Search

Background Sulfoxaflor is a new insecticide for controlling against Aphis gossypii in the field. ATP-binding cassette (ABC) transporters belong to a large superfamily of proteins and play an important role in the detoxification process. However, the potential role of ABC transporters in sulfoxaflor resistance in A. gossypii is unknown. Results In this study, an ABC transporter inhibitor, verapamil, dramatically increased the toxicity of sulfoxaflor in the resistant population with a synergistic ratio of 8.55. However, verapamil did not synergize sulfoxaflor toxicity in the susceptible population. The contents of ABC transporters were significantly increased in the Sul-R population. Based on RT-qPCR analysis, 10 of 23 ABC transcripts, ABCA1, ABCA2, ABCB1, ABCB5, ABCD1, ABCG7, ABCG16, ABCG26, ABCG27, and MRP7, were up-regulated in the Sul-R population compared to the Sus population. Meanwhile, inductive effects of ABCA1, ABCD1, ABCG7 and ABCG26 by sulfoxaflor were found in A. gossypii. Furthermore, knockdown of ABCA1 and ABCD1 using RNAi significantly increased the sulfoxaflor sensitivity in Sul-R aphids. Conclusion These results suggested that ABC transporters, especially the ABCA1 and ABCD1 genes, might be related with sulfoxaflor resistance in A. gossypii. This study will promote further work to validate the functional roles of these ABCs in sulfoxaflor resistance and might be helpful for the management of sulfoxaflor-resistant A. gossypii.

ABC transporters fulfill diverse physiological functions in different cellular localizations ranging from the plasma membrane to intracellular membranous compartments. Several ABC transporters have been spotted in the endolysosomal system, which consists of endosomes, autophagosomes, lysosomes, and lysosome-related organelles. In this review, we present an overview of lysosomal ABC transporters including ABCA2, ABCA3, ABCA5, ABCB6, ABCB9, and ABCD4, discussing their trafficking routes, putative substrates, potential physiological functions, and associated diseases. In addition, we offer a critical evaluation of the literature linking ABC transporters to lysosomal drug sequestration, examining pitfalls associated with in vitro models of drug resistance.

The occurrence of Alzheimer's disease (AD) worldwide has been progressively accelerating at an alarming rate, without any successful therapeutic strategy for the disease mitigation. The complexity of AD pathogenesis needs to be targeted with an alternative approach, as provided by the superfamily of ATP-binding cassette (ABC) transporters, which constitutes an extensive range of proteins, capable of transporting molecular entities across biological membranes. These protein moieties have been implicated in AD, based upon their potential in lipid transportation, resulting in maintenance of cholesterol homeostasis. These transporters have been reported to target the primary hallmark of AD pathogenesis, namely, beta-amyloid hypothesis, which is associated with accumulation of beta-amyloid (Aβ) plaques in AD patients. The ABC transporters have been observed to be localized to the capillary endothelial cells of the blood-brain barrier and neural parenchymal cells, where they exhibit different roles, consequently influencing the neuronal expression of Aβ peptides. The review highlights different families of ABC transporters, ABCB1 (P-glycoprotein), ABCA (ABCA1, ABCA2, and ABCA7), ABCG2 (BCRP; breast cancer resistance protein), ABCG1 and ABCG4, as well as ABCC1 (MRP; multidrug resistance protein) in the CNS, and their interplay in regulating cholesterol metabolism and Aβ peptide load in the brain, simultaneously exerting protective effects against neurotoxic substrates and xenobiotics. The authors aim to establish the significance of this alternative approach as a novel therapeutic target in AD, to provide the researchers an opportunity to evaluate the potential aspects of ABC transporters in AD treatment.

FoxM1 amplification in human pancreatic cancer predicts poor prognosis and resistance to paclitaxel. Here, a novel role between FoxM1 (FoxM1b and FoxM1c) and Prohibitin1 (PHB1) in paclitaxel resistance has been identified. We adopted a bioinformatics approach to predict the potential effector of FoxM1. It specifically bound to the promoter of PHB1, and it enhanced PHB1 expression at transcriptional and post-transcriptional levels. FoxM1 contributed to the PHB1/C-RAF interaction and phosphorylation of ERK1/2 kinases, thus promoting paclitaxel resistance. Notably, FoxM1 conferred tumor cell resistance to paclitaxel, but knocking down PHB1 could sensitize pancreatic cancer cells to it. Besides, we identified that ABCA2 promoted paclitaxel resistance under the regulation of FoxM1/PHB1/RAF-MEK-ERK. Thiostrepton, an inhibitor of FoxM1, significantly decreased the expression of PHB1, p-ERK1/2, and ABCA2. It increased the influx of paclitaxel into the cell, and it attenuated FoxM1-mediated paclitaxel resistance in vitro and in vivo. Collectively, our findings defined PHB1 as an important downstream effector of FoxM1. It was regulated by FoxM1 to maintain phosphorylation of ERK1/2 in drug-resistant cells, and FoxM1 simultaneously enhanced the function of ABCA2, which collectively contributed to paclitaxel resistance. Targeting FoxM1 and its downstream effector PHB1 increased the sensitivity of pancreatic cells to paclitaxel treatment, providing potential therapeutic strategies for patients with paclitaxel resistance. Keywords: pancreatic cancer, paclitaxel resistance, thiostrepton, FoxM1, PHB1, MAPK signaling, ABCA2

