Translation reinitiation at alternative open reading frames regulates gene expression in an integrated stress response

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.

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.

A Potential Role for c-MYC in the Regulation of Meibocyte Cell Stress

The integrated stress response (ISR) is a key regulator of cell survival, promoting apoptosis through the effector protein CHOP in instances of prolonged or severe stress. The ISR's role in the initiation and progression of epithelial malignancies has been investigated; however, the ISR has not been evaluated in ocular adnexal sebaceous carcinoma (SebCA). Though uncommon, mortality rates of up to 40% have been reported, and the mechanisms underlying SebCA tumorigenesis remain unresolved; however, c-MYC upregulation has been documented. Our objective was to determine the role of MYC in modulating the ISR in the Meibomian gland. Human Meibomian gland epithelial cells (HMGECs) were subject to both pharmacologic and genetic manipulations of MYC expression. Cytotoxicity, proliferation, and changes in protein and gene expression were assessed. Conditionally MYC-overexpressing mice were subject to topical 4-hydroxytamoxifen (4-OHT) induction of the eyelids prior to tissue harvest for histology, immunohistochemistry, immunoblotting, and qPCR. MYC-inhibited HMGECs exhibited dose-dependent decreased proliferation, increased CHOP expression, and increased apoptosis. Conversely, MYC-overexpressing HMGECs and Meibomian glands from 4-OHT-induced mice demonstrated suppressed CHOP expression, reduced apoptosis, and upregulated fatty acid synthase expression. These results suggest that MYC inhibition induces the ISR and promotes apoptosis, while MYC induction suppresses CHOP expression. High MYC expression may, therefore, serve as a mechanism for SebCA to elude cell death by promoting lipogenesis.

Plasticity of the mammalian integrated stress response

An increased level of phosphorylation of eukaryotic translation initiation factor 2 subunit-α (eIF2α, encoded by EIF2S1; eIF2α-p) coupled with decreased guanine nucleotide exchange activity of eIF2B is a hallmark of the 'canonical' integrated stress response (c-ISR)1. It is unclear whether impaired eIF2B activity in human diseases including leukodystrophies2, which occurs in the absence of eIF2α-p induction, is synonymous with the c-ISR. Here we describe a mechanism triggered by decreased eIF2B activity, distinct from the c-ISR, which we term the split ISR (s-ISR). The s-ISR is characterized by translational and transcriptional programs that are different from those observed in the c-ISR. Opposite to the c-ISR, the s-ISR requires eIF4E-dependent translation of the upstream open reading frame 1 and subsequent stabilization of ATF4 mRNA. This is followed by altered expression of a subset of metabolic genes (for example, PCK2), resulting in metabolic rewiring required to maintain cellular bioenergetics when eIF2B activity is attenuated. Overall, these data demonstrate a plasticity of the mammalian ISR, whereby the loss of eIF2B activity in the absence of eIF2α-p induction activates the eIF4E-ATF4-PCK2 axis to maintain energy homeostasis.

Sodium ferrous citrate in 5-Aminolevulinic acid supplements suppresses the effector function of feline lymphocytes by reducing the mitochondrial membrane potential

5-Aminolevulinic acid (5-ALA) is an endogenous amino acid in mammalian cells; it is the first amino acid in the heme biosynthesis pathway occurring in the mitochondria. 5-ALA with sodium ferrous citrate (SFC) possesses anti-inflammatory properties by inducing heme oxygenase (HO)-1 expression and releasing heme metabolites in humans and mice. Supplements containing 5-ALA and divalent iron is available in veterinary medicine. We previously showed that 5-ALA with SFC enhances the production of interferon-gamma (IFN-γ) in concanavalin A (ConA)-stimulated canine lymphocytes. However, the effects of 5-ALA/SFC on feline lymphocytes remain to be investigated. This study demonstrated that 5-ALA/SFC-induced HO-1 expression and decreased IFN-γ production in ConA-stimulated feline lymphocytes. Comprehensive RNA sequencing analysis revealed that the activating transcription factor 4 (ATF4) signaling pathway was inhibited by adding 5-ALA/SFC. Moreover, we confirmed that 5-ALA/SFC decreased ATF4 protein expression. Furthermore, separate analyses of the effects of 5-ALA and SFC on feline lymphocytes revealed that SFC, but not 5-ALA, induced AKT dephosphorylation and mitochondrial dysfunction in activated lymphocytes. Thus, SFC in 5-ALA supplements may suppress the effector function of feline lymphocytes via mitochondrial metabolism, thereby representing a novel mechanism in 5-ALA/SFC research.

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.

Inhibition of GLS1 and ASCT2 Synergistically Enhances the Anticancer Effects in Pancreatic Cancer Cells

Pancreatic cancer, a leading cause of cancer-related deaths, is characterized by increased dependence on glutamine metabolism. Telaglenastat (CB-839), a glutaminase (GLS) inhibitor targets glutamine metabolism; however, its efficacy as monotherapy is limited owing to metabolic adaptations. In this study, we demonstrated that CB-839 effectively inhibited cell growth in pancreatic cancer cells, but activated the general control nonderepressible 2 (GCN2)-activating transcription factor 4 (ATF4) signaling pathway. ATF4 knockdown reduced glutamine transporter alanine, serine, and cysteine transporter 2 (ASCT2) expression, glutamine uptake, and cell viability under glutamine deprivation-recovery conditions, confirming its protective role in mitigating glutamine-related metabolic stress. Notably, the combination of CB-839 and the ASCT2 inhibitor V-9302 demonstrated a synergistic effect, significantly suppressing pancreatic cancer cell survival. These findings highlight ATF4 and ASCT2 as crucial therapeutic targets and indicate that dual inhibition of GLS and ASCT2 may enhance treatment outcomes for pancreatic cancer.

