Vinca alkaloid drugs promote stress-induced translational repression and stress granule formation

Suppression of stress granule formation is a vulnerability imposed by mutant p53

Missense mutations in the TP53 (p53) gene have been linked to malignant progression. However, our in-silico analyses reveal that hepatocellular carcinoma (HCC) patients with mutant p53 (mutp53) have better overall survival compared to those with p53-null (p53null) HCC, unlike other cancer types. Given the historical use of sorafenib (SOR) monotherapy for advanced HCC, we hypothesize that mutp53 increases sensitivity to SOR, a multikinase inhibitor that induces endoplasmic reticulum (ER) stress. Here we show that mutp53 inhibits stress granule (SG) formation by binding to an ER stress sensor, PKR-like ER kinase (PERK), and a key SG component, GAP SH3 domain-binding protein 1 (G3BP1), contributing to increased sensitivity of SG-competent cells and xenografts to ER stress inducers including SOR. Our study identifies a unique vulnerability imposed by mutp53, suggesting mutp53 as a biomarker for ER stress-inducing agents and highlighting the importance of SG inhibition for cancer treatment.

Universal high-throughput image quantification of subcellular structure dynamics and spatial distributions within cells

Image analysis of subcellular structures and biological processes relies on specific, context-dependent pipelines, which are labor-intensive, constrained by the intricacies of the specific biological system, and inaccessible to broader applications. Here we introduce the application of dispersion indices, a statistical tool traditionally employed by economists, to analyze the spatial distribution and heterogeneity of subcellular structures. This computationally efficient high-throughput approach, termed GRID (Generalized Readout of Image Dispersion), is highly generalizable, compatible with open-source image analysis software, and adaptable to diverse biological scenarios. GRID readily quantifies diverse structures and processes to include autophagic puncta, mitochondrial clustering, and microtubule dynamics. Further, GRID is versatile, applicable to both 2D cell cultures and 3D multicellular organoids, and suitable for high-throughput screening and performance metric measurements, such as half-maximal effective concentration (EC50) values. The approach enables mechanistic analysis of critical subcellular structure processes of relevance for diseases ranging from metabolic and neuronal diseases to cancer as well as a first-pass screening method for identifying biologically active agents for drug discovery.

Caprin1 Bridges PRMT1 to G3BP1 and Spaces Them to Ensure Proper Stress Granule Formation

Stress granules (SGs) are dynamic biomolecular condensates that form in the cytoplasm in response to cellular stress, encapsulating proteins and RNAs. Methylation is a key factor in the assembly of SGs, with PRMT1, which acts as an arginine methyltransferase, localizing to SGs. However, the precise mechanism of PRMT1 localization within SGs remains unknown. In this study, we identified that Caprin1 plays a primary role in the recruitment of PRMT1 to SGs, particularly through its C-terminal domain. Our findings demonstrate that Caprin1 serves a dual function as both a linker, facilitating the formation of a PRMT1-G3BP1 complex, and as a spacer, preventing the aberrant formation of SGs under non-stress conditions. This study sheds new lights on the regulatory mechanisms governing SG formation and suggests that Caprin1 plays a critical role in cellular responses to stress.

PRMT1 and TDRD3 promote stress granule assembly by rebuilding the protein-RNA interaction network

Stress granules (SGs) are membrane-less organelles (MLOs) or cytosolic compartments formed upon exposure to environmental cell stress-inducing stimuli. SGs are based on ribonucleoprotein complexes from a set of cytoplasmic proteins and mRNAs, blocked in translation due to stress cell-induced polysome disassembly. Post-translational modifications (PTMs) such as methylation, are involved in SG assembly, with the methylation writer PRMT1 and its reader TDRD3 colocalizing to SGs. However, the role of this writer-reader system in SG assembly remains unclear. Here, we found that PRMT1 methylates SG constituent RNA-binding proteins (RBPs) on their RGG motifs. Besides, we report that TDRD3, as a reader of asymmetric dimethylarginines, enhances RNA binding to recruit additional RNAs and RBPs, lowering the percolation threshold and promoting SG assembly. Our study enriches our understanding of the molecular mechanism of SG formation by elucidating the functions of PRMT1 and TDRD3. We anticipate that our study will provide a new perspective for comprehensively understanding the functions of PTMs in liquid-liquid phase separation driven condensate assembly.

Biomolecular condensates and disease pathogenesis

Biomolecular condensates or membraneless organelles (MLOs) formed by liquid-liquid phase separation (LLPS) divide intracellular spaces into discrete compartments for specific functions. Dysregulation of LLPS or aberrant phase transition that disturbs the formation or material states of MLOs is closely correlated with neurodegeneration, tumorigenesis, and many other pathological processes. Herein, we summarize the recent progress in development of methods to monitor phase separation and we discuss the biogenesis and function of MLOs formed through phase separation. We then present emerging proof-of-concept examples regarding the disruption of phase separation homeostasis in a diverse array of clinical conditions including neurodegenerative disorders, hearing loss, cancers, and immunological diseases. Finally, we describe the emerging discovery of chemical modulators of phase separation.

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.

Stress granule-mediated sequestration of EGR1 mRNAs correlates with lomustine-induced cell death prevention

Some chemotherapy drugs modulate the formation of stress granules (SGs), which are RNA-containing cytoplasmic foci contributing to stress response pathways. How SGs mechanistically contribute to pro-survival or pro-apoptotic functions must be better defined. The chemotherapy drug lomustine promotes SG formation by activating the stress-sensing eIF2α kinase HRI (encoded by the EIF2AK1 gene). Here, we applied a DNA microarray-based transcriptome analysis to determine the genes modulated by lomustine-induced stress and suggest roles for SGs in this process. We found that the expression of the pro-apoptotic EGR1 gene was specifically regulated in cells upon lomustine treatment. The appearance of EGR1-encoding mRNA in SGs correlated with a decrease in EGR1 mRNA translation. Specifically, EGR1 mRNA was sequestered to SGs upon lomustine treatment, probably preventing its ribosome translation and consequently limiting the degree of apoptosis. Our data support the model where SGs can selectively sequester specific mRNAs in a stress-specific manner, modulate their availability for translation, and thus determine the fate of a stressed cell.

