relA over-expression reduces tumorigenicity and activates apoptosis in human cancer cells

Homoharringtonine synergizes with venetoclax in early T cell progenitor acute lymphoblastic leukemia: Bench and bed

BACKGROUND

Early T cell precursor acute lymphoblastic leukemia (ETP-ALL) is a distinct subtype of T-ALL with a poor prognosis. To find a cure, we examined the synergistic effect of homoharringtonine (HHT) in combination with the BCL-2 inhibitor venetoclax (VEN) in ETP-ALL.

METHODS

Using in vitro cellular assays and ETP-ALL xenograft models, we first investigated the synergistic activity of HHT and VEN in ETP-ALL. Next, to explore the underlying mechanism, we employed single-cell RNA sequencing of primary ETP-ALL cells treated with HHT or VEN alone or in combination and validated the results with western blot assays. Based on the promising preclinical results and given that both drugs have been approved for clinical use, we then assessed this combination in clinical practice.

FINDINGS

Our results showed that HHT synergizes strongly with VEN both in vitro and in vivo in ETP-ALL. Mechanistic studies demonstrated that the HHT/VEN combination concurrently downregulated key anti-apoptotic proteins, i.e., MCL1, leading to enhanced apoptosis. Importantly, the clinical results were very promising. Six patients with ETP-ALL with either refractory/relapsed (R/R) or newly diagnosed disease were treated with an HHT/VEN-based regimen. All patients achieved complete remission (CR) after only one cycle of treatment.

CONCLUSIONS

Our findings demonstrate that a combination of HHT/VEN is effective on ETP-ALL and represents the "backbone" of a promising and safe regimen for newly diagnosed and R/R patients with ETP-ALL.

FUNDING

This work was funded by the National Cancer Institute, Gehr Family Foundation, George Hoag Family Foundation, National Natural Science Foundation of China, and Key Research and Development Program of Zhejiang Province of China.

Secreted clusterin inhibits tumorigenesis by modulating tumor cells and macrophages in human meningioma

BACKGROUND

Meningioma is the most common primary intracranial tumor with a high frequency of postoperative recurrence, yet the biology of the meningioma malignancy process is still obscure.

METHODS

To identify potential therapeutic targets and tumor suppressors, we performed single-cell transcriptome analysis through meningioma malignancy, which included 18 samples spanning normal meninges, benign and high-grade in situ tumors, and lung metastases, for extensive transcriptome characterization. Tumor suppressor candidate gene and molecular mechanism were functionally validated at the animal model and cellular levels.

RESULTS

Comprehensive analysis and validation in mice and clinical cohorts indicated clusterin (CLU) had suppressive function for meningioma tumorigenesis and malignancy by inducing mitochondria damage and triggering type 1 interferon pathway dependent on its secreted isoform, and the inhibition effect was enhanced by TNFα as TNFα also induced type 1 interferon pathway. Meanwhile, both intra- and extracellular CLU overexpression enhanced macrophage polarization towards M1 phenotype and TNFα production, thus promoting tumor killing and phagocytosis.

CONCLUSIONS

CLU might be a key brake of meningioma malignance by synchronously modulating tumor cells and their microenvironment. Our work provides comprehensive insights into meningioma malignancy and a potential therapeutic strategy.

Genetic analysis of PALB2 gene WD40 domain in canine mammary tumour patients

BACKGROUND

DNA repair mechanisms are essential for tumorigenesis and disruption of HR mechanism is an important predisposing factor of human breast cancers (BC). PALB2 is an important part of the HR. There are similarities between canine mammary tumours (CMT) and BCs. As its human counterpart, PALB2 mutations could be a predisposing factor of CMT.

OBJECTIVES

In this study, we aimed to investigate the impacts of PALB2 variants on tumorigenesis and canine mammary tumor (CMT) malignancy.

METHODS

We performed Sanger sequencing to detect germline mutations in the WD40 domain of the canine PALB2 gene in CMT patients. We conducted in silico analysis to investigate the variants, and compared the germline PALB2 mutations in humans that cause breast cancer (BC) with the variants detected in dogs with CMT.

RESULTS

We identified an intronic (c.3096+8C>G) variant, two exonic (p.A1050V and p.R1354R) variants, and a 3' UTR variant (c.4071T>C). Of these, p.R1354R and c.4071T>C novel variants were identified for the first time in this study. We found that the p.A1050V mutation had a significant effect. However, we could not determine sufficient similarity due to the differences in nucleotide/amino acid sequences between two species. Nonetheless, possible variants of human sequences in the exact location as their dog counterparts are associated with several cancer types, implying that the variants could be crucial for tumorigenesis in dogs. Our results did not show any effect of the variants on tumor malignancy.

CONCLUSIONS

The current project is the first study investigating the relationship between the PALB2 gene WD40 domain and CMTs. Our findings will contribute to a better understanding of the pathogenic mechanism of the PALB2 gene in CMTs. In humans, variant positions in canines have been linked to cancer-related phenotypes such as familial BC, endometrial tumor, and hereditary cancer predisposition syndrome. The results of bioinformatics analyses should be investigated through functional tests or case-control studies.

A1CF Binding to the p65 Interaction Site on NKRF Decreased IFN-β Expression and p65 Phosphorylation (Ser536) in Renal Carcinoma Cells

Apobec-1 complementation factor (A1CF) functions as an RNA-binding cofactor for APO-BEC1-mediated C-to-U conversion during RNA editing and as a hepatocyte-specific regulator in the alternative pre-mRNA splicing of metabolic enzymes. Its role in RNA editing has not been clearly established. Western blot, co-immunoprecipitation (Co-IP), immunofluorescence (IF), methyl thiazolyl tetrazolium (MTT), and 5-ethynyl-2'-deoxyuridine (EdU) assays were used to examine the role of A1CF beyond RNA editing in renal carcinoma cells. We demonstrated that A1CF interacts with NKRF, independent of RNA and DNA, without affecting its expression or nuclear translocation; however, it modulates p65(Ser536) phosphorylation and IFN-β levels. Truncation of A1CF or deletion on NKRF revealed that the RRM1 domain of A1CF and the p65 binding motif of NKRF are required for their interaction. Deletion of RRM1 on A1CF abrogates NKRF binding, and the decrease in IFN-β expression and p65(Ser536) phosphorylation was induced by A1CF. Moreover, full-length A1CF, but not an RRM1 deletion mutant, promoted cell proliferation in renal carcinoma cells. Perturbation of A1CF levels in renal carcinoma cells altered anchorage-independent growth and tumor progression in nude mice. Moreover, p65(Ser536) phosphorylation and IFN-β expression were lower, but ki67 was higher in A1CF-overexpressing tumor tissues of a xenograft mouse model. Notably, primary and metastatic samples from renal cancer patients exhibited high A1CF expression, low p65(Ser536) phosphorylation, and decreased IFN-β levels in renal carcinoma tissues compared with the corresponding paracancerous tissues. Our results indicate that A1CF-decreased p65(Ser536) phosphorylation and IFN-β levels may be caused by A1CF competitive binding to the p65-combined site on NKRF and demonstrate the direct binding of A1CF independent of RNA or DNA in signal pathway regulation and tumor promotion in renal carcinoma cells.