Acute treadmill exercise induces mitochondrial unfolded protein response in skeletal muscle of male rats

Mitochondria are often referred to as the energy centers of the cell and are recognized as key players in signal transduction, sensing, and responding to internal and external stimuli. Under stress conditions, the mitochondrial unfolded protein response (UPRmt), a conserved mitochondrial quality control mechanism, is activated to maintain mitochondrial and cellular homeostasis. As a physiological stimulus, exercise-induced mitochondrial perturbations trigger UPRmt, coordinating mitochondria-to-nucleus communication and initiating a transcriptional program to restore mitochondrial function. The aim of this study was to evaluate the UPRmt signaling response to acute exercise in skeletal muscle. Male rats were subjected to acute treadmill exercise at 25 m/min for 60 min on a 0 % grade. Plantaris muscles were collected from both sedentary and exercise groups at various times: immediately (0), and at 1, 3, 6, 12, and 24 h post-exercise. Reactive oxygen species (ROS) production was assessed using hydrogen peroxide assay and dihydroethidium staining. Additionally, the mRNA and protein expression of UPRmt markers were measured using ELISA and real-time PCR. Mitochondrial activity was assessed using succinate dehydrogenase (SDH) and cytochrome c oxidase (COX) staining. Our results demonstrated that acute exercise increased ROS production and upregulated UPRmt markers at both gene and protein levels. Moreover, skeletal muscle exhibited an increase in mitochondrial activity in response to exercise, as indicated by SDH and COX staining. These findings suggest that acute treadmill exercise is sufficient to induce ROS production, activate UPRmt signaling, and enhance mitochondrial activity in skeletal muscle, expanding our understanding of mitochondrial adaptations to exercise.

Remodelled ribosomal populations synthesize a specific proteome in proliferating plant tissue during cold

Plant acclimation occurs through system-wide mechanisms that include proteome shifts, some of which occur at the level of protein synthesis. All proteins are synthesized by ribosomes. Rather than being monolithic, transcript-to-protein translation machines, ribosomes can be selective and cause proteome shifts. In this study, we use apical root meristems of germinating seedlings of the monocotyledonous plant barley as a model to examine changes in protein abundance and synthesis during cold acclimation. We measured metabolic and physiological parameters that allowed us to compare protein synthesis in the cold to optimal rearing temperatures. We demonstrated that the synthesis and assembly of ribosomal proteins are independent processes in root proliferative tissue. We report the synthesis and accumulation of various macromolecular complexes and propose how ribosome compositional shifts may be associated with functional proteome changes that are part of successful cold acclimation. Our study indicates that translation initiation is limiting during cold acclimation while the ribosome population is remodelled. The distribution of the triggered ribosomal protein heterogeneity suggests that altered compositions may confer 60S subunits selective association capabilities towards translation initiation complexes. To what extent selective translation depends on heterogeneous ribo-proteome compositions in barley proliferative root tissue remains a yet unresolved question.This article is part of the discussion meeting issue 'Ribosome diversity and its impact on protein synthesis, development and disease'.

Dysregulated ribosome quality control in human diseases

Precise regulation of mRNA translation is of fundamental importance for maintaining homeostasis. Conversely, dysregulated general or transcript-specific translation, as well as abnormal translation events, have been linked to a multitude of diseases. However, driven by the misconception that the transient nature of mRNAs renders their abnormalities inconsequential, the importance of mechanisms that monitor the quality and fidelity of the translation process has been largely overlooked. In recent years, there has been a dramatic shift in this paradigm, evidenced by several seminal discoveries on the role of a key mechanism in monitoring the quality of mRNA translation - namely, Ribosome Quality Control (RQC) - in the maintenance of homeostasis and the prevention of diseases. Here, we will review recent advances in the field and emphasize the biological significance of the RQC mechanism, particularly its implications in human diseases.

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.

Less is better: various means to reduce protein load in the endoplasmic reticulum

The endoplasmic reticulum (ER) is an important organelle that controls the intracellular and extracellular environments. The ER is responsible for folding almost one-third of the total protein population in the eukaryotic cell. Disruption of ER-protein folding is associated with numerous human diseases, including metabolic disorders, neurodegenerative diseases, and cancer. During ER perturbations, the cells deploy various mechanisms to increase the ER-folding capacity and reduce ER-protein load by minimizing the number of substrates entering the ER to regain homeostasis. These mechanisms include signaling pathways, degradation mechanisms, and other processes that mediate the reflux of ER content to the cytosol. In this review, we will discuss the recent discoveries of five different ER quality control mechanisms, including the unfolded protein response (UPR), ER-associated-degradation (ERAD), pre-emptive quality control, ER-phagy and ER to cytosol signaling (ERCYS). We will discuss the roles of these processes in decreasing ER-protein load and inter-mechanism crosstalk.

GCN2-Mediated eIF2α Phosphorylation Is Required for Central Nervous System Remyelination

Under conditions of amino acid deficiency, mammalian cells activate a nutrient-sensing kinase known as general control nonderepressible 2 (GCN2). The activation of GCN2 results in the phosphorylation of the alpha subunit of the eukaryotic initiation factor 2 (eIF2α), which can be phosphorylated by three other three integrated stress response (ISR) kinases, reducing overall protein synthesis. GCN2 activation also promotes the translation of specific mRNAs, some of which encode transcription factors that enhance the transcription of genes involved in the synthesis, transport, and metabolism of amino acids to restore cellular homeostasis. The phosphorylation of eIF2α has been shown to protect oligodendrocytes, the cells responsible for producing myelin in the central nervous system during remyelination. Here, we explore the potential role of the kinase GCN2 in the myelination process. We challenged mice deficient in the GCN2-encoding gene with a pharmacological demyelinating stimulus (cuprizone) and evaluated the recovery of myelin as well as ISR activation through the levels of eIF2α phosphorylation. Our findings indicate that GCN2 controls the establishment of myelin by fine-tuning its abundance and morphology in the central nervous system. We also found that GCN2 is essential for remyelination. Surprisingly, we discovered that GCN2 is necessary to maintain eIF2α levels during remyelination.

Mitigating effects of Jiawei Chaihu Shugan decoction on necroptosis and inflammation of hippocampal neurons in epileptic mice

Jiawei Chaihu Shugan decoction (JWCHSGD) is a traditional Chinese medicine well-known for its beneficial effects in treating epilepsy (Xianzheng in ancient Chinese), but the molecular mechanism of its action remains unclear. To investigate the molecular mechanism of JWCHSGD's prevention of epilepsy-mediated neuron from necroptosis and inflammation via the circRNA-Csnk1g3/Csnk1g3-85aa/ CK1γ3/TNF-α signal pathway. In vitro, murine neuronal HT22 cells were treated in six groups: control, model, carbamazepine, and three JWCHSGD doses (high, medium, low). Viability and apoptosis were assessed via CCK-8 and flow cytometry. In vivo, 60 C57BL/6J mice were divided into six groups: control, model, carbamazepine, JWCHSGD, JWCHSGD + Sh Circ_Csnk1g3, and JWCHSGD + Sh NC. An epilepsy model was induced, and treatments were administered for two weeks. Outcomes included EEG, hippocampal histopathology, apoptosis (TUNEL), and mRNA/protein expression of key pathway markers. In HT22 cells, the model group showed reduced viability, increased apoptosis, and elevated mRNA/protein levels of Csnk1g3-85aa, RIP1, RIP3, MLKL, TNF-α, IL-6, and IL-1β (P < 0.05). JWCHSGD and carbamazepine increased viability and decreased apoptosis, reversing these molecular changes (P < 0.05). In mice, the model group had heightened epileptic discharges, neuronal damage, and apoptosis, along with increased expression of the same markers (P < 0.05). JWCHSGD and carbamazepine mitigated these effects (P < 0.05). JWCHSGD reduces epileptic events by regulating the circRNA-Csnk1g3/Csnk1g3-85aa/CK1γ3/TNF-α signaling pathway, impacting necroptosis and inflammation in hippocampal neurons and HT22 cells.

