UBAP2L arginine methylation by PRMT1 modulates stress granule assembly. Cell Death Differ. 2020;27:227-241. [PMID: 31114027 PMCID: PMC7205891 DOI: 10.1038/s41418-019-0350-5]

Application of stress granule core element G3BP1 in various diseases: A review

Ras-GTPase-activating protein-binding protein 1 (G3BP1) is a core component and crucial regulatory switch in stress granules (SGs). When the concentration of free RNA within cells increases, it can trigger RNA-dependent liquid-liquid phase separation (LLPS) with G3BP1 as the core, thereby forming SGs that affect cell survival or death. In addition, G3BP1 interacts with various host proteins to regulate the expression of SGs. As a multifunctional binding protein, G3BP1 has diverse biological functions, influencing cell proliferation, differentiation, apoptosis, and RNA metabolism and serving as a crucial regulator in signaling pathways such as Rac1-PAK1, TSC-mTORC1, NF-κB, and STAT3. Therefore, it plays a significant role in the regulation of neurodegenerative diseases, myocardial hypertrophy, and congenital immunity, and is involved in the proliferation, invasion, and metastasis of cancer cells. G3BP1 is an important antiviral factor that interacts with viral proteins, and regulates SG assembly to exert antiviral effects. This article focuses on the recent discoveries and progress of G3BP1 in biology, including its structure and function, regulation of SG formation and dissolution, and its relationships with non-neoplastic diseases, tumors, and viruses.

Modulation of stress granule dynamics by phosphorylation and ubiquitination in plants

The Arabidopsis tandem CCCH zinc finger 1 (TZF1) is an RNA-binding protein that plays a pivotal role in plant growth and stress response. In this report, we show that TZF1 contains two intrinsically disordered regions necessary for its localization to stress granules (SGs). TZF1 recruits mitogen-activated protein kinase (MAPK) signaling components and an E3 ubiquitin ligase KEEP-ON-GOING (KEG) to SGs. TZF1 is phosphorylated by MPKs and ubiquitinated by KEG. Using a high throughput Arabidopsis protoplasts transient expression system, mutant studies reveal that the phosphorylation of specific residues plays differential roles in enhancing or reducing TZF1 SG assembly and protein-protein interaction with mitogen-activated kinase kinase 5 in SGs. Ubiquitination appears to play a positive role in TZF1 SG assembly, because mutations cause a reduction of typical SGs, while enhancing the assembly of large SGs encompassing the nucleus. Together, our results demonstrate that plant SG assembly is distinctively regulated by phosphorylation and ubiquitination.

UBAP2L contributes to formation of P-bodies and modulates their association with stress granules

Stress triggers the formation of two distinct cytoplasmic biomolecular condensates: stress granules (SGs) and processing bodies (PBs), both of which may contribute to stress-responsive translation regulation. Though PBs can be present constitutively, stress can increase their number and size and lead to their interaction with stress-induced SGs. The mechanism of such interaction, however, is largely unknown. Formation of canonical SGs requires the RNA binding protein Ubiquitin-Associated Protein 2-Like (UBAP2L), which is a central SG node protein in the RNA-protein interaction network of SGs and PBs. UBAP2L binds to the essential SG and PB proteins G3BP and DDX6, respectively. Research on UBAP2L has mostly focused on its role in SGs, but not its connection to PBs. We find that UBAP2L is not solely an SG protein but also localizes to PBs in certain conditions, contributes to PB biogenesis and SG-PB interactions, and can nucleate hybrid granules containing SG and PB components in cells. These findings inform a new model for SG and PB formation in the context of UBAP2L's role.

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.

Metal-polyphenol-network coated R612F nanoparticles reduce drug resistance in hepatocellular carcinoma by inhibiting stress granules

Stress granules (SGs) are considered to be the nonmembrane discrete assemblies present in the cytoplasm to cope with various environmental stress. SGs can promote the progression and drug resistance of hepatocellular carcinoma (HCC). Therefore, it is important to explore the mechanism of SG formation to reduce drug resistance in HCC. In this study, we demonstrate that p110α is required for SGs assembly. Mechanistically, the Arg-Gly (RG) motif of p110α is required for SG competence and regulates the recruitment of SG components. The methylation of p110α mediated by protein arginine methyltransferase 1 (PRMT1) interferes with the recruitment of p110α to SG components, thereby inhibiting the promotion of p110α to SGs. On this basis, we generated metal-polyphenol-network-coated R612F nanoparticles (MPN-R612F), which can efficiently enter HCC cells and maintain the hypermethylation state of p110α, thereby inhibiting the assembly of SGs and ultimately reducing the resistance of HCC cells to sorafenib. The combination of MPN-R612F nanoparticles and sorafenib can kill HCC cells more effectively and play a stronger anti-tumor effect. This study provides a new perspective for targeting SGs in the treatment of HCC.

Stress granules in cancer: Adaptive dynamics and therapeutic implications

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

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

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

The HRD1-SEL1L ubiquitin ligase regulates stress granule homeostasis in couple with distinctive signaling branches of ER stress

Stress granules (SGs) are membrane-less cellular compartments which are dynamically assembled via biomolecular condensation mechanism when eukaryotic cells encounter environmental stresses. SGs are important for gene expression and cell fate regulation. Dysregulation of SG homeostasis has been linked to human neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we report that the HRD1-SEL1L ubiquitin ligase complex specifically regulates the homeostasis of heat shock-induced SGs through the ubiquitin-proteasome system (UPS) and the UPS-associated ATPase p97. Mechanistically, the HRD1-SEL1L complex mediates SG homeostasis through the BiP-coupled PERK-eIF2α signaling axis of endoplasmic reticulum (ER) stress, thereby coordinating the unfolded protein response (UPR) with SG dynamics. Furthermore, we show that the distinctive branches of ER stress play differential roles in SG homeostasis. Our study indicates that the UPS and the UPR together via the HRD1-SEL1L ubiquitin ligase to maintain SG homeostasis in a stressor-dependent manner.

