Heat Shock Up-Regulates lmp2 and lmp7 and Enhances Presentation of Immunoproteasome-Dependent Epitopes

Mapping the interplay of immunoproteasome and autophagy in different heart failure phenotypes

Proper protein degradation is required for cellular protein homeostasis and organ function. Particularly, in post-mitotic cells, such as cardiomyocytes, unbalanced proteolysis due to inflammatory stimuli and oxidative stress contributes to organ dysfunction. To ensure appropriate protein turnover, eukaryotic cells exert two main degradation systems, the ubiquitin-proteasome-system and the autophagy-lysosome-pathway. It has been shown that proteasome activity affects the development of cardiac dysfunction differently, depending on the type of heart failure. Studies analyzing the inducible subtype of the proteasome, the immunoproteasome (i20S), demonstrated that the i20S plays a double role in diseased hearts. While i20S subunits are increased in cardiac hypertrophy, atrial fibrillation and partly in myocarditis, the opposite applies to diabetic cardiomyopathy and ischemia/reperfusion injury. In addition, the i20S appears to play a role in autophagy modulation depending on heart failure phenotype. This review summarizes the current literature on the i20S in different heart failure phenotypes, emphasizing the two faces of i20S in injured hearts. A selection of established i20S inhibitors is introduced and signaling pathways linking the i20S to autophagy are highlighted. Mapping the interplay of the i20S and autophagy in different types of heart failure offers potential approaches for developing treatment strategies against heart failure.

The Functional and Mechanistic Roles of Immunoproteasome Subunits in Cancer

Cell-mediated immunity is driven by antigenic peptide presentation on major histocompatibility complex (MHC) molecules. Specialized proteasome complexes called immunoproteasomes process viral, bacterial, and tumor antigens for presentation on MHC class I molecules, which can induce CD8 T cells to mount effective immune responses. Immunoproteasomes are distinguished by three subunits that alter the catalytic activity of the proteasome and are inducible by inflammatory stimuli such as interferon-γ (IFN-γ). This inducible activity places them in central roles in cancer, autoimmunity, and inflammation. While accelerated proteasomal degradation is an important tumorigenic mechanism deployed by several cancers, there is some ambiguity regarding the role of immunoproteasome induction in neoplastic transformation. Understanding the mechanistic and functional relevance of the immunoproteasome provides essential insights into developing targeted therapies, including overcoming resistance to standard proteasome inhibition and immunomodulation of the tumor microenvironment. In this review, we discuss the roles of the immunoproteasome in different cancers.

Out of Control: The Role of the Ubiquitin Proteasome System in Skeletal Muscle during Inflammation

The majority of critically ill intensive care unit (ICU) patients with severe sepsis develop ICU-acquired weakness (ICUAW) characterized by loss of muscle mass, reduction in myofiber size and decreased muscle strength leading to persisting physical impairment. This phenotype results from a dysregulated protein homeostasis with increased protein degradation and decreased protein synthesis, eventually causing a decrease in muscle structural proteins. The ubiquitin proteasome system (UPS) is the predominant protein-degrading system in muscle that is activated during diverse muscle atrophy conditions, e.g., inflammation. The specificity of UPS-mediated protein degradation is assured by E3 ubiquitin ligases, such as atrogin-1 and MuRF1, which target structural and contractile proteins, proteins involved in energy metabolism and transcription factors for UPS-dependent degradation. Although the regulation of activity and function of E3 ubiquitin ligases in inflammation-induced muscle atrophy is well perceived, the contribution of the proteasome to muscle atrophy during inflammation is still elusive. During inflammation, a shift from standard- to immunoproteasome was described; however, to which extent this contributes to muscle wasting and whether this changes targeting of specific muscular proteins is not well described. This review summarizes the function of the main proinflammatory cytokines and acute phase response proteins and their signaling pathways in inflammation-induced muscle atrophy with a focus on UPS-mediated protein degradation in muscle during sepsis. The regulation and target-specificity of the main E3 ubiquitin ligases in muscle atrophy and their mode of action on myofibrillar proteins will be reported. The function of the standard- and immunoproteasome in inflammation-induced muscle atrophy will be described and the effects of proteasome-inhibitors as treatment strategies will be discussed.

