Selective regulation of apoptosis: the cytotoxic lymphocyte serpin proteinase inhibitor 9 protects against granzyme B-mediated apoptosis without perturbing the Fas cell death pathway

Oropharyngeal squamous cell carcinomas differentially express granzyme inhibitors

Objectives

Patients with human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinomas (OPSCCs) have an improved prognosis compared to HPV-negative OPSCCs. Several theories have been proposed to explain this relatively good prognosis. One hypothesis is a difference in immune response. In this study, we compared tumor-infiltrating CD3+, CD4+, CD8+ T-cells, and granzyme inhibitors (SERPINB1, SERPINB4, and SERPINB9) between HPV-positive and HPV-negative tumors and the relation with survival.

Methods

Protein expression of tumor-infiltrating lymphocytes (TILs) (CD3, CD4, and CD8) and granzyme inhibitors was analyzed in 262 OPSCCs by immunohistochemistry (IHC). Most patients (67 %) received primary radiotherapy with or without chemotherapy. Cox regression analysis was carried out to compare overall survival (OS) of patients with low and high TIL infiltration and expression of granzyme inhibitors.

Results

HPV-positive OPSCCs were significantly more heavily infiltrated by TILs (p < 0.001) compared to HPV-negative OPSCCs. A high level of CD3+ TILs was correlated with a favorable outcome in the total cohort and in HPV-positive OPSCCs, while it reached no significance in HPV-negative OPSCCs. There was expression of all three granzyme inhibitors in OPSCCs. No differences in expression were found between HPV-positive and HPV-negative OPSCCs. Within the group of HPV-positive tumors, a high expression of SERPINB1 was associated with a significantly worse overall survival.

Conclusion

HPV-positive OPSCCs with a low count of CD3+ TILs or high expression of SERPINB1 have a worse OS, comparable with HPV-negative OPSCCs. This suggests that the immune system plays an important role in the carcinogenesis of the virally induced oropharynx tumors.

A Novel Serpin Regulatory Mechanism: SerpinB9 IS REVERSIBLY INHIBITED BY VICINAL DISULFIDE BOND FORMATION IN THE REACTIVE CENTER LOOP

The intracellular protease inhibitor Sb9 (SerpinB9) is a regulator of the cytotoxic lymphocyte protease GzmB (granzyme B). Although GzmB is primarily involved in the destruction of compromised cells, recent evidence suggests that it is also involved in lysosome-mediated death of the cytotoxic lymphocyte itself. Sb9 protects the cell from GzmB released from lysosomes into the cytosol. Here we show that reactive oxygen species (ROS) generated within cytotoxic lymphocytes by receptor stimulation are required for lyososomal permeabilization and release of GzmB into the cytosol. Importantly, ROS also inactivate Sb9 by oxidizing a highly conserved cysteine pair (P1-P1' in rodents and P1'-P2' in other mammals) in the reactive center loop to form a vicinal disulfide bond. Replacement of the P4-P3' reactive center loop residues of the prototype serpin, SERPINA1, with the P4-P5' residues of Sb9 containing the cysteine pair is sufficient to convert SERPINA1 into a ROS-sensitive GzmB inhibitor. Conversion of the cysteine pair to serines in either human or mouse Sb9 results in a functional serpin that inhibits GzmB and resists ROS inactivation. We conclude that ROS sensitivity of Sb9 allows the threshold for GzmB-mediated suicide to be lowered, as part of a conserved post-translational homeostatic mechanism regulating lymphocyte numbers or activity. It follows, for example, that antioxidants may improve NK cell viability in adoptive immunotherapy applications by stabilizing Sb9.

SERPINB12 Is a Slow-Binding Inhibitor of Granzyme A and Hepsin

The clade B/intracellular serpins protect cells from peptidase-mediated injury by forming covalent complexes with their targets. SERPINB12 is expressed in most tissues, especially at cellular interfaces with the external environment. This wide tissue distribution pattern is similar to that of granzyme A (GZMA). Because SERPINB12 inhibits trypsin-like serine peptidases, we determined whether it might also neutralize GZMA. SERPINB12 formed a covalent complex with GZMA and inhibited the enzyme with typical serpin slow-binding kinetics. SERPINB12 also inhibited Hepsin. SERPINB12 may function as an endogenous inhibitor of these peptidases.

Human SERPINB12 Is an Abundant Intracellular Serpin Expressed in Most Surface and Glandular Epithelia

The intracellular serine protease inhibitors (serpins) are an important family of proteins that protect cells form proteinase-mediated injury. Understanding the tissue and cellular expression pattern of this protein family can provide important insights into their physiologic roles. For example, high expression in epithelial tissues, such as lung, may suggest a biologic function in cellular defense, secretion, or selective absorption. Although the expression pattern of many of the intracellular serpins has been well described, one member of this class, SERPINB12, has not been carefully examined. We generated a mouse monoclonal antibody directed against human SERPINB12 and delineated its specificity and tissue and cell type distribution pattern through immunoblotting and immunohistochemistry, respectively. This monoclonal antibody was human specific and did not cross-react with other human intracellular serpins or mouse Serpinb12. SERPINB12 was found in nearly all the tissues investigated. In addition, this serpin was found in multiple cell types within individual tissues but primarily the epithelium. These data suggest that SERPINB12, like some other intracellular serpins, may play a vital role in barrier function by providing protection of epithelial cells.

The potential role of DNA methylation in abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is a complex disorder that has a significant impact on the aging population. While both genetic and environmental risk factors have been implicated in AAA formation, the precise genetic markers involved and the factors influencing their expression remain an area of ongoing investigation. DNA methylation has been previously used to study gene silencing in other inflammatory disorders and since AAA has an extensive inflammatory component, we sought to examine the genome-wide DNA methylation profiles in mononuclear blood cells of AAA cases and matched non-AAA controls. To this end, we collected blood samples and isolated mononuclear cells for DNA and RNA extraction from four all male groups: AAA smokers (n = 11), AAA non-smokers (n = 9), control smokers (n = 10) and control non-smokers (n = 11). Methylation data were obtained using the Illumina 450k Human Methylation Bead Chip and analyzed using the R language and multiple Bioconductor packages. Principal component analysis and linear analysis of CpG island subsets identified four regions with significant differences in methylation with respect to AAA: kelch-like family member 35 (KLHL35), calponin 2 (CNN2), serpin peptidase inhibitor clade B (ovalbumin) member 9 (SERPINB9), and adenylate cyclase 10 pseudogene 1 (ADCY10P1). Follow-up studies included RT-PCR and immunostaining for CNN2 and SERPINB9. These findings are novel and suggest DNA methylation may play a role in AAA pathobiology.

