Gene for human CD59 (likely Ly-6 homologue) is located on the short arm of chromosome 11

CD59 gene: 143 haplotypes of 22,718 nucleotides length by computational phasing in 113 individuals from different ethnicities

BACKGROUND

CD59 deficiency due to rare germline variants in the CD59 gene causes disabilities, ischemic strokes, neuropathy, and hemolysis. CD59 deficiency due to common somatic variants in the PIG-A gene in hematopoietic stem cells causes paroxysmal nocturnal hemoglobinuria. The ISBT database lists one nonsense and three missense germline variants that are associated with the CD59-null phenotype. To analyze the genetic diversity of the CD59 gene, we determined long-range CD59 haplotypes among individuals from different ethnicities.

METHODS

We determined a 22.7 kb genomic fragment of the CD59 gene in 113 individuals using next-generation sequencing (NGS), which covered the whole NM_203330.2 mRNA transcript of 7796 base pairs. Samples came from an FDA reference repository and our Ethiopia study cohorts. The raw genotype data were computationally phased into individual haplotype sequences.

RESULTS

Nucleotide sequencing of the CD59 gene of 226 chromosomes identified 216 positions with single nucleotide variants. Only three haplotypes were observed in homozygous form, which allowed us to assign them unambiguously as experimentally verified CD59 haplotypes. They were also the most frequent haplotypes among both cohorts. An additional 140 haplotypes were imputed computationally.

DISCUSSION

We provided a large set of haplotypes and proposed three verified long-range CD59 reference sequences, based on a population approach, using a generalizable rationale for our choice. Correct long-range haplotypes are useful as template sequences for allele calling in high-throughput NGS and precision medicine approaches, thus enhancing the reliability of clinical diagnostics. Long-range haplotypes can also be used to evaluate the influence of genetic variation on the risk of transfusion reactions or diseases.

Consequences of dysregulated complement regulators on red blood cells

The complement system represents the first line of defense that is involved in the clearance of pathogens, dying cells and immune complexes via opsonization, induction of an inflammatory response and the formation of a lytic pore. Red blood cells (RBCs) are very important for the delivery of oxygen to tissues and are continuously in contact with complement proteins in the blood plasma. To prevent complement activation on RBCs, various complement regulatory proteins can be found in plasma and on the cell membrane. RBCs are special cells without a nucleus and having a slightly different make-up of complement regulators than nucleated cells, as membrane cofactor protein (MCP) is not expressed and complement receptor 1 (CR1) is highly expressed. Decreased expression and/or function of complement regulatory proteins may result in unwanted complement activation and accelerated removal of RBCs. This review describes complement regulation on RBCs and the consequences when this regulation is out of balance.

Congenital CD59 Deficiency

The severe clinical symptoms of inherited CD59 deficiency confirm the importance of CD59 as essential complement regulatory protein for protection of cells against complement attack, in particular protection of hematopoietic cells and human neuronal tissue. Targeted complement inhibition might become a treatment option as suggested by a case report. The easy diagnostic approach by flow cytometry and the advent of a new treatment option should increase the awareness of this rare differential diagnosis and lead to further studies on their pathophysiology.

Spontaneous abortion is associated with elevated systemic C5a and reduced mRNA of complement inhibitory proteins in placenta

Spontaneous abortion in early pregnancy due to unknown reasons is a common problem. The excess complement activation and consequent placental inflammation and anti-angiogenic milieu is emerging as an important associated factor in many pregnancy-related complications. In the present study we sought to examine the expression of complement inhibitory proteins at the feto-maternal interface and levels of complement split products in the circulation to understand their role in spontaneous abortion. Consenting pregnant women who either underwent elective abortion due to non-clinical reasons (n = 13) or suffered miscarriage (n = 14) were recruited for the study. Systemic levels of complement factors C3a and C5a were measured by enzyme-linked immunosorbent assay (ELISA). Plasma C5 and C3 protein levels were examined by Western blot. Expressions of complement regulatory proteins such as CD46 and CD55 in the decidua were investigated by quantitative polymerase chain reaction (PCR) and Western blot. The median of plasma C3a level was 82·83 ng/ml and 66·17 ng/ml in elective and spontaneous abortion patients, respectively. Medians of plasma C5a levels in elective and spontaneous abortion patients were 0·96 ng/ml and 1·14 ng/ml, respectively. Only plasma C5a levels but not C3a levels showed significant elevation in spontaneous abortion patients compared to elective abortion patients. Further, there was a threefold decrease in the mRNA expressions of complement inhibitory proteins CD46 and CD55 in the decidua obtained from spontaneous abortion patients compared to that of elective abortion patients. These data suggested that dysregulated complement cascade may be associated with spontaneous abortion.

