Hijacking autophagy for infection by flaviviruses.

Autophagy is a lysosomal degradative pathway, which regulates the homeostasis of eukaryotic cells. This pathway can degrade misfolded or aggregated proteins, clear damaged organelles, and eliminate intracellular pathogens, including viruses, bacteria, and parasites. But, not all types of viruses are eliminated by autophagy. Flaviviruses (e.g., Yellow fever, Japanese encephalitis, Hepatitis C, Dengue, Zika, and West Nile viruses) are single-stranded and enveloped RNA viruses, and transmitted to humans primarily through the bites of arthropods, leading to severe and widespread illnesses. Like the coronavirus SARS-CoV-II, flaviviruses hijack autophagy for their infection and escape from host immune clearance. Thus, it is possible to control these viral infections by inhibiting autophagy. In this review, we summarize recent research progresses on hijacking of autophagy by flaviviruses and discuss the feasibility of antiviral therapies using autophagy inhibitors.

PA200-Mediated Proteasomal Protein Degradation and Regulation of Cellular Senescence.

Cellular senescence is closely related to DNA damage, proteasome inactivity, histone loss, epigenetic alterations, and tumorigenesis. The mammalian proteasome activator PA200 (also referred to as PSME4) or its yeast ortholog Blm10 promotes the acetylation-dependent degradation of the core histones during transcription, DNA repair, and spermatogenesis. According to recent studies, PA200 plays an important role in senescence, probably because of its role in promoting the degradation of the core histones. Loss of PA200 or Blm10 is a major cause of the decrease in proteasome activity during senescence. In this paper, recent research progress on the association of PA200 with cellular senescence is summarized, and the potential of PA200 to serve as a therapeutic target in age-related diseases is discussed.

Biochemical targets of the micropeptides encoded by lncRNAs.

Long non-coding RNAs (lncRNAs) are a group of transcripts longer than 200 nucleotides, which play important roles in regulating various cellular activities by the action of the RNA itself. However, about 40% of lncRNAs in human cells are potentially translated into micropeptides (also referred to as microproteins) usually shorter than 100 amino acids. Thus, these lncRNAs may function by both RNAs directly and their encoded micropeptides. The micropeptides encoded by lncRNAs may regulate transcription, translation, protein phosphorylation or degradation, or subcellular membrane functions. This review attempts to summarize the biochemical targets of the micropeptides-encoded by lncRNAs, which function by both RNAs and micropeptides, and discuss their associations with various diseases and their potentials as drug targets.

Molecular mechanisms underlying the BIRC6-mediated regulation of apoptosis and autophagy.

Procaspase 9 is the initiator caspase for apoptosis, but how its levels and activities are maintained remains unclear. The gigantic Inhibitor-of-Apoptosis Protein BIRC6/BRUCE/Apollon inhibits both apoptosis and autophagy by promoting ubiquitylation of proapoptotic factors and the key autophagic protein LC3, respectively. Here we show that BIRC6 forms an anti-parallel U-shaped dimer with multiple previously unannotated domains, including a ubiquitin-like domain, and the proapoptotic factor Smac/DIABLO binds BIRC6 in the central cavity. Notably, Smac outcompetes the effector caspase 3 and the pro-apoptotic protease HtrA2, but not procaspase 9, for binding BIRC6 in cells. BIRC6 also binds LC3 through its LC3-interacting region, probably following dimer disruption of this BIRC6 region. Mutation at LC3 ubiquitylation site promotes autophagy and autophagic degradation of BIRC6. Moreover, induction of autophagy promotes autophagic degradation of BIRC6 and caspase 9, but not of other effector caspases. These results are important to understand how the balance between apoptosis and autophagy is regulated under pathophysiological conditions.

Ubiquitin Ligase Nrdp1 Controls Autophagy-Associated Acrosome Biogenesis and Mitochondrial Arrangement during Spermiogenesis.

