Breaking BAG: The Co-Chaperone BAG3 in Health and Disease

BAG3 Regulation of RAB35 Mediates the Endosomal Sorting Complexes Required for Transport/Endolysosome Pathway and Tau Clearance

BACKGROUND

Declining proteostasis with aging contributes to increased susceptibility to neurodegenerative diseases, including Alzheimer's disease (AD). Emerging studies implicate impairment of the endosome-lysosome pathway as a significant factor in the pathogenesis of these diseases. Previously, we demonstrated that BAG3 regulates phosphorylated tau clearance. However, we did not fully define how BAG3 regulates endogenous tau proteostasis, especially in the early stages of disease progression.

METHODS

Mass spectrometric analyses were performed to identify neuronal BAG3 interactors. Multiple biochemical assays were used to investigate the BAG3-HSP70-TBC1D10B (EPI64B)-RAB35-HRS regulatory networks. Live-cell imaging was used to study the dynamics of the endosomal pathway. Immunohistochemistry and immunoblotting were performed in human AD brains and in P301S tau transgenic mice with BAG3 overexpressed.

RESULTS

The primary group of neuronal BAG3 interactors identified are involved in the endocytic pathway. Among them were key regulators of small GTPases, such as the RAB35 GTPase-activating protein TBC1D10B. We demonstrated that a BAG3-HSP70-TBC1D10B complex attenuates the ability of TBC1D10B to inactivate RAB35. Thus, BAG3 interacts with TBC1D10B to support the activation of RAB35 and recruitment of HRS, initiating endosomal sorting complex required for transport-mediated endosomal tau clearance. Furthermore, TBC1D10B shows significantly less colocalization with BAG3 in AD brains than in age-matched controls. Overexpression of BAG3 in P301S tau transgenic mice increased the colocalization of phosphorylated tau with the endosomal sorting complex required for transport III protein CHMP2B and reduced the levels of the mutant human tau.

CONCLUSIONS

We identified a novel BAG3-TBC1D10B-RAB35 regulatory axis that modulates endosomal sorting complex required for transport-dependent protein degradation machinery and tau clearance. Dysregulation of BAG3 could contribute to the pathogenesis of AD.

Protein Quality Control at the Sarcomere: Titin Protection and Turnover and Implications for Disease Development

Sarcomeres are mainly composed of filament and signaling proteins and are the smallest molecular units of muscle contraction and relaxation. The sarcomere protein titin serves as a molecular spring whose stiffness mediates myofilament extensibility in skeletal and cardiac muscle. Due to the enormous size of titin and its tight integration into the sarcomere, the incorporation and degradation of the titin filament is a highly complex task. The details of the molecular processes involved in titin turnover are not fully understood, but the involvement of different intracellular degradation mechanisms has recently been described. This review summarizes the current state of research with particular emphasis on the relationship between titin and protein quality control. We highlight the involvement of the proteasome, autophagy, heat shock proteins, and proteases in the protection and degradation of titin in heart and skeletal muscle. Because the fine-tuned balance of degradation and protein expression can be disrupted under pathological conditions, the review also provides an overview of previously known perturbations in protein quality control and discusses how these affect sarcomeric proteins, and titin in particular, in various disease states.

ERAS Is Constitutively Expressed in the Tissues of Adult Horses and May Be a Key Player in Basal Autophagy

ERas is a new gene of the Ras family found in murine embryonic stem (ES) cells. Its human ortholog is not expressed in human ES cells. So far ERas gene has only been found to be expressed in the tissues of adult cynomolgus monkeys and cattle; however, information about ERAS expression or its potential functions in equine tissues is lacking. This study was performed to investigate whether Eras is an equine functional gene and whether ERAS is expressed in the tissues of adult horses and determine its potential physiological role. Expression of the ERas gene was detected in all examined adult tissues, and the RT-PCR assay revealed ERAS transcripts. Protein expression was also detected by Western blot analysis. Quantitative real time RT-qPCR analysis revealed that different expression levels of ERAS transcripts were most highly expressed in the testis. Immunohistochemically, ERAS was found to be localized prevalently in the plasmatic membrane as well as cytoplasm of the cells. ERAS was a physical partner of activated PDGFβR leading to the AKT signaling. ERAS was found to interact with a network of proteins (BAG3, CHIP, Hsc70/Hsp70, HspB8, Synpo2, and p62) known to play a role in the chaperone-assisted selective autophagy (CASA), which is also known as BAG3-mediated selective macroautophagy, an adaptive mechanism to maintain cellular homeostasis. Furthermore, ERAS was found to interact with parkin. PINK1, BNIP3, laforin. All these proteins are known to play a role in parkin-dependent and -independent mitophagy. This is the first study demonstrating that Eras is a functional gene, and that ERAS is constitutively expressed in the tissues of adult horses. ERAS appears to play a physiological role in cellular proteostasis maintenance, thus mitigating the proteotoxicity of accumulated misfolded proteins and contributing to protection against disease. Finally, it is conceivable that activation of AKT pathway by PDGFRs promotes actin reorganization, directed cell movements, stimulation of cell growth.

Heat shock protein A4 ablation leads to skeletal muscle myopathy associated with dysregulated autophagy and induced apoptosis

BACKGROUND

Molecular chaperones assist protein folding, facilitate degradation of misfolded polypeptides, and thereby maintain protein homeostasis. Impaired chaperone activity leads to defective protein quality control that is implicated in multiple skeletal muscle diseases. The heat shock protein A4 (HSPA4) acts as a co-chaperone for HSP70. Previously, we showed that Hspa4 deletion causes impaired protein homeostasis in the heart. However, its functional role in skeletal muscle has not been explored.

METHODS

We performed a comparative phenotypic and biochemical analyses of Hspa4 knockout (KO) mice with wild-type (WT) littermates.

RESULTS

HSPA4 is markedly upregulated in regenerating WT muscle in vivo, and in differentiated myoblasts in vitro. Hspa4-KO mice are marked by growth retardation and increased variability in body weight, accompanied by 35% mortality rates during the peri-weaning period. The surviving Hspa4-KO mice experienced progressive skeletal muscle myopathy, characterized by increased number of muscle fibers with centralized nuclei, heterogeneous myofiber size distribution, inflammatory cell infiltrates and upregulation of embryonic and perinatal myosin heavy chain transcripts. Hspa4-KO muscles demonstrated an accumulation of autophagosome-associated proteins including microtubule associated protein1 light chain 3-II (LC3-II) and p62/sequestosome accompanied by increased number of TUNEL-positive nuclei.

CONCLUSIONS

Our findings underscore the indispensable role of HSPA4 in maintenance of muscle integrity through contribution in skeletal muscle autophagy and apoptosis, which might provide a novel therapeutic strategy for skeletal muscle morbidities.

Identification of an autophagy-related gene signature for predicting prognosis and immune activity in pancreatic adenocarcinoma

Adenocarcinoma of the pancreas (PAAD) is a cancerous growth that deteriorates rapidly and has a poor prognosis. Researchers are investigating autophagy in PAAD to identify a new biomarker and treatment target. An autophagy-related gene (ARG) model for overall survival (OS) was constructed using multivariate Cox regression analyses. A cohort of the Cancer Genome Atlas (TCGA)-PAAD was used as the training group as a basis for model construction. This prediction model was validated with several external datasets. To evaluate model performance, the analysis with receiver operating characteristic curves (ROC) was performed. The Human Protein Atlas (HPA) and Cancer Cell Line Encyclopedia (CCLE) were investigated to validate the effects of ARGs expression on cancer cells. Comparing the levels of immune infiltration between high-risk and low-risk groups was finished through the use of CIBERSORT. The differentially expressed genes (DEGs) between the low-/high-risk groups were analyzed further via Gene Ontology biological process (GO-BP) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, which were used to identify potential small-molecule compounds in Connectivity Map (CMap), followed by half-maximal inhibitory concentration (IC50) examination with PANC-1 cells. The risk score was finally calculated as follows: BAK1 × 0.34 + ITGA3 × 0.38 + BAG3 × 0.35 + APOL1 × 0.26-RAB24 × 0.67519. ITGA3 and RAB24 both emerged as independent prognostic factors in multivariate Cox regression. Each PAAD cohort had a significantly shorter OS in the high-risk group than in the low-risk group. The high-risk group exhibited infiltration of several immune cell types, including naive B cells (p = 0.003), plasma cells (p = 0.044), and CD8 T cells (nearly significant, p = 0.080). Higher infiltration levels of NK cells (p = 0.025), resting macrophages (p = 0.020), and mast cells (p = 0.007) were found in the high-risk group than the low-risk group. The in vitro and in vivo expression of signature ARGs was consistent in the CCLE and HPA databases. The top 3 enriched Gene Ontology biological processes (GO-BPs) were signal release, regulation of transsynaptic signaling, and modulation of chemical synaptic transmission, and the top 3 enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were MAPK, cAMP, and cell adhesion molecules. Four potential small-molecule compounds (piperacetazine, vinburnine, withaferin A and hecogenin) that target ARGs were also identified. Taking the results together, our research shows that the ARG signature may serve as a useful prognostic indicator and reveal potential therapeutic targets in patients with PAAD.

