Perturbation of maternal PIASy abundance disrupts zygotic genome activation and embryonic development via SUMOylation pathway

During the maternal-to-zygotic transition (MZT), mRNAs and proteins stored in oocytes are degraded and zygotic genes are activated. We have previously shown that the ubiquitin-proteasome system (UPS)-mediated degradation of maternal proteins plays a role in the onset of zygotic transcription. However, it is still unclear which maternal proteins should be degraded for zygotic genome activation and ensuring subsequent embryonic development. In this study, we screen for these maternal factors that are degraded via the UPS. We thus identified a maternal protein PIASy (protein inhibitor of activated STATy), which is an E3 SUMO ligase. The overexpression of PIASy in fertilized embryos causes developmental arrest at the two-cell stage due to severe abnormal chromosome segregation and impaired zygotic transcription. We find that this developmental role of PIASy is related to its SUMOylation activity. Moreover, PIASy overexpression leads to increased trimethylation of histone H3 lysine 9 (H3K9me3) in two-cell nuclei and enhanced translocation of H3K9me3 methyltransferase to the pronucleus. Hence, PIASy is a maternal factor that is degraded after fertilization and may be important for the proper induction of zygotic genome activation and embryonic development.

Poly(ADP-ribose)-dependent ubiquitination and its clinical implications

ADP-ribosylation-the addition of one or multiple ADP-ribose units onto proteins-is a therapeutically important post-translational modification implicated in cancer, neurodegeneration, and infectious diseases. The protein modification regulates a broad range of biological processes, including DNA repair, transcription, RNA metabolism, and the structural integrity of nonmembranous structures. The polymeric form of ADP-ribose, poly(ADP-ribose), was recently identified as a signal for triggering protein degradation through the ubiquitin-proteasome system. Using informatics analyses, we found that these ubiquitinated substrates tend to be low abundance proteins, which may serve as rate-limiting factors within signaling networks or metabolic processes. In this review, we summarize the current literature on poly(ADP-ribose)-dependent ubiquitination (PARdU) regarding its biological mechanisms, substrates, and relevance to diseases.

Natural alkaloid harmine promotes degradation of alpha-synuclein via PKA-mediated ubiquitin-proteasome system activation

BACKGROUND

Parkinson's disease (PD) is an age-dependent progressive movement disorder characterized by a profound and selective loss of nigrostriatal dopaminergic neurons. Accumulation of <alpha>-synuclein (<alpha>-syn) positive protein aggregates in the substantia nigra is a pathological hallmark of PD, indicating that protein turnover defect is implicated in PD pathogenesis.

PURPOSE

This study aims to identify neuroprotective compounds which can alleviate the accumulation of <alpha>-syn in neuronal cells and dissect the underlying mechanisms.

METHODS

High throughput screening was performed by dot blot assay. The degradation of different forms of <alpha>-syn by candidate compounds were assessed by western blot. The autophagy lysosome pathway and ubiquitin-proteasome system were examined to dissect the degradation pathway. The UPS activity was assessed by cellular UPS substrates degradation assay and biochemical proteasome activity assay. Q-PCR was performed to test the mRNA level of different proteasome subunits. Furthermore, Neuroprotective effect of candidate compound was tested by LDH assay and PI staining.

RESULTS

Through the high throughput screening, harmine was identified as a potent <alpha>-syn lowering compound. The time-dependent and dose-dependent effects of harmine on the degradation of different forms of <alpha>-syn were further confirmed. Harmine could dramatically promote the degradation of UPS substrates GFP-CL1, Ub-R-GFP and Ub-G76V-GFP, and activate cellular proteasome activity. Mechanistically, harmine dramatically enhanced PKA phosphorylation to enhance proteasome subunit PSMD1 expression. PKA inhibitor blocked the effects of harmine in activating UPS, up regulating PSMD1 and promoting <alpha>-syn degradation, indicating that harmine enhances UPS function via PKA activation. Moreover, harmine efficiently rescued cell death induced by over-expression of <alpha>-syn, via UPS-dependent manner.