Proteasome dysregulation in human cancer: implications for clinical therapies

Cancer cells show heightened dependency on the proteasome for their survival, growth, and spread. Proteasome dysregulation is therefore commonly selected in favor of the development of many types of cancer. The vast abnormalities in a cancer cell, on top of the complexity of the proteasome itself, have enabled a plethora of mechanisms gearing the proteasome to the oncogenic process. Here, we use selected examples to highlight some general mechanisms underlying proteasome dysregulation in cancer, including copy number variations, transcriptional control, epigenetic regulation, and post-translational modifications. Research in this field has greatly advanced our understanding of proteasome regulation and will shed new light on proteasome-based combination therapies for cancer treatment.

Antigen-adjuvant effects of icariin in enhancing tumor-specific immunity in mastocytoma-bearing DBA/2J mice

Cancer immunotherapy has attracted much attention in recent years because of the ability of immune system to identify tumor cells and limit their growth. Icariin (ICA) is a natural flavonoid glucoside isolated from Epimedium plants and has shown a variety of pharmacological activities such as anti-inflammatory effects, immunological regulation and anticancer potency. Furthermore, it has immunoadjuvant effects on enhancing Th1-immune response, suggesting that ICA may serve as an adjuvant for cancer immunotherapy. In this study, we used P815 mouse mastocytoma tumor model and immunized them with P815AB peptide and/or ICA. Our results demonstrated that ICA could increase the cytotoxic T lymphocytes (CTL) response for P815AB peptide on the tumor-bearing DBA/2J mice. In addition, the percentage of CD4⁺CD8⁺/CD3⁺CD69⁺/CD69⁺NKG2D⁺ positive cells in splenocytes of the tumor-bearing mice all significantly increased after combined immunization with ICA and P815AB peptide. This illustrated that ICA could enhance the immunogenicity of P815AB and improve the ability of T cells and CTLs in recognizing the tumor cells. Moreover, ICA improved the function of peritoneal macrophages with effects of inhibition on tumor growth. Besides, we discussed the possible mechanism of ICA to enhance body immunity by detecting the expression level of MHC-I and related genes in B16-F10 and RMA/S cells. The results suggested that ICA has the potential to up-regulate LMP/TAP related molecules and induce the expression of MHC-I, which increase the immune surveillance and keep cancer in remission. In conclusion, ICA showed an anti-tumor effect both in vitro and in vivo and may be an effective antigen adjuvant for cancer treatment by enhancing tumor-specific immunity.

The TRPV1 ion channel regulates thymocyte differentiation by modulating autophagy and proteasome activity

Autophagy and the ubiquitin-proteasome system (UPS) control thymus cell homeostasis under resting and endoplasmic reticulum (ER) stress conditions. Several evidence support a cross-talk between UPS and autophagy; abrogation of UPS responses stimulates autophagy, and vice versa the inhibition of autophagy alters the UPS functions.

Herein, we found that TRPV1 activation induces ER stress, proteasome dysfunction and autophagy in thymocytes by modulating the expression of UPR-related genes. The TRPV1-mediated autophagy prevents the UPR activation by inhibiting BiP, Grp94 and ERp57 chaperone protein expression.

Thymocytes from TRPV1 KO mice display both autophagy and proteasome dysfunctions, resulting in increased apoptotic cells and reduced total DP thymocyte number.

In addition, positive selection of thymocytes triggered by anti-TCRβ/CD2 Ab-mediated costimulation induces apoptosis in thymocytes from TRPV1 KO as compared with WT mice. Stimulation of TRPV1 KO thymocytes with anti-TCRβ/CD2 mAbs modulates the expression of CD4 antigen on purified DP thymocytes, with reduced number of mature, single positive (SP) CD4 and increased number of immature SP CD4^low and DP CD4^lowCD8⁺ thymocytes, further supporting the intrinsic role of TRPV1 in T cell maturation. Finally, a reduction in CD8⁺ and CD4⁺ T cells is evidenced in the peripheral blood and spleen of TRPV1 KO, as compared with WT mice. Therapeutic strategy by restraining or stimulating the TRPV1 expression and functions in thymocytes might represent a new pharmacological tool in the regulation of different inflammatory T cell responses.