MicroRNA regulation of BAG3

B-cell lymphoma 2 (Bcl-2)-associated athanogene 3 (BAG3) protein is a member of BAG family of co-chaperones that modulates major biological processes, including apoptosis, autophagy, and development to promote cellular adaptive responses to stress stimuli. Although BAG3 is constitutively expressed in several cell types, its expression is also inducible and is regulated by microRNAs (miRNAs). miRNAs are small non-coding RNAs that mostly bind to the 3'-UTR (untranslated region) of mRNAs to inhibit their translation or to promote their degradation. miRNAs can potentially regulate over 50% of the protein-coding genes in a cell and therefore are involved in the regulation of all major functions, including cell differentiation, growth, proliferation, apoptosis, and autophagy. Dysregulation of miRNA expression is associated with pathogenesis of numerous diseases, including peripheral artery disease (PAD). BAG3 plays a critical role in regulating the response of skeletal muscle cells to ischemia by its ability to regulate autophagy. However, the biological role of miRNAs in the regulation of BAG3 in biological processes has only been elucidated recently. In this review, we discuss how miRNA may play a key role in regulating BAG3 expression under normal and pathological conditions.

An unexpected role for BAG3 in regulating PARP1 ubiquitination in oxidative stress-related endothelial damage

Oxidative stress-associated endothelial damage is the initiation factor of cardiovascular disease, and protein posttranslational modifications play critical roles in this process. Bcl-2-associated athanogene 3 (BAG3) is a molecular chaperone regulator of the BAG family, which interacts with various proteins and influences cell survival by activating multiple pathways. BAG3 undergoes posttranslational modifications; however, research evaluating BAG3 acetylation and its regulatory mechanism is lacking. In addition, the interacting protein and regulatory mechanism of BAG3 in oxidative stress-associated endothelial damage remain unclear. Here, key molecular interactions and protein modifications of BAG3 were identified in oxidative stress-associated endothelial damage. Endothelial-specific BAG3 knockout in the mouse model starkly enhances oxidative stress-associated endothelial damage and vascular remodeling, while BAG3 overexpression in mice significantly relieves this process. Mechanistically, poly(ADP-ribose) polymerase 1 (PARP1), causing oxidative stress, was identified as a novel physiological substrate of BAG3. Indeed, BAG3 binds to PARP1's BRCT domain to promote its ubiquitination (K249 residue) by enhancing the E3 ubiquitin ligase WWP2, which leads to proteasome-induced PARP1 degradation. Furthermore, we surprisingly found that BAG3 represents a new substrate of the acetyltransferase CREB-binding protein (CBP) and the deacetylase Sirtuin 2 (SIRT2) under physiological conditions. CBP/SIRT2 interacted with BAG3 and acetylated/deacetylated BAG3's K431 residue. Finally, deacetylated BAG3 promoted the ubiquitination of PARP1. This work reveals a novel regulatory system, with deacetylation-dependent regulation of BAG3 promoting PARP1 ubiquitination and degradation via enhancing WWP2, which is one possible mechanism to decrease vulnerability of oxidative stress in endothelial cells.

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Endothelial-specific BAG3 knockout in mice aggravates oxidative stress endothelial injury.

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BAG3 transgenic mice relieves oxidative stress endothelial injury.

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BAG3 promotes ubiquitination at the K249 residue of PARP1 via mobilization of the E3 ubiquitin ligase WWP2.

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CBP/SIRT2 interacted with BAG3 and acetylated/deacetylated BAG3's K431 residue.

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Deacetylated BAG3 promoted the ubiquitination of PARP1.

BAG family proteins contributes to autophagy-mediated multidrug resistance of tumor

Multidrug resistance (MDR) is a significant cause of tumor treatment failure. Accumulating evidence suggests that autophagy plays a significant role in the development of MDR. Autophagy is a conserved mechanism that maintains tumor homeostasis by removing damaged mitochondria. However, the specific regulatory mechanism is unclear. Here, we summarize recent studies on the role of autophagy in the development of MDR and the initiation of mitophagy by Bcl-2-associated athanogene (BAG) family proteins. Additionally, this mini-review emphasizes the regulatory role of BAG family proteins, which maintain mitochondrial homeostasis by regulating the PINK1/Parkin pathway. Elucidation of the regulatory mechanisms of mitophagy may foster the development of clinical therapeutic strategies for MDR tumors.

Concerted BAG3 and SIRPα blockade impairs pancreatic tumor growth

The BAG3- and SIRPα- mediated pathways trigger distinct cellular targets and signaling mechanisms in pancreatic cancer microenvironment. To explore their functional connection, we investigated the effects of their combined blockade on cancer growth in orthotopic allografts of pancreatic cancer mt4–2D cells in immunocompetent mice. The anti-BAG3 + anti-SIRPα mAbs treatment inhibited (p = 0.007) tumor growth by about the 70%; also the number of metastatic lesions was decreased, mostly by the effect of the anti-BAG3 mAb. Fibrosis and the expression of the CAF activation marker α-SMA were reduced by about the 30% in animals treated with anti-BAG3 mAb compared to untreated animals, and appeared unaffected by treatment with the anti-SIRPα mAb alone; however, the addition of anti-SIRPα to anti-BAG3 mAb in the combined treatment resulted in a > 60% (p < 0.0001) reduction of the fibrotic area and a 70% (p < 0.0001) inhibition of CAF α-SMA positivity. Dendritic cells (DCs) and CD8+ lymphocytes, hardly detectable in the tumors of untreated animals, were modestly increased by single treatments, while were much more clearly observable (p < 0.0001) in the tumors of the animals subjected to the combined treatment. The effects of BAG3 and SIRPα blockade do not simply reflect the sum of the effects of the single blockades, indicating that the two pathways are connected by regulatory interactions and suggesting, as a proof of principle, the potential therapeutic efficacy of a combined BAG3 and SIRPα blockade in pancreatic cancer.

Functional characterization of BAG3 in orange-spotted grouper (Epinephelus coioides) during viral infection

Bcl-2-associated athanogene 3 (BAG3) is a cochaperone protein that interacts with Bcl-2 and mediate cell death. However, little is known about the roles of fish BAG3 during viral infection. In this study, we characterized a BAG3 homolog from orange-spotted grouper (Epinephelus coioides) (EcBAG3) and investigated its roles during viral infection. The EcBAG3 protein encoded 579 amino acids with typical WW, PXXP and BAG domains, which shared high identities with reported fish BAG3. Quantitative real-time PCR (qRT-PCR) analysis revealed that EcBAG3 was highly expressed in brain and heart. And the expression of EcBAG3 was significantly up-regulated after red-spotted grouper nervous necrosis virus (RGNNV) stimulation in vitro. EcBAG3 overexpression could promoted the expression of viral genes (coat protein (CP) and RNA-dependent RNA polymerase (RdRp)), which was enhanced by co-transfection with Hsp70 and Hsp22. Also, EcBAG3 overexpression up-regulated the expression of LC3-Ⅱ and down-regulated the expression of Bax and BNIP3, the IFN- (IRF1, IRF3, IRF7, IFP35, Mx1) or inflammation-related (IL-1β and TNFα) factors, as well as decreased the activities of NF-κB, ISRE and IFN-3. While knockdown of EcBAG3 decreased the transcripts of RGNNV CP gene and RdRp gene. Further studies showed that EcBAG3 knockdown impaired the expression level of autophagy factor LC3-Ⅱ, and promoted the expression level of Bax and BNIP3, inflammatory factors and interferon factors. These data indicate that EcBAG3 can affect viral infection through modulating virus-induced cell death, regulating the expression of IFN- and inflammation-related factors, which will be helpful to further explore the immune response of fish during viral infection.

