Nucleotide sequence of cDNA and derived amino acid sequence of human complement component C9

Killing of Microbes and Cancer by the Immune System with Three Mammalian Pore-Forming Killer Proteins

Immunology is the science of biological warfare between the defenses of our immune systems and offensive pathogenic microbes and cancers. Over the course of his scientific career, Eckhard R. Podack made several seminal discoveries that elucidated key aspects of this warfare at a molecular level. When Eckhard joined the complement laboratory of Müller-Eberhard in 1974, he was fascinated by two questions: (1) what is the molecular mechanism by which complement kills invasive bacteria? and (2) which one of the complement components is the killer molecule? Eckhard’s quest to answer these questions would lead to the discovery C9 and later, two additional pore-forming killer molecules of the immune system. Here is a brief account of how he discovered poly-C9, the pore-forming protein of complement in blood and interstitial fluids: Perforin-1, expressed by natural killer cells and cytotoxic T lymphocytes; and Perforin-2 (MPEG1), expressed by all cell types examined to date. All the three killing systems are crucial for our survival and health.

International Union of Basic and Clinical Pharmacology. XCV. Recent advances in the understanding of the pharmacology and biological roles of relaxin family peptide receptors 1-4, the receptors for relaxin family peptides

Relaxin, insulin-like peptide 3 (INSL3), relaxin-3, and INSL5 are the cognate ligands for the relaxin family peptide (RXFP) receptors 1-4, respectively. RXFP1 activates pleiotropic signaling pathways including the signalosome protein complex that facilitates high-sensitivity signaling; coupling to Gα(s), Gα(i), and Gα(o) proteins; interaction with glucocorticoid receptors; and the formation of hetero-oligomers with distinctive pharmacological properties. In addition to relaxin-related ligands, RXFP1 is activated by Clq-tumor necrosis factor-related protein 8 and by small-molecular-weight agonists, such as ML290 [2-isopropoxy-N-(2-(3-(trifluoromethylsulfonyl)phenylcarbamoyl)phenyl)benzamide], that act allosterically. RXFP2 activates only the Gα(s)- and Gα(o)-coupled pathways. Relaxin-3 is primarily a neuropeptide, and its cognate receptor RXFP3 is a target for the treatment of depression, anxiety, and autism. A variety of peptide agonists, antagonists, biased agonists, and an allosteric modulator target RXFP3. Both RXFP3 and the related RXFP4 couple to Gα(i)/Gα(o) proteins. INSL5 has the properties of an incretin; it is secreted from the gut and is orexigenic. The expression of RXFP4 in gut, adipose tissue, and β-islets together with compromised glucose tolerance in INSL5 or RXFP4 knockout mice suggests a metabolic role. This review focuses on the many advances in our understanding of RXFP receptors in the last 5 years, their signal transduction mechanisms, the development of novel compounds that target RXFP1-4, the challenges facing the field, and current prospects for new therapeutics.

Enteric pathogens deploy cell cycle inhibiting factors to block the bactericidal activity of Perforin-2

Perforin-2 (MPEG1) is an effector of the innate immune system that limits the proliferation and spread of medically relevant Gram-negative, -positive, and acid fast bacteria. We show here that a cullin-RING E3 ubiquitin ligase (CRL) complex containing cullin-1 and βTrCP monoubiquitylates Perforin-2 in response to pathogen associated molecular patterns such as LPS. Ubiquitylation triggers a rapid redistribution of Perforin-2 and is essential for its bactericidal activity. Enteric pathogens such as Yersinia pseudotuberculosis and enteropathogenic Escherichia coli disarm host cells by injecting cell cycle inhibiting factors (Cifs) into mammalian cells to deamidate the ubiquitin-like protein NEDD8. Because CRL activity is dependent upon NEDD8, Cif blocks ubiquitin dependent trafficking of Perforin-2 and thus, its bactericidal activity. Collectively, these studies further underscore the biological significance of Perforin-2 and elucidate critical molecular events that culminate in Perforin-2-dependent killing of both intracellular and extracellular, cell-adherent bacteria.

DOI:http://dx.doi.org/10.7554/eLife.06505.001

A wide range of bacteria and other microbes can infect animals and cause disease. Throughout evolution, these microbes and their hosts have been fighting never ending arms races in which the microbes deploy ever more elaborate weapons, while the hosts adapt to defend themselves. An animal's first line of defense is provided by its ‘innate’ immune system. This system is activated by the general features of microbial cells; for example, the molecules that make up the walls surrounding most bacteria. Microbes must defeat the innate immune system in order to cause disease, and ultimately to spread from one host to the next.

One component of innate immunity is a protein called Perforin-2 that is present in most, if not all, animal cells. This protein forms pores on bacterial cells, causing them to split open and die. However, it was not clear how Perforin-2 is switched on and what, if anything, bacteria do to counteract it. To address these questions, McCormack et al. infected human and mice cells with bacteria that cause serious diseases of the digestive tract.

The experiments show that when animal cells detect bacteria, or merely a fragment of their cell wall, a specific group of proteins, called the CRL complex, attaches a molecule called ubiquitin to Perforin-2. Ubiquitin works much like the shipping label of a package, enabling the efficient targeting of Perforin-2 to the invading bacteria. McCormack et al. also show that some bacteria use a protein called a cell cycle inhibiting factor (or Cif for short) to inhibit the CRL complex. This blocks the ubiquitin labeling of Perforin-2, which renders it a useless weapon that can no longer be directed towards bacteria.

Mice that are infected with a bacterium called Yersinia pseudotuberculosis become seriously unwell and often die. However, McCormack et al. found that mice infected with mutant Y. pseudotuberculosis that lacked Cif remained healthy. Also, mice that lacked Perforin-2 are highly susceptible to infectious diseases. McCormack et al.'s findings reveal how Perforin-2 is activated during the innate immune response and how some bacteria can defeat this pivotal defense. In the current age of antibiotic resistant bacteria, these studies may spur the development of new drugs that restore or increase the activity of Perforin-2.

DOI:http://dx.doi.org/10.7554/eLife.06505.002

Genetic Association of the Porcine C9 Complement Component with Hemolytic Complement Activity

The complement system is a part of the natural immune regulation mechanism against invading pathogens. Complement activation from three different pathways (classical, lectin, and alternative) leads to the formation of C5-convertase, an enzyme for cleavage of C5 into C5a and C5b, followed by C6, C7, C8, and C9 in membrane attack complex. The C9 is the last complement component of the terminal lytic pathway, which plays an important role in lysis of the target cells depending on its self-polymerization to form transmembrane channels. To address the association of C9 with traits related to disease resistance, the complete porcine C9 cDNA was comparatively sequenced to detect single nucleotide polymorphisms (SNPs) in pigs of the breeds Hampshire (HS), Duroc (DU), Berlin miniature pig (BMP), German Landrace (LR), Pietrain (PIE), and Muong Khuong (Vietnamese potbelly pig). Genotyping was performed in 417 F2 animals of a resource population (DUMI: DU×BMP) that were vaccinated with Mycoplasma hyopneumoniae, Aujeszky diseases virus and porcine respiratory and reproductive syndrome virus at 6, 14 and 16 weeks of age, respectively. Two SNPs were detected within the third exon. One of them has an amino acid substitution. The European porcine breeds (LR and PIE) show higher allele frequency of these SNPs than Vietnamese porcine breed (MK). Association of the substitution SNP with hemolytic complement activity indicated statistically significant differences between genotypes in the classical pathway but not in the alternative pathway. The interactions between eight time points of measurement of complement activity before and after vaccinations and genotypes were significantly different. The difference in hemolytic complement activity in the both pathways depends on genotype, kind of vaccine, age and the interaction to the other complement components. These results promote the porcine C9 (pC9) as a candidate gene to improve general animal health in the future.

