Transcriptional control of the multi-drug transporter ABCB1 by transcription factor Sp3 in different human tissues

Efflux ABC transporters in drug disposition and their posttranscriptional gene regulation by microRNAs

ATP-binding cassette (ABC) transporters are transmembrane proteins expressed commonly in metabolic and excretory organs to control xenobiotic or endobiotic disposition and maintain their homeostasis. Changes in ABC transporter expression may directly affect the pharmacokinetics of relevant drugs involving absorption, distribution, metabolism, and excretion (ADME) processes. Indeed, overexpression of efflux ABC transporters in cancer cells or bacteria limits drug exposure and causes therapeutic failure that is known as multidrug resistance (MDR). With the discovery of functional noncoding microRNAs (miRNAs) produced from the genome, many miRNAs have been revealed to govern posttranscriptional gene regulation of ABC transporters, which shall improve our understanding of complex mechanism behind the overexpression of ABC transporters linked to MDR. In this article, we first overview the expression and localization of important ABC transporters in human tissues and their clinical importance regarding ADME as well as MDR. Further, we summarize miRNA-controlled posttranscriptional gene regulation of ABC transporters and effects on ADME and MDR. Additionally, we discuss the development and utilization of novel bioengineered miRNA agents to modulate ABC transporter gene expression and subsequent influence on cellular drug accumulation and chemosensitivity. Findings on posttranscriptional gene regulation of ABC transporters shall not only improve our understanding of mechanisms behind variable ADME but also provide insight into developing new means towards rational and more effective pharmacotherapies.

Regulation of P-Glycoprotein in the Brain

Maintenance of the tightly regulated homeostatic environment of the brain is facilitated by the blood-brain barrier (BBB). P-glycoprotein (P-gp), an ATP-binding cassette transporter, is expressed on the luminal surface of the endothelial cells in the BBB, and actively exports a wide variety of substrates to limit exposure of the vulnerable brain environment to waste buildup and neurotoxic compounds. Downregulation of P-gp expression and activity at the BBB have been reported with ageing and in neurodegenerative diseases. Upregulation of P-gp at the BBB contributes to poor therapeutic outcomes due to altered pharmacokinetics of CNS-acting drugs. The regulation of P-gp is highly complex, but unravelling the mechanisms involved may help the development of novel and nuanced strategies to modulate P-gp expression for therapeutic benefit. This review summarises the current understanding of P-gp regulation in the brain, encompassing the transcriptional, post-transcriptional and post-translational mechanisms that have been identified to affect P-gp expression and transport activity.

The Roles of microRNAs in Cancer Multidrug Resistance

Simple Summary

The resistance of neoplastic cells to multiple drugs is a serious problem in cancer chemotherapy. The molecular causes of multidrug resistance in cancer are largely known, but less is known about the mechanisms by which cells deliver phenotypic changes that resist the attack of anticancer drugs. The findings of RNA interference based on microRNAs represented a breakthrough in biology and pointed to the possibility of sensitive and targeted regulation of gene expression at the post-transcriptional level. Such regulation is also involved in the development of multidrug resistance in cancer. The aim of the current paper is to summarize the available knowledge on the role of microRNAs in resistance to multiple cancer drugs.

Abstract

Cancer chemotherapy may induce a multidrug resistance (MDR) phenotype. The development of MDR is based on various molecular causes, of which the following are very common: induction of ABC transporter expression; induction/activation of drug-metabolizing enzymes; alteration of the expression/function of apoptosis-related proteins; changes in cell cycle checkpoints; elevated DNA repair mechanisms. Although these mechanisms of MDR are well described, information on their molecular interaction in overall multidrug resistance is still lacking. MicroRNA (miRNA) expression and subsequent RNA interference are candidates that could be important players in the interplay of MDR mechanisms. The regulation of post-transcriptional processes in the proteosynthetic pathway is considered to be a major function of miRNAs. Due to their complementarity, they are able to bind to target mRNAs, which prevents the mRNAs from interacting effectively with the ribosome, and subsequent degradation of the mRNAs can occur. The aim of this paper is to provide an overview of the possible role of miRNAs in the molecular mechanisms that lead to MDR. The possibility of considering miRNAs as either specific effectors or interesting targets for cancer therapy is also analyzed.

