Heat shock proteins-driven stress granule dynamics: yet another avenue for cell survival

Neurodevelopmental disorder-associated CYFIP2 regulates membraneless organelles and eIF2α phosphorylation via protein interactors and actin cytoskeleton

De novo variants in the Cytoplasmic FMR1-interacting protein 2 (CYFIP2) have been repeatedly associated with neurodevelopmental disorders and epilepsy, underscoring its critical role in brain development and function. While CYFIP2's role in regulating actin polymerization as part of the WAVE regulatory complex (WRC) is well-established, its additional molecular functions remain relatively unexplored. In this study, we performed unbiased quantitative proteomic analysis, revealing 278 differentially expressed proteins (DEPs) in the forebrain of Cyfip2 knock-out embryonic mice compared to wild-type mice. Unexpectedly, these DEPs, in conjunction with previously identified CYFIP2 brain interactors, included not only other WRC components but also numerous proteins associated with membraneless organelles (MLOs) involved in mRNA processing and translation within cells, including the nucleolus, stress granules, and processing bodies. Additionally, single-cell transcriptomic analysis of the Cyfip2 knock-out forebrain revealed gene expression changes linked to cellular stress responses and MLOs. We also observed morphological changes in MLOs in Cyfip2 knock-out brains and CYFIP2 knock-down cells under basal and stress conditions. Lastly, we demonstrated that CYFIP2 knock-down in cells, potentially through WRC-dependent actin regulation, suppressed the phosphorylation levels of the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α), thereby enhancing protein synthesis. These results suggest a physical and functional connection between CYFIP2 and various MLO proteins and also extend CYFIP2's role within the WRC from actin regulation to influencing eIF2α phosphorylation and protein synthesis. With these dual functions, CYFIP2 may fine-tune the balance between MLO formation/dynamics and protein synthesis, a crucial aspect of proper mRNA processing and translation.

Biological resilience in health and disease

All living organisms - from single-celled prokaryotes through to invertebrates and humans - are frequently exposed to numerous challenges during their lifetime, which could damage their molecular and cellular contents and threaten their survival. Nevertheless, these diverse organisms are, on the whole, remarkably resilient to potential threats. Recent years have seen rapid advances in our mechanistic understanding of this emerging phenomenon of biological resilience, which enables cells, tissues and whole organisms to bounce back from challenges or stress. In this At a Glance article, I discuss current knowledge on the diverse molecular mechanisms driving biological resilience across scales, with particular focus on its dynamic and adaptive nature. I highlight emerging evidence that loss of biological resilience could underly numerous pathologies, including age-related frailty and degenerative disease. Finally, I present the multi-disciplinary experimental approaches that are helping to unravel the causal mechanisms of resilience and how this emerging knowledge could be harnessed therapeutically in the clinic.

Protective effects of L-theanine and dihydromyricetin on reproductive function in male mice under heat stress

Heat stress can impair the male reproductive function. L-Theanine and dihydromyricetin have biological activities against heat stress; however, their effects on reproductive function in heat-stressed males are unclear. In this study, male mice were given L-theanine, dihydromyricetin, or a combination of both for 28 days, followed by 2 h of heat stress daily for 7 days. All interventions alleviated heat stress-induced testicular damage, improving the testicular organ index, sperm density, acrosome integrity, sperm deformity rate, and hormone levels. Treatment increased the antioxidant enzyme activity and decreased the markers of oxidative and inflammatory stress in the testes. A combination dose of 200 + 200 mg kg-1 d-1 showed the best protective effect. The potential mechanism involves the regulation of HSP27 and HSP70, which regulate the levels of reproductive hormones through the StAR/Cyp11a1/Hsd3b1/Cyp17a1/Hsd17b3 pathway, alleviate inflammation and oxidative stress through the P38/NF-κB/Nrf2/HO-1 pathway, and regulate the Bcl-2/Fas/Caspase3 apoptotic pathway. Overall, L-theanine and dihydromyricetin may play a protective role against heat stress-induced reproductive dysfunction, suggesting their potential use in heat stress-resistant foods.