CONCLUSION

Harmine, as a new proteasome enhancer, may have potential to be developed into therapeutic agent against neurodegenerative diseases associated with UPS dysfunction and aberrant proteins accumulation.

Oxidative attack during temperature fluctuation challenge compromises liver protein homeostasis of a temperate fish model

Seasonal variations in water temperature are a natural stressor of temperate fish that affect growth performance and metabolism globally. Gilthead sea bream is one of the most economically interesting species in the Mediterranean; but its liver metabolism is affected by the cold season. However, the effects of cold on protein turnover mechanisms have hardly been studied. Here, we study the relationship between liver oxidative status and protein homeostasis pathways during a 50-day low temperature period at 14 °C, and subsequent recovery at two times: 7 days (early recovery) and 30 days (late recovery). Liver redox status was determined by measuring oxidised lipids and proteins, the glutathione redox cycle and major antioxidant enzymes activities. Protein turnover was analysed via liver protein expression of HSP70 and HSP90; proteasome 26S subunits and polyubiquitination, as markers of the ubiquitin-proteasome system (UPS); and cathepsin D, as a lysosomal protease. Low temperature exposure depressed antioxidant enzyme activities, affecting the glutathione redox cycle and reducing total glutathione levels. Both the UPS and lysosomal pathways were also depressed and consequently, oxidised protein accumulated in liver. Interestingly, both protein oxidation and polyubiquitination tagging depended on protein molecular weight. Despite all these alterations, temperature recovery reverted most consequences of the cold at different rates: with delayed recovery of total glutathione levels and oxidised protein degradation with respect to enzyme activities recovery. All these findings demonstrate that protein liver homeostasis is compromised after chronic cold exposure and could be the cause of liver affectations reported in aquaculture of temperate fish.

Endo-lysosomal pathway and ubiquitin-proteasome system dysfunction in Alzheimer's disease pathogenesis

Several lines of evidence have shown that defects in the endo-lysosomal autophagy degradation pathway and the ubiquitin-proteasome system play a role in Alzheimer's Disease (AD) pathogenesis and pathophysiology. Early pathological changes, such as marked enlargement of endosomal compartments, gradual accumulation of autophagic vacuoles (AVs) and lysosome dyshomeostasis, are well-recognized in AD. In addition to these pathological indicators, many genetic variants of key regulators in the endo-lysosomal autophagy networks and the ubiquitin-proteasome system have been found to be associated with AD. Furthermore, altered expression levels of key proteins in these pathways have been found in AD human brain tissues, primary cells and AD mouse models. In this review, we discuss potential disease mechanisms underlying the dysregulation of protein homeostasis governing systems. While the importance of two major protein degradation pathways in AD pathogenesis has been highlighted, targeted therapy at key components of these pathways has great potential in developing novel therapeutic interventions for AD. Future investigations are needed to define molecular mechanisms by which these complex regulatory systems become malfunctional at specific stages of AD development and progression, which will facilitate future development of novel therapeutic interventions. It is also critical to investigate all key components of the protein degradation pathways, both upstream and downstream, to improve our abilities to manipulate transport pathways with higher efficacy and less side effects.

Scalable In Vitro Proteasome Activity Assay

We developed a degradation assay based on fluorescent protein substrates that are efficiently recognized, unfolded, translocated, and hydrolyzed by the proteasome. The substrates consist of three components: a proteasome-binding tag, a folded domain, and an initiation region. All the components of the model substrate can be changed to modulate degradation, and the assay can be performed in parallel in 384-well plates. These properties allow the assay to be used to explore a wide range of experimental conditions and to screen proteasome modulators.

The ubiquitin-proteasome system is necessary for the replication of duck Tembusu virus

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that has caused massive economic losses to the duck industry in China. The cellular factors required for DTMUV replication have been poorly studied. The ubiquitin-proteasome system (UPS), the major intracellular proteolytic pathway, mediates diverse cellular processes, including endocytosis and signal transduction, which may be involved in the entry of virus. In the present study, we explored the interplay between DTMUV replication and the UPS in BHK-21 cells and found that treatment with proteasome inhibitor (MG132 and lactacystin) significantly decreased the DTMUV progency at the early infection stage. We further revealed that inhibition of the UPS mainly occurs on the level of viral protein expression and RNA transcription. In addition, using specific siRNAs targeting ubiquitin reduces the production of viral progeny. In the presence of MG132 the staining for the envelope protein of DTMUV was dramatically reduced in comparison with the untreated control cells. Overall, our observations reveal an important role of the UPS in multiple steps of the DTMUV infection cycle and identify the UPS as a potential drug target to modulate the impact of DTMUV infection.

