Real-time reverse transcription-PCR expression profiling of the complete human ATP-binding cassette transporter superfamily in various tissues

Delayed endometrial preparation for the induction of luteolysis as a potential factor for improved reproductive performance in Angus beef heifers with high antral follicle counts†

Antral follicle count (AFC) and anti-Müllerian hormone (AMH) concentrations are reflective for ovarian reserve and have been associated with improved reproductive performance in cattle. Key events for regulation of uterine receptivity are orchestrated by progesterone. As progesterone concentrations are greater in animals with high than low AFC, we tested the hypothesis, if the resulting improved uterine environment will lead to improved conceptus elongation and endometrial response to interferon tau. For four years, 10 heifers with lowest and highest AFC, respectively, were selected from 120 heifers. Reproductive tracts and blood samples for progesterone and AMH analysis were collected after synchronization and insemination. For a recovered conceptus, length was determined, and interferon tau (IFNT) transcript abundance was analyzed. Endometrial transcript abundance of interferon-stimulated gene 15 (ISG15) and oxytocin receptor (OXTR) were analyzed. Progesterone concentrations did not differ between low and high AFC groups (P = 0.1). A difference in conceptus length was not observed. Endometrial abundance of ISG15 did not differ between pregnant low and high AFC heifers. Abundance of OXTR was greater in open low AFC than open high AFC heifers (P < 0.01). Interaction of AMH and pregnancy status was determined, with greater AMH in pregnant than open high AFC heifers (P < 0.05). Improved uterine environment in high vs. low AFC heifers did not result in longer conceptuses or improved endometrial response. As the increase in OXTR transcript abundance was only detected in low AFC heifers, reported differences in reproductive performance might be associated with earlier initiation of luteolysis.

Enhancing of cerebral Abeta clearance by modulation of ABC transporter expression: a review of experimental approaches

Clearance of amyloid-beta (Aβ) from the brain is impaired in both early-onset and late-onset Alzheimer's disease (AD). Mechanisms for clearing cerebral Aβ include proteolytic degradation, antibody-mediated clearance, blood brain barrier and blood cerebrospinal fluid barrier efflux, glymphatic drainage, and perivascular drainage. ATP-binding cassette (ABC) transporters are membrane efflux pumps driven by ATP hydrolysis. Their functions include maintenance of brain homeostasis by removing toxic peptides and compounds, and transport of bioactive molecules including cholesterol. Some ABC transporters contribute to lowering of cerebral Aβ. Mechanisms suggested for ABC transporter-mediated lowering of brain Aβ, in addition to exporting of Aβ across the blood brain and blood cerebrospinal fluid barriers, include apolipoprotein E lipidation, microglial activation, decreased amyloidogenic processing of amyloid precursor protein, and restricting the entrance of Aβ into the brain. The ABC transporter superfamily in humans includes 49 proteins, eight of which have been suggested to reduce cerebral Aβ levels. This review discusses experimental approaches for increasing the expression of these ABC transporters, clinical applications of these approaches, changes in the expression and/or activity of these transporters in AD and transgenic mouse models of AD, and findings in the few clinical trials which have examined the effects of these approaches in patients with AD or mild cognitive impairment. The possibility that therapeutic upregulation of ABC transporters which promote clearance of cerebral Aβ may slow the clinical progression of AD merits further consideration.

Peroxisome Proliferator-Activated Receptor α in Lipoprotein Metabolism and Atherosclerotic Cardiovascular Disease

Peroxisome proliferator-activated receptors (PPARs) are a group of ligand-binding transcription factors with pivotal action in regulating pleiotropic signaling pathways of energetic metabolism, immune responses and cell proliferation and differentiation. A significant body of evidence indicates that the PPARα receptor is an important modulator of plasma lipid and lipoprotein metabolism, with pluripotent effects influencing the lipid and apolipoprotein cargo of both atherogenic and antiatherogenic lipoproteins and their functionality. Clinical evidence supports an important role of PPARα agonists (fibric acid derivatives) in the treatment of hypertriglyceridemia and/or low high-density lipoprotein (HDL) cholesterol levels, although the effects of clinical trials are contradictory and point to a reduction in the risk of nonfatal and fatal myocardial infarction events. In this manuscript, we provide an up-to-date critical review of the existing relevant literature.

The Expression and Effect of ABCE1 in Gastric Adenocarcinoma

ATP-binding cassette E1 (ABCE1) is mainly related to the regulation of viral infection, cell multiplication, and anti-apoptosis. Previous reports confirmed the central role in the regulation of ABCE1 in liver and breast cancer; however, its potential role in gastric adenocarcinoma remains unclear. In our study, siRNA and plasmid were transfected to construct gastric cancer cell lines with low and overexpression of ABCE1, and Western blot, RT-qPCR, and immunohistochemical staining were used to detect ABCE1 expression levels in gastric cancer tissues and cell lines. The effects of ABCE1 on cell growth, metastasis, invasion, cell cycle, and drug resistance were investigated using CCK-8 test, wound healing assay, and clone formation experiment. Functional experiments indicated that si-ABCE1 decreased the proliferation, metastasis, and invasion of gastric adenocarcinoma. Meanwhile, si-ABCE1 has significantly promoted EMT process and enhanced the sensitivity of paclitaxel and cisplatin. In vivo experiments also confirmed that si-ABCE1 group had significantly smaller tumors, and immunohistochemical staining results showed the tumor growth in si-ABCE1 group was reduced obviously. In summary, we found ABCE1 is considered as a crucial role in the evolution of gastric adenocarcinoma and could be a viable therapeutic target for the disease.

Drug delivery strategies for management of women's health issues in the upper genital tract

The female upper genital tract (UGT) hosts important reproductive organs including the cervix, uterus, fallopian tubes, and ovaries. Several pathologies affect these organ systems such as infections, reproductive issues, structural abnormalities, cancer, and inflammatory diseases that could have significant impact on women's overall health. Effective disease management is constrained by the multifaceted nature of the UGT, complex anatomy and a dynamic physiological environment. Development of drug delivery strategies that can overcome mucosal and safety barriers are needed for effective disease management. This review introduces the anatomy, physiology, and mucosal properties of the UGT and describes drug delivery barriers, advances in drug delivery technologies, and opportunities available for new technologies that target the UGT.

Oxidative Stress and the Neurovascular Unit

The neurovascular unit (NVU) is a relatively recent concept that clearly describes the relationship between brain cells and their blood vessels. The components of the NVU, comprising different types of cells, are so interrelated and associated with each other that they are considered as a single functioning unit. For this reason, even slight disturbances in the NVU could severely affect brain homeostasis and health. In this review, we aim to describe the current state of knowledge concerning the role of oxidative stress on the neurovascular unit and the role of a single cell type in the NVU crosstalk.

