Characterization of the human ABO gene promoter in erythroid cell lineage

Serological and genetic analysis of a B3 phenotype caused by c.259G > T in the ABO gene

BACKGROUND

Mixed agglutination is a serological pattern in some ambiguous ABO blood type identification. This study focused on the serological and molecular genetic characteristics of a B3 phenotype induced by a c.259G > T mutation in the ABO gene.

STUDY DESIGN AND METHODS

Serological methods such as gel cards and tubes were used to identify the ABO blood type of the patient, with fluorescent PCR for ABO genotyping and Sanger sequencing for analysing the ABO exons. Protein 3D Structure was simulated and further analysed using SWISS-MODLE and PyMOL. Both the wild-type (VAL-87, ABO*B.01) and the mutant (p.Val87Leu) plasmids were transfected into Hela cells to assess the agglutination intensity of the transfected cells with anti-B antibodies.

RESULTS

Serological testing showed weak expression of the B antigen and mixed agglutination with anti-B antibodies. ABO genotyping indicated the presence of a B allele, but exon sequencing revealed an additional c.259G > T mutation in exon 6 based on the ABO*B.01 allele. The simulated three-dimensional structures of the proteins showed increased steric hindrance with mutations, leading to a relatively loose structure. The transfected Hela cells with the mutant (p.Val87Leu) plasmid exhibited a significantly reduced agglutination intensity with anti-B antibodies.

CONCLUSION

Based on comprehensive serological, genetic, and simulation analyses, it is concluded that the c.259G > T mutation in exon 6 of the ABO*B.01 allele results in an amino acid change within the enzymatic active site. This alteration likely impacts protein stability and reduces B antigen expression, leading to the B3 subtype phenotype.

Identification of an AweakB phenotype caused by significant ABO gene deletion in a Chinese woman

BACKGROUND AND OBJECTIVES

The AweakB is a rare phenotype in the ABO blood group system. Here, we first report a novel ABO mutation discovered in a Chinese woman with an AweakB. Third-generation sequencing was employed to investigate the molecular mechanisms underlying AweakB. By correctly identifying the phenotype, it was useful for increasing the safety of blood transfusion.

MATERIALS AND METHODS

ABO blood group was identified by the standard ABO serological test and polymerase chain reaction with sequence-specific primers (PCR-SSP). To analyse the ABO gene sequence, single-molecule real-time (SMRT) sequencing was performed to obtain full-length sequencing of the ABO gene.

RESULTS

The Chinese individual was serologically identified as AweakB subtype, and SMRT sequencing analysis revealed that there were large fragment deletion mutations in the promoter (c.1-1326_1-1321del, c.1-1010_1-975del, c.1-952_1-1del) and Exon 1 region (c.1_28del).

CONCLUSION

We report for the first time that large fragment deletions represent a novel molecular basis for the AweakB. These deletions may potentially influence the expression of the A antigen.

Serological and molecular characterization of novel ABO variants including an interesting B(A) subgroup

BACKGROUND

ABO grouping is the most important pretransfusion testing that is directly related to the safety of blood transfusion. A weak ABO subgroup is one of the important causes of an ABO grouping discrepancy. Here, we investigated the characterization of four novel ABO variants including a novel B(A) subgroup.

STUDY DESIGN AND METHODS

RBCs were phenotyped by standard serology methods. The full coding regions of the ABO gene and the erythroid cell-specific regulatory elements in intron one were sequenced. The effect of the possible splice site variant was predicted by Alamut software. The 3D structural modeling of three relative B(A) enzymes (p.Met214Thr, p.Met214Val, and p.Met214Leu) were performed by PyMOL software.

RESULTS

Four novel ABO alleles were identified with weak ABO expression in this study, in which two would lead to premature terminations, and two resulted in amino acid changes. In silico analysis revealed that the splice site variant c.155G>T had the potential to alter splice transcripts. 3D structural view shown that the variant amino acid position 214 was spatially adjacent to the donor recognition pocket residues (266Met and 268Ala) and just next to the 211DVD213 motif. The size of the side chain of Thr and Val is the smallest, Leu is medium, and Met is the largest, and the size changes in the critical position 214 may affect the donor recognition pocket.

CONCLUSION

Four ABO subgroup alleles were newly linked to different kinds of ABO variants and the possible mechanism through which they produce weak ABO subgroups was analyzed in silico.

Role of MiRNA in the Regulation of Blood Group Expression

Background

MicroRNAs (miRNAs) are small, endogenous non-coding RNA molecules that inhibit gene expression through either destabilization of the target mRNA or translational repression. MiRNAs recognize target sites, most commonly found in the 3'-untranslated regions of cognate mRNAs. This review aims to provide a state-of-the-art overview of the role of miRNAs in the regulation of major blood group antigens such as ABH as well as cancer-specific glycans.

Summary

Besides their known roles in the control of developmental processes, proliferation, apoptosis, and carcinogenesis, miRNAs have recently been identified to play a regulatory role during erythropoiesis and blood group antigen expression. Since only little is known about the function of the red cell membrane proteins carrying blood group antigens, it is of great interest to shed light on the regulatory mechanisms of blood group gene expression. Some carrier proteins of blood group antigens are not restricted to red blood cells and are widely expressed in other bodily fluids and tissues and quite a few play a crucial role in tumor cells, as either tumor suppressors or promoters.

Key Message

All available data point at a tremendous physiological as well as pathophysiological relevance of miRNAs in context of blood group regulation. Furthermore, miRNAs are involved in the regulation of pleiotropic genetic pathways such as hematopoiesis and tumorigenesis and thus have to be studied in future research on this subject.

Review of ABO Expression and Variations based on Transcriptional Regulation of the ABO Blood Group Gene

Background and Summary

We review the transcriptional regulation of ABO expression and discuss variants in the promoter and erythroid cell-specific regulatory region in individuals with weak ABO phenotypes such as Bm, Am, B3, and A3. We also review the molecular mechanisms responsible for variations in ABO expression in development and disease including the cell type-specific expression of ABO during erythroid cell differentiation, and reduction of A- or B-antigens in cancer cells or on red blood cells in patients with leukemia. Although the relationship between ABO blood group antigens and diseases has been characterized, the physiological significance of the ABO blood group system remains unclear.

