Extracellular matrix remodeling by human granzyme B via cleavage of vitronectin, fibronectin, and laminin

Perforin-independent extracellular granzyme B activity contributes to abdominal aortic aneurysm

Granzyme B (GZMB) is a serine protease that is abundantly expressed in advanced human atherosclerotic lesions and may contribute to plaque instability. Perforin is a pore-forming protein that facilitates GZMB internalization and the induction of apoptosis. Recently a perforin-independent, extracellular role for GZMB has been proposed. In the current study, the role of GZMB in abdominal aortic aneurysm (AAA) was assessed. Apolipoprotein E (APOE)(-/-) x GZMB(-/-) and APOE(-/-) x perforin(-/-) double knockout (GDKO, PDKO) mice were generated to test whether GZMB exerted a causative role in aneurysm formation. To induce aneurysm, mice were given angiotensin II (1000 ng/kg/min) for 28 days. GZMB was found to be abundant in both murine and human AAA specimens. GZMB deficiency was associated with a decrease in AAA and increased survival compared with APOE-KO and PDKO mice. Although AAA rupture was observed frequently in APOE-KO (46.7%; n = 15) and PDKO (43.3%; n = 16) mice, rupture was rarely observed in GDKO (7.1%; n = 14) mice. APOE-KO mice exhibited reduced fibrillin-1 staining compared with GDKO mice, whereas in vitro protease assays demonstrated that fibrillin-1 is a substrate of GZMB. As perforin deficiency did not affect the outcome, our results suggest that GZMB contributes to AAA pathogenesis via a perforin-independent mechanism involving extracellular matrix degradation and subsequent loss of vessel wall integrity.

Granzyme B cleavage of autoantigens in autoimmunity

The systemic autoimmune diseases are a complex group of disorders characterized by elaboration of high titer autoantibodies and immune-mediated damage of tissues. Two striking features of autoimmune rheumatic diseases are their self-sustaining nature and capacity for autoamplification, exemplified by disease flares. These features suggest the presence of a feed-forward cycle in disease propagation, in which immune effector pathways drive the generation/release of autoantigens, which in turn fuel the immune response. There is a growing awareness that structural modification during cytotoxic granule-induced cell death is a frequent and striking feature of autoantigens, and may be an important principle driving disease. This review focuses on granzyme B (GrB)-mediated cleavage of autoantigens including (i) features of GrB cleavage sites within autoantigens, (ii) co-location of cleavage sites with autoimmune epitopes, and (iii) GrB sensitivity of autoantigens in disease-relevant target tissue. The mechanisms whereby GrB-induced changes in autoantigen structure may contribute to the initiation and propagation of autoimmunity are reviewed and reveal that GrB has the potential to create or destroy autoimmune epitopes. As there remains no direct evidence showing a causal function for GrB cleavage of antigens in the generation of autoimmunity, this review highlights important outstanding questions about the function of GrB in autoantigen selection.

Granzymes in cancer and immunity

Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells are indispensable factors in the body's ongoing defence against viral infection and tumor development. CTL/NK cells recognize and kill infected or aberrant target cells by two major pathways: either through introduction of a battery of proteases - called granzymes - to the target cell cytosol, or through TNF superfamily-dependent killing. During granzyme-dependent killing, target cell death is quick and efficient and is mediated by multiple granzymes, acting via redundant cell death pathways. Although granzyme-mediated cell death has been intensively studied, recent work has also hinted at an alternative, proinflammatory role for these enzymes. Thus, in addition to their well-established role as intracellular effectors of target cell death, recent data suggest that granzymes may have an extracellular role in the propagation of immune signals. In this study, we discuss the role of granzymes as central factors in antitumor immunity, as well possible roles for these proteases as instigators of inflammation.

Endolysosomal proteases and their inhibitors in immunity

The cellular endolysosomal compartment is dynamic, complex and incompletely understood. Its organelles and constituents vary between different cell types, but endolysosomal proteases are key components of this compartment in all cells. In immune cells, these proteases function in pathogen recognition and elimination, signal processing and cell homeostasis, and they are regulated by dedicated inhibitors. Pathogens can produce analogous proteases to subvert the host immune response. The balance in activity between a protease and its inhibitor can tune the immune response or cause damage as a result of mislocalized proteolysis. In this Review, we highlight recent developments in this area and emphasize the importance of studying the role of endolysosomal proteases, and their natural inhibitors, in the initiation and regulation of immune responses.

Control of granzymes by serpins

Although proteolysis mediated by granzymes has an important role in the immune response to infection or tumours, unrestrained granzyme activity may damage normal cells. In this review, we discuss the role of serpins within the immune system, as specific regulators of granzymes. The well-characterised human granzyme B-SERPINB9 interaction highlights the cytoprotective function that serpins have in safeguarding lymphocytes from granzymes that may leak from granules. We also discuss some of the pitfalls inherent in using rodent models of granzyme-serpin interactions and the ways in which our understanding of serpins can help resolve some of the current, contentious issues in granzyme biology.

