Regulated translation initiation controls stress-induced gene expression in mammalian cells

The arginine metabolism and its deprivation in cancer therapy

Arginine deprivation has emerged as a promising therapeutic strategy in cancer treatment due to the auxotrophy of certain tumors. Many cancers, such as pancreatic, colorectal, and hepatocellular carcinoma, exhibit downregulated argininosuccinate synthetase, making them reliant on external arginine sources. This dependency allows targeted therapies that deplete arginine, inhibiting tumor growth while sparing normal cells. Arginine is crucial for various cellular processes, including protein synthesis and immune function. Its deprivation affects both tumor metabolism and immune responses, potentially enhancing cancer therapy. Studies have explored using enzymes like arginine deiminase and arginase, often modified for increased stability and reduced immunogenicity, to effectively lower arginine levels in the tumor microenvironment. These approaches show promise, particularly in tumors with low argininosuccinate synthetase expression. However, the impact on immune cells and the potential for resistance highlight the need for further research. Combining arginine deprivation with other treatments might improve outcomes, offering a novel approach to combat arginine-dependent cancers.

Crosstalk between ferroptosis and endoplasmic reticulum stress: A potential target for ovarian cancer therapy (Review)

Ferroptosis is a unique mode of cell death driven by iron‑dependent phospholipid peroxidation, and its mechanism primarily involves disturbances in iron metabolism, imbalances in the lipid antioxidant system and accumulation of lipid peroxides. Protein processing, modification and folding in the endoplasmic reticulum (ER) are closely related regulatory processes that determine cell function, fate and survival. The uncontrolled proliferative capacity of malignant cells generates an unfavorable microenvironment characterized by high metabolic demand, hypoxia, nutrient deprivation and acidosis, which promotes the accumulation of misfolded or unfolded proteins in the ER, leading to ER stress (ERS). Ferroptosis and ERS share common pathways in several diseases, and the two interact to affect cell survival and death. Additionally, cell death pathways are not linear signaling cascades, and different pathways of cell death may be interrelated at multiple levels. Ferroptosis and ERS in ovarian cancer (OC) have attracted increasing research interest; however, both are discussed separately regarding OC. The present review aims to summarize the associations and potential links between ferroptosis and ERS, aiming to provide research references for the development of therapeutic approaches for the management of OC.

Aminolevulinate/iron exposure elicited Nrf-2-mediated cytoprotection in DARS2 deficient fibroblasts with impaired energy and antioxidant metabolisms

Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) is a disorder caused by mutations in the mitochondrial aspartyl-tRNA synthetase gene DARS2, which compromises mitochondrial protein translation. The typical presentation is juvenile in onset with gradually progressive spasticity and ataxia. Only palliative treatment is available for LBSL individuals. Here we showed that the use of the Food and Drug Administration-approved heme precursors, aminolevulinate plus ferrous iron (ALA/Fe), can result in a novel pharmacological treatment that increases energy status in DARS2 deficient cells. The marked mitochondrial and antioxidant deficiencies observed in fibroblasts from two LBSL-affected brothers, harboring intron-2 (c.228-17C > G) and intron-5 (c.492 + 2 T > C) DARS2 mutations, were rescued by ALA/Fe exposure, and the use of dexamethasone, a known Nrf-2 inhibitor, blocked the positive effects of ALA/Fe. Altogether, this study showed that fibroblasts can be used as a biological system to identify potential new treatments for LBSL that can reduce morbidity and mortality, and that the activation of Nrf-2-mediated cytoprotection can be targeted for the treatment of LBSL and other mitochondrial diseases.

The Molecular Basis of Amino Acids Sensing

Amino acids are organic compounds that serve as the building blocks of proteins and peptides. Additionally, they function as bioactive molecules that play important roles in metabolic regulation and signal transduction. The ability of cells to sense fluctuations in intracellular and extracellular amino acid levels is vital for effectively regulating protein synthesis and catabolism, maintaining homeostasis, adapting to diverse nutritional environments and influencing cell fate decision. In this review, the recent molecular insights into amino acids sensing are discussed, along with the different sensing mechanisms in distinct organisms.

Unveiling the HSP90 inhibitor mediated effects on endoplasmic reticulum stress and redox signaling:from a cancer inhibitor to retinal degeneration catalyst

Retinal degeneration (RD) is a class of polygenic blind eye disease characterized by photoreceptors loss and dysfunction of retinal pigment epithelium. Thus far, there is no effective treatment to save the declining vision in RD patients. Animal models are highly precious tools for studying the pathological mechanisms of RD, and for screening potential therapeutics. AUY922 is a heat shock protein 90 inhibitor that exhibits potent anti-cancer effects. However, it causes adverse ocular reactions such as reduced visual acuity and night blindness. This study intends to explore the pathological mechanism underlying the AUY922 induced RD. In vitro study, AUY922 induced cytotoxic effects on the 661W cells, which are ascribed to endoplasmic reticulum (ER) stress and oxidative damages. ER stress inhibitor 4-PBA alleviated 661W cells apoptosis and oxidative stress. Subsequently, AUY922 was delivered into the vitreous cavity of mouse and induced selective photoreceptor death and visual impairments. Overactivation of neuroglial and retinal remodeling occurred during the degenerative process. Moreover, enhanced CHOP expression was tied to profound disturbances in redox homeostasis, which readied photoreceptors for apoptosis. The underlying mechanism should be attributed to the activation of the PERK-eIF2α-ATF4-CHOP pathway. AUY922 can compensate for the high toxicity and instability of traditional inducers in RD modeling. These results not only enrich our understanding of the toxicology of AUY922 but also provide clues for establishing reliable RD models.

Mitochondrial unfolded protein response (UPRmt) as novel therapeutic targets for neurological disorders

Neurological disorders, including brain cancer, neurodegenerative diseases and ischemic/reperfusion injury, pose a significant threat to global human health. Due to the high metabolic demands of nerve cells, mitochondrial dysfunction is a critical feature of these disorders. The mitochondrial unfolded protein response (UPRmt) is an evolutionarily conserved mitochondrial response, which is critical for maintaining mitochondrial and energetic homeostasis under stress. Previous studies have found that UPRmt participates in diverse physiological processes especially metabolism and immunity. Currently, increasing evidence suggest that targeted regulation of UPRmt can also effectively delay the progression of neurological diseases and improve patients' prognosis. This review provides a comprehensive overview of UPRmt in the context of neurological diseases, with a particular emphasis on its regulatory functions. Additionally, we summarize the mechanistic insights into UPRmt in neurological disorders as investigated in preclinical studies, as well as its potential as a therapeutic target in the clinical management of neurological tumors. By highlighting the importance of UPRmt in the complex processes underlying neurological disorders, this review aims to bridge current knowledge gaps and inspire novel therapeutic strategies for these conditions.