Key Messages

This review discusses accumulated knowledge of the ABO gene regulation and potential reasons for conservation of ABO during evolution.

Novel evidence that the ABO blood group shapes erythropoiesis and results in higher hematocrit for blood group B carriers

The ABO blood group (BG) system is of great importance for blood transfusion and organ transplantation. Since the same transcription factors (TFs) and microRNAs (miRNAs) govern the expression of ABO BG antigens and regulate erythropoiesis, we hypothesized functional connections between both processes. We found significantly higher hemoglobin and hematocrit values in BG B blood donors compared to BG A. Furthermore, we observed that erythropoiesis in BG B hematopoietic stem/progenitor cells (HSPCs) was accelerated compared to BG A HSPCs. Specifically, BG B HSPCs yielded more lineage-specific progenitors in a shorter time (B: 31.3 ± 2.2% vs. A: 22.5 ± 3.0%). Moreover, non-BG A individuals exhibited more terminally differentiated RBCs with higher enucleation rates containing more hemoglobin compared to BG A. Additionally, we detected increased levels of miRNA-215-5p and -182-5p and decreased expression of their target TFs RUNX1 and HES-1 mRNAs in erythroid BG B precursor cells compared to BG A. This highlights the important roles of these factors for the disappearance of differentiation-specific glycan antigens and the appearance of cancer-specific glycan antigens. Our work contributes to a deeper understanding of erythropoiesis gene regulatory networks and identifies its interference with BG-specific gene expression regulations particularly in diseases, where ABO BGs determine treatment susceptibility and disease progression.

Emergence of an erythroid cell-specific regulatory region in ABO intron 1 attributable to A- or B-antigen expression on erythrocytes in Hominoidea

A- and B-antigens are present on red blood cells (RBCs) as well as other cells and secretions in Hominoidea including humans and apes such as chimpanzees and gibbons, whereas expression of these antigens on RBCs is subtle in monkeys such as Japanese macaques. Previous studies have indicated that H-antigen expression has not completely developed on RBCs in monkeys. Such antigen expression requires the presence of H-antigen and A- or B-transferase expression in cells of erythroid lineage, although whether or not ABO gene regulation is associated with the difference of A- or B-antigen expression between Hominoidea and monkeys has not been examined. Since it has been suggested that ABO expression on human erythrocytes is dependent upon an erythroid cell-specific regulatory region or the + 5.8-kb site in intron 1, we compared the sequences of ABO intron 1 among non-human primates, and demonstrated the presence of sites orthologous to the + 5.8-kb site in chimpanzees and gibbons, and their absence in Japanese macaques. In addition, luciferase assays revealed that the former orthologues enhanced promoter activity, whereas the corresponding site in the latter did not. These results suggested that the A- or B-antigens on RBCs might be ascribed to emergence of the + 5.8-kb site or the corresponding regions in ABO through genetic evolution.

A Novel Mutation Eliminates GATA-1 and RUNX1-Mediated Promoter Activity in Galactosyltransferase Gene

Introduction

Mutations in the promoter region and exons of ABO gene may cause changes in the expression of blood group antigens, often showing a weak ABO phenotype. Here, we identified a novel weak ABO subgroup allele that caused B_el phenotype and explored its mechanisms.

Methods

The ABO phenotype of subjects (Chinese Han nationality) was classified by serological method. The plasma activity of erythrocyte glycosyltransferase was detected by the phosphate coupling method. ABO subtype genotyping was performed by PCR-SSP and exon sequencing. The activity of the promoter was evaluated by a dual-luciferase reporter assay.

Results

We identified a mutation exon 1 c.15_16insTGTTG of the B allele in a B_el subject. Genealogical investigation showed that the mutation was inherited from her mother. The mutation was located in the promoter region of the ABO gene. The dual-luciferase reporter assay showed that the mutation inactivated GATA-1 and RUNX1-mediated activity of the ABO gene promoter, leading to a decrease in the expression and activity of B glycosyltransferase.

Conclusion

A novel B_var ABO subgroup allele was identified. The novel mutation can reduce the promoter activity that activated by GATA-1 and RUNX1, subsequently causing the B_el phenotype.

A historical overview of advances in molecular genetic/genomic studies of the ABO blood group system

In 1990, 90 years after the discovery of ABO blood groups by Karl Landsteiner, my research team at the Molecular Biology Laboratory of the now-defunct Biomembrane Institute elucidated the molecular genetic basis of the ABO polymorphism. Henrik Clausen, Head of the Immunology Laboratory, initiated the project by isolating human group A transferase (AT), whose partial amino acid sequence was key to its success. Sen-itiroh Hakomori, the Scientific Director, provided all the institutional support. The characterization started from the 3 major alleles (A1, B, and O), and proceeded to the alleles of A2, A3, Ax and B3 subgroups and also to the cis-AB and B(A) alleles, which specify the expression of A and B antigens by single alleles. In addition to the identification of allele-specific single nucleotide polymorphism (SNP) variations, we also experimentally demonstrated their functional significance in glycosyltransferase activity and sugar specificity of the encoded proteins. Other scientists interested in blood group genes later characterized more than 250 ABO alleles. However, recent developments in next-generation sequencing have enabled the sequencing of millions of human genomes, transitioning from the era of genetics to the era of genomics. As a result, numerous SNP variations have been identified in the coding and noncoding regions of the ABO gene, making ABO one of the most studied loci for human polymorphism. As a tribute to Dr. Hakomori's scientific legacy, a historical overview in molecular genetic/genomic studies of the human ABO gene polymorphism is presented, with an emphasis on early discoveries made at his institute.

