A J-Protein Co-chaperone Recruits BiP to Monomerize IRE1 and Repress the Unfolded Protein Response

Metabolic reprogramming of interleukin-17-producing γδ T cells promotes ACC1-mediated de novo lipogenesis under psoriatic conditions

Metabolic reprogramming determines γδ T cell fate during thymic development; however, the metabolic requirements of interleukin (IL)-17A-producing γδ T cells (γδT17 cells) under psoriatic conditions are unclear. Combining high-throughput techniques, including RNA sequencing, SCENITH, proteomics and stable isotope tracing, we demonstrated that psoriatic inflammation caused γδT17 cells to switch toward aerobic glycolysis. Under psoriatic conditions, γδT17 cells upregulated ATP-citrate synthase to convert citrate to acetyl-CoA, linking carbohydrate metabolism and fatty acid synthesis (FAS). Accordingly, we used a pharmacological inhibitor, Soraphen A, which blocks acetyl-CoA carboxylase (ACC), to impair FAS in γδT17 cells, reducing their intracellular lipid stores and ability to produce IL-17A under psoriatic conditions in vitro. We pinpointed the pathogenic role of ACC1 in γδT17 cells in vivo by genetic ablation, ameliorating inflammation in a psoriatic mouse model. Furthermore, ACC inhibition limited human IL-17A-producing γδT17 cells. Targeting ACC1 to attenuate pathogenic γδT17 cell function has important implications for psoriasis management.

HaloPROTAC3 treatment activates the unfolded protein response of the endoplasmic reticulum in nonengineered mammalian cell lines

Proteins fused to HaloTag, an engineered haloalkane dehalogenase, can be depleted by a heterobifunctional degrader compound HaloPROTAC3. The binding of HaloPROTAC3 to both the HaloTag and the E3 ligase von Hippel-Lindau (VHL) brings them into proximity and mediates the degradation of the HaloTag fusion proteins. Here, we generated a colon cancer cell line HCT116 expressing HaloTag fused to the RNA-binding protein IGF2BP3 to study its function. HaloPROTAC3 treatment depleted 75% of HaloTag-IGF2BP3 in 5 h. Transcriptomics revealed that HaloPROTAC3 treatment resulted in the destabilization of IGF2BP3 target mRNAs and activated the unfolded protein response (UPR). Surprisingly, we found that HaloPROTAC3 results in UPR activation in nonengineered mammalian cells. Our data demonstrate that HaloPROTAC3 causes mild endoplasmic reticulum stress independent of IGF2BP3 function and shall guide future studies using the HaloPROTAC3 protein depletion strategy.

A nonenzymatic dependency on inositol-requiring enzyme 1 controls cancer cell cycle progression and tumor growth

Endoplasmic-reticulum resident inositol-requiring enzyme 1α (IRE1) supports protein homeostasis via its cytoplasmic kinase-RNase module. Known cancer dependency on IRE1 entails its enzymatic activation of the transcription factor XBP1s and of regulated RNA decay. We discovered surprisingly that some cancer cell lines require IRE1 but not its enzymatic activity. IRE1 knockdown but not enzymatic IRE1 inhibition or XBP1 disruption attenuated cell cycle progression and tumor growth. IRE1 silencing led to activation of TP53 and CDKN1A/p21 in conjunction with increased DNA damage and chromosome instability, while decreasing heterochromatin as well as DNA and histone H3K9me3 methylation. Immunoelectron microscopy detected some endogenous IRE1 protein at the nuclear envelope. Thus, cancer cells co-opt IRE1 either enzymatically or nonenzymatically, which has significant implications for IRE1's biological role and therapeutic targeting.

Homeostasis control in health and disease by the unfolded protein response

Cells rely on the endoplasmic reticulum (ER) to fold and assemble newly synthesized transmembrane and secretory proteins - essential for cellular structure-function and for both intracellular and intercellular communication. To ensure the operative fidelity of the ER, eukaryotic cells leverage the unfolded protein response (UPR) - a stress-sensing and signalling network that maintains homeostasis by rebalancing the biosynthetic capacity of the ER according to need. The metazoan UPR can also redirect signalling from cytoprotective adaptation to programmed cell death if homeostasis restoration fails. As such, the UPR benefits multicellular organisms by preserving optimally functioning cells while removing damaged ones. Nevertheless, dysregulation of the UPR can be harmful. In this Review, we discuss the UPR and its regulatory processes as a paradigm in health and disease. We highlight important recent advances in molecular and mechanistic understanding of the UPR that enable greater precision in designing and developing innovative strategies to harness its potential for therapeutic gain. We underscore the rheostatic character of the UPR, its contextual nature and critical open questions for its further elucidation.

A platform for multimodal in vivo pooled genetic screens reveals regulators of liver function

Organ function requires coordinated activities of thousands of genes in distinct, spatially organized cell types. Understanding the basis of emergent tissue function requires approaches to dissect the genetic control of diverse cellular and tissue phenotypes in vivo. Here, we develop paired imaging and sequencing methods to construct large-scale, multi-modal genotype-phenotypes maps in tissue with pooled genetic perturbations. Using imaging, we identify genetic perturbations in individual cells while simultaneously measuring their gene expression and subcellular morphology. Using single-cell sequencing, we measure transcriptomic responses to the same genetic perturbations. We apply this approach to study hundreds of genetic perturbations in the mouse liver. Our study reveals regulators of hepatocyte zonation and liver unfolded protein response, as well as distinct pathways that cause hepatocyte steatosis. Our approach enables new ways of interrogating the genetic basis of complex cellular and organismal physiology and provides crucial training data for emerging machine-learning models of cellular function.

Transmission of unfolded protein response-a regulator of disease progression, severity, and spread in virus infections

The unfolded protein response (UPR) is a cell-autonomous stress response aimed at restoring homeostasis due to the accumulation of misfolded proteins in the endoplasmic reticulum (ER). Viruses often hijack the host cell machinery, leading to an accumulation of misfolded proteins in the ER. The cell-autonomous UPR is the immediate response of an infected cell to this stress, aiming to restore normal function by halting protein translation, degrading misfolded proteins, and activating signaling pathways that increase the production of molecular chaperones. The cell-non-autonomous UPR involves the spreading of UPR signals from initially stressed cells to neighboring unstressed cells that lack the stressor. Though viruses are known modulators of cell-autonomous UPR, recent advancements have highlighted that cell-non-autonomous UPR plays a critical role in elucidating how local infections cause systemic effects, thereby contributing to disease symptoms and progression. Additionally, by utilizing cell-non-autonomous UPR, viruses have devised novel strategies to establish a pro-viral state, promoting virus spread. This review discusses examples that have broadened the understanding of the role of UPR in virus infections and disease progression by looking beyond cell-autonomous to non-autonomous processes and mechanistic details of the inducers, spreaders, and receivers of UPR signals.

Hepatitis B small surface protein hijacking Bip is initial and essential to promote lipid synthesis

To date, the molecular pathogenic mechanisms between HBsAg and liver metabolic disorders have not been fully understood. To explore the overall effects of HBsAg on liver tissues from HBV transgenic mice, proteome, interactome, and signal pathway analysis were employed to uncover the underlying mechanisms. Bioinformatics analysis of 191 differentially expressed proteins suggested that HBV upregulated the expression of multiple enzymes involved in lipid synthesis, and small HBs (SHBs) caused lipid accumulation in cells. Further studies showed that SHBs bound to binding immunoglobulin protein (Bip), which normally functions in cell homeostasis against the unfolded protein response (UPR) signaling via occupying inositol-requiring enzyme 1 (IRE1). Hijacking Bip by SHBs alleviated the inhibition of post-endoplasmic reticulum (ER) signaling and sequential activation of the IRE1 downstream transcription factors involved in lipid synthesis, such as spliced X-box binding protein 1 (sXBP1) and sterol regulatory element-binding protein 1 (SREBP1), leading to lipid metabolism disorder. The restoration of Bip can alleviate ER stress, and block the sequential post-ER signaling caused by SHBs. This study revealed a new pathway through which SHBs promote lipid disorder, and suggests that Bip may serve as a novel target for intervention in HBV related liver diseases. SIGNIFICANCE: In this study, we found a new pathway promoting the lipid disorder by SHBs through quantitative proteomics studies, and Bip may serve as a novel target for intervention in HBV related liver diseases. These findings highlight a novel role of SHBs in regulating cell lipid metabolism and provide an insight into the relationship between HBV infection and liver fatty disorders, which may serve as a potential therapeutic target for intervention of HBV related liver diseases.

