A novel mutation in the erythrocyte protein 4.2 gene of Japanese patients with hereditary spherocytosis (protein 4.2 Fukuoka)

Ankyrin-1 Gene Exhibits Allelic Heterogeneity in Conferring Protection Against Malaria

Allelic heterogeneity is a common phenomenon where a gene exhibits a different phenotype depending on the nature of its genetic mutations. In the context of genes affecting malaria susceptibility, it allowed us to explore and understand the intricate host–parasite interactions during malaria infections. In this study, we described a gene encoding erythrocytic ankyrin-1 (Ank-1) which exhibits allelic-dependent heterogeneous phenotypes during malaria infections. We conducted an ENU mutagenesis screen on mice and identified two Ank-1 mutations, one resulting in an amino acid substitution (MRI95845), and the other a truncated Ank-1 protein (MRI96570). Both mutations caused hereditary spherocytosis-like phenotypes and confer differing protection against Plasmodium chabaudi infections. Upon further examination, the Ank-1^(MRI96570) mutation was found to inhibit intraerythrocytic parasite maturation, whereas Ank-1^(MRI95845) caused increased bystander erythrocyte clearance during infection. This is the first description of allelic heterogeneity in ankyrin-1 from the direct comparison between two Ank-1 mutations. Despite the lack of direct evidence from population studies, this data further supported the protective roles of ankyrin-1 mutations in conferring malaria protection. This study also emphasized the importance of such phenomena in achieving a better understanding of host–parasite interactions, which could be the basis of future studies.

Investigating the key membrane protein changes during in vitro erythropoiesis of protein 4.2 (-) cells (mutations Chartres 1 and 2)

BACKGROUND

Protein 4.2 deficiency caused by mutations in the EPB42 gene results in hereditary spherocytosis with characteristic alterations of CD47, CD44 and RhAG. We decided to investigate at which stage of erythropoiesis these hallmarks of protein 4.2 deficiency arise in a novel protein 4.2 patient and whether they cause disruption to the band 3 macrocomplex.

DESIGN AND METHODS

We used immunoprecipitations and detergent extractability to assess the strength of protein associations within the band 3 macrocomplex and with the cytoskeleton in erythrocytes. Patient erythroblasts were cultured from peripheral blood mononuclear cells to study the effects of protein 4.2 deficiency during erythropoiesis.

RESULTS

We report a patient with two novel mutations in EPB42 resulting in complete protein 4.2 deficiency. Immunoprecipitations revealed a weakened ankyrin-1-band 3 interaction in erythrocytes resulting in increased band 3 detergent extractability. CD44 abundance and its association with the cytoskeleton were increased. Erythroblast differentiation revealed that protein 4.2 and band 3 appear simultaneously and associate early in differentiation. Protein 4.2 deficiency results in lower CD47, higher CD44 expression and increased RhAG glycosylation starting from the basophilic stage. The normal downregulation of CD44 expression was not seen during protein 4.2(-) erythroblast differentiation. Knockdown of CD47 did not increase CD44 expression, arguing against a direct reciprocal relationship.

CONCLUSIONS

We have established that the characteristic changes caused by protein 4.2 deficiency occur early during erythropoiesis. We postulate that weakening of the ankyrin-1-band 3 association during protein 4.2 deficiency is compensated, in part, by increased CD44-cytoskeleton binding.

Protein 4.2 Komatsu (D175Y) associated with the lack of interaction with ankyrin in human red blood cells

Membrane skeletal proteins play an important role in regulating the shape and function of the human red blood cell. Protein 4.2 interacts with cytoplasmic domain of band 3 (CDB3) and ankyrin for association between the skeleton network and the membrane. The deficiency of protein 4.2 may result in hereditary spherocytosis. In order to explore the molecular mechanism of the linkage of protein 4.2 Komatsu (D175Y) and protein 4.2 Nippon (A142T) with hereditary spherocytosis, a series of protein 4.2-derived mutants were designed and expressed in Escherichia coli. Their interactions with ankyrin and CDB3 were investigated by Far Western blot and pull-down assay in vitro. The results showed that the mutant D175Y of protein 4.2 cannot interact with ankyrin while mutant A142T, just like normal protein 4.2, can bind to ankyrin directly and can associate with CDB3 in the presence of ankyrin. Based on comparing the binding abilities of the protein 4.2 mutants D175F, D175A, D175K and D175Y with ankyrin and CDB3, we suggested that defective binding of protein 4.2 Komatsu to ankyrin is resulted from the charge effect of amino acid residue 175 substitution (D-->Y), which leads to significant structural change in protein 4.2 function domain.

