NF-κB and Human Cancer: What Have We Learned over the Past 35 Years?

Transcription factor NF-κB has been extensively studied for its varied roles in cancer development since its initial characterization as a potent retroviral oncogene. It is now clear that NF-κB also plays a major role in a large variety of human cancers, including especially ones of immune cell origin. NF-κB is generally constitutively or aberrantly activated in human cancers where it is involved. These activations can occur due to mutations in the NF-κB transcription factors themselves, in upstream regulators of NF-κB, or in pathways that impact NF-κB. In addition, NF-κB can be activated by tumor-assisting processes such as inflammation, stromal effects, and genetic or epigenetic changes in chromatin. Aberrant NF-κB activity can affect many tumor-associated processes, including cell survival, cell cycle progression, inflammation, metastasis, angiogenesis, and regulatory T cell function. As such, inhibition of NF-κB has often been investigated as an anticancer strategy. Nevertheless, with a few exceptions, NF-κB inhibition has had limited success in human cancer treatment. This review covers general themes that have emerged regarding the biological roles and mechanisms by which NF-κB contributes to human cancers and new thoughts on how NF-κB may be targeted for cancer prognosis or therapy.

Looking Down on NF-κB.

The diversified NF-κB transcription factor family has been extensively characterized in organisms ranging from flies to humans. However, homologs of NF-κB and many upstream signaling components have recently been characterized in basal phyla, including Cnidaria (sea anemones, corals, hydras, and jellyfish), Porifera (sponges), and single-celled protists, including Capsaspora owczarzaki and some choanoflagellates. Herein, we review what is known about basal NF-κBs and how that knowledge informs on the evolution and conservation of key sequences and domains in NF-κB, as well as the regulation of NF-κB activity. The structures and DNA-binding activities of basal NF-κB proteins resemble those of mammalian NF-κB p100 proteins, and their posttranslational activation appears to have aspects of both canonical and noncanonical pathways in mammals. Several studies suggest that the single NF-κB proteins found in some basal organisms have dual roles in development and immunity. Further research on NF-κB in invertebrates will reveal information about the evolutionary roots of this major signaling pathway, will shed light on the origins of regulated innate immunity, and may have relevance to our understanding of the responses of ecologically important organisms to changing environmental conditions and emerging pathogen-based diseases.

CRISPR/Cas9-based editing of a sensitive transcriptional regulatory element to achieve cell type-specific knockdown of the NEMO scaffold protein.

The use of alternative promoters for the cell type-specific expression of a given mRNA/protein is a common cell strategy. NEMO is a scaffold protein required for canonical NF-κB signaling. Transcription of the NEMO gene is primarily controlled by two promoters: one (promoter B) drives NEMO transcription in most cell types and the second (promoter D) is largely responsible for NEMO transcription in liver cells. Herein, we have used a CRISPR/Cas9-based approach to disrupt a core sequence element of promoter B, and this genetic editing essentially eliminates expression of NEMO mRNA and protein in 293T human kidney cells. By cell subcloning, we have isolated targeted 293T cell lines that express no detectable NEMO protein, have defined genomic alterations at promoter B, and do not support activation of canonical NF-κB signaling in response to treatment with tumor necrosis factor. Nevertheless, non-canonical NF-κB signaling is intact in these NEMO-deficient cells. Expression of ectopic wild-type NEMO, but not certain human NEMO disease mutants, in the edited cells restores downstream NF-κB signaling in response to tumor necrosis factor. Targeting of the promoter B element does not substantially reduce NEMO expression (from promoter D) in the human SNU-423 liver cancer cell line. Thus, we have created a strategy for selectively eliminating cell type-specific expression from an alternative promoter and have generated 293T cell lines with a functional knockout of NEMO. The implications of these findings for further studies and for therapeutic approaches to target canonical NF-κB signaling are discussed.

Evolutionary Origins of Toll-like Receptor Signaling.