The Differential Expressions and Associations of Intracellular and Extracellular GRP78/Bip with Disease Activity and Progression in Rheumatoid Arthritis

GRP78/BiP, a stress-induced protein and autoantigen in rheumatoid arthritis (RA), exhibits different expressions in various biological fluids and tissues, including blood, synovial fluid (SF), and synovium, all of which are pertinent to the disease activity and progression of RA; however, there is a scarcity of data linking both intracellular and extracellular GRP78/Bip to disease activity and progression of RA. This study was undertaken to investigate the differential expression of GRP78/Bip in blood, SF, and synovium, and to determine their association with disease activity and progression of RA. Patients with RA, osteoarthritis (OA), and traumatic meniscal injury (TMI) without radiographic OA were consecutively recruited for the study. Among patients with RA, six different subgroups were established based on their disease activity and progression. Disease activity was measured using the DAS28 (Disease activity scores in 28 joints) criterion, while disease progression was evaluated using the Steinbrocker classification grade. The levels of GRP78/Bip, TNF-α, and IL-10 were significantly elevated in the serum, SF, and synovium of patients with RA when compared to both the control (CON, TMI Patients) and the inflammation control (iCON, OA Patients) groups (p < 0.05). In terms of disease activity status, as opposed to remission status in RA, the levels of GRP78/Bip, TNF-α, and IL-10 were all elevated in serum and synovium (p < 0.05). However, GRP78/Bip and IL-10 levels were found to be reduced in SF, while TNF-α levels remained elevated. With respect to disease progression in RA, GRP78/Bip levels exhibited a positive correlation with both the stage of RA and the levels of TNF-α and IL-10 in serum and synovium. Nonetheless, a negative correlation was observed between GRP78/Bip levels and the stage of RA in SF, while positive correlations with the levels of TNF-α and IL-10 persisted. The differential expression of GRP78/Bip in blood, SF, and synovium indicated that the potential role and function of GRP78/Bip might vary depending on its specific location within these biological fluids and tissues. The presence of intracellular and extracellular GRP78/Bip was associated with disease activity and progression of RA, suggesting the involvement of GRP78/Bip in the pathogenesis and development of this debilitating autoimmune disorder, as well as its potential as a biomarker for monitoring disease activity and progression of RA.

Impaired insulin signaling and diet-induced type 3 diabetes pathophysiology increase amyloid β expression in the Drosophila model of Alzheimer's disease

Compelling evidence has strongly linked unregulated sugar levels to developing Alzheimer's disease, suggesting Alzheimer's to be 'diabetes of the brain or 'type 3 diabetes. Insulin resistance contributes to the pathogenesis of Alzheimer's disease due to uncontrolled and unchecked blood glucose, though the interrelatedness between Alzheimer's disease and type 2 diabetes is debatable. Here we describe the consequences of inducing type 3 diabetes by feeding Drosophila on a high sucrose diet, which effectively mimics the pathophysiology of diabetes. A high sucrose diet increases glycogen and lipid accumulation. Inducing type 3 diabetes worsened neurodegeneration and accelerated disease progression in Drosophila expressing the Alzheimer's Familial Arctic mutation. High sucrose milieu also negatively affected locomotor ability and reduced the lifespan in the Alzheimer's disease model of Drosophila. The results showed that creating diabetic conditions by using insulin receptor (InR) knockdown in the eyes of Drosophila led to a degenerative phenotype, indicating a genetic interaction between the insulin signaling pathway and Alzheimer's disease. The expression of PERK reflects disruption in the endoplasmic reticulum homeostasis due to amyloid-β (Aβ) under a high sucrose diet. These observations demonstrated an association between type 3 diabetes and Alzheimer's disease, and that a high sucrose environment has a degenerating effect on Alzheimer's disease condition.

Repurposing peripheral immunocytes of Bacillus Calmette Guerin-vaccinated melanoma patients to reveal preventive Alzheimer's disease mechanisms, possibly via the unfolded protein response

Background

Alzheimer's disease (AD) dysfunctional unfolded protein response (UPR) is revealed by amyloid-β aggregates. Normally, UPR reacts to endoplasmic reticulum stress by resolving misfolded/aggregated proteins, and UPR failure induces brain-cell apoptosis consistent with AD pathology. Peripheral blood mononuclear cells (PBMC) and immunocyte brain infiltrates are involved in AD pathogenesis, whose risk is lowered by the Bacillus Calmette Guerin (BCG) vaccine. Hypothetically, BCG prevents AD caused by UPR-driven apoptosis in PBMC brain infiltrates, corrected by BCG-vaccinated PBMC brain infiltrates.

Objective

To reveal whether BCG shifts the UPR towards cell survival. Method: PBMC proteins from 6 individuals were compared by immuno-electrophoresis before and after BCG hypervaccination. Cryopreserved PBMC provided an opportunity to analyze the BCG impact on the UPR, although their donor destiny to develop AD was unknown. UPR signaling responsive to BCG was recorded to examine if BCG can influence UPR signaling and thereby explain the previously demonstrated AD prevention by BCG.

Results

UPR signal levels were scored according to positive versus negative cell survival odds by the BCG impact on a dozen UPR signals. The balance between positive and negative scores of individuals emphasizes the impact of the BCG vaccine on the UPR. The antiapoptotic UPR signals under BCG show opposite trends to UPR signals in AD brains, reported by the literature. In conclusion, 3/6 individuals had superior PBMC survival chances under BCG.

Conclusions

These results suggest that the UPR is part of the mechanism responsible for reducing the risk of AD, as previously shown among BCG-treated bladder cancer patients.

Malate initiates a proton-sensing pathway essential for pH regulation of inflammation

Metabolites can double as a signaling modality that initiates physiological adaptations. Metabolism, a chemical language encoding biological information, has been recognized as a powerful principle directing inflammatory responses. Cytosolic pH is a regulator of inflammatory response in macrophages. Here, we found that L-malate exerts anti-inflammatory effect via BiP-IRF2BP2 signaling, which is a sensor of cytosolic pH in macrophages. First, L-malate, a TCA intermediate upregulated in pro-inflammatory macrophages, was identified as a potent anti-inflammatory metabolite through initial screening. Subsequent screening with DARTS and MS led to the isolation of L-malate-BiP binding. Further screening through protein‒protein interaction microarrays identified a L-malate-restrained coupling of BiP with IRF2BP2, a known anti-inflammatory protein. Interestingly, pH reduction, which promotes carboxyl protonation of L-malate, facilitates L-malate and carboxylate analogues such as succinate to bind BiP, and disrupt BiP-IRF2BP2 interaction in a carboxyl-dependent manner. Both L-malate and acidification inhibit BiP-IRF2BP2 interaction, and protect IRF2BP2 from BiP-driven degradation in macrophages. Furthermore, both in vitro and in vivo, BiP-IRF2BP2 signal is required for effects of both L-malate and pH on inflammatory responses. These findings reveal a previously unrecognized, proton/carboxylate dual sensing pathway wherein pH and L-malate regulate inflammatory responses, indicating the role of certain carboxylate metabolites as adaptors in the proton biosensing by interactions between macromolecules.

Role of AMPK2 in regulating the IRE1JNK pathway in metabolic dysfunctionassociated fatty liver disease

OBJECTIVES

Over 25% of the global population is affected by metabolic dysfunction-associated fatty liver disease (MAFLD), yet its pathogenesis remains unclear. Endoplasmic reticulum stress (ERS) may be involved in the onset and progression of MAFLD. Adenosine 5'-monophosphate-activated protein kinase α2 (AMPKα2), a key regulator of hepatic energy metabolism, may influence MAFLD development via ERS modulation. This study aims to investigate the role of AMPKα2 in a high-fat diet-induced MAFLD mouse model and its regulatory effect on the inositol-requiring enzyme 1 alpha (IRE1α)-c-Jun N-terminal kinase (JNK) signaling pathway.