Granzyme A Is Required for Regulatory T-Cell Mediated Prevention of Gastrointestinal Graft-versus-Host Disease

In our previous work we could identify defects in human regulatory T cells (Tregs) likely favoring the development of graft-versus-host disease (GvHD) following allogeneic stem cell transplantation (SCT). Treg transcriptome analyses comparing GvHD and immune tolerant patients uncovered regulated gene transcripts highly relevant for Treg cell function. Moreover, granzyme A (GZMA) also showed a significant lower expression at the protein level in Tregs of GvHD patients. GZMA induces cytolysis in a perforin-dependent, FAS-FASL independent manner and represents a cell-contact dependent mechanism for Tregs to control immune responses. We therefore analyzed the functional role of GZMA in a murine standard model for GvHD. For this purpose, adoptively transferred CD4+CD25+ Tregs from gzmA-/- mice were analyzed in comparison to their wild type counterparts for their capability to prevent murine GvHD. GzmA-/- Tregs home efficiently to secondary lymphoid organs and do not show phenotypic alterations with respect to activation and migration properties to inflammatory sites. Whereas gzmA-/- Tregs are highly suppressive in vitro, Tregs require GZMA to rescue hosts from murine GvHD, especially regarding gastrointestinal target organ damage. We herewith identify GZMA as critical effector molecule of human Treg function for gastrointestinal immune response in an experimental GvHD model.

Human T cell activation induces synaptic translocation and alters expression of the serine protease inhibitor neuroserpin and its target protease

Contact between T cells and APCs and activation of an effective immune response trigger cellular polarization and the formation of a structured interface known as the immunological synapse. Interactions across the synapse and secretion of T cell and APC-derived factors into the perisynaptic compartment regulate synapse formation and activation of T cells. We report that the serine protease inhibitor neuroserpin, an axonally secreted protein thought to play roles in the formation of the neuronal synapse and refinement of synaptic activity, is expressed in human naïve effector memory and central memory subsets of CD4(+) and CD8(+) T cells, as well as monocytes, B cells, and NK cells. Neuroserpin partially colocalized with a TGN38/LFA-1-positive vesicle population in T cells and translocates to the immunological synapse upon activation with TCR antibodies or antigen-pulsed APCs. Activation of T cells triggered neuroserpin secretion, a rapid, 8.4-fold up-regulation of the serine protease tissue plasminogen activator, the protease target for neuroserpin, and a delayed, 6.25-fold down-regulation of neuroserpin expression. Evidence of polarization and regulated neuroserpin expression was also seen in ex vivo analyses of human lymph nodes and blood-derived T cells. Increased neuroserpin expression was seen in clusters of T cells in the paracortex of human lymph nodes, with some showing polarization to areas of cell:cell interaction. Our results support a role for neuroserpin and tissue plasminogen activator in activation-controlled proteolytic cleavage of proteins in the synaptic or perisynaptic space to modulate immune cell function.

A natural genetic variant of granzyme B confers lethality to a common viral infection

Many immune response genes are highly polymorphic, consistent with the selective pressure imposed by pathogens over evolutionary time, and the need to balance infection control with the risk of auto-immunity. Epidemiological and genomic studies have identified many genetic variants that confer susceptibility or resistance to pathogenic micro-organisms. While extensive polymorphism has been reported for the granzyme B (GzmB) gene, its relevance to pathogen immunity is unexplored. Here, we describe the biochemical and cytotoxic functions of a common allele of GzmB (GzmB^W) common in wild mouse. While retaining ‘Asp-ase’ activity, GzmB^W has substrate preferences that differ considerably from GzmB^P, which is common to all inbred strains. In vitro, GzmB^W preferentially cleaves recombinant Bid, whereas GzmB^P activates pro-caspases directly. Recombinant GzmB^W and GzmB^P induced equivalent apoptosis of uninfected targets cells when delivered with perforin in vitro. Nonetheless, mice homozygous for GzmB^W were unable to control murine cytomegalovirus (MCMV) infection, and succumbed as a result of excessive liver damage. Although similar numbers of anti-viral CD8 T cells were generated in both mouse strains, GzmB^W-expressing CD8 T cells isolated from infected mice were unable to kill MCMV-infected targets in vitro. Our results suggest that known virally-encoded inhibitors of the intrinsic (mitochondrial) apoptotic pathway account for the increased susceptibility of GzmB^W mice to MCMV. We conclude that different natural variants of GzmB have a profound impact on the immune response to a common and authentic viral pathogen.

Granzymes (Gzm) are serine proteases expressed by cytotoxic T cells and natural killer cells, and are important for the destruction of virally infected cells. To date, the function of these molecules has been assessed exclusively in common laboratory mouse strains that express identical granzyme proteins. In wild mouse populations, variants of granzyme B have been identified, but how these function, especially in the context of infections, is unknown. We have generated a novel mouse strain expressing a granzyme B variant found in wild mice (GzmB^W), and exposed these mice to viral infections. The substrates cleaved by GzmB^W were found to differ significantly from those cleaved by the GzmB^P protein, which is normally expressed by laboratory mice. Alterations in substrate specificity resulted in GzmB^W mice being significantly more susceptible to infection with murine cytomegalovirus, a common mouse pathogen. Our findings demonstrate that polymorphisms in granzyme B can profoundly affect the outcome of infections with some viral pathogens.

A colorimetric assay that specifically measures Granzyme B proteolytic activity: hydrolysis of Boc-Ala-Ala-Asp-S-Bzl

The serine protease Granzyme B (GzmB) mediates target cell apoptosis when released by cytotoxic T lymphocytes (CTL) or natural killer (NK) cells. GzmB is the most studied granzyme in humans and mice and therefore, researchers need specific and reliable tools to study its function and role in pathophysiology. This especially necessitates assays that do not recognize proteases such as caspases or other granzymes that are structurally or functionally related. Here, we apply GzmB's preference for cleavage after aspartic acid residues in a colorimetric assay using the peptide thioester Boc-Ala-Ala-Asp-S-Bzl. GzmB is the only mammalian serine protease capable of cleaving this substrate. The substrate is cleaved with similar efficiency by human, mouse and rat GzmB, a property not shared by other commercially available peptide substrates, even some that are advertised as being suitable for this purpose. This protocol is demonstrated using unfractionated lysates from activated NK cells or CTL and is also suitable for recombinant proteases generated in a variety of prokaryotic and eukaryotic systems, provided the correct controls are used. This assay is a highly specific method to ascertain the potential pro-apoptotic activity of cytotoxic molecules in mammalian lymphocytes, and of their recombinant counterparts expressed by a variety of methodologies.