Toll-like receptors (TLRs) are transmembrane pattern recognition receptors that are best known for their roles in innate immunity for the detection of and defense against microbial pathogens. However, TLRs also have roles in many nonimmune processes, most notably development. TLRs direct both immune and developmental programs by activation of downstream signaling pathways, often by activation of the NF-κB pathway. There are two primary TLR subtypes: 1) TLRs with multiple cysteine clusters in their ectodomain (mccTLRs) and 2) TLRs with a single cysteine cluster in their ectodomain (sccTLRs). For some time, it has been known that TLRs and the biological processes that they control are conserved in organisms from insects to mammals. However, genome and transcriptome sequencing has revealed that many basal metazoans also have TLRs and downstream NF-κB signaling components. In this review, we discuss what is known about the structure, biological function, and downstream signaling pathways of TLRs found in phyla from Porifera through Annelida. From these analyses, we hypothesize that mccTLRs emerged in the phylum Cnidaria, that sccTLRs evolved in the phylum Mollusca, and that TLRs have dual immune and developmental biological functions in organisms as ancient as cnidarians.

Adaptive Significance of ERα Splice Variants in Killifish (Fundulus heteroclitus) Resident in an Estrogenic Environment.

The possibility that chronic, multigenerational exposure to environmental estrogens selects for adaptive hormone-response phenotypes is a critical unanswered question. Embryos/larvae of killifish from an estrogenic-polluted environment (New Bedford Harbor, MA [NBH]) compared with those from a reference site overexpress estrogen receptor alpha (ERα) mRNA but are hyporesponsive to estradiol. Analysis of ERα mRNAs in the two populations revealed differences in splicing of the gene encoding ERα (esr1). Here we tested the transactivation functions of four differentially expressed ERα mRNAs and tracked their association with the hyporesponsive phenotype for three generations after transfer of NBH parents to a clean environment. Deletion variants ERαΔ6 and ERαΔ6-8 were specific to NBH killifish, had dominant negative functions in an in vitro reporter assay, and were heritable. Morpholino-mediated induction of ERαΔ6 mRNA in zebrafish embryos verified its role as a dominant negative ER on natural estrogen-responsive promoters. Alternate long (ERαL) and short (ERαS) 5'-variants were similar transcriptionally but differed in estrogen responsiveness (ERαS ≫ ERαL). ERαS accounted for high total ERα expression in first generation (F1) NBH embryos/larvae but this trait was abolished by transfer to clean water. By contrast, the hyporesponsive phenotype of F1 NBH embryos/larvae persisted after long-term laboratory holding but reverted to a normal or hyper-responsive phenotype after two or three generations, suggesting the acquisition of physiological or biochemical traits that compensate for ongoing expression of negative-acting ERαΔ6 and ERαΔ6-8 isoforms. We conclude that a heritable change in the pattern of alternative splicing of ERα pre-mRNA is part of a genetic adaptive response to estrogens in a polluted environment.

Evidence for an oncogenic modifier role for mutant histone acetyltransferases in diffuse large B-cell lymphoma.

Mutations in histone acetyltransferases (HATs) are among the most common mutations in diffuse large B-cell lymphoma (DLBCL). We previously showed that two human DLBCL cell lines, RC-K8 and SUDHL2, express C-terminally truncated, HAT domain-deficient p300 proteins (p300ΔC) that are required for optimal cell proliferation. Microarray analysis of mRNA expression in RC-K8 cells following p300ΔC knockdown shows upregulation of NF-κB and p53 gene expression programs and downregulation of a MYC gene expression program. Experiments indicate that these gene expression changes are due to inhibitory effects of p300ΔC on NF-κB activity and on p53 protein levels and stimulatory effects on MYC protein levels, suggesting that p300ΔC mutants enhance the proliferation of DLBCL cells by adjusting the transcriptional output of cell-specific oncoproteins. We propose that p300/CBP gene truncation represents a new class of oncogenic mutation that optimizes the activity of context-specific oncogenic transcription factors. We propose 'oncogenic modifier' to describe such mutations.

Histone acetyltransferases and histone deacetylases in B- and T-cell development, physiology and malignancy.

The development of B and T cells from hematopoietic precursors and the regulation of the functions of these immune cells are complex processes that involve highly regulated signaling pathways and transcriptional control. The signaling pathways and gene expression patterns that give rise to these developmental processes are coordinated, in part, by two opposing classes of broad-based enzymatic regulators: histone acetyltransferases (HATs) and histone deacetylases (HDACs). HATs and HDACs can modulate gene transcription by altering histone acetylation to modify chromatin structure, and by regulating the activity of non-histone substrates, including an array of immune-cell transcription factors. In addition to their role in normal B and T cells, dysregulation of HAT and HDAC activity is associated with a variety of B- and T-cell malignancies. In this review, we describe the roles of HATs and HDACs in normal B- and T-cell physiology, describe mutations and dysregulation of HATs and HDACs that are implicated lymphoma and leukemia, and discuss HAT and HDAC inhibitors that have been explored as treatment options for leukemias and lymphomas.

