Isolation and expression of the full-length cDNA encoding CD59 antigen of human lymphocytes

Gecko CD59 is implicated in proximodistal identity during tail regeneration

Several adult reptiles, such as Gekko japonicus, have the ability to precisely re-create a missing tail after amputation. To ascertain the associated acquisition of positional information from blastemal cells and the underlying molecular mechanism of tail regeneration, a candidate molecule CD59 was isolated from gecko. CD59 transcripts displayed a graded expression in the adult gecko spinal cord with the highest level in the anterior segment, with a stable expression along the normal tail. After tail amputation, CD59 transcripts in the spinal cord proximal to the injury sites increased markedly at 1 day and 2 weeks; whereas in the regenerating blastema, strong CD59 positive signals were detected in the blastemal cells anterior to the blastema, with a gradual decrease along the proximodistal (PD) axis. When treated with RA following amputation, CD59 transcripts in the blastema were up-regulated. PD confrontation assays revealed that the proximal blastema engulfed the distal one after in vitro culture, and rabbit-anti human CD59 antibody was able to block this PD engulfment. Overexpression of the CD59 during tail regeneration causes distal blastemal cells to translocate to a more proximal location. Our results suggest that position identity is not restricted to amphibian limb regeneration, but has already been established in tail blastema of reptiles. The CD59, a cell surface molecule, acted as a determinant of proximal–distal cell identity.

Cutting edge: phosphatidylinositol 4,5-bisphosphate concentration at the APC side of the immunological synapse is required for effector T cell function

Little is known about the signaling that occurs in an APC during contact with a T cell. In this article we report the concentration of the signaling lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) at the APC side of the immunological synapse. In both human and mouse cells, a PI(4,5)P(2)-specific fluorescent reporter, PH-GFP (where PH is pleckstrin homology), detected an Ag-dependent enrichment of PI(4,5)P(2) at the synapse between Ag-specific T cells and APC. When PIP(4,5)P(2) was sequestered by a high concentration of PH-GFP reporter, cells were less susceptible to CTL-mediated lysis than control cells. These findings suggest a new regulatory target for modulating immune function that may be exploited for immune escape by pathogens and tumors.

Determination of CD59 protein in normal human serum by enzyme immunoassay, using octyl-glucoside detergent to release glycosyl-phosphatidylinositol-CD59 from lipid complex

In this study we have optimised the enzyme immunoassay (ELISA) to quantify CD59 antigen in human serum or plasma. The glycosyl-phosphatidylinositol (GPI)-linked form of CD59 is known to complex with serum high-density lipoprotein. For ELISA optimisation, therefore, we investigated the effect of detergents, added to the sample diluent, on the determined values of CD59. Values obtained in the presence of octyl-glucoside (OG) for 20 adults aged 18-35 years and 17 children 1-5 years old were, respectively, 33-119 ng/ml (mean +/- S.D.: 66+/-22 ng/ml) and 37-143 ng/ml (76+/-33 ng/ml). These results were higher than those measured without OG and were in contrast with published results showing absence, or eight to nine times lower levels, of the protein in serum. A known range for serum concentrations of CD59 in healthy individuals will establish an important reference point for clinical work and for the investigation of diseases involving the complement membrane attack complex (MAC) and its regulation.

First tryptophan-containing weak neurotoxin from cobra venom

With the purpose of studying structure-function relationships among weak neurotoxins (called so because of their low toxicity), we have isolated a toxin (WTX) from the venom of cobra Naja kaouthia using a combination of gel-filtration and ion-exchange chromatography. The amino acid sequence of the isolated toxin was determined by means of Edman degradation and MALDI mass spectrometry, the primary structure obtained being confirmed by 1H-NMR in the course of spatial structure analysis. The WTX sequence differs slightly from that of the toxin CM-9a isolated earlier from the same venom (Joubert and Taljaard, Hoppe-Seyler's Z. Physiol. Chem., 361 (1980) 425). The differences include an extra residue (Trp36) between Ser35 and Arg37 as well as interchanging of two residues (Tyr52 and Lys50) in the C-terminal part of the toxin molecule. These changes improve the alignment that can be made with other weak neurotoxin sequences. An extended sequence comparison reveals that WTX is the first case of a tryptophan-containing weak neurotoxin isolated from cobra venom. WTX was found to compete with radioiodinated alpha-bungarotoxin for binding to the membrane-bound nicotinic acetylcholine receptor from Torpedo californica.