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Treatment with proteasome inhibitor significantly decreased the DTMUV progency.

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Inhibition of the UPS mainly occurs on the level of viral protein expression and RNA transcription.

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Inhibit the expression of ubiquitin reduces the production of viral progeny.

Ethanol withdrawal limits fear memory reactivation-induced molecular events associated with destabilization phase: Influence of d-cycloserine

A 1-day fear memory in ethanol withdrawn (ETOH) rats is resistant to destabilization-reconsolidation process. However, d-cycloserine (DCS) reverts this disturbance. Considering that the formation of pathological fear memories in humans often occurs long time before the requirement of an intervention, the study of older memories is relevant in ETOH rats. In addition, the resistance to destabilization and DCS effect on this memory phase at molecular level in ETOH rats have not been corroborated yet. Firstly, we examined the effect of a pharmacological intervention after reactivation on reconsolidation of a 7-day fear memory in ETOH rats. Then, and considering that enhanced GluN2B expression and ubiquitin-proteasome system (UPS) activity are involved in destabilization, we evaluated them following reactivation in ETOH rats. Furthermore, DCS effect on such destabilization markers was examined. It was found that the pharmacological intervention after reactivation did not affect the 7-day fear memory in ETOH rats with DCS reversing this resistance. Memory reactivation increased GluN2B expression, polyubiquitination levels and proteasome activity in the basolateral amygdala complex (BLA) of control (CON) rats only; without affecting these molecular events in ETOH rats. Finally, ETOH rats treated with DCS and CON animals displayed elevated and similar UPS activities in the BLA after reactivation. In conclusion, the reactivation of an older fear memory formed during ethanol withdrawal does not trigger the molecular events associated with destabilization, and DCS facilitates this memory phase by enhancing the UPS activity.

Methods for genetic analysis of mammalian ER-associated degradation

Identification and degradation of misfolded proteins by the ubiquitin-proteasome system (UPS) is crucial for maintaining proteostasis, but only a handful of UPS components have been linked to the recognition of specific substrates. Studies in Saccharomyces cerevisiae using systematic perturbation of nonessential genes have uncovered UPS components that recognize and ubiquitylate model substrates of the UPS; however, similar analyses in metazoans have been limited. In this chapter, we describe methods for using CRISPR/Cas9 technology combined with genome-wide high complexity single guide (sgRNA) libraries and a transcriptional shutoff strategy for phenotypic selection based on kinetic measurements of protein turnover to identify the genes required to degrade model clients of the mammalian ER-associated degradation system. We also discuss considerations for screen design, execution, and interpretation.

Proteasome inhibitor b-AP15 induces enhanced proteotoxicity by inhibiting cytoprotective aggresome formation

Proteasome inhibitors have been shown to induce cell death in cancer cells by triggering an acute proteotoxic stress response characterized by accumulation of poly-ubiquitinated proteins, ER stress and the production of reactive oxygen species. The aggresome pathway has been described as an escape mechanism from proteotoxicity by sequestering toxic cellular aggregates. Here we show that b-AP15, a small-molecule inhibitor of proteasomal deubiquitinase activity, induces poly-ubiquitin accumulation in absence of aggresome formation. b-AP15 was found to affect organelle transport in treated cells, raising the possibility that microtubule-transport of toxic protein aggregates is inhibited, leading to enhanced cytotoxicity. In contrast to the antiproliferative effects of the clinically used proteasome inhibitor bortezomib, the effects of b-AP15 are not further enhanced by the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA). Our results suggest an inhibitory effect of b-AP15 on the transport of misfolded proteins, resulting in a lack of aggresome formation, and a strong proteotoxic stress response.