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.

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.

Stress in pregnancy alters hepatic unfolded protein responses in male adult offspring

Stress is considered an independent risk factor for the development of cardiometabolic disorders, especially when it occurs during pregnancy, and it may play an important role in stress-induced fetal programming on the protein-folding homeostasis in hepatic endoplasmic reticulum. The study aimed to determine the effects of prenatal stress on the unfolded protein responses in the liver of male and female offspring of Wistar rats. Pregnant Wistar rats at 90 days old were divided into control and stress groups. The unpredictable stress protocol was performed from the 14th to the 21st day of pregnancy. The offspring of each group were divided into four groups according to sex and intervention. After the lactation period, the dams were anesthetized and euthanized for blood collection to determine plasma corticosterone levels. At 90 days old, the offspring were anesthetized and euthanized for liver tissue collection to measure protein expression of the endoplasmic reticulum stress. Dams submitted to prenatal stress showed an increase in corticosterone levels when compared to the control group. In the male offspring, prenatal stress induced lower body mass at birth and at 90 days compared to control, while females presented lower body mass only at birth. Prenatal stress reduced eIF2α expression in males, while increased p-eIF2α expression similarly in both sexes. Furthermore, only males had a greater p-eIF2α/eIF2α ratio and androgen receptor expression when compared to its respective control group and females. Prenatal stress induced a hepatic programming in the reticulum endoplasmic responses only in males at 90 days old by increasing androgen receptor, eIF2α phosphorylation and activity, while in females stress during pregnancy reduced cHDL and had little impact on hepatic unfolded protein response.

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.

UGGT1-mediated reglucosylation of N-glycan competes with ER-associated degradation of unstable and misfolded glycoproteins

How the fate (folding versus degradation) of glycoproteins is determined in the endoplasmic reticulum (ER) is an intriguing question. Monoglucosylated glycoproteins are recognized by lectin chaperones to facilitate their folding, whereas glycoproteins exposing well-trimmed mannoses are subjected to glycoprotein ER-associated degradation (gpERAD); we have elucidated how mannoses are sequentially trimmed by EDEM family members (George et al., 2020; 2021 eLife). Although reglucosylation by UGGT was previously reported to have no effect on substrate degradation, here we directly tested this notion using cells with genetically disrupted UGGT1/2. Strikingly, the results showed that UGGT1 delayed the degradation of misfolded substrates and unstable glycoproteins including ATF6α. An experiment with a point mutant of UGGT1 indicated that the glucosylation activity of UGGT1 was required for the inhibition of early glycoprotein degradation. These and overexpression-based competition experiments suggested that the fate of glycoproteins is determined by a tug-of-war between structure formation by UGGT1 and degradation by EDEMs. We further demonstrated the physiological importance of UGGT1, since ATF6α cannot function properly without UGGT1. Thus, our work strongly suggests that UGGT1 is a central factor in ER protein quality control via the regulation of both glycoprotein folding and degradation.

Multiprotein bridging factor 1 is required for robust activation of the integrated stress response on collided ribosomes

In yeast, multiprotein bridging factor 1 (Mbf1) has been proposed to function in the integrated stress response (ISR) as a transcriptional coactivator by mediating a direct interaction between general transcription machinery and the process's key effector, Gcn4. However, mounting evidence has demonstrated that Mbf1 (and its human homolog EDF1) is recruited to collided ribosomes, a known activator of the ISR. In this study, we connect these otherwise seemingly disparate functions of Mbf1. Our biochemical and structural analyses reveal that Mbf1 functions as a core ISR factor by interacting with collided ribosomes to mediate Gcn2 activation. We further show that Mbf1 serves no role as a transcriptional coactivator of Gcn4. Instead, Mbf1 is required for optimal stress-induced eukaryotic initiation factor 2α (eIF2α) phosphorylation and downstream de-repression of GCN4 translation. Collectively, our data establish that Mbf1 functions in ISR signaling by acting as a direct sensor of stress-induced ribosome collisions.

Exploring the dual role of endoplasmic reticulum stress in urological cancers: Implications for tumor progression and cell death interactions

The endoplasmic reticulum (ER) is crucial for maintaining calcium balance, lipid biosynthesis, and protein folding. Disruptions in ER homeostasis, often due to the accumulation of misfolded or unfolded proteins, lead to ER stress, which plays a significant role in various diseases, especially cancer. Urological cancers, which account for high male mortality worldwide, pose a persistent challenge due to their incurability and tendency to develop drug resistance. Among the numerous dysregulated biological mechanisms, ER stress is a key factor in the progression and treatment response of these cancers. This review highlights the dual role of aberrant ER stress activation in urologic cancers, affecting both tumor growth and therapeutic outcomes. While ER stress can support tumor growth through pro-survival autophagy, it primarily inhibits cancer progression via apoptosis and pro-death autophagy. Interestingly, ER stress can paradoxically aid cancer progression through mechanisms such as exosome-mediated immune evasion. Additionally, the review examines how pharmacological interventions, particularly with phytochemicals, can stimulate ER stress-mediated tumor suppression. Key regulators, including PERK, IRE1α, and ATF6, are discussed for their roles in upregulating CHOP levels and triggering apoptosis. In conclusion, a deeper understanding of ER stress in urological cancers not only clarifies the complex interactions between cellular stress and cancer progression but also provides new opportunities for innovative therapeutic strategies.

Tiny but mighty: Diverse functions of uORFs that regulate gene expression

Upstream open reading frames (uORFs) are critical cis-acting regulators of downstream gene expression. Specifically, uORFs regulate translation by disrupting translation initiation or mediating mRNA decay. We herein summarize the effects of several uORFs that regulate gene expression in microbes to illustrate the detailed mechanisms mediating uORF functions. Microbes are ideal for uORF studies because of their prompt responses to stimuli. Recent studies revealed uORFs are ubiquitous in higher eukaryotes. Moreover, they influence various physiological processes in mammalian cells by regulating gene expression, mostly at the translational level. Research conducted using rapidly evolving methods for ribosome profiling combined with protein analyses and computational annotations showed that uORFs in mammalian cells control gene expression similar to microbial uORFs, but they also have unique tumorigenesis-related roles because of their protein-encoding capacities. We briefly introduce cutting-edge research findings regarding uORFs in mammalian cells.

