Exposure of Cultured Astrocytes to Menadione Triggers Rapid Radical Formation, Glutathione Oxidation and Mrp1-Mediated Export of Glutathione Disulfide

Observation of the neuroprotective efficacy of vitamin K in a streptozocin-induced diabetes model in chick embryos

Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia due to insulin deficiency and/or resistance. Vitamin K (VK) is a group of fat-soluble molecules, including naturally occurring vitamin K1 (phylloquinone). vitamin K2 (menaquinone), and synthetic vitamin K3 (menadione). Beyond coagulation, the health benefits of VK have been described to play different roles in both physiological and pathological processes such as inflammation, energy metabolism, neuroprotection, cellular growth, and survival. It was aimed to observe the antioxidant and/or neuroprotective activity of vitamin K1 in our model of chick embryo diabetic neuropathy (DN) induced by streptozotocin (STZ). Ninety White Leghorn, fertile and 0-day-old SPF (specific pathogen-free) eggs (57 ± 4 gr) were used in the study. Chick embryo blood brain tissues were taken for biochemical evaluation. Plasma insulin and glucose levels were measured. In addition, brain tissue total antioxidant level (TAS), total oxidant level (TOS), malondialdehyde (MDA), and vascular endothelial growth factor (VEGF) levels were measured. Plasma glucose levels were higher in the STZ-treated groups and lower in the treatment groups. Plasma insulin levels were observed to be higher in STZ groups in groups treated with high VK. Low TAS, high MDA, TOS, and VEGF levels were recorded in brain tissue STZ groups. Low VEGF, TOS, and MDA levels were recorded in the group treated with the highest VK, while high TAS levels were observed. In our STZ-induced chick embryo diabetic neuropathy model, we observed that VK1 reduced oxidant damage by showing antioxidant properties or by modulating antioxidant enzymes.

Modulation of Multidrug Resistance Protein 1-mediated Transport Processes by the Antiviral Drug Ritonavir in Cultured Primary Astrocytes

The Multidrug Resistance Protein 1 (Mrp1) is an ATP-dependent efflux transporter and a major facilitator of drug resistance in mammalian cells during cancer and HIV therapy. In brain, Mrp1-mediated GSH export from astrocytes is the first step in the supply of GSH precursors to neurons. To reveal potential mechanisms underlying the drug-induced modulation of Mrp1-mediated transport processes, we investigated the effects of the antiviral drug ritonavir on cultured rat primary astrocytes. Ritonavir strongly stimulated the Mrp1-mediated export of glutathione (GSH) by decreasing the Km value from 200 nmol/mg to 28 nmol/mg. In contrast, ritonavir decreased the export of the other Mrp1 substrates glutathione disulfide (GSSG) and bimane-glutathione. To give explanation for these apparently contradictory observations, we performed in silico docking analysis and molecular dynamics simulations using a homology model of rat Mrp1 to predict the binding modes of ritonavir, GSH and GSSG to Mrp1. The results suggest that ritonavir binds to the hydrophilic part of the bipartite binding site of Mrp1 and thereby differently affects the binding and transport of the Mrp1 substrates. These new insights into the modulation of Mrp1-mediated export processes by ritonavir provide a new model to better understand GSH-dependent detoxification processes in brain cells.

ABC transporter-mediated MXR mechanism in fish embryos and its potential role in the efflux of nanoparticles

ATP-binding cassette (ABC) transporters are believed to protect aquatic organisms by pumping xenobiotics out, and recent investigation has suggested their involvement in the detoxification and efflux of nanoparticles (NPs), but their roles in fish embryos are poorly understood. In this regard, this paper summarizes the recent advances in research pertaining to the development of ABC transporter-mediated multi-xenobiotic resistance (MXR) mechanism in fish embryos and the potential interaction between ABC transporters and NPs. The paper focuses on: (1) Expression, function, and modulation mechanism of ABC proteins in fish embryos; (2) Potential interaction between ABC transporters and NPs in cell models and fish embryos. ABC transporters could be maternally transferred to fish embryos and thus play an important role in the detoxification of various chemical pollutants and NPs. There is a need to understand the specific mechanism to benefit the protection of aquatic resources.

