BAG-1 interacts with the p50-p50 homodimeric NF-κB complex: implications for colorectal carcinogenesis

The Atypical MAP Kinase MAPK15 Is Required for Lung Adenocarcinoma Metastasis via Its Interaction with NF-κB p50 Subunit and Transcriptional Regulation of Prostaglandin E2 Receptor EP3 Subtype

Studying the relatively underexplored atypical MAP Kinase MAPK15 on cancer progression/patient outcomes and its potential transcriptional regulation of downstream genes would be highly valuable for the diagnosis, prognosis, and potential oncotherapy of malignant tumors such as lung adenocarcinoma (LUAD). Here, the expression of MAPK15 in LUAD was detected by immunohistochemistry and its correlation with clinical parameters such as lymph node metastasis and clinical stage was analyzed. The correlation between the prostaglandin E2 receptor EP3 subtype (EP3) and MAPK15 expression in LUAD tissues was examined, and the transcriptional regulation of EP3 and cell migration by MAPK15 in LUAD cell lines were studied using the luciferase reporter assay, immunoblot analysis, qRT-PCR, and transwell assay. We found that MAPK15 is highly expressed in LUAD with lymph node metastasis. In addition, EP3 is positively correlated with the expression of MAPK15 in LUAD tissues, and we confirmed that MAPK15 transcriptionally regulates the expression of EP3. Upon the knockdown of MAPK15, the expression of EP3 was down-regulated and the cell migration ability was decreased in vitro; similarly, the mesenteric metastasis ability of the MAPK15 knockdown cells was inhibited in in vivo animal experiments. Mechanistically, we demonstrate for the first time that MAPK15 interacts with NF-κB p50 and enters the nucleus, and NF-κB p50 binds to the EP3 promoter and transcriptionally regulates the expression of EP3. Taken together, we show that a novel atypical MAPK and NF-κB subunit interaction promotes LUAD cell migration through transcriptional regulation of EP3, and higher MAPK15 level is associated with lymph node metastasis in patients with LUAD.

Bcl-3: A Double-Edged Sword in Immune Cells and Inflammation

The NF-κB transcription factor family controls the transcription of many genes and regulates a number of pivotal biological processes. Its activity is regulated by the IκB family of proteins. Bcl-3 is an atypical member of the IκB protein family that regulates the activity of nuclear factor NF-κB. It can promote or inhibit the expression of NF-κB target genes according to the received cell type and stimulation, impacting various cell functions, such as proliferation and differentiation, induction of apoptosis and immune response. Bcl-3 is also regarded as an environment-dependent cell response regulator that has dual roles in the development of B cells and the differentiation, survival and proliferation of Th cells. Moreover, it also showed a contradictory role in inflammation. At present, in addition to the work aimed at studying the molecular mechanism of Bcl-3, an increasing number of studies have focused on the effects of Bcl-3 on inflammation, immunity and malignant tumors in vivo. In this review, we focus on the latest progress of Bcl-3 in the regulation of the NF-κB pathway and its extensive physiological role in inflammation and immune cells, which may help to provide new ideas and targets for the early diagnosis or targeted treatment of various inflammatory diseases, immunodeficiency diseases and malignant tumors.

Expression of BAG1 is associated with prognosis in kidney renal clear cell carcinoma based on bioinformatics

Background

BCL2 associated Athano-Gene 1 (BAG1) has been described to be involved in the development and progression of cancer. But the role of BAG1 in kidney renal clear cell carcinoma (KIRC) has remained largely unknown.

Methods

We performed bioinformatic analysis of data from TCGA and GEO dataset. The role of BAG1 in KIRC was explored by Logistic and Cox regression model. The molecular mechanisms of BAG1 was revealed by GSEA.

