An abundance of free regulatory (19S) proteasome particles regulates neuronal synapses

GDNF reduces fibril-induced early-stage alpha-synuclein pathology after delivery of 20S proteasome inhibitor lactacystin

Failures in protein homeostasis are linked to Parkinson's disease (PD) and other neurodegenerative diseases. Lewy bodies, proteinaceous inclusions rich in phosphorylated alpha-synuclein are a hallmark of PD. Glial cell line-derived neurotrophic factor (GDNF) can eliminate Lewy body-like inclusions in mouse dopamine neurons. This study explores whether GDNF has protective effects against alpha-synuclein protofibril toxicity under proteasome inhibition by lactacystin, both in vitro and in vivo. GDNF did not shield midbrain dopamine neurons from lactacystin-induced neurodegeneration, but still prevented phosphorylated alpha-synuclein accumulation. In vivo experiment with control or GDNF-expressing viral vectors assessed alpha-synuclein pathology spread in the nigrostriatal pathway and lactacystin-caused damage in the midbrain. GDNF overexpression reduced phosphorylated alpha-synuclein inclusions. Lactacystin-treated mice showed motor asymmetry and decreased spontaneous activity, exacerbated without AAV-GDNF pre-treatment. However, GDNF's neuroprotective effect could not be confirmed in vivo, due to side-effects from overexpression in the midbrain. Importantly, these findings show that GDNF continues to eliminate alpha-synuclein aggregation despite lactacystin-induced proteasome inhibition. Activating neurotrophic signaling pathways may protect against alpha-synuclein pathology in PD, even with impaired protein degradation mechanisms.

The Unified Theory of Neurodegeneration Pathogenesis Based on Axon Deamidation

Until now, neurodegenerative diseases like Alzheimer's and Parkinson's have been studied separately in biochemistry and therapeutic drug development, and no causal link has ever been established between them. This study has developed a Unified Theory, which establishes that the regulation of axon and dendrite-specific 4E-BP2 deamidation rates controls the occurrence and progression of neurodegenerative diseases. This is based on identifying axon-specific 4E-BP2 deamidation as a universal denominator for the biochemical processes of deamidation, translational control, oxidative stress, and neurodegeneration. This was achieved by conducting a thorough and critical review of 224 scientific publications regarding (a) deamidation, (b) translational control in protein synthesis initiation, (c) neurodegeneration and (d) oxidative stress, and by applying my discovery of the fundamental neurobiological mechanism behind neuron-specific 4E-BP2 deamidation to practical applications in medicine. Based on this newly developed Unified Theory and my critical review of the scientific literature, I also designed three biochemical flowsheets of (1) in-vivo deamidation, (2) protein synthesis initiation and translational control, and (3) 4E-BP2 deamidation as a control system of the four biochemical processes. The Unified Theory of Neurodegeneration Pathogenesis based on axon deamidation, developed in this work, paves the way to controlling the occurrence and progression of neurodegenerative diseases such as Alzheimer's and Parkinson's through a unique, neuron-specific regulatory system that is 4E-BP2 deamidation, caused by the proteasome-poor environment in neuronal projections, consisting mainly of axons.

Neuronal autophagy in the control of synapse function

Neurons are long-lived postmitotic cells that capitalize on autophagy to remove toxic or defective proteins and organelles to maintain neurotransmission and the integrity of their functional proteome. Mutations in autophagy genes cause congenital diseases, sharing prominent brain dysfunctions including epilepsy, intellectual disability, and neurodegeneration. Ablation of core autophagy genes in neurons or glia disrupts normal behavior, leading to motor deficits, memory impairment, altered sociability, and epilepsy, which are associated with defects in synapse maturation, plasticity, and neurotransmitter release. In spite of the importance of autophagy for brain physiology, the substrates of neuronal autophagy and the mechanisms by which defects in autophagy affect synaptic function in health and disease remain controversial. Here, we summarize the current state of knowledge on neuronal autophagy, address the existing controversies and inconsistencies in the field, and provide a roadmap for future research on the role of autophagy in the control of synaptic function.