Pharmacodynamic mechanisms of anti-inflammatory drugs on the chemosensitization of multidrug-resistant cancers and the pharmacogenetics effectiveness

Drug resistance as a remarkable issue in cancer treatment is associated with inflammation which occurs through complex chemical reactions in the tumor microenvironment. Recent studies have implicated that glucocorticoids and NSAIDs are mainly useful combinations for inflammatory response modulation in chemotherapeutic protocols for cancer treatment. Immunosuppressive actions of glucocorticoids and NSAIDs are mainly mediated by the transrepression or activation regulation of inflammatory genes with different DNA-bound transcription factors including AP-1, NFAT, NF-κB, STAT and also, varying functions of COX enzymes in cancer cells. Interestingly, many investigations have proved the benefits of these anti-inflammatory agents in the quenching of multidrug resistance pathways. Numerous analyses on the ABC transporter promoters showed conserved nucleotide sequences with several DNA response elements that participate in transcriptional regulation. Furthermore, genetic variations in nucleotide sequences of membrane transporters were strongly associated with changes in these transporters' expression or function and a substantial impact on systemic drug exposure and toxicity. It appeared that several polymorphisms in MDR transporter genes especially MDR1 have influenced the regulatory mechanisms and explained differences in glucocorticoid responses.

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.

10-Phenyltriazoyl Artemisinin is a Novel P-glycoprotein Inhibitor that Suppresses the Overexpression and Function of P-glycoprotein

Background:

The effect of drugs on ATP-binding cassette transporters, especially permeabilityglycoprotein (P-gp), is an important consideration during new anti-cancer drug development.

Objective:

In this context, the effects of a newly synthesized artemisinin derivative, 10-(4-phenyl-1H-1,2,3- triazol)-artemisinin (5a), were evaluated on P-gp expression and function.

Methods:

Reverse transcript polymerase chain reaction and immunoblotting techniques were used to determine the effect of 5a on P-gp expression in LS174T cells. In addition, the ability of 5a to work as either a substrate or an inhibitor of P-gp was investigated through different methods.

Results:

The results revealed that 5a acts as a novel P-gp inhibitor that dually suppresses the overexpression and function of P-glycoprotein. Co-treatment of LS174T cell line, human colon adenocarcinoma cell line, with 5a and paclitaxel recovered the anticancer effect of paclitaxel by controlling the acquired drug resistance pathway. The overexpression of P-gp induced by rifampin and paclitaxel in a colorectal cell line was suppressed by 5a which could be a novel inhibitory substrate inhibiting the transport of paclitaxel by P-gp.

Conclusion:

The results revealed that 5a can be classified as a type B P-gp inhibitor (with both substrate and inhibitor activities) with an additional function of suppressing P-gp overexpression. The results might be clinically useful in the development of anticancer drugs against cancers with multidrug resistance.

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.

Oestrogen-related receptor alpha mediates chemotherapy resistance of osteosarcoma cells via regulation of ABCB1

Chemotherapy resistance is one of the major challenges for the treatment of osteosarcoma (OS). The potential roles of oestrogenic signals in the chemoresistance of OS cells were investigated. As compare to the parental cells, the doxorubicin and cisplatin (CDDP) resistant OS cells had greater levels of oestrogen-related receptors alpha (ERRα). Targeted inhibition of ERRα by its specific siRNAs or inverse agonist XCT-790 can restore the sensitivity of OS resistant cells to chemotherapy. This might be due to that si-ERRα can decrease the expression of P-glycoprotein (P-gp, encoded by ABCB1), one important ABC membrane transporter for drug efflux. XCT-790 can decrease the transcription and mRNA stability of ABCB1, while had no effect on protein stability of P-gp. ERRα can bind to the transcription factor of SP3 to increase the transcription of ABCB1. Furthermore, XCT-790 treatment decreased the expression of miR-9, which can bind to the 3'UTR of ABCB1 and trigger its decay. Collectively, we found that ERRα can regulate the chemoresistance of OS cells via regulating the transcription and mRNA stability of ABCB1. Targeted inhibition of ERRα might be a potential approach for OS therapy.

Promoter Haplotypes of the ABCB1 Gene Encoding the P-Glycoprotein Differentially Affect Its Promoter Activity by Altering Transcription Factor Binding