Nuclear RNA-related processes modulate the assembly of cytoplasmic RNA granules

Stress granules (SGs) are cytoplasmic assemblies formed under various stress conditions as a consequence of translation arrest. SGs contain RNA-binding proteins, ribosomal subunits and messenger RNAs (mRNAs). It is well known that mRNAs contribute to SG formation; however, the connection between SG assembly and nuclear processes that involve mRNAs is not well established. Here, we examine the effects of inhibiting mRNA transcription, splicing and export on the assembly of SGs and the related cytoplasmic P body (PB). We demonstrate that inhibition of mRNA transcription, splicing and export reduces the formation of canonical SGs in a eukaryotic initiation factor 2α phosphorylation-independent manner, and alters PB size and quantity. We find that the splicing inhibitor madrasin promotes the assembly of stress-like granules. We show that the addition of synthetic mRNAs directly to the cytoplasm is sufficient for SG assembly, and that the assembly of these SGs requires the activation of stress-associated protein synthesis pathways. Moreover, we show that adding an excess of mRNA to cells that do not have active splicing, and therefore have low levels of cytoplasmic mRNAs, promotes SG formation under stress conditions. These findings emphasize the importance of the cytoplasmic abundance of newly transcribed mRNAs in the assembly of SGs.

Stress Granule Core Protein-Derived Peptides Inhibit Assembly of Stress Granules and Improve Sorafenib Sensitivity in Cancer Cells

Upon a variety of environmental stresses, eukaryotic cells usually recruit translational stalled mRNAs and RNA-binding proteins to form cytoplasmic condensates known as stress granules (SGs), which minimize stress-induced damage and promote stress adaptation and cell survival. SGs are hijacked by cancer cells to promote cell survival and are consequently involved in the development of anticancer drug resistance. However, the design and application of chemical compounds targeting SGs to improve anticancer drug efficacy have rarely been studied. Here, we developed two types of SG inhibitory peptides (SIPs) derived from SG core proteins Caprin1 and USP10 and fused with cell-penetrating peptides to generate TAT-SIP-C1/2 and SIP-U1-Antp, respectively. We obtained 11 SG-inducing anticancer compounds from cell-based screens and explored the potential application of SIPs in overcoming resistance to the SG-inducing anticancer drug sorafenib. We found that SIPs increased the sensitivity of HeLa cells to sorafenib via the disruption of SGs. Therefore, anticancer drugs which are competent to induce SGs could be combined with SIPs to sensitize cancer cells, which might provide a novel therapeutic strategy to alleviate anticancer drug resistance.

HuR-positive stress granules: Potential targets for age-related osteoporosis

Aging impairs osteoblast function and bone turnover, resulting in age-related bone degeneration. Stress granules (SGs) are membrane-less organelles that assemble in response to stress via the recruitment of RNA-binding proteins (RBPs), and have emerged as a novel mechanism in age-related diseases. Here, we identified HuR as a bone-related RBP that aggregated into SGs and facilitated osteogenesis during aging. HuR-positive SG formation increased during osteoblast differentiation, and HuR overexpression mitigated the reduction in SG formation observed in senescent osteoblasts. Moreover, HuR positively regulated the mRNA stability and expression of its target β-catenin by binding and recruiting β-catenin into SGs. As a potential therapeutic target, HuR activator apigenin (API) enhanced its expression and thus aided osteoblasts differentiation. API treatment increased HuR nuclear export, enhanced the recruitment of β-catenin into HuR-positive SGs, facilitated β-catenin nuclear translocation, and contributed osteogenesis. Our findings highlight the roles of HuR and its SGs in promoting osteogenesis during skeletal aging and lay the groundwork for novel therapeutic strategies against age-related skeletal disorders.

Time-resolved proteomic profiling reveals compositional and functional transitions across the stress granule life cycle

Stress granules (SGs) are dynamic, membrane-less organelles. With their formation and disassembly processes characterized, it remains elusive how compositional transitions are coordinated during prolonged stress to meet changing functional needs. Here, using time-resolved proteomic profiling of the acute to prolonged heat-shock SG life cycle, we identify dynamic SG proteins, further segregated into early and late proteins. Comparison of different groups of SG proteins suggests that their biochemical properties help coordinate SG compositional and functional transitions. In particular, early proteins, with high phase-separation-propensity, drive the rapid formation of the initial SG platform, while late proteins are subsequently recruited as discrete modules to further functionalize SGs. This model, supported by immunoblotting and immunofluorescence imaging, provides a conceptual framework for the compositional transitions throughout the acute to prolonged SG life cycle. Additionally, an early SG constituent, non-muscle myosin II, is shown to promote SG formation by increasing SG fusion, underscoring the strength of this dataset in revealing the complexity of SG regulation.

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.

Stress Granules as Causes and Consequences of Translation Suppression

Significance: Stress granules (SGs) are biomolecular condensates that form upon global translation suppression during stress. SGs are enriched in translation factors and messenger RNAs (mRNAs), which they may sequester away from the protein synthesis machinery. While this is hypothesized to remodel the functional transcriptome during stress, it remains unclear whether SGs are a cause, or simply a consequence, of translation repression. Understanding the function of SGs is particularly important because they are implicated in numerous diseases including viral infections, cancer, and neurodegeneration. Recent Advances: We synthesize recent SG research spanning biological scales, from observing single proteins and mRNAs within one cell to measurements of the entire transcriptome or proteome of SGs in a cell population. We use the emerging understanding from these studies to suggest that SGs likely have less impact on global translation, but instead may strongly influence the translation of individual mRNAs localized to them. Critical Issues: Development of a unified model that links stress-induced RNA-protein condensation to regulation of downstream gene expression holds promise for understanding the mechanisms of cellular resilience. Future Directions: Therefore, upcoming research should clarify what influence SGs exert on translation at all scales as well as the molecular mechanisms that enable this. The resulting knowledge will be required to drive discovery in how SGs allow organisms to adapt to challenges and support health or go awry and lead to disease. Antioxid. Redox Signal. 39, 390-409.

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: 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 enigma of ultraviolet radiation stress granules: Research challenges and new perspectives

Stress granules (SGs) are non-membrane bound cytoplasmic condensates that form in response to a variety of different stressors. Canonical SGs are thought to have a cytoprotective role, reallocating cellular resources during stress by activation of the integrated stress response (ISR) to inhibit translation and avoid apoptosis. However, different stresses result in compositionally distinct, non-canonical SG formation that is likely pro-apoptotic, though the exact function(s) of both SGs subtypes remain unclear. A unique non-canonical SG subtype is triggered upon exposure to ultraviolet (UV) radiation. While it is generally agreed that UV SGs are bona fide SGs due to their dependence upon the core SG nucleating protein Ras GTPase-activating protein-binding protein 1 (G3BP1), the localization of other key components of UV SGs are unknown or under debate. Further, the dynamics of UV SGs are not known, though unique properties such as cell cycle dependence have been observed. This Perspective compiles the available information on SG subtypes and on UV SGs in particular in an attempt to understand the formation, dynamics, and function of these mysterious stress-specific complexes. We identify key gaps in knowledge related to UV SGs, and examine the unique aspects of their formation. We propose that more thorough knowledge of the distinct properties of UV SGs will lead to new avenues of understanding of the function of SGs, as well as their roles in disease.