Structural biology of the membrane attack complex

The complement system is an intricate network of serum proteins that mediates humoral innate immunity through an amplification cascade that ultimately leads to recruitment of inflammatory cells or opsonisation or killing of pathogens. One effector arm of this network is the terminal pathway of complement, which leads to the formation of the membrane attack complex (MAC) composed of complement components C5b, C6, C7, C8 and C9. Upon formation of C5 convertases via the classical or alternative pathways of complement activation, C5b is generated from C5 by proteolytic cleavage, nucleating a series of association and polymerisation reactions of the MAC-constituting complement components that culminate in pore formation of pathogenic membranes. Recent structures of MAC components and homologous proteins significantly increased our understanding of oligomerisation, membrane association and integration, shedding light onto the molecular mechanism of this important branch of the innate immune system.

Killing machines: three pore-forming proteins of the immune system

The evolution of early multicellular eukaryotes 400-500 million years ago required a defensive strategy against microbial invasion. Pore-forming proteins containing the membrane-attack-complex-perforin (MACPF) domain were selected as the most efficient means to destroy bacteria or virally infected cells. The mechanism of pore formation by the MACPF domain is distinctive in that pore formation is purely physical and unspecific. The MACPF domain polymerizes, refolds, and inserts itself into bilayer membranes or bacterial outer cell walls. The displacement of surface lipid/carbohydrate molecules by the polymerizing MACPF domain creates clusters of large, water-filled holes that destabilize the barrier function and provide access for additional anti-bacterial or anti-viral effectors to sensitive sites that complete the destruction of the invader via enzymatic or chemical attack. The highly efficient mechanism of anti-microbial defense by a combined physical and chemical strategy using pore-forming MACPF-proteins has been retargeted during evolution of vertebrates and mammals for three purposes: (1) to kill extracellular bacteria C9/polyC9 evolved in conjunction with complement, (2) to kill virus infected and cancer cells perforin-1/polyperforin-1 CTL evolved targeted by NK and CTL, and (3) to kill intracellular bacteria transmembrane perforin-2/putative polyperforin-2 evolved targeted by phagocytic and nonphagocytic cells. Our laboratory has been involved in the discovery and description of each of the three pore-formers that will be reviewed here.

Molecular characterization and expression analysis of complement component C9 gene in the whitespotted bambooshark, Chiloscyllium plagiosum

Complement system is known as highly sophisticated immune defense mechanism for antigen recognition as well as effector functions. Activation of the terminal pathway of the complement system leads to the assembly of terminal complement complexes (C5b-9), which induces the characteristic complement-mediated cytolysis. The lytic activity of shark complement involves functional analogues of mammalian C8 and C9. In this article, a full-length cDNA of C9 (CpC9) is identified from cartilaginous species, the whitespotted bambooshark, Chiloscyllium plagiosum by RACE. The CpC9 cDNA is 2263 bp in length, encoding a protein of 603 amino acids, which shares 42% and 43% identity with human and Xenopus C9 respectively. Through sequence alignment and comparative analysis, the CpC9 protein was found well conserved, with the typical modular architecture in TCCs and nearly unanimous cysteine composition from fish to mammal. Phylogenetic analysis places it in a clade with C9 orthologs in higher vertebrate and as a sister taxa to the Xenopus. Expression analysis revealed that CpC9 is constitutively highly expressed in shark liver, with much less or even undetectable expression in other tissues; demonstrating liver is the primary tissue for C9synthesis. To sum up, the structural conservation and distinctive phylogenetics might indicate the potentially vital role of CpC9 in shark immune response, though it remains to be confirmed by further study.

Perforin-2 restricts growth of Chlamydia trachomatis in macrophages

Chlamydia trachomatis is a Gram-negative obligate intracellular bacterium that preferentially infects epithelial cells. Professional phagocytes provide C. trachomatis only a limited ability to survive and are proficient killers of chlamydiae. We present evidence herein that identifies a novel host defense protein, perforin-2, that plays a significant role in the eradication of C. trachomatis during the infection of macrophages. Knockdown of perforin-2 in macrophages did not alter the invasion of host cells but did result in chlamydial growth that closely mirrored that detected in HeLa cells. C trachomatis L2, serovar B, and serovar D and C. muridarum were all equally susceptible to perforin-2-mediated killing. Interestingly, induction of perforin-2 expression in epithelial cells is blocked during productive chlamydial growth, thereby protecting chlamydiae from bactericidal attack. Ectopic expression of perforin-2 in HeLa cells, however, does result in killing. Overall, our data implicate a new innate resistance protein in the control of chlamydial infection and may help explain why the macrophage environment is hostile to chlamydial growth.

Relaxin family peptides and their receptors

There are seven relaxin family peptides that are all structurally related to insulin. Relaxin has many roles in female and male reproduction, as a neuropeptide in the central nervous system, as a vasodilator and cardiac stimulant in the cardiovascular system, and as an antifibrotic agent. Insulin-like peptide-3 (INSL3) has clearly defined specialist roles in male and female reproduction, relaxin-3 is primarily a neuropeptide involved in stress and metabolic control, and INSL5 is widely distributed particularly in the gastrointestinal tract. Although they are structurally related to insulin, the relaxin family peptides produce their physiological effects by activating a group of four G protein-coupled receptors (GPCRs), relaxin family peptide receptors 1-4 (RXFP1-4). Relaxin and INSL3 are the cognate ligands for RXFP1 and RXFP2, respectively, that are leucine-rich repeat containing GPCRs. RXFP1 activates a wide spectrum of signaling pathways to generate second messengers that include cAMP and nitric oxide, whereas RXFP2 activates a subset of these pathways. Relaxin-3 and INSL5 are the cognate ligands for RXFP3 and RXFP4 that are closely related to small peptide receptors that when activated inhibit cAMP production and activate MAP kinases. Although there are still many unanswered questions regarding the mode of action of relaxin family peptides, it is clear that they have important physiological roles that could be exploited for therapeutic benefit.

