Thioflavin S (NSC71948) interferes with Bcl-2-associated athanogene (BAG-1)-mediated protein-protein interactions

Thio-2 Inhibits Key Signaling Pathways Required for the Development and Progression of Castration-resistant Prostate Cancer

Therapies that abrogate persistent androgen receptor (AR) signaling in castration-resistant prostate cancer (CRPC) remain an unmet clinical need. The N-terminal domain of the AR that drives transcriptional activity in CRPC remains a challenging therapeutic target. Herein we demonstrate that BCL-2-associated athanogene-1 (BAG-1) mRNA is highly expressed and associates with signaling pathways, including AR signaling, that are implicated in the development and progression of CRPC. In addition, interrogation of geometric and physiochemical properties of the BAG domain of BAG-1 isoforms identifies it to be a tractable but challenging drug target. Furthermore, through BAG-1 isoform mouse knockout studies, we confirm that BAG-1 isoforms regulate hormone physiology and that therapies targeting the BAG domain will be associated with limited "on-target" toxicity. Importantly, the postulated inhibitor of BAG-1 isoforms, Thio-2, suppressed AR signaling and other important pathways implicated in the development and progression of CRPC to reduce the growth of treatment-resistant prostate cancer cell lines and patient-derived models. However, the mechanism by which Thio-2 elicits the observed phenotype needs further elucidation as the genomic abrogation of BAG-1 isoforms was unable to recapitulate the Thio-2-mediated phenotype. Overall, these data support the interrogation of related compounds with improved drug-like properties as a novel therapeutic approach in CRPC, and further highlight the clinical potential of treatments that block persistent AR signaling which are currently undergoing clinical evaluation in CRPC.

BAG1, MGMT, FOXO1, and DNAJA1 as potential drug targets for radiosensitizing cancer cell lines

BACKGROUND AND PURPOSE

Activation of some signaling pathways can promote cell survival and have a negative impact on tumor response to radiotherapy. Here, the role of differences in expression levels of genes related to the poly(ADP-ribose) polymerase-1 (PARP-1), heat shock protein 90 (Hsp90), B-cell lymphoma 2 (Bcl-2), and phosphoinositide 3-kinase (PI3K) pathways in the survival or death of cells following X-ray exposure was investigated.

METHODS

Eight human cell cultures (MCF-7 and MDA-MB-231: breast cancers; MCF-12A: apparently normal breast; A549: lung cancer; L132: normal lung; G28, G44 and G112: glial cancers) were irradiated with X-rays. The colony-forming and real-time PCR based on a custom human pathway RT² Profiler PCR Array assays were used to evaluate cell survival and gene expression, respectively.

RESULTS

The surviving fractions at 2 Gy for the cell lines, in order of increasing radioresistance, were found to be as follows: MCF-7 (0.200 ± 0.011), G44 (0.277 ± 0.065), L132 (0.367 ± 0.023), MDA-MB-231 (0.391 ± 0.057), G112 (0.397 ± 0.113), A549 (0.490 ± 0.048), MCF-12A (0.526 ± 0.004), and G28 (0.633 ± 0.094). The rank order of radioresistance at 6 Gy was: MCF-7 < L132 < G44 < MDA-MB-231 < A549 < G28 < G112 < MCF-12A. PCR array data analysis revealed that several genes were differentially expressed between irradiated and unirradiated cell cultures. The following genes, with fold changes: BCL2A1 (21.91), TP53 (8743.75), RAD51 (11.66), FOX1 (65.86), TCP1 (141.32), DNAJB1 (3283.64), RAD51 (51.52), and HSPE1 (12887.29) were highly overexpressed, and BAX (-127.21), FOX1 (-81.79), PDPK1 (-1241.78), BRCA1 (-8.70), MLH1 (-12143.95), BCL2 (-18.69), CCND1 (-46475.98), and GJA1 (-2832.70) were highly underexpressed in the MDA-MB-231, MCF-7, MCF-12A, A549, L132, G28, G44, and G112 cell lines, respectively. The radioresistance in the malignant A549 and G28 cells was linked to upregulation in the apoptotic, DNA repair, PI3K, and Hsp90 pathway genes BAG1, MGMT, FOXO1, and DNAJA1, respectively, and inhibition of these genes resulted in significant radiosensitization.

