A BAG's life: Every connection matters in cancer

Exploring the Redox and pH Dimension of Carbonic Anhydrases in Cancer: A Focus on Carbonic Anhydrase 3

Significance: Both redox and pH are important regulatory processes that underpin cell physiological functions, in addition to influencing cancer cell development and tumor progression. The thioredoxin (Trx) and glutathione redox systems and the carbonic anhydrase (CA) proteins are considered key regulators of cellular redox and pH, respectively, with components of the Trx system and CAs regarded as cancer therapeutic targets. However, the redox and pH axis in cancer cells is an underexplored topic of research. Recent Advances: Structural studies of a CA family member, CA3, localized two of its five cysteine residues to the protein surface. Redox-regulated modifications to CA3 have been identified, including glutathionylation. CA3 has been shown to bind to other proteins, including B cell lymphoma-2-associated athanogene 3, and squalene epoxidase, which can modulate autophagy and proinflammatory signaling, respectively, in cancer cells. Critical Issues: CA3 has also been associated with epithelial-mesenchymal transition processes, which promote cancer cell metastasis, whereas CA3 overexpression activates the phosphatidylinositol-3 kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway, which upregulates cell growth and inhibits autophagy. It is not yet known if CA3 modulates cancer progression through its reported antioxidant functions. Future Directions: CA3 is one of the least studied CA isozymes. Further studies are required to assess the cellular antioxidant role of CA3 and its impact on cancer progression. Identification of other binding partners is also required, including whether CA3 binds to Trx in human cells. The development of specific CA3 inhibitors will facilitate these functional studies and allow CA3 to be investigated as a cancer therapeutic target.

BAG3 promotes proliferation and migration of arterial smooth muscle cells by regulating STAT3 phosphorylation in diabetic vascular remodeling

BACKGROUND

Diabetic vascular remodeling is the most important pathological basis of diabetic cardiovascular complications. The accumulation of advanced glycation end products (AGEs) caused by elevated blood glucose promotes the proliferation and migration of vascular smooth muscle cells (VSMCs), leading to arterial wall thickening and ultimately vascular remodeling. Therefore, the excessive proliferation and migration of VSMCs is considered as an important therapeutic target for vascular remodeling in diabetes mellitus. However, due to the lack of breakthrough in experiments, there is currently no effective treatment for the excessive proliferation and migration of VSMCs in diabetic patients. Bcl-2-associated athanogene 3 (BAG3) protein is a multifunctional protein highly expressed in skeletal muscle and myocardium. Previous research has confirmed that BAG3 can not only regulate cell survival and apoptosis, but also affect cell proliferation and migration. Since the excessive proliferation and migration of VSMCs is an important pathogenesis of vascular remodeling in diabetes, the role of BAG3 in the excessive proliferation and migration of VSMCs and its molecular mechanism deserve further investigation.

METHODS

In this study, BAG3 gene was manipulated in smooth muscle to acquire SM22αCre; BAG3FL/FL mice and streptozotocin (STZ) was used to simulate diabetes. Expression of proteins and aortic thickness of mice were detected by immunofluorescence, ultrasound and hematoxylin-eosin (HE) staining. Using human aorta smooth muscle cell line (HASMC), cell viability was measured by CCK-8 and proliferation was measured by colony formation experiment. Migration was detected by transwell, scratch experiments and Phalloidin staining. Western Blot was used to detect protein expression and Co-Immunoprecipitation (Co-IP) was used to detect protein interaction.

RESULTS

In diabetic vascular remodeling, AGEs could promote the interaction between BAG3 and signal transducer and activator of transcription 3 (STAT3), leading to the enhanced interaction between STAT3 and Janus kinase 2 (JAK2) and reduced interaction between STAT3 and extracellular signal-regulated kinase 1/2 (ERK1/2), resulting in accumulated p-STAT3(705) and reduced p-STAT3(727). Subsequently, the expression of matrix metallopeptidase 2 (MMP2) is upregulated, thus promoting the migration of VSMCs.

CONCLUSIONS

BAG3 upregulates the expression of MMP2 by increasing p-STAT3(705) and decreasing p-STAT3(727) levels, thereby promoting vascular remodeling in diabetes. This provides a new orientation for the prevention and treatment of diabetic vascular remodeling.

