The mTOR-S6 kinase pathway promotes stress granule assembly

Neuroprotective effects of ellorarxine in neuronal models of degeneration

Introduction

Retinoic acid (RA) was first recognised to be important for the central nervous system (CNS) in its developmental regulatory role and, given this action, it has been proposed in the adult CNS to regulate plasticity and promote regeneration. These types of roles have included support of neurogenesis, induction of neurite outgrowth, and protection from neuronal death. These functions are predominantly mediated by the retinoic acid receptor (RAR) transcription factor, and hence agonists for the RARs have been tested in a variety of models of neurodegeneration. This present study employs several in vitro models less explored for the action of RAR agonists to reverse neurodegeneration.

Methods

A series of assays are used in which neuronal cells are placed under the types of stress that have been linked to neurodegeneration, in particular amyotrophic lateral sclerosis (ALS), and the neuroprotective influence of a new potent agonist for RAR, ellorarxine, is tested out. In these assays, neuronal cells were subjected to excitotoxic stress induced by glutamate, proteostasis disruption caused by epoxomicin, and oxidative stress leading to stress granule formation triggered by sodium arsenite.

Results

Ellorarxine effectively reversed neuronal death in excitotoxic and proteostasis disruption assays and mitigated stress granule formation induced by sodium arsenite. This study also highlights for the first time the novel observation of RAR modulation of stress granules, although it is unknown whether this change in stress granules will be neuroprotective or potentially regenerative. Furthermore, the distribution of RAR agonists following intraperitoneal injection was assessed in mice, revealing preferential accumulation in the central nervous system, particularly in the spinal cord, compared to the liver. Gene expression studies in the spinal cord demonstrated that ellorarxine induces transcriptional changes at a low dose (0.01 mg/kg).

Discussion

These findings underscore the therapeutic potential of RAR agonists, such as ellorarxine, for ALS and potentially other neurodegenerative diseases.

Stress granules in cancer: Adaptive dynamics and therapeutic implications

Stress granules (SGs), membrane-less cellular organelles formed via liquid-liquid phase separation, are central to how cells adapt to various stress conditions, including endoplasmic reticulum stress, nutrient scarcity, and hypoxia. Recent studies have underscored a significant link between SGs and the process of tumorigenesis, highlighting that proteins, associated components, and signaling pathways that facilitate SG formation are often upregulated in cancer. SGs play a key role in enhancing tumor cell proliferation, invasion, and migration, while also inhibiting apoptosis, facilitating immune evasion, and driving metabolic reprogramming through multiple mechanisms. Furthermore, SGs have been identified as crucial elements in the development of resistance against chemotherapy, immunotherapy, and radiotherapy across a variety of cancer types. This review delves into the complex role of SGs in cancer development and resistance, bringing together the latest progress in the field and exploring new avenues for therapeutic intervention.

Friend or foe: The role of stress granule in neurodegenerative disease

Stress granules (SGs) are dynamic membraneless organelles that form in response to cellular stress. SGs are predominantly composed of RNA and RNA-binding proteins that assemble through liquid-liquid phase separation. Although the formation of SGs is considered a transient and protective response to cellular stress, their dysregulation or persistence may contribute to various neurodegenerative diseases. This review aims to provide a comprehensive overview of SG physiology and pathology. It covers the formation, composition, regulation, and functions of SGs, along with their crosstalk with other membrane-bound and membraneless organelles. Furthermore, this review discusses the dual roles of SGs as both friends and foes in neurodegenerative diseases and explores potential therapeutic approaches targeting SGs. The challenges and future perspectives in this field are also highlighted. A more profound comprehension of the intricate relationship between SGs and neurodegenerative diseases could inspire the development of innovative therapeutic interventions against these devastating diseases.

Myeloid PTEN loss affects the therapeutic response by promoting stress granule assembly and impairing phagocytosis by macrophages in breast cancer

Breast cancer (BRCA) has become the most common type of cancer in women. Improving the therapeutic response remains a challenge. Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a classic tumour suppressor with emerging new functions discovered in recent years, and myeloid PTEN loss has been reported to impair antitumour immunity. In this study, we revealed a novel mechanism by which myeloid PTEN potentially affects antitumour immunity in BRCA. We detected accelerated stress granule (SG) assembly under oxidative stress in PTEN-deficient bone marrow-derived macrophages (BMDMs) through the EGR1-promoted upregulation of TIAL1 transcription. PI3K/AKT/mTOR (PAM) pathway activation also promoted SG formation. ATP consumption during SG assembly in BMDMs impaired the phagocytic ability of 4T1 cells, potentially contributing to the disruption of antitumour immunity. In a BRCA neoadjuvant cohort, we observed a poorer response in myeloid PTENlow patients with G3BP1 aggregating as SGs in CD68+ cells, a finding that was consistent with the observation in our study that PTEN-deficient macrophages tended to more readily assemble SGs with impaired phagocytosis. Our results revealed the unconventional impact of SGs on BMDMs and might provide new perspectives on drug resistance and therapeutic strategies for the treatment of BRCA patients.

Liquid-liquid phase separation in diseases

Liquid-liquid phase separation (LLPS), an emerging biophysical phenomenon, can sequester molecules to implement physiological and pathological functions. LLPS implements the assembly of numerous membraneless chambers, including stress granules and P-bodies, containing RNA and protein. RNA-RNA and RNA-protein interactions play a critical role in LLPS. Scaffolding proteins, through multivalent interactions and external factors, support protein-RNA interaction networks to form condensates involved in a variety of diseases, particularly neurodegenerative diseases and cancer. Modulating LLPS phenomenon in multiple pathogenic proteins for the treatment of neurodegenerative diseases and cancer could present a promising direction, though recent advances in this area are limited. Here, we summarize in detail the complexity of LLPS in constructing signaling pathways and highlight the role of LLPS in neurodegenerative diseases and cancers. We also explore RNA modifications on LLPS to alter diseases progression because these modifications can influence LLPS of certain proteins or the formation of stress granules, and discuss the possibility of proper manipulation of LLPS process to restore cellular homeostasis or develop therapeutic drugs for the eradication of diseases. This review attempts to discuss potential therapeutic opportunities by elaborating on the connection between LLPS, RNA modification, and their roles in diseases.

Miao medicine Gu Yan Xiao tincture inhibits mTOR to stimulate chondrocyte autophagy in a rabbit model of osteoarthritis

ETHNOPHARMACOLOGICAL RELEVANCE

The Gu Yan Xiao tincture, a blend of traditional Chinese herbs, is traditionally used for osteoarthritis and related pain. This study investigated its mechanism of action in order to rationalize and validate its therapeutic use.

AIM OF THE STUDY

This study analyzed, in a rabbit model of knee osteoarthritis, whether and how Gu Yan Xiao tincture exerts therapeutic benefits by modulating chondrocyte autophagy.