METHODS

Liver-specific AMPKα2 knockout mice on a C57BL/6 background were generated and subjected to MAFLD induction. Mice were divided into four groups: wild-type control (WT+Chow, basic diet for 12 weeks), wild-type high-fat diet (WT+HFD, high-fat diet for 12 weeks), AMPKα2 knockout control (AMPKα2 KO+Chow), and AMPKα2 knockout high-fat diet (AMPKα2 KO+HFD). Blood glucose, lipid levels, and liver function were assessed post-treatment. Liver histology was analyzed using Oil Red O, hematoxylin-eosin, Masson, and Sirius Red staining. Western blotting was used to evaluate the expression of AMPKα2, ERS markers, autophagy, apoptosis, and ferroptosis-related proteins.

RESULTS

Compared with the WT+Chow group, the WT+HFD group showed significantly elevated blood glucose, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels (all P<0.01); histological analyses revealed hepatic steatosis, vacuolization, and fibrosis, with a significantly increased non-alcoholic steatohepatitis activity score (NAS) (P<0.001). Phosphorylated IRE1α and the autophagy marker microtubule-associated protein light chain (LC) 3II/LC3I were markedly upregulated, while apoptotic proteins (Cleaved-Caspase 3, BAX, Bcl-2) and ferroptosis markers (SLC7A11, GPX4) showed no significant change (P>0.05). In the AMPKα2 KO+HFD group, blood glucose, ALT, and AST levels were significantly reduced compared to the WT+HFD group. Histological improvements were observed with reduced vacuolization and lipid accumulation. Expression of p-IRE1α, JNK, and LC3II/LC3I was significantly decreased (P<0.05).

CONCLUSIONS

Hepatic AMPKα2 knockout alleviates high-fat induced MAFLD, potentially by inhibiting the IRE1α-JNK pathway and reducing autophagy.

Porcine epidemic diarrhea virus E protein induces unfolded protein response through activating both PERK and ATF6 rather than IRE1 signaling pathway

Porcine epidemic diarrhea virus (PEDV) small envelope protein (E) plays important roles in virus budding, assembly, and release. Our previous study found that PEDV E protein localizes in the endoplasmic reticulum (ER) to trigger the unfolded protein response (UPR). However, how UPR is directly regulated by PEDV E protein remains elusive. Thus, in this study, we investigated the expression of ER chaperone glucose-regulated protein 78 (GRP78) and activations of the three main UPR signaling pathways to elucidate the underlying mechanisms of UPR triggered by PEDV E protein. The results showed that over-expression of PEDV E protein increased expression of GRP78 and induced stronger phosphorylation of both protein kinase RNA-like ER kinase (PERK) and eukaryotic initiation factor-2α (eIF2α), as well as caused the significant degradation of activating transcription factor 6 (ATF6), in both dose- and time-dependent manners. However, PEDV E protein did not induce UPR through the inositol-requiring enzyme 1 (IRE1) signaling pathway, as revealed by the splicing of XBP1 remaining unaffected and unchanged when PEDV E protein was overexpressed. Taken together, these results demonstrate that PEDV E protein induces UPR through activation of both PERK and ATF6 pathways rather than IRE1 signaling. This study not only provides mechanistic details of UPR induced by the PEDV E protein, but also provides insights into these new biologic functions to help us better understand the interactions between PEDV and host cells.

Chaperone BiP controls ER stress sensor Ire1 through interactions with its oligomers

The complex multistep activation cascade of Ire1 involves changes in the Ire1 conformation and oligomeric state. Ire1 activation enhances ER folding capacity, in part by overexpressing the ER Hsp70 molecular chaperone BiP; in turn, BiP provides tight negative control of Ire1 activation. This study demonstrates that BiP regulates Ire1 activation through a direct interaction with Ire1 oligomers. Particularly, we demonstrated that the binding of Ire1 luminal domain (LD) to unfolded protein substrates not only trigger conformational changes in Ire1-LD that favour the formation of Ire1-LD oligomers but also exposes BiP binding motifs, enabling the molecular chaperone BiP to directly bind to Ire1-LD in an ATP-dependent manner. These transient interactions between BiP and two short motifs in the disordered region of Ire1-LD are reminiscent of interactions between clathrin and another Hsp70, cytoplasmic Hsc70. BiP binding to substrate-bound Ire1-LD oligomers enables unfolded protein substrates and BiP to synergistically and dynamically control Ire1-LD oligomerisation, helping to return Ire1 to its deactivated state when an ER stress response is no longer required.

IRE1α inhibits osteogenic differentiation of mouse embryonic fibroblasts by limiting Shh signaling

OBJECTIVES

This study aimed to investigate the effect of endoplasmic reticulum (ER) stress sensor inositol-requiring enzyme 1α (IRE1α) on the sonic hedgehog N-terminus (N-Shh)-enhanced-osteogenic differentiation process in mouse embryonic fibroblasts (MEFs).

MATERIALS AND METHODS

Osteogenesis of MEFs was observed by alkaline phosphatase (ALP) staining, alizarin red staining, and Von Kossa staining assays. Activation of unfolded protein response and Shh signaling were examined using real-time quantitative PCR and western blot assays. IRE1α-deficient MEFs were used to explore the effect of IRE1α on N-Shh-driven osteogenesis.

RESULTS

N-Shh increased ALP activity, matrix mineralization, and the expression of Alp and Col-I in MEFs under osteogenic conditions; notably, this was reversed when combined with the ER stress activator Tm treatment. Interestingly, the administration of N-Shh decreased the expression of IRE1α. Abrogation of IRE1α increased the expression of Shh pathway factors in osteogenesis-induced MEFs, contributing to the osteogenic effect of N-Shh. Moreover, IRE1α-deficient MEFs exhibited elevated levels of osteogenic markers.

CONCLUSIONS

Our findings suggest that the IRE1α-mediated unfolded protein response may alleviate the ossification of MEFs by attenuating Shh signaling. Our research has identified a strategy to inhibit excessive ossification, which may have clinical significance in preventing temporomandibular joint bony ankylosis.

Disordered regions in the IRE1α ER lumenal domain mediate its stress-induced clustering

Conserved signaling cascades monitor protein-folding homeostasis to ensure proper cellular function. One of the evolutionary conserved key players is IRE1, which maintains endoplasmic reticulum (ER) homeostasis through the unfolded protein response (UPR). Upon accumulation of misfolded proteins in the ER, IRE1 forms clusters on the ER membrane to initiate UPR signaling. What regulates IRE1 cluster formation is not fully understood. Here, we show that the ER lumenal domain (LD) of human IRE1α forms biomolecular condensates in vitro. IRE1α LD condensates were stabilized both by binding to unfolded polypeptides as well as by tethering to model membranes, suggesting their role in assembling IRE1α into signaling-competent stable clusters. Molecular dynamics simulations indicated that weak multivalent interactions drive IRE1α LD clustering. Mutagenesis experiments identified disordered regions in IRE1α LD to control its clustering in vitro and in cells. Importantly, dysregulated clustering of IRE1α mutants led to defects in IRE1α signaling. Our results revealed that disordered regions in IRE1α LD control its clustering and suggest their role as a common strategy in regulating protein assembly on membranes.