CONCLUSIONS

Targeting BAG1, MGMT, FOXO1, and DNAJA1 with specific inhibitors might effectively sensitize radioresistant tumors to radiotherapy.

Interactome analysis of Bag-1 isoforms reveals novel interaction partners in endoplasmic reticulum-associated degradation

Bag-1 is a multifunctional protein that regulates Hsp70 chaperone activity, apoptosis, and proliferation. The three major Bag-1 isoforms have different subcellular localizations and partly non-overlapping functions. To identify the detailed interaction network of each isoform, we utilized mass spectrometry-based proteomics and found that interactomes of Bag-1 isoforms contained many common proteins, with variations in their abundances. Bag-1 interactomes were enriched with proteins involved in protein processing and degradation pathways. Novel interaction partners included VCP/p97; a transitional ER ATPase, Rad23B; a shuttling factor for ubiquitinated proteins, proteasome components, and ER-resident proteins, suggesting a role for Bag-1 also in ER-associated protein degradation (ERAD). Bag-1 pull-down from cells and tissues from breast cancer patients validated these interactions and showed cancer-related prominence. Using in silico predictions we detected hotspot residues of Bag-1. Mutations of these residues caused loss of binding to protein quality control elements and impaired proteasomal activity in MCF-7 cells. Following CD147 glycosylation pattern, we showed that Bag-1 downregulated VCP/p97-dependent ERAD. Overall, our data extends the interaction map of Bag-1, and broadens its role in protein homeostasis. Targeting the interaction surfaces revealed in this study might be an effective strategy in the treatment of cancer.

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.

Advancement in Pharmacological Activities of Benzothiazole and its Derivatives: An Up to Date Review

Benzothiazole is a heterocyclic aromatic and bicyclic compound in which, benzene ring is attached with thiazole ring. This nucleus is established in marine as well as terrestrial natural compounds. The benzothiazole skeleton is established in a broad variety of bioactive heterocycles and natural products. The benzothiazole nucleus is considered as the principle moiety in several biologically active compounds. Over the decade, chemists are paying more attention towards the revision of the biological and therapeutic activities such as antimicrobial, analgesic, antiinflammatory, antitubercular, antiviral and antioxidant of benzothiazole containing compounds. The molecular structures of a number of potent drugs including Frentizole, Pramipexole, Thioflavin T and Riluzole etc., are based on benzothiazole skeleton. The present work is the compilation and presentation of all available information in a systematic manner with an aim to present the findings in a way, which may be beneficial for future research.

A BAG's life: Every connection matters in cancer

The members of the BCL-2 associated athanogene (BAG) family participate in the regulation of a variety of interrelated physiological processes, such as autophagy, apoptosis, and protein homeostasis. Under normal circumstances, the six BAG members described in mammals (BAG1-6) principally assist the 70 kDa heat-shock protein (HSP70) in protein folding; however, their role as oncogenes is becoming increasingly evident. Deregulation of the BAG multigene family has been associated with cell transformation, tumor recurrence, and drug resistance. In addition to BAG overexpression, BAG members are also involved in many oncogenic protein-protein interactions (PPIs). As such, either the inhibition of overloading BAGs or of specific BAG-client protein interactions could have paramount therapeutic value. In this review, we will examine the role of each BAG family member in different malignancies, focusing on their modular structure, which enables interaction with a variety of proteins to exert their pro-tumorigenic role. Lastly, critical remarks on the unmet needs for proposing effective BAG inhibitors will be pointed out.

Over-expression of Bcl2-associated athanogene 2 in oral cancer promotes cellular proliferation and is associated with poor prognosis

OBJECTIVE

The aim of the present study was to state the role of BAG2 in oral squamous cell carcinomas (OSCC).