Crops genetically engineered to produce insecticidal proteins from Bacillus thuringiensis (Bt) have many benefits and are important globally for managing insect pests. However, the evolution of pest resistance to Bt crops reduces their benefits. Understanding the genetic basis of such resistance is needed to better monitor, manage, and counter pest resistance to Bt crops. Previous work shows that resistance to Bt toxin Cry2Ab is associated with mutations in the gene encoding the ATP-binding cassette protein ABCA2 in lab- and field-selected populations of the pink bollworm (Pectinophora gossypiella), one of the world’s most destructive pests of cotton. Here we used CRISPR/Cas9 gene editing to test the hypothesis that mutations in the pink bollworm gene encoding ABCA2 (PgABCA2) can cause resistance to Cry2Ab. Consistent with this hypothesis, introduction of disruptive mutations in PgABCA2 in a susceptible strain of pink bollworm increased the frequency of resistance to Cry2Ab and facilitated creation of a Cry2Ab-resistant strain. All Cry2Ab-resistant individuals tested in this study had disruptive mutations in PgABCA2. Overall, we found 17 different disruptive mutations in PgABCA2 gDNA and 26 in PgABCA2 cDNA, including novel mutations corresponding precisely to single-guide (sgRNA) sites used for CRISPR/Cas9. Together with previous results, these findings provide the first case of practical resistance to Cry2Ab where evidence identifies a specific gene in which disruptive mutations can cause resistance and are associated with resistance in field-selected populations.

BackgroundAs the most common neurodegenerative disease, Alzheimer’s disease (AD) leads to progressive loss of cognition and memory. Presently, the underlying pathogenic genes of AD patients remain elusive, and effective disease-modifying therapy is not available. This study explored novel biomarkers that can affect diagnosis and treatment in AD based on immune infiltration.MethodsThe gene expression profiles of 139 AD cases and 134 normal controls were obtained from the NCBI GEO public database. We applied the computational method CIBERSORT to bulk gene expression profiles of AD to quantify 22 subsets of immune cells. Besides, based on the use of the Least Absolute Shrinkage Selection Operator (LASSO), this study also applied SVM-RFE analysis to screen key genes. GO-based semantic similarity and logistic regression model analyses were applied to explore hub genes further.ResultsThere was a remarkable significance in the infiltration of immune cells between the subgroups. The proportions for monocytes, M0 macrophages, and dendritic cells in the AD group were significantly higher than those in the normal group, while the proportion of some cells was lower than that of the normal group, such as NK cell resting, T-cell CD4 naive, T-cell CD4 memory activation, and eosinophils. Additionally, seven genes (ABCA2, CREBRF, CD72, CETN2, KCNG1, NDUFA2, and RPL36AL) were identified as hub genes. Then we performed the analysis of immune factor correlation, gene set enrichment analysis (GSEA), and GO based on seven hub genes. The AUC of ROC prediction model in test and validation sets were 0.845 and 0.839, respectively. Eventually, the mRNA expression analysis of ABCA2, NDUFA2, CREBRF, and CD72 revealed significant differences among the seven hub genes and then was confirmed by RT-PCR.ConclusionA model based on immune cell infiltration might be used to forecast AD patients’ diagnosis, and it provided a new perspective for AD treatment targets.

Multidrug resistance (MDR) is considered as the major obstacle for treating pediatric acute lymphoblastic leukemia (ALL). MicroRNAs (miRNAs) are small non coding RNAs which may potentially regulate response to chemotherapy. In this study, total RNA was isolated from bone marrow samples of 46 children with de novo ALL and 16 controls. Quantitative reverse transcriptase polymerase chain reaction was used to investigate the expression profile of the predicted miRNAs; miR-326 and miR-200c, and their predicted targets ABCA2, and ABCA3 transporters. The presence of minimal residual disease was studied using PCR-SSCP (single-strand conformation polymorphism) 1 year after treatment. The association between the miRNA expression and drug resistance was analyzed statistically. Results showed a significant down-regulation of both miR-326 and miR-200c expressions in ALL patients compared with non-cancer controls (P = 0.0002, AUC = 0.813 and P = 0.035, AUC = 0.79, respectively). A considerable negative association between miR-326 expression and MDR was identified which could raise the risk of chemoresistance by 4.8- fold. The expression profiles of miR-326 and ABCA2 transporter were inversely correlated. Data revealed, a novel diagnostic role for miR-326 and miR-200c as potential biomarkers of pediatric ALL. Down-regulation of miR-326 was introduced, for the first time, as a prognostic factor for drug resistance in childhood ALL. To the best of our knowledge, this is the first time that ABCA2 transporter is proposed as a target gene for miR-326, through which it can exert its impact on drug resistance. These data may provide novel approaches to new therapeutics and diagnostics.

The identification of drug transporters expressed in human skin and interindividual differences in gene expression is important for understanding the role of drug transporters in human skin. In the present study, we evaluated the expression of ATP-binding cassette (ABC) and solute carrier (SLC) transporters using human skin tissues. In skin samples, ABCC3 was expressed at the highest levels, followed by SLCO3A1, SLC22A3, SLC16A7, ABCA2, ABCC1, and SLCO2B1. Among the quantitated transporters, ABCC3 accounted for 20.0% of the total mean transporter mRNA content. The expression of ABCC3 mRNA showed large interindividual variability (9.5-fold). None of the single nucleotide polymorphisms tested (-1767G>A, -1328G>A, -1213C>G, -897delC, -260T>A, and -211C>T) in the promoter region of the ABCC3 gene showed a significant change in ABCC3 mRNA levels. ABCC3 expression levels negatively correlated with the methylation status of the CpG island (CGI) located approximately 10 kilobase pairs upstream of ABCC3 (Rs: -0.323, P < 0.05). The reporter gene assay revealed a significant increase in transcriptional activity in the presence of CGI. ABCC3 mRNA was upregulated in HaCaT cells by the demethylating agent 5-aza-2'-deoxycytidine. Furthermore, the deletion of the region surrounding CGI using the clustered regularly interspaced short palindromic repeat/Cas9 system resulted in significantly lower ABCC3 mRNA levels than those in control clones in HaCaT cells. Herein, we demonstrated large interindividual differences in the expression of drug transporters in human skin. CGI may function as an enhancer of the transcription of ABCC3, and methylation levels in CGI contribute to the variability of ABCC3 expression in human skin.

