ER stress affects processing of MHC class I-associated peptides

Differences in F pocket impact on HLA I genetic associations with autoimmune diabetes

Introduction

Human leukocyte antigen (HLA) I molecules present antigenic peptides to activate CD8+ T cells. Type 1 Diabetes (T1D) is an auto-immune disease caused by aberrant activation of the CD8+ T cells that destroy insulin-producing pancreatic β cells. Some HLA I alleles were shown to increase the risk of T1D (T1D-predisposing alleles), while some reduce this risk (T1D-protective alleles).

Methods

Here, we compared the T1D-predisposing and T1D-protective allotypes concerning peptide binding, maturation, localization and surface expression and correlated it with their sequences and energetic profiles using experimental and computational methods.

Results

T1D-predisposing allotypes had more peptide-bound forms and higher plasma membrane levels than T1D-protective allotypes. This was related to the fact that position 116 within the F pocket was more conserved and made more optimal contacts with the neighboring residues in T1D-predisposing allotypes than in protective allotypes.

Conclusion

Our work uncovers that specific polymorphisms in HLA I molecules potentially influence their susceptibility to T1D.

Chikungunya virus infection disrupts MHC-I antigen presentation via nonstructural protein 2

Infection by chikungunya virus (CHIKV), a mosquito-borne alphavirus, causes severe polyarthralgia and polymyalgia, which can last in some people for months to years. Chronic CHIKV disease signs and symptoms are associated with the persistence of viral nucleic acid and antigen in tissues. Like humans and nonhuman primates, CHIKV infection in mice results in the development of robust adaptive antiviral immune responses. Despite this, joint tissue fibroblasts survive CHIKV infection and can support persistent viral replication, suggesting that they escape immune surveillance. Here, using a recombinant CHIKV strain encoding the fluorescent protein VENUS with an embedded CD8+ T cell epitope, SIINFEKL, we observed a marked loss of both MHC class I (MHC-I) surface expression and antigen presentation by CHIKV-infected joint tissue fibroblasts. Both in vivo and ex vivo infected joint tissue fibroblasts displayed reduced cell surface levels of H2-Kb and H2-Db MHC-I proteins while maintaining similar levels of other cell surface proteins. Mutations within the methyl transferase-like domain of the CHIKV nonstructural protein 2 (nsP2) increased MHC-I cell surface expression and antigen presentation efficiency by CHIKV-infected cells. Moreover, expression of WT nsP2 alone, but not nsP2 with mutations in the methyltransferase-like domain, resulted in decreased MHC-I antigen presentation efficiency. MHC-I surface expression and antigen presentation was rescued by replacing VENUS-SIINFEKL with SIINFEKL tethered to β2-microglobulin in the CHIKV genome, which bypasses the requirement for peptide processing and TAP-mediated peptide transport into the endoplasmic reticulum. Collectively, this work suggests that CHIKV escapes the surveillance of antiviral CD8+ T cells, in part, by nsP2-mediated disruption of MHC-I antigen presentation.

The impact of tetrachlorobisphenol A exposure during puberty: Altered Leydig cell development and induced endoplasmic reticulum stress in male mice

Tetrachlorobisphenol A (TCBPA), a halogenated flame retardant and endocrine disruptor, has been detected in human urine and serum. While previous research has shown its impact on the reproductive system, investigations into its mechanisms during puberty remain limited. This study aims to explore the effects of TCBPA on Leydig cells in adolescent mice and potential underlying mechanisms. Male C57 mice of age 28 days were gavaged with 50, 100, and 200 mg/kg/day for 28 days. TCBPA did not alter body weight and testis weight but lowered testosterone levels at 100 and 200 mg/kg and reduced sperm count in the epididymis at 200 mg/kg. TCBPA lowered Leydig cell number at 200 mg/kg while it downregulated key Leydig cell gene (Lhcgr, Scarb1, Cyp11a1, Cyp17a1, Hsd3b6, Hsd17b3 and Insl3) as low as 50 mg/kg. Further study indicated that TCBPA induced reactive oxygen species and caused endoplasmic reticulum stress. In vitro study in TM3 mouse Leydig cells showed that TCBPA indeed induced reactive oxygen species and caused endoplasmic reticulum stress at 75 μM and inhibited testosterone production at this concentration and addition of antioxidant tocopherol can reverse it. These discoveries provide new insights and references for a deeper understanding of the toxic mechanisms of TCBPA on Leydig cells during puberty.

Interleukin-22 suppresses major histocompatibility complex II in mucosal epithelial cells

Major histocompatibility complex (MHC) II is dynamically expressed on mucosal epithelial cells and is induced in response to inflammation and parasitic infections, upon exposure to microbiota, and is increased in chronic inflammatory diseases. However, the regulation of epithelial cell-specific MHC II during homeostasis is yet to be explored. We discovered a novel role for IL-22 in suppressing epithelial cell MHC II partially via the regulation of endoplasmic reticulum (ER) stress, using animals lacking the interleukin-22-receptor (IL-22RA1), primary human and murine intestinal and respiratory organoids, and murine models of respiratory virus infection or with intestinal epithelial cell defects. IL-22 directly downregulated interferon-γ-induced MHC II on primary epithelial cells by modulating the expression of MHC II antigen A α (H2-Aα) and Class II transactivator (Ciita), a master regulator of MHC II gene expression. IL-22RA1-knockouts have significantly higher MHC II expression on mucosal epithelial cells. Thus, while IL-22-based therapeutics improve pathology in chronic disease, their use may increase susceptibility to viral infections.

Chikungunya virus infection disrupts MHC-I antigen presentation via nonstructural protein 2

Infection by chikungunya virus (CHIKV), a mosquito-borne alphavirus, causes severe polyarthralgia and polymyalgia, which can last in some people for months to years. Chronic CHIKV disease signs and symptoms are associated with the persistence of viral nucleic acid and antigen in tissues. Like humans and nonhuman primates, CHIKV infection in mice results in the development of robust adaptive antiviral immune responses. Despite this, joint tissue fibroblasts survive CHIKV infection and can support persistent viral replication, suggesting that they escape immune surveillance. Here, using a recombinant CHIKV strain encoding a chimeric protein of VENUS fused to a CD8+ T cell epitope, SIINFEKL, we observed a marked loss of both MHC class I (MHC-I) surface expression and antigen presentation by CHIKV-infected joint tissue fibroblasts. Both in vivo and ex vivo infected joint tissue fibroblasts displayed reduced cell surface levels of H2-Kb and H2-Db MHC proteins while maintaining similar levels of other cell surface proteins. Mutations within the methyl transferase-like domain of the CHIKV nonstructural protein 2 (nsP2) increased MHC-I cell surface expression and antigen presentation efficiency by CHIKV-infected cells. Moreover, expression of WT nsP2 alone, but not nsP2 with mutations in the methyltransferase-like domain, resulted in decreased MHC-I antigen presentation efficiency. MHC-I surface expression and antigen presentation could be rescued by replacing VENUS-SIINFEKL with SIINFEKL tethered to β2-microglobulin in the CHIKV genome, which bypasses the need for peptide processing and TAP-mediated peptide transport into the endoplasmic reticulum. Collectively, this work suggests that CHIKV escapes the surveillance of antiviral CD8+ T cells, in part, by nsP2-mediated disruption of MHC-I antigen presentation.

Enterotoxins A and B produced by Staphylococcus aureus increase cell proliferation, invasion and cytarabine resistance in acute myeloid leukemia cell lines

As in the case of cancer, the risk of infection increases when the host's immune system is not working properly. It has been shown that toxins produced by the bacteria responsible for bacterial infections can alter the properties of cancer cells as well as their sensitivity to chemotherapy agents. Staphylococcus aureus (S. aureus) is one of the most prevalent pathogens in acute myeloid leukemia (AML) patients and it produces several virulence factors, including Staphylococcal enterotoxin A (SEA) and Staphylococcal enterotoxin B (SEB). Cytotoxicity, transwell migration, invasion assays, and various transcriptomic and gene set enrichment (GSE) analyses were used to determine how SEA and SEB alter cell proliferation, migration, invasion, and Cytarabine (Cyt) resistance in AML cell lines. The treatment of AML cell lines with SEA/SEB caused an increase in cell proliferation and Cyt resistance. Toxins enhanced the proclivity of cells to migrate and invade, with around 50% of cells in the presence of SEA and SEB. Transcriptomic and gene set enrichment analyses, and subsequent PCR validations showed dysregulation of immune related genes and genesets. Apparently, this allows AML cells to escape and survive the undesirable environment created by toxins, possibly via the ER stress signaling pathway. Therefore, SEA and SEB can significantly alter the characteristics of AML cancer cells and evaluation of alterations in responsible immune genes and pathways may be crucial for controlling the progression of cancer. In addition, our results suggest that there may be a strong interaction between the immune related pathways and the ER signaling pathway.