PSMB8 as a Candidate Marker of Responsiveness to Preoperative Radiation Therapy in Rectal Cancer Patients

PURPOSE

The ability to predict individual responsiveness to cancer therapy is urgently needed. This is particularly true for patients with locally advanced rectal cancer (LARC) because a large proportion are resistant to preoperative chemoradiation therapy (CRT). In this study, we sought to identify markers that could predict response by comparing the gene expression profiles of the tumors of patients who received preoperative CRT.

METHODS AND MATERIALS

The basal gene expression profiles of tumors from 22 LARC patients who were responders (n=9) and nonresponders (n=13) to preoperative CRT were analyzed using RNA sequencing (RNA-Seq). To validate the RNA-Seq findings, real-time reverse transcriptase polymerase chain reaction (RT-PCR) was performed on tumor samples from an additional 40 LARC patients (n=20 responders; n=20 nonresponders). Candidate genes were stably overexpressed or knocked down in colorectal cancer (CRC) cell lines, and the effect on response to radiation was tested in vitro and also in vivo in a mouse xenograft model.

RESULTS

Eight differentially expressed (>16-fold) genes (B3GALT4, HSPA1B, KRBOX1, PPBP, PPP1R18, PSMB8, SLC39A7, and TAP2) associated with the preoperative CRT response were identified (P<.0005). Among these genes, real-time RT-PCR showed that PSMB8 and SLC39A7 were upregulated in the responsive group of the additional 40 LARC patients. In CRC cell lines, PSMB8 overexpression significantly reduced colony formation and increased the apoptosis-inducing molecules cleaved caspase-3 and cleaved PARP after 6-Gy irradiation. PSMB8 knockdown increased colony formation and decreased caspase-3 activation and cleaved PARP levels after irradiation. SLC39A7 overexpression had no significant effects on irradiated CSC cells. After irradiation of the xenografted mice, tumors that arose from CRC cell line HCT116 overexpressing PSMB8 grew more slowly than did those from HCT116 with vector alone.

CONCLUSION

These results suggest that PSMB8 is a predictive marker of preoperative radiosensitivity in LARC patients. Clinical validation in a larger cohort is now required.

Mammalian proteasome subtypes: Their diversity in structure and function

The 20S proteasome is a multicatalytic proteinase catalysing the degradation of the majority of intracellular proteins. Thereby it is involved in almost all basic cellular processes, which is facilitated by its association with various regulator complexes so that it appears in different disguises like 26S proteasome, hybrid-proteasome and others. The 20S proteasome has a cylindrical structure built up by four stacked rings composed of α- and β-subunits. Since the three active site-containing β-subunits can all or in part be replaced by immuno-subunits, three main subpopulations exist, namely standard-, immuno- and intermediate-proteasomes. Due to posttranslational modifications or/and genetic variations all α- and β-subunits occur in multiple iso- or proteoforms. This leads to the fact that each of the three subpopulations is composed of a variety of 20S proteasome subtypes. This review summarizes the knowledge of proteasome subtypes in mammalian cells and tissues and their possible biological and medical relevancy.

