Human ERMAP: an erythroid adhesion/receptor transmembrane protein

Proteomes of plasmodium knowlesi early and late ring-stage parasites and infected host erythrocytes

The emerging malaria parasite Plasmodium knowlesi threatens the goal of worldwide malaria elimination due to its zoonotic spread in Southeast Asia. After brief ex-vivo culture we used 2D LC/MS/MS to examine the early and late ring stages of infected Macaca mulatta red blood cells harboring P. knowlesi. The M. mulatta clathrin heavy chain and T-cell and macrophage inhibitor ERMAP were overexpressed in the early ring stage; glutaredoxin 3 was overexpressed in the late ring stage; GO term differential enrichments included response to oxidative stress and the cortical cytoskeleton in the early ring stage. P. knowlesi clathrin heavy chain and 60S acidic ribosomal protein P2 were overexpressed in the late ring stage; GO term differential enrichments included vacuoles in the early ring stage, ribosomes and translation in the late ring stage, and Golgi- and COPI-coated vesicles, proteasomes, nucleosomes, vacuoles, ion-, peptide-, protein-, nucleocytoplasmic- and RNA-transport, antioxidant activity and glycolysis in both stages. SIGNIFICANCE: Due to its zoonotic spread, cases of the emerging human pathogen Plasmodium knowlesi in southeast Asia, and particularly in Malaysia, threaten regional and worldwide goals for malaria elimination. Infection by this parasite can be fatal to humans, and can be associated with significant morbidity. Due to zoonotic transmission from large macaque reservoirs that are untreatable by drugs, and outdoor biting mosquito vectors that negate use of preventive measures such as bed nets, its containment remains a challenge. Its biology remains incompletely understood. Thus we examine the expressed proteome of the early and late ex-vivo cultured ring stages, the first intraerythrocyte developmental stages after infection of host rhesus macaque erythrocytes. We used GO term enrichment strategies and differential protein expression to compare early and late ring stages. The early ring stage is characterized by the enrichment of P. knowlesi vacuoles, and overexpression of the M. mulatta clathrin heavy chain, important for clathrin-coated pits and vesicles, and clathrin-mediated endocytosis. The M. mulatta protein ERMAP was also overexpressed in the early ring stage, suggesting a potential role in early ring stage inhibition of T-cells and macrophages responding to P. knowlesi infection of reticulocytes. This could allow expansion of the host P. knowlesi cellular niche, allowing parasite adaptation to invasion of a wider age range of RBCs than the preferred young RBCs or reticulocytes, resulting in proliferation and increased pathogenesis in infected humans. Other GO terms differentially enriched in the early ring stage include the M. mulatta cortical cytoskeleton and response to oxidative stress. The late ring stage is characterized by overexpression of the P. knowlesi clathrin heavy chain. Combined with late ring stage GO term enrichment of Golgi-associated and coated vesicles, and enrichment of COPI-coated vesicles in both stages, this suggests the importance to P. knowlesi biology of clathrin-mediated endocytosis. P. knowlesi ribosomes and translation were also differentially enriched in the late ring stage. With expression of a variety of heat shock proteins, these results suggest production of folded parasite proteins is increasing by the late ring stage. M. mulatta endocytosis was differentially enriched in the late ring stage, as were clathrin-coated vesicles and endocytic vesicles. This suggests that M. mulatta clathrin-based endocytosis, perhaps in infected reticulocytes rather than mature RBC, may be an important process in the late ring stage. Additional ring stage biology from enriched GO terms includes M. mulatta proteasomes, protein folding and the chaperonin-containing T complex, actin and cortical actin cytoskeletons. P knowlesi biology also includes proteasomes, as well as nucleosomes, antioxidant activity, a variety of transport processes, glycolysis, vacuoles and protein folding. Mature RBCs have lost internal organelles, suggesting infection here may involve immature reticulocytes still retaining organelles. P. knowlesi parasite proteasomes and translational machinery may be ring stage drug targets for known selective inhibitors of these processes in other Plasmodium species. To our knowledge this is the first examination of more than one timepoint within the ring stage. Our results expand knowledge of both host and parasite proteins, pathways and organelles underlying P. knowlesi ring stage biology.