Short chain fatty acids prime colorectal cancer cells to activate antitumor immunity

Introduction

Colorectal cancer (CRC) is a leading cause of death worldwide and its growth can either be promoted or inhibited by the metabolic activities of intestinal microbiota. Short chain fatty acids (SCFAs) are microbial metabolites with potent immunoregulatory properties yet there is a poor understanding of how they directly regulate immune modulating pathways within the CRC cells.

Methods

We used engineered CRC cell lines, primary organoid cultures, orthotopic in vivo models, and patient CRC samples to investigate how SCFA treatment of CRC cells regulates their ability to activate CD8+ T cells.

Results

CRC cells treated with SCFAs induced much greater activation of CD8+ T cells than untreated CRC cells. CRCs exhibiting microsatellite instability (MSI) due to inactivation of DNA mismatch repair were much more sensitive to SCFAs and induced much greater CD8+ T cell activation than chromosomally instable (CIN) CRCs with intact DNA repair, indicating a subtype-dependent response to SCFAs. This was due to SCFA-induced DNA damage that triggered upregulation of chemokine, MHCI, and antigen processing or presenting genes. This response was further potentiated by a positive feedback loop between the stimulated CRC cells and activated CD8+ T cells in the tumor microenvironment. The initiating mechanism in the CRCs was inhibition of histone deacetylation by the SCFAs that triggered genetic instability and led to an overall upregulation of genes associated with SCFA signaling and chromatin regulation. Similar gene expression patterns were found in human MSI CRC samples and in orthotopically grown MSI CRCs independent of the amount of SCFA producing bacteria in the intestine.

Discussion

MSI CRCs are widely known to be more immunogenic than CIN CRCs and have a much better prognosis. Our findings indicate that a greater sensitivity to microbially produced SCFAs contributes to the successful activation of CD8+ T cells by MSI CRCs, thereby identifying a mechanism that could be therapeutically targeted to improve antitumor immunity in CIN CRCs.

M2 macrophage-derived exosomes suppress tumor intrinsic immunogenicity to confer immunotherapy resistance

T-cell-based immune checkpoint blockade therapy (ICB) can be undermined by local immunosuppressive M2-like tumor-associated macrophages (TAMs). However, modulating macrophages has proved difficult as the molecular and functional features of M2-TAMs on tumor growth are still uncertain. Here we reported that immunosuppressive M2 macrophages render cancer cells resistant to CD8+ T-cell-dependent tumor-killing refractory ICB efficacy by secreting exosomes. Proteomics and functional studies revealed that M2 macrophage-derived exosome (M2-exo) transmitted apolipoprotein E (ApoE) to cancer cells conferring ICB resistance by downregulated MHC-I expression curbing tumor intrinsic immunogenicity. Mechanistically, M2 exosomal ApoE diminished the tumor-intrinsic ATPase activity of binding immunoglobulin protein (BiP) to decrease tumor MHC-I expression. Sensitizing ICB efficacy can be achieved by the administration of ApoE ligand, EZ-482, enhancing ATPase activity of BiP to boost tumor-intrinsic immunogenicity. Therefore, ApoE may serve as a predictor and a potential therapeutic target for ICB resistance in M2-TAMs-enriched cancer patients. Collectively, our findings signify that the exosome-mediated transfer of functional ApoE from M2 macrophages to the tumor cells confers ICB resistance. Our findings also provide a preclinical rationale for treating M2-enriched tumors with ApoE ligand, EZ-482, to restore sensitivity to ICB immunotherapy.

NLRC5-CIITA Fusion Protein as an Effective Inducer of MHC-I Expression and Antitumor Immunity

Aggressive tumors evade cytotoxic T lymphocytes by suppressing MHC class-I (MHC-I) expression that also compromises tumor responsiveness to immunotherapy. MHC-I defects strongly correlate to defective expression of NLRC5, the transcriptional activator of MHC-I and antigen processing genes. In poorly immunogenic B16 melanoma cells, restoring NLRC5 expression induces MHC-I and elicits antitumor immunity, raising the possibility of using NLRC5 for tumor immunotherapy. As the clinical application of NLRC5 is constrained by its large size, we examined whether a smaller NLRC5-CIITA fusion protein, dubbed NLRC5-superactivator (NLRC5-SA) as it retains the ability to induce MHC-I, could be used for tumor growth control. We show that stable NLRC5-SA expression in mouse and human cancer cells upregulates MHC-I expression. B16 melanoma and EL4 lymphoma tumors expressing NLRC5-SA are controlled as efficiently as those expressing full-length NLRC5 (NLRC5-FL). Comparison of MHC-I-associated peptides (MAPs) eluted from EL4 cells expressing NLRC5-FL or NLRC5-SA and analyzed by mass spectrometry revealed that both NLRC5 constructs expanded the MAP repertoire, which showed considerable overlap but also included a substantial proportion of distinct peptides. Thus, we propose that NLRC5-SA, with its ability to increase tumor immunogenicity and promote tumor growth control, could overcome the limitations of NLRC5-FL for translational immunotherapy applications.

EULAR study group on ‘MHC-I-opathy’: identifying disease-overarching mechanisms across disciplines and borders

The ‘MHC-I (major histocompatibility complex class I)-opathy’ concept describes a family of inflammatory conditions with overlapping clinical manifestations and a strong genetic link to the MHC-I antigen presentation pathway. Classical MHC-I-opathies such as spondyloarthritis, Behçet’s disease, psoriasis and birdshot uveitis are widely recognised for their strong association with certain MHC-I alleles and gene variants of the antigen processing aminopeptidases ERAP1 and ERAP2 that implicates altered MHC-I peptide presentation to CD8+T cells in the pathogenesis. Progress in understanding the cause and treatment of these disorders is hampered by patient phenotypic heterogeneity and lack of systematic investigation of the MHC-I pathway.

Here, we discuss new insights into the biology of MHC-I-opathies that strongly advocate for disease-overarching and integrated molecular and clinical investigation to decipher underlying disease mechanisms. Because this requires transformative multidisciplinary collaboration, we introduce the EULAR study group on MHC-I-opathies to unite clinical expertise in rheumatology, dermatology and ophthalmology, with fundamental and translational researchers from multiple disciplines such as immunology, genomics and proteomics, alongside patient partners. We prioritise standardisation of disease phenotypes and scientific nomenclature and propose interdisciplinary genetic and translational studies to exploit emerging therapeutic strategies to understand MHC-I-mediated disease mechanisms. These collaborative efforts are required to address outstanding questions in the etiopathogenesis of MHC-I-opathies towards improving patient treatment and prognostication.

Enhanced antitumor activity induced by a DNA vaccine encoding E7 antigen fused to an ERAD-targeting sequence

The endoplasmic reticulum (ER) is a key organelle in cell homeostasis and cell health through antigen presentation to immune cells. Thus, the ER has become a therapeutic target to induce cellular immune responses. We previously reported the antitumor effect of a DNA vaccine that expresses the E7 antigen fused to the cyclooxygenase-2 (COX-2) protein. This inflammation-related enzyme contains a degradation cassette associated with the endoplasmic reticulum-associated degradation (ERAD) pathway. To avoid the use of full-length COX-2 and any risk of adverse effects due to the activity of its catalytic site, we designed new versions of the fusion protein. These new constructs encode the E7 antigen fused to the signal peptide and the ERAD sequence of COX-2 with or without the membrane-binding domain (MBD) as well as deletion of the catalytic site. We evaluated the antigen-specific antitumor effect of these DNA constructs in murine prophylactic and therapeutic cancer models. These assays showed that the ERAD cassette is the minimum sequence in the COX-2 protein that induces an antitumor effect when fused to the E7 antigen with the advantage of eliminating any potential adverse effects from the use of full-length COX-2.