Stress response regulation of mRNA translation: Implications for antioxidant enzyme expression in cancer

From tumorigenesis to advanced metastatic stages, tumor cells encounter stress, ranging from limited nutrient and oxygen supply within the tumor microenvironment to extrinsic and intrinsic oxidative stress. Thus, tumor cells seize regulatory pathways to rapidly adapt to distinct physiologic conditions to promote cellular survival, including manipulation of mRNA translation. While it is now well established that metastatic tumor cells must up-regulate their antioxidant capacity to effectively spread and that regulation of antioxidant enzymes is imperative to disease progression, relatively few studies have assessed how translation and the hijacking of RNA systems contribute to antioxidant responses of tumors. Here, we review the major stress signaling pathways involved in translational regulation and discuss how these are affected by oxidative stress to promote prosurvival changes that manipulate antioxidant enzyme expression. We describe how tumors elicit these adaptive responses and detail how stress-induced translation can be regulated by kinases, RNA-binding proteins, RNA species, and RNA modification systems. We also highlight opportunities for further studies focused on the role of mRNA translation and RNA systems in the regulation of antioxidant enzyme expression, which may be of particular importance in the context of metastatic progression and therapeutic resistance.

Perturbations in eIF3 subunit stoichiometry alter expression of ribosomal proteins and key components of the MAPK signaling pathways

Protein synthesis plays a major role in homeostasis and when dysregulated leads to various pathologies including cancer. To this end, imbalanced expression of eukaryotic translation initiation factors (eIFs) is not only a consequence but also a driver of neoplastic growth. eIF3 is the largest, multi-subunit translation initiation complex with a modular assembly, where aberrant expression of one subunit generates only partially functional subcomplexes. To comprehensively study the effects of eIF3 remodeling, we contrasted the impact of eIF3d, eIF3e or eIF3h depletion on the translatome of HeLa cells using Ribo-seq. Depletion of eIF3d or eIF3e, but not eIF3h reduced the levels of multiple components of the MAPK signaling pathways. Surprisingly, however, depletion of all three eIF3 subunits increased MAPK/ERK pathway activity. Depletion of eIF3e and partially eIF3d also increased translation of TOP mRNAs that encode mainly ribosomal proteins and other components of the translational machinery. Moreover, alterations in eIF3 subunit stoichiometry were often associated with changes in translation of mRNAs containing short uORFs, as in the case of the proto-oncogene MDM2 and the transcription factor ATF4. Collectively, perturbations in eIF3 subunit stoichiometry exert specific effect on the translatome comprising signaling and stress-related transcripts with complex 5' UTRs that are implicated in homeostatic adaptation to stress and cancer.

Novel insights into the GCN2 pathway and its targeting. Therapeutic value in cancer and lessons from lung fibrosis development

Defining the mechanisms that allow cells to adapt to environmental stress is critical for understanding the progression of chronic diseases and identifying relevant drug targets. Among these, activation of the pathway controlled by the eIF2-alpha kinase GCN2 is critical for translational and metabolic reprogramming of the cell in response to various metabolic, proteotoxic, and ribosomal stressors. However, its role has frequently been investigated through the lens of a stress pathway signaling via the eIF2α-activating transcription factor 4 (ATF4) downstream axis, while recent advances in the field have revealed that the GCN2 pathway is more complex than previously thought. Indeed, this kinase can be activated through a variety of mechanisms, phosphorylate substrates other than eIF2α, and regulate cell proliferation in a steady state. This review presents recent findings regarding the fundamental mechanisms underlying GCN2 signaling and function, as well as the development of drugs that modulate its activity. Furthermore, by comparing the literature on GCN2's antagonistic roles in two challenging pathologies, cancer and pulmonary diseases, the benefits, and drawbacks of GCN2 targeting, particularly inhibition, are discussed.

The physiological role of the unfolded protein response in the nervous system

The unfolded protein response (UPR) is a cellular stress response pathway activated when the endoplasmic reticulum, a crucial organelle for protein folding and modification, encounters an accumulation of unfolded or misfolded proteins. The UPR aims to restore endoplasmic reticulum homeostasis by enhancing protein folding capacity, reducing protein biosynthesis, and promoting protein degradation. It also plays a pivotal role in coordinating signaling cascades to determine cell fate and function in response to endoplasmic reticulum stress. Recent research has highlighted the significance of the UPR not only in maintaining endoplasmic reticulum homeostasis but also in influencing various physiological processes in the nervous system. Here, we provide an overview of recent findings that underscore the UPR's involvement in preserving the function and viability of neuronal and myelinating cells under physiological conditions, and highlight the critical role of the UPR in brain development, memory storage, retinal cone development, myelination, and maintenance of myelin thickness.

Coordinated translational control of multiple immune checkpoints by the integrated stress response pathway in lung cancer

The integrated stress response (ISR) is an adaptive pathway hijacked by cancer cells to survive cellular stresses in the tumor microenvironment. ISR activation potently induces Programmed Death Ligand 1 (PD-L1), leading to suppression of anti-tumor immunity. Here we sought to uncover additional immune checkpoint proteins regulated by the ISR to elucidate mechanisms of tumor immune escape. We show that CD155 and PD-L1 are coordinately induced by the ISR, enhancing translation of both immune checkpoint proteins through bypass of inhibitory upstream open reading frames (uORFs) in their 5' UTRs. Analysis of primary human lung tumors identifies a significant correlation between PD-L1 and CD155 expression. ISR activation accelerates tumorigenesis and inhibits T cell function, effects that can be overcome by combining PD-1 blockade with the ISR inhibitor ISRIB. These studies uncover a novel mechanism by which two immune checkpoint proteins are coordinately regulated and suggest a new therapeutic strategy for lung cancer patients.

Statement of Significance

This study uncovers a novel mechanism for the coordinated translational regulation of the PD-L1/PD1 and CD155/TIGIT immune checkpoint pathways and highlights the ISR as a therapeutic vulnerability for lung cancer. Inhibition of the ISR pathway bolsters PD-1 blockade, potentially unveiling a new therapeutic strategy for lung cancer patients.

