Increased Proteasome Activity Research Articles

5-HT4 receptor agonists treatment reduces tau pathology and behavioral deficit in the PS19 mouse model of tauopathy.

Accumulation of tau in synapses in the early stages of Alzheimer's disease (AD) has been shown to cause synaptic damage, synaptic loss, and the spread of tau pathology through trans-synaptically connected neurons. Moreover, synaptic loss correlates with a decline in cognitive function, providing an opportunity to investigate therapeutic strategies to target synapses and synaptic tau to rescue or prevent cognitive decline in AD. One of the promising synaptic targets is the 5-HT4 serotonergic receptor present postsynaptically in the brain structures involved in the memory processes. 5-HT4R stimulation exerts synaptogenic and pro-cognitive effects involving synapse-to-nucleus signaling essential for synaptic plasticity. However, it is not known whether 5-HT4R activation has a therapeutic effect on tau pathology. The goal of this study was to investigate the impact of chronic stimulation of 5-HT4R by two agonists, prucalopride and RS-67333, in PS19 mice, a model of tauopathy. We utilized gradient assays to isolate pre- and post-synaptic compartments, followed by biochemical analyses for tau species and ubiquitinated proteins in the synaptic compartments and total brain tissue. Next, we performed kinetic assays to test the proteasome's hydrolysis capacity in treatment conditions. Moreover, behavioral tests such as the open field and non-maternal nest-building tests were used to evaluate anxiety-like behaviors and hippocampal-related cognitive functioning in the treatment paradigm. Our results show that 5-HT4R agonism reduced tauopathy, reduced synaptic tau, increased proteasome activity, and improved cognitive functioning in PS19 mice. Our data suggest that enhanced proteasome activity by synaptic mediated signaling leads to the enhanced turnover of tau initially within synapses where the receptors are localized, and over time, the treatment attenuated the accumulation of tau aggregation and improved cognitive functioning of the PS19 mice. Therefore, stimulation of 5-HT4R offers a promising therapy to rescue synapses from the accumulation of toxic synaptic tau, evident in the early stages of AD.

Tetramethylpyrazine Nitrone Promotes the Clearance of Alpha-Synuclein via Nrf2-Mediated Ubiquitin-Proteasome System Activation.

Aggregation of α-synuclein (α-syn) and α-syn cytotoxicity are hallmarks of sporadic and familial Parkinson's disease (PD). Nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-dependent enhancement of the expression of the 20S proteasome core particles (20S CPs) and regulatory particles (RPs) increases proteasome activity, which can promote α-syn clearance in PD. Activation of peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) may reduce oxidative stress by strongly inducing Nrf2 gene expression. In the present study, tetramethylpyrazine nitrone (TBN), a potent-free radical scavenger, promoted α-syn clearance by the ubiquitin-proteasome system (UPS) in cell models overexpressing the human A53T mutant α-syn. In the α-syn transgenic mice model, TBN improved motor impairment, decreased the products of oxidative damage, and down-regulated the α-syn level in the serum. TBN consistently up-regulated PGC-1α and Nrf2 expression in tested models of PD. Additionally, TBN similarly enhanced the proteasome 20S subunit beta 8 (Psmb8) expression, which is linked to chymotrypsin-like proteasome activity. Furthermore, TBN increased the mRNA levels of both the 11S RPs subunits Pa28αβ and a proteasome chaperone, known as the proteasome maturation protein (Pomp). Interestingly, specific siRNA targeting of Nrf2 blocked TBN's effects on Psmb8, Pa28αβ, Pomp expression, and α-syn clearance. In conclusion, TBN promotes the clearance of α-syn via Nrf2-mediated UPS activation, and it may serve as a potentially disease-modifying therapeutic agent for PD.

Abstract 5906: A new combinatorial therapy that synergistically targets the NuRD complex and proteostasis to eradicate quiescent ovarian cancer cells