MATERIALS AND METHODS

The active constituents within the GYX tincture were identified using liquid chromatography-mass spectrometry. The rabbit model was established by injecting animals with type II collagenase intra-articularly, and the effects of topically applied tincture were examined on osteoarthritis lesions of the knee using histopathology, micro-computed tomography and x-ray imaging. Effects of the tincture were also evaluated on levels of inflammatory cytokines, matrix metalloproteases, and autophagy in chondrocytes. As a positive control, animals were treated with sodium diclofenac.

RESULTS

The tincture mitigated the reduction in joint space, hyperplasia of the synovium and matrix metalloproteases in serum that occurred after injection of type II collagenase in rabbits. These therapeutic effects were associated with inhibition of mTOR and activation of autophagy in articular chondrocytes. Inhibiting mTOR with rapamycin potentiated the therapeutic effects of the tincture, while inhibiting autophagy with 3-methyladenine antagonized them.

CONCLUSIONS

Gu Yan Xiao tincture mitigates tissue injury in a rabbit model of osteoarthritis, at least in part by inhibiting mTOR and thereby promoting autophagy in chondrocytes. These results rationalize the use of the tincture not only against osteoarthritis but also potentially other diseases involving inhibition of autophagy in bones and joints.

ROS-responsive MSC-derived Exosome Mimetics Carrying MHY1485 Alleviate Renal Ischemia Reperfusion Injury through Multiple Mechanisms

Renal ischemia reperfusion (IR) injury is a prevalent inflammatory nephropathy in surgeries such as renal transplantation or partial nephrectomy, damaging renal function through inducing inflammation and cell death in renal tubules. Mesenchymal stromal/stem cell (MSC)-based therapies, common treatments to attenuate inflammation in IR diseases, fail to exhibit satisfying effects on cell death in renal IR. In this study, we prepared MSC-derived exosome mimetics (EMs) carrying the mammalian target of the rapamycin (mTOR) agonist to protect kidneys in proinflammatory environments under IR conditions. The thioketal-modified EMs carried the mTOR agonist and bioactive molecules in MSCs and responsively released them in kidney IR areas. MSC-derived EMs and mTOR agonists protected kidneys synergistically from IR through alleviating inflammation, apoptosis, and ferroptosis. The current study indicates that MSC-TK-MHY1485 EMs (MTM-EM) are promising therapeutic biomaterials for renal IR injury.

Targeting stress granules in neurodegenerative diseases: A focus on biological function and dynamics disorders

Stress granules (SGs) are membraneless organelles formed by eukaryotic cells in response to stress to promote cell survival through their pleiotropic cytoprotective effects. SGs recruit a variety of components to enhance their physiological function, and play a critical role in the propagation of pathological proteins, a key factor in neurodegeneration. Recent advances indicate that SG dynamic disorders exacerbate neuronal susceptibility to stress in neurodegenerative diseases (NDs) including Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Huntington's disease (HD) and Parkinson's disease (PD). Here, we outline the biological functions of SGs, highlight SG dynamic disorders in NDs, and emphasize therapeutic approaches for enhancing SG dynamics to provide new insights into ND intervention.

Translation regulation in response to stress

Cell stresses occur in a wide variety of settings: in disease, during industrial processes, and as part of normal day-to-day rhythms. Adaptation to these stresses requires cells to alter their proteome. Cells modify the proteins they synthesize to aid proteome adaptation. Changes in both mRNA transcription and translation contribute to altered protein synthesis. Here, we discuss the changes in translational mechanisms that occur following the onset of stress, and the impact these have on stress adaptation.

Role of stress granules in tumorigenesis and cancer therapy

Stress granules (SGs) are membrane-less organelles that cell forms via liquid-liquid phase separation (LLPS) under stress conditions such as oxidative stress, ER stress, heat shock and hypoxia. SG assembly is a stress-responsive mechanism by regulating gene expression and cellular signaling pathways. Cancer cells face various stress conditions in tumor microenvironment during tumorigenesis, while SGs contribute to hallmarks of cancer including proliferation, invasion, migration, avoiding apoptosis, metabolism reprogramming and immune evasion. Here, we review the connection between SGs and cancer development, the limitation of SGs on current cancer therapy and promising cancer therapeutic strategies targeting SGs in the future.

Cauliflower mosaic virus protein P6 is a multivalent node for RNA granule proteins and interferes with stress granule responses during plant infection

Biomolecular condensation is a multipurpose cellular process that viruses use ubiquitously during their multiplication. Cauliflower mosaic virus replication complexes are condensates that differ from those of most viruses, as they are nonmembranous assemblies that consist of RNA and protein, mainly the viral protein P6. Although these viral factories (VFs) were described half a century ago, with many observations that followed since, functional details of the condensation process and the properties and relevance of VFs have remained enigmatic. Here, we studied these issues in Arabidopsis thaliana and Nicotiana benthamiana. We observed a large dynamic mobility range of host proteins within VFs, while the viral matrix protein P6 is immobile, as it represents the central node of these condensates. We identified the stress granule (SG) nucleating factors G3BP7 and UBP1 family members as components of VFs. Similarly, as SG components localize to VFs during infection, ectopic P6 localizes to SGs and reduces their assembly after stress. Intriguingly, it appears that soluble rather than condensed P6 suppresses SG formation and mediates other essential P6 functions, suggesting that the increased condensation over the infection time-course may accompany a progressive shift in selected P6 functions. Together, this study highlights VFs as dynamic condensates and P6 as a complex modulator of SG responses.

Kinase regulation by liquid-liquid phase separation

Liquid-liquid phase separation (LLPS) is emerging as a mechanism of spatiotemporal regulation that could answer long-standing questions about how order is achieved in biochemical signaling. In this review we discuss how LLPS orchestrates kinase signaling, either by creating condensate structures that are sensed by kinases or by direct LLPS of kinases, cofactors, and substrates - thereby acting as a mechanism to compartmentalize kinase-substrate relationships, and in some cases also sequestering the kinase away from inhibitory factors. We also examine the possibility that selective pressure promotes genomic rearrangements that fuse pro-growth kinases to LLPS-prone protein sequences, which in turn drives aberrant kinase activation through LLPS.

Starvation Protects Hepatocytes from Inflammatory Damage through Paradoxical mTORC1 Signaling

Background and aims: Sepsis-related liver failure is associated with a particularly unfavorable clinical outcome. Calorie restriction is a well-established factor that can increase tissue resilience, protect against liver failure and improve outcome in preclinical models of bacterial sepsis. However, the underlying molecular basis is difficult to investigate in animal studies and remains largely unknown.

METHODS

We have used an immortalized hepatocyte line as a model of the liver parenchyma to uncover the role of caloric restriction in the resilience of hepatocytes to inflammatory cell damage. In addition, we applied genetic and pharmacological approaches to investigate the contribution of the three major intracellular nutrient/energy sensor systems, AMPK, mTORC1 and mTORC2, in this context.

