Interferon-gamma, the functional plasticity of the ubiquitin-proteasome system, and MHC class I antigen processing

Melanocytes: Target Cells of an HLA-C*06:02-Restricted Autoimmune Response in Psoriasis

HLA-C*06:02 is the main psoriasis risk allele. By the unbiased analysis of a Vα3S1/Vβ13S1 T-cell receptor from pathogenic psoriatic CD8⁺ T cells, we had recently proven that HLA-C*06:02 directs an autoimmune response against melanocytes through autoantigen presentation in psoriasis and identified ADAMTSL5 as a melanocyte autoantigen. We concluded that psoriasis is based on a melanocyte-specific immune response and that HLA-C*06:02 may predispose to psoriasis via this newly identified autoimmune pathway. Understanding this pathway, however, requires more detailed explanation. It is based on the fact that an HLA class I-restricted autoreactive CD8⁺ T-cell response must be directed against a particular target cell type, because HLA class I molecules present peptide antigens generated from cytoplasmic (i.e., intracellular) proteins. This review summarizes the findings on the melanocyte-specific autoimmune response in the context of the immune mechanisms related to HLA function and T-cell receptor-antigen recognition. Identifying melanocytes as target cells of the psoriatic immune response now explains psoriasis as a primary autoimmune skin disease.

Autoimmune aspects of psoriasis: Heritability and autoantigens

Chronic immune-mediated disorders (IMDs) constitute a major health burden. Understanding IMD pathogenesis is facing two major constraints: Missing heritability explaining familial clustering, and missing autoantigens. Pinpointing IMD risk genes and autoimmune targets, however, is of fundamental importance for developing novel causal therapies. The strongest association of all IMDs is seen with human leukocyte antigen (HLA) alleles. Using psoriasis as an IMD model this article reviews the pathogenic role HLA molecules may have within the polygenic predisposition of IMDs. It concludes that disease-associated HLA alleles account for both missing heritability and autoimmune mechanisms by facilitating tissue-specific autoimmune responses through autoantigen presentation.

Inhibiting DNA methylation activates cancer testis antigens and expression of the antigen processing and presentation machinery in colon and ovarian cancer cells

Innovative therapies for solid tumors are urgently needed. Recently, therapies that harness the host immune system to fight cancer cells have successfully treated a subset of patients with solid tumors. These responses have been strong and durable but observed in subsets of patients. Work from our group and others has shown that epigenetic therapy, specifically inhibiting the silencing DNA methylation mark, activates immune signaling in tumor cells and can sensitize to immune therapy in murine models. Here we show that colon and ovarian cancer cell lines exhibit lower expression of transcripts involved in antigen processing and presentation to immune cells compared to normal tissues. In addition, treatment with clinically relevant low doses of DNMT inhibitors (that remove DNA methylation) increases expression of both antigen processing and presentation and Cancer Testis Antigens in these cell lines. We confirm that treatment with DNMT inhibitors upregulates expression of the antigen processing and presentation molecules B2M, CALR, CD58, PSMB8, PSMB9 at the RNA and protein level in a wider range of colon and ovarian cancer cell lines and treatment time points than had been described previously. In addition, we show that DNMTi treatment upregulates many Cancer Testis Antigens common to both colon and ovarian cancer. This increase of both antigens and antigen presentation by epigenetic therapy may be one mechanism to sensitize patients to immune therapies.

Blockade of IDO-kynurenine-AhR metabolic circuitry abrogates IFN-γ-induced immunologic dormancy of tumor-repopulating cells

Interactions with the immune system may lead tumorigenic cells into dormancy. However, the underlying molecular mechanism is poorly understood. Using a 3D fibrin gel model, we show that IFN-γ induces tumour-repopulating cells (TRCs) to enter dormancy through an indolamine 2,3-dioxygenase 1 (IDO1)-kynurenine (Kyn)-aryl hydrocarbon receptor (AhR)-p27 dependent pathway. Mechanistically, IFN-γ signalling triggers differentiated tumour cell apoptosis via STAT1; however, when IDO1 and AhR are highly expressed as in TRCs, IFN-γ results in IDO1/AhR-dependent p27 induction that prevents STAT1 signalling, thus suppressing the process of cell death and activating the dormancy program. Blocking the IDO/AhR metabolic circuitry not only abrogates IFN-γ-induced dormancy but also results in enhanced repression of tumour growth by IFN-γ-induced apoptosis of TRCs both in vitro and in vivo. These data present a previously unrecognized mechanism of inducing TRC dormancy by IFN-γ, suggesting a potential effective cancer immunotherapeutic modality through the combination of IFN-γ and IDO/AhR inhibitors.

Tumour repopulating cells (TRC) are stem-like cells that can escape immune-mediated killing. Here, the authors show IFN-γ results in either dormancy or apoptosis of TRC depending on the activation of the IDO1 metabolic pathway, and that combining IFN-γ with IDO1 inhibitors results in enhanced tumour regression.

Noncovalent inhibitors of human 20S and 26S proteasome based on trypsin inhibitor SFTI-1

Sunflower trypsin inhibitor (SFTI-1) is recognized as an attractive scaffold to designed potent inhibitors of various proteases. We have recently found that its analogues inhibit noncovalently both human and yeast 20S proteasomes. Here, a set of novel and more potent in vitro inhibitors is presented. The inhibitory potency of the peptides was assessed with human 20S proteasome in the presence or absence of sodium dodecyl sulfate and with human 26 proteasome. Their antiproliferative action against tumor (human melanoma cells A375) and normal cells (46 BR.1N human fibroblasts and HaCaT keratinocytes) was determined. The selected fluoresceine-labeled inhibitors were able to internalize into A375 cells and were sometimes present as foci in the cells. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 685-696, 2016.

Immunoproteasome subunit deficiency has no influence on the canonical pathway of NF-κB activation

Activation of the pro-inflammatory transcription factor NF-κB requires signal-induced proteasomal degradation of the inhibitor of NF-κB (IκB) in order to allow nuclear translocation. Most cell types are capable of expressing two types of 20S proteasome core particles, the constitutive proteasome and immunoproteasome. Inducible under inflammatory conditions, the immunoproteasome is mainly characterized through an altered cleavage specificity compared to the constitutive proteasome. However, the question whether immunoproteasome subunits affect NF-κB signal transduction differently from constitutive subunits is still up for debate. To study the effect of immunoproteasomes on LPS- or TNF-α-induced NF-κB activation, we used IFN-γ stimulated peritoneal macrophages and mouse embryonic fibroblasts derived from mice deficient for the immunoproteasome subunits low molecular mass polypeptide (LMP) 2, or LMP7 and multicatalytic endopeptidase complex-like 1 (MECL-1). Along the canonical signaling pathway of NF-κB activation no differences in the extent and kinetic of IκB degradation were observed. Neither the nuclear translocation and DNA binding of NF-κB nor the production of the NF-κB dependent cytokines TNF-α, IL-6, and IL-10 differed between immunoproteasome deficient and proficient cells. Hence, we conclude that immunoproteasome subunits have no specialized function for canonical NF-κB activation.