Calycosin Enhances Heat Shock Related-Proteins in H9c2 Cells to Modulate Survival and Apoptosis against Heat Shock

Heat shock proteins (HSPs), which function as chaperones, are activated in response to various environmental stressors. In addition to their role in diverse aspects of protein production, HSPs protect against harmful protein-related stressors. Calycosin exhibits numerous beneficial properties. This study aims to explore the protective effects of calycosin in the heart under heat shock and determine its underlying mechanism. H9c2 cells, western blot, TUNEL staining, flow cytometry, and immunofluorescence staining were used. The time-dependent effects of heat shock analyzed using western blot revealed increased HSP expression for up to 2[Formula: see text]h, followed by protein degradation after 4[Formula: see text]h. Hence, a heat shock damage duration of 4[Formula: see text]h was chosen for subsequent investigations. Calycosin administered post-heat shock demonstrated dose-dependent recovery of cell viability. Under heat shock conditions, calycosin prevented the apoptosis of H9c2 cells by upregulating HSPs, suppressing p-JNK, enhancing Bcl-2 activation, and inhibiting cleaved caspase 3. Calycosin also inhibited Fas/FasL expression and activated cell survival markers (p-PI3K, p-ERK, p-Akt), indicating their cytoprotective properties through PI3K/Akt activation and JNK inhibition. TUNEL staining and flow cytometry confirmed that calycosin reduced apoptosis. Moreover, calycosin reversed the inhibitory effects of quercetin on HSF1 and Hsp70 expression, illustrating its role in enhancing Hsp70 expression through HSF1 activation during heat shock. Immunofluorescence staining demonstrated HSF1 translocation to the nucleus following calycosin treatment, emphasizing its cytoprotective effects. In conclusion, calycosin exhibits pronounced protective effects against heat shock-induced damages by modulating HSP expression and regulating key signaling pathways to promote cell survival in H9c2 cells.

The therapeutic efficacy of different configuration nano-polydopamine drug carrier systems with photothermal synergy against head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignant tumor worldwide. Considering its special anatomical site and the progressive resistance to chemotherapy drugs, the development of more effective, minimally invasive and precise treatment methods is urgently needed. Nanomaterials, given their special properties, can be used as drug carrier systems to improve the therapeutic effect and reduce the adverse effects. The drug carrier systems with photothermal effect can promote the killing of cancer cells and help overcome drug resistance through heat stress. We selected dopamine, a simple raw material, and designed and synthesized three different configurations of nano-polydopamine (nPDA) nanomaterials, including nPDA balls, nPDA plates and porous nPDA balls. In addition to the self-polymerization and self-assembly, nPDA has high photothermal conversion efficiency and can be easily modified. Moreover, we loaded cisplatin into three different configurations of nPDA, creating nPDA-cis (the nano-drug carrier system with cisplatin), and comparatively studied the properties and antitumor effects of all the nPDA and nPDA-cis materials in vitro and nPDA-cis in vivo. We found that the photothermal effect of the nPDA-cis balls drug carrier system had synergistic effect with cisplatin, resulting in excellent antitumor effect and good clinical application prospects. The comparison of the three different configurations of drug carrier systems suggested the importance of optimizing the spatial configuration design and examining the physical and chemical properties in the future development of nano-drug carrier systems. In this study, we also noted the duality and complexity of the influences of heat stress on tumors in vitro and in vivo. The specific mechanisms and the synergy with chemotherapy and immunotherapy will be an important research direction in the future.