Quantitative analysis of resistance to natural killer attacks reveals stepwise killing kinetics

Molecular mechanisms can protect cancer cells from immune attacks. At the level of bulk tissue, these survival mechanisms are often indistinguishable and simply appear as reduced cell death. However, by tracking individual cell survival and death times, we found broad variation in the kinetics of immune evasion. In response to attacks by natural killer cells, we observed that some cancer lines exhibited exponential survival time distributions. Slowly killed cancer lines had reduced exponential rate constants. In contrast, a line engineered to express the serpin protein PI-9, which is known to promote resistance to immune killing, exhibited a markedly nonexponential survival time distribution. By following the histories of individual cancer cells with multiplexed reporters, we obtained evidence that two or more immune attacks are likely required to kill serpin-expressing cells. Thus, resistance is a finite and measurable quantity, with a distinct kinetic signature. A quantitative model based on independently measured parameters is consistent with our conclusions.

Identification of Serpinb6b as a species-specific mouse granzyme A inhibitor suggests functional divergence between human and mouse granzyme A

The granzyme family serine proteases are key effector molecules expressed by cytotoxic lymphocytes. The physiological role of granzyme (Gzm) A is controversial, with significant debate over its ability to induce death in target cells. Here, we investigate the natural inhibitors of GzmA. We employed substrate phage display and positional proteomics to compare substrate specificities of mouse (m) and human (h) GzmA at the peptide and proteome-wide levels and we used the resulting substrate specificity profiles to search for potential inhibitors from the intracellular serpin family. We identified Serpinb6b as a potent inhibitor of mGzmA. Serpinb6b interacts with mGzmA, but not hGzmA, with an association constant of 1.9 ± 0.8 × 10(5) M(-1) s(-1) and a stoichiometry of inhibition of 1.8. Mouse GzmA is over five times more cytotoxic than hGzmA when delivered into P815 target cells with streptolysin O, whereas transfection of target cells with a Serpinb6b cDNA increases the EC50 value of mGzmA 13-fold, without affecting hGzmA cytotoxicity. Unexpectedly, we also found that Serpinb6b employs an exosite to specifically inhibit dimeric but not monomeric mGzmA. The identification of an intracellular inhibitor specific for mGzmA only indicates that a lineage-specific increase in GzmA cytotoxic potential has driven cognate inhibitor evolution.

The granzyme B-Serpinb9 axis controls the fate of lymphocytes after lysosomal stress

Cytotoxic lymphocytes (CLs) contain lysosome-related organelles (LROs) that perform the normal degradative functions of the lysosome, in addition to storage and release of powerful cytotoxins employed to kill virally infected or abnormal cells. Among these cytotoxins is granzyme B (GrB), a protease that has also been implicated in activation (restimulation)-induced cell death of natural killer (NK) and T cells, but the underlying mechanism and its regulation are unclear. Here we show that restimulation of previously activated human or mouse lymphocytes induces lysosomal membrane permeabilisation (LMP), followed by GrB release from LROs into the CL cytosol. The model lysosomal stressors sphingosine and Leu-Leu-methyl-ester, and CLs from gene-targeted mice were used to show that LMP releases GrB in both a time- and concentration-dependent manner, and that the liberated GrB is responsible for cell death. The endogenous GrB inhibitor Serpinb9 (Sb9) protects CLs against LMP-induced death but is decreasingly effective as the extent of LMP increases. We also used these model stressors to show that GrB is the major effector of LMP-mediated death in T cells, but that in NK cells additional effectors are released, making GrB redundant. We found that limited LMP and GrB release occurs constitutively in proliferating lymphocytes and in NK cells engaged with targets in vitro. In Ectromelia virus-infected lymph nodes, working NK cells lacking Sb9 are more susceptible to GrB-mediated death. Taken together, these data show that a basal level of LMP occurs in proliferating and activated lymphocytes, and is increased on restimulation. LMP releases GrB from LROs into the lymphocyte cytoplasm and its ensuing interaction with Sb9 dictates whether or not the cell survives. The GrB-Sb9 nexus may therefore represent an additional mechanism of limiting lymphocyte lifespan and populations.

A functional genomics screen identifies PCAF and ADA3 as regulators of human granzyme B-mediated apoptosis and Bid cleavage

The human lymphocyte toxins granzyme B (hGrzB) and perforin cooperatively induce apoptosis of virus-infected or transformed cells: perforin pores enable entry of the serine protease hGrzB into the cytosol, where it processes Bid to selectively activate the intrinsic apoptosis pathway. Truncated Bid (tBid) induces Bax/Bak-dependent mitochondrial outer membrane permeability and the release of cytochrome c and Smac/Diablo. To identify cellular proteins that regulate perforin/hGrzB-mediated Bid cleavage and subsequent apoptosis, we performed a gene-knockdown (KD) screen using a lentiviral pool of short hairpin RNAs embedded within a miR30 backbone (shRNAmiR). We transduced HeLa cells with a lentiviral pool expressing shRNAmiRs that target 1213 genes known to be involved in cell death signaling and selected cells with acquired resistance to perforin/hGrzB-mediated apoptosis. Twenty-two shRNAmiRs were identified in the positive-selection screen including two, PCAF and ADA3, whose gene products are known to reside in the same epigenetic regulatory complexes. Small interfering (si)RNA-mediated gene-KD of PCAF or ADA3 also conferred resistance to perforin/hGrzB-mediated apoptosis providing independent validation of the screen results. Mechanistically, PCAF and ADA3 exerted their pro-apoptotic effect upstream of mitochondrial membrane permeabilization, as indicated by reduced cytochrome c release in PCAF-KD cells exposed to perforin/hGrzB. While overall levels of Bid were unaltered, perforin/hGrzB-mediated cleavage of Bid was reduced in PCAF-KD or ADA3-KD cells. We discovered that PCAF-KD or ADA3-KD resulted in reduced expression of PACS2, a protein implicated in Bid trafficking to mitochondria and importantly, targeted PACS2-KD phenocopied the effect of PCAF-KD or ADA3-KD. We conclude that PCAF and ADA3 regulate Bid processing via PACS2, to modulate the mitochondrial cell death pathway in response to hGrzB.