UBAP2L ensures homeostasis of nuclear pore complexes at the intact nuclear envelope

Assembly of macromolecular complexes at correct cellular sites is crucial for cell function. Nuclear pore complexes (NPCs) are large cylindrical assemblies with eightfold rotational symmetry, built through hierarchical binding of nucleoporins (Nups) forming distinct subcomplexes. Here, we uncover a role of ubiquitin-associated protein 2-like (UBAP2L) in the assembly and stability of properly organized and functional NPCs at the intact nuclear envelope (NE) in human cells. UBAP2L localizes to the nuclear pores and facilitates the formation of the Y-complex, an essential scaffold component of the NPC, and its localization to the NE. UBAP2L promotes the interaction of the Y-complex with POM121 and Nup153, the critical upstream factors in a well-defined sequential order of Nups assembly onto NE during interphase. Timely localization of the cytoplasmic Nup transport factor fragile X-related protein 1 (FXR1) to the NE and its interaction with the Y-complex are likewise dependent on UBAP2L. Thus, this NPC biogenesis mechanism integrates the cytoplasmic and the nuclear NPC assembly signals and ensures efficient nuclear transport, adaptation to nutrient stress, and cellular proliferative capacity, highlighting the importance of NPC homeostasis at the intact NE.

Fragile X Messenger Ribonucleoprotein Protein and Its Multifunctionality: From Cytosol to Nucleolus and Back

Silencing of the fragile X messenger ribonucleoprotein 1 (FMR1) gene and a consequent lack of FMR protein (FMRP) synthesis are associated with fragile X syndrome, one of the most common inherited intellectual disabilities. FMRP is a multifunctional protein that is involved in many cellular functions in almost all subcellular compartments under both normal and cellular stress conditions in neuronal and non-neuronal cell types. This is achieved through its trafficking signals, nuclear localization signal (NLS), nuclear export signal (NES), and nucleolar localization signal (NoLS), as well as its RNA and protein binding domains, and it is modulated by various post-translational modifications such as phosphorylation, ubiquitination, sumoylation, and methylation. This review summarizes the recent advances in understanding the interaction networks of FMRP with a special focus on FMRP stress-related functions, including stress granule formation, mitochondrion and endoplasmic reticulum plasticity, ribosome biogenesis, cell cycle control, and DNA damage response.

A super-enhancer-regulated RNA-binding protein cascade drives pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy in need of new therapeutic options. Using unbiased analyses of super-enhancers (SEs) as sentinels of core genes involved in cell-specific function, here we uncover a druggable SE-mediated RNA-binding protein (RBP) cascade that supports PDAC growth through enhanced mRNA translation. This cascade is driven by a SE associated with the RBP heterogeneous nuclear ribonucleoprotein F, which stabilizes protein arginine methyltransferase 1 (PRMT1) to, in turn, control the translational mediator ubiquitin-associated protein 2-like. All three of these genes and the regulatory SE are essential for PDAC growth and coordinately regulated by the Myc oncogene. In line with this, modulation of the RBP network by PRMT1 inhibition reveals a unique vulnerability in Myc-high PDAC patient organoids and markedly reduces tumor growth in male mice. Our study highlights a functional link between epigenetic regulation and mRNA translation and identifies components that comprise unexpected therapeutic targets for PDAC.

Tudor-dimethylarginine interactions: the condensed version

Biomolecular condensates (BMCs) can facilitate or inhibit diverse cellular functions. BMC formation is driven by noncovalent protein-protein, protein-RNA, and RNA-RNA interactions. Here, we focus on Tudor domain-containing proteins - such as survival motor neuron protein (SMN) - that contribute to BMC formation by binding to dimethylarginine (DMA) modifications on protein ligands. SMN is present in RNA-rich BMCs, and its absence causes spinal muscular atrophy (SMA). SMN's Tudor domain forms cytoplasmic and nuclear BMCs, but its DMA ligands are largely unknown, highlighting open questions about the function of SMN. Moreover, DMA modification can alter intramolecular interactions and affect protein localization. Despite these emerging functions, the lack of direct methods of DMA detection remains an obstacle to understanding Tudor-DMA interactions in cells.

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.

Regulation of Biomolecular Condensates by Poly(ADP-ribose)

Biomolecular condensates are reversible compartments that form through a process called phase separation. Post-translational modifications like ADP-ribosylation can nucleate the formation of these condensates by accelerating the self-association of proteins. Poly(ADP-ribose) (PAR) chains are remarkably transient modifications with turnover rates on the order of minutes, yet they can be required for the formation of granules in response to oxidative stress, DNA damage, and other stimuli. Moreover, accumulation of PAR is linked with adverse phase transitions in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. In this review, we provide a primer on how PAR is synthesized and regulated, the diverse structures and chemistries of ADP-ribosylation modifications, and protein-PAR interactions. We review substantial progress in recent efforts to determine the molecular mechanism of PAR-mediated phase separation, and we further delineate how inhibitors of PAR polymerases may be effective treatments for neurodegenerative pathologies. Finally, we highlight the need for rigorous biochemical interrogation of ADP-ribosylation in vivo and in vitro to clarify the exact pathway from PARylation to condensate formation.