Evidence of an Antimicrobial Peptide Signature Encrypted in HECT E3 Ubiquitin Ligases

The ubiquitin-proteasome pathway (UPP) is a hallmark of the eukaryotic cell. In jawed vertebrates, it has been co-opted by the adaptive immune system, where proteasomal degradation produces endogenous peptides for major histocompatibility complex class I antigen presentation. However, proteolytic products are also necessary for the phylogenetically widespread innate immune system, as they often play a role as host defense peptides (HDPs), pivotal effectors against pathogens. Here, we report the identification of the arachnid HDP oligoventin, which shares homology to a core member of the UPP, E3 ubiquitin ligases. Oligoventin has broad antimicrobial activity and shows strong synergy with lysozymes. Using computational and phylogenetic approaches, we show high conservation of the oligoventin signature in HECT E3s. In silico simulation of HECT E3s self-proteolysis provides evidence that HDPs can be generated by fine-tuned 26S proteasomal degradation, and therefore are consistent with the hypothesis that oligoventin is a cryptic peptide released by the proteolytic processing of an Nedd4 E3 precursor protein. Finally, we compare the production of HDPs and endogenous antigens from orthologous HECT E3s by proteasomal degradation as a means of analyzing the UPP coupling to metazoan immunity. Our results highlight the functional plasticity of the UPP in innate and adaptive immune systems as a possibly recurrent mechanism to generate functionally diverse peptides.

Overexpression of Glutamate Decarboxylase in Mesenchymal Stem Cells Enhances Their Immunosuppressive Properties and Increases GABA and Nitric Oxide Levels

The neurotransmitter GABA has been recently identified as a potent immunosuppressive agent that targets both innate and adaptive immune systems and prevents disease progression of several autoimmunity models. Mesenchymal stem cells (MSCs) are self-renewing progenitor cells that differentiate into various cell types under specific conditions, including neurons. In addition, MSC possess strong immunosuppressive capabilities. Upon cytokine priming, undifferentiated MSC suppress T-cell proliferation via cell-to-cell contact mechanisms and the secretion of soluble factors like nitric oxide, prostaglandin E2 and IDO. Although MSC and MSC-derived neuron-like cells express some GABAergic markers in vitro, the role for GABAergic signaling in MSC-mediated immunosuppression remains completely unexplored. Here, we demonstrate that pro-inflammatory cytokines selectively regulate GAD-67 expression in murine bone marrow-MSC. However, expression of GAD-65 is required for maximal GABA release by MSC. Gain of function experiments using GAD-67 and GAD-65 co-expression demonstrates that GAD increases immunosuppressive function in the absence of pro-inflammatory licensing. Moreover, GAD expression in MSC evokes an increase in both GABA and NO levels in the supernatants of co-cultured MSC with activated splenocytes. Notably, the increase in NO levels by GAD expression was not observed in cultures of isolated MSC expressing GAD, suggesting crosstalk between these two pathways in the setting of immunosuppression. These results indicate that GAD expression increases MSC-mediated immunosuppression via secretion of immunosuppressive agents. Our findings may help reconsider GABAergic activation in MSC for immunological disorders.

Carfilzomib enhances natural killer cell-mediated lysis of myeloma linked with decreasing expression of HLA class I

Natural killer (NK) cell-based treatments are promising therapies for multiple myeloma (MM). Carfilzomib (CFZ), is a second-generation proteasome inhibitor, used to treat relapsed and refractory MM. In this study, we determined that CFZ treatment enhanced the sensitivity of MM cells to NK cell-mediated lysis. Here, we report that CFZ decreased the expression of human leukocyte antigen (HLA) class I in a time- and dose-dependent manner. CFZ also down-regulated the expression of newly formed HLA class I on MM cells. Treatment of MM with CFZ enhanced NK cell degranulation and significantly sensitized patients' MM cells to NK cell-mediated lysis. Furthermore, the enhancement of NK cell-mediated lysis was linked with the decreased expression of HLA class I. Our findings show a novel activity of CFZ as an immunomodulating agent and suggest a possible approach to therapeutically augment NK cell function in MM patients.

Whole Genome Pathway Analysis Identifies an Association of Cadmium Response Gene Loss with Copy Number Variation in Mutant p53 Bearing Uterine Endometrial Carcinomas

Background

Massive chromosomal aberrations are a signature of advanced cancer, although the factors promoting the pervasive incidence of these copy number alterations (CNAs) are poorly understood. Gatekeeper mutations, such as p53, contribute to aneuploidy, yet p53 mutant tumors do not always display CNAs. Uterine Corpus Endometrial Carcinoma (UCEC) offers a unique system to begin to evaluate why some cancers acquire high CNAs while others evolve another route to oncogenesis, since about half of p53 mutant UCEC tumors have a relatively flat CNA landscape and half have 20–90% of their genome altered in copy number.

Methods

We extracted copy number information from 68 UCEC genomes mutant in p53 by the GISTIC2 algorithm. GO term pathway analysis, via GOrilla, was used to identify suppressed pathways. Genes within these pathways were mapped for focal or wide distribution. Deletion hotspots were evaluated for temporal incidence.

Results

Multiple pathways contributed to the development of pervasive CNAs, including developmental, metabolic, immunological, cell adhesion and cadmium response pathways. Surprisingly, cadmium response pathway genes are predicted as the earliest loss events within these tumors: in particular, the metallothionein genes involved in heavy metal sequestration. Loss of cadmium response genes were associated with copy number changes and poorer prognosis, contrasting with 'copy number flat' tumors which instead exhibited substantive mutation.

Conclusion

Metallothioneins are lost early in the development of high CNA endometrial cancer, providing a potential mechanism and biological rationale for increased incidence of endometrial cancer with cadmium exposure. Developmental and metabolic pathways are altered later in tumor progression.

Exposure to Melan-A/MART-126-35 tumor epitope specific CD8(+)T cells reveals immune escape by affecting the ubiquitin-proteasome system (UPS)

Efficient processing of target antigens by the ubiquitin-proteasome-system (UPS) is essential for treatment of cancers by T cell therapies. However, immune escape due to altered expression of IFN-γ-inducible components of the antigen presentation machinery and consequent inefficient processing of HLA-dependent tumor epitopes can be one important reason for failure of such therapies. Here, we show that short-term co-culture of Melan-A/MART-1 tumor antigen-expressing melanoma cells with Melan-A/MART-126-35-specific cytotoxic T lymphocytes (CTL) led to resistance against CTL-induced lysis because of impaired Melan-A/MART-126-35 epitope processing. Interestingly, deregulation of p97/VCP expression, which is an IFN-γ-independent component of the UPS and part of the ER-dependent protein degradation pathway (ERAD), was found to be essentially involved in the observed immune escape. In support, our data demonstrate that re-expression of p97/VCP in Melan-A/MART-126-35 CTL-resistant melanoma cells completely restored immune recognition by Melan-A/MART-126-35 CTL. In conclusion, our experiments show that impaired expression of IFN-γ-independent components of the UPS can exert rapid immune evasion of tumor cells and suggest that tumor antigens processed by distinct UPS degradation pathways should be simultaneously targeted in T cell therapies to restrict the likelihood of immune evasion due to impaired antigen processing.

Major Histocompatibility Complex (MHC) Class I Processing of the NY-ESO-1 Antigen Is Regulated by Rpn10 and Rpn13 Proteins and Immunoproteasomes following Non-lysine Ubiquitination

The supply of MHC class I-restricted peptides is primarily ensured by the degradation of intracellular proteins via the ubiquitin-proteasome system. Depending on the target and the enzymes involved, ubiquitination is a process that may dramatically vary in terms of linkages, length, and attachment sites. Here we identified the unique lysine residue at position 124 of the NY-ESO-1 cancer/testis antigen as the acceptor site for the formation of canonical Lys-48-linkages. Interestingly, a lysine-less form of NY-ESO-1 was as efficient as its wild-type counterpart in supplying the HLA-A*0201-restricted NY-ESO-1157-165 antigenic peptide. In fact, we show that the regulation of NY-ESO-1 processing by the ubiquitin receptors Rpn10 and Rpn13 as a well as by the standard and immunoproteasome is governed by non-canonical ubiquitination on non-lysine sites. In summary, our data underscore the significance of atypical ubiquitination in the modulation of MHC class I antigen processing.