Activation of the 20S proteasome core particle prevents cell death induced by oxygen- and glucose deprivation in cultured cortical neurons

Neuronal damage in brain ischemia is characterized by a disassembly of the proteasome and a decrease in its proteolytic activity. However, to what extent these alterations are coupled to neuronal death is controversial since proteasome inhibitors were shown to provide protection in different models of stroke in rodents. This question was addressed in the present work using cultured rat cerebrocortical neurons subjected to transient oxygen- and glucose-deprivation (OGD) as a model for in vitro ischemia. Under the latter conditions there was a time-dependent loss in the proteasome activity, determined by cleavage of the Suc-LLVY-AMC fluorogenic substrate, and the disassembly of the proteasome, as assessed by native-polyacrylamide gel electrophoresis followed by western blot against Psma2 and Rpt6, which are components of the catalytic core and regulatory particle, respectively. Immunocytochemistry experiments against the two proteins also showed differential effects on their dendritic distribution. OGD also downregulated the protein levels of Rpt3 and Rpt10, two components of the regulatory particle, by a mechanism dependent on the activity of NMDA receptors and mediated by calpains. Activation of the proteasome activity, using an inhibitor of USP14, a deubiquitinase enzyme, inhibited OGD-induced cell death, and decreased calpain activity as determined by analysis of spectrin cleavage. Similar results were obtained in the presence of two oleic amide derivatives (B12 and D3) which directly activate the 20S proteasome core particle. Together, these results show that proteasome activation prevents neuronal death in cortical neurons subjected to in vitro ischemia, indicating that inhibition of the proteasome is a mediator of neuronal death in brain ischemia.

The adaptor protein AP-3β disassembles heat-induced stress granules via 19S regulatory particle in Arabidopsis

To survive under adverse conditions, plants form stress granules (SGs) to temporally store mRNA and halt translation as a primary response. Dysregulation in SG disassembly can have detrimental effects on plant survival after stress release, yet the underlying mechanism remains poorly understood. Using Arabidopsis as a model system, we demonstrate that the β subunit of adaptor protein (AP) -3 complex (AP-3β) interacts with the SG core RNA-binding proteins Tudor staphylococcal nuclease 1/2 (TSN1/2) both in vitro and in vivo. We also show that AP-3β is rapidly recruited to SGs upon heat induction and plays a key role in disassembling SGs during stress recovery. Genetic evidences support that AP-3β serves as an adaptor to recruit the 19S regulatory particle (RP) of the proteasome to SGs. Notably, the 19S RP promotes SG disassembly through RP-associated deubiquitylation, independent of its proteolytic activity. This deubiquitylation process of SG components is crucial for translation reinitiation and growth recovery after heat release. Our findings uncover a previously unexplored role of the 19S RP in regulating SG disassembly and highlights the importance of endomembrane proteins in supporting RNA granule dynamics in plants.

Understanding the molecular diversity of synapses

Synapses are composed of thousands of proteins, providing the potential for extensive molecular diversity to shape synapse type-specific functional specializations. In this Review, we explore the landscape of synaptic diversity and describe the mechanisms that expand the molecular complexity of synapses, from the genotype to the regulation of gene expression to the production of specific proteoforms and the formation of localized protein complexes. We emphasize the importance of examining every molecular layer and adopting a systems perspective to understand how these interconnected mechanisms shape the diverse functional and structural properties of synapses. We explore current frameworks for classifying synapses and methodologies for investigating different synapse types at varying scales, from synapse-type-specific proteomics to advanced imaging techniques with single-synapse resolution. We highlight the potential of synapse-type-specific approaches for integrating molecular data with cellular functions, circuit organization and organismal phenotypes to enable a more holistic exploration of neuronal phenomena across different scales.

19S proteasome loss causes monopolar spindles through ubiquitin-independent KIF11 degradation

To direct regulated protein degradation, the 26S proteasome recognizes ubiquitinated substrates through its 19S particle and then degrades them in the 20S enzymatic core. Despite this close interdependency between proteasome subunits, we demonstrate that knockouts from different proteasome subcomplexes result in distinct highly cellular phenotypes. In particular, depletion of 19S PSMD lid proteins, but not that of other proteasome subunits, prevents bipolar spindle assembly during mitosis, resulting in a mitotic arrest. We find that the monopolar spindle phenotype is caused by ubiquitin-independent proteasomal degradation of the motor protein KIF11 upon loss of 19S proteins. Thus, negative regulation of 20S-mediated proteasome degradation is essential for mitotic progression and 19S and 20S proteasome components can function independently outside of the canonical 26S structure. This work reveals a role for the proteasome in spindle formation and identifies the effects of ubiquitin-independent degradation on cell cycle control.