Promoter single nucleotide polymorphisms (SNPs) of the ABCB1 gene, encoding the placental efflux transporter P-glycoprotein, can alter its expression and affect fetal exposure to therapeutics and environmental xenobiotics. SNPs are not arrayed as independent variants but as combinations forming defined haplotypes. Recently, we defined the haplotypes encompassing ABCB1 promoter SNPs and found that ABCB1 haplotypes differentially affect its promoter activity. The mechanism(s) by which ABCB1 haplotypes alter its promoter activity are not known. We hypothesize that the haplotype-dependent differences in ABCB1 promoter activity are due to haplotype-specific alterations in transcription factor (TF) binding. To test our hypothesis, we used a TF binding profile array and determined whether differences in TF binding exist across different ABCB1 haplotypes. TFs showing significant haplotype binding differences were mechanistically evaluated using small interfering RNA (siRNA) in cultured human placental cells. Our data indicate significant haplotype-dependent differences in TF binding. Our siRNA studies showed that the regulatory effects of TFs on promoter activity are also haplotype dependent. Our data provide a mechanistic explanation for the differential effects of ABCB1 haplotypes on its promoter activity and underscore the importance of evaluating genetic variants in the context of haplotypes rather than individual SNPs when investigating their effects on gene/protein expression and disease risk.

The miR-491-3p/Sp3/ABCB1 axis attenuates multidrug resistance of hepatocellular carcinoma

As one of main obstacles in the treatment and prognosis of hepatocellular carcinoma (HCC), multidrug resistance (MDR) is usually associated with the overexpression of the drug efflux pump P-glycoprotein (P-gp/ABCB1) which is responsible for reducing the intracellular concentration of chemotherapeutic agents. In current work, we discovered the novel role of miR-491-3p in ABCB1-mediated multidrug resistance in HCC and revealed the underlying mechanism in which miR-491-3p downregulated the expression of ABCB1 and its transcription factor Sp3 by directly targeting their 3'-UTR. Moreover, overexpressing ABCB1 or Sp3 reversed the sensitivity to chemotherapeutics in Hep3B cells induced by miR-491-3p, confirming miR-491-3p/Sp3/ABCB1 regulatory loop plays an important role in enhancing the drugs sensitivity of HCC. Meanwhile, the discovery of that the expression level of miR-491-3p was inversely correlated with that of ABCB1 and Sp3 in HCC cell lines and clinical samples pointed out the possibility of miR-491-3p in clinical use. In summary, our results reveal a pivotal role of miR-491-3p in the regulation of MDR in HCC, and suggest the potential application of miR-491-3p as a therapeutic strategy for modulating MDR in cancer cells.

SP and KLF Transcription Factors in Digestive Physiology and Diseases

Specificity proteins (SPs) and Krüppel-like factors (KLFs) belong to the family of transcription factors that contain conserved zinc finger domains involved in binding to target DNA sequences. Many of these proteins are expressed in different tissues and have distinct tissue-specific activities and functions. Studies have shown that SPs and KLFs regulate not only physiological processes such as growth, development, differentiation, proliferation, and embryogenesis, but pathogenesis of many diseases, including cancer and inflammatory disorders. Consistently, these proteins have been shown to regulate normal functions and pathobiology in the digestive system. We review recent findings on the tissue- and organ-specific functions of SPs and KLFs in the digestive system including the oral cavity, esophagus, stomach, small and large intestines, pancreas, and liver. We provide a list of agents under development to target these proteins.

Resveratrol reverses P-glycoprotein-mediated multidrug resistance of U2OS/ADR cells by suppressing the activation of the NF-κB and p38 MAPK signaling pathways

The present study aimed to investigate the reversal effect of resveratrol on the phenomenon of multidrug resistance in U2OS/adriamycin (ADR) cells and to clarify the molecular mechanisms. To examine the cell survival and half-inhibitory concentration (IC50) of ADR in U2OS and U2OS/ADR cells, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used. The accumulation of ADR in U2OS and U2OS/ADR cells was investigated by flow cytometry. Reverse transcription-quantitative polymerase chain reaction and western blot analysis were used to detect the expression of multidrug resistance protein 1 (MDR1), P-glycoprotein (P-gp), p65 and p38. Compared with U2OS cells, the IC50 value of ADR was significantly increased in U2OS/ADR cells, which exhibited high levels of MDR1/P-gp. However, resveratrol could drastically reduce the IC50 value of ADR and the expression of MDR1/P-gp, and increased the accumulation of ADR in U2OS/ADR cells. In addition, the expression levels of p38 (phosphorylated) and p65 (acetylated and total) in U2OS/ADR cells were also significantly suppressed by resveratrol. These results suggested that the nuclear factor (NF)-κB and p38 mitogen-activated protein kinase (MAPK) signaling pathways are correlated with ADR-induced drug resistance in U2OS/ADR cells. Furthermore, resveratrol could downregulate the expression of MDR1/P-gp and reverse the drug resistance phenomenon in U2OS/ADR cells partly at least by suppressing the activation of the NF-κB and p38 MAPK signaling pathways.

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.

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.