BAG Family Members as Mitophagy Regulators in Mammals

The BCL-2-associated athanogene (BAG) family is a multifunctional group of co-chaperones that are evolutionarily conserved from yeast to mammals. In addition to their common BAG domain, these proteins contain, in their sequences, many specific domains/motifs required for their various functions in cellular quality control, such as autophagy, apoptosis, and proteasomal degradation of misfolded proteins. The BAG family includes six members (BAG1 to BAG6). Recent studies reported their roles in autophagy and/or mitophagy through interaction with the autophagic machinery (LC3, Beclin 1, P62) or with the PINK1/Parkin signaling pathway. This review describes the mechanisms underlying BAG family member functions in autophagy and mitophagy and the consequences in physiopathology.

A Glimpse of Programmed Cell Death Among Bacteria, Animals, and Plants

Programmed cell death (PCD) in animals mainly refers to lytic and non-lytic forms. Disruption and integrity of the plasma membrane are considered as hallmarks of lytic and apoptotic cell death, respectively. These lytic cell death programs can prevent the hosts from microbial pathogens. The key to our understanding of these cases is pattern recognition receptors, such as TLRs in animals and LRR-RLKs in plants, and nod-like receptors (NLRs). Herein, we emphatically discuss the biochemical and structural studies that have clarified the anti-apoptotic and pro-apoptotic functions of Bcl-2 family proteins during intrinsic apoptosis and how caspase-8 among apoptosis, necroptosis, and pyroptosis sets the switchable threshold and integrates innate immune signaling, and that have compared the similarity and distinctness of the apoptosome, necroptosome, and inflammasome. We recapitulate that the necroptotic MLKL pore, pyroptotic gasdermin pore, HR-inducing resistosome, and mitochondrial Bcl-2 family all can form ion channels, which all directly boost membrane disruption. Comparing the conservation and unique aspects of PCD including ferrroptosis among bacteria, animals, and plants, the commonly shared immune domains including TIR-like, gasdermin-like, caspase-like, and MLKL/CC-like domains act as arsenal modules to restructure the diverse architecture to commit PCD suicide upon stresses/stimuli for host community.

Valosin Containing Protein (VCP): A Multistep Regulator of Autophagy

Valosin containing protein (VCP) has emerged as a central protein in the regulation of the protein quality control (PQC) system. VCP mutations are causative of multisystem proteinopathies, which include neurodegenerative diseases (NDs), and share various signs of altered proteostasis, mainly associated with autophagy malfunctioning. Autophagy is a complex multistep degradative system essential for the maintenance of cell viability, especially in post-mitotic cells as neurons and differentiated skeletal muscle cells. Interestingly, many studies concerning NDs have focused on autophagy impairment as a pathological mechanism or autophagy activity boosting to rescue the pathological phenotype. The role of VCP in autophagy has been widely debated, but recent findings have defined new mechanisms associated with VCP activity in the regulation of autophagy, showing that VCP is involved in different steps of this pathway. Here we will discuss the multiple activity of VCP in the autophagic pathway underlying its leading role either in physiological or pathological conditions. A better understanding of VCP complexes and mechanisms in regulating autophagy could define the altered mechanisms by which VCP directly or indirectly causes or modulates different human diseases and revealing possible new therapeutic approaches for NDs.

Structural Refinement of 2,4-Thiazolidinedione Derivatives as New Anticancer Agents Able to Modulate the BAG3 Protein

The multidomain BAG3 protein is a member of the BAG (Bcl-2-associated athanogene) family of co-chaperones, involved in a wide range of protein-protein interactions crucial for many key cellular pathways, including autophagy, cytoskeletal dynamics, and apoptosis. Basal expression of BAG3 is elevated in several tumor cell lines, where it promotes cell survival signaling and apoptosis resistance through the interaction with many protein partners. In addition, its role as a key player of several hallmarks of cancer, such as metastasis, angiogenesis, autophagy activation, and apoptosis inhibition, has been established. Due to its involvement in malignant transformation, BAG3 has emerged as a potential and effective biological target to control multiple cancer-related signaling pathways. Recently, by using a multidisciplinary approach we reported the first synthetic BAG3 modulator interfering with its BAG domain (BD), based on a 2,4-thiazolidinedione scaffold and endowed with significant anti-proliferative activity. Here, a further in silico-driven selection of a 2,4-thiazolidinedione-based compound was performed. Thanks to a straightforward synthesis, relevant binding affinity for the BAG3BD domain, and attractive biological activities, this novel generation of compounds is of great interest for the development of further BAG3 binders, as well as for the elucidation of the biological roles of this protein in tumors. Specifically, we found compound 6 as a new BAG3 modulator with a relevant antiproliferative effect on two different cancer cell lines (IC₅₀: A375 = 19.36 μM; HeLa = 18.67 μM).

Global identification of phospho-dependent SCF substrates reveals a FBXO22 phosphodegron and an ERK-FBXO22-BAG3 axis in tumorigenesis

SKP1-CUL1-F-box (SCF) ubiquitin ligases play fundamental roles in cellular functions. Typically, substrate phosphorylation is required for SCF recognition and subsequent degradation. However, phospho-dependent substrates remain largely unidentified. Here, using quantitative phoshoproteome approach, we performed a system-wide investigation of phospho-dependent SCF substrates. This strategy identified diverse phospho-dependent candidates. Biochemical verification revealed a mechanism by which SCF^FBXO22 recognizes the motif XXPpSPXPXX as a conserved phosphodegron to target substrates for destruction. We further demonstrated BAG3, a HSP70 co-chaperone, is a bona fide substrate of SCF^FBXO22. FBXO22 mediates BAG3 ubiquitination and degradation that requires ERK-dependent BAG3 phosphorylation at S377. FBXO22 depletion or expression of a stable BAG3 S377A mutant promotes tumor growth via defects in apoptosis and cell cycle progression in vitro and in vivo. In conclusion, our study identified broad phosphorylation-dependent SCF substrates and demonstrated a phosphodegron recognized by FBXO22 and a novel ERK-FBXO22-BAG3 axis involved in tumorigenesis.

The Molecular Biodiversity of Protein Targeting and Protein Transport Related to the Endoplasmic Reticulum

Looking at the variety of the thousands of different polypeptides that have been focused on in the research on the endoplasmic reticulum from the last five decades taught us one humble lesson: no one size fits all. Cells use an impressive array of components to enable the safe transport of protein cargo from the cytosolic ribosomes to the endoplasmic reticulum. Safety during the transit is warranted by the interplay of cytosolic chaperones, membrane receptors, and protein translocases that together form functional networks and serve as protein targeting and translocation routes. While two targeting routes to the endoplasmic reticulum, SRP (signal recognition particle) and GET (guided entry of tail-anchored proteins), prefer targeting determinants at the N- and C-terminus of the cargo polypeptide, respectively, the recently discovered SND (SRP-independent) route seems to preferentially cater for cargos with non-generic targeting signals that are less hydrophobic or more distant from the termini. With an emphasis on targeting routes and protein translocases, we will discuss those functional networks that drive efficient protein topogenesis and shed light on their redundant and dynamic nature in health and disease.

Detection of sieric BAG3 in patients affected by cardiovascular diseases: State of art and perspectives

BAG3 is highly expressed in the heart and its functions are essential in maintaining cardiac muscle cells homeostasis. In the past, BAG3 was detected in serum from advanced heart failure patients and its higher levels were correlated to an increased death risk. Moreover, it has also been reported that BAG3 levels in serum are increased in patients with hypertension, a known cardiovascular risk marker. Evidence from different laboratories suggested the possibility to use BAG3-based strategies to improve the clinical outcome of cardiovascular disease patients. This review aims to highlight the biological roles of intracellular or secreted BAG3 in myocardiocytes and propose additional new data on the levels of sieric BAG3 in patients with acute myocardial infarction (AMI), never assessed before. We evaluated BAG3 serum levels in relation to cardiovascular risk parameters in 64 AMI patients aged ≥18 years of either sex. We observed significant (p < .01) correlations of BAG3 positivity with dyslipidemic status and diabetic disease. We did not observe any significant correlations of BAG3 levels with smoking habit, hypertension or familiarity for AMI, although BAG3-positive seemed to be more numerous than BAG3-negative patients among hypertensives and among patients with familiarity for AMI. Furthermore, a significant (p < .001) correlation of BAG3 positivity with diuretics assumption was also noted. In conclusion, 32.8% of the patients were BAG3-positive and were characterized by some particular features as comorbidity presence or concomitant therapies. The significance of these observations needs to be verified by more extensive studies and could help in the validation of the use of BAG3 as a biomarker in heart attack risk stratification.