The Role of the Hypoxia-Related Unfolded Protein Response (UPR) in the Tumor Microenvironment

Despite our understanding of the unfolded protein response (UPR) pathways, the crosstalk between the UPR and the complex signaling networks that different cancers utilize for cell survival remains to be, in most cases, a difficult research barrier. A major problem is the constant variability of different cancer types and the different stages of cancer as well as the complexity of the tumor microenvironments (TME). This complexity often leads to apparently contradictory results. Furthermore, the majority of the studies that have been conducted have utilized two-dimensional in vitro cultures of cancer cells that were exposed to continuous hypoxia, and this approach may not mimic the dynamic and cyclic conditions that are found in solid tumors. Here, we discuss the role of intermittent hypoxia, one of inducers of the UPR in the cellular component of TME, and the way in which intermittent hypoxia induces high levels of reactive oxygen species, the activation of the UPR, and the way in which cancer cells modulate the UPR to aid in their survival. Although the past decade has resulted in defining the complex, novel non-coding RNA-based regulatory networks that modulate the means by which hypoxia influences the UPR, we are now just to beginning to understand some of the connections between hypoxia, the UPR, and the TME.

Metabolic adaption of cancer cells toward autophagy: Is there a role for ER-phagy?

Autophagy is an evolutionary conserved catabolic pathway that uses a unique double-membrane vesicle, called autophagosome, to sequester cytosolic components, deliver them to lysosomes and recycle amino-acids. Essentially, autophagy acts as a cellular cleaning system that maintains metabolic balance under basal conditions and helps to ensure nutrient viability under stress conditions. It is also an important quality control mechanism that removes misfolded or aggregated proteins and mediates the turnover of damaged and obsolete organelles. In this regard, the idea that autophagy is a non-selective bulk process is outdated. It is now widely accepted that forms of selective autophagy are responsible for metabolic rewiring in response to cellular demand. Given its importance, autophagy plays an essential role during tumorigenesis as it sustains malignant cellular growth by acting as a coping-mechanisms for intracellular and environmental stress that occurs during malignant transformation. Cancer development is accompanied by the formation of a peculiar tumor microenvironment that is mainly characterized by hypoxia (oxygen < 2%) and low nutrient availability. Such conditions challenge cancer cells that must adapt their metabolism to survive. Here we review the regulation of autophagy and selective autophagy by hypoxia and the crosstalk with other stress response mechanisms, such as UPR. Finally, we discuss the emerging role of ER-phagy in sustaining cellular remodeling and quality control during stress conditions that drive tumorigenesis.

Mitochondrial fission induces immunoescape in solid tumors through decreasing MHC-I surface expression

Mitochondrial dynamics can regulate Major Histocompatibility Complex (MHC)-I antigen expression by cancer cells and their immunogenicity in mice and in patients with malignancies. A crucial role in the mitochondrial fragmentation connection with immunogenicity is played by the IRE1α-XBP-1s axis. XBP-1s is a transcription factor for aminopeptidase TPP2, which inhibits MHC-I complex cell surface expression likely by degrading tumor antigen peptides. Mitochondrial fission inhibition with Mdivi-1 upregulates MHC-I expression on cancer cells and enhances the efficacy of adoptive T cell therapy in patient-derived tumor models. Therefore mitochondrial fission inhibition might provide an approach to enhance the efficacy of T cell-based immunotherapy.

The Potential Role of Mitochondrial Acetaldehyde Dehydrogenase 2 in Urological Cancers From the Perspective of Ferroptosis and Cellular Senescence

Overproduction of reactive oxygen species (ROS) and superlative lipid peroxidation promote tumorigenesis, and mitochondrial aldehyde dehydrogenase 2 (ALDH2) is associated with the detoxification of ROS-mediated lipid peroxidation-generated reactive aldehydes such as 4-hydroxy-2-nonenal (4-HNE), malondialdehyde, and acrolein due to tobacco smoking. ALDH2 has been demonstrated to be highly associated with the prognosis and chemoradiotherapy sensitivity of many types of cancer, including leukemia, lung cancer, head and neck cancer, esophageal cancer, hepatocellular cancer, pancreatic cancer, and ovarian cancer. In this study, we explored the possible relationship between ALDH2 and urological cancers from the aspects of ferroptosis, epigenetic alterations, proteostasis, mitochondrial dysfunction, and cellular senescence.

The role of cellular proteostasis in anti-tumor immunity

Immune checkpoint blockade therapy is perhaps the most important development in cancer treatment in recent memory. It is based on decades of investigation into the biology of immune cells and the role of the immune system in controlling cancer growth. While the molecular circuitry that governs the immune system in general - and anti-tumor immunity in particular - is intensely studied, far less attention has been paid to the role of cellular stress in this process. Proteostasis, intimately linked to cell stress responses, refers to the dynamic regulation of the cellular proteome and is maintained through a complex network of systems that govern the synthesis, folding, and degradation of proteins in the cell. Disruption of these systems can result in the loss of protein function, altered protein function, the formation of toxic aggregates, or pathologies associated with cell stress. However, the importance of proteostasis extends beyond its role in maintaining proper protein function; proteostasis governs how tolerant cells may be to mutations in protein coding genes and the overall half-life of proteins. Such gene expression changes may be associated with human diseases including neurodegenerative diseases, metabolic disease, and cancer and manifest at the protein level against the backdrop of the proteostasis network in any given cellular environment. In this review, we focus on the role of proteostasis in regulating immune responses against cancer as well the role of proteostasis in determining immunogenicity of cancer cells.

Development of an Immortalized Porcine Fibroblast Cell Panel With Different Swine Leukocyte Antigen Genotypes

Immortalized cell lines are valuable resources to expand the molecular characterization of major histocompatibility complex genes and their presented antigens. We generated a panel of immortalized cell lines by transfecting human telomerase reverse transcriptase (hTERT) into primary fibroblast cells prepared from ear, fetal, and lung tissues of 10 pigs from five breeds and successfully cultured them for 30-45 passages. The cell growth characteristic of the immortalized fibroblasts was similar to that of primary fibroblast, which was unable to form colonies on soft agar. The genotypes of major swine leukocyte antigen (SLA) genes, including three classical class I (SLA-1, -2, and -3) and three class II genes (DQB1, DRB1, and DQA), were determined using high-resolution typing. A total of 58 alleles, including a novel allele for SLA-2, were identified. Each cell line was unique. A cell line derived from a National Institutes of Health miniature pig was homozygous across the six major SLA genes. The expression levels of SLA classical class I genes varied among the cell lines and were slightly upregulated in the immortalized compared to the primary cells based on semiquantitative reverse transcription polymerase chain reaction. The immortalized porcine fibroblast cell lines with diverse SLA haplotypes that were developed in this study have potential to be applied in studies regarding the molecular characteristics and genetic structure of SLA genes and epitope-major histocompatibility complex interactions in pigs.

Pharmacological Inhibition of IRE-1 Alpha Activity in Herpes Simplex Virus Type 1 and Type 2-Infected Dendritic Cells Enhances T Cell Activation

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) infections are life-long and highly prevalent in the human population. These viruses persist in the host, eliciting either symptomatic or asymptomatic infections that may occur sporadically or in a recurrent manner through viral reactivations. Clinical manifestations due to symptomatic infection may be mild such as orofacial lesions, but may also translate into more severe diseases, such as ocular infections that may lead to blindness and life-threatening encephalitis. A key feature of herpes simplex viruses (HSVs) is that they have evolved molecular determinants that hamper numerous components of the host’s antiviral innate and adaptive immune system. Importantly, HSVs infect and negatively modulate the function of dendritic cells (DCs), by inhibiting their T cell-activating capacity and eliciting their apoptosis after infection. Previously, we reported that HSV-2 activates the splicing of the mRNA of XBP1, which is related to the activity of the unfolded protein response (UPR) factor Inositol-Requiring Enzyme 1 alpha (IRE-1α). Here, we sought to evaluate if the activation of the IRE-1α pathway in DCs upon HSV infection may be related to impaired DC function after infection with HSV-1 or HSV-2. Interestingly, the pharmacological inhibition of the endonuclease activity of IRE-1α in HSV-1- and HSV-2-infected DCs significantly reduced apoptosis in these cells and enhanced their capacity to migrate to lymph nodes and activate virus-specific CD4⁺ and CD8⁺ T cells. These findings suggest that the activation of the IRE-1α-dependent UPR pathway in HSV-infected DCs may play a significant role in the negative effects that these viruses exert over these cells and that the modulation of this signaling pathway may be relevant for enhancing the function of DCs upon infection with HSVs.

An accomplice more than a mere victim: The impact of β-cell ER stress on type 1 diabetes pathogenesis

BACKGROUND

Pancreatic β-cells are the insulin factory of an organism with a mission to regulate glucose homeostasis in the body. Due to their high secretory activity, β-cells rely on a functional and intact endoplasmic reticulum (ER). Perturbations to ER homeostasis and unmitigated stress lead to β-cell dysfunction and death. Type 1 diabetes (T1D) is a chronic inflammatory disease caused by the autoimmune-mediated destruction of β-cells. Although autoimmunity is an essential component of T1D pathogenesis, accumulating evidence suggests an important role of β-cell ER stress and aberrant unfolded protein response (UPR) in disease initiation and progression.