DESIGN

Expression data of BAG2 in OSCC tissues were extracted from Oncomine and TCGA database. Expression levels of BAG2 mRNA and protein were examined by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot assay. The Kaplan-Meier method was conducted to evaluate the overall survival of OSCC patients. Small interfering RNAs (siRNAs) strategy was used to confirm the effect of BAG2 expression on proliferative, invasive, migrated capacities of OSCC cells by Cell Counting kit-8 (CCK-8), colon formation assay, wound healing and transwell assay.

RESULTS

Our results showed that BAG2 expression was up-regulated in oral squamous cell carcinomas tissues. Compared with OSCC patients with low BAG2 expression, poorer overall survival rate was found in OSCC patients with high BAG2 expression. Furthermore, proliferation, invasion and migration of HO-1-N-1 cells were significantly inhibited because of the knockdown of BAG2. Transfection of si-BAG2 has no impacts on proliferation in HNOEC cells. Inhibition of BAG2 downregulated the expression of relevant proteins, such as proliferating cell nuclear antigen (PCNA), c-Myc, matrix metalloproteinase-2 (MMP-2) and Vimentin. Additionally, the expression levels of the important protein phosphorylation (p-ERK1/2 and p-MEK) in mitogen-activated protein kinase (MAPK) pathway were reduced in HO-1-N-1 cells transfected with si-BAG2.

CONCLUSIONS

High-regulated BAG2 is related to poor prognosis and could promote proliferation, invasion and migration of OSCC cells by activating the MAPK signaling pathway. Thus, BAG2 may be a potential target for OSCC therapy.

Choose and Use Your Chemical Probe Wisely to Explore Cancer Biology

Small-molecule chemical probes or tools have become progressively more important in recent years as valuable reagents to investigate fundamental biological mechanisms and processes causing disease, including cancer. Chemical probes have also achieved greater prominence alongside complementary biological reagents for target validation in drug discovery. However, there is evidence of widespread continuing misuse and promulgation of poor-quality and insufficiently selective chemical probes, perpetuating a worrisome and misleading pollution of the scientific literature. We discuss current challenges with the selection and use of chemical probes, and suggest how biologists can and should be more discriminating in the probes they employ.

BAG-1 as a biomarker in early breast cancer prognosis: a systematic review with meta-analyses

BACKGROUND

The co-chaperone protein Bcl-2-associated athanogene-1 (BAG-1) is overexpressed in breast cancer and has been incorporated in the oncotype DX and PAM50 breast cancer prognostic assays. Bcl-2-associated athanogene-1 exists as multiple protein isoforms that interact with diverse partners, including chaperones Hsc70/Hsp70, Ser/Thr kinase Raf-1 and Bcl-2, to promote cancer cell survival. The BAG-1L isoform specifically binds to and increases the transcriptional activity of oestrogen receptor in cells, and in some, but not all studies, BAG-1 expression is predictive of clinical outcome in breast cancer.

METHODS

A systematic review of published studies reporting BAG-1 (mRNA and/or protein) expression and clinical outcome in early breast cancer. The REporting Recommendations for Tumour MARKer and Prognostic Studies (REMARK) criteria were used as a template against which data were assessed. Meta-analyses were performed for studies that provided a hazard ratio and 95% confidence intervals for clinical outcomes including disease-free survival or breast cancer-specific survival from univariate analysis.

RESULTS

Eighteen studies used differing methodologies and reported on differing outcomes. Meta-analyses were only possible on results from a subset of reported studies. Meta-analyses suggested improved outcome with high BAG-1 mRNA and high BAG-1 nuclear expression by immunohistochemisty.

CONCLUSIONS

Increased levels of BAG-1 are associated with better breast cancer outcomes.

A combination of trastuzumab and BAG-1 inhibition synergistically targets HER2 positive breast cancer cells