BACKGROUND ABCA2 has been genetically linked to Alzheimer's disease (AD) risk, but its mRNA expression and epigenetics in AD have not been investigated. MATERIAL AND METHODS To explore the diagnosis value of ABCA2 mRNA expression in AD, 2 datasets GES15222 and GSE33000 containing expression profile of brain cortex tissues and 2 datasets GSE63063 (Cohort 1) and GSE63063 (Cohort 2) containing expression profile of blood were downloaded from the NCBI GEO database and analyzed by receiver operating characteristic curve (ROC) analyses and logistic regression. The ABCA2 co-expressed genes were also analyzed by GO annotation to investigate the potential molecular mechanisms. RESULTS The analyses results suggested ABCA2 mRNA expression was upregulated significantly in AD compared with controls in all datasets. ROC analysis suggested that ABCA2 was associated with AD in all datasets, which were also proved by univariate and multivariate analyses. Next, the dataset GSE80970 containing methylation profiles of prefrontal cortex tissues from AD patients were downloaded and analyzed. Methylation of 2 of 36 CpG islands in ABCA2 gene with high diagnostic accuracy of AD from controls in ROC analyses were found to be negatively associated with AD risk in univariate analysis. One was still associated with AD risk after adjustment of confounding factors. Additional analyses indicated that ACBA2 mRNA expression could be used to diagnose mild cognitive impairment (MCI) and Huntington's disease (HD) from controls and to distinguish HD from AD, but not AD from MCI. Furthermore, the genes involved in AD during ABCA2 alteration were analyzed by GO analysis. CONCLUSIONS ABCA2 mRNA expression and methylation is associated AD risk. ABCA2 may be used as a biomarker for AD diagnosis and may be a potential therapeutic target of AD.

Cry toxins are insecticidal proteins produced by Bacillus thuringiensis (Bt). They are used commercially to control insect pests since they are very active in specific insects and are harmless to the environment and human health. The gene encoding ATP-binding cassette subfamily A member 2 (ABCA2) was identified in an analysis of Cry2A toxin resistance genes. However, we do not have direct evidence for the role of ABCA2 for Cry2A toxins or why Cry2A toxin resistance does not cross to other Cry toxins. Therefore, we performed two experiments. First, we edited the ABCA2 sequence in Bombyx mori using transcription activator-like effector-nucleases (TALENs) and confirmed the susceptibility-determining ability in a diet overlay bioassay. Strains with C-terminal half-deleted BmABCA2 showed strong and specific resistance to Cry2A toxins, even strains carrying a deletion of 1 to 3 amino acids showed resistance. However, the C-terminal half-deleted strains did not show cross-resistance to other toxins. Second, we conducted a cell swelling assay and confirmed the specific ability of BmABCA2 to Cry2A toxins in HEK239 cells. Those demonstrated that BmABCA2 is a functional receptor for Cry2A toxins and that BmABCA2 deficiency-dependent Cry2A resistance does not confer cross-resistance to Cry1A, Cry1F, Cry1Ca, Cry1Da, or Cry9Aa toxins.

ATP-binding cassette (ABC) transporters represent the largest known group of efflux pumps, utilizing ATP to translocate a broad spectrum of substrates across lipid membranes, which play an important role in phase III of the detoxification process. The presence of ABC transporters and their potential association with insecticide resistance have not been investigated in Aphis gossypii, one of the most economically important agricultural pests worldwide. In this study, the ABC transporter inhibitor-verapamil significantly increased thiamethoxam toxicity against resistant cotton aphids, suggesting that ABCs are involved in thiamethoxam resistance. ABC transporter genes were identified using the A. gossypii genome database and transcriptome data. A total of 69 ABC transporters were identified and grouped into seven subfamilies (A-G), including 4 ABCAs, 5 ABCBs, 25 ABCCs, 2 ABCDs, 1 ABCE, 4 ABCFs and 30 ABCGs. Of these ABC transporters, 53 were predicted to be functional, 19 were full transporters, 30 were half-transporters and 4 had two NBDs. Subfamilies C and G accounted for 77% (32 and 45%, respectively) of the genes. The transcripts of 20 of 26 ABCs based on the transcriptome were upregulated, and ABCA1, ABCA2, ABCB1, ABCB4, ABCB8, ABCD1, ABCD2, ABCE1, ABCF1, ABCF3, ABCG7, ABCG15, ABCG17, ABCG24, ABCG27, ABCG30, MRP1, MRP7, MRP14 and MRP21 transcripts were significantly increased in the thiamethoxan resistant strain compared to the susceptible strain with qRT-PCR. The suppression of overexpressed ABCs (ABCA2, ABCD1, ABCD2, ABCE1 and ABCG15) significantly increased the thiamethoxam sensitivity of resistant aphids. These results suggest that ABC transporters might be involved in thiamethoxam resistance in A. gossypii and will facilitate further work to validate the functional roles of these ABCs in thiamethoxam resistance. These results are useful for understanding the multiple resistance mechanisms of thiamethoxam and the management of insecticide-resistant cotton aphids.

