IFN-gamma increases cathepsin H mRNA levels in mouse macrophages

Transcriptomic and proteomic study of cancer cell lines exposed to actinomycin D and nutlin-3a reveals numerous, novel candidates for p53-regulated genes

Transcriptomic analyses have revealed hundreds of p53-regulated genes; however, these studies used a limited number of cell lines and p53-activating agents. Therefore, we searched for candidate p53-target genes by employing stress factors and cell lines never before used in a high-throughput search for p53-regulated genes. We performed RNA-Seq on A549 cells exposed to camptothecin, actinomycin D, nutlin-3a, as well as a combination of actinomycin D and nutlin-3a (A + N). The latter two substances synergise upon the activation of selected p53-target genes. A similar analysis was performed on other cell lines (U-2 OS, NCI-H460, A375) exposed to A + N. To identify proteins in cell lysates or those secreted into a medium of A549 cells in control conditions or treated with A + N, we employed mass spectrometry. The expression of selected genes strongly upregulated by A + N or camptothecin was examined by RT-PCR in p53-deficient cells and their controls. We found that p53 participates in the upregulation of: ACP5, APOL3, CDH3, CIBAR2, CRABP2, CTHRC1, CTSH, FAM13C, FBXO2, FRMD8, FRZB, GAST, ICOSLG, KANK3, KCNK6, KLRG2, MAFB, MR1, NDRG4, PTAFR, RETSAT, TMEM52, TNFRSF14, TRANK1, TYSND1, WFDC2, WFDC5, WNT4 genes. Twelve of these proteins were detected in the secretome and/or proteome of treated cells. Our data generated new hypotheses concerning the functioning of p53. Many genes activated by A + N or camptothecin are also activated by interferons, indicating a noticeable overlap between transcriptional programs of p53 and these antiviral cytokines. Moreover, several identified genes code for antagonists of WNT/β-catenin signalling pathways, which suggests new connections between these two cancer-related signalling systems. One of these antagonists is DRAXIN. Previously, we found that its gene is activated by p53. In this study, using mass spectrometry and Western blotting, we detected expression of DRAXIN in a medium of A549 cells exposed to A + N. Thus, this protein functions not only in the development of the nervous system, but it may also have a new cancer-related function.

Cathepsin H: molecular characteristics and clues to function and mechanism

Cathepsin H (CatH) is a lysosomal cysteine protease with a unique aminopeptidase activity that is extensively expressed in the lung, pancreas, thymus, kidney, liver, skin, and brain. Owing to its specific enzymatic activity, CatH has critical effects on the regulation of biological behaviours of cancer cells and pathological processes in brain diseases. Moreover, a neutral pH level is optimal for CatH activity, so it is expected to be active in the extra-lysosomal and extracellular space. In the present review, we describe the expression, maturation, and enzymatic properties of CatH, and summarize the available experimental evidence that mechanistically links CatH to various physiological and pathological processes. Finally, we discuss the challenges and potentials of CatH inhibitors in CatH-induced disease therapy.

Immune-related gene expression signatures in colorectal cancer

The immune system is crucial in regulating colorectal cancer (CRC) tumorigenesis. Identification of immune-related transcriptomic signatures derived from the peripheral blood of patients with CRC would provide insights into CRC pathogenesis, and suggest novel clues to potential immunotherapy strategies for the disease. The present study collected blood samples from 59 patients with CRC and 62 healthy control patients and performed whole blood gene expression profiling using microarray hybridization. Immune-related gene expression signatures for CRC were identified from immune gene datasets, and an algorithmic predictive model was constructed for distinguishing CRC from controls. Model performance was characterized using an area under the receiver operating characteristic curve (ROC AUC). Functional categories for CRC-specific gene expression signatures were determined using gene set enrichment analyses. A Kaplan-Meier plotter survival analysis was also performed for CRC-specific immune genes in order to characterize the association between gene expression and CRC prognosis. The present study identified five CRC-specific immune genes [protein phosphatase 3 regulatory subunit Bα (PPP3R1), amyloid β precursor protein, cathepsin H, proteasome activator subunit 4 and DEAD-Box Helicase 3 X-Linked]. A predictive model based on this five-gene panel showed good discriminatory power (independent test set sensitivity, 83.3%; specificity, 94.7%, accuracy, 89.2%; ROC AUC, 0.96). The candidate genes were involved in pathways associated with ‘adaptive immune responses’, ‘innate immune responses’ and ‘cytokine signaling’. The survival analysis found that a high level of PPP3R1 expression was associated with a poor CRC prognosis. The present study identified five CRC-specific immune genes that were potential diagnostic biomarkers for CRC. The biological function analysis indicated a close association between CRC pathogenesis and the immune system, and may reveal more information about the immunogenic and pathogenic mechanisms driving CRC in the future. Overall, the association between PPP3R1 expression and survival of patients with CRC revealed potential new targets for CRC immunotherapy.

