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

Unveiling gut microbiota's role: Bidirectional regulation of drug transport for improved safety

Drug safety is a paramount concern in the field of drug development, with researchers increasingly focusing on the bidirectional regulation of gut microbiota in this context. The gut microbiota plays a crucial role in maintaining drug safety. It can influence drug transport processes in the body through various mechanisms, thereby modulating their efficacy and toxicity. The main mechanisms include: (1) The gut microbiota directly interacts with drugs, altering their chemical structure to reduce toxicity and enhance efficacy, thereby impacting drug transport mechanisms, drugs can also change the structure and abundance of gut bacteria; (2) bidirectional regulation of intestinal barrier permeability by gut microbiota, promoting the absorption of nontoxic drugs and inhibiting the absorption of toxic components; (3) bidirectional regulation of the expression and activity of transport proteins by gut microbiota, selectively promoting the absorption of effective components or inhibiting the absorption of toxic components. This bidirectional regulatory role enables the gut microbiota to play a key role in maintaining drug balance in the body and reducing adverse reactions. Understanding these regulatory mechanisms sheds light on novel approaches to minimize toxic side effects, enhance drug efficacy, and ultimately improve drug safety. This review systematically examines the bidirectional regulation of gut microbiota in drug transportation from the aforementioned aspects, emphasizing their significance in ensuring drug safety. Furthermore, it offers a prospective outlook from the standpoint of enhancing therapeutic efficacy and reducing drug toxicity, underscoring the importance of further exploration in this research domain. It aims to provide more effective strategies for drug development and treatment.

Regulation of LAMTOR1 by oxidative stress in retinal pigment epithelium: Implications for age-related macular degeneration pathogenesis

Oxidative stress is a critical pathogenic factor for age-related macular degeneration (AMD). Autophagy serves as a mechanism to counteract oxidative stress. LAMTOR1 regulates mTORC1 activity by recruiting or disassembling it on the lysosome under the addition or deprivation of amino acids. This regulation inhibits or enhances autophagy. Our study investigates whether oxidative stress impacts LAMTOR1, thereby adapting to oxidative conditions. We employed oxidative stressors, menadione (VK3) and 4-hydroxynonenal (4-HNE), and observed a reduction of LAMTOR1 in both human and mouse retinal pigment epithelium (RPE) following short-term (1h) and prolonged exposures (24h). Nrf2 overexpression increased both lamtor1 mRNA and LAMTOR1 protein in the RPE. To determine if Nrf2 regulates lamtor1 transcription, we cloned the deletion mutants of the lamtor1 promoter into a luciferase reporter. Although the promoter contained antioxidant response elements, transcriptional activity depended on the interaction between Nrf2 and the constructs containing the transcriptional start site. Moreover, Nrf2-driven transcription was significantly reduced by an inhibitor of histone acetyltransferase, p300. Correspondingly, Nrf2 overexpression increased levels of acetylated histone 3 and p300. The reduction in LAMTOR1 by 4-HNE was reversed by pepstatin A and NH4Cl which block lysosomal degradation. 4-HNE increased TFEB nuclear translocation which was reversed by LAMTOR1 overexpression. In vivo, LAMTOR1 levels decreased in the photoreceptor and RPE layers of NaIO3-injected mice, compared to PBS-injected controls. In conclusion, oxidative injury reduces LAMTOR1, predominantly through lysosomal degradation although Nrf2-mediated histone acetylation enhances lamtor1 transcription. This study reveals a previously unrecognized regulatory mechanism of lamtor1 by oxidative stress, suggesting a novel role for LAMTOR1 in the pathogenesis of AMD.

Epigenetic modulation of doxorubicin resistance and strategies for enhancing chemotherapeutic sensitivity

With the rising global cancer burden, the dependency on chemotherapy also rises along with the complication of chemoresistance development. Studies on multi-drug resistant proteins provide a wide range of regulators, although the exact mechanism is not yet clearly understood. Epigenetic modifications play a vital role in the regulation of cellular processes and also in determining the efficacy of cancer therapy by modulating resistance development and tumor progression. Of the various epigenetic modifications, histone acetylation/deacetylation and DNA methylation are currently given more focus in evaluating their role in resistance development to doxorubicin. This chapter highlights the various studies conducted on the regulation of doxorubicin (dox) resistance based on these epigenetic modifications and the clinical trials conducted in evaluating its effectiveness as a potential combinational therapy.

A new strategy for overcoming drug resistance in liver cancer: Epigenetic regulation

Drug resistance in hepatocellular carcinoma has posed significant obstacles to effective treatment. Recent evidence indicates that, in addition to traditional gene mutations, epigenetic recoding plays a crucial role in HCC drug resistance. Unlike irreversible gene mutations, epigenetic changes are reversible, offering a promising avenue for preventing and overcoming drug resistance in liver cancer. This review focuses on various epigenetic modifications relevant to drug resistance in HCC and their underlying mechanisms. Additionally, we introduce current clinical epigenetic drugs and clinical trials of these drugs as regulators of drug resistance in other solid tumors. Although there is no clinical study to prevent the occurrence of drug resistance in liver cancer, the development of liquid biopsy and other technologies has provided a bridge to achieve this goal.

ABCB1 and ABCG2 Regulation at the Blood-Brain Barrier: Potential New Targets to Improve Brain Drug Delivery

The drug efflux transporters ABCB1 and ABCG2 at the blood-brain barrier limit the delivery of drugs into the brain. Strategies to overcome ABCB1/ABCG2 have been largely unsuccessful, which poses a tremendous clinical problem to successfully treat central nervous system (CNS) diseases. Understanding basic transporter biology, including intracellular regulation mechanisms that control these transporters, is critical to solving this clinical problem.In this comprehensive review, we summarize current knowledge on signaling pathways that regulate ABCB1/ABCG2 at the blood-brain barrier. In Section I, we give a historical overview on blood-brain barrier research and introduce the role that ABCB1 and ABCG2 play in this context. In Section II, we summarize the most important strategies that have been tested to overcome the ABCB1/ABCG2 efflux system at the blood-brain barrier. In Section III, the main component of this review, we provide detailed information on the signaling pathways that have been identified to control ABCB1/ABCG2 at the blood-brain barrier and their potential clinical relevance. This is followed by Section IV, where we explain the clinical implications of ABCB1/ABCG2 regulation in the context of CNS disease. Lastly, in Section V, we conclude by highlighting examples of how transporter regulation could be targeted for therapeutic purposes in the clinic. SIGNIFICANCE STATEMENT: The ABCB1/ABCG2 drug efflux system at the blood-brain barrier poses a significant problem to successful drug delivery to the brain. The article reviews signaling pathways that regulate blood-brain barrier ABCB1/ABCG2 and could potentially be targeted for therapeutic purposes.

Epigenetic modulation: Research progress on histone acetylation levels in major depressive disorders

Depression is a serious mental illness and a prevalent condition with multiple aetiologies. The impact of the current therapeutic strategies is limited and the pathogenesis of the illness is not well understood. According to previous studies, depression onset is influenced by a variety of environmental and genetic factors, including chronic stress, aberrant changes in gene expression, and hereditary predisposition. Transcriptional regulation in eukaryotes is closely related to chromosome packing and is controlled by histone post-translational modifications. The development of new antidepressants may proceed along a new path with medications that target epigenetics. Histone deacetylase inhibitors (HDACis) are a class of compounds that interfere with the function of histone deacetylases (HDACs). This review explores the relationship between HDACs and depression and focuses on the current knowledge on their regulatory mechanism in depression and the potential therapeutic use of HDACis with antidepressant efficacy in preclinical research. Future research on inhibitors is also proposed and discussed.