Protein-4.2 association with band 3 (AE1, SLCA4) in Xenopus oocytes: effects of three natural protein-4.2 mutations associated with hemolytic anemia

We have investigated the effects of coexpression of protein 4.2 and three protein-4.2 variants with band 3 in the Xenopus oocyte expression system. Normal protein 4.2 increased band-3–specific chloride transport in the oocytes. Protein 4.2 also coimmunoprecipitated with band 3 and colocalized with band 3 at the oocyte plasma membrane. The increase in band-3–mediated chloride transport and coimmunoprecipitation of protein 4.2 required the presence of the N-terminal cytoplasmic domain of band 3. Protein 4.2 also localized to the oocyte plasma membrane in the absence of band 3. The protein-4.2 variants 4.2 Tozeur (R310Q) and 4.2 Komatsu (D175Y) had impaired ability to bind to band 3 and these variants did not localize to the oocyte plasma membrane when expressed on their own or when coexpressed with band 3. Unexpectedly, 4.2 Nippon (A142T) behaved similarly to normal protein 4.2. In the absence of a crystal structure of protein 4.2, we propose a homology model of protein 4.2 based on the structure of the sequence-related protein transglutaminase. Using our results in oocytes and this homology model we speculate how these mutations affect protein 4.2 and result in hereditary spherocytosis.

Cysteine 10 is a key residue in amyloidogenesis of human transthyretin Val30Met

Type I familial amyloidotic polyneuropathy (FAP), a systemic amyloidosis, is characterized by aggregation of variant transthyretin (TTR Val30Met) into stable, insoluble fibrils. This aggregation is caused by genetic and environmental factors. Genetic factors have been studied extensively. However, little is known about environmental or physiological factors involved in the disease process, and their identification may be important for development of effective treatment. X-ray crystallography of normal and amyloidogenic human TTR Val30Met in type I FAP showed that the -SH side chain of cysteine at position 10 (Cys10) forms a hydrogen bond with Gly57 in normal TTR but not in TTR Val30Met. This result suggests a crucial role for the free Cys10 residue and possible involvement of physiological factors affecting Cys residue reactivity in TTR amyloidogenesis. To analyze amyloidogenesis in vivo, our group generated murine FAP models by transgenic technology, with human TTR Val30Met. The three lines of transgenic mice expressed amyloidogenic mutant TTR (Cys10/Met30), wild-type TTR (Cys10/Val30), and artificial Cys-free mutant TTR (Ser10/Met30). Histochemical investigation showed deposition of amyloid derived from human TTR only in amyloidogenic mutant TTR (Cys10/Met30) mice. Thus, the -SH residue in Cys10 plays a crucial role in TTR Val30Met amyloidogenesis in vivo. These data suggest the possibility of innovative treatment via physiological factors modulating Cys10 residue reactivity.

Induction of erythrocyte protein 4.2 gene expression during differentiation of murine erythroleukemia cells

Protein 4.2 (P4.2) is an important component in the erythrocyte membrane skeletal network that regulates the stability and flexibility of erythrocytes. Recently, we provided the evidence for specific P4.2 expression in erythroid cells during development (L. Zhu et al., 1998, Blood 91, 695-705). Using dimethyl sulfoxide (DMSO)-induced differentiation of murine erythroleukemia (MEL) cells as a model, transcription of the P4.2 gene was found to be induced during erythroid differentiation. To examine the mechanism for this induction, we isolated the mouse P4.2 genomic DNA containing the 5' flanking sequence and defined the location of the P4.2 promoter. Transcription of the mouse P4.2 gene initiates at multiple sites, with the major initiation site mapped at 174 nucleotides upstream of the ATG start codon. The mouse P4.2 promoter is TATA-less and contains multiple potential binding sites for erythroid transcription factors GATA-1, NF-E2, EKLF, and tal-1/SCL. Transient transfection experiments demonstrated that a 1.7-kb mouse P4.2 promoter fused with the luciferase coding regions was induced in DMSO-treated MEL cells. Deletion analysis showed that a 259-bp P4.2 promoter DNA (nucleotide position -88 to +171 relative to the major transcription initiation site designated +1), containing a GATA-binding site at position -29 to -24, could still respond to the induction in differentiated MEL cells. Importantly, mutations in the -29/-24 GATA motif rendered the promoter unresponsive to DMSO induction. Electrophoretic mobility shift assay revealed that GATA-1 could bind to the -29/-24 GATA motif and this was confirmed by the observation that the nuclear protein bound to the motif was supershifted by an anti-GATA-1 monoclonal antibody. Taken together, these results suggest that the erythroid transcription factor GATA-1 plays an important role in the induction of P4.2 gene expression during erythroid cell differentiation.