Where to start? Activity-dependent alternative translation initiation generates multifunctional proteoforms in the brain

In this issue of Molecular Cell, Lee et al.1 report that alternative translation initiation can generate new proteoforms with distinct localization patterns in a neuronal activity-dependent manner.

Chemical inhibition of the integrated stress response impairs the ubiquitin-proteasome system

Inhibitors of the integrated stress response (ISR) have been used to explore the potential beneficial effects of reducing the activation of this pathway in diseases. As the ISR is in essence a protective response, there is, however, a risk that inhibition may compromise the cell's ability to restore protein homeostasis. Here, we show that the experimental compound ISRIB impairs degradation of proteins by the ubiquitin-proteasome system (UPS) during proteotoxic stress in the cytosolic, but not nuclear, compartment. Accumulation of a UPS reporter substrate that is intercepted by ribosome quality control was comparable to the level observed after blocking the UPS with a proteasome inhibitor. Consistent with impairment of the cytosolic UPS, ISRIB treatment caused an accumulation of polyubiquitylated and detergent insoluble defective ribosome products (DRiPs) in the presence of puromycin. Our data suggest that the persistent protein translation during proteotoxic stress in the absence of a functional ISR increases the pool of DRiPs, thereby hindering the efficient clearance of cytosolic substrates by the UPS.

Specific activation of the integrated stress response uncovers regulation of central carbon metabolism and lipid droplet biogenesis

The integrated stress response (ISR) enables cells to cope with a variety of insults, but its specific contribution to downstream cellular outputs remains unclear. Using a synthetic tool, we selectively activate the ISR without co-activation of parallel pathways and define the resulting cellular state with multi-omics profiling. We identify time- and dose-dependent gene expression modules, with ATF4 driving only a small but sensitive subgroup that includes amino acid metabolic enzymes. This ATF4 response affects cellular bioenergetics, rerouting carbon utilization towards amino acid production and away from the tricarboxylic acid cycle and fatty acid synthesis. We also find an ATF4-independent reorganization of the lipidome that promotes DGAT-dependent triglyceride synthesis and accumulation of lipid droplets. While DGAT1 is the main driver of lipid droplet biogenesis, DGAT2 plays an essential role in buffering stress and maintaining cell survival. Together, we demonstrate the sufficiency of the ISR in promoting a previously unappreciated metabolic state.

The Proteostasis Network is a Therapeutic Target in Acute Myeloid Leukemia

Oncogenic growth places great strain and dependence on the proteostasis network. This has made proteostasis pathways attractive therapeutic targets in cancer, but efforts to drug these pathways have yielded disappointing clinical outcomes. One exception is proteasome inhibitors, which are approved for frontline treatment of multiple myeloma. However, proteasome inhibitors are largely ineffective for treatment of other cancers, including acute myeloid leukemia (AML), although reasons for these differences are unknown. Here, we determined that proteasome inhibitors are ineffective in AML due to inability to disrupt proteostasis. In response to proteasome inhibition, AML cells activated HSF1 and autophagy, two key stem cell proteostasis pathways, to prevent unfolded protein accumulation. Inactivation of HSF1 sensitized human AML cells to proteasome inhibition, marked by unfolded protein accumulation, activation of the PERK-mediated integrated stress response, severe reductions in protein synthesis, proliferation and cell survival, and significant slowing of disease progression and extension of survival in vivo . Similarly, combined autophagy and proteasome inhibition suppressed proliferation, synergistically killed AML cells, and significantly reduced AML burden and extended survival in vivo . Furthermore, autophagy and proteasome inhibition preferentially suppressed protein synthesis and induced apoptosis in primary patient AML cells, including AML stem/progenitor cells, without severely affecting normal hematopoietic stem/progenitor cells. Combined autophagy and proteasome inhibition also activated the integrated stress response, but surprisingly this occurred in a PKR-dependent manner. These studies unravel how proteostasis pathways are co-opted to promote AML growth, progression and drug resistance, and reveal that disabling the proteostasis network is a promising strategy to therapeutically target AML.

The signaling cascade of induction and maintenance of ES cell diapause

Nutrient deficiency during pregnancy in numerous animal species can induce the state of embryonic diapause. Diapause is characterized by changes in protein and gene expression that minimize the organism's reliance on external energy sources and ensure survival. Remarkably, the systematic changes associated with diapause appear to spare the gene expression program that supports embryonic cells' maintenance in the pluripotent state. The phenomenon of the differentiation "freeze" during diapause can be reproduced in vitro. Mimicking nutrient deficiency by pharmacological inhibition of mTOR induces the diapause-like state in ES cells without affecting ES cell pluripotency. We discovered a connection between mTOR signaling and the chromatin-bound bromodomain and extra-terminal (BET) transcriptional regulator BRD4, showing a key role of BET-protein in the induction of diapause-like state in ES cells. mTOR inhibition rapidly and negatively impacts BRD4 binding to chromatin, which is associated with changes in gene expression that can contribute to diapause. Conversely, pharmacological inhibition of BET-protein circumvents the diapause dependence on mTOR inhibition and causes the diapause-like state. BET-repressed diapause-like ES cells retain the undifferentiated pluripotent state, which is associated with upregulation of a functionally linked group of genes encoding negative regulators of MAP kinase (MAPK) signaling and inactivation of MAP kinase. The transcriptional switch-off of MAP kinase following chronic BET inhibition imitates the transcriptional de-repression of MAP kinase negative regulators in response to mTOR inhibition. Mechanistically, suppression of mTOR or BET-protein leads to a profound decline in Capicua transcriptional repressor (CIC) at promoters of key negative regulators of MAP kinase. The discovered mTOR-BRD4 axis in the induction of diapause and the rapid transcriptional shut-off of differentiation program is likely to play a major role in the maintenance of embryonic diapause in vivo, as well as in controlling of the undifferentiated state of various types of stem cells during diapause-like metabolic dormancy.

Endoplasmic reticulum stress in diseases

The endoplasmic reticulum (ER) is a key organelle in eukaryotic cells, responsible for a wide range of vital functions, including the modification, folding, and trafficking of proteins, as well as the biosynthesis of lipids and the maintenance of intracellular calcium homeostasis. A variety of factors can disrupt the function of the ER, leading to the aggregation of unfolded and misfolded proteins within its confines and the induction of ER stress. A conserved cascade of signaling events known as the unfolded protein response (UPR) has evolved to relieve the burden within the ER and restore ER homeostasis. However, these processes can culminate in cell death while ER stress is sustained over an extended period and at elevated levels. This review summarizes the potential role of ER stress and the UPR in determining cell fate and function in various diseases, including cardiovascular diseases, neurodegenerative diseases, metabolic diseases, autoimmune diseases, fibrotic diseases, viral infections, and cancer. It also puts forward that the manipulation of this intricate signaling pathway may represent a novel target for drug discovery and innovative therapeutic strategies in the context of human diseases.