SCAR: The high-prevalence antigen 013.008 in the Scianna blood group system

BACKGROUND

The Scianna (SC) blood group system comprises seven antigens. They reside on the erythroblast membrane-associated glycoprotein (ERMAP). The ERMAP and RHCE genes are juxtaposed to each other on chromosome 1. We report a novel SC antigen.

STUDY DESIGN AND METHODS

Blood samples came from a patient and his two sisters in Saudi Arabia. To investigate the antibody specificity we used the column agglutination technique and soluble recombinant ERMAP protein. The significance of anti-SCAR was evaluated by the transfusion history and a monocyte monolayer assay. We determined the genomic sequence of ERMAP and RHCE genes.

RESULTS

The patient's serum showed an antibody of titer 8 against a high-prevalence antigen. The soluble recombinant ERMAP protein inhibited the antibody. The propositus genotyped homozygous for an ERMAP:c.424C>G variant, for which his sisters were heterozygous. The c.424C>G variant occurred in the SC*01 allele in one haplotype with the RHCE*03 (RHCE*cE) allele. No signs of hemolysis occurred following an incompatible blood transfusion. The monocyte monolayer assay was negative.

CONCLUSIONS

We characterized a high-prevalence antigen, with the proposed name "SCAR," which is the eighth antigen of the Scianna blood group system (proposed designation 013.008). Individuals homozygous for ERMAP:p.(Gln142Glu) protein variant can produce anti-SCAR. Although we did not observe any sign of hemolysis at this time, the anti-SCAR prompted a change of the treatment regimen. A review of the known reports indicated that all SC alloantibodies of sufficient titer should be considered capable of causing hemolysis.

ERMAP is a B7 family-related molecule that negatively regulates T cell and macrophage responses

T cell activation and tolerance are tightly regulated by costimulatory and coinhibitory molecules. B7 family members play a crucial role in regulating immune responses. In this study, we identified erythroid membrane-associated protein (ERMAP) as a novel T cell inhibitory molecule. ERMAP shares significant sequence and structural homology with existing B7 family members in its extracellular domain. The ERMAP protein is expressed on the cell surface of resting and activated antigen-presenting cells (APCs) and in some tumor tissues. The putative ERMAP receptor is expressed on activated CD4 and CD8 T cells and macrophages. Both mouse and human ERMAP-IgG2a Fc (ERMAP-Ig) fusion proteins inhibit T cell functions in vitro. Administration of ERMAP-Ig protein ameliorates autoimmune diseases, including experimental autoimmune encephalomyelitis and type 1 diabetes, in mice. Anti-ERMAP antibody enhances macrophage phagocytosis of cancer cells in vitro. Furthermore, administration of an anti-ERMAP antibody inhibits tumor growth in mice likely by blocking the inhibitory effects of ERMAP on T cells and macrophages. Our results suggest that therapeutic interaction with the ERMAP inhibitory pathway may represent a novel strategy for treating patients with autoimmune disease or cancer.

The phylogeny of 48 alleles, experimentally verified at 21 kb, and its application to clinical allele detection

Background

Sequence information generated from next generation sequencing is often computationally phased using haplotype-phasing algorithms. Utilizing experimentally derived allele or haplotype information improves this prediction, as routinely used in HLA typing. We recently established a large dataset of long ERMAP alleles, which code for protein variants in the Scianna blood group system. We propose the phylogeny of this set of 48 alleles and identify evolutionary steps to derive the observed alleles.

Methods

The nucleotide sequence of > 21 kb each was used for all physically confirmed 48 ERMAP alleles that we previously published. Full-length sequences were aligned and variant sites were extracted manually. The Bayesian coalescent algorithm implemented in BEAST v1.8.3 was used to estimate a coalescent phylogeny for these variants and the allelic ancestral states at the internal nodes of the phylogeny.

Results

The phylogenetic analysis allowed us to identify the evolutionary relationships among the 48 ERMAP alleles, predict 4243 potential ancestral alleles and calculate a posterior probability for each of these unobserved alleles. Some of them coincide with observed alleles that are extant in the population.

Conclusions

Our proposed strategy places known alleles in a phylogenetic framework, allowing us to describe as-yet-undiscovered alleles. In this new approach, which relies heavily on the accuracy of the alleles used for the phylogenetic analysis, an expanded set of predicted alleles can be used to infer alleles when large genotype data are analyzed, as typically generated by high-throughput sequencing. The alleles identified by studies like ours may be utilized in designing of microarray technologies, imputing of genotypes and mapping of next generation sequencing data.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1791-9) contains supplementary material, which is available to authorized users.