Inhibition of intracellular bacterial replication in fibroblasts is dependent on the perforin-like protein (perforin-2) encoded by macrophage-expressed gene 1

Fibroblasts are known to eliminate intracellular bacteria, but the lethal hit of the bactericidal mechanism has not been defined. We show that primary embryonic and established fibroblasts can be induced by interferons or by intracellular bacterial infection to express a perforin-like mRNA previously described as macrophage-expressed gene 1 (Mpeg1). The presence and level of the perforin-like mRNA correlate with the ability of primary mouse embryonic fibroblasts (MEF) to eliminate intracellular bacteria. In addition, siRNA knockdown of the perforin-like molecule abolishes bactericidal activity and allows intracellular bacterial replication. Complementation of MEF in which the endogenous perforin-like molecule has been knocked down with a red fluorescent protein-tagged version restores bactericidal activity. The perforin-like molecule has broad bactericidal specificity for pathogenic and non-pathogenic bacteria, including Gram-positive and -negative, and acid fast bacteria. The perforin-like molecule renders previously lysozyme-resistant bacteria sensitive to lysis by lysozyme suggesting physical damage of the outer cell wall by the perforin-like protein. MEF damage cell walls of intracellular bacteria by insertion, polymerization, and pore formation of the perforin-like protein, analogous to pore formers of complement and perforin-1 of cytolytic lymphocytes. We propose the name perforin-2.

An unexpected loss of domains in the conservative evolution ninth complement component in a higher teleost, Miichthys miiuy

The complement systems of fish are well developed and play an important role in the innate immune response. C9 is the ninth member of complement components, involved in creating the membrane attack complex (MAC). In the present study, a truncated C9 cDNA sequence encoding 461 amino acids was cloned and characterized in the miiuy croaker (Miichthys miiuy). Typical fish C9 molecules have five characteristic modular domains, i.e. TSP1, LDLRA, MACPF, EGF, and a second TSP domain which is absent in mammalian counterparts. While in miiuy croaker, this truncated C9 presents only TSP1, LDLRA and MACPF domains. It is the first time of finding a truncated C9 in teleost components. RT-PCR analysis detected these C9 transcripts among all tissues examined, demonstrating its constitutive expression pattern in healthy fish. The highest levels of transcripts were detected in liver of both healthy and pathogen-infected miiuy croaker. Its constitutive and inducible expression pattern of this truncated C9 in liver is similar to most complement components which belong to the type of acute-phase proteins and are in general of hepatic origin. We cannot exclude the possibility that miiuy croaker presents the typical C9 although it has not yet been found. The molecular evolutionary analysis showed that this truncated C9 of miiuy croaker had a significantly higher omega value comparing with other fish and the positive selection pressure had happened on it after its divergence with other fish.

Topology of the membrane-bound form of complement protein C9 probed by glycosylation mapping, anti-peptide antibody binding, and disulfide modification

The two N-linked oligosaccharides in native human C9 were deleted by site-specific mutagenesis. This aglycosyl-C9 did not differ from its native form in hemolytic and bactericidal activity. A new N-glycosylation site (K311N/E313T) was introduced into the turn of a helix-turn-helix [HTH] fold that had been postulated to form a transmembrane hairpin in membrane-bound C9. This glycosylated form of human C9 was as active as the native protein suggesting that the glycan chain remains on the external side of the membrane and that translocation of this hairpin is not required for membrane anchoring. Furthermore, flow cytometry provided evidence for the recognition of membrane-bound C9 on complement-lysed ghosts by an antibody specific for the HTH fold. A new N-glycosylation site (P26N) was also introduced close to the N-terminus of C9 to test whether this region was involved in C9 polymerization, which is thought to be required for cytolytic activity of C9. Again, this glycosylated C9 was as active as native C9 and could be induced to polymerize by heating or incubation with metal ions. The two C-terminal cystines within the MACPF domain could be eliminated partially or completely without affecting the hemolytic activity. Free sulfhydryl groups of unpaired cysteines in such C9 mutants are blocked since they could not be modified with SH-specific reagents. These results are discussed with respect to a recently proposed model that, on the basis of the MACPF structure in C8alpha, envisions membrane insertion of C9 to resemble the mechanism by which cholesterol-dependent cytolysins enter a membrane.

Expression of terminal complement components by human keratinocytes

Human keratinocytes are important constituents of the skin immune system. They produce several cytokines, chemokines as well as some complement proteins. As regards soluble complement proteins, so far keratinocytes have been shown to synthesize only C3, factor B, factor H and factor I. Synthesis and regulation of synthesis of other complement proteins has not yet been studied. Here we studied the synthesis of terminal complement components, C5-C9 by human keratinocytes. We also studied the regulation of terminal complement synthesis in keratinocytes by several cytokines, namely, IL-1alpha, IL-2, IL-6, TGF-beta1, TNF-alpha, and IFN-gamma. Human keratinocytes constitutively expressed C5, C7, C8gamma and C9 mRNA but not C6, C8alpha and C8beta mRNA. They released C7 and C9, but not C5, C6 and C8. None of the cytokines tested had any influence on the synthesis of terminal components except TNF-alpha, which strongly upregulated C9 production. In conclusion, we demonstrate that keratinocytes are capable of synthesizing some of the terminal complement components and that the synthesis of C9 is regulated by TNF-alpha.

Gene structure and molecular phylogeny of the linker chains from the giant annelid hexagonal bilayer hemoglobins

Giant extracellular hexagonal bilayer hemoglobin (HBL-Hb), found only in annelids, is an approximately 3500-kDa heteropolymeric structure involved in oxygen transport. The HBL-Hbs are comprised of globin and linker chains, the latter being required for the assembly of the quaternary structure. The linker chains, varying in size from 225 to 283 amino acids, have a conserved cysteine-rich domain within their N-terminal moiety that is homologous to the cysteine-rich modules constituting the ligand binding domain of the low-density lipoprotein receptor (LDLR) protein family found in many metazoans. We have investigated the gene structure of linkers from Arenicola marina, Alvinella pompejana, Nereis diversicolor, Lumbricus terrestris, and Riftia pachyptila. We found, contrary to the results obtained earlier with linker genes from N. diversicolor and L. terrestris, that in all of the foregoing cases, the linker LDL-A module is flanked by two phase 1 introns, as in the human LDLR gene, with two more introns in the 3' side whose positions varied with the species. In addition, we obtained 13 linker cDNAs that have been determined experimentally or found in the EST database LumbriBASE. A molecular phylogenetic analysis of the linker primary sequences demonstrated that they cluster into two distinct families of linker proteins. We propose that the common gene ancestor to annelid linker genes exhibited a four-intron and five-exon structure and gave rise to the two families subsequent to a duplication event.

Extracellular phosphorylation of C9 by protein kinase CK2 regulates complement-mediated lysis

Ecto-protein kinases (ecto-PK) are expressed on many cell types, both normal and malignant, yet their functions are largely unknown. An ecto-PK capable of phosphorylating the C9 component of the complement system is described. This C9 ecto-PK could be inhibited by TBB, Emodin and DRB, selective inhibitors of protein kinase CK2. Treatment of Raji human B lymphoma cells with these CK2 inhibitors augmented cell killing by Rituximab (anti-CD20 antibodies) and human complement. Analysis of C5b-7-bearing Raji cells showed that extracellular inhibition of the ecto-CK2 enhanced cell lysis by C8 and C9. Blocking of the membrane complement regulator CD59 with monoclonal antibodies further enhanced the effect of the CK2 inhibitors on Raji cell death by complement. C9 ecto-CK2 activity was increased on cancer cells relative to normal fibroblasts and blood cells. Therefore, ecto-CK2 appears to be an additional factor protecting cells from complement-mediated lysis, probably by phosphorylation/inhibition of complement C9.