Abstract Despite advances in immune and targeted therapies, chemotherapy remains the primary treatment for ovarian cancer (OvCa) patients. Unfortunately, most OvCa patients develop chemotherapy-resistant disease that is inevitably fatal. Quiescence is an important yet poorly understood mechanism underlying chemotherapy resistance. Therefore, we aimed to characterize quiescent ovarian cancer (qOvCa) cells to identify novel therapeutic targets to improve OvCa patient outcomes. Primary patient-derived qOvCa cells and proliferating cells were isolated using a single-cell microfluidics culture device and collected for single-cell RNA-seq. scRNA-seq of qOvCa cells identified (i) downregulation of MBD3 and CHD4, which are components of the Nucleosome Remodeling and Deacetylase (NuRD) complex, and (ii) upregulation of proteasome-associated genes. Knockdown of either MBD3 or CHD4 by shRNA, or NuRD complex pharmacologic inhibition with the HDAC inhibitors such as Vorinostat resulted in significant cell growth arrest without cell death. Standard and Fucci reporter-based cell cycle analysis further confirmed that inhibition of the NuRD complex with Vorinostat induced 94.47% cells in the G0 phase (p<0.0001), suggesting a dense quiescent state. Through cell cycle phase maps produced by iterative immunofluorescence of 30 core cell cycle regulators and manifold learning, we found Vorinostat-treated OvCa cells demonstrated a completely different cell cycle structure from control cells, with most of the cells in an extreme G0 phase. Bulk RNA-seq of Vorinostat-treated cells in three OvCa cell lines validated the downregulation of pathways relating to cell cycle, cell division, and DNA replication (LFC<-1, p<0.05), which is consistent with stem cells. Upregulation of several pathways involved in proteostasis were also noted. We therefore performed a targeted drug screen for combinatorial therapy approaches to eradicate qOvCa. We found that Vorinostat combined with the proteasome inhibitor Carfilzomib demonstrated the most profound synergistic cell death (Loewe index synergy score 23-73). Increased proteasome activity was also found in both primary and Vorinostat-induced qOvCa, suggesting the essential role of the proteasome in qOvCa. Tumor xenograft studies confirmed that Vorinostat alone can delay tumor growth (p<0.05) and combinatorial therapy of Vorinostat and Carfilzomib is more efficacious (p=0.0049). Taken together, NuRD complex inhibition induces quiescence. Combination therapy with Vorinostat to induce quiescence combined with proteasome inhibitors resulted in the profound death of therapy-resistant quiescent cells. Our work suggests this is a novel therapeutic approach to eradicate chemoresistant qOvCa cells and increase cure rates. Citation Format: Qi Jiang, Michelle Ertel, Santiago Panesso- Gómez, Sara Sannino, April Sagan, Alexander J. Cole, Stacy C. McGonigal, Betsy Ann Varghese, Wayne Stallaert, Jeffrey L. Brodsky, Hatice U. Osmanbeyoglu, Ronald J. Buckanovich. A new combinatorial therapy that synergistically targets the NuRD complex and proteostasis to eradicate quiescent ovarian cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5906.

A novel autism-associated UBLCP1 mutation impacts proteasome regulation/activity

The landscape of autism spectrum disorder (ASD) in Lebanon is unique because of high rates of consanguinity, shared ancestry, and increased remote consanguinity. ASD prevalence in Lebanon is 1 in 68 with a male-to-female ratio of 2:1. This study aims to investigate the impact of an inherited deletion in UBLCP1 (Ubiquitin-Like Domain-Containing CTD Phosphatase 1) on the ubiquitin-proteasome system (UPS) and proteolysis. Whole exome sequencing in a Lebanese family with ASD without pathogenic copy number variations (CNVs) uncovered a deletion in UBLCP1. Functional evaluation of the identified variant is described in fibroblasts from the affected. The deletion in UBLCP1 exon 10 (g.158,710,261CAAAG > C) generates a premature stop codon interrupting the phosphatase domain and is predicted as pathogenic. It is absent from databases of normal variation worldwide and in Lebanon. Wild-type UBLCP1 is widely expressed in mouse brains. The mutation results in decreased UBLCP1 protein expression in patient-derived fibroblasts from the autistic patient compared to controls. The truncated UBLCP1 protein results in increased proteasome activity decreased ubiquitinated protein levels, and downregulation in expression of other proteasome subunits in samples from the affected compared to controls. Inhibition of the proteasome by using MG132 in proband cells reverses alterations in gene expression due to the restoration of protein levels of the common transcription factor, NRF1. Finally, treatment with gentamicin, which promotes premature termination codon read-through, restores UBLCP1 expression and function. Discovery of an ASD-linked mutation in UBLCP1 leading to overactivation of cell proteolysis is reported. This, in turn, leads to dysregulation of proteasome subunit transcript levels as a compensatory response.

Phosphorylation of RPT6 Controls Its Ability to Bind DNA and Regulate Gene Expression in the Hippocampus of Male Rats during Memory Formation.