Recruitment of ubiquitin E2 enzymes is determined jointly by the U-box domains and substrates of E3 ligases

Ubiquitination is a cascade reaction involving E1, E2, and E3 enzymes. The orthogonal ubiquitin transfer (OUT) method has been previously established to identify potential substrates of E3 ligases. In this study, we verified the ubiquitination of five substrates mediated by the E3 ligases CHIP and E4B. To further explore the activity of U-box domains of E3 ligases, two mutants with the U-box domains interchanged between CHIP and E4B were generated. They exhibited a significantly reduced ubiquitination ability. Additionally, different E3s recruited similar E2 ubiquitin-conjugating enzymes when ubiquitinating the same substrates, highlighting that U-box domains determined the E2 recruitment, while the substrate determined the E2 selectivity. This study reveals the influence of substrates and U-box domains on E2 recruitment, providing a novel perspective on the function of U-box domains of E3 ligases.

Unravelling the Intricate Roles of FAM111A and FAM111B: From Protease-Mediated Cellular Processes to Disease Implications

Proteases are critical enzymes in cellular processes which regulate intricate events like cellular proliferation, differentiation and apoptosis. This review highlights the multifaceted roles of the serine proteases FAM111A and FAM111B, exploring their impact on cellular functions and diseases. FAM111A is implicated in DNA replication and replication fork protection, thereby maintaining genome integrity. Additionally, FAM111A functions as an antiviral factor against DNA and RNA viruses. Apart from being involved in DNA repair, FAM111B, a paralog of FAM111A, participates in cell cycle regulation and apoptosis. It influences the apoptotic pathway by upregulating anti-apoptotic proteins and modulating cell cycle-related proteins. Furthermore, FAM111B's association with nucleoporins suggests its involvement in nucleo-cytoplasmic trafficking and plays a role in maintaining normal telomere length. FAM111A and FAM111B also exhibit some interconnectedness and functional similarity despite their distinct roles in cellular processes and associated diseases resulting from their dysfunction. FAM111A and FAM111B dysregulation are linked to genetic disorders: Kenny-Caffey Syndrome type 2 and Gracile Bone Dysplasia for FAM111A and POIKTMP, respectively, and cancers. Therefore, the dysregulation of these proteases in diseases emphasizes their potential as diagnostic markers and therapeutic targets. Future research is essential to unravel the intricate mechanisms governing FAM111A and FAM111B and explore their therapeutic implications comprehensively.

A Mitochondrial Localized Chaperone Regulator OsBAG6 Functions in Saline-Alkaline Stress Tolerance in Rice

B-cell lymphoma 2 (Bcl-2)-associated athanogene (BAG) family genes play prominent roles in regulating plant growth, development, and stress response. Although the molecular mechanism underlying BAG's response to abiotic stress has been studied in Arabidopsis, the function of OsBAG underlying saline-alkaline stress tolerance in rice remains unclear. In this study, OsBAG6, a chaperone regulator localized to mitochondria, was identified as a novel negative regulator of saline-alkaline stress tolerance in rice. The expression level of OsBAG6 was induced by high concentration of salt, high pH, heat and abscisic acid treatments. Overexpression of OsBAG6 in rice resulted in significantly reduced plant heights, grain size, grain weight, as well as higher sensitivity to saline-alkaline stress. By contrast, the osbag6 loss-of-function mutants exhibited decreased sensitivity to saline-alkaline stress. The transcriptomic analysis uncovered differentially expressed genes related to the function of "response to oxidative stress", "defense response", and "secondary metabolite biosynthetic process" in the shoots and roots of OsBAG6-overexpressing transgenic lines. Furthermore, cytoplasmic levels of Ca2+ increase rapidly in plants exposed to saline-alkaline stress. OsBAG6 bound to calcium sensor OsCaM1-1 under normal conditions, which was identified by comparative interactomics, but not in the presence of elevated Ca2+. Released OsCaM1-1 saturated with Ca2+ is then able to regulate downstream stress-responsive genes as part of the response to saline-alkaline stress. OsBAG6 also interacted with energy biosynthesis and metabolic pathway proteins that are involved in plant growth and saline-alkaline stress response mechanisms. This study reveals a novel function for mitochondrial localized OsBAG6 proteins in the saline-alkaline stress response alongside OsCaM1-1.