Autophagy is critical to acrosome biogenesis and mitochondrial quality control, but the underlying mechanisms remain unclear. The ubiquitin ligase Nrdp1/RNF41 promotes ubiquitination of the mitophagy-associated Parkin and interacts with the pro-autophagic protein SIP/CacyBP. Here, we report that global deletion of Nrdp1 leads to formation of the round-headed sperm and male infertility by disrupting autophagy. Quantitative proteome analyses demonstrated that the expression of many proteins associated with mitochondria, lysosomes, and acrosomes was dysregulated in either spermatids or sperm of the Nrdp1-deficient mice. Deletion of Nrdp1 increased the levels of Parkin but decreased the levels of SIP, the mitochondrial fission protein Drp1 and the mitochondrial protein Tim23 in sperm, accompanied by the inhibition of autophagy, the impairment of acrosome biogenesis and the disruption of mitochondrial arrangement in sperm. Thus, our results uncover an essential role of Nrdp1 in spermiogenesis and male fertility by promoting autophagy, providing important clues to cope with the related male reproductive diseases.

A descriptive study on clinical department managers' cognition of the Plan-Do-Check-Act cycle and factors influencing their cognition.

BACKGROUND: The mastery and application of the "Plan-Do-Check-Act" (PDCA) cycle by hospital clinical department managers are essential for hospitals to carry out total quality management and continuously improve medical quality. This study investigated the degree of cognition of the PDCA cycle by clinical department managers and the factors affecting their cognition. METHODS: A self-designed questionnaire was used to evaluate the cognition of clinical department managers regarding the PDCA cycle in 11 municipal public Class III Grade A hospitals in Western China. RESULTS: More than 25% of clinical department managers in the surveyed hospitals are unaware or partially aware of the PDCA cycle. Logistic regression analysis showed that sex (P = 0.049), education (P < 0.001), duty (P < 0.001), and tenure (P = 0.002) had a significant influence on managers' cognition of PDCA. Participants who were female (P < 0.001), undergraduate (P < 0.001), head nurses, or deputy head nurses (P < 0.001), with a tenure of 5-10 years (P = 0.024) had a better cognition of the PDCA cycle. In the daily management of the department, the vast majority of managers do not implement the Check and Action steps. Among the trained managers, only 65.44% applied the complete PDCA cycle in daily management. Nearly a third of managers thought PDCA was a response to hospital demands; 82.83% of the managers need to receive PDCA cycle training, and half of them indicated a preference for online training. CONCLUSIONS: The cognition level of hospital clinical department managers regarding the PDCA cycle is relatively low, especially among the clinical department heads, and most of them are willing to accept PDCA cycle training.

lncRNA LINC00960 promotes apoptosis by sponging ubiquitin ligase Nrdp1-targeting miR-183-5p.

The ubiquitin ligase Nrdp1/RNF41 promotes the ubiquitin-dependent degradation of multiple important substrates, including BRUCE/BIRC6, a giant ubiquitin-conjugating enzyme inhibiting both apoptosis and autophagy. miR-183-5p is associated with various malignancies potentially by targeting dozens of genes. Here, we show that the lncRNA LINC00960 binds to the Nrdp1-targeting miR-183-5p and promotes apoptosis. Compared to other known miR-183-5p targets, Nrdp1 mRNA is among the few with top scores to complement miR-183-5p. miR-183-5p binds to the 3'UTR of Nrdp1 mRNA and downregulates Nrdp1 at both the mRNA and protein levels. The miR-183-5p mimics inhibit DNA damage-induced apoptosis probably by upregulating BRUCE level, whereas the miR-183-5p inhibitor suppresses the effects of miR-183-5p. LINC00960 is the noncoding RNA with the highest score to complement miR-183-5p. LINC00960 overexpression reduces, but its knockdown increases, the level of miR-183-5p, whereas LINC00960 overexpression increases, but its knockdown decreases, the level of Nrdp1 and apoptosis. Importantly, the expression of LINC00960, which is associated with multiple types of tumors, positively correlates with that of Nrdp1 in several tumors but inversely correlates with that of miR-183-5p in multiple human tumor cell lines, as analysed by quantitative PCR. Thus, miR-183-5p downregulates Nrdp1 expression and inhibits apoptosis, whereas LINC00960 upregulates Nrdp1 and promotes apoptosis by inhibiting miR-183-5p. These results may provide new ideas for the prevention, diagnosis and treatment of apoptosis-related diseases, such as tumors and neurodegenerative diseases.