Epithelial ovarian cancer (EOC) has the highest mortality among gynecological carcinomas. The lack of specific markers for prognostic determination of EOC progression hinders the search for novel effective therapies. The aim of the present study was (i) to explore differences in expressions of ATP-binding cassette (ABC) and solute carrier (SLC) transporter genes, genes associated with drug metabolism and cell cycle regulation between control ovarian tissues (n = 14), primary EOCs (n = 44) and intraperitoneal metastases (n = 29); (ii) to investigate associations of gene expression levels with prognosis of patients with intraperitoneal metastases. In all tissue samples, transcript levels of the above target genes were assessed using quantitative real-time PCR. Gene expression levels were compared between particular tissue types and evaluated with regard to progression-free survival (PFS) and drug-resistance status of patients with metastases. Gene expression of ABCA7 significantly increased and that of ESR2 decreased in the order control ovarian tissues - primary EOCs - metastases. High expressions of ABCA2/8/9/10, ABCB1, ABCC9, ABCG2, ATP7A, SLC16A14, and SOD3 genes were significantly associated with longer progression-free survival of patients. In intraperitoneal metastases, expression of all of these genes highly correlated and indicated prognostic profile. Transporters from the ABCA family, ABCG2, and ESR2 are involved mainly in lipid metabolism, membrane transport, and cell proliferation. These processes are thus probably the most important for EOC progression. Based on these results, we have proposed novel markers of ovarian carcinoma progression and metastatic spread which might be potentially useful as therapeutic targets. Their significance should be further explored on a larger independent set of patients.

The ATP binding cassette transporter ABCA2 is primarily an endolysosomal membrane protein that demonstrates pleiotropic functionalities, coalescing around the maintenance of homeostasis of sterols, sphingolipids and cholesterol. It is most highly expressed in brain tissue and ABCA2 knockout mice express neurological defects consistent with aberrant myelination. Increased expression of the transporter has been linked with resistance to cancer drugs, particularly those possessing a steroid backbone and gene expression (in concert with other genes involved in cholesterol metabolism) was found to be regulated by sterols. Moreover, in macrophages ABCA2 is influenced by sterols and has a role in regulating cholesterol sequestration, potentially important in cardiovascular disease. Accumulating data indicate the critical importance of ABCA2 in mediating movement of sphingolipids within cellular compartments and these have been implicated in various aspects of cholesterol trafficking. Perhaps because the functions of ABCA2 are linked with membrane building blocks, there are reports linking it with human pathologies, including, cholesterolemias and cardiovascular disease, Alzheimer's and cancer. The present review addresses whether there is now sufficient information to consider ABCA2 as a plausible therapeutic target.

Narges Aberuyi,1 Soheila Rahgozar,1 Zohreh Khosravi Dehaghi,1 Alireza Moafi,2 Andrea Masotti,3,* Alessandro Paolini3,* 1Department of Biology, Faculty of Science, University of Isfahan, 2Department of Pediatric-Hematology-Oncology, Sayed-ol-Shohada Hospital, Isfahan University of Medical Sciences, Isfahan, Iran; 3Gene Expression – Microarrays Laboratory, Bambino Gesù Children’s Hospital-Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Rome, Italy *These authors contributed equally tothe manuscript Purpose: The aim of this work was to study the correlation between the expressions of the ABCA2 and ABCA3 genes at the mRNA and protein levels in children with acute lymphoblastic leukemia (ALL) and the effects of this association on multidrug resistance (MDR).Materials and methods: Sixty-nine children with de novo ALL and 25 controls were enrolled in the study. Mononuclear cells were isolated from the bone marrow. The mRNA levels of ABCA2 and ABCA3 were measured by real-time polymerase chain reaction (PCR). Samples with high mRNA levels were assessed for respective protein levels by Western blotting. Following the first year of treatment, persistent monoclonality of T-cell gamma receptors or immunoglobulin H (IgH) gene rearrangement was assessed and considered as the MDR. The tertiary structure of ABCA2 was predicted using Phyre2 and I-TASSER web systems and compared to that of ABCA3, which has been previously reported. Molecular docking was performed using DOCK 6.7.Results: Real-time quantitative PCR (qRT-PCR) showed high levels of ABCA2 and ABCA3 mRNAs in 13 and 17 samples, respectively. Among them, five and eight individuals demonstrated high levels of ABCA2 and ABCA3, respectively. Response to chemotherapy was significantly decreased (P=0.001) when the mRNA and protein of both genes were overexpressed compared to individuals with high transcriptional levels of either ABCA2 or ABCA3 alone. Close similarity between ABCA2 and ABCA3 structures was revealed by protein tertiary structure prediction, whereas molecular docking analysis suggested similar binding of chemotherapy drugs and therefore a potentially similar role in determining the MDR.Conclusion: Our findings suggested, for the first time, that quantification of the protein level of ABCA2 and ABCA3 transporters had a prognostic impact on pediatric ALL MDR. Furthermore, the tertiary structure of ABCA2 was predicted for the first time, and docking analysis revealed a possible compensatory effect between ABCA2 and ABCA3 transporters, which may contribute to the efflux of cytotoxic drugs and, ultimately, to chemoresistance. Keywords: ABCA2 transporter, ABCA3 transporter, multidrug resistance, childhood acute lymphoblastic leukemia, molecular docking, tertiary structure

The ATP binding cassette transporter-2 (ABCA2) has been genetically linked to Alzheimer's disease but the molecular mechanisms are unknown. In this study, the effects of expression of human ABCA2 on endogenous amyloid precursor protein (APP) expression, trafficking and processing were examined in mouse N2a neuronal cells. ABCA2 expression increased the steady-state APP mRNA levels through transcription. ABCA2 also induced increased synthesis of APP holoprotein and altered APP processing and metabolite generation. ABCA2 expression promoted b-secretase (BACE1) cleavage of APP not at the common Asp1 amino acid site (β-site) of Aβ in APP but at the Glu11 site (β'-site) to increase C89 carboxyl-terminal fragment levels (β'-CTF/C89). The levels of N-terminally truncated Aβ11-40 peptides were also increased by ABCA2 expression. The delivery of newly synthesized APP to the cell surface through the secretary pathway was not perturbed by ABCA2 expression; however, ABCA2 expression increased the amount of APP in early-endosomal compartments, which also contained the highest levels of β'-CTF/C89 and is likely the site of increased BACE1 processing of APP. This report identifies ABCA2 as a key regulator of endogenous APP expression and processing and suggests a possible biochemical mechanism linking ABCA2 expression, APP processing and Alzheimer's disease.

