Ayumi Yawata

Total absence of protein 4.2 and partial deficiency of band 3 in hereditary spherocytosis

Unlike previously reported cases with total protein 4.2 deficiency due to mutations in the EPB42 gene, we describe a total deficiency in protein 4.2 with normal EPB42 alleles. Hereditary spherocytosis (HS) was observed in a Japanese woman (unsplenectomized) and her daughter (splenectomized). The mother showed a partial deficiency in band 3 and a proportional reduction in protein 4.2. She was heterozygous for a novel allele of the EPB3 gene, allele Okinawa, which contains the two mutations that define the Memphis II polymorphism (K56E, AAG → GAG, and P854L, CCG → CTG) and, additionally, the mutation: G714R, GGG → AGG, located in a highly conserved position of transmembrane segment 9. The latter change was responsible for HS. In trans to allele Okinawa, the daughter displayed allele Fukuoka: G130R, GGA → AGA, an allele known to alter the binding of protein 4.2 to band 3. The daughter presented with a more pronounced decrease of band 3, and lacked protein 4.2, resulting in aggravated haemolytic features. Although the father was not available for study, heterozygosity for allele Fukuoka has been documented in another individual who showed no clinical or haematological signs, and a normal content of band 3. We suggest that band 3 Okinawa binds virtually all the protein 4.2 in red cell precursors, band 3 Fukuoka being unable to do so, and that the impossibility of band 3 Okinawa incorporation into the membrane leads to degradation of the band 3 Okinawa protein 4.2 complex. In contrast, band 3 Fukuoka, free of bound protein 4.2, could then incorporate normally into the bilayer. Thus, protein 4.2 would not appear in the daughters red cell membrane.

Ankyrin gene mutations in Japanese patients with hereditary spherocytosis

We studied mutations of theankyrin-1 (ANK-1) gene of genomic DNA from Japanese patients with hereditary spherocytosis (HS). Forty-nine patients from 46 unrelated families were included in this study. Of these patients, 19 cases from 16 unrelated families had HS of autosomal-dominant inheritance, and 30 patients had non-autosomal-dominant HS. Fifteen mutations of theANK-1 gene pathognomonic for HS were identified: 4 nonsense mutations, 7 frameshift mutations, and 4 abnormal splicing mutations. These 15 mutations have not been previously reported. The frameshift mutations were found from exon 1 to exon 26, corresponding particularly to the band 3-binding domain of ankyrin. The nonsense mutations, on the contrary, were present mostly at the 3′-terminal side, especially in the spectrin-binding domain and the regulatory domain.The patients with ankyrin gene mutations tended to be more anemic with a higher level of reticulocytosis than those without these mutations. Fifteen silent mutations of theANK-1 gene, most of which have previously been detected in HS patients in Western populations, were also found. The allele frequency of these silent mutations in the HS patients was nearly identical to that in normal subjects. There was no difference between the Japanese and Western populations in the allele frequency of these gene polymorphisms in healthy subjects or HS patients.

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.

Homozygous missense mutation (band 3 Fukuoka: G130R): a mild form of hereditary spherocytosis with near-normal band 3 content and minimal changes of membrane ultrastructure despite moderate protein 4.2 deficiency

The characteristics of phenotypic expression were studied in a Japanese family with hereditary spherocytosis and an extremely rare homozygous missense mutation of the band 3 gene (band 3 Fukuoka: G130R). The homozygous unsplenectomized proband was a 29‐year‐old male with compensated haemolytic anaemia (red cell count 4.21 × 1012/l, reticulocytes 278 × 109/l, and indirect bilirubin 44 μmol/l). His red cell band 3 (B3) protein demonstrated a 9.3% reduction and his protein 4.2 (P4.2) level was substantially reduced (45.0%), compared to normal subjects. P4.2 protein was composed mostly of a wild type (72 kD) with a trace of 68 kD peptide. The binding properties of the mutated B3 to normal P4.2 were significantly impaired, which probably resulted in the substantial reduction of P4.2 in this proband, since no abnormalities were detected on the P4.2 gene. Electron microscopy (EM) using the freeze‐fracture method demonstrated a mild decrease in intramembrane particles (IMPs) of near‐normal size (8 nm in diameter) with no substantial increases in their oligomerization. Their distribution on the membrane P face was almost normal, although most of the IMPs could represent the homozygously mutated B3 protein. EM (quick‐freeze deep‐etching method) disclosed a skeletal network of near‐normal size and size distribution of the skeletal units, suggesting that the mutated B3 protein itself did not have much effect on the skeletal network in situ. Therefore the reduced P4.2 content (45% of that of normal subjects), which remained on the red cell membrane of this proband, appeared to be nearly sufficient for maintaining the normal structure of the skeletal network and IMPs in situ, contrary to the marked abnormalities in both IMPs and the skeletal network in complete P4.2 deficiencies.

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

Summary. 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 kU and 72 kD isoforms in trace amounts. Other family members (daughters older and younger than the son) exhibited nearly normal amounts of 72 kD as a wild form of band 4.2 on SDS‐PAGE with the presence of the 74 kD 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 ovalostomato‐cytosis.