∆F508 CFTR interactome remodelling promotes rescue of cystic fibrosis

Deletion of phenylalanine 508 of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is the major cause of Cystic Fibrosis (CF), one of the most common inherited childhood diseases. The mutated CFTR anion channel is not fully glycosylated and shows minimal activity in bronchial epithelial cells of CF patients. Low temperature or inhibition of histone deacetylases (HDACi) can partially rescue ΔF508 CFTR cellular processing defects and function. A favorable change of ΔF508 CFTR protein-protein interactions was proposed as mechanism of rescue, however CFTR interactome dynamics during temperature-shift and HDACi rescue are unknown. Here, we report the first comprehensive analysis of the wt and ΔF508 CFTR interactome and its dynamics during temperature shift and HDACi. By using a novel deep proteomic analysis method (CoPIT), we identified 638 individual high-confidence CFTR interactors and discovered a mutation-specific interactome, which is extensively remodeled upon rescue. Detailed analysis of the interactome remodeling identified key novel interactors, whose loss promoted enhanced CFTR channel function in primary CF epithelia or which were critical for normal CFTR biogenesis. Our results demonstrate that global remodeling of ΔF508 CFTR interactions is crucial for rescue, and provide comprehensive insight into the molecular disease mechanisms of CF caused by deletion of F508.

The mammalian target of rapamycin modulates the immunoproteasome system in the heart

The mammalian target of rapamycin (mTOR) plays an important role in cardiac development and function. Inhibition of mTOR by rapamycin has been shown to attenuate pathological cardiac hypertrophy and improve the function of aging heart, accompanied by an inhibition of the cardiac proteasome activity. The current study aimed to determine the potential mechanism(s) by which mTOR inhibition modulates cardiac proteasome. Inhibition of mTOR by rapamycin was found to reduce primarily the immunoproteasome in both H9c2 cells in vitro and mouse heart in vivo, without significant effect on the constitutive proteasome and protein ubiquitination. Concurrent with the reduction of the immunoproteasome, rapamycin reduced two important inflammatory response pathways, the NF-κB and Stat3 signaling. In addition, rapamycin attenuated the induction of the immunoproteasome in H9c2 cells by inflammatory cytokines, including INFγ and TNFα, by suppressing NF-κB signaling. These data indicate that rapamycin indirectly modulated immunoproteasome through the suppression of inflammatory response pathways. Lastly, the role of the immunoproteasome during the development of cardiac hypertrophy was investigated. Administration of a specific inhibitor of the immunoproteasome ONX 0914 attenuated isoproterenol-induced cardiac hypertrophy, suggesting that the immunoproteasome may be involved in the development of cardiac hypertrophy and therefore could be a therapeutic target. In conclusion, rapamycin inhibits the immunoproteasome through its effect on the inflammatory signaling pathways and the immunoproteasome could be a potential therapeutic target for pathological cardiac hypertrophy.

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.

Pathophysiological importance of aggregated damaged proteins

Reactive oxygen species (ROS) are formed continuously in the organism even under physiological conditions. If the level of ROS in cells exceeds the cellular defense capacity, components such as RNA/DNA, lipids, and proteins are damaged and modified, thus affecting the functionality of organelles as well. Proteins are especially prominent targets of various modifications such as oxidation, glycation, or conjugation with products of lipid peroxidation, leading to the alteration of their biological function, nonspecific interactions, and the production of high-molecular-weight protein aggregates. To ensure the maintenance of cellular functions, two proteolytic systems are responsible for the removal of oxidized and modified proteins, especially the proteasome and organelles, mainly the autophagy-lysosomal systems. Furthermore, increased protein oxidation and oxidation-dependent impairment of proteolytic systems lead to an accumulation of oxidized proteins and finally to the formation of nondegradable protein aggregates. Accordingly, the cellular homeostasis cannot be maintained and the cellular metabolism is negatively affected. Here we address the current knowledge of protein aggregation during oxidative stress, aging, and disease.

Advanced-glycation-end-product-induced formation of immunoproteasomes: involvement of RAGE and Jak2/STAT1

AGEs (advanced glycation-end products) accumulate during aging and several pathologies such as Alzheimer's disease and diabetes. These protein products are known to inhibit proteolytic pathways. Moreover, AGEs are known to be involved in the activation of immune responses. In the present study we demonstrate that AGEs induce the expression of immunoproteasomal subunits. To elucidate a molecular basis underlying the observed effects we were able to demonstrate an activation of the Jak2 (Janus kinase 2)/STAT1 (signal transducer and activator of transcription 1) pathway. Inhibition of Jak2 by AG-490 and STAT1 by specific siRNA (small interfering RNA) abolished AGE-induced expression of immunoproteasomal subunits. Furthermore, silencing of RAGE (receptor for AGEs) revealed that AGE-induced up-regulation of the immunoproteasome is mediated by a RAGE signalling process. Thus we have described for the first time that the signalling pathway of Jak2 and STAT1 activated by AGEs via RAGE is involved in the induction of the immunoproteasome.