Treatment of HER2+ breast cancer with trastuzumab is effective and combination anti-HER2 therapies have demonstrated benefit over monotherapy in the neoadjuvant and metastatic settings. This study investigated the therapeutic potential of targeting the BAG-1 protein co-chaperone in trastuzumab-responsive or -resistant cells. In the METABRIC dataset, BAG-1 mRNA was significantly elevated in HER2+ breast tumors and predicted overall survival in a multivariate analysis (HR = 0.81; p = 0.022). In a breast cell line panel, BAG-1 protein was increased in HER2+ cells and was required for optimal growth as shown by siRNA knockdown. Overexpression of BAG-1S in HER2+ SKBR3 cells blocked growth inhibition by trastuzumab, whereas overexpression of a mutant BAG-1S protein (BAG-1S H3AB), defective in binding HSC70, potentiated the effect of trastuzumab. Injection of a Tet-On SKBR3 clone, induced to overexpress myc-BAG-1S into the mammary fat pads of immunocompromised mice, resulted in 2-fold larger tumors compared to uninduced controls. Induction of myc-BAG-1S expression in two Tet-On SKBR3 clones attenuated growth inhibition by trastuzumab in vitro. Targeting endogenous BAG-1 by siRNA enhanced growth inhibition of SKBR3 and BT474 cells by trastuzumab, while BAG-1 protein-protein interaction inhibitor (Thio-S or Thio-2) plus trastuzumab combination treatment synergistically attenuated growth. In BT474 cells this reduced protein synthesis, caused G1/S cell cycle arrest and targeted the ERK and AKT signaling pathways. In a SKBR3 subpopulation with acquired resistance to trastuzumab BAG-1 targeting remained effective and either Thio-2 or BAG-1 siRNA reduced growth more compared to trastuzumab-responsive parental cells. In summary, targeting BAG-1 function in combination with anti-HER2 therapy might prove beneficial.

Regulation of osteoblast development by Bcl-2-associated athanogene-1 (BAG-1)

BCL-2-associated athanogene-1 (BAG-1) is expressed by osteoblast-lineage cells; early embryonic lethality in Bag-1 null mice, however, has limited the investigation of BAG-1 function in osteoblast development. In the present study, bone morphogenetic protein-2/BMP-2-directed osteogenic differentiation of bone marrow stromal cells (BMSCs) of Bag-1^+/− (heterozygous) female mice was decreased significantly. Genes crucial for osteogenic differentiation, bone matrix formation and mineralisation were expressed at significantly lower levels in cultures of Bag-1^+/− BMSCs supplemented with BMP-2, while genes with roles in inhibition of BMP-2-directed osteoblastogenesis were significantly upregulated. 17-β-estradiol (E2) enhanced responsiveness of BMSCs of wild-type and Bag-1^+/− mice to BMP-2, and promoted robust BMP-2-stimulated osteogenic differentiation of BMSCs. BAG-1 can modulate cellular responses to E2 by regulating the establishment of functional estrogen receptors (ERs), crucially, via its interaction with heat shock proteins (HSC70/HSP70). Inhibition of BAG-1 binding to HSC70 by the small-molecule chemical inhibitor, Thioflavin-S, and a short peptide derived from the C-terminal BAG domain, which mediates binding with the ATPase domain of HSC70, resulted in significant downregulation of E2/ER-facilitated BMP-2-directed osteogenic differentiation of BMSCs. These studies demonstrate for the first time the significance of BAG-1-mediated protein-protein interactions, specifically, BAG-1-regulated activation of ER by HSC70, in modulation of E2-facilitated BMP-2-directed osteoblast development.

The Bag-1 inhibitor, Thio-2, reverses an atypical 3D morphology driven by Bag-1L overexpression in a MCF-10A model of ductal carcinoma in situ