Innate, adaptive, and cell-autonomous immunity against Toxoplasma gondii infection

Hosts have been fighting pathogens throughout the evolution of all infectious diseases. Toxoplasma gondii is one of the most common infectious agents in humans but causes only opportunistic infection in healthy individuals. Similar to antimicrobial immunity against other organisms, the immune response against T. gondii activates innate immunity and in turn induces acquired immune responses. After activation of acquired immunity, host immune cells robustly produce the proinflammatory cytokine interferon-γ (IFN-γ), which activates a set of IFN-γ-inducible proteins, including GTPases. IFN-inducible GTPases are essential for cell-autonomous immunity and are specialized for effective clearance and growth inhibition of T. gondii by accumulating in parasitophorous vacuole membranes. Recent studies suggest that the cell-autonomous immune response plays a protective role in host defense against not only T. gondii but also various intracellular bacteria. Moreover, the negative regulatory mechanisms of such strong immune responses are also important for host survival after infection. In this review, we will discuss in detail recent advances in the understanding of host defenses against T. gondii and the roles played by cell-autonomous immune responses.

Researchers are extensively studying immune responses to the single-celled parasite Toxoplasma gondii, which infects around one-third of humans, often harmlessly, but can cause life-threatening toxoplasmosis infections in patients with weakened immune systems. Masahiro Yamamoto and Miwa Sasai at Osaka University in Japan review recent advances in understanding the interactions between the immune system and the parasite. They consider non-specific ‘innate’ immune responses and also the ‘acquired’ responses that target specific parts of the parasite, referred to as antigens. Methods that selectively switch off genes in mice are revealing details presumed to also be relevant for humans. Significant molecules, molecular signaling pathways and immune-regulating processes are being identified. Recent studies suggest cell-autonomous immunity, the ability of host cells to defend themselves against attack, plays a significant role in fighting Toxoplasma gondii infection.

The proinflammatory effects of macrophage-derived NADPH oxidase function in autoimmune diabetes

Type 1 diabetes (T1D) is an autoimmune disease culminating in the destruction of insulin-producing pancreatic β-cells. While ultimately a T cell-mediated disease, macrophages play an indispensable role in disease initiation and progression. Infiltrating macrophages generate an inflammatory environment by releasing NADPH oxidase-derived superoxide and proinflammatory cytokines. The synthesis of reactive oxygen species (ROS) is acknowledged as putative factors contributing to autoimmunity and β-cell damage in T1D. In addition to direct lysis, free radicals collectively participate in β-cell destruction by providing a redox-dependent third signal necessary for islet-reactive CD4 and CD8 T cell maturation and by inducing oxidative post-translational modifications of β-cell epitopes to further exacerbate autoimmune responses. This review will provide an overview of macrophage function and a synergistic cross-talk with redox biology that contributes to autoimmune dysregulation in T1D.

Cathepsin H deficiency in mice induces excess Th1 cell activation and early-onset of EAE though impairment of toll-like receptor 3 cascade

OBJECTIVE

The objective of this study is to investigate the role of cathepsin H (CatH), a lysosomal cysteine protease, in the development of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis.

METHODS

EAE was induced in CatH-deficient mice (CatH^-/-) and wild-type littermates (+/+) using myelin oligodendrocyte glycoprotein (MOG) 35-55. The effects of CatH deficiency were determined by clinical scoring, mRNA expression levels of Tbx21, Rorc and FoxP3, protein levels of poly(I:C)-induced toll-like receptor 3 (TLR3) and phosphorylation of IRF3, and secretion of interferon-β (IFN-β) by splenocytes.

RESULTS AND CONCLUSIONS

CatH^-/- showed a significantly earlier disease onset of EAE and increased Th1 cell differentiation in splenocytes. Splenocytes prepared from immunized CatH^-/- showed a significant decrease in poly(I:C)-induced increased TLR3 expression, interferon regulatory factor 3 (IRF3) phospholylation and IFN-β secretion. Therefore, CatH deficiency impaired TLR3-mediated activation of IRF3 and consequent secretion of IFN-β from dendritic cells, leading to the enhancement of Th1 cell differentiation and consequent early disease onset of EAE.

The induction of neuronal death by up-regulated microglial cathepsin H in LPS-induced neuroinflammation

BACKGROUND

Neuroinflammation is a hallmark that leads to selective neuronal loss and/or dysfunction in neurodegenerative disorders. Microglia-derived lysosomal cathepsins are increasingly recognized as important inflammatory mediators to trigger signaling pathways that aggravate neuroinflammation. However, cathepsin H (Cat H), a cysteine protease, has been far less studied in neuroinflammation, compared to cathepsins B, D, L, and S. The expression patterns and functional roles of Cat H in the brain in neuroinflammation remain unknown.

METHODS

C57BL/6J mice were intraperitoneally injected with either 0.9% saline or lipopolysaccharide (LPS, 5 mg/kg). Immunohistochemistry (IHC) and in situ hybridization (ISH) were used to analyze expression and localization of Cat H in the brain. Nitrite assay was used to examine microglial activation in vitro; ELISA was used to determine the release of Cat H and proinflammatory cytokines (TNF-α, IL-1β, IL-6, IFN-γ). Cat H activity was analyzed by cellular Cat H assay kit. Flow cytometry and in situ cell death detection were used to investigate neuronal death. Data were evaluated for statistical significance with one-way ANOVA and t test.

