Down-regulation of Bcl-2-interacting protein BAG-1 confers resistance to anti-cancer drugs

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.

Pharmacological Effects of Verticine: Current Status

Verticine is the major bioactive constituent of Fritillaria as a kind of Traditional Chinese Medicine. Pharmacological researches have reported various benefits of verticine, including anticancer, anti-inflammatory, protecting against acute lung injury, tracheobronchial relaxation, antitussive, expectorant, sedative, and analgesic activities, in addition to inhibiting proliferation of cultured orbital fibroblast, angiotensin converting enzyme (ACE), and acetylcholinesterase (AChE) and inhibiting hERG potassium channels. The underlying mechanisms of verticine are still under investigation. This review will comprehensively summarize the metabolism, biological activities, and possible mechanism of verticine.

The role of expression and polymorphism of the BAG-1 gene in response to platinum-based chemotherapeutics in NSCLC

We investigated the correlation between BAG-1 expression and sensitivity to platinum-based chemotherapeutics in patients with non-small cell lung cancer (NSCLC). mRNA and protein expression of BAG-1 in lung tissue of NSCLC postoperative patients (I-IIIA stage) or healthy subjects were detected using reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Cox regression analysis was used to quantify the association of prognostic factors with survival in NSCLC patients. Venous blood samples from patients newly diagnosed with advanced NSCLC (IIIB-IV stage) were collected before chemotherapy to analyze allelic frequency and gene polymorphisms. Compared to healthy controls (11.67%, 14 cases), levels of mRNA and protein of BAG-1 in lung tissues was significantly higher in NSCLC patients (61.67%, 74 cases) (χ²=5.601, P<0.05). Moreover, BAG-1 expression was identified as an independent prognostic factor for survival in NSCLC patients. As time to progression and survival rate was dramatically increased, patients with a positive expression of BAG-1 exhibited a prolonged survival period (TTP, 49.3 months; 5-year survival rat, 16.21%) compared with those without BAG-1 expression (χ²=7.243, P<0.05). Two BAG-1 digestion patterns (CC and CT) were identified and confirmed. patients (77.46%) had a C/C genotype at BAG-1 codon 324, while 22.54% had the C/T genotype. The T/T genotype was not present in these patients. The progression risk of patients carrying the C/C genotype at Bag-1 codon 324 was 1.87 times higher than that of patients carrying the C/T genotype (P<0.001). Follow-up examination showed that the chemotherapeutic sensitivity of patients carrying the C/C genotype was 2.852 times higher than that of patients carrying the C/T genotype (95% CI, 1.133-7.182; P=0.026). Significant differences were found in the median progression-free survival (PFS) and overall survival (OS) of these two cohorts of patients. Compared to patients carrying the C/T genotype of BAG-1, patients carrying the C/C genotype at Bag-1 codon 324 exhibited better responses to platinum-based chemotherapy. Hence, the expression of BAG-1 was closely associated with the sensitivity to platinum-based chemotherapeutics in NSCLC patients.

Expression of BAG-1 and PARP-1 in precursor lesions and invasive cervical cancer associated with human papillomavirus (HPV)

Cervical cancer remains persistently the second most common malignancies among women worldwide, responsible for 500,000 new cases annually. Only in Brazil, the estimate is for 18,430 new cases in 2011. Several types of molecular markers have been studied in carcinogenesis including proteins associated with apoptosis such as BAG-1 and PARP-1. This study aims to demonstrate the expression of BAG-1 and PARP-1 in patients with low-grade squamous intraepithelial lesions (LSILs), high-grade squamous intraepithelial lesions (HSILs) and invasive squamous cell carcinomas (SCCs) of the uterine cervix and to verify a possible association with HPV infection. Fifty samples of LSILs, 50 samples of HSILs and 50 samples of invasive SCCs of the uterine cervix were analyzed by immunohistochemistry for BAG-1 and PARP-1 expression. PCR was performed to detect and type HPV DNA. BAG-1 expression levels were significantly different between LSILs and HSILs (p = 0,014) and between LSILs and SCCs (p = 0,014). In regards to PARP-1 expression, we found significant differences between the expression levels in HSILs and SCCs (p = 0,022). No association was found between BAG-1 expression and the presence of HPV. However, a significant association was found between PARP-1 expression and HPV positivity in the HSILs group (p = 0,021). In conclusion our research suggests that BAG-1 expression could contribute to the differentiation between LSIL and HSIL/SCC whereas PARP-1 could be useful to the differentiation between HSIL HPV-related and SCC. Further studies are needed to clarify the molecular aspects of the relationship between PARP-1 expression and HPV infection, with potential applications for cervical cancer prediction.