Results

The current study found that the KIRC tumor samples have a low level of BAG1 mRNA expression compared to the matched normal tissues based on TCGA data and GEO databases. Low expression of BAG1 in KIRC was significantly associated with Sex, clinical pathological stage, tumor-node-metastasis (TNM) stage, hemoglobin levels, cancer status and history of neoadjuvant treatment. Kaplan-Meier survival analysis indicated that KIRC patients with BAG1 high expression have a longer survival time than those with BAG1 low expression (p < 0.000). Cox regression analysis showed that BAG1 remained independently associated with overall survival, with a hazard ratio (HR) of 1.75(CI:1.05–2.90; p = 0.029). GSEA indicated that the signaling pathways including fatty acid metabolism and oxidative phosphorylation were differentially enriched in high BAG1 expression phenotype.

Conclusions

These findings suggested that BAG1 expression may act as a potential favorable prognostic marker and challenging therapeutic target.

The role of B-Cell Lymphoma-3 (BCL-3) in enabling the hallmarks of cancer: implications for the treatment of colorectal carcinogenesis

With its identification as a proto-oncogene in chronic lymphocytic leukaemia and central role in regulating NF-κB signalling, it is perhaps not surprising that there have been an increasing number of studies in recent years investigating the role of BCL-3 (B-Cell Chronic Lymphocytic Leukaemia/Lymphoma-3) in a wide range of human cancers. Importantly, this work has begun to shed light on our mechanistic understanding of the function of BCL-3 in tumour promotion and progression. Here, we summarize the current understanding of BCL-3 function in relation to the characteristics or traits associated with tumourigenesis, termed ‘Hallmarks of Cancer’. With the focus on colorectal cancer, a major cause of cancer related mortality in the UK, we describe the evidence that potentially explains why increased BCL-3 expression is associated with poor prognosis in colorectal cancer. As well as promoting tumour cell proliferation, survival, invasion and metastasis, a key emerging function of this proto-oncogene is the regulation of the tumour response to inflammation. We suggest that BCL-3 represents an exciting new route for targeting the Hallmarks of Cancer; in particular by limiting the impact of the enabling hallmarks of tumour promoting inflammation and cell plasticity. As BCL-3 has been reported to promote the stem-like potential of cancer cells, we suggest that targeting BCL-3 could increase the tumour response to conventional treatment, reduce the chance of relapse and hence improve the prognosis for cancer patients.

BCL‑3 promotes cyclooxygenase‑2/prostaglandin E2 signalling in colorectal cancer

First discovered as an oncogene in leukaemia, recent reports highlight an emerging role for the proto‑oncogene BCL‑3 in solid tumours. Importantly, BCL‑3 expression is upregulated in >30% of colorectal cancer cases and is reported to be associated with a poor prognosis. However, the mechanism by which BCL‑3 regulates tumorigenesis in the large intestine is yet to be fully elucidated. In the present study, it was shown for the first time that knocking down BCL‑3 expression suppressed cyclooxygenase‑2 (COX‑2)/prostaglandin E2 (PGE2) signalling in colorectal cancer cells, a pathway known to drive several of the hallmarks of cancer. RNAi‑mediated suppression of BCL‑3 expression decreased COX‑2 expression in colorectal cancer cells both at the mRNA and protein level. This reduction in COX‑2 expression resulted in a significant and functional reduction (30‑50%) in the quantity of pro‑tumorigenic PGE2 produced by the cancer cells, as shown by enzyme linked immunoassays and medium exchange experiments. In addition, inhibition of BCL‑3 expression also significantly suppressed cytokine‑induced (TNF‑α or IL‑1β) COX‑2 expression. Taken together, the results of the present study identified a novel role for BCL‑3 in colorectal cancer and suggested that expression of BCL‑3 may be a key determinant in the COX‑2‑meditated response to inflammatory cytokines in colorectal tumour cells. These results suggest that targeting BCL‑3 to suppress PGE2 synthesis may represent an alternative or complementary approach to using non‑steroidal anti‑inflammatory drugs [(NSAIDs), which inhibit cyclooxygenase activity and suppress the conversion of arachidonic acid to prostaglandin], for prevention and/or recurrence in PGE2‑driven tumorigenesis.