Role of BAG3 in bovine Deltapapillomavirus-mediated autophagy

Bovine Deltapapillomavirus genus (δPV), comprises four members that are highly pathogenic and are frequently associated with bladder tumors of adult cattle and water buffaloes. In particular, bovine δPV-2 and δPV-13 are commonly found in urinary bladder tumors in adult large ruminants reared fully or partially on hilly/mountain pasturelands rich in bracken fern (Pteridium spp.) as the urinary bladder of the herbivores is the specific target for bracken genotoxins such as ptaquiloside (PT). PT is a sesquiterpenoid responsible for alkylation of adenine of codon 61 of gene H-Ras, which results in Glutamine 61 substitution that is essential for guanosine triphosphate (GTP) hydrolysis. Glutamine substitution at position 61 impairs the intrinsic GTPase activity. Therefore, active GTP-bound conformations (Ras-GTP) accumulate in cells, thereby causing abnormal cell proliferation and differentiation. The aim of the present study is to stress how bovine δPVs upregulate different forms of selective autophagy, of which BAG3 is a key player. BAG3 plays a central role in autophagy and acts as a multifunctional hub for an interaction network at the cytosolic and mitochondrial level. BAG3 is a functional partner of bovine δPV E5 oncoprotein and forms a complex with molecular chaperones Hsc70/Hsp70/Hsp8B and with cochaperone CHIP. BAG3 interacts with Synpo2. It is believed that this interaction has a crucial role for autophagosome (mitophagosome) formation. Furthermore, in urothelial cells infected by bovine δPVs, BAG3 interacts with parkin and some receptors such as BNIP3/FUNDC1, which suggests that BAG3 is involved in both parkin-dependent and -independent mitophagy that appear upregulate in bladder carcinogenesis of cattle induced by bovine δPVs. Surprisingly, BAG3 interacts also with ERAS, a protein encoded by the ERas gene, a novel member of the RAS family. Unlike in humans, the ERas gene is a functional gene in the cells of adult cattle, and it appears to play a role in bovine BAG3-mediated selective autophagy, including mitophagy observed in urothelial cells spontaneously infected with bovine papillomavirus.

Molecular Signaling to Preserve Mitochondrial Integrity against Ischemic Stress in the Heart: Rescue or Remove Mitochondria in Danger

Cardiovascular diseases are one of the leading causes of death and global health problems worldwide, and ischemic heart disease is the most common cause of heart failure (HF). The heart is a high-energy demanding organ, and myocardial energy reserves are limited. Mitochondria are the powerhouses of the cell, but under stress conditions, they become damaged, release necrotic and apoptotic factors, and contribute to cell death. Loss of cardiomyocytes plays a significant role in ischemic heart disease. In response to stress, protective signaling pathways are activated to limit mitochondrial deterioration and protect the heart. To prevent mitochondrial death pathways, damaged mitochondria are removed by mitochondrial autophagy (mitophagy). Mitochondrial quality control mediated by mitophagy is functionally linked to mitochondrial dynamics. This review provides a current understanding of the signaling mechanisms by which the integrity of mitochondria is preserved in the heart against ischemic stress.

With or without You: Co-Chaperones Mediate Health and Disease by Modifying Chaperone Function and Protein Triage

Heat shock proteins (HSPs) are a family of molecular chaperones that regulate essential protein refolding and triage decisions to maintain protein homeostasis. Numerous co-chaperone proteins directly interact and modify the function of HSPs, and these interactions impact the outcome of protein triage, impacting everything from structural proteins to cell signaling mediators. The chaperone/co-chaperone machinery protects against various stressors to ensure cellular function in the face of stress. However, coding mutations, expression changes, and post-translational modifications of the chaperone/co-chaperone machinery can alter the cellular stress response. Importantly, these dysfunctions appear to contribute to numerous human diseases. Therapeutic targeting of chaperones is an attractive but challenging approach due to the vast functions of HSPs, likely contributing to the off-target effects of these therapies. Current efforts focus on targeting co-chaperones to develop precise treatments for numerous diseases caused by defects in protein quality control. This review focuses on the recent developments regarding selected HSP70/HSP90 co-chaperones, with a concentration on cardioprotection, neuroprotection, cancer, and autoimmune diseases. We also discuss therapeutic approaches that highlight both the utility and challenges of targeting co-chaperones.

Unraveling the role of tomato Bcl-2-associated athanogene (BAG) proteins during abiotic stress response and fruit ripening

B-cell lymphoma2 (Bcl-2)-associated athanogene (BAG) family proteins are evolutionary conserved across all eukaryotes. These proteins interact with HSP70/HSC70 and function as co-chaperones during stress response and developmental pathways. Compared to the animal counterpart, the BAG proteins in plants are much less studied and primarily Arabidopsis BAG proteins have been identified and characterized for their role in programmed cell death, homeostasis, growth and development, abiotic and biotic stress response. Here, we have identified BAG protein family (SlBAGs) in tomato, an economically important and a model fruit crop using genome-wide scanning. We have performed phylogenetic analysis, genes architecture assessment, chromosomal location and in silico promoter analysis. Our data suggest that SlBAGs show differential tissue specific expression pattern during plant development particularly fruit development and ripening. Furthermore, we reported that expression of SlBAGs is modulated during abiotic stresses and is regulated by stress hormones ABA and ethylene. In planta subcellular localization reveals their diverse subcellular localization, and many members are localized in nucleus and cytoplasm. Like previous reports, our protein-protein interaction network and yeast two-hybrid analysis uncover that SlBAGs interact with HSP70. The current study provides insights into role of SlBAGs in plant development particualry fruit ripening and abiotic stress response.

Drosophila p38 MAPK interacts with BAG-3/starvin to regulate age-dependent protein homeostasis

As organisms age, they often accumulate protein aggregates that are thought to be toxic, potentially leading to age‐related diseases. This accumulation of protein aggregates is partially attributed to a failure to maintain protein homeostasis. A variety of genetic factors have been linked to longevity, but how these factors also contribute to protein homeostasis is not completely understood. In order to understand the relationship between aging and protein aggregation, we tested how a gene that regulates lifespan and age‐dependent locomotor behaviors, p38 MAPK (p38Kb), influences protein homeostasis as an organism ages. We find that p38Kb regulates age‐dependent protein aggregation through an interaction with starvin, a regulator of muscle protein homeostasis. Furthermore, we have identified Lamin as an age‐dependent target of p38Kb and starvin.

CDK1-Mediated Phosphorylation of BAG3 Promotes Mitotic Cell Shape Remodeling and the Molecular Assembly of Mitotic p62 Bodies

The cochaperone BCL2-associated athanogene 3 (BAG3), in complex with the heat shock protein HSPB8, facilitates mitotic rounding, spindle orientation, and proper abscission of daughter cells. BAG3 and HSPB8 mitotic functions implicate the sequestosome p62/SQSTM1, suggesting a role for protein quality control. However, the interplay between this chaperone-assisted pathway and the mitotic machinery is not known. Here, we show that BAG3 phosphorylation at the conserved T285 is regulated by CDK1 and activates its function in mitotic cell shape remodeling. BAG3 phosphorylation exhibited a high dynamic at mitotic entry and both a non-phosphorylatable BAG3^T285A and a phosphomimetic BAG3^T285D protein were unable to correct the mitotic defects in BAG3-depleted HeLa cells. We also demonstrate that BAG3 phosphorylation, HSPB8, and CDK1 activity modulate the molecular assembly of p62/SQSTM1 into mitotic bodies containing K63 polyubiquitinated chains. These findings suggest the existence of a mitotically regulated spatial quality control mechanism for the fidelity of cell shape remodeling in highly dividing cells.

Molecular mechanisms of mammalian autophagy

The ubiquitin-proteasome pathway (UPP) and autophagy play integral roles in cellular homeostasis. As part of their normal life cycle, most proteins undergo ubiquitination for some form of redistribution, localization and/or functional modulation. However, ubiquitination is also important to the UPP and several autophagic processes. The UPP is initiated after specific lysine residues of short-lived, damaged or misfolded proteins are conjugated to ubiquitin, which targets these proteins to proteasomes. Autophagy is the endosomal/lysosomal-dependent degradation of organelles, invading microbes, zymogen granules and macromolecules such as protein, carbohydrates and lipids. Autophagy can be broadly separated into three distinct subtypes termed microautophagy, chaperone-mediated autophagy and macroautophagy. Although autophagy was once thought of as non-selective bulk degradation, advancements in the field have led to the discovery of several selective forms of autophagy. Here, we focus on the mechanisms of primary and selective mammalian autophagy pathways and highlight the current knowledge gaps in these molecular pathways.

