Hepatic deficiency of COP9 signalosome subunit 8 induces ubiquitin-proteasome system impairment and Bim-mediated apoptosis in murine livers

The Proteome Profile of Olfactory Ecto-Mesenchymal Stem Cells-Derived from Patients with Familial Alzheimer's Disease Reveals New Insights for AD Study

Alzheimer's disease (AD), the most common neurodegenerative disease and the first cause of dementia worldwide, has no effective treatment, and its pathological mechanisms are not yet fully understood. We conducted this study to explore the proteomic differences associated with Familial Alzheimer's Disease (FAD) in olfactory ecto-mesenchymal stem cells (MSCs) derived from PSEN1 (A431E) mutation carriers compared with healthy donors paired by age and gender through two label-free liquid chromatography-mass spectrometry approaches. The first analysis compared carrier 1 (patient with symptoms, P1) and its control (healthy donor, C1), and the second compared carrier 2 (patient with pre-symptoms, P2) with its respective control cells (C2) to evaluate whether the protein alterations presented in the symptomatic carrier were also present in the pre-symptom stages. Finally, we analyzed the differentially expressed proteins (DEPs) for biological and functional enrichment. These proteins showed impaired expression in a stage-dependent manner and are involved in energy metabolism, vesicle transport, actin cytoskeleton, cell proliferation, and proteostasis pathways, in line with previous AD reports. Our study is the first to conduct a proteomic analysis of MSCs from the Jalisco FAD patients in two stages of the disease (symptomatic and presymptomatic), showing these cells as a new and excellent in vitro model for future AD studies.

Roles of Cullin-RING Ubiquitin Ligases in Cardiovascular Diseases

Maintenance of protein homeostasis is crucial for virtually every aspect of eukaryotic biology. The ubiquitin-proteasome system (UPS) represents a highly regulated quality control machinery that protects cells from a variety of stress conditions as well as toxic proteins. A large body of evidence has shown that UPS dysfunction contributes to the pathogenesis of cardiovascular diseases. This review highlights the latest findings regarding the physiological and pathological roles of cullin-RING ubiquitin ligases (CRLs), an essential player in the UPS, in the cardiovascular system. To inspire potential therapeutic invention, factors regulating CRL activities are also discussed.

Cullin Deneddylation Suppresses the Necroptotic Pathway in Cardiomyocytes

Cardiomyocyte death in the form of apoptosis and necrosis represents a major cellular mechanism underlying cardiac pathogenesis. Recent advances in cell death research reveal that not all necrosis is accidental, but rather there are multiple forms of necrosis that are regulated. Necroptosis, the earliest identified regulated necrosis, is perhaps the most studied thus far, and potential links between necroptosis and Cullin-RING ligases (CRLs), the largest family of ubiquitin E3 ligases, have been postulated. Cullin neddylation activates the catalytic dynamic of CRLs; the reverse process, Cullin deneddylation, is performed by the COP9 signalosome holocomplex (CSN) that is formed by eight unique protein subunits, COPS1/CNS1 through COPS8/CNS8. As revealed by cardiomyocyte-restricted knockout of Cops8 (Cops8-cko) in mice, perturbation of Cullin deneddylation in cardiomyocytes impairs not only the functioning of the ubiquitin-proteasome system (UPS) but also the autophagic-lysosomal pathway (ALP). Similar cardiac abnormalities are also observed in Cops6-cko mice; and importantly, loss of the desmosome targeting of COPS6 is recently implicated as a pathogenic factor in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). Cops8-cko causes massive cardiomyocyte death in the form of necrosis rather than apoptosis and rapidly leads to a progressive dilated cardiomyopathy phenotype as well as drastically shortened lifespan in mice. Even a moderate downregulation of Cullin deneddylation as seen in mice with Cops8 hypomorphism exacerbates cardiac proteotoxicity induced by overexpression of misfolded proteins. More recently, it was further demonstrated that cardiomyocyte necrosis caused by Cops8-cko belongs to necroptosis and is mediated by the RIPK1-RIPK3 pathway. This article reviews these recent advances and discusses the potential links between Cullin deneddylation and the necroptotic pathways in hopes of identifying potentially new therapeutic targets for the prevention of cardiomyocyte death.