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].

Sexually dimorphic RNA helicases DDX3X and DDX3Y differentially regulate RNA metabolism through phase separation

Sex differences are pervasive in human health and disease. One major key to sex-biased differences lies in the sex chromosomes. Although the functions of the X chromosome proteins are well appreciated, how they compare with their Y chromosome homologs remains elusive. Herein, using ensemble and single-molecule techniques, we report that the sex chromosome-encoded RNA helicases DDX3X and DDX3Y are distinct in their propensities for liquid-liquid phase separation (LLPS), dissolution, and translation repression. We demonstrate that the N-terminal intrinsically disordered region of DDX3Y more strongly promotes LLPS than the corresponding region of DDX3X and that the weaker ATPase activity of DDX3Y, compared with DDX3X, contributes to the slower disassembly dynamics of DDX3Y-positive condensates. Interestingly, DDX3Y-dependent LLPS represses mRNA translation and enhances aggregation of FUS more strongly than DDX3X-dependent LLPS. Our study provides a platform for future comparisons of sex chromosome-encoded protein homologs, providing insights into sex differences in RNA metabolism and human disease.

Allergen protease-activated stress granule assembly and gasdermin D fragmentation control interleukin-33 secretion

Interleukin-33 (IL-33), an epithelial cell-derived cytokine that responds rapidly to environmental insult, has a critical role in initiating airway inflammatory diseases. However, the molecular mechanism underlying IL-33 secretion following allergen exposure is not clear. Here, we found that two cell events were fundamental for IL-33 secretion after exposure to allergens. First, stress granule assembly activated by allergens licensed the nuclear-cytoplasmic transport of IL-33, but not the secretion of IL-33. Second, a neo-form murine amino-terminal p40 fragment gasdermin D (Gsdmd), whose generation was independent of inflammatory caspase-1 and caspase-11, dominated cytosolic secretion of IL-33 by forming pores in the cell membrane. Either the blockade of stress granule assembly or the abolishment of p40 production through amino acid mutation of residues 309-313 (ELRQQ) could efficiently prevent the release of IL-33 in murine epithelial cells. Our findings indicated that targeting stress granule disassembly and Gsdmd fragmentation could reduce IL-33-dependent allergic airway inflammation.

Glucocorticoids enhance chemotherapy-driven stress granule assembly and impair granule dynamics leading to cell death

Stress granules (SGs) can assemble in cancer cells upon chemotoxic stress. Glucocorticoids function during stress responses and are administered with chemotherapies. The roles of glucocorticoids in SG assembly and disassembly pathways are unknown. We examined whether combining glucocorticoids such as cortisone with chemotherapies from the vinca alkaloid family, which dismantle the microtubule network, affects SG assembly and disassembly pathways and influences cell viability in cancer cells and human-derived organoids. Cortisone augmented SG formation when combined with vinorelbine (VRB). Live-cell imaging showed that cortisone increased SG assembly rates but reduced SG clearance rates after stress, by increasing protein residence times within the SGs. Mechanistically, VRB and cortisone signaled through the integrated stress response mediated by eIF2α (also known as EIF2S1), yet induced different kinases, with cortisone activating the GCN2 kinase (also known as EIF2AK4). Cortisone increased VRB-induced cell death and reduced the population of cells trapped in mitotic catastrophe. These effects were mediated by the core SG proteins G3BP1 and G3BP2. In conclusion, glucocorticoids induce SG assembly and cell death when administered with chemotherapies, suggesting that combining glucocorticoids with chemotherapies can enhance cancer cell chemosensitivity.

Summary: Combining cortisone with the chemotherapy vinorelbine enhances the assembly of stress granules that are less likely to be cleared from the cells, augmenting vinorelbine-induced cell death.

FAM98A promotes resistance to 5-fluorouracil in colorectal cancer by suppressing ferroptosis

BACKGROUND

FAM98A is a microtubule-associated protein involved in cell proliferation and migration, and is frequently dysregulated in epithelial cancers. But its role in the development of colorectal cancer (CRC) cancer remains unknown.

METHODS

Immunohistochemical analysis was performed to examine the expression of FAM98A in CRC samples. We also investigated the effects of abnormal expression on the biological behavior of colorectal cancer cells both in vitro and in vivo. Immunoblotting and immunoprecipitation were used to screen FAM98A-related signalling pathways and downstream factors.

RESULTS

FAM98A was upregulated in CRC tissues and CRC cell lines. Overexpression of FAM98A promoted cell proliferation and recovered 5-FU suppressed CRC cell proliferation both in vitro and in vivo. In addition, the Enhanced expression of FAM98A inhibited ferroptosis in CRC cells by activating the translation of xCT in stress granules (SGs). Furthermore, we identified that metformin could reverse FAM98A-mediated 5-FU resistance in CRC cells.

CONCLUSIONS

Our results for the first time indicate that FAM98A plays a critical role in promoting CRC progression, which provides a novel target for clinical drug resistance of colorectal cancer. And metformin may sensitize 5-FU in the treatment of colorectal cancer.

Collective Learnings of Studies of Stress Granule Assembly and Composition

Stress granules have gained considerable exposure and interest in recent years. These micron-sized entities, composed of RNA and protein, form following a stress exposure and have been linked to several pathologies. Understanding stress granule function is paramount but has been arduous due to the membraneless nature of these organelles. Several new methodologies have recently been developed to catalogue the protein and RNA composition of stress granules. Collectively, this work has provided important insights to potential stress granule functions as well as molecular mechanisms for their assembly and disassembly. This chapter reviews the latest advancements in the understanding of stress granule dynamics and discusses the various protocols developed to study their composition.