De Novo Serine Synthesis Is a Metabolic Vulnerability That Can Be Exploited to Overcome Sunitinib Resistance in Advanced Renal Cell Carcinoma

Sunitinib is an oral tyrosine kinase inhibitor used in treating advanced renal cell carcinoma (RCC) that exhibits significant efficacy but faces resistance in 30% of patients. Identifying the molecular mechanisms underlying resistance could enable the development of strategies to enhance sunitinib sensitivity. In this study, we showed that sunitinib induces a metabolic shift leading to increased serine synthesis in RCC cells. Activation of the GCN2-ATF4 stress response pathway was identified as the mechanistic link between sunitinib treatment and elevated serine production. The increased serine biosynthesis supported nucleotide synthesis and sustained cell proliferation, migration, and invasion following sunitinib treatment. Inhibiting key enzymes in the serine synthesis pathway, such as phosphoglycerate dehydrogenase and phosphoserine aminotransferase 1, enhanced the sensitivity of resistant cells to sunitinib. Beyond RCC, similar activation of serine synthesis following sunitinib treatment occurred in a variety of other cancer types, suggesting a shared adaptive response to sunitinib therapy. Together, this study identifies the de novo serine synthesis pathway as a potential target to overcome sunitinib resistance, offering insights into therapeutic strategies applicable across diverse cancer contexts. Significance: Sunitinib treatment induces metabolic reprogramming to provide essential metabolite building blocks for tumor survival, resistance, and progression by upregulating serine biosynthesis, which represents a targetable dependency to enhance therapeutic efficacy.

Narciclasine enhances cisplatin-induced apoptotic cell death by inducing unfolded protein response-mediated regulation of NOXA and MCL1

BACKGROUND

Platinum-based chemotherapy is commonly used to treat non-small cell lung cancer (NSCLC); however, innate and acquired resistance is clinically seen in many patients. Hence, a combinatorial approach with novel therapeutic agents to overcome chemoresistance is a promising option for improving patient outcomes. We investigated the combinational anticancer efficacy of cisplatin and narciclasine in three-dimensional NSCLC tumor spheroids.

METHODS

To assess the efficacy of cisplatin and narciclasine, cell viability assays, live/dead cell staining, cell death enzyme-linked immunosorbent assay (ELISA), western blot analysis for proteins related to apoptosis, and in vivo xenograft experiments were performed. The synergistic effects of cisplatin and narciclasine were elucidated through transcriptomic analysis and subsequent validation of candidate molecules by regulating their expression. To clarify the underlying molecular mechanisms, the activation of unfolded protein responses and kinetics of a candidate protein were assessed.

RESULTS

Narciclasine inhibited viability of NSCLC tumor spheroids and augmented the sensitivity of cisplatin-resistant tumor spheroids to cisplatin by inducing apoptosis. After conducting bioinformatic analysis using RNA sequencing data and functional validation experiments, we identified NOXA as a key gene responsible for the enhanced apoptosis observed with the combination of cisplatin and narciclasine. This treatment dramatically increased NOXA while downregulating anti-apoptotic MCL1 levels. Silencing NOXA reversed the enhanced apoptosis and restored MCL1 levels, while MCL1 overexpression protected tumor spheroids from combination treatment-induced apoptosis. Interestingly, narciclasine alone and in combination with cisplatin induced unfolded protein response and inhibited general protein synthesis. Furthermore, the combination treatment increased NOXA expression through the IRE1α-JNK/p38 axis and the activation of p53. Cisplatin alone and in combination with narciclasine destabilized MCL1 via NOXA-mediated proteasomal degradation.

CONCLUSIONS

We identified a natural product, narciclasine, that synergizes with cisplatin. The combination of cisplatin and narciclasine induced NOXA expression, downregulated MCL1, and ultimately induced apoptosis in NSCLC tumor spheroids. Our findings suggest that narciclasine is a potential natural product for combination with cisplatin for treatment of NSCLC.

Patient-derived models of UBA5-associated encephalopathy identify defects in neurodevelopment and highlight potential therapeutic avenues

UBA5 encodes for the E1 enzyme of the UFMylation cascade, which plays an essential role in endoplasmic reticulum (ER) homeostasis. The clinical phenotypes of UBA5-associated encephalopathy include developmental delays, epilepsy, and intellectual disability. To date, there is no humanized neuronal model to study the cellular and molecular consequences of UBA5 pathogenic variants. We developed and characterized patient-derived cortical organoid cultures from two patients with compound heterozygous variants in UBA5. Both shared the same missense variant, which encodes a hypomorphic allele (p.A371T), along with a nonsense variant (p.G267* or p.A123fs*4). Single-cell RNA sequencing of 100-day organoids identified defects in GABAergic interneuron development. We demonstrated aberrant neuronal firing and reduction in size of patient-derived organoids. Mechanistically, we showed that ER homeostasis is perturbed along with an exacerbated unfolded protein response pathway in engineered U87-MG cells and patient-derived organoids expressing UBA5 pathogenic variants. We also assessed two potential therapeutic modalities that augmented UBA5 protein abundance to rescue aberrant molecular and cellular phenotypes. We assessed SINEUP, a long noncoding RNA that augments translation efficiency, and CRISPRa, a modified CRISPR-Cas9 approach to augment transcription efficiency to increase UBA5 protein production. Our study provides a humanized model that allows further investigations of UBA5 variants in the brain and highlights promising approaches to alleviate cellular aberrations for this rare, developmental disorder.

Aggregates associated with amyotrophic lateral sclerosis sequester the actin-binding protein profilin 2

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disease characterized by the degeneration of upper and lower motoneurons. The four most frequently mutated genes causing familial ALS (fALS) are C9orf72, FUS, SOD1, and TARDBP. Some of the related wild-type proteins comprise intrinsically disordered regions (IDRs) which favor their assembly in liquid droplets-the biophysical mechanism behind the formation of physiological granules such as stress granules (SGs). SGs assemble and dissolve dependent on the cellular condition. However, it has been suggested that transition from reversible SGs to irreversible aggregates contributes to the toxic properties of ALS-related mutated proteins. Sequestration of additional proteins within these aggregates may then result in downstream toxicity. While the exact downstream mechanisms remain elusive, rare ALS-causing mutations in the actin binding protein profilin 1 suggest an involvement of the actin cytoskeleton. Here, we hypothesize that profilin isoforms become sequestered in aggregates of ALS-associated proteins which induce subsequent dysregulation of the actin cytoskeleton. Interestingly, localization of neuronal profilin 2 in SGs was more pronounced compared with the ubiquitously expressed profilin 1. Accordingly, FUS and C9orf72 aggregates prominently sequestered profilin 2 but not profilin 1. Moreover, we observed a distinct sequestration of profilin 2 and G-actin to C9orf72 aggregates in different cellular models. On the functional level, we identified dysregulated actin dynamics in cells with profilin 2-sequestering aggregates. In summary, our results suggest a more common involvement of profilins in ALS pathomechanisms than indicated from the rarely occurring profilin mutations.

An ISR-independent role of GCN2 prevents excessive ribosome biogenesis and mRNA translation

The integrated stress response (ISR) is a corrective physiological programme to restore cellular homeostasis that is based on the attenuation of global protein synthesis and a resource-enhancing transcriptional programme. GCN2 is the oldest of four kinases that are activated by diverse cellular stresses to trigger the ISR and acts as the primary responder to amino acid shortage and ribosome collisions. Here, using a broad multi-omics approach, we uncover an ISR-independent role of GCN2. GCN2 inhibition or depletion in the absence of discernible stress causes excessive protein synthesis and ribosome biogenesis, perturbs the cellular translatome, and results in a dynamic and broad loss of metabolic homeostasis. Cancer cells that rely on GCN2 to keep protein synthesis in check under conditions of full nutrient availability depend on GCN2 for survival and unrestricted tumour growth. Our observations describe an ISR-independent role of GCN2 in regulating the cellular proteome and translatome and suggest new avenues for cancer therapies based on unleashing excessive mRNA translation.