Memory formation requires coordinated control of gene expression, protein synthesis, and ubiquitin-proteasome system (UPS)-mediated protein degradation. The catalytic component of the UPS, the 26S proteasome, contains a 20S catalytic core surrounded by two 19S regulatory caps, and phosphorylation of the 19S cap regulatory subunit RPT6 at serine 120 (pRPT6-S120) has been widely implicated in controlling activity-dependent increases in proteasome activity. Recently, RPT6 was also shown to act outside the proteasome where it has a transcription factor-like role in the hippocampus during memory formation. However, little is known about the proteasome-independent function of "free" RPT6 in the brain or during memory formation and whether phosphorylation of S120 is required for this transcriptional control function. Here, we used RNA-sequencing along with novel genetic approaches and biochemical, molecular, and behavioral assays to test the hypothesis that pRPT6-S120 functions independently of the proteasome to bind DNA and regulate gene expression during memory formation. RNA-sequencing following siRNA-mediated knockdown of free RPT6 revealed 46 gene targets in the dorsal hippocampus of male rats following fear conditioning, where RPT6 was involved in transcriptional activation and repression. Through CRISPR-dCas9-mediated artificial placement of RPT6 at a target gene, we found that RPT6 DNA binding alone may be important for altering gene expression following learning. Further, CRISPR-dCas13-mediated conversion of S120 to glycine on RPT6 revealed that phosphorylation at S120 is necessary for RPT6 to bind DNA and properly regulate transcription during memory formation. Together, we reveal a novel function for phosphorylation of RPT6 in controlling gene transcription during memory formation.

Abstract C083: HDAC6 inhibition increases proteasome activity and modulates the myeloma immunopeptidome to promote cytotoxic T-cell activity

Abstract The proteasome functions as an essential component of immune surveillance by generating peptides from intracellular antigens that are then presented to cytotoxic T-cells. The vast majority of defined antitumor T-cell responses involves the proteasomal processing of intracellular proteins and their presentation in the context of major histocompatibility complex (MHC) class I molecules to antigenic peptide-specific CD8+ T-cells. Such antigenic peptides generated by the proteasome are generally 8-10 amino acids in length and mirror the linear sequence of the parental protein. However, immune evasion is a hallmark of cancer cells that disrupt the antigen processing and presentation machinery. Tumors develop strategies to evade host immunity and resist current immunotherapies, while others display a low tumor mutation burden limiting the presence of tumor antigenicity. Here, we postulated that pharmacologic enhancement of proteasome catalytic activity would increase MHC class I antigen presentation, modulate the myeloma immunopeptidome, and promote CD8+ T-cells anti-myeloma activity. A cell-based, high-throughput screen revealed that the histone deacetylase 6 (HDAC6) inhibitors tubastatin-A, ACY-738 and ACY-1215 increased proteasome activity in multiple myeloma (MM) cells. HDAC6 inhibitors increased pan-MHC class-I expression in MM cells as well as a panel of cancer cell lines. Treatment of MM patient tumor cells with HDAC6 inhibitors increased the cytotoxic effect of autologous patient-derived T-cells. Mechanism-based studies demonstrated that pharmacologic blockade or genetic ablation of the HDAC6 ubiquitin-binding (BUZ) domain disrupted HDAC6 association with HR23B, a substrate-shuttle factor that delivers ubiquitinylated cargo to proteasomes. HDAC6 inhibitors or HDAC6-BUZ domain deletion reduced the association of HR23B with HDAC6 and promoted binding of HR23B to proteasomes and a consequent increase in proteasome activity. The results validate the HDAC6-BUZ domain as an attractive drug discovery target and demonstrate that proteasome activators enhance antitumor immunity. Proteasome activators represent a paradigm-shifting approach to overcome mechanisms of immune escape in cancer cells. FDA-approved drugs that increase proteasome activity and boost antigen presentation and can be repositioned as cancer immunotherapeutics to overcome the existing bottlenecks in drug development. Taken together, our results highlight the breadth and magnitude of the proteasome in governing fundamental cellular processes and the immense potential of therapeutics that exploit proteasomes to treat human disease. Citation Format: Priyanka S. Rana, James J. Ignatz-Hoover, James J. Driscoll. HDAC6 inhibition increases proteasome activity and modulates the myeloma immunopeptidome to promote cytotoxic T-cell activity [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C083.