Co-overexpression of Bag-1 and heat shock protein 70 in human epidermal squamous cell carcinoma: Bag-1-mediated resistance to 5-fluorouracil-induced apoptosis

Background:

The aim was to determine whether Bcl-2-associated athanogene-1 (Bag-1) and/or its binding protein heat shock protein-70 (Hsp70) exhibit deregulated expression in epidermal squamous cell carcinoma (SCC) and whether Bag-1 confers apoptosis resistance.

Method:

Immunohistochemistry for Bag-1 and Hsp70 was performed on 60 epidermal SCC and 10 normal skin samples. The epidermal SCC cell line SCC-13 was treated with 5-fluorouracil (5-FU) after Bag-1 knockdown to determine whether high Bag-1 levels contribute to growth and/or apoptosis resistance.

Results:

Normal epithelium expressed primarily nuclear Bag-1. Most tumours showed reduced nuclear Bag-1 staining, but a subset exhibited strong Bag-1 staining, with cytoplasmic Bag-1 staining intensity correlating with cytoplasmic Hsp70 staining intensity (r_s=0.462; P<0.001) and less differentiation (P<0.001). Bag-1 knockdown resulted in markedly reduced SCC-13 cell yield, increased spontaneous apoptosis and enhanced sensitivity to 5-FU-induced apoptosis. Apoptosis induced by 5-FU in the Bag-1-knockdown cells was significantly greater than the additive apoptotic effect of 5-FU or Bag-1 knockdown alone.

Conclusions:

Overexpression of Bag-1 and Hsp70 in poorly differentiated SCC may confer both enhanced tumour cell growth and apoptosis resistance. Bag-1 may contribute to the resistance of more advanced epidermal SCC to chemotherapy.

Expressions of the anti-apoptotic genes Bag-1 and Bcl-2 in colon cancer and their relationship

BACKGROUND

The aims of this study were to investigate the expressions and significance of the antiapoptotic genes Bag-1 and Bcl-2 in colon cancer and to evaluate their relationship.

METHODS

The expressions of Bag-1 and Bcl-2 were examined in 128 colon cancer and 20 normal colon tissue samples by reverse-transcription polymerase chain reaction and immunohistochemical technique (streptavidin-biotin-peroxidase complex method).

RESULTS

Bag-1 and Bcl-2 were expressed in colorectal cancer tissues but not in normal colorectal tissues by reverse-transcription polymerase chain reaction. The expression of Bag-1 in colon cancer was closely correlated with pathologic grade, distance metastasis, Duke stage, and prognosis, but it had no effect on the pathologic type, tumor diameter, depth of invasion, and lymphoid node metastasis of the cancer. By contrast, Bcl-2 had no significant correlation with all the clinical and pathologic factors. There was a positive correlation between Bag-1 and Bcl-2 in the development of colon cancer.

CONCLUSIONS

High expressions of Bag-1 and Bcl-2 proteins in colon cancer were found. They might be regarded as biomarkers for the diagnosis of the early stage of colon cancer. In addition, they have significant relevance for the prognosis of colon cancer.

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

The C-terminal BAG domain is thought to play a key role in BAG-1-induced survival and proliferation by mediating protein-protein interactions, for example, with heat shock proteins HSC70 and HSP70, and with RAF-1 kinase. Here, we have identified thioflavin S (NSC71948) as a potential small-molecule chemical inhibitor of these interactions. NSC71948 inhibited the interaction of BAG-1 and HSC70 in vitro and decreased BAG-1:HSC70 and BAG-1:HSP70 binding in intact cells. NSC71948 also reduced binding between BAG-1 and RAF-1, but had no effect on the interaction between two unrelated proteins, BIM and MCL-1. NSC71948 functionally reversed the ability of BAG-1 to promote vitamin D3 receptor-mediated transactivation, an activity of BAG-1 that depends on HSC70/HSP70 binding, and reduced phosphorylation of p44/42 mitogen-activate protein kinase. NSC71948 can be used to stain amyloid fibrils; however, structurally related compounds, thioflavin T and BTA-1, had no effect on BAG-1:HSC70 binding, suggesting that structural features important for amyloid fibril binding and inhibition of BAG-1:HSC70 binding may be separable. We demonstrated that NSC71948 inhibited the growth of BAG-1 expressing human ZR-75-1 breast cancer cells and wild-type, but not BAG-1-deficient, mouse embryo fibroblasts. Taken together, these data suggest that NSC71948 may be a useful molecule to investigate the functional significance of BAG-1 C-terminal protein interactions. However, it is important to recognize that NSC71948 may exert additional "off-target" effects. Inhibition of BAG-1 function may be an attractive strategy to inhibit the growth of BAG-1-overexpressing cancers, and further screens of additional compound collections may be warranted.

