Increased tyrosine phosphorylation of band 3 in hemoglobinopathies

A perspective on exogenous redox regulation mediated by transfused RBCs subject to the storage lesion

Granted with a potent ability to interact with and tolerate oxidative stressors, RBCs scavenge most reactive oxygen and nitrogen species (RONS) generated in circulation. This essential non-canonical function, however, renders RBCs susceptible to damage when vascular RONS are generated in excess, making vascular redox imbalance a common etiology of anemia, and thus a common indication for transfusion. This accentuates the relevance of impairments in redox metabolism during hypothermic storage, as the exposure to chronic oxidative stressors upon transfusion could be exceedingly deleterious to stored RBCs. Herein, we review the prominent mechanisms of the hypothermic storage lesion that alter the ability of RBCs to scavenge exogenous RONS as well as the associated clinical relevance.

A Novel Frameshift Mutation of HBB Causing Dominant β-Thalassemia in a Chinese Individual

We reported a rare β-thalassemia patient, a 41-year-old Chinese male with small cell hypopigmentation anemia, jaundice and splenomegaly as the main clinical symptoms. By using Next-Generation Sequencing (NGS), we identified a novel de novo HBB mutation(c.358_365dup, p.Phe123Alafs*39) which resulted in an abnormally prolonged β-globin chain comprising 159 amino acid residues. The secondary and three-dimensional structures of the β-globin predicted that the novel prolonged β-globin chain has a considerable risk of instability in the hemoglobin, and leads to clinical phenotype. This study contributes to the enrichment of the genetic pathogenic mutation database for thalassemia and underscores the significance of NGS in the screening of mutations for thalassemia families.

Recent developments in the use of pyruvate kinase activators as a new approach for treating sickle cell disease

ABSTRACT

Pyruvate kinase (PK) is a key enzyme in glycolysis, the sole source of adenosine triphosphate, which is essential for all energy-dependent activities of red blood cells. Activating PK shows great potential for treating a broad range of hemolytic anemias beyond PK deficiency, because they also enhance activity of wild-type PK. Motivated by observations of sickle-cell complications in sickle-trait individuals with concomitant PK deficiency, activating endogenous PK offers a novel and promising approach for treating patients with sickle-cell disease.

Tyrosine phosphorylation of band 3 impairs the storage quality of suspended red blood cells in the Tibetan high-altitude polycythemia population

Due to environmental hypoxia on the Tibetan Plateau, local residents often exhibit a compensative increase in hemoglobin concentration to maintain the body's oxygen supply. However, increases in hemoglobin and hematocrit (Hct) pose a serious challenge to the quality of stored suspended red blood cells (SRBCs) prepared from the blood of high-hemoglobin populations, especially populations at high altitude with polycythemia in Tibet. To explore the difference in storage quality of SRBCs prepared from plateau residents with a high hemoglobin concentration, blood donors were recruited from Tibet (> 3600 m) and Chengdu (≈ 500 m) and divided into a high-altitude control (HAC) group, high-altitude polycythemia (HAPC) group and lowland control (LLC) group according to their hemoglobin concentration and altitude of residence. The extracellular acidification rate (ECAR), pyruvate kinase (PK) activity and band 3 tyrosine phosphorylation were analyzed on the day of blood collection. Then, whole-blood samples were processed into SRBCs, and storage quality parameters were analyzed aseptically on days 1, 14, 21 and 35 of storage. Overall, we found that tyrosine 21 phosphorylation activated glycolysis by releasing glycolytic enzymes from the cytosolic domain of band 3, thus increasing glucose consumption and lactate accumulation during storage, in the HAPC group. In addition, band 3 tyrosine phosphorylation impaired erythrocyte deformability, accompanied by the highest hemolysis rate in the HAPC group, during storage. We believe that these results will stimulate new ideas to further optimize current additive solutions for the high-hemoglobin population in Tibet and reveal new therapeutic targets for the treatment of HAPC populations.

Rapid degradation of protein tyrosine phosphatase 1B in sickle cells: Possible contribution to sickle cell membrane weakening

Although both protein tyrosine phosphatases and kinases are constitutively active in healthy human red blood cells (RBCs), the preponderance of phosphatase activities maintains the membrane proteins in a predominantly unphosphorylated state. We report here that unlike healthy RBCs, proteins in sickle cells are heavily tyrosine phosphorylated, raising the question regarding the mechanism underpinning this tyrosine phosphorylation. Upon investigating possible causes, we observe that protein tyrosine phosphatase 1B (PTP1B), the major erythrocyte tyrosine phosphatase, is largely digested to a lower molecular weight fragment in sickle cells. We further find that the resulting truncated form of PTP1B is significantly less active than its intact counterpart, probably accounting for the intense tyrosine phosphorylation of Band 3 in sickle erythrocytes. Because this tyrosine phosphorylation of Band 3 promotes erythrocyte membrane weakening that causes release of both membrane vesicles and cell free hemoglobin that in turn initiates vaso-occlusive events, we conclude that cleavage of PTP1B could contribute to the symptoms of sickle cell disease. We further posit that methods to inhibit proteolysis of PTP1B could mitigate symptoms of the disease.