A bacterial phospholipid phosphatase inhibits host pyroptosis by hijacking ubiquitin.

The inflammasome-mediated cleavage of gasdermin D (GSDMD) causes pyroptosis and inflammatory cytokine release to control pathogen infection, but how pathogens evade this immune response remains largely unexplored. Here we identify the known protein phosphatase PtpB from Mycobacterium tuberculosis as a phospholipid phosphatase inhibiting the host inflammasome-pyroptosis pathway. Mechanistically, PtpB dephosphorylated phosphatidylinositol-4-monophosphate and phosphatidylinositol-(4,5)-bisphosphate in host cell membrane, thus disrupting the membrane localization of the cleaved GSDMD to inhibit cytokine release and pyroptosis of macrophages. Notably, this phosphatase activity requires PtpB binding to ubiquitin. Disrupting phospholipid phosphatase activity or the ubiquitin-interacting motif of PtpB enhanced host GSDMD-dependent immune responses and reduced intracellular pathogen survival. Thus, pathogens inhibit pyroptosis and counteract host immunity by altering host membrane composition.

Mycobacterium tuberculosis protein kinase G acts as an unusual ubiquitinating enzyme to impair host immunity.

Upon Mycobacterium tuberculosis (Mtb) infection, protein kinase G (PknG), a eukaryotic-type serine-threonine protein kinase (STPK), is secreted into host macrophages to promote intracellular survival of the pathogen. However, the mechanisms underlying this PknG-host interaction remain unclear. Here, we demonstrate that PknG serves both as a ubiquitin-activating enzyme (E1) and a ubiquitin ligase (E3) to trigger the ubiquitination and degradation of tumor necrosis factor receptor-associated factor 2 (TRAF2) and TGF-ß-activated kinase 1 (TAK1), thereby inhibiting the activation of NF-κB signaling and host innate responses. PknG promotes the attachment of ubiquitin (Ub) to the ubiquitin-conjugating enzyme (E2) UbcH7 via an isopeptide bond (UbcH7 K82-Ub), rather than the usual C86-Ub thiol-ester bond. PknG induces the discharge of Ub from UbcH7 by acting as an isopeptidase, before attaching Ub to its substrates. These results demonstrate that PknG acts as an unusual ubiquitinating enzyme to remove key components of the innate immunity system, thus providing a potential target for tuberculosis treatment.

Proteasome activator PA200 maintains stability of histone marks during transcription and aging.

The epigenetic inheritance relies on stability of histone marks, but various diseases, including aging-related disorders, are usually associated with alterations of histone marks. Whether and how the proteasome is responsible for maintaining the histone marks during transcription and aging remain unclear. The core histones can be degraded by the atypical proteasome, which contains the proteasome activator PA200, in an acetylation-dependent manner during somatic DNA damage response and spermiogenesis. Methods: By utilizing a substitute of methionine to label proteins metabolically, we analyzed histone degradation genome-wide by sequencing the DNA fragments following pulse-chase assays. The genome-wide RNA-sequencing analysis was performed to analyze transcription and chromatin-immunoprecipitation (ChIP)-sequencing was used for analyses of histone marks. The experimental models included gene-manipulated cells (including both mouse and yeast), mouse liver, and mice. Results: Degradation of H4 or the transcription-coupled histone variant H3.3 could be suppressed by deletion of PA200 or its yeast ortholog Blm10. The histone deacetylase inhibitor accelerated the degradation rates of H3, while the mutations of the putative acetyl-lysine-binding region of PA200 abolished histone degradation in the G1-arrested cells. Deletion of PA200 dramatically altered deposition of the active transcriptional hallmarks (H3K4me3 and H3K56ac) and transcription, especially during cellular aging. Furthermore, deletion of PA200 or Blm10 accelerated cellular aging. Notably, the PA200-deficient mice displayed a range of aging-related deteriorations, including immune malfunction, anxiety-like behavior and shorter lifespan. Conclusion: PA200 promotes the transcription-coupled degradation of the core histones, and plays an important role in maintaining the stability of histone marks during transcription and aging.