Simultaneous quantitation of oxidized and reduced glutathione via LC-MS/MS to study the redox state and drug-mediated modulation in cells, worms and animal tissue

Alterations in reduced and oxidized glutathione (GSH/GSSG) levels represent an important marker for oxidative stress and potential disease progression in toxicological research. Since GSH can be oxidized rapidly, using a stable and reliable method for sample preparation and GSH/GSSG quantification is essential to obtain reproducible data. Here we describe an optimised sample processing combined with a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, validated for different biological matrices (lysates from HepG2 cells, C. elegans, and mouse liver tissue). To avoid autoxidation of GSH, samples were treated with the thiol-masking agent N-ethylmaleimide (NEM) and sulfosalicylic acid (SSA) in a single step. With an analysis time of 5 min, the developed LC-MS/MS method offers simultaneous determination of GSH and GSSG at high sample throughput with high sensitivity. This is especially interesting with respect of screening for oxidative and protective properties of substances in in vitro and in vivo models, e.g. C. elegans. In addition to method validation parameters (linearity, limit of detection (LOD), limit of quantification (LOQ), recovery, interday, intraday), we verified the method by using menadione and L-buthionine-(S,R)-sulfoximine (BSO) as well established modulators of cellular GSH and GSSG concentrations. Thereby menadione proved to be a reliable positive control also in C. elegans.

β-lapachone-mediated WST1 Reduction as Indicator for the Cytosolic Redox Metabolism of Cultured Primary Astrocytes

Electron cycler-mediated extracellular reduction of the water-soluble tetrazolium salt 1 (WST1) is frequently used as tool for the determination of cell viability. We have adapted this method to monitor by determining the extracellular WST1 formazan accumulation the cellular redox metabolism of cultured primary astrocytes via the NAD(P)H-dependent reduction of the electron cycler β-lapachone by cytosolic NAD(P)H:quinone oxidoreductase 1 (NQO1). Cultured astrocytes that had been exposed to β-lapachone in concentrations of up to 3 µM remained viable and showed an almost linear extracellular accumulation of WST1 formazan for the first 60 min, while higher concentrations of β-lapachone caused oxidative stress and impaired cell metabolism. β-lapachone-mediated WST1 reduction was inhibited by the NQO1 inhibitors ES936 and dicoumarol in a concentration-dependent manner, with half-maximal inhibition observed at inhibitor concentrations of about 0.3 µM. β-lapachone-mediated WST1 reduction depended strongly on glucose availability, while mitochondrial substrates such as lactate, pyruvate or ketone bodies allowed only residual β-lapachone-mediated WST1 reduction. Accordingly, the mitochondrial respiratory chain inhibitors antimycin A and rotenone hardly affected astrocytic WST1 reduction. Both NADH and NADPH are known to supply electrons for reactions catalysed by cytosolic NQO1. Around 60% of the glucose-dependent β-lapachone-mediated WST1 reduction was prevented by the presence of the glucose-6-phosphate dehydrogenase inhibitor G6PDi-1, while the glyceraldehyde-3-phosphate dehydrogenase inhibitor iodoacetate had only little inhibitory potential. These data suggest that pentose phosphate pathway-generated NADPH, and not glycolysis-derived NADH, is the preferred electron source for cytosolic NQO1-catalysed reductions in cultured astrocytes.

The critical role of nanoparticle sizes in the interactions between gold nanoparticles and ABC transporters in zebrafish embryos

Despite the increasing evidences for adenosine triphosphate-binding cassette (ABC transporters)-mediated efflux of nanoparticles, the universality of these phenomena and the determining factors for the process remained to be clarified. This paper aimed to systemically investigate the role of nanoparticle size in the interactions between adenosine triphosphate-binding cassette (ABC transporters) and gold nanoparticles (AuNPs, 3 nm, 19 nm, and 84 nm, named as Au-3, Au-19, and Au-84) in zebrafish embryos. The results showed that all the three AuNPs induced significant toxicity as reflected by delayed hatching of embryos, decreased glutathione (GSH) contents, and increased reactive oxygen species (ROS) levels. Under the hindrance of embryo chorions, smaller AuNPs could more easily accumulate in the embryos, causing higher toxicity. Addition of transporter inhibitors enhanced the accumulation and toxicity of Au-3 and Au-19, and these nanoparticles induced the expressions of abcc2 and abcb4, indicating a fact that Au-3 and Au-19 were the potential substrates of ABC transporters, but these phenomena were barely found for Au-84. On the contrary, Au-84 suppressed the gene expressions of various ABC transporters like abcc1, abcg5, and abcg8. With specific suppressors, transcription factors like nuclear factor-erythroid 2-related factor-2 (Nrf2) and pregnane X receptor (Pxr) were found to be important in the induction of ABC transporters by AuNPs. After all, these results revealed a vital role of nanoparticle sizes in the interactions between ABC transporters and AuNPs in zebrafish embryos, and the critical size could be around 19 nm. Such information would be beneficial in assessing the environmental risk of nanoparticles, as well as their interactions with other chemical toxicants.

