Perk is essential for translational regulation and cell survival during the unfolded protein response

Molecular and therapeutic insight into ER stress signalling in NSCLC

Endoplasmic Reticulum (ER) stress is intricately involved in cancer development, progression and response to chemotherapy. ER stress related genes might play an important role in predicting the prognosis in lung adenocarcinoma patients and may be manipulated to improve the treatment outcome and overall survival rate. In this review, we analysed the contribution of the three major ER stress pathways-IRE1, ATF6, and PERK-in lung cancer pathogenesis via modulation of tumour microenvironment (TME) and processes as metastasis, angiogenesis, apoptosis and N-glycosylation. Furthermore, we discuss the regulatory role of microRNAs in fine-tuning ER stress pathways in Non-Small Cell Lung Cancer (NSCLC). Our review also highlights various promising strategies to overcome chemoresistance by targeting ER stress pathways, offering new therapeutic opportunities.

Impact of proteostasis workload on sensitivity to proteasome inhibitors in multiple myeloma

Genomic alterations and enormous monoclonal immunoglobulin production cause multiple myeloma to heavily depend on proteostasis mechanisms, including protein folding and degradation. These findings support the use of proteasome inhibitors for treating multiple myeloma and mantle cell lymphoma. Myeloma treatment has evolved, especially with the availability of new drugs, such as proteasome inhibitors, into therapeutic strategies for both frontline and relapsed/refractory disease settings. However, proteasome inhibitors are generally not effective enough to cure most patients. Natural resistance and eventual acquired resistance led to relapsed/refractory disease and poor prognosis. Advances in the understanding of cellular proteostasis and the development of innovative drugs that also target other proteostasis network components offer opportunities to exploit the intrinsic vulnerability of myeloma cells. This review outlines recent findings on the molecular mechanisms regulating cellular proteostasis pathways, as well as resistance, sensitivity, and escape strategies developed against proteasome inhibitors and provides a rationale and examples for novel combinations of proteasome inhibitors with FDA-approved drugs and investigational drugs targeting the NRF1 (NFE2L1)-mediated proteasome bounce-back response, redox homeostasis, heat shock response, unfolding protein response, autophagy, and VCP/p97 to increase proteotoxic stress, which can improve the efficacy of antimyeloma therapy based on proteasome inhibitors.

Reticulon 4 reflects endoplasmic reticulum stress in arginine vasopressin neurons

Arginine vasopressin (AVP) is synthesized in the magnocellular supraoptic nucleus and paraventricular nuclei of the hypothalamus, where AVP neurons function under a consistently high demand for AVP production. AVP neurons are subject to endoplasmic reticulum (ER) stress even under basal conditions, and this ER stress is further exacerbated when AVP production increases due to dehydration. Reticulon (RTN) is essential for ER formation and stabilization and plays a critical role in membrane morphogenesis within the ER. This study aimed to investigate the expression of RTN family members in hypothalamic AVP neurons. Fluorescence immunohistochemistry and in-situ hybridization were employed to examine the expression of RTN family members in hypothalamic AVP neurons of adult male mice. Water deprivation and treatment with a chemical chaperone 4-phenylbutyric acid were used to increase and decrease the ER stress of AVP neurons, respectively. Among the RTN family members, only RTN4 was found to be expressed in hypothalamic AVP neurons. RTN4 was colocalized with ER organelle markers, including immunoglobulin heavy chain binding protein and calnexin. Furthermore, RTN4 expression increased during ER stress induced by water deprivation. On the other hand, increased RTN4 expression by water deprivation was attenuated by 4-phenylbutyric acid treatment. Our results suggest that RTN4 expression in AVP neurons is closely associated with ER stress caused by increased protein production in neuroendocrine cells.

m6A alters ribosome dynamics to initiate mRNA degradation

Degradation of mRNA containing N6-methyladenosine (m6A) is essential for cell growth, differentiation, and stress responses. Here, we show that m6A markedly alters ribosome dynamics and that these alterations mediate the degradation effect of m6A on mRNA. We find that m6A is a potent inducer of ribosome stalling, and these stalls lead to ribosome collisions that form a unique conformation unlike those seen in other contexts. We find that the degree of ribosome stalling correlates with m6A-mediated mRNA degradation, and increasing the persistence of collided ribosomes correlates with enhanced m6A-mediated mRNA degradation. Ribosome stalling and collision at m6A is followed by recruitment of YTHDF m6A reader proteins to promote mRNA degradation. We show that mechanisms that reduce ribosome stalling and collisions, such as translation suppression during stress, stabilize m6A-mRNAs and increase their abundance, enabling stress responses. Overall, our study reveals the ribosome as the initial m6A sensor for beginning m6A-mRNA degradation.

PERK-dependent reciprocal crosstalk between ER and non-centrosomal microtubules coordinates ER architecture and cell shape

The architecture of the endoplasmic reticulum (ER) is a key determinant of its function. Its dynamics are linked to those of the cytoskeleton, but our understanding of how this coordination occurs and what its functional relevance is, limited. Here, we report that the unfolded protein response (UPRER) transducer EIF2AK3/PERK (eukaryotic translation initiation factor 2-alpha kinase 3/protein kinase R-like endoplasmic reticulum kinase) is essential for acute-stress-induced peripheral redistribution and remodeling of the ER through eukaryotic initiation factor 2 alpha (eIF2α) phosphorylation and translation initiation shutdown. PERK-mediated eIF2α phosphorylation can be bypassed by blocking polysome assembly, depleting microtubule (MT)-anchoring ER proteins such as p180/RRBP1 (ribosome-binding protein 1), or disrupting the MT cytoskeleton. Specific disruption of non-centrosomal MTs, but not centrosome depletion, rescues ER redistribution in PERK-deficient cells. Conversely, PERK deficiency stabilizes non-centrosomal MTs against proteasomal degradation, promoting polarized protrusiveness in epithelial cells and neuroblasts. Thus, PERK coordinates ER architecture and homeostasis with cell morphogenesis by coupling ER remodeling and non-centrosomal MT stability and dynamics.

GRP94 is indispensable for definitive endoderm specification of human induced pluripotent stem cells

Human induced pluripotent stem cell (hiPSC)-derived insulin-producing β cell therapy shows promise in treating type 1 diabetes and potentially type 2 diabetes. Understanding the genetic factors controlling hiPSC differentiation could optimize this therapy. In this study, we investigated the role of glucose-regulated protein 94 (GRP94) in human β cell development by generating HSP90B1/GRP94 knockout (KO) hiPSCs, re-expressing GRP94 in the mutants and inducing their β cell differentiation. Our results revealed that GRP94 depletion hindered β cell generation by promoting cell death induced by endoplasmic reticulum (ER) stress and other stressors during definitive endoderm (DE) differentiation. Moreover, GRP94 deletion resulted in decreased activation of WNT/β-catenin signaling, which is critical for DE specification. Re-expression of GRP94 in GRP94 KO iPSCs partially reversed DE differentiation deficiency and alleviated cell death. These findings highlight the previously unrecognized indispensable role of GRP94 in human DE formation and consequent β cell development from hiPSCs. GRP94 mitigates ER stress-induced cell death and regulates the WNT/β-catenin signaling pathway, which is both crucial for successful β cell differentiation. These results provide new insights into the molecular mechanisms underlying β cell differentiation from hiPSCs and suggest that targeting GRP94 pathways could enhance the efficiency of hiPSC-derived insulin-producing cell therapies for diabetes treatment.

The Effect of Electroconvulsive Therapy on Hippocampal Endoplasmic Reticulum Stress in a Rat Model of Depression

OBJECTIVE

The mechanisms underlying the effectiveness of electroconvulsive therapy (ECT), one of the most effective treatments for depression, are still unknown. While the increasing endoplasmic reticulum (ER) stress in depression can retrieve with pharmacological agents, ECT's effectiveness has not been examined yet. In this study, we tested how hippocampal ER stress parameters change after repeated ECT in rats in the chronic unpredictable mild stress (CUMS) model.

METHODS

Rats were divided into 4 groups. Two groups were included in the experimental group, where the CUMS model was applied for 21 days. Then, the experimental ECT model was applied to 2 groups, one experimental and 1 control group, for 21 days. Weight changes results were evaluated at the end of the 21st and 42nd day. In the final step, 3 prominent ER stress-related proteins (Grp-78, Xbp1, and Atf-4) were measured by western blot in the removed hippocampus.