The pros and cons of ubiquitination on the formation of protein condensates

Ubiquitination, a post-translational modification that attaches one or more ubiquitin (Ub) molecules to another protein, plays a crucial role in the phase-separation processes. Ubiquitination can modulate the formation of membrane-less organelles in two ways. First, a scaffold protein drives phase separation, and Ub is recruited to the condensates. Second, Ub actively phase-separates through the interactions with other proteins. Thus, the role of ubiquitination and the resulting polyUb chains ranges from bystanders to active participants in phase separation. Moreover, long polyUb chains may be the primary driving force for phase separation. We further discuss that the different roles can be determined by the lengths and linkages of polyUb chains which provide preorganized and multivalent binding platforms for other client proteins. Together, ubiquitination adds a new layer of regulation for the flow of material and information upon cellular compartmentalization of proteins.

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.

The association of UBAP2L and G3BP1 mediated by small nucleolar RNA is essential for stress granule formation

Stress granules (SGs) are dynamic, non-membranous structures composed of non-translating mRNAs and various proteins and play critical roles in cell survival under stressed conditions. Extensive proteomics analyses have been performed to identify proteins in SGs; however, the molecular functions of these components in SG formation remain unclear. In this report, we show that ubiquitin-associated protein 2-like (UBAP2L) is a crucial component of SGs. UBAP2L localized to SGs in response to various stresses, and its depletion significantly suppressed SG organization. Proteomics and RNA sequencing analyses found that UBAP2L formed a protein-RNA complex with Ras-GTP-activating protein SH3 domain binding protein 1 (G3BP1) and small nucleolar RNAs (snoRNAs). In vitro binding analysis demonstrated that snoRNAs were required for UBAP2L association with G3BP1. In addition, decreased expression of snoRNAs reduced the interaction between UBAP2L and G3BP1 and suppressed SG formation. Our results reveal a critical role of SG component, the UBAP2L/snoRNA/G3BP1 protein-RNA complex, and provide new insights into the regulation of SG assembly.

SERBP1 Promotes Stress Granule Clearance by Regulating 26S Proteasome Activity and G3BP1 Ubiquitination and Protects Male Germ Cells from Thermostimuli Damage

Stress granules (SGs) are membraneless cytoplasmic condensates that dynamically assemble in response to various stressors and reversibly disassemble after stimulus removal; however, the mechanisms underlying SG dynamics and their physiological roles in germ cell development are elusive. Here, we show that SERBP1 (SERPINE1 mRNA binding protein 1) is a universal SG component and conserved regulator of SG clearance in somatic and male germ cells. SERBP1 interacts with the SG core component G3BP1 and 26S proteasome proteins PSMD10 and PSMA3 and recruits them to SGs. In the absence of SERBP1, reduced 20S proteasome activity, mislocalized valosin containing protein (VCP) and Fas associated factor family member 2 (FAF2), and diminished K63-linked polyubiquitination of G3BP1 during the SG recovery period were observed. Interestingly, the depletion of SERBP1 in testicular cells in vivo causes increased germ cell apoptosis upon scrotal heat stress. Accordingly, we propose that a SERBP1-mediated mechanism regulates 26S proteasome activity and G3BP1 ubiquitination to facilitate SG clearance in both somatic and germ cell lines.

Stress granules dynamics and promising functions in pancreatic cancer

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

A New Phase of Networking: The Molecular Composition and Regulatory Dynamics of Mammalian Stress Granules

Stress granules (SGs) are cytosolic biomolecular condensates that form in response to cellular stress. Weak, multivalent interactions between their protein and RNA constituents drive their rapid, dynamic assembly through phase separation coupled to percolation. Though a consensus model of SG function has yet to be determined, their perceived implication in cytoprotective processes (e.g., antiviral responses and inhibition of apoptosis) and possible role in the pathogenesis of various neurodegenerative diseases (e.g., amyotrophic lateral sclerosis and frontotemporal dementia) have drawn great interest. Consequently, new studies using numerous cell biological, genetic, and proteomic methods have been performed to unravel the mechanisms underlying SG formation, organization, and function and, with them, a more clearly defined SG proteome. Here, we provide a consensus SG proteome through literature curation and an update of the user-friendly database RNAgranuleDB to version 2.0 (http://rnagranuledb.lunenfeld.ca/). With this updated SG proteome, we use next-generation phase separation prediction tools to assess the predisposition of SG proteins for phase separation and aggregation. Next, we analyze the primary sequence features of intrinsically disordered regions (IDRs) within SG-resident proteins. Finally, we review the protein- and RNA-level determinants, including post-translational modifications (PTMs), that regulate SG composition and assembly/disassembly dynamics.

A little less aggregation a little more replication: Viral manipulation of stress granules

Recent exciting studies have uncovered how membrane-less organelles, also known as biocondensates, are providing cells with rapid response pathways, allowing them to re-organize their cellular contents and adapt to stressful conditions. Their assembly is driven by the phase separation of their RNAs and intrinsically disordered protein components into condensed foci. Among these, stress granules (SGs) are dynamic cytoplasmic biocondensates that form in response to many stresses, including activation of the integrated stress response or viral infections. SGs sit at the crossroads between antiviral signaling and translation because they concentrate signaling proteins and components of the innate immune response, in addition to translation machinery and stalled mRNAs. Consequently, they have been proposed to contribute to antiviral activities, and therefore are targeted by viral countermeasures. Equally, SGs components can be commandeered by viruses for their own efficient replication. Phase separation processes are an important component of the viral life cycle, for example, driving the assembly of replication factories or inclusion bodies. Therefore, in this review, we will outline the recent understanding of this complex interplay and tug of war between viruses, SGs, and their components. This article is categorized under: RNA in Disease and Development > RNA in Disease Translation > Regulation RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes.