Emerging concepts and treatments in autoinflammatory interferonopathies and monogenic systemic lupus erythematosus

Over the past two decades, the number of genetically defined autoinflammatory interferonopathies has steadily increased. Aicardi-Goutières syndrome and proteasome-associated autoinflammatory syndromes (PRAAS, also known as CANDLE) are caused by genetic defects that impair homeostatic intracellular nucleic acid and protein processing respectively. Research into these genetic defects revealed intracellular sensors that activate type I interferon production. In SAVI and COPA syndrome, genetic defects that cause chronic activation of the dinucleotide sensor stimulator of interferon genes (STING) share features of lung inflammation and fibrosis; and selected mutations that amplify interferon-α/β receptor signalling cause central nervous system manifestations resembling Aicardi-Goutières syndrome. Research into the monogenic causes of childhood-onset systemic lupus erythematosus (SLE) demonstrates the pathogenic role of autoantibodies to particle-bound extracellular nucleic acids that distinguishes monogenic SLE from the autoinflammatory interferonopathies. This Review introduces a classification for autoinflammatory interferonopathies and discusses the divergent and shared pathomechanisms of interferon production and signalling in these diseases. Early success with drugs that block type I interferon signalling, new insights into the roles of cytoplasmic DNA or RNA sensors, pathways in type I interferon production and organ-specific pathology of the autoinflammatory interferonopathies and monogenic SLE, reveal novel drug targets that could personalize treatment approaches.

Understanding ubiquitination in neurodevelopment by integrating insights across space and time

Ubiquitination regulates a myriad of eukaryotic signaling cascades by modifying substrate proteins, thereby determining their functions and fates. In this perspective, we discuss current challenges in investigating the ubiquitin system in the developing brain. We foster the concept that ubiquitination pathways are spatiotemporally regulated and tightly intertwined with molecular and cellular transitions during neurogenesis and neural circuit assembly. Focusing on the neurologically highly relevant class of homologous to E6AP C-terminus (HECT) ubiquitin ligases, we propose cross-disciplinary translational approaches bridging state-of-the-art cell biology, proteomics, biochemistry, structural biology and neuroscience to dissect ubiquitination in neurodevelopment and its specific perturbations in brain diseases. We highlight that a comprehensive understanding of ubiquitin signaling in the brain may reveal new horizons in basic neuroscience and clinical applications.

Localized molecular chaperone synthesis maintains neuronal dendrite proteostasis

Proteostasis is maintained through regulated protein synthesis and degradation and chaperone-assisted protein folding. However, this is challenging in neuronal projections because of their polarized morphology and constant synaptic proteome remodeling. Using high-resolution fluorescence microscopy, we discover that hippocampal and spinal cord motor neurons of mouse and human origin localize a subset of chaperone mRNAs to their dendrites and use microtubule-based transport to increase this asymmetric localization following proteotoxic stress. The most abundant dendritic chaperone mRNA encodes a constitutive heat shock protein 70 family member (HSPA8). Proteotoxic stress also enhances HSPA8 mRNA translation efficiency in dendrites. Stress-mediated HSPA8 mRNA localization to the dendrites is impaired by depleting fused in sarcoma-an amyotrophic lateral sclerosis-related protein-in cultured spinal cord mouse motor neurons or by expressing a pathogenic variant of heterogenous nuclear ribonucleoprotein A2/B1 in neurons derived from human induced pluripotent stem cells. These results reveal a neuronal stress response in which RNA-binding proteins increase the dendritic localization of HSPA8 mRNA to maintain proteostasis and prevent neurodegeneration.