RESULTS

Cat H mRNA was only present in perivascular microglia and non-parenchymal sites under normal conditions. After LPS injection, Cat H mRNA expression in activated microglia in different brain regions was increased. Twenty-four hours after LPS injection, Cat H mRNA expression was maximal in SNr; 72 h later, it peaked in cerebral cortex and hippocampus then decreased and maintained at a low level. The expression of Cat H protein exhibited the similar alterations after LPS injection. In vitro, inflammatory stimulation (LPS, TNF-α, IL-1β, IL-6, and IFN-γ) increased the release and activity of Cat H in microglia. Conversely, addition of Cat H to microglia promoted the production and release of NO, IL-1β, and IFN-γ which could be prevented by neutralizing antibody. Further, addition of Cat H to Neuro2a cells induced neuronal death.

CONCLUSIONS

Taken together, these data indicate that the up-regulated microglial Cat H expression, release, and activity in the brain lead to neuronal death in neuroinflammation. The functional link of Cat H with microglial activation might contribute to the initiation and maintenance of microglia-driven chronic neuroinflammation.

Enhanced Dendritic Cell-Mediated Antigen-Specific CD4+ T Cell Responses: IFN-Gamma Aids TLR Stimulation

Phenotypic maturation and T cell stimulation are two functional attributes of DCs critical for immune induction. The combination of antigens, including those from cancer, with Toll-like receptor (TLR) ligands induces far superior cellular immune responses compared to antigen alone. In this study, IFN-gamma treatment of bone marrow-derived DC, followed by incubation with the TLR2, TLR4, or TLR9 agonists, enhanced DC activation compared to TLR ligation alone. Most notably, the upregulation of CD40 with LPS stimulation and CD86 with CpG stimulation was observed in in vitro cultures. Similarly, IFN-gamma coinjected with TLR ligands was able to promote DC activation in vivo, with DCs migrating from the site of immunization to the popliteal lymph nodes demonstrating increased expression of CD80 and CD86. The heightened DC activation translated to a drastic increase in T cell stimulatory capacity in both antigen independent and antigen dependent fashions. This is the first time that IFN-gamma has been shown to have a combined effect with TLR ligation to enhance DC activation and function. The results demonstrate the novel use of IFN-gamma together with TLR agonists to enhance antigen-specific T cell responses, for applications in the development of enhanced vaccines and drug targets against diseases including cancer.

Deletion of cathepsin H perturbs angiogenic switching, vascularization and growth of tumors in a mouse model of pancreatic islet cell cancer

Proteases can regulate many aspects of tumor development as their actions, which include degradation of the extracellular matrix, proteolytic processing of chemokines and activation of other enzymes, influence several key tumorigenic processes. Members of one protease class, the cysteine cathepsins, have received increasing recognition for their involvement in cancer development, and numerous clinical studies have reported correlations between elevated cathepsin levels and malignant progression. This is also the case for cathepsin H, a member of the cysteine cathepsin family, and its utility as a prognostic marker has been analyzed extensively. However, there is limited information available on its specific functions in tumor development and progression. To gain further insight into the role of this protease in cancer, we crossed cathepsin H-deficient mice with the RIP1-Tag2 model of pancreatic islet carcinogenesis. Deletion of cathepsin H significantly impaired angiogenic switching of the pre-malignant hyperplastic islets and resulted in a reduction in the subsequent number of tumors that formed. Moreover, the tumor burden in cathepsin H null RT2 mice was significantly reduced, in association with defects in the blood vasculature and increased apoptosis. Thus, we demonstrate here for the first time important tumor-promoting roles for cathepsin H in vivo using a mouse model of human cancer.

Biomedical nanoparticles modulate specific CD4+ T cell stimulation by inhibition of antigen processing in dendritic cells

Understanding how nanoparticles may affect immune responses is an essential prerequisite to developing novel clinical applications. To investigate nanoparticle-dependent outcomes on immune responses, dendritic cells (DCs) were treated with model biomedical poly(vinylalcohol)-coated super-paramagnetic iron oxide nanoparticles (PVA-SPIONs). PVA-SPIONs uptake by human monocyte-derived DCs (MDDCs) was analyzed by flow cytometry (FACS) and advanced imaging techniques. Viability, activation, function, and stimulatory capacity of MDDCs were assessed by FACS and an in vitro CD4+ T cell assay. PVA-SPION uptake was dose-dependent, decreased by lipopolysaccharide (LPS)-induced MDDC maturation at higher particle concentrations, and was inhibited by cytochalasin D pre-treatment. PVA-SPIONs did not alter surface marker expression (CD80, CD83, CD86, myeloid/plasmacytoid DC markers) or antigen-uptake, but decreased the capacity of MDDCs to process antigen, stimulate CD4+ T cells, and induce cytokines. The decreased antigen processing and CD4+ T cell stimulation capability of MDDCs following PVA-SPION treatment suggests that MDDCs may revert to a more functionally immature state following particle exposure.

Channel catfish, Ictalurus punctatus, cysteine proteinases: cloning, characterisation and expression of cathepsin H and L

The antigen recognition by the host immune system is a complex biochemical process that requires a battery of enzymes. Cathepsins are one of the enzyme superfamilies involved in antigen degradation. We observed the up-regulation of catfish cathepsin H and L transcripts during the early stage of Edwardsiella ictaluri infection in preliminary studies, and speculated that cathepsin H and L may play roles in infection. We identified, sequenced and characterized the complete channel catfish cathepsin H and L cDNAs, which comprised 1415 and 1639 nucleotides, respectively. The open reading frames of cathepsin H appeared to encode a protein of 326-amino acid residues, which that of cathepsin L encoded a protein of 336 amino acids. The degree of conservation of the channel catfish cathepsin H and L amino acid sequences in comparison to other species ranged from 61% to 77%, and 67% to 85%, respectively. The catalytic triad and substrate binding sites are conserved in cathepsin H and L amino acid sequences. The cathepsin L transcript was expressed in all tissues examined, while the cathepsin H was expressed in restricted tissues. These results provide important information for further exploring the roles of channel catfish cathepsins in antigen processing.