RESULTS

We demonstrate that starvation reliably protects hepatocytes from cellular damage caused by pro-inflammatory cytokines. While the major nutrient- and energy-related signaling pathways AMPK, mTORC2/Akt and mTORC1 responded to caloric restriction as expected, mTORC1 was paradoxically activated by inflammatory stress in starved, energy-deprived hepatocytes. Pharmacological inhibition of mTORC1 or genetic silencing of the mTORC1 scaffold Raptor, but not its mTORC2 counterpart Rictor, abrogated the protective effect of starvation and exacerbated inflammation-induced cell death. Remarkably, mTORC1 activation in starved hepatocytes was uncoupled from the regulation of autophagy, but crucial for sustained protein synthesis in starved resistant cells.

CONCLUSIONS

AMPK engagement and paradoxical mTORC1 activation and signaling mediate protection against pro-inflammatory stress exerted by caloric restriction in hepatocytes.

RNA recruitment switches the fate of protein condensates from autophagic degradation to accumulation

Protein condensates can evade autophagic degradation under stress or pathological conditions. However, the underlying mechanisms are unclear. Here, we demonstrate that RNAs switch the fate of condensates in Caenorhabditis elegans. PGL granules undergo autophagic degradation in embryos laid under normal conditions and accumulate in embryos laid under heat stress conditions to confer stress adaptation. In heat-stressed embryos, mRNAs and RNA control factors partition into PGL granules. Depleting proteins involved in mRNA biogenesis and stability suppresses PGL granule accumulation and triggers their autophagic degradation, while loss of activity of proteins involved in RNA turnover facilitates accumulation. RNAs facilitate LLPS of PGL granules, enhance their liquidity, and also inhibit recruitment of the gelation-promoting scaffold protein EPG-2 to PGL granules. Thus, RNAs are important for controlling the susceptibility of phase-separated protein condensates to autophagic degradation. Our work provides insights into the accumulation of ribonucleoprotein aggregates associated with the pathogenesis of various diseases.

Stress granules: functions and mechanisms in cancer

Stress granules (SGs) are non-enveloped structures formed primarily via protein and RNA aggregation under various stress conditions, including hypoxia and viral infection, as well as oxidative, osmotic, and heat-shock stress. SGs assembly is a highly conserved cellular strategy to reduce stress-related damage and promote cell survival. At present, the composition and dynamics of SGs are well understood; however, data on the functions and related mechanisms of SGs are limited. In recent years, SGs have continued to attract attention as emerging players in cancer research. Intriguingly, SGs regulate the biological behavior of tumors by participating in various tumor-associated signaling pathways, including cell proliferation, apoptosis, invasion and metastasis, chemotherapy resistance, radiotherapy resistance, and immune escape. This review discusses the roles and mechanisms of SGs in tumors and suggests novel directions for cancer treatment.

Stress granules dynamics and promising functions in pancreatic cancer

Stress granules (SGs), non-membrane subcellular organelles made up of non-translational messenger ribonucleoproteins (mRNPs), assemble in response to various environmental stimuli in cancer cells, including pancreatic cancer, particularly pancreatic ductal adenocarcinoma (PDAC) which has a low 5-year survival rate of 10%. The pertinent research on SGs and pancreatic cancer has not, however, been compiled. In this review, we talk about the dynamics of SGs and their positive effects on pancreatic cancer such as SGs promote PDAC viability and repress apoptosis, meanwhile emphasizing the connection between SGs in pancreatic cancer and signature mutations such KRAS, P53, and SMAD4 as well as the functions of SGs in antitumor drug resistance. This novel stress management technique may open the door to better treatment options in the future.

RNA-targeted therapy corrects neuronal deficits in PACS1 syndrome mice

Neurodevelopmental disorders (NDDs) are frequently associated with dendritic abnormalities in pyramidal neurons that affect arbor complexity, spine density, and synaptic communication 1,2. The underlying genetic causes are often complex, obscuring the molecular pathways that drive these disorders 3. Next-generation sequencing has identified recurrent de novo missense mutations in a handful of genes associated with NDDs, offering a unique opportunity to decipher the molecular pathways 4. One such gene is PACS1, which encodes the multi-functional trafficking protein PACS1 (or PACS-1); a single recurrent de novo missense mutation, c607C>T (PACS1R203W), causes developmental delay and intellectual disability (ID) 5,6. The processes by which PACS1R203W causes PACS1 syndrome are unknown, and there is no curative treatment. We show that PACS1R203W increases the interaction between PACS1 and the α-tubulin deacetylase HDAC6, elevating enzyme activity and appropriating control of its posttranscriptional regulation. Consequently, PACS1R203W reduces acetylation of α-tubulin and cortactin, causing the Golgi to fragment and enter developing neurites, leading to increased dendrite arborization. The dendrites, however, are beset with diminished spine density and fewer functional synapses, characteristic of ID pathology. Treatment of PACS1 syndrome mice with PACS1- or HDAC6-targeting antisense oligonucleotides restores neuronal structure and synaptic transmission, suggesting PACS1R203W/HDAC6 may be targeted for treating PACS1 syndrome neuropathology.

Stress Granules in Cancer

The capacity of cells to organize complex biochemical reactions in intracellular space is a fundamental organizational principle of life. Key to this organization is the compartmentalization of the cytoplasm into distinct organelles, which is frequently achieved through intracellular membranes. Recent evidence, however, has added a new layer of flexibility to cellular compartmentalization. As such, in response to specific stimuli, liquid-liquid phase separations can lead to the rapid rearrangements of the cytoplasm to form membraneless organelles. Stress granules (SGs) are one such type of organelle that form specifically when cells are faced with stress stimuli, to aid cells in coping with stress. Inherently, altered SG formation has been linked to the pathogenesis of diseases associated with stress and inflammatory conditions, including cancer. Exciting discoveries have indicated an intimate link between SGs and tumorigenesis. Several pro-tumorigenic signaling molecules including the RAS oncogene, mTOR, and histone deacetylase 6 (HDAC6) have been shown to upregulate SG formation. Based on these studies, SGs have emerged as structures that can integrate oncogenic signaling and tumor-associated stress stimuli to enhance cancer cell fitness. In addition, growing evidence over the past decade suggests that SGs function not only to regulate the switch between survival and cell death, but also contribute to cancer cell proliferation, invasion, metastasis, and drug resistance. Although much remains to be learned about the role of SGs in tumorigenesis, these studies highlight SGs as a key regulatory hub in cancer and a promising therapeutic target.

Stress granules dynamics: benefits in cancer

Stress granules (SGs) are stress-induced subcellular compartments, which carry out a particular function to cope with stress. These granules protect cells from stress-related damage and cell death through dynamic sequestration of numerous ribonucleoproteins (RNPs) and signaling proteins, thereby promoting cell survival under both physiological and pathological condition. During tumorigenesis, cancer cells are repeatedly exposed to diverse stress stimuli from the tumor microenvironment, and the dynamics of SGs is often modulated due to the alteration of gene expression patterns in cancer cells, leading to tumor progression as well as resistance to anticancer treatment. In this mini review, we provide a brief discussion about our current understanding of the fundamental roles of SGs during physiological stress and the effect of dysregulated SGs on cancer cell fitness and cancer therapy. [BMB Reports 2022; 55(12): 577-586].