TRMT10A dysfunction perturbs codon translation of initiator methionine and glutamine and impairs brain functions in mice

In higher eukaryotes, tRNA methyltransferase 10A (TRMT10A) is responsible for N1-methylguanosine modification at position nine of various cytoplasmic tRNAs. Pathogenic mutations in TRMT10A cause intellectual disability, microcephaly, diabetes, and short stature in humans, and generate cytotoxic tRNA fragments in cultured cells; however, it is not clear how TRMT10A supports codon translation or brain functions. Here, we generated Trmt10a null mice and showed that tRNAGln(CUG) and initiator methionine tRNA levels were universally decreased in various tissues; the same was true in a human cell line lacking TRMT10A. Ribosome profiling of mouse brain revealed that dysfunction of TRMT10A causes ribosome slowdown at the Gln(CAG) codon and increases translation of Atf4 due to higher frequency of leaky scanning of its upstream open reading frames. Broadly speaking, translation of a subset of mRNAs, especially those for neuronal structures, is perturbed in the mutant brain. Despite not showing discernable defects in the pancreas, liver, or kidney, Trmt10a null mice showed lower body weight and smaller hippocampal postsynaptic densities, which is associated with defective synaptic plasticity and memory. Taken together, our study provides mechanistic insight into the roles of TRMT10A in the brain, and exemplifies the importance of universal tRNA modification during translation of specific codons.

Phosphorylation of GCN2 by mTOR confers adaptation to conditions of hyper-mTOR activation under stress

Adaptation to the shortage in free amino acids (AA) is mediated by 2 pathways, the integrated stress response (ISR) and the mechanistic target of rapamycin (mTOR). In response to reduced levels, primarily of leucine or arginine, mTOR in its complex 1 configuration (mTORC1) is suppressed leading to a decrease in translation initiation and elongation. The eIF2α kinase general control nonderepressible 2 (GCN2) is activated by uncharged tRNAs, leading to induction of the ISR in response to a broader range of AA shortage. ISR confers a reduced translation initiation, while promoting the selective synthesis of stress proteins, such as ATF4. To efficiently adapt to AA starvation, the 2 pathways are cross-regulated at multiple levels. Here we identified a new mechanism of ISR/mTORC1 crosstalk that optimizes survival under AA starvation, when mTORC1 is forced to remain active. mTORC1 activation during acute AA shortage, augmented ATF4 expression in a GCN2-dependent manner. Under these conditions, enhanced GCN2 activity was not dependent on tRNA sensing, inferring a different activation mechanism. We identified a labile physical interaction between GCN2 and mTOR that results in a phosphorylation of GCN2 on serine 230 by mTOR, which promotes GCN2 activity. When examined under prolonged AA starvation, GCN2 phosphorylation by mTOR promoted survival. Our data unveils an adaptive mechanism to AA starvation, when mTORC1 evades inhibition.

IGHMBP2 deletion suppresses translation and activates the integrated stress response

IGHMBP2 is a nonessential, superfamily 1 DNA/RNA helicase that is mutated in patients with rare neuromuscular diseases SMARD1 and CMT2S. IGHMBP2 is implicated in translational and transcriptional regulation via biochemical association with ribosomal proteins, pre-rRNA processing factors, and tRNA-related species. To uncover the cellular consequences of perturbing IGHMBP2, we generated full and partial IGHMBP2 deletion K562 cell lines. Using polysome profiling and a nascent protein synthesis assay, we found that IGHMBP2 deletion modestly reduces global translation. We performed Ribo-seq and RNA-seq and identified diverse gene expression changes due to IGHMBP2 deletion, including ATF4 up-regulation. With recent studies showing the integrated stress response (ISR) can contribute to tRNA metabolism-linked neuropathies, we asked whether perturbing IGHMBP2 promotes ISR activation. We generated ATF4 reporter cell lines and found IGHMBP2 knockout cells demonstrate basal, chronic ISR activation. Our work expands upon the impact of IGHMBP2 in translation and elucidates molecular mechanisms that may link mutant IGHMBP2 to severe clinical phenotypes.

Activating transcription factor 4 in erythroid development and β -thalassemia: a powerful regulator with therapeutic potential

Activating transcription factor 4 (ATF4) is a fundamental basic region/leucine zipper transcription factor, responds to various stress signals, and plays crucial roles in normal metabolic and stress response processes. Although its functions in human health and disease are not completely understood, compelling evidence underscores ATF4 is indispensable for multiple stages and lineages of erythroid development, including the regulation of fetal liver hematopoietic stem cells, induction of terminal erythroid differentiation, and maintenance of erythroid homeostasis. β -Thalassemia is a blood disorder arising from mutations in the β -globin gene. Reactivating the expression of the γ -globin gene in adult patients has emerged as a promising therapeutic strategy for ameliorating clinical symptoms associated with β -thalassemia. Recent research has suggested that ATF4 contributes to decreased fetal hemoglobin (HbF) level through its binding to potent negative regulators of HbF, such as BCL11A and MYB. Notably, evidence also suggests a contrasting outcome where increased ATF4 protein levels are associated with enhanced HbF at the transcriptional level. Consequently, the identification of mechanisms that modulate ATF4-mediated γ -globin transcription and its effects on erythroid development may unveil novel targets for β -thalassemia treatment.

Deubiquitylase OTUD3 regulates integrated stress response to suppress progression and sorafenib resistance of liver cancer

The integrated stress response (ISR) is activated in response to intrinsic and extrinsic stimuli, playing a role in tumor progression and drug resistance. The regulatory role and mechanism of ISR in liver cancer, however, remain largely unexplored. Here, we demonstrate that OTU domain-containing protein 3 (OTUD3) is a deubiquitylase of eukaryotic initiation factor 2α (eIF2α), antagonizing ISR and suppressing liver cancer. OTUD3 decreases interactions between eIF2α and the kinase EIF2ΑK3 by removing K27-linked polyubiquitylation on eIF2α. OTUD3 deficiency in mice leads to enhanced ISR and accelerated progression of N-nitrosodiethylamine-induced hepatocellular carcinoma. Additionally, decreased OTUD3 expression associated with elevated eIF2α phosphorylation correlates with the progression of human liver cancer. Moreover, ISR activation due to decreased OTUD3 expression renders liver cancer cells resistant to sorafenib, while the combined use of the ISR inhibitor ISRIB significantly improves their sensitivity to sorafenib. Collectively, these findings illuminate the regulatory mechanism of ISR in liver cancer and provide a potential strategy to counteract sorafenib resistance.