The Role of ABC Transporters in Lipid Metabolism and the Comorbid Course of Chronic Obstructive Pulmonary Disease and Atherosclerosis

Chronic obstructive pulmonary disease (COPD) ranks among the leading causes of morbidity and mortality worldwide. COPD rarely occurs in isolation and is often combined with various diseases. It is considered that systemic inflammation underlies the comorbid course of COPD. The data obtained in recent years have shown the importance of violations of the cross-links of lipid metabolism and the immune response, which are links in the pathogenesis of both COPD and atherosclerosis. The role of lipid metabolism disorders in the pathogenesis of the comorbid course of COPD and atherosclerosis and the participation of ATP-binding cassette (ABC) transporters in these processes is discussed in this article. It is known that about 20 representatives of a large family of ABC transporters provide lipid homeostasis of cells by moving lipids inside the cell and in its plasma membrane, as well as removing lipids from the cell. It was shown that some representatives of the ABC-transporter family are involved in various links of the pathogenesis of COPD and atherosclerosis, which can determine their comorbid course.

The Physiological Roles of Vitamin E and Hypovitaminosis E in the Transition Period of High-Yielding Dairy Cows

Simple Summary

In high-yield cows, most production diseases occur during transition periods. Alpha-tocopherol, the most biologically active form of vitamin E, declines in blood and reaches the lowest levels (hypovitaminosis E) around calving. Hypovitaminosis E is associated with the incidence of peripartum diseases. Therefore, many studies which have been published for more than 30 years have investigated the effects of α-tocopherol supplementation. This α-tocopherol deficiency was thought to be caused by complex factors. However, until recently, the physiological factors or pathways underlying hypovitaminosis E in the transition period have been poorly understood. In the last 10 years, the α-tocopherol-related genes expression, which regulate the metabolism, transportation, and tissue distribution of α-tocopherol in humans and rodents, has been reported in ruminant tissues. In this paper, we discuss at least six physiological phenomena that occur during the transition period and may be candidate factors predisposing to a decreased blood α-tocopherol level and hypovitaminosis E with changes in α-tocopherol-related genes expression.

Abstract

Levels of alpha-tocopherol (α-Toc) decline gradually in blood throughout prepartum, reaching lowest levels (hypovitaminosis E) around calving. Despite numerous reports about the disease risk in hypovitaminosis E and the effect of α-Toc supplementation on the health of transition dairy cows, its risk and supplemental effects are controversial. Here, we present some novel data about the disease risk of hypovitaminosis E and the effects of α-Toc supplementation in transition dairy cows. These data strongly demonstrate that hypovitaminosis E is a risk factor for the occurrence of peripartum disease. Furthermore, a study on the effectiveness of using serum vitamin levels as biomarkers to predict disease in dairy cows was reported, and a rapid field test for measuring vitamin levels was developed. By contrast, evidence for how hypovitaminosis E occurred during the transition period was scarce until the 2010s. Pioneering studies conducted with humans and rodents have identified and characterised some α-Toc-related proteins, molecular players involved in α-Toc regulation followed by a study in ruminants from the 2010s. Based on recent literature, the six physiological factors: (1) the decline in α-Toc intake from the close-up period; (2) changes in the digestive and absorptive functions of α-Toc; (3) the decline in plasma high-density lipoprotein as an α-Toc carrier; (4) increasing oxidative stress and consumption of α-Toc; (5) decreasing hepatic α-Toc transfer to circulation; and (6) increasing mammary α-Toc transfer from blood to colostrum, may be involved in α-Toc deficiency during the transition period. However, the mechanisms and pathways are poorly understood, and further studies are needed to understand the physiological role of α-Toc-related molecules in cattle. Understanding the molecular mechanisms underlying hypovitaminosis E will contribute to the prevention of peripartum disease and high performance in dairy cows.

The effect of gut microbiota on the intestinal lipidome of mice

Gut microbiota significantly influence the plasma and liver lipidome. An interconnecting metabolite is acetate generated after degradation and fermentation of dietary fiber by the gut microbiota, which is metabolized in the liver into longer chain fatty acids and complex lipids reaching the circulation. Whether these systemic changes are accompanied by alternations of the intestinal lipidome is unclear. Therefore, we quantified glycerophospholipids, sphingolipids and sterols in ileum and colon, the two segments containing the highest densities of microbes in the gastrointestinal tract, of germfree and specific pathogen free mice using mass spectrometry-based lipidomics. We found that the presence of gut microbes lowers the free cholesterol content in colon while elevating phosphatidylcholine levels. Further, PUFA-containing phosphatidylcholine and -ethanolamine fractions are increased in ileum and colon of germfree compared to SPF mice. A total fatty acid analysis by GC-MS revealed higher levels of arachidonic and docosahexaenoic acid in the ileum of germfree mice indicating that the gut microbiota inhibits PUFA metabolism in the small intestine.

The Bile Salt Export Pump: Molecular Structure, Study Models and Small-Molecule Drugs for the Treatment of Inherited BSEP Deficiencies

The bile salt export pump (BSEP/ABCB11) is responsible for the transport of bile salts from hepatocytes into bile canaliculi. Malfunction of this transporter results in progressive familial intrahepatic cholestasis type 2 (PFIC2), benign recurrent intrahepatic cholestasis type 2 (BRIC2) and intrahepatic cholestasis of pregnancy (ICP). Over the past few years, several small molecular weight compounds have been identified, which hold the potential to treat these genetic diseases (chaperones and potentiators). As the treatment response is mutation-specific, genetic analysis of the patients and their families is required. Furthermore, some of the mutations are refractory to therapy, with the only remaining treatment option being liver transplantation. In this review, we will focus on the molecular structure of ABCB11, reported mutations involved in cholestasis and current treatment options for inherited BSEP deficiencies.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

ABCB transporters in a leaf beetle respond to sequestered plant toxins

Phytophagous insects can tolerate and detoxify toxic compounds present in their host plants and have evolved intricate adaptations to this end. Some insects even sequester the toxins for their defence. This necessitates specific mechanisms, especially carrier proteins that regulate uptake and transport to specific storage sites or protect sensitive tissues from noxious compounds. We identified three ATP-binding cassette subfamily B (ABCB) transporters from the transcriptome of the cardenolide-sequestering leaf beetle Chrysochus auratus and analysed their functional role in the sequestration process. These were heterologously expressed and tested for their ability to interact with various potential substrates: verapamil (standard ABCB substrate), the cardenolides digoxin (commonly used), cymarin (present in the species's host plant) and calotropin (present in the ancestral host plants). Verapamil stimulated all three ABCBs and each was activated by at least one cardenolide, however, they differed as to which they were activated by. While the expression of the most versatile transporter fits with a protective role in the blood-brain barrier, the one specific for cymarin shows an extreme abundance in the elytra, coinciding with the location of the defensive glands. Our data thus suggest a key role of ABCBs in the transport network needed for cardenolide sequestration.

