EMBO Journal最新文献

Dysregulation of RNA processing has in recent years emerged as a significant contributor to neurodegeneration. The diverse mechanisms and molecular functions underlying RNA processing underscore the essential role of RNA regulation in maintaining neuronal health and function. RNA molecules are bound by RNA-binding proteins (RBPs), and interactions between RNAs and RBPs are commonly affected in neurodegeneration. In this review, we highlight recent progress in understanding dysregulated RNA-processing pathways and the causes of RBP dysfunction across various neurodegenerative diseases. We discuss both established and emerging mechanisms of RNA-mediated neuropathogenesis in this rapidly evolving field. Furthermore, we explore the development of potential RNA-targeting therapeutic approaches for the treatment of neurodegenerative diseases.

Cancer cells rely on invasive growth to survive in a hostile microenvironment; this growth is characterised by interconnected processes such as epithelial-to-mesenchymal transition and migration. A master regulator of these events is the MET oncogene, which is overexpressed in the majority of cancers; however, since mutations in the MET oncogene are seen only rarely in cancers and are relatively infrequent, the mechanisms that cause this widespread MET overexpression remain obscure. Here, we show that the 5' untranslated region (5'UTR) of MET mRNA harbours two functional stress-responsive elements, conferring translational regulation by the integrated stress response (ISR), regulated by phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α) at serine 52. ISR activation by serum starvation, leucine deprivation, hypoxia, irradiation, thapsigargin or gemcitabine is followed by MET protein overexpression. We mechanistically link MET translation to the ISR by (i) mutation of the two uORFs within the MET 5'UTR, (ii) CRISPR/Cas9-mediated mutation of eIF2α (S52A), or (iii) the application of ISR pathway inhibitors. All of these interventions reduce stress-induced MET overexpression. Finally, we show that blocking stress-induced MET translation blunts MET-dependent invasive growth. These findings indicate that upregulation of the MET oncogene is a functional requirement linking integrated stress response to cancer progression.

Mitochondrial carrier homolog 2 (MTCH2) is a regulator of apoptosis, mitochondrial dynamics, and metabolism. Loss of MTCH2 results in mitochondrial fragmentation, an increase in whole-body energy utilization, and protection against diet-induced obesity. In this study, we used temporal metabolomics on HeLa cells to show that MTCH2 deletion results in a high ATP demand, an oxidized cellular environment, and elevated utilization of lipids, amino acids, and carbohydrates, accompanied by a decrease in several metabolites. Lipidomics analysis revealed a strategic adaptive reduction in membrane lipids and an increase in storage lipids in MTCH2 knockout cells. Importantly, MTCH2 knockout cells showed an increase in mitochondrial oxidative function, which may explain the higher energy demand. Interestingly, this imbalance in energy metabolism and reductive potential triggered by MTCH2-deletion prevents NIH3T3L1 preadipocytes from differentiating into mature adipocytes, an energy consuming reductive biosynthetic process. In summary, the loss of MTCH2 leads to increased mitochondrial oxidative activity and energy demand, creating a catabolic and oxidative environment that fails to fuel the anabolic processes required for lipid accumulation and adipocyte differentiation.

The identification of pathways that control elimination of protein inclusions is essential to understand the cellular response to proteotoxicity, particularly in the nuclear compartment, for which our knowledge is limited. We report that stress-induced nuclear inclusions related to the nucleolus are eliminated upon stress alleviation during the recovery period. This process is independent of autophagy/lysosome and CRM1-mediated nuclear export pathways, but strictly depends on the ubiquitin-activating E1 enzyme, UBA1, and on nuclear proteasomes that are recruited into the formed inclusions. UBA1 activity is essential only for the recovery process but dispensable for nuclear inclusion formation. Furthermore, the E3 ligase HUWE1 and HSP70 are components of the ubiquitin/chaperone systems that promote inclusion elimination. The recovery process also requires RNA Pol I-dependent production of the lncRNA IGS₄₂ during stress. IGS₄₂ localises within the formed inclusions and promotes their elimination by preserving the mobility of resident proteins. These findings reveal a protein quality control system that operates within the nucleus for the elimination of stress-induced nucleolus-related inclusions.

Endoplasmic reticulum (ER) plasticity and ER-phagy are intertwined processes essential for maintaining ER dynamics. We investigated the interplay between two isoforms of the ER-phagy receptor FAM134B in regulating ER remodeling in differentiating myoblasts. During myogenesis, the canonical FAM134B1 is degraded, while its isoform FAM134B2 is transcriptionally upregulated. The switch, favoring FAM134B2, is an important regulator of ER morphology during myogenesis. FAM134B2 partial reticulon homology domain, with its rigid conformational characteristics, enables efficient ER reshaping. FAM134B2 action increases in the active phase of differentiation leading to ER restructuring via ER-phagy, which then reverts to physiological levels when myotubes are mature and the ER is reorganized. Knocking out both FAM134B isoforms in myotubes results in an aberrant proteome landscape and the formation of dilated ER structures, both of which are rescued by FAM134B2 re-expression. Our results underscore how the fine-tuning of FAM134B isoforms and ER-phagy orchestrate the ER dynamics during myogenesis providing insights into the molecular mechanisms governing ER homeostasis in muscle cells.