Identification and functional characterization of a new gene encoding the mouse terminal complement inhibitor CD59

CD59 is a 18- to 20-kDa, GPI-anchored membrane protein that functions as a key regulator of the terminal step of the complement activation cascade. It restricts binding of C9 to the C5b-8 complex, thereby preventing the formation of the membrane attack complex (C5b-9 of complement). A single human CD59 gene has been identified, and corresponding genetic homologues from rat, mouse, and pig have been characterized in previous studies. In this study, we report the discovery and functional characterization of a separate cd59 gene in the mouse (referred to as cd59b, the previously characterized mouse cd59 gene as cd59a). Mouse cd59b is 85% and 63% identical to cd59a at the nucleotide and amino acid level, respectively. In cDNA transfection experiments with Chinese hamster ovary cells, peptide-tagged cd59b was detected on the cell surface by flow cytometry and was shown to be susceptible to phosphatidylinositol-specific phospholipase C cleavage. Chinese hamster ovary cells expressing cd59b were significantly more resistant than control cells to human and mouse complement-mediated lysis. These results suggest that cd59b encodes a GPI-anchored protein that is functionally active as a membrane attack complex inhibitor. Northern blot analysis revealed that cd59b is expressed selectively in the mouse testis. In contrast, the major transcript of cd59a was shown to be expressed at high levels in the heart, kidney, liver, and lung, but only minimally in the testis. These results revealed the existence of two distinct cd59 genes in the mouse that are differentially regulated and that may have nonoverlapping physiological functions in vivo.

Molecular Cloning and Functional Characterization of the Pig Analogue of CD59: Relevance to Xenotransplantation

In this work, we report the cloning of the cDNA for the porcine analogue of human CD59. Degenerate primers, derived from the N-terminal sequence of pig erythrocyte CD59, were used to obtain the corresponding cDNA sequence. From this sequence, gene-specific primers were designed and used to amplify the 3′ and 5′ ends of the cDNA using the rapid amplification of cDNA ends (RACE) method. The complete 768-bp cDNA so obtained consisted of a 84-bp 5′ untranslated region, a 26-amino-acid NH2-signal peptide, a 98-amino-acid coding region, including putative N-glycosylation sites and a glycosylphosphatidylinositol-anchoring signal, and a 312-bp 3′ untranslated region. The mature protein sequence was 48% identical to human CD59 at the amino acid level. Northern blot analysis revealed several distinct CD59 transcripts, and a variability in expression levels of the different transcripts in the panel of tissues screened. Stable expression of pig CD59 in a CD59-negative human cell line conferred protection against lysis by complement from pig and several other species. Separate expression of pig and human CD59 at similar levels in the same cell line allowed a direct functional comparison between these two analogues. Pig CD59 and human CD59 showed similar activity in inhibiting lysis by complement from all species tested; in particular, expressed pig CD59 efficiently inhibited lysis by human complement. The relevance of these data to current work in the engineering of pig organs for xenotransplantation is discussed.

Structure-function relationships of the complement regulatory protein, CD59

CD59 (membrane inhibitor of reactive lysis, protectin) is a membrane protein whose functions include the inhibition of the insertion of the ninth component of complement into the target membrane. It belongs to a superfamily of proteins including Ly-6, elapid snake venom toxins, and urokinase receptor (UPAR); the members of the superfamily have a similar structure that includes four (in mammals five) disulfide bridges that maintain a three-dimensional conformation consisting of a central core, three finger-like "loops" extending from it and a small loop near the coboxyl end. We have used site directed mutagenesis to explore three aspects of the structure of CD59: 1) the role of the disulfide bridges in expression and function of the molecule; 2) the location of epitopes reacting with monoclonal antibodies to the molecule; and 3) the parts of the molecule that are critical to its function in inhibiting complement lysis. Mutant molecules in which the disulfides maintaining the finger-like loops (Cys3-Cys26, Cys19-Cys39, and Cys45-Cys63) were removed were not expressed on the cell surface. The mutation of the disulfide (Cys6-Cys13) resulted in no change in expression or function. The mutation of Cys64-Cys69 maintaining the small loop resulted in an expressed molecule with increased functional activity. The major epitope for 6 of 7 monoclonal antibodies was centered on Arg53 as the mutation 53Arg-->Ser resulted in a loss of interaction with these antibodies, as did the deletion of four nearby residues (Leu54-Asn57). The alteration 55Arg-->Ser resulted in loss of reactivity for some but not other antibodies. The reactivity with one monoclonal antibody, H19, was abrogated by the mutations 61Tyr-->Gly and 61Tyr-->Ala. Functional activity of the molecule was not adversely altered by mutations in the first and second loops; however, the 61Tyr-->Gly mutation was non-functional. The mutation of 61Tyr-->His diminished function but changes 61Tyr-->Ala and 61Tyr-->Phe had no effect on function. We conclude that the functional site of CD59 is located in this region of the molecule.