Redox control of the ubiquitin-proteasome system: from molecular mechanisms to functional significance

In their natural environments, cells are regularly exposed to oxidizing conditions that may lead to protein misfolding. If such misfolded proteins are allowed to linger, they may form insoluble aggregates and pose a serious threat to the cell. Accumulation of misfolded, oxidatively damaged proteins is characteristic of many diseases and during aging. To counter the adverse effects of oxidative stress, cells can initiate an antioxidative response in an attempt to repair the damage, or rapidly channel the damaged proteins for degradation by the ubiquitin-proteasome system (UPS). Recent studies have shown that elements of the oxidative stress response and the UPS are linked on many levels. To manage the extra burden of misfolded proteins, the UPS is induced by oxidative stress, and special proteasome subtypes protect cells against oxidative damage. In addition, the proteasome is directly associated with a thioredoxin and other cofactors that may adjust the particle's response during an oxidative challenge. Here, we give an overview of the UPS and a detailed description of the degradation of oxidized proteins and of the crosstalk between oxidative stress and protein degradation in health and disease.

Plant Hsp90 proteins interact with B-cells and stimulate their proliferation

BACKGROUND

The molecular chaperone heat shock protein 90 (Hsp90) plays an important role in folding stabilization and activation of client proteins. Besides, Hsp90 of mammals and mammalian pathogens displays immunostimulatory properties. Here, we investigated the role of plant-derived Hsp90s as B-cell mitogens by measuring their proliferative responses in vitro.

METHODOLOGY

Plant cytosolic Hsp90 isoforms from Arabidopsis thaliana (AtHsp81.2) and Nicotiana benthamiana (NbHsp90.3) were expressed in E. coli. Over-expression of recombinant plant Hsp90s (rpHsp90s) was confirmed by SDS-PAGE and western blot using and anti-AtHsp81.2 polyclonal anti-body. Both recombinant proteins were purified by Ni-NTA affinity chromatography and their identity confirmed by MALDI-TOF-TOF. Recombinant AtHsp81.2 and NbHsp90.3 proteins induced prominent proliferative responses in spleen cells form BALB/c mice. Polymyxin-B, a potent inhibitor of lipopolysaccharide (LPS), did not eliminate the rpHsp90-induced proliferation. In addition, in vitro incubation of spleen cells with rpHsp90 led to the expansion of CD19-bearing populations, suggesting a direct effect of these proteins on B lymphocytes. This effect was confirmed by immunofluorescence analysis, where a direct binding of rpHsp90 to B- but not to T-cells was observed in cells from BALB/c and C3H/HeN mice. Finally, we examined the involvement of Toll Like Receptor 4 (TLR4) molecules in the rpHsp90s induction of B-cell proliferation. Spleen cells from C3H/HeJ mice, which carry a point mutation in the cytoplasmic region of TLR4, responded poorly to prAtHsp90. However, the interaction between rpHsp90 and B-cells from C3H/HeJ mice was not altered, suggesting that the mutation on TLR4 would be affecting the signal cascade but not the rpHsp90-TLR4 receptor interaction.

CONCLUSIONS

Our results show for the first time that spleen cell proliferation can be stimulated by a non-pathogen-derived Hsp90. Furthermore, our data provide a new example of a non-pathogen-derived ligand for TLRs.