The hydroxyflavone, fisetin, suppresses mast cell activation induced by interaction with activated T cell membranes

BACKGROUND AND PURPOSE

Cell-to-cell interactions between mast cells and activated T cells are increasingly recognized as a possible mechanism in the aetiology of allergic or non-allergic inflammatory disorders. To determine the anti-allergic effect of fisetin, we examined the ability of fisetin to suppress activation of the human mast cell line, HMC-1, induced by activated Jurkat T cell membranes.

EXPERIMENTAL APPROACH

HMC-1 cells were incubated with or without fisetin for 15 min and then co-cultured with Jurkat T cell membranes activated by phorbol-12-myristate 13-acetate for 16 h. We determined gene expression in activated HMC-1 cells by DNA microarray and quantitative reverse transcription (RT)-PCR analysis. We also examined activation of the transcription factor NF-kappaB and MAP kinases (MAPKs) in activated HMC-1 cells.

KEY RESULTS

Fisetin suppresses cell spreading and gene expression in HMC-1 cells stimulated by activated T cell membranes. Additionally, we show that these stimulated HMC-1 cells expressed granzyme B. The stimulatory interaction also induced activation of NF-kappaB and MAPKs; these activations were suppressed by fisetin. Fisetin also reduced the amount of cell surface antigen CD40 and intercellular adhesion molecule-1 (ICAM-1) on activated HMC-1 cells.

CONCLUSIONS AND IMPLICATIONS

Fisetin suppressed activation of HMC-1 cells by activated T cell membranes by interfering with cell-to-cell interaction and inhibiting the activity of NF-kappaB and MAPKs and thereby suppressing gene expression. Fisetin may protect against the progression of inflammatory diseases by limiting interactions between mast cells and activated T cells.

Aberrant protein expression in plasma and kidney tissue during experimental obstructive nephropathy

Kidney failure is a major health problem worldwide. Patients with end-stage renal disease require intensive medical support by dialysis or kidney transplantation. Current methods for diagnosis of kidney disease are either invasive or insensitive, and renal function may decline by as much as 50% before it can be detected using current techniques. The goal of this study was, therefore, to identify biomarkers of kidney disease (associated with renal fibrosis) that can be used for the development of a non-invasive clinical test for early disease detection. We utilized two protein-profiling technologies (SELDI-TOF MS and 2-D) to screen the plasma and kidney proteome for aberrantly expressed proteins in an experimental mouse model of unilateral uretric obstruction, which mimics the pathology of human renal disease. Several differentially regulated proteins were detected at the plasma level of day-3-obstructed animals, which included serum amyloid A1, fibrinogen α, haptoglobin precursor protein, haptoglobin and major urinary proteins 11 and 8. Differentially expressed proteins detected at the tissue level included ras-like activator protein 2, haptoglobin precursor protein, malate dehydrogenase, α enolase and murine urinary protein (all p<0.05 versus controls). Immunohistochemistry was used to confirm the up-regulation of fibrinogen. Interestingly, these proteins are largely separated into four major classes: (i) acute-phase reactants (ii) cell-signaling molecules (iii) molecules involved in cell growth and metabolism and (iv) urinary proteins. These results provide new insights into the pathology of obstructive nephropathy and may facilitate the development of specific assay(s) to detect and monitor renal fibrosis.

The possible role of granzyme B in the pathogenesis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a highly prevalent inflammatory lung condition characterized by airways disease and emphysema, and the precise mechanism of pathogenesis is poorly understood. The consistent features of COPD include protease-antiprotease imbalance, inflammation and accelerated aging caused by apoptosis or senescence. One family of molecules involved in all of these processes is the granzymes, serine proteases with the best-known member being granzyme B (GzmB). The majority of GzmB is released unidirectionally towards target cells, but GzmB can also be released nonspecifically and escape into the extracellular environment. GzmB is capable of cleaving extracellular matrix (ECM) proteins in vitro, and the accumulation of GzmB in the extracellular milieu during chronic inflammation in COPD could contribute to ECM degradation and remodelling and, consequently, the emphysematous phenotype in the lung. Preliminary studies suggest that increased GzmB expression is associated with increased COPD severity, and this may represent a promising new target for drug and biomarker discovery in COPD. In this paper, we review the potential pathogenic contributions of GzmB to the pathogenesis of COPD.

CD2 distinguishes two subsets of human plasmacytoid dendritic cells with distinct phenotype and functions

Plasmacytoid dendritic cells (pDCs) are key regulators of antiviral immunity. They rapidly secrete IFN-alpha and cross-present viral Ags, thereby launching adaptive immunity. In this study, we show that activated human pDCs inhibit replication of cancer cells and kill them in a contact-dependent fashion. Expression of CD2 distinguishes two pDC subsets with distinct phenotype and function. Both subsets secrete IFN-alpha and express granzyme B and TRAIL. CD2(high) pDCs uniquely express lysozyme and can be found in tonsils and in tumors. Both subsets launch recall T cell responses. However, CD2(high) pDCs secrete higher levels of IL12p40, express higher levels of costimulatory molecule CD80, and are more efficient in triggering proliferation of naive allogeneic T cells. Thus, human blood pDCs are composed of subsets with specific phenotype and functions.