Early rRNA processing is a stress-dependent regulatory event whose inhibition maintains nucleolar integrity

The production of ribosomes is an energy-intensive process owing to the intricacy of these massive macromolecular machines. Each human ribosome contains 80 ribosomal proteins and four non-coding RNAs. Accurate assembly requires precise regulation of protein and RNA subunits. In response to stress, the integrated stress response (ISR) rapidly inhibits global translation. How rRNA is coordinately regulated with the rapid inhibition of ribosomal protein synthesis is not known. Here, we show that stress specifically inhibits the first step of rRNA processing. Unprocessed rRNA is stored within the nucleolus, and when stress resolves, it re-enters the ribosome biogenesis pathway. Retention of unprocessed rRNA within the nucleolus aids in the maintenance of this organelle. This response is independent of the ISR or inhibition of cellular translation but is independently regulated. Failure to coordinately control ribosomal protein translation and rRNA production results in nucleolar fragmentation. Our study unveils how the rapid translational shut-off in response to stress coordinates with rRNA synthesis production to maintain nucleolar integrity.

Stress Granules in the Anti-Cancer Medications Mechanism of Action: A Systematic Scoping Review

Stress granule (SG) formation is a well-known cellular mechanism for minimizing stress-related damage and increasing cell survival. In addition to playing a critical role in the stress response, SGs have emerged as critical mediators in human health. It seems logical that SGs play a key role in cancer cell formation, development, and metastasis. Recent studies have shown that many SG components contribute to the anti-cancer medications' responses through tumor-associated signaling pathways and other mechanisms. SG proteins are known for their involvement in the translation process, control of mRNA stability, and capacity to function in both the cytoplasm and nucleus. The current systematic review aimed to include all research on the impact of SGs on the mechanism of action of anti-cancer medications and was conducted using a six-stage methodological framework and the PRISMA guideline. Prior to October 2021, a systematic search of seven databases for eligible articles was performed. Following the review of the publications, the collected data were subjected to quantitative and qualitative analysis. Notably, Bortezomib, Sorafenib, Oxaliplatin, 5-fluorouracil, Cisplatin, and Doxorubicin accounted for the majority of the medications examined in the studies. Overall, this systematic scoping review attempts to demonstrate and give a complete overview of the function of SGs in the mechanism of action of anti-cancer medications by evaluating all research.

Translation inhibition and suppression of stress granules formation by cisplatin

Platinum-based antineoplastic drugs, such as cisplatin, are commonly used to induce tumor cell death. Cisplatin is believed to induce apoptosis as a result of cisplatin-DNA adducts that inhibit DNA and RNA synthesis. Although idea that DNA damage underlines anti-proliferative effects of cisplatin is dominant in cancer research, there is a poor correlation between the degree of the cell sensitivity to cisplatin and the extent of DNA platination. Here, we examined possible effects of cisplatin on post-transcriptional gene regulation that may contribute to cisplatin-mediated cytotoxicity. We show that cisplatin suppresses formation of stress granules (SGs), pro-survival RNA granules with multiple roles in cellular metabolism. Mechanistically, cisplatin inhibits cellular translation to promote disassembly of polysomes and aggregation of ribosomal subunits. As SGs are in equilibrium with polysomes, cisplatin-induced shift towards ribosomal aggregation suppresses SG formation. Our data uncover previously unknown effects of cisplatin on RNA metabolism.

MG53 suppresses tumor progression and stress granule formation by modulating G3BP2 activity in non-small cell lung cancer

Background

Cancer cells develop resistance to chemotherapeutic intervention by excessive formation of stress granules (SGs), which are modulated by an oncogenic protein G3BP2. Selective control of G3BP2/SG signaling is a potential means to treat non-small cell lung cancer (NSCLC).

Methods

Co-immunoprecipitation was conducted to identify the interaction of MG53 and G3BP2. Immunohistochemistry and live cell imaging were performed to visualize the subcellular expression or co-localization. We used shRNA to knock-down the expression MG53 or G3BP2 to test the cell migration and colony formation. The expression level of MG53 and G3BP2 in human NSCLC tissues was tested by western blot analysis. The ATO-induced oxidative stress model was used to examine the effect of rhMG53 on SG formation. Moue NSCLC allograft experiments were performed on wild type and transgenic mice with either knockout of MG53, or overexpression of MG53. Human NSCLC xenograft model in mice was used to evaluate the effect of MG53 overexpression on tumorigenesis.

Results

We show that MG53, a member of the TRIM protein family (TRIM72), modulates G3BP2 activity to control lung cancer progression. Loss of MG53 results in the progressive development of lung cancer in mg53^-/- mice. Transgenic mice with sustained elevation of MG53 in the bloodstream demonstrate reduced tumor growth following allograft transplantation of mouse NSCLC cells. Biochemical assay reveals physical interaction between G3BP2 and MG53 through the TRIM domain of MG53. Knockdown of MG53 enhances proliferation and migration of NSCLC cells, whereas reduced tumorigenicity is seen in NSCLC cells with knockdown of G3BP2 expression. The recombinant human MG53 (rhMG53) protein can enter the NSCLC cells to induce nuclear translation of G3BP2 and block arsenic trioxide-induced SG formation. The anti-proliferative effect of rhMG53 on NSCLC cells was abolished with knockout of G3BP2. rhMG53 can enhance sensitivity of NSCLC cells to undergo cell death upon treatment with cisplatin. Tailored induction of MG53 expression in NSCLC cells suppresses lung cancer growth via reduced SG formation in a xenograft model.

Conclusion

Overall, these findings support the notion that MG53 functions as a tumor suppressor by targeting G3BP2/SG activity in NSCLCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01418-3.

Thioredoxin 1 is required for stress granule assembly upon arsenite-induced oxidative stress

Arsenic is a major water pollutant and health hazard, leading to acute intoxication and, upon chronic exposure, several diseases including cancer development. Arsenic exerts its pronounced cellular toxicity through its trivalent oxide arsenite (ASN), which directly inhibits numerous proteins including Thioredoxin 1 (Trx1), and causes severe oxidative stress. Cells respond to arsenic by inhibition of protein synthesis and subsequent assembly of stress granules (SGs), cytoplasmic condensates of stalled mRNAs, translation factors and RNA-binding proteins. The biological role of SGs is diverse and not completely understood; they are important for regulation of cell signaling and survival under stress conditions, and for adapting de novo protein synthesis to the protein folding capacity during the recovery from stress. In this study, we identified Trx1 as a novel component of SGs. Trx1 is required for the assembly of ASN-induced SGs, but not for SGs induced by energy deprivation or heat shock. Importantly, our results show that Trx1 is essential for cell survival upon acute exposure to ASN, through a mechanism that is independent of translation inhibition.