Myoblast mechanotransduction and myotube morphology is dependent on BAG3 regulation of YAP and TAZ

Skeletal muscle tissue is mechanically dynamic with changes in stiffness influencing function, maintenance, and regeneration. We modeled skeletal muscle mechanical changes in culture with dynamically stiffening hydrogels demonstrating that the chaperone protein BAG3 transduces matrix stiffness by redistributing YAP and TAZ subcellular localization in muscle progenitor cells. BAG3 depletion increases cytoplasmic retention of YAP and TAZ, desensitizing myoblasts to changes in hydrogel elastic moduli. Upon differentiation, muscle progenitors depleted of BAG3 formed enlarged, round myotubes lacking the typical cylindrical morphology. The aberrant morphology is dependent on YAP/TAZ signaling, which was sequestered in the cytoplasm in BAG3-depleted myotubes but predominately nuclear in cylindrical myotubes of control cells. Control progenitor cells induced to differentiate on soft (E' = 4 and 12 kPa) hydrogels formed circular myotubes similar to those observed in BAG3-depleted cells. Inhibition of the Hippo pathway partially restored myotube morphologies, permitting nuclear translocation of YAP and TAZ in BAG3-depleted myogenic progenitors. Thus, BAG3 is a critical mediator of dynamic stiffness changes in muscle tissue, coupling mechanical alterations to intracellular signals and inducing changes in gene expression that influence muscle progenitor cell morphology and differentiation.

Understanding the Potential of Genome Editing in Parkinson's Disease

CRISPR is a simple and cost-efficient gene-editing technique that has become increasingly popular over the last decades. Various CRISPR/Cas-based applications have been developed to introduce changes in the genome and alter gene expression in diverse systems and tissues. These novel gene-editing techniques are particularly promising for investigating and treating neurodegenerative diseases, including Parkinson's disease, for which we currently lack efficient disease-modifying treatment options. Gene therapy could thus provide treatment alternatives, revolutionizing our ability to treat this disease. Here, we review our current knowledge on the genetic basis of Parkinson's disease to highlight the main biological pathways that become disrupted in Parkinson's disease and their potential as gene therapy targets. Next, we perform a comprehensive review of novel delivery vehicles available for gene-editing applications, critical for their successful application in both innovative research and potential therapies. Finally, we review the latest developments in CRISPR-based applications and gene therapies to understand and treat Parkinson's disease. We carefully examine their advantages and shortcomings for diverse gene-editing applications in the brain, highlighting promising avenues for future research.

Therapeutic targeting of BAG3: considering its complexity in cancer and heart disease

Bcl2-associated athanogene-3 (BAG3) is expressed ubiquitously in humans, but its levels are highest in the heart, the skeletal muscle, and the central nervous system; it is also elevated in many cancers. BAG3's diverse functions are supported by its multiple protein-protein binding domains, which couple with small and large heat shock proteins, members of the Bcl2 family, other antiapoptotic proteins, and various sarcomere proteins. In the heart, BAG3 inhibits apoptosis, promotes autophagy, couples the β-adrenergic receptor with the L-type Ca2+ channel, and maintains the structure of the sarcomere. In cancer cells, BAG3 binds to and supports an identical array of prosurvival proteins, and it may represent a therapeutic target. However, the development of strategies to block BAG3 function in cancer cells may be challenging, as they are likely to interfere with the essential roles of BAG3 in the heart. In this Review, we present the current knowledge regarding the biology of this complex protein in the heart and in cancer and suggest several therapeutic options.

RNA-Seq analysis reveals potential regulators of programmed cell death and leaf remodelling in lace plant (Aponogeton madagascariensis)

BACKGROUND

The lace plant (Aponogeton madagascariensis) is an aquatic monocot that develops leaves with uniquely formed perforations through the use of a developmentally regulated process called programmed cell death (PCD). The process of perforation formation in lace plant leaves is subdivided into several developmental stages: pre-perforation, window, perforation formation, perforation expansion and mature. The first three emerging "imperforate leaves" do not form perforations, while all subsequent leaves form perforations via developmentally regulated PCD. PCD is active in cells called "PCD cells" that do not retain the antioxidant anthocyanin in spaces called areoles framed by the leaf veins of window stage leaves. Cells near the veins called "NPCD cells" retain a red pigmentation from anthocyanin and do not undergo PCD. While the cellular changes that occur during PCD are well studied, the gene expression patterns underlying these changes and driving PCD during leaf morphogenesis are mostly unknown. We sought to characterize differentially expressed genes (DEGs) that mediate lace plant leaf remodelling and PCD. This was achieved performing gene expression analysis using transcriptomics and comparing DEGs among different stages of leaf development, and between NPCD and PCD cells isolated by laser capture microdissection.

RESULTS

Transcriptomes were sequenced from imperforate, pre-perforation, window, and mature leaf stages, as well as PCD and NPCD cells isolated from window stage leaves. Differential expression analysis of the data revealed distinct gene expression profiles: pre-perforation and window stage leaves were characterized by higher expression of genes involved in anthocyanin biosynthesis, plant proteases, expansins, and autophagy-related genes. Mature and imperforate leaves upregulated genes associated with chlorophyll development, photosynthesis, and negative regulators of PCD. PCD cells were found to have a higher expression of genes involved with ethylene biosynthesis, brassinosteroid biosynthesis, and hydrolase activity whereas NPCD cells possessed higher expression of auxin transport, auxin signalling, aspartyl proteases, cysteine protease, Bag5, and anthocyanin biosynthesis enzymes.

CONCLUSIONS

RNA sequencing was used to generate a de novo transcriptome for A. madagascariensis leaves and revealed numerous DEGs potentially involved in PCD and leaf remodelling. The data generated from this investigation will be useful for future experiments on lace plant leaf development and PCD in planta.

Identification and Quantification of Glutathionylated Cysteines under Ischemic Stress

Ischemia reperfusion injury contributes to adverse cardiovascular diseases in part by producing a burst of reactive oxygen species that induce oxidations of many muscular proteins. Glutathionylation is one of the major protein cysteine oxidations that often serve as molecular mechanisms behind the pathophysiology associated with ischemic stress. Despite the biological significance of glutathionylation in ischemia reperfusion, identification of specific glutathionylated cysteines under ischemic stress has been limited. In this report, we have analyzed glutathionylation under oxygen-glucose deprivation (OGD) or repletion of nutrients after OGD (OGD/R) by using a clickable glutathione approach that specifically detects glutathionylated proteins. Our data find that palmitate availability induces a global level of glutathionylation and decreases cell viability during OGD/R. We have then applied a clickable glutathione-based proteomic quantification strategy, which enabled the identification and quantification of 249 glutathionylated cysteines in response to palmitate during OGD/R in the HL-1 cardiomyocyte cell line. The subsequent bioinformatic analysis found 18 glutathionylated cysteines whose genetic variants are associated with muscular disorders. Overall, our data report glutathionylated cysteines under ischemic stress that may contribute to adverse outcomes or muscular disorders.

What's in the BAGs? Intrinsic disorder angle of the multifunctionality of the members of a family of chaperone regulators

In humans, the family of Bcl-2 associated athanogene (BAG) proteins includes six members characterized by exceptional multifunctionality and engagement in the pathogenesis of various diseases. All of them are capable of interacting with a multitude of often unrelated binding partners. Such binding promiscuity and related functional and pathological multifacetedness cannot be explained or understood within the frames of the classical "one protein-one structure-one function" model, which also fails to explain the presence of multiple isoforms generated for BAG proteins by alternative splicing or alternative translation initiation and their extensive posttranslational modifications. However, all these mysteries can be solved by taking into account the intrinsic disorder phenomenon. In fact, high binding promiscuity and potential to participate in a broad spectrum of interactions with multiple binding partners, as well as a capability to be multifunctional and multipathogenic, are some of the characteristic features of intrinsically disordered proteins and intrinsically disordered protein regions. Such functional proteins or protein regions lacking unique tertiary structures constitute a cornerstone of the protein structure-function continuum concept. The aim of this paper is to provide an overview of the functional roles of human BAG proteins from the perspective of protein intrinsic disorder which will provide a means for understanding their binding promiscuity, multifunctionality, and relation to the pathogenesis of various diseases.