Extracellular matrix-induced gene expression in human breast cancer cells

Extracellular matrix (ECM) molecules modify gene expression through attachment-dependent (focal adhesion-related) integrin receptor signaling. It was previously unknown whether the same molecules acting as soluble peptides could generate signal cascades without the associated mechanical anchoring, a condition that may be encountered during matrix remodeling and degradation and relevant to invasion and metastatic processes. In the current study, the role of ECM ligand-regulated gene expression through this attachment-independent process was examined. It was observed that fibronectin, laminin, and collagen type I and II induce Smad2 activation in MCF-10A and MCF-7 cells. This activation is not caused by transforming growth factor (TGF)-beta ligand contamination or autocrine TGF involvement and is 3- to 5-fold less robust than the TGF-beta1 ligand. The resulting nuclear translocation of Smad4 in response to ECM ligand indicates downstream transcriptional responses occurring. Coimmunoprecipitation experiments determined that collagen type II and laminin act through interaction with integrin alpha(2)beta(1) receptor complex. The ECM ligand-induced Smad activation (termed signaling crosstalk) resulted in cell type and ligand-specific transcriptional changes, which are distinct from the TGF-beta ligand-induced responses. These findings show that cell-matrix communication is more complex than previously thought. Soluble ECM peptides drive transcriptional regulation through corresponding adhesion and non-attachment-related processes. The resultant gene expressional patterns correlate with pathway activity and not by the extent of Smad activation. These results extend the complexity and the existing paradigms of ECM-cell communication to ECM ligand regulation without the necessity of mechanical coupling.

Elevation of plasma granzyme B levels after acute myocardial infarction

BACKGROUND

Apoptosis is reported to play an important role in left ventricular (LV) remodeling after acute myocardial infarction (AMI). Granzyme B is a member of the serine esterase family, which has an important role in cellular apoptosis and extracellular matrix degradation.

METHODS AND RESULTS

Peripheral blood samples were obtained from 33 patients with a first-onset AMI treated by percutaneous coronary intervention (mean age: 61.4+/-8.7 years old) on days 1, 7 and 14 after onset. Plasma levels of tumor necrosis factor (TNF)-alpha, a soluble form of the Fas ligand (sFasL), and granzyme B were measured. TIMI grade 3 recanalization was accomplished in all patients within 12 h after onset. The LV end-diastolic volume index (LVEDVI) was calculated on day 1 and at 6 months after onset. Plasma levels of TNF-alpha, sFasL and granzyme B increased significantly on days 7 and 14 after onset of AMI. Stepwise multivariate regression analysis showed that the plasma granzyme B level on day 14 is a significant explanatory variable for changes in the LVEDVI.

CONCLUSIONS

Plasma levels of granzyme B increased after AMI, which might be an important factor in the progression of late LV remodeling after AMI.

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

The cytotoxic granzyme B (GrB)/perforin pathway has been traditionally viewed as a primary mechanism that is used by cytotoxic lymphocytes to eliminate allogeneic, virally infected and/or transformed cells. Although originally proposed to have intracellular and extracellular functions, upon the discovery that perforin, in combination with GrB, could induce apoptosis, other potential functions for this protease were, for the most part, disregarded. As there are 5 granzymes in humans and 11 granzymes in mice, many studies used perforin knockout mice as an initial screen to evaluate the role of granzymes in disease. However, in recent years, emerging clinical and biochemical evidence has shown that the latter approach may have overlooked a critical perforin-independent, pathogenic role for these proteases in disease. This review focuses on GrB, the most characterized of the granzyme family, in disease. Long known to be a pro-apoptotic protease expressed by cytotoxic lymphocytes and natural killer cells, it is now accepted that GrB can be expressed in other cell types of immune and nonimmune origin. To the latter, an emerging immune-independent role for GrB has been forwarded due to recent discoveries that GrB may be expressed in nonimmune cells such as smooth muscle cells, keratinocytes, and chondrocytes in certain disease states. Given that GrB retains its activity in the blood, can cleave extracellular matrix, and its levels are often elevated in chronic inflammatory diseases, this protease may be an important contributor to certain pathologies. The implications of sustained elevations of intracellular and extracellular GrB in chronic vascular, dermatological, and neurological diseases, among others, are developing. This review examines, for the first time, the multiple roles of GrB in disease pathogenesis.