Ovarian cysteine proteinases in the teleost Fundulus heteroclitus: molecular cloning and gene expression during vitellogenesis and oocyte maturation

The cysteine proteinases cathepsins B and L are members of the multigene family of lysosomal proteases that have been implicated in the processing of yolk proteins (YPs) in teleost oocytes. However, the full identification of the type of cathepsins expressed in fish ovarian follicles and embryos, as well as their regulatory mechanisms and specific function(s), are not yet elucidated. In this study, cDNAs encoding cathepsins B, L, F, K, S, Z, C, and H have been isolated from the teleost Fundulus heteroclitus, and the analysis of their deduced amino acid sequences revealed highly similar structural features to vertebrate orthologs, and confirmed in this species the existence of cathepsin L-like, cathepsin B-like, and cathepsin F-like subfamilies of cysteine proteinases. While all identified cathepsins were expressed in ovarian follicles, the corresponding mRNAs showed different temporal expression patterns. Thus, similar mRNA levels of cathepsins L, F, S, B, C, and Z were found throughout the oocyte growth or vitellogenesis period, whereas those for cathepsin H and K appeared to decrease as vitellogenesis advanced. During oocyte maturation, a transient accumulation of cathepsins L, S, H, and F mRNAs, approximately a 3-, 1.5-, 1.6-, and 6-fold increase, respectively, was detected in ovarian follicles within the 20-25 hr after hormone stimulation, coincident with the maximum proteolysis of the oocyte major YPs. The specific temporal pattern of expression of these genes may indicate a potential role of cathepsin L-like and cathepsin F proteases in the YP processing events occurring during fish oocyte maturation and/or early embryogenesis.

Constitutive and regulated expression of platelet basic protein in human monocytes

Platelet basic protein (PBP) and several of its derivatives are known for their broad range of functions as signaling molecules and cationic antimicrobial peptides and were considered hitherto megakaryocyte- and platelet-specific. In search of glucocorticoid-regulated antimicrobial systems of monocytes, we found a 15-fold down-regulation of PBP mRNA by differential display. Regulation was confirmed in vivo even at low prednisone doses. Quantitative mRNA analyses confirmed down-regulation also for platelets. Western blotting and immunostains showed down-regulation at the protein level. Pro-PBP derivatives were in the size range of 7.5-14 kD and in immunostains, gave granular cytoplasmatic patterns. Interleukin (IL)-4 and IL-10 induced a similar down-regulation. Phagocytosis resulted in an increase of smaller derivatives in the range of 7.5 kD. Stimulation with interferon-gamma and lipopolysaccharide did decrease expression of PBP and affected derivatization. Expression of PBP and its derivatives is not restricted to the megakaryocytic cell lineage. PBP and some of its derivatives might contribute to the antimicrobial armamentarium of mononuclear phagocytes or have monokine functions. Our studies define PBPs as one among the many immunosuppressive targets of glucocorticoids.

Interferon-gamma: an overview of signals, mechanisms and functions

Interferon-gamma (IFN-gamma) coordinates a diverse array of cellular programs through transcriptional regulation of immunologically relevant genes. This article reviews the current understanding of IFN-gamma ligand, receptor, signal transduction, and cellular effects with a focus on macrophage responses and to a lesser extent, responses from other cell types that influence macrophage function during infection. The current model for IFN-gamma signal transduction is discussed, as well as signal regulation and factors conferring signal specificity. Cellular effects of IFN-gamma are described, including up-regulation of pathogen recognition, antigen processing and presentation, the antiviral state, inhibition of cellular proliferation and effects on apoptosis, activation of microbicidal effector functions, immunomodulation, and leukocyte trafficking. In addition, integration of signaling and response with other cytokines and pathogen-associated molecular patterns, such as tumor necrosis factor-alpha, interleukin-4, type I IFNs, and lipopolysaccharide are discussed.

Impaired electroretinogram (ERG) response in apolipoprotein E-deficient mice

PURPOSE

We investigated the effects of 35 weeks of a cholesterol diet in apolipoprotein E (apoE)-deficient mice on their ERG response.

METHODS

C57BL/6J and apoE-deficient mice were fed regular mouse chow (C57-R and ApoE-R, respectively) or a cholesterol-containing diet (C57-C and ApoE-C, respectively). Retinal function was assessed by dark-adapted electroretinography (ERG). Retina tissue was also analyzed by immunohistochemical staining and nucleic acid array expression analysis performed by gene array technology.

RESULTS

ApoE-C mice had diminished a- and b-wave amplitudes (60.7% +/- 8.4% (p < 0.005) and 44.8% +/- 10% (p < 0.005) of control values, respectively). Gene expression profiling revealed upregulation of several pro-apoptotic genes. Furthermore, immunohistochemistry showed increased Bax immunoreactivity.