Computational analysis of nuclear factor-κB and resveratrol in colorectal cancer

Nuclear factor κB (NF-κB), a dimeric transcription factor, is a major regulator and an important determinant of the biological characteristics of tumour cells. Some antioxidants or protease inhibitors have been found to act against NF-κB to suppress colorectal cancer (CRC). In the current investigation, a computational study was performed to investigate the molecular interaction between NF-κB and resveratrol. Molecular docking studies revealed that, resveratrol with NF-κB are predicted to be quite effective. The application of molecular dynamics simulation (MDS) tactics has considerably supported in increasing the prediction precision of the outcomes. Further, this study revealed that NF-κB could be a potential target for various anti-cancerous drugs for cancer therapeutics. Furthermore, animal investigations are necessary to confirm the efficacy and evaluate potency of target and drugs.Communicated by Ramaswamy H. Sarma.

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.

G-quadruplex located in the 5'UTR of the BAG-1 mRNA affects both its cap-dependent and cap-independent translation through global secondary structure maintenance

The anti-apoptotic BAG-1 protein isoforms are known to be overexpressed in colorectal tumors and are considered to be potential therapeutic targets. The isoforms are derived from alternative translation initiations occuring at four in-frame start codons of a single mRNA transcript. Its 5′UTR also contains an internal ribosome entry site (IRES) regulating the cap-independent translation of the transcript. An RNA G-quadruplex (rG4) is located at the 5′end of the BAG-1 5′UTR, upstream of the known cis-regulatory elements. Herein, we observed that the expression of BAG-1 isoforms is post-transcriptionally regulated in colorectal cancer cells and tumors, and that stabilisation of the rG4 by small molecules ligands reduces the expression of endogenous BAG-1 isoforms. We demonstrated a critical role for the rG4 in the control of both cap-dependent and independent translation of the BAG-1 mRNA in colorectal cancer cells. Additionally, we found an upstream ORF that also represses BAG-1 mRNA translation. The structural probing of the complete 5′UTR showed that the rG4 acts as a steric block which controls the initiation of translation at each start codon of the transcript and also maintains the global 5′UTR secondary structure required for IRES-dependent translation.

NFKB1 and Cancer: Friend or Foe?

Current evidence strongly suggests that aberrant activation of the NF-κB signalling pathway is associated with carcinogenesis. A number of key cellular processes are governed by the effectors of this pathway, including immune responses and apoptosis, both crucial in the development of cancer. Therefore, it is not surprising that dysregulated and chronic NF-κB signalling can have a profound impact on cellular homeostasis. Here we discuss NFKB1 (p105/p50), one of the five subunits of NF-κB, widely implicated in carcinogenesis, in some cases driving cancer progression and in others acting as a tumour-suppressor. The complexity of the role of this subunit lies in the multiple dimeric combination possibilities as well as the different interacting co-factors, which dictate whether gene transcription is activated or repressed, in a cell and organ-specific manner. This review highlights the multiple roles of NFKB1 in the development and progression of different cancers, and the considerations to make when attempting to manipulate NF-κB as a potential cancer therapy.

H3K4me3 mediates the NF-κB p50 homodimer binding to the pdcd1 promoter to activate PD-1 transcription in T cells