UPF3B modulates endoplasmic reticulum stress through interaction with inositol-requiring enzyme-1α

The unfolded protein response (UPR) is a conserved and adaptive intracellular pathway that relieves the endoplasmic reticulum (ER) stress by activating ER transmembrane stress sensors. As a consequence of ER stress, the inhibition of nonsense-mediated mRNA decay (NMD) is due to an increase in the phosphorylation of eIF2α, which has the effect of inhibiting translation. However, the role of NMD in maintaining ER homeostasis remains unclear. In this study, we found that the three NMD factors, up-frameshift (UPF)1, UPF2, or UPF3B, were required to negate the UPR. Among these three NMD factors, only UPF3B interacted with inositol-requiring enzyme-1α (IRE1α). This interaction inhibited the kinase activity of IRE1α, abolished autophosphorylation, and reduced IRE1α clustering for ER stress. BiP and UPF3B jointly control the activation of IRE1α on both sides of the ER membrane. Under stress conditions, the phosphorylation of UPF3B was increased and the phosphorylated sites were identified. Both the UPF3BY160D genetic mutation and phosphorylation at Thr169 of UPF3B abolished its interaction with IRE1α and UPF2, respectively, leading to activation of ER stress and NMD dysfunction. Our study reveals a key physiological role for UPF3B in the reciprocal regulatory relationship between NMD and ER stress.

Endoplasmic Reticulum Membrane Homeostasis and the Unfolded Protein Response

The endoplasmic reticulum (ER) is the key organelle for membrane biogenesis. Most lipids are synthesized in the ER, and most membrane proteins are first inserted into the ER membrane before they are transported to their target organelle. The composition and properties of the ER membrane must be carefully controlled to provide a suitable environment for the insertion and folding of membrane proteins. The unfolded protein response (UPR) is a powerful signaling pathway that balances protein and lipid production in the ER. Here, we summarize our current knowledge of how aberrant compositions of the ER membrane, referred to as lipid bilayer stress, trigger the UPR.

Exploring Evolutionary Adaptations and Genomic Advancements to Improve Heat Tolerance in Chickens

Climate change poses a significant threat to the poultry industry, especially in hot climates that adversely affect chicken growth, development, and productivity through heat stress. This literature review evaluates the evolutionary background of chickens with the specific genetic characteristics that can help chickens to cope with hot conditions. Both natural selection and human interventions have influenced the genetic characteristics of the breeds used in the current poultry production system. The domestication of chickens from the Red junglefowl (Gallus gallus) has resulted in the development of various breeds with distinct genetic differences. Over the past few years, deliberate breeding for desirable traits (such as meat production and egg quality) in chickens has resulted in the emergence of various economically valuable breeds. However, this selective breeding has also caused a decrease in the genetic diversity of chickens, making them more susceptible to environmental stressors like heat stress. Consequently, the chicken breeds currently in use may possess a limited ability to adapt to challenging conditions, such as extreme heat. This review focuses on evaluating potential genes and pathways responsible for heat tolerance, including heat shock response, antioxidant defense systems, immune function, and cellular homeostasis. This article will also discuss the physiological and behavioral responses of chicken varieties that exhibit genetic resistance to heat, such as the naked neck and dwarf traits in different indigenous chickens. This article intends to review the current genomic findings related to heat tolerance in chickens that used methods such as the genome-wide association study (GWAS) and quantitative trait loci (QTL) mapping, offering valuable insights for the sustainability of poultry in the face of global warming.

The Essential Functions of Molecular Chaperones and Folding Enzymes in Maintaining Endoplasmic Reticulum Homeostasis

It has been estimated that up to one-third of the proteins encoded by the human genome enter the endoplasmic reticulum (ER) as extended polypeptide chains where they undergo covalent modifications, fold into their native structures, and assemble into oligomeric protein complexes. The fidelity of these processes is critical to support organellar, cellular, and organismal health, and is perhaps best underscored by the growing number of disease-causing mutations that reduce the fidelity of protein biogenesis in the ER. To meet demands encountered by the diverse protein clientele that mature in the ER, this organelle is populated with a cadre of molecular chaperones that prevent protein aggregation, facilitate protein disulfide isomerization, and lower the activation energy barrier of cis-trans prolyl isomerization. Components of the lectin (glycan-binding) chaperone system also reside within the ER and play numerous roles during protein biogenesis. In addition, the ER houses multiple homologs of select chaperones that can recognize and act upon diverse peptide signatures. Moreover, redundancy helps ensure that folding-compromised substrates are unable to overwhelm essential ER-resident chaperones and enzymes. In contrast, the ER in higher eukaryotic cells possesses a single member of the Hsp70, Hsp90, and Hsp110 chaperone families, even though several homologs of these molecules reside in the cytoplasm. In this review, we discuss specific functions of the many factors that maintain ER quality control, highlight some of their interactions, and describe the vulnerabilities that arise from the absence of multiple members of some chaperone families.

Navigating the landscape of the unfolded protein response in CD8+ T cells

Endoplasmic reticulum stress occurs due to large amounts of misfolded proteins, hypoxia, nutrient deprivation, and more. The unfolded protein is a complex intracellular signaling network designed to operate under this stress. Composed of three individual arms, inositol-requiring enzyme 1, protein kinase RNA-like ER kinase, and activating transcription factor-6, the unfolded protein response looks to resolve stress and return to proteostasis. The CD8+ T cell is a critical cell type for the adaptive immune system. The unfolded protein response has been shown to have a wide-ranging spectrum of effects on CD8+ T cells. CD8+ T cells undergo cellular stress during activation and due to environmental insults. However, the magnitude of the effects this response has on CD8+ T cells is still understudied. Thus, studying these pathways is important to unraveling the inner machinations of these powerful cells. In this review, we will highlight the recent literature in this field, summarize the three pathways of the unfolded protein response, and discuss their roles in CD8+ T cell biology and functionality.

Endoplasmic reticulum: Monitoring and maintaining protein and membrane homeostasis in the endoplasmic reticulum by the unfolded protein response

The endoplasmic reticulum (ER) regulates essential cellular processes, including protein folding, lipid synthesis, and calcium homeostasis. The ER homeostasis is maintained by a conserved set of signaling cascades called the Unfolded Protein Response (UPR). How the UPR senses perturbations in ER homeostasis has been the subject of active research for decades. In metazoans, the UPR consists of three ER-membrane embedded sensors: IRE1, PERK and ATF6. These sensors detect the accumulation of misfolded proteins in the ER lumen and adjust protein folding capacity according to cellular needs. Early work revealed that the ER-resident chaperone BiP binds to all three UPR sensors in higher eukaryotes and BiP binding was suggested to regulate their activity. More recent data have shown that in higher eukaryotes the interaction of the UPR sensors with a complex network of chaperones and misfolded proteins modulates their activation and deactivation dynamics. Furthermore, emerging evidence suggests that the UPR monitors ER membrane integrity beyond protein folding defects. However, the mechanistic and structural basis of UPR activation by proteotoxic and lipid bilayer stress in higher eukaryotes remains only partially understood. Here, we review the current understanding of novel protein interaction networks and the contribution of the lipid membrane environment to UPR activation.

IRE1α recognizes a structural motif in cholera toxin to activate an unfolded protein response

IRE1α is an endoplasmic reticulum (ER) sensor that recognizes misfolded proteins to induce the unfolded protein response (UPR). We studied cholera toxin (CTx), which invades the ER and activates IRE1α in host cells, to understand how unfolded proteins are recognized. Proximity labeling colocalized the enzymatic and metastable A1 segment of CTx (CTxA1) with IRE1α in live cells, where we also found that CTx-induced IRE1α activation enhanced toxicity. In vitro, CTxA1 bound the IRE1α lumenal domain (IRE1αLD), but global unfolding was not required. Rather, the IRE1αLD recognized a seven-residue motif within an edge β-strand of CTxA1 that must locally unfold for binding. Binding mapped to a pocket on IRE1αLD normally occupied by a segment of the IRE1α C-terminal flexible loop implicated in IRE1α oligomerization. Mutation of the CTxA1 recognition motif blocked CTx-induced IRE1α activation in live cells, thus linking the binding event with IRE1α signal transduction and induction of the UPR.