Some New Aspects of Genetic Variability in Patients with Cutaneous T-Cell Lymphoma

AIM

Cutaneous T-cell lymphoma (CTCL) is a group of T-cell malignancies that develop in the skin. Though studied intensively, the etiology and pathogenesis of CTCL remain elusive. This study evaluated the survival of CTCL patients in the 1st Department of Dermatovenereology of St. Anne's University Hospital Brno. It included analysis of 19 polymorphic gene variants based on their expected involvement in CTCL severity.

MATERIAL AND METHODS

75 patients with CTCL, evaluated and treated at the 1st Department of Dermatovenereology of St. Anne´s University Hospital Brno, Faculty of Medicine, Masaryk University, were recruited for the study over the last 28 years (44 men and 31 women, average age 58 years, range 20-82 years). All patients were genotyped for 19 chosen gene polymorphisms by the conventional PCR method with restriction analysis. A multivariate Cox regression model was calculated to reveal genetic polymorphisms and other risk factors for survival.

RESULTS

The model identified MDR Ex21 2677 (rs2032582) as a significant genetic factor influencing the survival of the patients, with the T-allele playing a protective role. A multivariate stepwise Cox regression model confirmed the following as significant independent risk factors for overall survival: increased age at admission, clinical staging of the tumor, and male sex.

CONCLUSION

We showed that the TT genotype at position 2677 of the MDR1 gene exhibited statistically significant longer survival in CTCL patients. As such, the TT genotype of MDR1 confers a significant advantage for the CTCL patients who respond to treatment.

Microbial Metabolites Orchestrate a Distinct Multi-Tiered Regulatory Network in the Intestinal Epithelium That Directs P-Glycoprotein Expression

P-glycoprotein (P-gp) is a key component of the intestinal epithelium playing a pivotal role in removal of toxins and efflux of endocannabinoids to prevent excessive inflammation and sustain homeostasis. Recent studies revealed butyrate and secondary bile acids, produced by the intestinal microbiome, potentiate the induction of functional P-gp expression. We now aim to determine the molecular mechanism by which this functional microbiome output regulates P-gp. RNA sequencing of intestinal epithelial cells responding to butyrate and secondary bile acids in combination discovered a unique transcriptional program involving multiple pathways that converge on P-gp induction. Using shRNA knockdown and CRISPR/Cas9 knockout cell lines, as well as mouse models, we confirmed the RNA sequencing findings and discovered a role for intestinal HNF4α in P-gp regulation. These findings shed light on a sophisticated signaling network directed by intestinal microbial metabolites that orchestrate P-gp expression and highlight unappreciated connections between multiple pathways linked to colonic health. IMPORTANCE Preventing aberrant inflammation is essential to maintaining homeostasis in the mammalian intestine. Although P-glycoprotein (P-gp) expression in the intestine is critical for protecting the intestinal epithelium from toxins and damage due to neutrophil infiltration, its regulation in the intestine is poorly understood. Findings presented in our current study have now uncovered a sophisticated and heretofore unappreciated intracellular signaling network or "reactome" directed by intestinal microbial metabolites that orchestrate regulation of P-gp. Not only do we confirm the role of histone deacetylases (HDAC) inhibition and nuclear receptor activation in P-gp induction by butyrate and bile acids, but we also discovered new signaling pathways and transcription factors that are uniquely activated in response to the combination of microbial metabolites. Such findings shed new light into a multi-tiered network that maintains P-gp expression in the intestine in the context of the fluctuating commensal microbiome, to sustain a homeostatic tone in the absence of infection or insult.

Tumor-targeting pH/redox dual-responsive nanosystem epigenetically reverses cancer drug resistance by co-delivering doxorubicin and GCN5 siRNA

Multidrug resistance (MDR) is a major cause accounting for chemotherapy failure and recurrence of malignant tumors. A prominent mechanism underlying MDR is overexpression of P-glycoprotein (P-gp, a drug efflux pump). Promoting drug delivery efficacy by targeting tumor and concurrently suppressing drug efflux through down-regulating P-gp emerges as an effective strategy to enhance intracellular drug accumulation for combating MDR tumor. General Control Non-repressed 5 (GCN5), a histone acetyltransferase acting as an epigenetic regulator of multidrug resistance protein 1 (MDR1), positively regulates P-gp levels in drug-resistant cancer cells. Herein, a hyaluronic acid-coated, pH/redox dual-responsive nanosystem (HPMSNs) is fabricated for co-delivering doxorubicin (DOX) and GCN5 siRNA (siGCN5). This nanosystem can effectively encapsulate DOX and siRNA preventing premature leakage and releasing these therapeutics intracellularly via its pH/redox dual responsiveness. Through CD44-mediated targeting, DOX/siGCN5@HPMSNs increases drug internalization in CD44-overexpressing cancer cells, and markedly promotes DOX retention by down-regulating P-gp expression in drug-resistant cancers through silencing GCN5. Of note, in an MDR breast tumor model, DOX and siGCN5 co-delivered HPMSNs inhibits MDR tumor growth by 77%, abolishes P-gp-mediated drug resistance, and eliminates DOX's systemic toxicity. Thus, the tumor-targeting, stimuli-responsive nanosystem is an effective carrier for co-delivering anticancer drug and siRNA for combating cancer drug resistance. STATEMENT OF SIGNIFICANCE: We designed a tumor-targeting, pH/redox dual-responsive nanosystem (HPMSNs) for chemo-drug and siRNA co-delivery. This nanosystem efficiently co-delivered DOX and siGCN5 into drug-resistant cancer cells and significantly inhibited the tumor growth through: (1) HA shell enhanced the cellular internalization of loaded DOX and siGCN5 via CD44-mediated targeting; (2) the pH/redox dual-responsive nanosystem released the cargos in response to the intracellular environment; (3) the released siGCN5 downregulated P-gp epigenetically. In an MDR breast tumor model (MCF7/ADR), DOX and siGCN5 loaded HPMSNs markedly inhibited tumor growth, almost completely abolished P-gp expression, and minimized systemic toxicity of DOX.

Gut microbiota regulation of P-glycoprotein in the intestinal epithelium in maintenance of homeostasis

BACKGROUND

P-glycoprotein (P-gp) plays a critical role in protection of the intestinal epithelia by mediating efflux of drugs/xenobiotics from the intestinal mucosa into the gut lumen. Recent studies bring to light that P-gp also confers a critical link in communication between intestinal mucosal barrier function and the innate immune system. Yet, despite knowledge for over 10 years that P-gp plays a central role in gastrointestinal homeostasis, the precise molecular mechanism that controls its functional expression and regulation remains unclear. Here, we assessed how the intestinal microbiome drives P-gp expression and function.

RESULTS

We have identified a "functional core" microbiome of the intestinal gut community, specifically genera within the Clostridia and Bacilli classes, that is necessary and sufficient for P-gp induction in the intestinal epithelium in mouse models. Metagenomic analysis of this core microbial community revealed that short-chain fatty acid and secondary bile acid production positively associate with P-gp expression. We have further shown these two classes of microbiota-derived metabolites synergistically upregulate P-gp expression and function in vitro and in vivo. Moreover, in patients suffering from ulcerative colitis (UC), we find diminished P-gp expression coupled to the reduction of epithelial-derived anti-inflammatory endocannabinoids and luminal content (e.g., microbes or their metabolites) with a reduced capability to induce P-gp expression.

CONCLUSION

Overall, by means of both in vitro and in vivo studies as well as human subject sample analysis, we identify a mechanistic link between cooperative functional outputs of the complex microbial community and modulation of P-gp, an epithelial component, that functions to suppress overactive inflammation to maintain intestinal homeostasis. Hence, our data support a new cross-talk paradigm in microbiome regulation of mucosal inflammation. Video abstract.