Design, synthesis and biological evaluation of novel 2,4-thiazolidinedione derivatives able to target the human BAG3 protein

The Bcl-2-associated athanogene 3 (BAG3) protein plays multiple roles in controlling cellular homeostasis, and it has been reported to be deregulated in many cancers, leading tumor cell apoptosis escape. BAG3 protein is then an emerging target for its oncogenic activities in both leukemia and solid cancers, such as medulloblastoma. In this work a series of forty-four compounds were designed and successfully synthesized by the modification and optimization of a previously reported 2,4-thiazolidinedione derivative 28. Using an efficient cloning and transfection in human embryonic kidney HEK-293T cells, BAG3 was collected and purified by chromatographic techniques such as IMAC and SEC, respectively. Subsequently, through Surface Plasmon Resonance (SPR) all the compounds were evaluated for their binding ability to BAG3, highlighting the compound FB49 as the one having the greatest affinity for the protein (Kd = 45 ± 6 μM) also against the reference compound 28. Further analysis carried out by Saturation Transfer Difference (STD) Nuclear Magnetic Resonance (NMR) spectroscopy further confirmed the highest affinity of FB49 for the protein. In vitro biological investigation showed that compound FB49 is endowed with an antiproliferative activity in the micromolar range in three human tumoral cell lines and more importantly is devoid of toxicity in human peripheral mononuclear cell deriving from healthy donors. Moreover, FB49 was able to block cell cycle in G1 phase and to induce apoptosis as well as autophagy in medulloblastoma HD-MB03 treated cells. In addition, FB49 demonstrated a synergistic effect when combined with a chemotherapy cocktail of Vincristine, Etoposide, Cisplatin, Cyclophosphamide (VECC). In conclusion we have demonstrated that FB49 is a new derivative able to bind human BAG3 with high affinity and could be used as BAG3 modulator in cancers correlated with overexpression of this protein.

The oomycete-specific BAG subfamily maintains protein homeostasis and promotes pathogenicity in an atypical HSP70-independent manner

Protein homeostasis is vital for organisms and requires chaperones like the conserved Bcl-2-associated athanogene (BAG) co-chaperones that bind to the heat shock protein 70 (HSP70) through their C-terminal BAG domain (BD). Here, we show an unconventional BAG subfamily exclusively found in oomycetes. Oomycete BAGs feature an atypical N-terminal BD with a short and oomycete-specific α1 helix (α1'), plus a C-terminal small heat shock protein (sHSP) domain. In oomycete pathogen Phytophthora sojae, both BD-α1' and sHSP domains are required for P. sojae BAG (PsBAG) function in cyst germination, pathogenicity, and unfolded protein response assisting in 26S proteasome-mediated degradation of misfolded proteins. PsBAGs form homo- and heterodimers through their unique BD-α1' to function properly, with no recruitment of HSP70s to form the common BAG-HSP70 complex found in other eukaryotes. Our study highlights an oomycete-exclusive protein homeostasis mechanism mediated by atypical BAGs, which provides a potential target for oomycete disease control.

Identification of an Imidazopyridine-based Compound as an Oral Selective Estrogen Receptor Degrader for Breast Cancer Therapy

The pro-oncogenic activities of estrogen receptor alpha (ERα) drive breast cancer pathogenesis. Endocrine therapies that impair the production of estrogen or the action of the ERα are therefore used to prevent primary disease metastasis. Although recent successes with ERα degraders have been reported, there is still the need to develop further ERα antagonists with additional properties for breast cancer therapy. We have previously described a benzothiazole compound A4B17 that inhibits the proliferation of androgen receptor-positive prostate cancer cells by disrupting the interaction of the cochaperone BAG1 with the AR. A4B17 was also found to inhibit the proliferation of estrogen receptor-positive (ER+) breast cancer cells. Using a scaffold hopping approach, we report here a group of small molecules with imidazopyridine scaffolds that are more potent and efficacious than A4B17. The prototype molecule X15695 efficiently degraded ERα and attenuated estrogen-mediated target gene expression as well as transactivation by the AR. X15695 also disrupted key cellular protein-protein interactions such as BAG1-mortalin (GRP75) interaction as well as wild-type p53-mortalin or mutant p53-BAG2 interactions. These activities together reactivated p53 and resulted in cell-cycle block and the induction of apoptosis. When administered orally to in vivo tumor xenograft models, X15695 potently inhibited the growth of breast tumor cells but less efficiently the growth of prostate tumor cells. We therefore identify X15695 as an oral selective ER degrader and propose further development of this compound for therapy of ER+ breast cancers.

Significance

An imidazopyridine that selectively degrades ERα and is orally bioavailable has been identified for the development of ER+ breast cancer therapeutics. This compound also activates wild-type p53 and disrupts the gain-of-function tumorigenic activity of mutant p53, resulting in cell-cycle arrest and the induction of apoptosis.