Mammary MCF-10A cells seeded on reconstituted basement membrane form spherical structures with a hollow central lumen, termed acini, which are a physiologically relevant model of mammary morphogenesis. Bcl-2-associated athanogene 1 (Bag-1) is a multifunctional protein overexpressed in breast cancer and ductal carcinoma in situ. When present in the nucleus Bag-1 is predictive of clinical outcome in breast cancer. Bag-1 exists as three main isoforms, which are produced by alternative translation initiation from a single mRNA. The long isoform of Bag-1, Bag-1L, contains a nuclear localisation sequence not present in the other isoforms. When present in the nucleus Bag-1L, but not the other Bag-1 isoforms, can interact with and modulate the activities of estrogen-, androgen- and vitamin D-receptors. Overexpression of Bag-1 mRNA in MCF-10A is known to produce acini with luminal filling reminiscent of ductal carcinoma in situ. As this mRNA predominantly overexpresses the short isoform of Bag-1, Bag-1S, we set out to examine whether the nuclear Bag-1L isoform is sufficient to drive premalignant change by developing a Bag-1L-overexpressing MCF-10A model. Two clones differentially overexpressing Bag-1L were grown in two-dimensional (2D) and three-dimensional (3D) cultures and compared with an established model of HER2-driven transformation. In 2D cultures, Bag-1L overexpression reduced proliferation but did not affect growth factor responsiveness or clonogenicity. Acini formed by Bag-1L-overexpressing cells exhibited reduced luminal clearing when compared with controls. An abnormal branching morphology was also observed which correlated with the level of Bag-1L overexpression, suggesting further malignant change. Treatment with Thio-2, a small-molecule inhibitor of Bag-1, reduced the level of branching. In summary, 3D cultures of MCF-10A mammary epithelial cells overexpressing Bag-1L demonstrate a premalignant phenotype with features of ductal carcinoma in situ. Using this model to test the small-molecule Bag-1 inhibitor, Thio-2, reveals its potential to reverse the atypical branched morphology of acini that characterizes this premalignant change.

Bag-1 promotes cell survival through c-Myc-mediated ODC upregulation that is not preferred under apoptotic stimuli in MCF-7 cells

Bag-1, Bcl-2 associated athanogene-1, is a multifunctional protein that can regulate a wide variety of cellular processes: proliferation, cell survival, transcription, apoptosis and motility. Bag-1 interacts with various targets in the modulation of these pathways; yet molecular details of Bag-1's involvement in each cellular event are still unclear. We first showed that forced Bag-1 expression promotes cell survival and prevents drug-induced apoptosis in MCF-7 breast cancer cells. Increased mRNA expressions of c-myc protooncogene and ornithine decarboxylase (ODC), biosynthetic enzyme of polyamines, were detected in Bag-1L+ cells, and western blots against the protein product of c-Myc and ODC confirmed these findings. Once ODC, a c-Myc target, gets activated, polyamine biosynthesis increases. We observed enhanced polyamine content in the Bag-1L+ cells. On the contrary, when polyamine catabolic mechanisms were investigated, Bag-1 silencing suppressed biosynthesis of polyamines because of the downregulation of ODC and upregulation of PAO. Exposure of cells to apoptotic inducers enhances the cell death mechanism by producing toxic products such as H2 O2 and aldehydes. Bag-1L+ cells prevented drug-induced PAO activation leading to a decrease in H2 O2 production following cisplatin or paclitaxel treatment. In this line, our results suggested that Bag-1 indirectly affects cell survival through c-Myc activated signalling that causes elevation of ODC levels, leading to an increase of the polyamine content.

Targeting Proteasomal Degradation of Soluble, Misfolded Proteins

This chapter deals with small molecule modulators of the ubiquitin–proteasome system (UPS). They are designed to restore its impaired capacity to dispose of soluble, dysfunctional protein copies, and to fight its pathological impairment in proteinopathies in general and in tauopathies in particular. Two specific molecular targets belonging to the U-box E3 ligase family (C-terminus of Hsc70 interacting protein, CHIP) and to the proteasome-associated cysteine protease DUB family (USP14) are selected for their putative role against NDDs and tauopathies. The limited available structural information for the two targets, and for their interactions with members of UPS-driven protein complexes, is described. A small number of known modulators for each target (or even for structurally related targets, possibly to provide translatable examples) are portrayed in terms of their biological profile, and of their development potential as disease-modifying drugs against NDDs.