Inhibition of Oncogenic Transcription Factor REL by the Natural Product Derivative Calafianin Monomer 101 Induces Proliferation Arrest and Apoptosis in Human B-Lymphoma Cell Lines.

Increased activity of transcription factor NF-κB has been implicated in many B-cell lymphomas. We investigated effects of synthetic compound calafianin monomer (CM101) on biochemical and biological properties of NF-κB. In human 293 cells, CM101 selectively inhibited DNA binding by overexpressed NF-κB subunits REL (human c-Rel) and p65 as compared to NF-κB p50, and inhibition of REL and p65 DNA binding by CM101 required a conserved cysteine residue. CM101 also inhibited DNA binding by REL in human B-lymphoma cell lines, and the sensitivity of several B-lymphoma cell lines to CM101-induced proliferation arrest and apoptosis correlated with levels of cellular and nuclear REL. CM101 treatment induced both phosphorylation and decreased expression of anti-apoptotic protein Bcl-XL, a REL target gene product, in sensitive B-lymphoma cell lines. Ectopic expression of Bcl-XL protected SUDHL-2 B-lymphoma cells against CM101-induced apoptosis, and overexpression of a transforming mutant of REL decreased the sensitivity of BJAB B-lymphoma cells to CM101-induced apoptosis. Lipopolysaccharide-induced activation of NF-κB signaling upstream components occurred in RAW264.7 macrophages at CM101 concentrations that blocked NF-κB DNA binding. Direct inhibitors of REL may be useful for treating B-cell lymphomas in which REL is active, and may inhibit B-lymphoma cell growth at doses that do not affect some immune-related responses in normal cells.

Methods for assessing the in vitro transforming activity of NF-κB transcription factor c-Rel and related proteins.

Among NF-κB transcription factors, c-Rel and c-Rel-derived proteins, including v-Rel, are the only ones that have shown consistent and frank transforming activity in cell culture. In particular, viral, chicken, mouse, and human Rel proteins can rapidly transform primary chicken spleen and bone marrow cells. Overexpression of a human Rel protein missing a C-terminal transactivation domain can also enhance the transformed state of the human B-lymphoma cell line BJAB. As described in this chapter, these in vitro assays can be used to quantitatively assess the transforming activity of Rel proteins.

Histone acetyltransferase-deficient p300 mutants in diffuse large B cell lymphoma have altered transcriptional regulatory activities and are required for optimal cell growth.

BACKGROUND: Recent genome-wide studies have shown that approximately 30% of diffuse large B-cell lymphoma (DLBCL) cases harbor mutations in the histone acetyltransferase (HAT) coactivators p300 or CBP. The majority of these mutations reduce or eliminate the catalytic HAT activity. We previously demonstrated that the human DLBCL cell line RC-K8 expresses a C-terminally truncated, HAT-defective p300 protein (p300ΔC-1087), whose expression is essential for cell proliferation. METHODS: Using results from large-scale DLBCL studies, we have identified and characterized a second C-terminally truncated, HAT-defective p300 mutant, p300ΔC-820, expressed in the SUDHL2 DLBCL cell line. Properties of p300ΔC-820 were characterized in the SUDHL2 DLBCL cell line by Western blotting, co-immunoprecipitation, and shRNA gene knockdown, as well by using cDNA expression vectors for p300ΔC-820 in pull-down assays, transcriptional reporter assays, and immunofluorescence experiments. A mass spectrometry-based method was used to compare the histone acetylation profile of DLBCL cell lines expressing various levels of wild-type p300. RESULTS: We show that the SUDHL2 cell line expresses a C-terminally truncated, HAT-defective form of p300 (p300ΔC-820), but no wild-type p300. The p300ΔC-820 protein has a wild-type ability to localize to subnuclear "speckles," but has a reduced ability to enhance transactivation by transcription factor REL. Knockdown of p300ΔC-820 in SUDHL2 cells reduced their proliferation and soft agar colony-forming ability. In RC-K8 cells, knockdown of p300ΔC-1087 resulted in increased expression of mRNA and protein for REL target genes A20 and IκBα, two genes that have been shown to limit the growth of RC-K8 cells when overexpressed. Among a panel of B-lymphoma cell lines, low-level expression of full-length p300 protein, which is characteristic of the SUDHL2 and RC-K8 cells, was associated with decreased acetylation of histone H3 at lysines 14 and 18. CONCLUSIONS: The high prevalence of p300 mutations in DLBCL suggests that HAT-deficient p300 activity defines a subtype of DLBCL, which we have investigated using human DLBCL cell lines RC-K8 and SUDHL2. Our results suggest that truncated p300 proteins contribute to DLBCL cell growth by affecting the expression of specific genes, perhaps through a mechanism that involves alterations in global histone acetylation.