Immunohistochemical localization of C9 neoantigen and the terminal complement inhibitory protein CD59 in human endometrium

PROBLEM

Human endometrium expresses complement components, receptors, and regulatory proteins, many of which appear to be expressed in a hormone-dependent manner. Whether terminal complement components are also present in the endometrium is unknown. CD59, a broadly expressed protein that blocks association of C9 with C8 in the membrane attack complex, is localized in reproductive tissue to human spermatozoa, seminal plasma, amniotic fluid, and placenta. The present study examines human endometrium for the presence of CD59 and terminal complement proteins.

METHOD

Endometrial biopsies were obtained from six normal women from various phases of the menstrual cycle and analyzed by immunohistochemistry, using MEM-43 anti-human CD59 and anti-human SC5b-9 murine monoclonal antibodies and the immunoperoxidase technique.

RESULTS

Both CD59 protein and SC5b-9 (C9 neoantigen) were demonstrated to be present in endometrial glandular epithelium throughout the menstrual cycle. No specific staining was demonstrated in the stromal compartment.

CONCLUSION

CD59 protein and terminal complement proteins are expressed in glandular epithelial cells of normal human endometrium, in both proliferative and luteal phases, suggesting that expression is not hormonally dependent. These analyses further support the presence of a functionally active complement system in normal human endometrium.

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.

Gene structure of human CD59 and demonstration that discrete mRNAs are generated by alternative polyadenylation

We have isolated the CD59 gene from human genomic libraries. The gene is distributed over more than 27 x 10(3) base-pairs and consists of one 5'-untranslated exon and three coding exons. The gene structure is similar to that of mouse Ly-6 with the exception of the larger size of CD59 introns. Northern blot analysis using six different probes located in the 3'-region of the gene shows that more than four different CD59 mRNA molecules are generated by alternative polyadenylation. Three of these polyadenylation sites were predicted from previously published cDNA sequences. We have isolated a fourth from Jurkat poly(A)+ RNA by the procedure of rapid amplification of cDNA ends. Alternative polyadenylation may be due to the RNA secondary structure around the typical polyadenylation signal, AAUAAA.

Structural requirements for glycosyl-phosphatidylinositol-anchor attachment in the cellular receptor for urokinase plasminogen activator

The urokinase-plasminogen-activator receptor (u-PAR) is a glycosyl-phosphatidylinositol(glycosyl-PtdIns)-anchored membrane protein. Using site-directed mutagenesis, we have studied features in the u-PAR sequence important for successful glycosyl-PtdIns attachment. Two critical sequence elements were identified. In the sequence Ser282-Gly283-Ala284, simultaneous substitution of all of these residues prevented membrane anchoring. Individual substitution of each of the residues indicated that Gly283 is the more critical residue and the likely attachment site. However, it was unexpectedly found that mutation of this residue gave rise only to a partial impairment of glycosyl-PtdIns attachment. We therefore propose that more than one residue within this sequence can be utilized as glycosyl-PtdIns-attachment site. In the last eight COOH-terminal amino acids encoded in u-PAR cDNA, deletion of this sequence (residues 306-313) completely prevented glycosyl-PtdIns attachment. However, the remaining COOH-terminal region proved still to possess a potential glycosyl-PtdIns signal activity; it could be converted to a new functional glycosyl-PtdIns signal by substitution of a single positively charged residue (Arg304). Substitution of Arg304 by Leu converted this truntaced u-PAR to a glycosyl-PtdIns-anchored protein, indistinguishable from the wild type. Substitution of Arg304 by a negatively charged residue (Glu) led to a partial acquisition of the glycosyl-PtdIns-anchoring ability. These findings show that charged amino acids placed in the COOH-terminus interfere negatively with glycosyl-PtdIns-anchoring, and, furthermore, that this effect is more pronounced for positively charged than for negatively charged amino acid residues.