Granzyme M: behind enemy lines

The granule-exocytosis pathway is the major mechanism via which cytotoxic lymphocytes eliminate virus-infected and tumor cells. In this pathway, cytotoxic lymphocytes release granules containing the pore-forming protein perforin and a family of serine proteases known as granzymes into the immunological synapse. Pore-formation by perforin facilitates entry of granzymes into the target cell, where they can activate various (death) pathways. Humans express five different granzymes, of which granzymes A and B have been most extensively characterized. However, much less is known about granzyme M (GrM). Recently, structural analysis and advanced proteomics approaches have determined the primary and extended specificity of GrM. GrM functions have expanded over the past few years: not only can GrM efficiently induce cell death in tumor cells, it can also inhibit cytomegalovirus replication in a noncytotoxic manner. Finally, a role for GrM in lipopolysaccharide-induced inflammatory responses has been proposed. In this review, we recapitulate the current status of GrM expression, substrate specificity, functions, and inhibitors.

SerpinB1 regulates homeostatic expansion of IL-17+ γδ and CD4+ Th17 cells

SerpinB1 is an endogenous inhibitor of serine proteases recognized for its anti-inflammatory and host-protective properties. Although loss of serpinB1 in mice does not result in gross immune deregulation, serpinb1a(-/-) mice display increased mortality and inflammation-associated morbidity upon challenge with influenza virus. Here, we show that IL-17A(+) γδ and CD4(+) Th17 cells are already expanded in the lungs of serpinb1a(-/-) mice at steady-state. Both γδ and αβ(+) CD4(+) CCR6(+) T cells isolated from the lungs of naive serpinb1a(-/-) mice displayed a skewed transcriptional profile relative to WT cells, including increased Th17 signature transcripts [Il17a, l17f, and Rorc (RORγt)] and decreased Th1 signature transcripts [Ifng, Cxcr3, and Tbx21 (T-bet)] in γδ T cells. In addition to the lung, IL-17A(+) γδ and CD4(+) Th17 cells were increased in the spleen of naive serpinb1a(-/-) mice, despite normal αβ and γδ T cell development in the thymus. Within the γδ T cell compartment, loss of serpinb1a prompted selective expansion of Vγ4(+) and Vγ6/Vδ1(+) cells, which also displayed elevated expression of the proliferating cell nuclear antigen, Ki-67, and IL-17A. Given that serpinb1a is preferentially expressed in WT IL-17A(+) γδ and CD4(+) Th17 cell subsets vis-à-vis other T cell lineages, our findings reveal a novel function of serpinB1 in limiting untoward expansion of lymphocytes with a Th17 phenotype.

Granzyme M targets topoisomerase II alpha to trigger cell cycle arrest and caspase-dependent apoptosis

Cytotoxic lymphocyte protease granzyme M (GrM) is a potent inducer of tumor cell death. The apoptotic phenotype and mechanism by which it induces cell death, however, remain poorly understood and controversial. Here, we show that GrM-induced cell death was largely caspase-dependent with various hallmarks of classical apoptosis, coinciding with caspase-independent G2/M cell cycle arrest. Using positional proteomics in human tumor cells, we identified the nuclear enzyme topoisomerase II alpha (topoIIα) as a physiological substrate of GrM. Cleavage of topoIIα by GrM at Leu(1280) separated topoIIα functional domains from the nuclear localization signals, leading to nuclear exit of topoIIα catalytic activity, thereby rendering it nonfunctional. Similar to the apoptotic phenotype of GrM, topoIIα depletion in tumor cells led to cell cycle arrest in G2/M, mitochondrial perturbations, caspase activation, and apoptosis. We conclude that cytotoxic lymphocyte protease GrM targets topoIIα to trigger cell cycle arrest and caspase-dependent apoptosis.

Suppression of granzyme B activity and caspase-3 activation in leukaemia cells constitutively expressing the protease inhibitor 9

Immune surveillance against malignant cells is mediated by cytotoxic T-lymphocytes and NK-cells (CTL/NK) that induce apoptosis through the granzyme-B-dependent pathway. The serine protease inhibitor serpinB9/protease inhibitor-9 (PI-9) is a known inhibitor of granzyme B. Ectopic expression of PI-9 in tumour cells has been reported. However, the impact of PI-9 on granzyme-B-induced apoptosis in tumour cells remains unclear. The aim of this study was to investigate the influence of constitutive PI-9 expression in leukaemia cell lines on the activity of granzyme B and apoptosis induction. PI-9 negative (lymphoblastic Jurkat cells; myeloblastic U937 cells) and PI-9-expressing cell lines (myeloblastic K562 cells, EBV-transformed LCL-1 and LCL-2 B-cells, lymphoblastic Daudi cells, AML-R cells f leukaemia and the U937 subclone U937PI-9(+)). For accurate granzyme B activity determination a quantitative substrate (Ac-IEPD-pNA) cleavage assay was established and caspase-3 activation measured for apoptosis assessment. Cells were treated with a cytotoxic granule isolate that has previously been shown to induce apoptosis through granzyme B signalling. We found a robust correlation between constitutive PI-9 expression levels and the suppression of granzyme B activity. Further, inhibition of granzyme B translated into reduced caspase-3 activation. We conclude, suppression of granzyme B initiated apoptosis in PI-9-expressing cells could contribute to immune evasion and the measurement of granzyme B activity with our assay might be a useful predictive marker in immune-therapeutic approaches against cancer.

Ultrastructural and functional analysis of secretory goblet cells in the midgut of the lepidopteran Anticarsia gemmatalis

Defoliation caused by Anticarsia gemmatalis larvae affects the commercial production of the soybean. Although regulation of the digestion of soybean components has become part of the suggested strategy to overcome problems caused by Anticarsia larvae, few studies have focused on the morphological and cellular aspects of Anticarsia intestinal tissue. We have therefore further analyzed the morphology and ultrastructure of the midgut of 5th instar larvae of A. gemmatalis. Dissected midgut was subjected to chemical or cryo-fixation and then to several descriptive and analytical techniques associated with both light and electron microscopy in order to correlate anatomical and physiological aspects of this organ. Histological analysis revealed typical anatomy composed of a cell layer limited by a peritrophic membrane. The identified lepidoptera-specific goblet cells were shown to contain several mitochondria inside microvilli of the goblet cell cavity and a vacuolar H(+)-ATPase possibly coupled to a K(+)-pumping system. Columnar cells were present and exhibited microvilli dispersed along the apical region that also presented secretory characteristics. We additionally found evidence for the secretion of polyphosphate (PolyP) into the midgut, a result corroborating previous reports suggesting an excretion route from the goblet cell cavity toward the luminal space. Thus, our results suggest that the Anticarsia midgut not only possesses several typical lepidopteran features but also presents some unique aspects such as the presence of a tubular network and PolyP-containing apocrine secretions, plus an apparent route for the release of cellular debris by the goblet cells.