Advances in Circular RNA in the Pathogenesis of Epilepsy

Recent studies evidenced the involvement of circular RNA (circRNA) in neuroinflammation, apoptosis, and synaptic remodeling suggesting an important role for circRNA in the occurrence and development of epilepsy. This review provides an overview of circRNAs considered to be playing regulatory roles in the process of epilepsy and to be involved in multiple biological epilepsy-related processes, such as hippocampal sclerosis, inflammatory response, cell apoptosis, synaptic remodeling, and cell proliferation and differentiation. This review covers the current research status of differential expression of circRNA-mediated seizures, m6A methylation, demethylation-mediated seizures in post transcriptional circRNA modification, as well as the mechanisms of m5C- and m7G-modified circRNA. In summary, this article reviews the research progress on the relationship between circRNA in non-coding RNA and epilepsy.

Long non-coding RNA-mediated modulation of endoplasmic reticulum stress under pathological conditions

Endoplasmic reticulum (ER) stress, which ensues from an overwhelming protein folding capacity, activates the unfolded protein response (UPR) in an effort to restore cellular homeostasis. As ER stress is associated with numerous diseases, it is highly important to delineate the molecular mechanisms governing the ER stress to gain insight into the disease pathology. Long non-coding RNAs, transcripts with a length of over 200 nucleotides that do not code for proteins, interact with proteins and nucleic acids, fine-tuning the UPR to restore ER homeostasis via various modes of actions. Dysregulation of specific lncRNAs is implicated in the progression of ER stress-related diseases, presenting these molecules as promising therapeutic targets. The comprehensive analysis underscores the importance of understanding the nuanced interplay between lncRNAs and ER stress for insights into disease mechanisms. Overall, this review consolidates current knowledge, identifies research gaps and offers a roadmap for future investigations into the multifaceted roles of lncRNAs in ER stress and associated diseases to shed light on their pivotal roles in the pathogenesis of related diseases.

Ribosome rescue factor PELOTA modulates translation start site choice for C/EBPα protein isoforms

Translation initiation at alternative start sites can dynamically control the synthesis of two or more functionally distinct protein isoforms from a single mRNA. Alternate isoforms of the developmental transcription factor CCAAT/enhancer-binding protein α (C/EBPα) produced from different start sites exert opposing effects during myeloid cell development. This choice between alternative start sites depends on sequence features of the CEBPA transcript, including a regulatory uORF, but the molecular basis is not fully understood. Here, we identify the factors that affect C/EBPα isoform choice using a sensitive and quantitative two-color fluorescent reporter coupled with CRISPRi screening. Our screen uncovered a role of the ribosome rescue factor PELOTA (PELO) in promoting the expression of the longer C/EBPα isoform by directly removing inhibitory unrecycled ribosomes and through indirect effects mediated by the mechanistic target of rapamycin kinase. Our work uncovers further links between ribosome recycling and translation reinitiation that regulate a key transcription factor, with implications for normal hematopoiesis and leukemogenesis.

Molecular Mechanisms of the Therapeutic Effect of Selenium Nanoparticles in Hepatocellular Carcinoma

This review describes and summarizes, for the first time, the molecular mechanisms of the cytotoxic effect of selenium nanoparticles of various origins on hepatocellular carcinoma cells. The text provides information from recent years indicating the regulation of various signaling pathways and endoplasmic reticulum stress by selenium nanoparticles; the pathways of cell death of liver cancer cells as a result of exposure to selenium nanoparticles are considered. Particular attention is paid to the participation of selenoproteins and selenium-containing thioredoxin reductases and glutathione peroxidases in these processes. Previously, there were no reviews that fully reflected the cytotoxic effects of selenium nanoparticles specifically in hepatocellular carcinoma, despite the fact that many reviews and experimental articles have been devoted to the causes of this disease and the molecular mechanisms of regulation of cytotoxic effects by other agents. The relevance of this review is primarily explained by the fact that despite the development of various drugs and approaches for the treatment and prevention of hepatocellular carcinoma, this disease is still the fourth leading cause of death in the world. For this reason, a complete understanding of the latest trends in the treatment of oncology of various etiologies, especially hepatocellular carcinoma, is extremely important.

Depletion of cap-binding protein eIF4E dysregulates amino acid metabolic gene expression

Protein synthesis is metabolically costly and must be tightly coordinated with changing cellular needs and nutrient availability. The cap-binding protein eIF4E makes the earliest contact between mRNAs and the translation machinery, offering a key regulatory nexus. We acutely depleted this essential protein and found surprisingly modest effects on cell growth and recovery of protein synthesis. Paradoxically, impaired protein biosynthesis upregulated genes involved in the catabolism of aromatic amino acids simultaneously with the induction of the amino acid biosynthetic regulon driven by the integrated stress response factor GCN4. We further identified the translational control of Pho85 cyclin 5 (PCL5), a negative regulator of Gcn4, that provides a consistent protein-to-mRNA ratio under varied translation environments. This regulation depended in part on a uniquely long poly(A) tract in the PCL5 5' UTR and poly(A) binding protein. Collectively, these results highlight how eIF4E connects protein synthesis to metabolic gene regulation, uncovering mechanisms controlling translation during environmental challenges.

Upstream open reading frames: new players in the landscape of cancer gene regulation

The translation of RNA by ribosomes represents a central biological process and one of the most dysregulated processes in cancer. While translation is traditionally thought to occur exclusively in the protein-coding regions of messenger RNAs (mRNAs), recent transcriptome-wide approaches have shown abundant ribosome activity across diverse stretches of RNA transcripts. The most common type of this kind of ribosome activity occurs in gene leader sequences, also known as 5' untranslated regions (UTRs) of the mRNA, that precede the main coding sequence. Translation of these upstream open reading frames (uORFs) is now known to occur in upwards of 25% of all protein-coding genes. With diverse functions from RNA regulation to microprotein generation, uORFs are rapidly igniting a new arena of cancer biology, where they are linked to cancer genetics, cancer signaling, and tumor-immune interactions. This review focuses on the contributions of uORFs and their associated 5'UTR sequences to cancer biology.