Targeting BAG-1: a novel strategy to increase drug efficacy in acute myeloid leukemia

Overexpression of antiapoptotic proteins occurs frequently in cancer, resulting in defective apoptosis that may contribute to a poor chemosensitivity of tumor cells. B-cell lymphoma (BCL) 2-associated AthanoGene-1 (BAG-1) is a prosurvival chaperone recently found involved in the maintenance of acute myeloid leukemia (AML) cells survival in vitro. Here we reported BAG-1 upregulation in 87 of 99 analyzed AML patients with respect to healthy control samples applying reverse phase protein assay. Silencing of BAG-1 expression confirmed a decreased BCL-2 protein level but, in addition, provoked the increased transcription of GADD34 stress sensor. Furthermore, a dephosphorylation of eIF2α, as well as alteration of expression of IRE-1 and CHOP proteins, were documented, suggesting that a disruption of the endoplasmic reticulum stress/unfolded protein response was provoked by downregulation of BAG-1. A similar phenomenon was triggered after addition of Thioflavin S, which was shown to block BAG-1/BCL-2 interaction and to increase cell death, enforcing a prosurvival role of the BAG-1 protein in AML. Interestingly, synergic cytotoxic effects of doxorubicin, VP16 drugs, and ABT-737 compound were observed when Thioflavin S was coupled with these drugs. Taken together, our results gave further proof that upregulation of BAG-1 plays a critical role in AML and that BAG-1 targeting might be considered for a combined therapeutic strategy with conventional chemotherapy drugs in the treatment of AML patients.

Isolation of a novel thioflavin S-derived compound that inhibits BAG-1-mediated protein interactions and targets BRAF inhibitor-resistant cell lines

Protein-protein interactions mediated through the C-terminal Bcl-2-associated athanogene (BAG) domain of BAG-1 are critical for cell survival and proliferation. Thioflavin S (NSC71948)-a mixture of compounds resulting from the methylation and sulfonation of primulin base-has been shown to dose-dependently inhibit the interaction between BAG-1 and Hsc70 in vitro. In human breast cancer cell lines, with high BAG-1 expression levels, Thioflavin S reduces the binding of BAG-1 to Hsc70, Hsp70, or CRAF and decreases proliferation and viability. Here, we report the development of a protocol for the purification and isolation of biologically active constituents of Thioflavin S and the characterization of the novel compound Thio-2. Thio-2 blocked the growth of several transformed cell lines, but had much weaker effects on untransformed cells. Thio-2 also inhibited the proliferation of melanoma cell lines that had become resistant to treatment with PLX4032, an inhibitor of mutant BRAF. In transformed cells, Thio-2 interfered with intracellular signaling at the level of RAF, but had no effect on the activation of AKT. Thio-2 decreased binding of BAG-1 to Hsc70 and to a lesser extent BRAF in vitro and in vivo, suggesting a possible mechanism of action. Given that tumors frequently develop resistance to kinase inhibitors during treatment, Thio-2 and related compounds may offer promising alternative strategies to currently available therapies.

Hsp70 protein complexes as drug targets

Heat shock protein 70 (Hsp70) plays critical roles in proteostasis and is an emerging target for multiple diseases. However, competitive inhibition of the enzymatic activity of Hsp70 has proven challenging and, in some cases, may not be the most productive way to redirect Hsp70 function. Another approach is to inhibit Hsp70's interactions with important co-chaperones, such as J proteins, nucleotide exchange factors (NEFs) and tetratricopeptide repeat (TPR) domain-containing proteins. These co-chaperones normally bind Hsp70 and guide its many diverse cellular activities. Complexes between Hsp70 and co-chaperones have been shown to have specific functions, including roles in pro-folding, pro-degradation and pro-trafficking pathways. Thus, a promising strategy may be to block protein- protein interactions between Hsp70 and its co-chaperones or to target allosteric sites that disrupt these contacts. Such an approach might shift the balance of Hsp70 complexes and re-shape the proteome and it has the potential to restore healthy proteostasis. In this review, we discuss specific challenges and opportunities related to these goals. By pursuing Hsp70 complexes as drug targets, we might not only develop new leads for therapeutic development, but also discover new chemical probes for use in understanding Hsp70 biology.