Endogenous tagging enables the study of proteins within their native regulatory context, typically using CRISPR to insert tag sequences directly into the gene sequence. Here, we introduce qTAG, a collection of repair cassettes that makes endogenous tagging more accessible. The cassettes support N- and C-terminal tagging with commonly used selectable markers and feature restriction sites for easy modification. Lox sites also enable the removal of the marker gene after successful integration. We demonstrate the utility of qTAG with a range of diverse tags for applications in fluorescence imaging, proximity labeling, epitope tagging, and targeted protein degradation. The system includes novel tags like mStayGold, offering enhanced brightness and photostability for live-cell imaging of native protein dynamics. Additionally, we explore alternative cassette designs for conditional expression tagging, selectable knockout tagging, and safe-harbor expression. The plasmid collection is available through Addgene, featuring ready-to-use constructs for common subcellular markers and tagging cassettes to target genes of interest. The qTAG system will serve as an open resource for researchers to adapt and tailor their own experiments.

Genomes are organised into DNA loops by the Structural Maintenance of Chromosomes (SMC) proteins. SMCs establish functional chromosomal sub-domains for DNA repair, gene expression and chromosome segregation, but how SMC activity is specifically targeted is unclear. Here, we define the molecular mechanism targeting the condensin SMC complex to specific chromosomal regions in budding yeast. A conserved pocket on the condensin HAWK subunit Ycg1 binds to chromosomal receptors carrying a related motif, CR1. In early mitosis, CR1 motifs in receptors Sgo1 and Lrs4 recruit condensin to pericentromeres and rDNA, to facilitate sister kinetochore biorientation and rDNA condensation, respectively. We additionally find that chromosome arm condensation begins as sister kinetochores come under tension, in a manner dependent on the Ycg1 pocket. We propose that multiple CR1-containing proteins recruit condensin to chromosomes and identify several additional candidates based on their sequence. Overall, we uncover the molecular mechanism that targets condensin to functionalise chromosomal domains to achieve accurate chromosome segregation during mitosis.

Ribosomes scanning from the mRNA 5' cap to the start codon may initiate at upstream open reading frames (uORFs), decreasing protein biosynthesis. Termination at a uORF can lead to re-initiation, where 40S subunits resume scanning and initiate another translation event downstream. The noncanonical translation factors MCTS1-DENR participate in re-initiation at specific uORFs, but knowledge of other trans-acting factors or uORF features influencing re-initiation is limited. Here, we establish a cell-free re-initiation assay using HeLa lysates to address this question. Comparing in vivo and in vitro re-initiation on uORF-containing reporters, we validate MCTS1-DENR-dependent re-initiation in vitro. Using this system and ribosome profiling in cells, we found that knockdown of the MCTS1-DENR homolog eIF2D causes widespread gene deregulation unrelated to uORF translation, and thus distinct to MCTS1-DENR-dependent re-initiation regulation. Additionally, we identified MCTS2, encoded by an Mcts1 retrogene, as a DENR partner promoting re-initiation in vitro, providing a plausible explanation for clinical differences associated with DENR vs. MCTS1 mutations in humans.

ATR signaling is essential in sensing and responding to the replication stress; as such, any defects can impair cellular function and survival. ATR itself is activated via tightly regulated mechanisms. Here, we identify FOXP1, a forkhead-box-containing transcription factor, as a regulator coordinating ATR activation. We show that, unlike its role as a transcription factor, FOXP1 functions as a scaffold and directly binds to RPA-ssDNA and ATR-ATRIP complexes, facilitating the recruitment and activation of ATR. This process is regulated by FOXP1 O-GlcNAcylation, which represses its interaction with ATR, while CHK1-mediated phosphorylation of FOXP1 inhibits its O-GlcNAcylation upon replication stress. Supporting the physiological relevance of this loop, we find pathogenic FOXP1 mutants identified in various tumor tissues with compromised ATR activation and stalled replication fork stability. We thus conclude that FOXP1 may serve as a potential chemotherapeutic target in related tumors.

Entry of viral capsids into the nucleus induces the formation of biomolecular condensates called HIV-1 membraneless organelles (HIV-1-MLOs). Several questions remain about their persistence, in vivo formation, composition, and function. Our study reveals that HIV-1-MLOs persisted for several weeks in infected cells, and their abundance correlated with viral infectivity. Using an appropriate animal model, we show that HIV-1-MLOs were formed in vivo during acute infection. To explore the viral structures present within these biomolecular condensates, we used a combination of double immunogold labeling, electron microscopy and tomography, and unveiled a diverse array of viral core structures. Our functional analyses showed that HIV-1-MLOs remained stable during treatment with a reverse transcriptase inhibitor, maintaining the virus in a dormant state. Drug withdrawal restored reverse transcription, promoting efficient virus replication akin to that observed in latently infected patients on antiretroviral therapy. However, when HIV-1 MLOs were deliberately disassembled by pharmacological treatment, we observed a complete loss of viral infectivity. Our findings show that HIV-1 MLOs shield the final reverse transcription product from host immune detection.