Metformin alleviates ß-glycerophosphate-induced calcification of vascular smooth muscle cells via AMPK/mTOR-activated autophagy.

The aim of the present study was to investigate the effect of metformin on ß-glycerophosphate-induced calcification of vascular smooth muscle cells (VSMCs) and the possible mechanisms underlying this. Using an established VSMC calcification model, VSMCs were first treated with ß-glycerophosphate, before metformin, 3-methyladenine and compound C were added to the cell cultures in different combinations. Calcium deposition in the cells was examined by Alizarin Red S staining and using the O-cresolphthalein complexone method. To assess the occurrence of autophagy, autophagosomes inside the cells were studied using a transmission electron microscope and green fluorescent microtubule-associated protein 1 light chain 3 (LC3) puncta were examined using a fluorescent microscope. Additionally, protein expression levels of α-smooth muscle actin (α-SMA), runt-related transcription factor 2 (RUNX2), LC3II/I, beclin 1 and 5' adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway-associated proteins were determined by western blot analysis. Metformin increased the number of autophagosomes, green fluorescent LC3 puncta and the levels of LC3II/I, beclin 1, α-SMA and phosphorylated (p)-AMPK in the VSMCs that were treated with ß-glycerophosphate when compared to controls; whereas, calcium deposition and the expression levels of RUNX2 and p-mTOR were found to be decreased. Treating the VSMCs with 3-methyladenine or compound C reversed the effects of metformin. The results of the present study suggested that metformin may alleviate ß-glycerophosphate-induced calcification of VSMCs, which may be attributed to the activation of AMPK/mTOR signaling pathway-dependent autophagy.

Predictors, causes and outcome of 30-day readmission among acute ischemic stroke.

BACKGROUND AND PURPOSE: Readmission within 30 days of index acute ischemic stroke (AIS) after hospitalization increases the burden on patients and healthcare expense. The purpose of our study was to investigate predictors and causes of 30-day readmission after AIS and investigate hospitalization expenses, length of stay (LOS) and in-hospital mortality of 30-day readmission. METHODS: This is a multicenter retrospective study. AIS were captured by International Classification of Diseases, Tenth Revision (ICD-10) diagnosis codes, patients with readmitted within 30 days after discharge were identified as readmission group. Multivariable logistic regression was used to identify independent predictors of 30-day readmissions. Hospitalization expenses, LOS and in-hospital mortality were compared for index admission and readmission. RESULTS: We identified 2371 patients with AIS, 176 patients died before discharge, 504(23.0%) patients were admitted within 30 days. Older age, prior stroke, non-neurology floor during index admission, indwelling urinary catheter and diabetes were independently associated with increased risk of 30-day readmission (P<0.05). The most common causes for 30-day readmission were infection (28.8%) and recurrent stroke and TIA (22.8%). Patients with 30-day readmission have longer LOS and higher hospitalization expenses on readmission compared with the mean of these metrics on index admission (P<0.001). The in-hospital mortality after a within 30-day readmission was higher than index admission (13.1% vs 8.0%; OR 1.88, 95% CI 2.5-5.3; P<0.001). CONCLUSIONS: Older age, stroke severity, prior stroke, diabetes, indwelling urinary catheter and admission to non-neurology floor during index admission were associated with 30-day readmission. 30-readmission after AIS increased hospitalization expenses, LOS and in-hospital mortality.

Proteasome Activator Blm10 Regulates Transcription Especially During Aging.

