Inhibition Of Stress Granules Formation Research Articles

Critical role of G3BP1 in bovine parainfluenza virus type 3 (BPIV3)-inhibition of stress granules formation and viral replication.

It remains unclear whether BPIV3 infection leads to stress granules formation and whether G3BP1 plays a role in this process and in viral replication. This study aims to clarify the association between BPIV3 and stress granules, explore the effect of G3BP1 on BPIV3 replication, and provide significant insights into the mechanisms by which BPIV3 evades the host's antiviral immunity to support its own survival. Here, we use Immunofluorescence staining to observe the effect of BPIV3 infection on the assembly of stress granules. Meanwhile, the expression changes of eIF2α and G3BP1 were determined. Overexpression or siRNA silencing of intracellular G3BP1 levels was examined for its regulatory control of BPIV3 replication. We identify that the BPIV3 infection elicited phosphorylation of the eIF2α protein. However, it did not induce the assembly of stress granules; rather, it inhibited the formation of stress granules and downregulated the expression of G3BP1. G3BP1 overexpression facilitated the formation of stress granules within cells and hindered viral replication, while G3BP1 knockdown enhanced BPIV3 expression. This study suggest that G3BP1 plays a crucial role in BPIV3 suppressing stress granule formation and viral replication.

Abstract LB303: Suppression of stress granule formation is a novel vulnerability imposed by mutant p53

Abstract Mutation of the tumor suppressor p53 is the most common cancer specific event. Most of these mutations are missense mutations in the DNA-binding domain of p53, causing loss of wild-type p53 (wtp53) transcriptional activity. Missense mutant p53 (mutp53) also enhances cancer malignancy in a manner independent of wtp53. Hence, mutp53 is an ideal therapeutic target due to its uniqueness and high expression levels in cancers; however, directly targeting mutp53 protein itself has been challenging. To better understand the mechanism of oncogenic function of mutp53, we performed in silico TCGA database analysis and found that patients with missense mutp53-carrying hepatocellular carcinoma (HCC), but not other types of cancer, had unexpectedly better overall survival than patients with p53-null HCC. Since sorafenib (SOR) has historically been used as a single agent chemotherapy for HCC, unlike other cancer types, we hypothesized that SOR treatment may have yet unappreciated advantages for treating mutp53-expressing tumors. Indeed, knockdown of mutp53 rendered HCC cells and xenografts more resistant to SOR. Consistent with a report showing that SOR induces ER stress-mediated pro-survival stress granule (SG) formation, mutp53-expressing HCC cells, treated with SOR or other ER stress inducers, formed significantly fewer SGs with increased apoptosis, as compared with mutp53-knockdown cells. This result was partly due to mutp53’s ability to interact with an eIF2α kinase PERK and a key SG core protein, G3BP1. Moreover, the oligomerization domain of mutp53 was required for the interaction of mutp53 with G3BP1 and subsequent suppression of ER-stress-mediated SG formation and survival. These results suggest that inhibition of SG formation is a novel vulnerability imposed by mutp53, leading to sensitization of cancer cells to ER stress. Our results also emphasize the use of ER stress inducers to treat mutp53-expressing tumors and mutp53 as a biomarker of SOR sensitivity. Citation Format: Elizabeth Thoenen, Atul Ranjan, Alejandro Parrales, Shigeto Nishikawa, Dan Dixon, Sugako Oka, Tomoo Iwakuma. Suppression of stress granule formation is a novel vulnerability imposed by mutant p53 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB303.

Hollow copper sulfide nanoparticles carrying ISRIB for the sensitized photothermal therapy of breast cancer and brain metastases through inhibiting stress granule formation and reprogramming tumor-associated macrophages.