An abnormal but functionally active complement component C9 protein found in an Irish family with subtotal C9 deficiency

Two independently segregating C9 genetic defects have previously been reported in two siblings in an Irish family with subtotal C9 deficiency. One defect would lead to an abnormal C9 protein, with replacement of a cysteine by a glycine (C98G). The second defect is a premature stop codon at amino acid 406 which would lead to a truncated C9. However, at least one of two abnormal proteins was present in the circulation of the proband at 0.2% of normal C9 concentration. In this study, the abnormal protein was shown to have a molecular weight approximately equal to that of normal C9, and to carry the binding site for monoclonal antibody (mAb) Mc42 which is known to react with an epitope at amino acid positions 412-426, distal to 406. Therefore, the subtotal C9 protein carries the C98G defect. The protein was incorporated into the terminal complement complex, and was active in haemolytic, bactericidal and lipopolysaccharide release assays. A quantitative haemolytic assay indicated even slightly greater haemolytic efficiency than normal C9. Epitope mapping with six antihuman C9 mAbs showed the abnormal protein to react to these antibodies in the same way as normal C9. However, none of these mAbs have epitopes within the lipoprotein receptor A module, where the C98G defect is located. The role of this region in C9 functionality is still unclear. In conclusion, we have shown that the lack of a cysteine led to the production of a protein present in the circulation at very much reduced levels, but which was fully functionally active.

The human complement C9 gene: structural analysis of the 5' gene region and genetic polymorphism studies

C9 is the last of the human complement components creating the membrane attack complex. The single chain serum protein is encoded by a gene located on chromosome 5p13 that is composed of 11 exons. With the aid of inverse PCR, the hitherto unknown regions flanking exon 1 and the 3' part of exon 11 (3'UTR) have been sequenced. A computer-based analysis of the 300-bp region located just upstream of the AUG start codon showed homologies to known DNA modules which affect the transcriptional regulation of certain genes. The most striking of these is a sequence that may substitute the missing TATA box in initiating C9 transcription. In the 3'UTR, three successive polyadenylation signals were found. Although the C9 protein is invariant, four different single nucleotide polymorphisms (SNPs) have been observed at the DNA level by exon-specific PCR and direct sequencing. None of them changes the amino acid composition of the mature protein. Due to a C --> T transition in exon 1 at cDNA position 17, the fifth amino acid of the leader peptide may be either an arginine or a tryptophane. Using either PCR/ RFLP analysis (exons 1 and 11) or allele-specific PCR (intron 1 and exon 4), each polymorphism can be characterized without sequencing. All of the exon 1, intron 1 and exon 11 variants could be detected in small population samples of European, Thai or South American Indian origin. In contrast, the exon 4 C variant was observed only once in a European. The first three SNPs can be combined to designate eight different 'C9 alleles'. Of these, six have actually be found. These data provide strong evidence that several mutation and recombination events occurred in the course of C9 gene evolution.

Expression and folding of human very-low-density lipoprotein receptor fragments: neutralization capacity toward human rhinovirus HRV2

Minor group human rhinoviruses (HRVs) use members of the low-density lipoprotein receptor family for cell entry. To investigate the utility of receptor fragments as viral inhibitors, various polypeptide segments derived from the ligand binding domain of human very-low-density lipoprotein receptor (VLDLR) were expressed in a soluble form in bacteria. Whereas none of the fragments was active in virus binding immediately after recovery from the cell lysates, constructs encompassing complement type repeats 1-3, 1-6, and 1-8 spontaneously acquired virus binding activity by incubation at 4 degrees C in buffer containing Ca(2+) ions and lacking any redox system. When immobilized receptor-associated protein (RAP), a specific chaperone for VLDLR, was present during the incubation, the yield of protein active in ligand binding was substantially increased. A VLDLR fragment with repeats 4-6 failed to bind virus; however, it bound RAP. Bacterial expression of truncated VLDLR 1-3 at high yield, easy purification, and folding together with high inhibitory activity toward HRV2 makes this protein a promising starting point for the development of an oligopeptide-based antiviral agent. Using sucrose density gradient centrifugation, we demonstrate the formation of virus-receptor complexes. The recombinant receptors can thus be used for structure determination by electron cryo-microscopy.

An assay for high-sensitivity detection of thrombin activity and determination of proteases activating or inactivating protease-activated receptors

This paper describes the development of galactosidase protease-activated receptor (GPAR) as a recombinant protein obtained by fusion of beta-galactosidase, the extracellular domains of protease-activated receptors (PARs), and a biotin acceptor domain. Used as an immobilized substrate, this protein allows the detection of thrombin in the sub-picomolar range. A comparative analysis for proteolytic cleavage of murine PAR1, PAR2, and PAR3 and human PAR4 was performed, involving mutated and nonmutated GPAR fusion proteins. Thrombin cleaved GPAR1 (2.6 mol(beta-galactosidase)/(mol(thrombin) * min)), GPAR3 (410 mmol(beta-galactosidase)/(mol(thrombin) * min)), and GPAR4 (4.3 mmol(beta-galactosidase)/(mol(thrombin) * min)) specifically at the proteolytic activation site. A second possible cleavage site for thrombin is present in murine PAR1 and PAR3. Trypsin and plasmin cleaved all receptor fusion proteins with little specificity for the activation site, except for a marked preference of trypsin for cleavage at the activation site of GPAR2. Chymotrypsin cleaves GPAR1 at a rate (58 mmol(beta-galactosidase)/(mol(thrombin) * min)) that suggests the possibility of chymotryptic inactivation of PAR1. Elastase may inactivate PAR1 and PAR3, but probably not PAR2 and PAR4. Neither activated protein C nor the plasminogen activators cleave any GPAR fusion protein at considerable rates.

The four terminal components of the complement system are C-mannosylated on multiple tryptophan residues

C-Mannosylation is a unique form of protein glycosylation, involving the C-glycosidic attachment of a mannosyl residue to the indole moiety of Trp. In the two examples found so far, human RNase 2 and interleukin-12, only the first Trp in the recognition motif WXXW is specifically C-mannosylated. To establish the generality of protein C-mannosylation, and to learn more about its mechanism, the terminal components of the human complement system (C6, C7, C8,and C9), which contain multiple and complex recognition motifs, were examined. Together with C5b they form the cytolytic agent, the membrane attack complex. These are the first proteins that are C-mannosylated on more than one Trp residue as follows: six in C6, four in C7, C8alpha, and C8beta, and two in C9. Thus, from the 113 Trp residues in the complete membrane attack complex, 50 were found to undergo C-mannosylation. The other important finding is that in C6, C7, C8, and C9 Trp residues without a second Trp (or another aromatic residue) at the +3 position can be C-mannosylated. This shows that they must contain an additional C-mannosylation signal. Whether this is encoded in the primary or tertiary structure is presently unknown. Finally, all modified Trp residues are part of the highly conserved core of the thrombospondin type 1 repeats present in these proteins. Since this module has been found in a large number of other proteins, the results suggest further candidates for C-mannosylation.