SCOPE OF REVIEW

In this article, we introduce ER stress and the UPR, review β-cell ER stress in various mouse models, evaluate its involvement in inflammation, and discuss the effects of ER stress on β-cell plasticity and demise, and islet autoimmunity in T1D. We also highlight the relationship of ER stress with other stress response pathways and provide insight into ongoing clinical studies targeting ER stress and the UPR for the prevention or treatment of T1D.

MAJOR CONCLUSIONS

Evidence from ex vivo studies, in vivo mouse models, and tissue samples from patients suggest that β-cell ER stress and a defective UPR contribute to T1D pathogenesis. Thus, restoration of β-cell ER homeostasis at various stages of disease presents a plausible therapeutic strategy for T1D. Identifying the specific functions and regulation of each UPR sensor in β-cells and uncovering the crosstalk between stressed β-cells and immune cells during T1D progression would provide a better understanding of the molecular mechanisms of disease process, and may reveal novel targets for development of effective therapies for T1D.

High Glucose Concentrations Impair the Processing and Presentation of Mycobacterium tuberculosis Antigens In Vitro

Type 2 diabetes is an established risk factor for tuberculosis, but the underlying mechanisms are largely unknown. We established an in vitro model to analyze the effect of high glucose concentrations in antigen processing and presentation in antigen-presenting cells. Human monocyte-derived macrophages (MDMs) were exposed to high (11 mM and 30 mM) and low (5.5 mM) glucose concentrations and infected with Mycobacterium tuberculosis (Mtb). Flow cytometry was used to analyze the effect of high glucose concentrations in histocompatibility complex (MHC) class II molecules (HLA-DR) and co-stimulatory molecules (CD80 and CD86), indispensable for an adequate antigenic presentation and CD4+ T cell activation. HLA-DR and CD86 were significantly decreased by high glucose concentrations compared with low glucose concentrations. Confocal microscopy was used to detect Rab 5 and Lamp-1, proteins involved in the kinetics of antigen processing as early markers, and Rab 7 and cathepsin D as late markers. We observed a delay in the dynamics of the acquisition of Rab 7 and cathepsin D in high glucose concentrations. Moreover, the kinetics of the formation M. tuberculosis peptide-MHC II complexes in MDMs was decreased under high glucose concentrations, reducing their capacity for T cell activation. These findings suggest that high glucose concentrations directly affect antigenic processing, and therefore antigenic presentation.

Decidual NK cells kill Zika virus-infected trophoblasts

Zika virus (ZIKV) during pregnancy infects fetal trophoblasts and causes placental damage and birth defects including microcephaly. Little is known about the anti-ZIKV cellular immune response at the maternal-fetal interface. Decidual natural killer cells (dNK), which directly contact fetal trophoblasts, are the dominant maternal immune cells in the first-trimester placenta, when ZIKV infection is most hazardous. Although dNK express all the cytolytic molecules needed to kill, they usually do not kill infected fetal cells but promote placentation. Here, we show that dNK degranulate and kill ZIKV-infected placental trophoblasts. ZIKV infection of trophoblasts causes endoplasmic reticulum (ER) stress, which makes them dNK targets by down-regulating HLA-C/G, natural killer (NK) inhibitory receptor ligands that help maintain tolerance of the semiallogeneic fetus. ER stress also activates the NK activating receptor NKp46. ZIKV infection of Ifnar1 ^-/- pregnant mice results in high viral titers and severe intrauterine growth restriction, which are exacerbated by depletion of NK or CD8 T cells, indicating that killer lymphocytes, on balance, protect the fetus from ZIKV by eliminating infected cells and reducing the spread of infection.

Beneficial autoimmunity improves cancer prognosis

Many tumour antigens that do not arise from cancer cell-specific mutations are targets of humoral and cellular immunity despite their expression on non-malignant cells. Thus, in addition to the expected ability to detect mutations and stress-associated shifts in the immunoproteome and immunopeptidome (the sum of MHC class I-bound peptides) unique to malignant cells, the immune system also recognizes antigens expressed in non-malignant cells, which can result in autoimmune reactions against non-malignant cells from the tissue of origin. These autoimmune manifestations include, among others, vitiligo, thyroiditis and paraneoplastic syndromes, concurrent with melanoma, thyroid cancer and non-small-cell lung cancer, respectively. Importantly, despite the undesirable effects of these symptoms, such events can have prognostic value and correlate with favourable disease outcomes, suggesting 'beneficial autoimmunity'. Similarly, the occurrence of dermal and endocrine autoimmune adverse events in patients receiving immune-checkpoint inhibitors can have a positive predictive value for therapeutic outcomes. Neoplasias derived from stem cells deemed 'not essential' for survival (such as melanocytes, thyroid cells and most cells in sex-specific organs) have a particularly good prognosis, perhaps because the host can tolerate autoimmune reactions that destroy tumour cells at some cost to non-malignant tissues. In this Perspective, we discuss examples of spontaneous as well as therapy-induced autoimmunity that correlate with favourable disease outcomes and make a strong case in favour of this 'beneficial autoimmunity' being important not only in patients with advanced-stage disease but also in cancer immunosurveillance.

Deregulation of HLA-I in cancer and its central importance for immunotherapy

It is now well accepted that many tumors undergo a process of clonal selection which means that tumor antigens arising at various stages of tumor progression are likely to be represented in just a subset of tumor cells. This process is thought to be driven by constant immunosurveillance which applies selective pressure by eliminating tumor cells expressing antigens that are recognized by T cells. It is becoming increasingly clear that the same selective pressure may also select for tumor cells that evade immune detection by acquiring deficiencies in their human leucocyte antigen (HLA) presentation pathways, allowing important tumor antigens to persist within cells undetected by the immune system. Deficiencies in antigen presentation pathway can arise by a variety of mechanisms, including genetic and epigenetic changes, and functional antigen presentation is a hard phenomenon to assess using our standard analytical techniques. Nevertheless, it is likely to have profound clinical significance and could well define whether an individual patient will respond to a particular type of therapy or not. In this review we consider the mechanisms by which HLA function may be lost in clinical disease, we assess the implications for current immunotherapy approaches using checkpoint inhibitors and examine the prognostic impact of HLA loss demonstrated in clinical trials so far. Finally, we propose strategies that might be explored for possible patient stratification.

Chemoradiation induces upregulation of immunogenic cell death-related molecules together with increased expression of PD-L1 and galectin-9 in gastric cancer

Surgery alone or combined with chemo- and/or radiation therapy remains the primary treatment for gastric cancer (GC) to date and immunotherapeutic tools such as monoclonal antibodies are only slowly being implemented. This is partly due to the fact that the immune microenvironment in GC during chemoradiation and other treatment modalities is still poorly understood. 7 gastric cancer (GC) cell lines were tested for their response to chemoradiation using 5-FU in combination with X-ray irradiation. We conducted flow cytometric analysis to determine the cells’ ability to undergo immunogenic cell death (ICD) and their expression of the two immunosuppressive proteins programmed death-ligand 1 (PD-L1) and galectin-9 (Gal-9). We evaluated the overall immunogenicity of two cell lines (MKN7, MKN74) in co-culture experiments with human monocyte-derived dendritic cells (Mo-DCs). Chemoradiation induces distinct responses in different GC cell lines. We observe ICD in vitro in all tested GC cell lines in the form of calreticulin (CRT) translocation to the plasma membrane. As a resistance mechanism, these cells also upregulated Gal-9 and PD-L1. Mo-DC maturation experiments showed that GCs provoked the maturation of Mo-DCs after chemoradiation in vitro. The addition of α-PD-L1 blocking antibody further enhanced the immunogenicity of these cells while improving DC viability. Blocking Tim-3, as the main receptor for Gal-9, had no such effect. Our findings suggest that the benefits of chemoradiation can substantially depend on tumor subtype and these benefits can be offset by induced immune evasion in GC. Combination treatment using checkpoint inhibitors could potentially lead to enhanced immune responses and yield better patient outcomes.

