Human genes for complement components C1r and C1s in a close tail-to-tail arrangement

Combinatorial activation of the WNT-dependent fibrogenic program by distinct complement subunits in dystrophic muscle

Fibrosis is associated with compromised muscle functionality in Duchenne muscular dystrophy (DMD). We report observations with tissues from dystrophic patients and mice supporting a model to explain fibrosis in DMD, which relies on the crosstalk between the complement and the WNT signaling pathways and the functional interactions of two cellular types. Fibro-adipogenic progenitors and macrophages, which populate the inflamed dystrophic muscles, act as a combinatorial source of WNT activity by secreting distinct subunits of the C1 complement complex. The resulting aberrant activation of the WNT signaling in responsive cells, such as fibro-adipogenic progenitors, contributes to fibrosis. Indeed, pharmacological inhibition of the C1r/s subunits in a murine model of DMD mitigated the activation of the WNT signaling pathway, reduced the fibrogenic characteristics of the fibro-adipogenic progenitors, and ameliorated the dystrophic phenotype. These studies shed new light on the molecular and cellular mechanisms responsible for fibrosis in muscular dystrophy and open to new therapeutic strategies.

Inhibition of the Classical Pathway of Complement Activation Impairs Bacterial Clearance during Enterococcus faecalis Infection

Enterococcus faecalis infections are considered a major public health concern worldwide. The complement system has a crucial role in the protection against different microbial pathogens, including E. faecalis Complement can be activated through three different pathways, including the classical, lectin, and alternative pathways. There is limited information on the role of the classical pathway (CP) in protection against infections caused by E. faecalis In the present study, we generated Fab fragments that successfully block the CP in mouse via inhibition of a key enzyme, C1s-A. Our results showed that anti-C1s-A Fab fragments block CP-mediated C3b and C4b deposition in vitro We further showed that administration of anti-C1s-A Fab fragments significantly impairs the CP functional activity in vivo Moreover, treatment of mice infected with E. faecalis using anti-C1s-A Fab fragments significantly impairs bacterial clearance as determined from the viable bacterial counts recovered from blood, kidneys, spleens, livers, and lungs of infected mice. Overall, this study highlights the essential role of the CP in host defense against E. faecalis.

Analyzing the lncRNA, miRNA, and mRNA-associated ceRNA networks to reveal potential prognostic biomarkers for glioblastoma multiforme

Background

Glioblastoma multiforme (GBM) is the most seriously brain tumor with extremely poor prognosis. Recent research has demonstrated that competitive endogenous RNA (ceRNA) network which long noncoding RNAs (lncRNAs) act as microRNA (miRNA) sponges to regulate mRNA expression were closely related to tumor development. However, the regulatory mechanisms and functional roles of ceRNA network in the pathogenesis of GBM are remaining poorly understood.

Methods

In this study, we systematically analyzed the expression profiles of lncRNA and mRNA (GSE51146 dataset) and miRNA (GSE65626 dataset) from GEO database. Then, we constructed a ceRNA network with the dysregulated genes by bioinformatics methods. The TCGA and GSE4290 dataset were used to confirm the expression and prognostic value of candidate mRNAs.

Results

In total, 3413 differentially expressed lncRNAs and mRNAs, 305 differentially expressed miRNAs were indentified in GBM samples. Then a ceRNA network containing 3 lncRNAs, 5 miRNAs, and 60 mRNAs was constructed. The overall survival analysis of TCGA databases indicated that two mRNAs (C1s and HSD3B7) were remarkly related with the prognosis of GBM.

Conclusion

The ceRNA network may increase our understanding to the pathogenesis of GBM. In general, the candidate mRNAs from the ceRNA network can be predicted as new therapeutic targets and prognostic biomarkers for GBM.

Molecular features and the transcriptional and functional delineation of complement system activators C1r and C1s from Sebastes schlegelii