Reduction of blood group A antigen on erythrocytes in a patient with myelodysplastic syndrome harboring somatic mutations in RUNX1 and GATA2

BACKGROUND

Reduction of blood group ABO antigens on red blood cells (RBCs) is well known in patients with leukemias, and this reduction of ABO expression is strongly associated with DNA methylation of the ABO promoter. Previously, we reported a two-nucleotide deletion in RUNX1 encoding an abnormally elongated protein lacking the trans-activation domain in a patient with myelodysplastic syndrome (MDS) showing A-antigen loss on RBCs. This prompted us to investigate the underlying mechanism responsible for A-antigen reduction on RBCs in another patient with MDS.

STUDY DESIGN AND METHODS

Screening of somatic mutations was carried out using a targeted sequencing panel with genomic DNA from peripheral blood mononuclear cells from the patient and eleven MDS controls without A- or B-antigen loss. DNA methylation of the ABO promoter was examined by bisulfite genomic sequencing. Transient transfection assays were performed for functional evaluation of mutations.

RESULTS

Screening of somatic mutations showed missense mutations in RUNX1 and GATA2 in the patient, while no mutation was found in exons of those genes in the controls. There was no significant difference in ABO promoter methylation between the patient and the controls. Transient transfection experiments into COS-7 and K562 cells suggested that the amino acid substitutions encoded by those mutations reduced or lost the trans-activation potential of the ABO expression.

CONCLUSION

Considering the discrepancy between the variant frequencies of these mutations and the ratios of the RBCs with A-antigens loss, the antigen reduction might be associated with these somatic mutations and hypermethylation of the ABO promoter.

A cell-specific regulatory region of the human ABO blood group gene regulates the neighborhood gene encoding odorant binding protein 2B

The human ABO blood group system is of great importance in blood transfusion and organ transplantation. ABO transcription is known to be regulated by a constitutive promoter in a CpG island and regions for regulation of cell-specific expression such as the downstream + 22.6-kb site for epithelial cells and a site in intron 1 for erythroid cells. Here we investigated whether the + 22.6-kb site might play a role in transcriptional regulation of the gene encoding odorant binding protein 2B (OBP2B), which is located on the centromere side 43.4 kb from the + 22.6-kb site. In the gastric cancer cell line KATOIII, quantitative PCR analysis demonstrated significantly reduced amounts of OBP2B and ABO transcripts in mutant cells with biallelic deletions of the site created using the CRISPR/Cas9 system, relative to those in the wild-type cells, and Western blotting demonstrated a corresponding reduction of OBP2B protein in the mutant cells. Moreover, single-molecule fluorescence in situ hybridization assays indicated that the amounts of both transcripts were correlated in individual cells. These findings suggest that OBP2B could be co-regulated by the + 22.6-kb site of ABO.

Regulation of ABO blood group antigen expression by miR-331-3p and miR-1908-5p during hematopoietic stem cell differentiation

The ABO blood group system is the most important factor in clinical transfusion medicine and is implicated in a number of human diseases. ABO antigens are not confined to red blood cells (RBCs) and are widely expressed in a variety of human cells and tissues. To date, many alleles with variant ABO expression have been identified and in many cases traced to one of the >250 reported genetic variations in the respective glycosyltransferase. The role of microRNAs (miRNAs) in the regulation of blood group antigens during erythropoiesis has not been addressed, however. Here, we show that miR-331-3p and miR-1908-5p directly target the mRNA of glycosyltransferases A and B. Expression levels of miR-331-3p and miR-1908-5p inversely correlated with levels of blood group A antigen. In addition, we found that overexpression of these miRNAs in hematopoietic stem cells led to a significantly reduced number of blood group A antigens per RBC. Simultaneous targeting of the transcription factor (TF) SP1 by miR-331-3p further enhanced these effects. The targeting rendered SP1 incapable of binding to the ABO gene promoter, causing further downregulation of blood group A antigen expression by up to 70%. Taken together, expression changes in these miRNAs may account for rare cases of weak A/B phenotypes that genetic variations in the glycosyltransferase coding region cannot explain. These results also suggest an explanation for the disappearance of ABH antigens during carcinogenesis and point to new therapeutic targets in ABO mismatched organ transplantation.

Genomic analysis of blood samples with serologic ABO discrepancy identifies 12 novel alleles in a Chinese Han population

OBJECTIVES

This study aimed at identifying new ABO alleles from155 unrelated blood samples with potential ABO discrepancy in a Chinese Han population of 835 144 donors.

BACKGROUND

Serological strategies and genotyping are crucial for the precise determination of ABO discrepancy.

METHODS

Their ABO phenotypes and plasma glycosyltransferase activity were determined by standard forward and reverse typing and dilution tests. The genomic DNA of the ABO gene was amplified by polymerase chain reaction and sequenced. The frequency of ABO subgroup alleles associated with ABO discrepancy was analysed.

RESULTS

Serological analysis indicated that 53, 96 and 6 samples with ABO discrepancy were identified in the A, B and O subgroups, respectively. Genetic analysis revealed 12 novel alleles among the 46 associated with serologic ABO discrepancy. The majority of novel alleles was obtained from point mutations or single base insertion in Exons 6 to 7 of the ABO gene. The most frequent alleles were ABO*cisAB.01 (14/53, 26.42%) and ABO*A2.05 (7/53, 13.2%) in the A subgroup and ABO*BA.02 (34/96, 35.42%) and ABO*BEL.11 (15/96, 15.62%) in the B subgroup. Samples with the same ABO subgroup allele displayed different phenotypes, such as ABO*AX.13, ABO*BW.03, ABO*BW.12, ABO*BW.15, ABO*BEL.03, ABO*BEL.10 and ABO*BEL.11.

CONCLUSION

This study identified 12 novel alleles among the 46 associated with serologic ABO discrepancies. ABO genotyping is needed for the accurate evaluation of blood phenotype to improve the safety of blood transfusion.