Full-length nucleotide sequence of ERMAP alleles encoding Scianna (SC) antigens

BACKGROUND

Scianna (SC) blood group system comprises two antithetical antigens, Sc1 and Sc2, and five additional antigens. The antigens reside on a glycoprotein encoded by the erythroblast membrane-associated protein (ERMAP) gene. For the common ERMAP alleles, we determined the full-length nucleotide sequence that encodes the Scianna glycoprotein.

STUDY DESIGN AND METHODS

Blood donor samples from five populations were analyzed including 20 African Americans, 10 Caucasians, 10 Thai, five Asians, and five Hispanics for a total of 100 chromosomes. An assay was devised to determine the genomic sequence of the ERMAP gene in one amplicon, spanning 21.4 kb and covering Exons 2 to 12 and the intervening sequence (IVS). All alleles (confirmed haplotypes) were resolved without ambiguity.

RESULTS

Among 50 blood donors, we found 80 single-nucleotide polymorphisms (SNPs), including six novel SNPs, in 21,308 nucleotides covering the coding sequence of the ERMAP gene and including the introns. The noncoding sequences harbored 75 SNPs (68 in the introns and seven in the 3'-UTR). No SNP indicative of a nonfunctional allele was detected. The nucleotide sequences for 48 ERMAP alleles (confirmed haplotypes) were determined by allele-specific polymerase chain reaction and sequencing in 100 chromosomes.

CONCLUSIONS

We documented 48 ERMAP alleles of 21,308 nucleotides each. The two nucleotide sequences available in GenBank for ERMAP alleles of similar length have not been found in our 100 chromosomes. Alleles determined without ambiguity can be used as templates to analyze next generation sequencing data, which will enhance the reliability in clinical diagnostics.

Easy identification of antibodies to high-prevalence Scianna antigens and detection of admixed alloantibodies using soluble recombinant Scianna protein

BACKGROUND

Identification of antibodies against high-prevalence Scianna (Sc; ERMAP) antigens, like Sc1 and Sc5, is difficult and may incur delays in blood procurement and costs. The detection of additional clinically significant alloantibodies is hampered in the presence of anti-Scianna. Soluble recombinant Scianna protein is demonstrated to facilitate antibody diagnostics in both cases.

STUDY DESIGN AND METHODS

Soluble recombinant Scianna protein (Sc:1,-2,3,-4,5,6,7) was produced comprising the antigenic extracellular domain fused to a V5-His tag. The protein was isolated from eukaryotic cell culture supernatants of stably transfected HEK293 cells. Seven serum samples with anti-Sc1, anti-Sc2, and anti-Sc5 and 30 serum samples with antibodies to other blood group antigens were evaluated in hemagglutination inhibition assays. Antisera with mixed antibody specificities and autoantibodies were also tested.

RESULTS

Soluble Scianna protein inhibited specifically antibodies to the high-prevalence Scianna antigens Sc1 and Sc5. No antibodies were neutralized that were directed to the low-prevalence Sc2 antigen or to a large representative set of antigens from other blood group systems. Clinically relevant antibodies could be identified despite being masked by anti-Sc1 and anti-Sc5. A mixture of Scianna and JMH proteins allowed detecting a common antibody despite the presence of antibodies to high-prevalence antigens of the Scianna or JMH blood group systems.

CONCLUSION

Antibody detection systems comprising soluble recombinant Scianna protein provide an easy single-step method for detection and identification of antibodies to high-prevalence Scianna antigens. Reagents with Scianna and other recombinant blood group proteins and mixtures of such proteins would be useful routine reagents in immunohematology.