A longitudinal biomarker for the extent of skin disease in patients with diffuse cutaneous systemic sclerosis

OBJECTIVE

To define a pharmacodynamic biomarker based on gene expression in skin that would provide a biologic measure of the extent of disease in patients with diffuse cutaneous systemic sclerosis (dcSSc) and could be used to monitor skin disease longitudinally.

METHODS

Skin biopsy specimens obtained from a cohort of patients with dcSSc (including longitudinal specimens) were analyzed by microarray. Expression of genes correlating with the modified Rodnan skin thickness score (MRSS) were examined for change over time using a NanoString platform, and a generalized estimating equation (GEE) was used to define and validate longitudinally measured pharmacodynamic biomarkers composed of multiple genes.

RESULTS

Microarray analysis of genes parsed to include only those correlating with the MRSS revealed prominent clusters of profibrotic/transforming growth factor β-regulated, interferon-regulated/proteasome, macrophage, and vascular marker genes. Using genes changing longitudinally with the MRSS, we defined 2 multigene pharmacodynamic biomarkers. The first was defined mathematically by applying a GEE to longitudinal samples. This modeling method selected cross-sectional THBS1 and longitudinal THBS1 and MS4A4A. The second model was based on a weighted selection of genes, including additional genes that changed statistically significantly over time: CTGF, CD163, CCL2, and WIF1. In an independent validation data set, biomarker levels calculated using both models correlated highly with the MRSS.

CONCLUSION

Skin gene expression can be used effectively to monitor changes in SSc skin disease over time. We implemented 2 relatively simple models on a NanoString platform permitting highly reproducible assays that can be applied directly to samples from patients or collected as part of clinical trials.

Gnidimacrin, a Potent Anti-HIV Diterpene, Can Eliminate Latent HIV-1 Ex Vivo by Activation of Protein Kinase C β

HIV-1-latency-reversing agents, such as histone deacetylase inhibitors (HDACIs), were ineffective in reducing latent HIV-1 reservoirs ex vivo using CD4 cells from patients as a model. This deficiency poses a challenge to current pharmacological approaches for HIV-1 eradication. The results of this study indicated that gnidimacrin (GM) was able to markedly reduce the latent HIV-1 DNA level and the frequency of latently infected cells in an ex vivo model using patients peripheral blood mononuclear cells. GM induced approximately 10-fold more HIV-1 production than the HDACI SAHA or romidepsin, which may be responsible for the effectiveness of GM in reducing latent HIV-1 levels. GM achieved these effects at low picomolar concentrations by selective activation of protein kinase C βI and βII. Notably, GM was able to reduce the frequency of HIV-1 latently infected cells at concentrations without global T cell activation or stimulating inflammatory cytokine production. GM merits further development as a clinical trial candidate for latent HIV-1 eradication.

Targeting of MYCN by means of DNA vaccination is effective against neuroblastoma in mice

The MYCN oncogene is a strong genetic marker associated with poor prognosis in neuroblastoma (NB). Therefore, MYCN gene amplification and subsequent overexpression provide a possible target for new treatment approaches in NB. We first identified an inverse correlation of MYCN expression with CD45 mRNA in 101 NB tumor samples. KEGG mapping further revealed that MYCN expression was associated with immune-suppressive pathways characterized by a down-regulation of T cell activation and up-regulation of T cell inhibitory gene transcripts. We then aimed to investigate whether DNA vaccination against MYCN is effective to induce an antigen-specific and T cell-mediated immune response. For this purpose, we generated a MYCN-expressing syngeneic mouse model by MYCN gene transfer to NXS2 cells. MYCN-DNA vaccines were engineered based on the pCMV-F3Ub plasmid backbone to drive ubiquitinated full-length MYCN-cDNA and minigene expression. Vaccines were delivered orally with attenuated S. typhimurium strain SL7207 as a carrier. Immunization with both MYCN-DNA vaccines significantly reduced primary tumor growth of MYCN-expressing NB cells in contrast to negative controls. The immune response was mediated by tumor-infiltrating T cells in vivo, which revealed MYCN-specific and MHC class I-restricted lysis of inducible MYCN-expressing NB target cells in vitro. Finally, these antigen-specific T cells also killed MYCN-negative mammary carcinoma cells pulsed with MYCN peptides in contrast to controls. In summary, we demonstrate proof of concept that MYCN can be targeted by DNA vaccination, which may provide an approach to overcoming MYCN immune-suppressive activities in patients with MYCN-amplified disease.

Blimp1/Prdm1 Functions in Opposition to Irf1 to Maintain Neonatal Tolerance during Postnatal Intestinal Maturation

The neonatal intestine is a very complex and dynamic organ that must rapidly adapt and remodel in response to a barrage of environmental stimuli during the first few postnatal weeks. Recent studies demonstrate that the zinc finger transcriptional repressor Blimp1/Prdm1 plays an essential role governing postnatal reprogramming of intestinal enterocytes during this period. Functional loss results in global changes in gene expression patterns, particularly in genes associated with metabolic function. Here we engineered a knock-in allele expressing an eGFP-tagged fusion protein under control of the endogenous regulatory elements and performed genome wide ChIP-seq analysis to identify direct Blimp1 targets and further elucidate the function of Blimp1 in intestinal development. Comparison with published human and mouse datasets revealed a highly conserved core set of genes including interferon-inducible promoters. Here we show that the interferon-inducible transcriptional activator Irf1 is constitutively expressed throughout fetal and postnatal intestinal epithelium development. ChIP-seq demonstrates closely overlapping Blimp1 and Irf1 peaks at key components of the MHC class I pathway in fetal enterocytes. The onset of MHC class I expression coincides with down-regulated Blimp1 expression during the suckling to weaning transition. Collectively, these experiments strongly suggest that in addition to regulating the enterocyte metabolic switch, Blimp1 functions as a gatekeeper in opposition to Irf1 to prevent premature activation of the MHC class I pathway in villus epithelium to maintain tolerance in the neonatal intestine.

The transcriptional repressor Blimp1/Prdm1 plays a pivotal role in the metabolic switch that occurs in the small intestine during the suckling to weaning transition. Notably, expression profiling of perinatal Blimp1-deficient small intestine revealed premature activation of metabolic genes normally restricted to post-weaning enterocytes. To further elucidate the function of Blimp1 in intestinal development, we engineered a novel Blimp1-eGFP-fusion knock-in mouse strain to perform ChIP-seq analysis. In addition to identifying which metabolic genes are direct Blimp1 targets, ChIP-seq analysis revealed a highly conserved Blimp1/Irf-1 overlapping sites that function to control MHC class I antigen processing during acquisition of neonatal tolerance in the first weeks after birth during early colonization of the intestinal tract by commensal microorganisms. Moreover, immunohistochemical analysis of human fetal intestine suggests that a BLIMP1/IRF-1 axis may also function in human intestinal epithelium development.