Nanotechnology-Enabled Targeted Protein Degradation for Cancer Therapeutics

Targeted protein degradation (TPD) represents an innovative therapeutic strategy that has garnered considerable attention from both academic and industrial sectors due to its promising developmental prospects. Approximately 85% of human proteins are implicated in disease pathogenesis, and the FDA has approved around 400 drugs targeting these disease-related proteins, predominantly enzymes, transcription factors, and non-enzymatic proteins. However, existing therapeutic modalities fail to address certain "high-value" targets, such as c-Myc and Ras. The emergence of proteolysis-targeting chimeras (PROTAC) technology has introduced TPD into a new realm. The capability to target non-druggable sites has expanded the therapeutic horizon of protein-based drugs, although challenges related to bioavailability, safety, and adverse side effects have constrained their clinical progression. Nano-delivery systems and emerging TPD modalities, such as molecular glues, lysosome-targeted chimeras (LYTACs), autophagy system compounds (ATTEC), and antibody PROTAC (AbTACs), have mitigated some of these limitations. This paper reviews the latest advancements in TPD, highlighting their applications and benefits in cancer therapy, and concludes with a forward-looking perspective on the future development of this field.

Understanding neurodevelopmental proteasomopathies as new rare disease entities: A review of current concepts, molecular biomarkers, and perspectives

The recent advances in high throughput sequencing technology have drastically changed the practice of medical diagnosis, allowing for rapid identification of hundreds of genes causing human diseases. This unprecedented progress has made clear that most forms of intellectual disability that affect more than 3% of individuals worldwide are monogenic diseases. Strikingly, a substantial fraction of the mendelian forms of intellectual disability is associated with genes related to the ubiquitin-proteasome system, a highly conserved pathway made up of approximately 1200 genes involved in the regulation of protein homeostasis. Within this group is currently emerging a new class of neurodevelopmental disorders specifically caused by proteasome pathogenic variants which we propose to designate "neurodevelopmental proteasomopathies". Besides cognitive impairment, these diseases are typically associated with a series of syndromic clinical manifestations, among which facial dysmorphism, motor delay, and failure to thrive are the most prominent ones. While recent efforts have been made to uncover the effects exerted by proteasome variants on cell and tissue landscapes, the molecular pathogenesis of neurodevelopmental proteasomopathies remains ill-defined. In this review, we discuss the cellular changes typically induced by genomic alterations in proteasome genes and explore their relevance as biomarkers for the diagnosis, management, and potential treatment of these new rare disease entities.

Localized synthesis of molecular chaperones sustains neuronal proteostasis

Neurons are challenged to maintain proteostasis in neuronal projections, particularly with the physiological stress at synapses to support intercellular communication underlying important functions such as memory and movement control. Proteostasis is maintained through regulated protein synthesis and degradation and chaperone-assisted protein folding. Using high-resolution fluorescent microscopy, we discovered that neurons localize a subset of chaperone mRNAs to their dendrites, particularly more proximal regions, and increase this asymmetric localization following proteotoxic stress through microtubule-based transport from the soma. The most abundant chaperone mRNA in dendrites encodes the constitutive heat shock protein 70, HSPA8. Proteotoxic stress in cultured neurons, induced by inhibiting proteasome activity or inducing oxidative stress, enhanced transport of Hspa8 mRNAs to dendrites and the percentage of mRNAs engaged in translation on mono and polyribosomes. Knocking down the ALS-related protein Fused in Sarcoma (FUS) and a dominant mutation in the heterogenous nuclear ribonucleoprotein A2/B1 (HNRNPA2B1) impaired stress-mediated localization of Hspa8 mRNA to dendrites in cultured murine motor neurons and human iPSC-derived neurons, respectively, revealing the importance of these RNA-binding proteins in maintaining proteostasis. These results reveal the increased dendritic localization and translation of the constitutive HSP70 Hspa8 mRNA as a crucial neuronal stress response to uphold proteostasis and prevent neurodegeneration.

Neuronal UBE3A substrates hold therapeutic potential for Angelman syndrome

Emerging therapies for Angelman syndrome, a severe neurodevelopmental disorder, are focused on restoring UBE3A gene expression in the brain. Further therapeutic opportunities may arise from a better understanding of how UBE3A gene products-both long and short isoforms of the ubiquitin ligase E3A (UBE3A)-function in neurons. Great strides have been made recently toward identifying ubiquitin substrates of UBE3A in vitro and in heterologous expression systems. From this work, a particularly close relationship between UBE3A and subunits of the 19S regulatory particle of the proteasome has become evident. We propose that further research cognizant of isoform-specific UBE3A functional roles will be instrumental in elucidating key UBE3A/substrate relationships within distinct neuronal compartments, lending to the discovery of novel therapeutic targets and valuable clinical biomarkers for the treatment of Angelman syndrome.