C1r and C1s are serine proteases responsible for activating the classical complement pathway to initiate the complement cascade, which plays a crucial role in eliminating invading pathogenic microbes. In this study, cDNA sequences of C1r and C1s were identified from black rockfish and designated as SsC1r and SsC1s, respectively. In both sequences, two CUB domains, an EGF-like domain, two CCP domains, and a trypsin-like serine protease domain were identified. Multiple sequence alignments with known vertebrate homologs demonstrated that both sequences were highly conserved and, especially, the catalytic and substrate binding residues were completely conserved. In the constructed phylogenetic tree, C1r and C1s formed two separate clusters, which further branched into groups of related organisms. SsC1r and SsC1s joined with their respective teleostean clusters. Transcriptional analysis showed that the highest mRNA expression level was in the liver under normal physiological conditions. Significantly upregulated expression of both mRNAs in spleen and liver after pathologic stress, by intraperitoneal injection with different stimuli, suggested their vital role in immunity. The serine protease domains of SsC1r and SsC1s were cloned and the recombinant proteins were expressed and purified. A protease assay, conducted to confirm their functionality, indicated that both recombinant proteins had proteolytic activity. Taken together, these results indicate that SsC1r and SsC1s have significant properties to aid in the immunity of black rockfish by activating the complement system by proteolytic cleavage.

C1r/C1s deficiency is insufficient to induce murine systemic lupus erythematosus

C1s deficiency is strongly associated with the development of human systemic lupus erythematosus (SLE); however, the mechanisms by which C1s deficiency contributes to the development of SLE have not yet been elucidated in detail. Using ICR-derived-glomerulonephritis (ICGN) mouse strain that develops SLE and very weakly expresses C1s in the liver, we investigated the protective roles of C1s against SLE. A genetic sequence analysis revealed complete deletion of the C1s1 gene, a mouse homolog of the human C1s gene, with partial deletion of the C1ra and C1rb genes in the ICGN strain. This deletion led to the absence of C1r/C1s and a low level of C1q in the circulation. In order to investigate whether the C1r/C1s deficiency induces SLE, we produced a congenic mouse strain by introducing the deletion region of ICGN into the C57BL/6 strain. Congenic mice exhibited no C1r/C1s and a low level of C1q in the circulation, but did not have any autoimmune defects. These results suggest that C1r/C1s deficiency is not sufficient to drive murine SLE and also that other predisposing genes exist in ICGN mice.

C1 Complex: An Adaptable Proteolytic Module for Complement and Non-Complement Functions

Complement C1 is the defining component of the classical pathway. Within the C1qC1r₂C1s₂ complex, C1q functions as a molecular scaffold for C1r₂C1s₂ and C1q binding to its ligands activates these two serine proteases. The classic C1q ligands are antigen-bound antibodies and activated C1s cleaves C4 and C2 to initiate the complement cascade. Recent studies suggest broad C1 functions beyond the complement system. C1q binds to the Frizzled receptors to activate C1s, which cleaves lipoprotein receptor-related protein 6 to trigger aging-associated Wnt receptor signaling. C1q binds to apoptotic cells and the activated C1 proteases cleave nuclear antigens. C1s also cleaves MHC class I molecule and potentially numerous other proteins. The diversity of C1q ligands and C1 protease substrates renders C1 complex versatile and modular so that it can adapt to multiple molecular and cellular processes besides the complement system.

Early Components of the Complement Classical Activation Pathway in Human Systemic Autoimmune Diseases

The complement system consists of effector proteins, regulators, and receptors that participate in host defense against pathogens. Activation of the complement system, via the classical pathway (CP), has long been recognized in immune complex-mediated tissue injury, most notably systemic lupus erythematosus (SLE). Paradoxically, a complete deficiency of an early component of the CP, as evidenced by homozygous genetic deficiencies reported in human, are strongly associated with the risk of developing SLE or a lupus-like disease. Similarly, isotype deficiency attributable to a gene copy-number (GCN) variation and/or the presence of autoantibodies directed against a CP component or a regulatory protein that result in an acquired deficiency are relatively common in SLE patients. Applying accurate assay methodologies with rigorous data validations, low GCNs of total C4, and heterozygous and homozygous deficiencies of C4A have been shown as medium to large effect size risk factors, while high copy numbers of total C4 or C4A as prevalent protective factors, of European and East-Asian SLE. Here, we summarize the current knowledge related to genetic deficiency and insufficiency, and acquired protein deficiencies for C1q, C1r, C1s, C4A/C4B, and C2 in disease pathogenesis and prognosis of SLE, and, briefly, for other systemic autoimmune diseases. As the complement system is increasingly found to be associated with autoimmune diseases and immune-mediated diseases, it has become an attractive therapeutic target. We highlight the recent developments and offer a balanced perspective concerning future investigations and therapeutic applications with a focus on early components of the CP in human systemic autoimmune diseases.