Overexpression of ATP-binding cassette (ABC) transporters is a major adaptive advantage used by tumor cells to evade the accumulation of cytotoxic agents. ABCA2, a transporter highly expressed in the cells of the nervous and haematopoetic systems, is associated with lipid transport and drug resistance in cancer cells, including tumor stem cells. Recently, a single nucleotide polymorphism (SNP) in Abca2 was linked to early onset Alzheimer's disease (AD). The characterization of two independent knockout mouse models has shed light on putative in vivo functions of this transporter in the development and maintenance of myelin membrane lipids in the CNS.The objective of this review is to guide the reader through the existing scope of literature on the ABCA2 transporter, focusing on its potential as a future target in human pathologies, specifically cancer and neurological disease.An NCBI PubMed literature search was conducted to address the growing body of ABCA2 literature that, at the time of publication, included 39 reports. From these, we focused on papers that provided insight into the functional importance of this transporter in tumor stem cells, cancer, drug resistance, Alzheimer's disease and myelination.These studies have implicated ABCA2 as a therapeutic target in modulating the drug resistance phenotype prevalent in human cancers and in the treatment of neuropathies, including Alzheimer's disease and myelin-related disorders.

ATP-binding cassette (ABC) transporters comprise a family of critical membrane bound proteins functioning in the translocation of molecules across cellular membranes. Substrates for transport include lipids, cholesterol and pharmacological agents. Mutations in ABC transporter genes cause a variety of human pathologies and elicit drug resistance phenotypes in cancer cells. ABCA2, the second member the A subfamily to be identified, was highly expressed in ovarian carcinoma cells resistant to the anti-cancer agent, estramustine, and more recently, in human vestibular schwannomas. Cells expressing elevated levels of ABCA2 show resistance to variety of compounds, including estradiol, mitoxantrone and a free radical initiator, 2,2'-azobis-(2-amidinopropane). ABCA2 is expressed in a variety of tissues, with greatest abundance in the central nervous system and macrophages. This transporter, along with other proteins that have a high degree of homology to ABCA2, including ABCA1 and ABCA7, are up-regulated in human macrophages during cholesterol import. Recent studies have shown ABCA2 also plays a role in the trafficking of low-density lipoprotein (LDL)-derived free cholesterol and to be coordinately expressed with sterol-responsive genes. A single nucleotide polymorphism in exon 14 of the ABCA2 gene was shown to be linked to early onset Alzheimer disease (AD) in humans, supporting an earlier study showing ABCA2 expression influences levels of APP and beta-amyloid peptide, the primary component of senile plaques. Studies thus far implicate ABCA2 as a sterol transporter, the deregulation of which may affect a cellular phenotype conducive to the pathogenesis of a variety of human diseases including AD, atherosclerosis and cancer.

Membrane transporters (such as ABCs, SLCs and ATPases) act in carcinogenesis and chemoresistance development, but their relevance for prognosis of epithelial ovarian cancer (EOC) remains poorly understood. We evaluated the gene expression profile of 39 ABC and 12 SLC transporters and three ATPases in EOC tissues and addressed their putative role in prognosis and clinical course of EOC patients. Relative gene expression in a set of primary EOC (n=57) and in control ovarian tissues (n=14) was estimated and compared with clinical data and survival of patients. Obtained data were validated in an independent set of patients (n=60). Six ABCs and SLC22A18 gene were significantly overexpressed in carcinomas when compared with controls, while expression of 12 ABCs, five SLCs, ATP7A and ATP11B was decreased. Expression of ABCA12, ABCC3, ABCC6, ABCD3, ABCG1 and SLC22A5 was higher in high grade serous carcinoma compared with other subtypes. ABCA2 gene expression significantly associated with EOC grade in both sets of patients. Notably, expression level of ABCA9, ABCA10, ABCC9 and SLC16A14 significantly associated with progression-free survival (PFS) of the disease in either pilot or validation sets. ABCG2 level associated with PFS in the pooled set of patients. In conclusion, ABCA2, ABCA9, ABCA10, ABCC9, ABCG2 and SLC16A14 present novel putative markers of EOC progression and together with the revealed relationship between ABCA12, ABCC3, ABCC6, ABCD3, ABCG1 and SLC22A5 expression, and high grade serous type of EOC should be further examined by larger follow-up study.

ATP-binding cassette (ABC) transporters are a family of proteins that translocate molecules across cellular membranes. Substrates can include lipids, cholesterol and drugs. Mutations in ABC transporter genes can cause human pathologies and drug resistance phenotypes in cancer cells. ABCA2, the second member the A sub-family to be identified, was found at high levels in ovarian carcinoma cells resistant to the anti-cancer agent, estramustine (EM). In vitro models with elevated levels of ABCA2 are resistant to a variety of compounds, including estradiol, mitoxantrone and a free radical initiator, 2,2'-azobis-(2-amidinopropane) (AAPH). ABCA2 is most abundant in the central nervous system (CNS), ovary and macrophages. Enhanced expression of ABCA2 and related proteins, including ABCA1, ABCA4 and ABCA7, is found in human macrophages upon bolus cholesterol treatment. ABCA2 also plays a role in the trafficking of low-density lipoprotein (LDL)-derived free cholesterol and is coordinately expressed with genes involved in cholesterol homeostasis. Additionally, ABCA2 expression has been linked with gene cluster patterns consistent with pathologies including Alzheimer's disease (AD). A single-nucleotide polymorphism (SNP) in exon 14 of the ABCA2 gene was shown to be linked to early onset AD in humans, supporting the observation that ABCA2 expression influences levels of beta-amyloid peptide (Abeta), the primary component of senile plaques. ABCA2 may play a role in cholesterol transport and affect a cellular phenotype conducive to the pathogenesis of a variety of human diseases including AD, atherosclerosis and cancer.