Effect of sodium butyrate on ABC transporters in lung cancer A549 and colorectal cancer HCT116 cells

Histone deacetylase (HDAC) inhibitors and DNA alkylators are effective components of combination chemotherapy. The aim of the present study was to investigate the possible mechanism of their synergism by detecting the effect of HDAC inhibitors on the expression levels of drug transporters that export DNA alkylators. It was demonstrated that the HDAC inhibitor sodium butyrate (NaB) induced the differential expression of multidrug resistant ATP-binding cassette (ABC) transporters in lung cancer and colorectal cancer cells. Specifically, NaB increased the mRNA expression levels of ABC subfamily B member 1 (ABCB1), ABCC10 and ABCC12, and protein expression levels of multidrug resistance-1 (MDR1), multidrug resistance-associated protein 7 (MRP7) and MRP9. Moreover, NaB decreased the expression levels of ABCC1, ABCC2 and ABCC3 mRNAs, as well as those of MRP1, MRP2 and MRP3 proteins. The molecular mechanism underlying this process was subsequently investigated. NaB decreased the expression of HDAC4, but not HDAC1, HDAC2 or HDAC3. In addition, NaB promoted histone H3 acetylation and methylation at lysine 9, as well as MDR1 acetylation, suggesting that acetylation and methylation may be involved in NaB-mediated ABC transporter expression. Thus, the present results indicated that the synergism of the HDAC inhibitors with the DNA alkylating agents may due to the inhibitory effect of MRPs by HDAC inhibitors. The findings also suggested the possibility of antagonistic effects following the combined treatment of HDAC inhibitors with MDR1 ligands.

Transcription factor NFYA promotes G1/S cell cycle transition and cell proliferation by transactivating cyclin D1 and CDK4 in clear cell renal cell carcinoma

NFYA (nuclear transcription factor Y, subunit A) is a CCAAT-binding transcription factor. Accumulating evidence suggests that NFYA plays an important role in breast, ovarian, lung and gastric cancer. However, the role of NFYA in clear cell renal cell carcinoma (ccRCC) remains unclear. In this study, it was discovered that the expression of NFYA is elevated in tissues of ccRCC patient and high NFYA expression is linked to poor overall survival in ccRCC patient. Inhibition of G1/S cell cycle transition and decreased cell proliferation were observed upon NFYA knockdown in ccRCC cells. Moreover, further investigation revealed that NFYA binds directly to the promoter region of both CDK4 and cyclin D1 (CCND1) thus transactivating their expression, resulting in RB phosphorylation and the activation of subsequent E2F pathway activation. Taken together, these findings imply the oncogenic role of NFYA in ccRCC progression and its potential as a target for ccRCC therapy.

Natural HDAC-1/8 inhibitor baicalein exerts therapeutic effect in CBF-AML

BACKGROUND

Although targeting histone deacetylases (HDACs) may be an effective strategy for core binding factor-acute myeloid leukemia (CBF-AML) harboring t(8;21) or inv(16), HDAC inhibitors are reported to be limited by drug-resistant characteristic. Our purpose is to evaluate the anti-leukemia effects of Baicalein on CBF-AML and clarify its underlying mechanism.

METHODS

Enzyme activity assay was used to measure the activity inhibition of HDACs. Rhodamine123 and RT-qPCR were employed to evaluate the distribution of drugs and the change of ATP-binding cassette (ABC) transporter genes. CCK8, Annexin V/PI, and FACS staining certified the effects of Baicalein on cell growth, apoptosis, and differentiation. Duolink and IP assay assessed the interaction between HDAC-1 and ubiquitin, HSP90 and AML1-ETO, and Ac-p53 and CBFβ-MYH11. AML cell lines and primary AML cells-bearing NOD/SCID mice models were used to evaluate the anti-leukemic efficiency and potential mechanism of Baicalein in vivo.

RESULTS

Baicalein showed HDAC-1/8 inhibition to trigger growth suppression and differentiation induction of AML cell lines and primary AML cells. Although the inhibitory action on HDAC-1 was mild, Baicalein could induce the degradation of HDAC-1 via ubiquitin proteasome pathway, thereby upregulating the acetylation of Histone H3 without promoting ABC transporter genes expression. Meanwhile, Baicalein increased the acetylation of HSP90 and lessened its connection to AML1/ETO, consequently leading to degradation of AML1-ETO in t(8;21)q(22;22) AML cells. In inv(16) AML cells, Baicalein possessed the capacity of apoptosis induction accompanied with p53-mediated apoptosis genes expression. Moreover, CBFβ-MYH11-bound p53 acetylation was restored via HDAC-8 inhibition induced by Baicalein contributing the diminishing of survival of CD34+  inv(16) AML cells.

CONCLUSIONS

These findings improved the understanding of the epigenetic regulation of Baicalein, and warrant therapeutic potential of Baicalein for CBF-AML.

Epigenetic Regulation of Multidrug Resistance Protein 1 and Breast Cancer Resistance Protein Transporters by Histone Deacetylase Inhibition

Multidrug resistance protein 1 (MDR1, ABCB1, P-glycoprotein) and breast cancer resistance protein (BCRP, ABCG2) are key efflux transporters that mediate the extrusion of drugs and toxicants in cancer cells and healthy tissues, including the liver, kidneys, and the brain. Altering the expression and activity of MDR1 and BCRP influences the disposition, pharmacodynamics, and toxicity of chemicals, including a number of commonly prescribed medications. Histone acetylation is an epigenetic modification that can regulate gene expression by changing the accessibility of the genome to transcriptional regulators and transcriptional machinery. Recently, studies have suggested that pharmacological inhibition of histone deacetylases (HDACs) modulates the expression and function of MDR1 and BCRP transporters as a result of enhanced histone acetylation. This review addresses the ability of HDAC inhibitors to modulate the expression and the function of MDR1 and BCRP transporters and explores the molecular mechanisms by which HDAC inhibition regulates these transporters. While the majority of studies have focused on histone regulation of MDR1 and BCRP in drug-resistant and drug-sensitive cancer cells, emerging data point to similar responses in nonmalignant cells and tissues. Elucidating epigenetic mechanisms regulating MDR1 and BCRP is important to expand our understanding of the basic biology of these two key transporters and subsequent consequences on chemoresistance as well as tissue exposure and responses to drugs and toxicants. SIGNIFICANCE STATEMENT: Histone deacetylase inhibitors alter the expression of key efflux transporters multidrug resistance protein 1 and breast cancer resistance protein in healthy and malignant cells.

Restoring Treatment Response in Colorectal Cancer Cells by Targeting MACC1-Dependent ABCB1 Expression in Combination Therapy

Treatment failure of solid cancers, represented by the development of drug resistance in the primary tumor or later outgrowth of drug resistant metastases, is the major cause of death for cancer patients. It represents an urgent clinical need for predictive biomarkers which indicate the success or failure of standard treatment regimens. Besides treatment prediction, interfering with cellular processes associated with drug resistance might improve treatment response by applying combination therapies. Metastasis-associated in colon cancer (MACC) 1 was identified in our group as a prognostic biomarker in human colorectal cancer, and has been established as key player, prognostic, and predictive biomarker for tumor progression and metastasis in a variety of solid cancers. Besides increased cell proliferation and motility, subsequently contributing to growth and metastatic spread of the primary tumor, MACC1 has also been shown to dysregulate apoptosis and is contributing to treatment resistance. Here we report the MACC1 dependent treatment resistance of colorectal cancer (CRC) cells to standard therapeutics like doxorubicin by upregulating ATP-binding cassette subfamily B member 1 (ABCB1) protein. Overexpression of MACC1 in CRC cells increased both its presence on the ABCB1 promoter and its transcriptional activity, resulting in elevated ABCB1 expression and thus treatment resistance to standard therapeutics. In contrast, depleting MACC1 increased intracellular drug concentrations, leading to better treatment response. We already identified the first MACC1 transcriptional inhibitors, such as lovastatin, by high-throughput screening of clinically approved small molecule drugs. These compounds inhibited cell motility in vitro but also restricted metastasis development in xenograft mouse models by reducing MACC1 expression. Here we report, that treating high MACC1 expressing CRC cells with a combination of statins and standard therapeutics increased the rate of cytotoxicity and resulted in higher treatment response.