CONCLUSIONS

In the hypercholesterolemic mice, we demonstrated a loss of ERG response and induction of apoptotic activity at the gene and protein levels. Our current and previous findings suggest that cholesterol metabolism plays an important role in retinal function.

Purification and some properties of cathepsin H from rabbit skeletal muscle

Rabbit muscle cathepsin H classified as an aminoendopeptidase was purified and its properties were investigated to clarify its contribution to the proteolysis of postmortem muscle. The purification was performed by ammonium sulfate fractionation and successive chromatographies on Sephadex G-75, phosphocelluose, DEAE-Sephadex A-50 and Sephadex G-100. The purified enzyme gave a single protein band on SDS-PAGE. Its molecular mass was found to be 28 kDa by gel permeation and 30 kDa by SDS-PAGE. The optimum pHs for alpha-N-benzoyl-DL-arginine-beta-naphthylamide (BANA)- and L-leucine-beta-naphthylamide (Leu-NA)-hydrolyzing activities were 6.6 and 7.0, respectively. This enzyme was almost stable in the range of pH 4-5 and up to 50 degrees C at pH 5.0. The Km values of BANA- and Leu-NA-hydrolyzing activities were 0.367 and 0.203 mM, respectively. The enzyme was inhibited by monoiodoacetic acid, antipain, leupeptin, TLCK and TPCK, but was not affected by pepstatin, bestatin, puromycin, PMSF or trypsin inhibitor. This enzyme strongly acted on Arg-, Lys-, Met-, Ala-, Ser- and Leu-NAs, weakly acted on Val- and Glu-NAs, and hardly acted on Pro- and Gly-NAs. The amount of cathepsin H in muscle was estimated to be less than one-fourth of the sum of the amount of aminopeptidases C and H by the Leu-NA-hydrolyzing activity on the chromatography. This enzyme degraded myosin heavy chain, actin, tropomyosin and troponin I clearly at pH 4.0, while it slightly degraded troponin I at pH 5.0-5.6. Therefore, the contribution of cathepsin H to the proteolysis of postmortem muscle is presumed to be relatively small.

Serpin 2a is induced in activated macrophages and conjugates to a ubiquitin homolog

After i.p. infection of mice with the intracellular bacterium Mycobacterium bovis bacillus Calmette-Guérin, macrophages recovered from the peritoneal cavity display classical signs of immune activation. We have identified a member of the serine protease inhibitor (serpin) family which is highly induced in macrophages during bacillus Calmette-Guérin infection. Serpin 2a (spi2a) expression is also induced in macrophages in vivo during infection with Salmonella typhimurium and Listeria monocytogenes, and in vitro by a variety of bacteria and bacterial products. The cytokine IFN-gamma also induces spi2a expression in macrophages, and this induction is synergistic with bacterial products. We also demonstrate here that a ubiquitin homolog, IFN-stimulated gene of 15-kDa (ISG15), is strongly induced during in vitro and in vivo activation of macrophages and that it conjugates to spi2a in activated macrophages. The ISG15-spi2a conjugates were identified by tandem mass spectrometry and contained spi2a conjugated to either one or two molecules of ISG15. Whereas spi2a was induced by either bacterial products or IFN-gamma, ISG15 was induced only by bacterial products. Although many protein targets have been described for ubiquitin conjugation, spi2a is the first ISG15-modified protein to be reported. Macrophage activation is accompanied by the activation of a variety of proteases. It is of interest that a member of the serine protease inhibitor family is concomitantly induced and modified by a ubiquitin-like protein.

Efficient in vivo presentation of Listeria monocytogenes- derived CD4 and CD8 T cell epitopes in the absence of IFN-gamma

IFN-gamma is an essential component of the early Listeria monocytogenes-specific immune response, and is also an important regulator of Ag processing and presentation. Ag presentation is required for the induction and also the effector function of antimicrobial T cells. To evaluate the effect of IFN-gamma on bacterial Ag presentation in vivo, macrophages and dendritic cells were separated from L. monocytogenes-infected tissues and analyzed with peptide-specific CD4 and CD8 T cell lines in a sensitive ELISPOT-based ex vivo Ag presentation assay. The comparison of professional APCs isolated from infected IFN-gamma-deficient and wild-type mice revealed different peptide presentation patterns of L. monocytogenes-derived CD8 T cell epitopes, while the presentation pattern of CD4 T cell epitopes remained unchanged. The further in vitro analysis of the generation of CD8 T cell epitopes revealed a peptide-specific effect of IFN-gamma on MHC class I-restricted Ag presentation. These results show that despite this modulation of the Ag presentation pattern of CD8 T cell epitopes, IFN-gamma is not generally required for the MHC class I- and MHC class II-restricted presentation of L. monocytogenes-derived antigenic peptides by professional APCs in vivo.

Proteolysis and antigen presentation by MHC class II molecules

Proteolysis is the primary mechanism used by all cells not only to dispose of unwanted proteins but also to regulate protein function and maintain cellular homeostasis. Proteases that reside in the endocytic pathway are the principal actors of terminal protein degradation. The proteases contained in the endocytic pathway are classified into four major groups based on the active-site amino acid used by the enzyme to hydrolyze amide bonds of proteins: cysteine, aspartyl, serine, and metalloproteases. The presentation of peptide antigens by major histocompatibility complex (MHC) class II molecules is strictly dependent on the action of proteases. Class II molecules scour the endocytic pathway for antigenic peptides to bind and present at the cell surface for recognition by CD4⁺ T cells. The specialized cell types that support antigen presentation by class II molecules are commonly referred to as professional antigen presenting cells (APCs), which include bone marrow-derived B lymphocytes, dendritic cells (DCs), and macrophages. In addition, the expression of certain endocytic proteases is regulated either at the level of gene transcription or enzyme maturation and their activity is controlled by the presence of endogenous protease inhibitors.