Toward the understanding of the role of CDC48, a major component of the protein quality control, in plant immunity

The evolutionally conserved chaperone-like protein CDC48 (cell division cycle 48) is a major component of ubiquitin-dependent protein degradation pathways in animal and yeast and, more generally, of the protein quality control machinery. In plants, CDC48 plays essential regulatory functions in development and the possibly that it contributes to protein degradation through the ubiquitin-proteasome system (UPS) and the endoplasmic reticulum-associated protein degradation (ERAD) system has been reported. In this review we described recent findings highlighting a role for CDC48 in plant immunity. First data indicated that CDC48 is S-nitrosylated in plant cells undergoing an immune response, regulates the turnover of immune receptors and mediates the degradation of viral proteins. Furthermore its overexpression was associated to an exacerbated hypersensitive-like cell death. We also designed and reported here the first CDC48 interactome. The corresponding data confirm the closed interaction of CDC48 with components of the UPS and shed light on its putative regulatory function of S-adenosyl-methionine synthesis and metabolism. More generally, these investigations further support the concept that plant cells facing pathogen attack finely regulate the protein quality control machinery.

Targeted substrate degradation by Kelch controls the actin cytoskeleton during ring canal expansion

During Drosophila oogenesis, specialized actin-based structures called ring canals form and expand to accommodate growth of the oocyte. Previous work demonstrated that Kelch and Cullin 3 function together in a Cullin 3-RING ubiquitin ligase complex (CRL3^Kelch) to organize the ring canal cytoskeleton, presumably by targeting a substrate for proteolysis. Here, we use tandem affinity purification followed by mass spectrometry to identify HtsRC as the CRL3^Kelch ring canal substrate. CRISPR-mediated mutagenesis of HtsRC revealed its requirement in the recruitment of the ring canal F-actin cytoskeleton. We present genetic evidence consistent with HtsRC being the CRL3^Kelch substrate, as well as biochemical evidence indicating that HtsRC is ubiquitylated and degraded by the proteasome. Finally, we identify a short sequence motif in HtsRC that is necessary for Kelch binding. These findings uncover an unusual mechanism during development wherein a specialized cytoskeletal structure is regulated and remodeled by the ubiquitin-proteasome system.

Possible Association of the Ubiquitin-Specific Peptidase 46 Gene (USP46) with Affective Temperamental Traits in Healthy Korean Volunteers

OBJECTIVE

Ubiquitin-specific peptidase 46 gene (USP46) polymorphisms is part of ubiquitin-proteasome system, which is responsible for dynamic cellular processes such as the regulation of cell cycle. USP46 has been reported to be associated with major depressive disorder. The objective of the present study was to investigate the association of USP46 polymorphisms with affective temperamental traits in healthy subjects.

METHODS

A total of 557 Korean healthy volunteers were recruited, and 545 subjects (328 male, 217 female) were included in the final analysis. The DNA of the subjects was isolated from saliva samples. Two single-nucleotide polymorphisms (SNPs) rs346005, rs2244291 in USP46 were genotyped. Affective temperaments were assessed using the Korean version of Temperament Evaluation of the Memphis, Pisa, Paris, and San Diego Autoquestionnaire (TEMPS-A).

RESULTS

A significant association was found between rs346005 genotypes and TEMPS-A only in male subjects. In particular, subjects with the CC genotype of rs346005 showed a more depressive temperament than subjects with AA or CA genotypes in males. For rs2244291, there were no associations between the rs2244291 genotypes and TEMPS-A scores.

CONCLUSION

Some affective temperaments may serve as a genetic predisposing factors for affective disorders, such as depressive disorder, via vulnerability genes related to the ubiquitin-proteasome system.

The physiological role of the free 20S proteasome in protein degradation: A critical review

BACKGROUND

It has been almost three decades since the removal of oxidized proteins by the free 20S catalytic unit of the proteasome (20SPT) was proposed. Since then, experimental evidence suggesting a physiological role of proteolysis mediated by the free 20SPT has being gathered.

SCOPE OF REVIEW

Experimental data that favors the hypothesis of free 20SPT as playing a role in proteolysis are critically reviewed.