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.

DNA Methylation in Promoter Regions of Red Cell Membrane Protein Genes in Healthy Individuals and Patients with Hereditary Membrane Disorders

The methylation state of 5′-CG-3′ sites is known to be linked to the regulation of promoter function by modulating DNA-protein interactions and to the structure of chromatin. As part of a project to determine methylation patterns in the human genome, we examined the methylation profiles of several genes for human erythroid membrane proteins: ELB42 (protein 4.2), EPB3 (band 3), SPTB gene (β-spectrin), and ANK1 (ankyrin). The bisulfite protocol of the genomic sequencing method was applied. The number of 5′-CG-3′ dinucleotides was the most abundant in SPTB and ANK1, much less in EPB3, and the least in ELB42. In the DNA of peripheral blood mononuclear cells from healthy individuals, the promoter regions of EPB3 and ELB42 were extensively methylated, but the SPTB and ANK1 promoters were totally unmethylated. We also investigated methylation profiles in peripheral blood mononuclear cells from patients with red cell membrane diseases, such as complete protein 4.2 deficiency due to ELB42 mutations, hereditary spherocytosis with EPB3 mutations, and hereditary elliptocytosis with SPTB mutations. The DNA methylation states in these genes of erythroid cells, which we obtained at the second phase of the 2-phase liquid culture of erythroid precursor cells in the peripheral blood, were essentially identical or very similar to those of peripheral blood mononuclear cells. In disease states, the DNA methylation profiles of these red cell membrane protein genes were essentially not different from those in healthy individuals (statistically not significant).

Hereditary elliptocytosis associated with spectrin Le Puy in a Japanese family: Ultrastructural aspect of the red cell skeleton

Abstract:  A dominantly‐inherited hereditary elliptocytosis of intermediate severity was recorded in a Japanese family from Yamagata. The condition was associated with a spectrin truncated β‐chain (MW: 214 kD; 31% of total β‐spectrin), and a defect of mutant spectrin as regards tetramerization and phosphorylation. cDNA analysis revealed skipping of exon X, the third‐to‐last exon of the spectrin β‐gene. At the gene level, a one‐base substitution (A→G) changed position +4 of the 5′ donor splice site consensus sequence of intron X. This mutation has been described before in a French kindred, defining spectrin Le Puy. Electron micrographs following quick‐freeze deep‐etching showed that the skeletal network was disorganized.

A surface replica method: a useful tool for studies of the cytoskeletal network in red cell membranes of normal subjects and patients with a β-spectrin mutant (spectrin Le Puy: β220/214)

Visualization of the components of the red cell membranes, and especially the structure of cytoskeletal proteins in situ, has become a requisite in studies of red cell membrane disorders. There has been a search for a consistent and dependable method for detecting these structures. In the present study, the surface replica method was used with transmission electron microscopy to examine the cytoskeletal network of the red cell ghosts of a normal control and patients with a β-spectrin mutant (β-spectrin Le Puy). The surface replica method is well-suited to observation of the cytoskeletal network of the membranes in a nearly native in situ condition. Immunogold labelling with anti-membrane protein antibodies is easily applicable to the identification of each component of the cytoskeletal proteins. The findings obtained under normal and pathological conditions using the surface replica method corresponded with those made by the quick-freeze, deep-etching method.

The state of DNA methylation in the promoter regions of the human red cell membrane protein (band 3, protein 4.2, andβ-spectrin) genes

The state of methylation of the 5′-CpG-3′ sites is known to be linked to the regulation of promoter function by modulating DNA-protein interactions and to the structure of chromatin. As part of a project to determine methylation patterns in the human genome, the methylation profiles were examined in genes for the human erythroid membrane proteins; protein 4.2 (P4.2), gene (ELB42), band 3 (B3), gene (EPB3), and β-spectrin (β-Sp), gene (SPTB). The bisulfite protocol of the genomic sequencing method was applied.(1) In the DNA from peripheral white blood cells, the promoter regions of EPB3 and ELB42 were extensively methylated, but the promoter of SPTB was totally unmethylated. (2) During erythroid differentiation, (i) ELB42 was unmethylated in DNAs from the cell line UT-7/EPO, but became methylated (55−93 %) in cultured erythroblasts from peripheral BFU-E. The mRNA from ELB42 was first detected in early erythroblasts and protein 4.2 was expressed in late erythroblasts. (ii) EPB3 was consistently methylated in UT-7/EPO and also in cultured erythroblasts from burst forming unit erythroid (BFU-E) from peripheral blood. EPB3 and ELB42 were efficiently transcribed in UT-7 cells only after erythropoietin stimulation. (iii) SPTB remained unmethylated in DNAs from UT-7/EPO and cultured erythroblasts. (3) We also investigated methylation profiles in peripheral white blood cells from patients with erythroid diseases, like complete P4.2 deficiency due to ELB42 mutations, hereditary spherocytosis with EPB3 mutations, and hereditary elliptocytosis with SPTB mutations. The methylation profiles of the promoter regions of these three genes were essentially identical to those in healthy individuals.