Transcriptomic analysis reveals different responses to ammonia stress and subsequent recovery between Coilia nasus larvae and juveniles

Excessive ammonia triggered negative effects on aquatic animals' health, growth, and mass death, especially at different developmental periods. However, the underlying responses to ammonia stress in fish larvae and juveniles were much less explored. Transcriptomic analysis of Coilia nasus larvae and juveniles treated with ammonia stress and subsequent recovery in freshwater were performed. Total 958,213,132 clean reads were obtained. A total of 234,830 unigenes with an average length of 1397 bp and N50 value 2521 bp were assembled. 831 and 952 DEGs were identified in C. nasus larvae and juveniles, respectively. Transcriptomic analysis revealed that genes associated with purine metabolism, immune, inflammation, epigenetic modification, and nerve conduction presented different expression trends between C. nasus larvae and juveniles. Other genes related to purine metabolism (XDH) and epigenetic modifications (DNMT1, DNMT3A, and DNMT3B) detected by RT-qPCR also displayed different expression trends. These results indicated that ammonia detoxify strategies and gene regulation patterns were different in C. nasus larvae and juveniles. Higher TNF-α, ILF-2, and ILF-3 expression and reduced LZM, AKP, and ACP activities suggested that inflammation and declined immunity were triggered by ammonia stress. Additionally, nervous conduction was severely affected under ammonia stress in C. nasus juveniles. Furthermore, recovery in freshwater had positive effects on nervous conduction. However, it was worth noting that reduced immunity and inflammation were still existed after recovery in freshwater. In conclusion, our study would be beneficial to reveal the different responses to ammonia stress between larvae and juveniles.

Perplexing Role of P-Glycoprotein in Tumor Microenvironment

Development of multidrug resistance (MDR) still remains a major obstacle to the long-term success of cancer therapy. P-glycoprotein (P-gp) is a well-identified membrane transporter with capability to efflux drug molecules out of the cancer cell leading to reduced efficiency of chemotherapy. Cancer cells upregulate P-gp expression as an adaptive response to evade chemotherapy mediated cell death. While several P-gp inhibitors have been discovered by in silico and pre-clinical studies, very few have successfully passed all phases of the clinical trials. Studies show that application of P-gp inhibitors in cancer therapy regimen following development of MDR achieved limited beneficial outcomes. While, the non-specific substrate binding to P-gp has made the drug-design a challenge, a bigger perplexing challenge comes from its role in tumor immunology. Expression of P-gp was noted immune cell phenotypes with apparently antagonistic functionality. Both pro-tumor MΦ2-macrophages and, anti-tumor NK-cell and Th17/CD4⁺T cell subsets have shown enhanced expression of P-gp. While drug based inhibition of P-gp in pro-tumor immune cell phenotypes could promote tumor elimination, however, it would not be a rational choice to exert inhibition of P-gp on anti-tumor immune cell phenotypes. This mutually exclusive paradigm of P-gp functionality requires a more comprehensive and detailed understanding of its role in tumor microenvironment with active interplay of cancer and immune cells in the tumor mileu. In this review, we focus on the current understanding of the role of P-gp in cancer cells and immune cells and finally attempt to highlight some caveats in the current understanding of its role in comprehensive tumor microenvironment along with challenges in the development of P-gp inhibitors toward anti-cancer therapy.

ABC Transporters in Extrahepatic Tissues: Pharmacological Regulation in Heart and Intestine

ATP binding cassette (ABC) transporters are transmembrane proteins expressed in secretory epithelia like the liver, kidneys and intestine, in the epithelia exhibiting barrier function such as the blood-brain barrier and placenta, and to a much lesser extent, in tissues like reproductive organs, lungs, heart and pancreas, among others. They regulate internal distribution of endogenous metabolites and xenobiotics including drugs of therapeutic use and also participate in their elimination from the body. We here describe the function and regulation of ABC transporters in the heart and small intestine, as examples of extrahepatic tissues, in which ABC proteins play clearly different roles. In the heart, they are involved in tissue pathogenesis as well as in protecting this organ against toxic compounds and druginduced oxidative stress. The small intestine is highly exposed to therapeutic drugs taken orally and, consequently, ABC transporters localized on its surface strongly influence drug absorption and pharmacokinetics. Examples of the ABC proteins currently described are Multidrug Resistance-associated Proteins 1 and 2 (MRP1 and 2) for heart and small intestine, respectively, and P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) for both organs.

Brain region-specific regulation of histone acetylation and efflux transporters in mice

Multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP) protect the brain by restricting the passage of chemicals across the blood-brain barrier. Prior studies have demonstrated the epigenetic regulation of MDR1 and BCRP in cancer cells treated with histone deacetylase (HDAC) inhibitors that enhance histone acetylation and gene transcription. In the present study, we tested the in vivo effects of two HDAC inhibitors, valproic acid (VPA; 400 mg/kg) and apicidin (5 mg/kg), on Mdr1 and Bcrp transporter expression in brain regions of adult male mice injected intraperitoneally daily for 7 days. VPA increased Mdr1 protein expression in the striatum (70%) and Bcrp protein in the midbrain (30%). Apicidin enhanced striatal Mdr1 protein (30%) and hippocampal Bcrp protein (20%). Transporter induction correlated with increased histone H3 acetylation in discrete brain regions. In conclusion, HDAC inhibitors upregulate transporter proteins in vivo, which may be important in regulating regional xenobiotic disposition within the brain.

Increased MDR1 Transporter Expression in Human Brain Endothelial Cells Through Enhanced Histone Acetylation and Activation of Aryl Hydrocarbon Receptor Signaling

Multidrug resistance protein 1 (MDR1, ABCB1, P-glycoprotein) is a critical efflux transporter that extrudes chemicals from the blood-brain barrier (BBB) and limits neuronal exposure to xenobiotics. Prior studies in malignant cells demonstrated that MDR1 expression can be altered by inhibition of histone deacetylases (HDAC), enzymes that modify histone structure and influence transcription factor binding to DNA. Here, we sought to identify the mechanisms responsible for the up-regulation of MDR1 by HDAC inhibitors in human BBB cells. Immortalized human brain capillary endothelial (hCMEC/D3) cells were treated with HDAC inhibitors and assessed for MDR1 expression and function. Of the HDAC inhibitors profiled, valproic acid (VPA), apicidin, and suberoylanilide hydroxamic acid (SAHA) increased MDR1 mRNA and protein levels by 30-200%, which corresponded with reduced intracellular accumulation of the MDR1 substrate rhodamine 123. Interestingly, induction of MDR1 mRNA by HDAC inhibitors mirrored increases in the expression of the aryl hydrocarbon receptor (AHR) and its target gene cytochrome P450 1A1. To explore the role of AHR in HDAC inhibitor-mediated regulation of MDR1, a pharmacological activator (β-naphthoflavone, βNF) and inhibitor (CH-223191, CH) of AHR were tested. The induction of MDR1 in cells treated with SAHA was amplified by βNF and attenuated by CH. Furthermore, SAHA increased the binding of acetylated histone H3K9/K14 and AHR proteins to regions of the MDR1 promoter that contain AHR response elements. In conclusion, HDAC inhibitors up-regulate the expression and activity of the MDR1 transporter in human brain endothelial cells by increasing histone acetylation and facilitating AHR binding at the MDR1 promoter.