Cell Physiology and Molecular Mechanism of Anion Transport by Erythrocyte Band 3/AE1

The major transmembrane protein of the red blood cell, known as band 3, AE1, and SLC4A1, has two main functions: 1) catalysis of Cl^-/HCO₃^- exchange, one of the steps in CO₂ excretion; 2) anchoring the membrane skeleton. This review summarizes the 150 year history of research on red cell anion transport and band 3 as an experimental system for studying membrane protein structure and ion transport mechanisms. Important early findings were that red cell Cl^- transport is a tightly coupled 1:1 exchange and band 3 is labeled by stilbenesulfonate derivatives that inhibit anion transport. Biochemical studies showed that the protein is dimeric or tetrameric (paired dimers) and that there is one stilbenedisulfonate binding site per subunit of the dimer. Transport kinetics and inhibitor characteristics supported the idea that the transporter acts by an alternating access mechanism with intrinsic asymmetry. The sequence of band 3 cDNA provided a framework for detailed study of protein topology and amino acid residues important for transport. The identification of genetic variants produced insights into the roles of band 3 in red cell abnormalities and distal renal tubular acidosis. The publication of the membrane domain crystal structure made it possible to propose concrete molecular models of transport. Future research directions include improving our understanding of the transport mechanism at the molecular level and of the integrative relationships among band 3, hemoglobin, carbonic anhydrase, and gradients (both transmembrane and subcellular) of HCO₃^-, Cl^-, O₂, CO₂, pH, and NO metabolites during pulmonary and systemic capillary gas exchange.

Post-translational modification as a response to cellular stress induced by hemoglobin oxidation in sickle cell disease

Intracellular oxidative stress and oxidative modification of sickle hemoglobin (HbS) play a role in sickle cell disease (SCD) pathogenesis. Recently, we reported that Hb-dependent oxidative stress induced post-translational modifications (PTMs) of Hb and red blood cell (RBC) membrane proteins of transgenic SCD mice. To identify the mechanistic basis of these protein modifications, we followed in vitro oxidative changes occurring in intracellular Hb obtained from RBCs and RBC-derived microparticles (MPs) from the blood of 23 SCD patients (HbSS) of which 11 were on, and 12, off hydroxyurea (HU) treatment, and 5 ethnic matched controls. We used mass spectrometry-based proteomics to characterize these oxidative PTMs on a cross-sectional group of these patients (n = 4) and a separate subgroup of patients (n = 2) studied prior to initiation and during HU treatment. Collectively, these data indicated that band-3 and its interaction network involved in MPs formation exhibited more protein phosphorylation and ubiquitination in SCD patients than in controls. HU treatment reversed these oxidative PTMs back to level observed in controls. These PTMs were also confirmed using orthogonal immunoprecipitation experiments. Moreover, we observed specific markers reflective of oxidative stress, including irreversible oxidation of βCys93 and ubiquitination of Hb βLys145 (and βLys96). Overall, these studies strongly suggest that extensive erythrocyte membrane protein phosphorylation and ubiquitination are involved in SCD pathogenesis and provide further insight into the multifaceted effects of HU treatment.

Differential red blood cell age fractionation and Band 3 phosphorylation distinguish two different subtypes of warm autoimmune hemolytic anemia

Warm autoimmune hemolytic anemia (wAIHA) is a blood disorder characterized by the increased destruction of autologous red blood cells (RBCs) due to the presence of opsonizing pathogenic autoantibodies. Preliminary reports published more than three decades ago proposed the presence of two wAIHA subtypes: Type I, in which autoantibodies preferentially recognize the oldest, most dense RBCs; and Type II, characterized by autoantibodies that show no preference.

STUDY DESIGN AND METHODS

We evaluated patients having wAIHA for Type I and II subtype using discontinuous Percoll gradient age fractionation and direct antiglobulin test (DAT). We performed Western immunoblotting and mass spectrometry to show autoantibody specificity for Band 3. We investigated Band 3 tyrosine phosphorylation in different Percoll fractions to determine aging associated with oxidative stress.

RESULTS

We confirm the existence of two subtypes of wAIHA, Type I and Type II, and that autoantibodies recognize Band 3. Type I patients were characterized by five Percoll fractions, with a DAT showing IgG opsonization F₁ < F₅ and elevated Band 3 phosphorylation compared to healthy controls (HCs). In contrast, Type II wAIHA patients were characterized by three to four Percoll fractions, where the DAT IgG opsonization shows F₁ ≥ F_3/4 and Band 3 phosphorylation was absent or significantly decreased compared to HC.

CONCLUSIONS

Type I patients have increased Band 3 tyrosine phosphorylation that may represent accelerated aging of their RBCs resulting in exacerbation of a pathologic form of RBC senescence. Type II patients show decreased Band 3 tyrosine phosphorylation and lack the oldest, most dense RBCs suggesting premature RBC clearance and a more severe wAIHA.