Analysis of protein processing by N-terminal proteomics reveals novel species-specific substrate determinants of granzyme B orthologs

Using a targeted peptide-centric proteomics approach, we performed in vitro protease substrate profiling of the apoptotic serine protease granzyme B resulting in the delineation of more than 800 cleavage sites in 322 human and 282 mouse substrates, encompassing the known substrates Bid, caspase-7, lupus La protein, and fibrillarin. Triple SILAC (stable isotope labeling by amino acids in cell culture) further permitted intra-experimental evaluation of species-specific variations in substrate selection by the mouse or human granzyme B ortholog. For the first time granzyme B substrate specificities were directly mapped on a proteomic scale and revealed unknown cleavage specificities, uncharacterized extended specificity profiles, and macromolecular determinants in substrate selection that were confirmed by molecular modeling. We further tackled a substrate hunt in an in vivo setup of natural killer cell-mediated cell death confirming in vitro characterized granzyme B cleavages next to several other unique and hitherto unreported proteolytic events in target cells.

Granzyme B delivery via perforin is restricted by size, but not by heparan sulfate-dependent endocytosis

How granzymes gain entry into the cytosol of target cells during killer cell attack has been the subject of several studies in the past, but the effective delivery mechanism during target cell encounter has not been clarified. Here we show that granzyme B (GzmB) mutants lacking binding to negatively charged, essentially heparan-sulfate-containing membrane receptors are poorly endocytosed yet are delivered to the cytosol with efficacy similar to that of WT GzmB. In a cell-based system GzmB-deficient natural killer cells provided perforin (pfn) by natural polarized secretion and synergized with externally added GzmB. Whereas receptor (heparan sulfate)-dependent endocytosis was dispensable, delivery of larger cargo like that of GzmB fusion proteins and GzmB-antibody complexes was restricted by their size. Our data support the model in which granzymes are primarily translocated through repairable membrane pores of finite size and not by the disruption of endocytosed vesicles. We conclude that structurally related translocators, i.e., perforin and cholesterol-dependent cytolysins, deliver deathly cargo across host cell membranes in a similar manner.

Dendritic cells as killers: mechanistic aspects and potential roles

Dendritic cells (DC) are professional APC endowed with the unique capacity to activate naive T cells. DC also have important effector functions during the innate immune response, such as pathogen recognition and cytokine production. In fact, DC represent the crucial link between innate and adaptive immune responses. However, DC are quite heterogeneous and various subsets endowed with specific pathogen recognition mechanisms, locations, phenotypes, and functions have been described both in rodents and in humans. A series of studies indicated that rodent as well as human DC could also mediate another important innate function, i.e., cell-mediated cytotoxicity, mostly toward tumor cells. In this article, we will review the phenotypes of these so-called killer DC, their killing mechanism, and putative implication in the immune response.

Antihemostatic activity of human granzyme B mediated by cleavage of von Willebrand factor

The cytotoxic lymphocyte protease granzyme B (GrB) is elevated in the plasma of individuals with diseases that elicit a cytotoxic lymphocyte-mediated immune response. Given the recently recognized ability of GrB to cleave extracellular matrix proteins, we examined the effect of GrB on the pro-hemostatic molecule von Willebrand factor (VWF). GrB delays ristocetin-induced platelet aggregation and inhibits platelet adhesion and spreading on immobilized VWF under static conditions. It efficiently cleaves VWF at two sites within the A1-3 domains that are essential for the VWF-platelet interaction. Like the VWF regulatory proteinase ADAMTS-13, GrB-mediated cleavage is dependent upon VWF conformation. In vitro, GrB cannot cleave the VWF conformer found in solution, but cleavage is induced when VWF is artificially unfolded or presented as a matrix. GrB cleaves VWF with comparable efficiency to ADAMTS-13 and rapidly processes ultra-large VWF multimers released from activated endothelial cells under physiological shear. GrB also cleaves the matrix form of fibrinogen at several sites. These studies suggest extracellular GrB may help control localized coagulation during inflammation.

Death by a thousand cuts: granzyme pathways of programmed cell death

The granzymes are cell death-inducing enzymes, stored in the cytotoxic granules of cytotoxic T lymphocytes and natural killer cells, that are released during granule exocytosis when a specific virus-infected or transformed target cell is marked for elimination. Recent work suggests that this homologous family of serine esterases can activate at least three distinct pathways of cell death. This redundancy likely evolved to provide protection against pathogens and tumors with diverse strategies for evading cell death. This review discusses what is known about granzyme-mediated pathways of cell death as well as recent studies that implicate granzymes in immune regulation and extracellular proteolytic functions in inflammation.