Karyotype Aberrations in Action: The Evolution of Cancer Genomes and the Tumor Microenvironment

Cancer is a disease of cellular evolution. For this cellular evolution to take place, a population of cells must contain functional heterogeneity and an assessment of this heterogeneity in the form of natural selection. Cancer cells from advanced malignancies are genomically and functionally very different compared to the healthy cells from which they evolved. Genomic alterations include aneuploidy (numerical and structural changes in chromosome content) and polyploidy (e.g., whole genome doubling), which can have considerable effects on cell physiology and phenotype. Likewise, conditions in the tumor microenvironment are spatially heterogeneous and vastly different than in healthy tissues, resulting in a number of environmental niches that play important roles in driving the evolution of tumor cells. While a number of studies have documented abnormal conditions of the tumor microenvironment and the cellular consequences of aneuploidy and polyploidy, a thorough overview of the interplay between karyotypically abnormal cells and the tissue and tumor microenvironments is not available. Here, we examine the evidence for how this interaction may unfold during tumor evolution. We describe a bidirectional interplay in which aneuploid and polyploid cells alter and shape the microenvironment in which they and their progeny reside; in turn, this microenvironment modulates the rate of genesis for new karyotype aberrations and selects for cells that are most fit under a given condition. We conclude by discussing the importance of this interaction for tumor evolution and the possibility of leveraging our understanding of this interplay for cancer therapy.

Tackling HLA Deficiencies Head on with Oncolytic Viruses

Dysregulation of HLA (human leukocyte antigen) function is increasingly recognized as a common escape mechanism for cancers subject to the pressures exerted by immunosurveillance or immunotherapeutic interventions. Oncolytic viruses have the potential to counter this resistance by upregulating HLA expression or encouraging an HLA-independent immunological responses. However, to achieve the best therapeutic outcomes, a prospective understanding of the HLA phenotype of cancer patients is required to match them to the characteristics of different oncolytic strategies. Here, we consider the spectrum of immune competence observed in clinical disease and discuss how it can be best addressed using this novel and powerful treatment approach.

Endoplasmic reticulum stress signals in the tumour and its microenvironment

Protein handling, modification and folding in the endoplasmic reticulum (ER) are tightly regulated processes that determine cell function, fate and survival. In several tumour types, diverse oncogenic, transcriptional and metabolic abnormalities cooperate to generate hostile microenvironments that disrupt ER homeostasis in malignant and stromal cells, as well as infiltrating leukocytes. These changes provoke a state of persistent ER stress that has been demonstrated to govern multiple pro-tumoural attributes in the cancer cell while dynamically reprogramming the function of innate and adaptive immune cells. Aberrant activation of ER stress sensors and their downstream signalling pathways have therefore emerged as key regulators of tumour growth and metastasis as well as response to chemotherapy, targeted therapies and immunotherapy. In this Review, we discuss the physiological inducers of ER stress in the tumour milieu, the interplay between oncogenic signalling and ER stress response pathways in the cancer cell and the profound immunomodulatory effects of sustained ER stress responses in tumours.

Negative feedback and modern anti-cancer strategies targeting the ER stress response

Endoplasmic reticulum (ER) stress is a cell state in which misfolded or unfolded proteins are aberrantly accumulated in the ER. ER stress induces an evolutionarily conserved adaptive response, named the ER stress response, that deploys a self-regulated machinery to maintain cellular proteostasis. However, compared to its well-established canonical activation mechanism, the negative feedback mechanisms regulating the ER stress response remain unclear and no accepted methods or markers have been established. Several studies have documented that both endogenous and exogenous insults can induce ER stress in cancer. Based on this evidence, small molecule inhibitors targeting ER stress response have been designed to kill cancer cells, with some of them showing excellent curative effects. Here, we review recent advances in our understanding of negative feedback of the ER stress response and compare the markers used to date. We also summarize therapeutic inhibitors targeting ER stress response and highlight the promises and challenges ahead.

Acetaldehyde suppresses HBV-MHC class I complex presentation on hepatocytes via induction of ER stress and Golgi fragmentation

Alcohol consumption worsens hepatitis B virus (HBV) infection pathogenesis. We have recently reported that acetaldehyde suppressed HBV peptide-major histocompatibility complex I (MHC class I) complex display on hepatocytes, limiting recognition and subsequent removal of the infected hepatocytes by HBV-specific cytotoxic T lymphocytes (CTLs). This suppression was attributed to impaired processing of antigenic peptides by the proteasome. However, in addition to proteasome dysfunction, alcohol may induce endoplasmic reticulum (ER) stress and Golgi fragmentation in HBV-infected liver cells to reduce uploading of viral peptides to MHC class I and/or trafficking of this complex to the hepatocyte surface. Hence, the aim of this study was to elucidate whether alcohol-induced ER stress and Golgi fragmentation affect HBV peptide-MHC class I complex presentation on HBV+ hepatocytes. Here, we demonstrate that, while both acetaldehyde and HBV independently cause ER stress and Golgi fragmentation, the combined exposure provided an additive effect. Thus we observed an activation of the inositol-requiring enzyme 1α-X-box binding protein 1 and activation transcription factor (ATF)6α, but not the phospho PKR-like ER kinase-phospho eukaryotic initiation factor 2α-ATF4-C/EBP homologous protein arms of ER stress in HBV-transfected cells treated with acetaldehyde-generating system (AGS). In addition, Golgi proteins trans-Golgi network 46, GM130, and Giantin revealed punctate distribution, indicating Golgi fragmentation upon AGS exposure. Furthermore, the effects of acetaldehyde were reproduced by treatment with ER stress inducers, thapsigargin and tunicamycin, which also decreased the display of this complex and MHC class I turnover in HepG2.2.15 cells and HBV-infected primary human hepatocytes. Taken together, alcohol-induced ER stress and Golgi fragmentation contribute to the suppression of HBV peptide-MHC class I complex presentation on HBV+ hepatocytes, which may diminish their recognition by CTLs and promote persistence of HBV infection in hepatocytes.NEW & NOTEWORTHY Our current findings show that acetaldehyde accelerates endoplasmic reticulum (ER) stress by activating the unfolded protein response arms inositol-requiring enzyme 1α-X-box binding protein 1 and activation transcription factor (ATF)6α but not phospho PKR-like ER kinase-p eukaryotic initiation factor 2α-ATF4-C/EBP homologous protein in hepatitis B virus (HBV)-transfected HepG2.2.15 cells. It also potentiates Golgi fragmentation, as evident by punctate distribution of Golgi proteins, GM130, trans-Golgi network 46, and Giantin. While concomitantly increasing HBV DNA and HBV surface antigen titers, acetaldehyde-induced ER stress suppresses the presentation of HBV peptide-major histocompatibility complex I complexes on hepatocyte surfaces, thereby promoting the persistence of HBV infection in the liver.

HIV-1 induced changes in HLA-C*03 : 04-presented peptide repertoires lead to reduced engagement of inhibitory natural killer cell receptors

OBJECTIVE

Viral infections influence intracellular peptide repertoires available for presentation by HLA-I. Alterations in HLA-I/peptide complexes can modulate binding of killer immunoglobuline-like receptors (KIRs) and thereby the function of natural killer (NK) cells. Although multiple studies have provided evidence that HLA-I/KIR interactions play a role in HIV-1 disease progression, the consequence of HIV-1 infection for HLA-I/KIR interactions remain largely unknown.

DESIGN

We determined changes in HLA-I presented peptides resulting from HIV-1-infection of primary human CD4 T cells and assessed the impact of changes in peptide repertoires on HLA-I/KIR interactions.

METHODS

Liquid chromatography-coupled tandem mass spectrometry to identify HLA-I presented peptides, cell-based in-vitro assays to evaluate functional consequences of alterations in immunopeptidome and atomistic molecular dynamics simulations to confirm experimental data.

RESULTS

A total of 583 peptides exclusively presented on HIV-1-infected cells were identified, of which only 0.2% represented HIV-1 derived peptides. Focusing on HLA-C*03 : 04/KIR2DL3 interactions, we observed that HLA-C*03 : 04-presented peptides derived from noninfected CD4 T cells mediated stronger binding of inhibitory KIR2DL3 than peptides derived from HIV-1-infected cells. Furthermore, the most abundant peptide presented by HLA-C*03 : 04 on noninfected CD4 T cells (VIYPARISL) mediated the strongest KIR2DL3-binding, while the most abundant peptide presented on HIV-1-infected cells (YAIQATETL) did not mediate KIR2DL3-binding. Molecular dynamics simulations of HLA-C*03 : 04/KIR2DL3 interactions in the context of these two peptides revealed that VIYPARISL significantly enhanced the HLA-C*03 : 04/peptide contact area to KIR2DL3 compared with YAIQATETL.

