Structure and differential mechanisms of regulation of expression of a serine esterase gene in activated human T lymphocytes

Microscopic polyangiitis triggered by recurrent methicillin-resistant Staphylococcus aureus bacteremia

Most of the purported links between microbial agents and primary small-vessel anti-neutrophilic antibody-positive (ANCA) vasculitides remain speculative. There is strong circumstantial evidence for the role of Staphylococcus aureus in the development of Wegener's granulomatosis, but its role in other ANCA-positive vasculitis syndromes is less clear. We describe a patient who developed a non-granulomatous, necrotizing small-vessel vasculitis with a positive anti-neutrophil cytoplasmic antibody of a perinuclear type (p-ANCA), along with anti-myeloperoxidase antibodies after recurrent episodes of methicillin-resistant Staphylococcus aureus bacteremia.

Hypotheses on the etiology of antineutrophil cytoplasmic autoantibody associated vasculitis: the cause is hidden, but the result is known

The first description of what is now known as antineutrophil cytoplasmic autoantibody-associated necrotizing vasculitis appeared more than 140 yr ago. Since then, many aspects of the pathogenic pathway have been elucidated, indicating the involvement of antineutrophil cytoplasmic autoantibodies, but why antineutrophil cytoplasmic autoantibodies are produced in the first place remains unknown. Over the years, many hypotheses have emerged addressing the etiology of antineutrophil cytoplasmic antibody production, but no exclusive factor or set of factors can so far be held responsible. Herein is reviewed the most influential hypotheses regarding the causes of antineutrophil cytoplasmic antibody-associated vasculitis with the aim of placing in an epidemiologic background the different hypotheses that are centered on environmental and genetic influences.

Correlated fragile site expression allows the identification of candidate fragile genes involved in immunity and associated with carcinogenesis

Background

Common fragile sites (cfs) are specific regions in the human genome that are particularly prone to genomic instability under conditions of replicative stress. Several investigations support the view that common fragile sites play a role in carcinogenesis. We discuss a genome-wide approach based on graph theory and Gene Ontology vocabulary for the functional characterization of common fragile sites and for the identification of genes that contribute to tumour cell biology.

Results

Common fragile sites were assembled in a network based on a simple measure of correlation among common fragile site patterns of expression. By applying robust measurements to capture in quantitative terms the non triviality of the network, we identified several topological features clearly indicating departure from the Erdos-Renyi random graph model. The most important outcome was the presence of an unexpected large connected component far below the percolation threshold. Most of the best characterized common fragile sites belonged to this connected component. By filtering this connected component with Gene Ontology, statistically significant shared functional features were detected. Common fragile sites were found to be enriched for genes associated to the immune response and to mechanisms involved in tumour progression such as extracellular space remodeling and angiogenesis.

Moreover we showed how the internal organization of the graph in communities and even in very simple subgraphs can be a starting point for the identification of new factors of instability at common fragile sites.

Conclusion

We developed a computational method addressing the fundamental issue of studying the functional content of common fragile sites. Our analysis integrated two different approaches. First, data on common fragile site expression were analyzed in a complex networks framework. Second, outcomes of the network statistical description served as sources for the functional annotation of genes at common fragile sites by means of the Gene Ontology vocabulary. Our results support the hypothesis that fragile sites serve a function; we propose that fragility is linked to a coordinated regulation of fragile genes expression.

Crystal structure of the caspase activator human granzyme B, a proteinase highly specific for an Asp-P1 residue

Granzyme B is the prototypic member of the granzymes, a family of trypsin-like serine proteinases localized in the dense cytoplasmic granules of activated natural killer cells and cytotoxic T lymphocytes. Granzyme B directly triggers apoptosis in target cells by activating the caspase pathway, and has been implicated in the etiology of rheumatoid arthritis. Human granzyme B expressed in a baculovirus system has been crystallized without inhibitor and its structure has been determined to 3.1 A resolution, after considerably improving the diffraction power of the crystals by controlled humidity changes. The granzyme B structure reveals an overall fold similar to that found in cathepsin G and human chymase. The guanidinium group of Arg226, anchored at the back of the S1-specificity pocket, can form a salt bridge with the P1-Asp side chain of a bound peptide substrate. The architecture of the substrate binding site of granzyme B appears to be designed to accommodate and cleave hexapeptides such as the sequence Ile-Glu-Thr-Asp-/Ser-Gly present in the activation site of pro-caspase-3, a proven physiological substrate of granzyme B. These granzyme B crystals, with fully accessible active sites, are well suited for soaking with small synthetic inhibitors that might be used for a treatment of chronic inflammatory disorders.