A new blood group antigen is defined by anti-CD59, detected in a CD59-deficient patient

BACKGROUND

CD59 is a cell surface glycoprotein of approximately 20 kDa limiting the lytic activity of the terminal complement complex C5b-9. Although CD59 is known as a red blood cell (RBC) antigen defined by monoclonal antibodies, it so far has not been identified as a blood group antigen, since the description of a human alloantibody was missing. In this study we show the presence of an anti-CD59 in a patient affected by a homozygous CD59 deficiency.

STUDY DESIGN AND METHODS

RBC CD59 and CD55 were determined by flow cytometry or by the column agglutination technique using monoclonal antisera. Commercially available His-tagged recombinant soluble CD59 protein was used to inhibit anti-CD59.

RESULTS

Seven cases of an isolated CD59 deficiency due to three distinct null alleles of the CD59 gene have been published so far. Recently we described the CD59-null allele c.146delA in a young child of heterozygous parents. Her plasma contained an alloantibody directed against the high-prevalence RBC antigen CD59. The antibody specificity was identified using soluble recombinant human CD59 protein, which blocked the reactivity of the patient's antibody and of monoclonal anti-CD59 but not of monoclonal anti-CD55. In addition, RBC alloantibodies such as anti-K, anti-C, anti-c, or anti-Fy(a) remained unaffected. Therefore, inhibition by recombinant CD59 is a useful diagnostic tool to detect alloantibodies in the presence of anti-CD59.

CONCLUSION

This is the first demonstration of a human anti-CD59 alloantibody, which defines CD59 as an RBC blood group antigen. CD59 represents a candidate for a new blood group system.

P53 possibly upregulates the expression of CD58 (LFA-3) and CD59 (MIRL)

P53 is an oncosuppressor protein which acts via transcriptional and non-transcriptional mechanisms. The transcriptional function of p53 is mediated by specific responsive elements (RE). In the present study we found one perfect p53 RE located in the first intron of the gene encoding for CD58 (lymphocyte function Antigen-3/LFA-3) membrane protein. Additionally, we detected one perfect p53 RE within the promoter region and one imperfect p53 RE placed in the first intron of the gene encoding for CD59 (membrane inhibitor of reactive lysis/MIRL). The results of our investigation suggest that p53 may enhance the transcription of both CD59 and CD58 and imply a novel role for p53 as a direct regulator of the immune response.

Structural and phylogenetic characterization of human SLURP-1, the first secreted mammalian member of the Ly-6/uPAR protein superfamily

Members of the Ly-6/uPAR protein family share one or several repeat units of the Ly-6/uPAR domain that is defined by a distinct disulfide bonding pattern between 8 or 10 cysteine residues. The Ly-6/uPAR protein family can be divided into two subfamilies. One comprises GPI-anchored glycoprotein receptors with 10 cysteine residues. The other subfamily includes the secreted single-domain snake and frog cytotoxins, and differs significantly in that its members generally possess only eight cysteines and no GPI-anchoring signal sequence. We report the purification and structural characterization of human SLURP-1 (secreted mammalian Ly-6/uPAR related protein 1) from blood and urine peptide libraries. SLURP-1 is encoded by the ARS (component B)-81/s locus, and appears to be the first mammalian member of the Ly-6/uPAR family lacking a GPI-anchoring signal sequence. A phylogenetic analysis based on the SLURP-1 primary protein structure revealed a closer relationship to the subfamily of cytotoxins. Since the SLURP-1 gene maps to the same chromosomal region as several members of the Ly-6/uPAR subfamily of glycoprotein receptors, it is suggested that both biologically distinct subfamilies might have co-evolved from local chromosomal duplication events.