Sam68 is a druggable vulnerability point in cancer stem cells

Sam68 (Src associated in mitosis of 68 kDa) is an RNA-binding and multifunctional protein extensively characterized in numerous cellular functions, such as RNA processing, cell cycle regulation, kinase- and growth factor signaling. Recent investigations highlighted Sam68 as a primary target of a class of reverse-turn peptidomimetic drugs, initially developed as inhibitors of Wnt/β-catenin mediated transcription. Further investigations on such compounds revealed their capacity to selectively eliminate cancer stem cell (CSC) activity upon engaging Sam68. This work highlighted previously unappreciated roles for Sam68 in the maintenance of neoplastic self-renewal and tumor-initiating functions. Here, we discuss the implication of Sam68 in tumorigenesis, where central findings support its contribution to chromatin regulation processes essential to CSCs. We also review advances in CSC-targeting drug discovery aiming to modulate Sam68 cellular distribution and protein-protein interactions. Ultimately, Sam68 constitutes a vulnerability point of CSCs and an attractive therapeutic target to impede neoplastic stemness in human tumors.

Critical and distinct roles of cell type-specific NF-κB2 in lung cancer

Different from the well-studied canonical NF-κB member RelA, the role of the noncanonical NF-κB member NF-κB2 in solid tumors, and lung cancer in particular, is poorly understood. Here we report that in contrast to the tumor-promoting role of RelA, NF-κB2 intrinsic to lung epithelial and tumor cells had no marked effect on lung tumorigenesis and progression. On the other hand, NF-κB2 limited dendritic cell number and activation in the lung but protected lung macrophages and drove them to promote lung cancer through controlling activation of noncanonical and canonical NF-κB, respectively. NF-κB2 was also required for B cell maintenance and T cell activation. The antitumor activity of lymphocyte NF-κB2 was dominated by the protumor function of myeloid NF-κB2; thus, NF-κB2 has an overall tumor-promoting activity. These studies reveal a cell type-dependent role for NF-κB2 in lung cancer and help understand the complexity of NF-κB action and lung cancer pathogenesis for better design of NF-κB-targeted therapy against this deadliest cancer.

Investigation into the Role of Long-Non-Coding RNA MIAT in Leukemia

Myocardial Infarction Associated Transcript (MIAT) is a nuclear long non-coding RNA (LncRNA) with four different splicing variants. MIAT dysregulation is associated with carcinogenesis, mainly acting as an oncogene regulating cellular growth, invasion, and metastasis. The aim of the current study is to investigate the role of MIAT in the regulation of T and chronic myeloid leukemic cell survival. To this end, MIAT was silenced using MIAT-specific siRNAs in leukemic cell lines, and functional assays were performed thereafter. This investigation also aims to investigate the effects of MIAT silencing on the expression of core genes involved in cancer. Functional studies and gene expression determination confirm that MIAT knockdown not only affects short- and long-term survival and the apoptosis of leukemic cells but also plays a pivotal role in the alteration of key genes involved in cancer, including c-MYC and HIF-1A. Our observations suggest that MIAT could act as an oncogene and it has the potential to be used not only as a reliable biomarker for leukemia, but also be employed for prognostic and therapeutic purposes.

Hepatocyte Nuclear Factor 1α Proinflammatory Effect Linked to the Overexpression of Liver Nuclear Factor–κB in Experimental Model of Chronic Kidney Disease

Chronic kidney disease (CKD) is associated with low-grade inflammation that activates nuclear factor–κB (NF–κB), which upregulates the expression of numerous NF–κB responsive genes, including the genes encoding IL-6, ICAM-1, VCAM-1, and MCP-1. Herein, we found the coordinated overexpression of genes encoding RelA/p65 (a subunit of NF–κB) and HNF1α in the livers of chronic renal failure (CRF) rats—an experimental model of CKD. The coordinated overexpression of RelA/p65 and HNF1α was associated with a significant increase in IL-6, ICAM-1, VCAM-1, and MCP-1 gene expressions. A positive correlation between liver RelA/p65 mRNA levels and a serum concentration of creatinine and BUN suggest that RelA/p65 gene transcription is tightly related to the progression of renal failure. The knockdown of HNF1α in the HepG2 cell line by siRNA led to a decrease in Rel A/p65 mRNA levels. This was associated with a decrease in IL-6, ICAM-1, VCAM-1, and MCP-1 gene expressions. The simultaneous repression of HNF-1α and RelA/p65 by clofibrate is tightly associated with the downregulation of IL-6, ICAM-1, VCAM-1, and MCP-1 gene expression. In conclusion, our findings suggest that NF–κB could be a downstream component of the HNF1α-initiated signaling pathway in the livers of CRF rats.

Evaluation of chemo-preventive efficacy of Ficus religiosa latex extract by flow cytometry analysis and gene expression studies performed by RT-PCR in various cell lines

Background

An extract of Ficus religiosa latex has been previously found to possess potent pharmacological activity with high antioxidant content phytochemical. The present research was conducted to investigate the chemo-preventive efficacy of latex extract on human breast adenocarcinoma MDA MB 231, human neroblastoma IMR 32, and human colorectal HCT 116 cell lines.

Results

The results showed that the latex crude extract induced cytotoxicity in all the selected cell lines with IC50 value 4.8 ± 1.13 μg/ml against the IMR 32 cell line. The cell cycle analysis results indicated the arrest and accumulation of cells at G1 phase in case of MDA MB 231 cells and HCT 116 cells whereas in the case of IMR 32 cells the arrest was in G2/M phase. The clear bands of fragments observed in DNA ladder experiments showed that apoptosis is induced by extracts in the cell lines. This could be correlated with the gene level expression studies on selected pro-apoptotic (p53 and caspase-3) and anti-apoptotic (Bcl-2, AKT) genes, which got upregulated and downregulated, respectively.

Conclusion

Based on the experimental evidence, Ficus religiosa contains phytochemicals with potent antitumor activities.