RESULTS

We found that rats administered CUMS exhibited depression-like behavioral responses such as weight loss. In CUMS-treated rats (group 3), Grp-78 levels increased, ATF4 levels did not change, and Xbp1 levels decreased. While ECT increased Grp-78 levels in normal rats, it did not change Atf-4 levels and reduced Xbp1 levels (group 2). When ECT was applied to rats undergoing the CUMS model, Grp-78 and Xbp1 levels decreased, while Atf-4 levels did not change (group 4).

CONCLUSIONS

These findings show that increased ER stress may play a role in the pathophysiology of depression and that this increase can be reversed with ECT treatment. These findings need to be confirmed by clinical studies in humans.

The unfolded protein response is a potential therapeutic target in pathogenic fungi

Pathogenic fungal infections cause significant morbidity and mortality, particularly in immunocompromised patients. The frequent emergence of multidrug-resistant strains challenges existing antifungal therapies, driving the need to investigate novel antifungal agents that target new molecular moieties. Pathogenic fungi are subjected to various environmental stressors, including pH, temperature, and pharmacological agents, both in natural habitats and the host body. These stressors elevate the risk of misfolded or unfolded protein production within the endoplasmic reticulum (ER) which, if not promptly mitigated, can lead to the accumulation of these proteins in the ER lumen. This accumulation triggers an ER stress response, potentially jeopardizing fungal survival. The unfolded protein response (UPR) is a critical cellular defense mechanism activated by ER stress to restore the homeostasis of protein folding. In recent years, the regulatory role of the UPR in pathogenic fungi has garnered significant attention, particularly for its involvement in fungal adaptation, regulation of virulence, and drug resistance. In this review, we comparatively analyze the UPRs of fungi and mammals and examine the potential utility of the UPR as a molecular antifungal target in pathogenic fungi. By clarifying the specificity and regulatory functions of the UPR in pathogenic fungi, we highlight new avenues for identifying potential therapeutic targets for antifungal treatments.

MiR-204-5p mediates PERK inhibition to suppress growth and induce apoptosis in ovarian cancer through the eIF2α/ATF-4/CHOP pathway

The unfolded protein response (UPR) is crucial in maintaining cell survival during stressful conditions, but prolonged ER stress can lead to apoptosis. Based on the evidence acquired, it has been suggested that inhibiting the protein kinase RNA-like ER kinase (PERK) pathway, which constitutes an adaptive branch of UPR, may represent a viable approach for impeding the proliferation of neoplastic cells. This study assesses the influence of PERK inhibition mediated by miR-204-5p on the growth of ovarian cancer cell lines, OVCAR3 and SKOV3. We demonstrated that miR-204-5p significantly downregulated the expression of PERK at the RNA and protein levels. The suppression of PERK, mediated by miR-204-5p, significantly diminished cellular viability and enhanced apoptotic cell death in cells exposed to Tunicamycin (Tm). We ascertained that the inhibition of PERK by miR-204-5p decreased eukaryotic initiation factor 2alpha (eIF2α) phosphorylation. Moreover, activating transcription factor 4 (ATF4) and CCAAT-enhancer-binding homologous protein (CHOP) expression levels were notably elevated in response to miR-204-5p. The expression of Bax and caspase-12 was found to be upregulated, while the expression of Bcl-2 was reduced. This study is the first to demonstrate that silencing the PERK gene through miR-204-5p significantly inhibits cell growth and promotes ER-stress-induced apoptosis in ovarian cancer cells.

Cytosolic and endoplasmic reticulum chaperones inhibit wt-p53 to increase cancer cells' survival by refluxing ER-proteins to the cytosol

The endoplasmic reticulum (ER) is an essential sensing organelle responsible for the folding and secretion of almost one-third of eukaryotic cells' total proteins. However, environmental, chemical, and genetic insults often lead to protein misfolding in the ER, accumulating misfolded proteins, and causing ER stress. To solve this, several mechanisms were reported to relieve ER stress by decreasing the ER protein load. Recently, we reported a novel ER surveillance mechanism by which proteins from the secretory pathway are refluxed to the cytosol to relieve the ER of its content. The refluxed proteins gain new prosurvival functions in cancer cells, thereby increasing cancer cell fitness. We termed this phenomenon ER to CYtosol Signaling (or 'ERCYS'). Here, we found that in mammalian cells, ERCYS is regulated by DNAJB12, DNAJB14, and the HSC70 cochaperone SGTA. Mechanistically, DNAJB12 and DNAJB14 bind HSC70 and SGTA - through their cytosolically localized J-domains to facilitate ER-protein reflux. DNAJB12 is necessary and sufficient to drive this phenomenon to increase AGR2 reflux and inhibit wt-p53 during ER stress. Mutations in DNAJB12/14 J-domain prevent the inhibitory interaction between AGR2-wt-p53. Thus, targeting the DNAJB12/14-HSC70/SGTA axis is a promising strategy to inhibit ERCYS and impair cancer cell fitness.

The ability of dietary essential oils to mitigate nickel-induced growth retardation, immune-antioxidant suppression, and endoplasmic reticulum stress activation in Nile tilapia

Fish immunity is significantly impacted by waterborne metal intoxication. Nickel is a ubiquitous metal in aquatic bodies which badly impacts fish immune responses and survival. In the current research, we looked into the possible protective effects of essential oils of tea tree (TTO) and basil (BEO) against nickel exposure in Nile tilapia, or Oreochromis niloticus. To achieve this, 240 Nile tilapia (27.92 ± 0.22 g) were categorized into six groups for 45 days; three groups were fed on basal control, TTO, and BEO diets without Ni exposure. The other three groups were subjected to Ni at a level of 3.6 mg/L and fed on basal, TTO, and BEO diets. The outcomes showed a substantial decrease in the growth measures and survival % in the Ni-exposed fish. Oxidative stress (higher splenic malondialdehyde and lower splenic catalase, reduced glutathione, and superoxide dismutase), immune suppression (lower serum lysozyme, myeloperoxidase, and nitric oxide), and elevated serum cortisol levels were observed in the Ni-intoxicated group. The Ni-intoxicated group exhibited various pathological alterations detected in the intestinal tissue mainly inflammatory and necrotic changes, moreover, moderate depletion of lymphoid elements represented by necrotic lymphocytes in the splenic tissue. Ni-exposure induced endoplasmic reticulum stress through up-regulation of the splenic expression of protein kinase R-like endoplasmic reticulum kinase, activating transcription factor 6, CCAAT/enhancer-binding protein homologous protein, X-box binding protein 1, α-subunit of eukaryotic initiation factor 2, inositol-requiring kinase 1a, mitogen-activated protein kinase, c-JunN-terminal kinase, and binding protein for immunoglobulins. Feeding on the TTO and BEO diets improved the growth measures, survival, and antioxidant capacity. Immunomodulation, enhancement of the intestinal and splenic architecture, and relief of the endoplasmic reticulum stress condition were noticed when the Ni-intoxicant groups were fed on TTO and BEO diets. Overall, the effect of the TTO diet was more pronounced than the BEO diet in mitigating the negative consequences of Ni-intoxication in Nile tilapia. Dietary fortification of 0.1% TTO and/or 0.1% BEO is recommended during Ni exposure in aquaculture practices.

Cannabinoids Activate Endoplasmic Reticulum Stress Response and Promote the Death of Avian Retinal Müller Cells in Culture

BACKGROUND/OBJECTIVES

Activation of cannabinoid CB1 or CB2 receptors induces the death of glial progenitors from the chick retina in culture. Here, by using an enriched retinal glial cell culture, we characterized some mechanisms underlying glial death promoted by cannabinoids.