A high-resolution genetic map of mouse chromosome 15 encompassing the Dominant megacolon (Dom) locus

Dominant megacolon (Dom) is one of four mutations in the mouse that can produce a phenotype similar to Hirschsprung disease in human. The Dom gene product is not known, and no candidate region has been defined for a possible human homolog. In this publication we report mapping the Dom locus with high definition, using several intra-and interspecific crosses and a set of 16 Chr 15-specific microsatellites flanking this locus.

Tissue expression, structure and function of the murine Ly-6 family of molecules

Murine Ly-6 molecules are a family of cell surface glycoproteins which have interesting patterns of tissue expression during haematopoiesis from multipotential stem cells to lineage committed precursor cells, and on specific leucocyte subpopulations in the peripheral lymphoid tissues. These interesting patterns of tissue expression suggest an intimate association between the regulation of Ly-6 expression and the development and homeostasis of the immune system. Ly-6 molecules are low molecular weight phosphatidyl inositol anchored glycoproteins with remarkable amino acid homology throughout a distinctive cysteine rich protein domain that is associated predominantly with O-linked carbohydrate. These molecules are encoded by multiple tightly linked genes located on Chr. 15 which have conserved geneomic organization. The in vivo functions of Ly-6 molecules are not known although in vitro studies suggest a role in cellular activation. This review will summarize our understanding of Ly-6 with regard to tissue expression, molecular structure, gene organization and function.

The human E48 antigen, highly homologous to the murine Ly-6 antigen ThB, is a GPI-anchored molecule apparently involved in keratinocyte cell-cell adhesion

The E48 antigen, a putative human homologue of the 20-kD protein present in desmosomal preparations of bovine muzzle, and formerly called desmoglein III (dg4), is a promising target antigen for antibody-based therapy of squamous cell carcinoma in man. To anticipate the effect of high antibody dose treatment, and to evaluate the possible biological involvement of the antigen in carcinogenesis, we set out to molecularly characterize the antigen. A cDNA clone encoding the E48 antigen was isolated by expression cloning in COS cells. Sequence analysis revealed that the clone contained an open reading frame of 128 amino acids, encoding a core protein of 13,286 kD. Database searching showed that the E48 antigen has a high level of sequence similarity with the mouse ThB antigen, a member of the Ly-6 antigen family. Phosphatidylinositol-specific (PI-specific) phospholipase-C treatment indicated that the E48 antigen is glycosylphosphatidylinositol-anchored (GPI-anchored) to the plasma membrane. The gene encoding the E48 antigen is a single copy gene, located on human chromosome 8 in the 8q24-qter region. The expression of the gene is confined to keratinocytes and squamous tumor cells. The putative mouse homologue, the ThB antigen, originally identified as an antigen on cells of the lymphocyte lineage, was shown to be highly expressed in squamous mouse epithelia. Moreover, the ThB expression level is in keratinocytes, in contrast to that in lymphocytes, not mouse strain related. Transfection of mouse SV40-polyoma transformed mouse NIH/3T3 cells with the E48 cDNA confirmed that the antigen is likely to be involved in cell-cell adhesion.