Proteasomes in the brain of β2-microglobulin knockout mice

MHC class I molecules play an important role in synaptic plasticity of the mammalian nervous system. Proteolytic complexes (proteasomes) produce oligopeptides that are presented on cell surfaces in complexes with MHC class I molecules and regulate many cellular processes beside this. The goal of the present work was to study peculiarities in functioning of proteasomes and associated signaling pathways along with evaluation of NeuN and gFAP expression in different sections of the brain in mice with knockout of β2-microglobulin, a constituent of MHC class I molecules. It was found that the frontal cortex and the brainstem, structures with different ratio of NeuN and gFAP expression, are characterized by opposite changes in the proteasome pool under constant total proteasome levels in B2m-knockout mice in comparison with those in control animals. ChTL-activity as well as expression of LMP7 immune subunit and PA28 regulator of proteasomes was elevated in the cortex of B2m-knockout mice, while these indicators were decreased in the brainstem. The concentrations of the signaling molecules nNOS and HSP70 in B2m-knockout mice were increased in the cortex, while being decreased in the brainstem, and this indicates the possibility of control of expression of the LMP7 subunit and the regulator PA28 by these molecules. Changes in the proteasome pool observed in striatum of B2m-knockout mice are similar to those observed in the brainstem. At the same time, the cerebellum is characterized by a specific pattern of proteasome functioning in comparison with that in all other brain structures. In cerebellum the expression of immune subunits LMP7 and LMP2 and the regulator PA28 was increased, while expression of regulator PA700 was decreased. Deficiency of NeuN and gFAP was revealed in most brain compartments of B2m-knockout mice. Thus, increased expression of the above-mentioned immune subunits and the proteasome regulator PA28 in the cortex and cerebellum may compensate disturbances revealed in the brain structures and the absence of MHC class I molecules. Apparently, this promotes production of peptides necessary for cell-to-cell interactions and maintains nervous system plasticity in B2m-knockout mice.

Interferon gamma in autoimmunity: A complicated player on a complex stage

Early views of autoimmune disease cast IFNγ as a prototypic pro-inflammatory factor. It is now clear that IFNγ is capable of both pro- and anti-inflammatory activities with the functional outcome dependent on the physiological and pathological setting examined. Here, the major immune modulatory activities of IFNγ are reviewed and current evidence for the impact of IFNγ on pathology and regulation of several autoimmune diseases and disease models is summarized.

Human natural killer cells promote cross-presentation of tumor cell-derived antigens by dendritic cells

Dendritic cells (DCs) cross-present antigen (Ag) to initiate T-cell immunity against most infections and tumors. Natural killer (NK) cells are innate cytolytic lymphocytes that have emerged as key modulators of multiple DC functions. Here, we show that human NK cells promote cross-presentation of tumor cell-derived Ag by DC leading to Ag-specific CD8(+) T-cell activation. Surprisingly, cytotoxic function of NK cells was not required. Instead, we highlight a critical and nonredundant role for IFN-γ and TNF-α production by NK cells to enhance cross-presentation by DC using two different Ag models. Importantly, we observed that NK cells promote cell-associated Ag cross-presentation selectively by monocytes-derived DC (Mo-DC) and CD34-derived CD11b(neg) CD141(high) DC subsets but not by myeloid CD11b(+) DC. Moreover, we demonstrate that triggering NK cell activation by monoclonal antibodies (mAbs)-coated tumor cells leads to efficient DC cross-presentation, supporting the concept that NK cells can contribute to therapeutic mAbs efficiency by inducing downstream adaptive immunity. Taken together, our findings point toward a novel role of human NK cells bridging innate and adaptive immunity through selective induction of cell-associated Ag cross-presentation by CD141(high) DC, a process that could be exploited to better harness Ag-specific cellular immunity in immunotherapy.

An analysis of the safety profile of proteasome inhibitors for treating various cancers

INTRODUCTION

Emerging evidence demonstrates that the ubiquitin-proteasome pathway is a promising target for cancer therapy. Bortezomib (Velcade) exhibits great efficacy against multiple myeloma (MM) since the first clinical application. However, there are still several limitations associated with the use of bortezomib, including severe toxicities. To overcome bortezomib's shortcomings and to improve its safety profile, several second-generation proteasome inhibitors, for example, carfilzomib, ixazomib, oprozomib and marizomib, have been developed and currently tested in various clinical trials.

AREAS COVERED

A literature search was carried out using PubMed and Google Scholar. The activity and safety profiling of proteasome inhibitors in treatment of various cancers were reviewed.

EXPERT OPINION

Bortezomib, as a single or in combination therapy, demonstrates efficacy against MM or other hematological malignancies in clinical settings. However, it encounters two major problems, the acquired resistance and the severe side effects. Future direction in bortezomib-based therapy should focus on how to increase or retain its efficacy but improve its safety profile through, for example, rational combination therapies. Second-generation proteasome inhibitors have shown benefits in both overcoming bortezomib resistance and reducing related side effects, although these encouraging results should be further confirmed in a larger clinic population.

Proteasomes associated with the Blm10 activator protein antagonize mitochondrial fission through degradation of the fission protein Dnm1

The conserved Blm10/PA200 activators bind to the proteasome core particle gate and facilitate turnover of peptides and unfolded proteins in vitro. We report here that Blm10 is required for the maintenance of functional mitochondria. BLM10 expression is induced 25-fold upon a switch from fermentation to oxidative metabolism. In the absence of BLM10, Saccharomyces cerevisiae cells exhibit a temperature-sensitive growth defect under oxidative growth conditions and produce colonies with dysfunctional mitochondria at high frequency. Loss of BLM10 leads to reduced respiratory capacity, increased mitochondrial oxidative damage, and reduced viability in the presence of oxidative stress or death stimuli. In the absence of BLM10, increased fragmentation of the mitochondrial network under oxidative stress is observed indicative of elevated activity of the mitochondrial fission machinery. The degradation of Dnm1, the main factor mediating mitochondrial fission, is impaired in the absence of BLM10 in vitro and in vivo. These data suggest that the mitochondrial functional and morphological changes observed are related to elevated Dnm1 levels. This hypothesis is supported by the finding that cells that constitutively overexpress DNM1 display the same mitochondrial defects as blm10Δ cells. The data are consistent with a model in which Blm10 proteasome-mediated turnover of Dnm1 is required for the maintenance of mitochondrial function and provides cytoprotection under conditions that induce increased mitochondrial damage and programmed cell death.

Inhibition of human and yeast 20S proteasome by analogues of trypsin inhibitor SFTI-1

Starting from the primary structure of sunflower trypsin inhibitor SFTI-1, we designed novel non-covalent inhibitors of human and yeast 20S proteasomes. Peptides with Arg residue in P₁ position and two basic amino acid residues (Lys or/and Arg) in P₂′ and P₃′ positions strongly inhibited chymotrypsin-like and caspase-like activities, while trypsin-like activity was poorly modified. We found that some SFTI-1 analogues up-regulated exclusively the chymotrypsin-like activity of latent yeast 20S proteasome.

The proteasome complex and the maintenance of pluripotency: sustain the fate by mopping up?

The proteasome is a multi-enzyme complex responsible for orchestrating protein quality control by degrading misfolded, damaged, abnormal and foreign proteins. Studies related to the association of the proteasomal system in the preservation of self-renewal in both human and mouse pluripotent cells are sparse, and therefore a clear indication of the emergence of a new and important field of research. Under specific conditions the standard proteasome switches to the newly synthesized immunoproteasome, a catalytically active protein chamber also involved in the regulation of protein homeostasis, cell signaling and gene expression. Herein we review recent data to help elucidate and highlight the pivotal role of the proteasome complex, constitutive as well as inducible, in the regulation of self-renewal, pluripotency and differentiation of both embryonic and induced pluripotent stem cells. The proteasome that is endowed with enhanced proteolytic activity maintains self-renewal by regulating gene expression. In addition to protein degradation, the proteasome activator PA28, compartments of the 19S regulatory particle and key members of the ubiquitin pathway dictate the fate of a pluripotent stem cell. We anticipate that our observations will stimulate active research in this new and emerging theme related to stem cell biology, disease and regenerative medicine.