METHODS AND RESULTS

Retinal cultures obtained from 8-day-old (E8) chick embryos and maintained for 12-15 days (C12-15) were used. MTT assays revealed that the CB1/CB2 agonist WIN 55,212-2 (WIN) decreased cell viability in the cultures in a time-dependent manner, with a concomitant increase in extracellular LDH activity, suggesting membrane integrity loss. Cell death was also dose-dependently induced by cannabidiol (CBD), Δ9-tetrahydrocannabinol (THC), and CP55940, another CB1/CB2 agonist. In contrast to WIN-induced cell death that was not blocked by either antagonist, the deleterious effect of CBD was blocked by the CB2 receptor antagonist SR144528, but not by PF514273, a CB1 receptor antagonist. WIN-treated cultures showed glial cells with large vacuoles in cytoplasm that were absent in cultures incubated with WIN plus 4-phenyl-butyrate (PBA), a chemical chaperone. Since cannabinoids induced the phosphorylation of eukaryotic initiation factor 2-alfa (eIF2α), these results suggest a process of endoplasmic reticulum (ER) swelling and stress. Incubation of the cultures with WIN for 4 h induced a ~five-fold increase in the number of cells labeled with the ROS indicator CM-H2DCFDA. WIN induced the phosphorylation of JNK but not of p38 in the cultures, and also induced an increase in the number of glial cells expressing cleaved-caspase 3 (c-CASP3). The decrease in cell viability and the expression of c-CASP3 was blocked by salubrinal, an inhibitor of eIF2α dephosphorylation.

CONCLUSIONS

These data suggest that cannabinoids induce the apoptosis of glial cells in culture by promoting ROS production, ER stress, JNK phosphorylation, and caspase-3 processing. The graphical abstract was created at Biorender.com.

Sinapic acid alleviates glutamate-induced excitotoxicity by inhibiting neuroinflammation and endoplasmic reticulum stress pathway in C6 glioma cells

Sinapic acid (SA) is a polyphenol compound derived from hydroxycinnamic acid found in various foods such as cereals and vegetables and has antioxidant, anti-inflammatory and neuroprotective properties. However, its effects on glutamate-induced excitotoxicity, which is important in neurodegenerative diseases, have not been fully elucidated. This study aimed to investigate the effect of SA on glutamate excitotoxicity and the possible role of proinflammatory cytokines and the endoplasmic reticulum (ER) stress pathway. In the study, C6 rat glioma cell line was used and the cells were divided into 4 groups: control, glutamate, SA and glutamate+SA. Cells were treated with 10 mM glutamate for 24 h to induce excitotoxicity. Additionally, SA was applied to cells at concentrations of 12.5 to 100 μM to examine its effects on glutamate excitotoxicity. XTT test was used for cell viability, and apoptotic cells were determined by immunofluorescence and flow cytometry methods. Proinflammatory cytokines (tumor necrosis factor-alpha, TNF-α and interleukin-beta, IL-1β), ER stress markers (glucose regulatory protein 78, GRP78; C/EBP homologous protein, CHOP and activating transcription factor-4, ATF-4) and caspase-3 was used to measure ELISA method. Findings indicated that SA (50 μM) significantly increased cell viability against glutamate-induced excitotoxicity (p < 0.05). Also, SA caused a significant decrease in TNF-α, IL-1β, GRP78, CHOP, ATF-4 and caspase-3 levels in glutamate-treated cells (p < 0.05). Flow cytometry and immunofluorescence staining results showed that SA reduced apoptosis in C6 glioma cells. In conclusion, our findings suggested that SA attenuated glutamate-induced excitotoxicity by preventing apoptosis through reducing proinflammatory cytokines and ER stress protein levels.

Unfolded protein responses: Dynamic machinery in wound healing

Skin wound healing is a dynamic process consisting of multiple cellular and molecular events that must be tightly coordinated to repair the injured tissue efficiently. The healing pace is decided by the type of injuries, the depth and size of the wounds, and whether wound infections occur. However, aging, comorbidities, genetic factors, hormones, and nutrition also impact healing outcomes. During wound healing, cells undergo robust processes of synthesizing new proteins and degrading multifunctional proteins. This imposes an increasing burden on the endoplasmic reticulum (ER), causing ER stress. Unfolded protein response (UPR) represents a collection of highly conserved stress signaling pathways originated from the ER to maintain protein homeostasis and modulate cell physiology. UPR is known to be beneficial for tissue healing. However, when excessive ER stress exceeds ER's folding potential, UPR pathways trigger cell apoptosis, interrupting tissue regeneration. Understanding how UPR pathways modulate the skin's response to injuries is critical for new interventions toward the control of acute and chronic wounds. Herein, in this review, we focus on the participation of the canonical and noncanonical UPR pathways during different stages of wound healing, summarize the available evidence demonstrating UPR's unique position in balancing homeostasis and pathophysiology of healing tissues, and highlight the understudied areas where therapeutic opportunities may arise.

IRE1 is a promising therapeutic target in pancreatic cancer

[Figure: see text].

Aging and voluntary exercise's effects on Aβ1-42 levels, endoplasmic reticulum stress factors, and apoptosis in the hippocampus of old male rats

Within the aging cortex, amyloid beta peptide (Aβ) is a crucial element of the senile plaques, a hallmark feature often observed in cases of Alzheimer's disease (AD). The UPR (unfolded protein response), a cellular mechanism for protein folding, is switched on by Aβ accumulation. Endoplasmic reticulum (ER) stress has been identified as playing a role in aging and the development of neurodegenerative diseases. The exact molecular pathways leading to perishing of cells from Aβ-induced ER stress, as well as the impact of voluntary exercise on these mechanisms, are still subjects awaiting a definitive answer yet. In the current study, 18 male Wistar rats were included: 6 young rats (3 months old; 200-250 g) in the Young Control group, and 12 old rats (18 months old; 400-430 g) randomly allocated to the Old Control and Old Exercise groups. The rat cages had running wheels for them to voluntarily run on for 8 weeks. This was followed by Western blotting, immunohistochemical staining, biochemical as well as morphological analyses. Voluntary exercise reduced Aβ1-42 deposition (P < 0.001) and inhibited the activation of caspase-8 (P < 0.001) and caspase-12 (P < 0.01), and on top of that down-regulated the expression of ATF6 (P < 0.001), CHOP (P < 0.01), and p-PERK (P < 0.05) proteins in the hippocampus of old male rats. Exercise amplified the population of Bcl-2-expressing cells and decreased the population of Bax-expressing cells in the hippocampus of the Old Exercise group (P < 0.001). Voluntary exercise inhibited the apoptotic pathways and suppressed the activation of UPR signaling pathways. Hence, voluntary exercise may be a therapeutic strategy and a promising approach to prevent AD through modulation of Aβ-induced ER stress.

Cytoplasmic regulation of the poly(A) tail length as a potential therapeutic target

Virtually all mRNAs acquire a poly(A) tail cotranscriptionally, but its length is dynamically regulated in the cytoplasm in a transcript-specific manner. The length of the poly(A) tail plays a crucial role in determining mRNA translation, stability, and localization. This dynamic regulation of poly(A) tail length is widely used to create posttranscriptional gene expression programs, allowing for precise temporal and spatial control. Dysregulation of poly(A) tail length has been linked to various diseases, including cancers, inflammatory and cardiovascular disorders, and neurological syndromes. Cytoplasmic poly(A) tail length is maintained by a dynamic equilibrium between cis-acting elements and cognate factors that promote deadenylation or polyadenylation, enabling rapid gene expression reprogramming in response to internal and external cellular cues. While cytoplasmic deadenylation and its pathophysiological implications have been extensively studied, cytoplasmic polyadenylation and its therapeutic potential remain less explored. This review discusses the distribution, regulation, and mechanisms of cytoplasmic polyadenylation element-binding proteins(CPEBs), highlighting their dual roles in either promoting or repressing gene expression depending on cellular context. We also explore their involvement in diseases such as tumor progression and metastasis, along with their potential as targets for novel therapeutic strategies.