Mitonuclear Communication in Stem Cell Function

Mitochondria perform multiple functions within the cell, including the production of ATP and a great deal of metabolic intermediates, while also contributing to the cellular stress response. The majority of mitochondrial proteins are encoded by nuclear genomes, highlighting the importance of mitonuclear communication for sustaining mitochondrial homeostasis and functional. As a crucial part of the intracellular signalling network, mitochondria can impact stem cell fate determinations. Considering the essential function of stem cells in tissue maintenance, regeneration and aging, it is important to understand how mitochondria influence stem cell fate. This review explores the significant roles of mitonuclear communication and mitochondrial proteostasis, highlighting their influence on stem cells. We also examine how mitonuclear interactions contribute to cellular homeostasis, stem cell therapies, and the potential for extending lifespan.

Activation of the mitochondrial unfolded protein response regulates the dynamic formation of stress granules

To rapidly adapt to harmful changes to their environment, cells activate the integrated stress response (ISR). This results in an adaptive transcriptional and translational rewiring, and the formation of biomolecular condensates named stress granules (SGs), to resolve stress. In addition to this first line of defence, the mitochondrial unfolded protein response (UPRmt) activates a specific transcriptional programme to maintain mitochondrial homeostasis. We present evidence that the SG formation and UPRmt pathways are intertwined and communicate. UPRmt induction results in eIF2α phosphorylation and the initial and transient formation of SGs, which subsequently disassemble. The induction of GADD34 (also known as PPP1R15A) during late UPRmt protects cells from prolonged stress by impairing further assembly of SGs. Furthermore, mitochondrial functions and cellular survival are enhanced during UPRmt activation when SGs are absent, suggesting that UPRmt-induced SGs have an adverse effect on mitochondrial homeostasis. These findings point to a novel crosstalk between SGs and the UPRmt that might contribute to restoring mitochondrial functions under stressful conditions.

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.

Endoplasmic reticulum stress disrupts signaling via altered processing of transmembrane receptors

Cell communication systems based on polypeptide ligands use transmembrane receptors to transmit signals across the plasma membrane. In their biogenesis, receptors depend on the endoplasmic reticulum (ER)-Golgi system for folding, maturation, transport and localization to the cell surface. ER stress, caused by protein overproduction and misfolding, is a well-known pathology in neurodegeneration, cancer and numerous other diseases. How ER stress affects cell communication via transmembrane receptors is largely unknown. In disease models of multiple myeloma, chronic lymphocytic leukemia and osteogenesis imperfecta, we show that ER stress leads to loss of the mature transmembrane receptors FGFR3, ROR1, FGFR1, LRP6, FZD5 and PTH1R at the cell surface, resulting in impaired downstream signaling. This is caused by downregulation of receptor production and increased intracellular retention of immature receptor forms. Reduction of ER stress by treatment of cells with the chemical chaperone tauroursodeoxycholic acid or by expression of the chaperone protein BiP resulted in restoration of receptor maturation and signaling. We show a previously unappreciated pathological effect of ER stress; impaired cellular communication due to altered receptor processing. Our findings have implications for disease mechanisms related to ER stress and are particularly important when receptor-based pharmacological approaches are used for treatment.

Regulation of translation elongation and integrated stress response in heat-shocked neurons

Neurons deviate from a canonical heat shock response (HSR). Here, we revealed that neuronal adaptation to heat shock accompanies a brake on mRNA translation, slowed elongating ribosomes, phosphorylation of eukaryotic elongation factor-2 (p-eEF2), and suppressed the integrated stress response (ISR). Returning neurons to control temperature within 1 h of starting heat shock was necessary for survival and allowed for restored translation following dephosphorylation of eEF2. Subsequent to recovery, neurons briefly activated the ISR and were sensitive to the ISR inhibitor ISRIB, which enhanced protein synthesis and survival. Ribosome profiling and RNA sequencing (RNA-seq) identified newly synthesized and existing transcripts associated with ribosomes during heat shock. Preservation of these transcripts for translation during recovery was in part mediated by p-eEF2 and slowed ribosomes. Our work supports a neuronal heat shock model of a partially suspended state of translation poised for rapid reversal if recovery becomes an option and provides insight into regulation between the HSR and the ISR.

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.

Ribosomal protein deficiencies linked to Diamond-Blackfan anemia induce distinctive alterations of ATF4 expression

Ribosomal protein haploinsufficiency causes Diamond-Blackfan anemia (DBA) and other ribosomopathies. DBA has been linked to p53 activation and reduced GATA1 expression, but these mechanisms do not fully explain the disease. This study unveils that deficiencies in small (RPS) or large (RPL) ribosomal subunit proteins cause a p53-independent loss of ATF4, a master regulator of stress responses and erythropoiesis, by reducing the pool of actively translating ATF4 mRNAs. This defect is more pronounced in RPS deficiencies because the loss of 40S, but not 60S, subunits cause a destabilization of ATF4 transcripts. ATF4 downregulation occurs in early hematopoietic progenitors and correlates with the severity of erythroid differentiation defects in patients with DBA. It is also linked to the de-repression of fetal hemoglobin in erythroid cells, a frequent feature in patients with DBA. Our findings indicate that impaired ATF4 expression might be a primary contributor to DBA and explain the aggravated erythroid failure of RPS-mutant patients.

Potential threat of environmental toxin palytoxin to cerebral nerves: A mechanism study in vitro and in vivo

Palytoxin (PTX), a toxin naturally synthesized by marine organisms like Palythoa, Ostreopsis and Trichodesmium spp. in tropical and temperate seas, bioaccumulates in fish and crustaceans, thereby exposing humans through the food chain. Although growing evidence highlights PTX's lethal hepatotoxicity, nephrotoxicity, and cardiotoxicity, its neurotoxic effects and the underlying mechanisms remain elusive. In this study, we assessed the cerebral neurotoxicity of PTX by using HT22 neuronal cells and a chronic mouse model, conducting a comprehensive analysis of phenotypic alterations and gene expression changes. Phenotypic analysis revealed significant damage to mitochondria, endoplasmic reticulum, and axons and disruptions in energy metabolism in PTX-treated neuronal cells and mouse brains. Transcriptome sequencing and real-time quantitative reverse transcription polymerase chain reaction indicated that key genes in the JNK/p38 MAPK signaling, mitochondrial stress, and endoplasmic reticulum stress pathways were significantly altered. Furthermore, pretreatment with JNK and p38 inhibitors significantly restored mitochondrial membrane potential, ATP content, and cell viability, while reducing the expression of pro-apoptotic genes in HT22 cells. These findings confirm that JNK/p38 MAPK signaling pathways activation, leading to mitochondrial stress, is a major contributor to PTX-induced neuronal cell death at the cellular level. Chronic exposure to PTX was shown to damage mammalian cerebral nerves, carrying a potential risk for neurodegenerative diseases. Our study provides insights into the environmental and health risks associated with PTX exposure and offers a foundation for risk assessment and intervention strategies.