PD-1 is a co-repressive receptor that curbs T cell activation and thereby serves as a protection mechanism against autoimmunity under physiological conditions. Under pathological conditions, tumor cells express PD-L1 as an adaptive resistant mechanism to suppress PD-1⁺ T cells to evade host immunosurveillance. PD-1 therefore is a key target in cancer immunotherapy. Despite the extensive studies of PD-1 expression regulation, the pdcd1 transcription machinery and regulatory mechanisms are still not fully understood. We report here that the NF-κB p50 homodimer is a transcription regulator of PD-1 in activated T cells. A putative κB sequence exists at the pdcd1 promoter. All five NF-κB Rel subunits are activated in activated T cells. However, only the p50 homodimer directly binds to the κB sequence at the pccd1 promoter in CD4⁺ and CD8⁺ T cells. Deficiency in p50 results in reduced PD-1 expression in both CD4⁺ and CD8⁺ T cells in vitro. Using an in vivo mixed bone marrow chimera mouse model, we show that p50 regulates PD-1 expression in a cell-intrinsic way and p50 deficiency leads to decreased PD-1 expression in both antigen-specific CD4⁺ and CD8⁺ T cells in vivo. The expression levels of H3K4me3-specific histone methyltransferase increased significantly, resulting in a significant increase in H3K4me3 deposition at the pdcd1 promoter in activated CD4⁺ and CD8⁺ T cells. Inhibition of H3K4me3 significantly decreased p50 binding to the pdcd1 promoter and PD-1 expression in a T cell line. Our findings determine that the p50-H3K4me3 axis regulates pdcd1 transcription activation in activated T cells.

Protumor Steering of Cancer Inflammation by p50 NF-κB Enhances Colorectal Cancer Progression

Although tumor-associated macrophages (TAM) display a M2-skewed tumor-promoting phenotype in most cancers, in colorectal cancer, both TAM polarization and its impact remain controversial. We investigated the role of the M2-polarizing p50 NF-κB subunit in orchestrating TAM phenotype, tumor microenvironment composition, and colorectal cancer progression. We first demonstrated, by parallel studies in colitis-associated cancer (CAC) and in genetically driven Apc^Min mouse models, that the p50-dependent inhibition of M1-polarized gut inflammation supported colorectal cancer development. In accordance with these studies, p50^-/- mice displayed exacerbated CAC with fewer and smaller tumors, along with enhanced levels of M1/Th1 cytokines/chemokines, including IL12 and CXCL10, whose administration restrained CAC development in vivo The inflammatory profile supporting tumor resistance in colons from p50^-/- tumor bearers correlated inversely with TAM load and positively with both recruitment of NK, NKT, CD8⁺ T cells and number of apoptotic tumor cells. In agreement, myeloid-specific ablation of p50 promoted tumor resistance in mice, whereas in colorectal cancer patients, a high number of p50⁺ TAMs at the invasive margin was associated with decreased IL12A and TBX21 expression and worse postsurgical outcome. Our findings point to p50 involvement in colorectal cancer development, through its engagement in the protumor activation of macrophages, and identify a candidate for prognostic and target therapeutic intervention. Cancer Immunol Res; 6(5); 578-93. ©2018 AACR.

BAG-1M co-activates BACE1 transcription through NF-κB and accelerates Aβ production and memory deficit in Alzheimer's disease mouse model

Accumulation of amyloid β protein (Aβ)-containing neuritic plaques in the brain is a neuropathological feature of Alzheimer's disease (AD). The β-site APP-cleaving enzyme 1 (BACE1) is essential for Aβ generation and dysregulation of BACE1 expression may lead to AD pathogenesis. Bcl-2-associated athanogen 1M (BAG-1M), initially identified as an anti-apoptotic protein, has also been found to be highly expressed in the same neurons that contain intracellular amyloid in the hippocampus of AD patient. In this report, we found that over-expression of BAG-1M enhances BACE1-mediated cleavage of amyloid precursor protein (APP) and Aβ production by up-regulating BACE1 gene transcription. The regulation of BACE1 transcription by BAG-1M was dependent on NF-κB, as BAG-1M complexes NF-κB at the promoter of BACE1 gene and co-activates NF-κB-facilitated BACE1 transcription. Moreover, expression of BAG-1M by lentiviral vector in the hippocampus of AD transgenic model mice promotes Aβ generation and formation of neuritic plaque, and subsequently accelerates memory deficits of the mice. These results provide evidence for an emerging role of BAG-1M in the regulation of BACE1 expression and AD pathogenesis and that targeting the BAG-1M-NF-κB complex may provide a mechanism for inhibiting Aβ production and plaque formation.