The role of Bag3 in cell signaling

Bag3 has been implicated in a wide variety of physiological processes from autophagy to aggresome formation and from cell transformation to survival. We argue that involvement of Bag3 in many of these processes is due to its distinct function in cell signaling. The structure of Bag3 suggests that it can serve as a scaffold that links molecular chaperones Hsp70 and small Hsps with components of a variety of signaling pathways. Major protein-protein interaction motifs of Bag3 that recruit components of signaling pathways are WW domain and PXXP motif that interacts with SH3-domain proteins. Furthermore, Hsp70-Bag3 appears to be a sensor of abnormal polypeptides during the proteotoxic stress. It also serves as a sensor of a mechanical force during mechanotransduction. Common feature of these and probably certain other sensory mechanisms is that they represent responses to specific kinds of abnormal proteins, i.e. unfolded filamin A in case of mechanotransduction or stalled translating polypeptides in case of sensing proteasome inhibition. Overall Hsp70-Bag3 module represents a novel signaling node that responds to multiple stimuli and controls multiple physiological processes.

Different roles of BAG3 in cardiac physiological hypertrophy and pathological remodeling

Heart failure is one of the leading causes of death worldwide. A stimulated heart undergoes either adaptive physiological hypertrophy, which can maintain a normal heart function, or maladaptive pathological remodeling, which can deteriorate heart function. These 2 kinds of remodeling often co-occur at the early stages of many heart diseases and have important effects on cardiac function. The Bcl2-associated athanogene 3 (BAG3) protein is highly expressed in the heart and has many functions. However, it is unknown how BAG3 is regulated and what its function is during physiological hypertrophy and pathological remodeling. We generated tamoxifen-induced, heart-specific heterozygous and homozygous BAG3 knockout mouse models (BAG3 protein level decreased by approximately 40% and 80% in the hearts after tamoxifen administration). BAG3 knockout models were subjected to swimming training or phenylephrine (PE) infusion to induce cardiac physiological hypertrophy and pathological remodeling. Neonatal rat ventricular cardiomyocytes (NRVCs) were used to study BAG3 functions and mechanisms in vitro. We found that BAG3 was upregulated in physiological hypertrophy and in pathological remodeling both in vivo and in vitro. Heterozygous or homozygous knockout BAG3 in mouse hearts and knockdown of BAG3 in the NRVCs blunted physiological hypertrophy and aggravated pathological remodeling, while overexpression of BAG3 promoted physiological hypertrophy and inhibited pathological remodeling in NRVCs. Mechanistically, BAG3 overexpression in NRVCs promoted physiological hypertrophy by activating the protein kinase B (AKT)/mammalian (or mechanistic) target of rapamycin (mTOR) pathway. BAG3 knockdown in NRVCs aggravated pathological remodeling through activation of the calcineurin/nuclear factor of activated T cells 2 (NFATc2) pathway. Because BAG3 has a dual role in cardiac remodeling, heart-specific regulation of BAG3 may be an effective therapeutic strategy to protect against deterioration of heart function and heart failure caused by many heart diseases.

Lysosome dysfunction as a cause of neurodegenerative diseases: Lessons from frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are fatal neurodegenerative disorders that are thought to exist on a clinical and pathological spectrum. FTD and ALS are linked by shared genetic causes (e.g. C9orf72 hexanucleotide repeat expansions) and neuropathology, such as inclusions of ubiquitinated, misfolded proteins (e.g. TAR DNA-binding protein 43; TDP-43) in the CNS. Furthermore, some genes that cause FTD or ALS when mutated encode proteins that localize to the lysosome or modulate endosome-lysosome function, including lysosomal fusion, cargo trafficking, lysosomal acidification, autophagy, or TFEB activity. In this review, we summarize evidence that lysosomal dysfunction, caused by genetic mutations (e.g. C9orf72, GRN, MAPT, TMEM106B) or toxic-gain of function (e.g. aggregation of TDP-43 or tau), is an important pathogenic disease mechanism in FTD and ALS. Further studies into the normal function of many of these proteins are required and will help uncover the mechanisms that cause lysosomal dysfunction in FTD and ALS. Mutations or polymorphisms in genes that encode proteins important for endosome-lysosome function also occur in other age-dependent neurodegenerative diseases, including Alzheimer's (e.g. APOE, PSEN1, APP) and Parkinson's (e.g. GBA, LRRK2, ATP13A2) disease. A more complete understanding of the common and unique features of lysosome dysfunction across the spectrum of neurodegeneration will help guide the development of therapies for these devastating diseases.

Regular football training down-regulates miR-1303 muscle expression in veterans

PURPOSE

Regular exercise affects the expression of several genes, proteins and microRNAs (miRNAs) in time- and intensity-dependent manner promoting longevity. We previously identified from GeneChip Array analysis several differentially expressed genes and miRNAs in muscle from veteran football players (VPG) compared to active untrained elderly subjects (CG); here we focussed on miRNA-1303 (miR-1303). The aims of the present research were: to analyse the effects of football training on the expression of miR-1303 and to identify its putative target involved in the longevity pathways in skeletal muscle from VPG compared to CG.

METHODS

RNA samples from 12 VPG and 12 CG muscle biopsies were used to validate miR-1303 expression. Crossing four different bioinformatic algorithms, we identified 16 putative targets of miR-1303; from these, BAG-2, KLHL7 and KBTBD6 were chosen for further validation by Western blot analysis in LHCN-M2 human myoblasts transiently transfected with miR-1303.

RESULTS

Football training down-regulates miR-1303 expression in muscle from VPG compared to CG and the expression of BAG-2, a chaperon protein involved in the autophagy pathway, inversely correlated to overexpression of miR-1303 in a time-dependent manner, indicating that it is a miR-1303 potential target.

CONCLUSIONS

This is the first report, to our knowledge, describing miR-1303 regulation in skeletal muscle by football training and the identification of a target protein, BAG-2, involved in the autophagy pathway. This result contributes to the enlargement of knowledge on the molecular mechanisms linking football training, autophagy and longevity.

Proteostasis Dysfunction in Aged Mammalian Cells. The Stressful Role of Inflammation

Aging is a biological and multifactorial process characterized by a progressive and irreversible deterioration of the physiological functions leading to a progressive increase in morbidity. In the next decades, the world population is expected to reach ten billion, and globally, elderly people over 80 are projected to triple in 2050. Consequently, it is also expected an increase in the incidence of age-related pathologies such as cancer, diabetes, or neurodegenerative disorders. Disturbance of cellular protein homeostasis (proteostasis) is a hallmark of normal aging that increases cell vulnerability and might be involved in the etiology of several age-related diseases. This review will focus on the molecular alterations occurring during normal aging in the most relevant protein quality control systems such as molecular chaperones, the UPS, and the ALS. Also, alterations in their functional cooperation will be analyzed. Finally, the role of inflammation, as a synergistic negative factor of the protein quality control systems during normal aging, will also be addressed. A better comprehension of the age-dependent modifications affecting the cellular proteostasis, as well as the knowledge of the mechanisms underlying these alterations, might be very helpful to identify relevant risk factors that could be responsible for or contribute to cell deterioration, a fundamental question still pending in biomedicine.

Implication of BAG5 downregulation in metabolic reprogramming of cisplatin-resistant ovarian cancer cells via mTORC2 signaling pathway

Ovarian cancer is the most frequent cause of gynecologic malignancies associated death. Primary or acquired cisplatin resistance is frequently occurred during ovarian cancer therapy. Cancer stem cells (CSC) tend to form minimal residual disease after chemotherapy and are implicated in relapse. The ability of cancer cells to reprogram their metabolism has recently been related with maintenance of CSC and resistance to chemotherapies. The current study found that BAG5 expression was decreased in cisplatin-resistant ovarian cancer cells and clinical tissues. Our data demonstrated that BAG5 knockdown was implicated in metabolic reprogramming and maintenance of cancer stem cell (CSC)-like features of ovarian cancer cells via regulation of Rictor and subsequent mTORC2 signaling pathway. In addition, the current study demonstrated that Bcl6 upregulation was responsible for repression of BAG5 transactivation via recruitment on the BAG5 promoter in cisplatin-resistant ovarian cancer. The current study also demonstrated reverse correlations between BAG5 and Bcl6, BAG5 and Rictor in ovarian serous adenocarcinoma tissues. Collectively, the current study identified the implication of Bcl6/BAG5/Rictor-mTORC2 signaling pathway in metabolic reprograming and maintenance of CSC-like features in cisplatin-resistant ovarian cancer cells. Therefore, further studies on the mechanism underlying regulation of metabolic reprogramming and CSC-like characteristics of cisplatin-resistant ovarian cancer cells may contribute to the establishment of novel therapeutic strategy for cisplatin-resistance.