The interferon-inducible Staf50 gene is downregulated during T cell costimulation by CD2 and CD28

It is well established that interferons (IFN) exert potent regulatory effects on the immune system. We have recently isolated a new IFN-induced human cDNA coding for a member of the Ring finger B-box/B30.2 subfamily that localizes to the chromosome band 11p15. We have named it Staf50. We show in this report that Staf50 is expressed in resting T cells in the absence of exogenous IFN treatment and is strongly repressed during T cell activation by anti-CD28 and anti-CD2 monoclonal antibodies (mAb) at both messenger and protein levels. In addition, we show that several members of the Ring finger B-box/B30.2 subfamily, including the 52-kDa SSA/Ro autoantigen, localize to the same chromosome band, 11p15, and are upregulated by IFN. These data led us to define a family of IFN-induced genes clustered on chromosome 11p15 that may be involved in T cell regulatory processes.

Delta(9)-tetrahydrocannabinol selectively increases aspartyl cathepsin D proteolytic activity and impairs lysozyme processing by macrophages

Delta(9)-tetrahydrocannabinol (THC) causes an antigen-dependent defect in the ability of macrophages to activate helper T cells, and this drug-induced impairment is mediated through the peripheral CB2 receptor. Various requirements for the processing of the antigen, lysozyme, were examined to determine where along the pathway THC exerts its influence. A THC-exposed macrophage hybridoma inefficiently stimulated interleukin-2 secretion by a helper T cell hybridoma in response to native lysozyme and its reduced form, suggesting that disulfide bond reduction was unaffected. Cell surface expression of major histocompatibility complex class II molecules was normal on THC-exposed macrophages. The drug-exposed macrophages also competently presented a lysozyme peptide to the T cells, indicating that the class II molecules were functional. The proteolytic activity of two thiol cathepsins was unaltered, but aspartyl cathepsin D activity was significantly increased in THC-exposed macrophages. Thus, selective up-regulation of aspartyl cathepsin activity accompanied the deficiency in lysozyme processing and may contribute, at least in part, to the antigen-dependent processing defect in THC-exposed macrophages.

Alterations in cathepsin H activity and protein patterns in human colorectal carcinomas

Our analyses of cathepsin H activity levels and protein forms in human colorectal cancers compared to matched control mucosa support the concept that altered proteinase expression patterns may reflect both cancer stage and site. Cathepsin H-specific activity was significantly increased in colorectal cancers compared to control mucosa (P = 0.003; n = 77). Highest specific activities and cancer/normal ratios (C/N) for activity were measured in Dukes' B and C stage carcinomas, cancers involved in local spread and invasion to lymph nodes. In contrast, cathepsin B and L activities analysed in the same paired extracts had been shown to be most frequently elevated in earlier stage carcinomas (Dukes' A and B), confirming that cathepsin H demonstrates a distinct pattern of expression during colorectal cancer progression. Although cathepsin H activities were most commonly elevated in Dukes' C cancers at all colon sites, both specific activity and C/N ratios were significantly higher for cancers of the left colon compared to other colon locations. A subset of 43 paired extracts analysed on Western blots also revealed consistent changes in cathepsin H protein forms in cancers. Normal mucosa typically showed a strong protein doublet at 31 and 29 kDa while cancers demonstrated decreased expression or total loss of the 31 kDa protein (90% of cases), equal or increased expression of the 29-kDa protein (67% of cases) and the new appearance or up-regulation of a cathepsin H band at 22 kDa (78% of cases). C/N ratios for cathepsin H enzyme activity correlated significantly with C/N ratios for the 29 kDa mature single-chain protein form (P < 0.001), with increased activity most commonly associated with elevated expression of 29-kDa cathepsin H but also with up-regulation of the 22-kDa band, suggesting a shift to more fully processed, mature active cathepsin H protein forms in cancers. Changes in cathepsin H expression were also detected by immunohistochemistry as elevated cathepsin H staining in tumour epithelial cells.

Cloning of DLM-1, a novel gene that is up-regulated in activated macrophages, using RNA differential display

Tumors interact with their environment, reprogramming host cells to induce responses such as angiogenesis, inflammation, immunity and immune suppression. To understand these processes, it is important to identify and isolate new genes whose expression is induced in host tissues in response to tumors. Ascites tumors offer an attractive model for isolating such genes, because responding host peritoneal lining tissues can be cleanly separated from tumor cells growing in suspension within the peritoneal cavity. We here report the cloning by differential display of a novel gene, DLM-1, that is highly up-regulated in the peritoneal lining tissue of mice bearing MOT ascites tumors. Mouse peritoneal macrophages, stimulated by IFN-gamma or LPS, also expressed significant amounts of DLM-1. Up-regulation of DLM-1 became evident by 4h after stimulation with IFN-gamma and was not blocked by cycloheximide, suggesting the presence of IFN responding elements in its transcription regulation region. DLM-1 RNA was detected at significant levels in normal mouse lung, intestinal epithelium, liver and thymus by Northern blot analysis. In situ hybridization of MOT and HT-29 mouse subcutaneous transplanted solid tumors revealed strong DLM-1 expression in the host reactive stromal cells, but not the tumor cells. Sequence analysis of the full-length cDNA clone revealed that it encodes a protein of approx. M(r) 44330 with multiple potential protein kinase C and casein kinase II phosphorylation sites. Our data suggest that DLM-1 plays a role in such important processes as host response in neoplasia.