An association between high Ly-6A/E expression on tumor cells and a highly malignant phenotype

Murine Ly-6 is a molecule expressed by various cells, including several types of hematopoietic cells such as pluripotent stem cells, and activated T cells. Ly-6 is also expressed on tumor cells originating from a variety of tissues. Preliminary observations suggested that the expression of Ly-6A/E is up-regulated on highly tumorigenic variants of polyoma-virus(PyV)-transformed BALB/c 3T3 cells as compared with weakly tumorigenic variants. On the basis of these observations, we sorted PyV-transformed A3C cells or DA3 mammary adenocarcinoma cells into stable sub-populations expressing high or low levels of membrane or mRNA Ly-6A/E. In vivo studies indicated that the high-Ly-6A/E-expressing cells in both tumor systems expressed a considerably more malignant phenotype (higher efficiency in local tumor production as well as in lung colonization) than low-Ly-6A/E expressors. Since the high-Ly-6A/E expressors did not exhibit any growth advantage in vitro over low Ly-6A/E expressors, we concluded that interactions of the former cells with micro-environmental factors operating in vivo (e.g., Ly-6A/E ligands) conferred upon these cells a highly malignant phenotype. Apart from the difference in Ly-6A/E expression, no other phenotypic characteristics distinguished highly from weakly malignant tumor cells. Similarly to T cells, where antibodies to Ly-6 transduce (or co-transduce) a proliferative signal, antibodies to Ly-6A/E were found to transduce a mitogenic signal to high-Ly-6A/E-expressing tumor cells but not to low-Ly-6A/E expressors. Taken together, these results show that Ly-6A/E expression is directly or indirectly associated in vivo with a highly malignant phenotype of 2 types of non-lymphoid murine tumors.

Molecular cloning of the rat analogue of human CD59: structural comparison with human CD59 and identification of a putative active site

We have previously described the purification and partial characterization of the rat analogue of the human complement regulatory molecule CD59 [Hughes, Piddlesden, Williams, Harrison and Morgan (1992) Biochem. J. 284, 169-176]. We present here the molecular cloning and full sequence analysis of this molecule. A PCR-based approach utilizing primers designed from the amino-terminal protein sequence was used to isolate a full-length cDNA clone from a rat kidney cDNA library. This clone encoded a 92 bp 5'-flanking sequence, a 66 bp signal peptide and a 315 bp coding region containing putative glycosylation and GPI-anchor signals. The 3' untranslated flanking region was approximately 1.1 kbp long and included the poly-A tail and a CATA repeating sequence. The coding region was 58% identical with the human cDNA at the nucleotide level and 44% identical at the amino acid level. Despite this relatively low overall sequence conservation, several highly conserved stretches were apparent, particularly in the N-terminal portion of the molecule, in the cysteine-rich region immediately preceding the site of glycolipid attachment and in the C-terminal peptide removed during glycolipid attachment. An N-glycosylation site was identified at Asn-16 and a putative glycosylphosphatidylinositol anchor addition site at Asn-79, indicating that the mature processed protein was two residues longer than human CD59. Comparison of the sequences of rat and human CD59, together with consideration of the published three-dimensional structure of human CD59 and functional data, implicates specific regions of the protein in interactions with C-8 and/or C-9.

Membrane defence against complement lysis: the structure and biological properties of CD59

The complement system is an important branch of the innate immune response, constituting a first line of defence against invading microorganisms which activate complement via both antibody-dependent and -independent mechanisms. Activation of complement leads to (a) a direct attack upon the activating cell surface by assembly of the pore-forming membrane attack complex (MAC), and (b) the generation of inflammatory mediators which target and recruit other branches of the immune system. However, uncontrolled complement activation can lead to widespread tissue damage in the host, since certain of the activation products, notably the fragment C3b and the C5b-7 complex, can bind nonspecifically to any nearby cell membranes. Therefore it is important that complement activation is tightly regulated. Our own cells express a number of membrane-bound control proteins which limit complement activation at the cell surface and prevent accidental complement-mediated damage. These include decay-accelerating factor, complement receptor 1 and membrane cofactor protein, all of which are active at the level of C3/C5 convertase formation. Until recently, cell surface control of MAC assembly had been attributed to a single 65-kD membrane protein called homologous restriction factor (alternatively named C8-binding protein and MAC-inhibiting protein). However a second MAC-inhibiting protein has since been discovered and it is now clear that this protein plays a major role in the control of membrane attack. This review charts the rapid progress made in elucidating the protein and gene structure, and the mechanism of action of this most recently discovered complement inhibitor, CD59.