Physiological responses to cold and starvation stresses in the liver of yellow drum (Nibea albiflora) revealed by LC-MS metabolomics

As global climate changes, mass mortality in farmed fish associated with the severely cold weather has aroused growing concerns. Yellow drum (Nibea albiflora) is an important maricultured fish in China, whereby its aquaculture suffered from overwinter mortality associated with cold and cold-induced-fasting stresses. Here, by using LC-MS metabolomics combined with transcriptomics, we investigated the physiological responses of yellow drum liver to cold and starvation stresses. The experiment involved four groups: 16 °C fed group (CG1), 16 °C unfed group (CG2), 8 °C fed group (EG1), and 8 °C unfed group (EG2). Under cold stress, a total of 308 and 257 differential metabolites were identified in EG1 vs. CG1 and EG2 vs. CG2, respectively, showing 5 overlapping significant pathways: glutathione metabolism, biosynthesis of unsaturated fatty acids, galactose metabolism, arginine and proline metabolism, and ABC transporters. Intersection analysis identified that glutamate, oxidized glutathione (GSSG), and eicosenoic acid were the common metabolites induced by cold stress. Under starvation stress, a total of 300 and 215 differential metabolites were identified in CG2 vs. CG1 and EG2 vs. EG1, respectively, showing 2 overlapping significant pathways: glutathione metabolism and galactose metabolism. Intersection analysis revealed that glutamate and GSSG were the common metabolites caused by fasting. Under cold and starvation combined stresses, 286 differential metabolites were identified in EG2 vs. CG1, showing 7 influenced pathways: glycerophospholipid metabolism, biosynthesis of unsaturated fatty acids, glutathione metabolism, sphingolipid metabolism, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, autophagy, and purine metabolism. Interestingly, the glutamate and GSSG were induced by both single and combined stresses of cold and starvation treatments. These findings suggest that glutathione metabolism and its related metabolites (glutamate and GSSG) could be potential biomarkers of cold and starvation stresses in yellow drum. Overall, the results of this study provided insights into the physiological regulation in response to cold and starvation stresses in this fish.

In-depth proteome analysis of more than 12,500 proteins in buffalo mammary epithelial cell line identifies protein signatures for active proliferation and lactation

The mature mammary gland is made up of a network of ducts that terminates in alveoli. The innermost layer of alveoli is surrounded by the differentiated mammary epithelial cells (MECs), which are responsible for milk synthesis and secretion during lactation. However, the MECs are in a state of active proliferation during pregnancy, when they give rise to network like structures in the mammary gland. Buffalo (Bubalus bubalis) constitute a major source of milk for human consumption, and the MECs are the major precursor cells which are mainly responsible for their lactation potential. The proteome of MECs defines their functional state and suggests their role in various cellular activities such as proliferation and lactation. To date, the proteome profile of MECs from buffalo origin is not available. In the present study, we have profiled in-depth proteome of in vitro cultured buffalo MECs (BuMECs) during active proliferation using high throughput tandem mass spectrometry (MS). MS analysis identified a total of 8330, 5970, 5289, 4818 proteins in four sub-cellular fractions (SCFs) that included cytosolic (SCF-I), membranous and membranous organelle’s (SCF-II), nuclear (SCF-III), and cytoskeletal (SCF-IV). However, 792 proteins were identified in the conditioned media, which represented the secretome. Altogether, combined analysis of all the five fractions (SCFs- I to IV, and secretome) revealed a total of 12,609 non-redundant proteins. The KEGG analysis suggested that these proteins were associated with 325 molecular pathways. Some of the highly enriched molecular pathways observed were metabolic, MAPK, PI3-AKT, insulin, estrogen, and cGMP-PKG signalling pathway. The newly identified proteins in this study are reported to be involved in NOTCH signalling, transport and secretion processes.

Characterizing Iranian Pediatric Patients With Relapsed Acute Lymphoblastic Leukemia Through Gene Expression Profiling of Common ATP Binding Cassette Transporters Subfamily C

BACKGROUND

The correlation between gene expression of ABCC transporters and recurrence as a treatment failure in pediatric patients with acute lymphoblastic leukemia (ALL) is an unsolved problem in scientific associations. The aim of this study was to evaluate the predictive value of ABCC1-6 gene expression pattern for estimating recurrence in Iranian pediatric patients with ALL.

MATERIALS AND METHODS

Iranian pediatric patients with approved ALL enrolled in this study as 2 groups of case (relapsed ALL) and control (treated individuals who lasted for >3 years following their final treatment). Real-time polymerase chain reaction was done with GAPDH for expressing ABCC1-6 transporter genes. Cumulative doses of Vincristine, Daunorubicin, and L-Asparginase were checked for each patient. Gathered data analyzed with SPSS version 22 and REST 2009 software.

RESULTS

Thirty-nine samples as 23 relapsed ALL and 16 controls enrolled. High expression of ABCC2-6 and low expression of ABCC1 were detected in pediatric patients with relapse. ABCC3 and ABCC4 had significant relation with high-risk patients of NCI group. Also, ABCC4 and ABCC6 had more expression with high doses of Daunorubicin and L-Asparginase.

CONCLUSIONS

Designed expression pattern have the predictive value for estimating of conferring relapse in Iranian pediatric patients with diagnosed ALL. The authors suggest of designing a multiple childhood malignancy center project to evaluate this pattern in a cohort study.

Comparative Loss-of-Function Screens Reveal ABCE1 as an Essential Cellular Host Factor for Efficient Translation of Paramyxoviridae and Pneumoviridae

The Paramyxoviridae and Pneumoviridae families include important human and animal pathogens. To identify common host factors, we performed genome-scale siRNA screens with wild-type-derived measles, mumps, and respiratory syncytial viruses in the same cell line. A comparative bioinformatics analysis yielded different members of the coatomer complex I, translation factors ABCE1 and eIF3A, and several RNA binding proteins as cellular proteins with proviral activity for all three viruses. A more detailed characterization of ABCE1 revealed its essential role for viral protein synthesis. Taken together, these data sets provide new insight into the interactions between paramyxoviruses and pneumoviruses and host cell proteins and constitute a starting point for the development of broadly effective antivirals.