Expression of granzyme B in peripheral blood polymorphonuclear neutrophils (PMN), myeloid cell lines and in PMN derived from haemotopoietic stem cells in vitro

Granzyme B and perforin are the major protagonists of cytotoxicity mediated by natural killer (NK) cells or cytotoxic T cells. More recent we described the presence of granzyme B and perforin in polymorphonuclear neutrophils (PMN), a finding in discrepancy with the credo that granzyme B and perforin expression is restricted to cytotoxic T cells and NK cells. In extension of our previous study, we now provide evidence that granzyme B is not only present in mature PMN, but also in the myeloid cell lines HL-60 and U937, in CD34+ stem cells, and in PMN derived from CD34+ cells in vitro. In agreement with the "targeting by time" hypothesis we found the bulk of granzyme B in association with primary granules, in addition to a minor membrane expression. Granzyme B, on one hand might, enhance the cytotoxic potential of PMN, on the other, it may provide PMN with additional means to degrade extracellular matrices.

Impaired expression of perforin and granulysin in CD8+ T cells at the site of infection in human chronic pulmonary tuberculosis

Protective immunity in tuberculosis is dependent on the coordinated release of cytolytic effector molecules from effector T cells and the subsequent granule-associated killing of infected target cells. In this study, we investigated the expression of cytolytic (perforin and granzyme A) and antimicrobial (granulysin) molecules at the single-cell level in cryopreserved lung tissue from patients with chronic, progressive tuberculosis disease. Quantification of protein-expressing cells was performed by in situ imaging, while mRNA levels in the infected tissue were analyzed by real-time PCR. Persistent inflammation, including excessive expression of inducible nitric oxide synthase in CD68+ macrophages and significant infiltration of CD3+, CD8+ and CD4+ T cells, was evident in tuberculosis lesions in all patients. However, despite the accumulation of CD3+ T cells, perforin- and granulysin-expressing CD3+ T cells were detected at two- to threefold-lower ratios in the tuberculosis lesions than in distal lung parenchyma and uninfected control lungs, respectively. This was evident at both the protein and mRNA levels. Moreover, perforin- and granulysin-expressing CD8+ T cells were scarce in individual granulomas within the tuberculosis lesions. In contrast, significant up-regulation of granzyme A-expressing CD3+ T cells was evident in the lesions from all patients. Confocal microscopy revealed coexpression of perforin and granulysin, primarily in CD8+ T cells; however, this expression was lower in the tuberculosis lesions. These findings suggest that symptomatic, chronic tuberculosis disease is associated with insufficient up-regulation of perforin and granulysin coexpression in CD8+ T cells at the local site of infection.

Current concepts in normal and defective angiogenesis: implications for systemic sclerosis

Vascular abnormalities are a major component of systemic sclerosis, but little is known about the events or mechanisms that initiate vascular injury and prevent its repair. Early stages of systemic sclerosis are characterized by an exaggerated angiogenic response later replaced by defective wound healing and fibrosis. In this review, we summarize the current knowledge of the angiogenic imbalance in systemic sclerosis.

Autoimmunity in systemic sclerosis: current concepts

Systemic sclerosis (SSc) is characterized by tissue fibrosis, obliterative microangiopathy, and immune abnormalities. The role of autoimmunity in generating the clinical and pathologic phenotype in SSc remains uncertain. Distinct subsets of antinuclear antibodies are selectively associated with unique disease manifestations but do not have a proven pathogenic role. A new class of autoantibodies recognizing cellular or extracellular matrix antigens has been recognized in SSc patients. They seem to directly activate pathways that may contribute to SSc-specific tissue and vascular damage. Data confirms that activation and polarization of T cells can contribute to a profibrotic environment. Also, activated immune effector cells can promote vascular obliterative damage through direct cytotoxic pathways targeting the endothelium or by inducing proinflammatory molecules. Technologies are emerging to accurately measure the autoantigen-specific T-cell response in SSc patients. Perturbed B-cell homeostasis has been reported in SSc. If confirmed in-vivo, these advances could lead to new disease-modifying therapeutic strategies directed at SSc-specific immune effector pathways.

Macrophages express granzyme B in the lesion areas of atherosclerosis and rheumatoid arthritis

Granzyme B is a major mediator of the cytotoxic immune response by inducing target cell death when internalized in the presence of perforin. Recently, several studies have focused on another role of granzyme B, which is extracellular matrix (ECM) remodeling through the degradation of ECM proteins. In order to investigate the expression pattern of granzyme B in the lesion areas of atherosclerosis and rheumatoid arthritis, we performed immunohistochemistry and in situ hybridization analyses using human atherosclerotic plaques and the synovial tissues of rheumatoid arthritic- and osteoarthritic-joints. In atherosclerotic plaques, granzyme B was expressed by macrophages in areas such as the boundary regions between media and intima, areas around necrotic cores, and in shoulder regions. In the synovial tissues of rheumatoid arthritic-joints, the expression of granzyme B was strongly observed in the lining layers where the majority of cells are macrophages and also in perivascular areas where macrophages and a small number of lymphocytes were mixed to form diffuse cellular aggregates. Granzyme B-positive cells were not detected in osteoarthritic synovium. Furthermore, the expression of granzyme B has been induced in the human macrophage cell line, THP-1, by ECM proteins or agents which induce macrophage differentiation. These observations indicate that macrophages should be added to the list of cell types that express granzyme B in human inflammatory diseases and that granzyme B may play a role in macrophage functions that are associated with disease progression.