Crosstalk Between the Oxidative Stress and Glia Cells After Stroke: From Mechanism to Therapies

Stroke is the second leading cause of global death and is characterized by high rates of mortality and disability. Oxidative stress is accompanied by other pathological processes that together lead to secondary brain damage in stroke. As the major component of the brain, glial cells play an important role in normal brain development and pathological injury processes. Multiple connections exist in the pathophysiological changes of reactive oxygen species (ROS) metabolism and glia cell activation. Astrocytes and microglia are rapidly activated after stroke, generating large amounts of ROS via mitochondrial and NADPH oxidase pathways, causing oxidative damage to the glial cells themselves and neurons. Meanwhile, ROS cause alterations in glial cell morphology and function, and mediate their role in pathological processes, such as neuroinflammation, excitotoxicity, and blood-brain barrier damage. In contrast, glial cells protect the Central Nervous System (CNS) from oxidative damage by synthesizing antioxidants and regulating the Nuclear factor E2-related factor 2 (Nrf2) pathway, among others. Although numerous previous studies have focused on the immune function of glial cells, little attention has been paid to the role of glial cells in oxidative stress. In this paper, we discuss the adverse consequences of ROS production and oxidative-antioxidant imbalance after stroke. In addition, we further describe the biological role of glial cells in oxidative stress after stroke, and we describe potential therapeutic tools based on glia cells.

Oxidative stress-mediated up-regulation of ABC transporters in lung cancer cells

This paper aimed to evaluate the role of oxidative stress in the regulation of ABC transporters in human lung cancer (A549) cells facing substrate (doxorubicin, DOX) and non-substrate (ethanol, ETH and hydrogen peroxide, HP) chemicals. After 24-h treatment, all the chemicals caused significant cytotoxicity as reflected by the reduction in cell viability and the increase in reactive oxygen species (ROS) levels. Depending on the rescuing effects of ROS scavenger including glutathione (GSH) and Vitamin C (VC), the toxicity dependence on oxidative stress were found to be HP>ETH>DOX. Addition of transporter inhibitors significantly enhanced the ROS levels and death-inducing effects of chemicals, indicating the universal detoxification function of ABC transporters. At moderate ROS levels (about 3-4 folds of control levels, caused by 10 μM DOX, 400 mM ETH, and 400 μM HP), all the three chemicals induced the gene expressions and activities of ABC transporters, but these values decreased at too high ROS levels (8.36 folds of control levels) caused by HP at LC₅₀ (800 μM). Such induction could be attenuated by GSH and KCZ, and was completely abolished by 50 μM KCZ, indicating an important role of oxidative stress and pregnane X receptor (PXR) in the induction of ABC transporters. After all, this paper revealed a critical role of oxidative stress in the modulation of ABC transporters by either substrate or non-substrate chemicals during 24-h treatment. Such information should be beneficial for overcoming ABC transporter-mediated multidrug resistance (MDR). This article is protected by copyright. All rights reserved.

Confined growth of ZIF-8 in dendritic mesoporous organosilica nanoparticles as bioregulators for enhanced mRNA delivery in vivo

Zeolitic imidazolate framework-8 (ZIF-8) and its composites have diverse applications. However, ZIF-8-based nanocomposites are mainly used as carriers in biomolecular delivery, with the functions of metal ions and ligands rarely used to modulate the biofunctions. In this work, dendritic mesoporous organosilica nanoparticles (DMONs) with tetrasulfide bond were used to confine ZIF-8 growth partially inside mesopores as a novel nanocomposite for mRNA delivery. Each component in the resultant DMONs-ZIF-8 contributed to mRNA delivery applications, including high loading benefitting from positively charged ZIF-8 and large mesopores of DMONs, endosomal escape promoted by the imidazole ring of ZIF-8, and long-term glutathione depletion mediated by both zinc ions and tetrasulfide bond. Combined together, DMONs-ZIF-8 demonstrated enhanced mRNA translation and better transfection efficiency than commercial products and toxic polymer-modified DMONs in vitro and in vivo.