As known, the benefits of photothermal therapy (PTT) are greatly limited by the heat tolerance of cancer cells resulting from overexpressed heat shock proteins (HSPs). Then HSPs further trigger the formation of stress granules (SGs) that regulate protein expression and cell viability under various stress conditions. Inhibition of SG formation can sensitize tumor cells to PTT. Herein, we developed PEGylated pH (low) insertion peptide (PEG-pHLIP)-modified hollow copper sulfide nanoparticles (HCuS NPs) encapsulating the SG inhibitor ISRIB, with the phase-change material lauric acid (LA) as a gate-keeper, to construct a pH-driven and NIR photo-responsive controlled smart drug delivery system (IL@H-PP). The nanomedicine could specifically target slightly acidic tumor sites. Upon irradiation, IL@H-PP realized PTT, and the light-controlled release of ISRIB could effectively inhibit the formation of PTT-induced SG to sensitize tumor cells to PTT, thereby increasing the antitumor effect and inducing potent immunogenic cell death (ICD). Moreover, IL@H-PP could promote the production of reactive oxygen species (ROS) by tumor-associated macrophages (TAMs), repolarizing them towards the M1 phenotype and remodeling the immunosuppressive microenvironment. Invitro/vivo results revealed the potential of PTT combined with SG inhibitors, which provides a new paradigm for antitumor and anti-metastases.

African swine fever virus pS273R antagonizes stress granule formation by cleaving the nucleating protein G3BP1 to facilitate viral replication

Cytoplasmic stress granules (SGs) are generally triggered by stress-induced translation arrest for storing mRNAs. Recently, it has been shown that SGs are regulated by different stimulators including viral infection, which is involved in the antiviral activity of host cells to limit viral propagation. To survive, several viruses have been reported to execute various strategies, such as modulating SG formation, to create optimal surroundings for viral replication. African swine fever virus (ASFV) is one of the most notorious pathogens in the global pig industry. However, the interplay between ASFV infection and SG formation remains largely unknown. In this study, we found that ASFV infection inhibited SG formation. Through SG inhibitory screening, we found that several ASFV-encoded proteins are involved in inhibition of SG formation. Among them, an ASFV S273R protein (pS273R), the only cysteine protease encoded by the ASFV genome, significantly affected SG formation. ASFV pS273R interacted with G3BP1 (Ras-GTPase-activating protein [SH3 domain] binding protein 1), a vital nucleating protein of SG formation. Furthermore, we found that ASFV pS273R cleaved G3BP1 at the G140-F141 to produce two fragments (G3BP1-N1-140 and G3BP1-C141-456). Interestingly, both the pS273R-cleaved fragments of G3BP1 lost the ability to induce SG formation and antiviral activity. Taken together, our finding reveals that the proteolytic cleavage of G3BP1 by ASFV pS273R is a novel mechanism by which ASFV counteracts host stress and innate antiviral responses.

FUS ALS neurons activate major stress pathways and reduce translation as an early protective mechanism against neurodegeneration.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder causing progressive loss of motor neurons. Mutations in Fused in sarcoma (FUS) leading to its cytoplasmic mislocalization cause a subset of ALS. Under stress, mutant FUS localizes to stress granules (SGs)-cytoplasmic condensates composed of RNA and various proteins. Aberrant dynamics of SGs is linked to the pathology of ALS. Here, using motor neurons (MNs) derived from human induced pluripotent stem cells, we show that, in mutant FUS, MN dynamics of SGs is disturbed. Additionally, heat-shock response (HSR) and integrated stress response (ISR) involved in the regulation of SGs are upregulated in mutant MNs. HSR activation correlates with the amount of cytoplasmic FUS mislocalization. While inhibition of SG formation, translation, or ISR does not influence survival of FUS ALS neurons, proteotoxicity that cannot be compensated with the activation of stress pathways is the main driver of neurodegeneration in early FUS ALS.