Anti-viral strategies of cytotoxic T lymphocytes are manifested through a variety of granule-bound pathways of apoptosis induction

Cytotoxic T cells and natural killer cells together constitute a major defence against virus infection, through their ability to induce apoptotic death in infected cells. These cytolytic lymphocytes kill their targets through two principal mechanisms, and one of these, granule exocytosis, is essential for an effective in vivo immune response against many viruses. In recent years, the authors and other investigators have identified several distinct mechanisms that can induce death in a targeted cell. In the present article, it is postulated that the reason for this redundancy of lethal mechanisms is to deal with the array of anti-apoptotic molecules elaborated by viruses to extend the life of infected cells. The fate of such a cell therefore reflects the balance of pro-apoptotic (immune) and anti-apoptotic (viral) strategies that have developed over eons of evolutionary time.

Down-regulation of human granzyme B expression by glucocorticoids. Dexamethasone inhibits binding to the Ikaros and AP-1 regulatory elements of the granzyme B promoter

The serine protease granzyme B is an essential component of the granule exocytosis pathway, a major apoptotic mechanism used by cytotoxic T lymphocytes and natural killer cells to induce target cell apoptosis. Granzyme B gene transcription is induced in activated lymphocytes upon antigenic stimulation, and several regulatory regions including CBF, AP-1, and Ikaros binding sites have been shown to be essential in the control of granzyme B promoter activation. Dexamethasone, a glucocorticoid that is widely used as an immunomodulatory and anti-inflammatory agent, inhibits granzyme B mRNA transcript in phytohemagglutinin-activated peripheral blood mononuclear cells. Transfection of a reporter construct containing the -148 to +60 region of the human granzyme B promoter demonstrated that this region was the target for dexamethasone repression. Mutation of Ikaros or AP-1 binding sites in the context of the granzyme B promoter demonstrated that both sites participate in dexamethasone-mediated inhibition of the granzyme B promoter activity. Electromobility shift assay revealed that dexamethasone abolished the binding of nuclear transcription factors to the Ikaros binding site and reduced AP-1 binding activity. These results indicate that dexamethasone is able to abrogate the transcriptional activity of the human granzyme B gene promoter by inhibiting the binding of nuclear factors at the AP-1 and Ikaros sites.

Residual cytotoxicity and granzyme K expression in granzyme A-deficient cytotoxic lymphocytes

Cytotoxic lymphocytes contain granules that have the ability to induce apoptosis in susceptible target cells. The granule contents include perforin, a pore-forming molecule, and several granzymes, including A and B, which are the most abundant serine proteases in these granules. Granzyme B-deficient cytotoxic T lymphocytes (CTL) have a severe defect in their ability to rapidly induce apoptosis in their targets, but have an intact late cytotoxicity pathway that is in part perforin-dependent. In this report, we have created mice that are deficient for granzyme A and characterized their phenotype. These mice have normal growth and development and normal lymphocyte development, activation, and proliferation. Granzyme A-deficient CTL have a small but reproducible defect in their ability to induce 51Cr and 125I-UdR release from susceptible allogeneic target cells. Since other granzyme A-like tryptases could potentially account for the residual cytotoxicity in granzyme A-deficient CTL, we cloned the murine granzyme K gene, which is linked to granzyme A in humans, and proved that it is also tightly linked with murine granzyme A. The murine granzyme K gene (which encodes a tryptase similar to granzyme A) is expressed at much lower levels than granzyme A in CTL and LAK cells, but its expression is unaltered in granzyme A-/- mice. The minimal cytotoxic defect in granzyme A-/- CTL could be due to the existence of an intact, functional early killing pathway (granzyme B dependent), or to the persistent expression of additional granzyme tryptases like granzyme K.

Expression of human recombinant granzyme A zymogen and its activation by the cysteine proteinase cathepsin C

Human granzyme A is one of the serine proteinases present in the granules of cytotoxic T lymphocytes and natural killer cells. Granzymes are synthesized as inactive proenzymes with an amino-terminal prodipeptide, which is processed during transport of granzymes to the cytotoxic granules, where they are stored as active proteinases. In this study, we explored the possibility of producing recombinant granzymes. Recombinant human granzyme A zymogen was expressed in several eukaryotic cell lines (HepG2, Jurkat, and COS-1) after infection with a recombinant vaccinia virus containing full-length granzyme A cDNA. Immunoblot analysis of cell lysates showed that all infected cells produced a disulfide-linked homodimer of identical molecular weight as natural granzyme A. Infected HepG2 cells produced the largest amount of this protease (approximately 160 times more than lymphokine activated killer (LAK) cells). The recombinant protein only had high mannose type oligosaccharides as did the natural protein. Although infected HepG2 and COS cells contained high granzyme A antigen levels, lysates from these cells did not show any granzyme A proteolytic activity. However, the inactive proenzyme could be converted into active granzyme A by incubation with the thiol proteinase cathepsin C (dipeptidyl peptidase I). This study is the first to demonstrate expression of an active recombinant human cytotoxic lymphocyte proteinase and conversion of inactive progranzyme A into an active enzyme by cathepsin C. We suggest that a similar approach can be used for the production of other granzymes and related proteinases.