Inhibition of Band 3 tyrosine phosphorylation: a new mechanism for treatment of sickle cell disease

Many hypotheses have been proposed to explain how a glutamate to valine substitution in sickle haemoglobin (HbS) can cause sickle cell disease (SCD). We propose and document a new mechanism in which elevated tyrosine phosphorylation of Band 3 initiates sequelae that cause vaso-occlusion and the symptoms of SCD. In this mechanism, denaturation of HbS and release of heme generate intracellular oxidants which cause inhibition of erythrocyte tyrosine phosphatases, thus permitting constitutive tyrosine phosphorylation of Band 3. This phosphorylation in turn induces dissociation of the spectrin-actin cytoskeleton from the membrane, leading to membrane weakening, discharge of membrane-derived microparticles (which initiate the coagulation cascade) and release of cell-free HbS (which consumes nitric oxide) and activates the endothelium to express adhesion receptors). These processes promote vaso-occlusive events which cause SCD. We further show that inhibitors of Syk tyrosine kinase block Band 3 tyrosine phosphorylation, prevent release of cell-free Hb, inhibit discharge of membrane-derived microparticles, increase sickle cell deformability, reduce sickle cell adhesion to human endothelial cells, and enhance sickle cell flow through microcapillaries. In view of reports that imatinib (a Syk inhibitor) successfully treats symptoms of sickle cell disease, we suggest that Syk tyrosine kinase inhibitors warrant repurposing as potential treatments for SCD.

Hemoglobin oxidation-dependent reactions promote interactions with band 3 and oxidative changes in sickle cell-derived microparticles

The contribution of intracellular hemoglobin (Hb) oxidation to RBC-derived microparticle (MP) formation is poorly defined in sickle cell disease (SCD). Here we report that sickle Hb (HbS) oxidation, coupled with changes in cytosolic antioxidative proteins, is associated with membrane alterations and MP formation in homozygous Townes-sickle cell (Townes-SS) mice. Photometric and proteomic analyses confirmed the presence of high levels of Hb oxidation intermediates (ferric/ferryl) and consequent β-globin posttranslational modifications, including the irreversible oxidation of βCys93 and the ubiquitination of βLys96 and βLys145. This is the first report to our knowledge to link the UPS (via ubiquitinated Hb and other proteins) to oxidative stress. Ferryl Hb also induced complex formation with band 3 and RBC membrane proteins. Incubation of Townes-SS MPs with human endothelial cells caused greater loss of monolayer integrity, apoptotic activation, heme oxygenase-1 induction, and concomitant bioenergetic imbalance compared with control Townes-AA MPs. MPs obtained from Townes-SS mice treated with hydroxyurea produced fewer posttranslational Hb modifications. In vitro, hydroxyurea reduced the levels of ferryl Hb and shielded its target residue, βCys93, by a process of S-nitrosylation. These mechanistic analyses suggest potential antioxidative therapeutic modalities that may interrupt MP heme-mediated pathophysiology in SCD patients.

Squeezing for Life - Properties of Red Blood Cell Deformability

Deformability is an essential feature of blood cells (RBCs) that enables them to travel through even the smallest capillaries of the human body. Deformability is a function of (i) structural elements of cytoskeletal proteins, (ii) processes controlling intracellular ion and water handling and (iii) membrane surface-to-volume ratio. All these factors may be altered in various forms of hereditary hemolytic anemia, such as sickle cell disease, thalassemia, hereditary spherocytosis and hereditary xerocytosis. Although mutations are known as the primary causes of these congenital anemias, little is known about the resulting secondary processes that affect RBC deformability (such as secondary changes in RBC hydration, membrane protein phosphorylation, and RBC vesiculation). These secondary processes could, however, play an important role in the premature removal of the aberrant RBCs by the spleen. Altered RBC deformability could contribute to disease pathophysiology in various disorders of the RBC. Here we review the current knowledge on RBC deformability in different forms of hereditary hemolytic anemia and describe secondary mechanisms involved in RBC deformability.

Global transformation of erythrocyte properties via engagement of an SH2-like sequence in band 3

Src homology 2 (SH2) domains are composed of weakly conserved sequences of ∼100 aa that bind phosphotyrosines in signaling proteins and thereby mediate intra- and intermolecular protein-protein interactions. In exploring the mechanism whereby tyrosine phosphorylation of the erythrocyte anion transporter, band 3, triggers membrane destabilization, vesiculation, and fragmentation, we discovered a SH2 signature motif positioned between membrane-spanning helices 4 and 5. Evidence that this exposed cytoplasmic sequence contributes to a functional SH2-like domain is provided by observations that: (i) it contains the most conserved sequence of SH2 domains, GSFLVR; (ii) it binds the tyrosine phosphorylated cytoplasmic domain of band 3 (cdb3-PO₄) with K_d = 14 nM; (iii) binding of cdb3-PO₄ to erythrocyte membranes is inhibited both by antibodies against the SH2 signature sequence and dephosphorylation of cdb3-PO₄; (iv) label transfer experiments demonstrate the covalent transfer of photoactivatable biotin from isolated cdb3-PO₄ (but not cdb3) to band 3 in erythrocyte membranes; and (v) phosphorylation-induced binding of cdb3-PO₄ to the membrane-spanning domain of band 3 in intact cells causes global changes in membrane properties, including (i) displacement of a glycolytic enzyme complex from the membrane, (ii) inhibition of anion transport, and (iii) rupture of the band 3-ankyrin bridge connecting the spectrin-based cytoskeleton to the membrane. Because SH2-like motifs are not retrieved by normal homology searches for SH2 domains, but can be found in many tyrosine kinase-regulated transport proteins using modified search programs, we suggest that related cases of membrane transport proteins containing similar motifs are widespread in nature where they participate in regulation of cell properties.