The pleiotropic roles of eIF5A in cellular life and its therapeutic potential in cancer

Protein synthesis is dysregulated in the majority of cancers and this process therefore provides a good therapeutic target. Many novel anti-cancer agents are directed to target the initiation stage of translation, however, translation elongation also holds great potential as a therapeutic target. The elongation factor eIF5A that assists the formation of peptidyl bonds during the elongation process is of considerable interest in this regard. Overexpression of eIF5A has been linked with the development of a variety of cancers and inhibitors of the molecule have been proposed for anti-cancer clinical applications. eIF5A is the only protein in the cell that contains the post-translational modification hypusine. Hypusination is a two-step enzymatic process catalysed by the Deoxyhypusine Synthase (DHPS) and Deoxyhypusine Hydroxylase (DOHH). In addition, eIF5A can be acetylated by p300/CBP-associated factor (PCAF) which leads to translocation of the protein to the nucleus and its deactivation. In addition to the nucleus, eIF5A has been found in the mitochondria and the endoplasmic reticulum (ER) with eIF5A localisation related to function from regulation of mitochondrial activity and apoptosis to maintenance of ER integrity and control of the unfolded protein response (UPR). Given the pleiotropic functions of eIF5A and by extension the hypusination enzymes, this system is being considered as a target for a range of cancers including multiple myeloma, B-Cell lymphoma, and neuroblastoma. In this review, we explore the role of eIF5A and discuss the therapeutic strategies that are currently developing both in the pre- and the clinical stage.

An emerging role for stress granules in neurodegenerative disease and hearing loss

Stress granules (SGs) are membrane-less cytosolic assemblies that form in response to stress (e.g., heat, oxidative stress, hypoxia, viral infection and UV). Composed of mRNA, RNA binding proteins and signalling proteins, SGs minimise stress-related damage and promote cell survival. Recent research has shown that the stress granule response is vital to the cochlea's response to stress. However, emerging evidence suggests stress granule dysfunction plays a key role in the pathophysiology of multiple neurodegenerative diseases, several of which present with hearing loss as a symptom. Hearing loss has been identified as the largest potentially modifiable risk factor for dementia. The underlying reason for the link between hearing loss and dementia remains to be established. However, several possible mechanisms have been proposed including a common pathological mechanism. Here we will review the role of SGs in the pathophysiology of neurodegenerative diseases and explore possible links and emerging evidence that they may play an important role in maintenance of hearing and may be a common mechanism underlying age-related hearing loss and dementia.

Stress granules dynamics: benefits in cancer

Stress granules (SGs) are stress-induced subcellular compartments, which carry out a particular function to cope with stress. These granules protect cells from stress-related damage and cell death through dynamic sequestration of numerous ribonucleoproteins (RNPs) and signaling proteins, thereby promoting cell survival under both physiological and pathological condition. During tumorigenesis, cancer cells are repeatedly exposed to diverse stress stimuli from the tumor microenvironment, and the dynamics of SGs is often modulated due to the alteration of gene expression patterns in cancer cells, leading to tumor progression as well as resistance to anticancer treatment. In this mini review, we provide a brief discussion about our current understanding of the fundamental roles of SGs during physiological stress and the effect of dysregulated SGs on cancer cell fitness and cancer therapy. [BMB Reports 2022; 55(12): 577-586].

S6 kinase 1 at the central node of cell size and ageing

Genetic evidence in living organisms from yeast to plants and animals, including humans, unquestionably identifies the Target Of Rapamycin kinase (TOR or mTOR for mammalian/mechanistic) signal transduction pathway as a master regulator of growth through the control of cell size and cell number. Among the mTOR targets, the activation of p70 S6 kinase 1 (S6K1) is exquisitely sensitive to nutrient availability and rapamycin inhibition. Of note, in vivo analysis of mutant flies and mice reveals that S6K1 predominantly regulates cell size versus cell proliferation. Here we review the putative mechanisms of S6K1 action on cell size by considering the main functional categories of S6K1 targets: substrates involved in nucleic acid and protein synthesis, fat mass accumulation, retrograde control of insulin action, senescence program and cytoskeleton organization. We discuss how S6K1 may be involved in the observed interconnection between cell size, regenerative and ageing responses.

Stress Granules Determine the Development of Obesity-Associated Pancreatic Cancer

Obesity is a global epidemic and a major predisposing factor for cancer. Increasing evidence shows that obesity-associated stress is a key driver of cancer risk and progression. Previous work has identified the phase-separation organelles, stress granules (SG), as mutant KRAS-dependent mediators of stress adaptation. However, the dependence of tumorigenesis on these organelles is unknown. Here, we establish a causal link between SGs and pancreatic ductal adenocarcinoma (PDAC). Importantly, we uncover that dependence on SGs is drastically heightened in obesity-associated PDAC. Furthermore, we identify a previously unknown regulator and component of SGs, namely, the serine/arginine protein kinase 2 (SRPK2), as a specific determinant of SG formation in obesity-associated PDAC. We show that SRPK2-mediated SG formation in obesity-associated PDAC is driven by hyperactivation of the IGF1/PI3K/mTOR/S6K1 pathway and that S6K1 inhibition selectively attenuates SGs and impairs obesity-associated PDAC development.

SIGNIFICANCE

: We show that stress adaptation via the phase-separation organelles SGs mediates PDAC development. Moreover, preexisting stress conditions such as obesity are a driving force behind tumor SG dependence, and enhanced SG levels are key determinants and a chemopreventive target for obesity-associated PDAC. This article is highlighted in the In This Issue feature, p. 1825.

Beyond controlling cell size: functional analyses of S6K in tumorigenesis

As a substrate and major effector of the mammalian target of rapamycin complex 1 (mTORC1), the biological functions of ribosomal protein S6 kinase (S6K) have been canonically assigned for cell size control by facilitating mRNA transcription, splicing, and protein synthesis. However, accumulating evidence implies that diverse stimuli and upstream regulators modulate S6K kinase activity, leading to the activation of a plethora of downstream substrates for distinct pathobiological functions. Beyond controlling cell size, S6K simultaneously plays crucial roles in directing cell apoptosis, metabolism, and feedback regulation of its upstream signals. Thus, we comprehensively summarize the emerging upstream regulators, downstream substrates, mouse models, clinical relevance, and candidate inhibitors for S6K and shed light on S6K as a potential therapeutic target for cancers.

High expression of eIF4A1 predicts unfavorable prognosis in clear cell renal cell carcinoma

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is a worldwide malignancy with high morbidity and mortality. Translation initiation factor 4A1 (eIF4A1), which is an ATP-dependent RNA helicase as a part of eIF4F complex, has been linked to malignant transformation and progression, and a variety of cancers display dysregulation of this enzyme. However, its role in ccRCC remains unclear. In our study, we examined its potential effects in ccRCC.