Paramyxoviruses and pneumoviruses have similar life cycles and share the respiratory tract as a point of entry. In comparative genome-scale siRNA screens with wild-type-derived measles, mumps, and respiratory syncytial viruses in A549 cells, a human lung adenocarcinoma cell line, we identified vesicular transport, RNA processing pathways, and translation as the top pathways required by all three viruses. As the top hit in the translation pathway, ABCE1, a member of the ATP-binding cassette transporters, was chosen for further study. We found that ABCE1 supports replication of all three viruses, confirming its importance for viruses of both families. More detailed characterization revealed that ABCE1 is specifically required for efficient viral but not general cellular protein synthesis, indicating that paramyxoviral and pneumoviral mRNAs exploit specific translation mechanisms. In addition to providing a novel overview of cellular proteins and pathways that impact these important pathogens, this study highlights the role of ABCE1 as a host factor required for efficient paramyxovirus and pneumovirus translation.

Nonglucuronidated Ezetimibe Disrupts CD13- and CD64-Coassembly in Membrane Microdomains and Decreases Cellular Cholesterol Content in Human Monocytes/Macrophages

Ezetimibe (EZE) and glucuronidated EZE (EZE-Glu) differentially target Niemann-Pick C1-like 1 (NPC1L1) and CD13 (aminopeptidase-N) to inhibit intestinal cholesterol absorption and cholesterol processing in other cells, although the precise molecular mechanisms are not fully elucidated. Cellular effects of EZE, EZE-Glu, and the low-absorbable EZE-analogue S6130 were investigated on human monocyte-derived macrophages upon loading with atherogenic lipoproteins. EZE and S6130, but not EZE-Glu disturbed the colocalization of CD13 and its coreceptor CD64 (Fcγ receptor I) in membrane microdomains, and decreased the presence of both receptors in detergent-resistant membrane fractions. Biotinylated cholesterol absorption inhibitor C-5 (i.e., derivative of EZE) was rapidly internalized to perinuclear tubular structures of cells, resembling endoplasmic reticulum (ER), but CD13 was detected on extracellular sites of the plasma membrane and endolysosomal vesicles. Administration of EZE, but not of EZE-Glu or S6130, was associated with decreased cellular cholesteryl ester content, indicating the sterol-O acyltransferase 1 (SOAT1)-inhibition by EZE. Furthermore, EZE decreased the expression of molecules involved in cholesterol uptake and synthesis, in parallel with increased apolipoprotein A-I-mediated cholesterol efflux and upregulation of efflux-effectors. However, NPC1L1 the other claimed molecular target of EZE, was not detected in macrophages, thereby excluding this protein as target for EZE in macrophages. Thus, EZE is very likely a CD13-linked microdomain-disruptor and SOAT1-inhibitor in macrophages leading to in vitro anti-atherosclerotic effects through a decrease of net cellular cholesterol content. © 2019 International Society for Advancement of Cytometry.

Abcc6 deficiency in mice leads to altered ABC transporter gene expression in metabolic active tissues

Background

ATP-binding cassette (ABC) transporters are involved in a huge range of physiological processes. Mutations in the ABCC6 gene cause pseudoxanthoma elasticum, a metabolic disease with progressive soft tissue calcification.

Methods

The aim of the present study was to analyze gene expression levels of selected ABC transporters associated with cholesterol homeostasis in metabolic active tissues, such as the liver, kidney and white adipose tissue (WAT) of Abcc6^−/− mice from an early and late disease stage (six-month-old and 12-month-old mice).

Results

The strongest regulation of ABC transporter genes was observed in the liver tissue of six-month-old Abcc6^−/− mice. Here, we found a significant increase of mRNA expression levels of phospholipid, bile salt and cholesterol/sterol transporters Abcb1b, Abcb11, Abcg1, Abcg5 and Abcg8. Abcd2 mRNA expression was increased by 3.2-fold in the liver tissue. We observed strong upregulation of Abca3 and Abca1 mRNA expression up to 3.3-fold in kidney and WAT, and a 2-fold increase of Abca9 mRNA in the WAT of six-month-old Abcc6 knockout mice. Gene expression levels of Abcb1b and Abcg1 remained increased in the liver tissue after an age-related disease progression, while we observed lower mRNA expression of Abca3 and Abca9 in the kidney and WAT of 12-month-old Abcc6^−/− mice.

Conclusions

These data support previous findings that Abcc6 deficiency leads to an altered gene expression of other ABC transporters depending on the status of disease progression. The increased expression of fatty acid, bile salt and cholesterol/sterol transporters may be linked to an altered cholesterol and lipoprotein metabolism due to a loss of Abcc6 function.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0943-x) contains supplementary material, which is available to authorized users.

Beyond Competitive Inhibition: Regulation of ABC Transporters by Kinases and Protein-Protein Interactions as Potential Mechanisms of Drug-Drug Interactions

ATP-binding cassette (ABC) transporters are transmembrane efflux transporters mediating the extrusion of an array of substrates ranging from amino acids and lipids to xenobiotics, and many therapeutic compounds, including anticancer drugs. The ABC transporters are also recognized as important contributors to pharmacokinetics, especially in drug-drug interactions and adverse drug effects. Drugs and xenobiotics, as well as pathologic conditions, can influence the transcription of ABC transporters, or modify their activity or intracellular localization. Kinases can affect the aforementioned processes for ABC transporters as do protein interactions. In this review, we focus on the ABC transporters ABCB1, ABCB11, ABCC1, ABCC4, and ABCG2 and illustrate how kinases and protein-protein interactions affect these transporters. The clinical relevance of these factors is currently unknown; however, these examples suggest that our understanding of drug-drug interactions will benefit from further knowledge of how kinases and protein-protein interactions affect ABC transporters.

Gene Expression and Methylation Analysis of ABCA7 in Patients with Alzheimer's Disease

BACKGROUND/OBJECTIVE

The aim of this study was to examine the blood gene expression and methylation of ATP-binding cassette sub-family A member 7 gene (ABCA7) as a biological marker of AD.

METHODS

AD subjects (n = 50; 11 males, 77.7±6.05 years old) and age- and sex-matched healthy controls (n = 50) were recruited. A single nucleotide polymorphism in ABCA7 (rs3764650), methylation rates of CpG sites in the ABCA7 promoter region, and ABCA7 mRNA expression levels in peripheral blood were examined.