BAG-1 suppresses expression of the key regulatory cytokine transforming growth factor β (TGF-β1) in colorectal tumour cells

As colorectal cancer remains the second highest cause of cancer-related deaths in much of the industrialised world, identifying novel strategies to prevent colorectal tumour development remains an important challenge. BAG-1 is a multi-functional protein, the expression of which is up-regulated at relatively early stages in colorectal tumorigenesis. Importantly, BAG-1 is thought to enhance colorectal tumour progression through promoting tumour cell survival. Here we report for the first time a novel role for BAG-1, establishing it as a suppressor of transforming growth factor beta [TGF-β1] expression in colorectal tumour cells. Microarray analysis first highlighted the possibility that BAG-1 may regulate TGF-β1 expression, a key cytokine in normal colonic tissue homeostasis. Q-RT-PCR and ELISA demonstrated TGFB1 mRNA and protein expression to be significantly increased when BAG1 levels were reduced by siRNA; additionally, induction of BAG-1L caused suppression of TGFB1 mRNA in colorectal tumour cells. Using reporter and ChIP assays, a direct association of BAG-1 with the TGFB1 gene regulatory region was identified. Immunohistochemistry and Weiser fraction data indicated levels of BAG-1 and TGF-β1 are inversely correlated in the normal colonic epithelium in vivo, consistent with a role for BAG-1-mediated repression of TGF-β1 production. In vitro studies showed that the change in TGF-β1 production following manipulation of BAG-1 is functionally relevant; through induction of anchorage-independent growth in TGF-β1 dependent NRK fibroblasts and regulation of SMAD2 phosphorylation in TGF-β1 sensitive adenoma cells. Taken together, this study identifies the anti-apoptotic protein BAG-1 as a suppressor of the inhibitory growth factor TGF-β1, suggesting that high expression of BAG-1 can impact on a number of the hallmarks of cancer, of potential importance in promoting the early stages of colorectal tumorigenesis. Establishing BAG-1 as a repressor of TGF-β1 has important biological implications, and highlights a new role for BAG-1 in colorectal tumorigenesis.

Functional amyloid formation by Streptococcus mutans

Dental caries is a common infectious disease associated with acidogenic and aciduric bacteria, including Streptococcus mutans. Organisms that cause cavities form recalcitrant biofilms, generate acids from dietary sugars and tolerate acid end products. It has recently been recognized that micro-organisms can produce functional amyloids that are integral to biofilm development. We now show that the S. mutans cell-surface-localized adhesin P1 (antigen I/II, PAc) is an amyloid-forming protein. This conclusion is based on the defining properties of amyloids, including binding by the amyloidophilic dyes Congo red (CR) and Thioflavin T (ThT), visualization of amyloid fibres by transmission electron microscopy and the green birefringent properties of CR-stained protein aggregates when viewed under cross-polarized light. We provide evidence that amyloid is present in human dental plaque and is produced by both laboratory strains and clinical isolates of S. mutans. We provide further evidence that amyloid formation is not limited to P1, since bacterial colonies without this adhesin demonstrate residual green birefringence. However, S. mutans lacking sortase, the transpeptidase enzyme that mediates the covalent linkage of its substrates to the cell-wall peptidoglycan, including P1 and five other proteins, is not birefringent when stained with CR and does not form biofilms. Biofilm formation is inhibited when S. mutans is cultured in the presence of known inhibitors of amyloid fibrillization, including CR, Thioflavin S and epigallocatechin-3-gallate, which also inhibited ThT uptake by S. mutans extracellular proteins. Taken together, these results indicate that S. mutans is an amyloid-forming organism and suggest that amyloidogenesis contributes to biofilm formation by this oral microbe.

The retinoblastoma protein (Rb) as an anti-apoptotic factor: expression of Rb is required for the anti-apoptotic function of BAG-1 protein in colorectal tumour cells

Although the retinoblastoma-susceptibility gene RB1 is inactivated in a wide range of human tumours, in colorectal cancer, the retinoblastoma protein (Rb) function is often preserved and the RB locus even amplified. Importantly, we have previously shown that Rb interacts with the anti-apoptotic Bcl-2 associated athanogene 1 (BAG-1) protein, which is highly expressed in colorectal carcinogenesis. Here we show for the first time that Rb expression is critical for BAG-1 anti-apoptotic activity in colorectal tumour cells. We demonstrate that Rb expression not only increases the nuclear localisation of the anti-apoptotic BAG-1 protein, but that expression of Rb is required for inhibition of apoptosis by BAG-1 both in a γ-irradiated Saos-2 osteosarcoma cell line and colorectal adenoma and carcinoma cell lines. Further, consistent with the fact that nuclear BAG-1 has previously been shown to promote cell survival through increasing nuclear factor (NF)-κB activity, we demonstrate that the ability of BAG-1 to promote NF-κB activity is significantly inhibited by repression of Rb expression. Taken together, data presented suggest a novel function for Rb, promoting cell survival through regulating the function of BAG-1. As BAG-1 is highly expressed in the majority of colorectal tumours, targeting the Rb–BAG-1 complex to promote apoptosis has exciting potential for future therapeutic development.