Expression of CREB3L1 blocks key cancer pathways and suppresses metastasis of lung squamous cell carcinoma cells

Lung cancer is the leading cause of death due to cancer, with higher mortality rates than cancers of the colon, breast and prostate combined. About one quarter of lung cancers are lung squamous cell carcinomas (LUSC), with a five-year survival rate of only 16 %. We discovered that the majority of LUSCs have reduced expression of a key transcription factor CREB3L1 (cAMP responsive element binding protein 3 like 1), known to function as a metastasis suppressor in breast, bladder and ovarian cancers. In this report, we set out to determine if CREB3L1 functions as a metastasis suppressor in LUSCs. A differential gene expression analysis showed that ectopic expression of CREB3L1 in NCI-H2170 and NCI-1703 cells caused significant reductions in many signaling pathway genes involved in promoting cell viability, survival, migration and angiogenesis. Expression of CREB3L1 was able to reduce cell migration and anchorage-independent growth in soft agar in NCI-H2170, NCI-H1703 and NCI-H226 LUSC cells. Expression of CREB3L1 had less impact on the growth of primary xenograft tumors for NCI-H2170 and NCI-H1703 cells, the latter of which formed atypical masses filled with blood. In contrast, xenografts of NCI-H226 expressing CREB3L1 showed significant reductions in primary tumor growth. Finally, in a mouse metastasis assay, expression of CREB3L1 in NCI-H2170 cells significantly reduced the formation of liver metastases and in NCI-H226 cells, lung metastases, as compared to their respective CREB3L1-deficient parental LUSC cells. Taken together, these results strongly support a role for CREB3L1 as a metastasis suppressor in lung squamous cell carcinoma cells.

ADAR1 p150 prevents HSV-1 from triggering PKR/eIF2α-mediated translational arrest and is required for efficient viral replication

Adenosine deaminase acting on dsRNA 1 (ADAR1) catalyzes the deamination of adenosines to inosines in double-stranded RNAs (dsRNA) and regulates innate immunity by preventing the hyperactivation of cytosolic dsRNA sensors such as MDA5, PKR or ZBP1. ADAR1 has been shown to exert pro- and antiviral, editing-dependent and editing-independent functions in viral infections, but little is known about its function in herpesvirus replication. We now demonstrate that herpes simplex virus 1 (HSV-1) hyperactivates PKR in the absence of ADAR1, resulting in eIF2α mediated translational arrest and reduced viral replication. Silencing of PKR or inhibition of its downstream effectors by viral (ICP34.5) or pharmacological (ISRIB) inhibitors rescues viral replication in ADAR1-deficient cells. Upon infection, ADAR1 p150 interacts with PKR and prevents its hyperactivation. Our findings demonstrate that ADAR1 is an important proviral factor that raises the activation threshold for sensors of innate immunity.

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.

Modulation of CREB3L2-ATF4 heterodimerization via proteasome inhibition and HRI activation in Alzheimer's disease pathology

Alzheimer's disease (AD) pathology includes transcriptional changes in the neurons, which are in part caused by the heterodimerization of two stress response transcription factors, CREB3L2 and ATF4. We investigated the role of proteasome inhibition and the eIF2α-kinase HRI in the formation of CREB3L2-ATF4 in neurons exposed to soluble oligomeric Aβ42. While HRI activation increased ATF4 expression, it decreased CREB3L2 and CREB3L2-ATF4 levels. Proteasome inhibition, induced by Aβ42, leads to increased levels of both transcription factors in the nucleus. These findings suggest that CREB3L2 levels are normally kept low due to rapid degradation, but proteasome inhibition in response to Aβ42 disrupts this balance, increasing CREB3L2 and heterodimer levels. Activation of HRI not only reduced CREB3L2 and heterodimer levels but also prevented the transcriptional dysregulation of a CREB3L2-ATF4 target, SNX3. Our results suggest that manipulating the HRI pathway during proteasome inhibition could help restore normal gene expression in the context of AD-related protein accumulation.

Dissecting Branch-Specific Unfolded Protein Response Activation in Drug-Tolerant BRAF-Mutant Melanoma using Data-Independent Acquisition Mass Spectrometry

Cells rely on the Unfolded Protein Response (UPR) to maintain ER protein homeostasis (proteostasis) when faced with elevated levels of misfolded and aggregated proteins. The UPR is comprised of three main branches-ATF6, IRE1, and PERK-that coordinate the synthesis of proteins involved in folding, trafficking, and degradation of nascent proteins to restore ER function. Dysregulation of the UPR is linked to numerous diseases, including neurodegenerative disorders, cancer, and diabetes. Despite its importance, identifying UPR targets has been challenging due to their heterogeneous induction, which varies by cell type and tissue. Additionally, defining the magnitude and range of UPR-regulated genes is difficult because of intricate temporal regulation, feedback between UPR branches, and extensive cross-talk with other stress-signaling pathways. To comprehensively identify UPR-regulated proteins and determine their branch specificity, we developed a data-independent acquisition (DIA) liquid-chromatography mass spectrometry (LC-MS) pipeline. Our optimized workflow improved identifications of low-abundant UPR proteins and leveraged an automated SP3-based protocol on the Biomek i5 liquid handler for label-free peptide preparation. Using engineered stable cell lines that enable selective pharmacological activation of each UPR branch without triggering global UPR activation, we identified branch-specific UPR proteomic targets. These targets were subsequently applied to investigate proteomic changes in multiple patient-derived BRAF-mutant melanoma cell lines treated with a BRAF inhibitor (PLX4720, i.e., vemurafenib). Our findings revealed differential regulation of the XBP1s branch of the UPR in the BRAF-mutant melanoma cell lines after PLX4720 treatment, likely due to calcium activation, suggesting that the UPR plays a role as a non-genetic mechanism of drug tolerance in melanoma. In conclusion, the validated branch-specific UPR proteomic targets identified in this study provide a robust framework for investigating this pathway across different cell types, drug treatments, and disease conditions in a high-throughput manner.

The natural alkaloid nitidine chloride targets RNA polymerase I to inhibit ribosome biogenesis and repress cancer cell growth

Nature is an abundant and largely untapped source of potent bioactive molecules. Ribosome biogenesis modulators have proven effective in suppressing cancer cell growth and are currently being evaluated in clinical trials for anticancer therapies. In this study, we characterized the alkaloid nitidine chloride (NC), produced by the endemic Cameroonian plant Fagara (and other plants). We demonstrate that NC kills cancer cells regardless of their p53 status and inhibits tumor growth in vitro. Furthermore, NC profoundly suppresses global protein synthesis. Treatment of human cells with NC causes severe nucleolar disruption and inhibits pre-rRNA synthesis by destabilizing key factors required for recruitment of RNA polymerase I to ribosomal DNA promoters. In vitro, NC intercalates into DNA and inhibits topoisomerases I and II. Consistently, NC treatment activates a DNA damage response. We propose that the torsional stress on rDNA caused by topoisomerase inhibition leads to loss of RNA polymerase I function and to shutdown of ribosome biogenesis. Although NC has long been suspected of possessing anticancer properties, here we provide a molecular explanation for its mechanism of action. In budding yeast cells, interestingly, NC inhibits cell growth, impairs ribosome biogenesis, and disrupts nucleolar structure. This suggests that its mode of action is at least partially evolutionarily conserved.

Pre-cachectic changes in amino acid homeostasis precede activation of eIF2α signaling in the liver at the onset of C26 cancer-induced cachexia

The sequence of events associated with cancer cachexia induction needs to be further characterized. Using the C26 mouse model, we found that prior to cachexia, cancer progression was associated with increased levels of IL-6 and growth differentiation factor 15 (GDF15), highly induced production of positive acute phase proteins (APPs) and reduced levels of most amino acids in the systemic circulation, while signal transducer and activator of transcription 3 (STAT3) signaling was induced (1) in the growing spleen, alongside activation of ribosomal protein S6 (rpS6) and alpha subunit of eukaryotic translation initiation factor-2 (eIF2α) signalings, and (2) in the liver, alongside increased positive-APP expression, decreased albumin expression, and upregulation of autophagy. At the onset of cachexia, rpS6 and eIF2α signalings were concomitantly activated in the liver, with increased expression of activating transcription factor 4 (ATF4) target genes involved in amino acid synthesis and transport, as well as autophagy. Data show that pre-cachectic (pre-Cx) alterations in protein/aa homeostasis are followed by activation of eIF2α signaling in the liver, an adaptive mechanism likely regulating protein/amino acid metabolism upon progression to cachexia.