RESULTS

The distribution of the rs3764650 polymorphism in AD subjects was not different from that of controls. Although the methylation rates of AD subjects were not significantly different from those of controls, the ABCA7 mRNA expression level in AD subjects was significantly higher than that in controls. Additionally, the ABCA7 mRNA expression level in AD subjects was significantly correlated with Mini-Mental State Examination recall, the Alzheimer's Disease Assessment Scale total score, and the Clinical Dementia Rating score. We also found a significant correlation between the ABCA7 mRNA expression level and duration of illness.

CONCLUSION

The ABCA7 mRNA expression level in peripheral blood may be a marker for early stages of AD and disease progression regardless of rs3764650 and the methylation rate of its promoter.

MDR1 and BCRP Transporter-Mediated Drug-Drug Interaction between Rilpivirine and Abacavir and Effect on Intestinal Absorption

Rilpivirine (TMC278) is a highly potent nonnucleoside reverse transcriptase inhibitor (NNRTI) representing an effective component of combination antiretroviral therapy (cART) in the treatment of HIV-positive patients. Many antiretroviral drugs commonly used in cART are substrates of ATP-binding cassette (ABC) and/or solute carrier (SLC) drug transporters and, therefore, are prone to pharmacokinetic drug-drug interactions (DDIs). The aim of our study was to evaluate rilpivirine interactions with abacavir and lamivudine on selected ABC and SLC transporters in vitro and assess its importance for pharmacokinetics in vivo Using accumulation assays in MDCK cells overexpressing selected ABC or SLC drug transporters, we revealed rilpivirine as a potent inhibitor of MDR1 and BCRP, but not MRP2, OCT1, OCT2, or MATE1. Subsequent transport experiments across monolayers of MDCKII-MDR1, MDCKII-BCRP, and Caco-2 cells demonstrated that rilpivirine inhibits MDR1- and BCRP-mediated efflux of abacavir and increases its transmembrane transport. In vivo experiments in male Wistar rats confirmed inhibition of MDR1/BCRP in the small intestine, leading to a significant increase in oral bioavailability of abacavir. In conclusion, rilpivirine inhibits MDR1 and BCRP transporters and may affect pharmacokinetic behavior of concomitantly administered substrates of these transporters, such as abacavir.

Lipidomic and metabolic changes in the P4-type ATPase ATP10D deficient C57BL/6J wild type mice upon rescue of ATP10D function

Background

Sequence variants near the human gene for P4-type ATPase, class V, type 10D (ATP10D) were shown to significantly associate with circulating hexosylceramide d18:1/16:0 and d18:1/24:1 levels, obesity, insulin resistance, plasma high density lipoprotein (HDL), coronary stenotic index and intracranial atherosclerotic index. In mice Atp10d is associated with HDL modulation and C57BL/6 mice expressing a truncated, non-functional form of ATP10D easily develop obesity and insulin resistance on high-fat diet.

Results

We analyzed metabolic differences of ATP10D deficient C57BL/6J wild type and ATP10D transgenic C57BL/6J BAC129 mice. ATP10D transgenic mice gain 25% less weight on high-fat diet concomitant with a reduced increase in fat cell mass but independent of adipocyte size change. ATP10D transgenic mice also had 26% lower triacylglycerol levels with approximately 76% bound to very low density lipoprotein while in ATP10D deficient wild type mice 57% are bound to low density lipoprotein. Furthermore increased oxygen consumption and CO₂ production, 38% lower glucose and 69% lower insulin levels and better insulin sensitivity were observed in ATP10D transgenic mice. Besides decreased hexosylceramide species levels were detected. Part of these effects may be due to reduced hepatic stearoyl-CoA desaturase 1 (SCD1) expression in ATP10D transgenic mice, which was reflected by altered fatty acid and lipid species patterns. There was a significant decrease in the hepatic 18:1 to 18:0 free fatty acid ratio in transgenic mice. The ratio of 16:1 to 16:0 was not significantly different. Interestingly both ratios were significantly reduced in plasma total fatty acids.

Summary

In summary we found that ATP10D reduces high-fat diet induced obesity and improves insulin sensitivity. ATP10D transgenic mice showed altered hepatic expression of lipid-metabolism associated genes, including Scd1, along with changes in hepatic and plasma lipid species and plasma lipoprotein pattern.

Cellular Models and In Vitro Assays for the Screening of modulators of P-gp, MRP1 and BCRP

Adenosine triphosphate (ATP)-binding cassette (ABC) transporters are highly expressed in tumor cells, as well as in organs involved in absorption and secretion processes, mediating the ATP-dependent efflux of compounds, both endogenous substances and xenobiotics, including drugs. Their expression and activity levels are modulated by the presence of inhibitors, inducers and/or activators. In vitro, ex vivo and in vivo studies with both known and newly synthesized P-glycoprotein (P-gp) inducers and/or activators have shown the usefulness of these transport mechanisms in reducing the systemic exposure and specific tissue access of potentially harmful compounds. This article focuses on the main ABC transporters involved in multidrug resistance [P-gp, multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP)] expressed in tissues of toxicological relevance, such as the blood-brain barrier, cardiovascular system, liver, kidney and intestine. Moreover, it provides a review of the available cellular models, in vitro and ex vivo assays for the screening and selection of safe and specific inducers and activators of these membrane transporters. The available cellular models and in vitro assays have been proposed as high throughput and low-cost alternatives to excessive animal testing, allowing the evaluation of a large number of compounds.

Peroxisomal ATP-binding cassette transporters form mainly tetramers

ABCD1 and its homolog ABCD2 are peroxisomal ATP-binding cassette (ABC) half-transporters of fatty acyl-CoAs with both distinct and overlapping substrate specificities. Although it is established that ABC half-transporters have at least to dimerize to generate a functional unit, functional equivalents of tetramers (i.e. dimers of full-length transporters) have also been reported. However, oligomerization of peroxisomal ABCD transporters is incompletely understood but is of potential significance because more complex oligomerization might lead to differences in substrate specificity. In this work, we have characterized the quaternary structure of the ABCD1 and ABCD2 proteins in the peroxisomal membrane. Using various biochemical approaches, we clearly demonstrate that both transporters exist as both homo- and heterotetramers, with a predominance of homotetramers. In addition to tetramers, some larger molecular ABCD assemblies were also found but represented only a minor fraction. By using quantitative co-immunoprecipitation assays coupled with tandem mass spectrometry, we identified potential binding partners of ABCD2 involved in polyunsaturated fatty-acid metabolism. Interestingly, we identified calcium ATPases as ABCD2-binding partners, suggesting a role of ABCD2 in calcium signaling. In conclusion, we have shown here that ABCD1 and its homolog ABCD2 exist mainly as homotetramers in the peroxisomal membrane.