RUNX1 mutation in a patient with myelodysplastic syndrome and decreased erythrocyte expression of blood group A antigen

BACKGROUND

Loss of blood group ABO antigens on red blood cells (RBCs) is well known in patients with leukemias, and such decreased ABO expression has been reported to be strongly associated with hypermethylation of the ABO promoter. We investigated the underlying mechanism responsible for A-antigen reduction on RBCs in a patient with myelodysplastic syndrome.

STUDY DESIGN AND METHODS

Genetic analysis of ABO was performed by PCR and sequencing using peripheral blood. RT-PCR were carried out using cDNA prepared from total bone marrow (BM) cells. Bisulfite genomic sequencing was performed using genomic DNA from BM cells. Screening of somatic mutations was carried out using a targeted sequencing panel with genomic DNA from BM cells, followed by transient transfection assays.

RESULTS

Genetic analysis of ABO did not reveal any mutation in coding regions, splice sites, or regulatory regions. RT-PCR demonstrated reduction of A-transcripts when the patient's RBCs were not agglutinated by anti-A antibody and did not indicate any significant increase of alternative splicing products in the patient relative to the control. DNA methylation of the ABO promoter was not obvious in erythroid cells. Targeted sequencing identified somatic mutations in ASXL1, EZH2, RUNX1, and WT1. Experiments involving transient transfection into K562 cells showed that the expression of ABO was decreased by expression of the mutated RUNX1.

CONCLUSION

Because the RUNX1 mutation encoded an abnormally elongated protein without a transactivation domain which could act as dominant negative inhibitor, this frame-shift mutation in RUNX1 may be a genetic candidate contributing to A-antigen loss on RBCs.

An exonic missense mutation c.28G>A is associated with weak B blood group by affecting RNA splicing of the ABO gene

BACKGROUND

The amino acid substitutions caused by ABO gene mutations are usually predicted to impact glycosyltransferase's function or its biosynthesis. Here we report an ABO exonic missense mutation that affects B-antigen expression by decreasing the mRNA level of the ABO gene rather than the amino acid change.

STUDY DESIGN AND METHODS

Serologic studies including plasma total GTB transfer capacity were performed. The exon sequences of the ABO gene were analyzed by Sanger sequencing. B³¹⁰ cDNA with c.28G>A (p.G10R) mutation was expressed in HeLa cells and total GTB transfer capacity in cell supernatant was measured. Flow cytometry was performed on these HeLa cells after transfection, and agglutination of Hela-B_weak cells was also examined. The mRNA of the ABO gene was analyzed by direct sequencing and real-time reverse transcriptase-polymerase chain reaction. A minigene construct was prepared to evaluate the potential of splicing.

RESULTS

While plasma total GTB transfer capacity was undetectable in this B₃ -like individual, the relative percentage of antigen-expressing cells and mean fluorescence index of the B_weak red blood cells (RBCs) were 19 and 14% of normal B RBCs, respectively. There was no significant difference of total GTB transfer capacity in cell supernatant and B-antigen expression on cell surfaces between HeLa cells transfected with B³¹⁰ cDNA and B cDNA. The mRNA expression level of B³¹⁰ in peripheral whole blood was significantly reduced. The amount of splicing is significantly lower in c.28G>A construct compared to that in wild-type construct after transfection in K562 cells.

CONCLUSION

ABO c.28G>A mutation may cause B₃ -like subgroup by affecting RNA splicing of the ABO gene.

Histone deacetylase inhibitors suppress ABO transcription in vitro, leading to reduced expression of the antigens

BACKGROUND

The ABO system is of fundamental importance in the fields of transfusion and transplantation and has apparent associations with certain diseases, including cardiovascular disorders. ABO expression is reduced in the late phase of erythroid differentiation in vitro, whereas histone deacetylase inhibitors (HDACIs) are known to promote cell differentiation. Therefore, whether or not HDACIs could reduce the amount of ABO transcripts and A or B antigens is an intriguing issue.

STUDY DESIGN AND METHODS

Quantitative polymerase chain reactions were carried out for the ABO transcripts in erythroid-lineage K562 and epithelial-lineage KATOIII cells after incubation with HDACIs, such as sodium butyrate, panobinostat, vorinostat, and sodium valproate. Flow cytometric analysis was conducted to evaluate the amounts of antigen in KATOIII cells treated with panobinostat. Quantitative chromatin immunoprecipitation (ChIP) assays and luciferase assays were performed on both cell types to examine the mechanisms of ABO suppression.

RESULTS

HDACIs reduced the ABO transcripts in both K562 and KATOIII cells, with panobinostat exerting the most significant effect. Flow cytometric analysis demonstrated a decrease in B-antigen expression on panobinostat-treated KATOIII cells. ChIP assays indicated that panobinostat altered the modification of histones in the transcriptional regulatory regions of ABO, and luciferase assays demonstrated reduced activity of these elements.

CONCLUSION

ABO transcription seems to be regulated by an epigenetic mechanism. Panobinostat appears to suppress ABO transcription, reducing the amount of antigens on the surface of cultured cells.

Epithelial Expression of Human ABO Blood Group Genes Is Dependent upon a Downstream Regulatory Element Functioning through an Epithelial Cell-specific Transcription Factor, Elf5

The human ABO blood group system is of great importance in blood transfusion and organ transplantation. The ABO system is composed of complex carbohydrate structures that are biosynthesized by A- and B-transferases encoded by the ABO gene. However, the mechanisms regulating ABO gene expression in epithelial cells remain obscure. On the basis of DNase I-hypersensitive sites in and around ABO in epithelial cells, we prepared reporter plasmid constructs including these sites. Subsequent luciferase assays and histone modifications indicated a novel positive regulatory element, designated the +22.6-kb site, downstream from ABO, and this was shown to enhance ABO promoter activity in an epithelial cell-specific manner. Expression of ABO and B-antigen was reduced in gastric cancer KATOIII cells by biallelic deletion of the +22.6-kb site using the CRISPR/Cas9 system. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that the site bound to an epithelial cell-specific transcription factor, Elf5. Mutation of the Ets binding motifs to abrogate binding of this factor reduced the regulatory activity of the +22.6-kb site. Furthermore, ELF5 knockdown with shRNA reduced both endogenous transcription from ABO and B-antigen expression in KATOIII cells. Thus, Elf5 appeared to be involved in the enhancer potential of the +22.6-kb site. These results support the contention that ABO expression is dependent upon a downstream positive regulatory element functioning through a tissue-restricted transcription factor, Elf5, in epithelial cells.