Band 3 Erythrocyte Membrane Protein Acts as Redox Stress Sensor Leading to Its Phosphorylation by p (72) Syk

In erythrocytes, the regulation of the redox sensitive Tyr phosphorylation of band 3 and its functions are still partially defined. A role of band 3 oxidation in regulating its own phosphorylation has been previously suggested. The current study provides evidences to support this hypothesis: (i) in intact erythrocytes, at 2 mM concentration of GSH, band 3 oxidation, and phosphorylation, Syk translocation to the membrane and Syk phosphorylation responded to the same micromolar concentrations of oxidants showing identical temporal variations; (ii) the Cys residues located in the band 3 cytoplasmic domain are 20-fold more reactive than GSH; (iii) disulfide linked band 3 cytoplasmic domain docks Syk kinase; (iv) protein Tyr phosphatases are poorly inhibited at oxidant concentrations leading to massive band 3 oxidation and phosphorylation. We also observed that hemichromes binding to band 3 determined its irreversible oxidation and phosphorylation, progressive hemolysis, and serine hyperphosphorylation of different cytoskeleton proteins. Syk inhibitor suppressed the phosphorylation of band 3 also preventing serine phosphorylation changes and hemolysis. Our data suggest that band 3 acts as redox sensor regulating its own phosphorylation and that hemichromes leading to the protracted phosphorylation of band 3 may trigger a cascade of events finally leading to hemolysis.

Targeting the redox metabolism of Plasmodium falciparum

Targeting the redox metabolism of Plasmodium falciparum to create a fatal overload of oxidative stress is a route to explore the discovery of new antimalarial drugs. There are three main possibilities to target the redox metabolism of P. falciparum at the erythrocytic stage: selective targeting and inhibition of a redox P. falciparum protein or enzyme; oxidant drugs targeting essential parasite components and heme by-products; and redox cycler drugs targeting the parasitized red blood cell. Oxidants and redox cycler agents, with or without specific targets, may disrupt the fragile parasitized erythrocyte redox-dependent architecture given that: redox equilibrium plays a vital role at the erythrocytic stage; P. falciparum possesses major NADPH-dependent redox systems, such as glutathione and thioredoxin ones; and the protein-NADPH-dependent phosphorylation-dephosphorylation process is involved in building new permeation pathways and channels for the nutrient-waste import-export traffic of the parasite.

Proteomic analysis of ERK1/2-mediated human sickle red blood cell membrane protein phosphorylation

BACKGROUND

In sickle cell disease (SCD), the mitogen-activated protein kinase (MAPK) ERK1/2 is constitutively active and can be inducible by agonist-stimulation only in sickle but not in normal human red blood cells (RBCs). ERK1/2 is involved in activation of ICAM-4-mediated sickle RBC adhesion to the endothelium. However, other effects of the ERK1/2 activation in sickle RBCs leading to the complex SCD pathophysiology, such as alteration of RBC hemorheology are unknown.

RESULTS

To further characterize global ERK1/2-induced changes in membrane protein phosphorylation within human RBCs, a label-free quantitative phosphoproteomic analysis was applied to sickle and normal RBC membrane ghosts pre-treated with U0126, a specific inhibitor of MEK1/2, the upstream kinase of ERK1/2, in the presence or absence of recombinant active ERK2. Across eight unique treatment groups, 375 phosphopeptides from 155 phosphoproteins were quantified with an average technical coefficient of variation in peak intensity of 19.8%. Sickle RBC treatment with U0126 decreased thirty-six phosphopeptides from twenty-one phosphoproteins involved in regulation of not only RBC shape, flexibility, cell morphology maintenance and adhesion, but also glucose and glutamate transport, cAMP production, degradation of misfolded proteins and receptor ubiquitination. Glycophorin A was the most affected protein in sickle RBCs by this ERK1/2 pathway, which contained 12 unique phosphorylated peptides, suggesting that in addition to its effect on sickle RBC adhesion, increased glycophorin A phosphorylation via the ERK1/2 pathway may also affect glycophorin A interactions with band 3, which could result in decreases in both anion transport by band 3 and band 3 trafficking. The abundance of twelve of the thirty-six phosphopeptides were subsequently increased in normal RBCs co-incubated with recombinant ERK2 and therefore represent specific MEK1/2 phospho-inhibitory targets mediated via ERK2.

CONCLUSIONS

These findings expand upon the current model for the involvement of ERK1/2 signaling in RBCs. These findings also identify additional protein targets of this pathway other than the RBC adhesion molecule ICAM-4 and enhance the understanding of the mechanism of small molecule inhibitors of MEK/1/2/ERK1/2, which could be effective in ameliorating RBC hemorheology and adhesion, the hallmarks of SCD.