MAJOR CONCLUSIONS

Protein degradation by the proteasome may proceed through multiple proteasome complexes with different requirements though the unequivocal role of the free 20SPT in cellular proteolysis towards native or oxidized proteins remains to be demonstrated.

GENERAL SIGNIFICANCE

The biological significance of proteolysis mediated by the free 20SPT has been elusive since its discovery. The present review critically analyzes the available experimental data supporting the proteolytic role of the free or single capped 20SPT.

Small-molecule PROTACs: An emerging and promising approach for the development of targeted therapy drugs

There are several challenges towards the development and clinical use of small molecule inhibitors, which are currently the main type of targeted therapies towards intracellular proteins. PROteolysis-TArgeting Chimeras (PROTACs) exploit the intracellular ubiquitin-proteasome system to selectively degrade target proteins. Recently, small-molecule PROTACs with high potency have been frequently reported. In this review, we summarize the emerging characteristics of small-molecule PROTACs, such as inducing a rapid, profound and sustained degradation, inducing a robust inhibition of downstream signals, displaying enhanced target selectivity, and overcoming resistance to small molecule inhibitors. In tumor xenografts, small-molecule PROTACs can significantly attenuate tumor progression. In addition, we also introduce recent developments of the PROTAC technology such as homo-PROTACs. The outstanding advantages over traditional small-molecule drugs and the promising preclinical data suggest that small-molecule PROTAC technology has the potential to greatly promote the development of targeted therapy drugs.

The N-recognin UBR4 of the N-end rule pathway is targeted to and required for the biogenesis of the early endosome

The N-end rule pathway is a proteolytic system in which single N-terminal residues of proteins act as N-degrons. These degrons are recognized by N-recognins, facilitating substrate degradation via the ubiquitin (Ub) proteasome system (UPS) or autophagy. We have previously identified a set of N-recognins [UBR1, UBR2, UBR4 (also known as p600) and UBR5 (also known as EDD)] that bind N-degrons through their UBR boxes to promote proteolysis by the proteasome. Here, we show that the 570 kDa N-recognin UBR4 is associated with maturing endosomes through an interaction with Ca²⁺-bound calmodulin. The endosomal recruitment of UBR4 is essential for the biogenesis of early endosomes (EEs) and endosome-related processes, such as the trafficking of endocytosed protein cargos and degradation of extracellular cargos by endosomal hydrolases. In mouse embryos, UBR4 marks and plays a role in the endosome-lysosome pathway that mediates the heterophagic proteolysis of endocytosed maternal proteins into amino acids. By screening 9591 drugs through the DrugBank database, we identify picolinic acid as a putative ligand for UBR4 that inhibits the biogenesis of EEs. Our results suggest that UBR4 is an essential modulator in the endosome-lysosome system.This article has an associated First Person interview with the first author of the paper.

Mechanistic targeting of advanced glycation end-products in age-related diseases

Glycative stress, caused by the accumulation of cytotoxic and irreversibly-formed sugar-derived advanced glycation end-products (AGEs), contributes to morbidity associated with aging, age-related diseases, and metabolic diseases. In this review, we summarize pathways leading to formation of AGEs, largely from sugars and glycolytic intermediates, and discuss detoxification of AGE precursors, including the glyoxalase system and DJ-1/Park7 deglycase. Disease pathogenesis downstream of AGE accumulation can be cell autonomous due to aggregation of glycated proteins and impaired protein function, which occurs in ocular cataracts. Extracellular AGEs also activate RAGE signaling, leading to oxidative stress, inflammation, and leukostasis in diabetic complications such as diabetic retinopathy. Pharmaceutical agents have been tested in animal models and clinically to diminish glycative burden. We summarize existing strategies and point out several new directions to diminish glycative stress including: plant-derived polyphenols as AGE inhibitors and glyoxalase inducers; improved dietary patterns, particularly Mediterranean and low glycemic diets; and enhancing proteolytic capacities of the ubiquitin-proteasome and autophagy pathways that are involved in cellular clearing of AGEs.