Rat complement factor I: molecular cloning, sequencing and expression in tissues and isolated cells

Factor I (FI) is a regulatory serine protease of the complement system which cleaves three peptide bonds in the alpha-chain of C3b and two bonds in the alpha-chain of C4b thereby inactivating these proteins. The human protein and the recently characterized mouse factor I are heterodimers of about 88,000 MW which consist of a non-catalytic heavy chain of 50,000 MW which is linked to a catalytic light chain of 38,000 MW by a disulphide bond. For the screening of a rat liver cDNA library we used a hybridization probe produced by polymerase chain reaction (PCR) using degenerated primers which corresponded to conserved parts of the human and the murine factor I nucleotide sequences. One of the identified sequences, which had a length of 2243 base pairs (bp), contained the complete coding region and the whole 3' untranslated region. The length of the coding region in rat consisted of 1812 bp followed by a 3' untranslated region of 207 bp including the polyadenylation signal and the beginning of the poly A tail. Comparison of the rat cDNA-derived coding sequence revealed identities of 87% to the mouse and of 78% to the human FI nucleotide sequence. The translation product of rat FI mRNA was 604 amino acid residues (aa) in length with an identity of 85% to the mouse (603 aa) and 69% to the human protein (583 aa). The comparison of the molecular mass predicted by the primary structure and derived from rat FI isolated from rat serum as detected in immunoblot analyses suggested a glycosylation of more than 20% of the total mass of the FI protein. Expression studies using reverse transcription (RT)-PCR assays indicated that FI-specific mRNA could neither be identified in B cells, nor in T cells, monocytes or granulocytes from rat and human peripheral blood nor in rat peritoneal macrophages. These data were in agreement with the results of RT-PCR obtained with several human lymphoma cell lines (Jurkat, MOLT-4, HUT102, Wil 2-NS, Ramos, Raji, U937) all of which were devoid of FI-specific mRNA. In accord with our data from two rat hepatoma cell lines (FAO and H4IIE) and one from man (HepG2) only isolated rat hepatocytes (HC) but neither Kupffer cells (KC), hepatic stellate cells (HSC; Ito cells) nor sinusoidal endothelial cells (SEC) expressed FI-specific mRNA. FI mRNA was also detected in human umbilical vein endothelial cells (HUVEC) and in the uterus and small intestine of the rat. Spleen and lymph nodes did not contain any detectable FI-specific mRNA.

Increased complement biosynthesis by microglia and complement activation on neurons in Huntington's disease

In this study complement activation and biosynthesis have been analysed in the brains of Huntington's disease (HD) (n = 9) and normal (n = 3) individuals. In HD striatum, neurons, myelin and astrocytes were strongly stained with antibodies to C1q, C4, C3, iC3b-neoepitope and C9-neoepitope. In contrast, no staining for complement components was found in the normal striatum. Marked astrogliosis and microgliosis were observed in all HD caudate and the internal capsule samples but not in normal brain. RT-PCR analysis and in-situ hybridisation were carried out to determine whether complement was synthesised locally by activated glial cells. By RT-PCR, we found that complement activators of the classical pathway C1q C chain, C1r, C4, C3, as well as the complement regulators, C1 inhibitor, clusterin, MCP, DAF, CD59, were all expressed constitutively and at much higher level in HD brains compared to normal brain. Complement anaphylatoxin receptor mRNAs (C5a receptor and C3a receptor) were strongly expressed in HD caudate. In general, we found that the level of complement mRNA in normal control brains was from 2 to 5 fold lower compared to HD striatum. Using in-situ hybridisation, we confirmed that C3 mRNA and C9 mRNA were expressed by reactive microglia in HD internal capsule. We propose that complement produced locally by reactive microglia is activated on the membranes of neurons, contributing to neuronal necrosis but also to proinflammatory activities. Complement opsonins (iC3b) and anaphylatoxins (C3a, C5a) may be involved in the recruitment and stimulation of glial cells and phagocytes bearing specific complement receptors.

Phosphorylation of the complement component, C9, by an ecto-protein kinase of human leukemic cells

Ecto-protein kinases (ecto-PK) are surface constituents of many, if not all, animal cell types; normal, transformed or malignant. The occurrence of ecto-PK on the surface of human leukemia cell lines was described [Paas, Y., Fishelson, Z., 1995. Shedding of tyrosine and serine/threonine ecto-PK from human leukemic cells. Arch. Biochem. Biophys. 316 780-788.]. These ecto-PKs have been shown to phosphorylate several exogenous substrates, including the complement C9 protein, an essential component of the terminal complement system. C9 is phosphorylated by ecto-PK of K562 cells on serine residue(s). Phosphorylation occurs in the N-terminal C9a portion produced by cleavage of phosphorylated C9 with human alpha-thrombin. C9 polymers generated upon incubation of C9 with ZnCl2 do not serve as substrates for the K562 ecto-PK. In contrast, unfolded C9, obtained by reduction and alkylation, serves as a superior substrate for the K562 ecto-PK. Native C9 phosphorylation produced a rather low stoichiometry of incorporated phosphate (around 3%) per C9. Despite that, the phosphorylated C9 expressed reduced hemolytic activity. The complement-sensitive variant of K562 (K562/S) did not express the C9 phosphorylating activity. Various PK inhibitors tested failed to block C9 phosphorylation. Only heparin and 2,3-diphosphoglycerate (dpGA) prevented C9 phosphorylation, indicating that the ecto-PK is related to the casein kinase CK2. C9 can be phosphorylated by ecto-PK from other tumor cells, including Jurkat, SK-OV-3 and BT-474. These results suggest that extracellular phosphorylation of C9 may serve as a protective mechanism against complement in tumor cells.

Hexagonal bilayer structuring activity of linker chains of an annelid giant hemoglobin from the polychaete Perinereis aibuhitensis

Preferential activity of linker chains to clamp submultiples to form hexagonal bilayer (HBL) assembly of the multisubunit hemoglobin (Hb) of the polychaete Perinereis aibuhitensis (approximately 3.4 MDa) was demonstrated. To understand the HBL assembly that should rely on structuring activity of each subunit, reassociation in response to combining isolated subunits was monitored using gel filtration, SDS-PAGE, and transmission electron microscopy. The isolation of each subunit L, T, and M (L, linker chains; T, disulfide-bonded trimer A-b-B; M, monomeric chain a) of Perinereis Hb was made simply by exposing Hb to pH 10.5, where Hb was completely dissociated into its subunits L, T, and M. As a result, it was concluded that (i) subunits T and M have strong affinity to form an intermediate complex, submultiple D, which is a dodecamer of globin chains, 3[a. A-b-B], (ii) addition of subunit L to submultiple D brings about the formation of whole molecule, similarly (iii) addition of subunit M to T+L forms the whole molecule, and (iv) addition of subunit T to M+L brings about the formation of the whole molecule, too. The results obtained lead us to conclude that linkers do function to clamp 12 submultiples D up to a whole molecule at the final step of formation of Perinereis Hb. In summary, linkers appeared to have high affinity for submultiple D, a little affinity for subunit T, but no affinity for subunit M at all. Thus linker chains were demonstrated to preferentially clamp submultiples D together to form the HBL disc of the whole molecule.