Protein disulfide isomerase-9 interacts with the lumenal region of the transmembrane endoplasmic reticulum stress sensor kinase, IRE1, to modulate the unfolded protein response in Arabidopsis

Environmental stressors disrupt secretory protein folding and proteostasis in the endoplasmic reticulum (ER), leading to ER stress. The unfolded protein response (UPR) senses ER stress and restores proteostasis by increasing the expression of ER-resident protein folding chaperones, such as protein disulfide isomerases (PDIs). In plants, the transmembrane ER stress sensor kinase, IRE1, activates the UPR by unconventionally splicing the mRNA encoding the bZIP60 transcription factor, triggering UPR gene transcription. The induced PDIs catalyze disulfide-based polypeptide folding to restore the folding capacity in the ER; however, the substrates with which PDIs interact are largely unknown. Here, we demonstrate that the Arabidopsis PDI-M subfamily member, PDI9, modulates the UPR through interaction with IRE1. This PDI9-IRE1 interaction was largely dependent on Cys63 in the first dithiol redox active domain of PDI9, and Cys233 and Cys107 in the ER lumenal domain of IRE1A and IRE1B, respectively. In vitro and in vivo, PDI9 coimmunoprecipitated with IRE1A and IRE1B. Moreover, the PDI9:RFP and Green Fluorescence Protein (GFP):IRE1 fusions exhibited strong interactions as measured by fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer (FLIM-FRET) when coexpressed in mesophyll protoplasts. The UPR-responsive PDI9 promoter:mCherry reporter and the UPR-dependent splicing of the bZIP60 intron from the mRNA of the 35S::bZIP60-intron:GFP reporter were both significantly induced in the pdi9 mutants, indicating a derepression and hyperactivation of UPR. The inductions of both reporters were substantially attenuated in the ire1a-ire1b mutant. We propose a model in which PDI9 modulates the UPR through two competing activities: secretory protein folding and via interaction with IRE1 to maintain proteostasis in plants.

IRE1α: from the function to the potential therapeutic target in atherosclerosis

Inositol requiring enzyme 1 (IRE1) is generally thought to control the most conserved pathway in the unfolded protein response (UPR). Two isoforms of IRE1, IRE1α and IRE1β, have been reported in mammals. IRE1α is a ubiquitously expressed protein whose knockout shows marked lethality. In contrast, the expression of IRE1β is exclusively restricted in the epithelial cells of the respiratory and gastrointestinal tracts, and IRE1β-knockout mice are phenotypically normal. As research continues to deepen, IRE1α was showed to be tightly linked to inflammation, lipid metabolism regulation, cell death and so on. Growing evidence also suggests an important role for IRE1α in promoting atherosclerosis (AS) progression and acute cardiovascular events through disrupting lipid metabolism balance, facilitating cells apoptosis, accelerating inflammatory responses and promoting foam cell formation. In addition, IRE1α was recognized as novel potential therapeutic target in AS prevention. This review provides some clues about the relationship between IRE1α and AS, hoping to contribute to further understanding roles of IRE1α in atherogenesis and to be helpful for the design of novel efficacious therapeutics agents targeting IRE1α-related pathways.

Exploring the IRE1 interactome: From canonical signaling functions to unexpected roles

The unfolded protein response is a mechanism aiming at restoring endoplasmic reticulum (ER) homeostasis and is likely involved in other adaptive pathways. The unfolded protein response is transduced by three proteins acting as sensors and triggering downstream signaling pathways. Among them, inositol-requiring enzyme 1 alpha (IRE1α) (referred to as IRE1 hereafter), an endoplasmic reticulum-resident type I transmembrane protein, exerts its function through both kinase and endoribonuclease activities, resulting in both X-box binding protein 1 mRNA splicing and RNA degradation (regulated ire1 dependent decay). An increasing number of studies have reported protein-protein interactions as regulators of these signaling mechanisms, and additionally, driving other noncanonical functions. In this review, we deliver evolutive and structural insights on IRE1 and further describe how this protein interaction network (interactome) regulates IRE1 signaling abilities or mediates other cellular processes through catalytic-independent mechanisms. Moreover, we focus on newly discovered targets of IRE1 kinase activity and discuss potentially novel IRE1 functions based on the nature of the interactome, thereby identifying new fields to explore regarding this protein's biological roles.

Loss of Grp170 results in catastrophic disruption of endoplasmic reticulum function

GRP170 (Hyou1) is required for mouse embryonic development, and its ablation in kidney nephrons leads to renal failure. Unlike most chaperones, GRP170 is the lone member of its chaperone family in the ER lumen. However, the cellular requirement for GRP170, which both binds nonnative proteins and acts as nucleotide exchange factor for BiP, is poorly understood. Here, we report on the isolation of mouse embryonic fibroblasts obtained from mice in which LoxP sites were engineered in the Hyou1 loci (Hyou1LoxP/LoxP). A doxycycline-regulated Cre recombinase was stably introduced into these cells. Induction of Cre resulted in depletion of Grp170 protein which culminated in cell death. As Grp170 levels fell we observed a portion of BiP fractionating with insoluble material, increased binding of BiP to a client with a concomitant reduction in its turnover, and reduced solubility of an aggregation-prone BiP substrate. Consistent with disrupted BiP functions, we observed reactivation of BiP and induction of the unfolded protein response (UPR) in futile attempts to provide compensatory increases in ER chaperones and folding enzymes. Together, these results provide insights into the cellular consequences of controlled Grp170 loss and provide hypotheses as to why mutations in the Hyou1 locus are linked to human disease.

Keeping goblet cells unstressed: new insights into a general principle

Two new studies reveal how the unfolded protein response is regulated in mucin-secreting gut epithelial cells.

Activation of goblet-cell stress sensor IRE1β is controlled by the mucin chaperone AGR2

Intestinal goblet cells are secretory cells specialized in the production of mucins, and as such are challenged by the need for efficient protein folding. Goblet cells express Inositol-Requiring Enzyme-1β (IRE1β), a unique sensor in the unfolded protein response (UPR), which is part of an adaptive mechanism that regulates the demands of mucin production and secretion. However, how IRE1β activity is tuned to mucus folding load remains unknown. We identified the disulfide isomerase and mucin chaperone AGR2 as a goblet cell-specific protein that crucially regulates IRE1β-, but not IRE1α-mediated signaling. AGR2 binding to IRE1β disrupts IRE1β oligomerization, thereby blocking its downstream endonuclease activity. Depletion of endogenous AGR2 from goblet cells induces spontaneous IRE1β activation, suggesting that alterations in AGR2 availability in the endoplasmic reticulum set the threshold for IRE1β activation. We found that AGR2 mutants lacking their catalytic cysteine, or displaying the disease-associated mutation H117Y, were no longer able to dampen IRE1β activity. Collectively, these results demonstrate that AGR2 is a central chaperone regulating the goblet cell UPR by acting as a rheostat of IRE1β endonuclease activity.

The IRE1β-mediated unfolded protein response is repressed by the chaperone AGR2 in mucin producing cells

Effector mechanisms of the unfolded protein response (UPR) in the endoplasmic reticulum (ER) are well-characterised, but how ER proteostasis is sensed is less well understood. Here, we exploited the beta isoform of the UPR transducer IRE1, that is specific to mucin-producing cells in order to gauge the relative regulatory roles of activating ligands and repressing chaperones of the specialised ER of goblet cells. Replacement of the stress-sensing luminal domain of endogenous IRE1α in CHO cells (normally expressing neither mucin nor IRE1β) with the luminal domain of IRE1β deregulated basal IRE1 activity. The mucin-specific chaperone AGR2 repressed IRE1 activity in cells expressing the domain-swapped IRE1β/α chimera, but had no effect on IRE1α. Introduction of the goblet cell-specific client MUC2 reversed AGR2-mediated repression of the IRE1β/α chimera. In vitro, AGR2 actively de-stabilised the IRE1β luminal domain dimer and formed a reversible complex with the inactive monomer. These features of the IRE1β-AGR2 couple suggest that active repression of IRE1β by a specialised mucin chaperone subordinates IRE1 activity to a proteostatic challenge unique to goblet cells, a challenge that is otherwise poorly recognised by the pervasive UPR transducers.