Crosstalk between ubiquitination and translation in neurodevelopmental disorders

Ubiquitination is one of the most conserved post-translational modifications and together with mRNA translation contributes to cellular protein homeostasis (proteostasis). Temporal and spatial regulation of proteostasis is particularly important during synaptic plasticity, when translation of specific mRNAs requires tight regulation. Mutations in genes encoding regulators of mRNA translation and in ubiquitin ligases have been associated with several neurodevelopmental disorders. RNA metabolism and translation are regulated by RNA-binding proteins, critical for the spatial and temporal control of translation in neurons. Several ubiquitin ligases also regulate RNA-dependent mechanisms in neurons, with numerous ubiquitination events described in splicing factors and ribosomal proteins. Here we will explore how ubiquitination regulates translation in neurons, from RNA biogenesis to alternative splicing and how dysregulation of ubiquitin signaling can be the underlying cause of pathology in neurodevelopmental disorders, such as Fragile X syndrome. Finally we propose that targeting ubiquitin signaling is an attractive novel therapeutic strategy for neurodevelopmental disorders where mRNA translation and ubiquitin signaling are disrupted.

⍺-Synuclein levels in Parkinson's disease - Cell types and forms that contribute to pathogenesis

Parkinson's disease (PD) has two main pathological hallmarks, the loss of nigral dopamine neurons and the proteinaceous aggregations of ⍺-synuclein (⍺Syn) in neuronal Lewy pathology. These two co-existing features suggest a causative association between ⍺Syn aggregation and the underpinning mechanism of neuronal degeneration in PD. Both increased levels and post-translational modifications of ⍺Syn can contribute to the formation of pathological aggregations of ⍺Syn in neurons. Recent studies have shown that the protein is also expressed by multiple types of non-neuronal cells in the brain and peripheral tissues, suggesting additional roles of the protein and potential diversity in non-neuronal pathogenic triggers. It is important to determine (1) the threshold levels triggering ⍺Syn to convert from a biological to a pathologic form in different brain cells in PD; (2) the dominant form of pathologic ⍺Syn and the associated post-translational modification of the protein in each cell type involved in PD; and (3) the cell type associated biological processes impacted by pathologic ⍺Syn in PD. This review integrates these aspects and speculates on potential pathological mechanisms and their impact on neuronal and non-neuronal ⍺Syn in the brains of patients with PD.

PSMD11 loss-of-function variants correlate with a neurobehavioral phenotype, obesity, and increased interferon response

Primary proteasomopathies have recently emerged as a new class of rare early-onset neurodevelopmental disorders (NDDs) caused by pathogenic variants in the PSMB1, PSMC1, PSMC3, or PSMD12 proteasome genes. Proteasomes are large multi-subunit protein complexes that maintain cellular protein homeostasis by clearing ubiquitin-tagged damaged, misfolded, or unnecessary proteins. In this study, we have identified PSMD11 as an additional proteasome gene in which pathogenic variation is associated with an NDD-causing proteasomopathy. PSMD11 loss-of-function variants caused early-onset syndromic intellectual disability and neurodevelopmental delay with recurrent obesity in 10 unrelated children. Our findings demonstrate that the cognitive impairment observed in these individuals could be recapitulated in Drosophila melanogaster with depletion of the PMSD11 ortholog Rpn6, which compromised reversal learning. Our investigations in subject samples further revealed that PSMD11 loss of function resulted in impaired 26S proteasome assembly and the acquisition of a persistent type I interferon (IFN) gene signature, mediated by the integrated stress response (ISR) protein kinase R (PKR). In summary, these data identify PSMD11 as an additional member of the growing family of genes associated with neurodevelopmental proteasomopathies and provide insights into proteasomal biology in human health.

Proteasome Inhibition Reprograms Chromatin Landscape in Breast Cancer

The 26S proteasome is the major protein degradation machinery in cells. Cancer cells use the proteasome to modulate gene expression networks that promote tumor growth. Proteasome inhibitors have emerged as effective cancer therapeutics, but how they work mechanistically remains unclear. Here, using integrative genomic analysis, we discovered unexpected reprogramming of the chromatin landscape and RNA polymerase II (RNAPII) transcription initiation in breast cancer cells treated with the proteasome inhibitor MG132. The cells acquired dynamic changes in chromatin accessibility at specific genomic loci termed differentially open chromatin regions (DOCR). DOCRs with decreased accessibility were promoter proximal and exhibited unique chromatin architecture associated with divergent RNAPII transcription. Conversely, DOCRs with increased accessibility were primarily distal to transcription start sites and enriched in oncogenic superenhancers predominantly accessible in non-basal breast tumor subtypes. These findings describe the mechanisms by which the proteasome modulates the expression of gene networks intrinsic to breast cancer biology.