Optimization of potent hepatitis C virus NS3 helicase inhibitors isolated from the yellow dyes thioflavine S and primuline

A screen for hepatitis C virus (HCV) NS3 helicase inhibitors revealed that the commercial dye thioflavine S was the most potent inhibitor of NS3-catalyzed DNA and RNA unwinding in the 827-compound National Cancer Institute Mechanistic Set. Thioflavine S and the related dye primuline were separated here into their pure components, all of which were oligomers of substituted benzothiazoles. The most potent compound (P4), a benzothiazole tetramer, inhibited unwinding >50% at 2 ± 1 μM, inhibited the subgenomic HCV replicon at 10 μM, and was not toxic at 100 μM. Because P4 also interacted with DNA, more specific analogues were synthesized from the abundant dimeric component of primuline. Some of the 32 analogues prepared retained ability to inhibit HCV helicase but did not appear to interact with DNA. The most potent of these specific helicase inhibitors (compound 17) was active against the replicon and inhibited the helicase more than 50% at 2.6 ± 1 μM.

Inhibition of the single downstream target BAG1 activates the latent apoptotic potential of MYC

Aberrant MYC expression is a common oncogenic event in human cancer. Paradoxically, MYC can either drive cell cycle progression or induce apoptosis. The latent ability of MYC to induce apoptosis has been termed "intrinsic tumor suppressor activity," and reactivating this apoptotic function in tumors is widely considered a valuable therapeutic goal. As a transcription factor, MYC controls the expression of many downstream targets, and for the majority of these, it remains unclear whether or not they play direct roles in MYC function. To identify the subset of genes specifically required for biological activity, we conducted a screen for functionally important MYC targets and identified BAG1, which encodes a prosurvival chaperone protein. Expression of BAG1 is regulated by MYC in both a mouse model of breast cancer and transformed human cells. Remarkably, BAG1 induction is essential for protecting cells from MYC-induced apoptosis. Ultimately, the synthetic lethality we have identified between MYC overexpression and BAG1 inhibition establishes a new pathway that might be exploited to reactivate the latent apoptotic potential of MYC as a cancer therapy.

BAG-1 enhances cell-cell adhesion, reduces proliferation and induces chaperone-independent suppression of hepatocyte growth factor-induced epidermal keratinocyte migration

Cell motility is important in maintaining tissue homeostasis, facilitating epithelial wound repair and in tumour formation and progression. The aim of this study was to determine whether BAG-1 isoforms regulate epidermal cell migration in in vitro models of wound healing. In the human epidermal cell line HaCaT, endogenous BAG-1 is primarily nuclear and increases with confluence. Both transient and stable p36-Bag-1 overexpression resulted in increased cellular cohesion. Stable transfection of either of the three human BAG-1 isoforms p36-Bag-1 (BAG-1S), p46-Bag-1 (BAG-1M) and p50-Bag-1 (BAG-1L) inhibited growth and wound closure in serum-containing medium. However, in response to hepatocyte growth factor (HGF) in serum-free medium, BAG-1S/M reduced communal motility and colony scattering, but BAG-1L did not. In the presence of HGF, p36-Bag-1 transfectants retained proliferative response to HGF with no change in ERK1/2 activation. However, the cells retained E-cadherin localisation at cell-cell junctions and exhibited pronounced cortical actin. Point mutations in the BAG domain showed that BAG-1 inhibition of motility is independent of its function as a chaperone regulator. These findings are the first to suggest that BAG-1 plays a role in regulating cell-cell adhesion and suggest an important function in epidermal cohesion.