Background: Histones are basic elements of the chromatin and are critical to controlling chromatin structure and transcription. The proteasome activator PA200 promotes the acetylation-dependent proteasomal degradation of the core histones during spermatogenesis, DNA repair, transcription, and cellular aging and maintains the stability of histone marks. Objective: The study aimed to explore whether the yeast ortholog of PA200, Blm10, promotes degradation of the core histones during transcription and regulates transcription especially during aging. Methods: Protein degradation assays were performed to detect the role of Blm10 in histone degradation during transcription. mRNA profiles were compared in WT and mutant BY4741 or MDY510 yeast cells by RNA-sequencing. Results: The core histones can be degraded by the Blm10-proteasome in the non-replicating yeast, suggesting that Blm10 promotes the transcription-coupled degradation of the core histones. Blm10 preferentially regulates transcription in aged yeast, especially transcription of genes related to translation, amino acid metabolism, and carbohydrate metabolism. Mutations of Blm10 at F2125/N2126 in its putative acetyl-lysine binding region abolished the Blm10-mediated regulation of gene expression. Conclusion: Blm10 promotes degradation of the core histones during transcription and regulates transcription, especially during cellular aging, further supporting the critical role of PA200 in maintaining the stability of histone marks from the evolutionary view. These results should provide meaningful insights into the mechanisms underlying aging and the related diseases.

Proteasome subunit α4s is essential for formation of spermatoproteasomes and histone degradation during meiotic DNA repair in spermatocytes.

Meiosis, which produces haploid progeny, is critical to ensuring both faithful genome transmission and genetic diversity. Proteasomes play critical roles at various stages of spermatogenesis, including meiosis, but the underlying mechanisms remain unclear. The atypical proteasomes, which contain the activator PA200, catalyze the acetylation-dependent degradation of the core histones in elongated spermatids and DNA repair in somatic cells. We show here that the testis-specific proteasome subunit α4s/PSMA8 is essential for male fertility by promoting proper formation of spermatoproteasomes, which harbor both PA200 and constitutive catalytic subunits. Immunostaining of a spermatocyte marker, SYCP3, indicated that meiosis was halted at the stage of spermatocytes in the α4s-deficient testes. α4s stimulated the in vitro degradation of the acetylated core histones, instead of nonacetylated histones, by the PA200-proteasome. Deletion of α4s blocked degradation of the core histones at DNA damage loci in spermatocytes, leading to meiotic arrest at metaphase I. Thus, α4s is required for histone degradation at meiotic DNA damage loci, proper progression of meiosis, and fertility in males by promoting proper formation of spermatoproteasomes. These results are important for understanding male infertility and might provide potential targets for male contraception or treatment of male infertility.

OGT-Mediated KEAP1 Glycosylation Accelerates NRF2 Degradation Leading to High Phosphate-Induced Vascular Calcification in Chronic Kidney Disease.

Unraveling the complex regulatory pathways that mediate the effects of phosphate on vascular smooth muscle cells (VSMCs) may provide novel targets and therapies to limit the destructive effects of vascular calcification (VC) in patients with chronic kidney disease (CKD). Our previous studies have highlighted several signaling networks associated with VSMC autophagy, but the underlying mechanisms remain poorly understood. Thereafter, the current study was performed to characterize the functional relevance of O-linked N-acetylglucosamine (GlcNAc) transferase (OGT) in high phosphate-induced VC in CKD settings. We generated VC models in 5/6 nephrectomized rats in vivo and VSMC calcification models in vitro. Artificial modulation of OGT (knockdown and overexpression) was performed to explore the role of OGT in VSMC autophagy and VC in thoracic aorta, and in vivo experiments were used to substantiate in vitro findings. Mechanistically, co-immunoprecipitation (Co-IP) assay was performed to examine interaction between OGT and kelch like ECH associated protein 1 (KEAP1), and in vivo ubiquitination assay was performed to examine ubiquitination extent of nuclear factor erythroid 2-related factor 2 (NRF2). OGT was highly expressed in high phosphate-induced 5/6 nephrectomized rats and VSMCs. OGT silencing was shown to suppress high phosphate-induced calcification of VSMCs. OGT enhances KEAP1 glycosylation and thereby results in degradation and ubiquitination of NRF2, concurrently inhibiting VSMC autophagy to promote VSMC calcification in 5/6 nephrectomized rats. OGT inhibits VSMC autophagy through the KEAP1/NRF2 axis and thus accelerates high phosphate-induced VC in CKD.