METHODS

Based on Proteomic data, TCGA and ONCOMINE database, RCC cell lines and tissues, the expression of eIF4A1 between ccRCC and normal tissues were investigated. A correlation was evaluated between the prognostic model for OS and ccRCC progression. Analysis of functional enrichment and PPI network were performed. After examining differentially expressed genes between the eIF4A1 high and low-expression groups, we performed GSEA analysis. Furthermore, we investigated immune cell infiltration of eIF4A1. Then we determined eIF4A1 functions in the establishment and maintenance of cell viability, migration and invasion of cell lines. Flow cytometry was utilized to detect cell cycle.

RESULTS

The eIF4A1 was up-regulated in ccRCC tissues and cell lines. An increased level of eIF4A1 was linked to lower survival rates and impaired immunity. Depletion of eIF4A1 could arrest tumor cells in G1 phase, so as to seriously limit cell proliferation and weaken the capacity of cell migration.

CONCLUSION

ccRCC patients with high eIF4A1 expression are at increased risk of poor prognosis, furthermore eIF4A1 plays a prominent role in facilitating tumor cell proliferation and migration which may further be a potential prognostic biomarker and therapeutic target.

Regulation of Cellular Ribonucleoprotein Granules: From Assembly to Degradation via Post-translational Modification

Cells possess membraneless ribonucleoprotein (RNP) granules, including stress granules, processing bodies, Cajal bodies, or paraspeckles, that play physiological or pathological roles. RNP granules contain RNA and numerous RNA-binding proteins, transiently formed through the liquid–liquid phase separation. The assembly or disassembly of numerous RNP granules is strongly controlled to maintain their homeostasis and perform their cellular functions properly. Normal RNA granules are reversibly assembled, whereas abnormal RNP granules accumulate and associate with various neurodegenerative diseases. This review summarizes current studies on the physiological or pathological roles of post-translational modifications of various cellular RNP granules and discusses the therapeutic methods in curing diseases related to abnormal RNP granules by autophagy.

CRISPR/Cas9-Mediated Constitutive Loss of VCP (Valosin-Containing Protein) Impairs Proteostasis and Leads to Defective Striated Muscle Structure and Function In Vivo

Valosin-containing protein (VCP) acts as a key regulator of cellular protein homeostasis by coordinating protein turnover and quality control. Mutations in VCP lead to (cardio-)myopathy and neurodegenerative diseases such as inclusion body myopathy with Paget’s disease of the bone and frontotemporal dementia (IBMPFD) or amyotrophic lateral sclerosis (ALS). To date, due to embryonic lethality, no constitutive VCP knockout animal model exists. Here, we generated a constitutive CRISPR/Cas9-induced vcp knockout zebrafish model. Similar to the phenotype of vcp morphant knockdown zebrafish embryos, we found that vcp-null embryos displayed significantly impaired cardiac and skeletal muscle function. By ultrastructural analysis of skeletal muscle cells and cardiomyocytes, we observed severely disrupted myofibrillar organization and accumulation of inclusion bodies as well as mitochondrial degeneration. vcp knockout was associated with a significant accumulation of ubiquitinated proteins, suggesting impaired proteasomal function. Additionally, markers of unfolded protein response (UPR)/ER-stress and autophagy-related mTOR signaling were elevated in vcp-deficient embryos, demonstrating impaired proteostasis in VCP-null zebrafish. In conclusion, our findings demonstrate the successful generation of a stable constitutive vcp knockout zebrafish line that will enable characterization of the detailed mechanistic underpinnings of vcp loss, particularly the impact of disturbed protein homeostasis on organ development and function in vivo.

Pathophysiology of stress granules: An emerging link to diseases (Review)

Under unfavorable environmental conditions, eukaryotic cells may form stress granules (SGs) in the cytosol to protect against injury and promote cell survival. The initiation, mRNA and protein composition, distribution and degradation of SGs are subject to multiple intracellular post-translational modifications and signaling pathways to cope with stress damage. Despite accumulated comprehensive knowledge of their composition and dynamics, the function of SGs remains poorly understood. When the stress persists, aberrant and/or persistent intracellular SGs and aggregation of SGs-related proteins may lead to various diseases. In the present article, the research progress regarding the generation, modification and function of SGs was reviewed. The regulatory effects and influencing factors of SGs in the development of tumors, cardiovascular diseases, viral infections and neurodegenerative diseases were also summarized, which may provide novel insight for preventing and treating SG-related diseases.

Harnessing stress granule formation by small molecules to inhibit the cellular replication of SARS-CoV-2

We identified small-molecule enhancers of cellular stress granules by observing molecular crowding of proteins and RNAs in a time-dependent manner. Hit molecules sensitized the IRF3-mediated antiviral mechanism in the presence of poly(I:C) and inhibited the replication of SARS-CoV-2 by inducing stress granule formation. Thus, modulating multimolecular crowding can be a promising strategy against SARS-CoV-2.

PQN-59 and GTBP-1 contribute to stress granule formation but are not essential for their assembly in C. elegans embryos

When exposed to stressful conditions, eukaryotic cells respond by inducing the formation of cytoplasmic ribonucleoprotein complexes called stress granules. Here, we use C. elegans to study two proteins that are important for stress granule assembly in human cells – PQN-59, the human UBAP2L ortholog, and GTBP-1, the human G3BP1 and G3BP2 ortholog. Both proteins assemble into stress granules in the embryo and in the germline when C. elegans is exposed to stressful conditions. Neither of the two proteins is essential for the assembly of stress-induced granules, as shown by the single and combined depletions by RNAi, and neither pqn-59 nor gtbp-1 mutant embryos show higher sensitivity to stress than control embryos. We find that pqn-59 mutants display reduced progeny and a high percentage of embryonic lethality, phenotypes that are not dependent on stress exposure and that are not shared with gtbp-1 mutants. Our data indicate that, in contrast to human cells, PQN-59 and GTBP-1 are not required for stress granule formation but that PQN-59 is important for C. elegans development.

Summary: In contrast to human cells, where the UBAP2L and G3BP1 and G3BP2 proteins are crucial nucleators of stress granules, the C. elegans orthologs are not essential for this process in worms.

Resveratrol and related stilbene derivatives induce stress granules with distinct clearance kinetics

Stress granules (SGs) are ribonucleoprotein functional condensates that form under stress conditions in all eukaryotic cells. Although their stress-survival function is far from clear, SGs have been implicated in the regulation of many vital cellular pathways. Consequently, SG dysfunction is thought to be a mechanistic point of origin for many neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). Additionally, SGs are thought to play a role in pathogenic pathways as diverse as viral infection and chemotherapy resistance. There is a growing consensus on the hypothesis that understanding the mechanistic regulation of SG physical properties is essential to understanding their function. Although the internal dynamics and condensation mechanisms of SGs have been broadly investigated, there have been fewer investigations into the timing of SG formation and clearance in live cells. Because the lifetime of SG persistence can be a key factor in their function and tendency toward pathological dysregulation, SG clearance mechanisms deserve particular attention. Here we show that resveratrol and its analogues piceatannol, pterostilbene, and 3,4,5,4'-tetramethoxystilbene induce G3BP-dependent SG formation with atypically rapid clearance kinetics. Resveratrol binds to G3BP, thereby reducing its protein-protein association valency. We suggest that altering G3BP valency is a pathway for the formation of uniquely transient SGs.