Effects of pre-storage leukoreduction on stored red blood cells signaling: a time-course evaluation from shape to proteome

The introduction of pre-storage leukoreduction in the preparation of standard RBCs intended for transfusion provided significant improvement in the quality of labile products and their post transfusion viability and effects, although the literature data are controversial. To elucidate the issue of the probable leukoreduction effects on RBCs storage lesion, we evaluated various storage quality measures in RBCs stored in either leukoreduced (L) or non-leukoreduced (N) units, with emphasis to senescence and oxidative stress associated modifications. Our data suggest that the residual leukocytes/platelets of the labile products represent a stressful storage factor, countering the structural and functional integrity of stored RBCs. Hemolysis, irreversible echinocytosis, microvesiculation, removal signaling, ROS/calcium accumulation, band 3-related senescence modifications, membrane proteome stress biomarkers as well as emergence of a senescence phenotype in young RBCs that is disproportionate to their age, are all encountered more or mostly in N-RBCs compared to the L-RBCs, either for a part or for the whole of the storage period. The partial, yet significant, alleviation of so many storage-related manifestations in the L-RBCs compared to the N-RBCs, is presented for the first time and provides a rational mechanistic interpretation of the improved storage quality and transfusions observed by the introduction of pre-storage leukoreduction. This article is part of a Special Issue entitled: Integrated omics.

Regulation of membrane-cytoskeletal interactions by tyrosine phosphorylation of erythrocyte band 3

The cytoplasmic domain of band 3 serves as a center of erythrocyte membrane organization and constitutes the major substrate of erythrocyte tyrosine kinases. Tyrosine phosphorylation of band 3 is induced by several physiologic stimuli, including malaria parasite invasion, cell shrinkage, normal cell aging, and oxidant stress (thalassemias, sickle cell disease, glucose-6-phosphate dehydrogenase deficiency, etc). In an effort to characterize the biologic sequelae of band 3 tyrosine phosphorylation, we looked for changes in the polypeptide's function that accompany its phosphorylation. We report that tyrosine phosphorylation promotes dissociation of band 3 from the spectrin-actin skeleton as evidenced by: (1) a decrease in ankyrin affinity in direct binding studies, (2) an increase in detergent extractability of band 3 from ghosts, (3) a rise in band 3 cross-linkability by bis-sulfosuccinimidyl-suberate, (4) significant changes in erythrocyte morphology, and (5) elevation of the rate of band 3 diffusion in intact cells. Because release of band 3 from its ankyrin and adducin linkages to the cytoskeleton can facilitate changes in multiple membrane properties, tyrosine phosphorylation of band 3 is argued to enable adaptive changes in erythrocyte biology that permit the cell to respond to the above stresses.

Irreversible AE1 tyrosine phosphorylation leads to membrane vesiculation in G6PD deficient red cells

BACKGROUND

While G6PD deficiency is one of the major causes of acute hemolytic anemia, the membrane changes leading to red cell lysis have not been extensively studied. New findings concerning the mechanisms of G6PD deficient red cell destruction may facilitate our understanding of the large individual variations in susceptibility to pro-oxidant compounds and aid the prediction of the hemolytic activity of new drugs.

METHODOLOGY/PRINCIPAL FINDINGS

Our results show that treatment of G6PD deficient red cells with diamide (0.25 mM) or divicine (0.5 mM) causes: (1) an increase in the oxidation and tyrosine phosphorylation of AE1; (2) progressive recruitment of phosphorylated AE1 in large membrane complexes which also contain hemichromes; (3) parallel red cell lysis and a massive release of vesicles containing hemichromes. We have observed that inhibition of AE1 phosphorylation by Syk kinase inhibitors prevented its clustering and the membrane vesiculation while increases in AE1 phosphorylation by tyrosine phosphatase inhibitors increased both red cell lysis and vesiculation rates. In control RBCs we observed only transient AE1 phosphorylation.

CONCLUSIONS/SIGNIFICANCE

Collectively, our findings indicate that persistent tyrosine phosphorylation produces extensive membrane destabilization leading to the loss of vesicles which contain hemichromes. The proposed mechanism of hemolysis may be applied to other hemolytic diseases characterized by the accumulation of hemoglobin denaturation products.

Intercellular adhesion molecule-4 and CD36 are implicated in the abnormal adhesiveness of sickle cell SAD mouse erythrocytes to endothelium

BACKGROUND

Abnormal adhesiveness of red blood cells to endothelium has been implicated in vaso-occlusive crisis of sickle cell disease. The present study examined whether the SAD mouse model exhibits the same abnormalities of red blood cell adhesion as those found in human sickle cell disease.

DESIGN AND METHODS

The repertoire of adhesive molecules on murine erythrocytes and bEnd.3 microvascular endothelial cells was determined by flow cytometry using monoclonal antibodies or by western blotting. Adhesion was investigated in dynamic conditions and measured at different shear stresses.