Granzyme B is expressed in mouse mast cells in vivo and in vitro and causes delayed cell death independent of perforin

Mast cells respond to pathogens and allergens by secreting a vast array of preformed and newly synthesized mediators, including enzymes, vasoactive amines, lipid mediators, cytokines and chemokines, thereby affecting innate and adaptive immune responses and pathogenesis. Here, we present evidence that skin-, but not lung-associated primary mast cells as well as in vitro-differentiated bone marrow-derived mast cells (BMMC) express granzyme (gzm) B, but not gzmA or perforin (perf). GzmB is associated with cytoplasmic granules of BMMC and secreted after Fcepsilon-receptor-mediated activation. BMMC from wild type but not gzmB-deficient mice cause cell death in susceptible adherent target cells, indicating that the perf-independent cytotoxicity of BMMC is executed by gzmB. Furthermore, gzmB induces a disorganization of endothelial cell-cell contacts. The data suggest that activated mast cells contribute, via secreted gzmB, to cell death, increased vascular permeability, leukocyte extravasation and subsequent inflammatory processes in affected tissues.

The role of Granzyme B in atheromatous diseases

The mechanism and role of apoptotic cell death in the pathogenesis of atheromatous diseases is an area of intense research. Atherosclerosis is an inflammatory disease and as such, immune-mediated cell killing plays an important role. Recent studies have suggested that Granzyme B and perforin play an important role in atherogenesis. The current manuscript reviews our current understanding pertaining to the role of Granzyme B in cardiac allograft vasculopathy and atherosclerosis.

Human mast cells produce and release the cytotoxic lymphocyte associated protease granzyme B upon activation

Mast cells are widely distributed throughout the body and express effector functions in allergic reactions, inflammatory diseases, and host defense. Activation of mast cells results in exocytosis of preformed chemical mediators and leads to novel synthesis and secretion of lipid mediators and cytokines. Here, we show that human mast cells also express and release the cytotoxic lymphocyte-associated protease, granzyme B. Granzyme B was active and localized in cytoplasmic granules, morphologically resembling those present in cytotoxic lymphocytes. Expression and release of granzyme B by mast cell-lines HMC-1 and LAD 2 and by cord blood- and mature skin-derived human mast cells depended on the mode of activation of these cells. In mast cell lines and cord blood-derived mast cells, granzyme B expression was mainly induced by non-physiological stimuli (A23187/PMA, Compound 48/80) and substance P. In contrast, mature skin-derived mast cells only produced granzyme B upon IgE-dependent stimulation. We conclude that granzyme B is expressed and released by human mast cells upon physiologic stimulation. This suggests a role for granzyme B as a novel mediator in mast cell biology.

Natural killer cell-derived human granzyme H induces an alternative, caspase-independent cell-death program

Granzyme H (GzmH) belongs to a family of 5 human serine proteases that are expressed by cytotoxic immune effector cells. Although GzmH is most closely related to the caspase-activating granzyme B (GzmB), neither a natural substrate nor a role in immune defense reactions has been demonstrated for this orphan granzyme. In rodents, multiple related genes exist, but none of these can be regarded as functional homologs. Here we show that host cells are efficiently killed by GzmH after perforin and streptolysin O-mediated delivery into the cytosol. Dying cells show typical hallmarks of programmed cell death, such as mitochondrial depolarization, reactive oxygen species (ROS) generation, DNA degradation, and chromatin condensation. Contrary to GzmB, cell death by GzmH does not involve the activation of executioner caspases, the cleavage of Bid or inhibitor of caspase-activated DNase (ICAD), or the release of cytochrome c. The high expression levels of GzmH in naive natural killer (NK) cells and its potent killing ability strongly support the role of the protease in triggering an alternative cell-death pathway in innate immunity.

The major human and mouse granzymes are structurally and functionally divergent

Approximately 2% of mammalian genes encode proteases. Comparative genomics reveals that those involved in immunity and reproduction show the most interspecies diversity and evidence of positive selection during evolution. This is particularly true of granzymes, the cytotoxic proteases of natural killer cells and CD8+ T cells. There are 5 granzyme genes in humans and 10 in mice, and it is suggested that granzymes evolve to meet species-specific immune challenge through gene duplication and more subtle alterations to substrate specificity. We show that mouse and human granzyme B have distinct structural and functional characteristics. Specifically, mouse granzyme B is 30 times less cytotoxic than human granzyme B and does not require Bid for killing but regains cytotoxicity on engineering of its active site cleft. We also show that mouse granzyme A is considerably more cytotoxic than human granzyme A. These results demonstrate that even "orthologous" granzymes have species-specific functions, having evolved in distinct environments that pose different challenges.