A novel link between silent information regulator 1 and autophagy in cerebral ischemia-reperfusion

Cerebral ischemia is one of the leading causes of death and disability worldwide. Although revascularization via reperfusion combined with advanced anticoagulant therapy is currently a gold standard treatment for patients, the reperfusion itself also results in a serious dysfunction termed cerebral ischemia-reperfusion (I/R) injury. Silent information regulator 1 (sirtuin 1, SIRT1), is a classic NAD⁺-dependent deacetylase, which has been proposed as an important mediator in the alleviation of cerebral ischemia through modulating multiple physiological processes, including apoptosis, inflammation, DNA repair, oxidative stress, and autophagy. Recent growing evidence suggests that SIRT1-mediated autophagy plays a key role in the pathophysiological process of cerebral I/R injury. SIRT1 could both activate and inhibit the autophagy process by mediating different autophagy pathways, such as the SIRT1-FOXOs pathway, SIRT1-AMPK pathway, and SIRT1-p53 pathway. However, the autophagic roles of SIRT1 in cerebral I/R injury have not been systematically summarized. Here, in this review, we will first introduce the molecular mechanisms and effects of SIRT1 in cerebral ischemia and I/R injury. Next, we will discuss the involvement of autophagy in the pathogenesis of cerebral I/R injury. Finally, we will summarize the latest advances in the interaction between SIRT1 and autophagy in cerebral I/R injury. A good understanding of these relationships would serve to consolidate a framework of mechanisms underlying SIRT1's neuroprotective effects and provides evidence for the development of drugs targeting SIRT1.

Protein Quality Control in Glioblastoma: A Review of the Current Literature with New Perspectives on Therapeutic Targets

Protein quality control allows eukaryotes to maintain proteostasis under the stress of constantly changing conditions. In this review, we discuss the current literature on PQC, highlighting flaws that must exist for malignancy to occur. At the nidus of PQC, the expression of BAG1-6 reflects the cell environment; each isoform directs proteins toward different, parallel branches of the quality control cascade. The sum of these branches creates a net shift toward either homeostasis or apoptosis. With an established role in ALP, Bag3 is necessary for cell survival in stress conditions including those of the cancerous niche (i.e., hypoxia, hypermutation). Evidence suggests that excessive Bag3–HSP70 activity not only sustains, but also propagates cancers. Its role is anti-apoptotic—which allows malignant cells to persist—and intercellular—with the production of infectious ‘oncosomes’ enabling cancer expansion and recurrence. While Bag3 has been identified as a key prognostic indicator in several cancer types, its investigation is limited regarding glioblastoma. The cochaperone HSP70 has been strongly linked with GBM, while ALP inhibitors have been shown to improve GBM susceptibility to chemotherapeutics. Given the highly resilient, frequently recurrent nature of GBM, the targeting of Bag3 is a necessary consideration for the successful and definitive treatment of GBM.

Unraveling the mystery: How bad is BAG3 in hematological malignancies?

BAG3, also known as BIS and CAIR-1, interacts with Hsp70 via its BAG domain and with other molecules through its WW domain, PXXP repeats and IPV motifs. BAG3 can participate in major cellular pathways including apoptosis, autophagy, cytoskeleton structure, and motility by regulating the expression, location, and activity of its chaperone proteins. As a multifunctional protein, BAG3 is highly expressed in skeletal muscle, cardiomyocytes and multiple tumors, and its intracellular expression can be stimulated by stress. The functions and mechanisms of BAG3 in hematological malignancies have recently been a topic of interest. BAG3 has been confirmed to be involved in the development and chemoresistance of hematological malignancies and to act as a prognostic indicator. Modulation of BAG3 and its corresponding proteins has thus emerged as a promising therapeutic and experimental target. In this review, we consider the characteristics of BAG3 in hematological malignancies as a reference for further clinical and fundamental investigations.

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.

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.