Vincristine attenuates cardiac fibrosis through the inhibition of NLRP3 inflammasome activation

Vincristine (VCR) is widely used in cancer therapies, although its benefits on cardiac fibrosis remain unknown. Here, we investigated VCR's efficacy on cardiac fibrosis and elucidated the underlying mechanism of action. Network pharmacology was employed to predict the mechanism of VCR action on cardiac fibrosis. We induced cardiac fibrosis in adult male Sprague-Dawley (SD) rats via isoproterenol (ISO) injection, followed by treatment with VCR or vehicle. After 10 days of treatment, VCR-treated rats exhibited a significantly lower heart/body weight ratio relative to those treated with the vehicle. Moreover, cardiac fibrosis was alleviated in VCR-treated rats relative to vehicle-treated rats. The results revealed the down-regulation of mature caspase-1, interleukin (IL)-1β, and IL-18 in VCR-treated rats relative to vehicle-treated rats. We also observed less colocalization between the nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) and apoptosis-associated speck-like protein containing a CARD (ASC) in VCR-treated rats compared with vehicle-treated rats. We then cultured neonatal rat cardiac fibroblasts (NRCFs) and exposed them to lipopolysaccharide (LPS) and adenosine triphosphate (ATP) in the presence or absence of VCR. The results indicated that VCR mediated the down-regulation of caspase-1, IL-1β, and IL-18 and the colocalization of NLRP3 and ASC in LPS+ATP-stimulated cardiac fibroblasts (CFs). We found evidence that VCR attenuates cardiac fibrosis by directly suppressing the activation of the NLRP3 inflammasome. These findings provide novel insights into VCR's mechanism of action in alleviating cardiac fibrosis.

Quantification of eIF2α Phosphorylation Associated with Mitotic Catastrophe by Immunofluorescence Microscopy

Mitotic catastrophe is an oncosuppressive mechanism that drives cells toward senescence or death when an error occurs during mitosis. Eukaryotic cells have developed adaptive signaling pathways to cope with stress. The phosphorylation on serine 51 of the eukaryotic translation initiation factor (eIF2α) is a highly conserved event in stress responses, including the one that is activated upon treatment with mitotic catastrophe inducing agents, such as microtubular poisons or actin blockers. The protocol described herein details a method to quantify the phosphorylation of eIF2α by high-throughput immunofluorescence microscopy. This method is useful to capture the 'integrated stress response', which is characterized by eIF2α phosphorylation in the context of mitotic catastrophe.

Complex Interactions Between Membrane-Bound Organelles, Biomolecular Condensates and the Cytoskeleton

Membrane-bound and membraneless organelles/biomolecular condensates ensure compartmentalization into functionally distinct units enabling proper organization of cellular processes. Membrane-bound organelles form dynamic contacts with each other to enable the exchange of molecules and to regulate organelle division and positioning in coordination with the cytoskeleton. Crosstalk between the cytoskeleton and dynamic membrane-bound organelles has more recently also been found to regulate cytoskeletal organization. Interestingly, recent work has revealed that, in addition, the cytoskeleton and membrane-bound organelles interact with cytoplasmic biomolecular condensates. The extent and relevance of these complex interactions are just beginning to emerge but may be important for cytoskeletal organization and organelle transport and remodeling. In this review, we highlight these emerging functions and emphasize the complex interplay of the cytoskeleton with these organelles. The crosstalk between membrane-bound organelles, biomolecular condensates and the cytoskeleton in highly polarized cells such as neurons could play essential roles in neuronal development, function and maintenance.

Raloxifene prevents stress granule dissolution, impairs translational control and promotes cell death during hypoxia in glioblastoma cells

Glioblastoma (GBM) is the most common primary malignant brain tumor, and it has a uniformly poor prognosis. Hypoxia is a feature of the GBM microenvironment, and previous work has shown that cancer cells residing in hypoxic regions resist treatment. Hypoxia can trigger the formation of stress granules (SGs), sites of mRNA triage that promote cell survival. A screen of 1120 FDA-approved drugs identified 129 candidates that delayed the dissolution of hypoxia-induced SGs following a return to normoxia. Amongst these candidates, the selective estrogen receptor modulator (SERM) raloxifene delayed SG dissolution in a dose-dependent manner. SG dissolution typically occurs by 15 min post-hypoxia, however pre-treatment of immortalized U251 and U3024 primary GBM cells with raloxifene prevented SG dissolution for up to 2 h. During this raloxifene-induced delay in SG dissolution, translational silencing was sustained, eIF2α remained phosphorylated and mTOR remained inactive. Despite its well-described role as a SERM, raloxifene-mediated delay in SG dissolution was unaffected by co-administration of β-estradiol, nor did β-estradiol alone have any effect on SGs. Importantly, the combination of raloxifene and hypoxia resulted in increased numbers of late apoptotic/necrotic cells. Raloxifene and hypoxia also demonstrated a block in late autophagy similar to the known autophagy inhibitor chloroquine (CQ). Genetic disruption of the SG-nucleating proteins G3BP1 and G3BP2 revealed that G3BP1 is required to sustain the raloxifene-mediated delay in SG dissolution. Together, these findings indicate that modulating the stress response can be used to exploit the hypoxic niche of GBM tumors, causing cell death by disrupting pro-survival stress responses and control of protein synthesis.

Targeting stress granules: A novel therapeutic strategy for human diseases

Stress granules (SGs) are assemblies of mRNA and proteins that form from mRNAs stalled in translation initiation in response to stress. Chronic stress might even induce formation of cytotoxic pathological SGs. SGs participate in various biological functions including response to apoptosis, inflammation, immune modulation, and signalling pathways; moreover, SGs are involved in pathogenesis of neurodegenerative diseases, viral infection, aging, cancers and many other diseases. Emerging evidence has shown that small molecules can affect SG dynamics, including assembly, disassembly, maintenance and clearance. Thus, targeting SGs is a potential therapeutic strategy for the treatment of human diseases and the promotion of health. The established methods for detecting SGs provided ready tools for large-scale screening of agents that alter the dynamics of SGs. Here, we describe the effects of small molecules on SG assembly, disassembly, and their roles in the disease. Moreover, we provide perspective for the possible application of small molecules targeting SGs in the treatment of human diseases.

Revisiting the Concept of Stress in the Prognosis of Solid Tumors: A Role for Stress Granules Proteins?

