P-gp expression seems to be dependent on phosphatidylinositol 3-kinase activity. Taken together, our findings show that HDAC inhibitor treatment leads to an increase in P-gp expression through dynamic changes in chromatin structure and transcription factor association within the promoter region.

Involvement of extracellular signal-regulated kinase activation in human osteosarcoma cell resistance to the histone deacetylase inhibitor FK228 [(1S,4S,7Z,10S,16E,21R)-7-ethylidene-4,21-bis(propan-2-yl)-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8.7.6]tricos-16-ene-3,6,9,19,22-pentone]

The histone deacetylase inhibitor depsipeptide [(1S,4S,7Z,10S, 16E,21R)-7-ethylidene-4,21-bis(propan-2-yl)-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8.7.6]tricos-16-ene-3,6,9,19, 22-pentone] (FK228) has attracted a great deal of interest because of its antiproliferative and apoptotic properties in various malignancies. Histone deacetylase inhibitors induce the expression of the multidrug resistance transporter P-glycoprotein (P-gp), and FK228 is a known P-gp substrate. Thus, FK228 seems to induce its own mechanism of drug resistance by up-regulating P-gp. The goal of this study was to establish human FK228-resistant osteosarcoma cell lines and to investigate whether there are mechanisms of FK228 resistance in addition to P-gp up-regulation. After 72 h in culture, the 50% inhibitory concentrations (IC(50)) of FK228 were 4.8 and 991 nM in HOS and HOS/FK8 cells, respectively, and 3.6 and 1420 nM in U2OS and U2OS/FK11 cells, respectively. Increased histone H3 acetylation was observed in FK228-resistant cell lines after a 1-h treatment with 10 nM FK228. Unlike in parental cells, significant P-gp overexpression was detected in FK228-resistant cells, and 10 nM FK228 treatment activated the mitogen-activated protein kinase (MAPK) pathway but did not induce Fas ligand (FasL) up-regulation or c-FLIP down-regulation. However, treatment of FK228-resistant cells with a combination of FK228 and mitogen-activated protein kinase kinase (MEK) inhibitors induced apoptosis, up-regulated FasL, and down-regulated c-FLIP. The expression and function of P-gp were unaltered by treatment with MEK inhibitors. These results indicate that the FK228 resistance of osteosarcoma cells is related to P-gp overexpression and MAPK pathway activation by FK228. MEK or P-gp inhibitors may be useful in overcoming this resistance.

Hyaluronan-mediated CD44 interaction with p300 and SIRT1 regulates beta-catenin signaling and NFkappaB-specific transcription activity leading to MDR1 and Bcl-xL gene expression and chemoresistance in breast tumor cells

In this study we have investigated hyaluronan (HA)-mediated CD44 (an HA receptor) interactions with p300 (a histone acetyltransferase) and SIRT1 (a histone deacetylase) in human breast tumor cells (MCF-7 cells). Specifically, our results indicate that HA binding to CD44 up-regulates p300 expression and its acetyltransferase activity that, in turn, promotes acetylation of beta-catenin and NFkappaB-p65 leading to activation of beta-catenin-associated T-cell factor/lymphocyte enhancer factor transcriptional co-activation and NFkappaB-specific transcriptional up-regulation, respectively. These changes then cause the expression of the MDR1 (P-glycoprotein/P-gp) gene and the anti-apoptotic gene Bcl-x(L) resulting in chemoresistance in MCF-7 cells. Our data also show that down-regulation of p300, beta-catenin, or NFkappaB-p65 in MCF-7 cells (by transfecting cells with p300-, beta-catenin-, or NFkappaB-p65-specific small interfering RNA) inhibits the HA/CD44-mediated beta-catenin/NFkappaB-p65 acetylation and abrogates the aforementioned transcriptional activities. Subsequently, there is a significant decrease in both MDR1 and Bcl-x(L) gene expression and an enhancement in caspase-3 activity and chemosensitivity in the breast tumor cells. Further analyses indicate that activation of SIRT1 (deacetylase) by resveratrol (a natural antioxidant) induces SIRT1-p300 association and acetyltransferase inactivation, leading to deacetylation of HA/CD44-induced beta-catenin and NFkappaB-p65, inhibition of beta-catenin-T-cell factor/lymphocyte enhancer factor and NFkappaB-specific transcriptional activation, and the impairment of MDR1 and Bcl-x(L) gene expression. All these multiple effects lead to an activation of caspase-3 and a reduction of chemoresistance. Together, these findings suggest that the interactions between HA/CD44-stimulated p300 (acetyltransferase) and resveratrol-activated SIRT1 (deacetylase) play pivotal roles in regulating the balance between cell survival versus apoptosis, and multidrug resistance versus sensitivity in breast tumor cells.

Redox regulation of multidrug resistance in cancer chemotherapy: molecular mechanisms and therapeutic opportunities

The development of multidrug resistance to cancer chemotherapy is a major obstacle to the effective treatment of human malignancies. It has been established that membrane proteins, notably multidrug resistance (MDR), multidrug resistance protein (MRP), and breast cancer resistance protein (BCRP) of the ATP binding cassette (ABC) transporter family encoding efflux pumps, play important roles in the development of multidrug resistance. Overexpression of these transporters has been observed frequently in many types of human malignancies and correlated with poor responses to chemotherapeutic agents. Evidence has accumulated showing that redox signals are activated in response to drug treatments that affect the expression and activity of these transporters by multiple mechanisms, including (a) conformational changes in the transporters, (b) regulation of the biosynthesis cofactors required for the transporter's function, (c) regulation of the expression of transporters at transcriptional, posttranscriptional, and epigenetic levels, and (d) amplification of the copy number of genes encoding these transporters. This review describes various specific factors and their relevant signaling pathways that are involved in the regulation. Finally, the roles of redox signaling in the maintenance and evolution of cancer stem cells and their implications in the development of intrinsic and acquired multidrug resistance in cancer chemotherapy are discussed.