CONCLUSION

These data demonstrate that HIV-1 infection-induced changes in HLA-I-presented peptides can reduce engagement of inhibitory KIRs, providing a mechanism for enhanced activation of NK cells by virus-infected cells.

Characterizing diversity in the tumor-immune microenvironment of distinct subclasses of gastroesophageal adenocarcinomas

BACKGROUND

Gastroesophageal adenocarcinomas (GEAs) are heterogeneous cancers where immune checkpoint inhibitors have robust efficacy in heavily inflamed microsatellite instability (MSI) or Epstein-Barr virus (EBV)-positive subtypes. Immune checkpoint inhibitor responses are markedly lower in diffuse/genome stable (GS) and chromosomal instable (CIN) GEAs. In contrast to EBV and MSI subtypes, the tumor microenvironment of CIN and GS GEAs have not been fully characterized to date, which limits our ability to improve immunotherapeutic strategies.

PATIENTS AND METHODS

Here we aimed to identify tumor-immune cell association across GEA subclasses using data from The Cancer Genome Atlas (N = 453 GEAs) and archival GEA resection specimen (N = 71). The Cancer Genome Atlas RNAseq data were used for computational inferences of immune cell subsets, which were correlated to tumor characteristics within and between subtypes. Archival tissues were used for more spatial immune characterization spanning immunohistochemistry and mRNA expression analyses.

RESULTS

Our results confirmed substantial heterogeneity in the tumor microenvironment between distinct subtypes. While MSI-high and EBV+ GEAs harbored most intense T cell infiltrates, the GS group showed enrichment of CD4+ T cells, macrophages and B cells and, in ∼50% of cases, evidence for tertiary lymphoid structures. In contrast, CIN cancers possessed CD8+ T cells predominantly at the invasive margin while tumor-associated macrophages showed tumor infiltrating capacity. Relatively T cell-rich 'hot' CIN GEAs were often from Western patients, while immunological 'cold' CIN GEAs showed enrichment of MYC and cell cycle pathways, including amplification of CCNE1.

CONCLUSIONS

These results reveal the diversity of immune phenotypes of GEA. Half of GS gastric cancers have tertiary lymphoid structures and are therefore promising candidates for immunotherapy. The majority of CIN GEAs, however, exhibit T cell exclusion and infiltrating macrophages. Associations of immune-poor CIN GEAs with MYC activity and CCNE1 amplification may enable new studies to determine precise mechanisms of immune evasion, ultimately inspiring new therapeutic modalities.

Unraveling the regulatory role of endoplasmic-reticulum-associated degradation in tumor immunity

During malignant transformation and cancer progression, tumor cells face both intrinsic and extrinsic stress, endoplasmic reticulum (ER) stress in particular. To survive and proliferate, tumor cells use multiple stress response pathways to mitigate ER stress, promoting disease aggression and treatment resistance. Among the stress response pathways is ER-associated degradation (ERAD), which consists of multiple components and steps working together to ensure protein quality and quantity. In addition to its established role in stress responses and tumor cell survival, ERAD has recently been shown to regulate tumor immunity. Here we summarize current knowledge on how ERAD promotes protein degradation, regulates immune cell development and function, participates in antigen presentation, exerts paradoxical roles on tumorigenesis and immunity, and thus impacts current cancer therapy. Collectively, ERAD is a critical protein homeostasis pathway intertwined with cancer development and tumor immunity. Of particular importance is the need to further unveil ERAD's enigmatic roles in tumor immunity to develop effective targeted and combination therapy for successful treatment of cancer.

Beyond the cell factory: Homeostatic regulation of and by the UPRER

The endoplasmic reticulum (ER) is commonly referred to as the factory of the cell, as it is responsible for a large amount of protein and lipid synthesis. As a membrane-bound organelle, the ER has a distinct environment that is ideal for its functions in synthesizing these primary cellular components. Many different quality control machineries exist to maintain ER stability under the stresses associated with synthesizing, folding, and modifying complex proteins and lipids. The best understood of these mechanisms is the unfolded protein response of the ER (UPR^ER), in which transmembrane proteins serve as sensors, which trigger a coordinated transcriptional response of genes dedicated for mitigating the stress. As the name suggests, the UPR^ER is most well described as a functional response to protein misfolding stress. Here, we focus on recent findings and emerging themes in additional roles of the UPR^ER outside of protein homeostasis, including lipid homeostasis, autophagy, apoptosis, and immunity.

ER stress activates immunosuppressive network: implications for aging and Alzheimer's disease

The endoplasmic reticulum (ER) contains stress sensors which recognize the accumulation of unfolded proteins within the lumen of ER, and subsequently these transducers stimulate the unfolded protein response (UPR). The ER sensors include the IRE1, PERK, and ATF6 transducers which activate the UPR in an attempt to restore the quality of protein folding and thus maintain cellular homeostasis. If there is excessive stress, UPR signaling generates alarmins, e.g., chemokines and cytokines, which activate not only tissue-resident immune cells but also recruit myeloid and lymphoid cells into the affected tissues. ER stress is a crucial inducer of inflammation in many pathological conditions. A chronic low-grade inflammation and cellular senescence have been associated with the aging process and many age-related diseases, such as Alzheimer’s disease. Currently, it is known that immune cells can exhibit great plasticity, i.e., they are able to display both pro-inflammatory and anti-inflammatory phenotypes in a context-dependent manner. The microenvironment encountered in chronic inflammatory conditions triggers a compensatory immunosuppression which defends tissues from excessive inflammation. Recent studies have revealed that chronic ER stress augments the suppressive phenotypes of immune cells, e.g., in tumors and other inflammatory disorders. The activation of immunosuppressive network, including myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg), has been involved in the aging process and Alzheimer’s disease. We will examine in detail whether the ER stress-related changes found in aging tissues and Alzheimer’s disease are associated with the activation of immunosuppressive network, as has been observed in tumors and many chronic inflammatory diseases.

Beta Cell Dedifferentiation Induced by IRE1α Deletion Prevents Type 1 Diabetes

Immune-mediated destruction of insulin-producing β cells causes type 1 diabetes (T1D). However, how β cells participate in their own destruction during the disease process is poorly understood. Here, we report that modulating the unfolded protein response (UPR) in β cells of non-obese diabetic (NOD) mice by deleting the UPR sensor IRE1α prior to insulitis induced a transient dedifferentiation of β cells, resulting in substantially reduced islet immune cell infiltration and β cell apoptosis. Single-cell and whole-islet transcriptomics analyses of immature β cells revealed remarkably diminished expression of β cell autoantigens and MHC class I components, and upregulation of immune inhibitory markers. IRE1α-deficient mice exhibited significantly fewer cytotoxic CD8⁺ T cells in their pancreata, and adoptive transfer of their total T cells did not induce diabetes in Rag1^-/- mice. Our results indicate that inducing β cell dedifferentiation, prior to insulitis, allows these cells to escape immune-mediated destruction and may be used as a novel preventive strategy for T1D in high-risk individuals.

The Impact of the ER Unfolded Protein Response on Cancer Initiation and Progression: Therapeutic Implications

Cellular stress induced by the accumulation of misfolded proteins in the endoplasmic reticulum (ER) activates an elaborate signalling network termed the unfolded protein response (UPR). This adaptive response is mediated by the transmembrane signal transducers IRE1, PERK, and ATF6 to decide cell fate of recovery or death. In malignant cells, UPR signalling may be required to maintain ER homeostasis and survival in the tumor microenvironment characterized by oxidative stress, hypoxia, lactic acidosis and compromised protein folding. Here we provide an overview of the ER response to cellular stress and how the sustained activation of this network enables malignant cells to develop tumorigenic, metastatic and drug-resistant capacities to thrive under adverse conditions. Understanding the complexity of ER stress responses and how to target the UPR in disease will have significant potential for novel future therapeutics.

Understanding and leveraging cell metabolism to enhance mesenchymal stem cell transplantation survival in tissue engineering and regenerative medicine applications

In tissue engineering and regenerative medicine, stem cell-specifically, mesenchymal stromal/stem cells (MSCs)-therapies have fallen short of their initial promise and hype. The observed marginal, to no benefit, success in several applications has been attributed primarily to poor cell survival and engraftment at transplantation sites. MSCs have a metabolism that is flexible enough to enable them to fulfill their various cellular functions and remarkably sensitive to different cellular and environmental cues. At the transplantation sites, MSCs experience hostile environments devoid or, at the very least, severely depleted of oxygen and nutrients. The impact of this particular setting on MSC metabolism ultimately affects their survival and function. In order to develop the next generation of cell-delivery materials and methods, scientists must have a better understanding of the metabolic switches MSCs experience upon transplantation. By designing treatment strategies with cell metabolism in mind, scientists may improve survival and the overall therapeutic potential of MSCs. Here, we provide a comprehensive review of plausible metabolic switches in response to implantation and of the various strategies currently used to leverage MSC metabolism to improve stem cell-based therapeutics.