Better Together: Interorganellar Communication in the Regulation of Proteostasis

An extensive network of chaperones and folding factors is responsible for maintaining a functional proteome, which is the basis for cellular life. The underlying proteostatic mechanisms are not isolated within organelles, rather they are connected over organellar borders via signalling processes or direct association via contact sites. This review aims to provide a conceptual understanding of proteostatic mechanisms across organelle borders, not focussing on individual organelles. This discussion highlights the precision of these finely tuned systems, emphasising the complicated balance between cellular protection and adaptation to stress. In this review, we discuss widely accepted aspects while shedding light on newly discovered perspectives.

Recent advances in small molecule and peptide inhibitors of glucose-regulated protein 78 for cancer therapy

Glucose-regulated protein 78 (GRP78) is one of key endoplasmic reticulum (ER) chaperone proteins that regulates the unfolded protein response (UPR) to maintain ER homeostasis. As a core factor in the regulation of the UPR, GRP78 takes a critical part in the cellular processes required for tumorigenesis, such as proliferation, metastasis, anti-apoptosis, immune escape and chemoresistance. Overexpression of GRP78 is closely correlated with tumorigenesis and poor prognosis in various malignant tumors. Targeting GRP78 is regarded as a potentially promising therapeutic strategy for cancer therapy. Although none of the GRP78 inhibitors have been approved to date, there have been several studies of GRP78 inhibitors. Herein, we comprehensively review the structure, physiological functions of GRP78 and the recent progress of GRP78 inhibitors, and discuss the structures, in vitro and in vivo efficacies, and merits and demerits of these inhibitors to inspire further research. Additionally, the feasibility of GRP78-targeting proteolysis-targeting chimeras (PROTACs), disrupting GRP78 cochaperone interactions, or covalent inhibition are also discussed as novel strategies for drugs discovery targeting GRP78, with the hope that these strategies can provide new opportunities for targeted GRP78 antitumor therapy.

The Role of Endoplasmic Reticulum in Lipotoxicity during Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) Pathogenesis

Perturbations in lipid and protein homeostasis induce endoplasmic reticulum (ER) stress in metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as nonalcoholic fatty liver disease. Lipotoxic and proteotoxic stress can activate the unfolded protein response (UPR) transducers: inositol requiring enzyme1α, PKR-like ER kinase, and activating transcription factor 6α. Collectively, these pathways induce expression of genes that encode functions to resolve the protein folding defect and ER stress by increasing the protein folding capacity of the ER and degradation of misfolded proteins. The ER is also intimately connected with lipid metabolism, including de novo ceramide synthesis, phospholipid and cholesterol synthesis, and lipid droplet formation. Following their activation, the UPR transducers also regulate lipogenic pathways in the liver. With persistent ER stress, cellular adaptation fails, resulting in hepatocyte apoptosis, a pathological marker of liver disease. In addition to the ER-nucleus signaling activated by the UPR, the ER can interact with other organelles via membrane contact sites. Modulating intracellular communication between ER and endosomes, lipid droplets, and mitochondria to restore ER homeostasis could have therapeutic efficacy in ameliorating liver disease. Recent studies have also demonstrated that cells can convey ER stress by the release of extracellular vesicles. This review discusses lipotoxic ER stress and the central role of the ER in communicating ER stress to other intracellular organelles in MASLD pathogenesis.

Loss of Grp170 results in catastrophic disruption of endoplasmic reticulum functions

GRP170, a product of the Hyou1 gene, is required for mouse embryonic development, and its ablation in kidney nephrons leads to renal failure. Unlike most chaperones, GRP170 is the lone member of its chaperone family in the ER lumen. However, the cellular requirement for GRP170, which both binds non-native proteins and acts as nucleotide exchange factor for BiP, is poorly understood. Here, we report on the isolation of embryonic fibroblasts from mice in which LoxP sites were engineered in the Hyou1 loci ( Hyou1 LoxP/LoxP ). A doxycycline-regulated Cre recombinase was also stably introduced into these cells. Induction of Cre resulted in excision of Hyou1 and depletion of Grp170 protein, culminating in apoptotic cell death. As Grp170 levels fell we observed increased steady-state binding of BiP to a client, slowed degradation of a misfolded BiP substrate, and BiP accumulation in NP40-insoluble fractions. Consistent with disrupted BiP functions, we observed reactivation of BiP storage pools and induction of the unfolded protein response (UPR) in futile attempts to provide compensatory increases in ER chaperones and folding enzymes. Together, these results provide insights into the cellular consequences of controlled Grp170 loss and insights into mutations in the Hyou1 locus and human disease.

The unfolded protein response links ER stress to cancer-associated thrombosis

Thrombosis is a common complication of advanced cancer, yet the cellular mechanisms linking malignancy to thrombosis are poorly understood. The unfolded protein response (UPR) is an ER stress response associated with advanced cancers. A proteomic evaluation of plasma from patients with gastric and non-small cell lung cancer who were monitored prospectively for venous thromboembolism demonstrated increased levels of UPR-related markers in plasma of patients who developed clots compared with those who did not. Release of procoagulant activity into supernatants of gastric, lung, and pancreatic cancer cells was enhanced by UPR induction and blocked by antagonists of the UPR receptors inositol-requiring enzyme 1α (IRE1α) and protein kinase RNA-like endoplasmic reticulum kinase (PERK). Release of extracellular vesicles bearing tissue factor (EVTFs) from pancreatic cancer cells was inhibited by siRNA-mediated knockdown of IRE1α/XBP1 or PERK pathways. Induction of UPR did not increase tissue factor (TF) synthesis, but rather stimulated localization of TF to the cell surface. UPR-induced TF delivery to EVTFs was inhibited by ADP-ribosylation factor 1 knockdown or GBF1 antagonism, verifying the role of vesicular trafficking. Our findings show that UPR activation resulted in increased vesicular trafficking leading to release of prothrombotic EVTFs, thus providing a mechanistic link between ER stress and cancer-associated thrombosis.

Targeted inhibition of protein synthesis renders cancer cells vulnerable to apoptosis by unfolded protein response

Cellular stress responses including the unfolded protein response (UPR) decide over the fate of an individual cell to ensure survival of the entire organism. During physiologic UPR counter-regulation, protective proteins are upregulated to prevent cell death. A similar strategy induces resistance to UPR in cancer. Therefore, we hypothesized that blocking protein synthesis following induction of UPR substantially enhances drug-induced apoptosis of malignant cells. In line, upregulation of the chaperone BiP was prevented by simultaneous arrest of protein synthesis in B cell malignancies. Cytotoxicity by immunotoxins-approved inhibitors of protein synthesis-was synergistically enhanced in combination with UPR-inducers in seven distinct hematologic and three solid tumor entities in vitro. Synergistic cell death depended on mitochondrial outer membrane permeabilization via BAK/BAX, which correlated with synergistic, IRE1α-dependent reduction of BID, accompanied by an additive fall of MCL-1. The strong synergy was reproduced in vivo against xenograft mouse models of mantle cell lymphoma, Burkitt's lymphoma, and patient-derived acute lymphoblastic leukemia. In contrast, synergy was absent in blood cells of healthy donors suggesting a tumor-specific vulnerability. Together, these data support clinical evaluation of blocking stress response counter-regulation using inhibitors of protein synthesis as a novel therapeutic strategy.

Enhanced SARS-CoV-2 entry via UPR-dependent AMPK-related kinase NUAK2

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) remodels the endoplasmic reticulum (ER) to form replication organelles, leading to ER stress and unfolded protein response (UPR). However, the role of specific UPR pathways in infection remains unclear. Here, we found that SARS-CoV-2 infection causes marginal activation of signaling sensor IRE1α leading to its phosphorylation, clustering in the form of dense ER-membrane rearrangements with embedded membrane openings, and XBP1 splicing. By investigating the factors regulated by IRE1α-XBP1 during SARS-CoV-2 infection, we identified stress-activated kinase NUAK2 as a novel host-dependency factor for SARS-CoV-2, HCoV-229E, and MERS-CoV entry. Reducing NUAK2 abundance or kinase activity impaired SARS-CoV-2 particle binding and internalization by decreasing cell surface levels of viral receptors and viral trafficking likely by modulating the actin cytoskeleton. IRE1α-dependent NUAK2 levels were elevated in SARS-CoV-2-infected and bystander non-infected cells, promoting viral spread by maintaining ACE2 cell surface levels and facilitating virion binding to bystander cells.