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.

De novo variants in genes regulating stress granule assembly associate with neurodevelopmental disorders

Stress granules (SGs) are cytoplasmic assemblies in response to a variety of stressors. We report a new neurodevelopmental disorder (NDD) with common features of language problems, intellectual disability, and behavioral issues caused by de novo likely gene-disruptive variants in UBAP2L, which encodes an essential regulator of SG assembly. Ubap2l haploinsufficiency in mouse led to social and cognitive impairments accompanied by disrupted neurogenesis and reduced SG formation during early brain development. On the basis of data from 40,853 individuals with NDDs, we report a nominally significant excess of de novo variants within 29 genes that are not implicated in NDDs, including 3 essential genes (G3BP1, G3BP2, and UBAP2L) in the core SG interaction network. We validated that NDD-related de novo variants in newly implicated and known NDD genes, such as CAPRIN1, disrupt the interaction of the core SG network and interfere with SG formation. Together, our findings suggest the common SG pathology in NDDs.

Stress Granule Homeostasis, Aberrant Phase Transition, and Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease. In recent years, a large number of ALS-related mutations have been discovered to have a strong link to stress granules (SGs). SGs are cytoplasmic ribonucleoprotein condensates mediated by liquid-liquid phase separation (LLPS) of biomacromolecules. They help cells cope with stress. The normal physiological functions of SGs are dependent on three key aspects of SG "homeostasis": SG assembly, disassembly, and SG components. Any of these three aspects can be disrupted, resulting in abnormalities in the cellular stress response and leading to cytotoxicity. Several ALS-related pathogenic mutants have abnormal LLPS abilities that disrupt SG homeostasis, and some of them can even cause aberrant phase transitions. As a result, ALS-related mutants may disrupt various aspects of SG homeostasis by directly disturbing the intermolecular interactions or affecting core SG components, thus disrupting the phase equilibrium of the cytoplasm during stress. Considering that the importance of the "global view" of SG homeostasis in ALS pathogenesis has not received enough attention, we first systematically summarize the physiological regulatory mechanism of SG homeostasis based on LLPS and then examine ALS pathogenesis from the perspective of disrupted SG homeostasis and aberrant phase transition of biomacromolecules.

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

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

MicroRNA-1224-5p Aggravates Sepsis-Related Acute Lung Injury in Mice

Oxidative stress and inflammation are implicated in the development of sepsis-related acute lung injury (ALI). MicroRNA-1224-5p (miR-1224-5p) plays critical roles in regulating inflammatory response and reactive oxygen species (ROS) production. The present study is aimed at investigating the role and underlying mechanisms of miR-1224-5p in sepsis-related ALI. Mice were intratracheally injected with lipopolysaccharide (LPS, 5 mg/kg) for 12 h to induce sepsis-related ALI. To manipulate miR-1224-5p level, mice were intravenously injected with the agomir, antagomir, or matched controls for 3 consecutive days. Murine peritoneal macrophages were stimulated with LPS (100 ng/mL) for 6 h to further validate the role of miR-1224-5p in vitro. To inhibit adenosine 5′-monophosphate-activated protein kinase alpha (AMPKα) or peroxisome proliferator activated receptor-gamma (PPAR-γ), compound C or GW9662 was used in vivo and in vitro. We found that miR-1224-5p levels in lungs were elevated by LPS injection, and that the miR-1224-5p antagomir significantly alleviated LPS-induced inflammation, oxidative stress, and ALI in mice. Conversely, the miR-1224-5p agomir aggravated inflammatory response, ROS generation, and pulmonary dysfunction in LPS-treated mice. In addition, the miR-1224-5p antagomir reduced, while the miR-1224-5p agomir aggravated LPS-induced inflammation and oxidative stress in murine peritoneal macrophages. Further findings revealed that miR-1224-5p is directly bound to the 3′-untranslated regions of PPAR-γ and subsequently suppressed PPAR-γ/AMPKα axis, thereby aggravating LPS-induced ALI in vivo and in vitro. We demonstrate for the first time that endogenous miR-1224-5p is a critical pathogenic factor for inflammation and oxidative damage during LPS-induced ALI through inactivating PPAR-γ/AMPKα axis. Targeting miR-1224-5p may help to develop novel approaches to treat sepsis-related ALI.

Ubiquitin Binding Protein 2-Like (UBAP2L): is it so NICE After All?

Ubiquitin Binding Protein 2-like (UBAP2L, also known as NICE-4) is a ubiquitin- and RNA-binding protein, highly conserved in metazoans. Despite its abundance, its functions have only recently started to be characterized. Several studies have demonstrated the crucial involvement of UBAP2L in various cellular processes such as cell cycle regulation, stem cell activity and stress-response signaling. In addition, UBAP2L has recently emerged as a master regulator of growth and proliferation in several human cancers, where it is suggested to display oncogenic properties. Given that this versatile protein is involved in the regulation of multiple and distinct cellular pathways, actively contributing to the maintenance of cell homeostasis and survival, UBAP2L might represent a good candidate for future therapeutic studies. In this review, we discuss the current knowledge and latest advances on elucidating UBAP2L cellular functions, with an aim to highlight the importance of targeting UBAP2L for future therapies.