Cytosolic protein quality control machinery: Interactions of Hsp70 with a network of co-chaperones and substrates

The chaperone heat shock protein 70 (Hsp70) and its network of co-chaperones serve as a central hub of cellular protein quality control mechanisms. Domain organization in Hsp70 dictates ATPase activity, ATP dependent allosteric regulation, client/substrate binding and release, and interactions with co-chaperones. The protein quality control activities of Hsp70 are classified as foldase, holdase, and disaggregase activities. Co-chaperones directly assisting protein refolding included J domain proteins and nucleotide exchange factors. However, co-chaperones can also be grouped and explored based on which domain of Hsp70 they interact. Here we discuss how the network of cytosolic co-chaperones for Hsp70 contributes to the functions of Hsp70 while closely looking at their structural features. Comparison of domain organization and the structures of co-chaperones enables greater understanding of the interactions, mechanisms of action, and roles played in protein quality control.

On the origin of BAG(3) and its consequences for an expansion of BAG3's role in protein homeostasis

The B-cell CLL 2-associated athanogene (BAG) protein family in general and BAG3, in particular, are pivotal elements of cellular protein homeostasis, with BAG3 playing a major role in macroautophagy. In particular, in the contexts of senescence and degeneration, BAG3 has exhibited an essential role often related to its capabilities to organize and remove aggregated proteins. Exciting studies in different species ranging from human, murine, zebrafish, and plant samples have delivered vital insights into BAG3s' (and other BAG proteins') functions and their regulations. However, so far no studies have addressed neither BAG3's evolution nor its phylogenetic position in the BAG family.

Neuromodulation of BAG co-chaperones by HIV-1 viral proteins and H2O2: implications for HIV-associated neurological disorders

Despite increasing numbers of aged individuals living with HIV, the mechanisms underlying HIV-associated neurological disorders (HANDs) remain elusive. As HIV-1 pathogenesis and aging are characterized by oxidative stress as well as altered protein quality control (PQC), reactive oxygen species (ROS) themselves might constitute a molecular mediator of neuronal PQC by modulating BCL-2 associated athanogene (BAG) family members. Present results reveal H2O2 replicated and exacerbated a reduction in neuronal BAG3 induced by the expression of HIV-1 viral proteins (i.e., Tat and Nef), while also causing an upregulation of BAG1. Such a reciprocal regulation of BAG3 and BAG1 levels was also indicated in two animal models of HIV, the doxycycline-inducible Tat (iTat) and the Tg26 mouse. Inhibiting oxidative stress via antioxidants in primary culture was capable of partially preserving neuronal BAG3 levels as well as electrophysiological functioning otherwise altered by HIV-1 viral proteins. Current findings indicate HIV-1 viral proteins and H2O2 may mediate neuronal PQC by exerting synergistic effects on complementary BAG family members, and suggest novel therapeutic targets for the aging HIV-1 population.

The Vault Nanoparticle: A Gigantic Ribonucleoprotein Assembly Involved in Diverse Physiological and Pathological Phenomena and an Ideal Nanovector for Drug Delivery and Therapy

Simple Summary

In recent decades, a molecular complex referred to as vault nanoparticle has attracted much attention by the scientific community, due to its unique properties. At the molecular scale, it is a huge assembly consisting of 78 97-kDa polypeptide chains enclosing an internal cavity, wherein enzymes involved in DNA integrity maintenance and some small noncoding RNAs are accommodated. Basically, two reasons justify this interest. On the one hand, this complex represents an ideal tool for the targeted delivery of drugs, provided it is suitably engineered, either chemically or genetically; on the other hand, it has been shown to be involved in several cellular pathways and mechanisms that most often result in multidrug resistance. It is therefore expected that a better understanding of the physiological roles of this ribonucleoproteic complex may help develop new therapeutic strategies capable of coping with cancer progression. Here, we provide a comprehensive review of the current knowledge.

Abstract

The vault nanoparticle is a eukaryotic ribonucleoprotein complex consisting of 78 individual 97 kDa-“major vault protein” (MVP) molecules that form two symmetrical, cup-shaped, hollow halves. It has a huge size (72.5 × 41 × 41 nm) and an internal cavity, wherein the vault poly(ADP-ribose) polymerase (vPARP), telomerase-associated protein-1 (TEP1), and some small untranslated RNAs are accommodated. Plenty of literature reports on the biological role(s) of this nanocomplex, as well as its involvement in diseases, mostly oncological ones. Nevertheless, much has still to be understood as to how vault participates in normal and pathological mechanisms. In this comprehensive review, current understanding of its biological roles is discussed. By different mechanisms, vault’s individual components are involved in major cellular phenomena, which result in protection against cellular stresses, such as DNA-damaging agents, irradiation, hypoxia, hyperosmotic, and oxidative conditions. These diverse cellular functions are accomplished by different mechanisms, mainly gene expression reprogramming, activation of proliferative/prosurvival signaling pathways, export from the nucleus of DNA-damaging drugs, and import of specific proteins. The cellular functions of this nanocomplex may also result in the onset of pathological conditions, mainly (but not exclusively) tumor proliferation and multidrug resistance. The current understanding of its biological roles in physiological and pathological processes should also provide new hints to extend the scope of its exploitation as a nanocarrier for drug delivery.

The Role of HSPB8, a Component of the Chaperone-Assisted Selective Autophagy Machinery, in Cancer

The cellular response to cancer-induced stress is one of the major aspects regulating cancer development and progression. The Heat Shock Protein B8 (HSPB8) is a small chaperone involved in chaperone-assisted selective autophagy (CASA). CASA promotes the selective degradation of proteins to counteract cell stress such as tumor-induced stress. HSPB8 is also involved in (i) the cell division machinery regulating chromosome segregation and cell cycle arrest in the G0/G1 phase and (ii) inflammation regulating dendritic cell maturation and cytokine production. HSPB8 expression and role are tumor-specific, showing a dual and opposite role. Interestingly, HSPB8 may be involved in the acquisition of chemoresistance to drugs. Despite the fact the mechanisms of HSPB8-mediated CASA activation in tumors need further studies, HSPB8 could represent an important factor in cancer induction and progression and it may be a potential target for anticancer treatment in specific types of cancer. In this review, we will discuss the molecular mechanism underlying HSPB8 roles in normal and cancer conditions. The basic mechanisms involved in anti- and pro-tumoral activities of HSPB8 are deeply discussed together with the pathways that modulate HSPB8 expression, in order to outline molecules with a beneficial effect for cancer cell growth, migration, and death.

An Adult Mouse Model of Dilated Cardiomyopathy Caused by Inducible Cardiac-Specific Bis Deletion

BCL-2 interacting cell death suppressor (BIS) is a multifunctional protein that has been implicated in cancer and myopathy. Various mutations of the BIS gene have been identified as causative of cardiac dysfunction in some dilated cardiomyopathy (DCM) patients. This was recently verified in cardiac-specific knock-out (KO) mice. In this study, we developed tamoxifen-inducible cardiomyocyte-specific BIS-KO (Bis-iCKO) mice to assess the role of BIS in the adult heart using the Cre-loxP strategy. The disruption of the Bis gene led to impaired ventricular function and subsequent heart failure due to DCM, characterized by reduced left ventricular contractility and dilatation that were observed using serial echocardiography and histology. The development of DCM was confirmed by alterations in Z-disk integrity and increased expression of several mRNAs associated with heart failure and remodeling. Furthermore, aggregation of desmin was correlated with loss of small heat shock protein in the Bis-iCKO mice, indicating that BIS plays an essential role in the quality control of cardiac proteins, as has been suggested in constitutive cardiac-specific KO mice. Our cardiac-specific BIS-KO mice may be a useful model for developing therapeutic interventions for DCM, especially late-onset DCM, based on the distinct phenotypes and rapid progressions.

Chaperone-Assisted Mitotic Actin Remodeling by BAG3 and HSPB8 Involves the Deacetylase HDAC6 and Its Substrate Cortactin

The fidelity of actin dynamics relies on protein quality control, but the underlying molecular mechanisms are poorly defined. During mitosis, the cochaperone BCL2-associated athanogene 3 (BAG3) modulates cell rounding, cortex stability, spindle orientation, and chromosome segregation. Mitotic BAG3 shows enhanced interactions with its preferred chaperone partner HSPB8, the autophagic adaptor p62/SQSTM1, and HDAC6, a deacetylase with cytoskeletal substrates. Here, we show that depletion of BAG3, HSPB8, or p62/SQSTM1 can recapitulate the same inhibition of mitotic cell rounding. Moreover, depletion of either of these proteins also interfered with the dynamic of the subcortical actin cloud that contributes to spindle positioning. These phenotypes were corrected by drugs that limit the Arp2/3 complex or HDAC6 activity, arguing for a role for BAG3 in tuning branched actin network assembly. Mechanistically, we found that cortactin acetylation/deacetylation is mitotically regulated and is correlated with a reduced association of cortactin with HDAC6 in situ. Remarkably, BAG3 depletion hindered the mitotic decrease in cortactin–HDAC6 association. Furthermore, expression of an acetyl-mimic cortactin mutant in BAG3-depleted cells normalized mitotic cell rounding and the subcortical actin cloud organization. Together, these results reinforce a BAG3′s function for accurate mitotic actin remodeling, via tuning cortactin and HDAC6 spatial dynamics.