ER-stressed MSC displayed more effective immunomodulation in RA CD4+CXCR5+ICOS+ follicular helper-like T cells through higher PGE2 binding with EP2/EP4

Objectives: To analyze the further immunomodulatory effects of endoplasmic reticulum (ER)-stressed umbilical cord-derived mesenchymal stem cells MSCs (UC-MSCs) on rheumatoid arthritis (RA) CD4⁺CXCR5⁺ICOS⁺ T (follicular helper-like T, Tfh) cells.Methods: MSCs were isolated from umbilical cord and surface markers were identified by flow cytometry. CD4⁺ T cells were purified from RA patients' peripheral blood mononuclear cells (PBMCs) using immunomagnetic beads. Thapsigargin (Tg)-stimulated or unstimulated MSCs were co-cultured with RA CD4⁺ T cells. CD4⁺CXCR5⁺ICOS⁺ T cells were analyzed with fluorescence activating cell sorter (FACS) and major soluble factors secreted by MSCs were detected by qRT-PCR as well as ELISA. Receptors of prostanoid E2 (PGE2), known as EP1-4, on CD4⁺ T cells were tested with RT-PCR and FACS. Proportion of CD4⁺CXCR5⁺ICOS⁺ T cells was determined after EP2/EP4 antagonists and anti-IL-6R antibody was added into co-cultured system, respectively.Results: ER-stressed MSCs further down-regulated peripheral CD4⁺CXCR5⁺ICOS⁺ T cells compared with Tg-stimulated MSCs and CD4⁺ T co-cultured group. PGE2 and IL-6 increased obviously in the supernatants. EP2/EP4 could be detected on CD4⁺ T cells and frequencies of CD4⁺CXCR5⁺ICOS⁺ T cells were upregulated when EP2 and/or EP4 antagonists rather than anti-IL-6R antibody were added.Conclusions: ER-stressed MSCs exhibited better inhibition effect on RA CD4⁺CXCR5⁺ICOS⁺ T cells by releasing PGE2, indicating the immunosuppressive effect of MSCs could be enhanced by induction of ER stress.

Integrative genomic and transcriptomic analysis of genetic markers in Dupuytren's disease

Background

Dupuytren’s disease (DD) is a fibroproliferative disorder characterized by thickening and contracting palmar fascia. The exact pathogenesis of DD remains unknown.

Results

In this study, we identified co-expressed gene set (DD signature) consisting of 753 genes via weighted gene co-expression network analysis. To confirm the robustness of DD signature, module enrichment analysis and meta-analysis were performed. Moreover, this signature effectively classified DD disease samples. The DD signature were significantly enriched in unfolded protein response (UPR) related to endoplasmic reticulum (ER) stress. Next, we conducted multiple-phenotype regression analysis to identify trans-regulatory hotspots regulating expression levels of DD signature using Genotype-Tissue Expression data. Finally, 10 trans-regulatory hotspots and 16 eGenes genes that are significantly associated with at least one cis-eQTL were identified.

Conclusions

Among these eGenes, major histocompatibility complex class II genes and ZFP57 zinc finger protein were closely related to ER stress and UPR, suggesting that these genetic markers might be potential therapeutic targets for DD.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0518-3) contains supplementary material, which is available to authorized users.

Metabolic stress in cancer cells induces immune escape through a PI3K-dependent blockade of IFNγ receptor signaling

BACKGROUND

T-cell mediated immunotherapy brought clinical success for many cancer patients. Nonetheless, downregulation of MHC class I antigen presentation, frequently occurring in solid cancers, limits the efficacy of these therapies. Unraveling the mechanisms underlying this type of immune escape is therefore of great importance. We here investigated the immunological effects of metabolic stress in cancer cells as a result of nutrient deprivation.

METHODS

TC1 and B16F10 tumor cell lines were cultured under oxygen- and glucose-deprivation conditions that mimicked the tumor microenvironment of solid tumors. Presentation of peptide antigens by MHC class I molecules was measured by flow cytometry and via activation of tumor-specific CD8 T cell clones. The proficiency of the IFNy-STAT1 pathway was investigated by Western blots on phosphorylated proteins, transfection of constitutive active STAT1 constructs and qPCR of downstream targets. Kinase inhibitors for PI3K were used to examine its role in IFNy receptor signal transduction.

RESULTS

Combination of oxygen- and glucose-deprivation resulted in decreased presentation of MHC class I antigens on cancer cells, even in the presence of the stimulatory cytokine IFNy. This unresponsiveness to IFNy was the result of failure to phosphorylate the signal transducer STAT1. Forced expression of constitutive active STAT1 fully rescued the MHC class I presentation. Furthermore, oxygen- and glucose-deprivation increased PI3K activity in tumor cells. Pharmacological inhibition of this pathway not only restored signal transduction through IFNy-STAT1 but also improved MHC class I presentation. Importantly, PI3K inhibitors also rendered tumor cells sensitive for recognition by CD8 T cells in culture conditions of metabolic stress.

CONCLUSIONS

These data revealed a strong impact of metabolic stress on the presentation of tumor antigens by MHC class I and suggest that this type of tumor escape takes place at hypoxic areas even during times of active T cell immunity and IFNy release.

Negative effects on newborn piglets caused by excess dietary tryptophan in the morning in sows

BACKGROUND

This study investigated the effect of dynamic feeding models of dietary tryptophan on sows' performance during late pregnancy.

RESULTS

The average piglet birth weight and live farrowing rate from sows consuming a high-low tryptophan diet (0.39% Trp in the morning and 0.13% Trp in the afternoon) were decreased compared with those fed a 2×tryptophan diet (0.26% Trp in the morning and afternoon). Compared with the 2×tryptophan group, sow serum kynurenic acid and the newborn liver n-6:n-3 polyunsaturated fatty acid ratio were significantly higher, and sow serum taurine and newborn serum taurine, phosphoserine, cysteine and proline were lower in the high-low tryptophan diet group. Eighty-eight genes were differentially expressed in newborn piglets' livers between the 2×tryptophan and high-low groups. Genes related to cytotoxic effector regulation (major histocompatibility complex class I proteins), NADH oxidation, reactive oxygen species (ROS) metabolism and tissue development were differentially expressed between these two groups.

CONCLUSION

Together, the results provide information on new biomarkers in serum or liver and provide novel insights into variations in the fetal liver during exogenous stimulus response and biological processes of ROS metabolism in fetuses during late pregnancy caused by a single excessive tryptophan ingestion daily in the morning. © 2018 Society of Chemical Industry.

Molecular Insights Into the Relationship Between Autoimmune Thyroid Diseases and Breast Cancer: A Critical Perspective on Autoimmunity and ER Stress

The etiopathologies behind autoimmune thyroid diseases (AITDs) unravel misbehavior of immune components leading to the corruption of immune homeostasis where thyroid autoantigens turn foe to the self. In AITDs lymphocytic infiltration in the thyroid shows up a deranged immune system charging the follicular cells of the thyroid gland (thyrocytes) leading to the condition of either hyperthyroidism or hypothyroidism. The inflammation in AITDs consistently associate with ER function due to which disturbances in the ER protein homeostasis leads to unfolded protein response (UPR) that promotes pathogenesis of autoimmunity. The roles of ER stress in the instantaneous downregulation of MHC class I molecules on thyrocytes and the relevance of IFN γ in the pathogenesis of AITD has been well-documented. Thyroglobulin being the major target of autoantibodies in most of the AITDs is because of its unusual processing in the ER. Autoimmune disorders display a conglomeration of ER stress-induced UPR activated molecules. Several epidemiological data highlight the preponderance of AITDs in women as well as its concurrence with breast cancer. Both being an active glandular system displaying endocrine activity, thyroid as well as breast tissue show various commonalities in the expression pattern of heterogenous molecules that not only participate in the normal functioning but at the same time share the blame during disease establishment. Studies on the development and progression of breast carcinoma display a deranged and uncontrolled immune response, which is meticulously exploited during tumor metastasis. The molecular crosstalks between AITDs and breast tumor microenvironment rely on active participation of immune cells. The induction of ER stress by Tunicamycin advocates to provide a model for cancer therapy by intervening glycosylation. Therefore, this review attempts to showcase the molecules that are involved in feeding up the relationship between breast carcinoma and AITDs.