Unravelling the antitumor mechanism of Ocoxin through cancer cell genomics

Cancer is one of the leading causes of death worldwide. Many therapies are being used to treat this disease, however, new treatments are now being implemented, since they are not always effective and their secondary effects represent one of the main reasons for cancer patients' loss of life quality during the progression of the disease. In this scenario, Ocoxin is a mixture of plant extracts, amino acids, vitamins and minerals, known for its antioxidant, anti-inflammatory and immunoregulatory properties, which has shown to exert antitumor effects in many cancers. The aim of this study is to elucidate the mechanism of action of the compound in colorectal cancer, triple negative breast cancer, pancreatic cancer and prostate cancer. Analyses performed through RNA sequencing revealed that the main effect of Ocoxin appears to be the alteration of cell metabolism, especially inducing the process of ferroptosis. Nevertheless, the modulation of the cell cycle was also remarkable. Ocoxin altered 13 genes in common in all the four cancers that were not only associated to metabolism and cell cycle but were also involved in the integrated stress response and unfolded protein response, suggesting that the compound causes the induction of cell death through several pathways. Although the mechanisms vary according to the type of cancer, this study highlights the potential of Ocoxin as an adjunctive treatment to improve outcomes in cancer therapy.

Fine-Tuning of ATF4 DNA Binding Activity by a Secondary Basic Motif Unique to the ATF-X Subfamily of bZip Transcription Factors

The fine-tuning of transcription factor DNA-binding activity is often governed by transient intramolecular interactions between the transactivation domain and the DNA-binding domain. An example of such interaction is found in the transcription factor ATF4, a central regulator of the Integrated Stress Response. In ATF4, dynamic coupling between the transactivation domain and the basic-leucine zipper (bZip) domain modulates the phosphorylation levels of the disordered transactivation domain by casein kinase 2. However, the structural and molecular basis of these interdomain interactions remains poorly understood. This study focuses on a secondary basic motif at the C-terminus of ATF4, which is shared exclusively with its closest paralogue, ATF5. Through a combination of solution NMR spectroscopy, fluorescence polarization assays, and long-timescale molecular simulations, we demonstrate that this secondary basic motif is the primary driver of interdomain coupling between the transactivation and bZip domains of ATF4. Moreover, this motif enhances ATF4's DNA-binding specificity via interaction with the transactivation domain while also potentially facilitating rapid DNA scanning. Our findings reveal the pivotal role of a conserved motif in establishing disorder-mediated interactions that critically modulate ATF4's DNA-binding activity.

Role of endoplasmic reticulum stress in cell apoptosis induced by duck hepatitis A virus type 1 infection

The endoplasmic reticulum (ER), an elaborate cellular organelle that interweaves the cytosol, nucleus, mitochondria and plasma membrane, is essential for cell function and survival. Disruption of ER function can trigger unfolded protein response (UPR), which is activated by ER stress (ERS). In this study, we investigated the role of ERS in cell apoptosis induced by duck hepatitis A virus type 1 (DHAV-1) infection. Our findings revealed that DHAV-1 infection led to the activation of ERS. Specially, the expression of glucose-regulated protein 78 (GRP78) was upregulated, activating two pathways of UPR: the protein kinase R-like ER kinase (PERK) pathway and the inositol-requiring enzyme 1(IRE1) pathway. Consequently, phosphorylation of eukaryotic initiation factor 2 alpha (p-eIF2α) was increased, and transcription factor 4 (ATF4) was up-regulated, resulting in the induction of the apoptotic C/EBP homologous protein (CHOP). DHAV-1-infected cells exhibited various apoptotic phenotypes, including growth arrest, induction of the DNA damage-inducible protein 34 (GADD34), activation of caspase-3, and suppression of antiapoptotic protein B cell lymphoma-2 (Bcl-2). Importantly, inhibition of PERK or protein kinase R (PKR) activity suppressed CHOP activation and DHAV-1 replication, indicating that the PERK/PKR-eIF2α pathway played a crucial role in ERS-induced apoptosis. Collectively, our study provides novel insights into the mechanism of DHAV-1-induced apoptosis and reveals a potential defense mechanism against DHAV-1 replication.

Leandro A, Leandro M, Peralta J, Williams-Blangero S, Sanchez EE, Galan JA, Blangero J, Curran JE. Neurocellular Stress Response to Mojave Type A Rattlesnake Venom: Study of Molecular Mechanisms Using Human iPSC-Derived Neural Stem Cell Model

The Mojave rattlesnake venom shows significant geographical variability. The venom of Type A animals primarily contains β-neurotoxin referred to as Mojave Toxin (MTX), which makes bites from this snake particularly feared. We performed a genome-wide transcriptomic analysis of the neurocellular response to Mojave Type A rattlesnake venom using induced pluripotent stem cell-derived neural stem cells to unveil the molecular mechanisms underlying the damage caused by this snake's envenomation. Our results suggest that snake venom metalloproteases, although having a limited repertoire in Type A venom, facilitate venom spread by digesting the tissue's extracellular matrix. The MTX, which is composed of heterodimers of basic and acidic phospholipase-A2, co-opts the host arachidonic acid and Ca2+ second messenger mechanisms and triggers multiple signaling cascades, such as the activation of MAPKs and NF-κB-regulated proinflammatory genes; the neurotransmitter overload in excitatory synapses leading to a presynaptic blockade of nerve signals; and the upregulation of unfolded protein response (UPR) due to the depletion of Ca2+ from the endoplasmic reticulum. The upregulated UPR and the oxidative stress caused by reactive oxygen species generated in cytochromeP4501A1-mediated hydroxylation of arachidonic acid contribute to mitochondrial toxicity. The activation of UPR, mitochondrial toxicity, and oxidative stress synergistically contributed to apoptotic and ferroptotic cell death.

Unlocking the dual role of autophagy: A new strategy for treating lung cancer

Lung cancer exhibits the highest incidence and mortality rates among cancers globally, with a five-year overall survival rate alarmingly below 20%. Targeting autophagy, though a controversial therapeutic strategy, is extensively employed in clinical practice. Current research is actively pursuing various therapeutic strategies using small molecules to exploit the dual function of autophagy. Nevertheless, the pivotal question of enhancing or inhibiting autophagy in cancer therapy merits further attention. This review aims to provide a comprehensive overview of the mechanisms of autophagy in lung cancer. It also explores recent advances in targeting cytotoxic autophagy and inhibiting protective autophagy with small molecules to induce cell death in lung cancer cells. Notably, most autophagy-targeting drugs, primarily natural small molecules, have demonstrated that activating cytotoxic autophagy effectively induces cell death in lung cancer, as opposed to inhibiting protective autophagy. These insights contribute to identifying druggable targets and drug candidates for potential autophagy-related lung cancer therapies, offering promising approaches to combat this disease.