Clinical presentations and molecular basis of complement C1r deficiency in a male African-American patient with systemic lupus erythematosus

Homozygous deficiencies of early components for complement activation are among the strongest genetic risk factors for human systemic lupus erythematosus (SLE). Eleven cases of C1r deficiency are documented but this is the first report on the molecular basis of C1r deficiency. The proband is an African-American male who developed SLE at 3 months of age. He had a discoid lupus rash and diffuse proliferative glomerulonephritis. Serum complement analysis of the patient showed zero CH50 activity, undetectable C1r, and reduced levels of C1s, but highly elevated levels of complement C4, C2, and C1-inhibitor. The coding regions of the mutant C1R gene with 11 exons located at chromosome 12p13 were polymerase chain reaction (PCR)-amplified and sequenced to completion. DNA sequencing revealed a homozygous C→T mutation at nucleotide-6392 in exon 10 of the C1R gene, resulting in a nonsense mutation from Arg-380 (R380X). The patient's clinically normal mother was heterozygous for this mutation. A sequence-specific primer (SSP) PCR coupled with StuI-restriction fragment length polymorphism (RFLP) was developed to detect the novel mutation. Screening of 209 African-American SLE patients suggested that the R380X mutation is a rare causal variant. Mutations leading to early complement component deficiencies in SLE are mostly private variants with large effects.

Complement deficiency and systemic lupus erythematosus: consensus and dilemma

The involvement of the complement system in the pathogenesis of autoimmune diseases is a matter of debate. However, the link between complement abnormalities and systemic lupus erythematosus (SLE) is well established and widely described. Homozygous and/or heterozygous complement-component deficiencies of the classical pathway (C1q, C1r, C1s, C4A, C4B and C2) are causally associated with susceptibility to the development of SLE. Although the severity of the disease and the strength of the association are heterogeneous for deficiencies of these proteins, they commonly cause peculiar SLE syndromes with an early age of onset, a susceptibility to bacterial infections and negative anti-dsDNA antibodies. In this review, we highlight the available data on complement deficiency and SLE with a focus on deficiencies in classical complement pathway components. We also discuss the paradox of the link between complement deficiency and lupus. The complement system acts as a 'friend' through the clearance of immune complexes and apoptotic cells, which explains the close association between complement deficiency and lupus. It also acts as an 'enemy' by participating in the effector inflammatory phase of the autoimmune response. Understanding the importance of complement deficiencies should provide novel targets for therapeutic interventions in the modulation of the immune response.

Genetic analysis of complement C1s deficiency associated with systemic lupus erythematosus highlights alternative splicing of normal C1s gene

Deficiencies of complement proteins of the classical pathway are strongly associated with the development of autoimmune diseases. Deficiency of C1r has been observed to occur concomitantly with deficiency in C1s and 9 out of 15 reported cases presented systemic lupus erythematosus (SLE). Here, we describe a family in which all four children are deficient in C1s but only two of them developed SLE. Hemolytic activity mediated by the alternative and the lectin pathways were normal, but classical pathway activation was absent in all children's sera. C1s was undetectable, while in the parents' sera it was lower than in the normal controls. The levels of C1r observed in the siblings and parents sera were lower than in the control, while the concentrations of other complement proteins (C3, C4, MBL and MASP-2) were normal in all family members. Impairment of C1s synthesis was observed in the patients' fibroblasts when analyzed by confocal microscopy. We show that all four siblings are homozygous for a mutation at position 938 in exon 6 of the C1s cDNA that creates a premature stop codon. Our investigations led us to reveal the presence of previously uncharacterized splice variants of C1s mRNA transcripts in normal human cells. These variants are derived from the skipping of exon 3 and from the use of an alternative 3' splice site within intron 1 which increases the size of exon 2 by 87 nucleotides.

Butyrylcholinesterase, paraoxonase, and albumin esterase, but not carboxylesterase, are present in human plasma