Interplay between calcium and endoplasmic reticulum stress

Cellular homeostasis is crucial for the healthy functioning of the organism. Disruption of cellular homeostasis activates endoplasmic reticulum (ER) stress coping responses including the unfolded protein response (UPR). There are three ER resident stress sensors responsible for UPR activation - IRE1α, PERK and ATF6. Ca²⁺ signaling plays an important role in stress responses including the UPR and the ER is the main Ca²⁺ storage organelle and a source of Ca²⁺ for cell signaling. The ER contains many proteins involved in Ca²⁺ import/export/ storage, Ca²⁺ movement between different cellular organelles and ER Ca²⁺ stores refilling. Here we focus on selected aspects of ER Ca²⁺ homeostasis and its role in activation of the ER stress coping responses.

Adenosine 2 receptor regulates autophagy and apoptosis to alleviate ischemia reperfusion injury in type 2 diabetes via IRE-1 signaling

PURPOSE

This study aimed to determine the effect and mechanism of action of adenosine 2 receptor (A2R) activation on myocardial ischemia reperfusion injury (MIRI) under diabetic conditions.

METHODS

MIRI type 2 diabetic rats and H9C2 cardiomyocytes were treated with A2R agonist and then subjected to hypoxia for 6 h and reoxygenation for 18 h. Myocardial damage, and infarct size were determined by cardiac ultrasound. Indicators of cardiomyocyte injury, creatine kinase-MB and cardiac troponin I were detected by Enzyme Linked Immunosorbent Assay. Endoplasmic reticulum stress (ERS) was determined through measuring the expression levels of ERS related genes GRP78, p-IRE1/IRE1, and p-JNKJNK. The mechanism of A2R cardio protection in MIRI through regulating ERS induced autophagy was determined by investigating the ER resident protein IRE-1. The ER-stress inducer Tunicamycin, and the IRE-1 inhibitor STF in combination with the A2R agonist NECA were used, and the cellular responses were assessed through autophagy proteins expression Beclin-1, p62, LC3 and apoptosis.

RESULTS

NECA improved left ventricular function post MIRI, limited myocardial infarct size, reduced myocardial damage, decreased cardiomyocytes apoptosis, and attenuated ERS induced autophagy through regulating the IRE-XBP1s-CHOP pathway. These actions resulted into overall protection of the myocardium against MIRI.

CONCLUSION

In summary, A2R activation by NECA prior to ischemia attenuates apoptosis, reduces ERS induced autophagy and restores left ventricular function. This protective effect occurs through regulating the IRE1-XBPs-CHOP related mechanisms. NECA is thus a potential target for the treatment of MIRI in patient with type 2 diabetes.

Atg8 and Ire1 in combination regulate the autophagy-related endoplasmic reticulum stress response in Candida albicans

The unfolded protein response (UPR) is an important pathway to prevent endoplasmic reticulum (ER) stress in eukaryotic cells. In Saccharomyces cerevisiae, Ire1 is a key regulatory factor required for HAC1 gene splicing for further production of functional Hac1 and activation of UPR gene expression. Autophagy is another mechanism involved in the attenuation of ER stress by ER-phagy, and Atg8 is a core protein in autophagy. Both autophagy and UPR are critical for ER stress response, but whether they act individually or in combination in Candida albicans is unknown. In this study, we explored the interaction between Ire1 and the autophagy protein Atg8 for the ER stress response by constructing the atg8Δ/Δire1Δ/Δ double mutant in the pathogenic fungus C. albicans. Compared to the single mutants atg8Δ/Δ or ire1Δ/Δ, atg8Δ/Δire1Δ/Δ exhibited much higher sensitivity to various ER stress-inducing agents and more severe attenuation of UPR gene expression under ER stress. Further investigations showed that the double mutant had a defect in ER-phagy, which was associated with attenuated vacuolar fusion under ER stress. This study revealed that Ire1 and Atg8 in combination function in the activation of the UPR and ER-phagy to maintain ER homeostasis under ER stress in C. albicans.

MANF regulates neuronal survival and UPR through its ER-located receptor IRE1α

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER)-located protein with cytoprotective effects in neurons and pancreatic β cells in vitro and in models of neurodegeneration and diabetes in vivo. However, the exact mode of MANF action has remained elusive. Here, we show that MANF directly interacts with the ER transmembrane unfolded protein response (UPR) sensor IRE1α, and we identify the binding interface between MANF and IRE1α. The expression of wild-type MANF, but not its IRE1α binding-deficient mutant, attenuates UPR signaling by decreasing IRE1α oligomerization; phosphorylation; splicing of Xbp1, Atf6, and Txnip levels; and protecting neurons from ER stress-induced death. MANF-IRE1α interaction and not MANF-BiP interaction is crucial for MANF pro-survival activity in neurons in vitro and is required to protect dopamine neurons in an animal model of Parkinson's disease. Our data show IRE1α as an intracellular receptor for MANF and regulator of neuronal survival.

Persistent Endoplasmic Reticulum Stress Stimulated by Peptide Assemblies for Sensitizing Cancer Chemotherapy

Pharmacological targeting of endoplasmic reticulum (ER) stress represents one of important methods for disease therapy, which, however, is significantly suppressed by the ER homeostatic processe. Herein, a proof-of-concept strategy is reported for persistent stimulation of ER stress via preventing ER stress adaptation by utilizing multifunctional peptide assemblies. The strategy is established via creation of peptide assemblies with ER-targeting and chaperone glucose-regulated protein 78 (GRP78)-inhibiting functions. The peptides assemblies form well-defined nanofibers that are retrieved by ER organelles in human cervical cancer cell. The underlying mechanism studies unravel that the ER-accumulated peptide assemblies simultaneously stimulate ER stress and inhibit GRP78 refolding activity and thereby promoting endogenous protein aggregation. Combining the internalized peptide assemblies with the induced protein aggregates leads to the persistent stimulation of ER stress. The persistent ER stress induced by the peptide assemblies bestows their application in sensitizing cancer chemotherapy. Both in vitro and in vivo results confirm the enhanced cytotoxicity of drug toyocamycin against HeLa cells by peptide assemblies, thus efficiently inhibiting in vivo tumor growth. The strategy reported here discloses the fundamental keys for efficient promotion of ER stress, thus providing the guidance for development of ER-targeting-assisted cancer chemotherapy in the future.

Protective role of PERK-eIF2α-ATF4 pathway in chronic renal failure induced injury of rat hippocampal neurons

PURPOSE

Chronic renal failure (CRF) is associated with impairment of hippocampal neurons. This study investigated the effect of PERK-eIF2α-ATF4 pathway in CRF.

METHODS

Rat CRF model was established and rat hippocampal neurons were separated. Xanthine Oxidase method, fluorescence spectrophotometry and flow cytometry were applied to detect superoxide dismutase (SOD) content, reactive oxygen species (ROS) level and apoptosis in hippocampal neurons, respectively. The levels of phosphorylated (p)-PERK, phosphorylated (p)-eIF2α, CHOP, Bax, C-Caspase-3 and Bcl-2 in rats were measured using Western blot. Then, the neurotoxicity of serum from CRF rats was assessed in rat hippocampal neurons after treatment with rat CRF serum and transfection with or without PERK overexpression or knockdown plasmid.

RESULTS

SOD activity was reduced, while ROS level and apoptosis rate were increased in hippocampal tissues of CRF rats. PERK-eIF2α-ATF4 and apoptosis pathways were activated in CRF rats. Cells treated with serum from CRF rats showed increases in apoptosis rate and LDH and ROS levels, and decreases in cell viability and SOD activity. However, overexpressed PERK could reverse the cytotoxic effect of serum from CRF rats. PERK overexpression could enhance the activation of PERK-eIF2α-ATF4 pathway in hippocampal neurons induced by serum from CRF rats. Furthermore, PERK overexpression could alleviate the increases in CHOP, Bax, C-Caspase-3 expressions and the reduction of Bcl-2 expression in hippocampal neurons induced by serum from CRF rats.