HSPA6 is Correlated With the Malignant Progression and Immune Microenvironment of Gliomas

Gliomas are primary intracranial space lesions with a high mortality rate. Current treatments for glioma are very limited. Recently, immunotargeted therapy of the glioma microenvironment has been developed. Members of the 70 kDa heat shock protein (HSP70) family are involved in the development of many tumors and immunity. HSPA6 protein belongs to the HSP70 family; However, the biological function of this protein in gliomas has yet to be evaluated. In the present study, a range of analyses, involving protein networks, survival, clinical correlation, and function, revealed that the expression of HSPA6 was negatively correlated with clinical prognosis and closely associated with immunity, invasion, and angiogenesis. Quantitative protein analysis confirmed that HSPA6 was expressed at high levels in patients with glioblastoma. Vitro experiments further verified that HSPA6 enhanced the malignant progression of glioma cells by promoting proliferation, invasion and anti-apoptosis. We also found that HSPA6 was closely correlated with genomic variations and tumor microenvironment. Collectively, we demonstrated that HSPA6 may represent a new therapeutic target to improve the prognosis of patients with gliomas.

Neurodegenerative Disease-Associated TDP-43 Fragments Are Extracellularly Secreted with CASA Complex Proteins

Extracellular vesicles (EVs) play a central role in neurodegenerative diseases (NDs) since they may either spread the pathology or contribute to the intracellular protein quality control (PQC) system for the cellular clearance of NDs-associated proteins. Here, we investigated the crosstalk between large (LVs) and small (SVs) EVs and PQC in the disposal of TDP-43 and its FTLD and ALS-associated C-terminal fragments (TDP-35 and TDP-25). By taking advantage of neuronal cells (NSC-34 cells), we demonstrated that both EVs types, but particularly LVs, contained TDP-43, TDP-35 and TDP-25. When the PQC system was inhibited, as it occurs in NDs, we found that TDP-35 and TDP-25 secretion via EVs increased. In line with this observation, we specifically detected TDP-35 in EVs derived from plasma of FTLD patients. Moreover, we demonstrated that both neuronal and plasma-derived EVs transported components of the chaperone-assisted selective autophagy (CASA) complex (HSP70, BAG3 and HSPB8). Neuronal EVs also contained the autophagy-related MAP1LC3B-II protein. Notably, we found that, under PQC inhibition, HSPB8, BAG3 and MAP1LC3B-II secretion paralleled that of TDP-43 species. Taken together, our data highlight the role of EVs, particularly of LVs, in the disposal of disease-associated TDP-43 species, and suggest a possible new role for the CASA complex in NDs.

BAG1 down-regulation increases chemo-sensitivity of acute lymphoblastic leukaemia cells

BCL2‐associated athanogene‐1 (BAG1) is a multi‐functional protein that is found deregulated in several solid cancers and in paediatric acute myeloid leukaemia. The investigation of BAG1 isoforms expression and intracellular localization in B‐cell acute lymphoblastic leukaemia (B‐ALL) patient‐derived specimens revealed that BAG1 levels decrease during disease remission, compared to diagnosis, but drastically increase at relapse. In particular, at diagnosis both BAG1‐L and BAG1‐M isoforms are mainly nuclear, while during remission the localization pattern changes, having BAG1‐M almost exclusively in the cytosol indicating its potential cytoprotective role in B‐ALL. In addition, knockdown of BAG1/BAG3 induces cell apoptosis and G1‐phase cell cycle arrest and, more intriguingly, shapes cell response to chemotherapy. BAG1‐depleted cells show an increased sensitivity to the common chemotherapeutic agents, dexamethasone or daunorubicin, and to the BCL2 inhibitor ABT‐737. Moreover, the BAG1 inhibitor Thio‐2 induces a cytotoxic effect on RS4;11 cells both in vitro and in a zebrafish xenograft model and strongly synergizes with pan‐BCL inhibitors. Collectively, these data sustain BAG1 deregulation as a critical event in assuring survival advantage to B‐ALL cells.

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.

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.

Deciphering the selective binding mechanisms of anaplastic lymphoma kinase-derived neuroblastoma tumor neoepitopes to human leukocyte antigen

Neuroblastoma (NB), as a metastatic form of solid tumor, has a high fatality rate found in early childhood. The two anaplastic lymphoma kinase (ALK) neoepitopes nonamer and decamer used in cancer immunotherapy against NB cancer can selectively bind to the human leukocyte antigen (HLA-B*15:01) groove with high affinities, whereas the native self-peptide is unable to interact with the HLA-B*15:01. Here, we performed molecular dynamics (MD) simulations and subsequent molecular mechanics-generalized born surface area (MM-GBSA) binding free energy calculations to explore the selective binding mechanisms of nonamer and decamer to the HLA-B*15:01 against the self-peptide. MD simulations revealed the significant conformational dynamics of the self-peptide in the HLA-B*15:01 groove against the nonamer and decamer. Binding free energy calculations showed that the binding affinities of HLA-B*15:01-neoepitope complexes were followed in the order decamer > nonamer > self-peptide. Detailed analysis of HLA-B*15:01-neoepitope structural complexes showed that compared to the nonamer, the self-peptide tended to move outward to the solvent, whereas the decamer moved deep to the HLA-B*15:01 groove. These different dynamic observations of the ALK neoepitopes can explain the distinct binding affinities of self-peptide, nonamer, and decamer to the HLA-B*15:01. The results may be useful for the design of more selective ALK neoepitopes.