Intranuclear delivery of synthetic nuclear factor-kappa B p65 reduces inflammasomes after surgery

Patients undergoing surgery can suffer from various complications, including post-operative bleeding, local or systematic infection, and neurologic disorders. Major surgery can initiate innate immune responses and trigger overproduction of inflammatory mediators, which can contribute to organ dysfunction. Inflammasomes are innate immune complexes, which are connected to the pathogenesis of various diseases, including atherosclerosis, hemorrhagic brain injury, and Alzheimer's disease. In the present study, we hypothesized that nucleotide-binding oligomerization domain-containing-like receptor protein (NLRP) inflammasomes may have a role in the pathological effects of surgery. Therefore, we designed a protein inhibitor of nuclear factor kappa B (NF-κB) p65 transcripts, called nt-p65-TMD (nuclear transducible (nt) transcription modulated domain (TMD) of RelA (p65)), that can penetrate the nucleus, and evaluated its therapeutic efficacy for dampening surgery-induced inflammasome activation. It was found that the nt-p65-TMD significantly reduced the NLRP1 inflammasome complex components (NLRP1, ASC, and Caspase-1) and interleukin (IL)-1β and IL-18 productions in the spleen after surgery. In the spleen, specific cell population and selective mediators were altered after surgery with/without nt-p65-TMD treatment. Also, we found that treatment of nt-p65-TMD decreased cell death in the spleen after surgery. Therefore, nt-p65-TMD is a potential novel strategy for reducing surgery-induced NLRP1 inflammasome and complications.

Network analysis of pseudogene-gene relationships: from pseudogene evolution to their functional potentials

Pseudogenes are fossil relatives of genes. Pseudogenes have long been thought of as "junk DNAs", since they do not code proteins in normal tissues. Although most of the human pseudogenes do not have noticeable functions, ∼20% of them exhibit transcriptional activity. There has been evidence showing that some pseudogenes adopted functions as lncRNAs and work as regulators of gene expression. Furthermore, pseudogenes can even be "reactivated" in some conditions, such as cancer initiation. Some pseudogenes are transcribed in specific cancer types, and some are even translated into proteins as observed in several cancer cell lines. All the above have shown that pseudogenes could have functional roles or potentials in the genome. Evaluating the relationships between pseudogenes and their gene counterparts could help us reveal the evolutionary path of pseudogenes and associate pseudogenes with functional potentials. It also provides an insight into the regulatory networks involving pseudogenes with transcriptional and even translational activities.In this study, we develop a novel approach integrating graph analysis, sequence alignment and functional analysis to evaluate pseudogene-gene relationships, and apply it to human gene homologs and pseudogenes. We generated a comprehensive set of 445 pseudogene-gene (PGG) families from the original 3,281 gene families (13.56%). Of these 438 (98.4% PGG, 13.3% total) were non-trivial (containing more than one pseudogene). Each PGG family contains multiple genes and pseudogenes with high sequence similarity. For each family, we generate a sequence alignment network and phylogenetic trees recapitulating the evolutionary paths. We find evidence supporting the evolution history of olfactory family (both genes and pseudogenes) in human, which also supports the validity of our analysis method. Next, we evaluate these networks in respect to the gene ontology from which we identify functions enriched in these pseudogene-gene families and infer functional impact of pseudogenes involved in the networks. This demonstrates the application of our PGG network database in the study of pseudogene function in disease context.

Dihydroorotate dehydrogenase (DHODH) inhibitors affect ATP depletion, endogenous ROS and mediate S-phase arrest in breast cancer cells

Dihydroorotate dehydrogenase (DHODH) is the key enzyme in de novo biosynthesis of pyrimidine in both prokaryotes and eukaryotes. The de novo pathway of pyrimidine biosynthesis is essential in cancer cells proliferation. Leflunomide is an approved DHODH inhibitor that has been widely used for the treatment of arthritis. Similarly, brequinar sodium is another DHODH inhibitor that showed anti-tumour effect in MC38 colon carcinoma cells when used in combination with fluorouracil. Despite the potential role of DHODH inhibitors in cancer therapy, their mechanisms of action remain obscure and await further elucidation. Here, we evaluated the effect of DHODH inhibitors on the production of ATP and ROS in sensitive and non-sensitive breast cancer cells. Subsequently, the effects of DHODH inhibitors on cell cycle as well as on signalling molecules such as p53, p65 and STAT6 were evaluated in sensitive T-47D and non-sensitive MDAMB-436 cells. The correlations between DHODH protein expression, proliferation speed and sensitivity to DHODH inhibitors were also investigated in a panel of cancer cell lines. DHODH inhibitors-sensitive T-47D and MDAMB-231 cells appeared to preserve ROS production closely to endogenous ROS level whereas the opposite was observed in non-sensitive MDAMB-436 and W3.006 cells. In addition, we observed approximately 90% of intracellular ATP depletion in highly sensitive T-47D and MDAMB-231 cells compared to non-sensitive MDAMB-436 cells. There was significant over-expression of p53, p65 and STAT6 signalling molecules in sensitive cells which may be involved in mediating the S-phase arrest in cell cycle progression. The current study suggests that DHODH inhibitors are most effective in cells that express high levels of DHODH enzyme. The inhibition of cell proliferation by these inhibitors appears to be accompanied by ROS production as well as ATP depletion. The increase in expression of signalling molecules observed may be due to pyrimidine depletion which subsequently leads to cell cycle arrest at S-phase.

Differential Response of Two Human Breast Cancer Cell Lines to the Phenolic Extract from Flaxseed Oil

Many studies have evidenced that the phenolic components from flaxseed (FS) oil have potential health benefits. The effect of the phenolic extract from FS oil has been evaluated on two human breast cancer cell lines, MCF7 and MDA-MB231, and on the human non-cancerous breast cell line, MCF10A, by SRB assay, cellular death, cell cycle, cell signaling, lipid peroxidation and expression of some key genes. We have evidenced that the extract shows anti-proliferative activity on MCF7 cells by inducing cellular apoptosis, increase of the percentage of cells in G0/G1 phase and of lipid peroxidation, activation of the H2AX signaling pathway, and upregulation of a six gene signature. On the other hand, on the MDA-MB2131 cells we verified only an anti-proliferative activity, a weak lipid peroxidation, the activation of the PI3K signaling pathway and an up-regulation of four genes. Overall these data suggest that the extract has both cytotoxic and pro-oxidant effects only on MCF7 cells, and can act as a metabolic probe, inducing differences in the gene expression. For this purpose, we have performed an interactomic analysis, highlighting the existing associations. From this approach, we show that the phenotypic difference between the two cell lines can be explained through their differential response to the phenolic extract.