Effect of Heat Shock Treatment on the Virulence of Grass Carp Reovirus in Rare Minnow Gobiocypris rarus

The mode and outcome of fish-virus interactions are influenced by many abiotic factors, among which water temperature is especially important in poikilothermic fish. Rare minnow Gobiocypris rarus is a eurythermal small cyprinid fish that is sensitive to infection with genotype II grass carp reovirus (GCRV). HSP70, a conservative and key player in heat shock response, is previously identified as an induced pro-viral factor during GCRV infection in vitro. Here, rare minnow was subjected to heat shock treatment (HST), 1 h treatment at 32 °C followed by reverting to a normal temperature of 24 °C, and subsequently challenged with GCRV-II at a dosage of 1 × LD50. The effect of HST on GCRV virulence in vivo was evaluated by calculating virus-associated mortality and viral load in both dead and survival fish. The results revealed that HST enhanced the mortality of rare minnow infected with GCRV; the fact that viral loads in the tissue samples of HST-treated fish were significantly higher than those in samples of the control group at 6, 8 d p.i. reflected a faster infection process due to HST. Quantitative gene expression analysis was further employed to show that the expression levels of Hsp70 in intestine and liver tissues from the HST group declined faster than muscle tissue after HST. HST W/O GCRV challenge upregulated proinflammatory cytokines such as MyD88 and Nf-κB, which was in consistence with the inflammation observed in histopathological analysis. This study shed light on the complexity of the interaction between fish abiotic and biotic stress response, which suggested that HST, an abiotic stress, could enhance the virulence of GCRV in Gobiocypris rarus that involved modulating the gene expression of host heat shock, as well as a pro-inflammatory response.

Pifithrin-µ Induces Stress Granule Formation, Regulates Cell Survival, and Rewires Cellular Signaling

(1) Background: Stress granules (SGs) are cytoplasmic protein-RNA condensates that assemble in response to various insults. SG production is driven by signaling pathways that are relevant to human disease. Compounds that modulate SG characteristics are therefore of clinical interest. Pifithrin-µ is a candidate anti-tumor agent that inhibits members of the hsp70 chaperone family. While hsp70s are required for granulostasis, the impact of pifithrin-µ on SG formation is unknown. (2) Methods: Using HeLa cells as model system, cell-based assays evaluated the effects of pifithrin-µ on cell viability. Quantitative Western blotting assessed cell signaling events and SG proteins. Confocal microscopy combined with quantitative image analyses examined multiple SG parameters. (3) Results: Pifithrin-µ induced bona fide SGs in the absence of exogenous stress. These SGs were dynamic; their properties were determined by the duration of pifithrin-µ treatment. The phosphorylation of eIF2α was mandatory to generate SGs upon pifithrin-µ exposure. Moreover, the formation of pifithrin-µ SGs was accompanied by profound changes in cell signaling. Pifithrin-µ reduced the activation of 5'-AMP-activated protein kinase, whereas the pro-survival protein kinase Akt was activated. Long-term pifithrin-µ treatment caused a marked loss of cell viability. (4) Conclusions: Our study identified stress-related changes in cellular homeostasis that are elicited by pifithrin-µ. These insights are important knowledge for the appropriate therapeutic use of pifithrin-µ and related compounds.

Impact of Polyethylene Terephthalate Microplastics on Drosophila melanogaster Biological Profiles and Heat Shock Protein Levels

Microplastics and nanoplastics are abundant in the environment. Further research is necessary to examine the consequences of microplastic contamination on living species, given its widespread presence. In our research, we determined the toxic effects of PET microplastics on Drosophila melanogaster at the cellular and genetic levels. Our study revealed severe cytotoxicity in the midgut of larvae and the induction of oxidative stress after 24 and 48 h of treatment, as indicated by the total protein, Cu-Zn SOD, CAT, and MDA contents. For the first time, cell damage in the reproductive parts of the ovaries of female flies, as well as in the accessory glands and testes of male flies, has been observed. Furthermore, a decline in reproductive health was noted, resulting in decreased fertility among the flies. By analyzing stress-related genes such as hsp83, hsp70, hsp60, and hsp26, we detected elevated expression of hsp83 and hsp70. Our study identified hsp83 as a specific biomarker for detecting early redox changes in cells caused by PET microplastics in all the treated groups, helping to elucidate the primary defense mechanism against PET microplastic toxicity. This study offers foundational insights into the emerging environmental threats posed by microplastics, revealing discernible alterations at the genetic level.