Investigating the antimicrobial, antioxidant and cytotoxic activities of the biological synthesized glutathione selenium nano-incorporation

Aqueous glutathione selenium nano-incorporation (GSH-SeN-Inco) was prepared by gamma radiation in presence of microbial glutathione (GSH) and selenium dioxide. The novel prepared GSH-SeN-Inco are validated by UV-vis spectroscopy, TEM (17.5 nm), DLS, XRD, EDX and FTIR spectrum reveals the presence of GSH moiety that coating the selenium nanoparticles (SeNPs) forming GSH-SeN-Inco. The XRD analysis verified the presence of metallic SeNPs. The nucleation and radiolysis mechanism of GSH-SeN-Inco formation are also discussed. The size GSH-SeN-Inco (17.5 nm) is affected by certain factors such as concentration of GSH, selenium dioxide, and absorbed dose of gamma radiation. The present study explored the positive role of GSH-SeN-Inco as an antitumor activity against HepG-2 and MCF-7, with IC₅₀ at a concentration of 1.00 and 0.9 mM, respectively. The GSH-SeN-Inco show significant scavenging activity at 33%. The GSH-SeN-Inco shows antimicrobial potential against Gram-negative and Gram-positive bacteria with significant MIC especially Escherichia coli ATCC 25922 at 5.20 µg/ml.

Involvement of ABC transporters in the detoxification of non-substrate nanoparticles in lung and cervical cancer cells

This paper aimed to systemically investigate the role of adenosine triphosphate-binding cassette (ABC transporters) in the detoxification of non-substrate nanoparticles including titanium dioxide (n-TiO₂, 5-10 nm) and gold (AuNPs, 3 nm, 15 nm, and 80 nm, named as Au-3, Au-15 and Au-80) in human lung cancer (A549) and human cervical cancer (HeLa) cells. All these nanoparticles were of larger hydrophilic diameters than the channel sizes of ABC transporters, thus should not be the substrates of membrane proteins. After 24-h treatment, they induced significant cytotoxicity as reflected by the reduction in cell viability and glutathione (GSH) contents, as well as the increase in reactive oxygen species (ROS) level. At median-lethal concentrations (10 mg/L n-TiO₂, 2 mg/L Au-3, 5 mg/L Au-15, and 10 mg/L Au-80 for A549 cells; 20 mg/L n-TiO₂, 2 mg/L Au-3, 5 mg/L Au-15, and 10 mg/L Au-80 for Hela cells), all the nanoparticles significantly induced the gene expressions and activities of ABC transporters including P-glycoprotein (PGP) and multidrug resistance associated protein 1 (MRP1). Addition of transporter inhibitors enhanced the ROS levels produced by nanoparticles, but didn't alter their death-inducing effects and intracellular accumulations. With specific suppressors, transcription factors like nuclear factor-erythroid 2-related factor-2 (NRF2) and pregnane X receptor (PXR) were proved to be important in the induction of ABC transporters by nanoparticles. After all, this paper revealed a damage-dependent modulation of ABC transporters by non-substrate nanoparticles. The up-regulated ABC transporters could help in reducing the oxidative stress produced by nanoparticles. Such information should be useful in assessing the environmental risk of nanoparticles, as well as their interactions with other chemical toxicants or drugs.