RelA-Induced Interferon Response Negatively Regulates Proliferation

Both oncogenic and tumor-suppressor activities are attributed to the Nuclear Factor kappa B (NF-kB) pathway. Moreover, NF-kB may positively or negatively regulate proliferation. The molecular determinants of these opposing roles of NF-kB are unclear. Using primary human mammary epithelial cells (HMEC) as a model, we show that increased RelA levels and consequent increase in basal transcriptional activity of RelA induces IRF1, a target gene. Induced IRF1 upregulates STAT1 and IRF7, and in consort, these factors induce the expression of interferon response genes. Activation of the interferon pathway down-regulates CDK4 and up-regulates p27 resulting in Rb hypo-phosphorylation and cell cycle arrest. Stimulation of HMEC with IFN-γ elicits similar phenotypic and molecular changes suggesting that basal activity of RelA and IFN-γ converge on IRF1 to regulate proliferation. The anti-proliferative RelA-IRF1-CDK4 signaling axis is retained in ER+/HER2- breast tumors analyzed by The Cancer Genome Atlas (TCGA). Using immuno-histochemical analysis of breast tumors, we confirm the negative correlation between RelA levels and proliferation rate in ER+/HER2- breast tumors. These findings attribute an anti-proliferative tumor-suppressor role to basal RelA activity. Inactivation of Rb, down-regulation of RelA or IRF1, or upregulation of CDK4 or IRF2 rescues the RelA-IRF1-CDK4 induced proliferation arrest in HMEC and are points of disruption in aggressive tumors. Activity of the RelA-IRF1-CDK4 axis may explain favorable response to CDK4/6 inhibition observed in patients with ER+ Rb competent tumors.

Sustained, neuron-specific IKK/NF-κB activation generates a selective neuroinflammatory response promoting local neurodegeneration with aging

Background

Increasing evidence indicates that neuroinflammation is a critical factor contributing to the progression of various neurodegenerative diseases. The IKK/NF-κB signalling system is a central regulator of inflammation, but it also affects neuronal survival and differentiation. A complex interplay between different CNS resident cells and infiltrating immune cells, which produce and respond to various inflammatory mediators, determines whether neuroinflammation is beneficial or detrimental. The IKK/NF-κB system is involved in both production of and responses to these mediators, although the precise contribution depends on the cell type as well as the cellular context, and is only partially understood. Here we investigated the specific contribution of neuronal IKK/NF-κB signalling on the regulation of neuroinflammatory processes and its consequences. To address this issue, we established and analysed a conditional gain-of-function mouse model that expresses a constitutively active allele of IKK2 in principal forebrain neurons (IKK2^nCA). Proinflammatory gene and growth factor expression, histopathology, microgliosis, astrogliosis, immune cell infiltration and spatial learning were assessed at different timepoints after persistent canonical IKK2/NF-κB activation.

Results

In contrast to other cell types and organ systems, chronic IKK2/NF-κB signalling in forebrain neurons of adult IKK2^nCA animals did not cause a full-blown inflammatory response including infiltration of immune cells. Instead, we found a selective inflammatory response in the dentate gyrus characterized by astrogliosis, microgliosis and Tnf-α upregulation. Furthermore, downregulation of the neurotrophic factor Bdnf correlated with a selective and progressive atrophy of the dentate gyrus and a decline in hippocampus-dependent spatial learning. Neuronal degeneration was associated with increased Fluoro-jade staining, but lacked activation of apoptosis. Remarkably, neuronal loss could be partially reversed when chronic IKK2/NF-κB signalling was turned off and Bdnf expression was restored.

Conclusion

Our results demonstrate that persistent IKK2/NF-κB signalling in forebrain neurons does not induce overall neuroinflammation, but elicits a selective inflammatory response in the dentate gyrus accompanied by decreased neuronal survival and impaired learning and memory. Our findings further suggest that chronic activation of neuronal IKK2/NF-κB signalling, possibly as a consequence of neuroinflammatory conditions, is able to induce apoptosis-independent neurodegeneration via paracrine suppression of Bdnf synthesis.

Targeting nuclear factor-kappa B to overcome resistance to chemotherapy

Intrinsic or acquired resistance to chemotherapeutic agents is a common phenomenon and a major challenge in the treatment of cancer patients. Chemoresistance is defined by a complex network of factors including multi-drug resistance proteins, reduced cellular uptake of the drug, enhanced DNA repair, intracellular drug inactivation, and evasion of apoptosis. Pre-clinical models have demonstrated that many chemotherapy drugs, such as platinum-based agents, antracyclines, and taxanes, promote the activation of the NF-κB pathway. NF-κB is a key transcription factor, playing a role in the development and progression of cancer and chemoresistance through the activation of a multitude of mediators including anti-apoptotic genes. Consequently, NF-κB has emerged as a promising anti-cancer target. Here, we describe the role of NF-κB in cancer and in the development of resistance, particularly cisplatin. Additionally, the potential benefits and disadvantages of targeting NF-κB signaling by pharmacological intervention will be addressed.

Overexpression of p65 attenuates celecoxib-induced cell death in MDA-MB-231 human breast cancer cell line

BACKGROUND

Celecoxib is a selective cyclooxygenase (COX)-2 inhibitor that has been reported to reduce the risk of breast cancer. In our previous study, celecoxib induced apoptosis and caused cell cycle arrest at the G0/G1 phase in the breast cancer cell line MDA-MB-231, and its effects were mediated by downregulation of NF-κB signaling. The NF-κB p65/RelA subunit may play a role in cell death through the activation of anti-apoptotic target genes including the inhibitor of apoptosis (IAP) and Bcl-2 families, and inhibition of protein kinase B/Akt. The aim of the present study was to investigate p65 as the potential target of celecoxib treatment and determine whether p65 overexpression can override the inhibitory effect of celecoxib on NF-κB activity and affect cell survival.

METHODS

The effects of p65 overexpression on celecoxib-inhibited NF-κB transcriptional activity were examined by western blotting, electrophoretic mobility shift assay (EMSA) and luciferase reporter gene assay. Cell viability and cell death were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay, and the levels of cleaved poly(ADP-ribose) polymerase (PARP) and caspase. Anti-apoptotic NF-κB target genes and cell cycle regulators were examined by western blotting to screen for the expression of target genes under direct regulation by p65.

RESULTS

Overexpression of p65 increased NF-κB transcriptional activity and interfered with celecoxib-mediated apoptosis as assessed by MTT assay and caspase-3, caspase-9, and PARP expressions. Exogenously overexpressed p65 upregulated NF-κB-responsive genes, including anti-apoptotic genes such as survivin and XIAP, and the cell cycle regulatory gene cyclin D1. However, p65 overexpression did not affect celecoxib-induced p-Akt inactivation, suggesting that celecoxib might have separate molecular mechanisms for regulating Akt signaling independently of its inhibition of NF-κB transcriptional activity.