The Role of Ubiquitin in Regulating Stress Granule Dynamics

Stress granules (SGs) are dynamic, reversible biomolecular condensates, which assemble in the cytoplasm of eukaryotic cells under various stress conditions. Formation of SGs typically occurs upon stress-induced translational arrest and polysome disassembly. The increase in cytoplasmic mRNAs triggers the formation of a protein-RNA network that undergoes liquid-liquid phase separation when a critical interaction threshold has been reached. This adaptive stress response allows a transient shutdown of several cellular processes until the stress is removed. During the recovery from stress, SGs disassemble to re-establish cellular activities. Persistent stress and disease-related mutations in SG components favor the formation of aberrant SGs that are impaired in disassembly and prone to aggregation. Recently, posttranslational modifications of SG components have been identified as major regulators of SG dynamics. Here, we summarize new insights into the role of ubiquitination in affecting SG dynamics and clearance and discuss implications for neurodegenerative diseases linked to aberrant SG formation.

The lncRNA PILA promotes NF-κB signaling in osteoarthritis by stimulating the activity of the protein arginine methyltransferase PRMT1

Inflammatory cytokine-induced activation of nuclear factor κB (NF-κB) signaling plays a critical role in the pathogenesis of osteoarthritis (OA). We identified PILA as a long noncoding RNA (lncRNA) that enhances NF-κB signaling and OA. The abundance of PILA was increased in damaged cartilage from patients with OA and in human articular chondrocytes stimulated with the proinflammatory cytokine tumor necrosis factor (TNF). Knockdown of PILA inhibited TNF-induced NF-κB signaling, extracellular matrix catabolism, and apoptosis in chondrocytes, whereas ectopic expression of PILA promoted NF-κB signaling and matrix degradation. PILA promoted PRMT1-mediated arginine methylation of DExH-box helicase 9 (DHX9), leading to an increase in the transcription of the gene encoding transforming growth factor β-activated kinase 1 (TAK1), an upstream activator of NF-κB signaling. Furthermore, intra-articular injection of an adenovirus vector encoding PILA triggered spontaneous cartilage loss and exacerbated posttraumatic OA in mice. This study provides insight into the regulation of NF-κB signaling in OA and identifies a potential therapeutic target for this disease.

Role of the Ubiquitin System in Stress Granule Metabolism

Eukaryotic cells react to various stress conditions with the rapid formation of membrane-less organelles called stress granules (SGs). SGs form by multivalent interactions between RNAs and RNA-binding proteins and are believed to protect stalled translation initiation complexes from stress-induced degradation. SGs contain hundreds of different mRNAs and proteins, and their assembly and disassembly are tightly controlled by post-translational modifications. The ubiquitin system, which mediates the covalent modification of target proteins with the small protein ubiquitin (‘ubiquitylation’), has been implicated in different aspects of SG metabolism, but specific functions in SG turnover have only recently emerged. Here, we summarize the evidence for the presence of ubiquitylated proteins at SGs, review the functions of different components of the ubiquitin system in SG formation and clearance, and discuss the link between perturbed SG clearance and the pathogenesis of neurodegenerative disorders. We conclude that the ubiquitin system plays an important, medically relevant role in SG biology.

UBAP2L promotes gastric cancer metastasis by activating NF-κB through PI3K/AKT pathway

Ubiquitin-associated protein 2-like (UBAP2L) is highly expressed in various types of tumors and has been shown to participate in tumor growth and metastasis; however, its role in gastric cancer (GC) remains unknown. In this study, we observed that UBAP2L expression was markedly elevated in GC tissues and five GC cell lines. Higher expression of UBAP2L was associated with poor prognosis as revealed by bioinformatics analysis on online websites and laboratory experiments. Knockdown of UBAP2L impeded the migration and invasion abilities of GC cell lines. In contrast, its overexpression enhanced the migration and invasion abilities of GC cell lines. Overexpression of UBAP2L also increased the number and size of lung metastatic nodules in vivo. According to the results of mass spectrometry and pathway annotation of the identified proteins, the PI3K/AKT pathway was found to be related to UBAP2L regulation. Further exploration and rescue experiments revealed that UBAP2L stimulates the expression and nuclear aggregation of p65 and promotes the expression of SP1 by activating the PI3K/AKT pathway. In summary, our findings indicate that UBAP2L regulates GC metastasis through the PI3K/AKT/SP1/NF-κB axis. Thus, targeting UBAP2L may be a potential therapeutic strategy for GC.

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

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

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

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

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

Systematic Analysis of the Impact of R-Methylation on RBPs-RNA Interactions: A Proteomic Approach

RNA binding proteins (RBPs) bind RNAs through specific RNA-binding domains, generating multi-molecular complexes known as ribonucleoproteins (RNPs). Various post-translational modifications (PTMs) have been described to regulate RBP structure, subcellular localization, and interactions with other proteins or RNAs. Recent proteome-wide experiments showed that RBPs are the most representative group within the class of arginine (R)-methylated proteins. Moreover, emerging evidence suggests that this modification plays a role in the regulation of RBP-RNA interactions. Nevertheless, a systematic analysis of how changes in protein-R-methylation can affect globally RBPs-RNA interactions is still missing. We describe here a quantitative proteomics approach to profile global changes of RBP-RNA interactions upon the modulation of type I and II protein arginine methyltransferases (PRMTs). By coupling the recently described Orthogonal Organic Phase Separation (OOPS) strategy with the Stable Isotope Labelling with Amino acids in Cell culture (SILAC) and pharmacological modulation of PRMTs, we profiled RNA-protein interaction dynamics in dependence of protein-R-methylation. Data are available via ProteomeXchange with identifier PXD024601.