Simple Summary

Stress Granules (SGs) were discovered in 1999 and while the first decade of research has focused on some fundamental questions, the field is now investigating their role in human pathogenesis. Since then, evidences of a link between SGs and cancerology are accumulating in vitro and in vivo. In this work we summarized the role of SGs proteins in cancer development and their prognostic values. We find that level of expression of protein involved in SGs formation (and not mRNA level) could serve a prognostic marker in cancer. With this review we strongly suggest that SGs (proteins) could be targets of choice to block cancer development and counteract resistance to improve patients care.

Abstract

Cancer treatments are constantly evolving with new approaches to improve patient outcomes. Despite progresses, too many patients remain refractory to treatment due to either the development of resistance to therapeutic drugs and/or metastasis occurrence. Growing evidence suggests that these two barriers are due to transient survival mechanisms that are similar to those observed during stress response. We review the literature and current available open databases to study the potential role of stress response and, most particularly, the involvement of Stress Granules (proteins) in cancer. We propose that Stress Granule proteins may have prognostic value for patients.

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.

Treatment of cancer cells with Lapatinib negatively regulates general translation and induces stress granules formation

Stress granules (SG) are cytoplasmic RNA granules that form during various types of stress known to inhibit general translation, including oxidative stress, hypoxia, endoplasmic reticulum stress (ER), ionizing radiations or viral infection. Induction of these SG promotes cell survival in part through sequestration of proapoptotic molecules, resulting in the inactivation of cell death pathways. SG also form in cancer cells, but studies investigating their formation upon treatment with chemotherapeutics are very limited. Here we identified Lapatinib (Tykerb / Tyverb®), a tyrosine kinase inhibitor used for the treatment of breast cancers as a new inducer of SG in breast cancer cells. Lapatinib-induced SG formation correlates with the inhibition of general translation initiation which involves the phosphorylation of the translation initiation factor eIF2α through the kinase PERK. Disrupting PERK-SG formation by PERK depletion experiments sensitizes resistant breast cancer cells to Lapatinib. This study further supports the assumption that treatment with anticancer drugs activates the SG pathway, which may constitute an intrinsic stress response used by cancer cells to resist treatment.

Stress granules and neurodegeneration

Recent advances suggest that the response of RNA metabolism to stress has an important role in the pathophysiology of neurodegenerative diseases, particularly amyotrophic lateral sclerosis, frontotemporal dementias and Alzheimer disease. RNA-binding proteins (RBPs) control the utilization of mRNA during stress, in part through the formation of membraneless organelles termed stress granules (SGs). These structures form through a process of liquid-liquid phase separation. Multiple biochemical pathways regulate SG biology. The major signalling pathways regulating SG formation include the mammalian target of rapamycin (mTOR)-eukaryotic translation initiation factor 4F (eIF4F) and eIF2α pathways, whereas the pathways regulating SG dispersion and removal are mediated by valosin-containing protein and the autolysosomal cascade. Post-translational modifications of RBPs also strongly contribute to the regulation of SGs. Evidence indicates that SGs are supposed to be transient structures, but the chronic stresses associated with ageing lead to chronic, persistent SGs that appear to act as a nidus for the aggregation of disease-related proteins. We suggest a model describing how intrinsic vulnerabilities within the cellular RNA metabolism might lead to the pathological aggregation of RBPs when SGs become persistent. This process might accelerate the pathophysiology of many neurodegenerative diseases and myopathies, and it suggests new targets for disease intervention.

DDX3X acts as a live-or-die checkpoint in stressed cells by regulating NLRP3 inflammasome

The cellular stress response has a vital role in regulating homeostasis by modulating cell survival and death. Stress granules are cytoplasmic compartments that enable cells to survive various stressors. Defects in the assembly and disassembly of stress granules are linked to neurodegenerative diseases, aberrant antiviral responses and cancer1-5. Inflammasomes are multi-protein heteromeric complexes that sense molecular patterns that are associated with damage or intracellular pathogens, and assemble into cytosolic compartments known as ASC specks to facilitate the activation of caspase-1. Activation of inflammasomes induces the secretion of interleukin (IL)-1β and IL-18 and drives cell fate towards pyroptosis-a form of programmed inflammatory cell death that has major roles in health and disease6-12. Although both stress granules and inflammasomes can be triggered by the sensing of cellular stress, they drive contrasting cell-fate decisions. The crosstalk between stress granules and inflammasomes and how this informs cell fate has not been well-studied. Here we show that the induction of stress granules specifically inhibits NLRP3 inflammasome activation, ASC speck formation and pyroptosis. The stress granule protein DDX3X interacts with NLRP3 to drive inflammasome activation. Assembly of stress granules leads to the sequestration of DDX3X, and thereby the inhibition of NLRP3 inflammasome activation. Stress granules and the NLRP3 inflammasome compete for DDX3X molecules to coordinate the activation of innate responses and subsequent cell-fate decisions under stress conditions. Induction of stress granules or loss of DDX3X in the myeloid compartment leads to a decrease in the production of inflammasome-dependent cytokines in vivo. Our findings suggest that macrophages use the availability of DDX3X to interpret stress signals and choose between pro-survival stress granules and pyroptotic ASC specks. Together, our data demonstrate the role of DDX3X in driving NLRP3 inflammasome and stress granule assembly, and suggest a rheostat-like mechanistic paradigm for regulating live-or-die cell-fate decisions under stress conditions.

Stress Granules and Processing Bodies in Translational Control

Stress granules (SGs) and processing bodies (PBs) are non-membrane-enclosed RNA granules that dynamically sequester translationally inactive messenger ribonucleoprotein particles (mRNPs) into compartments that are distinct from the surrounding cytoplasm. mRNP remodeling, silencing, and/or storage involves the dynamic partitioning of closed-loop polyadenylated mRNPs into SGs, or the sequestration of deadenylated, linear mRNPs into PBs. SGs form when stress-activated pathways stall translation initiation but allow elongation and termination to occur normally, resulting in a sudden excess of mRNPs that are spatially condensed into discrete foci by protein:protein, protein:RNA, and RNA:RNA interactions. In contrast, PBs can exist in the absence of stress, when specific factors promote mRNA deadenylation, condensation, and sequestration from the translational machinery. The formation and dissolution of SGs and PBs reflect changes in messenger RNA (mRNA) metabolism and allow cells to modulate the proteome and/or mediate life or death decisions during changing environmental conditions.