Duodenase, a new serine protease of unusual specificity from bovine duodenal mucosa. Purification and properties

In this paper, data are presented on purification and properties of a new serine endopeptidase (duodenase) isolated from bovine duodenum mucosa. The enzyme has been purified to homogeneity by combinations of ammonium sulphate fractionation, carboxymethyl-cellulose 52 chromatography, and affinity chromatography on Sepharose 4B with Kunitz soybean trypsin inhibitor as a ligand. Some physicochemical properties of this protease have been investigated. The molecular mass of the purified duodenase was determined to be 29 +/- 0.5 kDa by SDS/PAGE and G-2000 SW column chromatography. The enzyme molecule is a single chain and the native enzyme is a monomeric protein. Its isoelectric point was estimated to be 10 +/- 0.2. Duodenase has two forms (I and II) which possess similar properties but differ in their amino acid composition. The new protease is a glycoprotein and contains approximately 3.5% sugars. The enzyme displays trypsin-like and chymotrypsin-like activities and hydrolyzes the amide bonds of substrates having Lys, Arg, Tyr, Phe and Leu residues at the P1 position. Duodenase is most active at pH 7.9-8.2. Duodenase was irreversibly inhibited by diisopropylphosphofluoridate and phenylmethanesulphonyl fluoride, indicative of an active-site serine in this protease. alpha-N-Tosyl-L-lysine chloromethane and alpha-N-tosyl-L-phenylalanine chloromethane, which react with an active His, caused marked inhibition of trypsin-like and chymotrypsin-like activities of duodenase. The enzyme activity was strongly suppressed by trypsin inhibitors from different sources (soybeans, bovine lungs and Lima beans). Chicken egg white ovomucoid had no effect on the duodenase activity. The N-terminal sequence of the native duodenase (24 amino acid residues) shows high similarity with those of human and murine cytotoxic T-lymphocyte granzymes, human leukocyte cathepsin G and rat mast cell chymases. The biological role of duodenase is discussed.

Duodenase, a new serine protease of unusual specificity from bovine duodenal mucosa. Primary structure of the enzyme

The complete amino acid sequence of duodenase, a new serine endopeptidase from bovine duodenal mucosa, has been determined. The sequence was reconstructed by the automated sequence analysis of the peptides obtained after cleavage with trypsin, Staphylococcus aureus V8 protease, cyanogen bromide and duodenase. The enzyme is composed of 226 amino acid residues yielding a molecular mass of 29.06 kDa. The presence of six cysteine residues and one potential sugar-chain-binding site at Asn50 was revealed. A predicted catalytic triade characteristic of the serine proteases was traced in the duodenase primary structure at the corresponding positions (His44, Asp87 and Ser181 in the sequence). Comparison of the sequence of duodenase with the other known primary structures of mammalian serine proteinases reveales the duodenase identity to granzymes from human and mice, human cathepsin G and mast cell chymases from rat, and gives an overall sequence identity of 47-55% with the mentioned enzymes. Alignment of the known serine protease and duodenase primary structures showed unique amino acid residues within the duodenase substrate-binding pocket at positions 189 (Asn) and 226 (Asp) (the bovine chymotrypsinogen A numbering). These results are discussed with respect to the relation between the duodenase unique residues within the primary specificity pocket S1 and the unusual dual specificity of the enzyme.

Production and characterization of monoclonal antibodies raised against recombinant human granzymes A and B and showing cross reactions with the natural proteins

The human serine proteases granzymes A and B are expressed in cytoplasmic granules of activated cytotoxic T lymphocytes and natural killer cells. Recombinant granzyme A and granzyme B proteins were produced in bacteria, purified and then used to raise specific mouse monoclonal antibodies. Seven monoclonal antibodies (mAb) were raised against granzyme A, which all recognized the same or overlapping epitopes. They reacted specifically in an immunoblot of interleukin-2 (IL-2) stimulated PBMNC with a disulfide-linked homodimer of 43 kDa consisting of 28 kDa subunits. Seven mAb against granzyme B were obtained, which could be divided into two groups, each recognizing a different epitope. On an immunoblot, all mAb reacted with a monomer of 33 kDa protein. By immunohistochemistry, these mAb could be used to detect granzymes A and B expression in activated CTL and NK cells. The availability of these mAb may facilitate studies on the role of human cytotoxic cells in various immune reactions and may contribute to a better understanding of the role of granzymes A and B in the cytotoxic response in vivo.