BCL-3 expression promotes colorectal tumorigenesis through activation of AKT signalling

OBJECTIVE

Colorectal cancer remains the fourth most common cause of cancer-related mortality worldwide. Here we investigate the role of nuclear factor-κB (NF-κB) co-factor B-cell CLL/lymphoma 3 (BCL-3) in promoting colorectal tumour cell survival.

DESIGN

Immunohistochemistry was carried out on 47 tumour samples and normal tissue from resection margins. The role of BCL-3/NF-κB complexes on cell growth was studied in vivo and in vitro using an siRNA approach and exogenous BCL-3 expression in colorectal adenoma and carcinoma cells. The question whether BCL-3 activated the AKT/protein kinase B (PKB) pathway in colorectal tumour cells was addressed by western blotting and confocal microscopy, and the ability of 5-aminosalicylic acid (5-ASA) to suppress BCL-3 expression was also investigated.

RESULTS

We report increased BCL-3 expression in human colorectal cancers and demonstrate that BCL-3 expression promotes tumour cell survival in vitro and tumour growth in mouse xenografts in vivo, dependent on interaction with NF-κB p50 or p52 homodimers. We show that BCL-3 promotes cell survival under conditions relevant to the tumour microenvironment, protecting both colorectal adenoma and carcinoma cells from apoptosis via activation of the AKT survival pathway: AKT activation is mediated via both PI3K and mammalian target of rapamycin (mTOR) pathways, leading to phosphorylation of downstream targets GSK-3β and FoxO1/3a. Treatment with 5-ASA suppressed BCL-3 expression in colorectal cancer cells.

CONCLUSIONS

Our study helps to unravel the mechanism by which BCL-3 is linked to poor prognosis in colorectal cancer; we suggest that targeting BCL-3 activity represents an exciting therapeutic opportunity potentially increasing the sensitivity of tumour cells to conventional therapy.

Silencing Bag-1 gene via magnetic gold nanoparticle-delivered siRNA plasmid for colorectal cancer therapy in vivo and in vitro

Apoptosis disorder is generally regarded as an important mechanism of carcinogenesis. Inducement of tumor cell apoptosis can be an effectual way to treat cancer. Bcl-2-associated athanogene 1 (Bag-1) is a positive regulator of Bcl-2 which is an anti-apoptotic gene. Bag-1 is highly expressed in colorectal cancer, which plays a critical role in promoting metastasis, poor prognosis, especially in anti-apoptotic function, and is perhaps a valuable gene target for colorectal cancer therapy. Recently, we applied a novel non-viral gene carrier, magnetic gold nanoparticle, and mediated plasmid pGPH1/GFP/Neo-Bag-1-homo-825 silencing Bag-1 gene for treating colorectal cancer in vivo and in vitro. By mediating with magnetic gold nanoparticle, siRNA plasmid was successfully transfected into cell. In 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay, magnetic gold nanoparticle had no significant cytotoxicity and by which delivered RNA plasmid inhibited cell viability significantly (P < 0.05). Downregulation of Bag-1 promoted cell apoptosis (∼47.0 %) in vitro and significantly decreased tumor growth when the cells were injected into nude mice. Based on the studies in vivo, the relative expression of Bag-1 was 0.165 ± 0.072 at mRNA level and ∼60 % at protein level. In further study, C-myc and β-catenin, mainly molecules of Wnt/β-catenin pathway, were decreased notably when Bag-1 were silenced in nanoparticle plasmid complex-transfected Balb c/nude tumor xenograft. In conclusion, Bag-1 is confirmed an anti-apoptosis gene that functioned in colorectal cancer, and the mechanism of Bag-1 gene causing colorectal cancer may be related to Wnt/β-catenin signaling pathway abnormality and suggested that magnetic gold nanoparticle-delivered siRNA plasmid silencing Bag-1 is an effective gene therapy method for colorectal cancer.