Multiple, but concerted cellular activities of the human protein Hap46/BAG-1M and isoforms

The closely related human and murine proteins Hap46/BAG-1M and BAG-1, respectively, were discovered more than a decade ago by molecular cloning techniques. These and the larger isoform Hap50/BAG-1L, as well as shorter isoforms, have the ability to interact with a seemingly unlimited array of proteins of completely unrelated structures. This problem was partially resolved when it was realized that molecular chaperones of the hsp70 heat shock protein family are major primary association partners, binding being mediated by the carboxy terminal BAG-domain and the ATP-binding domain of hsp70 chaperones. The latter, in turn, can associate with an almost unlimited variety of proteins through their substrate-binding domains, so that ternary complexes may result. The protein folding activity of hsp70 chaperones is affected by interactions with Hap46/BAG-1M or isoforms. However, there also exist several proteins which bind to Hap46/BAG-1M and isoforms independent of hsp70 mediation. Moreover, Hap46/BAG-1M and Hap50/BAG-1L, but not the shorter isoforms, can bind to DNA in a sequence-independent manner by making use of positively charged regions close to their amino terminal ends. This is the molecular basis for their effects on transcription which are of major physiological relevance, as discussed here in terms of a model. The related proteins Hap50/BAG-1L and Hap46/BAG-1M may thus serve as molecular links between such diverse bioactivities as regulation of gene expression and protein quality control. These activities are coordinated and synergize in helping cells to cope with conditions of external stress. Moreover, they recently became markers for the aggressiveness of several cancer types.

Bag-1 proteins in oral squamous cell carcinoma

Bag-1 is an anti-apoptotic protein that exhibits altered expression in many malignancies, including oral squamous cell carcinoma. The bag-1 gene gives rise to different protein products with different subcellular localisations through alternative translational initiation sites. In oral squamous cell carcinoma, cytoplasmic expression has been associated with metastasis to regional lymph nodes and poor prognosis. In contrast, the longest Bag-1 isoform is nuclear and may regulate differentiation in oral epithelium. In this review, the functions of the three isoforms of Bag-1 expressed in oral epithelial cells are discussed in relation to their contribution to oral carcinogenesis.

DNA methyltransferase 1 and 3B activate BAG-1 expression via recruitment of CTCFL/BORIS and modulation of promoter histone methylation

In a previous genomic analysis, using somatic methyltransferase (DNMT) knockout cells, we showed that hypomethylation decreased the expression of as many genes as were observed to increase, suggesting a previously unknown mechanism for epigenetic regulation. To address this idea, the expression of the BAG family genes was used as a model. These genes were used because their expression was decreased in DNMT1(-/-), DNMT3B(-/-), and double knockout cells and increased in DNMT1-overexpressing and DNMT3B-overexpressing cells. Chromatin immunoprecipitation analysis of the BAG-1 promoter in DNMT1-overexpressing or DNMT3B-overexpressing cells showed a permissive dimethyl-H3-K4/dimethyl-H3-K9 chromatin status associated with DNA-binding of CTCFL/BORIS, as well as increased BAG-1 expression. In contrast, a nonpermissive dimethyl-H3-K4/dimethyl-H3-K9 chromatin status was associated with CTCF DNA-binding and decreased BAG-1 expression in the single and double DNMT knockout cells. BORIS short hairpin RNA knockdown decreased both promoter DNA-binding, as well as BAG-1 expression, and changed the dimethyl-H3-K4/dimethyl-H3-K9 ratio to that characteristic of a nonpermissive chromatin state. These results suggest that DNMT1 and DNMT3B regulate BAG-1 expression via insulator protein DNA-binding and chromatin dynamics by regulating histone dimethylation.