Bcl-2 Associated Athanogene 2 (BAG2) is Associated With Progression and Prognosis of Hepatocellular Carcinoma: A Bioinformatics-Based Analysis

Background: Bcl-2 associated athanogene2 (BAG2) is reported to act as an oncogene or a tumor-suppressor in tumors in a context-dependent way; however, its function in hepatocellular carcinoma (HCC) remains unclear.

Methods: Immunohistochemistry (IHC) staining, cell counting kit-8 (CCK-8) assay, apoptotic assay, cell invasion assay and a set of bioinformatics tools were integrated to analyze the role of BAG2 in hepatocellular carcinoma.

Results: BAG2 was significantly up-regulated in HCC. Prognostic analysis indicated that HCC patients with high expression of BAG2 had significantly shorter overall survival, progression free survival and disease specific survival. Besides, silencing BAG2 in HCC cells impaired cell proliferation, facilitated apoptosis and repressed invasion of the cells. Bioinformatics analysis showed that BAG2 might regulate ribosome biogenesis in HCC.

Conclusion: This study revealed that the up-regulated BAG2 in HCC was associated with a worse prognosis and might favor the progression of the disease.

Co-Chaperone Bag-1 Plays a Role in the Autophagy-Dependent Cell Survival through Beclin 1 Interaction

Expression levels of the major mammalian autophagy regulator Beclin 1 and its interaction with Bcl-2 regulate the switch between autophagic cell survival and apoptotic cell death pathways. However, some of the regulators and the precise mechanisms of these processes still remain elusive. Bag-1 (Bcl-2 associated athanogene-1), a member of BAG family proteins, is a multifunctional pro-survival molecule that possesses critical functions in vital cellular pathways. Herein, we report the role of Bag-1 on Bcl-2/Beclin 1 crosstalk through indirectly interacting with Beclin 1. Pull-down experiments suggested a molecular interaction between Bag-1 and Beclin 1 in breast cancer cell lines. On the other hand, in vitro binding assays showed that Bag-1/Beclin 1 interaction does not occur directly but occurs through a mediator molecule. Bag-1 interaction with p-Beclin 1 (T119), indicator of early autophagy, is increased during nutrient starvation suggesting involvement of Bag-1 in the autophagic regulation. Furthermore, CRISPR/Cas9-mediated Bag-1 knock-out in MCF-7 cells hampered cell survival and proliferation and resulted in decreased levels of total LC3 under starvation. Collectively, we suggest that Bag-1 modulates cell survival/death decision through maintaining macroautophagy as a component of Beclin 1-associated complexes.

Co-Chaperones in Targeting and Delivery of Misfolded Proteins to the 26S Proteasome

Protein homeostasis (proteostasis) is essential for the cell and is maintained by a highly conserved protein quality control (PQC) system, which triages newly synthesized, mislocalized and misfolded proteins. The ubiquitin-proteasome system (UPS), molecular chaperones, and co-chaperones are vital PQC elements that work together to facilitate degradation of misfolded and toxic protein species through the 26S proteasome. However, the underlying mechanisms are complex and remain partly unclear. Here, we provide an overview of the current knowledge on the co-chaperones that directly take part in targeting and delivery of PQC substrates for degradation. While J-domain proteins (JDPs) target substrates for the heat shock protein 70 (HSP70) chaperones, nucleotide-exchange factors (NEFs) deliver HSP70-bound substrates to the proteasome. So far, three NEFs have been established in proteasomal delivery: HSP110 and the ubiquitin-like (UBL) domain proteins BAG-1 and BAG-6, the latter acting as a chaperone itself and carrying its substrates directly to the proteasome. A better understanding of the individual delivery pathways will improve our ability to regulate the triage, and thus regulate the fate of aberrant proteins involved in cell stress and disease, examples of which are given throughout the review.