The human Kell blood group binds the erythroid 4.1R protein: new insights into the 4.1R-dependent red cell membrane complex

Clonal hematopoiesis and acquired genetic abnormalities of the red cell: An historical review

Several syndromes affecting the red cell that mimic those induced by germline mutations may result from a somatic mutation that accompanies a myeloid malignancy. These syndromes are most notable in cases of myelodysplastic syndrome, but they are not limited to any one category of myeloid neoplasm. Their occurrence in males exceed the male predominance that is evident in myeloid neoplasms. The syndromes include disorders of globin chain synthesis (α- and β-thalassemia), heme synthesis (erythropoietic porphyria and erythropoietic uroporphyria), red cell membrane structure (elliptocytosis and spherocytosis), red cell enzyme activity (pyruvate kinase deficiency, glucose-6-phosphate dehydrogenase deficiency) and lowered expression of red cell ABO blood group antigens. This historical review describes the path to uncovering these acquired syndromes and their causal somatic mutations, where known. These syndromes often go unrecognized because of the dominant concern of the primary neoplasm. They may add to the healthcare needs of the patient.

Acquired elliptocytosis in chronic myeloid neoplasms: An enigmatic relationship to acquired red cell membrane protein and genetic abnormalities

Nineteen reports of 41 cases of acquired red cell elliptocytosis associated with a chronic myeloid neoplasm are described. Although the majority of cases have an abnormality of the long arm of chromosome 20, del(q20), several cases do not. Moreover, in one case a specific qualitative abnormality of red cell protein band 4.1(4.1R) was reported; however, several subsequent cases could find no abnormality of a red cell membrane protein or found a different abnormality, usually quantitative. Thus, this striking red cell phenotypic feature, acquired elliptocytosis, seen in myelodysplastic syndrome and other chronic myeloproliferative diseases, closely simulating the red cell phenotype of hereditary elliptocytosis, has an unexplained genetic basis, presumably as the result of an acquired mutation(s) in some chronic myeloid neoplasms.

Prior immunization against an intracellular antigen enhances subsequent red blood cell alloimmunization in mice

Antibodies against red blood cell (RBC) alloantigens can increase morbidity and mortality among transfusion recipients. However, alloimmunization rates can vary dramatically, as some patients never generate alloantibodies after transfusion, whereas others not only become alloimmunized but may also be prone to generating additional alloantibodies after subsequent transfusion. Previous studies suggested that CD4 T-cell responses that drive alloantibody formation recognize the same alloantigen engaged by B cells. However, because RBCs express numerous antigens, both internally and externally, it is possible that CD4 T-cell responses directed against intracellular antigens may facilitate subsequent alloimmunization against a surface RBC antigen. Here, we show that B cells can acquire intracellular antigens from RBCs. Using a mouse model of donor RBCs expressing 2 distinct alloantigens, we demonstrate that immune priming to an intracellular antigen, which would not be detected by any currently used RBC compatibility assays, can directly influence alloantibody formation after exposure to a subsequent distinct surface RBC alloantigen. These findings suggest a previously underappreciated mechanism whereby transfusion recipient responders may exhibit an increased rate of alloimmunization because of prior immune priming toward intracellular antigens.

Molecular and structural characterization of a novel high-prevalence antigen of the Augustine blood group system

BACKGROUND

An antibody directed against a high-prevalence red blood cell (RBC) antigen was detected in a 67-year-old female patient of North African ancestry with a history of a single pregnancy and blood transfusion. So far, the specificity of the proband's alloantibody remained unknown in our immunohematology reference laboratory.

STUDY DESIGN AND METHODS

Whole-exome sequencing (WES) was performed on the proband's DNA. The reactivity to the SLC29A1-encoded ENT1 adenosine transporter was investigated by flow cytometry analyses of ENT1-expressing HEK293 cells, and RBCs from Augustine-typed individuals. Erythrocyte protein expression level, nucleoside-binding capacity, and molecular structure of the proband's ENT1 variant were further explored by western blot, flow cytometry, and molecular dynamics calculations, respectively.