Expression of complement C4 and C9 genes by human astrocytes

Evidence exists that complement activation is involved in the pathogenesis of Alzheimer's disease (AD). It has been previously demonstrated that central nervous system (CNS) resident cells can synthesize complement proteins. Two key proteins in the complement pathway are the complement C4 and C9 proteins. Using reverse transcription-polymerase chain reaction, ELISA, immunocytochemical and immunoblot techniques, we showed that primary human astrocytes constitutively expressed complement C4 mRNA and protein, and that this was increased when cells were treated with interferon-gamma, but inhibited when cells were treated with interleukin-1beta (IL-1beta). C4 immunoreactivity could be localized to GFAP-positive astrocytes when protein secretion was inhibited. These results indicated that astrocytes could be a source of complement C4 in the human CNS. In addition it was shown that stimulated astrocytes could also express complement C9 mRNA, though C9 protein was not detectable in culture supernatants.

A Non-Sense Mutation at Arg95 Is Predominant in Complement 9 Deficiency in Japanese

Deficiency of the ninth component of complement (C9D) is one of the most common genetic abnormalities in Japan, with an incidence of one homozygote in 1000. Although C9D individuals are usually healthy, it has been shown that they have an significantly increased risk of developing meningococcal meningitis. In the present study we report the molecular bases for C9D in 10 unrelated Japanese subjects. As a screening step for mutations, exons 2 to 11 of the C9 gene were analyzed using exon-specific PCR/single-strand conformation polymorphism analysis, which demonstrated aberrantly migrating DNA bands in exon 4 in all the C9D subjects. Subsequent direct sequencing of exon 4 of the C9D subjects revealed that eight of the 10 C9D subjects were homozygous for a C to T transition at nucleotide 343, the first nucleotide of the codon CGA for Arg95, leading to a TGA stop codon (R95X). R95X is a novel mutation different from those recently identified in a Swiss family with C9D. Cases 6 and 7 were heterozygous for the R95X mutation. Family study in case 10 confirmed the genetic nature of the defect. In case 6, the second mutation for C9D of the C9 gene was identified to be the substitution of Cys to Tyr at amino acid residue 507 (C507Y), while the genetic defect(s) in the other allele in case 7 remains unknown. Our results indicate that a novel mutation, R95X, is present in most cases of C9D in Japan.

Dependence of the lytic activity of the N-terminal domain of human perforin on membrane lipid composition--implications for T-cell self-preservation

The kinetics and thermodynamics of pore formation by the 22-residue N-terminal domain of human perforin-(1-22)-peptide have been studied for a variety of model phospholipid membranes. Peptide binding and aggregation, and cell lysis were monitored through the change in the fluorescence of Trp, or vesicle-encapsulated carboxyfluorescein, respectively. Peptide binding was analyzed in terms of a model that incorporates non-ideal interactions and aggregation in a membrane bilayer. The minimum number of peptide monomers required to form an active pore averaged from four to six, according to the lipid composition of the vesicle. This combined kinetic and thermodynamic approach has provided quantitative information that allows a direct comparison of the binding behavior of the perforin-(1-22)-peptide in different lipid vesicles and affords molecular insight on the factors controlling pore formation. Pore formation is most favorable in thinner membranes with low melting temperatures. No significant difference in activity is observed for different zwitterionic headgroups. Rather, the gel state of the lipid chain, which diminishes the incorporation and aggregation of the perforin-(1-22)-peptide shows the strongest influence. This effect is observed in both the thermodynamic (incorporation isotherm) and kinetic (carboxyfluorescein release) studies. Insertion and aggregation are more facile in membranes with less densely packed lipids. The dependence of pore-forming activity on lipid composition provides important clues to understanding the self-protection mechanism employed by cytotoxic T lymphocytes (CTL) against perforin-mediated lysis.

Neuronal expression of mRNAs for complement proteins of the classical pathway in Alzheimer brain

To determine possible sources of complement proteins in the brain, we investigated by in situ hybridization expression of the mRNAs of C1q, C2, C3, C4, C5, C6, C7, C8 and C9 in postmortem Alzheimer disease (AD) and control brain tissue. We found detectable hybridization for all these components in the temporal cortex and hippocampus, with significantly higher levels being found in AD tissue. Hybridization signals were strongest over pyramidal neurons. Low or absent hybridization was seen in the visual cortex or cerebellum. These results suggest that the activated complement components found in association with AD lesions may be, in part, derived from neurons.

Molecular and cellular characterization of the membrane attack complex, C5b-9, in Alzheimer's disease

The membrane attack complex, C5b-9, is of considerable importance in many inflammatory reactions. It is the terminal, cytolytic component of both classical and alternative pathway activation, and its presence presupposes other potentially destructive complement constituents, including anaphylotoxins and opsonins. We have characterized C5b-9 and its C9 constituent in the Alzheimer's disease (AD) and nondemented elderly (ND) brain using immunohistochemistry at the light and electron microscopic levels, Western blot analysis, and the reverse transcriptase polymerase chain reaction. We have also conducted in vitro ELISA assays of amyloid beta-peptide-stimulated SC5b-9 production. C5b-9 is abundantly present in Alzheimer's disease cortex, associated with neurofibrillary tangle containing neurons, dystrophic neurites within neuritic plaques, and neuropil threads, but is weakly detected, if at all, in nondemented elderly cortex under the same conditions. Staining of Alzheimer's disease sections is abolished both by deletion of primary antibody or preabsorption with purified SC5b-9.

Carbohydrate gluing, an architectural mechanism in the supramolecular structure of an annelid giant hemoglobin

We report a carbohydrate-dependent supramolecular architecture in the extracellular giant hemoglobin (Hb) from the marine worm Perinereis aibuhitensis; we call this architectural mechanism carbohydrate gluing. This study is an extension of our accidental discovery of deterioration in the form of the Hb caused by a high concentration of glucose. The giant Hbs of annelids are natural supramolecules consisting of about 200 polypeptide chains that associate to form a double-layered hexagonal structure. This Hb has 0.5% (wt) carbohydrates, including mannose, xylose, fucose, galactose, glucose, N-acetylglucosamine (GlcNAc), and N-acetylgalactosamine (GalNAc). Using carbohydrate-staining assays, in conjunction with two-dimensional polyacrylamide gel electrophoresis, we found that two types of linker chains (L1 and L2; the nomenclature of the Hb subunits followed that for another marine worm, Tylorrhynchus heterochaetus) contained carbohydrates with both GlcNAc and GalNAc. Furthermore, two types of globins (a and A) have only GlcNAc-containing carbohydrates, whereas the other types of globins (b and B) had no carbohydrates. Monosaccharides including mannose, fucose, glucose, galactose, GlcNAc, and GalNAc reversibly dissociated the intact form of the Hb, but the removal of carbohydrate with N-glycanase resulted in irreversible dissociation. These results show that carbohydrate acts noncovalently to glue together the components to yield the complete quaternary supramolecular structure of the giant Hb. We suggest that this carbohydrate gluing may be mediated through lectin-like carbohydrate-binding by the associated structural chains ("linkers").