Heritable Variants in the Chromosome 1q22 Locus Increase Gastric Cancer Risk via Altered Chromatin Looping and Increased UBAP2L Expression

Genome-wide association studies (GWAS) have implicated the 1q22 gastric cancer risk locus in disease, but little is known about its underlying oncogenic functions. This study represents a systematic investigation of the biological significance and potential mechanism associated with the gastric cancer risk of SNP rs2075570(C>T) in 1q22. We identified two functional germline variations (rs2049805-C and rs2974931-G) in an active enhancer in a 64.8 kb high-linkage disequilibrium block of rs2075570. The enhancer upregulated ubiquitin associated protein 2 like (UBAP2L) gene expression over a 960 kb distance by chromatin looping. Gastric cancer tissues expressed significantly higher levels of UBAP2L than was observed in the matched noncancerous tissues, and the UBAP2L expression was negatively correlated with patient survival. Downregulation of UBAP2L inhibited the proliferation and invasion of human gastric cancer cells in vitro and in a xenograft mouse model. Notably, the two mutant variations significantly enforced the enhancer activity and UBAP2L expression. In conclusion, this study revealed two causal variations in the 1q22 region using tag-SNP rs2075570 as a genetic marker. These variations may affect the occurrence and progression of gastric cancer by reinforcing the expression of the 1q22-Enh enhancer-regulated UBAP2L target gene. IMPLICATIONS: Our study provides an important clue of how noncoding germline variations contribute to gastric cancer, which gives a novel insight into understanding the genetic mechanism of gastric cancer.

The Emerging Role of Stress Granules in Hepatocellular Carcinoma

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

Plant Stress Granules: Trends and Beyond

Stress granules (SGs) are dynamic membrane-less condensates transiently assembled through liquid-liquid phase separation (LLPS) in response to stress. SGs display a biphasic architecture constituted of core and shell phases. The core is a conserved SG fraction fundamental for its assembly and consists primarily of proteins with intrinsically disordered regions and RNA-binding domains, along with translational-related proteins. The shell fraction contains specific SG components that differ among species, cell type, and developmental stage and might include metabolic enzymes, receptors, transcription factors, untranslated mRNAs, and small molecules. SGs assembly positively correlates with stalled translation associated with stress responses playing a pivotal role during the adaptive cellular response, post-stress recovery, signaling, and metabolic rewire. After stress, SG disassembly releases mRNA and proteins to the cytoplasm to reactivate translation and reassume cell growth and development. However, under severe stress conditions or aberrant cellular behavior, SG dynamics are severely disturbed, affecting cellular homeostasis and leading to cell death in the most critical cases. The majority of research on SGs has focused on yeast and mammals as model organism. Nevertheless, the study of plant SGs has attracted attention in the last few years. Genetics studies and adapted techniques from other non-plant models, such as affinity capture coupled with multi-omics analyses, have enriched our understanding of SG composition in plants. Despite these efforts, the investigation of plant SGs is still an emerging field in plant biology research. In this review, we compile and discuss the accumulated progress of plant SGs regarding their composition, organization, dynamics, regulation, and their relation to other cytoplasmic foci. Lastly, we will explore the possible connections among the most exciting findings of SGs from mammalian, yeast, and plants, which might help provide a complete view of the biology of plant SGs in the future.

The N-terminal domain of the Schaaf-Yang syndrome protein MAGEL2 likely has a role in RNA metabolism

MAGEL2 encodes the L2 member of the melanoma-associated antigen gene (MAGE) protein family, truncating mutations of which can cause Schaaf-Yang syndrome, an autism spectrum disorder. MAGEL2 is also inactivated in Prader-Willi syndrome, which overlaps clinically and mechanistically with Schaaf-Yang syndrome. Studies to date have only investigated the C-terminal portion of the MAGEL2 protein, containing the MAGE homology domain that interacts with RING-E3 ubiquitin ligases and deubiquitinases to form protein complexes that modify protein ubiquitination. In contrast, the N-terminal portion of the MAGEL2 protein has never been studied. Here, we find that MAGEL2 has a low-complexity intrinsically disordered N-terminus rich in Pro-Xn-Gly motifs that is predicted to mediate liquid-liquid phase separation to form biomolecular condensates. We used proximity-dependent biotin identification (BioID) and liquid chromatography-tandem mass spectrometry to identify MAGEL2-proximal proteins, then clustered these proteins into functional networks. We determined that coding mutations analogous to disruptive mutations in other MAGE proteins alter these networks in biologically relevant ways. Proteins identified as proximal to the N-terminal portion of MAGEL2 are primarily involved in mRNA metabolic processes and include three mRNA N 6-methyladenosine (m6A)-binding YTHDF proteins and two RNA interference-mediating TNRC6 proteins. We found that YTHDF2 coimmunoprecipitates with MAGEL2, and coexpression of MAGEL2 reduces the nuclear accumulation of YTHDF2 after heat shock. We suggest that the N-terminal region of MAGEL2 may have a role in RNA metabolism and in particular the regulation of mRNAs modified by m6A methylation. These results provide mechanistic insight into pathogenic MAGEL2 mutations associated with Schaaf-Yang syndrome and related disorders.