Silencing of Bcl-XL expression in human MGC-803 gastric cancer cells by siRNA

To investigate the inhibitory effect of the Bcl-XL small interfering RNA (siRNA) on Bcl-XL gene expression in the human gastric cancer cell line MGC-803, green fluorescent protein (GFP) siRNA was constructed and transfected into MGC-803 cells, together with GFP expression vector pTrace SV40. GFP expression levels were observed using fluorescence microscopy. Bcl-XL siRNA and negative siRNA were then constructed and stably transfected into MGC-803 cells. RT-PCR and immunofluorescence were used to detect the expression of Bcl-XL. Spontaneous apoptosis was detected by acridine orange (AO) and flow cytometry. Results were as follows: (1) 48 h after GFP expression vector and GFP siRNA co-transfection, the expression level of GFP in the GFP siRNA group was much lower than the negative siRNA group, according to fluorescence microscopy results. The mRNA and protein levels of Bcl-XL in Bcl-XL siRNA stable transfectants were reduced to almost background level compared with negative siRNA transfectants or untreated cells. (2) Changes in nucleus morphology was observed by AO staining nucleic and flow cytometry analysis, which showed that stable Bcl-XL siRNA transfectants have an increased spontaneous apoptosis (21.17%+/-1.26% vs. 1.19%+/-0.18% and 1.56%+/-0.15% respectively, P < 0.05 vs. negative siRNA or untreated control). siRNA targeting GFP or Bcl-XL genes can specifically suppress GFP or Bcl-XL expression in MGC-803 cells, and Bcl-XL siRNA can increase spontaneous apoptosis. Bcl-XL siRNA may be a beneficial agent against human gastric adenocarcinoma.

Biological activities of HAP46/BAG-1. The HAP46/BAG-1 protein: regulator of HSP70 chaperones, DNA-binding protein and stimulator of transcription

HAP46/BAG-1M and its isoforms affect the protein-folding activities of mammalian HSP70 chaperones. They interact with the ATP-binding domain of HSP70 or HSC70, leaving the substrate-binding site available for further interactions. Trimeric complexes can therefore form with, for example, transcription factors. Moreover, HAP46/BAG-1M and the larger isoform HAP50/BAG-1L bind to DNA non-specifically and enhance transcription in vitro and upon overexpression in intact cells. These factors are linked to positive effects on cell proliferation and survival. This review focuses on DNA-binding activity and transcriptional stimulation by HAP46/BAG-1M, and presents a molecular model for the underlying mechanism. It is proposed that transcription factors are recruited into complexes with HAP46/BAG-1M or HAP50/BAG-1L through HSP70/HSC70 and that response-element-bound complexes that contain HAP46/BAG-1M and/or HAP50/BAG-1L along with HSP70s target and affect the basal transcription machinery.

Antisense BAG-1 sensitizes HeLa cells to apoptosis by multiple pathways

To study the mechanism of action of BAG-1 in drug-induced apoptosis, we constructed an antisense BAG-1 vector and established a stably transfected cell line from BAG-1-over-expressing HeLa cells. Reduced BAG-1 protein was confirmed by Western blot. Treatment of the antisense BAG-1-transfected cells with the anti-cancer drugs staurosporine, paclitaxel, all-trans retinoic acid (ATRA), and N-(4-hydroxyphenyl) retinamide (4-HPR) resulted in significantly enhanced apoptosis and reduced cell viability relative to vector-transfected cells. While the expression of p53 was increased, the level of Bcl-2 and Bax was decreased. Cells underexpressing BAG-1 had reduced cytosolic cytochrome c level. Treatment with staurosporine and paclitaxel resulted in increased cytochrome c release from mitochondria, whereas there was no change induced by treatment with ATRA and 4-HPR. Our experiments suggest that BAG-1 inhibits anti-cancer drug-induced apoptosis through apoptosis regulation pathways that may involve the mitochondrial Bcl-2/Bax ratio, p53, and differential anti-cancer drug-mediated cytochrome c release.

RNAi as a gene therapy approach

RNA duplexes of 21 - 23 nucleotides (nts), with approximately 2 nt 3' overhangs (called small interfering RNAs or siRNAs), have recently been shown to mediate sequence-specific inhibition of gene expression in mammalian cells via a post-transcriptional gene silencing (PTGS) mechanism termed RNA interference (RNAi). RNAi has been rapidly adopted as a functional genomics tool in a wide range of species, has been adapted to allow for the transient or stable knockdown of gene expression generation in cell lines and animals, and has been developed for high-throughput analysis of gene function in Caenorhabditis elegans. With an increasing list of genes successfully knocked-down by RNAi in mammalian cells and improvements in the delivery of siRNAs to cells, including in vivo delivery to mice, attention is now turning to assessing the potential RNAi has as a gene therapy approach. RNAi is likely to have the greatest impact as a therapeutic tool in two key clinical areas, cancer and infectious disease, but it also has the potential as a therapy for other disorders including some dominant genetic diseases. This review will describe the status of the science behind this novel mechanism and will illustrate the therapeutic potential of RNAi-based technologies, using examples from these critical clinical research areas.