Molecular genetic analysis of ABO blood group variations reveals 29 novel ABO subgroup alleles

BACKGROUND

Identifying genetic variants of the ABO gene may reveal new biologic mechanisms underlying variant phenotypes of the ABO blood group. We report the molecular genetic analysis of 322 apparently unrelated ABO subgroup individuals in an estimated 2.1 million donors.

STUDY DESIGN AND METHODS

We performed phenotype investigations by serology studies, analyzed the DNA sequence of the ABO gene by direct sequencing or sequencing after cloning, and evaluated promoter activity by reporter assays.

RESULTS

In 62 rare ABO alleles, we identified 29 novel ABO subgroup alleles in 43 apparently unrelated subgroup individuals and their four available pedigrees. Of these alleles, one was a deletion-mutation allele, four were hybrid alleles, and 24 were point-mutation alleles. Most of the point mutations were detected in Exons 6 to 7, while several others were also detected in Exons 1 to 5 or splicing regions. One ABO promoter mutation, -35 to -18 del, was found and verified to reduce promoter activity, as determined by dual luciferase assays. Two mutations, 7G>T and 52C>T, carrying the premature terminal codons E3X and R18X in the 5'-region, were found to be associated with the very weak ABO subgroups "Ael" and "Bel."

CONCLUSION

Twenty-nine ABO subgroup alleles were newly linked to different kinds of ABO variations. We provide the first evidence that promoter abnormality is involved in the formation of weak ABO phenotypes. We also described the first naturally occurring ABO alleles with premature terminal codons in the 5'-region that led to Ael and Bel phenotypes.

Expression of ABO blood-group genes is dependent upon an erythroid cell–specific regulatory element that is deleted in persons with the Bm phenotype

The ABO blood group is of great importance in blood transfusion and organ transplantation. However, the mechanisms regulating human ABO gene expression remain obscure. On the basis of DNase I–hypersensitive sites in and upstream of ABO in K562 cells, in the present study, we prepared reporter plasmid constructs including these sites. Subsequent luciferase assays indicated a novel positive regulatory element in intron 1. This element was shown to enhance ABO promoter activity in an erythroid cell–specific manner. Electrophoretic mobility–shift assays demonstrated that it bound to the tissue-restricted transcription factor GATA-1. Mutation of the GATA motifs to abrogate binding of this factor reduced the regulatory activity of the element. Therefore, GATA-1 appears to be involved in the cell-specific activity of the element. Furthermore, we found that a partial deletion in intron 1 involving the element was associated with Bm phenotypes. Therefore, it is plausible that deletion of the erythroid cell–specific regulatory element could down-regulate transcription in the Bm allele, leading to reduction of B-antigen expression in cells of erythroid lineage, but not in mucus-secreting cells. These results support the contention that the enhancer-like element in intron 1 of ABO has a significant function in erythroid cells.

Genetic and mechanistic evaluation for the mixed-field agglutination in B3 blood type with IVS3+5G>A ABO gene mutation

BACKGROUND

The ABO blood type B(3) is the most common B subtype in the Chinese population with a frequency of 1/900. Although IVS3+5G>A (rs55852701) mutation of B gene has been shown to associate with the development of B(3) blood type, genetic and mechanistic evaluation for the unique mixed-field agglutination phenotype has not yet been completely addressed.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we analyzed 16 cases of confirmed B(3) individuals and found that IVS3+5G>A attributes to all cases of B(3). RT-PCR analyses revealed the presence of at least 7 types of aberrant B(3) splicing transcripts with most of the transcripts causing early termination and producing non-functional protein during translation. The splicing transcript without exon 3 that was predicted to generate functional B(3) glycosyltransferase lacking 19 amino acids at the N-terminal segment constituted only 0.9% of the splicing transcripts. Expression of the B(3) cDNA with exon 3 deletion in the K562 erythroleukemia cells revealed that the B(3) glycosyltransferase had only 40% of B(1) activity in converting H antigen to B antigen. Notably, the typical mixed-field agglutination of B(3)-RBCs can be mimicked by adding anti-B antibody to the K562-B(3) cells.

CONCLUSIONS/SIGNIFICANCE

This study thereby demonstrates that both aberrant splicing of B transcripts and the reduced B(3) glycosyltransferase activity contribute to weak B expression and the mixed-field agglutination of B(3), adding to the complexity for the regulatory mechanisms of ABO gene expression.

Association between ABO blood groups and osteoporosis severity in Chinese adults aged 50 years and over

This study investigated whether the ABO blood groups contributed to the severity of osteoporosis in 1452 community-dwelling Chinese adults aged 50-85 years. Osteoporosis severity was scored as: F(0), no osteoporosis; F(1), osteopenia; F(2), osteoporosis; and F(3), severe osteoporosis. The proportions of adults with a non-O blood group were 55.0%, 62.0%, 70.8% and 72.6% for the groups with F(0), F(1), F(2) and F(3) osteoporosis scores, respectively. Having a non-O blood group was associated with an increased severity of osteoporosis, even after adjustment for gender, age and cigarette consumption (odds ratio 1.8; 95% confidence interval 1.0, 2.9). This study demonstrated that having a non-O blood group was an independent risk factor for the progression of osteoporosis in Chinese adults with osteoporosis aged ≥ 50 years.