A major issue in the treatment of T-cell acute lymphoblastic leukemia (T-ALL) is resistance to chemotherapeutic drugs. Multidrug resistance can be caused by ATP-binding cassette (ABC) transporters. The majority of these proteins have not yet been examined in T-ALL. Using a newly developed microarray for the simultaneous quantification of 38 ABC transporter genes, we observed a consistent overexpression of ABCA2/ABCA3 in clinical samples of ALL. Therefore, we analyzed the association of these two genes with drug resistance. Treatment of CCRF-CEM and Jurkat cells with methotrexate, vinblastine, or doxorubicin led to an induction of ABCA3 expression, whereas a significant increase of ABCA2 expression was only observed in Jurkat cells. To study the causal relationship of ABCA2/A3 overexpression with drug resistance, we applied RNA interference (RNAi) technology. RNAi specific for ABCA2 or ABCA3 led to a partial decrease of expression in these two ABC transporters. Upon cotreatment of RNAi for ABCA2 with methotrexate and vinblastine, a partial decrease of ABCA2 expression as well as a simultaneous increase of ABCA3 expression was observed. Vice versa, ABCA3 RNAi plus drugs decreased ABCA3 and increased ABCA2 expression. This indicates that down-regulation of one ABC transporter was compensated by the up-regulation of the other. Application of RNAi for both ABCA2 and ABCA3 resulted in a more efficient reduction of the expression of both transporters. As a consequence, a significant sensitization of cells to cytostatic drugs was achieved. In conclusion, ABCA2 and ABCA3 are expressed in many T-ALL and contribute to drug resistance. [Mol Cancer Ther 2006;5(8):1986–94]

Five ATP-binding cassette (ABC) subfamily-A transporters (ABCA1, ABCA2, ABCA3, ABCA7 and ABCA8) are expressed in the brain. These transporters may regulate brain lipid transport; however, their relative expression level in isolated human brain cells is unknown. We developed real-time polymerase chain reaction assays to quantify the expression of these genes in human neurons, astrocytes, oligodendrocytes, microglia and cell lines. Neurons expressed predominantly ABCA1 and ABCA3; astrocytes ABCA1, ABCA2 and ABCA3; microglia ABCA1 and oligodendrocytes ABCA2 and ABCA3. Although ABCA7 and ABCA8 expression was relatively low in all cells, the highest expression occurred in microglia and neurons, respectively. ABCA gene expression in the NTERA-2 and MO3.13 cell lines closely resembled the ABCA expression pattern of primary neurons and oligodendrocytes, respectively.

ABCA2 protein belongs to the ABCA subclass of ATP-binding cassette (ABC) transporters proposed to exert critical functions in transmembrane transport of endogenous lipids. In this study, we found by immunoblot analyses that approximately 260 kDa of ABCA2 protein is expressed predominantly in oligodendrocytes, and that the expression of the protein is upregulated in the brain during maturation, especially between postnatal days 6 and 19. Parallel to the changes in expression of ABCA2, immunohistochemical analyses showed rapid spatial spread of ABCA2-immunolabeled oligodendrocytes in the brain during this period. These temporal and spatial changes in ABCA2 expression were in good agreement with findings in myeloarchitectonics reported previously. Further, double immunolabeling with ABCA2 and a major structural protein of myelin, myelin basic protein, demonstrated that onset of ABCA2 expression in oligodendrocytes coincides with the appearance of thick myelin segments immunolabeled with myelin basic protein. Because ABCA2 was abundantly expressed in adult cortex in white matter and gray matter, coexpression of ABCA2 and a marker for the oligodendroglial progenitors NG2 or platelet-derived growth factor α receptor was investigated. No cells coexpressing ABCA2 and the marker were observed, suggesting that ABCA2 is expressed predominantly in myelin-forming oligodendrocytes distinct from the adult oligodendroglial progenitors tested. These results suggested a role for ABCA2 in membrane transport of substrates such as the lipids that are closely linked to myelination processes. J. Comp. Neurol. 455:353–367, 2003. © 2002 Wiley-Liss, Inc.

The ABC1 (ABCA) subfamily of the ATP-binding cassette (ABC) transporter superfamily has a structural feature that distinguishes it from other ABC transporters. Here we report the cloning, molecular characterization and tissue distribution of ABC2/ABCA2, which belongs to the ABC1 subfamily. Rat ABC2 is a protein of 2434 amino acids that has 44.5%, 40.0% and 40.8% identity with mouse ABC1/ABCA1, human ABC3/ABCA3 and human ABCR/ABCA4 respectively. Immunoblot analysis showed that proteins of 260 and 250kDa were detected in COS-1 cells transfected with ABC2 having a haemagglutinin tag, while no band was detected in mock-transfected cells. After incubation with N-glycosidase F, the mobilities of the two proteins increased and a single band was detected, suggesting that ABC2 is a glycoprotein. Photoaffinity labelling with 8-azido-[α-32P]ATP confirmed that ATP binds to the ABC2 protein in the presence of Mg2+. RNA blot analysis showed that ABC2 mRNA is most abundant in rat brain. Examination of brain by in situ hybridization determined that ABC2 is expressed at high levels in the white matter, indicating that it is expressed in the oligodendrocytes. ABC2, therefore, is a glycosylated ABC transporter protein, and may play an especially important role in the brain. In addition, the N-terminal 60-amino-acid sequence of the human ABC1, which was missing from previous reports, has been determined.