The goal of this work was to identify the esterases in human plasma and to clarify common misconceptions. The method for identifying esterases was nondenaturing gradient gel electrophoresis stained for esterase activity. We report that human plasma contains four esterases: butyrylcholinesterase (EC 3.1.1.8), paraoxonase (EC 3.1.8.1), acetylcholinesterase (EC 3.1.1.7), and albumin. Butyrylcholinesterase (BChE), paraoxonase (PON1), and albumin are in high enough concentrations to contribute significantly to ester hydrolysis. However, only trace amounts of acetylcholinesterase (AChE) are present. Monomeric AChE is seen in wild-type as well as in silent BChE plasma. Albumin has esterase activity with alpha- and beta-naphthylacetate as well as with p-nitrophenyl acetate. Misconception #1 is that human plasma contains carboxylesterase. We demonstrate that human plasma contains no carboxylesterase (EC 3.1.1.1), in contrast to mouse, rat, rabbit, horse, cat, and tiger that have high amounts of plasma carboxylesterase. Misconception #2 is that lab animals have BChE but no AChE in their plasma. We demonstrate that mice, unlike humans, have substantial amounts of soluble AChE as well as BChE in their plasma. Plasma from AChE and BChE knockout mice allowed identification of AChE and BChE bands without the use of inhibitors. Human BChE is irreversibly inhibited by diisopropylfluorophosphate, echothiophate, and paraoxon, but mouse BChE spontaneously reactivates. Since human plasma contains no carboxylesterase, only BChE, PON1, and albumin esterases need to be considered when evaluating hydrolysis of an ester drug in human plasma.

The human complement component C1R gene: the exon-intron structure and the molecular basis of allelic diversity

Human C1r is a component of the complement system, which is a major mediator of innate immunity. In this study we investigated the exon-intron organization of the human C1R gene, which spans 11 kb from the initiation codon to the stop codon, and is very similar in exon-intron structure to the C1S gene. Six common and rare alleles, C1R*1, C1R*2, C1R*5, C1R*8, C1R*9, and C1R*13, were characterized by five mutations at amino acid positions 114, 135, 146, 167 and 244, in exons 4, 5 and 7 where the CUB1, EGF and CUB2 domains are encoded, respectively. A comparison with the cDNA of the mouse C1r gene showed that C1R*2is likely to be an ancestral allele. In addition, nine nucleotide substitutions and one length polymorphism were found in introns 2, 3, 4, 8 and 10.

A novel murine complement-related gene encoding a C1r-like serum protein

C1r and C1s are highly specific serine proteases that initiate the classical pathway of complement activation. We recently demonstrated that, in the mouse, the genes encoding these proteins are duplicated. Analysis of the 5'-flanking region of the murine C1rA gene, the homologue of human C1r, revealed the presence of a novel gene encoding a C1r-like protein (c1r-LP). Although this gene carries a large deletion, it shows an overall structure similar to that of c1rA, suggesting that it may have arisen from a duplication of the C1r gene. The c1r-LP gene is expressed primarily in the liver, and is not regulated by lipopolysaccharide. The open reading frame of full-length cDNA clones encodes a pre-protein with a calculated molecular mass of 50.6 kDa which, except for an internal deletion of several modules, has a modular organization similar to that of C1r and shows 51% overall amino acid identity to corresponding regions of C1rA. Western blot analysis demonstrates the presence of C1r-LP in mouse serum. The serine protease domain of C1r-LP displays 60% amino acid residue identity to that of C1rA, however, certain atypical features of the active center, and primarily the absence of the activation/cleavage site, suggest that C1r-LP is either an atypical enzyme, or it lacks proteolytic activity, perhaps serving a regulatory function in the classical pathway.

Complement C1r and C1s genes are duplicated in the mouse: differential expression generates alternative isomorphs in the liver and in the male reproductive system

C1r and C1s are the serine proteases that form the catalytic unit of the C1 complex, the first component of complement. In the present study, we found that the genes encoding murine C1r and C1s are duplicated. One set of these genes, referred to as c1rA and c1sA, are primarily expressed in the liver and are therefore the homologues of the human C1r and C1s genes. The other two genes, termed c1rB and c1sB, are expressed exclusively in male reproductive tissues, specifically the coagulating gland and the prostate. The predicted C1rB and C1sB proteins share 96 and 93% amino acid identity with C1rA and C1sA respectively. Most of the substitutions are clustered in the serine protease domains, suggesting differences in catalytic efficiencies and/or substrate specificities or alternatively adaptation to different physiological environments. The high homology of C1rB and C1sB with C1rA and C1sA in the non-catalytic regions indicates that they are probably capable of assembling the C1 complex. The expression of alternative genes encoding isomorphs of activating components of complement in male reproductive tissues raises the possibility of new mechanisms of complement activation in the male genital tract or of novel functions for complement proteases in reproduction.