The 3' flanking region of the human ABO histo-blood group gene is involved in negative regulation of gene expression

Gene expression is driven by promoters, enhancers, silencers, and other cis-regulatory elements upstream and downstream of the gene. Previous studies of the regulation of human ABO gene transcription have focused mainly on the 5' region, including the core promoter and the region proximal to it. However, as the involvement of the 3' flanking region in transcriptional regulation has not yet been examined, we focused on this issue. The 3' region approximately 2.2kb downstream of the ABO gene was PCR-amplified and inserted into a cloning vector, followed by sequence determination and preparation of luciferase reporter vectors. Transient transfections into KATOIII and K562 cells were performed using various reporter plasmids containing the 3' region. The 3' region of the ABO gene, which was characterized by a high degree of sequence repetition, was effectively cloned by a single-copy cloning method. Transfections in KATOIII and K562 cells showed that negative elements were demonstrable within the 3' region. These observations suggest that negative regulatory elements seem to be present in the 3' region of ABO in both epithelial and erythroid lineages. As we had observed a negative region just upstream of the ABO promoter, transcription from ABO could be negatively regulated by repressive regions just upstream of the promoter and downstream of the gene. Further studies of the enhancer will be required for elucidating the molecular basis of ABO gene expression.

DNA methylation of the ABO promoter underlies loss of ABO allelic expression in a significant proportion of leukemic patients

Background

Loss of A, B and H antigens from the red blood cells of patients with myeloid malignancies is a frequent occurrence. Previously, we have reported alterations in ABH antigens on the red blood cells of 55% of patients with myeloid malignancies.

Methodology/Principal Findings

To determine the underlying molecular mechanisms of this loss, we assessed ABO allelic expression in 21 patients with ABH antigen loss previously identified by flow cytometric analysis as well as an additional 7 patients detected with ABH antigen changes by serology. When assessing ABO mRNA allelic expression, 6/12 (50%) patients with ABH antigen loss detected by flow cytometry and 5/7 (71%) of the patients with ABH antigen loss detected by serology had a corresponding ABO mRNA allelic loss of expression. We examined the ABO locus for copy number and DNA methylation alterations in 21 patients, 11 with loss of expression of one or both ABO alleles, and 10 patients with no detectable allelic loss of ABO mRNA expression. No loss of heterozygosity (LOH) at the ABO locus was observed in these patients. However in 8/11 (73%) patients with loss of ABO allelic expression, the ABO promoter was methylated compared with 2/10 (20%) of patients with no ABO allelic expression loss (P = 0.03).

Conclusions/Significance

We have found that loss of ABH antigens in patients with hematological malignancies is associated with a corresponding loss of ABO allelic expression in a significant proportion of patients. Loss of ABO allelic expression was strongly associated with DNA methylation of the ABO promoter.

Sequences variations in 5'-flanking region of ABO gene and correlation with ABO alleles in the indigenous Chinese

BACKGROUND AND OBJECTIVES

5'-flanking sequences of the ABO gene play important role in the regulation of gene expression, but polymorphism of 5'-flanking sequence of ABO gene is rarely known. Here, we further characterize the molecular genetic basis and ABO allele-related polymorphism of the 5'-untranslated regions (5'-UTR) of the human ABO gene.

MATERIALS AND METHODS

Collecting blood samples from 72 blood donors in Hangzhou, China, we analysed sequences of exons 6 and 7 of ABO gene and amplified an enhanced segment of 43 bp repeats in the 5'-UTR. Subsequently, we selected 25 homozygotes [of genotypes A101/A101 (two), A102/A102 (seven), B101/B101 (seven) and O01/O01 (nine)] and five heterozygotes [A102/O01 (two), B101/O01 (two) and O01/O105 (one)] for sequencing 5 -kb amplicons spanning the 5'-UTR and partial exon 1 of the ABO gene. We sequenced the amplicons bidirectionally and, when pertinent, analysed selected haplotypes by cloning.

RESULTS

As a result, we identified 11 new polymorphic sites (10 point mutations, one 8-bp deletion) in the 5'-UTR of the A102, B101 and O01 alleles of common ABO phenotypes. Five A102 alleles carry four tandem repeats of a 43-bp minisatellite unit that deviated from previous reports.

CONCLUSION

The results revealed the DNA polymorphisms in the 5'-UTRs correlated with the common ABO alleles. Elucidation of the diversity of the 5'-UTRs is an important supplement to existing methods for increasing our understanding of the molecular basis of the ABO blood group system.

ABO transcript levels in peripheral blood and erythropoietic culture show different allele-related patterns independent of the CBF/NF-Y enhancer motif and multiple novel allele-specific variations in the 5'- and 3'-noncoding regions

BACKGROUND

Mechanisms regulating the ABO gene are unclear, especially in the hematopoietic compartment. The number of 43-bp repeats in the CBF/NF-Y-binding enhancer region is considered to have a major influence on transcription.

STUDY DESIGN AND METHODS

Transcript levels in peripheral blood and in erythropoietic culture of CD34+ cells from marrow donors were measured with TaqMan assays. The 5'-regulatory region and 3'-downstream sequences were investigated to determine if allelic variations occur.

RESULTS

Surprisingly, transcripts from A(1) and A(2) alleles could not be detected in peripheral blood, although transcripts from B/O(1)/O(1v)/O(2) alleles were readily observed. Sequencing of approximately 4 kb upstream and 1.8 kb downstream of the coding region showed multiple novel allele-specific and allele-related motifs. No correlation between these sequence variations and transcript levels was found, however. Contradictory to the results with peripheral blood, in erythropoietic culture of CD34+ cells from healthy marrow donors transcripts from A(1) and A(2) alleles were found at higher levels than transcripts from B/O(1)/O(1v) alleles.

CONCLUSION

These data do not support previous suggestions that nonsense-mutated O(1)/O(1v) transcripts are eliminated first. Furthermore, our results contradict the notion that the number of repeats in the upstream CBF/NF-Y-binding enhancer region, which contains four 43-bp repeats in A(2)/B/O(1)/O(1v) but only one 43-bp unit in A(1)/O(2) alleles, determines the transcription rate. The reason for the remarkable discrepancy between blood and marrow remains to be elucidated.