The sticky business of Alphavirus capsid-host interactions

Alphaviruses are a serious threat to global health and can cause lethal encephalitic or arthritogenic disease in humans and animals. As there are no licensed antivirals, it is critical to improve our understanding of alphavirus interactions with the host cell. Here, we focus on the essential alphavirus protein capsid. While its roles in genome packaging and virus assembly have been well-studied, much less is known about capsid's interactions with host proteins and their functional relevance for infection. Recently, several new capsid interactor candidates were identified, collectively emphasising the complexity of capsid-host biology. In this review we summarise these novel interactor candidates, highlight capsid's emerging role in immune evasion, and discuss the challenges and opportunities arising from capsid-host interactions.

Cellular responses to RNA damage

RNA plays a central role in protein biosynthesis and performs diverse regulatory and catalytic functions, making it essential for all processes of life. Like DNA, RNA is constantly subjected to damage from endogenous and environmental sources. However, while the DNA damage response has been extensively studied, it was long assumed that RNA lesions are relatively inconsequential due to the transient nature of most RNA molecules. Here, we review recent studies that challenge this view by revealing complex RNA damage responses that determine survival when cells are exposed to nucleic acid-damaging agents and promote the resolution of RNA lesions.

The integrated stress response engages a cell-autonomous, ligand-independent, DR5-driven apoptosis switch

The integrated stress response (ISR) is a fundamental signaling network that leverages the cell's biosynthetic capacity against different stresses to restore homeostasis. However, when homeostasis is unattainable, the ISR switches to drive cell death and eliminate irreparably damaged cells. Previous work has shown that persistent activity of the ISR kinase PERK during unyielding endoplasmic reticulum (ER) stress induces apoptosis downstream of death receptor 5 (DR5) [1]. ER stress provides activating signals that engage the ectodomain (ED) of DR5 to drive its unconventional activation in the Golgi apparatus [1, 2]. Here, using chemical genetics to uncouple stress sensing from ISR activation, we found that DR5 signaling from the Golgi apparatus is integral to the ISR and not specific to ER stress. Furthermore, we show that DR5 activation can be driven solely by increased expression and does not require its ED. These findings indicate that a general ISR kill switch eliminates irreversibly injured cells.

GRP78 in Glioma Progression and Therapy: Implications for Targeted Approaches

Glioma is the most common primary malignant brain tumor, accounting for the majority of brain cancer-related deaths. Considering the limited efficacy of conventional therapies, novel molecular targeted therapies have been developed to improve outcomes and minimize toxicity. Glucose-regulated protein 78 (GRP78), a molecular chaperone primarily localized in the endoplasmic reticulum (ER), has received increasing attention for its role in glioma progression and resistance to conventional therapies. Overexpressed in gliomas, GRP78 supports tumor growth, survival, and therapeutic resistance by maintaining cellular homeostasis and regulating multiple signaling pathways. Its aberrant expression correlates with higher tumor grades and poorer patient prognosis. Beyond its intracellular functions, GRP78's presence on the cell surface and its role in the tumor microenvironment underscore its potential as a therapeutic target. Recent studies have explored innovative strategies to target GRP78, including small molecule inhibitors, monoclonal antibodies, and chimeric antigen receptor (CAR) T cell therapy, showing significant potential in glioma treatment. This review explores the biological characteristics of GRP78, its role in glioma pathophysiology, and the potential of GRP78-targeted therapy as a novel strategy to overcome treatment resistance and improve clinical outcomes. GRP78-targeted therapy, either alone or in combination with conventional treatments, could be a novel and attractive strategy for future glioma treatment.

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.

Autophagy-related 7 (ATG7) regulates food intake and liver health during asparaginase exposure

Amino acid starvation by the chemotherapy agent asparaginase is a potent activator of the integrated stress response (ISR) in the liver and can upregulate autophagy in some cell types. We hypothesized that autophagy-related 7 (ATG7), a protein that is essential for autophagy and an ISR target gene, was necessary during exposure to asparaginase to maintain liver health. We knocked down Atg7 systemically (Atg7Δ/Δ) or in hepatocytes only (ls-Atg7KO) in mice before exposure to pegylated asparaginase for 5 days. Intact mice injected with asparaginase lost body weight due to reduced food intake and increased energy expenditure. Systemic Atg7 ablation reduced liver protein synthesis and increased liver injury in vehicle-injected mice but did not further reduce liver protein synthesis, exacerbate steatosis or liver injury, or alter energy expenditure following 5 days of asparaginase exposure. Atg7Δ/Δ mice were unexpectantly protected from asparaginase-induced anorexia and weight loss. This protection corresponded with reduced phosphorylation of hepatic GCN2 and blunted increases in ISR gene targets including growth differentiation factor 15 (GDF15), a negative regulator of food intake. Interestingly, asparaginase elevated serum GDF15 and reduced food intake in ls-Atg7KO mice, similar to intact mice. Liver triglycerides and production of the hepatokine fibroblast growth factor 21, another ISR gene target, were suppressed in asparaginase-exposed Atg7Δ/Δ and ls-Atg7KO mice. This work identifies a bidirectional relationship between autophagy and the ISR in the liver during asparaginase, affecting food intake and liver health.

The integrated stress response drives MET oncogene overexpression in cancers

Cancer cells rely on invasive growth to survive in a hostile microenvironment; this growth is characterised by interconnected processes such as epithelial-to-mesenchymal transition and migration. A master regulator of these events is the MET oncogene, which is overexpressed in the majority of cancers; however, since mutations in the MET oncogene are seen only rarely in cancers and are relatively infrequent, the mechanisms that cause this widespread MET overexpression remain obscure. Here, we show that the 5' untranslated region (5'UTR) of MET mRNA harbours two functional stress-responsive elements, conferring translational regulation by the integrated stress response (ISR), regulated by phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α) at serine 52. ISR activation by serum starvation, leucine deprivation, hypoxia, irradiation, thapsigargin or gemcitabine is followed by MET protein overexpression. We mechanistically link MET translation to the ISR by (i) mutation of the two uORFs within the MET 5'UTR, (ii) CRISPR/Cas9-mediated mutation of eIF2α (S52A), or (iii) the application of ISR pathway inhibitors. All of these interventions reduce stress-induced MET overexpression. Finally, we show that blocking stress-induced MET translation blunts MET-dependent invasive growth. These findings indicate that upregulation of the MET oncogene is a functional requirement linking integrated stress response to cancer progression.

Polysulfide and persulfide-mediated activation of the PERK-eIF2α-ATF4 pathway increases Sestrin2 expression and reduces methylglyoxal toxicity

Unfolded protein response (UPR) is activated in cells under endoplasmic reticulum (ER) stress. One sensor protein involved in this response is PERK, which is activated through its redox-dependent oligomerization. Prolonged UPR activation is associated with the development and progression of various diseases, making it essential to understanding the redox regulation of PERK. Sulfane sulfur, such as polysulfides and persulfides, can modify the cysteine residues and regulate the function of various proteins. However, the regulatory mechanism and physiological effects of sulfane sulfur on the PERK-eIF2α-ATF4 pathway remain poorly understood. This study focuses on the persulfidation of PERK to elucidate the effects of polysulfides on the PERK-eIF2α-ATF4 pathway and investigate its cytoprotective mechanism. Here, we demonstrated that polysulfide treatment promoted the oligomerization of PERK and PTP1B in neuronal cells using western blotting under nonreducing conditions. We also observed that l-cysteine, a biological source of sulfane sulfur, promoted the oligomerization of PERK and the knockdown of CBS and 3-MST, two sulfane sulfur-producing enzymes, and reduced PERK oligomerization induced by l-cysteine treatment. Furthermore, the band shift assay and LC-MS/MS studies revealed that polysulfides and persulfides induce PTP1B and PERK persulfidation. Additionally, polysulfides promoted eIF2α phosphorylation and ATF4 accumulation in the nucleus, suggesting that polysulfides activate the PERK-eIF2α-ATF4 pathway in neuronal cells. Moreover, polysulfides protected neuronal cells from methylglyoxal-induced toxicity, and this protective effect was reduced when the expression of Sestrin2, regulated by ATF4 activity, was suppressed. This study identified a novel mechanism for the activation of the PERK-eIF2α-ATF4 pathway through persulfidation by polysulfides and persulfides. Interestingly, activation of this pathway overcame the toxicity of methylglyoxal in dependence on Sestrin2 expression. These findings deepen our understanding of neuronal diseases involving ER stress and UPR disturbance and may inspire new therapeutic strategies.