CONCLUSION

PERK-eIF2α-ATF4 pathway induced by increased endoplasmic reticulum stress may alleviate CRF-induced hippocampal neuronal damage.

Discovery and Development of a Selective Inhibitor of the ER Resident Chaperone Grp78

A recent study illustrated that a fluorescence polarization assay can be used to identify substrate-competitive Hsp70 inhibitors that can be isoform-selective. Herein, we use that assay in a moderate-throughput screen and report the discovery of a druglike amino-acid-based inhibitor with reasonable specificity for the endoplasmic reticular Hsp70, Grp78. Using traditional medicinal chemistry approaches, the potency and selectivity were further optimized through structure-activity relationship (SAR) studies in parallel assays for six of the human Hsp70 isoforms. The top compounds were all tested against a panel of cancer cell lines and disappointingly showed little effect. The top-performing compound, 8, was retested using a series of endoplasmic reticulum (ER) stress-inducing agents and found to synergize with these agents. Finally, 8 was tested in a spheroid tumor model and found to be more potent than in two-dimensional models. The optimized Grp78 inhibitors are the first reported isoform-selective small-molecule-competitive inhibitors of an Hsp70-substrate interaction.

Co-chaperones of the Human Endoplasmic Reticulum: An Update

In mammalian cells, the rough endoplasmic reticulum (ER) plays central roles in the biogenesis of extracellular plus organellar proteins and in various signal transduction pathways. For these reasons, the ER comprises molecular chaperones, which are involved in import, folding, assembly, export, plus degradation of polypeptides, and signal transduction components, such as calcium channels, calcium pumps, and UPR transducers plus adenine nucleotide carriers/exchangers in the ER membrane. The calcium- and ATP-dependent ER lumenal Hsp70, termed immunoglobulin heavy-chain-binding protein or BiP, is the central player in all these activities and involves up to nine different Hsp40-type co-chaperones, i.e., ER membrane integrated as well as ER lumenal J-domain proteins, termed ERj or ERdj proteins, two nucleotide exchange factors or NEFs (Grp170 and Sil1), and NEF-antagonists, such as MANF. Here we summarize the current knowledge on the ER-resident BiP/ERj chaperone network and focus on the interaction of BiP with the polypeptide-conducting and calcium-permeable Sec61 channel of the ER membrane as an example for BiP action and how its functional cycle is linked to ER protein import and various calcium-dependent signal transduction pathways.

Expression of DNAJB9 and some other genes is more sensitive to SWCNTs in normal human astrocytes than glioblastoma cells

Objective. Single-walled carbon nanotubes (SWCNTs) are considered to be one of the nanomaterials attractive for biomedical applications, particularly in the health sciences as imaging probes and drug carriers, especially in the field of cancer therapy. The increasing exploitation of nanotubes necessitates a comprehensive evaluation of the potential impact of these nanomaterials, which purposefully accumulate in the cell nucleus, on the human health and the function of the genome in the normal and tumor tissues. The aim of this study was to investigate the sensitivity of the expression of DNAJB9 and some other genes associated with the endoplasmic reticulum (ER) stress and cell proliferation to low doses of SWCNTs in normal human astrocytes (NHA/TS) and glioblastoma cells (U87MG) with and without an inhibition of ERN1 signaling pathway of the ER stress. Methods. Normal human astrocytes, line NHA/TS and U87 glioblastoma cells stable transfected by empty vector or dnERN1 (dominant-negative construct of ERN1) were exposed to low doses of SWCNTs (2 and 8 ng/ml) for 24 h. RNA was extracted from the cells and used for cDNA synthesis. The expression levels of DNAJB9, TOB1, BRCA1, DDX58, TFPI2, CLU, and P4HA2 mRNAs were measured by a quantitative polymerase chain reaction and normalized to ACTB mRNA. Results. It was found that the low doses of SWCNTs up-regulated the expression of DNAJB9, TOB1, BRCA1, DDX58, TFPI2, CLU, and P4HA2 genes in normal human astrocytes in dose-dependent (2 and 8 ng/ml) and gene-specific manner. These nanotubes also increased the expression of most studied genes in control (transfected by empty vector) U87 glioblastoma cells, but with much lesser extent than in NHA/TS. However, the expression of CLU gene in control U87 glioblastoma cells treated with SWCNTs was down-regulated in a dose-dependent manner. Furthermore, the expression of TOB1 and P4HA2 genes did not significantly change in these glioblastoma cells treated by lower dose of SWCNTs only. At the same time, inhibition of ERN1 signaling pathway of ER stress in U87 glioblastoma cells led mainly to a stronger resistance of DNAJB9, TOB1, BRCA1, DDX58, TFPI2, and P4HA2 gene expression to both doses of SWCNTs. Conclusion. The data obtained demonstrate that the low doses of SWCNTs disturbed the genome functions by changing the levels of key regulatory gene expressions in gene-specific and dose-dependent manner, but their impact was much stronger in the normal human astrocytes in comparison with the tumor cells. It is possible that ER stress, which is constantly present in tumor cells and responsible for multiple resistances, also created a partial resistance to the SWCNTs action. Low doses of SWCNTs induced more pronounced changes in the expression of diverse genes in the normal human astrocytes compared to glioblastoma cells indicating for a possible both genotoxic and neurotoxic effects with a greater extent in the normal cells.

Volleying plasma membrane proteins from birth to death: Role of J-domain proteins

The function, stability, and turnover of plasma membrane (PM) proteins are crucial for cellular homeostasis. Compared to soluble proteins, quality control of plasma membrane proteins is extremely challenging. Failure to meet the high quality control standards is detrimental to cellular and organismal health. J-domain proteins (JDPs) are among the most diverse group of chaperones that collaborate with other chaperones and protein degradation machinery to oversee cellular protein quality control (PQC). Although fragmented, the available literature from different models, including yeast, mammals, and plants, suggests that JDPs assist PM proteins with their synthesis, folding, and trafficking to their destination as well as their degradation, either through endocytic or proteasomal degradation pathways. Moreover, some JDPs interact directly with the membrane to regulate the stability and/or functionality of proteins at the PM. The deconvoluted picture emerging is that PM proteins are relayed from one JDP to another throughout their life cycle, further underscoring the versatility of the Hsp70:JDP machinery in the cell.

Comprehensive Transcriptome Analysis Reveals Genome-Wide Changes Associated with Endoplasmic Reticulum (ER) Stress in Potato (Solanum tuberosum L.)

We treated potato (Solanum tuberosum L.) plantlets with TM and performed gene expression studies to identify genome-wide changes associated with endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). An extensive network of responses was identified, including chromatin remodeling, transcriptional reprogramming, as well as changes in the structural components of the endomembrane network system. Limited genome-wide changes in alternative RNA splicing patterns of protein-coding transcripts were also discovered. Significant changes in RNA metabolism, components of the translation machinery, as well as factors involved in protein folding and maturation occurred, which included a broader set of genes than expected based on Arabidopsis research. Antioxidant defenses and oxygen metabolic enzymes are differentially regulated, which is expected of cells that may be experiencing oxidative stress or adapting to protect proteins from oxidation. Surges in protein kinase expression indicated early signal transduction events. This study shows early genomic responses including an array of differentially expressed genes that have not been reported in Arabidopsis. These data describe novel ER stress responses in a solanaceous host.

The role of heat shock proteins in metastatic colorectal cancer: A review

Heat shock proteins (HSPs) are a large molecular chaperone family classified by their molecular weights, including HSP27, HSP40, HSP60, HSP70, HSP90, and HSP110. HSPs are likely to have antiapoptotic properties and participate actively in various processes such as tumor cell proliferation, invasion, metastases, and death. In this review, we discuss comprehensively the functions of HSPs associated with the progression of colorectal cancer (CRC) and metastasis and resistance to cancer therapy. Taken together, HSPs have numerous clinical applications as biomarkers for cancer diagnosis and prognosis and potential therapeutic targets for CRC and its related metastases.