A new risk score based on twelve hepatocellular carcinoma-specific gene expression can predict the patients' prognosis

A large panel of molecular biomarkers have been identified to predict the prognosis of hepatocellular carcinoma (HCC), yet with limited clinical application due to difficult extrapolation. We here generated a genetic risk score system comprised of 12 HCC-specific genes to better predict the prognosis of HCC patients. Four genomics profiling datasets (GSE5851, GSE28691, GSE15765 and GSE14323) were searched to seek HCC-specific genes by comparisons between cancer samples and normal liver tissues and between different subtypes of hepatic neoplasms. Univariate survival analysis screened HCC-specific genes associated with overall survival (OS) in the training dataset for next-step risk model construction. The prognostic value of the constructed HCC risk score system was then validated in the TCGA dataset. Stratified analysis indicated this scoring system showed better performance in elderly male patients with HBV infection and preoperative lower levels of creatinine, alpha-fetoprotein and platelet and higher level of albumin. Functional annotation of this risk model in high-risk patients revealed that pathways associated with cell cycle, cell migration and inflammation were significantly enriched. In summary, our constructed HCC-specific gene risk model demonstrated robustness and potentiality in predicting the prognosis of HCC patients, especially among elderly male patients with HBV infection and relatively better general conditions.

Murine Myocardial Transcriptome Analysis Reveals a Critical Role of COPS8 in the Gene Expression of Cullin-RING Ligase Substrate Receptors and Redox and Vesicle Trafficking Pathways

Background: The COP9 signalosome (CSN) consisting of 8 unique protein subunits (COPS1 through COPS8) serves as the cullin deneddylase, regulating the catalytic dynamics of cullin RING ligases (CRLs), the largest family of ubiquitin ligases Background: The COP9 signalosome (CSN) consisting of 8 unique protein subunits (COPS1 through COPS8) serves as the cullin deneddylase, regulating the catalytic dynamics of cullin RING ligases (CRLs), the largest family of ubiquitin ligases. Supported primarily by the decrease of substrate receptor (SR) proteins of CRLs in cells deficient of a CSN subunit, CSN-mediated cullin deneddylation is believed to prevent autoubiquitination and self-destruction of the SR in active CRLs. However, it is unclear whether the decrease in SRs is solely due to protein destabilization. Moreover, our prior studies have demonstrated that cardiac specific knockout of Cops8 (Cops8-CKO) impairs autophagosome maturation and causes massive necrosis in cardiomyocytes but the underlying mechanism remains poorly understood. Given that Cops8 is nucleus-enriched and a prior report showed its binding to the promoter of several genes and association of its ablation with decreased mRNA levels of these genes, we sought to determine the dynamic changes of myocardial transcriptome in mice with perinatal Cops8-CKO and to explore their functional implications. Methods and Results: Myocardial transcriptomes of Cops8^flox/flox , Cops8^flox/+::Myh6-Cre, and Cops8^flox/flox::Myh6-Cre littermate mice at postnatal 2 and 3 weeks were analyzed. The data were imported into an in-house analysis pipeline using Bioconductor for quantile normalization and statistical analysis. Differentially expressed genes (DEGs) between groups at each time point or between time points within the group were revealed by t-test. Genes with p < 0.05 after Benjamini and Hochberg false discovery rate correction for multiple hypothesis testing were considered as significant DEGs. We found that (1) the Ingenuity Pathway Analysis (IPA) revealed significant enrichment of DEGs in multiple pathways, especially those responding to oxidative stress, in homozygous Cops8-CKO hearts at both 2 and 3 weeks, corroborating the occurrence of massive cardiomyocyte necrosis at 3 weeks; (2) the decreases in multiple CRL SR proteins were associated with decreased transcript levels; and (3) enrichment of DEGs in the chromatin remodeling pathway and the microtubule motility and vesicle trafficking pathways. Conclusions: Our data are consistent with the notion that Cops8/CSN plays a role in the transcriptional regulation of CRL SRs and in the redox and vesicle trafficking pathways.

Roles of Multifunctional COP9 Signalosome Complex in Cell Fate and Implications for Drug Discovery

The eight subunits containing COP9 signalosome (CSN) complex, is highly conserved among eukaryotes. CSN, identified as a negative regulator of photomorphogenesis, has also been demonstrated to be important in proteolysis, cellular signal transduction and cell cycle regulation in various eukaryotic organisms. This review mainly summarizes the roles of CSN in cell cycle regulation, signal transduction and apoptosis, and its potential as diagnostic biomarkers, drug targets for cancer and infectious diseases. J. Cell. Physiol. 232: 1246-1253, 2017. © 2016 Wiley Periodicals, Inc.