NFKB1: a suppressor of inflammation, ageing and cancer

The pleiotropic consequences of nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) pathway activation result from the combinatorial effects of the five subunits that form the homo- and heterodimeric NF-κB complexes. Although biochemical and gene knockout studies have demonstrated overlapping and distinct functions for these proteins, much is still not known about the mechanisms determining context-dependent functions, the formation of different dimer complexes and transcriptional control in response to diverse stimuli. Here we discuss recent results that reveal that the nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NFKB1) (p105/p50) subunit is an important regulator of NF-κB activity in vivo. These effects are not restricted to being a dimer partner for other NF-κB subunits. Rather p50 homodimers have a critical role as suppressors of the NF-κB response, while the p105 precursor has a variety of NF-κB-independent functions. The importance of Nfkb1 function can be seen in mouse models, where Nfkb1(-/-) mice display increased inflammation and susceptibility to certain forms of DNA damage, leading to cancer, and a rapid ageing phenotype. In humans, low expression of Kip1 ubiquitination-promoting complex 1 (KPC1), a ubiquitin ligase required for p105 to p50 processing, was shown to correlate with a reduction in p50 and glioblastoma incidence. Therefore, while the majority of research in this field has focused on the upstream signalling pathways leading to NF-κB activation or the function of other NF-κB subunits, such as RelA (p65), these data demonstrate a critical role for NFKB1, potentially revealing new strategies for targeting this pathway in inflammatory diseases and cancer.

Integrated transcriptional profiling and genomic analyses reveal RPN2 and HMGB1 as promising biomarkers in colorectal cancer

Colorectal cancer (CRC) is a heterogeneous disease that is associated with a gradual accumulation of genetic and epigenetic alterations. Among all CRC stages, stage II tumors are highly heterogeneous with a high relapse rate in about 20–25 % of stage II CRC patients following surgery. Thus, a comprehensive analysis of gene signatures to identify aggressive and metastatic phenotypes in stage II CRC is desired for a more accurate disease classification and outcome prediction. By utilizing a Cancer Array, containing 440 oncogenes and tumor suppressors to profile mRNA expression, we identified a larger number of differentially expressed genes in poorly differentiated stage II colorectal adenocarcinoma tissues, compared to their matched normal tissues. Ontology and Ingenuity Pathway Analysis (IPA) indicated that these genes are involved in functional mechanisms associated with several transcription factors. Genomic alterations of these genes were also investigated through The Cancer Genome Atlas (TCGA) database, utilizing 195 published CRC specimens. The percentage of genomic alterations in these genes was ranked based on their mRNA expression, copy number variations and mutations. This data was further combined with published microarray studies from a large set of CRC tumors classified based on prognostic features. This led to the identification of eight candidate genes including RPN2, HMGB1, AARS, IGFBP3, STAT1, HYOU1, NQO1 and PEA15 that were associated with the progressive phenotype. In particular, RPN2 and HMGB1 displayed a higher genomic alteration frequency in CRC, compared to eight other major solid cancers. Immunohistochemistry was performed on additional 78 stage I–IV CRC samples, where RPN2 protein immunostaining exhibited a significant association with stage III/IV tumors, distant metastasis, and poor differentiation, indicating that RPN2 expression is associated with poor prognosis. Further, our study revealed significant transcriptional regulatory mechanisms, networks and gene signatures, underlying CRC malignant progression and phenotype warranting future clinical investigations.

Inhibition of transcription by B cell Leukemia 3 (Bcl-3) protein requires interaction with nuclear factor κB (NF-κB) p50