The prognostic significance of insulin resistance in COVID-19: a review

Objectives

Emerging publications indicate that diabetes predisposes patients with COVID-19 to more severe complications, which is partly attributed to inflammatory condition. In the current review, we reviewed recent published literature to provide evidence on the role of insulin resistance (IR) in diabetes, the association between diabetes and COVID-19 severity and mortality, the impact of COVID-19 infection on incident new-onset diabetes, mechanisms responsible for IR in COVID-19 patients, and the predictive value of different surrogates of IR in COVID-19.

Method

The literature search performs to find out studies that have assessed the association between IR surrogates and morbidity and mortality in patients with COVID-19.

Results

We showed that there is a bulk of evidence in support of the fact that diabetes is a potent risk factor for enhanced morbidity and mortality in COVID-19 patients. COVID-19 patients with diabetes are more prone to remarkable dysglycemia compared to those without diabetes, which is associated with an unfavourable prognosis. Furthermore, SARS-COV2 can make patients predispose to IR and diabetes via activating ISR, affecting RAAS signaling pathway, provoking inflammation, and changing the expression of PPARɣ and SREBP-1. Additionally, higher IR is associated with increased morbidity and mortality in COVID-19 patients and different surrogates of IR can be utilized as a prognostic biomarker for COVID-19 patients.

Conclusion

Different surrogates of IR can be utilized as predictors of COVID-19 complications and death.

Mammalian integrated stress responses in stressed organelles and their functions

The integrated stress response (ISR) triggered in response to various cellular stress enables mammalian cells to effectively cope with diverse stressful conditions while maintaining their normal functions. Four kinases (PERK, PKR, GCN2, and HRI) of ISR regulate ISR signaling and intracellular protein translation via mediating the phosphorylation of eukaryotic translation initiation factor 2 α (eIF2α) at Ser51. Early ISR creates an opportunity for cells to repair themselves and restore homeostasis. This effect, however, is reversed in the late stages of ISR. Currently, some studies have shown the non-negligible impact of ISR on diseases such as ischemic diseases, cognitive impairment, metabolic syndrome, cancer, vanishing white matter, etc. Hence, artificial regulation of ISR and its signaling with ISR modulators becomes a promising therapeutic strategy for relieving disease symptoms and improving clinical outcomes. Here, we provide an overview of the essential mechanisms of ISR and describe the ISR-related pathways in organelles including mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. Meanwhile, the regulatory effects of ISR modulators and their potential application in various diseases are also enumerated.

Genetics and Molecular Biology of Memory Suppression

The brain is designed not only with molecules and cellular processes that help to form memories but also with molecules and cellular processes that suppress the formation and retention of memory. The latter processes are critical for an efficient memory management system, given the vast amount of information that each person experiences in their daily activities and that most of this information becomes irrelevant with time. Thus, efficiency dictates that the brain should have processes for selecting the most critical information for storage and suppressing the irrelevant or forgetting it later should it escape the initial filters. Such memory suppressor molecules and processes are revealed by genetic or pharmacologic insults that lead to enhanced memory expression. We review here the predominant memory suppressor molecules and processes that have recently been discovered. They are diverse, as expected, because the brain is complex and employs many different strategies and mechanisms to form memories. They include the gene-repressive actions of small noncoding RNAs, repressors of protein synthesis, cAMP-mediated gene expression pathways, inter- and intracellular signaling pathways for normal forgetting, and others. A deep understanding of memory suppressor molecules and processes is necessary to fully comprehend how the brain forms, stabilizes, and retrieves memories and to reveal how brain disorders disrupt memory.

Cardiac-specific deletion of heat shock protein 60 induces mitochondrial stress and disrupts heart development in mice

Congenital heart diseases are the most common birth defects around the world. Emerging evidence suggests that mitochondrial homeostasis is required for normal heart development. In mitochondria, a series of molecular chaperones including heat shock protein 60 (HSP60) are engaged in assisting the import and folding of mitochondrial proteins. However, it remains largely obscure whether and how these mitochondrial chaperones regulate cardiac development. Here, we generated a cardiac-specific Hspd1 deletion mouse model by αMHC-Cre and investigated the role of HSP60 in cardiac development. We observed that deletion of HSP60 in embryonic cardiomyocytes resulted in abnormal heart development and embryonic lethality, characterized by reduced cardiac cell proliferation and thinner ventricular walls, highlighting an essential role of cardiac HSP60 in embryonic heart development and survival. Our results also demonstrated that HSP60 deficiency caused significant downregulation of mitochondrial ETC subunits and induced mitochondrial stress. Analysis of gene expression revealed that P21 that negatively regulates cell proliferation is significantly upregulated in HSP60 knockout hearts. Moreover, HSP60 deficiency induced activation of eIF2α-ATF4 pathway, further indicating the underlying mitochondrial stress in cardiomyocytes after HSP60 deletion. Taken together, our study demonstrated that regular function of mitochondrial chaperones is pivotal for maintaining normal mitochondrial homeostasis and embryonic heart development.

l-2-Hydroxyglutarate remodeling of the epigenome and epitranscriptome creates a metabolic vulnerability in kidney cancer models

Tumor cells are known to undergo considerable metabolic reprogramming to meet their unique demands and drive tumor growth. At the same time, this reprogramming may come at a cost with resultant metabolic vulnerabilities. The small molecule l-2-hydroxyglutarate (l-2HG) is elevated in the most common histology of renal cancer. Similarly to other oncometabolites, l-2HG has the potential to profoundly impact gene expression. Here, we demonstrate that l-2HG remodels amino acid metabolism in renal cancer cells through combined effects on histone methylation and RNA N6-methyladenosine. The combined effects of l-2HG result in a metabolic liability that renders tumors cells reliant on exogenous serine to support proliferation, redox homeostasis, and tumor growth. In concert with these data, high-l-2HG kidney cancers demonstrate reduced expression of multiple serine biosynthetic enzymes. Collectively, our data indicate that high-l-2HG renal tumors could be specifically targeted by strategies that limit serine availability to tumors.

Socialized mitochondria: mitonuclear crosstalk in stress

Traditionally, mitochondria are considered sites of energy production. However, recent studies have suggested that mitochondria are signaling organelles that are involved in intracellular interactions with other organelles. Remarkably, stressed mitochondria appear to induce a beneficial response that restores mitochondrial function and cellular homeostasis. These mitochondrial stress-centered signaling pathways have been rapidly elucidated in multiple organisms. In this review, we examine current perspectives on how mitochondria communicate with the rest of the cell, highlighting mitochondria-to-nucleus (mitonuclear) communication under various stresses. Our understanding of mitochondria as signaling organelles may provide new insights into disease susceptibility and lifespan extension.