HDAC6 Inhibition Activates Proteasomes to Modulate the MHC Class I Immunopeptidome and Promote Antimyeloma Immunity

The evasion of host immunity is a hallmark of cancer. Tumor cells develop strategies to evade host immunity and to resist currently available immunotherapies, while others present a low tumor mutation burden limiting the presence of tumor antigenicity. Proteasomes are exquisitely complex, intricately regulated protein-degrading machines that are responsible for the overwhelming majority of intracellular proteolysis in eukaryotic cells. Proteasomes are also essential for the efficient processing of intracellular proteins to generate antigenic epitopes that complex with MHC-class I molecules and are displayed on antigen-presenting cells (APCs) to activate CD8 + cytotoxic T-lymphocytes (CTLs). We hypothesized that pharmacologic activation of proteasomes would modulate the tumor immunopeptidome to increase MHC class I antigen presentation and promote CTL activity. Here, we developed a cell-based, high-throughput screen (HTS) to identify FDA-approved pharmacologics and bioactive molecules that increased proteasomal activity to promote the presentation of MHC class I antigens. The HTS revealed that the histone deacetylase 6 (HDAC6)-selective inhibitors tubastatin-A, ACY-738 and ACY-1215 increased proteasome activity in a panel of multiple myeloma (MM) cell lines. The HDAC6 inhibitors also significantly enhanced MHC-class I antigen presentation pan-MHC class-I expression in a diverse panel of cancer cell lines. Pretreatment of MM patient CD138 + tumor cells with HDAC6 inhibitors promoted the cytotoxic activity of autologous patient-derived T-cells. Mechanistic studies revealed that pharmacologic blockade or genetic ablation of HDAC6 or the HDAC6 ubiquitin-binding (BUZ) domain disrupted the association of HDAC6 with the ubiquitin-like protein HR23B, a substrate-shuttle factor that delivers ubiquitinylated cargo to proteasomes. Taken together, the results validate the HDAC6-BUZ domain as an attractive drug discovery target and demonstrate the immediate translational impact of proteasome activators to modulate the immunopeptidome and enhance antitumor immunity. Proteasome activators also represent a paradigm-shifting approach to overcome mechanisms of immune escape. FDA-approved drugs that increase proteasome activity and boost antigen presentation can now be repositioned as cancer immunotherapeutics to overcome the existing bottlenecks in drug development.

PSMC2 Overexpression Enhances Proteasome Activity, Mitigates ER Stress, and Correleates with Reduced Overall Survival in Multiple Myeloma

Background: Multiple myeloma (MM) remains a highly treatable but generally incurable plasma cell dyscrasia. These plasma cells synthesize massive amounts of paraprotein relying heavily on the ubiquitin proteasome system to maintain homeostasis and are exquisitely sensitive to proteasome inhibition to avoid terminal ER stress. We postulated that increased expression of clinically relevant proteasome subunits would correlate with reduced overall survival in MM patients treated with proteasome inhibitors. Objective: To correlate proteasome gene expression levels to clinicals outcomes in both the phase III APEX trial and the MMRF COMMPASS Trial. To model the effects of these hits on MMCL UPS function. Results: We identified that 19S regulatory ATPases PSMC2 and PSMC6 correlated with poorer OS, outperforming the proteasome inhibitor (PI) target, PSMB5, in this analysis. We focused on modeling the more frequently upregulated PSMC2. We created PSMC2 overexpressing multiple myeloma cell lines, noting PSMC2 is readily incorporated in the higher order proteasome complexes. PSMC2 overexpressing cells exhibit higher levels of 20S proteasome activity (1.6 fold increase in ARH77 and 3 fold increase in U266 cell line compared to control, p< 0.01 in each case) and are more resistant to PI challenge (Bortezomib LD 50 of 30 nM v 15 nM in U266 overexpressed and control cells respectively, Bortezomib LD 50 of 18 nM v 10 nM in ARH77 overexpressed v control cells respectively). PIs are known to increase ER stress, and PSMC2 overexpressing cells are better able to mitigate PI mediated ER stress with PSMC2 overexpressing cells exhibiting less induction of ER stress sensors p-IRE1α and ATF4 compared to PSMC2 knockdown cells on bortezomib or tunicamycin challenge as quantitated by western blotting and utilizing an fluorescent ER stress sensor that models the conversion of XBP1u to XBP1s by pIRE1α. Mechanistically, PSMC subunits play a key role in the recognition and degradation of misfolded ER proteins, and increased 19S subunits may allow more effective ER associated protein degradation (ERAD) Conclusions: Taken together, our results suggest PSMC2 overexpression correlates with reduced OS in MM patients treated with bortezomib and that PSMC2 may represent an actionable therapeutic target to prevent or overcome PI resistance. PSMC2 overexpression increases proteasome activity in MM cells, mitigates ER stress on PI challenge and promotes PI resistance. mitigates ER stress upon PI challenge, and portending poorer clinical prognosis and more drug resistance, suggesting that 19S targeted agents may help overcome drug resistance in MM. Figure 1 A. PSMC2 overexpression increases chymotrypsin-like proteasome activity at baseline in U266 and ARH77 cells with a similar effect of residual proteasome activity after challenge with bortezomib or carfilzomib. B. ARH77 and U266 FLAG and vector cells were challenged with bortezomib for 18 hrs and then assayed by annexin PI staining. LD50 increased from 10 nm to 15 nm in ARH77 cells and from 12 to 25 in U266 Cells.