CONCLUSIONS

p65 is a pivotal anti-apoptotic factor that can reverse celecoxib-induced growth inhibition in MDA-MB-231 cells.

Involvement of interleukin-1β mediated nuclear factor κB signalling pathways to down-regulate prostate-specific antigen and cell proliferation in LNCaP prostate cancer cells

Involvement of NF-κB (nuclear factor κB) mediated by IL-1β (interleukin-1β) on cell proliferation and PSA (prostate-specific antigen) production of LNCaP prostate cell lines and the possible cross-talk with Akt (also known as protein kinase B) signalling pathway has been investigated. NF-κB and Akt were analysed by Western blotting from LNCaP cells treated by IL-1β before proliferation and PSA production were measured. IL-1β inhibited proliferation and decreased PSA production. The Akt pathway was not sensitive, whereas NF-κB phosphorylation occurred as a result of treatment. PSA production and proliferation of LNCaP cells were down-regulated by NF-κB mediated by IL-1β promoting anti-apoptotic signalling and co-suppressor factors of PSA expression. IL-1β through NF-κB activation provides a rationale for therapeutic approaches in the anticancer treatment of prostate.

Upsides and downsides of reactive oxygen species for cancer: the roles of reactive oxygen species in tumorigenesis, prevention, and therapy

SIGNIFICANCE

Extensive research during the last quarter century has revealed that reactive oxygen species (ROS) produced in the body, primarily by the mitochondria, play a major role in various cell-signaling pathways. Most risk factors associated with chronic diseases (e.g., cancer), such as stress, tobacco, environmental pollutants, radiation, viral infection, diet, and bacterial infection, interact with cells through the generation of ROS.

RECENT ADVANCES

ROS, in turn, activate various transcription factors (e.g., nuclear factor kappa-light-chain-enhancer of activated B cells [NF-κB], activator protein-1, hypoxia-inducible factor-1α, and signal transducer and activator of transcription 3), resulting in the expression of proteins that control inflammation, cellular transformation, tumor cell survival, tumor cell proliferation and invasion, angiogenesis, and metastasis. Paradoxically, ROS also control the expression of various tumor suppressor genes (p53, Rb, and PTEN). Similarly, γ-radiation and various chemotherapeutic agents used to treat cancer mediate their effects through the production of ROS. Interestingly, ROS have also been implicated in the chemopreventive and anti-tumor action of nutraceuticals derived from fruits, vegetables, spices, and other natural products used in traditional medicine.

CRITICAL ISSUES

These statements suggest both "upside" (cancer-suppressing) and "downside" (cancer-promoting) actions of the ROS. Thus, similar to tumor necrosis factor-α, inflammation, and NF-κB, ROS act as a double-edged sword. This paradox provides a great challenge for researchers whose aim is to exploit ROS stress for the development of cancer therapies.

FUTURE DIRECTIONS

the various mechanisms by which ROS mediate paradoxical effects are discussed in this article. The outstanding questions and future directions raised by our current understanding are discussed.

Rhein induces apoptosis in human breast cancer cells

Human breast cancers cells overexpressing HER2/neu are more aggressive tumors with poor prognosis, and resistance to chemotherapy. This study investigates antiproliferation effects of anthraquinone derivatives of rhubarb root on human breast cancer cells. Of 7 anthraquinone derivatives, only rhein showed antiproliferative and apoptotic effects on both HER2-overexpressing MCF-7 (MCF-7/HER2) and control vector MCF-7 (MCF-7/VEC) cells. Rhein induced dose- and time-dependent manners increase in caspase-9-mediated apoptosis correlating with activation of ROS-mediated activation of NF-κB- and p53-signaling pathways in both cell types. Therefore, this study highlighted rhein as processing anti-proliferative activity against HER2 overexpression or HER2-basal expression in breast cancer cells and playing important roles in apoptotic induction of human breast cancer cells.

Nucleolar NF-κB/RelA mediates apoptosis by causing cytoplasmic relocalization of nucleophosmin

In a number of contexts, and particularly in response to cellular stress, stimulation of the NF-kappaB (NF-κB) pathway promotes apoptosis. One mechanism underlying this pro-apoptotic activity is nucleolar sequestration of RelA, which is reported to cause cell death by repressing NF-κB-driven transcription. Here, we identify a novel and distinct nucleolar activity of RelA that induces apoptosis. We demonstrate, using a viral nucleolar localization signal (NoLS)-RelA fusion protein, that direct targeting of RelA to the nucleolus mediates apoptosis, independent of NF-κB transcriptional activity. We demonstrate a requirement for nucleophosmin (NPM, B23.1) in this apoptotic effect, and the apoptotic effect of stress-induced nucleolar RelA. We show by multiple approaches that nucleolar translocation of RelA is causally involved in the relocalization of NPM from the nucleolus to the cytoplasm and that RelA-induced cytoplasmic NPM mediates apoptosis by facilitating the mitochondrial accumulation of BAX. These data uncover a novel stress-response pathway and mechanism by which RelA promotes apoptosis, independent of its effects on NF-κB transcriptional activity. These findings are relevant to the design of novel anticancer agents that target RelA to this compartment.

Gadd45 proteins as critical signal transducers linking NF-kappaB to MAPK cascades

The growth arrest and DNA damage-inducible 45 (Gadd45) proteins are a group of critical signal transducers that are involved in regulations of many cellular functions. Accumulated data indicate that all three Gadd45 proteins (i.e., Gadd45alpha, Gadd45beta, and Gadd45gamma) play essential roles in connecting an upstream sensor module, the transcription Nuclear Factor-kappaB (NF-kappaB), to a transcriptional regulating module, mitogen-activated protein kinase (MAPK). This NF-kappaB-Gadd45(s)-MAPK pathway responds to various kinds of extracellular stimuli and regulates such cell activities as growth arrest, differentiation, cell survival, and apoptosis. Defects in this pathway can also be related to oncogenesis. In the first part of this review, the functions of Gadd45 proteins, and briefly NF-kappaB and MAPK, are summarized. In the second part, the mechanisms by which Gadd45 proteins are regulated by NF-kappaB, and how they affect MAPK activation, are reviewed.