BAG3 Proteomic Signature under Proteostasis Stress

The multifunctional HSP70 co-chaperone BAG3 (BCL-2-associated athanogene 3) represents a key player in the quality control of the cellular proteostasis network. In response to stress, BAG3 specifically targets aggregation-prone proteins to the perinuclear aggresome and promotes their degradation via BAG3-mediated selective macroautophagy. To adapt cellular homeostasis to stress, BAG3 modulates and functions in various cellular processes and signaling pathways. Noteworthy, dysfunction and deregulation of BAG3 and its pathway are pathophysiologically linked to myopathies, cancer, and neurodegenerative disorders. Here, we report a BAG3 proteomic signature under proteostasis stress. To elucidate the dynamic and multifunctional action of BAG3 in response to stress, we established BAG3 interactomes under basal and proteostasis stress conditions by employing affinity purification combined with quantitative mass spectrometry. In addition to the identification of novel potential BAG3 interactors, we defined proteins whose interaction with BAG3 was altered upon stress. By functional annotation and protein-protein interaction enrichment analysis of the identified potential BAG3 interactors, we confirmed the multifunctionality of BAG3 and highlighted its crucial role in diverse cellular signaling pathways and processes, ensuring cellular proteostasis and cell viability. These include protein folding and degradation, gene expression, cytoskeleton dynamics (including cell cycle and transport), as well as granulostasis, in particular.

Genetic compensation prevents myopathy and heart failure in an in vivo model of Bag3 deficiency

Mutations in the molecular co-chaperone Bcl2-associated athanogene 3 (BAG3) are found to cause dilated cardiomyopathy (DCM), resulting in systolic dysfunction and heart failure, as well as myofibrillar myopathy (MFM), which is characterized by protein aggregation and myofibrillar disintegration in skeletal muscle cells. Here, we generated a CRISPR/Cas9-induced Bag3 knockout zebrafish line and found the complete preservation of heart and skeletal muscle structure and function during embryonic development, in contrast to morpholino-mediated knockdown of Bag3. Intriguingly, genetic compensation, a process of transcriptional adaptation which acts independent of protein feedback loops, was found to prevent heart and skeletal muscle damage in our Bag3 knockout model. Proteomic profiling and quantitative real-time PCR analyses identified Bag2, another member of the Bag protein family, significantly upregulated on a transcript and protein level in bag3^-/- mutants. This implied that the decay of bag3 mutant mRNA in homozygous bag3^-/- embryos caused the transcriptional upregulation of bag2 expression. We further demonstrated that morpholino-mediated knockdown of Bag2 in bag3^-/- embryos evoked severe functional and structural heart and skeletal muscle defects, which are similar to Bag3 morphants. However, Bag2 knockdown in bag3^+/+ or bag3^+/- embryos did not result in (cardio-)myopathy. Finally, we found that inhibition of the nonsense-mediated mRNA decay (NMD) machinery by knockdown of upf1, an essential NMD factor, caused severe heart and skeletal muscle defects in bag3^-/- mutants due to the blockade of transcriptional adaptation of bag2 expression. Our findings provide evidence that genetic compensation might vitally influence the penetrance of disease-causing bag3 mutations in vivo.

One form of genetic compensation is described as transcriptional adaptation of gene expression triggered by deleterious gene mutations. Although the precise molecular mechanism that induces genetic compensation needs to be defined, it represents a powerful biological phenomenon that warrants genetic robustness. We find that antisense-mediated knockdown of Bag3 in zebrafish embryos causes heart failure and myopathy. By contrast, CRISPR/Cas9-induced depletion of Bag3 does not result in the abrogation of heart and skeletal muscle function in zebrafish embryos. We find here that transcriptional activation of the Bag family member bag2 is capable of restoring heart and skeletal muscle function in bag3 mutant embryos, whereas this compensatory mechanism is not present in the bag3 morphants. Furthermore, we show that nonsense-mediated decay of bag3 mRNA is the molecular trigger for the compensatory upregulation of bag2. Our study provides evidence that genetic compensation via transcriptional adaptation is a vital modulator of disease peculiarity and penetrance in bag3 mutant zebrafish and that this biological phenomenon might also be active in certain human BAG3 mutation carriers.

Centrality of BAGs in Plant PCD, Stress Responses, and Host Defense

Programmed cell death (PCD) is a genetically regulated process for the selective demise of unwanted and damaged cells. Although our understanding of plant PCD pathways has advanced significantly, doubts remain on the extent of conservation of animal apoptosis in plants. At least at the primary sequence level, plants do not encode the regulators of animal apoptosis. Structural analyses have enabled the identification of the B cell lymphoma 2 (Bcl-2)-associated athanogene (BAG) family of co-chaperones in plants. This discovery suggests that some aspects of animal PCD are conserved in plants, while the varied subcellular localization of plant BAGs indicates that they may have evolved distinct functions. Here we review plant BAG proteins, with an emphasis on their roles in the regulation of plant PCD.

Novel BAG3 Variants in African American Patients With Cardiomyopathy: Reduced β-Adrenergic Responsiveness in Excitation-Contraction

BACKGROUND

We reported 3 novel nonsynonymous single nucleotide variants of Bcl2-associated athanogene 3 (BAG3) in African Americans with heart failure (HF) that are associated with a 2-fold increase in cardiac events (HF hospitalization, heart transplantation, or death).

METHODS AND RESULTS

We expressed BAG3 variants (P63A, P380S, and A479V) via adenovirus-mediated gene transfer in adult left ventricular myocytes isolated from either wild-type (WT) or cardiac-specific BAG3 haploinsufficient (cBAG3^+/-) mice: the latter to simulate the clinical situation in which BAG3 variants are only found on 1 allele. Compared with WT myocytes, cBAG3^+/- myocytes expressed approximately 50% of endogenous BAG3 levels and exhibited decreased [Ca²⁺]_i and contraction amplitudes after isoproterenol owing to decreased L-type Ca²⁺ current. BAG3 repletion with WT BAG3 but not P380S, A479V, or P63A/P380S variants restored contraction amplitudes in cBAG3^+/- myocytes to those measured in WT myocytes, suggesting excitation-contraction abnormalities partly account for HF in patients harboring these mutants. Because P63A is near the WW domain (residues 21-55) and A479V is in the BAG domain (residues 420-499), we expressed BAG3 deletion mutants (Δ1-61 and Δ421-575) in WT myocytes and demonstrated that the BAG but not the WW domain was involved in enhancement of excitation-contraction by isoproterenol.

CONCLUSIONS

The BAG3 variants contribute to HF in African American patients partly by decreasing myocyte excitation-contraction under stress, and that both the BAG and PXXP domains are involved in mediating β-adrenergic responsiveness in myocytes.

Induction of BIS Protein During Astroglial and Fibrotic Scar Formation After Mitochondrial Toxin-Mediated Neuronal Injury in Rats

B cell leukemia/lymphoma-2 (Bcl-2)-interacting death suppressor (BIS), also identified as Bcl-2-associated athanogene 3 (BAG3), has been reported to be upregulated in reactive astrocytes after brain insults. The present study was designed to further substantiate the involvement of BIS protein in the astroglial reaction in the striatum of rats treated with the mitochondrial toxin, 3-nitropropionic acid. Weak constitutive immunoreactivity for BIS was observed in astrocytes in the control striatum, whereas its expression was upregulated, along with that of nestin, in the lesioned striatum. In the lesion core, where astrocytes are virtually absent, BIS/nestin double-labeled cells were associated with the vasculature and were identified as perivascular adventitial fibroblasts. By contrast, BIS/nestin double-labeled cells in the perilesional area were reactive astrocytes, which were confined to the border zone contributing to the formation of the astroglial scar; this was evident 3 days post-lesion and increased thereafter progressively throughout the 28-day experimental period. At the ultrastructural level, BIS protein was diffusely localized throughout the cytoplasm within the stained cells. Collectively, our results demonstrate the phenotypic and functional heterogeneity of BIS-positive cells in the lesioned striatum, suggesting the involvement of BIS in the formation of astroglial scar and its potential role in the development of fibrotic scar after brain insults.