A recent study demonstrated a significant genetic association between the ATP-binding cassette transporter A2 (ABCA2) and the risk for Alzheimer's disease (AD) in a large Caucasian sample. The rare T allele of the synonymous exonic single nucleotide polymorphism (SNP) rs908832 was overrepresented in early-onset AD patients as compared to cognitively healthy controls. Here we confirm the association of rs908832 with AD in a Western European population (n = 291, P = 0.008). In a second sample from Southern Europe, rs908832 was not associated with AD. Interestingly, rs908832 was not polymorphic in a Japanese sample. Furthermore, rs908832 was not associated with either serum cholesterol levels or with the risk for coronary artery disease, but seemed to be related to cholesterol levels in the cerebrospinal fluid. These data suggest that ABCA2 may exert population-dependent effects on the genetic risk for sporadic AD and support a role of ABC lipid transporters in the pathogenesis of this disease.

Multidrug resistance (MDR) is an important cause of treatment failure in acute lymphoblastic leukemia (ALL). The ABC family of membrane transporters is proposed, albeit with controversy, to be involved in this process. The present study aims to investigate the mRNA expression profile of several genes of this family, including ABCA2, ABCA3, ABCB1/MDR1, MRP1/ABCC1, MRP3/ABCC3, ABCG2/BCRP, and the intracellular transporter MVP/LRP, in childhood ALL, and to evaluate their association with response to therapy. Some genes in the present research are being studied for the first time in Iran. Using quantitative real-time PCR, we evaluated 27 children with ALL at diagnosis and 15 children with normal bone marrow. The status of response to therapy was assessed one year after the onset of therapy through investigating the IgH/TCRγ gene rearrangements. Our findings indicate a considerable and direct relationship between mRNA expression levels of ABCA2, ABCA3, MDR1, and MRP1 genes and positive minimal residual disease (MRD) measured after one year of treatment. Statistical analysis revealed that expression of these genes higher than the cutoff point will raise the risk of MRD by 15-, 6.25-, 12-, and 9-fold, respectively. No relationship was found between of MVP/LRP, MRP3 and ABCG2 genes expression and ALL prognoses. Considering the direct and significant relationship between the increased expression of ABCA2, ABCA3, MDR1, and MRP1 genes and positive risk of MRD in children with ALL, evaluating the expression profile of these genes on diagnosis may identify high risk individuals and help plan a more efficient treatment strategy.

Aim: ATP-binding cassette (ABC) transporters contribute to development of resistance to anticancer drugs via ATP-dependent drug efflux. A major goal of our study was to investigate associations between the expression of ABC transporters and outcome of breast carcinoma patients. Patients & methods: Transcript levels of all 49 human ABC transporters were determined in post-treatment tumor and non-neoplastic tissue samples from 68 breast carcinoma patients treated by neoadjuvant chemotherapy. Six ABC transporters were then evaluated in independent series of 100 pretreatment patients. Results:ABCA5/6/8/9/10, ABCB1/5/11, ABCC6/9, ABCD2/4, ABCG5 and ABCG8 were significantly downregulated and ABCA2/3/7/12, ABCB2/3/8/9/10, ABCC1/4/5/10/11/12, ABCD1/3, ABCE1, ABCF1/2/3 and ABCG1 were upregulated in post-treatment tumors compared with non-neoplastic tissues. Significant associations of intratumoral levels of ABCC1 and ABCC8 with grade and expression of hormonal receptors were found in both sets of patients. ABCA12, ABCA13 and ABCD2 levels were significantly associated with the response to neoadjuvant chemotherapy in post-treatment patients. Protein expression of ABCA12, ABCC8 and ABCD2 in tumor tissues of patients with breast carcinoma was observed by immunoblotting for the first time. Conclusion:ABCA12, ABCA13, ABCC1, ABCC8 and ABCD2 present potential modifiers of progression and response to the chemotherapy of breast carcinoma. Original submitted 27 July 2012; Revision submitted 5 February 2013

Objective The ABCA2 transporter shares high structural homology to ABCA1, which is crucial for the removal of excess cholesterol from macrophages and, by extension, in atherosclerosis. It has been suggested that ABCA2 sequesters cholesterol inside the lysosomes, however, little is known of the macrophage-specific role of ABCA2 in regulating lipid homeostasis in vivo and in modulating susceptibility to atherosclerosis. Methods Chimeras with dysfunctional macrophage ABCA2 were generated by transplantation of bone marrow from ABCA2 knockout (KO) mice into irradiated LDL receptor (LDLr) KO mice. Results Interestingly, lack of ABCA2 in macrophages resulted in a diminished lesion size in the aortic root (−24.5%) and descending thoracic aorta (−36.6%) associated with a 3-fold increase in apoptotic cells, as measured by both caspase 3 and TUNEL. Upon oxidized LDL exposure, macrophages from wildtype (WT) transplanted animals developed filipin-positive droplets in lysosomal-like compartments, corresponding to free cholesterol (FC) accumulation. In contrast, ABCA2-deficient macrophages displayed an abnormal diffuse distribution of FC over peripheral regions. The accumulation of neutral sterols in lipid droplets was increased in ABCA2-deficient macrophages, but primarily in cytoplasmic clusters and not in lysosomes. Importantly, apoptosis of oxLDL loaded macrophages lacking ABCA2 was increased 2.7-fold, probably as a consequence of the broad cellular distribution of FC. Conclusions Lack of functional ABCA2 generates abnormalities in intracellular lipid distribution/trafficking in macrophages consistent with its lysosomal sequestering role, leading to an increased susceptibility to apoptosis in response to oxidized lipids and reduced atherosclerotic lesion development.