Aβ42 induces stress granule formation via PACT/PKR pathway

Stress granule (SG) formation has been linked to several neurodegenerative disorders, such as Alzheimer's disease (AD). Amyloid-β42 (Aβ42) is a key player in the pathogenesis of AD and is known to trigger various stress-related signaling pathways. However, the impact of Aβ on SG formation has not been fully understood. The primary aim of this study is to analyze the SG-inducing properties of Aβ42 and to uncover the molecular mechanisms underlying this process. Our results revealed that exposure to 20 μM Aβ42 led to a significant SG formation in neuroblastoma-derived (SH-SY5Y) and glioma-derived (U87) cell lines. Interestingly, we observed elevated levels of p-eIF2α, while overall protein translation levels remained unchanged. Monomeric and oligomeric forms of Aβ42 exhibited a 4-5 times stronger ability to induce SG formation compared to fibrillar forms. Additionally, treatment with familial mutants of Aβ42 (Dutch and Flemish) showed distinct effects on SG induction. Moreover, our findings using eIF2α kinases knockout (KO) cell lines demonstrated that Aβ-induced SG formation is primarily dependent on Protein Kinase R (PKR). Subsequent proximity ligation assay (PLA) analysis revealed a close proximity of PACT and PKR in Aβ-treated cells and in AD mouse hippocampus. Taken together, our study suggests that Aβ42 promotes SG formation through PKR kinase activation, which in turn requires PACT involvement.

CRISPuRe-seq: pooled screening of barcoded ribonucleoprotein reporters reveals regulation of RNA polymerase III transcription by the integrated stress response via mTOR

Genetic screens using CRISPR (Clustered Regularly Interspaced Palindromic Repeats) provide valuable information about gene function. Nearly all pooled screening technologies rely on the cell to link genotype to phenotype, making it challenging to assay mechanistically informative, biochemically defined phenotypes. Here, we present CRISPuRe-seq (CRISPR PuRification), a novel pooled screening strategy that expands the universe of accessible phenotypes through the purification of ribonucleoprotein complexes that link genotypes to expressed RNA barcodes. While screening for regulators of the integrated stress response (ISR), we serendipitously discovered that the ISR represses transfer RNA (tRNA) production under conditions of reduced protein synthesis. This regulation is mediated through inhibition of mTORC1 and corresponding activation of the RNA polymerase III inhibitor MAF1. These data demonstrate that coherent downregulation of tRNA expression and protein synthesis is achieved through cross-talk between the ISR and mTOR, two master integrators of cell state.

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.

Unfolded protein response: An essential element of intestinal homeostasis and a potential therapeutic target for inflammatory bowel disease

Different physiological and pathological situations can produce alterations in the cell's endoplasmic reticulum (ER), leading to a condition known as ER stress, which can trigger an intricate intracellular signal transduction system known as the unfolded protein response (UPR). UPR is primarily tailored to restore proteostasis and ER equilibrium; otherwise, if ER stress persists, it can cause programmed cell death as a cytoprotective mechanism and drive inflammatory processes. Therefore, since intestinal cells strongly rely on UPR for their biological functions and unbalanced UPR has been linked to inflammatory, metabolic, and immune disorders, here we discussed the role of the UPR within the intestinal tract, focusing on the UPR contribution to inflammatory bowel disease development. Importantly, we also highlighted the promising potential of UPR components as therapeutic targets for intestinal inflammatory diseases.

G3BP1/2-Targeting PROTAC Disrupts Stress Granules Dependent ATF4 Migracytosis as Cancer Therapy

Stress granules (SGs) are membraneless cytoplasmic compartments that form in response to stress stimuli. In these compartments, most translation factors stall, except for activating transcription factor 4 (ATF4), which is preferentially translated to ensure cell survival under stressful conditions. Cancer cells encounter various stress conditions in the tumor microenvironment during tumorigenesis; however, how they exploit the pro-survival effects of ATF4 in SGs remains unclear. G3BP1/2 are central nodes of the SG network, regulating SG dynamics. In this study, we designed two small molecules, #129 and PROTAC (Proteolysis Targeting Chimera) degrader 129 (PT-129), which specifically target the NTF2L domain of G3BP1/2, a crucial hub for protein and RNA interactions. These compounds inhibit the formation of stress granules in stressed cells and disassemble pre-existing stress granules. Furthermore, pharmacological inhibition by PT-129 suppressed fibroblast-mediated cancer cell growth in vitro and reduced tumor growth in vivo. Mechanistically, SG facilitates the delivery of ATF4 from fibroblasts to tumor cells via migracytosis, a primary mediator of fibroblast-associated tumor growth. PT-129-mediated disassembly of stress granules disrupts ATF4 delivery, thereby preventing cancer cell proliferation. These compounds, therefore, represent powerful tools for gaining molecular insights into SGs and hold promise for cancer therapeutic interventions by modulating stress granule dynamics.

Palmitic acid-induced cell death: impact of endoplasmic reticulum and oxidative stress, mitigated by L-citrulline

OBJECTIVE

Palmitic acid (PA), the most abundant saturated free fatty acids, induces apoptosis in bovine mammary epithelial cells (MECs). It is suggested that oxidative stress and endoplasmic reticulum (ER) stress are key mechanisms underlying PA-induced cell death. This study aimed to investigate the interaction between ER stress and oxidative stress during PA-induced cell death in mammary alveolar cell-T (MAC-T) cells. Additionally, we examined whether L-citrulline can protect against PA-induced damage of MAC-T cells.

METHODS

MAC-T cells were treated with 4-phenyl butyric acid (4-PBA) or N-acetyl-Lcysteine (NAC) to inhibit PA-induced ER stress and oxidative stress, respectively. MAC-T cells were pretreated with or without L-citrulline for 48 h followed by PA treatment. Cell viability was measured with MTT assays. Intracellular reactive oxygen species (ROS) levels in MAC-T cells were assessed using 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluores cein diacetate acetyl ester dye. Real-time quantitative polymerase chain reaction was used to explore the regulation of genes associated with oxidative stress, and ER stress genes. Western blotting analysis was also carried out.

RESULTS

4-PBA significantly reduced PA-induced mRNA expressions of activating transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), nuclear factor (erythroid-derived 2)-like 2 (NRF2), and intracellular ROS levels. Furthermore, NAC dramatically reduced PA-induced ROS levels and the mRNA expressions of NRF2, ATF4, and CHOP. L-citrulline pretreatment effectively rescued cell viability decreased by PA. Moreover, L-citrulline pretreatment significantly downregulated the PA-induced upregulation of GRP78, ATF4, and CHOP mRNA expression, and protein expression of p-PERK and cleaved caspase-3. PA increased intracellular ROS levels and NRF2 mRNA expression, whereas L-citrulline pretreatment remarkably reduced these levels.

CONCLUSION

Both ER and oxidative stresses interact during PA-induced cell death in MAC-T cells, and L-citrulline could attenuate this cell death by inhibiting ER and oxidative stresses. Therefore, L-citrulline may be a promising supplement for protecting against PA-induced cell death in bovine MECs during the lactation period of dairy cows.

Chronic hyperglycemia induces hepatocyte pyroptosis via Gα12/Gα13-associated endoplasmic reticulum stress: Effect of pharmacological intervention

AIMS

Hyperglycemia induces pathophysiological changes. Endoplasmic reticulum (ER) stress with Gα12 overexpression may promote hepatocyte death. This study investigated whether sustained hyperglycemia triggers ER stress-associated pyroptosis and fibrosis in the liver alongside an overexpression of Gα12, and examined the potential link with VEGF-A levels.

MAIN METHODS

Mice were subjected to a high-fat diet (60 kcal% fat) with streptozotocin (50 mg/kg body weight, three consecutive times, between 12-13th weeks). AZ2 (a functional Gα12 inhibitor) was treated at 10 mg/kg body weight (5 times/week, 3 weeks). Immunoblotting and immunohistochemistry analyses were performed.

KEY FINDINGS

Hepatic Gα12/Gα13 were overexpressed in the diabetic mice. The following proteins downstream from the Gα12 axis were upregulated: PGC1α, PPARα, and SIRT1. Sustained hyperglycemia promoted ER stress marker levels. Histopathological and biochemical assays showed large-sized lipid droplet accumulation, hepatocyte degeneration, and damage as blood transaminase activities increased. Moreover, the diabetic condition increased IL-1β, caspase-1, and NLRP3 levels, which were supportive of pyroptosis. Consistently, the intensities of Masson's trichrome, collagen-1A1, α-SMA, vimentin, and fibronectin all increased. VEGF-A and VEGFR2 levels also increased in the liver and/or sera. The levels of hepatic pigment epithelial-derived factor (PEDF), a physiological antagonist of VEGF-A, decreased with its reciprocal increase in serum. These events were reversed by AZ2 treatment, supporting the role of Gα12 in hyperglycemic stress in the liver.