Placental ABC Transporters: Biological Impact and Pharmaceutical Significance

The human placenta fulfills a variety of essential functions during prenatal life. Several ABC transporters are expressed in the human placenta, where they play a role in the transport of endogenous compounds and may protect the fetus from exogenous compounds such as therapeutic agents, drugs of abuse, and other xenobiotics. To date, considerable progress has been made toward understanding ABC transporters in the placenta. Recent studies on the expression and functional activities are discussed. This review discusses the placental expression and functional roles of several members of ABC transporter subfamilies B, C, and G including MDR1/P-glycoprotein, the MRPs, and BCRP, respectively. Since placental ABC transporters modulate fetal exposure to various compounds, an understanding of their functional and regulatory mechanisms will lead to more optimal medication use when necessary in pregnancy.

Role of family D ATP-binding cassette transporters (ABCD) in cancer

ATP-binding cassette (ABC) transporters, belonging to the family D, are expressed in peroxisomes, endoplasmic reticulum or lysosomes. ABCD transporters play a role in transport of lipids, bile acids and vitamin B12 and associate with peroxisomal disorders. ABCD1 performs transport of coenzyme A esters of very-long-chain fatty acids (VLCFA) in peroxisomes and a number of mutations in ABCD1 gene were linked to an X-linked adrenoleucodystrophy (X-ALD). The role of ABCD transporters in tumour growth has not been studied in detail, but there is some evidence that ABCDs levels differ between undifferentiated stem or tumour cells and differentiated cells suggesting a possible link to tumorigenesis. In this mini-review, we discuss the available information about the role of ABCD transporters in cancer.

Abcb1 in Pigs: Molecular cloning, tissues distribution, functional analysis, and its effect on pharmacokinetics of enrofloxacin

P-glycoprotein (P-gp) is one of the best-known ATP-dependent efflux transporters, contributing to differences in pharmacokinetics and drug-drug interactions. Until now, studies on pig P-gp have been scarce. In our studies, the full-length porcine P-gp cDNA was cloned and expressed in a Madin-Darby Canine Kidney (MDCK) cell line. P-gp expression was then determined in tissues and its role in the pharmacokinetics of oral enrofloxacin in pigs was studied. The coding region of pig Abcb1 gene was 3,861 bp, encoding 1,286 amino acid residues (Mw = 141,966). Phylogenetic analysis indicated a close evolutionary relationship between porcine P-gp and those of cow and sheep. Pig P-gp was successfully stably overexpressed in MDCK cells and had efflux activity for rhodamine 123, a substrate of P-gp. Tissue distribution analysis indicated that P-gp was highly expressed in brain capillaries, small intestine, and liver. In MDCK-pAbcb1 cells, enrofloxacin was transported by P-gp with net efflux ratio of 2.48 and the efflux function was blocked by P-gp inhibitor verapamil. High expression of P-gp in the small intestine could modify the pharmacokinetics of orally administrated enrofloxacin by increasing the Cmax, AUC and Ka, which was demonstrated using verapamil, an inhibitor of P-gp.

ABCA7 frameshift deletion associated with Alzheimer disease in African Americans

Objective:

To identify a causative variant(s) that may contribute to Alzheimer disease (AD) in African Americans (AA) in the ATP-binding cassette, subfamily A (ABC1), member 7 (ABCA7) gene, a known risk factor for late-onset AD.

Methods:

Custom capture sequencing was performed on ∼150 kb encompassing ABCA7 in 40 AA cases and 37 AA controls carrying the AA risk allele (rs115550680). Association testing was performed for an ABCA7 deletion identified in large AA data sets (discovery n = 1,068; replication n = 1,749) and whole exome sequencing of Caribbean Hispanic (CH) AD families.

Results:

A 44-base pair deletion (rs142076058) was identified in all 77 risk genotype carriers, which shows that the deletion is in high linkage disequilibrium with the risk allele. The deletion was assessed in a large data set (531 cases and 527 controls) and, after adjustments for age, sex, and APOE status, was significantly associated with disease (p = 0.0002, odds ratio [OR] = 2.13 [95% confidence interval (CI): 1.42–3.20]). An independent data set replicated the association (447 cases and 880 controls, p = 0.0117, OR = 1.65 [95% CI: 1.12–2.44]), and joint analysis increased the significance (p = 1.414 × 10⁻⁵, OR = 1.81 [95% CI: 1.38–2.37]). The deletion is common in AA cases (15.2%) and AA controls (9.74%), but in only 0.12% of our non-Hispanic white cohort. Whole exome sequencing of multiplex, CH families identified the deletion cosegregating with disease in a large sibship. The deleted allele produces a stable, detectable RNA strand and is predicted to result in a frameshift mutation (p.Arg578Alafs) that could interfere with protein function.

Conclusions:

This common ABCA7 deletion could represent an ethnic-specific pathogenic alteration in AD.

Prolonged Oral Administration of a Pan-Retinoic Acid Receptor Antagonist Inhibits Spermatogenesis in Mice With a Rapid Recovery and Changes in the Expression of Influx and Efflux Transporters

We have previously shown that oral administration of a pan-retinoic acid receptor antagonist in mice daily at 2.5 mg/kg for 4 weeks reversibly inhibited spermatogenesis, with no detectable side effects. To elucidate the lowest dose and the longest dosing regimen that inhibits spermatogenesis but results in complete restoration of fertility upon cessation of administration of the drug, we examined the effects of daily doses as low as 1.0 mg/kg with dosing periods of 4, 8, and 16 weeks. We observed 100% sterility in all regimens, with restoration of fertility upon cessation of the drug treatment even for as long as 16 weeks. There was no change in testosterone levels in these males and the progeny examined from 2 of the recovered males were healthy and fertile, with normal testicular weight and testicular histology. Strikingly, a more rapid recovery, as assessed by mating studies, was observed at the lower dose and longer dosing periods. Insight into possible mechanisms underlying this rapid recovery was obtained at 2 levels. First, histological examination revealed that spermatogenesis was not as severely disrupted at the lower dose and with the longer treatment regimens. Second, gene expression analysis revealed that the more rapid recovery may involve the interplay of ATP-binding cassette efflux and solute carrier influx transporters in the testes.

Associations Between Genetic Variants in 19p13 and 19q13 Regions and Susceptibility to Alzheimer Disease: A Meta-Analysis

BACKGROUND

Alzheimer disease (AD) has become an epidemic within the growing elderly population and effective therapies of AD have not been discovered. Genetic factors accounted for over 70% of the incidence of AD and the disease-related polymorphisms are located on chromosome 19, which is one of several prominent chromosomes related to the development of AD. Many inconsistent associations between polymorphisms in ABCA7, CD33, and TOMM40 genes and the susceptibility to AD have been suggested by several independent studies.