Small molecule BKM1972 inhibits human prostate cancer growth and overcomes docetaxel resistance in intraosseous models

Bone metastasis is a major cause of prostate cancer (PCa) mortality. Although docetaxel chemotherapy initially extends patients' survival, in most cases PCa becomes chemoresistant and eventually progresses without a cure. In this study, we developed a novel small-molecule compound BKM1972, which exhibited potent in vitro cytotoxicity in PCa and other cancer cells regardless of their differences in chemo-responsiveness. Mechanistic studies demonstrated that BKM1972 effectively inhibited the expression of anti-apoptotic protein survivin and membrane-bound efflux pump ATP binding cassette B 1 (ABCB1, p-glycoprotein), presumably via signal transducer and activator of transcription 3 (Stat3). BKM1972 was well tolerated in mice and as a monotherapy, significantly inhibited the intraosseous growth of chemosensitive and chemoresistant PCa cells. These results indicate that BKM1972 is a promising small-molecule lead to treat PCa bone metastasis and overcome docetaxel resistance.

Role of Yin Yang-1 (YY1) in the transcription regulation of the multi-drug resistance (MDR1) gene

Resistance to chemotherapy hinders the successful treatment of acute lymphoblastic leukemia (ALL). The multi-drug resistance-1 (MDR1/ABCB1) gene encodes P-glycoprotein (P-gp), which plays an important role in chemoresistance; however, its transcriptional regulation remains unclear. We investigated the role of YY1 in the regulation of MDR1 and its relation to ALL outcomes. Analysis of the MDR1 promoter revealed four putative YY1-binding sites, which we analyzed using a reporter system and ChIP analysis. YY1 silencing resulted in the inhibition of MDR1 expression and function. The clinical roles of YY1 and MDR1 expression were evaluated in children with ALL. Expression of both proteins was increased in ALL patients compared to controls. We identified a positive correlation between YY1 and MDR1 expression. High levels of YY1 were associated with decreased overall survival. Our results demonstrated that YY1 regulates the transcription of MDR1. Therefore, YY1 may serve as a useful prognostic and/or therapeutic target.

Androgen receptor transcriptional activity and chromatin modifications on the ABCB1/MDR gene are critical for taxol resistance in ovarian cancer cells

We report here that the androgen receptor (AR) and ABCB1 are upregulated in a model of acquired taxol resistance (txr) in ovarian carcinoma cells. AR silencing sensitizes txr cells to taxol threefold, whereas ectopic AR expression in AR-null HEK293 cells induces resistance to taxol by 1.7-fold. AR activation using the agonist dihydrotestosterone (DHT) or sublethal taxol treatment upregulates ABCB1 expression in both txr cells and AR-expressing HEK293 cells. In contrast, AR inactivation using the antagonist bicalutamide downregulates ABCB1 expression and enhances cytotoxicity to taxol. A functional ABCB1 promoter containing five predicted androgen-response elements (AREs) is cloned. Deletion assays reveal a taxol-responsive promoter segment which harbors ARE4. Notably, DHT- or taxol-activated AR potentiates binding of the AR to ARE4 as revealed by the chromatin immunoprecipitation. On the other hand, txr cells display an increase in chromatin remodeling. AR/H3K9ac and AR/H3K14ac complexes bind specifically to ARE4 in response to taxol. Furthermore, acetyltransferase protein levels (p300 and GCN5) are upregulated in txr cells. Silencing of p300 or GCN5 reduces chromatin modification and enhances cytotoxicity in both parental and txr SKOV3 cells. While the phosphatidylinositol 3-kinase (PI3K)/serine/threonine protein kinase (AKT) pathway is significantly activated by taxol, taxol-induced ABCB1 expression, histone posttranslational modifications, and p300 binding to ARE4 are suppressed following inhibition of the PI3K/AKT cellular pathway. These results demonstrate that the AKT/p300/AR axis can be activated to target ABCB1 gene expression in response to taxol, thus revealing a new treatment target to counter taxol resistance.

Enhancement of transgene expression by nuclear transcription factor Y and CCCTC-binding factor

If a transgene is effectively delivered to a cell, its expression may still be limited by epigenetic mechanisms that silence the transgene. Indeed, once the transgene reaches the nucleus, it may be bound by histone proteins and condensed into heterochromatin or associated with repressor proteins that block transcription. In this study, we sought to enhance transgene expression by adding binding motifs for several different epigenetic enzymes either upstream or downstream of two promoters (CMV and EF1α). Screening these plasmids revealed that luciferase expression was enhanced 10-fold (10.4 ± 5.8) by the addition of a CCAAT box just upstream of the EF1α promoter to recruit nuclear transcription factor Y (NF-Y), while inserting a CCCTC-binding factor (CTCF) motif downstream of the EF1α promoter enhanced expression at least 14-fold (14.03 ± 6.54). ChIP assays confirmed that NF-Y and CTCF bound to the motifs that were added to each plasmid, but the presence of NF-Y and CTCF did not significantly affect the levels of histone acetylation (H3K9ac) or methylation (H3K9me3). Overall, these results show that transgene expression from the EF1α promoter can be significantly increased with motifs that recruit NF-Y or CTCF. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1581-1588, 2018.

Knockdown of TWIST enhances the cytotoxicity of chemotherapeutic drugs in doxorubicin-resistant HepG2 cells by suppressing MDR1 and EMT

The transcription factor twist family bHLH transcription factor 1 (TWIST), which is a member of the basic helix-loop-helix class of proteins, is known to induce epithelial-mesenchymal transition (EMT) and promote cancer metastasis. TWIST has previously been reported to be associated with multidrug resistance (MDR), since its depletion increases drug sensitivity. Although these previous studies have established a strong association between EMT and MDR, the molecular mechanism remains obscure. The present study demonstrated that TWIST protein expression was elevated in liver cancer, and was positively correlated with multidrug resistance protein 1 (MDR1) expression. Conversely, MDR1 was negatively correlated with E‑cadherin expression in liver cancer samples. In addition, the present study indicated that doxorubicin-resistant HepG2 (R‑HepG2) cells acquired an EMT phenotype. TWIST was also more highly expressed in R‑HepG2 cells compared with in parental HepG2 cells. Knockdown of TWIST increased the sensitivity of R‑HepG2 cells to 5-fluroracil, cisplatin and doxorubicin through a reduction in MDR1 expression and drug efflux ability. Furthermore, knockdown of TWIST in R‑HepG2 cells inhibited the migratory ability of cells and suppressed the EMT phenotype. These findings demonstrated that targeting TWIST may be considered a novel strategy to overcome drug resistance in liver cancer.

The animal nuclear factor Y: an enigmatic and important heterotrimeric transcription factor

Nuclear factor Y (NF-Y) is a heterotrimeric transcription factor with the ability to bind to CCAAT boxes in nearly all eukaryotes and has long been a topic of interest since it is first identified. In plants, due to each subunit of NF-Y is encoded by multiple gene families, there are a wide variety NF-Y complex combinations that fulfill many pivotal functions. However, the animal NF-Y complex usually has only one type of combination, as each subunit is generally encoded by a single gene. Even though, mounting evidence points to that the animal NF-Y complex is also essential for numerous biological processes involved in proliferation and apoptosis, cancer and tumor, stress responses, growth and development. Therefore, a relatively comprehensive functional dissection of animal NF-Y will enable a deeper comprehension of how lesser combinations of the NF-Y complex regulate diverse aspects of biology processes in animal. Here, we focus mainly on reviewing recent advances related to NF-Y in the animal field, including subunit structural characteristics, expression regulation models and biological functions, and we also discuss future directions.