A mechanism that transduces lysosomal damage signals to stress granule formation for cell survival

Lysosomal damage poses a significant threat to cell survival. Our previous work has reported that lysosomal damage induces stress granule (SG) formation. However, the importance of SG formation in determining cell fate and the precise mechanisms through which lysosomal damage triggers SG formation remains unclear. Here, we show that SG formation is initiated via a novel calcium-dependent pathway and plays a protective role in promoting cell survival in response to lysosomal damage. Mechanistically, we demonstrate that during lysosomal damage, ALIX, a calcium-activated protein, transduces lysosomal damage signals by sensing calcium leakage to induce SG formation by controlling the phosphorylation of eIF2α. ALIX modulates eIF2α phosphorylation by regulating the association between PKR and its activator PACT, with galectin-3 exerting a negative effect on this process. We also found this regulatory event of SG formation occur on damaged lysosomes. Collectively, these investigations reveal novel insights into the precise regulation of SG formation triggered by lysosomal damage, and shed light on the interaction between damaged lysosomes and SGs. Importantly, SG formation is significant for promoting cell survival in the physiological context of lysosomal damage inflicted by SARS-CoV-2 ORF3a, adenovirus infection, Malaria hemozoin, proteopathic tau as well as environmental hazard silica.

Heat-shock proteins, oxidative stress, and antioxidants in one-humped camels

One-humped camels (Camelus dromedarius) exhibit remarkable adaptability to harsh desert environments through various physiological adaptations. This study aimed to assess variations and reference values of Heat-shock proteins (HSPs), physiological parameters, mineral concentrations, total antioxidant capacity (TAC), and malondialdehyde (MDA) in 90 healthy female one-humped camels from Zabol's outskirts in Iran. The objective was to understand how these camels adapt to heat stress. Blood samples were collected from camels located at five geographical regions and analyzed using standard kits and methods. Reference intervals for heat-shock protein 30 (HSP30), heat-shock protein 40 (HSP40), heat-shock protein 70 (HSP70), and heat-shock protein 90 (HSP90) were determined using the reference value advisor (RVA). The study found significant differences among different regions for HSPs (P < 0.05), MDA (P = 0.021), and TAC (P = 0.042) levels, indicating variations in adaptation mechanisms. However, no notable differences were observed for other measured parameters between these regions. There were no significant differences observed in the evaluated parameters between the age categories of > 36 months and < 36 months. The positive correlation between HSPs and MDA levels (ranging from 0.754 to 0.884) suggests that the synthesis of HSPs is triggered as a response to oxidative stress caused by an imbalance between the production of reactive oxygen species (ROS) and the body's antioxidant defenses. This oxidative stress, in turn, is a consequence of thermal stress. Additionally, the study reveals a negative association between TAC and HSP levels (ranging from - 0.660 to - 0.820), emphasizing the role of antioxidants in mitigating heat stress. The findings of this research offer compelling support for the critical role that HSPs play in protecting cells from heat-induced damage. Additionally, the presence of higher levels of HSPs in regions with more severe climate conditions serves as evidence of camels' adaptation to heat stress. These findings emphasize the substantial impact of environmental factors on HSP production and further reinforce the crucial role of HSPs in bolstering the resilience of camels. Further research is needed to explore HSP expression and mechanisms to effectively manage and enhance camel resilience in extreme temperatures.