Smad7 induces plasticity in tumor-infiltrating Th17 cells and enables TNF-alpha-mediated killing of colorectal cancer cells

Transforming growth factor-beta (TGF-β) is deeply involved in colorectal cancer development and the disruption of the TGF-β signaling in dysplastic cells is required for tumor to grow. Nevertheless, tumor cells express TGF-β to escape the immune surveillance mediated by T cells. T-cell expression of Smad7, an intracellular inhibitor of the TGF-β signaling, protects against colitis-associated colorectal cancer. However, whether Smad7 in T cells might influence colorectal cancer growth independently of chronic inflammation and which T-cell subset is involved in this process is unknown. To address this issue, T-cell-specific Smad7 transgenic mice and wild-type (WT) littermates were subcutaneously transplanted with syngenic MC38 colon carcinoma cells. Smad7Tg mice were resistant to tumor development compared with WT mice and protection was dependent on CD4(+) T cells. Smad7 expression in T cells increased the number of tumor-infiltrating Tbet/ROR-γ-t double-positive CD4 T cells characterized by the expression of tumor necrosis factor-alpha (TNF-α) and interferon-gamma but lower IL17A. The low expression of IL17A caused by the Smad7 expression in tumor-infiltrating CD4(+) T cells enabled the TNF-α-mediated killing of cancer cells both in vitro and in vivo, thus indicating that the Smad7-mediated plastic effect on T-cell phenotype induces protection against colorectal cancer.

Overview of proteasome inhibitor-based anti-cancer therapies: perspective on bortezomib and second generation proteasome inhibitors versus future generation inhibitors of ubiquitin-proteasome system

Over the past ten years, proteasome inhibition has emerged as an effective therapeutic strategy for treating multiple myeloma (MM) and some lymphomas. In 2003, Bortezomib (BTZ) became the first proteasome inhibitor approved by the U.S. Food and Drug Administration (FDA). BTZ-based therapies have become a staple for the treatment of MM at all stages of the disease. The survival rate of MM patients has improved significantly since clinical introduction of BTZ and other immunomodulatory drugs. However, BTZ has several limitations. Not all patients respond to BTZ based therapies and relapse occurs in many patients who initially responded. Solid tumors, in particular, are often resistant to BTZ. Furthermore, BTZ can induce dose-limiting peripheral neuropathy (PN). The second generation proteasome inhibitor Carfizomib (CFZ; U.S. FDA approved in August 2012) induces responses in a minority of MM patients relapsed from or refractory to BTZ. There is less PN compared to BTZ. Four other second-generation proteasome inhibitors (Ixazomib, Delanzomib, Oprozomib and Marizomib) with different pharmacologic properties and broader anticancer activities, have also shown some clinical activity in bortezomib-resistant cancers. While the mechanism of resistance to bortezomib in human cancers still remains to be fully understood, targeting the immunoproteasome, ubiquitin E3 ligases, the 19S proteasome and deubiquitinases in pre-clinical studies represents possible directions for future generation inhibitors of ubiquitin-proteasome system in the treatment of MM and other cancers.

In vitro and ex vivo evaluation of a multi-epitope heparinase vaccine for various malignancies

Previous studies have indicated that heparanase (Hpa) might represent a candidate universal tumor-associated antigen. However, vaccine therapy targeting only one cytotoxic T lymphocyte (CTL) epitope is suboptimal in preventing cancer. In the present study, we designed heparanase multi-epitope vaccines to increase the immune response to standard single heparanase epitopes. The results showed that multi-epitope vaccines Hpa525 + 277 + 405 + 16 and Hpa8 + 310 + 315 + 363 induced higher Hpa-specific lysis of various cancer cells from different tissues in a HLA-A2-restricted and heparanase-specific manner compared with the single epitope vaccines Hpa525, Hpa277, Hpa405, Hpa16, Hpa8, Hpa310, Hpa315 and Hpa363, both in vitro and ex vivo. Heparanase multi-epitope vaccines not only induced the heparanase-specific CTL to lyse tumor cells but also increased CTL secretion of interferon-γ. However, these heparanase-specific CTL did not lyse heparanase-expressing autologous lymphocytes and dendritic cells, which confirms the safety of these multi-epitope vaccines. Therefore, the present study provides theoretical evidence for the use of heparanase multi-epitope vaccines for clinical application.

The unique functions of tissue-specific proteasomes

The 26S proteasome is the main protease in eukaryotes. Proteolysis occurs within the cylindrical 20S proteasome that is constitutively expressed in most tissues. However, three tissue-specific versions of the 20S proteasome have been discovered to date. The immunoproteasome is optimized to process antigens and it directs the differentiation of T helper (Th) cells. The thymoproteasome is selectively expressed in cortical epithelial cells of the thymus where it plays an essential role in the positive selection of T lymphocytes. Finally, the spermatoproteasome is found in the testes where it is required during spermatogenesis. Here, we outline how tissue-specific proteasomes adapt to functional needs in their respective tissues and how their selective inhibition may be used to interfere with autoimmune diseases and cancer.

Removal of damaged proteins during ES cell fate specification requires the proteasome activator PA28

In embryonic stem cells, removal of oxidatively damaged proteins is triggered upon the first signs of cell fate specification but the underlying mechanism is not known. Here, we report that this phase of differentiation encompasses an unexpected induction of genes encoding the proteasome activator PA28αβ (11S), subunits of the immunoproteasome (20Si), and the 20Si regulator TNFα. This induction is accompanied by assembly of mature PA28-20S(i) proteasomes and elevated proteasome activity. Inhibiting accumulation of PA28α using miRNA counteracted the removal of damaged proteins demonstrating that PA28αβ has a hitherto unidentified role required for resetting the levels of protein damage at the transition from self-renewal to cell differentiation.

The VHSE-based prediction of proteasomal cleavage sites

Prediction of proteasomal cleavage sites has been a focus of computational biology. Up to date, the predictive methods are mostly based on nonlinear classifiers and variables with little physicochemical meanings. In this paper, the physicochemical properties of 14 residues both upstream and downstream of a cleavage site are characterized by VHSE (principal component score vector of hydrophobic, steric, and electronic properties) descriptors. Then, the resulting VHSE descriptors are employed to construct prediction models by support vector machine (SVM). For both in vivo and in vitro datasets, the performance of VHSE-based method is comparatively better than that of the well-known PAProC, MAPPP, and NetChop methods. The results reveal that the hydrophobic property of 10 residues both upstream and downstream of the cleavage site is a dominant factor affecting in vivo and in vitro cleavage specificities, followed by residue’s electronic and steric properties. Furthermore, the difference in hydrophobic potential between residues flanking the cleavage site is proposed to favor substrate cleavages. Overall, the interpretable VHSE-based method provides a preferable way to predict proteasomal cleavage sites.

Targeting the ubiquitin-proteasome system for cancer therapy

INTRODUCTION

The ubiquitin-proteasome system (UPS) degrades 80 - 90% of intracellular proteins. Cancer cells take advantage of the UPS for their increased growth and decreased apoptotic cell death. Thus, the components that make up the UPS represent a diverse group of potential anti-cancer targets. The success of the first-in-class proteasome inhibitor bortezomib not only proved that the proteasome is a feasible and valuable anti-cancer target, but also inspired researchers to extensively explore other potential targets of this pathway.

AREAS COVERED

This review provides a broad overview of the UPS and its role in supporting cancer development and progression, especially in aspects of p53 inactivation, p27 turnover and NF-κB activation. Also, efforts toward the development of small molecule inhibitors (SMIs) targeting different steps in this pathway for cancer treatment are reviewed and discussed.