The Role of the Proteasome in Limiting Cellular Stress Associated with Protein Accumulation

AbstractThe proteasome is comprised of multiple subunits that catalyze the degradation of proteins to maintain cellular homeostasis. The proteasome targets protein substrates by two different pathways. The ubiquitin‐dependent pathway requires proteins to be labeled with a ubiquitin tag to signal for degradation by the 26S isoform of the proteasome. Protein degradation through this pathway declines during age progression. The ubiquitin‐independent pathway utilizes the 20S proteasome isoform. It can degrade misfolded and intrinsically disordered proteins to decrease cellular stress. Age‐related protein accumulation and aggregation can occur due to the decreased activity and expression of the proteasome. Protein accumulation causes increased cellular stress which can contribute to disease progression. Increasing proteasome activity could serve as a solution to eliminating and preventing protein accumulation. Studies have shown the value of the proteasome as a therapeutic entity to mitigate cellular stress. This perspective explores the link between proteasome activity and cellular stress caused by age‐related misfolded protein accumulation.

Klotho increases antioxidant defenses in astrocytes and ubiquitin–proteasome activity in neurons

Klotho is an antiaging protein, and its levels decline with age and chronic stress. The exogenous administration of Klotho can enhance cognitive performance in mice and negatively modulate the Insulin/IGF1/PI3K/AKT pathway in terms of metabolism. In humans, insulin sensitivity is a hallmark of healthy longevity. Therefore, this study aimed to determine if exogenous Klotho, when added to neuronal and astrocytic cell cultures, could reduce the phosphorylation levels of certain insulin signaling effectors and enhance antioxidant strategies in these cells. Primary cell cultures of cortical astrocytes and neurons from mice were exposed to 1 nM Klotho for 24 h, with or without glucose. Klotho decreased pAKT and mTOR levels. However, in astrocytes, Klotho increased FOXO-3a activity and catalase levels, shielding them from intermediate oxidative stress. In neurons, Klotho did not alter FOXO-3 phosphorylation levels but increased proteasome activity, maintaining lower levels of PFKFB3. This study offers new insights into the roles of Klotho in regulating energy metabolism and the redox state in the brain.

TCH-165 attenuates cardiac ischaemia/reperfusion injury by balancing mitochondrial dynamics via increasing proteasome activity

The proteasome is the main complex responsible for maintaining intracellular protein homeostasis, impairment of which is associated with cardiac ischaemia/reperfusion (I/R) injury. The small molecule TCH-165 has been found to activate the 20S proteasome to remove disordered proteins in multiple myeloma and glioblastoma. However, the preventive effect of TCH-165 against I/R-mediated cardiac impairment in mice remains largely unknown. Here, a cardiac I/R model was established in mice. Heart function was assessed with echocardiography. Cardiac infarction, myocyte death, and superoxide level were evaluated by 2,3,5-triphenyltetrazolium chloride (TTC)-Evans blue staining, terminal deoxynucleotidyl transferase-mediated dUTP nick and labelling (TUNEL) assay and immunostaining, respectively. Our results showed that TCH-165 treatment markedly ameliorated I/R-mediated cardiac dysfunction and decreased the infarct size, apoptosis, and superoxide levels. Mechanistically, TCH-165 increased immunoproteasome subunit expression/activity, increasing pro-fission protein dynamin-1-like protein (DNM1L, also known as DRP1) degradation and the expression of the pro-fusion proteins mitofusin 1/2 (Mfn1/2) and thereby leading to mitochondrial fission/fusion balance. In vitro experiments confirmed that inhibition of proteasome activity by epoxomicin abolished the protective effect of TCH-165 against hypoxia/reoxygenation (H/R)-induced increases in cardiomyocyte apoptosis, superoxide production and mitochondrial fission. In summary, TCH-165 is a newly discovered inducer of immunoproteasome activity that exerts a preventive effect against cardiac I/R damage by targeting Drp1 degradation, indicating that it may be as a potential therapeutic candidate for ischaemic heart disease.

Juniper berry extract containing Anthricin and Yatein suppresses lipofuscin accumulation in human epidermal keratinocytes through proteasome activation, increases brightness, and decreases spots in human skin.