The TSC Complex-mTORC1 Axis: From Lysosomes to Stress Granules and Back

The tuberous sclerosis protein complex (TSC complex) is a key integrator of metabolic signals and cellular stress. In response to nutrient shortage and stresses, the TSC complex inhibits the mechanistic target of rapamycin complex 1 (mTORC1) at the lysosomes. mTORC1 is also inhibited by stress granules (SGs), RNA-protein assemblies that dissociate mTORC1. The mechanisms of lysosome and SG recruitment of mTORC1 are well studied. In contrast, molecular details on lysosomal recruitment of the TSC complex have emerged only recently. The TSC complex subunit 1 (TSC1) binds lysosomes via phosphatidylinositol-3,5-bisphosphate [PI(3,5)P2]. The SG assembly factors 1 and 2 (G3BP1/2) have an unexpected lysosomal function in recruiting TSC2 when SGs are absent. In addition, high density lipoprotein binding protein (HDLBP, also named Vigilin) recruits TSC2 to SGs under stress. In this mini-review, we integrate the molecular mechanisms of lysosome and SG recruitment of the TSC complex. We discuss their interplay in the context of cell proliferation and migration in cancer and in the clinical manifestations of tuberous sclerosis complex disease (TSC) and lymphangioleiomyomatosis (LAM).

Phosphorylation Regulates CIRBP Arginine Methylation, Transportin-1 Binding and Liquid-Liquid Phase Separation

Arginine-glycine(-glycine) (RG/RGG) regions are highly abundant in RNA-binding proteins and involved in numerous physiological processes. Aberrant liquid-liquid phase separation (LLPS) and stress granule (SGs) association of RG/RGG regions in the cytoplasm have been implicated in several neurodegenerative disorders. LLPS and SG association of these proteins is regulated by the interaction with nuclear import receptors, such as transportin-1 (TNPO1), and by post-translational arginine methylation. Strikingly, many RG/RGG proteins harbour potential phosphorylation sites within or close to their arginine methylated regions, indicating a regulatory role. Here, we studied the role of phosphorylation within RG/RGG regions on arginine methylation, TNPO1-binding and LLPS using the cold-inducible RNA-binding protein (CIRBP) as a paradigm. We show that the RG/RGG region of CIRBP is in vitro phosphorylated by serine-arginine protein kinase 1 (SRPK1), and discovered two novel phosphorylation sites in CIRBP. SRPK1-mediated phosphorylation of the CIRBP RG/RGG region impairs LLPS and binding to TNPO1 in vitro and interferes with SG association in cells. Furthermore, we uncovered that arginine methylation of the CIRBP RG/RGG region regulates in vitro phosphorylation by SRPK1. In conclusion, our findings indicate that LLPS and TNPO1-mediated chaperoning of RG/RGG proteins is regulated through an intricate interplay of post-translational modifications.

mTORC1 Crosstalk With Stress Granules in Aging and Age-Related Diseases

The mechanistic target of rapamycin complex 1 (mTORC1) kinase is a master regulator of metabolism and aging. A complex signaling network converges on mTORC1 and integrates growth factor, nutrient and stress signals. Aging is a dynamic process characterized by declining cellular survival, renewal, and fertility. Stressors elicited by aging hallmarks such as mitochondrial malfunction, loss of proteostasis, genomic instability and telomere shortening impinge on mTORC1 thereby contributing to age-related processes. Stress granules (SGs) constitute a cytoplasmic non-membranous compartment formed by RNA-protein aggregates, which control RNA metabolism, signaling, and survival under stress. Increasing evidence reveals complex crosstalk between the mTORC1 network and SGs. In this review, we cover stressors elicited by aging hallmarks that impinge on mTORC1 and SGs. We discuss their interplay, and we highlight possible links in the context of aging and age-related diseases.

Stress Granules Involved in Formation, Progression and Metastasis of Cancer: A Scoping Review

The assembly of stress granules (SGs) is a well-known cellular strategy for reducing stress-related damage and promoting cell survival. SGs have become important players in human health, in addition to their fundamental role in the stress response. The critical role of SGs in cancer cells in formation, progression, and metastasis makes sense. Recent researchers have found that several SG components play a role in tumorigenesis and cancer metastasis via tumor-associated signaling pathways and other mechanisms. Gene-ontology analysis revealed the role of these protein components in the structure of SGs. Involvement in the translation process, regulation of mRNA stability, and action in both the cytoplasm and nucleus are among the main features of SG proteins. The present scoping review aimed to consider all studies on the effect of SGs on cancer formation, proliferation, and metastasis and performed based on a six-stage methodology structure and the PRISMA guideline. A systematic search of seven databases for qualified articles was conducted before July 2021. Publications were screened, and quantitative and qualitative analysis was performed on the extracted data. Go analysis was performed on seventy-one SGs protein components. Remarkably G3BP1, TIA1, TIAR, and YB1 have the largest share among the proteins considered in the studies. Altogether, this scoping review tries to demonstrate and provide a comprehensive summary of the role of SGs in the formation, progression, and metastasis of cancer by reviewing all studies.

The Emerging Role of Stress Granules in Hepatocellular Carcinoma

Stress granules (SGs) are small membrane-free cytosolic liquid-phase ordered entities in which mRNAs are protected and translationally silenced during cellular adaptation to harmful conditions (e.g., hypoxia, oxidative stress). This function is achieved by structural and functional SG components such as scaffold proteins and RNA-binding proteins controlling the fate of mRNAs. Increasing evidence indicates that the capacity of cells to assemble/disassemble functional SGs may significantly impact the onset and the development of metabolic and inflammatory diseases, as well as cancers. In the liver, the abnormal expression of SG components and formation of SG occur with chronic liver diseases, hepatocellular carcinoma (HCC), and selective hepatic resistance to anti-cancer drugs. Although, the role of SG in these diseases is still debated, the modulation of SG assembly/disassembly or targeting the expression/activity of specific SG components may represent appealing strategies to treat hepatic disorders and potentially cancer. In this review, we discuss our current knowledge about pathophysiological functions of SGs in HCC as well as available molecular tools and drugs capable of modulating SG formation and functions for therapeutic purposes.