Three-dimensional structure of a cysteine-rich repeat from the low-density lipoprotein receptor

The low-density lipoprotein (LDL) receptor plays a central role in mammalian cholesterol metabolism, clearing lipoproteins which bear apolipoproteins E and B-100 from plasma. Mutations in this molecule are associated with familial hypercholesterolemia, a condition which leads to an elevated plasma cholesterol concentration and accelerated atherosclerosis. The N-terminal segment of the LDL receptor contains a heptad of cysteine-rich repeats that bind the lipoproteins. Similar repeats are present in related receptors, including the very low-density lipoprotein receptor and the LDL receptor-related protein/alpha 2-macroglobulin receptor, and in proteins which are functionally unrelated, such as the C9 component of complement. The first repeat of the human LDL receptor has been expressed in Escherichia coli as a glutathione S-transferase fusion protein, and the cleaved and purified receptor module has been shown to fold to a single, fully oxidized form that is recognized by the monoclonal antibody IgG-C7 in the presence of calcium ions. The three-dimensional structure of this module has been determined by two-dimensional NMR spectroscopy and shown to consist of a beta-hairpin structure, followed by a series of beta turns. Many of the side chains of the acidic residues, including the highly conserved Ser-Asp-Glu triad, are clustered on one face of the module. To our knowledge, this structure has not previously been described in any other protein and may represent a structural paradigm both for the other modules in the LDL receptor and for the homologous domains of several other proteins. Calcium ions had only minor effects on the CD spectrum and no effect on the 1H NMR spectrum of the repeat, suggesting that they induce no significant conformational change.

Genomic organization of human complement protein C8 alpha and further examination of its linkage to C8 beta

Human C8 is one of five complement components (C5b, C6, C7, C8, C9) that interact to form the cytolytic C5b-9 complex on target membranes. It is composed of three nonidentical subunits (C8 alpha, C8 beta, C8 gamma) encoded by separate genes. C8 alpha and C8 beta are linked on chromosome 1p32, whereas C8 gamma is located on 9q22.3-q32. In this study, overlapping genomic clones were isolated and used to decipher the organization of the human C8 alpha gene. The gene contains at least 11 exons spanning approximately 70 kb of DNA. When compared to C6, C8 beta and C9, there is a remarkable similarity in genomic organization, consistent with amino acid sequence comparisons that suggest these proteins are ancestrally related. Regions of each protein that are structurally similar are encoded in exons of correspondingly similar lengths with highly conserved boundaries and phases. Availability of genomic sequence also facilitated a more detailed analysis of C8 alpha and C8 beta linkage. Based on analysis of genomic digests with cDNA probes, the loci were previously reported to be physically linked (< 2.5 kb) and in a 5' alpha-beta 3' orientation. In the present study, results obtained using exon-specific probes indicate the loci are not as closely linked as initially believed. Furthermore, they suggest that cDNA probes used earlier yielded misleading information because they encode exons that are distributed across large segments of genomic DNA.

Complement and cytokine gene expression in cultured microglial derived from postmortem human brains

Microglia were successfully cultured from human brain tissue from normal and neurologically diseased cases obtained 3.5-10 hours postmortem. Final cell preparations were more than 99% pure as judged by latex bead phagocytosis, expression of microglial phenotypic markers, and absence of astrocytic markers. The expression of complement genes C1qB, C3, and C4 as well as genes for interleukin-(IL-)1 alpha, IL-1 beta, IL-6, tumor necrosis factor (TNF)alpha, IL-1 receptor antagonist, and transforming growth factor beta, but not inducible nitric oxide synthase, by these cells was detected by polymerase chain reaction (PCR) analysis. The pattern of gene expression was evaluated following stimulation of the cells with lipopolysaccharide, phorbol myristate acetate, gamma interferon, and beta amyloid peptide. There was considerable variation in gene response to these activating agents. However, it was of interest that beta-amyloid peptide (1-40) increased the expression of IL-1 beta mRNA in these cells. The number of cases in this study was too small to permit evaluation of microglial response according to the disease state, but the results demonstrate the potential for such studies in the future.

Genetic detection of the silent allele (*Q0) in hereditary deficiencies of the human complement C6, C7, and C9 components

DNA polymorphisms (RFLPs) of the human complement component C6, C7, and C9 genes were studied in three C7-deficient (C7D) families, one C6-deficient (C6D) family, and one C9-deficient (C9D) family. The 3 loci are closely linked on human chromosome 5. The haplotypes carrying the "silent" allele (C7*Q0, C6*Q0, and C9*Q0) were defined in each family, allowing for the detection of carriers among asymptomatic relatives. This paper describes familial studies on a type of hereditary trait, characterized by recurrent Neisseria infections in individuals homozygous for "silent" alleles at the C6, C7, or C9 loci.

Molecular characterization of an apical early endosomal glycoprotein from developing rat intestinal epithelial cells

The apical endosomal compartment is thought to be involved in the sorting and selective transport of receptors and ligands across polarized epithelia. To learn about the protein components of this compartment, we have isolated and sequenced a cDNA that encodes a glycoprotein that is located in the apical endosomal tubules of developing rat intestinal epithelial cells. The deduced amino acid sequence predicts a protein of 1216 amino acids with a molecular mass of 133,769 Da. The deduced amino acid sequence together with amino-terminal amino acid sequencing indicate that there is a cleaved 21-amino acid signal sequence at the NH2-terminal portion of the molecule. There is a single hydrophobic region near the carboxyl terminus that has the characteristics of a membrane-spanning domain and a 36-amino acid cytoplasmic tail. We have found that the major form of this protein in intestinal epithelial cells has a molecular mass of 55-60 kDa, which is significantly smaller than the size predicted from the cDNA sequence, suggesting that the protein is synthesized as a large precursor and processed to the smaller form. The smaller form remains associated with the membrane, however, possibly through noncovalent association with the transmembrane portion of the molecule or with another membrane protein. The extracytoplasmic domain is cysteine-rich, with three cysteine-rich repeats that are similar to cysteine repeats present in several receptor proteins. However, there is no other significant similarity to other proteins in the GenBank. The cytoplasmic tail contains a possible internalization motif and several consensus motifs for serine/threonine kinases. Northern blot analysis suggests a single abundant message, and Southern blot analysis is consistent with a single gene and the absence of pseudogenes for this unique endosomal protein.