Role of caprin-1 in carcinogenesis

RNA-binding proteins serve an essential role in post-transcriptional gene regulation. Cytoplasmic activation/proliferation-associated protein-1 (caprin-1) is an RNA-binding protein that participates in the regulation of cell cycle control-associated genes. Caprin-1 acts alone or in combination with other RNA-binding proteins, such as RasGAP SH3-domain-binding protein 1 and fragile X mental retardation protein. In the tumorigenesis process, caprin-1 primarily functions by activating cell proliferation and upregulating the expression of immune checkpoint proteins. Through the formation of stress granules, caprin-1 is also involved in the process by which tumor cells adapt to adverse conditions, which contributes to radiation and chemotherapy resistance. Given its role in various clinical malignancies, caprin-1 holds the potential to be used as a biomarker and a target for the development of novel therapeutics. The present review describes this newly identified putative oncogenic protein and its possible impact on tumorigenesis.

Translational control in brain pathologies: biological significance and therapeutic opportunities

Messenger RNA (mRNA) translation is the terminal step in protein synthesis, providing a crucial regulatory checkpoint for this process. Translational control allows specific cell types to respond to rapid changes in the microenvironment or to serve specific functions. For example, neurons use mRNA transport to achieve local protein synthesis at significant distances from the nucleus, the site of RNA transcription. Altered expression or functions of the various components of the translational machinery have been linked to several pathologies in the central nervous system. In this review, we provide a brief overview of the basic principles of mRNA translation, and discuss alterations of this process relevant to CNS disease conditions, with a focus on brain tumors and chronic neurological conditions. Finally, synthesizing this knowledge, we discuss the opportunities to exploit the biology of altered mRNA translation for novel therapies in brain disorders, as well as how studying these alterations can shed new light on disease mechanisms.

Nitric oxide triggers the assembly of "type II" stress granules linked to decreased cell viability

We show that 3-morpholinosydnonimine (SIN-1)-induced nitric oxide (NO) triggers the formation of SGs. Whereas the composition of NO-induced SGs is initially similar to sodium arsenite (SA)-induced type I (cytoprotective) SGs, the progressive loss of eIF3 over time converts them into pro-death (type II) SGs. NO-induced SG assembly requires the phosphorylation of eIF2α, but the transition to type II SGs is temporally linked to the mTOR-regulated displacement of eIF4F complexes from the m⁷ guanine cap. Whereas SA does not affect mitochondrial morphology or function, NO alters mitochondrial integrity and function, resulting in increased ROS production, decreased cytoplasmic ATP, and plasma membrane permeabilization, all of which are supported by type II SG assembly. Thus, cellular energy balance is linked to the composition and function of NO-induced SGs in ways that determine whether cells live or die.

Gle1 mediates stress granule-dependent survival during chemotoxic stress

Stress granules (SGs) are non-membrane bound organelles that form in response to multiple different stress stimuli, including exposure to sodium arsenite. SGs are postulated to support cells during periods of stress and provide a protective effect, allowing survival. Gle1 is a highly conserved, essential modulator of RNA-dependent DEAD-box proteins that exists as at least two distinct isoforms in human cells. Gle1A is required for proper SG formation, whereas Gle1B functions in mRNA export at the nuclear pore complex. Since Gle1A is required for SG function, we hypothesized that SG-dependent survival responses would also be Gle1-dependent. We describe here an experimental system for quantifying and testing the SG-associated survival response to sodium arsenite stress in HeLa cells. Gle1A was required for the sodium arsenite survival response, and overexpression of Gle1A supported the survival response. Overexpression of the SG-component G3BP also enabled the response. Next, we analyzed whether cells undergoing multiple rounds of stress yield a subpopulation with a higher propensity for SG formation and an increased resistance to undergoing apoptosis. After ten doses of sodium arsenite treatment, cells became resistant to sodium arsenite and to diclofenac sodium (another SG-inducing drug). The sodium arsenite-resistant cells exhibited changes in SG biology and had an increased survival response that was conferred in a paracrine manner. Changes in secreted factors occurred including a significantly lower level of MCP-1, a known regulator of stress granules and stress-induced apoptosis. This study supports models wherein SGs play a role in cell evasion of apoptosis and further reveal Gle1A and SG functions as targets for clinical approaches directed at chemoresistant/refractory cells.

The Role of RNA in Biological Phase Separations

Phase transitions that alter the physical state of ribonucleoprotein particles contribute to the spacial and temporal organization of the densely packed intracellular environment. This allows cells to organize biologically coupled processes as well as respond to environmental stimuli. RNA plays a key role in phase separation events that modulate various aspects of RNA metabolism. Here, we review the role that RNA plays in ribonucleoprotein phase separations.

Translational control of aberrant stress responses as a hallmark of cancer

Altered mRNA translational control is emerging as a critical factor in cancer development and progression. Targeting specific elements of the translational machinery, such as mTORC1 or eIF4E, is emerging as a new strategy for innovative cancer therapy. While translation of most mRNAs takes place through cap-dependent mechanisms, a sub-population of cellular mRNA species, particularly stress-inducible mRNAs with highly structured 5'-UTR regions, are primarily translated through cap-independent mechanisms. Intriguingly, many of these mRNAs encode proteins that are involved in tumour cell adaptation to microenvironmental stress, and thus linked to aggressive behaviour including tumour invasion and metastasis. This necessitates a rigorous search for links between microenvironmental stress and aggressive tumour phenotypes. Under stress, cells block global protein synthesis to preserve energy while maintaining selective synthesis of proteins that support cell survival. One highly conserved mechanism to regulate protein synthesis under cell stress is to sequester mRNAs into cytosolic aggregates called stress granules (SGs), where their translation is silenced. SGs confer survival advantages and chemotherapeutic resistance to tumour cells under stress. Recently, it has been shown that genetically blocking SG formation dramatically reduces tumour invasive and metastatic capacity in vivo. Therefore, targeting SG formation might represent a potential treatment strategy to block cancer metastasis. Here, we present the critical link between selective mRNA translation, stress adaptation, SGs, and tumour progression. Further, we also explain how deciphering mechanisms of selective mRNA translation occurs under cell stress holds great promise for the identification of new targets in the treatment of cancer. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Mechanistic insights into mammalian stress granule dynamics

The accumulation of stalled translation preinitiation complexes (PICs) mediates the condensation of stress granules (SGs). Interactions between prion-related domains and intrinsically disordered protein regions found in SG-nucleating proteins promote the condensation of ribonucleoproteins into SGs. We propose that PIC components, especially 40S ribosomes and mRNA, recruit nucleators that trigger SG condensation. With resolution of stress, translation reinitiation reverses this process and SGs disassemble. By cooperatively modulating the assembly and disassembly of SGs, ribonucleoprotein condensation can influence the survival and recovery of cells exposed to unfavorable environmental conditions.