Gallium Arsenide Modulates Proteolytic Cathepsin Activities and Antigen Processing by Macrophages

Gallium arsenide (GaAs) is a semiconductor utilized in the electronics industry. Chemical exposure of animals causes a local inflammatory reaction, but systemic immunosuppression. Mice were administered i.p. 200 mg/kg GaAs crystals or latex beads, or vehicle. Five days after exposure, splenic macrophages were defective, whereas thioglycolate-elicited peritoneal macrophages (PEC) were more efficient in processing the Ag, pigeon cytochrome c, than vehicle control macrophages. Various aspects of the MHC class II Ag-processing pathway were examined. Both macrophage populations normally presented a peptide fragment to the CD4+ T cells. Surface MHC class II expression on the PEC was up-regulated, but splenic cells had normal MHC class II expression. PEC had elevated levels of glutathione and cysteine, major physiologic reducing thiols. However, the cysteine content of splenic macrophages was diminished. Proteolytic activities of aspartyl cathepsin D, and thiol cathepsins B and L were decreased significantly in splenic macrophages. On the other hand, thiol cathepsin activities were increased selectively in PEC. Latex bead-exposed PEC were not more potent APC, and their thiol cathepsin activities were unchanged, indicating that phagocytosis and nonspecific irritation were not responsible. The phenotype of PEC directly exposed to GaAs mirrored cytokine-activated macrophages, in contrast to splenic macrophages from a distant site. Therefore, GaAs exposure differentially modulated cathepsin activities in splenic macrophages and PEC, which correlated with their Ag-processing efficiency. Perhaps such distinct alterations may contribute to the local inflammation and systemic immunotoxicity caused by chemical exposure.

Epitope dominance: evidence for reciprocal determinant spreading to glutamic acid decarboxylase in non-obese diabetic mice

Autoimmune T-cell responses to peptide determinants of several autoantigens have recently been characterized. These data suggest that, in some autoimmune models, such as experimental autoimmune encephalomyelitis, T-cell responses may diversify from a nested set of peptides to include many other peptide regions. A similar immune phenomenon pertaining to autoimmune diabetes (IDDM) is observed in NOD mice. We have explored a similar pattern of T-cell responses related to age and disease status in NOD mice termed epitope dominance, which describes immune responses toward a pronounced subset of determinants of the autoantigen glutamic acid decarboxylase (GAD). Our studies have identified a total of five GAD epitopes between the 65 and 67 kDa isoforms. The magnitude of T-cell responses to these various determinants was dependent on the stage of disease as well as on whether mice were protected from disease. The T-cell responses of these epitopes in NOD mice correlated with the predicted binding of these peptides to the NOD class II molecule I-Ag7. We therefore propose a model which implicates antigen presenting cells as critical entities in the propagation of dominant responses to the presentation of autoantigens to T cells, particularly in the Th 1 environment of the NOD mouse. This hypothesis presents a new framework for the discussion and interpretation of the kinetics of T-cell responses to different peptide epitopes in autoimmune diseases such as IDDM.

Endosomal proteolysis and MHC class II function

Newly synthesized MHC class II alpha and beta chains associate with a protein chaperone, the invariant chain, which promotes the proper assembly of MHC class II complexes and their trafficking through cells and prevents their untimely loading with peptides. Efficient loading of MHC class II heterodimers with antigenic peptides requires concurrent proteolytic processing of both the invariant chain and endocytosed proteins. Recent studies have elucidated the critical roles of specific cysteine proteases, especially cathepsins S and L, in degrading the invariant chain and regulating the convergence of processed antigen and MHC class II dimers competent for peptide loading.

Crystal structure of porcine cathepsin H determined at 2.1 A resolution: location of the mini-chain C-terminal carboxyl group defines cathepsin H aminopeptidase function

BACKGROUND

Cathepsin H is a lysosomal cysteine protease, involved in intracellular protein degradation. It is the only known mono-aminopeptidase in the papain-like family and is reported to be involved in tumor metastasis. The cathepsin H structure was determined in order to investigate the structural basis for its aminopeptidase activity and thus to provide the basis for structure-based design of synthetic inhibitors.

RESULTS

The crystal structure of native porcine cathepsin H was determined at 2.1 A resolution. The structure has the typical papain-family fold. The so-called mini-chain, the octapeptide EPQNCSAT, is attached via a disulfide bond to the body of the enzyme and bound in a narrowed active-site cleft, in the substrate-binding direction. The mini-chain fills the region that in related enzymes comprises the non-primed substrate-binding sites from S2 backwards.