Paradoxical effects of mutant ubiquitin on Aβ plaque formation in an Alzheimer mouse model

Amyloid-β (Aβ) plaques are a prominent pathological hallmark of Alzheimer's disease (AD). They consist of aggregated Aβ peptides, which are generated through sequential proteolytic processing of the transmembrane protein amyloid precursor protein (APP) and several Aβ-associated factors. Efficient clearance of Aβ from the brain is thought to be important to prevent the development and progression of AD. The ubiquitin-proteasome system (UPS) is one of the major pathways for protein breakdown in cells and it has been suggested that impaired UPS-mediated removal of protein aggregates could play an important role in the pathogenesis of AD. To study the effects of an impaired UPS on Aβ pathology in vivo, transgenic APP_Swe/PS1ΔE9 mice (APPPS1) were crossed with transgenic mice expressing mutant ubiquitin (UBB⁺¹), a protein-based inhibitor of the UPS. Surprisingly, the APPPS1/UBB⁺¹ crossbreed showed a remarkable decrease in Aβ plaque load during aging. Further analysis showed that UBB⁺¹ expression transiently restored PS1-NTF expression and γ-secretase activity in APPPS1 mice. Concurrently, UBB⁺¹ decreased levels of β-APP-CTF, which is a γ-secretase substrate. Although UBB⁺¹ reduced Aβ pathology in APPPS1 mice, it did not improve the behavioral deficits in these animals.

Protein kinase C δ-dependent regulation of Ubiquitin-proteasome system function in breast cancer

Besides the crucial role of hyperinsulinemia in the development of breast cancer with Type 2 diabetes mellitus (T2DM), it has been shown that hyperglycemia could contribute to promote cancer progression. A remarkable association within hyperglycemia, PKCδ and Ubiquitin-proteasome system (UPS) has been reported, suggesting that PKCδ may mediate high glucose-induced UPS activation in breast cancer cells. Although the independent effects of PKCδ or UPS on breast cancer and T2DM are increasingly supported by experimental evidence, the complex interactional link between PKCδ and UPS is still unclear. Hence, we focus on the relationship between PKCδ and UPS in breast cancer with T2DM. We hypothesize that PKCδ may have the function to regulate the activity of UPS. Further, we speculate that PKCδ combine with proteasome α2 promoter, that indicate PKCδ regulate the function of UPS by change the composition of proteasome. Therefore, we surmise that PKCδ mediated high glucose-induced UPS activation in breast cancer cells, and specific PKCδ inhibitor rottlerin significantly suppressed elevated glucose induced the activity of UPS. We hope that our paper will stimulate further studies the relationship between PKCδ and UPS, and a new targeted therapy and early medical intervention for PKCδ could be a useful option for breast cancer cases complicated with T2DM or hyperglycemia.

Untying the knot: protein quality control in inherited cardiomyopathies

Mutations in genes encoding sarcomeric proteins are the most important causes of inherited cardiomyopathies, which are a major cause of mortality and morbidity worldwide. Although genetic screening procedures for early disease detection have been improved significantly, treatment to prevent or delay mutation-induced cardiac disease onset is lacking. Recent findings indicate that loss of protein quality control (PQC) is a central factor in the disease pathology leading to derailment of cellular protein homeostasis. Loss of PQC includes impairment of heat shock proteins, the ubiquitin-proteasome system, and autophagy. This may result in accumulation of misfolded and aggregation-prone mutant proteins, loss of sarcomeric and cytoskeletal proteins, and, ultimately, loss of cardiac function. PQC derailment can be a direct effect of the mutation-induced activation, a compensatory mechanism due to mutation-induced cellular dysfunction or a consequence of the simultaneous occurrence of the mutation and a secondary hit. In this review, we discuss recent mechanistic findings on the role of proteostasis derailment in inherited cardiomyopathies, with special focus on sarcomeric gene mutations and possible therapeutic applications.