Contribution of the yeast bi-chaperone system in the restoration of the RNA helicase Ded1 and translational activity under severe ethanol stress

Preexposure to mild stress often improves cellular tolerance to subsequent severe stress. Severe ethanol stress (10% v/v) causes persistent and pronounced translation repression in Saccharomyces cerevisiae. However, it remains unclear whether preexposure to mild stress can mitigate translation repression in yeast cells under severe ethanol stress. We found that the translational activity of yeast cells pretreated with 6% (v/v) ethanol was initially significantly repressed under subsequent 10% ethanol but was then gradually restored even under severe ethanol stress. We also found that 10% ethanol caused the aggregation of Ded1, which plays a key role in translation initiation as a DEAD-box RNA helicase. Pretreatment with 6% ethanol led to the gradual disaggregation of Ded1 under subsequent 10% ethanol treatment in wild-type cells but not in fes1Δhsp104Δ cells, which are deficient in Hsp104 with significantly reduced capacity for Hsp70. Hsp104 and Hsp70 are key components of the bi-chaperone system that play a role in yeast protein quality control. fes1Δhsp104Δ cells did not restore translational activity under 10% ethanol, even after pretreatment with 6% ethanol. These results indicate that the regeneration of Ded1 through the bi-chaperone system leads to the gradual restoration of translational activity under continuous severe stress. This study provides new insights into the acquired tolerance of yeast cells to severe ethanol stress and the resilience of their translational activity.

Intrinsically disordered regions and RNA binding domains contribute to protein enrichment in biomolecular condensates in Xenopus oocytes

Proteins containing both intrinsically disordered regions (IDRs) and RNA binding domains (RBDs) can phase separate in vitro, forming bodies similar to cellular biomolecular condensates. However, how IDR and RBD domains contribute to in vivo recruitment of proteins to biomolecular condensates remains poorly understood. Here, we analyzed the roles of IDRs and RBDs in L-bodies, biomolecular condensates present in Xenopus oocytes. We show that a cytoplasmic isoform of hnRNPAB, which contains two RBDs and an IDR, is highly enriched in L-bodies. While both of these domains contribute to hnRNPAB self-association and phase separation in vitro and mediate enrichment into L-bodies in oocytes, neither the RBDs nor the IDR replicate the localization of full-length hnRNPAB. Our results suggest a model where the additive effects of the IDR and RBDs regulate hnRNPAB partitioning into L-bodies. This model likely has widespread applications as proteins containing RBD and IDR domains are common biomolecular condensate residents.

The boundary of life and death: changes in mitochondrial and cytosolic proteomes associated with programmed cell death of Arabidopsis thaliana suspension culture cells

Introduction

Despite the critical role of programmed cell death (PCD) in plant development and defense responses, its regulation is not fully understood. It has been proposed that mitochondria may be important in the control of the early stages of plant PCD, but the details of this regulation are currently unknown.

Methods

We used Arabidopsis thaliana cell suspension culture, a model system that enables induction and precise monitoring of PCD rates, as well as chemical manipulation of this process to generate a quantitative profile of the alterations in mitochondrial and cytosolic proteomes associated with early stages of plant PCD induced by heat stress. The cells were subjected to PCD-inducing heat levels (10 min, 54°C), with/without the calcium channel inhibitor and PCD blocker LaCl3. The stress treatment was followed by separation of cytosolic and mitochondrial fractions and mass spectrometry-based proteome analysis.

Results

Heat stress induced rapid and extensive changes in protein abundance in both fractions, with release of mitochondrial proteins into the cytosol upon PCD induction. In our system, LaCl3 appeared to act downstream of cell death initiation signal, as it did not affect the release of mitochondrial proteins, but instead partially inhibited changes occurring in the cytosolic fraction, including upregulation of proteins with hydrolytic activity.

Discussion

We characterized changes in protein abundance and localization associated with the early stages of heat stress-induced PCD. Collectively, the generated data provide new insights into the regulation of cell death and survival decisions in plant cells.

Acute and chronic impacts of heat stress on planetary health

Heat waves are increasing in intensity, frequency, and duration causing significant heat stress in all living organisms. Heat stress has multiple negative effects on plants affecting photosynthesis, respiration, growth, development, and reproduction. It also impacts animals leading to physiological and behavioral alterations, such as reduced caloric intake, increased water intake, and decreased reproduction and growth. In humans, epidemiological studies have shown that heat waves are associated with increased morbidity and mortality. There are many biological effects of heat stress (structural changes, enzyme function disruption, damage through reactive oxygen or nitrogen species). While plants and animals can mitigate some of these effects through adaptive mechanisms such as the generation of heat shock proteins, antioxidants, stress granules, and others, these mechanisms may likely be inadequate with further global warming. This review summarizes the effects of heat stress on plants and animals and the adaptative mechanisms that have evolved to counteract this stress.