RESULTS

CD36, CD47 and intercellular adhesion molecular-4, but not Lutheran blood group antigen/basal cell adhesion molecule, are present on mouse mature erythrocytes. alpha(4)beta(1) are not expressed on SAD and wild type reticulocytes. Endothelial bEnd.3 cells express alpha(V)beta(3), alpha(4)beta(1), CD47, vascular cell adhesion molecule-1, and Lutheran blood group antigen/basal cell adhesion molecule, but not CD36. Adhesion of SAD red cells is: (i) 2- to 3-fold higher than that of wild type red cells; (ii) further increased on platelet activating factor-activated endothelium; (iii) not stimulated by epinephrine; (iv) inhibited after treating the endothelium with a peptide reproducing one of the binding sequences of mouse intercellular adhesion molecular-4, or with mon-oclonal antibody against murine alpha(v) integrin; and (v) inhibited after pretreatment of red blood cells with anti-mouse CD36 monoclonal antibodies. The combination of treatments with intercellular adhesion molecular-4 peptide and anti-CD36 monoclonal antibodies eliminates excess adhesion of SAD red cells. The phosphorylation state of intercellular adhesion molecular-4 and CD36 is probably not involved in the over-adhesiveness of SAD erythrocytes.

CONCLUSIONS

Intercellular adhesion molecular-4/alpha(v)beta(3) and CD36/thrombospondin interactions might contribute to the abnormally high adhesiveness of SAD red cells. The SAD mouse is a valuable animal model for investigating adhesion processes of sickle cell disease.

Current knowledge about the functional roles of phosphorylative changes of membrane proteins in normal and diseased red cells

With the advent of proteomic techniques the number of known post-translational modifications (PTMs) affecting red cell membrane proteins is rapidly growing but the understanding of their role under physiological and pathological conditions is incompletely established. The wide range of hereditary diseases affecting different red cell membrane functions and the membrane modifications induced by malaria parasite intracellular growth represent a unique opportunity to study PTMs in response to variable cellular stresses. In the present review, some of the major areas of interest in red cell membrane research have been considered as modifications of erythrocyte deformability and maintenance of the surface area, membrane transport alterations, and removal of diseased and senescent red cells. In all mentioned research areas the functional roles of PTMs are prevalently restricted to the phosphorylative changes of the more abundant membrane proteins. The insufficient information about the PTMs occurring in a large majority of the red membrane proteins and the general lack of mass spectrometry data evidence the need of new comprehensive, proteomic approaches to improve the understanding of the red cell membrane physiology.

Oxidative effects of gemfibrozil on anion influx and metabolism in normal and Beta-thalassemic erythrocytes: physiological implications

To further clarify some peculiar molecular mechanisms related to the physiology and pathophysiology of erythrocytes with respect to oxygen binding and release, metabolism and senescence, we investigated the oxidative effects of gemfibrozil in normal and beta-thalassemic red blood cells. Our results showed that the oxidative stress promoted by the drug, through a direct interaction with hemoglobin, may lead to activation of caspase 3, which in turn influences the band 3 anion flux and glucose metabolism. In a comparative context, we also evaluated the effect on band 3 and caspase 3 activation of orthovanadate (a phosphatase inhibitor) and t-butylhydroperoxide (a known oxidant). The results support the hypothesis that gemfibrozil influences band 3 function through several mechanisms of action, centered on oxidative stress, which induces significant alterations of glucose metabolism.

Modulation of glyceraldehyde 3 phosphate dehydrogenase activity and tyr-phosphorylation of Band 3 in human erythrocytes treated with ferriprotoporphyrin IX

Erythrocyte glyceraldehyde-3-phosphate dehydrogenase (G3PD), is a glycolytic enzyme normally inhibited upon binding to the anion transporter Band 3 and activated when free in the cytosol. We have previously reported that ferric protoporphyrin IX (FP) enhances G3PD activity in human erythrocytes (RBC). This could be due to two mechanisms considered in this work: Band 3 tyrosine phosphorylation or oxidative damage of specific G3PD binding sites in the membrane. In both cases binding of G3PD to the membrane would be prevented, leading to the enhancement of G3PD activity. Here, we show that FP induces a dose- and time-dependent phosphorylation of tyrosine 8 and 21 of Band 3, as confirmed by the recruitment of SHP2 phosphatase to the membrane. It appears that Band 3 phosphorylation is due to the oxidation of critical sulfydryl groups of a membrane phosphatase (PTP). Data on membrane localization, Mg2+ dependence, sensitivity to thiol oxidizing agents and protection by N-acetylcysteine (NAC) and DTT strongly suggest the involvement of PTP1B, the major PTP of human RBC associated to and acting on Band 3. However, FP activates G3PD even when Band 3 phosphorylation is inhibited, therefore phosphorylation is not the mechanism underlying G3PD activation by FP. The capacity of NAC of counteracting the stimulatory activity of FP, supports the hypothesis that FP might induce the oxidative damage of specific G3PD binding sites in the membrane, causing the displacement of the enzyme into the cytosol and/or the release from its binding site and therefore its activation.