Weak blood group B phenotypes may be caused by variations in the CCAAT-binding factor/NF-Y enhancer region of the ABO gene

BACKGROUND

Binding of CCAAT-binding factor NF-Y (CBF/NF-Y) to a 43-bp repeat unit in the minisatellite region in the 5' region of the ABO gene (CBF/NF-Y enhancer region) plays an important role in regulating the transcription of ABO genes. The common ABO alleles were found to have CBF/NF-Y enhancer regions with specific numbers of 43-bp minisatellite repeats.

MATERIAL AND METHODS

Blood samples from four healthy blood donors with weak B phenotypes were subjected to extensive ABO genotyping, including nucleotide sequencing of the 5' regulatory region containing the CBF/NF-Y enhancer.

RESULTS

The coding region of the ABO genes exhibited common ABO*B101-heterozygous genotypes in all samples, but unexpected variations were observed in the CBF/NF-Y enhancer region. In two cases, the CBF/NF-Y enhancer motifs did not exhibit the expected ABO allele dependency. One, an AB(weak) sample was heterozygous for ABO*A101 and ABO*B101 but homozygous for the ABO*B101-specific CBF/NF-Y motif. The second had a common ABO*B101/ABO*O01 genotype but was heterozygous for ABO*A101- and ABO*O01-specific enhancer motifs. In the other two samples, novel CBF/NF-Y motifs were found. One contained a shortened version of an otherwise ABO*B101-specific CBF/NF-Y motif, and the other had a single-base substitution located 12 bp upstream from the beginning of the first 43-bp repeat of an ABO*B101-specific CBF/NF-Y enhancer sequence.

CONCLUSION

The frequency of variations in the CBF/NF-Y region of the ABO gene in these samples with presumably common ABO*B101 alleles suggests that weak blood group B phenotypes may be caused by sequence variations in the CBF/NF-Y regulatory region.

Identification and characterization of a novel antisense RNA transcribed from the opposite strand of the human blood group ABO gene

BACKGROUND

To elucidate the molecular basis of control of the ABO gene in cell type-specific expression, during normal cell differentiation, and in cancer cells lacking A/B antigen, the mechanisms responsible for regulation of human ABO gene expression have been studied. Recently, naturally occurring antisense transcriptions have been reported to regulate gene expression through a variety of biological mechanisms. Therefore, RNA transcribed from the opposite strand of the ABO gene was investigated.

STUDY DESIGN AND METHODS

The presence of antisense RNA to the ABO-coding strand in human cancer cell lines and normal tissues was examined by strand-specific reverse transcription-polymerase chain reaction. The 5'- and 3'-ends of the transcript were determined by the rapid amplification of cDNA ends (RACE) system. KATOIII cells were treated with mithramycin A, followed by quantitative analysis of both sense and antisense ABO transcripts.

RESULTS

The endogenous antisense RNA to the ABO coding strand was found to start within the first intron of the ABO gene, and the expression coincided with ABO gene expression in various cultured cells and normal tissues. This novel gene was named ABOAS. Treatment of KATOIII cells with mithramycin A repressed transcription from the ABO exon 1 promoter, while it increased the ABOAS transcript.

CONCLUSION

These results suggest that ABOAS transcribed from the opposite strand of the ABO gene might be involved in the regulation of ABO gene expression.

Expression of the histo-blood group B gene predominates in AB-genotype cells

BACKGROUND

It has been demonstrated that the 43-bp minisatellite sequence in the 5' region of the ABO gene plays an important role in its transcriptional regulation. It was determined in previous investigations that the structure of the minisatellite enhancer was specific to A, B, and O alleles.

STUDY DESIGN AND METHODS

Real-time polymerase chain reaction (PCR) detection and a PCR-restriction fragment length polymorphism (RFLP) strategy were used to compare the quantities of the A and B transcripts in AB-genotype cells, including peripheral blood cells and cancer cell line with the group AB phenotype. The 5' 3.7-kb regions of the A and B genes were cloned and the sequences compared. The transcriptional activities of the 5' segments of the A and B genes were compared with luciferase reporter assay.

RESULTS

Both real-time PCR and PCR-RFLP analyses show that there is evidently more of the B transcript in the AB-genotype cells. It was demonstrated that the 5' segment of the B gene had a markedly higher transcription-activation activity relative to the A gene. This difference in transcription capability appears to result from the variation in minisatellite-enhancer structures in the A and B genes, which contain one and four repeats of the 43-bp enhancer unit, respectively.

CONCLUSION

Our study indicates that the majority of steady-state mRNA within AB-genotype cells is composed of the B transcript and that this phenomenon is due to the predominant expression of the B gene relative to the A gene.

Characterization of human deoxyribonuclease I gene (DNASE1) promoters reveals the utilization of two transcription-starting exons and the involvement of Sp1 in its transcriptional regulation

Levels of deoxyribonuclease I (DNase I) activity in vivo have been shown to be altered by physiological and/or pathological processes. However, no information is available on the regulation of DNase I gene (DNASE1) expression in vivo or in vitro. We first mapped the transcription start sites of DNASE1 in human pancreas and in the DNase I-producing human pancreatic cancer cell line QGP-1, and revealed a novel site approximately 12 kb upstream of exon 1, which was previously believed to be the single transcription-starting exon. This initiation site marks an alternative starting exon, designated 1a. Exons 1 and 1a were used simultaneously as transcription-starting exons in pancreas and QGP-1 cells. Promoter assay, EMSA and chromatin immunoprecipitation analysis with QGP-1 cells showed the promoter region of exon 1a in which the Sp1 transcription factor is specifically involved in promoter activity. This is the first to be identified as a transcription factor responsible for gene expression of vertebrate DNase I genes. Furthermore, RT-PCR analysis indicated alternative splicing of human DNASE1 pre-mRNA in pancreas and QGP-1 cells. Only two transcripts among eight alternative splicing products identified can be translated to produce intact DNase I protein. These results suggest that human DNASE1 expression is regulated through the use of alternative promoter and alternative splicing.