RESULTS

A missense variant was identified in the SLC29A1 gene, which encodes the Augustine blood group system. It arises from homozygosity for a rare c.242A > G missense mutation that results in a nonsynonymous p.Asn81Ser substitution within the large extracellular loop of ENT1. Flow cytometry analyses demonstrated that the proband's antibody was reactive against HEK-293 cells transfected with control but not proband's SLC29A1 cDNA. Consistent with this finding, proband's antibody was found to be reactive with At(a-) (AUG:-2), but not AUG:-1 (null phenotype) RBCs. Data from structural analysis further supported that the proband's p.Asn81Ser variation does not alter ENT1 binding of its specific inhibitor NBMPR.

CONCLUSION

Our study provides evidence for a novel high-prevalence antigen, AUG4 (also called ATAM after the proband's name) in the Augustine blood group system, encoded by the rare SLC29A1 variant allele AUG*04 (c.242A > G, p.Asn81Ser).

The equilibrative nucleoside transporter ENT1 is critical for nucleotide homeostasis and optimal erythropoiesis

The tight regulation of intracellular nucleotides is critical for the self-renewal and lineage specification of hematopoietic stem cells (HSCs). Nucleosides are major metabolite precursors for nucleotide biosynthesis and their availability in HSCs is dependent on their transport through specific membrane transporters. However, the role of nucleoside transporters in the differentiation of HSCs to the erythroid lineage and in red cell biology remains to be fully defined. Here, we show that the absence of the equilibrative nucleoside transporter (ENT1) in human red blood cells with a rare Augustine-null blood type is associated with macrocytosis, anisopoikilocytosis, an abnormal nucleotide metabolome, and deregulated protein phosphorylation. A specific role for ENT1 in human erythropoiesis was demonstrated by a defective erythropoiesis of human CD34+ progenitors following short hairpin RNA-mediated knockdown of ENT1. Furthermore, genetic deletion of ENT1 in mice was associated with reduced erythroid progenitors in the bone marrow, anemia, and macrocytosis. Mechanistically, we found that ENT1-mediated adenosine transport is critical for cyclic adenosine monophosphate homeostasis and the regulation of erythroid transcription factors. Notably, genetic investigation of 2 ENT1null individuals demonstrated a compensation by a loss-of-function variant in the ABCC4 cyclic nucleotide exporter. Indeed, pharmacological inhibition of ABCC4 in Ent1-/- mice rescued erythropoiesis. Overall, our results highlight the importance of ENT1-mediated nucleotide metabolism in erythropoiesis.

Home Sweet Home: Plasmodium vivax-Infected Reticulocytes-The Younger the Better?

After a century of constant failure to produce an in vitro culture of the most widespread human malaria parasite Plasmodium vivax, recent advances have highlighted the difficulties to provide this parasite with a healthy host cell to invade, develop, and multiply under in vitro conditions. The actual level of understanding of the heterogeneous populations of cells—framed under the name ‘reticulocytes’—and, importantly, their adequate in vitro progression from very immature reticulocytes to normocytes (mature erythrocytes) is far from complete. The volatility of its individual stability may suggest the reticulocyte as a delusory cell, particularly to be used for stable culture purposes. Yet, the recent relevance gained by a specific subset of highly immature reticulocytes has brought some hope. Very immature reticulocytes are characterized by a peculiar membrane harboring a plethora of molecules potentially involved in P. vivax invasion and by an intracellular complexity dynamically changing upon its quick maturation into normocytes. We analyze the potentialities offered by this youngest reticulocyte subsets as an ideal in vitro host cell for P. vivax.