Late expression of red cell membrane protein 4.2 in normal human erythroid maturation with seven isoforms of the protein 4.2 gene

The expression of protein 4.2 in normal human erythroid cells was studied utilizing erythroblasts from bone marrow and erythroid cells cultured by the two-phase liquid culture method from burst-forming unit erythroid (BFU-E) in peripheral blood. As opposed to spectrin, which was expressed in erythroid progenitors or very early erythroblasts, protein 4.2 was first detected in late erythroblasts with a morphology nearly identical to orthochromatic erythroblasts. Among the various major membrane proteins, the expression of protein 4.2 was the latest. At the gene level, protein 4.2 gene mRNA was expressed in early erythroblasts. During normal erythroid maturation, the expression of seven different protein 4.2 gene products was observed by Southern blot analysis. These seven gene products appeared to be derived from protein 4.2 gene in the presence or absence of skipping of the 90 bp in exon 1, exon 3, and/or exon 5, as judged by deduction from the protein 4.2 sequence. Therefore, it can be speculated that protein 4.2 is expressed after the cytoskeletal network has been constructed and assembled with integral proteins in the membrane lipid bilayer.

Red blood cell membrane disorders

The recent discovery of the specific molecular defects in many patients with hereditary spherocytosis and hereditary elliptocytosis/pyropoikilocytosis partially clarifies the molecular pathology of these diseases. HE and HPP are caused by defects in the horizontal interactions that hold the membrane skeleton together, particularly the critical spectrin self-association reaction. Single gene defects cause red cells to elongate as they circulate, by a unknown mechanism, and are clinically harmless. The combination of two defective genes or one severe alpha spectrin defect and a thalassaemia-like defect in the opposite allele (alphaLELY) results in fragile cells that fragment into bizarre shapes in the circulation, with haemolysis and sometimes life-threatening anaemia. A few of the alpha spectrin defects are common, suggesting they provide an advantage against malaria or some other threat. HS, in contrast, is nearly always caused by family-specific private mutations. These involve the five proteins that link the membrane skeleton to the overlying lipid bilayer: alpha and beta spectrin, ankyrin, band 3 and protein 4.2. Somehow, perhaps through loss of the anchorage band 3 provides its lipid neighbours (Peters et al, 1996), microvesiculation of the membrane surface ensues, leading to spherocytosis, splenic sequestration and haemolysis. Future research will need to focus on how each type of defect causes its associated disease, how the spleen aggravates membrane skeleton defects (a process termed 'conditioning'), how defective red, cells are recognized and removed in the spleen, and why patients with similar or even identical defects can have different clinical severity. Emphasis also needs to be given to improving diagnostic tests, particularly for HS, and exploring new options for therapy, like partial splenectomy, which can ameliorate symptoms while better protecting patients from bacterial sepsis and red cell parasites, and perhaps from atherosclerosis (Robinette & Franmeni, 1977) and venous thrombosis (Stewart et al, 1996).

Combination of two mutant alpha spectrin alleles underlies a severe spherocytic hemolytic anemia