Regulation of tumor immunity by tumor/dendritic cell fusions

The goal of cancer vaccines is to induce antitumor immunity that ultimately will reduce tumor burden in tumor environment. Several strategies involving dendritic cells- (DCs)- based vaccine incorporating different tumor-associated antigens to induce antitumor immune responses against tumors have been tested in clinical trials worldwide. Although DCs-based vaccine such as fusions of whole tumor cells and DCs has been proven to be clinically safe and is efficient to enhance antitumor immune responses for inducing effective immune response and for breaking T-cell tolerance to tumor-associated antigens (TAAs), only a limited success has occurred in clinical trials. This paper reviews tumor immune escape and current strategies employed in the field of tumor/DC fusions vaccine aimed at enhancing activation of TAAs-specific cytotoxic T cells in tumor microenvironment.

Immunoproteasomes preserve protein homeostasis upon interferon-induced oxidative stress

Interferon (IFN)-induced immunoproteasomes (i-proteasomes) have been associated with improved processing of major histocompatibility complex (MHC) class I antigens. Here, we show that i-proteasomes function to protect cell viability under conditions of IFN-induced oxidative stress. IFNs trigger the production of reactive oxygen species, which induce protein oxidation and the formation of nascent, oxidant-damaged proteins. We find that the ubiquitylation machinery is concomitantly upregulated in response to IFNs, functioning to target defective ribosomal products (DRiPs) for degradation by i-proteasomes. i-proteasome-deficiency in cells and in murine inflammation models results in the formation of aggresome-like induced structures and increased sensitivity to apoptosis. Efficient clearance of these aggregates by the enhanced proteolytic activity of the i-proteasome is important for the preservation of cell viability upon IFN-induced oxidative stress. Our findings suggest that rather than having a specific role in the production of class I antigens, i-proteasomes increase the peptide supply for antigen presentation as part of a more general role in the maintenance of protein homeostasis.

Cancer vaccine by fusions of dendritic and cancer cells

Dendritic cells (DCs) are potent antigen-presenting cells and play a central role in the initiation and regulation of primary immune responses. Therefore, their use for the active immunotherapy against cancers has been studied with considerable interest. The fusion of DCs with whole tumor cells represents in many ways an ideal approach to deliver, process, and subsequently present a broad array of tumor-associated antigens, including those yet to be unidentified, in the context of DCs-derived costimulatory molecules. DCs/tumor fusion vaccine stimulates potent antitumor immunity in the animal tumor models. In the human studies, T cells stimulated by DC/tumor fusion cells are effective in lysis of tumor cells that are used as the fusion partner. In the clinical trials, clinical and immunological responses were observed in patients with advanced stage of malignant tumors after being vaccinated with DC/tumor fusion cells, although the antitumor effect is not as vigorous as in the animal tumor models. This review summarizes recent advances in concepts and techniques that are providing new impulses to DCs/tumor fusions-based cancer vaccination.

Functional alterations of cardiac proteasomes under physiological and pathological conditions

The cardiac proteasome is a complex, heterogeneous, and dynamic organelle. Its function is regulated by its molecular organization, post-translational modifications, and associated partner proteins. Pressure overload, ischaemic heart disease, or genetic mutations in contractile proteins can cause heart failure, during which misfolded protein levels are elevated. At the same time, numerous interconnected signal transduction pathways are activated that may modulate any of the three proteasomal regulatory mechanisms mentioned above, resulting in functional changes in cardiac proteasomes. Many lines of evidence support the important role of the ubiquitin-proteasome system (UPS) in the development of heart diseases. Many researchers have focused on the UPS, applying new drug discovery methods not only in the field of cancer research but also in cardiovascular fields such as cardiac hypertrophy and ischaemic heart diseases. More understanding of UPS in the pathophysiology of heart diseases will lead to new routes for therapy.

Cardiovascular inflammation and lesion cell apoptosis: a novel connection via the interferon-inducible immunoproteasome

OBJECTIVE

Increasing evidence suggests that chronic inflammation contributes to atherogenesis, and that acute inflammatory events cause plaque rupture, thrombosis, and myocardial infarction. The present studies examined how inflammatory factors, such as interferon-gamma (IFNgamma), cause increased sensitivity to apoptosis in vascular lesion cells.