Mental disorders have a complex etiology resulting from interactions between multiple genetic risk factors and stressful life events. Orphan G protein-coupled receptor 50 (GPR50) has been identified as a genetic risk factor for bipolar disorder and major depression in women, and there is additional genetic and functional evidence linking GPR50 to neurite outgrowth, lipid metabolism, and adaptive thermogenesis and torpor. However, in the absence of a ligand, a specific function has not been identified. Adult GPR50 expression has previously been reported in brain regions controlling the HPA axis, but its developmental expression is unknown. In this study, we performed extensive expression analysis of GPR50 and three protein interactors using rt-PCR and immunohistochemistry in the developing and adult mouse brain. Gpr50 is expressed at embryonic day 13 (E13), peaks at E18, and is predominantly expressed by neurons. Additionally we identified novel regions of Gpr50 expression, including brain stem nuclei involved in neurotransmitter signaling: the locus coeruleus, substantia nigra, and raphe nuclei, as well as nuclei involved in metabolic homeostasis. Gpr50 colocalizes with yeast-two-hybrid interactors Nogo-A, Abca2, and Cdh8 in the hypothalamus, amygdala, cortex, and selected brain stem nuclei at E18 and in the adult. With this study, we identify a link between GPR50 and neurotransmitter signaling and strengthen a likely role in stress response and energy homeostasis.

Clinical, pharmacological, biochemical, and genetic evidence support the notion that alteration of cholesterol homeostasis strongly predisposes to Alzheimer disease (AD). The ATP-binding cassette transporter-2 (Abca2), which plays a role in intracellular sterol trafficking, has been genetically linked to AD. It is unclear how these two processes are related. Here we demonstrate that down-regulation of Abca2 in mammalian cells leads to decreased amyloid-β (Aβ) generation. In vitro studies revealed altered γ-secretase complex formation in Abca2 knock-out cells due to the altered levels, post-translational modification, and subcellular localization of Nicastrin. Reduced Abca2 levels in mammalian cells in vitro, inDrosophila melanogaster and in mice resulted in altered γ-secretase processing of APP, and thus Aβ generation, without affecting Notch cleavage. © 2012 by The American Society for Biochemistry and Molecular Biology, Inc., Fund for Scientific Research Flanders (FWO); Federal Office for Scientific Affairs (IUAP P6/43/); Stichting voor Alzheimer Onderzooek/Fondation pour la Recherche sur Maladie d’ Alzheimer (SAO/FRMA), the Flemish Government (Methusalem grant); Spanish Government Grants Ministerio de Ciencia e Innovación (Ingenio Consolider CSD2010-00064); Ministerio de Ciencia e Innovación (SAF2010-14906)

We have investigated the transcriptomic and/or proteomic patterns of 71 solute carrier (SLC) and organic solute (OST) transporters, 34 ATP-binding cassette (ABC) transporters, and 51 metabolizing enzymes in human brain microvessels. We used quantitative RT-PCR and LC-MS/MS to examine isolated brain microvessels and cortex biopsies from 12 patients with epilepsia or glioma. SLC2A1/GLUT1, SLC1A3/EAAT1, and SLC1A2/EAAT2 were the main SLC proteins whereas ABCG2/BCRP, ABCB1/MDR1, ABCA2 and ABCA8 were the main ABC quantified in isolated brain microvessels; ABCG2/BCRP was 1.6-fold more expressed than ABCB1/MDR1, and ABCC4/MRP4 was 10 times less abundant than ABCB1/MDR1. CYP1B1 and CYP2U1 were the only quantifiable CYPs. Finally, GSTP1, COMT, GSTM3, GSTO1 and GSTM2 proteins were the main phase II enzymes quantified; UGTs and NATs were not detected. Our extensive investigation of gene and protein patterns of transporters and metabolizing enzymes provides new molecular information for understanding drug entry and metabolism in the human blood-brain barrier.

The ATP binding cassette transporter subtype A5 (ABCA5)-like transporters ABCA5, ABCA6, ABCA8, ABCA9 and ABCA10 form a unique gene cluster within the ABC transporter superfamily, though their function is still poorly understood. The purpose of this study is to examine whether ABCA5-like transporters may play a role in tumor development by measuring their mRNA levels in human tissues and tumors. Intense mRNA expression of human ABCA5-like transporters was detected in the brain. ABCA5 and ABCA8 mRNAs were detected in spleen, testis and ovary. ABCA5 mRNA was also detected in liver and pancreas. ABCA6 mRNA was detected in lung and liver, and ABCA8 was detected in lung. ABCA6, ABCA7 and ABCA8 mRNAs were not detected in any tumors, but weak mRNA expression of ABCA10 was detected in all tumors examined. ABCA5 mRNA was detected in poorly differentiated colon adenocarcinoma (GI-112) and undifferentiated ovarian carcinoma (GI-102), but not in normal colon. ABCB1 mRNA was also detected in GI-112, while ABCC1 and ABCA2 mRNAs were not. In contrast, ABCC1 and ABCA2 mRNAs, but not ABCA5 or ABCB1 mRNA, were detected in well differentiated colon adenocarcinoma (CX-1). Thus, induction of ABCA5, together with ABCB1, appears to be correlated with the differentiation state of human colon tumors, and may have a role in tumor development.

ABCA2, which belongs to the A subclass of the ATP-binding cassette (ABC) transporter superfamily, is predominantly expressed in the cytoplasm of oligodendrocytes and Schwann cells, the myelin-forming cells in brain and peripheral nerve, respectively. Here, we demonstrate by immunoblot and immunohistochemistry that ABCA2 is expressed in benign vestibular schwannomas, which contain neither axons nor compact myelin. The expression patterns of ABCA2 in combination with other markers showed phenotypic heterogeneity in schwannomas. The majority of cells in fascicular Antoni type A areas coexpressed ABCA2, Ca 2+ -binding protein S100β, and p75 nerve growth factor receptor. In contrast, considerably varied expression levels of ABCA2 and p75 were more prominent in hypocellular type B areas than in type A areas. These data suggest that ABCA2 may be useful as a marker for cellular characterization of schwannomas.