The Menadione-Mediated WST1 Reduction by Cultured Astrocytes Depends on NQO1 Activity and Cytosolic Glucose Metabolism

The reduction of water-soluble tetrazolium salts (WSTs) is frequently used to determine the metabolic integrity and the viability of cultured cells. Recently, we have reported that the electron cycler menadione can efficiently connect intracellular oxidation reactions in cultured astrocytes with the extracellular reduction of WST1 and that this menadione cycling reaction involves an enzyme. The enzymatic reaction involved in the menadione-dependent WST1 reduction was found strongly enriched in the cytosolic fraction of cultured astrocytes and is able to efficiently use both NADH and NADPH as electron donors. In addition, the reaction was highly sensitive towards dicoumarol with Kic values in the low nanomolar range, suggesting that the NAD(P)H:quinone oxidoreductase 1 (NQO1) catalyzes the menadione-dependent WST1 reduction in astrocytes. Also, in intact astrocytes, dicoumarol inhibited the menadione-dependent WST1 reduction in a concentration-dependent manner with half-maximal inhibition observed at around 50 nM. Moreover, the menadione-dependent WST1 reduction by viable astrocytes was strongly affected by the availability of glucose. In the absence of glucose only residual WST1 reduction was observed, while a concentration-dependent increase in WST1 reduction was found during a 30 min incubation with maximal WST1 reduction already determined in the presence of 0.5 mM glucose. Mannose could fully replace glucose as substrate for astrocytic WST1 reduction, while other hexoses, lactate and the mitochondrial substrate β-hydroxybutyrate failed to provide electrons for the cell-dependent WST1 reduction. These results demonstrate that the menadione-mediated WST1 reduction involves cytosolic NQO1 activity and that this process is strongly affected by the availability of glucose as metabolic substrate.

In vitro function and in situ localization of Multidrug Resistance-associated Protein (MRP)1 (ABCC1) suggest a protective role against methyl mercury-induced oxidative stress in the human placenta

Methyl mercury (MeHg) is an organic highly toxic compound that is transported efficiently via the human placenta. Our previous data suggest that MeHg is taken up into placental cells by amino acid transporters while mercury export from placental cells mainly involves ATP binding cassette (ABC) transporters. We hypothesized that the ABC transporter multidrug resistance-associated protein (MRP)1 (ABCC1) plays an essential role in mercury export from the human placenta. Transwell transport studies with MRP1-overexpressing Madin-Darby Canine Kidney (MDCK)II cells confirmed the function of MRP1 in polarized mercury efflux. Consistent with this, siRNA-mediated MRP1 gene knockdown in the human placental cell line HTR-8/SVneo resulted in intracellular mercury accumulation, which was associated with reduced cell viability, accompanied by increased cytotoxicity, apoptosis, and oxidative stress as determined via the glutathione (GSH) status. In addition, the many sources claiming different localization of MRP1 in the placenta required a re-evaluation of its localization in placental tissue sections by immunofluorescence microscopy using an MRP1-specific antibody that was validated in-house. Taken together, our results show that (1) MRP1 preferentially mediates apical-to-basolateral mercury transport in epithelial cells, (2) MRP1 regulates the GSH status of placental cells, (3) MRP1 function has a decisive influence on the viability of placental cells exposed to low MeHg concentrations, and (4) the in situ localization of MRP1 corresponds to mercury transport from maternal circulation to the placenta and fetus. We conclude that MRP1 protects placental cells from MeHg-induced oxidative stress by exporting the toxic metal and by maintaining the placental cells' GSH status in equilibrium.

β-Lapachone Induces Acute Oxidative Stress in Rat Primary Astrocyte Cultures that is Terminated by the NQO1-Inhibitor Dicoumarol

β-lapachone (β-lap) is reduced in tumor cells by the enzyme NAD(P)H: quinone acceptor oxidoreductase 1 (NQO1) to a labile hydroquinone which spontaneously reoxidises to β-lap, thereby generating reactive oxygen species (ROS) and oxidative stress. To test for the consequences of an acute exposure of brain cells to β-lap, cultured primary rat astrocytes were incubated with β-lap for up to 4 h. The presence of β-lap in concentrations of up to 10 µM had no detectable adverse consequences, while higher concentrations of β-lap compromised the cell viability and the metabolism of astrocytes in a concentration- and time-dependent manner with half-maximal effects observed for around 15 µM β-lap after a 4 h incubation. Exposure of astrocytes to β-lap caused already within 5 min a severe increase in the cellular production of ROS as well as a rapid oxidation of glutathione (GSH) to glutathione disulfide (GSSG). The transient cellular accumulation of GSSG was followed by GSSG export. The β-lap-induced ROS production and GSSG accumulation were completely prevented in the presence of the NQO1 inhibitor dicoumarol. In addition, application of dicoumarol to β-lap-exposed astrocytes caused rapid regeneration of the normal high cellular GSH to GSSG ratio. These results demonstrate that application of β-lap to cultured astrocytes causes acute oxidative stress that depends on the activity of NQO1. The sequential application of β-lap and dicoumarol to rapidly induce and terminate oxidative stress, respectively, is a suitable experimental paradigm to study consequences of a defined period of acute oxidative stress in NQO1-expressing cells.