Arginine methylation of SARS-Cov-2 nucleocapsid protein regulates RNA binding, its ability to suppress stress granule formation, and viral replication

Viral proteins are known to be methylated by host protein arginine methyltransferases (PRMTs) necessary for the viral life cycle, but it remains unknown whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins are methylated. Herein, we show that PRMT1 methylates SARS-CoV-2 nucleocapsid (N) protein at residues R95 and R177 within RGG/RG motifs, preferred PRMT target sequences. We confirmed arginine methylation of N protein by immunoblotting viral proteins extracted from SARS-CoV-2 virions isolated from cell culture. Type I PRMT inhibitor (MS023) or substitution of R95 or R177 with lysine inhibited interaction of N protein with the 5'-UTR of SARS-CoV-2 genomic RNA, a property required for viral packaging. We also defined the N protein interactome in HEK293 cells, which identified PRMT1 and many of its RGG/RG substrates, including the known interacting protein G3BP1 as well as other components of stress granules (SGs), which are part of the host antiviral response. Methylation of R95 regulated the ability of N protein to suppress the formation of SGs, as R95K substitution or MS023 treatment blocked N-mediated suppression of SGs. Also, the coexpression of methylarginine reader Tudor domain-containing protein 3 quenched N protein-mediated suppression of SGs in a dose-dependent manner. Finally, pretreatment of VeroE6 cells with MS023 significantly reduced SARS-CoV-2 replication. Because type I PRMT inhibitors are already undergoing clinical trials for cancer treatment, inhibiting arginine methylation to target the later stages of the viral life cycle such as viral genome packaging and assembly of virions may represent an additional therapeutic application of these drugs.

Response to stress in biological disorders: Implications of stress granule assembly and function

It is indispensable for cells to adapt and respond to environmental stresses, in order for organisms to survive. Stress granules (SGs) are condensed membrane‐less organelles dynamically formed in the cytoplasm of eukaryotes cells to cope with diverse intracellular or extracellular stress factors, with features of liquid‐liquid phase separation. They are composed of multiple constituents, including translationally stalled mRNAs, translation initiation factors, RNA‐binding proteins and also non‐RNA‐binding proteins. SG formation is triggered by stress stimuli, viral infection and signal transduction, while aberrant assembly of SGs may contribute to tissue degenerative diseases. Recently, a growing body of evidence has emerged on SG response mechanisms for cells facing high temperatures, oxidative stress and osmotic stress. In this review, we aim to summarize factors affecting SGs assembly, present the impact of SGs on germ cell development and other biological processes. We particularly emphasize the significance of recently reported RNA modifications in SG stress responses. In parallel, we also review all current perspectives on the roles of SGs in male germ cells, with a particular focus on the dynamics of SG assembly.

Cancer cell adaptability: turning ribonucleoprotein granules into targets

Stress granules (SGs) and processing bodies (P-bodies) are membraneless cytoplasmic condensates of ribonucleoproteins (RNPs). They both regulate RNA fate under physiological and pathological conditions, and are thereby involved in the regulation and maintenance of cellular integrity. During tumorigenesis, cancer cells use these granules to thrive, to adapt to the harsh conditions of the tumor microenvironment (TME), and to protect themselves from anticancer treatments. This ability to provide multiple outcomes not only makes RNP granules promising targets for cancer therapy but also emphasizes the need for more knowledge about the biology of these granules to achieve clinical use. In this review we focus on the role of RNP granules in cancer, and on how their composition and regulation might be used to elaborate therapeutic strategies.

Polyphasic linkage and the impact of ligand binding on the regulation of biomolecular condensates

Cellular matter can be spatially and temporally organized into membraneless biomolecular condensates. The current thinking is that these condensates form and dissolve via phase transitions driven by one or more condensate-specific multivalent macromolecules known as scaffolds. Cells likely regulate condensate formation and dissolution by exerting control over the concentrations of regulatory molecules, which we refer to as ligands. Wyman and Gill introduced the framework of polyphasic linkage to explain how ligands can exert thermodynamic control over phase transitions. This review focuses on describing the concepts of polyphasic linkage and the relevance of such a mechanism for controlling condensate formation and dissolution. We describe how ligand-mediated control over scaffold phase behavior can be quantified experimentally. Further, we build on recent studies to highlight features of ligands that make them suppressors vs drivers of phase separation. Finally, we highlight areas where advances are needed to further understand ligand-mediated control of condensates in complex cellular environments. These advances include understanding the effects of networks of ligands on condensate behavior and how ligands modulate phase transitions controlled by different combinations of homotypic and heterotypic interactions among scaffold macromolecules. Insights gained from the application of polyphasic linkage concepts should be useful for designing novel pharmaceutical ligands to regulate condensates.

Discovery of Arginine Methylation, Phosphorylation, and Their Co-occurrence in Condensate-Associated Proteins in Saccharomyces cerevisiae

The formation of condensates in membraneless organelles is thought to be driven by protein phase separation. Arginine methylation and serine/threonine phosphorylation are important in the phase separation process; however, these post-translational modifications are often present in intrinsically disordered regions that are difficult to analyze with standard proteomic techniques. To understand their presence and co-occurrence in condensate-associated proteins, here, we use a multiprotease and multi-tandem mass spectrometry (MS/MS) fragmentation approach, coupled with heavy methyl stable isotope labeling of amino acids in cell culture (SILAC) and phospho- or methyl-peptide enrichment. For Saccharomyces cerevisiae, we report a 50% increase in the known arginine methylproteome, involving 15 proteins that are all condensate-associated. Importantly, some of these proteins have arginine methylation on all predicted sites-providing evidence that this modification can be pervasive. We explored whether arginine-methylated, condensate-associated proteins are also phosphorylated and found 12 such proteins to carry phosphorylated serine or threonine. In Npl3, Ded1, and Sbp1, single peptides were found to carry both modifications, indicating a co-occurrence in close proximity and on the same protein molecule. These co-modifications occur in regions of disorder, whereas arginine methylation is typically on regions of disorder that are also basic. For phosphorylation, its association with charged regions of condensate-associated proteins was less consistent, although some regions with multisite phosphorylation sites were strongly acidic. We conclude that arginine-methylated proteins associated with condensates are typically also modified with protein phosphorylation.