Promising new therapeutic targets for regulation of inflammation and immunity: RING-type E3 ubiquitin ligases

Ubiquitin-proteasome system (UPS) is a primary signaling pathway for regulation of protein turnover and removal of misfolded proteins in eukaryotic cells. Enzymes of the UPS pathway - E1 activating, E2 conjugating, E3 ligating - act together to covalently tag substrate proteins with a chain of ubiquitins, small regulatory proteins. The poly-ubiquitin chain then serves as a recognition motif for 26S proteasome to recognize and degrade the substrate. In recent years UPS has emerged as attractive enzymatic cascade for development of novel therapeutics against various human diseases. Building on the previous success of targeting this pathway in cancer - the broader scientific community is currently looking for ways to elucidate functions of E3 ligases, substrate-specific members of the UPS. RING-type E3 ubiquitin ligases, the largest class of E3s, represent prospective targets for small molecule modulation and their importance is reinforced by ever growing evidence of playing role in non-cancer diseases, primarily associated with inflammatory and immune disorders. In this review, we aim to briefly cover the current knowledge of biological functions of RING-type E3 ligases in inflammation and immunity.

ZMPSTE24 missense mutations that cause progeroid diseases decrease prelamin A cleavage activity and/or protein stability

The human zinc metalloprotease ZMPSTE24 is an integral membrane protein crucial for the final step in the biogenesis of the nuclear scaffold protein lamin A, encoded by LMNA. After farnesylation and carboxyl methylation of its C-terminal CAAX motif, the lamin A precursor (prelamin A) undergoes proteolytic removal of its modified C-terminal 15 amino acids by ZMPSTE24. Mutations in LMNA or ZMPSTE24 that impede this prelamin A cleavage step cause the premature aging disease Hutchinson-Gilford progeria syndrome (HGPS), and the related progeroid disorders mandibuloacral dysplasia type B (MAD-B) and restrictive dermopathy (RD). Here, we report the development of a ‘humanized yeast system’ to assay ZMPSTE24-dependent cleavage of prelamin A and examine the eight known disease-associated ZMPSTE24 missense mutations. All mutations show diminished prelamin A processing and fall into three classes, with defects in activity, protein stability or both. Notably, some ZMPSTE24 mutants can be rescued by deleting the E3 ubiquitin ligase Doa10, involved in endoplasmic reticulum (ER)-associated degradation of misfolded membrane proteins, or by treatment with the proteasome inhibitor bortezomib. This finding may have important therapeutic implications for some patients. We also show that ZMPSTE24-mediated prelamin A cleavage can be uncoupled from the recently discovered role of ZMPSTE24 in clearance of ER membrane translocon-clogged substrates. Together with the crystal structure of ZMPSTE24, this humanized yeast system can guide structure-function studies to uncover mechanisms of prelamin A cleavage, translocon unclogging, and membrane protein folding and stability.

Summary: The zinc metalloprotease ZMPSTE24 performs the final step of prelamin A processing. Here, a yeast-based system shows differences in protein stability and activity for alleles of ZMPSTE24 that cause progeria disease.

PSMD2 regulates breast cancer cell proliferation and cell cycle progression by modulating p21 and p27 proteasomal degradation

Alterations in the ubiquitin-proteasome system (UPS) and UPS-associated proteins have been implicated in the development of many human malignancies. In this study, we investigated the expression profiles of 797 UPS-related genes using HiSeq data from The Cancer Genome Atlas and identified that PSMD2 was markedly upregulated in breast cancer. High PSMD2 expression was significantly correlated with poor prognosis. Gene set enrichment analysis revealed that transcriptome signatures involving proliferation, cell cycle, and apoptosis were critically enriched in specimens with elevated PSMD2. Consistently, PSMD2 knockdown inhibited cell proliferation and arrested cell cycle at G0/G1 phase in vitro, as well as suppressed tumor growth in vivo. Rescue assays demonstrated that the cell cycle arrest caused by silencing PSMD2 partially resulted from increased p21 and/or p27. Mechanically, PSMD2 physically interacted with p21 and p27 and mediated their ubiquitin-proteasome degradation with the cooperation of USP14. Notably, intratumor injection of therapeutic PSMD2 small interfering RNA effectively delayed xenograft tumor growth accompanied by p21 and p27 upregulation. These data provide novel insight into the role of PSMD2 in breast cancer and suggest that PSMD2 may be a potential therapeutic target.