Research progresses in the pathogenesis of anaplastic large cell lymphoma

Anaplastic large cell lymphoma (ALCL) is a distinct subset of T-cell non-Hodgkin's lymphoma. As a consequence of its low incidence, general pathogenic consideration of ALCL is lacking. In this review, we summarize the pathogenesis, epidemiology, clinical manifestations, and treatment of ALCL, so as to better understand key stages of the development of this disease and provide valuable information for future treatment.

Design of human granzyme B variants resistant to serpin B9

Human granzyme B (hGB) is a serine protease involved in immune-mediated apoptosis. Its cytotoxicity makes it potentially applicable in cancer therapy. However, the effectiveness of hGB can be hampered by the cytosolic expression of a natural protein inhibitor, human Serpin B9 (hSB9). Here, we used computational approaches to identify hGB mutations that can affect its binding to hSB9 without significantly decreasing its catalytic efficiency. Alanine-scanning calculations allowed us to identify residues of hGB important for the interaction with hSB9. Some variants were selected, and molecular dynamic simulations on the mutated hGB in complex with hSB9 in aqueous solution were carried out to investigate the effect of these variants on the stability of the complex. The R28K, R201A, and R201K mutants significantly destabilized the interaction of the protein with hSB9. Consistently, all of these variants also retained their activity in the presence of the Serpin B9 inhibitor in subsequent in vitro assays of wild-type and mutated hGB. In particular, the activity of R201K hGB with and without Serpin B9 is very similar to that of the wild-type protein. Hence, R201K hGB emerges as a promising species for antitumoral therapy applications.

Serpinb9 (Spi6)-deficient mice are impaired in dendritic cell-mediated antigen cross-presentation

Serpinb9 (Sb9, also called Spi6) is an intracellular inhibitor of granzyme B (GrB) that protects activated cytotoxic lymphocytes from apoptosis. We show here that the CD8(+) subset of splenic dendritic cells (DC), specialized in major histocompatibility complex class I (MHC I) presentation of exogenous antigens (cross-presentation), produce high levels of Sb9. Mice deficient in Sb9 are unable to generate a cytotoxic T-cell response against cell-associated antigen by cross-presentation, but maintain normal MHC-II presentation to helper T cells. This impaired cross-priming ability is autonomous to DC and is evident in animals deficient in both Sb9 and GrB, indicating that this role of Sb9 in DC is GrB-independent. In Sb9-deficient mice, CD8(+) DC develop normally, survive as well as wild-type DC after antigenic challenge, and exhibit unimpaired capacity to take up antigen. Although the core processing machinery is unaffected, Sb9-deficient DC appear to process antigen faster. Our results point to a novel, GrB-independent role for Sb9 in DC cross-priming.

Granzyme B triggers a prolonged pressure to die in Bcl-2 overexpressing cells, defining a window of opportunity for effective treatment with ABT-737

Overexpression of Bcl-2 contributes to resistance of cancer cells to human cytotoxic lymphocytes (CL) by blocking granzyme B (GraB)-induced mitochondrial outer membrane permeabilization (MOMP). Drugs that neutralise Bcl-2 (e.g., ABT-737) may therefore be effective adjuvants for immunotherapeutic strategies that use CL to kill cancer cells. Consistent with this we found that ABT-737 effectively restored MOMP in Bcl-2 overexpressing cells treated with GraB or natural killer cells. This effect was observed even if ABT-737 was added up to 16 h after GraB, after which the cells reset their resistant phenotype. Sensitivity to ABT-737 required initial cleavage of Bid by GraB (gctBid) but did not require ongoing GraB activity once Bid had been cleaved. This gctBid remained detectable in cells that were sensitive to ABT-737, but Bax and Bak were only activated if ABT-737 was added to the cells. These studies demonstrate that GraB generates a prolonged pro-apoptotic signal that must remain active for ABT-737 to be effective. The duration of this signal is determined by the longevity of gctBid but not activation of Bax or Bak. This defines a therapeutic window in which ABT-737 and CL synergise to cause maximum death of cancer cells that are resistant to either treatment alone, which will be essential in defining optimum treatment regimens.

Protecting a serial killer: pathways for perforin trafficking and self-defence ensure sequential target cell death

Considerable progress has been made in understanding how cytotoxic lymphocytes use the highly toxic pore-forming protein perforin to eliminate dangerous cells, while remaining refractory to lysis. At least two mechanisms jointly preserve the killer cell: the C-terminal residues of perforin dictate its rapid export from the endoplasmic reticulum (ER), whose milieu otherwise favours pore formation; perforin is then stored in secretory granules whose acidity prevent its oligomerisation. Following exocytosis, perforin delivers the proapoptotic protease, granzyme B, into the target cell by disrupting its plasma membrane. Although the precise mechanism of perforin/granzyme synergy remains controversial, the recently defined crystal structure of the perforin monomer and cryo-electron microscopy (EM) of the entire pore suggest that passive transmembrane granzyme diffusion is the dominant proapoptotic mechanism.

Immunodetection of granzyme B tissue distribution and cellular localisation

Investigation of Granzyme B (GrB) function and pathophysiology in both human settings and rodent models increasingly involve the use of indirect immunofluorescence imaging and fluorescence-activated cell sorting, which requires reliable GrB antibodies that do not recognise other closely related granzymes. Here, we describe the validation (using a set of recombinant granzymes, and GrB-deficient cells) and application of widely available monoclonal antibodies to specifically monitor GrB in human or mouse cells.