SIGNIFICANCE

Our study provides a strong basis for understanding the mechanisms by which proteasome inhibitors exert anticancer effects. We find open chromatin regions that change during proteasome inhibition, are typically accessible in non-basal breast cancers.

Single-Molecule-Resolution Approaches in Synaptic Biology

Synapses between neurons are the primary loci for information transfer and storage in the brain. An individual neuron, alone, can make over 10000 synaptic contacts. It is, however, not easy to investigate what goes on locally within a synapse because many synaptic compartments are only a few hundred nanometers wide in size─close to the diffraction limit of light. To observe the biomolecular machinery and processes within synapses, in situ single-molecule techniques are emerging as powerful tools. Guided by important biological questions, this Perspective will highlight recent advances in using these techniques to obtain in situ measurements of synaptic molecules in three aspects: the cell-biological machinery within synapses, the synaptic architecture, and the synaptic neurotransmitter receptors. These advances showcase the increasing importance of single-molecule-resolution techniques for accessing subcellular biophysical and biomolecular information related to the brain.

Pan-cellular organelles and suborganelles-from common functions to cellular diversity?

Cell diversification is at the base of increasing multicellular organism complexity in phylogeny achieved during ontogeny. However, there are also functions common to all cells, such as cell division, cell migration, translation, endocytosis, exocytosis, etc. Here we revisit the organelles involved in such common functions, reviewing recent evidence of unexpected differences of proteins at these organelles. For instance, centrosomes or mitochondria differ significantly in their protein composition in different, sometimes closely related, cell types. This has relevance for development and disease. Particularly striking is the high amount and diversity of RNA-binding proteins at these and other organelles, which brings us to review the evidence for RNA at different organelles and suborganelles. We include a discussion about (sub)organelles involved in translation, such as the nucleolus and ribosomes, for which unexpected cell type-specific diversity has also been reported. We propose here that the heterogeneity of these organelles and compartments represents a novel mechanism for regulating cell diversity. One reason is that protein functions can be multiplied by their different contributions in distinct organelles, as also exemplified by proteins with moonlighting function. The specialized organelles still perform pan-cellular functions but in a cell type-specific mode, as discussed here for centrosomes, mitochondria, vesicles, and other organelles. These can serve as regulatory hubs for the storage and transport of specific and functionally important regulators. In this way, they can control cell differentiation, plasticity, and survival. We further include examples highlighting the relevance for disease and propose to examine organelles in many more cell types for their possible differences with functional relevance.

Exploiting Bacterial Effector Proteins to Uncover Evolutionarily Conserved Antiviral Host Machinery

Arboviruses are a diverse group of insect-transmitted pathogens that pose global public health challenges. Identifying evolutionarily conserved host factors that combat arbovirus replication in disparate eukaryotic hosts is important as they may tip the balance between productive and abortive viral replication, and thus determine virus host range. Here, we exploit naturally abortive arbovirus infections that we identified in lepidopteran cells and use bacterial effector proteins to uncover host factors restricting arbovirus replication. Bacterial effectors are proteins secreted by pathogenic bacteria into eukaryotic hosts cells that can inhibit antimicrobial defenses. Since bacteria and viruses can encounter common host defenses, we hypothesized that some bacterial effectors may inhibit host factors that restrict arbovirus replication in lepidopteran cells. Thus, we used bacterial effectors as molecular tools to identify host factors that restrict four distinct arboviruses in lepidopteran cells. By screening 210 effectors encoded by seven different bacterial pathogens, we identify six effectors that individually rescue the replication of all four arboviruses. We show that these effectors encode diverse enzymatic activities that are required to break arbovirus restriction. We further characterize Shigella flexneri-encoded IpaH4 as an E3 ubiquitin ligase that directly ubiquitinates two evolutionarily conserved proteins, SHOC2 and PSMC1, promoting their degradation in insect and human cells. We show that depletion of either SHOC2 or PSMC1 in insect or human cells promotes arbovirus replication, indicating that these are ancient virus restriction factors conserved across invertebrate and vertebrate hosts. Collectively, our study reveals a novel pathogen-guided approach to identify conserved antimicrobial machinery, new effector functions, and conserved roles for SHOC2 and PSMC1 in virus restriction.