EXPERT OPINION

Whereas some of the targets in the UPS, such as the 20S proteasome, Nedd8 activating enzyme and HDM2, have been well-established and validated, there remains a large pool of candidates waiting to be investigated. Development of SMIs targeting the UPS has been largely facilitated by state-of-the-art technologies such as high-throughput screening and computer-assisted drug design, both of which require a better understanding of the targets of interest.

The immunoproteasome as a target in hematologic malignancies

Suppression of proteasome function with the first-in-class small molecule inhibitor bortezomib is a rational therapeutic strategy against several hematologic malignancies, including multiple myeloma and mantle cell lymphoma. Second-generation inhibitors such as carfilzomib, ixazomib, and marizomib that, like bortezomib, target both the constitutive proteasome and the immunoproteasome, are also in clinical trials and showing encouraging activity. While the efficacy of these agents is well documented, toxicities associated with their use, such as peripheral neuropathy and gastrointestinal effects, can necessitate dose reductions or even discontinuations, possibly hampering their anti-neoplastic effects. These findings suggested that it could be possible to improve the therapeutic index of this class of drugs by specifically targeting only the immunoproteasome. Since the immunoproteasome is a unique target found in lymphoid-derived cells, immunoproteasome-specific inhibitors (IPSIs) could preserve efficacy while reducing treatment-emergent toxicities since they would spare other tissues with little to no immunoproteasome expression. This review discusses the current state of development of IPSIs, and the potential of using such agents for the treatment of hematologic malignancies.

Nitric oxide and KLF4 protein epigenetically modify class II transactivator to repress major histocompatibility complex II expression during Mycobacterium bovis bacillus Calmette-Guerin infection

Pathogenic mycobacteria employ several immune evasion strategies such as inhibition of class II transactivator (CIITA) and MHC-II expression, to survive and persist in host macrophages. However, precise roles for specific signaling components executing down-regulation of CIITA/MHC-II have not been adequately addressed. Here, we demonstrate that Mycobacterium bovis bacillus Calmette-Guérin (BCG)-mediated TLR2 signaling-induced iNOS/NO expression is obligatory for the suppression of IFN-γ-induced CIITA/MHC-II functions. Significantly, NOTCH/PKC/MAPK-triggered signaling cross-talk was found critical for iNOS/NO production. NO responsive recruitment of a bifunctional transcription factor, KLF4, to the promoter of CIITA during M. bovis BCG infection of macrophages was essential to orchestrate the epigenetic modifications mediated by histone methyltransferase EZH2 or miR-150 and thus calibrate CIITA/MHC-II expression. NO-dependent KLF4 regulated the processing and presentation of ovalbumin by infected macrophages to reactive T cells. Altogether, our study delineates a novel role for iNOS/NO/KLF4 in dictating the mycobacterial capacity to inhibit CIITA/MHC-II-mediated antigen presentation by infected macrophages and thereby elude immune surveillance.

Antigen presentation by small intestinal epithelial cells uniquely enhances IFN-γ secretion from CD4+ intestinal intraepithelial lymphocytes

Small intestinal epithelial cells (sIECs) express major histocompatibility complex class II molecules even in a normal condition, and are known to function as antigen presenting cells (APCs) at least in vitro. These findings raised the possibility that sIECs play an important role in inducing immune responses against luminal antigens, especially those of intestinal intraepithelial lymphocytes (IELs) and lamina propria lymphocytes (LPLs). We herein showed that antigenic stimulation with sIECs induced markedly greater secretion of interferon-gamma (IFN-γ) by CD4(+) IELs, but not interleukin (IL)-4, IL-10 and IL-17 although the proliferative response was prominently lower than that with T cell-depleted splenic APCs. In contrast, no enhanced IFN-γ secretion by CD4(+) LPLs and primed splenic CD4(+) T cells was observed when stimulated with sIECs. Taken together, these results suggest that sIECs uniquely activate CD4(+) IELs and induce remarkable IFN-γ secretion upon antigenic stimulation in vivo.

IFNγ in combination with IL-7 enhances immunotherapy in two rat glioma models

Peripheral immunization, using a combination of interferon-gamma (IFNγ)- and interleukin-7 (IL-7)-producing tumor cells, eradicated 75% of pre-established intracerebral N32 rat glioma tumors, and prolonged survival in the more aggressive RG2 model. Rats immunized with IFNγ- and IL7-transduced N32 cells displayed increases in IFNγ plasma levels and proliferating circulating T cells when compared with rats immunized with N32-wild type cells. Following irradiation, the expression of MHC I and II was high on N32-IFNγ cells, but low on RG2-IFNγ cells. In conclusion, IFNγ and IL-7 immunizations prolong survival in two rat glioma models.

Suppression of the macrophage proteasome by ethanol impairs MHC class I antigen processing and presentation

Alcohol binge-drinking (acute ethanol consumption) is immunosuppressive and alters both the innate and adaptive arms of the immune system. Antigen presentation by macrophages (and other antigen presenting cells) represents an important function of the innate immune system that, in part, determines the outcome of the host immune response. Ethanol has been shown to suppress antigen presentation in antigen presenting cells though mechanisms of this impairment are not well understood. The constitutive and immunoproteasomes are important components of the cellular proteolytic machinery responsible for the initial steps critical to the generation of MHC Class I peptides for antigen presentation. In this study, we used an in-vitro cell culture model of acute alcohol exposure to study the effect of ethanol on the proteasome function in RAW 264.7 cells. Additionally, primary murine peritoneal macrophages obtained by peritoneal lavage from C57BL/6 mice were used to confirm our cell culture findings. We demonstrate that ethanol impairs proteasome function in peritoneal macrophages through suppression of chymotrypsin-like (Cht-L) proteasome activity as well as composition of the immunoproteasome subunit LMP7. Using primary murine peritoneal macrophages, we have further demonstrated that, ethanol-induced impairment of the proteasome function suppresses processing of antigenic proteins and peptides by the macrophage and in turn suppresses the presentation of these antigens to cells of adaptive immunity. The results of this study provide an important mechanism to explain the immunosuppressive effects of acute ethanol exposure.

Reduction in ATP levels triggers immunoproteasome activation by the 11S (PA28) regulator during early antiviral response mediated by IFNβ in mouse pancreatic β-cells

Autoimmune destruction of insulin producing pancreatic β-cells is the hallmark of type I diabetes. One of the key molecules implicated in the disease onset is the immunoproteasome, a protease with multiple proteolytic sites that collaborates with the constitutive 19S and the inducible 11S (PA28) activators to produce immunogenic peptides for presentation by MHC class I molecules. Despite its importance, little is known about the function and regulation of the immunoproteasome in pancreatic β-cells. Of special interest to immunoproteasome activation in β-cells are the effects of IFNβ, a type I IFN secreted by virus-infected cells and implicated in type I diabetes onset, compared to IFNγ, the classic immunoproteasome inducer secreted by cells of the immune system. By qPCR analysis, we show that mouse insulinoma MIN6 cells and mouse islets accumulate the immune proteolytic β1_i, β2_i and β5_i, and 11S mRNAs upon exposure to IFNβ or IFNγ. Higher concentrations of IFNβ than IFNγ are needed for similar expression, but in each case the expression is transient, with maximal mRNA accumulation in 12 hours, and depends primarily on Interferon Regulatory Factor 1. IFNs do not alter expression of regular proteasome genes, and in the time frame of IFNβ-mediated response, the immune and regular proteolytic subunits co-exist in the 20S particles. In cell extracts with ATP, these particles have normal peptidase activities and degrade polyubiquitinated proteins with rates typical of the regular proteasome, implicating normal regulation by the 19S activator. However, ATP depletion rapidly stimulates the catalytic rates in a manner consistent with levels of the 11S activator. These findings suggest that stochastic combination of regular and immune proteolytic subunits may increase the probability with which unique immunogenic peptides are produced in pancreatic β-cells exposed to IFNβ, but primarily in cells with reduced ATP levels that stimulate the 11S participation in immunoproteasome function.