Augmented erythrocyte band-3 phosphorylation in septic mice

Infection-induced RBC dysfunction has been shown to play a role in the modulation of host response to injury and infection. The underlying biochemical mechanisms are not known. This study investigated alterations in RBC band-3 phosphorylation status and its relationship to anion exchange activity in vitro as well as under in vivo septic conditions induced by cecal ligation and puncture (CLP) in mice. Pervanadate treatment in vitro increased band-3 tyrosine phosphorylation that was accompanied by decreased RBC deformability and anion exchange activity. Following sepsis, band-3 tyrosine phosphorylation in whole RBC ghosts as well as in cytoskeleton-bound or soluble RBC protein fractions were elevated as compared to controls. Although anion exchange activity was similar in RBCs from septic and control animals, band-3 interaction with eosin-5-maleimide (EMA), which binds to band-3 lysine moieties, was increased in cells from septic animals as compared to controls, indicating that sepsis altered band 3 organization within the RBC membrane. Since glucose-6-phosphate dehydrogenase is a major antioxidant enzyme in RBC, in order to assess the potential role of oxidative stress in band-3 tyrosine phosphorylation, sepsis-induced RBC responses were also compared between WT and (G6PD) mutant animals (20% of normal G6PD activity). Band-3 membrane content and EMA staining were elevated in G6PD mutant mice compared to WT under control non-septic conditions. Following sepsis, G6PD mutant animals showed lessened responses in band-3 tyrosine phosphorylation and EMA staining compared to WT. RBC anion exchange activity was similar between mutant and WT animals under all tested conditions. In summary, these studies indicate that sepsis results in elevated band-3 tyrosine phosphorylation and alters band-3 membrane organization without grossly affecting RBC anion exchange activity. The observations also suggest that factors other than oxidative stress are responsible for the sepsis-induced increase in RBC band-3 tyrosine phosphorylation.

Phosphotyrosine phosphatases acting on band 3 in human erythrocytes of different age: PTP1B processing during cell ageing

The phosphorylation of tyrosine residues of human red blood cell (RBC) band 3 is regulated in vivo by constitutively active tyrosine-kinases (PTKs) and phosphotyrosine-phosphatases (PTPs), identified so far as, respectively, p72(syk) and p56/53(lyn), and PTP1B and SHPTP-2. Tyr-phosphorylation of band 3 increases upon reduction of cell volume as in hypertonic media or during Ca(2+)-induced membrane vesiculation. We show here that old RBCs display higher Tyr-phosphorylation levels of band 3 than younger cells under hypertonic conditions, at least in part due to the reduced cell volume of old RBCs, a condition of lowered threshold for activation of volume-sensitive PTKs. We have also analysed the membrane-bound PTP activity and the relative abundance of PTP1B (as the main membrane-associated PTP) in RBCs of different age. Immunodetection of PTP1B in purified ghost membranes revealed that the catalytic, N-terminal domain of the PTP is partially cleaved, in an age-dependent manner, from the membrane-bound domain, and it is lost during the preparation of ghost membranes. This suggests that erythrocytes may undergo in vivo activation of the Ca(2+)-dependent calpain system that proteolytically regulates PTP1B activity, as already documented for other cell types. On the other hand, the assay of the PTP activity that remains associated with the membranes of RBCs of different age indicated that the PTP undergoes oxidative inactivation that can be further differentiated into reversible and irreversible components.

Chemical and pathological oxidative influences on band 3 protein anion-exchanger

BACKGROUND/AIMS

The erythrocyte is a cell exposed to a high level of oxygen pressure and to oxidative chemical agents. This stress involves SH-groups oxidation, cell shrinkage by activation of K-Cl co-transport (KCC) and elevation of the band 3 tyrosine phosphorylation level. The aim of our study was to test whether oxidative stress could influence band 3-mediated anion transport in human red blood cells.

METHODS

To evaluate this hypothesis, normal and pathological (glucose 6 phosphate dehydrogenase (G6PDH) defficient) erythrocytes were treated with known sulphydryl-blocking or thiol-oxidizing agents, such as N-ethylmaleimide (NEM), azodicarboxylic acid bis[dimethylamide] (diamide), orthovanadate, Mg2+ and tested for sulphate (SO4-) uptake, K+ efflux, G6PDH activity and glutathione (GSH) concentration.

RESULTS

In normal red blood cells, the rate constants of SO4- uptake decreased by about 28 % when cells were incubated with NEM, diamide and orthovanadate. In G6PDH-deficient red blood cells, in which oxidative stress occurs naturally, the rate constant of sulphate uptake was decreased by about 40% that of normal red cells. Addition of oxidizing and phosphatase inhibitor agents to pathological erythrocytes further decreased anion transport. In contrast, G6PDH activity was increased under oxidative stress in normal as well as in pathological cells and was lower in the presence of exogenous Mg2+ in parallel to a significant increase in sulphate transport. In both cells, the oxidizing agents increased K+ efflux with depletion of GSH.

CONCLUSION

The data are discussed in light of the possible opposite effects exerted by oxidative agents and Mg2+ on KCC and on the protein tyrosine kinase (PTK)-protein tyrosine phosphatase (PTP) equilibrium. The decreased sulphate uptake observed in the experimental and pathological conditions could be due to band 3 SH-groups oxidation or to oxidative stress-induced K-Cl symport-mediated cell shrinkage with concomitant band 3 tyrosine phosphorylation.