Cloning and Transcriptional Activity Analysis of the Porcine Abcb1 Gene Promoter: Transcription Factor Sp1 Regulates the Expression of Porcine Abcb1

P-Glycoprotein (P-gp, Abcb1) plays a crucial role in drug disposition and functions by hydrolyzing ATP. However, little is known about the regulatory elements governing the transcription of the porcine Abcb1 gene. In this study, the transcription start site of the pig Abcb1 gene was identified by 5'-RACE. A 1.9-kb fragment of the 5'-flanking region of the Abcb1 gene was cloned from pig genomic DNA and sequenced. The region critical for its promoter activity was investigated via progressive deletions. Further, using mutation assays, two proximal Sp1 binding sites within the 5'-flanking region of Abcb1 were proven to be important cis-regulatory elements involved in regulating the constitutive expression of porcine Abcb1. RNA interference experiments showed that Sp1 regulated the expression of the porcine P-gp at both mRNA and protein levels. Hence, the current work provides valuable information on the regulatory mechanisms of pig Abcb1.

LTR12 promoter activation in a broad range of human tumor cells by HDAC inhibition

A considerable proportion of the human genome consists of transposable elements, including the long terminal repeats (LTRs) of endogenous retroviruses. During evolution, such LTRs were occasionally inserted upstream of protein-coding genes, contributing to their regulation. We previously identified the LTR12 from endogenous retrovirus 9 (ERV9) as a regulator of proapoptotic genes such as TP63 or TNFRSF10B. The promoter activity of LTR12 is largely confined to the testes, silenced in testicular carcinoma, but reactivated in testicular cancer cells by broad-range histone deacetylase (HDAC) inhibitors. Here we show that inhibition of HDAC1-3 is sufficient for LTR12 activation. Importantly, HDAC inhibitors induce LTR12 activity not only in testicular cancer cells, but also in cells derived from many additional tumor species. Finally, we characterize the transcription factor NF-Y as a mediator of LTR12 promoter activity and HDAC inhibitor-induced apoptosis, in the context of widespread genomic binding of NF-Y to specific LTR12 sequences. Thus, HDAC inhibitor-driven LTR12 activation represents a generally applicable means to induce proapoptotic genes in human cancer cells.

Growth Hormone Receptor Knockdown Sensitizes Human Melanoma Cells to Chemotherapy by Attenuating Expression of ABC Drug Efflux Pumps

Melanoma remains one of the most therapy-resistant forms of human cancer despite recent introductions of highly efficacious targeted therapies. The intrinsic therapy resistance of human melanoma is largely due to abundant expression of a repertoire of xenobiotic efflux pumps of the ATP-binding cassette (ABC) transporter family. Here, we report that GH action is a key mediator of chemotherapeutic resistance in human melanoma cells. We investigated multiple ABC efflux pumps (ABCB1, ABCB5, ABCB8, ABCC1, ABCC2, ABCG1, and ABCG2) reportedly associated with melanoma drug resistance in different human melanoma cells and tested the efficacy of five different anti-cancer compounds (cisplatin, doxorubicin, oridonin, paclitaxel, vemurafenib) with decreased GH action. We found that GH treatment of human melanoma cells upregulates expression of multiple ABC transporters and increases the EC50 of melanoma drug vemurafenib. Also, vemurafenib-resistant melanoma cells had upregulated levels of GH receptor (GHR) expression as well as ABC efflux pumps. GHR knockdown (KD) using siRNA in human melanoma cells treated with sub-EC50 doses of anti-tumor compounds resulted in significantly increased drug retention, decreased cell proliferation and increased drug efficacy, compared to mock-transfected controls. Our set of findings identify an unknown mechanism of GH regulation in mediating melanoma drug resistance and validates GHR as a unique therapeutic target for sensitizing highly therapy-resistant human melanoma cells to lower doses of anti-cancer drugs.

Targeting CD133 improves chemotherapeutic efficacy of recurrent pediatric pilocytic astrocytoma following prolonged chemotherapy

Background

Pilocytic astrocytomas (PAs) are the most common pediatric central nervous system neoplasms. In the majority of cases these tumors are benign and receive favorable prognosis following gross total surgical resection. In patients with progressive or symptomatic tumors, aggressive surgical resection is generally not feasible, thus radiation or chemotherapy are accepted initial or adjuvant interventions. Due to serious long-lasting side-effects, radiation is limited in young children; therefore, chemotherapy is widely practiced as an adjuvant treatment for these patients. However, chemotherapy can promote the emergence of multidrug resistant tumor cells that are more malignant than those of the original tumor. CD133, a putative stem cell marker in normal tissue and malignant brain tumors, enhances multidrug resistant gene 1 (MDR1) expression following chemotherapy in adult malignant glioblastomas. This study examines the relationship between CD133 and MDR1 in pediatric PAs exposed to chemotherapy, with the goal of identifying therapeutic targets that manifest as a result of chemotherapy.

Methods

Slides were obtained for 15 recurrent PAs, seven of which had received chemotherapy prior to surgical treatment for the recurrent tumor. These samples, as well as primary tumor tissue slides from the same patients were used to investigate CD133 and MDR1 expression via immunofluorescence. Archived frozen tissue samples from the same patients were used to examine CD133, MDR1 and PI3K-Akt-NF-κB signaling mediators, via western blot. Two drug resistant pediatric PA cell lines Res186 and Res199 were also used to evaluate the role of CD133 on cell response to cytotoxic therapy.

Results

CD133 and MDR1 were co-expressed and their expression was elevated in recurrent PAs from patients that had received chemotherapy, compared to patients that had not received chemotherapy. PI3K-Akt-NF-κB signaling mediator expression was also elevated in recurrent, chemotherapy-treated PA. Suppressing CD133 expression with siCD133 decreased levels of PI3K-Akt-NF-κB signaling mediators and MDR1, while increasing cell chemosensitivity, as indicated by quantification of apoptotic cells following chemotherapy.

Conclusions

CD133 contributes to multidrug resistance by regulating MDR1 levels via the PI3K-Akt-NF-κB signal pathway not only in adult glioblastomas, but also in pediatric PAs. Targeting CD133, adjuvant to conventional chemotherapy may improve outcomes for children with recurrent PA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0593-z) contains supplementary material, which is available to authorized users.

MiR-138 indirectly regulates the MDR1 promoter by NF-κB/p65 silencing

MicroRNAs (miRNAs) are known to mediate post-transcriptional gene silencing in the cytoplasm and recent evidence indicates that may also possess nuclear roles in regulating gene expression. A previous study showed that miR-138 is involved in the multidrug resistance of leukemia cells through down-regulation of the drug efflux pump P-glycoprotein (P-gp), the protein encoded by the human multidrug-resistant ABCB1/MDR1 gene. However, the transcriptional regulatory mechanisms responsible remain to be elucidated. To deepen the description of the mechanism of transcriptional gene silencing on the MDR1 promoter, we initially performed a bioinformatics search for potential miR-138 binding sites in the MDR1 gene promoter sequence. Interestingly, we did not find miR-138 binding sites in this region, suggesting an indirect regulation. From six representative transcriptional factors involved in MDR1 gene regulation, an in silico analysis revealed that NF-κB/p65 has a specific binding site for miR-138. The results of luciferase reporter assay, western blot and flow cytometry shown here suggest that miR-138 might modulate the human MDR1 expression by inhibiting NF-κB/p65 as an indirect mechanism of MDR1 regulation. Furthermore, employing the human macrophage-like cell line U937 we observed comparable results with NF-κB/p65 down-regulation and we also observed a significant reduction in the IL-6 and TNF-α mRNA, as well as in their secreted pro-inflammatory cytokines following miR-138 expression, suggesting that canonical NF-κB target genes might also be potential targets for miR-138 in leukemia cells.