Reelin is a serine protease of the extracellular matrix

Reelin is an extracellular matrix protein that plays a pivotal role in development of the central nervous system. Reelin is also expressed in the adult brain, notably in the cerebral cortex, where it might play a role in synaptic plasticity. The mechanism of action of reelin at the molecular level has been the subject of several hypotheses. Here we show that reelin is a serine protease and that proteolytic activity is relevant to its function, since (i) Reelin expression in HEK 293T cells impairs their ability to adhere to fibronectin-coated surfaces, and adhesion to fibronectin is restored by micromolar concentrations of diisopropyl phosphorofluoridate, a serine hydrolase inhibitor; (ii) purified Reelin binds FP-Peg-biotin, a trap probe which irreversibly binds to serine residues located in active catalytic sites of serine hydrolases; (iii) purified Reelin rapidly degrades fibronectin and laminin, while collagen IV is degraded at a much slower rate; fibronectin degradation is inhibited by inhibitors of serine proteases, and by monoclonal antibody CR-50, an antibody known to block the function of Reelin both in vitro and in vivo. The proteolytic activity of Reelin on adhesion molecules of the extracellular matrix and/or receptors on neurons may explain how Reelin regulates neuronal migration and synaptic plasticity.

Molecular basis of a selective C1s deficiency associated with early onset multiple autoimmune diseases

We have investigated the molecular basis of selective and complete C1s deficiency in 2-year-old girl with complex autoimmune diseases including lupus-like syndrome, Hashimoto's thyroiditis, and autoimmune hepatitis. This patient's complement profile was characterized by the absence of CH50 activity, C1 functional activity <10%, and undetectable levels of C1s Ag associated with normal levels of C1r and C1q Ags. Exon-specific amplification of genomic DNA by PCR followed by direct sequence analysis revealed a homozygous nonsense mutation in the C1s gene exon XII at codon 534, caused by a nucleotide substitution from C (CGA for arginine) to T (TGA for stop codon). Both parents were heterozygous for this mutation. We used the new restriction site for endonuclease Fok-1 created by the mutation to detect this mutation in the genomic DNA of seven healthy family members. Four additional heterozygotes for the mutation were identified in two generations. Our data characterize for the first time the genetic defect of a selective and complete C1s deficiency in a Caucasian patient.

The human gene for mannan-binding lectin-associated serine protease-2 (MASP-2), the effector component of the lectin route of complement activation, is part of a tightly linked gene cluster on chromosome 1p36.2-3

The proteases of the lectin pathway of complement activation, MASP-1 and MASP-2, are encoded by two separate genes. The MASP1 gene is located on chromosome 3q27, the MASP2 gene on chromosome 1p36.23-31. The genes for the classical complement activation pathway proteases, C1r and C1s, are linked on chromosome 12p13. We have shown that the MASP2 gene encodes two gene products, the 76 kDa MASP-2 serine protease and a plasma protein of 19 kDa, termed MAp19 or sMAP. Both gene products are components of the lectin pathway activation complex. We present the complete primary structure of the human MASP2 gene and the tight cluster that this locus forms with non-complement genes. A comparison of the MASP2 gene with the previously characterised C1s gene revealed identical positions of introns separating orthologous coding sequences, underlining the hypothesis that the C1s and MASP2 genes arose by exon shuffling from one ancestral gene.

A novel PCR-based technique using expressed sequence tags and gene homology for murine genetic mapping: localization of the complement genes

The complement system is a cascade of serum proteins and receptors which forms a vital arm of innate immunity and enhances the adaptive immune response. This work establishes the chromosomal localization of four key genes of the murine complement system. Mapping was performed using a novel and rapid PCR restriction length polymorphism method which was developed to exploit the murine expressed sequence tag (EST) database. This technique circumvents the laborious cDNA or genomic cloning steps of other mapping methods by relying on EST data and the prediction of exon-intron boundaries. This method can be easily applied to the genes of other systems, ranging from the interests of the individual researcher to large-scale gene localization projects. Here the complement system, probably one of the most well-characterized areas of immunology, was used as a model system. It was shown that the C3a receptor C1r and C1s genes form an unexpected complement gene cluster towards the telomeric end of chromosome 6. The second mannose binding lectin-associated serine protease gene was mapped to the telomeric end of chromosome 4, which is distinct from other complement-activating serine proteases. These results provide new insights into the evolution of this group of proteins.