Bifenthrin reduces pregnancy potential via induction of oxidative stress in porcine trophectoderm and uterine luminal epithelial cells

Exposure to pesticides has become a serious concern for the environment and human health. Bifenthrin, a synthetic pyrethroid pesticide, is one of the most frequently used pesticides worldwide. Despite the toxic potential of bifenthrin, no studies have elucidated the cytotoxic response of bifenthrin in maternal and fetal cells that are involved in the implantation process. In this study, the cytotoxic effect of bifenthrin was investigated using porcine trophectoderm (pTr) and uterine luminal epithelial (pLE) cells. The results showed that bifenthrin suppressed cell proliferation and viability in pTr and pLE cells. In particular, bifenthrin induced cell cycle arrest, resulting in apoptosis in both cell lines. We found that bifenthrin damaged the mitochondria and induced the production of reactive oxygen species, causing endoplasmic reticulum stress and calcium dysregulation in pTr and pLE cells. Finally, bifenthrin altered the MAPK/PI3K signaling pathway and pregnancy-related gene expression. Collectively, our results suggest that bifenthrin reduces the implantation potential of embryos and may help elucidate the mechanisms underlying toxin-derived cytotoxicity in maternal and fetal cells.

Lamin regulates the dietary restriction response via the mTOR pathway in Caenorhabditis elegans

Animals subjected to dietary restriction (DR) have reduced body size, low fecundity, slower development, lower fat content and longer life span. We identified lamin as a regulator of multiple dietary restriction phenotypes. Downregulation of lmn-1, the single Caenorhabditis elegans lamin gene, increased animal size and fat content specifically in DR animals. The LMN-1 protein acts in the mTOR pathway, upstream of RAPTOR and S6 kinase β1 (S6K), a key component of and target of the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1), respectively. DR excludes the mTORC1 activator RAGC-1 from the nucleus. Downregulation of lmn-1 restores RAGC-1 to the nucleus, a necessary step for the activation of the mTOR pathway. These findings further link lamin to metabolic regulation.

Summary: Downregulation of the single C. elegans lamin gene increases animal size and fat content specifically in dietary restricted animals. The lamin protein acts in the mTOR pathway to regulate these phenotypes.

Stress granules inhibit fatty acid oxidation by modulating mitochondrial permeability

The formation of stress granules (SGs) is an essential aspect of the cellular response to many kinds of stress, but its adaptive role is far from clear. SG dysfunction is implicated in aging-onset neurodegenerative diseases, prompting interest in their physiological function. Here, we report that during starvation stress, SGs interact with mitochondria and regulate metabolic remodeling. We show that SG formation leads to a downregulation of fatty acid β-oxidation (FAO) through the modulation of mitochondrial voltage-dependent anion channels (VDACs), which import fatty acids (FAs) into mitochondria. The subsequent decrease in FAO during long-term starvation reduces oxidative damage and rations FAs for longer use. Failure to form SGs, whether caused by the genetic deletion of SG components or an amyotrophic lateral sclerosis (ALS)-associated mutation, translates into an inability to downregulate FAO. Because metabolic dysfunction is a common pathological element of neurodegenerative diseases, including ALS, our findings provide a direction for studying the clinical relevance of SGs.

Hiding in Plain Sight: Formation and Function of Stress Granules During Microbial Infection of Mammalian Cells

Stress granule (SG) formation is a host cell response to stress-induced translational repression. SGs assemble with RNA-binding proteins and translationally silent mRNA. SGs have been demonstrated to be both inhibitory to viruses, as well as being subverted for viral roles. In contrast, the function of SGs during non-viral microbial infections remains largely unexplored. A handful of microbial infections have been shown to result in host SG assembly. Nevertheless, a large body of evidence suggests SG formation in hosts is a widespread response to microbial infection. Diverse stresses caused by microbes and their products can activate the integrated stress response in order to inhibit translation initiation through phosphorylation of the eukaryotic translation initiation factor 2α (eIF2α). This translational response in other contexts results in SG assembly, suggesting that SG assembly can be a general phenomenon during microbial infection. This review explores evidence for host SG formation in response to bacterial, fungal, and protozoan infection and potential functions of SGs in the host and for adaptations of the pathogen.

TSC2 Interacts with HDLBP/Vigilin and Regulates Stress Granule Formation

Tuberous sclerosis complex (TSC) is caused by mutations of either the TSC1 or TSC2 tumor suppressor gene. TSC causes tumors of the brain, heart, kidney, skin and lymphangioleiomyomatosis (LAM). Here we report that the TSC2 protein physically binds to high-density lipoprotein binding protein (HDLBP), also called vigilin, a core stress granule (SG) protein, and that TSC2 localizes to SGs. SGs contain mRNAs and translation initiation complexes, and regulate gene expression by sequestering specific transcripts, thereby serving a cytoprotective role. TSC2 has never before been shown to localize to SGs and knocking down vigilin impacts SG translocation of TSC2. TSC2-deficient cells showed a striking increase in the number of SGs after thermal shock and arsenite treatment relative to Tsc2-expressing cells. Our findings also show that murine kidney lysates from a model of TSC have increased levels of SG components including G3BP1 and Caprin1. G3BP1 and Caprin are elevated in renal angiomyolipomas (a renal tumor common in patients with TSC) compared with control normal kidney. G3BP1 is also elevated in TSC-associated subependymal giant cell astrocytomas. We found that genetic inhibition of G3BP1 inhibits the proliferation of TSC2-deficient cells in vitro. Finally, in a mouse model of TSC, genetic inhibition of SGs suppresses cell growth, suggesting that targeting SGs may have efficacy in the therapy of TSC. IMPLICATIONS: This study demonstrates that TSC2 physically interacts with HDLBP/vigilin, a component of SGs, that TSC2 localizes to SG and that TSC2-deficient cells have more SGs, suggesting that SGs represent a novel therapeutic target in TSC.

Small Molecule Screen Reveals Joint Regulation of Stress Granule Formation and Lipid Droplet Biogenesis

Metabolic regulation is a necessary component of all stress response pathways, because all different mechanisms of stress-adaptation place high-energy demands on the cell. Mechanisms that integrate diverse stress response pathways with their metabolic components are therefore of great interest, but few are known. We show that stress granule (SG) formation, a common adaptive response to a variety of stresses, is reciprocally regulated by the pathways inducing lipid droplet accumulation. Inability to upregulate lipid droplets reduces stress granule formation. Stress granule formation in turn drives lipid droplet clustering and fatty acid accumulation. Our findings reveal a novel connection between stress response pathways and new modifiers of stress granule formation.

G3BPs tether the TSC complex to lysosomes and suppress mTORC1 signaling

Ras GTPase-activating protein-binding proteins 1 and 2 (G3BP1 and G3BP2, respectively) are widely recognized as core components of stress granules (SGs). We report that G3BPs reside at the cytoplasmic surface of lysosomes. They act in a non-redundant manner to anchor the tuberous sclerosis complex (TSC) protein complex to lysosomes and suppress activation of the metabolic master regulator mechanistic target of rapamycin complex 1 (mTORC1) by amino acids and insulin. Like the TSC complex, G3BP1 deficiency elicits phenotypes related to mTORC1 hyperactivity. In the context of tumors, low G3BP1 levels enhance mTORC1-driven breast cancer cell motility and correlate with adverse outcomes in patients. Furthermore, G3bp1 inhibition in zebrafish disturbs neuronal development and function, leading to white matter heterotopia and neuronal hyperactivity. Thus, G3BPs are not only core components of SGs but also a key element of lysosomal TSC-mTORC1 signaling.