NF-Y in cancer: Impact on cell transformation of a gene essential for proliferation

NF-Y is a ubiquitous heterotrimeric transcription factor with a binding affinity for the CCAAT consensus motif, one of the most common cis-acting element in the promoter and enhancer regions of eukaryote genes in direct (CCAAT) or reverse (ATTGG) orientation. NF-Y consists of three subunits, NF-YA, the regulatory subunit of the trimer, NF-YB, and NF-YC, all required for CCAAT binding. Growing evidence in cells and animal models support the notion that NF-Y, driving transcription of a plethora of cell cycle regulatory genes, is a key player in the regulation of proliferation. Proper control of cellular growth is critical for cancer prevention and uncontrolled proliferation is a hallmark of cancer cells. Indeed, during cell transformation aberrant molecular pathways disrupt mechanisms controlling proliferation and many growth regulatory genes are altered in tumors. Here, we review bioinformatics, molecular and functional evidence indicating the involvement of the cell cycle regulator NF-Y in cancer-associated pathways. This article is part of a Special Issue entitled: Nuclear Factor Y in Development and Disease, edited by Prof. Roberto Mantovani.

Diversity, expansion, and evolutionary novelty of plant DNA-binding transcription factor families

Plant transcription factors (TFs) that interact with specific sequences via DNA-binding domains are crucial for regulating transcriptional initiation and are fundamental to plant development and environmental response. In addition, expansion of TF families has allowed functional divergence of duplicate copies, which has contributed to novel, and in some cases adaptive, traits in plants. Thus, TFs are central to the generation of the diverse plant species that we see today. Major plant agronomic traits, including those relevant to domestication, have also frequently arisen through changes in TF coding sequence or expression patterns. Here our goal is to provide an overview of plant TF evolution by first comparing the diversity of DNA-binding domains and the sizes of these domain families in plants and other eukaryotes. Because TFs are among the most highly expanded gene families in plants, the birth and death process of TFs as well as the mechanisms contributing to their retention are discussed. We also provide recent examples of how TFs have contributed to novel traits that are important in plant evolution and in agriculture.This article is part of a Special Issue entitled: Plant Gene Regulatory Mechanisms and Networks, edited by Dr. Erich Grotewold and Dr. Nathan Springer.

MDR1 mediated chemoresistance: BMI1 and TIP60 in action

Chemotherapy-induced emergence of drug resistant cells is frequently observed and is exemplified by the expression of family of drug resistance proteins including, multidrug resistance protein 1 (MDR1). However, a concise mechanism for chemotherapy-induced MDR1 expression is unclear. Mechanistically, mutational selection, epigenetic alteration, activation of the Wnt pathway or impaired p53 function have been implicated. The present study describes that the surviving fraction of cisplatin resistant cells co- upregulate MDR1, BMI1 and acetyl transferase activity of TIP60. Using complementary gain and loss of function approaches, we demonstrate that the expression of MDR1 is positively regulated by BMI1, a stem-cell factor classically known as a transcriptional repressor. Our study establishes a functional interaction between TIP60 and BMI-1 resulting in upregulation of MDR1 expression. Chromatin immunoprecipitation (ChIP) assays further establish that the proximal MDR1 promoter responds to cisplatin in a BMI1 dependent manner. BMI1 interacts with a cluster of E-box elements on the MDR1 promoter and recruits TIP60 resulting in acetylation of histone H2A and H3. Collectively, our data establish a hitherto unknown liaison among MDR1, BMI1 and TIP60 and provide mechanistic insights into cisplatin-induced MDR1 expression resulting in acquired cross-resistance against paclitaxel, doxorubicin and likely other drugs. In conclusion, our results advocate utilizing anti-BMI1 strategies to alleviate acquired resistance to chemotherapy.

Histone acetylation regulates orphan nuclear receptor NR4A1 expression in hypercholesterolaemia

Hypercholesterolaemia and inflammation are correlated with atherogenesis. Orphan nuclear receptor NR4A1, as a key regulator of inflammation, is closely associated with lipid levels in vivo. However, the mechanism by which lipids regulate NR4A1 expression remains unknown. We aimed to elucidate the underlying mechanism of NR4A1 expression in monocytes during hypercholesterolaemia, and reveal the potential role of NR4A1 in hypercholesterolaemia-induced circulating inflammation. Circulating leucocytes were collected from blood samples of 139 patients with hypercholesterolaemia and 139 sex- and age-matched healthy subjects. We found that there was a low-grade inflammatory state and higher expression of NR4A1 in patients. Both total cholesterol and low-density lipoprotein cholesterol levels in plasma were positively correlated with NR4A1 mRNA level. ChIP revealed that acetylation of histone H3 was enriched in the NR4A1 promoter region in patients. Human mononuclear cell lines THP-1 and U937 were treated with cholesterol. Supporting our clinical observations, cholesterol enhanced p300 acetyltransferase and decreased HDAC7 (histone deacetylase 7) recruitment to the NR4A1 promoter region, resulting in histone H3 hyperacetylation and further contributing to NR4A1 up-regulation in monocytes. Moreover, cytosporone B, an NR4A1 agonist, completely reversed cholesterol-induced IL-6 (interleukin 6) and MCP-1 (monocyte chemoattractant protein 1) expression to below basal levels, and knockdown of NR4A1 expression by siRNA not only mimicked, but also exaggerated the effects of cholesterol on inflammatory biomarker up-regulation. Thus we conclude that histone acetylation contributes to the regulation of NR4A1 expression in hypercholesterolaemia, and that NR4A1 expression reduces hypercholesterolaemia-induced inflammation.

ZHX2 enhances the cytotoxicity of chemotherapeutic drugs in liver tumor cells by repressing MDR1 via interfering with NF-YA

We previously reported the tumor suppressor function of Zinc-fingers and homeoboxes 2 (ZHX2) in hepatocellular carcinoma (HCC). Other studies indicate the association of increased ZHX2 expression with improved response to high dose chemotherapy in multiple myeloma. Here, we aim to test whether increased ZHX2 levels in HCC cells repress multidrug resistance 1(MDR1) expression resulting in increased sensitivity to chemotherapeutic drugs. We showed evidence that increased ZHX2 levels correlated with reduced MDR1 expression and enhanced the cytotoxicity of CDDP and ADM in different HCC cell lines. Consistently, elevated ZHX2 significantly reduced ADM efflux in HepG2 cells and greatly increased the CDDP-mediated suppression of liver tumor growth in vivo. Furthermore, immunohistochemical staining demonstrated the inverse correlation of ZHX2 and MDR1 expression in HCC tissues. Luciferase report assay showed that ZHX2 repressed the MDR1 promoter activity, while knockdown of NF-YA or mutating the NF-Y binding site eliminated this ZHX2-mediated repression of MDR1 transcription. Co-IP and ChIP assay further suggested that ZHX2 interacted with NF-YA and reduced NF-Y binding to the MDR1 promoter. Taken together, we clarify that ZHX2 represses NF-Y-mediated activation of MDR1 transcription and, in doing so, enhances the effects of chemotherapeutics in HCC cells both in vitro and in vivo.

A structure-activity relationship of non-peptide macrocyclic histone deacetylase inhibitors and their anti-proliferative and anti-inflammatory activities

Inhibition of the enzymatic activity of histone deacetylase (HDAC) is a promising therapeutic strategy for cancer treatment and several distinct small molecule histone deacetylase inhibitors (HDACi) have been reported. We have previously identified a new class of non-peptide macrocyclic HDACi derived from 14- and 15-membered macrolide skeletons. In these HDACi, the macrocyclic ring is linked to the zinc chelating hydroxamate moiety through a para-substituted aryl-triazole cap group. To further delineate the depth of the SAR of this class of HDACi, we have synthesized series of analogous compounds and investigated the influence of various substitution patterns on their HDAC inhibitory, anti-proliferative and anti-inflammatory activities. We identified compounds 25b and 38f with robust anti-proliferative activities and compound 26f (IC50 47.2 nM) with superior anti-inflammatory (IC50 88 nM) activity relative to SAHA.