Transcriptional upregulation of proteasome activator Blm10 antagonizes cellular aging.

Cellular aging is associated with the damage to DNA, decline in proteasome activity, loss of histones and alteration of epigenetic marks. The atypical proteasome with the activator PA200 in mammals or its ortholog Blm10 in yeast promotes the acetylation-dependent degradation of the core histones during DNA repair or spermiogenesis. We show here that loss of PA200 or Blm10 is the leading cause of the decline in proteasome activity during aging, the latter of which conversely induces the transcription of Blm10. The transcription factor Crt1 suppressed, but the proteasome subunit Rpn4 promoted, the transcription of Blm10. On the contrary to deletion of Rpn4, deletion of Crt1 elevated Blm10 transcription upon DNA damage, reduced core histone levels during aging, and prolonged replicative lifespan. These results suggest that cells can antagonize aging by up-regulating transcription of Blm10, providing important insights into the mechanisms of aging and the aging-related diseases.

OGT knockdown counteracts high phosphate-induced vascular calcification in chronic kidney disease through autophagy activation by downregulating YAP.

AIMS: Pathological vascular calcification (VC), a major risk factor for cardiovascular mortality, is a highly prevalent finding in patients with chronic kidney disease (CKD). We previously analyzed several pathways protecting against high phosphate-induced VC through induction of autophagy. Here, we explored how O-GlcNAc transferase (OGT) affected high phosphate-induced VC of CKD though mediation of autophagy. MAIN METHODS: In the rats with CKD induced by 5/6 nephrectomy, the VC process was accelerated by a high phosphate diet. The calcification of vascular smooth muscle cells (VSMCs) was induced by high phosphate treatment. We then experimentally tested the effect of OGT on high phosphate-induced VC by conducting loss-of-function experiments. Co-immunoprecipitation and GST pull-down assays were performed to evaluate interaction between OGT and Yes-associated protein (YAP). In mechanistic studies of this pathway, we measured autophagy protein expression and autophagosome formation, as well as calcium deposition and calcium content in VSMCs and in vivo in response to altered expression of OGT and/or YAP. KEY FINDINGS: OGT was up-regulated in high phosphate-induced VC models in vitro and in vivo. High phosphate-induced calcification in the rat aorta and VSMCs were suppressed by OGT silencing. OGT promoted the glycosylation of YAP to enhance its stability. Importantly, over-expressing YAP reduced autophagy and OGT expedited high phosphate-induced VC by inhibiting autophagy through upregulation of YAP. SIGNIFICANCE: OGT silencing downregulated YAP to induce autophagy activation, thus suppressing high phosphate-induced VC, which highlighted a promising preventive target against high phosphate-induced VC in CKD.

Effectiveness of Bailing capsules in the treatment of lupus nephritis: A meta­analysis.

Previous studies have explored the treatment of lupus nephritis with Bailing capsules; however, due to limited sample sizes and inconsistent results across these studies, no definitive conclusions have been drawn. Thus, the present study aimed to provide evidence for the effectiveness of Bailing capsules in the treatment of lupus nephritis. To obtain relevant clinical studies (published before 20 July 2019), PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure, WanFang and the Chinese Biomedical Literature Database were searched, and relevant studies concerning the use of Bailing capsules for treating lupus nephritis were selected. The extracted data were general characteristics such as the first author, publication year, study year, follow­up time, age, sex, course of the disease and a number of outcome indicators. These included systemic lupus erythematosus disease activity index (SLEDAI) score, serum albumin (Alb), 24­h urinary protein, serum creatinine, anti­ds­DNAIgM, complement component 3 (C3), and the number of effective treatments and complications. Meta­analysis was performed using R­3.12 software. Publication bias was assessed using Egger's test. A total of 14 studies comprising 1,301 participants were combined for analysis in the present study. The results demonstrated that with the exception of anti­ds­DNAIgM and complement C3, other indicators, such as SLEDAI score, Alb, 24­h urinary protein, serum creatinine, and the number of effective treatments and complications) in the Bailing capsule treatment group were improved compared with those in the control group. The results of the present meta­analysis suggested that Bailing capsules may be effective in the treatment of lupus nephritis.