Host nuclear factor-kappaB activation potentiates lung cancer metastasis

Epidemiologic and experimental evidence suggests that a link exists between inflammation and cancer, although this relationship has only recently begun to be elucidated for lung cancer, the most frequently fatal human tumor. Nuclear factor-kappaB (NF-kappaB), a transcription factor that controls innate immune responses in the lungs, has been implicated as an important determinant of cancer cell proliferative and metastatic potential; however, its role in lung tumorigenesis is uncertain. Here, we specifically examine the role of NF-kappaB-induced airway inflammation in lung cancer metastasis using a model of intravenous injection of Lewis lung carcinoma cells into immunocompetent C57Bl/6 mice. Induction of lung inflammation by direct and specific NF-kappaB activation in airway epithelial cells potentiates lung adenocarcinoma metastasis. Moreover, we identify resident lung macrophages as crucial effectors of lung susceptibility to metastatic cancer growth. We conclude that NF-kappaB activity in host tissue is a significant factor in the development of lung metastasis.

Use of bioluminescent imaging to investigate the role of nuclear factor-kappaBeta in experimental non-small cell lung cancer metastasis

Nuclear factor (NF)-kappaB is frequently over-expressed in non-small cell lung cancer (NSCLC), but the exact role of this observation remains unclear. In this regard, activation of the transcription factor may govern distinct steps of NSCLC progression, such as carcinogenesis, angiogenesis, and metastasis. In these studies we attempted to dissect the effects of two proteins of the NF-kappaB pathway (p65/RelA and IkappaBetaalpha) on experimental metastasis of murine NSCLC, using a novel approach of bioluminescent detection of NF-kappaB activation in tumor cells. Stable integration of a NF-kappaBeta reporter confirmed high basal activation of the transcription factor in mouse NSCLC cells in vitro and during experimental metastasis to the lungs, like human NSCLC. In the mouse model of NSCLC metastasis, NF-kappaBeta-dependent luciferase expression served as a reliable indicator of tumor cell delivery to the lungs, establishment of metastatic tumors, and lung tumor burden. In vitro transient p65/RelA and IkappaBetaalpha gene transfer to mouse NSCLC cells resulted, respectively, in significant NF-kappaB activation and inhibition, without affecting cell growth. However, p65/RelA overexpression in NSCLC cells drastically reduced in vivo metastasis to the lungs, while overexpression of IkappaBetaalpha had no effect. In conclusion, using bioluminescent detection of NF-kappaB activation in mouse lug adenocarcinoma cells, we found a negative impact of p65/RelA on NSCLC metastasis.

Phosphoprotein levels, MAPK activities and NFkappaB expression are affected by fisetin

Flavonoids, polyphenolic phytochemicals, are ubiquitous in plants and are commonly present in the human diet. They may exert diverse beneficial effects, including antioxidant and anticarcinogenic activities. The present study was designed to evaluate three biomolecules that play important roles in the apoptotic process: mitogen-activated protein kinases, protein phosphatases and NFkappaB, using HL60 cells treated with fisetin as an experimental model. Our results demonstrated that cells treated with fisetin presented high expression of NFkappaB, activation of MAPK p38 and an increase of phosphoprotein levels; inhibition of enzymes involved in redox status maintenance were also observed. Our findings reinforce the hypothesis that fisetin is likely to exert beneficial and/or toxic actions on cells not through its potential as antioxidant but rather through its modulation of protein kinase and phosphatase signaling cascades. Additionally, our results also indicate that the cellular effects of fisetin will ultimately depend on the cell type and on the extent to which they associate with the cells, either by interactions at the membrane or by uptake into the cytosol.

Inflammation and cancer: How hot is the link?

Although inflammation has long been known as a localized protective reaction of tissue to irritation, injury, or infection, characterized by pain, redness, swelling, and sometimes loss of function, there has been a new realization about its role in a wide variety of diseases, including cancer. While acute inflammation is a part of the defense response, chronic inflammation can lead to cancer, diabetes, cardiovascular, pulmonary, and neurological diseases. Several pro-inflammatory gene products have been identified that mediate a critical role in suppression of apoptosis, proliferation, angiogenesis, invasion, and metastasis. Among these gene products are TNF and members of its superfamily, IL-1alpha, IL-1beta, IL-6, IL-8, IL-18, chemokines, MMP-9, VEGF, COX-2, and 5-LOX. The expression of all these genes are mainly regulated by the transcription factor NF-kappaB, which is constitutively active in most tumors and is induced by carcinogens (such as cigarette smoke), tumor promoters, carcinogenic viral proteins (HIV-tat, HIV-nef, HIV-vpr, KHSV, EBV-LMP1, HTLV1-tax, HPV, HCV, and HBV), chemotherapeutic agents, and gamma-irradiation. These observations imply that anti-inflammatory agents that suppress NF-kappaB or NF-kappaB-regulated products should have a potential in both the prevention and treatment of cancer. The current review describes in detail the critical link between inflammation and cancer.

NF-κB in solid tumors

Cancer is a multistep process during which cells acquire genetic alterations that drive the progressive transformation of normal cells into highly malignant cells. Self-sufficiency in growth, insensitivity to anti-growth signals, evasion of apoptosis, limitless replicative potential, sustained angiogenesis, tissue invasion and metastasis, are signatures of transformed cells. NF-kappaB is a key actor in tumorigenesis given its ability to control the expression and the function of a number of genes involved in these processes. Indeed, constitutive activation of NF-kappaB is a common feature of many human tumors, while its sustained activation during inflammation predisposes normal cells to neoplastic transformation. Since suppression of NF-kappaB has been shown to inhibit oncogenic potential of transformed cells, targeting it should be effective in the prevention and treatment of cancer.

Can targeting apoptosis resolve the cancer saga?

A defect in apoptosis is almost always linked to many pathologies, including cancer. Carcinogenesis has been linked to abnormalities in the apoptotic pathway, and many drugs that are targeted at different parts of this pathway are being developed. There have been many promising drugs that target the extrinsic death receptor pathway as well as the intrinsic mitochondrial apoptotic pathway. There have also been developments in targeting initiator and effector caspases, as well as the death domains that are involved in transducing the apoptotic signals. In this review, the authors will briefly explain how apoptosis deregulation can lead to cancer and discuss drugs that promise success in targeting this anomaly. This article shall also explain how co-treatments with chemotherapy can increase survival of cancer patients. There is a problem of acquired resistance in some of these therapies but there may be ways to overcome this.

Pro-apoptotic role of NF-kappaB: implications for cancer therapy

Nuclear factor-kappaB (NF-kappaB) is generally viewed as anti-apoptotic and oncogenic, leading to a quest for its inhibitors. However, recent evidence suggests that in some situations NF-kappaB may promote apoptosis. Depending on the specific cell type and the stimulus involved, NF-kappaB activation may lead to either anti- or pro-apoptotic response. Both these effects can be mediated by NF-kappaB in a context-dependent manner by selectively regulating its target genes. In this review, we discuss the evidence for NF-kappaB's pro-apoptotic role and explore the possible mechanisms behind it. We emphasize that rather than trying to inhibit NF-kappaB in cancer therapy, agents should be developed to unleash its pro-apoptotic ability.