Activities of the MBL-associated serine proteases (MASPs) and their regulation by natural inhibitors

There has been rapid progress in determining the mechanism by which complement is activated by the complex formed between Mannose-Binding Lectin and its associated proteases (MASPs). MBL and the MASPs are of low abundance, but are similar to the more abundant C1q-C1r2s2 complex (C1), which has been extensively investigated. In this review we summarise recent findings on MBL-MASPs' structure. enzymic activity and regulation, and compare MBL-MASPs with C1.

Complement systems in invertebrates. The ancient alternative and lectin pathways

The complement system in higher vertebrates is composed of about thirty proteins that function in three activation cascades and converge in a single terminal pathway. It is believed that these cascades, as they function in the higher vertebrates, evolved from a few ancestral genes through a combination of gene duplications and divergences plus pathway duplication (perhaps as a result of genome duplication). Evidence of this evolutionary history is based on sequence analysis of complement components from animals in the vertebrate lineage. There are fewer components and reduced or absent pathways in lower vertebrates compared to mammals. Modern examples of the putatively ancestral complement system have been identified in sea urchins and tunicates, members of the echinoderm phylum and the protochordate subphylum, which are sister groups to the vertebrates. Thus far, this simpler system is composed of homologues of C3, factor B, and mannose binding protein associated serine protease suggesting the presence of simpler alternative and lectin pathways. Additional components are predicted to be present. A complete analysis of this invertebrate defense system, which evolved before the invention of rearranging genes, will provide keys to the primitive beginnings of innate immunity in the deuterostome lineage of animals.

Two Constituents of the Initiation Complex of the Mannan-Binding Lectin Activation Pathway of Complement Are Encoded by a Single Structural Gene

Mannan-binding lectin (MBL) forms a multimolecular complex with at least two MBL-associated serine proteases, MASP-1 and MASP-2. This complex initiates the MBL pathway of complement activation by binding to carbohydrate structures present on bacteria, yeast, and viruses. MASP-1 and MASP-2 are composed of modular structural motifs similar to those of the C1q-associated serine proteases C1r and C1s. Another protein of 19 kDa with the same N-terminal sequence as the 76-kDa MASP-2 protein is consistently detected as part of the MBL/MASP complex. In this study, we present the primary structure of this novel MBL-associated plasma protein of 19 kDa, MAp19, and demonstrate that MAp19 and MASP-2 are encoded by two different mRNA species generated by alternative splicing/polyadenylation from one structural gene.

Molecular Basis of Human Complement C1s Deficiency

This is the first report on the molecular basis of human complement C1s deficiency. Two abnormalities in the C1s gene were identified in a Japanese family, including one patient, by using exon-specific PCR, single-strand conformation polymorphism analysis, and nucleotide sequencing. A deletion of 4 bp, TTTG, was identified in exon X when using genomic DNA from the patient, his father, and his paternal grandmother. They were all heterozygous for the mutation. The mutant gene encodes a truncated C1s from the N terminus to the short consensus repeat domain. By further sequencing the PCR products, a nonsense mutation from G to T was identified at codon 608 in exon XII in the patient, his mother, and his sister. They were all heterozygous for the nonsense mutation. The mutant gene encodes a truncated form of C1s that lacks the C-terminal 80 amino acids. These results indicate that the patient was a compound heterozygote with the 4-bp deletion on the paternal allele and the nonsense mutation on the maternal allele. The levels of serum C1s seem to be correlated to the genotypes of the C1s gene in which no C1s was detected in the patient, and one-half of the normal level in the family members who are heterozygous for either mutation. The present study demonstrates that the disease is inherited in an autosomal recessive mode.

Characterization of the plasmid encoded virulence region pat-1 of phytopathogenic Clavibacter michiganensis subsp. michiganensis