We studied a patient with a severe spherocytic hemolytic anemia without family history of spherocytosis. Analysis of patient's erythrocyte membrane proteins revealed spectrin deficiency and a truncated alpha spectrin protein. We determined that the patient is a compound heterozygote with two mutations in alpha spectrin gene. Mutation in the paternal allele, designated alpha spectrin(PRAGUE), is a transition A to G in the penultimate position of intron 36 that leads to skipping of exon 37, frameshift, and production of the truncated alpha spectrin protein. The maternal allele, designated alpha spectrin(LEPRA), contains transition C-->T in position -99 of intron 30. This mutation enhances an alternative acceptor splice site 70 nucleotides upstream from the regular site. The alternative splicing causes a frameshift and premature termination of translation leading to a significant decrease in alpha spectrin production. The alpha(LEPRA) mutation is linked to a spectrin alphaIIa marker that was found to be associated with recessive or nondominant spectrin-deficient hereditary spherocytosis in approximately 50% of studied families. We conclude that the alpha(LEPRA) mutation combined in trans with the alpha(PRAGUE) mutation underlie the severe hemolytic anemia in the proband. We suggest that allele alpha spectrin(LEPRA) may be frequently involved in pathogenesis of recessive or nondominant spectrin-deficient hereditary spherocytosis.

Hereditary spherocytosis: a review of the clinical and molecular aspects of the disease

Hereditary spherocytosis is a common and very heterogeneous hemolytic anemia caused by defects of the red cell membrane proteins. In recent years, major advances in our understanding of the red cell membrane skeleton and a better characterization of its individual components have allowed a brighter insight into the pathogenesis of the disease. In this article, we present an overview of the erythrocyte skeleton and its individual constituents. We also review the clinical aspects of the disease and describe the currently known molecular defects involving the membrane proteins which have been shown to play an essential role in the underlying mechanism of hereditary spherocytosis. Finally we examine several models that have been proposed in an attempt to clarify the mechanism leading from the initial molecular insult to the clinical phenotype.

Control of band 3 lateral and rotational mobility by band 4.2 in intact erythrocytes: release of band 3 oligomers from low-affinity binding sites

Band 4.2 is a human erythrocyte membrane protein of incompletely characterized structure and function. Erythrocytes deficient in band 4.2 protein were used to examine the functional role of band 4.2 in intact erythrocyte membranes. Both the lateral and the rotational mobilities of band 3 were increased in band 4.2-deficient erythrocytes compared to control cells. In contrast, the lateral mobility of neither glycophorins nor a fluorescent phospholipid analog was altered in band 4.2-deficient cells. Compared to controls, band 4.2-deficient erythrocytes manifested a decreased ratio of band 3 to spectrin, and band 4.2-deficient membrane skeletons had decreased extractability of band 3 under low-salt conditions. Normal band 4.2 was found to bind to spectrin in solution and to promote the binding of spectrin to ankyrin-stripped inside-out vesicles. We conclude that band 4.2 provides low-affinity binding sites for both band 3 oligomers and spectrin dimers on the human erythrocyte membrane. Band 4.2 may serve as an accessory linking protein between the membrane skeleton and the overlying lipid bilayer.

Electron microscopic evidence of impaired intramembrane particles and instability of the cytoskeletal network in band 4.2 deficiency in human red cells

To obtain direct evidence of impaired intramembrane particles (IMPs) and a deranged cytoskeletal network in situ in human red cells of band 4.2 deficiency, electron microscopic studies were performed utilizing the freeze fracture method for IMPs and the quick-freeze deep-etching method for the cytoskeletal network. Three patients with three different previously identified mutations of the band 4.2 gene, i.e., band 4.2 Komatsu (homozygous; codon 175 GAT --> TAT), band 4.2 Nippon (homozygous; codon 142 GCT --> ACT), and band 4.2 Shiga (compound heterozygous; codon 317 CGC --> TGC and codon 142 GCT --> ACT), were selected for this study. The decrease in the number of IMPs with increase in their size was most marked in band 4.2 Komatsu, which was clinically most severe with no band 4.2 protein. In this regard, in band 4.2 Nippon, which showed moderate severity in clinical hematology with a nearly missing band 4.2 protein, increased sizing was less marked. The abnormalities in IMPs were the least in band 4.2 Shiga, which demonstrated compensated hemolysis with band 4.2 protein in a trace amount. The extent of the impairment of IMPs may be reflected by the total absence or the presence of band 4.2 protein even in a trace amount and/or by the specific site(s) of the mutation of the band 4.2 gene. Derangement of the cytoskeletal network was also observed in these three patients. It was most abnormal in band 4.2 Komatsu, and less so in band 4.2 Nippon and in band 4.2 Shiga. These results clearly indicate that 1) band 4.2 plays an important role not only in its binding to band 3 but also to the skeletal network (mostly to spectrins) vertically, and 2) its deficiency produces critical abnormality in maintenance of the structural and functional integrity of the integral proteins (such as band 3), as well as the cytoskeletal network.