METHODS AND RESULTS

Cells from the fibrous cap of human atherosclerotic lesions were sensitized by interferon-gamma (IFNgamma) to Fas-induced apoptosis, in a Bcl-X(L) reversible manner. Microarray profiling identified 72 INFgamma-induced transcripts with potential relevance to apoptosis. Half could be excluded because they were induced by IRF-1 overexpression, which did not sensitize to apoptosis. IFNgamma treatment strongly reduced Mcl-1, phospho-Bcl-2 (ser70), and phospho-Bcl-X(L) (ser62) protein levels. Candidate transcripts were modulated by siRNA, overexpression, or inhibitors to assess the effect on IFNgamma-induced Fas sensitivity. Surprisingly, siRNA knockdown of PSMB8 (LMP7), an "immunoproteasome" component, reversed IFNgamma-induced sensitivity to Fas ligation and prevented Fas/IFNgamma-induced degradation of Mcl-1, but did not protect p-Bcl-2 or p-Bcl-X(L). Proteasome inhibition markedly increased Mcl-1, p-Bcl-2, and p-Bcl-X(L) levels after IFNgamma treatment.

CONCLUSIONS

Although critical for antigen presentation, the immunoproteasome appears to be a key link between inflammatory factors and the control of vascular cell apoptosis and may thus be an important factor in plaque rupture and myocardial infarction.

Ischemic preconditioning-induced cardioprotection is lost in mice with immunoproteasome subunit low molecular mass polypeptide-2 deficiency

The ubiquitin-proteasome system plays an important role in many cellular processes through degradation of specific proteins. Low molecular mass polypeptide 2 (LMP-2 or beta(1i)) is one important subunit of the immunoproteasome. Ischemic preconditioning (IPC) activates cell signaling pathways and generates cardioprotection but has not been linked to LMP-2 function previously. LMP-2 knockout mice (C57BL6 background) and wild-type C57BL6 mice were subjected to 30 min of ischemia (I-30) and 120 min of reperfusion (R-120) with or without preceding IPC (10 min of infusion and 5 min of reperfusion). IPC significantly increased left ventricular developed pressure and decreased infarct size in wild-type mice, but this protective effect of IPC was lost in LMP-2 knockout mice. IPC-mediated degradation of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and activation of the downstream protein kinase Akt were impaired in LMP-2 knockout hearts. The impairment of PTEN degradation was associated with defective immunoproteasomes and decreased proteolytic activities. When LMP-2 knockout mice were pretreated with the PTEN inhibitor bpV(HOpic), cardiac function was significantly improved, and myocardial infarct size was significantly reduced after I-30/R-120. In conclusion, LMP-2 is required for normal proteasomal function and IPC induction in the heart. Its action may be related to PTEN protein degradation.

Hyperthermia on immune regulation: a temperature's story

Over the last decade the linkage between hyperthermia, heat shock proteins and fever with the body's immune system has been well investigated. The immunomodulatory function of hyperthermia has been found to be quite sensitively regulated by temperature, as different levels of heating can bring different modulatory effect on different sensitive targets. Understanding these intrinsic mechanisms could bring new inspirations on the design of clinical trials combining local tumor hyperthermia with immunotherapy in cancer patients. This review will attempt to tell the story about the effect of temperature on immune regulation, with special emphasis on the clinical application of hyperthermia and the feasibility of combining it with immunotherapy in the clinic.