bloodthirsty, an RBCC/TRIM gene required for erythropoiesis in zebrafish

The Antarctic icefishes (family Channichthyidae, suborder Notothenioidei) constitute the only vertebrate taxon that fails to produce red blood cells. These fishes can be paired with closely related, but erythrocyte-producing, notothenioids to discover erythropoietic genes via representational difference analysis. Using a B30.2-domain-encoding DNA probe so derived from the hematopoietic kidney (pronephros) of a red-blooded Antarctic rockcod, Notothenia coriiceps, we discovered a related, novel gene, bloodthirsty (bty), that encoded a 547-residue protein that contains sequential RING finger, B Box, coiled-coil, and B30.2 domains. bty mRNA was expressed by the pronephric kidney of N. coriiceps at a steady-state level 10-fold greater than that found in the kidney of the icefish Chaenocephalus aceratus. To test the function of bty, we cloned the orthologous zebrafish gene from a kidney cDNA library. Whole-mount in situ hybridization of zebrafish embryos showed that bty mRNA was present throughout development and, after the mid-blastula transition, was expressed in the head and in or near the site of primitive erythropoiesis in the tail just prior to red cell production. One- to four-cell embryos injected with two distinct antisense morpholino oligonucleotides (MOs) targeted to the 5'-end of the bty mRNA failed to develop red cells, whereas embryos injected with 4- and 5-bp mismatch control MOs produced wild-type quantities of erythrocytes. The morphant phenotype was rescued by co-injection of synthetic bty mRNA containing an artificial 5'-untranslated region (UTR) with the antisense MO that bound the 5'-UTR of the wild-type bty transcript. Furthermore, the expression of genes that mark terminal erythroid differentiation was greatly reduced in the antisense-MO-treated embryos. We conclude that bty is likely to play a role in differentiation of the committed red cell progenitor.

Human blood group genes 2004: chromosomal locations and cloning strategies

Of the 29 human blood group system genes, 27 have been localized to 14 autosomes and 2 have been assigned to the X chromosome. It is remarkable that 28 of the 29 system genes have now been localized to a single cytogenetic band on a specific chromosome. In this review, we summarize the chromosomal locations and cloning strategies used for those genes encoding blood group systems. We highlight such information about the 3 most recently defined blood group systems (I, GLOB, and GIL). In addition, we provide new information about 2 older blood group systems (SC and RAPH) whose polymorphisms have been defined in cloned genes.

Red blood cell blood group antigens: structure and function

Red blood cell (RBC) blood group antigens are polymorphic, inherited, carbohydrate or protein structures located on the extracellular surface of the RBC membrane. They contribute to the architecture of the RBC membrane, and their individual function(s) are being slowly revealed. The biological qualities assigned to these RBC membrane structures are based on observed physiological alteration in RBCs that lack the component, by documenting similarities in its protein sequence (predicted from the nucleotide sequence of the gene) to proteins of known function and by extrapolation to identified functional homologues in other cells. The varied roles of RBC antigens include membrane structural integrity, the transport of molecules through the membrane, as receptors for extracellular ligands, adhesion molecules, enzymes, complement components and regulators, and in glycocalyx formation.

Scianna antigens including Rd are expressed by ERMAP

The Scianna blood group encompasses the high-frequency antigens Sc1 and Sc3 and the low-frequency antigen Sc2. Another low-frequency antigen Rd (Radin) was suggested to belong to the Scianna blood group. The molecular basis of the Scianna blood group was unknown. The erythrocyte membrane-associated protein (ERMAP) shared the genomic location, protein product size, and localization to the red blood cell (RBC) membrane surface with Scianna. The ERMAP gene was sequenced in probands with known Scianna and Radin phenotypes. In a Sc:-1,-2 proband, only an ERMAP allele with a 2-bp deletion in exon 3 causing a frameshift could be detected. A Sc:-1,2 proband was homozygous for the ERMAP(Gly57Arg) allele. An Rd(+) proband was heterozygous for the ERMAP(Pro60Ala) allele. Polymerase chain reaction with sequence-specific priming (PCR-SSP) systems was developed to detect the Sc2 and Rd alleles of the ERMAP gene. The 2 alleles occurred with about 1% and less than 1% frequency in the population, which was compatible with the frequency of the Sc2 and Rd antigens known in whites. Two Sc2(+) and one Rd(+) samples that were found by genotyping were confirmed by serology. The antigens of the Scianna blood group include Rd and are expressed by the human ERMAP protein. Sc2 is caused by an ERMAP(Gly57Arg) allele and Rd by an ERMAP(Pro60Ala) allele. Scianna is the last of the previously characterized protein-based blood group systems whose molecular basis was discerned. Hence, the phenotype prediction by genotyping became possible for all human blood group systems encoded by proteins.