Emetine‐Loaded Black Phosphorus Hydrogel Sensitizes Tumor to Photothermal Therapy through Inhibition of Stress Granule Formation

AbstractDuring photothermal therapy (PTT), hyperthermia up to 50 °C is required for efficient induction of tumor cell death. Additional increases in temperature can lead to severe damage to adjacent tissues. Conversely, insufficient heating of deep‐seated tumor tissues results in tumor recurrence. Sensitization of tumor cells to PTT may solve this problem. Stress granules (SGs) function in integration of various internal and external stresses to regulate cell viability. However, the role of SGs in PTT is currently unknown. Here, with black phosphorus (BP) nanosheets as photothermal agents, it is found that SGs are induced in tumor by PTT through eukaryotic initiation factor 2α‐dependent pathway and participate in tumor resistance to PTT. To modulate SG formation in tumor, a BP hydrogel is prepared for tumor‐specific delivery and near‐infrared (NIR) light‐controlled release of the SG inhibitor Emetine. Upon NIR‐light irradiation, photothermal conversion of BP nanosheets enables PTT of tumor. Meanwhile, light‐controlled release of Emetine in tumor tissues effectively inhibits PTT‐induced SG formation and sensitizes tumor to PTT, resulting in enhanced tumor inhibition. These results reveal the role of SGs in PTT and present a novel strategy for tumor sensitization to enhance the therapeutic efficacy and reduce the side effects of PTT.

The Different Tactics of Foot-and-Mouth Disease Virus to Evade Innate Immunity.

Like all pathogens, foot-and-mouth disease virus (FMDV) is recognized by the immune system inducing a heightened immune response mainly mediated by type I and type III IFNs. To overcome the strong antiviral response induced by these cytokines, FMDV has evolved many strategies exploiting each region of its small RNA genome. These include: (a) inhibition of IFN induction at the transcriptional and translational level, (b) inhibition of protein trafficking; (c) blockage of specific post-translational modifications in proteins that regulate innate immune signaling; (d) modulation of autophagy; (e) inhibition of stress granule formation; and (f) in vivo modulation of immune cell function. Here, we summarize and discuss FMDV virulence factors and the host immune footprint that characterize infection in cell culture and in the natural hosts.

Inhibition of Stress Granule Formation by Middle East Respiratory Syndrome Coronavirus 4a Accessory Protein Facilitates Viral Translation, Leading to Efficient Virus Replication.

Stress granule (SG) formation is generally triggered as a result of stress-induced translation arrest. The impact of SG formation on virus replication varies among different viruses, and the significance of SGs in coronavirus (CoV) replication is largely unknown. The present study examined the biological role of SGs in Middle East respiratory syndrome (MERS)-CoV replication. The MERS-CoV 4a accessory protein is known to inhibit SG formation in cells in which it was expressed by binding to double-stranded RNAs and inhibiting protein kinase R (PKR)-mediated phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α). Replication of MERS-CoV lacking the genes for 4a and 4b (MERS-CoV-Δp4), but not MERS-CoV, induced SG accumulation in MERS-CoV-susceptible HeLa/CD26 cells, while replication of both viruses failed to induce SGs in Vero cells, demonstrating cell type-specific differences in MERS-CoV-Δp4-induced SG formation. MERS-CoV-Δp4 replicated less efficiently than MERS-CoV in HeLa/CD26 cells, and inhibition of SG formation by small interfering RNA-mediated depletion of the SG components promoted MERS-CoV-Δp4 replication, demonstrating that SG formation was detrimental for MERS-CoV replication. Inefficient MERS-CoV-Δp4 replication was not due to either the induction of type I and type III interferons or the accumulation of viral mRNAs in the SGs. Rather, it was due to the inefficient translation of viral proteins, which was caused by high levels of PKR-mediated eIF2α phosphorylation and likely by the confinement of various factors that are required for translation in the SGs. Finally, we established that deletion of the 4a gene alone was sufficient for inducing SGs in infected cells. Our study revealed that 4a-mediated inhibition of SG formation facilitates viral translation, leading to efficient MERS-CoV replication.IMPORTANCE Middle East respiratory syndrome coronavirus (MERS-CoV) causes respiratory failure with a high case fatality rate in patients, yet effective antivirals and vaccines are currently not available. Stress granule (SG) formation is one of the cellular stress responses to virus infection and is generally triggered as a result of stress-induced translation arrest. SGs can be beneficial or detrimental for virus replication, and the biological role of SGs in CoV infection is unclear. The present study showed that the MERS-CoV 4a accessory protein, which was reported to block SG formation in cells in which it was expressed, inhibited SG formation in infected cells. Our data suggest that 4a-mediated inhibition of SG formation facilitates the translation of viral mRNAs, resulting in efficient virus replication. To our knowledge, this report is the first to show the biological significance of SG in CoV replication and provides insight into the interplay between MERS-CoV and antiviral stress responses.