Induction of serine protease inhibitor 9 by Mycobacterium tuberculosis inhibits apoptosis and promotes survival of infected macrophages

Our recent microarray analysis of infected human alveolar macrophages (AMs) found serine protease inhibitor 9 (PI-9) to be the most prominently expressed of a cluster of apoptosis-associated genes induced by virulent Mycobacterium tuberculosis. In the current study, we show that induction of PI-9 occurs within hours of infection with M. tuberculosis H37Rv and is maintained through 7 days of infection in both AMs and blood monocytes. Inhibition of PI-9 by small inhibitory RNA decreased M. tuberculosis-induced expression of the antiapoptotic molecule Bcl-2 and resulted in a corresponding increase in production of caspase 3, a terminal effector molecule of apoptosis. Further, PI-9 small inhibitory RNA mediated a significant reduction in the subsequent survival of M. tuberculosis within AMs. Thus PI-9 induction within human mononuclear phagocytes by virulent M. tuberculosis serves to protect these primary targets of infection from elimination by apoptosis and thereby promotes intracellular survival of the organism.

Intracellular serine protease inhibitor SERPINB4 inhibits granzyme M-induced cell death

Granzyme-mediated cell death is the major pathway for cytotoxic lymphocytes to kill virus-infected and tumor cells. In humans, five different granzymes (i.e. GrA, GrB, GrH, GrK, and GrM) are known that all induce cell death. Expression of intracellular serine protease inhibitors (serpins) is one of the mechanisms by which tumor cells evade cytotoxic lymphocyte-mediated killing. Intracellular expression of SERPINB9 by tumor cells renders them resistant to GrB-induced apoptosis. In contrast to GrB, however, no physiological intracellular inhibitors are known for the other four human granzymes. In the present study, we show that SERPINB4 formed a typical serpin-protease SDS-stable complex with both recombinant and native human GrM. Mutation of the P2-P1-P1′ triplet in the SERPINB4 reactive center loop completely abolished complex formation with GrM and N-terminal sequencing revealed that GrM cleaves SERPINB4 after P1-Leu. SERPINB4 inhibited GrM activity with a stoichiometry of inhibition of 1.6 and an apparent second order rate constant of 1.3×10⁴ M⁻¹s⁻¹. SERPINB4 abolished cleavage of the macromolecular GrM substrates α-tubulin and nucleophosmin. Overexpression of SERPINB4 in tumor cells inhibited recombinant GrM-induced as well as NK cell-mediated cell death and this inhibition depended on the reactive center loop of the serpin. As SERPINB4 is highly expressed by squamous cell carcinomas, our results may represent a novel mechanism by which these tumor cells evade cytotoxic lymphocyte-induced GrM-mediated cell death.

Protection from endogenous perforin: glycans and the C terminus regulate exocytic trafficking in cytotoxic lymphocytes

Cytotoxic lymphocyte-mediated apoptosis is dependent on the delivery of perforin to secretory granules and its ability to form calcium-dependent pores in the target cell after granule exocytosis. It is unclear how cytotoxic lymphocytes synthesize and store perforin without incurring damage or death. We discovered that the extreme C terminus of perforin was essential for rapid trafficking from the endoplasmic reticulum to the Golgi compartment. Substitution of the C-terminal tryptophan residue resulted in retention of perforin in the ER followed by calcium-dependent toxic activity that eliminated host cells. We also found that N-linked glycosylation of perforin was critical for transport from the Golgi to secretory granules. Overall, an intact C terminus and N-linked glycosylation provide accurate and efficient export of perforin from the endoplasmic reticulum to the secretory granules and are critical for cytotoxic lymphocyte survival.

Inhibition of lung serine proteases in mice: a potentially new approach to control influenza infection

BACKGROUND

Host serine proteases are essential for the influenza virus life cycle because the viral haemagglutinin is synthesized as a precursor which requires proteolytic maturation. Therefore, we studied the activity and expression of serine proteases in lungs from mice infected with influenza and evaluated the effect of serine protease inhibitors on virus replication both in cell culture and in infected mice.

RESULTS

Two different inbred mouse strains were investigated: DBA/2J as a highly susceptible and C57Bl/6J as a more resistant strain to influenza virus infection. The serine proteases from lung homogenates of mice exhibited pH optima of 10.00. Using the substrate Bz-Val-Gly-Arg-p-nitroanilide or in zymograms, the intensities of proteolysis increased in homogenates from both mouse strains with time post infection (p.i.) with the mouse-adapted influenza virus A/Puerto Rico/8/34 (H1N1; PR8). In zymograms at day 7 p.i., proteolytic bands were stronger and numerous in lung homogenates from DBA/2J than C57Bl/6J mice. Real-time PCR results confirmed differential expression of several lung proteases before and after infecting mice with the H1N1 virus. The most strongly up-regulated proteases were Gzma, Tmprss4, Elane, Ctrl, Gzmc and Gzmb. Pretreatment of mouse and human lung cell lines with the serine protease inhibitors AEBSF or pAB or a cocktail of both prior to infection with the H1N1 or the A/Seal/Massachusetts/1/80 (H7N7; SC35M) virus resulted in a decrease in virus replication. Pretreatment of C57Bl/6J mice with either AEBSF or a cocktail of AEBSF and pAB prior to infection with the H1N1 virus significantly reduced weight loss and led to a faster recovery of treated versus untreated mice while pAB alone exerted a very poor effect. After infection with the H7N7 virus, the most significant reduction of weight loss was obtained upon pretreatment with either the protease inhibitor cocktail or pAB. Furthermore, pretreatment of C57BL/6J mice with AEBSF prior to infection resulted in a significant reduction in the levels of both the H1N1 and H7N7 nucleoproteins in mice lungs and also a significant reduction in the levels of the HA transcript in the lungs of the H1N1--but not the H7N7-infected mice.

CONCLUSION

Multiple serine protease activities might be implicated in mediating influenza infection. Blocking influenza A virus infection in cultured lung epithelia and in mice by the used serine protease inhibitors may provide an alternative approach for treatment of influenza infection.

Regulation of proteases by protein inhibitors of the serpin superfamily

The serpins comprise an ancient superfamily of proteins, found abundantly in eukaryotes and even in some bacteria and archea, that have evolved to regulate proteases of both serine and cysteine mechanistic classes. Unlike the thermodynamically determined lock-and-key type inhibitors, such as those of the Kunitz and Kazal families, serpins use conformational change and consequent kinetic trapping of an enzyme intermediate to effect inhibition. By combining interactions of both an exposed reactive center loop and exosites outside this loop with the active site and complementary exosites on the target protease, serpins can achieve remarkable specificity. Together with the frequent use of regulatory cofactors, this permits a sophisticated time- and location-dependent mode of protease regulation. An understanding of the structure and function of serpins has suggested that they may provide novel scaffolds for engineering protease inhibitors of desired specificity for therapeutic use.