An interspecific linkage map of mouse chromosome 15 positioned with respect to the centromere

We have used an interspecific backcross between C57BL/6J and Mus spretus to derive a molecular genetic linkage map of chromosome 15 that includes 25 molecular markers and spans 93% of the estimated length of chromosome 15. Using a second interspecific backcross that was analyzed with a centromere-specific marker, we were also able to position our map with respect to the chromosome 15 centromere. This map provides molecular access to many discrete regions on chromosome 15, thus providing a framework for establishing relationships between cloned DNA markers and known mouse mutations and for identifying homologous genes in mice and humans that may be involved in disease.

Phosphatidylinositol-glycan linked proteins of the erythrocyte membrane

The human erythrocyte bears a number of proteins anchored to the outer membrane surface via a phosphatidylinositol-glycan linkage. This class of proteins includes several complement regulatory proteins (including decay-accelerating factor, CD59 antigen (protectin), and C8 binding protein) as well as several enzymes and at least one protein important in cell-cell interaction. In addition, a number of blood group antigens have been identified to reside on proteins with phosphatidylinositol anchors. One blood group (Cromer) resides on DAF. Study of variants in this blood group system has led to interesting information about the function and expression of this protein. Several other blood groups, such as JMH and Holley/Gregory, appear to reside on as yet unidentified phosphatidylinositol-linked proteins. In paroxysmal nocturnal haemoglobinuria, a variable proportion of red cells fail to express or express weakly all phosphatidylinositol-linked proteins. The origin of this deficiency is now being worked out. In addition, individuals with inherited deficiency of DAF or CD59 (protectin) have been identified. Only the latter deficiency leads to a PNH-like syndrome.

The control of homologous lysis

Complement activation unleashes powerful effector mechanisms against which host cells are protected by homologous restriction factors. These factors are glycolipid-anchored membrane proteins that either induce C3 convertase dissociation (for example decay-accelerating factor) or prevent the full development of the membrane attack complex (for example homologous restriction factor and CD59). In this article Peter Lachmann explores the biology and biochemistry of these important and intriguing molecules.

Susceptibility to type I diabetes in women is associated with the CD3 epsilon locus on chromosome 11

Type I diabetes is associated with the DQ loci of the MHC and to a lesser extent with the T cell antigen receptor (TcR) beta chain genes. The non-obese diabetic (NOD) mouse is an animal model of human diabetes, in which up to 90% of female mice develop overt insulin-dependent diabetes. Genetic studies in the NOD mouse suggest that there are at least three diabetogenic genes; one that maps to the MHC, another that may map to the mouse Thy-I locus, and a third that has still to be identified. We have investigated loci in the vicinity of the human Thy-I locus on chromosome 11q23 and report here the results of restriction fragment length polymorphism (RFLP) analysis of the CD3 epsilon locus of 168 Caucasoid patients with type I diabetes. While no association was found between this locus and type I diabetes, a significant difference in the frequency of the CD3 epsilon 8-kb allele was found between male and female patients (0.268 versus 0.430; P less than 0.0025, Pc = 0.02) and between female patients and healthy female controls (0.430 versus 0.267; P less than 0.015). These results suggest that a gene residing on chromosome 11q23 may confer susceptibility to type I diabetes in women.

Localization of gene for human syndecan, an integral membrane proteoglycan and a matrix receptor, to chromosome 2

Syndecan, a cell surface proteoglycan, is an integral membrane protein acting as a receptor for the extracellular matrix. For chromosomal localization of the human syndecan gene, a panel of mouse-human somatic cell hybrids was analyzed by Southern blotting using the cDNA probe for human syndecan. The hybrids were karyotyped at the time of DNA extraction. A band corresponding to the human syndecan gene in Southern blots was found only in a hybrid cell line containing human chromosome 2. This hybrid was subcloned and its subclones were analyzed by Southern blotting and karyotyped. Subclones carrying human chromosome 2 contained the syndecan gene, while subclones not carrying this chromosome did not. The human syndecan gene is thus assigned to chromosome 2.