Skin brightness and spot have a significant impact on youthful and beautiful appearance. One important factor influencing skin brightness is the amount of internal reflected light from the skin. Observers recognize the total surface-reflected light and internal reflected light as skin brightness. The more internal reflected light from the skin, the more attractive and brighter the skin appears. This study aims to identify a new natural cosmetic ingredient that increases the skin's internal reflected light, decreases spot, and provides a youthful and beautiful skin appearance. Lipofuscin in epidermal keratinocytes, the aggregating complex of denatured proteins and peroxidized lipids, is one factor that decreases skin brightness and causes of spot. Aggregates block light transmission, and peroxidized lipids lead to skin yellowness, dullness, and age spot. Lipofuscin is known to accumulate intracellularly with aging. Rapid removal of intracellular denatured proteins prevents lipofuscin formation and accumulation in cells. We focused a proteasome system that efficiently removes intracellular denatured proteins. To identify natural ingredients that increase proteasome activity, we screened 380 extracts derived from natural products. The extract with the desired activity was fractionated and purified to identify active compounds that lead to proteasome activation. Finally, the efficacy of the proteasome-activating extract was evaluated in a human clinical study. We discovered that Juniperus communis fruits (Juniper berry) extract (JBE) increases proteasome activity and suppresses lipofuscin accumulation in human epidermal keratinocytes. We found Anthricin and Yatein, which belong to the lignan family, to be major active compounds responsible for the proteasome-activating effect of JBE. In a human clinical study, an emulsion containing 1% JBE was applied to half of the face twice daily for 4 weeks, resulting in increased internal reflected light, brightness improvement (L-value), and reduction in yellowness (b-value) and spot in the cheek area. This is the first report demonstrating that JBE containing Anthricin and Yatein decreases lipofuscin accumulation in human epidermal keratinocytes through proteasome activation, increases brightness, and decreases surface spots in human skin. JBE would be an ideal natural cosmetic ingredient for creating a more youthful and beautiful skin appearance with greater brightness and less spot.

Overexpression of Nfe2l1 increases proteasome activity and delays vision loss in a preclinical model of human blindness.

Proteasomes are the central proteolytic machines that are critical for breaking down most of the damaged and abnormal proteins in human cells. Although universally applicable drugs are not yet available, the stimulation of proteasomal activity is being analyzed as a proof-of-principle strategy to increase cellular resistance to a broad range of proteotoxic stressors. These approaches have included the stimulation of proteasomes through the overexpression of individual proteasome subunits, phosphorylation, or conformational changes induced by small molecules or peptides. In contrast to these approaches, we evaluated a transcription-driven increase in the total proteasome pool to enhance the proteolytic capacity of degenerating retinal neurons. We show that overexpression of nuclear factor erythroid-2-like 1 (Nfe2l1) transcription factor stimulated proteasome biogenesis and activity, improved the clearance of the ubiquitin-proteasomal reporter, and delayed photoreceptor neuron loss in a preclinical mouse model of human blindness caused by misfolded proteins. The findings highlight Nfe2l1 as an emerging therapeutic target to treat neurodegenerative diseases linked to protein misfolding.

Minimal mechanistic component of HbYX-dependent proteasome activation that reverses impairment by neurodegenerative-associated oligomers

The implication of reduced proteasomal function in neurodegenerative diseases combined with studies showing the protective effects of increasing proteasome activity in animal models highlight the need to understand the capacity for proteasome activation by small molecules. The C-terminal HbYX motif is present on many proteasome binding proteins and functions to tether activators to the 20S core particle. Previous studies have shown that peptides with a HbYX motif can autonomously activate 20S gate-opening to allow protein degradation. In this study, through an iterative process of peptide synthesis, we design a HbYX-like dipeptide mimetic that represents only the fundamental components of the HbYX motif. The mimetic robustly induces gate-opening in archaeal, yeast, and mammalian proteasomes. We identify multiple proteasome α subunit residues in the archaeal proteasome involved in HbYX-dependent activation. When stimulated by the mimetic, the mammalian 20S can degrade unfolded proteins such as tau. Findings using our peptide mimetic suggest the HbYX-dependent mechanism requires cooperative binding in at least two intersubunit pockets of the α ring. Most significantly, our peptide mimetic reverses proteasome impairment by neurodegenerative disease-associated oligomers. Collectively, these results validate HbYX-like molecules as having robust potential to stimulate proteasome function, which are potentially useful for treating neurodegenerative diseases.