CONCLUSIONS

The crystal structure of cathepsin H reveals that the mini-chain has a definitive role in substrate recognition and that carbohydrate residues attached to the body of the enzyme are involved in positioning the mini-chain in the active-site cleft. Modeling of a substrate into the active-site cleft suggests that the negatively charged carboxyl group of the C terminus of the mini-chain acts as an anchor for the positively charged N-terminal amino group of a substrate. The observed displacements of the residues within the active-site cleft from their equivalent positions in the papain-like endopeptidases suggest that they form the structural basis for the positioning of both the mini-chain and the substrate, resulting in exopeptidase activity.

The genes of the lysosomal cysteine proteinases cathepsin B, H, L, and S map to different mouse chromosomes

The mouse genes for the lysosomal cysteine proteinases cathepsin B, H, L, and S were mapped to Chromosomes (Chrs) 14, 9, 13, and 3, respectively. Two of the DNA probes used in this study detected an additional, independently segregating locus. The cathepsin B-specific probe hybridized to a locus on Chr 2, and the cathepsin H probe to a locus on the X Chr. These loci either correspond to pseudogenes or to cathepsin B- and cathepsin H-related genes. The four cysteine proteinases mapped in this study lie within known regions of conserved synteny between mouse and human chromosomes, when compared with the corresponding positions of their human homologs. Assuming that the genes of the cysteine proteinase gene family arose from a common ancestral gene, our results suggest that these four cysteine proteinases had been dispersed over different chromosomes before separation of mouse and human in evolution.

Stabilized expression of mRNA is associated with mycobacterial resistance controlled by Nramp1

Control of innate resistance to the growth of mycobacteria is mediated by a gene termed Nramp1. Although the role of the protein product of Nramp1 in mediating resistance to mycobacterial growth is not known, the effect of the gene is pleiotropic and it has been suggested that the gene controls macrophage priming for activation. We have found that the functional capacity of macrophages from Mycobacterium bovis BCG-susceptible mice can be suppressed by corticosterone, while the function of macrophages from BCG-resistant mice remains unaffected. In this study, we show that corticosterone differentially affects the stability of mRNAs of several recombinant gamma interferon (rIFN-gamma)-induced genes. Treatment of macrophages from BCG-susceptible mice with corticosterone accelerates the decay of Nramp1 mRNA. The mRNA of IFN-gamma-induced genes of macrophages from BCG-resistant mice was more stable than the mRNA of macrophages from BCG-susceptible mice in the presence or absence of corticosterone. The results of this investigation suggest that Nramp1 acts by stabilizing the mRNA of genes associated with macrophage activation, thus accounting for the functional differences that have been attributed to these macrophage populations.

Cellular responses to interferon-gamma

Interferons are cytokines that play a complex and central role in the resistance of mammalian hosts to pathogens. Type I interferon (IFN-alpha and IFN-beta) is secreted by virus-infected cells. Immune, type II, or gamma-interferon (IFN-gamma) is secreted by thymus-derived (T) cells under certain conditions of activation and by natural killer (NK) cells. Although originally defined as an agent with direct antiviral activity, the properties of IFN-gamma include regulation of several aspects of the immune response, stimulation of bactericidal activity of phagocytes, stimulation of antigen presentation through class I and class II major histocompatibility complex (MHC) molecules, orchestration of leukocyte-endothelium interactions, effects on cell proliferation and apoptosis, as well as the stimulation and repression of a variety of genes whose functional significance remains obscure. The implementation of such a variety of effects by a single cytokine is achieved by complex patterns of cell-specific gene regulation: Several IFN-gamma-regulated genes are themselves components of transcription factors. The IFN-gamma response is itself regulated by interaction with responses to other cytokines including IFN-alpha/beta, TNF-alpha, and IL-4. Over 200 genes are now known to be regulated by IFN-gamma and they are listed in a World Wide Web document that accompanies this review. However, much of the cellular response to IFN-gamma can be described in terms of a set of integrated molecular programs underlying well-defined physiological systems, for example the induction of efficient antigen processing for MHC-mediated antigen presentation, which play clearly defined roles in pathogen resistance. A promising approach to the complexity of the IFN-gamma response is to extend the analysis of the less understood IFN-gamma-regulated genes in terms of molecular programs functional in pathogen resistance.

Pattern of expression and characteristics of a cysteine proteinase cDNA from germinating seeds of pea (Pisum sativum L.)

A thiol proteinase cDNA clone with homology to barley aleurain and rice oryzain gamma and mammalian cathepsin H was isolated from a germinating pea (Pisum saticum L.) cotyledon library. The corresponding mRNA was present in late developing seeds, decreased in dry seeds and rose considerably as germination proceeded.

Essential role for cathepsin S in MHC class II-associated invariant chain processing and peptide loading

Destruction of li by proteolysis is required for MHC class II molecules to bind antigenic peptides, and for transport of the resulting complexes to the cell surface. The cysteine protease cathepsin S is highly expressed in spleen, lymphocytes, monocytes, and other class II-positive cells, and is inducible with interferon-gamma. Specific inhibition of cathepsin S in B lymphoblastoid cells prevented complete proteolysis of li, resulting in accumulation of a class II-associated 13 kDa li fragment in vivo. Consequently, the formation of SDS-stable complexes was markedly reduced. Purified cathepsin S, but not cathepsin B, H, or D, specifically digested li from alpha beta li trimers, generating alpha beta-CLIP complexes capable of binding exogenously added peptide in vitro. Thus, cathepsin S is essential in B cells for effective li proteolysis necessary to render class II molecules competent for binding peptides.