B cell leukemia 3 (Bcl-3) is an essential negative regulator of NF-κB during Toll-like receptor and TNF receptor signaling. Bcl-3 also interacts with a number of transcriptional regulators, including homodimers of the NF-κB p50 subunit. Deletion of Bcl-3 results in increased NF-κB p50 ubiquitination and proteasomal degradation and increased inflammatory gene expression. We employed immobilized peptide array technology to define a region of p50 required for the formation of a Bcl-3·p50 homodimer immunosuppressor complex. Our data demonstrate that amino acids 359-361 and 363 of p50 are critical for interaction with Bcl-3 and essential for Bcl-3-mediated inhibition of inflammatory gene expression. Bcl-3 is unable to interact with p50 when these amino acids are mutated, rendering it incapable of inhibiting the transcriptional activity of NF-κB. Bcl-3 interaction-defective p50 is hyperubiquitinated and has a significantly reduced half-life relative to wild-type p50. Nfkb1(-/-) cells reconstituted with mutated p50 precursor p105 are hyperresponsive to TNFα stimulation relative to wild-type p105, as measured by inflammatory gene expression. Mutant p105 recapitulates a Bcl3(-/-) phenotype. This study demonstrates that interaction with p50 is necessary and sufficient for the anti-inflammatory properties of Bcl-3 and further highlights the importance of p50 homodimer stability in the control of NF-κB target gene expression.

Overexpressed nuclear BAG-1 in human hepatocellular carcinoma is associated with poor prognosis and resistance to doxorubicin

Bcl-2-associated athanogene-1 (BAG-1) is a multifunctional anti-apoptotic protein which regulates an array of cellular processes, including apoptosis, signaling, proliferation, transcription, and cell motility and has been reported to be over-expressed in a number of human malignancies. To investigate the possible involvement of BAG-1 in tumorigenesis of hepatocellular carcinoma (HCC), we performed Western blot analysis in eight paired samples of HCC and adjacent peritumoral tissues and immunohistochemistry in 65 paraffin sections of HCC, which both showed an enhanced expression of nuclear BAG-1 isoform in HCC tissues. Statistical analysis confirmed that overexpression of nuclear BAG-1 in HCC tissues was significantly associated with histological grading (P < 0.001), poor prognosis (P = 0.004), and was found to be an independent prognostic indicator for HCC (P = 0.023). We also noted that BAG-1 was overexpressed in four HCC cell lines compared with a normal hepatocyte cell line, and BAG-1 overexpression increased resistance of HCC cells to doxorubicin, a common chemotherapeutic agent for HCC. Furthermore, we observed that knock down of BAG-1 with siRNA in HepG2 cells increased the chemosensitivity of cells, a process mediated through inhibition of doxorubicin-triggered NF-κB activation; and knock down of BAG-1 suppressed proliferation and cell cycle transition of HepG2 cells. In consequence, our results for the first time indicated that BAG-1 was dysregulated in HCC and suppression of BAG-1 expression which resulted in inhibiting of NF-κB signaling might be developed into a new strategy in HCC therapy.

NF-κB in colorectal cancer

Colorectal cancer (CRC) is a leading cause of morbidity and mortality worldwide, responsible for more than half a million deaths annually. CRC is a multistep process that entails the accumulation of genetic/epigenetic aberrations, which lead to the simultaneous failure of protective mechanisms and the activation of tumorigenic pathways. In most cases of CRC a deregulation of the Wnt-signaling pathway is required. The transcription factor nuclear factor κB (NF-κB) has been recognized as a key player in the initiation and propagation of CRC. Under physiological conditions, NF-κB orchestrates the inflammatory process and participates in the modulation of various steps of cell cycle and survival. It is normally kept in an inactive state in the cytoplasm by binding to a group of inhibitory proteins. Upon receipt of a signal, its inhibitor is phosphorylated and proteolytically degraded and NF-κB is actively translocated to the nucleus, where it facilitates target-gene transcription. Recent experimental data reveal the important role of NF-κB in tumor cells as well as in the surrounding "cancerous" and reactive microenvironment. Various tumor cell-derived and contextual cues feed constantly this vicious circuitry sustaining inflammation and promoting proliferation, angiogenesis, invasion and eventually metastasis. Therefore NF-κB along with its upstream and downstream network presents a rational target for therapeutic interventions. Numerous small molecules, inhibitory peptides, antisense RNAs, natural compounds, as well as gene therapy strategies interfere with multiple steps of the NF-κΒ signaling cascade. The design of NF-κΒ-targeted treatment may aid the efforts towards the pursuit of more efficient therapeutic measures devoid of severe systemic side-effects.

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.

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.