Hypothesis and Theory: Roles of Arginine Methylation in C9orf72-Mediated ALS and FTD

Hexanucleotide repeat expansion (G4C2_n) mutations in the gene C9ORF72 account for approximately 30% of familial cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), as well as approximately 7% of sporadic cases of ALS. G4C2_n mutations are known to result in the production of five species of dipeptide repeat proteins (DRPs) through non-canonical translation processes. Arginine-enriched dipeptide repeat proteins, glycine-arginine (polyGR), and proline-arginine (polyPR) have been demonstrated to be cytotoxic and deleterious in multiple experimental systems. Recently, we and others have implicated methylation of polyGR/polyPR arginine residues in disease processes related to G4C2_n mutation-mediated neurodegeneration. We previously reported that inhibition of asymmetric dimethylation (ADMe) of arginine residues is protective in cell-based models of polyGR/polyPR cytotoxicity. These results are consistent with the idea that PRMT-mediated arginine methylation in the context of polyGR/polyPR exposure is harmful. However, it remains unclear why. Here we discuss the influence of arginine methylation on diverse cellular processes including liquid-liquid phase separation, chromatin remodeling, transcription, RNA processing, and RNA-binding protein localization, and we consider how methylation of polyGR/polyPR may disrupt processes essential for normal cellular function and survival.

Ubiquitin-Modulated Phase Separation of Shuttle Proteins: Does Condensate Formation Promote Protein Degradation?

Liquid-liquid phase separation (LLPS) has recently emerged as a possible mechanism that enables ubiquitin-binding shuttle proteins to facilitate the degradation of ubiquitinated substrates via distinct protein quality control (PQC) pathways. Shuttle protein LLPS is modulated by multivalent interactions among their various domains as well as heterotypic interactions with polyubiquitin chains. Here, the properties of three different shuttle proteins (hHR23B, p62, and UBQLN2) are closely examined, unifying principles for the molecular determinants of their LLPS are identified, and how LLPS is connected to their functions is discussed. Evidence supporting LLPS of other shuttle proteins is also found. In this review, it is proposed that shuttle protein LLPS leads to spatiotemporal regulation of PQC activities by mediating the recruitment of PQC machinery (including proteasomes or autophagic components) to biomolecular condensates, assembly/disassembly of condensates, selective enrichment of client proteins, and extraction of ubiquitinated proteins from condensates in cells.

Molecular mechanisms of stress granule assembly and disassembly

Stress granules (SGs) are membrane-less ribonucleoprotein (RNP)-based cellular compartments that form in the cytoplasm of a cell upon exposure to various environmental stressors. SGs contain a large set of proteins, as well as mRNAs that have been stalled in translation as a result of stress-induced polysome disassembly. Despite the fact that SGs have been extensively studied for many years, their function is still not clear. They presumably help the cell to cope with the encountered stress, and facilitate the recovery process after stress removal upon which SGs disassemble. Aberrant formation of SGs and impaired SG disassembly majorly contribute to various pathological phenomena in cancer, viral infections, and neurodegeneration. The assembly of SGs is largely driven by liquid-liquid phase separation (LLPS), however, the molecular mechanisms behind that are not fully understood. Recent studies have proposed a novel mechanism for SG formation that involves the interplay of a large interaction network of mRNAs and proteins. Here, we review this novel concept of SG assembly, and discuss the current insights into SG disassembly.

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

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

G3BP1-linked mRNA partitioning supports selective protein synthesis in response to oxidative stress

Cells limit energy-consuming mRNA translation during stress to maintain metabolic homeostasis. Sequestration of mRNAs by RNA binding proteins (RBPs) into RNA granules reduces their translation, but it remains unclear whether RBPs also function in partitioning of specific transcripts to polysomes (PSs) to guide selective translation and stress adaptation in cancer. To study transcript partitioning under cell stress, we catalogued mRNAs enriched in prostate carcinoma PC-3 cell PSs, as defined by polysome fractionation and RNA sequencing (RNAseq), and compared them to mRNAs complexed with the known SG-nucleator protein, G3BP1, as defined by spatially-restricted enzymatic tagging and RNAseq. By comparing these compartments before and after short-term arsenite-induced oxidative stress, we identified three major categories of transcripts, namely those that were G3BP1-associated and PS-depleted, G3BP1-dissociated and PS-enriched, and G3BP1-associated but also PS-enriched. Oxidative stress profoundly altered the partitioning of transcripts between these compartments. Under arsenite stress, G3BP1-associated and PS-depleted transcripts correlated with reduced expression of encoded mitochondrial proteins, PS-enriched transcripts that disassociated from G3BP1 encoded cell cycle and cytoprotective proteins whose expression increased, while transcripts that were both G3BP1-associated and PS-enriched encoded proteins involved in diverse stress response pathways. Therefore, G3BP1 guides transcript partitioning to reprogram mRNA translation and support stress adaptation.

Dance with the Devil: Stress Granules and Signaling in Antiviral Responses

Cells have evolved highly specialized sentinels that detect viral infection and elicit an antiviral response. Among these, the stress-sensing protein kinase R, which is activated by double-stranded RNA, mediates suppression of the host translation machinery as a strategy to limit viral replication. Non-translating mRNAs rapidly condensate by phase separation into cytosolic stress granules, together with numerous RNA-binding proteins and components of signal transduction pathways. Growing evidence suggests that the integrated stress response, and stress granules in particular, contribute to antiviral defense. This review summarizes the current understanding of how stress and innate immune signaling act in concert to mount an effective response against virus infection, with a particular focus on the potential role of stress granules in the coordination of antiviral signaling cascades.