Inhibition of the Integrated stress response by Epstein-Barr virus oncoprotein LMP1 attenuates epithelial cell differentiation and lytic viral reactivation

EBV infects normal oral keratinocytes (NOKs) and plays an essential role in undifferentiated nasopharyngeal carcinoma (NPC). We previously showed that the EBV oncogene, LMP1, promotes proliferation and inhibits spontaneous differentiation in telomerase-immortalized NOKs grown in growth factor-restricted conditions. Here we have further examined the phenotypes of NOKs infected with wild-type EBV (WT EBV) versus an LMP1-deleted EBV mutant (ΔLMP1 EBV) in growth factor-restricted conditions. RNA-seq results show that WT EBV-infected NOKs not only have reduced differentiation, but also decreased expression of genes activated by the integrated stress response (ISR) pathway, in comparison to the ΔLMP1 EBV-infected cells. The ISR pathway is mediated by increased phosphorylation of the eIF2α translation initiation factor, leading to decreased translation of most cellular proteins but increased expression of some proteins, including ATF4 and CHOP. Immunoblot analyses confirmed that WT EBV-infected NOKs have decreased phosphorylation of eIF2α in comparison to uninfected and ΔLMP1 EBV-infected cells and showed that expression of LMP1 alone is sufficient to inhibit eIF2α phosphorylation. We found that LMP1 decreases the activity of two different eIF2α kinases, PERK and GCN2, in WT EBV-infected NOKs, resulting in decreased expression of the ISR-induced transcription factors, ATF4 and CHOP, in WT EBV-infected versus uninfected and ΔLMP1 EBV-infected NOKs. Furthermore, we found that both GCN2 and PERK activity are required for efficient TPA-induced lytic EBV reactivation and TPA-mediated epithelial cell differentiation. In addition, we demonstrate that over-expression of CHOP is sufficient to induce both lytic EBV reactivation and epithelial cell differentiation in WT EBV-infected NOKs and NPC cells and show that this effect is mediated by CHOP activation of the differentiation-inducing transcription factors, KLF4 and BLIMP1. Our results suggest that inhibition of the ISR pathway by the EBV oncoprotein, LMP1, may promote early NPC development by preventing epithelial cell differentiation and lytic EBV reactivation.

Taurine mechanism in preventing retinal cell damage from acute ocular hypertension through GTPBP3 regulation

We aimed to explore the protective effects and underlying mechanisms of taurine on retinal cells during acute ocular hypertension (AOH)-induced damage. Retinal morphology, apoptosis, mitochondrial structure, electroretinography, expression of GTP binding protein 3 (GTPBP3), and molecules in the unfolded protein response (UPR) were examined in an AOH mouse model and wild-type (WT) mice with or without intravitreal injection of taurine. For in vitro experiments, the GTPBP3 expression and endoplasmic reticulum (ER) stress were examined in R28 cell line under hydrogen peroxide (H2O2)-induced damage or hypoxia/reoxygenation (H/R)-induced damage, with or without taurine pretreatment. Taurine pretreatment alleviated retinal damage caused by AOH modeling. The GTPBP3 expression level decreased after AOH injury, and taurine pretreatment reversed this reduction. Retinas with decreased GTPBP3 expression showed reduced retinal ganglion cell (RGC) function, which could be reversed by intravitreal taurine injection. In H2O2-, H/R-, and AOH-induced damage, UPR were activated and alleviated by taurine pretreatment. GTPBP3 knockdown in R28 cells also activated the UPR, which was alleviated by taurine. A UPR activator downregulated GTPBP3 levels in normal R28 cells, whereas a UPR inhibitor upregulated GTPBP3 levels in GTPBP3 knockdown R28 cells. In conclusion, this study provides important evidence that taurine prevents retinal cell damage in mice exposed to AOH and modulates GTPBP3 expression via the UPR pathway. Interventions targeting this mechanism can be used as potential therapeutic targets for AOH damage.

TUDCA modulates drug bioavailability to regulate resistance to acute ER stress in Saccharomyces cerevisiae

Cells counter accumulation of misfolded secretory proteins in the endoplasmic reticulum (ER) through activation of the Unfolded Protein Response (UPR). Small molecules termed chemical chaperones can promote protein folding to alleviate ER stress. The bile acid tauroursodeoxycholic acid (TUDCA) has been described as a chemical chaperone. While promising in models of protein folding diseases, TUDCA's mechanism of action remains unclear. Here, we found TUDCA can rescue growth of yeast treated with the ER stressor tunicamycin (Tm), even in the absence of a functional UPR. In contrast, TUDCA failed to rescue growth on other ER stressors. Nor could TUDCA attenuate chronic UPR associated with specific gene deletions or overexpression of a misfolded mutant secretory protein. Neither pretreatment with nor delayed addition of TUDCA conferred protection against Tm. Importantly, attenuation of Tm-induced toxicity required TUDCA's critical micelle forming concentration, suggesting a mechanism where TUDCA directly sequesters drugs. Indeed, in several assays, TUDCA-treated cells closely resembled cells treated with lower doses of Tm. In addition, we found TUDCA can inhibit dyes from labeling intracellular compartments. Thus, our study challenges the model of TUDCA as a chemical chaperone and suggests that TUDCA decreases drug bioavailability, allowing cells to adapt to ER stress.

A nociceptor-specific RNAi screen in Drosophila larvae identifies RNA-binding proteins that regulate thermal nociception

Nociception is the process by which sensory neurons detect and encode potentially harmful environmental stimuli to generate behavioral responses. Nociceptor neurons exhibit plasticity in which their sensitivity to noxious stimuli and subsequent ability to drive behavior may be altered by environmental conditions, injury, infection, and inflammation. In some cases, nociceptor sensitization requires regulated changes in gene expression, and recent studies have indicated roles for post-transcriptional mechanisms in regulating these changes as an aspect of nociceptor plasticity. The larvae of Drosophila melanogaster have been developed as a powerful model for studying mechanisms of nociception, nociceptor plasticity, and nociceptor development. Diverse RNA-binding proteins regulate the development and morphology of larval nociceptors, implying important roles for post-transcriptional regulation of gene expression in these neurons, but the importance of these mechanisms for nociceptive behavior has not been investigated systematically. In this study, we conducted a nociceptor-specific RNAi screen of 112 candidate RNA-binding protein genes to identify those that are required for normal sensitivity to noxious thermal stimuli. The screen and subsequent validation experiments identified nine candidate genes (eIF2α, eIF4A, eIF4AIII, eIF4G2, mbl, SC35, snf, Larp4B and CG10445) that produce defects in nociceptive response latency when knocked down in larval nociceptors. Some of the genes identified have well-understood roles in the regulation of translation initiation and regulation of nociceptor sensitization in vertebrate and invertebrate animal models, suggesting an evolutionarily conserved role for these mechanisms in regulating nociceptor sensitivity. Other screen isolates have previously described roles in regulating nociceptor morphology and mRNA processing, but less clear roles in regulating nociceptor function. Further studies will be necessary to identify the mechanisms by which the identified RNA-binding proteins regulate sensory neuron function and the identities of the mRNAs that they target.