Structure of the CD59-encoding gene: further evidence of a relationship to murine lymphocyte antigen Ly-6 protein

The gene for CD59 [membrane inhibitor of reactive lysis (MIRL), protectin], a phosphatidylinositol-linked surface glycoprotein that regulates the formation of the polymeric C9 complex of complement and that is deficient on the abnormal hematopoietic cells of patients with paroxysmal nocturnal hemoglobinuria, consists of four exons spanning 20 kilobases. The untranslated first exon is preceded by a G+C-rich promoter region that lacks a consensus TATA or CAAT motif. The second exon encodes the hydrophobic leader sequence of the protein, and the third exon encodes the amino-terminal portion of the mature protein. The fourth exon encodes the remainder of the mature protein, including the hydrophobic sequence necessary for glycosyl-phosphatidylinositol anchor attachment. The structure of the CD59 gene is very similar to that encoding Ly-6, a murine glycoprotein with which CD59 has some structural similarity. The striking similarity in gene structure is further evidence that the two proteins belong to a superfamily of proteins that may also include the urokinase plasminogen-activator receptor and a squid glycoprotein of unknown function.

Herpesvirus saimiri has a gene specifying a homologue of the cellular membrane glycoprotein CD59

Herpesvirus saimiri (HSV) is a T-lymphotropic tumor virus that causes fulminant lymphomas and leukemias in various New World primates other than its natural host, the squirrel monkey (Saimiri sciureus). In the course of completing the nucleotide sequence of its genome, we identified an open reading frame of 363 nucleotides, designated HVS-15, that has no detectable homology to any other viral sequences to date. HVS-15 encodes a 121-amino-acid protein which shows significant similarities to human CD59, a phosphatidyl-inositol-glycan-anchored glycoprotein involved in T-cell activation and restriction of complement-mediated lysis. The predicted HVS-15 gene product is more similar to human CD59 than to the related murine Ly-6 antigens. A nucleotide sequence identity of 64% was found between HVS-15 and the CD59 reading frame, and a 48% identity exists between the corresponding protein sequences. The comparison of the amino acid sequences revealed a number of conserved structural features such as a similar pattern of hydrophobic termini and an identical cysteine skeleton.

Primary structure of the herpesvirus saimiri genome

This report describes the complete nucleotide sequence of the genome of herpesvirus saimiri, the prototype of gammaherpesvirus subgroup 2 (rhadinoviruses). The unique low-G + C-content DNA region has 112,930 bp with an average base composition of 34.5% G + C and is flanked by about 35 noncoding high-G + C-content DNA repeats of 1,444 bp (70.8% G + C) in tandem orientation. We identified 76 major open reading frames and a set of seven U-RNA genes for a total of 83 potential genes. The genes are closely arranged, with only a few regions of sizable noncoding sequences. For 60 of the predicted proteins, homologous sequences are found in other herpesviruses. Genes conserved between herpesvirus saimiri and Epstein-Barr virus (gammaherpesvirus subgroup 1) show that their genomes are generally collinear, although conserved gene blocks are separated by unique genes that appear to determine the particular phenotype of these viruses. Several deduced protein sequences of herpesvirus saimiri without counterparts in most of the other sequenced herpesviruses exhibited significant homology with cellular proteins of known function. These include thymidylate synthase, dihydrofolate reductase, complement control proteins, the cell surface antigen CD59, cyclins, and G protein-coupled receptors. Searching for functional protein motifs revealed that the virus may encode a cytosine-specific methylase and a tyrosine-specific protein kinase. Several herpesvirus saimiri genes are potential candidates to cooperate with the gene for saimiri transformation-associated protein of subgroup A (STP-A) in T-lymphocyte growth stimulation.

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.

Transfection of human CD59 complementary DNA into rat cells confers resistance to human complement

We have examined the role of the human CD59 antigen in inhibiting complement-mediated lysis by transfer and expression of a CD59 cDNA in rat cells. A cDNA encoding CD59 was subcloned into the expression vector pSFSVneo and stably transfected into the rat T cell line NB2-6TG. Indirect immunofluorescence staining using the anti-CD59 monoclonal antibody YTH53.1 demonstrated the presence of human CD59 antigen on transfected cells and its attachment to the cell surface by a rat glycolipid anchor. Transfected cells were found to contain a single 3.3-kb species of CD59 mRNA by Northern blot hybridization. Immunoblotting revealed that this encoded a protein band of the same size as that observed in human erythrocytes. To determine the biological effect of expression of human CD59 in rat cells, an assay was devised which measured the relative lysis of transfected cells compared to untransfected cells in the presence of human complement and a lytic monoclonal antibody. It was observed that CD59-transfected rat cells are less susceptible to lysis by human complement and that this effect was blocked by a F(ab')2 fragment of YTH53.1. These experiments provide a direct demonstration that CD59 can function as an homologous complement restriction factor for nucleated cells.