Ultraviolet irradiation represses TGF-β type II receptor transcription through a 38-bp sequence in the proximal promoter in human skin fibroblasts

Transforming growth factor-β (TGF-β) is a major regulator of collagen gene expression in human skin fibroblasts. Cellular responses to TGF-β are mediated primarily through its cell surface type I (TβRI) and type II (TβRII) receptors. Ultraviolet (UV) irradiation impairs TGF-β signalling largely due to reduced TβRII gene expression, thereby decreasing type I procollagen synthesis, in human skin fibroblasts. UV irradiation does not alter either TβRII mRNA or protein stability, indicating that UV reduction in TβRII expression likely results from transcriptional or translational repression. To understand how UV irradiation regulates TβRII transcription, we used a series of TβRII promoter-luciferase 5'-deletion constructs (covering 2 kb of the TβRII proximal promoter) to determine transcriptional rate in response to UV irradiation. We identified a 137-bp region upstream of the transcriptional start site that exhibited high promoter activity and was repressed 60% by UV irradiation, whereas all other TβRII promoter reporter constructs exhibited either low promoter activities or no regulation by UV irradiation. Mutation of potential transcription factor binding sites within the promoter region revealed that an inverted CCAAT box (-81 bp from transcription start site) is required for promoter activity. Mutation of the CCAAT box completely abolished UV irradiation regulation of the TβRII promoter. Protein-binding assay, as determined by electrophoretic mobility-shift assays (EMSAs) using the inverted CCAAT box as probe (-100/-62), demonstrated significantly enhanced protein binding in response to UV irradiation. Super shift experiments indicated that nuclear factor Y (NFY) is able to binding to this sequence, but NFY binding was not altered in response to UV irradiation, indicating additional protein(s) are capable of binding this sequence in response to UV irradiation. Taken together, these data indicate that UV irradiation reduces TβRII expression, at least partially, through transcriptional repression. This repression is mediated by a 38-bp sequence in TβRII promoter, in human skin fibroblasts.

Modulation of P-glycoprotein efflux pump: induction and activation as a therapeutic strategy

P-glycoprotein (P-gp) is an ATP-dependent efflux pump encoded by the MDR1 gene in humans, known to mediate multidrug resistance of neoplastic cells to cancer therapy. For several decades, P-gp inhibition has drawn many significant research efforts in an attempt to overcome this phenomenon. However, P-gp is also constitutively expressed in normal human epithelial tissues and, due to its broad substrate specificity, to its cellular polarized expression in many excretory and barrier tissues, and to its great efflux capacity, it can play a crucial role in limiting the absorption and distribution of harmful xenobiotics, by decreasing their intracellular accumulation. Such a defense mechanism can be of particular relevance at the intestinal level, by significantly reducing the intestinal absorption of the xenobiotic and, consequently, avoiding its access to the target organs. In this review, the current knowledge on this important efflux pump is summarized, and a new focus is brought on the therapeutic interest of inducing and/or activating P-gp for limiting the toxicity caused by its substrates. Several in vivo and in vitro studies validating the use of such a therapeutic strategy are discussed. An extensive literature search for reported P-gp inducers/activators and for the experimental models used in their characterization was conducted. Those studies demonstrate that effective antidotal pathways can be achieved by efficiently promoting the P-gp-mediated efflux of deleterious xenobiotics, resulting in a significant reduction in their intracellular levels and, consequently, in a significant reduction of their toxicity.

Identification of trichlormethiazide as a Mdr1a/b gene expression enhancer via a dual secretion-based promoter assay

Transporters of the ATP-binding cassette (ABC) family such as MDR1 play a pivotal role in persistence of brain homeostasis by contributing to the strict permeability properties of the blood–brain barrier. This barrier on one hand compromises treatment of central nervous system diseases by restricting access of drugs; on the other hand, an impaired or altered function of barrier building cells has been described in neurological disorders. The latter might contribute to increased vulnerability of the brain under pathological conditions or even enforce pathogenesis. Here, we present a novel approach for a systematic examination of drug impact on Mdr1 gene expression by establishing a dual reporter gene assay for the murine upstream core promoters of Mdr1a and b. We validated the time-resolved assay in comparison with single reporter gene constructs and applied it to analyze effects of a Food and Drug Administration (FDA)-approved drug library consisting of 627 substances. The chemo-preventive synthetic dithiolethione oltipraz was reidentified with our assay as an already known inducer of Mdr1 gene expression. Together with two newly characterized modifiers – gemcitabine and trichlormethiazide – we prove our findings in a blood–brain barrier culture model as well as in wild-type and Mdr1 knockout mice. In sum, we could demonstrate that our dual reporter gene assay delivers results, which also persist in the living animal and consequently is applicable for further analysis and prediction of Mdr1 regulation in vivo.

MiR-338-3p inhibits hepatocarcinoma cells and sensitizes these cells to sorafenib by targeting hypoxia-induced factor 1α

Hypoxia is a common feature of solid tumors and an important contributor to anti-tumor drug resistance. Hypoxia inducible factor-1 (HIF-1) is one of the key mediators of the hypoxia signaling pathway, and was recently proven to be required for sorafenib resistance in hepatocarcinoma (HCC). MicroRNAs have emerged as important posttranslational regulators in HCC. It was reported that miR-338-3p levels are associated with clinical aggressiveness of HCC. However, the roles of miR-338-3p in HCC disease and resistance to its therapeutic drugs are unknown. In this study, we found that miR-338-3p was frequently down-regulated in 14 HCC clinical samples and five cell lines. Overexpression of miR-338-3p inhibited HIF-1α 3'-UTR luciferase activity and HIF-1α protein levels in HepG2, SMMC-7721, and Huh7 cells. miR-338-3p significantly reduced cell viability and induced cell apoptosis of HCC cells. Additionally, HIF-1α overexpression rescued and HIF-1α knock-down abrogated the anti-HCC activity of miR-338-3p. Furthermore, miR-338-3p sensitized HCC cells to sorafenib in vitro and in a HCC subcutaneous nude mice tumor model by inhibiting HIF-1α. Collectively, miR-338-3p inhibits HCC tumor growth and sensitizes HCC cells to sorafenib by down-regulating HIF-1α. Our data indicate that miR-338-3p could be a potential candidate for HCC therapeutics.

Antagonistic controls of chromatin and mRNA start site selection by Tup family corepressors and the CCAAT-binding factor

The Tup family corepressors contribute to critical cellular responses, such as the stress response and differentiation, presumably by inducing repressive chromatin, though the precise repression mechanism remains to be elucidated. The Schizosaccharomyces pombe fission yeast Tup family corepressors Tup11 and Tup12 (Tup11/12), which are orthologs of Tup1 in Saccharomyces cerevisiae budding yeast and Groucho in Drosophila, negatively control chromatin and the transcriptional activity of some stress-responsive genes. Here, we demonstrate that Tup11/12 repress transcription of a gluconeogenesis gene, fbp1⁺, by three distinct mechanisms. First, Tup11/12 inhibit chromatin remodeling in the fbp1⁺ promoter region where the Atf1 and Rst2 transcriptional activators bind. Second, they repress the formation of an open chromatin configuration at the fbp1⁺ TATA box. Third, they repress mRNA transcription per se by regulating basic transcription factors. These inhibitory actions of Tup11/12 are antagonized by three different types of transcriptional activators: CREB/ATF-type Atf1, C₂H₂zinc finger-type Rst2, and CBF/NF-Y-type Php5 proteins. We also found that impaired chromatin remodeling and fbp1⁺ mRNA transcription in php5Δ strains are rescued by the double deletions of tup11⁺ and tup12⁺, although the distribution of the transcription start sites becomes broader than that in wild-type cells. These data reveal a new mechanism of precise determination of the mRNA start site by Tup family corepressors and CBF/NF-Y proteins.