Immunoproteasome Activation During Early Antiviral Response in Mouse Pancreatic β-cells: New Insights into Auto-antigen Generation in Type I Diabetes?

Type 1 diabetes results from autoimmune destruction of the insulin producing pancreatic β-cells. The immunoproteasome, a version of the proteasome that collaborates with the 11S/PA28 activator to generate immunogenic peptides for presentation by MHC class I molecules, has long been implicated in the onset of the disease, but little is known about immunoproteasome function and regulation in pancreatic β-cells. Interesting insight into these issues comes from a recent analysis of the immunoproteasome expressed in pancreatic β-cells during early antiviral defenses mediated by interferon β (IFNβ), a type I IFN implicated in the induction of the diabetic state in human and animal models. Using mouse islets and the MIN6 insulinoma cell line, Freudenburg et al. found that IFNβ stimulates expression of the immunoproteasome and the 11S/PA28 activator in a manner fundamentally similar to the classic immuno-inducer IFNγ, with similar timing of mRNA accumulation and decline; similar transcriptional activation mediated primarily by the IRF1 and similar mRNA and protein levels. Furthermore, neither IFNβ nor IFNγ altered the expression of regular proteolytic subunits or prevented their incorporation into proteolytic cores. As a result, immunoproteasomes had stochastic combinations of immune and regular proteolytic sites, an arrangement that would likely increase the probability with which unique immunogenic peptides are produced. However, immunoproteasomes were activated by the 11S/PA28 only under conditions of ATP depletion. A mechanism that prevents the activation of immunoproteasome at high ATP levels has not been reported before and could have a major regulatory significance, as it could suppress the generation of immunogenic peptides as cell accumulate immunoproteasome and 11S/PA28, and activate antigen processing only when ATP levels drop. We discuss implications of these new findings on the link between early antiviral response and the onset of type 1 diabetes.

Evaluation of the enhancing ability of three adjuvants for DNA vaccination using the porcine circovirus type 2 ORF2 (capsid) gene in mice

Molecular adjuvants were used to augment the amplitude of the immune response in many studies recently. Ubiquitin (ub), the peptide binding truncated C-terminal portion of heat shock protein 70 (hsp70c) and interleukin-2 (IL-2) are widely investigated adjuvants which have been proved to be efficient. In our study, we compared the enhancing ability of these three adjuvants based on DNA vaccination using the porcine circovirus type 2 ORF2 (capsid) gene in mice. The results of lymphocyte proliferation assay, flow cytometric analysis (FCM), antibody titer and cytokine production showed that ub conjugated plasmid induced a stronger Th1 type cellular immune response and an observably higher level of Cap-specific serum immunoglobulin G antibody compared with hsp70c or IL-2 conjugated plasmids during the period of post-immunization. Meanwhile, the ub conjugation vaccinated group elicited stronger specific immunity against PCV2 challenge than the others during most of the time of post-challenge. Thus, these data indicate that ub is a superior adjuvant for a PCV2 DNA vaccination than the hsp70c and IL-2 molecules.

Dendritic cell based PSMA immunotherapy for prostate cancer using a CD40-targeted adenovirus vector

Human prostate tumor vaccine and gene therapy trials using ex vivo methods to prime dendritic cells (DCs) with prostate specific membrane antigen (PSMA) have been somewhat successful, but to date the lengthy ex vivo manipulation of DCs has limited the widespread clinical utility of this approach. Our goal was to improve upon cancer vaccination with tumor antigens by delivering PSMA via a CD40-targeted adenovirus vector directly to DCs as an efficient means for activation and antigen presentation to T-cells. To test this approach, we developed a mouse model of prostate cancer by generating clonal derivatives of the mouse RM-1 prostate cancer cell line expressing human PSMA (RM-1-PSMA cells). To maximize antigen presentation in target cells, both MHC class I and TAP protein expression was induced in RM-1 cells by transduction with an Ad vector expressing interferon-gamma (Ad5-IFNγ). Administering DCs infected ex vivo with CD40-targeted Ad5-huPSMA, as well as direct intraperitoneal injection of the vector, resulted in high levels of tumor-specific CTL responses against RM-1-PSMA cells pretreated with Ad5-IFNγ as target cells. CD40 targeting significantly improved the therapeutic antitumor efficacy of Ad5-huPSMA encoding PSMA when combined with Ad5-IFNγ in the RM-1-PSMA model. These results suggest that a CD-targeted adenovirus delivering PSMA may be effective clinically for prostate cancer immunotherapy.

Nitric oxide-dependent CYP2B degradation is potentiated by a cytokine-regulated pathway and utilizes the immunoproteasome subunit LMP2

CYP2B proteins in rat hepatocytes undergo NO-dependent proteolytic degradation, but the mechanisms and the reasons for the specificity towards only certain P450 (cytochrome P450) enzymes are yet unknown. In the present study we found that down-regulation of CYP2B proteins by the NO donor NOC-18 is accelerated by pretreatment of the hepatocytes with IL-1 (interleukin-1β) in the presence of an NO synthase inhibitor, suggesting that an NO-independent action of IL-1 contributes to the lability of CYP2B proteins. The immunoproteasome subunit LMP2 (large multifunctional peptidase 2) was significantly expressed in hepatocytes under basal conditions, and IL-1 induced LMP2 within 6-12 h of treatment. CYP2B protein degradation in response to IL-1 was attenuated by the selective LMP2 inhibitor UK-101, but not by the LMP7 inhibitor IPSI. The results show that LMP2 contributes to the NO-dependent degradation of CYP2B proteins, and suggest that induction of LMP2 may be involved in the potentiation of this degradation by IL-1.

A novel HLA-B18 restricted CD8+ T cell epitope is efficiently cross-presented by dendritic cells from soluble tumor antigen

NY-ESO-1 has been a major target of many immunotherapy trials because it is expressed by various cancers and is highly immunogenic. In this study, we have identified a novel HLA-B*1801-restricted CD8⁺ T cell epitope, NY-ESO-1_88–96 (LEFYLAMPF) and compared its direct- and cross-presentation to that of the reported NY-ESO-1_157–165 epitope restricted to HLA-A*0201. Although both epitopes were readily cross-presented by DCs exposed to various forms of full-length NY-ESO-1 antigen, remarkably NY-ESO-1_88–96 is much more efficiently cross-presented from the soluble form, than NY-ESO-1_157–165. On the other hand, NY-ESO-1_157–165 is efficiently presented by NY-ESO-1-expressing tumor cells and its presentation was not enhanced by IFN-γ treatment, which induced immunoproteasome as demonstrated by Western blots and functionally a decreased presentation of Melan A_26–35; whereas NY-ESO-1_88–96 was very inefficiently presented by the same tumor cell lines, except for one that expressed high level of immunoproteasome. It was only presented when the tumor cells were first IFN-γ treated, followed by infection with recombinant vaccinia virus encoding NY-ESO-1, which dramatically increased NY-ESO-1 expression. These data indicate that the presentation of NY-ESO-1_88–96 is immunoproteasome dependent. Furthermore, a survey was conducted on multiple samples collected from HLA-B18⁺ melanoma patients. Surprisingly, all the detectable responses to NY-ESO-1_88–96 from patients, including those who received NY-ESO-1 ISCOMATRIX™ vaccine were induced spontaneously. Taken together, these results imply that some epitopes can be inefficiently presented by tumor cells although the corresponding CD8⁺ T cell responses are efficiently primed in vivo by DCs cross-presenting these epitopes. The potential implications for cancer vaccine strategies are further discussed.