MATERIAL/METHODS

A comprehensive literature search for studies involving the association between gene polymorphisms and AD was performed, and we finally selected 3 genes (4 polymorphisms) for the meta-analysis: ABCA7 (rs3764650), CD33 (rs3865444), and TOMM40 (rs157580, rs2075650).

RESULTS

A total of 25 articles investigating 3 genes (4 polymorphisms) were included in the meta-analysis. The pooled results of 4 polymorphisms were all significantly associated with the susceptibility to AD. The pooled effect of ABCA7 rs3764605 allele G was significantly associated with an increased the risk of AD (OR=1.20, 95% CI: 1.14-1.26, P value <0.001). Similarly, our evidence suggested that allele A of TOMM40 rs2075650 polymorphism was a risk factor for AD (OR=2.87, 95% CI: 2.46-3.34, P value <0.001). Alleles A of CD33 rs3865444 and A of TOMM40 rs157580 were both protective factors for AD onset (OR=0.94, 95% CI: 0.90-0.98, P value=0.003; OR=0.62, 95% CI: 0.57-0.66, P value <0.001). CONCLUSIONS" Results from the meta-analysis revealed that the pooled ABCA7 rs376465, CD33 rs3865444, TOMM40 rs157580, and rs2075650 variants were significantly associated with the susceptibility to AD. However, the association differed significantly between Asian and Caucasian groups for SNPs of CD33 rs3865444, TOMM40 rs157580, and rs2075650.

Peroxisomes in brain development and function

Peroxisomes contain numerous enzymatic activities that are important for mammalian physiology. Patients lacking either all peroxisomal functions or a single enzyme or transporter function typically develop severe neurological deficits, which originate from aberrant development of the brain, demyelination and loss of axonal integrity, neuroinflammation or other neurodegenerative processes. Whilst correlating peroxisomal properties with a compilation of pathologies observed in human patients and mouse models lacking all or individual peroxisomal functions, we discuss the importance of peroxisomal metabolites and tissue- and cell type-specific contributions to the observed brain pathologies. This enables us to deconstruct the local and systemic contribution of individual metabolic pathways to specific brain functions. We also review the recently discovered variability of pathological symptoms in cases with unexpectedly mild presentation of peroxisome biogenesis disorders. Finally, we explore the emerging evidence linking peroxisomes to more common neurological disorders such as Alzheimer’s disease, autism and amyotrophic lateral sclerosis. This article is part of a Special Issue entitled: Peroxisomes edited by Ralf Erdmann.

Drug transporters in tissues and cells relevant to sexual transmission of HIV: Implications for drug delivery

Efflux and uptake transporters of drugs are key regulators of the pharmacokinetics of many antiretroviral drugs. A growing body of literature has revealed the expression and functionality of multiple transporters in female genital tract (FGT), colorectal tissue, and immune cells. Drug transporters could play a significant role in the efficacy of preventative strategies for HIV-1 acquisition. Pre-exposure prophylaxis (PrEP) is a promising strategy, which utilizes topically (vaginally or rectally), orally or other systemically administered antiretroviral drugs to prevent the sexual transmission of HIV to receptive partners. The drug concentration in the receptive mucosal tissues and target immune cells for HIV is critical for PrEP effectiveness. Hence, there is an emerging interest in utilizing transporter information to explain tissue disposition patterns of PrEP drugs, to interpret inter-individual variability in PrEP drug pharmacokinetics and effectiveness, and to improve tissue drug exposure through modulation of the cervicovaginal, colorectal, or immune cell transporters. In this review, the existing literature on transporter expression, functionality and regulation in the transmission-related tissues and cells is summarized. In addition, the relevance of transporter function for drug delivery and strategies that could exploit transporters for increased drug concentration at target locales is discussed. The overall goal is to facilitate an understanding of drug transporters for PrEP optimization.

ABCA1 rs1883025 polymorphism and risk of age-related macular degeneration

PURPOSE

To evaluate the association of the ABCA1 rs1883025 polymorphism and susceptibility to age-related macular degeneration (AMD).

METHODS

A systematic search of the PubMed, EMBASE, and ISI web of science databases was performed to identify eligible published studies without language restrictions up to September 2015. Pooled odds ratios (ORs) with 95 % confidence intervals (CIs) were estimated under different genetic models using meta-analytic methods. Stratified analysis and sensitivity analysis were performed to explore potential sources of heterogeneity.

RESULTS

A total of 12 articles with 25,445 cases and 36,460 controls were eligible in this meta-analysis. The ABCA1 rs1883025 variant showed significant association with the lower risk of overall AMD under the allelic model (OR= 0.81, 95   %   CI=0.74-0.89). Stratified analysis based on ethnicity demonstrated a strong association between rs1883025 polymorphism and AMD in the Caucasian population, but not in Asian population. For late AMD, the ABCA1 rs1883025 variant was observed to have a significant association with the lower risk of this disease (OR = 0.81, 95 % CI, 0.72-0.91). In early-stage AMD, significant associations of the rs1883025 polymorphism with lower risk of early AMD were observed in different genetic models (OR ranging from 0.45 to 0.65, all P < 0.05).

CONCLUSIONS

The present meta-analysis indicated that the T allelic in rs1883025 variant was significantly associated with the risk of developing AMD, particularly at the early stage. The associations of the ABCA1 locus with AMD risk in various populations need further exploration.

Recent advances in the exploration of the bile salt export pump (BSEP/ABCB11) function

INTRODUCTION

The bile salt export pump (BSEP/ABCB11), residing in the apical membrane of hepatocyte, mediates the secretion of bile salts into the bile. A range of human diseases is associated with the malfunction of BSEP, including fatal hereditary liver disorders and mild cholestatic conditions. Manifestation of these diseases primarily depends on the mutation type; however, other factors such as hormonal changes and drug interactions can also trigger or influence the related diseases.

AREAS COVERED

Here, we summarize the recent knowledge on BSEP by covering its transport properties, cellular localization, regulation and major mutations/polymorphisms, as well as the hereditary and acquired diseases associated with BSEP dysfunction. We discuss the different model expression systems employed to understand the function of the BSEP variants, their drug interactions and the contemporary therapeutic interventions.

EXPERT OPINION

The limitations of the available model expression systems for BSEP result in controversial conclusions, and obstruct our deeper insight into BSEP deficiencies and BSEP-related drug interactions. The knowledge originating from different methodologies, such as clinical studies, molecular genetics, as well as in vitro and in silico modeling, should be integrated and harmonized. Increasing availability of robust molecular biological tools and our better understanding of the mechanism of BSEP deficiencies should make the personalized, mutation-based therapeutic interventions more attainable.