Ca2+ promotes erythrocyte band 3 tyrosine phosphorylation via dissociation of phosphotyrosine phosphatase from band 3

The anion-exchange band 3 protein is the main erythrocyte protein that is phosphorylated by protein tyrosine kinase (PTK). We have previously identified a band 3-associated phosphotyrosine phosphatase (PTP) that is normally highly active and prevents the accumulation of band 3 phosphotyrosine. Band 3 tyrosine phosphorylation can be induced by inhibition of PTP (vanadate, thiol oxidation), activation of PTK (hypertonic NaCl) or intracellular increased Ca(2+) (mechanism unknown). We now show that there is inhibition of dephosphorylation of band 3 in Ca(2+)/ionophore-treated erythrocytes and in membranes isolated from the treated cells. These membranes exhibit phosphatase activity upon the addition of exogenous substrate. Dephosphorylation of the endogenous substrate (band 3) can be activated in these membranes by the addition of Mg(2+). Thus the inability of PTP to dephosphorylate the band 3 phosphotyrosine is not due to inhibition of the enzyme itself. Ca(2+) rise in the erythrocyte causes dissociation of PTP from band 3, thus leaving the kinase unopposed. This is shown by a significant diminution in band 3/PTP co-precipitation. Addition of Mg(2+) to these membranes leads to reassociation of band 3 with PTP. The Ca(2+)-induced inhibition of band 3 dephosphorylation may be due to Ca(2+)-dependent alterations in membrane components and structure, affecting the interaction of band 3 with PTP. The Ca(2+)-induced tyrosine phosphorylation, involving an apparent PTP inhibition via dissociation from the substrate, may play a role in signal transduction pathways and in certain pathological disorders associated with increased cell Ca(2+).

Band 3 is an anchor protein and a target for SHP-2 tyrosine phosphatase in human erythrocytes

Tyr phosphorylation of the multifunctional transmembrane protein band 3 has been implicated in several erythrocyte functions and disorders. We previously demonstrated that pervanadate treatment of human erythrocytes induces band-3 Tyr phosphorylation, which is catalyzed by the sequential action of tyrosine kinase Syk and tyrosine kinase(s) belonging to the Src family. In this study, we show that Tyr phosphorylation of band 3, elicited by pervanadate, N-ethylmaleimide, or diamide, greatly increases band-3 interaction with the tyrosine phosphatase SHP-2 in parallel with the translocation of SHP-2 to erythrocyte membranes. These events seem to be mediated by Src-like catalyzed phosphorylation of band 3 because both SHP-2 translocation to cellular membranes and its interaction with Tyr-phosphorylated protein are greatly counteracted by PP2, a specific inhibitor of Src kinases. Binding-competition experiments demonstrate that SHP-2 recruitment to band 3 occurs via its SH2 domain(s). In particular, our data support the view that SHP-2 docks specifically with P-Y359 of band 3. Experiments performed with intact erythrocytes in the presence of the SHP-2 inhibitor calpeptin suggest that, once recruited to Tyr-phosphorylated band 3, the tyrosine phosphatase dephosphorylates the protein. P-Y8, 21, and 904 are the residues affected by SHP-2, as judged by (32)P-peptide mapping of band 3 digested with trypsin. These results indicate that in treated erythrocytes, recruitment of cytosolic SHP-2 to band 3 is a prerequisite for the subsequent dephosphorylation of the transmembrane protein.

beta-Spectrin S(ta) Bárbara: a novel frameshift mutation in hereditary spherocytosis associated with detectable levels of mRNA and a germ cell line mosaicism

Hereditary spherocytosis (HS) is a common inherited anaemia characterized by the presence of spherocytic red cells and by a heterogeneous nature in terms of its clinical presentation, molecular basis and inheritance. Defects in several membrane protein genes have been involved in the pathogenesis of HS, including defects in the beta-spectrin gene. We detected a novel frameshift mutation in the beta-spectrin gene, a C deletion at codon 638, in a patient presenting with HS and spectrin deficiency. The mutant protein was not detected in the membrane or in other cellular compartments, but detectable levels of mutant mRNA were found in the patient. Interestingly, this mutation was not present in the patient's parents, suggesting a genetic mosaicism, especially as the patient has an affected brother with the same molecular defect. We analysed DNA from different tissues of the parents and the mutation was absent from all tissues analysed. This mutation seems to be confined to the germ cell lineage of the patient's mother and must present a mosaic pattern in these cells as the patient also has unaffected siblings.

Deoxygenation and elevation of intracellular magnesium induce tyrosine phosphorylation of band 3 in human erythrocytes

Deoxygenation increases the level of tyrosine phosphorylation of band 3 by approximately 25% in human red blood cells (RBCs), as determined by Western blotting. The effect is much more pronounced in osmotically shrunken RBCs or in the presence of vanadate. When the rise in intracellular free Mg2+ concentration in deoxygenated RBCs is simulated via clamping of the intracellular magnesium in oxygenated RBCs by ionomycin, band 3 phosphorylation is elevated by up to 10-fold. Phosphorylated band 3 is preferentially retained by RBC skeletons, after mild extraction with Triton X-100. Elevation of intracellular free Mg2+ leads to band 3 phosphorylation and is accompanied by rigidification of the membrane skeleton as determined by analysis of RBC membrane mechanical fluctuations. These findings suggest that the visco-elastic properties of human erythrocytes may be regulated by band 3 tyrosine phosphorylation.