Immunoproteasome-specific subunit PSMB9 induction is required to regulate cellular proteostasis upon mitochondrial dysfunction

Perturbed cellular protein homeostasis (proteostasis) and mitochondrial dysfunction play an important role in neurodegenerative diseases, however, the interplay between these two phenomena remains unclear. Mitochondrial dysfunction leads to a delay in mitochondrial protein import, causing accumulation of non-imported mitochondrial proteins in the cytosol and challenging proteostasis. Cells respond by increasing proteasome activity and molecular chaperones in yeast and C. elegans. Here, we demonstrate that in human cells mitochondrial dysfunction leads to the upregulation of a chaperone HSPB1 and, interestingly, an immunoproteasome-specific subunit PSMB9. Moreover, PSMB9 expression is dependent on the translation elongation factor EEF1A2. These mechanisms constitute a defense response to preserve cellular proteostasis under mitochondrial stress. Our findings define a mode of proteasomal activation through the change in proteasome composition driven by EEF1A2 and its spatial regulation, and are useful to formulate therapies to prevent neurodegenerative diseases.

Substrate-specific effects of natural genetic variation on proteasome activity.

Protein degradation is an essential biological process that regulates protein abundance and removes misfolded and damaged proteins from cells. In eukaryotes, most protein degradation occurs through the stepwise actions of two functionally distinct entities, the ubiquitin system and the proteasome. Ubiquitin system enzymes attach ubiquitin to cellular proteins, targeting them for degradation. The proteasome then selectively binds and degrades ubiquitinated substrate proteins. Genetic variation in ubiquitin system genes creates heritable differences in the degradation of their substrates. However, the challenges of measuring the degradative activity of the proteasome independently of the ubiquitin system in large samples have limited our understanding of genetic influences on the proteasome. Here, using the yeast Saccharomyces cerevisiae, we built and characterized reporters that provide high-throughput, ubiquitin system-independent measurements of proteasome activity. Using single-cell measurements of proteasome activity from millions of genetically diverse yeast cells, we mapped 15 loci across the genome that influence proteasomal protein degradation. Twelve of these 15 loci exerted specific effects on the degradation of two distinct proteasome substrates, revealing a high degree of substrate-specificity in the genetics of proteasome activity. Using CRISPR-Cas9-based allelic engineering, we resolved a locus to a causal variant in the promoter of RPT6, a gene that encodes a subunit of the proteasome's 19S regulatory particle. The variant increases RPT6 expression, which we show results in increased proteasome activity. Our results reveal the complex genetic architecture of proteasome activity and suggest that genetic influences on the proteasome may be an important source of variation in the many cellular and organismal traits shaped by protein degradation.

Development of demetia therapeutics regurating synaptic plasticity

Alzheimer's disease (AD) is the most common dementia in the world characterized by the neuropathological hallmarks consisting of an accumulation of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFT). There is no fundamental therapeutic treatment. We have developed a novel AD therapeutic candidate SAK3 which improves neuronal plasticity in the brain. SAK3 enhanced the acetylcholine release via T-type calcium channels. T-type calcium channels is highly expressed in neuro-progenitor cells in the hippocampal dentate gyrus. SAK3 enhanced the proliferation and differentiation of the neuro-progenitor cells, thereby improving depressive behaviors. The Cav3.1 null mice impaired the proliferation and differentiation of the neuro-progenitor cells. In addition, SAK3 activated CaMKII involving neuronal plasticity, thereby improving spine regeneration and proteasome activities impaired in AD related AppNL-F/NL-F knock-in mice. The improvement of the decreased proteasome activity through enhancement CaMKII/Rpt6 signaling by SAK3 treatment contributed to the amelioration of synaptic abnormalities and cognitive decline. The increased proteasome activity also accounted for inhibition of Aβ deposition. Taken together, the proteasome activation via enhancement of CaMKII/Rpt6 signaling is a new strategy for AD treatment, which rescues the AD pathology including cognitive impairments and Aβ deposition. SAK3 may be a new hopeful drug candidate rescuing dementia patients.

Abstract 6235: Discovery of novel HDAC6 inhibitors that enhance proteasomal activity to boost antigen presentation and trigger anti-myeloma T-cell immunity