Chemical compounds that suppress hypoxia-induced stress granule formation enhance cancer drug sensitivity of human cervical cancer HeLa cells.

In eukaryotic cells, when exposed to certain types of stress including hypoxia, eIF2α is phosphorylated by several kinases including protein kinase R (PKR) and PKR-like endoplasmic reticulum kinase (PERK). Subsequently, protein translation is stopped and stress granules (SGs) are formed. Cancer cells form SGs under hypoxia. SGs accumulate apoptosis-related molecules and play anti-apoptotic roles. Thus, hypoxia-induced SG formation contributes to drug resistance in cancer cells. For this reason, inhibition of SG formation is expected to be beneficial in cancer therapy. To prove this concept, chemical reagents that inhibit SG formation are required as experimental tools. We searched for chemical compounds that suppress SG formation and identified that β-estradiol, progesterone, and stanolone (hereafter described as EPS) inhibit SG formation in human cervical cancer HeLa cells. As it turned out, EPS block PKR but not PERK, thus fail to suppress SG formation in most cancer cells, where SGs are formed via PERK. Nevertheless, in this study, we used HeLa cells as a model and demonstrated that EPS block hypoxia-induced SG formation in HeLa cells and consequently reduce drug resistance that HeLa cells acquire under hypoxia. Our findings support that inhibition of SG formation is a useful method to control cancers.

Inclusion bodies of human parainfluenza virus type 3 inhibit antiviral stress granule formation by shielding viral RNAs.

Viral invasion triggers the activation of the host antiviral response. Besides the innate immune response, stress granules (SGs) also act as an additional defense response to combat viral replication. However, many viruses have evolved various strategies to suppress SG formation to facilitate their own replication. Here, we show that viral mRNAs derived from human parainfluenza virus type 3 (HPIV3) infection induce SG formation in an eIF2α phosphorylation- and PKR-dependent manner in which viral mRNAs are sequestered and viral replication is inhibited independent of the interferon signaling pathway. Furthermore, we found that inclusion body (IB) formation by the interaction of the nucleoprotein (N) and phosphoprotein (P) of HPIV3 correlated with SG suppression. In addition, co-expression of P with NL478A (a point mutant of N, which is unable to form IBs with P) or with NΔN10 (lacking N-terminal 10 amino acids of N, which could form IBs with P but was unable to synthesize or shield viral RNAs) failed to inhibit SG formation, suggesting that inhibition of SG formation also correlates with the capacity of IBs to synthesize and shield viral RNAs. Therefore, we provide a model whereby viral IBs escape the antiviral effect of SGs by concealing their own newly synthesized viral RNAs and offer new insights into the emerging role of IBs in viral replication.

KSHV inhibits stress granule formation by viral ORF57 blocking PKR activation

TIA-1 positive stress granules (SG) represent the storage sites of stalled mRNAs and are often associated with the cellular antiviral response. In this report, we provide evidence that Kaposi’s sarcoma-associated herpesvirus (KSHV) overcomes the host antiviral response by inhibition of SG formation via a viral lytic protein ORF57. By immunofluorescence analysis, we found that B lymphocytes with KSHV lytic infection are refractory to SG induction. KSHV ORF57, an essential post-transcriptional regulator of viral gene expression and the production of new viral progeny, inhibits SG formation induced experimentally by arsenite and poly I:C, but not by heat stress. KSHV ORF37 (vSOX) bearing intrinsic endoribonuclease activity also inhibits arsenite-induced SG formation, but KSHV RTA, vIRF-2, ORF45, ORF59 and LANA exert no such function. ORF57 binds both PKR-activating protein (PACT) and protein kinase R (PKR) through their RNA-binding motifs and prevents PACT-PKR interaction in the PKR pathway which inhibits KSHV production. Consistently, knocking down PKR expression significantly promotes KSHV virion production. ORF57 interacts with PKR to inhibit PKR binding dsRNA and its autophosphorylation, leading to inhibition of eIF2α phosphorylation and SG formation. Homologous protein HSV-1 ICP27, but not EBV EB2, resembles KSHV ORF57 in the ability to block the PKR/eIF2α/SG pathway. In addition, KSHV ORF57 inhibits poly I:C-induced TLR3 phosphorylation. Altogether, our data provide the first evidence that KSHV ORF57 plays a role in modulating PKR/eIF2α/SG axis and enhances virus production during virus lytic infection.