A quantitative proteomic approach for unveiling novel mechanisms associated with MeHg-induced toxicity: effects on the methylation cycle

Methylmercury (MeHg) is still a major threat for human health and the environment due to its extremely high toxicity that mainly affects the nervous system. Despite the great efforts made during the last few decades, the specific molecular mechanisms involved in MeHg-induced toxicity are still not completely unveiled. In this work we explored such mechanisms using neuroblastoma cells (Neuro-2a) and SILAC as a quantitative proteomic approach. We found that exposure of Neuro-2a cells to 2 mg L-1 MeHg for 8 h decreased the cell viability to 70% and caused significant changes in the morphology of the cells, specially regarding neurite development. Our proteomic results showed different proteins altered upon MeHg exposure that helped to identify pathways related to the toxicity exerted by MeHg. Specifically, we have found that MeHg affects the methylation cycle by inhibiting the expression of key enzymes including MTHFD1 and MTR. Moreover, we demonstrate that inhibition of MTHFD1 is not observed when exposing the cells to inorganic Hg and other heavy metals such as Pb or Cu. Thus, this work sets the stage for dissecting a specific molecular mechanism for MeHg-induced toxicity.

The COP9 signalosome and cullin-RING ligases in the heart

Alteration of ubiquitin-proteasome system (UPS) mediated protein degradation has been implicated in the progression from a large subset of heart disease to congestive heart failure, rendering it extremely important to elucidate the cellular and molecular mechanism by which the UPS is regulated. Cullin-RING ligases (CRLs) represent the largest family of ubiquitin ligases crucial for UPS-dependent proteolysis. Serving as a cullin deneddylase, the COP9 signalosome (CSN) regulates the activity and assembly of CRLs. In the past several years, emerging studies have begun to unveil the role of the CSN and some of the CRLs in cardiomyocytes or the heart under physiological and pathological conditions. This review article will highlight and analyze these recent progresses and provide the author's perspective on the future directions for this research field.

Neddylation and deneddylation in cardiac biology

Neddylation is a post-translational protein modification that conjugates a ubiquitin-like protein NEDD8 to target proteins. Similar to ubiquitination, neddylation is mediated by a cascade of three NEDD8 specific enzymes, an E1 activating enzyme, an E2 conjugating enzyme and one of the several E3 ligases. Neddylation is countered by the action of deneddylases via a process termed deneddylation. By altering the substrate's conformation, stability, subcellular localization or binding affinity to DNA or proteins, neddylation regulates diverse cellular processes including the ubiquitin-proteasome system-mediated protein degradation, protein transcription, cell signaling etc. Dysregulation of neddylation has been linked to cancer, neurodegenerative disorders, and more recently, cardiac disease. Here we comprehensively overview the biochemistry, the proteome and the biological function of neddylation. We also summarize the recent progress in revealing the physiological and pathological role of neddylation and deneddylation in the heart.

Autophagic-lysosomal inhibition compromises ubiquitin-proteasome system performance in a p62 dependent manner in cardiomyocytes

Intracellular protein degradation is primarily performed by the ubiquitin-proteasome system (UPS) and the autophagic-lysosomal pathway (ALP). The interplay between these two pathways has been rarely examined in intact animals and the mechanism underlying the interplay remains unclear. Hence, we sought to test in vivo and in vitro the impact of inhibition of the ALP on UPS proteolytic performance in cardiomyocytes and to explore the underlying mechanism. Transgenic mice ubiquitously expressing a surrogate UPS substrate (GFPdgn) were treated with bafilomycin-A1 (BFA) to inhibit the ALP. Myocardial and renal GFPdgn protein levels but not mRNA levels were increased at 24 hours but not 3 hours after the first injection of BFA. Myocardial protein abundance of key proteasome subunits and the activities of proteasomal peptidases were not discernibly altered by the treatment. In cultured neonatal rat ventricular myocytes (NRVMs), the surrogate UPS substrate GFPu and a control red fluorescence protein (RFP) were co-expressed to probe UPS performance. At 12 hours or 24 hours after ALP inhibition by 3-methyladenine (3-MA) or BFA, GFPu/RFP protein ratios and the protein half-life of GFPu were significantly increased, which is accompanied by increases in p62 proteins. Similar findings were obtained when ALP was inhibited genetically via silencing Atg7 or Rab7. ALP inhibition-induced increases in GFPu and p62 are co-localized in NRVMs. siRNA-mediated p62 knockdown prevented ALP inhibition from inducing GFPu accumulation in NRVMs. We conclude that in a p62-dependent fashion, ALP inhibition impairs cardiac UPS proteolytic performance in cardiomyocytes in vitro and in vivo.