The tomato pathogen Clavibacter michiganensis subsp. michiganensis NCPPB382, causing bacterial wilt and canker, harbors two plasmids, pCM1 (27.5 kb) and pCM2 (72 kb), carrying genes involved in virulence. The region of plasmid pCM2 encoding the pathogenicity locus pat-1 was mapped by deletion analysis and complementation studies to a 1.5-kb Bg/II/SmaI DNA fragment. Introduction of the pat-1 region into endophytic, plasmid-free isolates of C. michiganensis subsp. michiganensis converted these bacteria into virulent pathogens. Based on the nucleotide sequence of the pat-1 region, an open reading frame (ORF1) can be predicted, coding for a protein of 280 amino acids and 29.7 kDa with homology to serine proteases. Introduction of a frame-shift mutation in ORF1 leads to a loss of the pathogenic phenotype. Northern (RNA) hybridizations identified an 1.5-knt transcript of the pat-1 structural gene. The site of transcription initiation was mapped by primer extension and a typical -10/-35 region was located with significant homology to the consensus Escherichia coli sigma 70 and Bacillus subtilis sigma 43 promoters. Downstream of the pat-1 structural gene, a peculiar repetitive sequence motif (pat-1rep) is located, consisting of 20 direct tandem repeats preceded by a run of 14 guanosine residues. DNA sequences homologous to pat-1rep were isolated and characterized from four virulent C. michiganensis subsp. michiganensis strains exhibiting a high extent of structural conservation. The deletion of this repetitive sequence reduced virulence significantly but did not lead to a complete loss of the virulence phenotype.

Localization of the genes for the 100-kDa complement-activating components of Ra-reactive factor (CRARF and Crarf) to human 3q27-q28 and mouse 16B2-B3

Human and mouse genes for the complement-activating component (P100) of Ra-reactive factor, a novel bactericidal factor (CRARF and Crarf), were mapped to R-banded metaphase chromosomes by fluorescence in situ hybridization with human and mouse P100 cDNA 2.7 and 2.0 kb long, respectively. The localization of fluorescent signals showed that CRARF and Crarf mapped to human 3q27-q28 and mouse 16B2-B3, respectively. This evidence is consistent with the previous assumption that the distal portion of the long arm of human chromosome 3 is homologous to the proximal portion of mouse chromosome 16.

Non-coordinated biosynthesis of early complement components in a deficiency of complement proteins C1r and C1s

We report on a 60-year-old woman with systemic lupus erythematosus and a total (95%) C1r and a partial (36%) C1s deficiency. The patient complained about cutaneous lesions on forearms and legs without other systemic involvement. Elevated anti-nuclear, anti-native DNA and anti-SSA antibodies were present. The finding of persistently depressed levels of haemolytic complement activity (CH50) on both serum and plasma, associated with normal levels of C3, C4 and C2 components, and normal alternative pathway haemolytic activity showed a deficiency of an early component of the classical pathway. Indeed C1r component was below the limits of detection whereas C1s component was lowered (36%). The depressed CH50 was only corrected by purified C1r. Biosynthesis of C1r and C1s by patient's monocytes was spontaneously normal but not up-regulated by interferon-gamma for C1r alone, whereas the biosynthesis of C1s, but also of interleukin-6, was increased, indicating a specific disregulation of C1r. The deficiency was associated with a lupus syndrome and a fatal assumed septic shock. This is in agreement with other reported cases.

Complement biosynthesis by mononuclear phagocytes

Mononuclear phagocytes are an important in vivo source of a wide range of complement components. They are able to rapidly up-regulate or down-regulate complement synthesis in response to many different pharmacological and biological stimuli. This ability is likely to make a significant contribution to maintaining host defences particularly in peripheral tissues. The important role of molecular biology in the study of complement biosynthesis by mononuclear phagocytes will be emphasised.

Genetic deficiencies of the complement system and association with disease--early components

Genetic deficiency of one of the early components of the classical pathway of complement (C1q, C1r, C1s, C4 and C2) is often associated with clinical symptoms and immunochemical abnormalities common in idiopathic autoimmune diseases, such as lupus erythematosus, but also with an increased incidence of various, local and generalized infections. These observations are consistent with the current view of the complement system's role in handling immune complexes and combating microbial invasion. However, the absence of absolute correlations in these experiments of nature suggests that genetic defects of the classical pathway act only epistatically to other host factors and the primary etiologies of the associated diseases. In contrast, the strong association of properdin and factor D deficiency with serious infections caused by encapsulated Gram-negative bacteria suggests a more immediate involvement of the alternative pathway in a specific segment of immunity and its pathology. This concept is also supported by the primordial role of the alternative pathway in the evolution of the complement system and the apparent lethality of factor B deficiency. The gene structures of most of these early components have now been elucidated providing the basis for detailed analyses of the defective alleles, the determination of carrier status, and prenatal diagnosis.