Localized molecular chaperone synthesis maintains neuronal dendrite proteostasis

Proteostasis is maintained through regulated protein synthesis and degradation and chaperone-assisted protein folding. However, this is challenging in neuronal projections because of their polarized morphology and constant synaptic proteome remodeling. Using high-resolution fluorescence microscopy, we discovered that neurons localize a subset of chaperone mRNAs to their dendrites and use microtubule-based transport to increase this asymmetric localization following proteotoxic stress. The most abundant dendritic chaperone mRNA encodes a constitutive heat shock protein 70 family member (HSPA8). Proteotoxic stress also enhanced HSPA8 mRNA translation efficiency in dendrites. Stress-mediated HSPA8 mRNA localization to the dendrites was impaired by depleting fused in sarcoma-an amyotrophic lateral sclerosis-related protein-in cultured mouse motor neurons and expressing a pathogenic variant of heterogenous nuclear ribonucleoprotein A2/B1 in neurons derived from human induced pluripotent stem cells. These results reveal a crucial and unexpected neuronal stress response in which RNA-binding proteins increase the dendritic localization of HSPA8 mRNA to maintain proteostasis and prevent neurodegeneration.

Synaptic proteasome is inhibited in Alzheimer's disease models and associates with memory impairment in mice

The proteasome plays key roles in synaptic plasticity and memory by regulating protein turnover, quality control, and elimination of oxidized/misfolded proteins. Here, we investigate proteasome function and localization at synapses in Alzheimer's disease (AD) post-mortem brain tissue and in experimental models. We found a marked increase in ubiquitinylated proteins in post-mortem AD hippocampi compared to controls. Using several experimental models, we show that amyloid-β oligomers (AβOs) inhibit synaptic proteasome activity and trigger a reduction in synaptic proteasome content. We further show proteasome inhibition specifically in hippocampal synaptic fractions derived from APPswePS1ΔE9 mice. Reduced synaptic proteasome activity instigated by AβOs is corrected by treatment with rolipram, a phosphodiesterase-4 inhibitor, in mice. Results further show that dynein inhibition blocks AβO-induced reduction in dendritic proteasome content in hippocampal neurons. Finally, proteasome inhibition induces AD-like pathological features, including reactive oxygen species and dendritic spine loss in hippocampal neurons, inhibition of hippocampal mRNA translation, and memory impairment in mice. Results suggest that proteasome inhibition may contribute to synaptic and memory deficits in AD.

Proteasome inhibition reprograms chromatin landscape in breast cancer

The 26S proteasome is the major protein degradation machinery in cells. Cancer cells use the proteasome to modulate gene expression networks that promote tumor growth. Proteasome inhibitors have emerged as effective cancer therapeutics, but how they work mechanistically remains unclear. Here, using integrative genomic analysis, we discovered unexpected reprogramming of the chromatin landscape and RNAPII transcription initiation in breast cancer cells treated with the proteasome inhibitor MG132. The cells acquired dynamic changes in chromatin accessibility at specific genomic loci termed Differentially Open Chromatin Regions (DOCRs). DOCRs with decreased accessibility were promoter proximal and exhibited unique chromatin architecture associated with divergent RNAPII transcription. Conversely, DOCRs with increased accessibility were primarily distal to transcription start sites and enriched in oncogenic super enhancers predominantly accessible in non-basal breast tumor subtypes. These findings describe the mechanisms by which the proteasome modulates the expression of gene networks intrinsic to breast cancer biology.

Highlights

Proteasome inhibition uncovers de novo Differential Open Chromatin Regions (DOCRs) in breast cancer cells. Proteasome inhibitor sensitive promoters exhibit a distinctive chromatin architecture with discrete transcription initiation patterns.Proteasome inhibition reprograms accessibility of super enhancers.Proteasome inhibitor sensitive super enhancers distinguish basal from non-basal breast cancer subtypes.