Targeting HPV-16 antigens to the endoplasmic reticulum induces an endoplasmic reticulum stress response

Very promising results have been observed with a deoxyribonucleic acid (DNA) vaccine based on human papillomavirus type-16 (HPV-16) antigen retention and delivery system in the endoplasmic reticulum (ER). However, the mechanism by which these antigens are processed once they reach this organelle is still unknown. Therefore, we evaluated whether this system awakens a stress response in the ER. Different DNA constructs based on E6 and E7 mutant antigens fused to an ER signal peptide (SP), a signal for retention in the ER (KDEL), or both signals (SPK), were transfected into HEK-293 cells. Overexpression of E6 and E7 antigens targeted to the ER (SP, and SPK constructs) induced ER stress, which was indicated by an increase of the ER-stress markers GRP78/BiP and CHOP. Additionally, the ER stress response was mediated by the ATF4 transcription factor, which was translocated into the nucleus. Besides, the overexpressed antigens were degraded by the proteasome. Through a cycloheximide-chase assay, we demonstrated that when both protein synthesis and proteasome were inhibited, the overexpressed antigens were degraded. Interestingly, when proteasome was blocked autophagy was increased and the ER stress response decreased. Taken together, these results indicate that the antigens are initially degraded by the ERAD pathway, and autophagy degradation pathway can be induced to compensate the proteasome inhibition. Therefore, we provided a new insight into the mechanism by which E6 and E7 mutant antigens are processed once they reach the ER, which will help to improve the development of more effective vaccines against cancer.

Overview of Bile Acids Signaling and Perspective on the Signal of Ursodeoxycholic Acid, the Most Hydrophilic Bile Acid, in the Heart

Bile acids (BA) are classically known as an important agent in lipid absorption and cholesterol metabolism. Nowadays, their role in glucose regulation and energy homeostasis are widely reported. BAs are involved in various cellular signaling pathways, such as protein kinase cascades, cyclic AMP (cAMP) synthesis, and calcium mobilization. They are ligands for several nuclear hormone receptors, including farnesoid X-receptor (FXR). Recently, BAs have been shown to bind to muscarinic receptor and Takeda G-protein-coupled receptor 5 (TGR5), both G-protein-coupled receptor (GPCR), independent of the nuclear hormone receptors. Moreover, BA signals have also been elucidated in other nonclassical BA pathways, such as sphingosine-1-posphate and BK (large conductance calcium- and voltage activated potassium) channels. Hydrophobic BAs have been proven to affect heart rate and its contraction. Elevated BAs are associated with arrhythmias in adults and fetal heart, and altered ratios of primary and secondary bile acid are reported in chronic heart failure patients. Meanwhile, in patients with liver cirrhosis, cardiac dysfunction has been strongly linked to the increase in serum bile acid concentrations. In contrast, the most hydrophilic BA, known as ursodeoxycholic acid (UDCA), has been found to be beneficial in improving peripheral blood flow in chronic heart failure patients and in protecting the heart against reperfusion injury. This review provides an overview of BA signaling, with the main emphasis on past and present perspectives on UDCA signals in the heart.

The role of the unfolded protein response in cancer progression: From oncogenesis to chemoresistance

Tumour cells endure both oncogenic and environmental stresses during cancer progression. Transformed cells must meet increased demands for protein and lipid production needed for rapid proliferation and must adapt to exist in an oxygen- and nutrient-deprived environment. To overcome such challenges, cancer cells exploit intrinsic adaptive mechanisms such as the unfolded protein response (UPR). The UPR is a pro-survival mechanism triggered by accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER), a condition referred to as ER stress. IRE1, PERK and ATF6 are three ER anchored transmembrane receptors. Upon induction of ER stress, they signal in a coordinated fashion to re-establish ER homoeostasis, thus aiding cell survival. Over the past decade, evidence has emerged supporting a role for the UPR in the establishment and progression of several cancers, including breast cancer, prostate cancer and glioblastoma multiforme. This review discusses our current knowledge of the UPR during oncogenesis, tumour growth, metastasis and chemoresistance.

Unresolved endoplasmic reticulum stress engenders immune-resistant, latent pancreatic cancer metastases

The majority of patients with pancreatic ductal adenocarcinoma (PDA) develop metastatic disease after resection of their primary tumor. We found that livers from patients and mice with PDA harbor single disseminated cancer cells (DCCs) lacking expression of cytokeratin 19 (CK19) and major histocompatibility complex class I (MHCI). We created a mouse model to determine how these DCCs develop. Intraportal injection of immunogenic PDA cells into preimmunized mice seeded livers only with single, nonreplicating DCCs that were CK19^- and MHCI^- The DCCs exhibited an endoplasmic reticulum (ER) stress response but paradoxically lacked both inositol-requiring enzyme 1α activation and expression of the spliced form of transcription factor XBP1 (XBP1s). Inducible expression of XBP1s in DCCs, in combination with T cell depletion, stimulated the outgrowth of macrometastatic lesions that expressed CK19 and MHCI. Thus, unresolved ER stress enables DCCs to escape immunity and establish latent metastases.

Elucidation of Gene Expression Patterns in the Brain after Spinal Cord Injury

Spinal cord injury (SCI) is a devastating neurological disease. The pathophysiological mechanisms of SCI have been reported to be relevant to central nervous system injury such as brain injury. In this study, gene expression of the brain after SCI was elucidated using transcriptome analysis to characterize the temporal changes in global gene expression patterns in a SCI mouse model. Subjects were randomly classified into 3 groups: sham control, acute (3 h post-injury), and subacute (2 wk post-injury) groups. We sought to confirm the genes differentially expressed between post-injured groups and sham control group. Therefore, we performed transcriptome analysis to investigate the enriched pathways associated with pathophysiology of the brain after SCI using Database for Annotation Visualization, and Integrated Discovery (DAVID), which yielded Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. Following enriched pathways were found in the brain: oxidative phosphorylation pathway; inflammatory response pathways—cytokine–cytokine receptor interaction and chemokine signaling pathway; and endoplasmic reticulum (ER) stress-related pathways—antigen processing and presentation and mitogen-activated protein kinase signaling pathway. Oxidative phosphorylation pathway was identified at acute phase, while inflammation response and ER stress-related pathways were identified at subacute phase. Since the following pathways—oxidative phosphorylation pathway, inflammatory response pathways, and ER stress-related pathways—have been well known in the SCI, we suggested a link between SCI and brain injury. These mechanisms provide valuable reference data for better understanding pathophysiological processes in the brain after SCI.

Immune regulation of the unfolded protein response at the mucosal barrier in viral infection

Protein folding in the endoplasmic reticulum (ER) is subject to stringent quality control. When protein secretion demand exceeds the protein folding capacity of the ER, the unfolded protein response (UPR) is triggered as a consequence of ER stress. Due to the secretory function of epithelial cells, UPR plays an important role in maintaining epithelial barrier function at mucosal sites. ER stress and activation of the UPR are natural mechanisms by which mucosal epithelial cells combat viral infections. In this review, we discuss the important role of UPR in regulating mucosal epithelium homeostasis. In addition, we review current insights into how the UPR is involved in viral infection at mucosal barriers and potential therapeutic strategies that restore epithelial cell integrity following acute viral infections via cytokine and cellular stress manipulation.

Inhibition of the Deubiquitinase Usp14 Diminishes Direct MHC Class I Antigen Presentation

Infected or transformed cells must present peptides derived from endogenous proteins on MHC class I molecules to be recognized and targeted for elimination by Ag-specific cytotoxic T cells. In the first step of peptide generation, proteins are degraded by the proteasome. In this study, we investigated the role of the ubiquitin-specific protease 14 (Usp14), a proteasome-associated deubiquitinase, in direct Ag presentation using a ligand-stabilized model protein expressed as a self-antigen. Chemical inhibition of Usp14 diminished direct presentation of the model antigenic peptide, and the effect was especially pronounced when presentation was restricted to the defective ribosomal product (DRiP) form of the protein. Additionally, presentation specifically from DRiP Ags was diminished by expression of a catalytically inactive form of Usp14. Usp14 inhibition did not appreciably alter protein synthesis and only partially delayed protein degradation as measured by a slight increase in the half-life of the model protein when its degradation was induced. Taken together, these data indicate that functional Usp14 enhances direct Ag presentation, preferentially of DRiP-derived peptides, suggesting that the processing of DRiPs is in some ways different from other forms of Ag.