ATP-binding cassette transporters in reproduction: a new frontier

BACKGROUND

The transmembrane ATP-binding cassette (ABC) transporters actively efflux an array of clinically relevant compounds across biological barriers, and modulate biodistribution of many physiological and pharmacological factors. To date, over 48 ABC transporters have been identified and shown to be directly and indirectly involved in peri-implantation events and fetal/placental development. They efflux cholesterol, steroid hormones, vitamins, cytokines, chemokines, prostaglandins, diverse xenobiotics and environmental toxins, playing a critical role in regulating drug disposition, immunological responses and lipid trafficking, as well as preventing fetal accumulation of drugs and environmental toxins.

METHODS

This review examines ABC transporters as important mediators of placental barrier functions and key reproductive processes. Expression, localization and function of all identified ABC transporters were systematically reviewed using PubMed and Google Scholar websites to identify relevant studies examining ABC transporters in reproductive tissues in physiological and pathophysiological states. Only reports written in English were incorporated with no restriction on year of publication. While a major focus has been placed on the human, extensive evidence from animal studies is utilized to describe current understanding of the regulation and function of ABC transporters relevant to human reproduction.

RESULTS

ABC transporters are modulators of steroidogenesis, fertilization, implantation, nutrient transport and immunological responses, and function as 'gatekeepers' at various barrier sites (i.e. blood-testes barrier and placenta) against potentially harmful xenobiotic factors, including drugs and environmental toxins. These roles appear to be species dependent and change as a function of gestation and development. The best-described ABC transporters in reproductive tissues (primarily in the placenta) are the multidrug transporters p-glycoprotein and breast cancer-related protein, the multidrug resistance proteins 1 through 5 and the cholesterol transporters ABCA1 and ABCG1.

CONCLUSIONS

The ABC transporters have various roles across multiple reproductive tissues. Knowledge of efflux direction, tissue distribution, substrate specificity and regulation of the ABC transporters in the placenta and other reproductive tissues is rapidly expanding. This will allow better understanding of the disposition of specific substrates within reproductive tissues, and facilitate development of novel treatments for reproductive disorders as well as improved approaches to protecting the developing fetus.

Correlation between the promoter methylation status of ATP-binding cassette sub-family G member 2 and drug sensitivity in colorectal cancer cell lines

Resistance to chemotherapeutic agents has been considered as a major reason for the high incidence rate of recurrence and metastasis suffered by colorectal cancer (CRC) patients. ATP-binding cassette sub-family G member 2 (ABCG2) is involved in drug resistance. DNA methylation of the ABCG2 promoter site has a significant influence on the regulation of epigenetic gene expression. In the present study, we investigated whether the methylation status of the ABCG2 promoter is related to drug sensitivity in CRC cell lines. In order to examine the ABCG2 expression level and identify the methylation status, RT-PCR, qRT-PCR analysis, MS-PCR and bisulfite sequencing were conducted on 32 CRC cell lines. SNU-C4, LS174T and NCI-H716 were selected as low ABCG2-expressing and high promoter methylated cell lines. The cell proliferation assay for 5-fluorouracil, oxaliplatin and irinotecan was performed after 5-aza-2'-deoxycytidine (5-aza) treatment in these cell lines. In the 32 CRC cell lines, 25% of the cell lines expressed low or no ABCG2 expression. Of these cell lines, SNU-C4, LS174T and NCI-H716 were hypermethylated at the promoter region, ~20%. Demethylation of ABCG2 was induced by 5-aza, which enhanced the ABCG2 expression level and influenced the cell proliferation similar to treatment with the anticancer agents. Our data suggest that the ABCG2 expression level regulated by methylation is related to anticancer drug sensitivity. Based on these results, it can be applied to predict the anticancer drug response.

ATP-binding cassette proteins BCRP, MRP1 and P-gp expression and localization in the human umbilical cord

1. The umbilical cord is a direct conduit to the fetus hence transporters could have roles in partitioning substances between the maternal-placental-fetal units. Here we determined the expression and localization of the ATP-Binding Cassette (ABC) transporters BCRP (ABCG2), P-gp (ABCB1) and MRP1 (ABCC1) in human umbilical cords. 2. The mRNA for BCRP and MRP1 was detected in 25/25 samples, but P-gp was detected in only 5/25. ABC transporter mRNA expression relative to 18S was 25.6 ± 0.3, 26.5 ± 0.6 and 22.2 ± 0.2 cycles for BCRP, MRP1 and P-gp respectively. 3. Using a subset of 10 umbilical cords, BCRP protein was present in all samples (immunoblot) with positive correlation between mRNA and proteins (p = 0.07, r = 0.62) and between immunoblotting and immunohistochemistry (IHC) (p = 0.03, r = 0.67). P-gp protein was observed in 4/10 samples by both immunoblot and IHC, with no correlation between mRNA and protein (p = 0.45, r = 0.55) or immunoblotting and IHC (p = 0.2, r = 0.72), likely due to small sample size. MRP1 protein was not observed. 4. Localization of BCRP and P-gp proteins was to Wharton's jelly with no specific staining in arterial or venous endothelia. 5. Understanding ABC transporter expression in the umbilical cord may be useful for determining fetal exposures to xenobiotics if functional properties can be defined.

Regulation of HDL genes: transcriptional, posttranscriptional, and posttranslational

HDL regulation is exerted at multiple levels including regulation at the level of transcription initiation by transcription factors and signal transduction cascades; regulation at the posttranscriptional level by microRNAs and other noncoding RNAs which bind to the coding or noncoding regions of HDL genes regulating mRNA stability and translation; as well as regulation at the posttranslational level by protein modifications, intracellular trafficking, and degradation. The above mechanisms have drastic effects on several HDL-mediated processes including HDL biogenesis, remodeling, cholesterol efflux and uptake, as well as atheroprotective functions on the cells of the arterial wall. The emphasis is on mechanisms that operate in physiologically relevant tissues such as the liver (which accounts for 80% of the total HDL-C levels in the plasma), the macrophages, the adrenals, and the endothelium. Transcription factors that have a significant impact on HDL regulation such as hormone nuclear receptors and hepatocyte nuclear factors are extensively discussed both in terms of gene promoter recognition and regulation but also in terms of their impact on plasma HDL levels as was revealed by knockout studies. Understanding the different modes of regulation of this complex lipoprotein may provide useful insights for the development of novel HDL-raising therapies that could be used to fight against atherosclerosis which is the underlying cause of coronary heart disease.