SIGNIFICANCE

Chronic hyperglycemia causes hepatic pyroptosis and fibrosis related to ER stress with Gα12/Gα13 and VEGF overexpression, which may be overcome by AZ2 treatments.

Reticulophagy and viral infection

All viruses are obligate intracellular parasites that use host machinery to synthesize viral proteins. In infected eukaryotes, viral secreted and transmembrane proteins are synthesized at the endoplasmic reticulum (ER). Many viruses refashion ER membranes into bespoke factories where viral products accumulate while evading host pattern recognition receptors. ER processes are tightly regulated to maintain cellular homeostasis, so viruses must either conform to ER regulatory mechanisms or subvert them to ensure efficient viral replication. Reticulophagy is a catabolic process that directs lysosomal degradation of ER components. There is accumulating evidence that reticulophagy serves as a form of antiviral defense; we call this defense "xERophagy" to acknowledge its relationship to xenophagy, the catabolic degradation of microorganisms by macroautophagy/autophagy. In turn, viruses can subvert reticulophagy to suppress host antiviral responses and support efficient viral replication. Here, we review the evidence for functional interplay between viruses and the host reticulophagy machinery.Abbreviations: AMFR: autocrine motility factor receptor; ARF4: ADP-ribosylation factor 4; ARL6IP1: ADP-ribosylation factor-like 6 interacting protein 1; ATL3: atlastin GTPase 3; ATF4: activating transcription factor 4; ATF6: activating transcription factor 6; BPIFB3: BPI fold containing family B, member 3; CALCOCO1: calcium binding and coiled coil domain 1; CAMK2B: calcium/calmodulin-dependent protein kinase II, beta; CANX: calnexin; CDV: canine distemper virus; CCPG1: cell cycle progression 1; CDK5RAP3/C53: CDK5 regulatory subunit associated protein 3; CIR: cargo-interacting region; CoV: coronavirus; CSNK2/CK2: casein kinase 2; CVB3: coxsackievirus B3; DAPK1: death associated protein kinase 1; DENV: dengue virus; DMV: double-membrane vesicles; EBOV: Ebola virus; EBV: Epstein-Barr Virus; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; EMCV: encephalomyocarditis virus; EMV: extracellular microvesicle; ER: endoplasmic reticulum; ERAD: ER-associated degradation; ERN1/IRE1: endoplasmic reticulum to nucleus signalling 1; EV: extracellular vesicle; EV71: enterovirus 71; FIR: RB1CC1/FIP200-interacting region; FMDV: foot-and-mouth disease virus; HCMV: human cytomegalovirus; HCV: hepatitis C virus; HMGB1: high mobility group box 1; HSPA5/BiP: heat shock protein 5; IFN: interferon; IFNG/IFN-γ: interferon gamma; KSHV: Kaposi's sarcoma-associated herpesvirus; LIR: MAP1LC3/LC3-interacting region; LNP: lunapark, ER junction formation factor; MAP1LC3: microtubule-associated protein 1 light chain 3; MAP3K5/ASK1: mitogen-activated protein kinase kinase kinase 5; MAPK/JNK: mitogen-activated protein kinase; MeV: measles virus; MHV: murine hepatitis virus; NS: non-structural; PDIA3: protein disulfide isomerase associated 3; PRR: pattern recognition receptor; PRRSV: porcine reproductive and respiratory syndrome virus; RB1CC1/FIP200: RB1-inducible coiled-coil 1; RETREG1/FAM134B: reticulophagy regulator 1; RHD: reticulon homology domain; RTN3: reticulon 3; RTN3L: reticulon 3 long; sAIMs: shuffled Atg8-interacting motifs; SARS-CoV: severe acute respiratory syndrome coronavirus; SINV: Sindbis virus; STING1: stimulator of interferon response cGAMP interactor 1; SVV: Seneca Valley virus; SV40: simian virus 40; TEX264: testis expressed gene 264 ER-phagy receptor; TFEB: transcription factor EB; TRAF2: TNF receptor-associated factor 2; UIM: ubiquitin-interacting motif; UFM1: ubiquitin-fold modifier 1; UPR: unfolded protein response; VAPA: vesicle-associated membrane protein, associated protein A; VAPB: vesicle-associated membrane protein, associated protein B and C; VZV: varicella zoster virus; WNV: West Nile virus; XBP1: X-box binding protein 1; XBP1s: XBP1 spliced; xERophagy: xenophagy involving reticulophagy; ZIKV: Zika virus.

Tubulin-Binding Region Modulates Cholesterol-Triggered Aggregation of Tau Proteins

A hallmark of Alzheimer disease (AD) and tauopathies, severe neurodegenerative diseases, is the progressive aggregation of Tau, also known as microtubule-associated Tau protein. Full-length Tau1-441, also known as 2N4R, contains two N-terminal inserts that bind to tubulin. This facilitates the self-assembly of tubulin simultaneously enhancing stability of cell microtubules. Other Tau isoforms have one (1N4R) or zero (0N4R) N-terminal inserts, which makes 2N4R Tau more and 0N4R less effective in promoting microtubule self-assembly. A growing body of evidence indicates that lipids can alter the aggregation rate of Tau isoforms. However, the role of N-terminal inserts in Tau-lipid interactions remains unclear. In this study, we utilized a set of biophysical methods to determine the extent to which N-terminal inserts alter interactions of Tau isoforms with cholesterol, one of the most important lipids in plasma membranes. Our results showed that 2 N insert prevents amyloid-driven aggregation of Tau at the physiological concentration of cholesterol, while the absence of this N-terminal repeat (1N4R and 0N4R Tau) resulted in the self-assembly of Tau into toxic amyloid fibrils. We also found that the presence of cholesterol in the lipid bilayers caused a significant increase in the cytotoxicity of 1N4R and 0N4R Tau to neurons. This effect was not observed for 2N4R Tau fibrils formed in the presence of lipid membranes with low, physiological, and elevated concentrations of cholesterol. Using molecular assays, we found that Tau aggregates primarily exert cytotoxicity by damaging cell endosomes, endoplasmic reticulum, and mitochondria.

Thioctic acid shield against lipopolysaccharide depression and endoplasmic reticulum stress: GR7M/Homer/ATF6 signaling

Aim: Endoplasmic reticulum stress triggers neuronal unfolded protein accumulation, contributing to the pathophysiology of depression psychiatric illnesses.Materials & methods: The brain-derived neurotrophic factor (BDNF), metabotropic glutamate receptor type 7 (GRM7), phosphoinisitol kinase-3 (PIK3), serine/threonine kinase 1 (AKT) and Homer1 may afford an important signaling pathways in LPS induced depression rat model. Herein, thioctic acid, Burdock and propolis therapeutic index on lipopolysaccharide (LPS)-induced depression was monitored. BDNF/PI3K/GR7M/ATF6/CHOP/XBP/AKT/Homer-1 signaling pathways also opened a novel avenue in the integration of synaptic neurotransmission.Results: The aforementioned treatments elevated GR7M/BDNF/GABA gene expression meanwhile decreased reactive oxygen species generation (Malondialdehyde/glutathione reductase/Total antioxidant capacity) and reduced the expression of ATF6/CHOP/PI3K/AKT/XBP/Homer-1 post LPS elevation.Conclusion: Thioctic acid, propolis and Burdock are prospective therapeutic agents via GRM7/BDNF/AKT/PI3K/ATF6/XBP/homer -1 signaling pathways in LPS-induced depression.

Mapping the Genetic Architecture of the Adaptive Integrated Stress Response in S. cerevisiae

The integrated stress response (ISR) is a conserved eukaryotic signaling pathway that responds to diverse stress stimuli to restore proteostasis. The strength and speed of ISR activation must be tuned properly to allow protein synthesis while maintaining proteostasis. Here, we describe how genetic perturbations change the dynamics of the ISR in budding yeast. We treated ISR dynamics, comprising timecourses of ISR activity across different levels of stress, as a holistic phenotype. We profiled changes in ISR dynamics across thousands of genetic perturbations in parallel using CRISPR interference with barcoded expression reporter sequencing (CiBER-seq). We treated cells with sulfometuron methyl, a titratable inhibitor of branched-amino acid synthesis, and measured expression of an ISR reporter. Perturbations to translation such as depletion of aminoacyl-tRNA synthetases or tRNA biogenesis factors reduced cell growth and caused a strikingly proportionate activation of the ISR activation. In contrast, impaired ribosome biogenesis reduced basal ISR activity and weakened ISR dynamics. Reduced ribosome capacity may lower the demand for amino acids and thereby explain these changes. Our work illustrates how CiBER-seq enables high-throughput measurements of complex and dynamic phenotypes that shed light on adaptive and homeostatic mechanisms.