Activity-based near-infrared fluorescent probe for LMP7: a chemical proteomics tool for the immunoproteasome in living cells

Probing the unknown: The immunoproteasome, an alternative form of the constitutive proteasome, has been implicated in a number of pathological states such as cancer and autoimmune diseases. In an effort to understand the role of the immunoproteasome in cells, the first immunoproteasome-specific near-infrared fluorescent probe has been developed.

Interferon gamma upregulates frataxin and corrects the functional deficits in a Friedreich ataxia model

Friedreich's ataxia (FRDA) is the most common hereditary ataxia, affecting ∼3 in 100 000 individuals in Caucasian populations. It is caused by intronic GAA repeat expansions that hinder the expression of the FXN gene, resulting in defective levels of the mitochondrial protein frataxin. Sensory neurons in dorsal root ganglia (DRG) are particularly damaged by frataxin deficiency. There is no specific therapy for FRDA. Here, we show that frataxin levels can be upregulated by interferon gamma (IFNγ) in a variety of cell types, including primary cells derived from FRDA patients. IFNγ appears to act largely through a transcriptional mechanism on the FXN gene. Importantly, in vivo treatment with IFNγ increases frataxin expression in DRG neurons, prevents their pathological changes and ameliorates the sensorimotor performance in FRDA mice. These results disclose new roles for IFNγ in cellular metabolism and have direct implications for the treatment of FRDA.

A selective inhibitor of the immunoproteasome subunit LMP2 induces apoptosis in PC-3 cells and suppresses tumour growth in nude mice

BACKGROUND

Although the proteasome is a validated anticancer target, the clinical application of its inhibitors has been limited because of inherent systemic toxicity. To broaden clinical utility of proteasome inhibitors as anticancer agents, it is critical to develop strategies to selectively target proteasomes in cancer cells. The immunoproteasome is an alternative form of the constitutive proteasome that is expressed at high levels in cancer tissues, but not in most normal cells in the body.

METHODS

To validate the immunoproteasome as a chemotherapeutic target, an immunoproteasome catalytic subunit LMP2-targeting inhibitor and siRNA were used. The sensitivity of PC-3 prostate cancer cells to these reagents was investigated using viability assays. Further, a xenograft model of prostate cancer was studied to test the in vivo effects of LMP2 inhibition.

RESULTS

A small molecule inhibitor of the immunoproteasome subunit LMP2, UK-101, induced apoptosis of PC-3 cells and resulted in significant inhibition (~50-60%) of tumour growth in vivo. Interestingly, UK-101 did not block degradation of IκBα in PC-3 cells treated with TNF-α, suggesting that its mode of action may be different from that of general proteasome inhibitors, such as bortezomib, which block IκBα degradation.

CONCLUSION

These results strongly suggest that the immunoproteasome has important roles in cancer cell growth and thus provide a rationale for targeting the immunoproteasome in the treatment of prostate cancer.

Lipopolysaccharide-induced neuroinflammation leads to the accumulation of ubiquitinated proteins and increases susceptibility to neurodegeneration induced by proteasome inhibition in rat hippocampus

Background

Neuroinflammation and protein accumulation are characteristic hallmarks of both normal aging and age-related neurodegenerative diseases. However, the relationship between these factors in neurodegenerative processes is poorly understood. We have previously shown that proteasome inhibition produced higher neurodegeneration in aged than in young rats, suggesting that other additional age-related events could be involved in neurodegeneration. We evaluated the role of lipopolysaccharide (LPS)-induced neuroinflammation as a potential synergic risk factor for hippocampal neurodegeneration induced by proteasome inhibition.

Methods

Young male Wistar rats were injected with 1 μL of saline or LPS (5 mg/mL) into the hippocampus to evaluate the effect of LPS-induced neuroinflammation on protein homeostasis. The synergic effect of LPS and proteasome inhibition was analyzed in young rats that first received 1 μL of LPS and 24 h later 1 μL (5 mg/mL) of the proteasome inhibitor lactacystin. Animals were sacrificed at different times post-injection and hippocampi isolated and processed for gene expression analysis by real-time polymerase chain reaction; protein expression analysis by western blots; proteasome activity by fluorescence spectroscopy; immunofluorescence analysis by confocal microscopy; and degeneration assay by Fluoro-Jade B staining.

Results

LPS injection produced the accumulation of ubiquitinated proteins in hippocampal neurons, increased expression of the E2 ubiquitin-conjugating enzyme UB2L6, decreased proteasome activity and increased immunoproteasome content. However, LPS injection was not sufficient to produce neurodegeneration. The combination of neuroinflammation and proteasome inhibition leads to higher neuronal accumulation of ubiquitinated proteins, predominant expression of pro-apoptotic markers and increased neurodegeneration, when compared with LPS or lactacystin (LT) injection alone.

Conclusions

Our results identify neuroinflammation as a risk factor that increases susceptibility to neurodegeneration induced by proteasome inhibition. These results highlight the modulation of neuroinflammation as a mechanism for neuronal protection that could be relevant in situations where both factors are present, such as aging and neurodegenerative diseases.

Proteins of Leishmania (Viannia) shawi confer protection associated with Th1 immune response and memory generation

BACKGROUND

Leishmania (Viannia) shawi parasite was first characterized in 1989. Recently the protective effects of soluble leishmanial antigen (SLA) from L. (V.) shawi promastigotes were demonstrated using BALB/c mice, the susceptibility model for this parasite. In order to identify protective fractions, SLA was fractionated by reverse phase HPLC and five antigenic fractions were obtained.

METHODS

F1 fraction was purified from L. (V.) shawi parasite extract by reverse phase HPLC. BALB/c mice were immunized once a week for two consecutive weeks by subcutaneous routes in the rump, using 25 μg of F1. After 1 and 16 weeks of last immunization, groups were challenged in the footpad with L. (V.) shawi promastigotes. After 2 months, those same mice were sacrificed and parasite burden, cellular and humoral immune responses were evaluated.

RESULTS

The F1 fraction induced a high degree of protection associated with an increase in IFN-γ, a decrease in IL-4, increased cell proliferation and activation of CD8+T lymphocytes. Long-term protection was acquired in F1-immunized mice, associated with increased CD4+ central memory T lymphocytes and activation of both CD4+ and CD8+ T cells. In addition, F1-immunized groups showed an increase in IgG2a levels.

CONCLUSIONS

The inductor capability of antigens to generate memory lymphocytes that can proliferate and secrete beneficial cytokines upon infection could be an important factor in the development of vaccine candidates against American Tegumentary Leishmaniasis.

The ubiquitin proteasome system in neurodegenerative diseases: culprit, accomplice or victim?

A shared hallmark for many neurodegenerative disorders is the accumulation of toxic protein species which is assumed to be the cause for these diseases. Since the ubiquitin proteasome system (UPS) is the most important pathway for selective protein degradation it is likely that it is involved in the aetiology neurodegenerative disorders. Indeed, impairment of the UPS has been reported to occur during neurodegeneration. Although accumulation of toxic protein species (amyloid β) are in turn known to impair the UPS the relationship is not necessarily causal. We provide an overview of the most recent insights in the roles the UPS plays in protein degradation and other processes. Additionally, we discuss the role of the UPS in clearance of the toxic proteins known to accumulate in the hallmarks of neurodegenerative diseases. The present paper will focus on critically reviewing the involvement of the UPS in specific neurodegenerative diseases and will discuss if UPS impairment is a cause, a consequence or both of the disease.