Phospho-Rasputin Stabilization by Sec16 Is Required for Stress Granule Formation upon Amino Acid Starvation

Most cellular stresses induce protein translation inhibition and stress granule formation. Here, using Drosophila S2 cells, we investigate the role of G3BP/Rasputin in this process. In contrast to arsenite treatment, where dephosphorylated Ser142 Rasputin is recruited to stress granules, we find that, upon amino acid starvation, only the phosphorylated Ser142 form is recruited. Furthermore, we identify Sec16, a component of the endoplasmic reticulum exit site, as a Rasputin interactor and stabilizer. Sec16 depletion results in Rasputin degradation and inhibition of stress granule formation. However, in the absence of Sec16, pharmacological stabilization of Rasputin is not enough to rescue the assembly of stress granules. This is because Sec16 specifically interacts with phosphorylated Ser142 Rasputin, the form required for stress granule formation upon amino acid starvation. Taken together, these results demonstrate that stress granule formation is fine-tuned by specific signaling cues that are unique to each stress. These results also expand the role of Sec16 as a stress response protein.

Staufen1 impairs stress granule formation in skeletal muscle cells from myotonic dystrophy type 1 patients.

Myotonic dystrophy (DM1) is caused by an expansion of CUG repeats (CUG(exp)) in the DMPK mRNA 3'UTR. CUG(exp)-containing mRNAs become toxic to cells by misregulating RNA-binding proteins. Here we investigated the consequence of this RNA toxicity on the cellular stress response. We report that cell stress efficiently triggers formation of stress granules (SGs) in proliferating, quiescent, and differentiated muscle cells, as shown by the appearance of distinct cytoplasmic TIA-1- and DDX3-containing foci. We show that Staufen1 is also dynamically recruited into these granules. Moreover, we discovered that DM1 myoblasts fail to properly form SGs in response to arsenite. This blockage was not observed in DM1 fibroblasts, demonstrating a cell type-specific defect. DM1 myoblasts display increased expression and sequestration of toxic CUG(exp) mRNAs compared with fibroblasts. Of importance, down-regulation of Staufen1 in DM1 myoblasts rescues SG formation. Together our data show that Staufen1 participates in the inhibition of SG formation in DM1 myoblasts. These results reveal that DM1 muscle cells fail to properly respond to stress, thereby likely contributing to the complex pathogenesis of DM1.

Is the microtubule disruption-induced alteration of peroxide concentration a factor inhibiting the assembly of ribonucleoprotein stress granules?

It has been examined whether the destruction of cell microtubules affects the increase in the intracellular hydrogen peroxide concentration caused by sodium arsenite, which induces the formation of stress ribonucleoprotein granules. As expected, sodium arsenite caused a 50% increase in hydrogen peroxide concentration in HeLa cells; on the other hand, another stress granule inducer tert-buthylhydroquinone did not affect the peroxide concentration. The disruption of microtubules by nocodazole or vinblastine also resulted in some increase in the intracellular peroxide concentration,y taxol did not affect it. The combined treatment of cells with and the microtubule stabilization by taxol did not affect it. The combined treatment of cells with arsenite and antimicrotubule drugs caused an additive effect, and the peroxide concentration increased twice or more. Thus, the inhibition of stress granule formation after microtubule disruption cannot be explained by a decrease in peroxide concentration as compared with the affect of arsenite.