Overexpression of p65/RelA potentiates curcumin-induced apoptosis in HCT116 human colon cancer cells

Curcumin, the yellow pigment in the spice turmeric, has potent chemopreventive activities that involve diverse molecular pathways. It is widely believed that curcumin pro-apoptotic properties are mediated by downregulation of NF kappa B (NFkappaB). The p65/RelA subunit of NFkappaB may influence cell death, in part by activation of NFkappaB anti-apoptotic target genes including X-linked inhibitor of apoptosis (XIAP), A20, bcl-xL and inhibition of sustained activation of c-Jun N-terminal kinase (JNK). We have shown previously that curcumin inhibits NFkappaB, activates JNK and promotes apoptosis in HCT116 colorectal cancer cells. Here, we show that forced overexpression of p65 does not affect curcumin-induced JNK activation. Indeed, overexpression of p65 enhanced curcumin-mediated apoptosis as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay and poly(ADP-ribose) polymerase (PARP) cleavage. This potentiating effect of p65 upon curcumin-mediated apoptosis was reversed by transfection of cells with an IkappaB super-repressor (DeltaNIkappaB). Curcumin treatment inhibited expression of NFkappaB anti-apoptotic target genes in mock-transfected and in p65-overexpressing HCT116 cells, although expression levels remained higher in the latter. Taken together, these results show that curcumin-mediated activation of JNK or induction of apoptosis does not require inhibition of p65. Furthermore, curcumin/p65 synergy in promotion of apoptosis cannot be attributed to active repression of NFkappaB anti-apoptotic genes.

Bcl-2 overexpression in melanoma cells increases tumor progression-associated properties and in vivo tumor growth

In this study, we demonstrated that bcl-2 overexpression in human melanoma cells consistently enhanced the activity of multiple metastasis-related proteinases, in vitro cell invasion, and in vivo tumor growth. In particular, by using the M14 parental cell line, the MN8 control clone, and two bcl-2 overexpressing derivatives, we found that bcl-2 overexpressing cells exposed to hypoxia, when compared to parental cells, expressed higher level of several metalloproteases (MMPs) such as MMP-2, MMP-7, MT1-MMP, and tissue inhibitors of metalloproteases-1 and -2. Moreover, bcl-2 overexpression in melanoma cells enhanced in vitro invasion on matrigel and, in vivo tumor growth. The more aggressive behavior of bcl-2 transfectants tumors is significantly associated to an increase in MMP-2 expression as well as in a more elevated microvessel density as compared to the parental line. Taken together, our data suggest that bcl-2 plays a pivotal role in the regulation of molecules associated with the migratory and invasive phenotype, contributing, in cooperation to hypoxia, to tumor progression.

Nuclear factor kappaB is downregulated and correlates with p53 in the Min mouse mucosa during an accelerated tumor growth

The nuclear factor kappaB signaling pathway has gained attention for its role in the carcinogenic process. We have measured the protein levels of the p65 subunit during a growth of adenomas in the Min mouse model for colon cancer. To study how an accelerated growth of adenomas affect cell signalling, adenoma growth was increased by an inulin diet (10%) that we have shown previously to be a promotor of adenoma formation. In our study, the association between NF-kappaB, p53, beta-catenin, Fas and COX-2 were evaluated by measuring their protein levels in 9- and 15-week old Min mouse adenomas and surrounding mucosa. The amount of p65 rouse between 9- and 15-weeks in the mucosa of the control-fed mice (p = 0.032). The inulin-fed mice had less p65 in the nucleus of the mucosa at 15 weeks of age compared to the control (p = 0.064), although the adenomas were significantly larger (1.46 mm +/- 0.12 for inulin, 0.97 mm +/- 0.12 for control, p < 0.001). Nuclear p65 correlated positively with nuclear p53 in the mucosa (p < 0.001) and adenoma (p < 0.001) tissues. Also, p65 correlated positively with nuclear beta-catenin in the mucosa (p = 0.012) and the adenoma (p = 0.001). Fas expression increased in the inulin group between 9-15 weeks (p = 0.034) and correlated negatively with p65 (p = 0.03). The amount of COX-2 in the adenoma tissue increased between 9-15 weeks and did not correlate with p65. The results suggest that p65 is involved in a p53-dependent apoptotic response in the Min mouse.

Increased expression of NF-κB p65 in CagA+ H. pylori-related gastric precancerous lesions and carcinoma

AIM: To determine the expression of nuclear factor kappa B (NF-κB) in human gastric precancerous lesions and carcinoma and its correlation with CagA⁺H. pylori infection.

METHODS: The expression of NF-κB p65 was detected by immunohistochemistry (SABC assay), and H. pylori were examined using 14C-breath test, rapid urease test and Warthin-Starry staining in patients with chronic superficial gastritis (CSG: n = 34), intestinal metaplasia (IM: n = 31), atypical dysplasia (AD: n = 34) and gastric cancer (GC: n = 55). Serum CagA IgG antibody was detected by dot immunogold filtration assay. The correlations of NF-κB p65 expression with CagA⁺H. pylori infection as well as the histological types, clinicopathological stages and lymph node metastasis were analyzed.

RESULTS: The expression of NF-κB p65 in CSG, IM, AD, GC was 15.0%, 41.9%, 64.7%, and 78.2%, respectively, and there were significant differences between them (χ² = 43.98, P <0.01). The rates of H. pylori infection were 70.0%, 67.7%, 73.5%, and 54.5%, respectively, and there were no significant differences between them (P > 0.05). The percentage of CagA⁺H. pylori infection were 53.6%, 61.9%, 68.0%, and 73.3%, respectively, and there were no significantdifferences (P > 0.05). In IM, the positive rate of NF-κB p65 expression in H. pylori or CagA⁺H. pylori positive patients were significantly higher than that in patients without H. pylori infection or with CagA- H. pylori infection (57.1%, 76.9% vs 10%, 25.0%, P <0.05). In GC patients, the positive expression of NF-κB p65 was correlation with the T stages(χ² = 5.91, P <0.05)and lymph node metastasis (χ² = 7.47, P <0.01), but not with the pathohistological types (P > 0.05).

CONCLUSION: NF-κB is constitutively activated in human gastric precancerous lesions and carcinoma tissue and correlates with tumor progression. The early activation may be related to CagA⁺H. pylori infection.