A truncating mutation in SERPINB6 is associated with autosomal-recessive nonsyndromic sensorineural hearing loss

More than 270 million people worldwide have hearing loss that affects normal communication. Although astonishing progress has been made in the identification of more than 50 genes for deafness during the past decade, the majority of deafness genes are yet to be identified. In this study, we mapped a previously unknown autosomal-recessive nonsyndromic sensorineural hearing loss locus (DFNB91) to chromosome 6p25 in a consanguineous Turkish family. The degree of hearing loss was moderate to severe in affected individuals. We subsequently identified a nonsense mutation (p.E245X) in SERPINB6, which is located within the linkage interval for DFNB91 and encodes for an intracellular protease inhibitor. The p.E245X mutation cosegregated in the family as a completely penetrant autosomal-recessive trait and was absent in 300 Turkish controls. The mRNA expression of SERPINB6 was reduced and production of protein was absent in the peripheral leukocytes of homozygotes, suggesting that the hearing loss is due to loss of function of SERPINB6. We also demonstrated that SERPINB6 was expressed primarily in the inner ear hair cells. We propose that SERPINB6 plays an important role in the inner ear in the protection against leakage of lysosomal content during stress and that loss of this protection results in cell death and sensorineural hearing loss.

Perforin: more than just a pore-forming protein

Cellular apoptosis induced by T cells is mainly mediated by two pathways. One, granule exocytosis utilizes perforin/granzymes. The other involves signaling through death receptors of the TNF-alpha R super-family, especially FasL. Perforin plays a central role in apoptosis induced by granzymes. However, the mechanisms of perforin-mediated cytotoxicity are still not elucidated completely. Perforin is not only a pore-forming protein, but also performs multiple biological functions or perforin performs one biological function (cytolysis), but has multiple biological implications in the cellular immune responses, including regulation of proliferation of CD8+ CTLs.

Perforin deficiency and susceptibility to cancer

Cytotoxic lymphocytes (CLs) are the killer cells that destroy intracellular pathogen-infected and transformed cells, predominantly through the cytotoxic granule-mediated death pathway. Soluble cytotoxic granule components, including pore-forming perforin and pro-apoptotic serine proteases, granzymes, synergize to induce unscheduled apoptosis of the target cell. A complete loss of CL function results in an aggressive immunoregulatory disorder, familial hemophagocytic lymphohistiocytosis, whereas a partial loss of function seems to be a factor strongly predisposing to hematological malignancies. This review discusses the pathological manifestations of CL deficiencies due to impaired perforin function and describes novel aspects of perforin biology.

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.

Inhibition of human initiator caspase 8 and effector caspase 3 by cross-class inhibitory bovSERPINA3-1 and A3-3

Serpins are a superfamily of structurally conserved proteins. Inhibitory serpins use a suicide substrate-like mechanism. Some are able to inhibit cysteine proteases in cross-class inhibition. Here, we demonstrate for the first time the strong inhibition of initiator and effector caspases 3 and 8 by two purified bovine SERPINA3s. SERPINA 3-1 (uniprotkb:Q9TTE1) binds tighly to human CASP3 (uniprotkb:P42574) and CASP8 (uniprotkb:Q14790) with k(ass) of 4.2x10(5) and 1.4x10(6) M(-1)s(-1), respectively. A wholly similar inhibition of human CASP3 and CASP8 by SERPINA3-3 (uniprotkb:Q3ZEJ6) was also observed with k(ass) of 1.5x10(5) and 2.7x10(6) M(-1)s(-1), respectively and form SDS-stable complexes with both caspases. By site-directed mutagenesis of bovSERPINA3-3, we identified Asp(371) as the potential P1 residue for caspases. The ability of other members of this family to inhibit trypsin and caspases was analysed and discussed.

The role of cathepsins in involution and breast cancer

Cysteine cathepsins are proteolytic enzymes that reside in endolysosomal vesicles. Some are expressed constitutively while others are transcriptionally regulated. However, the expression and subcellular localization of cathepsins changes during cancer progression and cathepsins have been shown to be causally involved in various aspects of tumorigenesis including metastasis. The use of mouse models of breast cancer genetically ablated for cathepsin B has shown that both the growth of the primary tumor and the extend of lung metastasis is reduced by the loss of cathepsin B. The role of cathepsins in involution of the mammary gland has received little attention although it is clear that cathepsins are involved in tissue remodeling in the second phase of involution. We discuss here the roles of cathepsins and their endogenous inhibitors in breast tumorigenesis and post-lactational involution.

HBZ is an immunogenic protein, but not a target antigen for human T-cell leukemia virus type 1-specific cytotoxic T lymphocytes

Recently, HBZ has been reported to play an important role in the proliferation of adult T-cell leukaemia (ATL) cells and might be a target of novel therapy for ATL. To develop a novel immunotherapy for ATL, we verified the feasibility of cellular immunotherapy targeting HBZ. We established an HBZ-specific and HLA-A*0201-restricted cytotoxic T lymphocyte (CTL) clone. Detailed study using this CTL clone clearly showed that HBZ is certainly an immunogenic protein recognizable by human CTLs; however, HBZ-specific CTLs could not lyse ATL cells. Failure of HBZ-specific CTLs to recognize human T-cell leukemia virus type 1 (HTLV-1)-infected cells might be due to a low level of HBZ protein expression in ATL cells and resistance of HTLV-1-infected cells to CTL-mediated cytotoxicity. Although HBZ plays an important role in the proliferation of HTLV-1-infected cells, it may also provide a novel mechanism that allows them to evade immune recognition.

SERPINB3, apoptosis and autoimmunity

SERPINB3 (Squamous Cell Carcinoma Antigen, SCCA1) is a member of the ov-serpins, a serine protease inhibitors family expressed in many cell types including normal epithelium, leukocytes, tumors of epithelial origin and primary liver cancer. Several studies, carried out in vitro and in vivo, have documented an important role of SERPINB3 in the modulation of programmed cell death by different mechanisms, both in inflammatory processes and in cancer. SERPINB3 significantly attenuates apoptosis by contrasting cytochrome c release from the mitochondria and by antichemotactic effect for NK cells. Mechanisms involved in apoptosis induction and regulation play a key role in the balance between cell proliferation and death. Imbalance of this equilibrium may contribute to the development of autoimmune diseases, as defective apoptosis of immune cells leads to deregulated autoreactive cell proliferation. Since defective programmed cell death represents a critical feature of autoimmunity, the involvement of SERPINB3 in this pathological field deserves further studies.