Stress granule formation inhibits stress-induced apoptosis by selectively sequestering executioner caspases

Cytoplasmic stress granules (SGs) are phase-separated membrane-less organelles that form in response to various stress stimuli. SGs are mainly composed of non-canonical stalled 48S preinitiation complexes. In addition, many other proteins also accumulate into SGs, but the list is still incomplete. SG assembly suppresses apoptosis and promotes cell survival under stress. Furthermore, hyperformation of SGs is frequently observed in various human cancers and accelerates tumor development and progression by reducing stress-induced damage of cancer cells. Therefore, they are of clinical importance. However, the precise mechanism underlying SG-mediated inhibition of apoptosis remains ill-defined. Here, using a proximity-labeling proteomic approach, we comprehensively analyzed SG-resident proteins and identified the executioner caspases, caspase-3 and -7, as SG components. We demonstrate that accumulation of caspase-3/7 into SGs is mediated by evolutionarily conserved amino acid residues within their large catalytic domains and inhibits caspase activities and consequent apoptosis induced by various stresses. Expression of an SG-localization-deficient caspase-3 mutant in cells largely counteracted the anti-apoptotic effect of SGs, whereas enforced relocalization of the caspase-3 mutant to SGs restored it. Thus, SG-mediated sequestration of executioner caspases is a mechanism underlying the broad cytoprotective function of SGs. Furthermore, using a mouse xenograft tumor model, we show that this mechanism prevents cancer cells from apoptosis in tumor tissues, thereby promoting cancer progression. Our results reveal the functional crosstalk between SG-mediated cell survival and caspase-mediated cell death signaling pathways and delineate a molecular mechanism that dictates cell-fate decisions under stress and promotes tumorigenesis.

Comprehensive Profiling of ceRNA (circRNA-miRNA-mRNA) Networks in Hypothalamic-Pituitary-Mammary Gland Axis of Dairy Cows under Heat Stress

Heat stress (HS) is directly correlated with mammary gland dysfunction and the hypothalamic-pituitary-mammary gland (HPM) axis is involved in regulating stress responses and lactation in dairy cows. Circular RNAs (circRNAs) play major roles in regulating transcription and post-transcription but their expression in the HPM axis of dairy cows under HS is still unclear. In the present study, we performed RNA sequencing to identify diferentially expressed (DE) circRNAs, DE microRNAs(miRNAs) and DEmRNAs, and performed bioinformatics analysis on those in HPM axis-related tissues of heat-stressed and normal cows. A total of 1680, 1112 and 521 DEcircRNAs, 120, 493 and 108 DEmiRNAs, 274, 6475 and 3134 DEmRNAs were identified in the hypothalamic, pituitary, and mammary gland tissues, respectively. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses indicated that the MAPK signaling pathway is potentially a key pathway. Competitive endogenous RNA (ceRNA) networks related to HS response and lactation regulation were established in three tissues. In conclusion, our results indicate that HS induces differential circRNA expression profiles in HPM axis-related tissues, and the predicted ceRNA network provides a molecular basis for regulating the stress response and lactation regulation in heat-stressed dairy cows.