SIP/CacyBP promotes autophagy by regulating levels of BRUCE/Apollon, which stimulates LC3-I degradation.

BRUCE/Apollon is a membrane-associated inhibitor of apoptosis protein that is essential for viability and has ubiquitin-conjugating activity. On initiation of apoptosis, the ubiquitin ligase Nrdp1/RNF41 promotes proteasomal degradation of BRUCE. Here we demonstrate that BRUCE together with the proteasome activator PA28γ causes proteasomal degradation of LC3-I and thus inhibits autophagy. LC3-I on the phagophore membrane is conjugated to phosphatidylethanolamine to form LC3-II, which is required for the formation of autophagosomes and selective recruitment of substrates. SIP/CacyBP is a ubiquitination-related protein that is highly expressed in neurons and various tumors. Under normal conditions, SIP inhibits the ubiquitination and degradation of BRUCE, probably by blocking the binding of Nrdp1 to BRUCE. On DNA damage by topoisomerase inhibitors, Nrdp1 causes monoubiquitination of SIP and thus promotes apoptosis. However, on starvation, SIP together with Rab8 enhances the translocation of BRUCE into the recycling endosome, formation of autophagosomes, and degradation of BRUCE by optineurin-mediated autophagy. Accordingly, deletion of SIP in cultured cells reduces the autophagic degradation of damaged mitochondria and cytosolic protein aggregates. Thus, by stimulating proteasomal degradation of LC3-I, BRUCE also inhibits autophagy. Conversely, SIP promotes autophagy by blocking BRUCE-dependent degradation of LC3-I and by enhancing autophagosome formation and autophagic destruction of BRUCE. These actions of BRUCE and SIP represent mechanisms that link the regulation of autophagy and apoptosis under different conditions.

Proteasomal deubiquitinase UCH37 inhibits degradation of ß-catenin and promotes cell proliferation and motility.

The ubiquitin-proteasome system degrades most cellular proteins in eukaryotes. UCH37, also known as UCH-L5, is a deubiquitinase binding to Rpn13, a receptor for ubiquitinated substrates in the 26 S proteasome. But, it remains unclear how UCH37 influences the proteasomal degradation of the ubiquitinated substrates. Because deletion of UCH37 is embryonically lethal in mice, this study aims to investigate the role of UCH37 in proteasomal degradation by constructing the UCH37-deficient cell lines using CRISPR/Cas9 technology. Our results demonstrated that deletion of UCH37 decreased the levels of proteasomal Rpn13, implying that UCH37 might facilitate incorporation of Rpn13 into the proteasome. Meanwhile, deletion of UCH37 decreased the levels of ß-catenin and the early endosomal protein Rab8. ß-Catenin interacts with TCF/LEF to control transcription, and is involved in development, tissue homeostasis and tumorigenesis. We further found that deletion of UCH37 increased the levels of the ubiquitinated ß-catenin and accelerated the hydrogen peroxide-stimulated degradation of ß-catenin. Deletion of UCH37 also down-regulated the transcription of c-Myc, a downstream effector of ß-catenin, and inhibited cell proliferation and motility. These results raise the possibility that UCH37 maintains the homeostasis of proteasomal degradation reciprocally by assisting the recruitment of the ubiquitin receptor Rpn13 into the proteasome and by reversing ubiquitination of certain critical substrates of the 26 S proteasome.