Compatibility of Tanshinone IIA and Astragaloside IV in attenuating hypoxia-induced cardiomyocytes injury

ETHNOPHARMACOLOGICAL RELEVANCE

Herbal medicines including Tanshinone IIA (TanIIA) and Astragaloside IV (AsIV) are widely used in Asia as therapeutic agents for cardiovascular diseases, due to their complementary roles and shared properties based on the theory of traditional Chinese medicine and pharmacological researches. However, the underlying pathological mechanisms for their efficacy are still unclear. In addition, the compatibility or incompatibility of the herbal medicines when administered with other herbal remedies or with prescription drugs is unknown.

AIM OF THE STUDY

We aimed to investigate the compatibility of TanIIA and AsIV in protecting cardiomyocytes against hypoxia-induced injury.

MATERIALS AND METHODS

Cultured cardiomyocytes were stimulated in hypoxia condition, in the absence or presence of the two herbal compounds, TanIIA and AsIV. Indicators were determined by cytotoxicity assay, quantitative PCR, ELISA, flow cytometry assay, immunofluorescence staining and western blot.

RESULTS

Either TanIIA alone or the combined herbal compounds inhibited hypoxia-triggered chemokines production including CCL2/5/19, CXCL2 and Transwell assay-indicated monocyte/macrophage recruitment, cytokines production including TNF-α and IL-6. While AsIV alone or the combined herbal compounds attenuated hypoxia-induced cell apoptosis indicated by decreased Annexin V⁺ cells and the ratio of Bax/Bcl-2, but no significant effect of the herbal compounds was observed in modulating cell apoptosis following both hypoxia and TNF-α stimulation. As an anti-apoptotic factor, stress granule formation was further enhanced by AsIV alone or the combined herbal compounds in hypoxia or heat shock stress. Moreover, immunoblotting analysis indicated that stress-responsive mitogen-activated protein kinases (MAPK) pathways including the phosphorylation of ERK1/2, p38 and JNK were inhibited while the phosphorylation of Akt in phosphatidylinositol 3-kinase (PI3K) -Akt pathway for cell survival was restored by the herbal compounds. Among these results, the combination of TanIIA and AsIV comprised most of the beneficial properties tested, although their combination did not improve the maximal effects achieved by any of the compounds alone.

CONCLUSIONS

Taken together, these data suggest a compatibility of TanIIA and AsIV in protecting cardiomyocyte against hypoxia-induced injury.

Methods to Classify Cytoplasmic Foci as Mammalian Stress Granules

Cells are often challenged by sudden environmental changes. Stress Granules (SGs), cytoplasmic ribonucleoprotein complexes that form in cells exposed to stress conditions, are implicated in various aspects of cell metabolism and survival. SGs modulate cellular signaling pathways, post-transcriptional gene expression, and stress response programs. The formation of these mRNA-containing granules is directly connected to cellular translation. SG assembly is triggered by inhibited translation initiation, and SG disassembly is promoted by translation activation or by inhibited translation elongation. This relationship is further highlighted by SG composition. Core SG components are stalled translation pre-initiation complexes, mRNA, and selected RNA-binding Proteins (RBPs). The purpose of SG assembly is to conserve cellular energy by sequestering translationally stalled housekeeping mRNAs, allowing for the enhanced translation of stress-responsive proteins. In addition to the core constituents, such as stalled translation preinitiation complexes, SGs contain a plethora of other proteins and signaling molecules. Defects in SG formation can impair cellular adaptation to stress and can thus promote cell death. SGs and similar RNA-containing granules have been linked to a number of human diseases, including neurodegenerative disorders and cancer, leading to the recent interest in classifying and defining RNA granule subtypes. This protocol describes assays to characterize and quantify mammalian SGs.

Lycorine Induces Apoptosis of A549 Cells via AMPK-Mammalian Target of Rapamycin (mTOR)-S6K Signaling Pathway

BACKGROUND This study was designed to investigate the effect of lycorine (LY) on the AMPK-mTOR-S6K signaling pathway and to clarify its role in autophagy and apoptosis. MATERIAL AND METHODS Various concentrations of LY were used to treat non-small cell lung carcinoma A549 cells. The MTT assay was used to measure cell viability and acridine orange staining was used to detect cell morphology changes. Western blot analysis was used to test the effect of LY on the expression levels of LC3, caspase 3, and other proteins involved in the AMPK-mTOR-S6K signaling pathway. RESULTS The half maximal inhibitory concentration (IC50) of LY after 24-h treatment was 8.5 μM, with stronger inhibitory effect of 24-h LY treatment over 12-h LY treatment. Morphological observation showed that lower doses (4 μM and 8 μM) of LY treatment induced A549 cell death mainly caused by autophagy, whereas the higher dose (16 μM) of LY treatment induced A549 cell death, mainly caused by apoptosis. Furthermore, 8 μM LY caused the highest conversion of LC3-II from LC3-I. All LY treatments activated caspase-3. LY treatment also promoted AMPK phosphorylation (Thr172) and inhibited the phosphorylation of mTOR and S6K. CONCLUSIONS LY induced apoptosis of A549 cells by regulating the AMPK-mTOR-S6K signaling pathway. Lower levels (4~8 μM) of LY-induced autophagy contributed to LY-induced apoptosis.

Cytoplasmic stress granules: Dynamic modulators of cell signaling and disease

Stress granule (SG) assembly is a conserved cellular strategy to minimize stress-related damage and promote cell survival. Beyond their fundamental role in the stress response, SGs have emerged as key players for human health. As such, SG assembly is associated with cancer, neurodegenerative disorders, ischemia, and virus infections. SGs and granule-related signaling circuits are therefore promising targets to improve therapeutic intervention for several diseases. This is clinically relevant, because pharmacological drugs can affect treatment outcome by modulating SG formation. As membraneless and highly dynamic compartments, SGs regulate translation, ribostasis and proteostasis. Moreover, they serve as signaling hubs that determine cell viability and stress recovery. Various compounds can modulate SG formation and dynamics. Rewiring cell signaling through SG manipulation thus represents a new strategy to control cell fate under various physiological and pathological conditions.