Oxidative Stress Induction Is a Rational Strategy to Enhance the Productivity of Antrodia cinnamomea Fermentations for the Antioxidant Secondary Metabolite Antrodin C

Antioxidant metabolites contribute to alleviating oxidative stress caused by reactive oxygen species (ROS) in microorganisms. We utilized oxidative stressors such as hydrogen peroxide supplementation to increase the yield of the bioactive secondary metabolite antioxidant antrodin C in submerged fermentations of the medicinal mushroom Antrodia cinnamomea. Changes in the superoxide dismutase and catalase activities of the cells indicate that ROS are critical to promote antrodin C biosynthesis, while the ROS production inhibitor diphenyleneiodonium cancels the productivity-enhancing effects of H2O2. Transcriptomic analysis suggests that key enzymes in the mitochondrial electron transport chain are repressed during oxidative stress, leading to ROS accumulation and triggering the biosynthesis of antioxidants such as antrodin C. Accordingly, rotenone, an inhibitor of the electron transport chain complex I, mimics the antrodin C productivity-enhancing effects of H2O2. Delineating the steps connecting oxidative stress with increased antrodin C biosynthesis will facilitate the fine-tuning of strategies for rational fermentation process improvement.

Interactions of TiO2 Nanoparticles with Ingredients from Modern Lifestyle Products and Their Effects on Human Skin Cells

The number of consumer products containing nanoparticles (NPs) experienced a rapid increase during the past decades. However, most studies of nanosafety have been conducted using only pure NPs produced in the laboratory, while the interactions with other ingredients in consumer products have rarely been considered so far. In the present study, we investigated such interactions—with a special focus on modern lifestyle products (MLPs) used by adolescents. An extensive survey was undertaken at different high schools all over Austria to identify MLPs that either contain NPs or that could come easily in contact with NPs from other consumer products (such as TiO₂ from sunscreens). Based on the results from a survey among secondary schools students, we focused on ingredients from Henna tattoos (2-hydroxy-1,4-naphtoquinone, HNQ, and p-phenylenediamine, PPD), fragrances (butylphenyl methylpropional, known as Lilial), cosmetics and skin-care products (four different parabens). As a cellular model, we decided to use neonatal normal human dermal fibroblasts (nNHDF), since skin contact is the main route of exposure for these compounds. TiO₂ NPs interacted with these compounds as evidenced by alterations in their hydrodynamic diameter observed by nanoparticle tracking analysis. Combinations of TiO₂ NPs with the different MLP components did not show altered cytotoxicity profiles compared to MLP components without TiO₂ NPs. Nevertheless, altered cellular glutathione contents were detected after incubation of the cells with Lilial. This effect was independent of the presence of TiO₂ NPs. Testing mixtures of NPs with other compounds from consumer products is an important approach to achieve a more reliable safety assessment.

GATA-1 isoforms differently contribute to the production and compartmentation of reactive oxygen species in the myeloid leukemia cell line K562

Maintenance of a balanced expression of the two isoforms of the transcription factor GATA‐1, the full‐length protein (GATA‐1_FL) and a shorter isoform (GATA‐1 _S), contributes to control hematopoiesis, whereas their dysregulation can alter the differentiation/proliferation potential of hematopoietic precursors thereby eventually leading to a variety of hematopoietic disorders. Although it is well established that these isoforms play opposite roles in these remarkable processes, most of the molecular pathways involved remain unknown.

Here, we demonstrate that GATA‐1_FL and GATA‐1_S are able to differently influence intracellular redox states and reactive oxygen species (ROS) compartmentation in the erythroleukemic K562 cell line, thus shedding novel mechanistic insights into the processes of cell proliferation and apoptosis resistance in myeloid precursors. Furthermore, given the role played by ROS signaling as a strategy to escape apoptosis and evade cell‐mediated immunity in myeloid cells, this study highlights a mechanism through which aberrant expression of GATA‐1 isoforms could play a role in the leukemogenic process.