Abstract Transformative success of cancer immunotherapy has revolutionized cancer treatment and can induce long lasting responses in patients with cancers from a wide range of histologies. However, only a fraction of patients respond to immunotherapy and cancer cells escape immunosurveillance through molecular mechanisms that remain elusive. Proteasomes play a central role in the immune response by generating peptides from intracellular antigens which are presented on the cell surface for recognition by CD8+ cytotoxic T lymphocytes (CTLs). Malignant cells employ strategies to downregulate antigen presentation and impair CTL-mediated tumor recognition and lysis. Recently, we discovered that HDAC6-specific inhibitors increased intracellular proteasome activity and the generation of antigenic class I MHC peptides. However, current HDAC6 inhibitors have pharmacologic liabilities that limit efficacy, e.g., low potency and solubility, poor pharmacokinetic properties and potential genotoxicity. Therefore, we performed a cell-based, high-throughput screen (HTS) of 9,600 HDAC-specific compounds to identify novel compounds that increased proteasomal activity in myeloma cells. We identified 8 hits that increased proteasomal activity at least two-fold. Importantly, two novel molecules identified in the HTS increased proteasome activity more potently and more rapidly than the HDAC6-specific inhibitors Tubastatin-A and ACY-1215 (Ricolinostat) with comparatively low cytotoxicity. Proteasomes degrade chicken ovalbumin (Ova) to generate the immunodominant antigen SIINFEKL presented at the cell surface complexed with the MHC-class I molecule H-2Kb. Treatment of tumor cells with Tubastatin-A and ACY-1215 increased levels of the MHC-class I-SIINFEKL complex by ~3-fold. Tumor cells were pretreated with Tubastatin-A and ACY-1215 and then co-cultured with CTLs that had been genetically-engineered to express a SIINFEKL-restricted T-cell receptor (TCR). Pre-treatment of lymphoma or multiple myeloma cells with novel HDAC6 inhibitors also increased tumor lysis by CTLs that expressed the SIINFEKL-restricted TCR by 2-fold. Taken together, our results support repositioning pharmacologics that inhibit HDAC6 to activate proteasomal generation of antigenic peptides and boost antigen presentation as cancer immunotherapeutics. Citation Format: Priyanka S. Rana, James Ignatz-Hoover, James J. Driscoll. Discovery of novel HDAC6 inhibitors that enhance proteasomal activity to boost antigen presentation and trigger anti-myeloma T-cell immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6235.

Abstract 1354: Proteasome activation prevents T cell exhaustion and improves antitumor activity

Abstract Tumor infiltrating lymphocytes (TILs) exert their antitumor activity in the tumor microenvironment (TME). Chronic TCR stimulation, together with features of the tumor microenvironment such as hypoxia, result in T cell exhaustion. Exhausted T cells (TEX) are characterized by oxidative stress that leads to cellular accumulation of oxidized proteins. Because the proteasome complex clears oxidized proteins, we hypothesized that its capacity might be overloaded in TEX, limiting their fitness. Analysis of single-cell transcriptomics data from 19 tumor types indicated an increased proteasome activity in TEX compared to non-exhausted TILs. Higher levels of ROS-induced protein oxidation, expression of proteasome genes and proteasome activity were confirmed in human TEX, suggesting that increased proteasome activity might be a compensatory mechanism to exhaustion-associated oxidative stress. We show that pharmacological activation of the proteasome prevented T cell exhaustion, and lead to superior anti-tumor control in the context of adoptive cell therapy in mouse models. Thus, modulation of the proteasome activity is an attractive strategy to prevent T cell dysfunction promoted by the TME, and to potentially overcome this major obstacle in cancer immunotherapies against solid tumors. Citation Format: Ander de Blas, Massimo Andreatta, Asier Antoñana-Vildosola, Paloma Velasco, Leire Egia-Mendikute, Borja Jimenez-Lasheras, Samanta Romina Zanetti, Santiago J. Carmona, Endika Prieto-Fernández, Asis Palazon. Proteasome activation prevents T cell exhaustion and improves antitumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1354.

Hematopoietic stem cells preferentially traffic misfolded proteins to aggresomes and depend on aggrephagy to maintain protein homeostasis.

Hematopoietic stem cells (HSCs) regenerate blood cells throughout life. To preserve their fitness, HSCs are particularly dependent on maintaining protein homeostasis (proteostasis). However, how HSCs purge misfolded proteins is unknown. Here, we show that in contrast to most cells that primarily utilize the proteasome to degrade misfolded proteins, HSCs preferentially traffic misfolded proteins to aggresomes in a Bag3-dependent manner and depend on aggrephagy, a selective form of autophagy, to maintain proteostasis invivo. When autophagy is disabled, HSCs compensate by increasing proteasome activity, but proteostasis is ultimately disrupted as protein aggregates accumulate and HSC function is impaired. Bag3-deficiency blunts aggresome formation in HSCs, resulting in protein aggregate accumulation, myeloid-biased differentiation, and diminished self-renewal activity. Furthermore, HSC aging is associated with a severe loss of aggresomes and reduced autophagic flux. Protein degradation pathways are thus specifically configured in young adult HSCs to preserve proteostasis and fitness but become dysregulated during aging.