Altered glycosylation and selected mutation in recombinant human complement component C9: effects on haemolytic activity

Recombinant wild-type and mutated forms of human complement component C9 have been synthesized in baculovirus-infected insect cells. Wild-type recombinant C9 was indistinguishable from native C9, as judged by haemolytic activity, trypsin and alpha-thrombin digestion, reaction with antibodies to C9, enzymatic deglycosylation to the same core size and polymerization in the presence of Zn2+. Replacement of the native signal peptide with the honey-bee melittin signal peptide, and replacement of Spodoptera frugiperda (Sf9) cells with Trichoplusia ni cells produced yields of 5 micrograms C9/ml supernatant. Three C9 mutants were generated; one mutant, with four acidic residues changed to alanines in a putative calcium-binding site, had the same biological activity as recombinant C9. Another mutant, lacking 23 N-terminal amino acids, previously showing increased polymerization when produced in vitro, polymerized on secretion, rendering it inactive. It was not possible to demonstrate haemolytic activity of the third mutant, cysteines 33 and 36 mutated to alanine, as it was secreted a hundredfold less than the wild-type protein.

The human complement component C8B gene: structure and phylogenetic relationship

The eighth component of human complement (C8) is a serum protein that consists of three chains (alpha, beta and gamma), encoded by three separate genes, viz., C8A, C8B, and C8G. In serum, the beta-subunit is non-covalently bound to the disulfide-linked alpha-gamma subunit. Using a full-length C8 beta cDNA probe, we isolated several clones from human genomic lambda DNA libraries. Four lambda clones covering the complete cDNA sequence were characterized by TaqI restriction mapping and were "shotgun" subcloned into M13. C8 beta-cDNA-positive clones were partially sequenced to characterize the 12 exons of the gene with sizes from 69 to 347 bp. All intron-exon junctions followed the GT-AG rule. By using polymerase chain reaction (PCR) primers located in the adjacent intron sequences, all 12 exons of the C8B gene could be amplified from genomic DNA. All fragments showed the expected sizes. The sizes of eight introns could be determined by using primer pairs that amplified two exons and the enclosed intron, and by restriction mapping. These analyses and the insert sizes of the genomic lambda clones indicate that the C8B gene has a total size of approximately 40 kb. The polymorphic TaqI site of the C8B gene localized in intron 11 could be demonstrated by direct restriction fragment analysis of a PCR fragment containing exons 11 and 12, and the enclosed intron 11. Homology comparison of the C8B gene with C8A and C9 on the basis of the exon structure confirmed the ancestral relationship known from the protein level.

A physical map of the human complement component C6, C7, and C9 genes

The genes for human complement components C6, C7, and C9 are linked on chromosome 5. In this report we describe the physical linkage between C6 and C7 genes. DNA fragments obtained by digestion with several rare-cutting restriction enzymes were separated through pulsed field gel electrophoresis. Hybridization with probes corresponding to the 5' and 3' ends of the three cDNAs showed common bands for the C6 and C7 genes. Both genes are contained in a NotI fragment of 500 kilobases (kb). Moreover, the presence of common 3' C6 and 3' C7 fragments indicates that both genes are oriented in a tail-to-tail, reverse way relative to transcription. No evidence of physical linkage between C9 and C6 or C7 was found in the range 50 kb-2.5 megabases (Mb).

Synthesis and regulation of complement components by human monocytes/macrophages and by acute monocytic leukemia

Proteins of the complement system (C2, C3) are synthesized by human monocytes and macrophages, thus providing an important local source of these proteins in vivo which serve as a first-line host defense mechanism. In this study, we investigated the production of complement components C2, C4, and C9 by human monocytes/macrophages and by the pathologic cells of acute monocytic leukemia which represent a source of immature monocytic precursors. Human blood monocytes were collected and purified by cytapheresis and elutriation and leukemic cells by Ficoll gradient. Secretion of complement components was measured by a hemolytic assay. The evaluation of the mRNAs of the various complement components in the cells was performed by polymerase chain reaction (PCR) by adding 32P labeled deoxycytidinetriphosphate (dCTP) to the amplification step. Functional C2 was found to increase during in vitro maturation of macrophages up to the fourth week of culture. C2 mRNA was detected after amplification and increased during the maturation. Interferon-gamma (IFN-gamma) mediated a marked increase of the C2 mRNA. We found a decrease in synthesis of C4 mRNA during in vitro differentiation of human monocytes. The effect of IFN-gamma resulted in an increase in C4 mRNA. C9 mRNA was not detected although it was detected in the HepG2 hepatoma-derived cell line. Functional C2 was not detected by leukemic cells after 24 h of culture but little functional C4 was present in the cell supernatants. As they were by human monocytes and macrophages, C2 and C4 mRNAs were detected after amplification but C9 mRNAs were not detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Deletion of IRF-1, mapping to chromosome 5q31.1, in human leukemia and preleukemic myelodysplasia

One of the most frequent cytogenetic abnormalities in human leukemia and myelodysplasia is an interstitial deletion within chromosome 5q. A tumor suppressor gene has been hypothesized to lie in 5q31, the smallest commonly deleted region. IRF-1, a gene whose product manifests anti-oncogenic activity, was mapped to 5q31.1. IRF-1 lies between IL-5 and CDC25C and is centromeric to IL-3 and GM-CSF. Among these genes, only IRF-1 was consistently deleted at one or both alleles in 13 cases of leukemia or myelodysplasia with aberrations of 5q31. Inactivating rearrangements of one IRF-1 allele, accompanied by deletion of the second allele, were also identified in one case of acute leukemia. Thus, IRF-1 may be a critically deleted gene in human leukemia and myelodysplasia.

Expression of the components and regulatory proteins of the alternative complement pathway and the membrane attack complex in normal and diseased synovium

We have studied synthesis of the complement components and regulatory proteins of the alternative pathway and the membrane attack complex in synovial membrane. RNA was extracted from synovial tissue of patients with rheumatoid arthritis (RA) or osteoarthritis (OA) as well as from normal synovial membrane. Dot blot analysis showed the presence of mRNAs for all the complement components and regulatory proteins (C3, factor B, factor D, C5, C6, C7, C9, factor H, factor I, S-protein, SP-40, 40, DAF, MCP, CR1, CD59), except for properdin, C8 alpha, C8 beta and C8 gamma in all three types of synovial membrane studied. In an attempt to determine which components were synthesised by each cell type, monocytes (mononuclear phagocytes), human umbilical vein endothelial cells (HUVEC), synovial membrane fibroblasts (from normal, OA and RA synovial membrane) and peripheral blood lymphocytes were cultured in vitro and secretion rates of individual components were measured and total cellular RNA analysed by northern blotting. Monocytes secreted properdin, C3, and factor H but not factor B, factor I, C5, C6, C7, C8 or C9. Fibroblasts and endothelial cells secreted factor B, factor H and factor I, but not properdin, C5, C6, C7, C8 or C9. Lymphocytes did not secrete any of these components. mRNAs encoding C3, factor B, factor H, S-protein, SP-40, 40, MCP and DAF were detected in all three other cell types (monocytes, fibroblasts and HU-VEC), but factor I and CD59 mRNAs were not detected in monocytes. C5, C6, C7, C8 alpha, C8 beta, CD8 gamma and C9 mRNAs were not detected in any of the cell types studied.(ABSTRACT TRUNCATED AT 250 WORDS)