Sickle Cell Trait Modulates the Proteome and Phosphoproteome of Plasmodium falciparum-Infected Erythrocytes

The high prevalence of sickle cell disease in some human populations likely results from the protection afforded against severe Plasmodium falciparum malaria and death by heterozygous carriage of HbS. P. falciparum remodels the erythrocyte membrane and skeleton, displaying parasite proteins at the erythrocyte surface that interact with key human proteins in the Ankyrin R and 4.1R complexes. Oxidative stress generated by HbS, as well as by parasite invasion, disrupts the kinase/phosphatase balance, potentially interfering with the molecular interactions between human and parasite proteins. HbS is known to be associated with abnormal membrane display of parasite antigens. Studying the proteome and the phosphoproteome of red cell membrane extracts from P. falciparum infected and non-infected erythrocytes, we show here that HbS heterozygous carriage, combined with infection, modulates the phosphorylation of erythrocyte membrane transporters and skeletal proteins as well as of parasite proteins. Our results highlight modifications of Ser-/Thr- and/or Tyr- phosphorylation in key human proteins, such as ankyrin, β-adducin, β-spectrin and Band 3, and key parasite proteins, such as RESA or MESA. Altered phosphorylation patterns could disturb the interactions within membrane protein complexes, affect nutrient uptake and the infected erythrocyte cytoadherence phenomenon, thus lessening the severity of malaria symptoms.

Overexpression of miR-669m inhibits erythroblast differentiation

MicroRNAs (miRNAs), one of small non-coding RNAs, regulate many cell functions through their post-transcriptionally downregulation of target genes. Accumulated studies have revealed that miRNAs are involved in hematopoiesis. In the present study, we investigated effects of miR-669m overexpression on hematopoiesis in mouse in vivo, and found that erythroid differentiation was inhibited by the overexpression. Our bioinformatic analyses showed that candidate targets of miR-669m which are involved in the erythropoiesis inhibition are A-kinase anchoring protein 7 (Akap7) and X-linked Kx blood group (Xk) genes. These two genes were predicted as targets of miR-669m by two different in silico methods and were upregulated in late erythroblasts in a public RNA-seq data, which was confirmed with qPCR. Further, miR-669m suppressed luciferase reporters for 3′ untranslated regions of Akap7 and Xk genes, which supports these genes are direct targets of miR-669m. Physiologically, miR-669m was not expressed in the erythroblast. In conclusion, using miR-669m, we found Akap7 and Xk, which may be involved in erythroid differentiation, implying that manipulating these genes could be a therapeutic way for diseases associated with erythropoiesis dysfunction.

Lack of the multidrug transporter MRP4/ABCC4 defines the PEL-negative blood group and impairs platelet aggregation

The rare PEL-negative phenotype is one of the last blood groups with an unknown genetic basis. By combining whole-exome sequencing and comparative global proteomic investigations, we found a large deletion in the ABCC4/MRP4 gene encoding an ATP-binding cassette (ABC) transporter in PEL-negative individuals. The loss of PEL expression on ABCC4-CRISPR-Cas9 K562 cells and its overexpression in ABCC4-transfected cells provided evidence that ABCC4 is the gene underlying the PEL blood group antigen. Although ABCC4 is an important cyclic nucleotide exporter, red blood cells from ABCC4null/PEL-negative individuals exhibited a normal guanosine 3',5'-cyclic monophosphate level, suggesting a compensatory mechanism by other erythroid ABC transporters. Interestingly, PEL-negative individuals showed an impaired platelet aggregation, confirming a role for ABCC4 in platelet function. Finally, we showed that loss-of-function mutations in the ABCC4 gene, associated with leukemia outcome, altered the expression of the PEL antigen. In addition to ABCC4 genotyping, PEL phenotyping could open a new way toward drug dose adjustment for leukemia treatment.