Activation of the classical complement pathway by mannose-binding protein in association with a novel C1s-like serine protease

Serum mannose-binding protein (MBP) is a C-type lectin that binds to terminal mannose and N-acetylglucosamine moieties present on surfaces of certain pathogens and activates the classical complement pathway. In the present study, we describe the mechanism underlying the activation triggered by MBP. The human serum MBP fraction was obtained by sequential affinity chromatography on mannan-Sepharose, anti-IgM-Sepharose and anti-MBP-Sepharose in the presence of calcium ions. This fraction contained a C1s-like serine protease as assessed by C4 consumption. The C1s-like serine protease, designated MBP-associated serine protease (MASP), was separated from MBP by rechromatography on anti-MBP-Sepharose in the presence of ethylenediaminetetraacetic acid. MASP exhibited both C4- and C2-consuming activities. The molecular mass of MASP was estimated to be 83 kD with two polypeptides of heavy (66 kD) and light (L) (31 kD) chains linked by disulfide bonds. The serine residue responsible for protease activity is located on the L chain. Reconstitution experiments using MASP and MBP revealed that combination of the two components restores C4- and C2-activating capacity on mannan. Based on analyses of molecular size, antigenicity, and 11 NH2-terminal amino acid sequences of the L chain, we conclude that MASP is a novel protein different from C1r or C1s. Our findings are not in accord with a proposed mechanism by which MBP utilizes the C1r2-C1s2 complex to initiate the classical complement pathway.

Expression of human factor IX in rat capillary endothelial cells: toward somatic gene therapy for hemophilia B

In aiming to develop a gene therapy approach for hemophilia B, we expressed and characterized human factor IX in rat capillary endothelial cells (CECs). Moloney murine leukemia virus-derived retrovirus vectors that contain human factor IX cDNA linked to heterologous promoters and the neomycin-resistant gene were constructed and employed to prepare recombinant retroviruses. Rat CECs and NIH 3T3 cells infected with these viruses were selected with the neomycin analogue, G418 sulfate, and tested for expression of factor IX. A construct with the factor IX cDNA under direct control by long terminal repeat gave the highest level of expression (0.84 and 3.6 micrograms per 10(6) cells per day for CECs and NIH 3T3 cells, respectively) as quantitated by immunoassays as well as clotting activity assays. A single RNA transcript of 4.4 kilobases predicted by the construct and a recombinant factor IX of 68 kilodaltons identical to purified plasma factor IX were found. The recombinant human factor IX produced showed full clotting activity, demonstrating that CECs have an efficient mechanism for posttranslational modifications, including gamma-carboxylation, essential for its biological activity. These results, in addition to other properties of the endothelium, including large number of cells, accessibility, and direct contact with the circulating blood, suggest that CECs can serve as an efficient drug delivery vehicle producing factor IX in a somatic gene therapy for hemophilia B.

Degradation of type I and II collagen by human activated C1-s

The activated first component of human complement, C1-s, was shown to cleave type I and II collagen and gelatin. The proteolytic activity was heat labile and was inhibited by a monoclonal antibody (M241) which recognized light chain of active human C1-s or by a serine protease inhibitor, DFP, but not by a chelating agent.

Identification of a human non-interferon lymphokine activating monocyte complement biosynthesis

A monocyte-stimulating activity produced by mitogen-induced mononuclear cells has been defined by its ability to enhance the synthesis in vitro of complement C1 subcomponents, C2 and C3. A lymphokine responsible for this activity was purified from culture supernatants of peripheral blood mononuclear cells activated by staphylococcal enterotoxin A. From 0.5 litre of supernatant the purification procedure [(NH4)2SO4 precipitation, phenyl-Sepharose chromatography and preparative electrofocusing] yielded about 100 pmol of purified lymphokine. Its pI is 7.9 and its Mr, estimated by SDS/polyacrylamide-gel electrophoresis, is 14,600, 27,000 and 56,000, the high-Mr species representing oligomeric forms of the Mr-14,600 molecule. Its amino acid analysis reveals a high percentage of hydrophobic amino acids (34%); the absence of histidine residues suggests that it is a novel monocyte-activating lymphokine. It enhances C1r and C1s biosynthesis at a pretranslational level. From its structure and activity this lymphokine appears different from gamma-interferon.

The scanning model for translation: an update

The small (40S) subunit of eukaryotic ribosomes is believed to bind initially at the capped 5'-end of messenger RNA and then migrate, stopping at the first AUG codon in a favorable context for initiating translation. The first-AUG rule is not absolute, but there are rules for breaking the rule. Some anomalous observations that seemed to contradict the scanning mechanism now appear to be artifacts. A few genuine anomalies remain unexplained.