Reorganization of Cell Compartmentalization Induced by Stress

The discovery of intrinsically disordered proteins (IDPs) that do not have an ordered structure and nevertheless perform essential functions has opened a new era in the understanding of cellular compartmentalization. It threw the bridge from the mostly mechanistic model of the organization of the living matter to the idea of highly dynamic and functional "soft matter". This paradigm is based on the notion of the major role of liquid-liquid phase separation (LLPS) of biopolymers in the spatial-temporal organization of intracellular space. The LLPS leads to the formation of self-assembled membrane-less organelles (MLOs). MLOs are multicomponent and multifunctional biological condensates, highly dynamic in structure and composition, that allow them to fine-tune the regulation of various intracellular processes. IDPs play a central role in the assembly and functioning of MLOs. The LLPS importance for the regulation of chemical reactions inside the cell is clearly illustrated by the reorganization of the intracellular space during stress response. As a reaction to various types of stresses, stress-induced MLOs appear in the cell, enabling the preservation of the genetic and protein material during unfavourable conditions. In addition, stress causes structural, functional, and compositional changes in the MLOs permanently present inside the cells. In this review, we describe the assembly of stress-induced MLOs and the stress-induced modification of existing MLOs in eukaryotes, yeasts, and prokaryotes in response to various stress factors.

Aberrant HSF1 signaling activation underlies metformin amelioration of myocardial infarction in mice

Myocardial infarction (MI) is a cardiovascular disease with high morbidity and mortality. Clinically, rehabilitation after massive MI often has a poor prognosis. Therefore, it is necessary to explore the therapeutic methods of myocardial protection after MI. As a first-line treatment for type 2 diabetes, metformin has been found to have a certain protective effect on myocardial tissue. However, its pharmacological mechanism remains unclear. In this study, we investigated key factors that reduced MI with metformin. Through in vivo, in vitro, and in silico analyses, we identified HSF1 as a key target for metformin. HSF1 could up-regulate the transcriptional level of AMPKα2 through transcriptional activation and stimulate the activity of the downstream AMPK/mTOR signaling pathway. Metformin stimulated cardiomyocytes to form stress granules (SGs), and knockdown of HSF1 reversed this process. Furthermore, HSF1 exhibited better in vitro affinity for metformin than AMPK, suggesting that HSF1 may be a more sensitive target for metformin.

Stress-Induced Membraneless Organelles in Eukaryotes and Prokaryotes: Bird’s-Eye View

Stress is an inevitable part of life. An organism is exposed to multiple stresses and overcomes their negative consequences throughout its entire existence. A correlation was established between life expectancy and resistance to stress, suggesting a relationship between aging and the ability to respond to external adverse effects as well as quickly restore the normal regulation of biological processes. To combat stress, cells developed multiple pro-survival mechanisms, one of them is the assembly of special stress-induced membraneless organelles (MLOs). MLOs are formations that do not possess a lipid membrane but rather form as a result of the “liquid–liquid” phase separation (LLPS) of biopolymers. Stress-responsive MLOs were found in eukaryotes and prokaryotes, they form as a reaction to the acute environmental conditions and are dismantled after its termination. These compartments function to prevent damage to the genetic and protein material of the cell during stress. In this review, we discuss the characteristics of stress-induced MLO-like structures in eukaryotic and prokaryotic cells.

Regulation of spatially restricted gene expression: linking RNA localization and phase separation

Subcellular restriction of gene expression is crucial to the functioning of a wide variety of cell types. The cellular machinery driving spatially restricted gene expression has been studied for many years, but recent advances have highlighted novel mechanisms by which cells can generate subcellular microenvironments with specialized gene expression profiles. Particularly intriguing are recent findings that phase separation plays a role in certain RNA localization pathways. The burgeoning field of phase separation has revolutionized how we view cellular compartmentalization, revealing that, in addition to membrane-bound organelles, phase-separated cytoplasmic microenvironments - termed biomolecular condensates - are compositionally and functionally distinct from the surrounding cytoplasm, without the need for a lipid membrane. The coupling of phase separation and RNA localization allows for precise subcellular targeting, robust translational repression and dynamic recruitment of accessory proteins. Despite the growing interest in the intersection between RNA localization and phase separation, it remains to be seen how exactly components of the localization machinery, particularly motor proteins, are able to associate with these biomolecular condensates. Further studies of the formation, function, and transport of biomolecular condensates promise to provide a new mechanistic understanding of how cells restrict gene expression at a subcellular level.