PHGDH Induction by MAPK Is Essential for Melanoma Formation and Creates an Actionable Metabolic Vulnerability

Overexpression of phosphoglycerate dehydrogenase (PHGDH), the rate-limiting enzyme in the serine synthesis pathway, promotes melanomagenesis, melanoma cell proliferation, and survival of metastases in serine-low environments such as the brain. Here, we found that PHGDH is universally increased in melanoma cells and required for melanomagenesis. Although PHGDH amplification explained PHGDH overexpression in a subset of melanomas, oncogenic BRAFV600E also promoted PHGDH transcription through mTORC1-mediated translation of ATF4. Importantly, depletion of PHGDH in genetic mouse melanoma models blocked tumor formation. In addition to BRAFV600E-mediated upregulation, PHGDH was further induced by exogenous serine restriction. Surprisingly, BRAFV600E inhibition diminished serine restriction-mediated PHGDH expression by preventing ATF4 induction. Consequently, melanoma cells could be specifically starved of serine by combining BRAFV600E inhibition with exogenous serine restriction, which promoted cell death in vitro and attenuated melanoma growth in vivo. In summary, this study identified that PHGDH is essential for melanomagenesis and regulated by BRAFV600E, revealing a targetable vulnerability in BRAFV600E-mutant melanoma. Significance: BRAFV600E promotes the expression of the serine synthesis enzyme PHGDH, which is required for melanoma formation, and can be targeted to sensitize melanoma to dietary serine restriction, providing a melanoma cell-specific treatment strategy.

Mitochondrial diseases: from molecular mechanisms to therapeutic advances

Mitochondria are essential for cellular function and viability, serving as central hubs of metabolism and signaling. They possess various metabolic and quality control mechanisms crucial for maintaining normal cellular activities. Mitochondrial genetic disorders can arise from a wide range of mutations in either mitochondrial or nuclear DNA, which encode mitochondrial proteins or other contents. These genetic defects can lead to a breakdown of mitochondrial function and metabolism, such as the collapse of oxidative phosphorylation, one of the mitochondria's most critical functions. Mitochondrial diseases, a common group of genetic disorders, are characterized by significant phenotypic and genetic heterogeneity. Clinical symptoms can manifest in various systems and organs throughout the body, with differing degrees and forms of severity. The complexity of the relationship between mitochondria and mitochondrial diseases results in an inadequate understanding of the genotype-phenotype correlation of these diseases, historically making diagnosis and treatment challenging and often leading to unsatisfactory clinical outcomes. However, recent advancements in research and technology have significantly improved our understanding and management of these conditions. Clinical translations of mitochondria-related therapies are actively progressing. This review focuses on the physiological mechanisms of mitochondria, the pathogenesis of mitochondrial diseases, and potential diagnostic and therapeutic applications. Additionally, this review discusses future perspectives on mitochondrial genetic diseases.

Human DBR1 deficiency impairs stress granule-dependent PKR antiviral immunity

The molecular mechanism by which inborn errors of the human RNA lariat-debranching enzyme 1 (DBR1) underlie brainstem viral encephalitis is unknown. We show here that the accumulation of RNA lariats in human DBR1-deficient cells interferes with stress granule (SG) assembly, promoting the proteasome degradation of at least G3BP1 and G3BP2, two key components of SGs. In turn, impaired assembly of SGs, which normally recruit PKR, impairs PKR activation and activity against viruses, including HSV-1. Remarkably, the genetic ablation of PKR abolishes the corresponding antiviral effect of DBR1 in vitro. We also show that Dbr1Y17H/Y17H mice are susceptible to similar viral infections in vivo. Moreover, cells and brain samples from Dbr1Y17H/Y17H mice exhibit decreased G3BP1/2 expression and PKR phosphorylation. Thus, the debranching of RNA lariats by DBR1 permits G3BP1/2- and SG assembly-mediated PKR activation and cell-intrinsic antiviral immunity in mice and humans. DBR1-deficient patients are prone to viral disease because of intracellular lariat accumulation, which impairs G3BP1/2- and SG assembly-dependent PKR activation.

Targeting Asparagine Metabolism in Solid Tumors

Reprogramming of energy metabolism to support cellular growth is a "hallmark" of cancer, allowing cancer cells to balance the catabolic demands with the anabolic needs of producing the nucleotides, amino acids, and lipids necessary for tumor growth. Metabolic alterations, or "addiction", are promising therapeutic targets and the focus of many drug discovery programs. Asparagine metabolism has gained much attention in recent years as a novel target for cancer therapy. Asparagine is widely used in the production of other nutrients and plays an important role in cancer development. Nutritional inhibition therapy targeting asparagine has been used as an anticancer strategy and has shown success in the treatment of leukemia. However, in solid tumors, asparagine restriction alone does not provide ideal therapeutic efficacy. Tumor cells initiate reprogramming processes in response to asparagine deprivation. This review provides a comprehensive overview of asparagine metabolism in cancers. We highlight the physiological role of asparagine and current advances in improving survival and overcoming therapeutic resistance.

Sensory quiescence induces a cell-non-autonomous integrated stress response curbed by condensate formation of the ATF4 and XRP1 effectors

Sensory disabilities have been identified as significant risk factors for dementia but underlying molecular mechanisms are unknown. In different Drosophila models with loss of sensory input, we observe non-autonomous induction of the integrated stress response (ISR) deep in the brain, as indicated by eIF2αS50 phosphorylation-dependent elevated levels of the ISR effectors ATF4 and XRP1. Unlike during canonical ISR, however, the ATF4 and XRP1 transcription factors are enriched in cytosolic granules that are positive for RNA and the stress granule markers Caprin, FMR1, and p62, and are reversible upon restoration of vision for blind flies. Cytosolic restraint of the ATF4 and XRP1 transcription factors dampens expression of their downstream targets including genes of cell death pathways activated during chronic cellular stress and thus constitutes a chronic stress protective response (CSPR). Cytosolic granules containing both p62 and ATF4 are also evident in the thalamus and hippocampus of mouse models of congenital or degenerative blindness. These data indicate a conserved link between loss of sensory input and curbed stress responses critical for protein quality control in the brain.

An Overview of Research Advances in Oncology Regarding the Transcription Factor ATF4

This review provides a comprehensive overview of the recent advancements in research on ATF4 (Activating Transcription Factor 4) within the field of oncology. As a crucial transcription factor, ATF4 has garnered increasing attention for its role in cancer research. The review begins with an exploration of the regulatory mechanisms of ATF4, including its transcriptional control, post-translational modifications, and interactions with other transcription factors. It then highlights key research findings on ATF4's involvement in various aspects of tumor biology, such as cell proliferation, differentiation, apoptosis and survival, invasion and metastasis, and the tumor microenvironment. Furthermore, the review discusses the potential of targeting ATF4 as a novel therapeutic strategy for cancer treatment. It also explores how ATF4's interactions with existing anticancer drugs could inform the development of more effective therapeutic agents. By elucidating the role of ATF4 in tumor biology and its potential clinical applications, this review aims to provide new insights and strategies for cancer treatment.

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.