ICAM-1 has a critical role in the regulation of metastatic melanoma tumor susceptibility to CTL lysis by interfering with PI3K/AKT pathway

Human primary melanoma cells (T1) were found to be more susceptible to lysis by a Melan-A/MART-1-specific CTL clone (LT12) than their metastatic derivative (G1). We show that this differential susceptibility does not involve antigen presentation by target cells, synapse formation between the metastatic target and CTL clone, or subsequent granzyme B (GrB) polarization. Although PI-9, an inhibitor of GrB, was found to be overexpressed in metastatic G1 cells, knockdown of the PI-9 gene did not result in the attenuation of G1 resistance to CTL-induced killing. Interestingly, we show that whereas T1 cells express high levels of intercellular adhesion molecule-1 (ICAM-1), a dramatically reduced expression was noted on G1 cells. We also showed that sorted ICAM-1+ G1 cells were highly sensitive to CTL-induced lysis compared with ICAM-1- G1 cells. Furthermore, incubation of metastatic G1 cells with IFN-gamma resulted in the induction of ICAM-1 and the potentiation of their susceptibility to lysis by LT12. More importantly, we found that the level of ICAM-1 expression by melanoma cells correlated with decreased PTEN activity. ICAM-1 knockdown in T1 cells resulted in increased phosphorylation of PTEN and the subsequent activation of AKT. We have additionally shown that inhibition of the phosphatidylinositol (3,4,5)-triphosphate kinase (PI3K)/AKT pathway by the specific inhibitor wortmannin induced a significant potentiation of susceptibility of G1 and ICAM-1 small interfering RNA-treated T1 cells to CTL-induced lysis. The present study shows that a shift in ICAM-1 expression, which was associated with an activation of the PI3K/AKT pathway, can be used by metastatic melanoma cells to escape CTL-mediated killing.

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.

The serpin saga; development of a new class of virus derived anti-inflammatory protein immunotherapeutics

Serine proteinase inhibitors, also called serpins, are an ancient grouping of proteins found in primitive organisms from bacteria, protozoa and horseshoe crabs and thus likely present at the time of the dinosaurs, up to all mammals living today. The innate or inflammatory immune system is also an ancient metazoan regulatory system, providing the first line of defense against infection or injury. The innate inflammatory defense response evolved long before acquired, antibody dependent immunity. Viruses have developed highly effective stratagems that undermine and block a wide variety of host inflammatory and immune responses. Some of the most potent of these immune modifying strategies utilize serpins that have also been developed over millions of years, including the hijacking by some viruses for defense against host immune attacks. Serpins represent up to 2-10 percent of circulating plasma proteins, regulating actions as wide ranging as thrombosis, inflammation, blood pressure control and even hormone transport. Targeting serpin-regulated immune or inflammatory pathways makes evolutionary sense for viral defense and many of these virus-derived inhibitory proteins have proven to be highly effective, working at very low concentrations--even down to the femptomolar to picomolar range. We are studying these viral anti-inflammatory proteins as a new class of immunomodulatory therapeutic agents derived from their native viral source. One such viral serpin, Serp-1 is now in clinical trial (conducted by VIRON Therapeutics, Inc.) for acute unstable coronary syndromes (unstable angina and small heart attacks), representing a 'first in class' therapeutic study. Several other viral serpins are also currently under investigation as anti-inflammatory or anti-immune therapeutics. This chapter describes these original studies and the ongoing analysis of viral serpins as a new class of virus-derived immunotherapeutic.

Granzyme C supports efficient CTL-mediated killing late in primary alloimmune responses

It is well established that granzymes A and B play a role in CTL killing of target cells by the perforin-dependent granule exocytosis pathway. The functions of multiple additional granzymes expressed in CTL are less well defined. In the present studies, CTL generated from mice deficient in dipeptidyl peptidase 1 (DPP1) were used to investigate the contribution of granzyme C to CTL killing of allogeneic target cells. DPP1 is required for activation of granzymes A and B by proteolytic removal of their N-terminal dipeptide prodomains while a significant portion of granzyme C is processed normally in the absence of DPP1. Cytotoxicity of DPP1(-/-) CTL generated in early (5-day) MLC in vitro and in peritoneal exudate cells 5 days after initial allogeneic sensitization in vivo was significantly impaired compared with wild-type CTL. Following 3 days of restimulation with fresh allogeneic stimulators however, cytotoxicity of these DPP1(-/-) effector cells was comparable to that of wild-type CTL. Killing mediated by DPP1(-/-) CTL following restimulation was rapid, perforin dependent, Fas independent and associated with early mitochondrial injury, phosphatidyl serine externalization, and DNA degradation, implicating a granzyme-dependent apoptotic pathway. The increased cytotoxicity of DPP1(-/-) CTL following restimulation coincided with increased expression of granzyme C. Moreover, small interfering RNA inhibition of granzyme C expression during restimulation significantly decreased cytotoxicity of DPP1(-/-) but not wild-type CTL. These results indicate that during late primary alloimmune responses, granzyme C can support CTL-mediated killing by the granule exocytosis pathway in the absence of functional granzymes A or B.

Transplantation survival is maintained by granzyme B+ regulatory cells and adaptive regulatory T cells

Granzyme B (GZB) has been implicated as an effector mechanism in regulatory T cells (T(reg)) suppression. In a model of T(reg)-dependent graft tolerance, it is shown that GZB- deficient mice are unable to establish long-term tolerance. Moreover, mice overexpressing the inhibitor of GZB, serine protease inhibitor 6, are also resistant to tolerization to alloantigen. Graft survival was shorter in bone marrow-mixed chimeras reconstituted with GZB-deficient T(reg) as compared with wild-type T(reg). Whereas there was no difference in graft survival in mixed chimeras reconstituted with wild-type, perforin-deficient, or Fas ligand-deficient T(reg). Finally, data also show that if alloreactive effectors cannot express FoxP3 and be induced to convert in the presence of competent T(reg), then graft tolerance is lost. Our data are the first in vivo data to implicate GZB expression by T(reg) in sustaining long-lived graft survival.