Structure and evolution of the cytotoxic cell proteinase genes CCP3, CCP4 and CCP5

A family of serine proteinases is believed to be important in cell-mediated cytotoxicity. Presented here are the genomic sequences for three murine members of this cytotoxic cell proteinase (CCP) family: the CCP3, CCP4 and CCP5 genes. All three of these genes have introns inserted at the same codon sites and the same exon distribution of the active site residues. These characteristics are also shared with the CCP1 and CCP2 genes, the charter members of the CCP gene family. Phylogenetic analysis using intron and exon sequences suggests that all five genes arose by various duplication events. This analysis also indicates that the recently described HuCCPX and CCP2 genes originated from recombination events between genes of different lineages. A phylogenetic and Southern analysis of the recombinant HuCCPX gene suggests that the human genome contains an additional CCP gene that has yet to be described. Finally, evidence is presented suggesting that the cDNA clone originally describing the CCP5 gene was derived from an alternately spliced transcript.

Characterization of a novel, human cytotoxic lymphocyte-specific serine protease cDNA clone (CSP-C)

A human cDNA clone encoding a novel serine protease, cytotoxic serine protease-C(CSP-C), has been isolated from a cDNA library prepared from recombinant interleukin-2 (IL-2)-activated lymphocytes of a patient with a large granular lymphoproliferative disorder. The clone has a 741-base pair open reading frame encoding a putative 246-amino acid protein. The protein sequence contains the catalytic charge relay system characteristic of a serine protease and the conserved N-terminal amino acid sequence of the mature cytotoxic lymphocyte serine proteases found in both mouse and human. The amino acid sequence of CSP-C has 71% identity with the previously reported cytotoxic serine protease-B(CSP-B)/human lymphocyte protease (HLP)/SECT and 57% identity with the granulocyte-specific serine protease cathepsin G. The homology with another lymphocyte-specific serine protease, human Hanukah factor (HF)/Granzyme A was 41%. The transcript is expressed in lymphocytes stimulated with IL-2 or IL-2 plus phytohemagglutinin (PHA). CSP-C is not expressed in B-lymphoblastoid cell lines or in the T-leukemia cell line MOLT4. The cDNA sequence suggests that the protein is expressed as a prepropeptide, as has been found in the other murine and human serine proteases of lymphocyte origin. It has recently been reported that human chromosome 14q11, in addition to containing the genes encoding cytotoxic serine protease B (CSP-B), cathepsin G, and the T-cell receptor alpha and delta genes, also includes an additional genomic DNA clone which cross-hybridized with CSP-B and cathepsin G, cathepsin-like gene-2 (CGL-2). It is likely that the CSP-C cDNA clone reported in this study corresponds to CGL-2.

Structural organization of the hCTLA-1 gene encoding human granzyme B

Cytotoxic T lymphocytes (CTLs) and natural killer/lymphokine-activated cells produce granzymes, a family of serine esterase proteins located in cytoplasmic granules. These might be involved in different cytotoxic pathways. We report the structural organization of the human gene encoding granzyme B (hCTLA-1). A 4.75-kb genomic DNA fragment containing all the sequences of granzyme B-encoding cDNA clones has been sequenced. The gene is composed of five exons and four introns. A comparison with the genomic organization of murine CCP1/CTLA-1 showed very similar structure and a 76% nucleotide homology in the coding sequences. This suggests that both genes may have a common ancestor. No typical regulatory element was detected in the 1160 bp upstream from the ATG start codon. The detection of a second locus related to hCTLA-1 is also described.

Contingent genetic regulatory events in T lymphocyte activation

Interaction of antigen in the proper histocompatibility context with the T lymphocyte antigen receptor leads to an orderly series of events resulting in morphologic change, proliferation, and the acquisition of immunologic function. In most T lymphocytes two signals are required to initiate this process, one supplied by the antigen receptor and the other by accessory cells or agents that activate protein kinase C. Recently, DNA sequences have been identified that act as response elements for one or the other of the two signals, but do not respond to both signals. The fact that these sequences lie within the control regions of the same genes suggests that signals originating from separate cell membrane receptors are integrated at the level of the responsive gene. The view is put forth that these signals initiate a contingent series of gene activations that bring about proliferation and impart immunologic function.