A stress paradox: the dual role of the unfolded protein response in the placenta

The placenta is a temporary organ that forms during pregnancy and is essential for fetal development and maternal health. As an endocrine organ, proper placental function requires continual production, folding, and transport of proteins and lipids. Central to these processes is the endoplasmic reticulum (ER), a dynamic organelle responsible for maintaining cellular protein and lipid synthesis and processing. ER stress occurs when there is an accumulation of unfolded or misfolded proteins, which triggers the activation of cellular pathways collectively called the unfolded protein response. Unfolded protein response pathways act to alleviate the misfolded protein burden and restore ER homeostasis, or if unresolved, initiate cell death. While prolonged ER stress has been linked to deficient placental function and adverse pregnancy outcomes, basal activation of unfolded protein response pathways is required for placental development and function. This review explores the importance of ER homeostasis in placental development and function, examining how disruptions in ER stress responses may contribute to adverse pregnancy outcomes.

Endoplasmic reticulum stress in acute lung injury and pulmonary fibrosis

Pulmonary fibrosis (PF) is a progressive and irreversible lung disease that leads to diminished lung function, respiratory failure, and ultimately death and typically has a poor prognosis, with an average survival time of 2 to 5 years. Related articles suggested that endoplasmic reticulum (ER) stress played a critical role in the occurrence and progression of PF. The ER is responsible for maintaining protein homeostasis. However, factors such as aging, hypoxia, oxidative stress, or inflammation can disrupt this balance, promoting the accumulation of misfolded proteins in the ER and triggering ER stress. To cope with this situation, cells activate the unfolded protein response (UPR). Since acute lung injury (ALI) is one of the key onset events of PF, in this review, we will discuss the role of ER stress in ALI and PF by activating multiple signaling pathways and molecular mechanisms that affect the function and behavior of different cell types, with a focus on epithelial cells, fibroblasts, and macrophages. Linking ER stress to these cell types may broaden our understanding of the mechanisms underlying lung fibrosis and help us target these cells through these mechanisms. The relationship between ER stress and PF is still evolving, and future research will explore new strategies to regulate UPR pathways, providing novel therapeutic targets.

MAM-mediated mitophagy and endoplasmic reticulum stress: the hidden regulators of ischemic stroke

Ischemic stroke (IS) is the predominant subtype of stroke and a leading contributor to global mortality. The mitochondrial-associated endoplasmic reticulum membrane (MAM) is a specialized region that facilitates communication between the endoplasmic reticulum and mitochondria, and has been extensively investigated in the context of neurodegenerative diseases. Nevertheless, its precise involvement in IS remains elusive. This literature review elucidates the intricate involvement of MAM in mitophagy and endoplasmic reticulum stress during IS. PINK1, FUNDC1, Beclin1, and Mfn2 are highly concentrated in the MAM and play a crucial role in regulating mitochondrial autophagy. GRP78, IRE1, PERK, and Sig-1R participate in the unfolded protein response (UPR) within the MAM, regulating endoplasmic reticulum stress during IS. Hence, the diverse molecules on MAM operate independently and interact with each other, collectively contributing to the pathogenesis of IS as the covert orchestrator.

Polystyrene microplastics cause reproductive toxicity in male mice

Microplastics are a common environmental pollutant that disrupts the reproductive system of living organisms. We investigated the reproductive toxicity of 2 μm polystyrene microplastics (PS-MPs) in mice and treated them with PS-MPs for 6 weeks. We demonstrated that PS-MPs decreased the gonadosomatic index and the serum concentration of pituitary-testicular axis hormones (Follicle-stimulating hormone, Luteinizing hormone, and testosterone). The PS-MPs treatment also reduced viable epididymal sperm number and sperm motility. Our results also demonstrated a marked decrease in tubular differentiation index, spermatogenesis index, repopulation index, and steroidogenic foci. The PS-MPs treated mice demonstrated marketed tissue damage in the testis. We also found that reproductive abnormality in PS-MPs treated mice accompanied by reduced antioxidant capacity elevated oxidative stress, and, elevated apoptotic signaling. It was observed that Endoplasmic reticulum (ER) stress markers, including GRP78 and Chop, were upregulated. Based on these findings, oxidative stress and endoplasmic reticulum stress may contribute to the decline in the steroidogenic function of Leydig cells with PS-MPs treated.

Origins and molecular effects of hypoxia in cancer

Hypoxia (insufficient O2) is a pivotal factor in cancer progression, triggering genetic, transcriptional, translational and epigenetic adaptations associated to therapy resistance, metastasis and patient mortality. In this review, we outline the microenvironmental origins and molecular mechanisms responsible for hypoxic cancer cell adaptations in situ and in vitro, whilst outlining current approaches to stratify, quantify and therapeutically target hypoxia in the context of precision oncology.

Why is next-generation sequencing essential in modern virology?

A contaminated viral stock results in considerable loss of time, resources and financial means and is generally discovered only by chance after years of research. Thus, it is necessary to implement a technique that can detect contamination without prior knowledge or assumptions, such as next-generation sequencing (NGS). Here, we describe the discovery of a cross-contaminated viral stock from a biological repository of an African Zika virus isolate with Toscana virus after performing NGS on infected cells. In addition, we also describe the consequences that we faced using this contaminated stock. These included the economic and time loss to the lab that needed to repeat all previously performed experiments, the generation of biologically flawed results with a subsequent potential retraction and the severe risk of infection of lab members who manipulated the contaminated stock.

Lost in translation? Evidence for a muted proteomic response to thermal stress in a stenothermal Antarctic fish and possible evolutionary mechanisms

Stenothermal Antarctic notothenioid fishes are noteworthy for their history of isolation in extreme cold and their corresponding lack of the canonical heat shock response. Despite extensive transcriptomic studies, the mechanistic basis for stenothermy has not been fully elucidated. Given that the proteome better represents an organism's physiology, the possibility exists that some aspects of stenothermy arise posttranscriptionally. Here, Antarctic emerald rockcod (Trematomus bernacchii) were sampled after exposure to chronic and/or acute high temperatures, followed by a thorough assessment of proteomic responses in the brain, gill, and kidney. Few cellular stress response proteins were induced, and overall responses were modest in terms of the numbers of differentially expressed proteins and their fold changes. Inconsistencies in protein induction across treatments and tissues are suggestive of dysregulation, rather than an adaptive response. Changes in regulation of the translational machinery in Antarctic notothenioids could explain these patterns. Some components of translational regulatory pathways are highly conserved [e.g., Ser-52, eukaryotic translation initiation factor 2α (eIF2α)], but other proteins comprising the cellular "integrated stress response," specifically, the eIF2α kinases general control nonderepressible 2 (GCN2) and PKR-like endoplasmic reticulum kinase (PERK), may have evolved along different trajectories in Antarctic fishes. Taken together, these observations suggest a novel hypothesis for stenothermy and the absence of a coordinated cellular stress response in Antarctic fishes.NEW & NOTEWORTHY Antarctic fishes have some of the lowest known heat tolerances among vertebrates, but the molecular mechanisms underlying this pattern are not fully understood. By combining detailed analyses of protein expression patterns in several tissues under various heat treatments with a broader evolutionary perspective, this study offers a novel hypothesis to explain the narrow range of temperature tolerance in this extraordinary group of fishes.