UVA induces granzyme B in human keratinocytes through MIF: implication in extracellular matrix remodeling

In a previous study, we have described that UVB induces granzyme B (GrB) in human keratinocyte cells, and that confers potent cellular cytotoxicity against various cellular models, including immune cells (Hernandez-Pigeon, H., Jean, C., Charruyer, A., Haure, M. J., Titeux, M., Tonasso, L., Quillet-Mary, A., Baudouin, C., Charveron, M., and Laurent, G. (2006) J. Biol. Chem. 281, 13525-13532). Herein, we have found that, in contrast to UVB, UVA failed to enhance keratinocyte cellular cytotoxicity but was still able to trigger GrB production. We show that GrB is accumulated through a p38 MAPK-dependent transcriptional mechanism stimulated by redox-dependent migration inhibitory factor release. Moreover, GrB purified from UVA-treated cellular extracts was found to degrade fibronectin in vitro. Treatment with antisense oligonucleotide directed against GrB resulted in the inhibition of UVA-induced cell detachment and cell death and facilitated cell migration through fibronectin and vitronectin matrix upon UVA exposure. Altogether, these results suggest another function for GrB in the context of the UV response. Indeed, combined with our previous study, it appears that, whereas this enzyme mediates keratinocyte cellular cytotoxicity following UVB irradiation, GrB supports the capacity of keratinocyte to degrade extracellular matrix components following UVA irradiation. UV-mediated GrB production may thus have important consequences in photoaging and photocarcinogenesis.

Increased granzyme A expression in type II pneumocytes of patients with severe chronic obstructive pulmonary disease

RATIONALE

Chronic obstructive pulmonary disease (COPD) is associated with increased numbers of CD8(+) cytotoxic T lymphocytes (CTLs) in the lung, but the functional activity of CTLs remains unknown. Granzyme A (GrA) and B (GrB) are serine proteases considered to be important effector molecules of CTLs and natural killer cells.

OBJECTIVE

To investigate protein and mRNA expression of GrA and GrB in peripheral lung tissue from patients with COPD and control subjects with normal lung function.

METHODS

Paraffin-embedded sections of surgical lung specimens from 22 patients with COPD (FEV(1), 22% predicted; GOLD stage 4) and 15 control subjects (FEV(1), 108% predicted) were immunostained for GrA and GrB, and semiquantified on a 3-point scale. Messenger RNA expression in total lung, specific cell types enriched for by laser capture microdissection, and freshly isolated primary cells were determined by reverse transcriptase-polymerase chain reaction.

MEASUREMENTS AND MAIN RESULTS

GrA and GrB immunoreactivity was observed in CD8(+) CTLs and CD57(+) natural killer cells, but also in type II pneumocytes and alveolar macrophages in both groups. Bronchiolar epithelium stained positive for GrA, but negative for GrB. These observations were confirmed by reverse transcriptase-polymerase chain reaction on total lung, laser capture microdissection-enriched specific cell types and freshly isolated primary type II pneumocytes. The scores of GrA-expressing type II pneumocytes were significantly higher in patients with COPD versus control subjects.

CONCLUSIONS

GrA and GrB mRNA and protein are detectable in human lung tissue. GrA expression is increased in type II pneumocytes of patients with very severe COPD. These results indicate that GrA may be important in the development of COPD.

Presence of plasma complement regulatory proteins clusterin (Apo J) and vitronectin (S40) on circulating immune complexes (CIC)

The complement regulatory (CR) proteins clusterin and vitronectin bind to the membrane attack complex (MAC) and thus prevent cytolysis. In this report, we demonstrate the presence of both of these CR proteins on MAC bound to circulating immune complexes (CIC). We measured the amount of clusterin and vitronectin on MAC in plasma, also referred to as soluble MAC (SMAC), as well as on MAC bound to CIC (MAC-CIC), using antibody directed to polymerized C9 in systemic lupus erythematosus (SLE) patients. We observed a strong correlation among the quantities of SMAC and MAC-CIC. The amount of both clusterin and vitronectin associated with MAC-CIC was two- to threefold higher in comparison to the SMAC. Patients with high levels of clusterin and vitronectin demonstrated renal involvement. We hypothesize that these complement regulatory proteins besides regulating the insertion of MAC play other critical roles, in disease pathogenesis.