Regulation of ABO gene expression

The ABO blood group system is important in blood transfusions and in identifying individuals during criminal investigations. Two carbohydrate antigens, the A and B antigens, and their antibodies constitute this system. Although biochemical and molecular genetic studies have demonstrated the molecular basis of the histo-blood group ABO system, some aspects remain to be elucidated. To explain the molecular basis of how the ABO genes are controlled in cell type-specific expression, during normal cell differentiation, and in cancer cells with invasive and metastatic potential that lack A/B antigens, it is essential to understand the regulatory mechanism of ABO gene transcription. We review the transcriptional regulation of the ABO gene, including positive and negative elements in the upstream region of the gene, and draw some inferences that help to explain the phenomena described above.

Genetic and epigenetic alterations of the blood group ABO gene in oral squamous cell carcinoma

Loss of histo-blood group A and B antigen expression is a frequent event in oral carcinomas and is associated with decreased activity of glycosyltransferases encoded by the ABO gene. We examined 30 oral squamous cell carcinomas for expression of A and B antigens and glycosyltransferases. We also examined DNA from these tumors for loss of heterozygosity (LOH) at markers surrounding the ABO locus at chromosome 9q34, for loss of specific ABO alleles, and for hypermethylation of the ABO promoters. Loss of A or B antigen expression was found in 21 of 25 tumors (84%) and was a consistent feature of tumors lacking expression of A/B glycosyltransferases. LOH at 9q34 was found in 7 of 27 cases (26%), and one case showed microsatellite instability. Among 20 AO/BO cases, 3 showed loss of the A/B allele and 3 showed loss of the O allele. Analysis of the proximal ABO promoter by methylation-specific PCR and melting curve analysis showed hypermethylation in 10 of 30 tumors (33.3%), which was associated with loss of A/B antigen expression. ABO promoter hypermethylation was also found in hyperplastic or dysplastic tissues adjacent to the tumors, suggesting that it is an early event in tumorigenesis. Collectively, we have identified molecular events that may account for loss of A/B antigen expression in 67% of oral squamous cell carcinomas.

ABO exon and intron analysis in individuals with the AweakB phenotype reveals a novel O1v-A2 hybrid allele that causes four missense mutations in the A transferase

Background

Since the cloning in 1990 of cDNA corresponding to mRNA transcribed at the blood-group ABO locus, polymorphisms due to ethnic and/or phenotypic variations have been reported. Some subgroups have been explained at the molecular level, but unresolved samples are frequently encountered in the reference laboratory.

Results

ABO blood grouping discrepancies were investigated serologically and by ABO genotyping [duplex polymerase-chain-reaction (PCR) – restriction-fragment-length-polymorphism (RFLP) and PCR – allele-specific-primer (ASP) across intron 6] and DNA sequencing of the ABO gene and its proposed regulatory elements. Blood samples from five individuals living in Portugal, Switzerland, Sweden and the USA were analysed. These individuals were confirmed to be of Black ethnic origin and had the unusual A_weakB phenotype but appeared to have the A²B genotype without previously reported mutations associated with weak A or B expression. Sequencing of this A allele (having 467C>T and 1061delC associated with the common A² [A201] allele) revealed three mutations regularly encountered in the O^1v [O02] allele: 106C>T (Val36Phe), 188G>A (Arg63His), 220C>T (Pro74Ser) in exons 3, 4 and 5, respectively. The additional presence of 46G>A (Ala16Thr) was noted, whilst 189C>T that normally accompanies 188G>A in O^1v was missing, as were all O^1v-related mutations in exons 6 and 7 (261delG, 297A>G, 646T>A, 681G>A, 771C>T and 829G>A). On screening other samples, 46G>A was absent, but two new O alleles were found, a Jordanian O¹ and an African O^1v allele having 188G>A but lacking 189C>T. Sequencing of introns 2, 3, 4 and 5 in common alleles (A¹ [A101], A², B [B101], O¹, O^1vand O² [O03]) revealed 7, 12, 17 and 8 polymorphic positions, respectively, suggesting that alleles could be defined by intronic sequences. These polymorphic sites allowed definition of a breakpoint in intron 5 where the O^1v-related sequence was fused with A² to form the new hybrid. Intron 6 has previously been sequenced. Four new mutations were detected in the hybrid allele and these were subsequently also found in intron 6 of A² alleles in other Black African samples.

Conclusions

A novel O^1v-A² hybrid was defined by ABO exon/intron analysis in five unrelated individuals of African descent with the A_weakB blood group phenotype.

Alternative promoter identified between a hypermethylated upstream region of repetitive elements and a CpG island in human ABO histo-blood group genes

We have studied the expression of human histo-blood group ABO genes during erythroid differentiation, using an ex vivo culture of AC133(-)CD34(+) cells obtained from peripheral blood. 5'-Rapid amplification of cDNA ends analysis of RNA from those cells revealed a novel transcription start site, which appeared to mark an alternative starting exon (1a) comprising 27 bp at the 5'-end of a CpG island in ABO genes. Results from reverse transcription-PCR specific to exon 1a indicated that the cells of both erythroid and epithelial lineages utilize this exon as the transcription starting exon. Transient transfection experiments showed that the region just upstream from the transcription start site possesses promoter activity in a cell type-specific manner when placed 5' adjacent to the reporter luciferase gene. Results from bisulfite genomic sequencing and reverse transcription-PCR analysis indicated that hypermethylation of the distal promoter region correlated with the absence of transcripts containing exon 1a, whereas hypermethylation in the interspersed repeats 5' adjacent to the distal promoter was commonly observed in all of the cell lines examined. These results suggest that a functional alternative promoter is located between the hypermethylated region of repetitive elements and the CpG island in the ABO genes.