Mechanism and effect of stress granule formation in cancer and its potential roles in breast cancer therapy

Stress granules are non-membranous cytoplasmic foci induced by various stress conditions. It is a protective strategy used by cells to suppress overall translation during stress. In cancer cells, it was thought that the formation of stress granules could protect them from apoptosis and induces resistance towards anti-cancer drugs or radiation treatment which makes the stress granules a potential target for cancer treatment. However, most of our understanding of stress granules are still in the stage of molecular and cell biology, and a transitional gap for its actual effect on clinical settings remains. In this review, we summarize the mechanism and effect of stress granules formation in cancer and try to illuminate its potential applications in cancer therapy, using breast cancer as an example.

A prion-like domain of Tpk2 catalytic subunit of protein kinase A modulates P-body formation in response to stress in budding yeast

Low complexity regions are involved in the assembly and disassembly of P-bodies (PBs). Saccharomyces cerevisiae contains three genes encoding the protein kinase A (PKA) catalytic subunit: TPK1, TPK2 and TPK3. Tpk2 and Tpk3 isoforms localize to PBs upon glucose starvation showing different mechanisms and kinetics of accumulation. In contrast to the other two isoforms, Tpk2 harbors a glutamine-rich prion-like domain (PrLD) at the N-terminus. Here we show that the appearance of Tpk2 foci in response to glucose starvation, heat stress or stationary phase was dependent on its PrLD. Moreover, the PrLD of Tpk2 was necessary for efficient PB and stress granule aggregation during stress conditions and in quiescent cells. Deletion of PrLD does not affect the in vitro and in vivo kinase activity of Tpk2 or its interaction with the regulatory subunit Bcy1. We present evidence that the PrLD of Tpk2 serves as a scaffold domain for PB assembly in a manner that is independent of Pat1 phosphorylation by PKA. In addition, a mutant strain where Tpk2 lacks PrLD showed a decrease of turnover of mRNA during glucose starvation. This work therefore provides new insight into the mechanism of stress-induced cytoplasmic mRNP assembly, and the role of isoform specific domains in the regulation of PKA catalytic subunit specificity and dynamic localization to cytoplasmic RNPs granules.

LSM12-EPAC1 defines a neuroprotective pathway that sustains the nucleocytoplasmic RAN gradient

Nucleocytoplasmic transport (NCT) defects have been implicated in neurodegenerative diseases such as C9ORF72-associated amyotrophic lateral sclerosis and frontotemporal dementia (C9-ALS/FTD). Here, we identify a neuroprotective pathway of like-Sm protein 12 (LSM12) and exchange protein directly activated by cyclic AMP 1 (EPAC1) that sustains the nucleocytoplasmic RAN gradient and thereby suppresses NCT dysfunction by the C9ORF72-derived poly(glycine-arginine) protein. LSM12 depletion in human neuroblastoma cells aggravated poly(GR)-induced impairment of NCT and nuclear integrity while promoting the nuclear accumulation of poly(GR) granules. In fact, LSM12 posttranscriptionally up-regulated EPAC1 expression, whereas EPAC1 overexpression rescued the RAN gradient and NCT defects in LSM12-deleted cells. C9-ALS patient-derived neurons differentiated from induced pluripotent stem cells (C9-ALS iPSNs) displayed low expression of LSM12 and EPAC1. Lentiviral overexpression of LSM12 or EPAC1 indeed restored the RAN gradient, mitigated the pathogenic mislocalization of TDP-43, and suppressed caspase-3 activation for apoptosis in C9-ALS iPSNs. EPAC1 depletion biochemically dissociated RAN-importin β1 from the cytoplasmic nuclear pore complex, thereby dissipating the nucleocytoplasmic RAN gradient essential for NCT. These findings define the LSM12-EPAC1 pathway as an important suppressor of the NCT-related pathologies in C9-ALS/FTD.

A post-transcriptional circuit comprising LSM12 and EPAC1 suppresses neurodegenerative pathologies in C9ORF72-associated amyotrophic lateral sclerosis by establishing the RAN gradient and sustaining nucleocytoplasmic transport.

Stress granules in colorectal cancer: Current knowledge and potential therapeutic applications

Stress granules (SGs) represent important non-membrane cytoplasmic compartments, involved in cellular adaptation to various stressful conditions (e.g., hypoxia, nutrient deprivation, oxidative stress). These granules contain several scaffold proteins and RNA-binding proteins, which bind to mRNAs and keep them translationally silent while protecting them from harmful conditions. Although the role of SGs in cancer development is still poorly known and vary between cancer types, increasing evidence indicate that the expression and/or the activity of several key SGs components are deregulated in colorectal tumors but also in pre-neoplastic conditions (e.g., inflammatory bowel disease), thus suggesting a potential role in the onset of colorectal cancer (CRC). It is therefore believed that SGs formation importantly contributes to various steps of colorectal tumorigenesis but also in chemoresistance. As CRC is the third most frequent cancer and one of the leading causes of cancer mortality worldwide, development of new therapeutic targets is needed to offset the development of chemoresistance and formation of metastasis. Abolishing SGs assembly may therefore represent an appealing therapeutic strategy to re-sensitize colon cancer cells to anti-cancer chemotherapies. In this review, we summarize the current knowledge on SGs in colorectal cancer and the potential therapeutic strategies that could be employed to target them.

Fasnall Induces Atypically Transient Stress Granules Independently of FASN Inhibition

Stress Granule formation has been linked to the resistance of some cancer cells to chemotherapeutic intervention. A number of studies have proposed that certain anti-tumor compounds promote cancer cell survival by inducing Stress Granule formation, leading to increased cellular fitness and apoptosis avoidance. Here we show that a potent fatty acid synthase inhibitor, fasnall, known for its anti-tumor capabilities, triggers the formation of atypical Stress Granules, independently of fatty acid synthase inhibition, characterized by high internal mobility and rapid turnover.

Understanding the roles of stress granule during chemotherapy for patients with malignant tumors

The assembly of stress granules (SGs) is a conserved mechanism to regulate protein synthesis under cell stress, where the translation of global protein is silenced and selective protein synthesis for survival maintains. SG formation confers survival advantages and chemotherapeutic resistance to malignant cells. Targeting SG assembly may represent a potential treatment strategy to overcome the primary and acquired chemotherapeutic resistance and enhance curative effect. We conduct a comprehensive review of the published literatures focusing on the drugs that potentially induce SGs and the related mechanism, retrospect the relationship between SGs and drug resistance related proteins, illuminate the regulated pathways and potential targets for SG assembly, and discuss future directions of overcoming the resistance to chemotherapy.