The proteasome and proteasome inhibitors in multiple myeloma

Proteasome inhibitors are one of the most important classes of agents to have emerged for the treatment of multiple myeloma in the past two decades, and now form one of the backbones of treatment. Three agents in this class have been approved by the United States Food and Drug Administration-the first-in-class compound bortezomib, the second-generation agent carfilzomib, and the first oral proteasome inhibitor, ixazomib. The success of this class of agents is due to the exquisite sensitivity of myeloma cells to the inhibition of the 26S proteasome, which plays a critical role in the pathogenesis and proliferation of the disease. Proteasome inhibition results in multiple downstream effects, including the inhibition of NF-κB signaling, the accumulation of misfolded and unfolded proteins, resulting in endoplasmic reticulum stress and leading to the unfolded protein response, the downregulation of growth factor receptors, suppression of adhesion molecule expression, and inhibition of angiogenesis; resistance to proteasome inhibition may arise through cellular responses mediating these downstream effects. These multiple biologic consequences of proteasome inhibition result in synergistic or additive activity with other chemotherapeutic and targeted agents for myeloma, and proteasome inhibitor-based combination regimens have become established as a cornerstone of therapy throughout the myeloma treatment algorithm, incorporating agents from the other key classes of antimyeloma agents, including the immunomodulatory drugs, monoclonal antibodies, and histone deacetylase inhibitors. This review gives an overview of the critical role of the proteasome in myeloma and the characteristics of the different proteasome inhibitors and provides a comprehensive summary of key clinical efficacy and safety data with the currently approved proteasome inhibitors.

An herbal formula consisting of Schisandra chinensis (Turcz.) Baill, Lycium chinense Mill and Eucommia ulmoides Oliv alleviates disuse muscle atrophy in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Schisandra chinensis (Turcz.) Baill (SC), Lycium chinense Mill (LC) and Eucommia ulmoides Oliv (EU) are representative tonic herbal medicines that help to strengthen body muscles and bones making them stronger according to the Donguibogam, a tradition medical book of the Joseon Dynasty in Korea.

AIM OF THE STUDY

To evaluate effects of an herbal formula consisting of SC, LC and EU on muscle atrophy in C2C12 myotubes and in a rat model of immobilization-induced muscle atrophy.

MATERIALS AND METHODS

Muscle atrophy was developed by cast immobilization of unilateral hindlimb on rats for 3 weeks. Treatments were administered orally 14 times over 3 weeks. After treatments, we compared the change of body weight, muscle weight, grip strength, muscle fiber size, muscle fiber type shift by Grip strength meter, H&E stain and ATPase stain. And western blot was used for evaluating molecular mechanism in muscle atrophy on C2C12 cells.

RESULTS

When taken individually, SC was the most effective of the three in inhibiting tumor necrosis factor alpha (TNF-α)-induced degeneration of C2C12 myogenesis. The formulation with a mass ratio of 2:1:1 SC: LC: EU (SSLE) was more effective against TNF-α-induced muscle atrophy than was a 1:1:1 SC: LC: EU (SLE) formula or any of the single herbal extracts. In a rat model of disuse muscle atrophy, the SSLE formula significantly inhibited reductions in muscle weight, grip strength and muscle fiber size induced by hindlimb immobilization, in a dose-dependent manner. The formula also inhibited immobilization-induced shifting of the muscle fiber type in soleus muscle. Treatment with SSLE inhibited TNF-α-induced expression of the atrogenes atrogin-1 and muscle RING-finger protein 1 in C2C12 cells. The SSLE formula also increased myoblast differentiation markers (myoD and myogenin) and activation of the Akt and mammalian target of rapamycin (mTOR) signaling pathway.

CONCLUSION

These findings suggest that the SSLE formula prevents muscle atrophy through inhibition of the ubiquitin-proteasome system as well as upregulation of myoblast differentiation and muscle protein synthesis in C2C12 cells. Taken together, we conclude that the SSLE formula is invaluable for the development of therapeutic medicines to prevent disuse muscle atrophy and its accompanying muscle weakness.