Understanding neurodevelopmental proteasomopathies as new rare disease entities: A review of current concepts, molecular biomarkers, and perspectives

The recent advances in high throughput sequencing technology have drastically changed the practice of medical diagnosis, allowing for rapid identification of hundreds of genes causing human diseases. This unprecedented progress has made clear that most forms of intellectual disability that affect more than 3% of individuals worldwide are monogenic diseases. Strikingly, a substantial fraction of the mendelian forms of intellectual disability is associated with genes related to the ubiquitin-proteasome system, a highly conserved pathway made up of approximately 1200 genes involved in the regulation of protein homeostasis. Within this group is currently emerging a new class of neurodevelopmental disorders specifically caused by proteasome pathogenic variants which we propose to designate "neurodevelopmental proteasomopathies". Besides cognitive impairment, these diseases are typically associated with a series of syndromic clinical manifestations, among which facial dysmorphism, motor delay, and failure to thrive are the most prominent ones. While recent efforts have been made to uncover the effects exerted by proteasome variants on cell and tissue landscapes, the molecular pathogenesis of neurodevelopmental proteasomopathies remains ill-defined. In this review, we discuss the cellular changes typically induced by genomic alterations in proteasome genes and explore their relevance as biomarkers for the diagnosis, management, and potential treatment of these new rare disease entities.

Temporal alterations of the nascent proteome in response to mitochondrial stress

Under stress, protein synthesis is attenuated to preserve energy and mitigate challenges to protein homeostasis. Here, we describe, with high temporal resolution, the dynamic landscape of changes in the abundance of proteins synthesized upon stress from transient mitochondrial inner membrane depolarization. This nascent proteome was altered when global translation was attenuated by stress and began to normalize as translation was recovering. This transition was associated with a transient desynchronization of cytosolic and mitochondrial translation and recovery of cytosolic and mitochondrial ribosomal proteins. Further, the elongation factor EEF1A1 was downregulated upon mitochondrial stress, and its silencing mimicked the stress-induced nascent proteome remodeling, including alterations in the nascent respiratory chain proteins. Unexpectedly, the stress-induced alterations in the nascent proteome were independent of physiological protein abundance and turnover. In summary, we provide insights into the physiological and pathological consequences of mitochondrial function and dysfunction.

Peroxisomal import stress activates integrated stress response and inhibits ribosome biogenesis

Impaired organelle-specific protein import triggers a variety of cellular stress responses, including adaptive pathways to balance protein homeostasis. Most of the previous studies focus on the cellular stress response triggered by misfolded proteins or defective protein import in the endoplasmic reticulum or mitochondria. However, little is known about the cellular stress response to impaired protein import in the peroxisome, an understudied organelle that has recently emerged as a key signaling hub for cellular and metabolic homeostasis. To uncover evolutionarily conserved cellular responses upon defective peroxisomal import, we carried out a comparative transcriptomic analysis on fruit flies with tissue-specific peroxin knockdown and human HEK293 cells expressing dominant-negative PEX5C11A. Our RNA-seq results reveal that defective peroxisomal import upregulates integrated stress response (ISR) and downregulates ribosome biogenesis in both flies and human cells. Functional analyses confirm that impaired peroxisomal import induces eIF2α phosphorylation and ATF4 expression. Loss of ATF4 exaggerates cellular damage upon peroxisomal import defects, suggesting that ATF4 activation serves as a cellular cytoprotective mechanism upon peroxisomal import stress. Intriguingly, we show that peroxisomal import stress decreases the expression of rRNA processing genes and inhibits early pre-rRNA processing, which leads to the accumulation of 47S precursor rRNA and reduction of downstream rRNA intermediates. Taken together, we identify ISR activation and ribosome biogenesis inhibition as conserved adaptive stress responses to defective peroxisomal import and uncover a novel link between peroxisomal dysfunction and rRNA processing.

Endoplasmic reticulum stress and associated apoptosis are linked with the pathogenesis of white striping in broiler breast muscles

White striping (WS) that appears as white stripes parallel to the muscle fibrils is an emerging growth-related abnormality of broiler breast meat. The pathomechanism of this defect has not been fully understood despite intensive studies over the past decade. In the present study, endoplasmic reticulum (ER) stress and its associated apoptotic pathways were investigated to elucidate the potential role of these pathways in the development of WS. To this end, a total of 60 Pectoralis major (Pm) muscle samples were collected from 55-d-old Ross 308 male broiler chickens according to the severity of gross WS lesions (normal, mild, and severe). Histopathological and molecular analyses were conducted to evaluate the lesions and genes involved in the ER stress and related apoptosis. All the Pm samples, both with and without macroscopic WS lesions, showed varying degrees of myodegenerative lesions. Molecular analysis revealed that the transcript abundances of many components related to protein kinase R-like ER kinase (PERK) and inositol-requiring enzyme type 1 (IRE-1) signals of the ER stress response were significantly greater in severely WS-affected breast tissues compared to their mildly affected and normal counterparts. Similarly, the transcript abundances of apoptotic markers related to both signaling pathways were significantly greater in severe WS lesions than those of mildly affected and normal Pm tissues. Besides these, a significant increase in caspase-3 transcript abundance was seen in severe WS lesions in comparison with mild WS and normal breast muscles. Findings of this study suggest that ER stress response and its related apoptotic pathways are possibly activated in the breast muscle of broiler chickens with severe WS lesions. Based on these findings, it is speculated that ER stress-mediated apoptosis occupies a central role in the progression of WS in broiler chickens.

ATF6 Promotes Colorectal Cancer Growth and Stemness by Regulating the Wnt Pathway

SIGNIFICANCE

ATF6 intervention reduces colorectal cancer cell and organoid viability by interrupting dysregulated Wnt signaling, identifying a novel facilitator and potential therapeutic target in colorectal cancer.

FicD regulates adaptation to the unfolded protein response in the murine liver

The unfolded protein response (UPR) is a cellular stress response that is activated when misfolded proteins accumulate in the endoplasmic reticulum (ER). Regulation of the UPR response must be adapted to the needs of the cell as prolonged UPR responses can result in disrupted cellular function and tissue damage. Previously, we discovered that the enzyme FicD (also known as Fic or HYPE) through its AMPylation and deAMPylation activity can modulate the UPR response via post-translational modification of BiP. FicD AMPylates BiP during homeostasis and deAMPylates BiP during stress. We hypothesized that FicD regulation of the UPR will play a role in mitigating the deleterious effects of UPR activation in tissues with frequent physiological stress. Here, we explore the role of FicD in the murine liver. As seen in our pancreatic studies, livers lacking FicD exhibit enhanced UPR signaling in response to short term physiologic fasting and feeding stress. However, in contrast to studies on the pancreas, livers, as a more regenerative tissue, remained remarkably resilient in the absence of FicD. The livers of FicD-/- did not show marked changes in UPR signaling or damage after either chronic high fat diet (HFD) feeding or acute pathological UPR induction. Intriguingly, FicD-/- mice showed changes in UPR induction and weight loss patterns following repeated pathological UPR induction. These findings indicate that FicD regulates UPR responses during mild physiological stress and in adaptation to repeated stresses, but there are tissue specific differences in the requirement for FicD regulation.

IRE1 is implicated in protein synthesis regulation under ER stress conditions in plants

The unfolded protein response (UPR) is a crucial cellular mechanism for maintaining protein folding homeostasis during endoplasmic reticulum (ER) stress. In this study, the role of IRE1, a key component of the UPR, was investigated in protein translation regulation under ER stress conditions in Arabidopsis. We discovered that the loss of IRE1A and IRE1B leads to diminished protein translation, indicating a significant role for IRE1 in this process. However, this regulation was not solely dependent on the interaction with bZIP60, a key transcription factor in the UPR. Interestingly, while chemical chaperones TUDCA and PBA effectively alleviated the translation inhibition observed in ire1a ire1b mutants, this effect was more pronounced than the mitigation observed from suppressing GCN2 expression or introducing a non-phosphorylatable eIF2α variant. Additionally, the kinase and ribonuclease activities of IRE1B were demonstrated to be crucial for plant adaptation and protein synthesis regulation under ER stress conditions. Overall, this study not only highlights the complex regulatory mechanisms of IRE1 in plant ER stress responses but also provides insights into its multifaceted roles in protein translation regulation.