On the antioxidant mechanisms of Bcl-2: a retrospective of NF-kappaB signaling and oxidative stress

Antioxidant and prooxidant signaling pathways are emanating as major players in, and regulators of, cell death and apoptosis. Redox conception of the critical role of oxidative stress in determining cell fate is being established-a foundation that craves deeper than the basic understanding of physiochemical interactions to extend beyond that into the realms of deciphering the molecular codes implicated with apoptosis. The proto-oncogene Bcl-2 is no stranger being a major player and decoder in controlling apoptosis, ostensibly via the regulation of redox equilibrium and disequilibrium. One of those potential mechanisms exhibited by Bcl-2 is its ability to counteract the detrimental effects of cell damage caused by free radicals, thereby gaining its well-known property of being an antioxidant. But the question is: what are the molecular mechanisms involved with the antioxidant role of Bcl-2 in the face of cell damage and apoptosis? Currently, a stance is being upheld in that the Bcl-2 antioxidant efficacy should be weighed against its ability to manipulate transcriptional control, through the regulation of specific transcription factors. NF-kappaB is no doubt one of the best candidates when it comes to the arena of oxidative stress, inflammation, and apoptosis. Therein, current themes in the burgeoning antioxidant role of Bcl-2 are exposed within the context of transcriptional control of NF-kappaB, thereby holding potential avenues for alleviating therapeutic approaches in the regulation of apoptosis.

Regulation of NF-κB by atypical activators and tumour suppressors

The RelA(p65) NF-κB (nuclear factor κB) subunit is typically thought of as being antiapoptotic and tumour-promoting. However, in our laboratory, we have discovered that RelA can inhibit, rather than induce, antiapoptotic gene expression when activated by certain chemotherapeutic drugs, UV light or through the action of the ARF tumour suppressor. These observations explain why RelA can sometimes facilitate rather than inhibit apoptosis and also exhibits tumour-suppressor characteristics in vivo. A better understanding of these processes and an ability to analyse RelA function in tumours could lead to improved cancer diagnosis, choice of therapy and, ultimately, development of new drugs.

NF-kappaB: tumor promoter or suppressor?

A role for the NF-kappaB family of transcription factors as tumor promoters is firmly established. However, other data suggest that NF-kappaB can also inhibit tumor growth. Moreover, NF-kappaB activity is modulated by tumor suppressors, such as p53 and ARF, whereby NF-kappaB subunits repress, rather than activate, the expression of tumor-promoting genes. This suggests a dual function of NF-kappaB during tumor progression - in the early stages, NF-kappaB inhibits tumor growth but, as further mutations lead to a loss of tumor suppressor expression, the oncogenic functions of NF-kappaB become unleashed, allowing it to actively contribute to tumorigenesis. Here, I discuss this hypothesis, its implications for NF-kappaB function, and how this might influence the use of NF-kappaB-based anticancer therapies.

Crossregulation of NF-kappaB by the APC/GSK-3beta/beta-catenin pathway

Glycogen synthase kinase-3beta (GSK-3beta) and adenomatous polyposis coli (APC) play an important role in the regulation of beta-catenin. Inhibition of or defects in their functions can lead to activation of beta-catenin. beta-catenin has been recently found to interact with and inhibit nuclear factor kappa B (NF-kappaB). However, the regulatory roles of GSK-3beta/APC on the NF-kappaB signaling pathway are unknown because of their diverse effects. In this study, we investigated whether GSK-3beta/APC might regulate NF-kappaB activity through beta-catenin. We found that inhibition of GSK-3beta suppressed NF-kappaB activity, whereas reexpression of APC restored NF-kappaB activity in APC mutated cells. The regulatory effects were through beta-catenin because depletion of beta-catenin with small interfering RNA (siRNA) in the same systems reversed the effects. The regulatory relationship was further supported by the analysis of primary breast tumor tissues in vivo in which NF-kappaB target TRAF1 was inversely correlated with activated beta-catenin. Thus, APC/GSK-3beta, through beta-catenin, may crossregulate NF-kappaB signaling pathway.

Divergent C-terminal transactivation domains of Rel/NF-κB proteins are critical determinants of their oncogenic potential in lymphocytes

rel/nf-kappaB genes are amplified, overexpressed, or constitutively activated in many human hematopoietic tumors; however, the molecular mechanisms by which they contribute to tumorigenesis remain to be determined. Here, we explored the oncogenic potential of cellular Rel/NF-kappaB proteins in vitro and in vivo. We show that overexpression of wild-type mouse and human c-rel genes suffices to malignantly transform primary spleen cells in stringent soft agar assays and produce fatal tumors in vivo. In contrast relA and a constitutively active form of IKKbeta did not. Importantly, a hybrid RelA protein with its C-terminal transactivation domain substituted by that of v-Rel was potently oncogenic in vitro and in vivo. The transactivation domain of v-Rel selectively conferred an oncogenic phenotype upon the Rel homology domain (RHD) of RelA, but not to the more divergent RHDs of p50/NF-kappaB1, p52/NF-kappaB2, or RelB. Collectively, our results highlight important differences in the intrinsic oncogenic activity of mammalian c-Rel and RelA proteins, and indicate that critical determinants of their differential oncogenicity reside in their divergent transactivation domains. These findings provide experimental evidence for a role of mammalian Rel/NF-kappaB factors in leukemia/lymphomagenesis in an in vivo animal model, and are consistent with the implication of c-rel in many human lymphomas.

Immortalized embryonic mouse fibroblasts lacking the RelA subunit of transcription factor NF-kappaB have a malignantly transformed phenotype

The RelA transcription factor is part of dimeric complexes, most commonly either p50-RelA (NF-kappaB) heterodimers or RelA homodimers, that control a variety of cellular processes. Immortalized embryonic fibroblasts established from rela knockout mice have previously been shown to be more sensitive to apoptosis induced by tumor necrosis factor (TNF) than are control fibroblasts. In this report, we show that one line of rela-/- fibroblasts has additional phenotypes that distinguish them from control mouse fibroblasts. As compared to normal 3T3 cells, RelA-deficient fibroblasts have a spindled morphology, are less adherent to culture dishes, grow to a higher saturation density, and can form colonies in soft agar. These properties are consistent with a weakly transformed phenotype for rela-/- cells. Furthermore, RelA-deficient fibroblasts can form tumors in immunodeficient mice, but these tumors regress, probably because of the sensitivity of these cells to TNF. The ability of rela-/- fibroblasts to form colonies in soft agar can be reverted by re-expression of wild-type mouse RelA, but not by expression of RelA mutants that cannot form homodimers. There is no clear correlation between the absence of RelA and the levels of expression of other Rel/NF-kappaB family members or adhesion proteins (ICAM-1 and VCAM-1) whose genes have upstream kappaB sites. Taken together, these results suggest that RelA has tumor suppressing activity under some circumstances and that RelA complexes are involved in the control of a variety of cellular properties associated with oncogenesis.