Regulation of antigen presentation machinery in human dendritic cells by recombinant adenovirus

Recombinant adenoviral vectors (AdV) are potent vehicles for antigen engineering of dendritic cells (DC). DC engineered with AdV to express full length tumor antigens are capable stimulators of antigen-specific polyclonal CD8+ and CD4+ T cells. To determine the impact of AdV on the HLA class I antigen presentation pathway, we investigated the effects of AdV transduction on antigen processing machinery (APM) components in human DC. Interactions among AdV transduction, maturation, APM regulation and T cell activation were investigated. The phenotype and cytokine profile of DC transduced with AdV was intermediate, between immature (iDC) and matured DC (mDC). Statistically significant increases in expression were observed for peptide transporters TAP-1 and TAP-2, and HLA class I peptide-loading chaperone ERp57, as well as co-stimulatory surface molecule CD86 due to AdV transduction. AdV transduction enhanced the expression of APM components and surface markers on mDC, and these changes were further modulated by the timing of DC maturation. Engineering of matured DC to express a tumor-associated antigen stimulated a broader repertoire of CD8+ T cells, capable of recognizing immunodominant and subdominant epitopes. These data identify molecular changes in AdV-transduced DC (AdV/DC) that could influence T cell priming and should be considered in design of cancer vaccines.

Synergistic Induction of Antigen-Specific CTL by Fusions of TLR-Stimulated Dendritic Cells and Heat-Stressed Tumor Cells

Dendritic cell (DC)/tumor cell fusion cells (FCs) can induce potent CTL responses. The therapeutic efficacy of a vaccine requires the improved immunogenicity of both DCs and tumor cells. The DCs stimulated with the TLR agonist penicillin-killed Streptococcus pyogenes (OK-432; OK-DCs) showed higher expression levels of MHC class I and II, CD80, CD86, CD83, IL-12, and heat shock proteins (HSPs) than did immature DCs. Moreover, heat-treated autologous tumor cells displayed a characteristic phenotype with increased expression of HSPs, carcinoembryonic Ag (CEA), MUC1, and MHC class I (HLA-A2 and/or A24). In this study, we have created four types of FC preparation by alternating fusion cell partners: 1) immature DCs fused with unheated tumor cells; 2) immature DCs fused with heat-treated tumor cells; 3) OK-DCs fused with unheated tumor cells; and 4) OK-DCs fused with heat-treated tumor cells. Although OK-DCs fused with unheated tumor cells efficiently enhanced CTL induction, OK-DCs fused with heat-treated tumor cells were most active, as demonstrated by: 1) up-regulation of multiple HSPs, MHC class I and II, CEA, CD80, CD86, CD83, and IL-12; 2) activation of CD4+ and CD8+ T cells able to produce IFN- gamma at higher levels; 3) efficient induction of CTL activity specific for CEA or MUC1 or both against autologous tumor; and 4) superior abilities to induce CD107+ IFN-gamma+ CD8+ T cells and CD154+ IFN-gamma+ CD4+ T cells. These results strongly suggest that synergism between OK-DCs and heat-treated tumor cells enhances the immunogenicity of FCs and provides a promising means of inducing therapeutic antitumor immunity.

Intermediate-type 20 S proteasomes in HeLa cells: "asymmetric" subunit composition, diversity and adaptation

The 20 S proteasomes are cylinder-shaped heteromeric dimers with a subunit configuration of alpha7, beta7, beta7, alpha7. Replacement of the three active site-containing standard beta-subunits (beta1, beta2, beta5) by immuno-beta-subunits (beta1i, beta2i, beta5i) results in formation of 20 S immuno-proteasomes, while only partial replacement leads to intermediate-type proteasomes. Synthesis of immuno-subunits can be induced by interferon-gamma, which causes a complete transformation of three subtypes of standard proteasomes into three subtypes of intermediate-type proteasomes in HeLa cells, a process that results in a change in the proteolytic activities of the enzymes. HeLa cells producing the proteasome beta1-subunit tagged with the Fc region-binding ZZ domain of protein A were grown in the presence of interferon-gamma. From these cells, we have purified 20 S proteasomes by using IgG-affinity resin and analysed them by 2D PAGE. Our study showed that subunit replacement can be confined to one half of the proteasome cylinder, resulting in the formation of intermediate-type proteasomes with "asymmetric" subunit composition. Analysis of proteasomes purified from the cytoplasm, nucleoplasm, and microsomes of HeLa S3 cells reveals that all three compartments are furnished with intermediate-type proteasomes of different subtype and subunit composition, exhibiting different specific proteolytic activities.