Band 4.2 Shiga: 317 CGC-->TGC in compound heterozygotes with 142 GCT-->ACT results in band 4.2 deficiency and microspherocytosis

A novel compound heterozygous mutation of 317 CGC-->TGC with 142 GCT-->ACT in human red cell band 4.2 deficiency is described. A proband and his son suffered from compensated haemolysis with nearly complete deficiency of red cell band 4.2. Their red cell morphology exhibited microspherocytosis resembling classic hereditary spherocytosis (HS). Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) showed band 4.2 to be nearly missing (< 1% of normal controls) with the presence of 74 kD and 72 kD isoforms in trace amounts. Other family members (daughters older and younger than the son) exhibited nearly normal amounts of 72kD as a wild form of band 4.2 on SDS-PAGE with the presence of the 74kD isoform in a trace amount. The proband and his son demonstrated two compound heterozygous mutations in trans: i.e. nucleotide (nt) 949 CGC-->TGC (codon 317 Arg-->Cys) in exon 7 and nt 424 GCT--ACT (codon 142 Ala-->Thr) in exon 3 of the band 4.2 gene. The two daughters demonstrated only the mutation of nt 949 CGC-->TGC in exon 7 in heterozygous states, but no 142 mutation. Therefore the proband and his son were compound heterozygotes of these two mutations in trans. It is interesting to note that the 74 kD isoform of band 4.2 protein existed in a trace amount in the two daughters in spite of the absence of the 142 Ala-->Thr mutation. In addition, even in the presence of the 142 mutation in one allele in the proband and his son, their red cell morphology demonstrated classic HS with microspherocytosis, although a homozygous state of the 142 mutation known as the Nippon type of band 4.2 deficiency exhibits ovalostomatocytosis.

Red cell membrane polypeptides under normal conditions and in genetic disorders

Broadly speaking, the red cell membrane is comprised of --a cholesterol-rich phospholipid bilayer that is studded by a large number of trans-bilayer proteins, --of glycosylphosphatidylinositol-anchored proteins (GPI-proteins) standing outside, and --an important protein assembly, the erythrocyte or membrane skeleton, that laminates the inner surface of the bilayer. Among the trans-bilayer proteins, one finds the anion exchanger, the glycophorins, the glucose transporter, a variety of cation transporters and pumps, and of course proteins carrying the epitopes of many blood groups. Among the GPI-proteins, one encounters the acetylcholinesterase and the decay-accelerating factor (CD 55). Among the skeletal proteins, finally, one recognises spectrin, actin (and a number of actin-binding proteins other than spectrin: dematin, tropomyosin, tropomodulin, etc.), protein 4.1 and protein p55. Spectrin heterotetramer organizes into a bidimensional network with a hexagonal mesh on the average. This network is linked to trans-bilayer proteins, through the complex beta-spectrin-ankyrin-anion exchanger (+ protein 4.2) on the one hand and, on the other hand, through the triangular interaction between protein 4.1, glycophorin C and protein p55. The sequence of the above proteins and the exon-intron organisation of their genes are known in most cases. Many proteins have a widespread tissue distribution in the form of variants adapted to their local functions. Such variants may be the products of multigene families (anion exchanger, ankyrin, spectrin), or derive from a single gene (protein 4.1, protein 4.2), the transcripts of which undergo cell-specific alternative splicing. It has been established that many congenital haemolytic anaemias result from mutations altering the above-mentioned genes. We will provide two examples. Hereditary elliptocytosis stems from an array of mutations located at, or near the head-to-head self-association region of two spectrin alpha beta dimers, or from mutations which, most often, yield a reduction (heterozygous state) or the lack (homozygous state) of protein 4.1. The aggravation of elliptocytosis associated with alpha-spectrin mutations frequently yields poikilocytosis and usually stems from the occurrence, in trans, of a low expression allele, allele alpha LELY. Hereditary spherocytosis derives from mutations in the ankyrin gene (80% of the cases), the anion exchanger gene (10-15% of the cases), the protein 4.2 gene (rare cases) and the alpha- and beta-spectrin genes (rare cases). Anion exchanger mutations usually cause the decrease in this protein (heterozygous state).(ABSTRACT TRUNCATED AT 250 WORDS)