Granzyme B, a novel mediator of allergic inflammation: its induction and release in blood basophils and human asthma

Histamine, leukotriene C4, IL-4, and IL-13 are major mediators of allergy and asthma. They are all formed by basophils and are released in particularly large quantities after stimulation with IL-3. Here we show that supernatants of activated mast cells or IL-3 qualitatively change the makeup of granules of human basophils by inducing de novo synthesis of granzyme B (GzmB), without induction of other granule proteins expressed by cytotoxic lymphocytes (granzyme A, perforin). This bioactivity of IL-3 is not shared by other cytokines known to regulate the function of basophils or lymphocytes. The IL-3 effect is restricted to basophil granulocytes as no constitutive or inducible expression of GzmB is detected in eosinophils or neutrophils. GzmB is induced within 6 to 24 hours, sorted into the granule compartment, and released by exocytosis upon IgE-dependent and -independent activation. In vitro, there is a close parallelism between GzmB, IL-13, and leukotriene C4 production. In vivo, granzyme B, but not the lymphoid granule marker granzyme A, is released 18 hours after allergen challenge of asthmatic patients in strong correlation with interleukin-13. Our study demonstrates an unexpected plasticity of the granule composition of mature basophils and suggests a role of granzyme B as a novel mediator of allergic diseases.

Granzyme B-mediated death of pancreatic beta-cells requires the proapoptotic BH3-only molecule bid

Perforin-deficient NOD mice are protected from diabetes, suggesting that cytotoxic granule contents of CD8(+) T-cells have a significant role in killing beta-cells. Despite this, cytotoxic granule effects on human or mouse pancreatic islets have not been reported. We tested the susceptibility of human and mouse islet cells to purified recombinant perforin and granzyme B and measured apoptotic death using a number of assays. Perforin and granzyme B impaired insulin secretion from islet cells, and this was accompanied by cytochrome c release, caspase activation, and DNA fragmentation. Granzyme B-mediated apoptotic changes only occurred in the presence of perforin. When compared with hemopoietic cells, traditionally used as targets to measure cytotoxic T-cell function in vitro, islet cells were relatively resistant to perforin and granzyme B. Inhibition of caspases prevented DNA fragmentation but not cytochrome c release, indicating that mitochondrial disruption due to granzyme B is independent of caspase activation. Consistent with this, islet cells from mice deficient in the BH3-only protein Bid were resistant to cytochrome c release and were protected from apoptosis after exposure to perforin/granzyme B. Our data suggest that Bid cleavage by granzyme B precedes mitochondrial disruption and apoptosis in pancreatic islets.

Role of Bid-induced mitochondrial outer membrane permeabilization in granzyme B-induced apoptosis

Cytotoxic lymphocytes (CL) induce death of their targets by granule exocytosis. During this process, enzymes contained within cytotoxic granules (granzymes) are delivered to the target cell where the enzymes trigger the cell death by cleaving specific substrates. Granzyme B is the only granzyme that has been shown to induce cell death by apoptosis, but the exact pathway by which this is achieved has been the subject of hot debate. Furthermore, several other death-inducing granzymes have been identified; therefore, the exact contribution of granzyme B to CL-induced death is unclear. In this study, we discuss our recent findings on granzyme B-induced cell death and discuss the potential relevance of this pathway to CL-induced death of viral-infected and transformed cells.

Human keratinocytes acquire cellular cytotoxicity under UV-B irradiation. Implication of granzyme B and perforin

Ultraviolet (UV) radiation from the sun is widely considered as a major cause of human skin photoaging and skin cancer. Granzyme B (GrB) and perforin (PFN) are two proteins contained in granules and implicated in one of the mechanisms by which cytotoxic lymphocytes and natural killer cells exert their cytotoxicity against virus-infected, alloreactive, or transformed cells. The distribution of GrB and PFN in the skin has received little attention. However, Berthou and co-workers (Berthou, C., Michel, L., Soulie, A., Jean-Louis, F., Flageul, B., Dubertret, L., Sigaux, F., Zhang, Y., and Sasportes, M. (1997) J. Immunol. 159, 5293-5300) described that, whereas freshly isolated epidermal cells did not express GrB or PFN, keratinocyte growth to confluence was associated with GrB and PFN mRNA and protein synthesis. In this work, we have investigated the possible role of UV-B on GrB and PFN expression in keratinocytes. We found that UV-B induces GrB and PFN expression in these cells through redox-, epidermal growth factor receptor-, and mitogen-activated protein kinase-dependent signaling. Furthermore, under UV irradiation, keratinocytes acquire a significant cytotoxicity, which is GrB and PFN dependent, toward a variety of cellular targets including transformed T-lymphocytes, melanocytes, and keratinocytes. This phenomenon may have important functional consequences in the regulation of skin inflammatory response and in the emergence of cancer skin.

Extracellular granzymes: current perspectives

Granzyme A (GrA) and granzyme B (GrB) play key roles in the induction of target cell death induced by cytotoxic lymphocytes. Whilst these roles have been extensively studied, it is becoming apparent that both granzymes also possess extracellular activities. Soluble granzymes are found extracellularly in normal plasma and are elevated in a number of diseases, ranging from viral and bacterial infections to autoimmune diseases. Here, we discuss the current knowledge of extracellular granzyme substrates, inhibitors and functions; and the pathological consequences of extracellular granzymes in disease. In addition, we provide new evidence for the role of glycosaminoglycan-binding sites of granzymes in extracellular matrix remodeling.