Research advances in understanding crosstalk between organs and pancreatic β-cell dysfunction

Obesity has increased dramatically worldwide. Being overweight or obese can lead to various conditions, including dyslipidaemia, hypertension, glucose intolerance and metabolic syndrome (MetS), which may further lead to type 2 diabetes mellitus (T2DM). Previous studies have identified a link between β-cell dysfunction and the severity of MetS, with multiple organs and tissues affected. Identifying the associations between pancreatic β-cell dysfunction and organs is critical. Research has focused on the interaction between the liver, gut and pancreatic β-cells. However, the mechanisms and related core targets are still not perfectly elucidated. The aims of this review were to summarize the mechanisms of β-cell dysfunction and to explore the potential pathogenic pathways and targets that connect the liver, gut, adipose tissue, muscle, and brain to pancreatic β-cell dysfunction.

The Involvement of Endoplasmic Reticulum Stress during the Interaction between Calcium Oxalate Crystals and Renal Tubular Epithelial Cells

Our study aimed to elucidate the mechanisms behind the interaction between calcium oxalate (CaOx) crystals and renal tubular epithelial cells through transcriptome sequencing analysis. HK-2 cells were stimulated with or without CaOx monohydrate crystals and subjected to RNA-seq to assess the effects of CaOx crystals on gene expression changes, key pathways, and molecular players during this interaction. A total of 629 differentially expressed genes (DEGs) were identified between the control group and experimental group, with 491 genes up-regulated and 138 down-regulated. Functional enrichment analysis indicated that the DEGs were significantly associated with endoplasmic reticulum stress (ERS) and unfolded protein response. To validate our findings, we compared our results with the public dataset GSE73680 and confirmed the increased expression of two ERS-related DEGs, CHAC1 and FGF21, in renal papillary tissues from patients with CaOx stones. Collectively, these findings suggest that ERS plays a crucial role in the crystal-cell interaction and highlight the potential for developing therapeutic strategies aimed at reducing CaOx stone formation by targeting ERS-related molecules and pathways.

An Essential Role for Calnexin in ER-Phagy and the Unfolded Protein Response

ER-phagy is a specialized form of autophagy, defined by the lysosomal degradation of ER subdomains. ER-phagy has been implicated in relieving the ER from misfolded proteins during ER stress upon activation of the unfolded protein response (UPR). Here, we identified an essential role for the ER chaperone calnexin in regulating ER-phagy and the UPR in neurons. We showed that chemical induction of ER stress triggers ER-phagy in the somata and axons of primary cultured motoneurons. Under basal conditions, the depletion of calnexin leads to an enhanced ER-phagy in axons. However, upon ER stress induction, ER-phagy did not further increase in calnexin-deficient motoneurons. In addition to increased ER-phagy under basal conditions, we also detected an elevated proteasomal turnover of insoluble proteins, suggesting enhanced protein degradation by default. Surprisingly, we detected a diminished UPR in calnexin-deficient early cortical neurons under ER stress conditions. In summary, our data suggest a central role for calnexin in orchestrating both ER-phagy and the UPR to maintain protein homeostasis within the ER.

GABAergic interneurons in the hippocampal CA1 mediate contextual fear generalization in PTSD rats

Fear overgeneralization is widely accepted as a pathogenic marker of post-traumatic stress disorder (PTSD). Recently, GABAergic interneurons have been regarded as key players in the regulation of fear memory. The role of hippocampal GABAergic interneurons in contextual fear generalization of PTSD remains incompletely understood. In the present study, we established a rat model of PTSD with inescapable foot shocks (IFS) and observed the loss of GABAergic interneuron phenotype in the hippocampal cornu ammonis-1 (CA1) subfield. To determine whether the loss of GABAergic interneuron phenotype was associated with fear generalization in PTSD rats, we used adeno-associated virus (AAV) to reduce the expression of GAD67 in CA1 and observed its effect on fear generalization. The results showed that the reduction of GAD67 in CA1 enhanced contextual fear generalization in rats. We investigated whether the PERK pathway was involved in the GABAergic interneuron injury. Increased expression of p-PERK, CHOP, and Caspase12 in GABAergic interneurons of PTSD rats was observed. Then, we used salubrinal, an endoplasmic reticulum stress inhibitor, to modulate the PERK pathway. The salubrinal treatment significantly protected the GABAergic interneurons and relieved fear generalization in PTSD rats. In addition, the results showed that salubrinal down-regulated the expression of CHOP and Caspase12 in GABAergic interneurons of PTSD rats. In conclusion, this study provided evidence that the loss of GABAergic interneuron phenotype in CA1 may contribute to contextual fear generalization in PTSD. The PERK pathway is involved in the GABAergic interneuron injury of PTSD rats and modulating it can protect GABAergic interneurons and constrain contextual fear generalization.

Modulation of endoplasmic reticulum stress response pathways by respiratory viruses

Acute respiratory infections (ARIs) are amongst the leading causes of death and disability, and the greatest burden of disease impacts children, pregnant women, and the elderly. Respiratory viruses account for the majority of ARIs. The unfolded protein response (UPR) is a host homeostatic defence mechanism primarily activated in response to aberrant endoplasmic reticulum (ER) resident protein accumulation in cell stresses including viral infection. The UPR has been implicated in the pathogenesis of several respiratory diseases, as the respiratory system is particularly vulnerable to chronic and acute activation of the ER stress response pathway. Many respiratory viruses therefore employ strategies to modulate the UPR during infection, with varying effects on the host and the pathogens. Here, we review the specific means by which respiratory viruses affect the host UPR, particularly in association with the high production of viral glycoproteins, and the impact of UPR activation and subversion on viral replication and disease pathogenesis. We further review the activation of UPR in common co-morbidities of ARIs and discuss the therapeutic potential of modulating the UPR in virally induced respiratory diseases.

The Role of Endoplasmic Reticulum Stress in Metabolic Diseases

The endoplasmic reticulum (ER), the center of protein folding, also controls the cell's life-and-death signaling mechanisms. ER stress caused by unfolded or misfolded proteins leads to the activation of the unfolded protein response (UPR) in the cell. The UPR utilizes three main signaling pathways to restore disrupted ER homeostasis. These signaling pathways are protein kinase R-like endoplasmic reticulum kinase, inositol-requiring enzyme 1, and activating transcription factor 6. Studies have reported that ER stress (ERS) plays a role in the pathogenesis of metabolic disorders such as diabetes, obesity, atherosclerosis, and nonalcoholic liver disease. This review will briefly discuss the ERS response in these metabolic diseases.

PERK-ATAD3A interaction provides a subcellular safe haven for protein synthesis during ER stress

Endoplasmic reticulum (ER) stress induces the repression of protein synthesis throughout the cell. Attempts to understand how localized stress leads to widespread repression have been limited by difficulties in resolving translation rates at the subcellular level. Here, using live-cell imaging of reporter mRNA translation, we unexpectedly found that during ER stress, active translation at mitochondria was significantly protected. The mitochondrial protein ATPase family AAA domain-containing protein 3A (ATAD3A) interacted with protein kinase RNA-like endoplasmic reticulum kinase (PERK) and mediated this effect on localized translation by competing for binding with PERK's target, eukaryotic initiation factor 2 (eIF2). PERK-ATAD3A interactions increased during ER stress, forming mitochondria-ER contact sites. Furthermore, ATAD3A binding attenuated local PERK signaling and rescued the expression of some mitochondrial proteins. Thus, PERK-ATAD3A interactions can control translational repression at a subcellular level, mitigating the impact of ER stress on the cell.

Advancements in unravelling the fundamental function of the ATAD3 protein in multicellular organisms

ATPase family AAA domain containing protein 3, commonly known as ATAD3 is a versatile mitochondrial protein that is involved in a large number of pathways. ATAD3 is a transmembrane protein that spans both the inner mitochondrial membrane and outer mitochondrial membrane. It, therefore, functions as a connecting link between the mitochondrial lumen and endoplasmic reticulum facilitating their cross-talk. ATAD3 contains an N-terminal domain which is amphipathic in nature and is inserted into the membranous space of the mitochondria, while the C-terminal domain is present towards the lumen of the mitochondria and contains the ATPase domain. ATAD3 is known to be involved in mitochondrial biogenesis, cholesterol transport, hormone synthesis, apoptosis and several other pathways. It has also been implicated to be involved in cancer and many neurological disorders making it an interesting target for extensive studies. This review aims to provide an updated comprehensive account of the role of ATAD3 in the mitochondria especially in lipid transport, mitochondrial-endoplasmic reticulum interactions, cancer and inhibition of mitophagy.