Expression of Protein 4.1 Family in Breast Cancer: Database Mining for 4.1 Family Members in Malignancies

BACKGROUND The protein 4.1 family is a family of cytoskeletal proteins that play an important role in maintaining normal cell morphology and cell adhesion, migration, division, and intercellular signaling. The main aim of this study was to explore the prognostic significance of the protein 4.1 family in breast cancer (BC) patients and to provide new biomarkers and therapeutic targets for the diagnosis and treatment of BC. MATERIAL AND METHODS The expression of 4.1 family members in various tumor types was compared to normal controls using the ONCOMINE and GOBO databases. The prognostic significance of the 4.1 family in BC patients was determined by Kaplan-Meier Plotter. RESULTS EPB41L2 (4.1G) was expressed at higher levels in normal tissues compared with BC patients for all 4.1 family members. In survival analysis, 4.1G and EPB41 (4.1R) mRNA high expressions were associated with better survival in BC patients. Moreover, 4.1G high expression was significantly associated with longer overall survival (OS) in luminal A and protracted relapse-free survival (RFS) in luminal B subtype BC patients who received Tamoxifen treatment. In addition, high expression of each 4.1 family member also showed better prognostic value in different molecular subtypes of BC. CONCLUSIONS These results indicate that the protein 4.1 family can be regarded as novel biomarkers and potential therapeutic targets for BC. Further research is needed to explore the detailed biological functions.

The Gerbich blood group system: old knowledge, new importance

Antigens of the Gerbich blood group system are expressed on glycophorin C (GPC) and glycophorin D (GPD), minor sialoglycoproteins of human erythrocytes. GPC and GPD help maintain erythrocyte shape of and contributes to the stability of its membrane. There are six high-prevalence Gerbich antigens: Ge2, Ge3, Ge4, GEPL (GE10), GEAT (GE11), GETI (GE12) and five low-prevalence Gerbich antigens: Wb (GE5), Ls^a (GE6), An^a (GE7), Dh^a (GE8), GEIS (GE9). Some Gerbich antigens (Ge4, Wb, Dh^a, GEAT) are expressed only on GPC, two (Ge2, An^a) are expressed only on GPD, while others (Ge3, Ls^a, GEIS, GEPL, GETI) are expressed on both GPC and GPD. Antibodies recognizing GPC/GPD may arise naturally (so-called "naturally-occurring RBC antibodies") or as the result of alloimmunization, and some of them may be clinically relevant. Gerbich antibodies usually do not cause serious hemolytic transfusion reactions (HTR); autoantibodies of anti-Ge2- or anti-Ge3 specificity can cause autoimmune hemolytic anemia (AIHA).

DARC extracellular domain remodeling in maturating reticulocytes explains Plasmodium vivax tropism

Plasmodium vivax is the most prevalent parasite species that causes malaria in humans and exclusively infects reticulocytes. Reticulocyte infection is facilitated by P vivax Duffy binding protein (DBP), which utilizes DARC (Duffy antigen receptor for chemokines) as an entry point. However, the selective tropism of P vivax for transferrin receptor (CD71)-positive reticulocytes remained unexplained, given the constitutive expression of DARC during reticulocyte maturation. CD71/RNA double staining of reticulocytes enriched from adult peripheral blood reveals 4 distinct reticulocyte populations: CD71^high/RNA^high (∼0.016%), CD71^low/RNA^high (∼0.059%), CD71^neg/RNA^high (∼0.37%), CD71^neg/RNA^low (∼0.55%), and erythrocytes CD71^neg/RNA^neg (∼99%). We hypothesized that selective association of DBP with a small population of immature reticulocytes could explain the preference of P vivax for reticulocytes. Binding of specific monoclonal anti-DARC antibodies and recombinant DBP to CD71^high/RNA^high reticulocytes was significantly higher compared with other reticulocyte populations and erythrocytes. Interestingly, the total DARC protein throughout reticulocyte maturation was constant. The data suggest that selective exposure of the DBP binding site within DARC is key to the preferential binding of DBP to immature reticulocytes, which is the potential mechanism underlying the preferential infection of a reticulocyte subset by P vivax.