Mutation of nonessential cysteines shows that the NF-κB essential modulator forms a constitutive noncovalent dimer that binds IκB kinase-ß with high affinity.

NEMO (NF-κB essential modulator) associates with catalytic subunits IKKα and IKKß to form the IκB kinase (IKK) complex and is a key regulator of NF-κB pathway signaling. Biochemical and structural characterization of NEMO has been challenging, however, leading to conflicting data about basic biochemical properties such as the oligomeric state of active NEMO and its binding affinity for IKKß. We show that up to seven of NEMO's 11 cysteine residues can be mutated to generate recombinant full-length NEMO that is highly soluble and active. Using a fluorescence anisotropy binding assay, we show that full-length NEMO binds a 44-mer peptide encompassing residues 701-745 of IKKß with a K(D) of 2.2 ± 0.8 nM. The IKKß binding affinities of mutants with five and seven Cys-to-Ala substitutions are indistinguishable from that of wild-type NEMO. Moreover, when expressed in NEMO -/- fibroblasts, the five-Ala and seven-Ala NEMO mutants can interact with cellular IKKß and restore NF-κB signaling to provide protection against tumor necrosis factor α-induced cell death. Treatment of the NEMO-reconstituted cells with H2O2 led to the formation of covalent dimers for wild-type NEMO and the five-Ala mutant, but not for the seven-Ala mutant, confirming that Cys54 and/or Cys347 can mediate interchain disulfide bonding. However, the IKKß binding affinity of NEMO is unaffected by the presence or absence of interchain disulfide bonding at Cys54, which lies within the IKKß binding domain of NEMO, or at Cys347, indicating that NEMO exists as a noncovalent dimer independent of the redox state of its cysteines. This conclusion was corroborated by the observation that the secondary structure content of NEMO and its thermal stability were independent of the presence or absence of interchain disulfide bonds.

Identification of an NF-κB p50/p65-responsive site in the human MIR155HG promoter.

BACKGROUND: MicroRNA-155 (miR-155) is the diced product of the MIR155HG gene. miR-155 regulates the expression of many immune-specific transcripts, is overexpressed in many human lymphomas, and has oncogenic activity in mouse transgenic models. MIR155HG has been proposed to be a target gene for transcription factor NF-κB largely due to the positive correlation between high nuclear NF-κB activity and increased miR-155 expression following treatment with NF-κB inducers or in subsets of hematopoietic cancers. Nevertheless, direct regulation of the human MIR155HG promoter by NF-κB has not been convincingly demonstrated previously. RESULTS: This report shows that induction of NF-κB activity rapidly leads to increased levels of both primary MIR155HG mRNA and mature miR-155 transcripts. We have mapped an NF-κB-responsive element to a position approximately 178 nt upstream of the MIR155HG transcription start site. The -178 site is specifically bound by the NF-κB p50/p65 heterodimer and is required for p65-induced reporter gene activation. Moreover, the levels of miR-155 in nine human B-lymphoma cell lines generally correlate with increased nuclear NF-κB proteins. CONCLUSION: Overall, the identification of an NF-κB-responsive site in the MIR155HG proximal promoter suggests that MIR155HG is a direct NF-κB target gene in vivo. Understanding NF-κB-mediated regulation of miR-155 could lead to improved immune cell-related diagnostic tools and targeted therapies.

The sensitivity of diffuse large B-cell lymphoma cell lines to histone deacetylase inhibitor-induced apoptosis is modulated by BCL-2 family protein activity.

BACKGROUND: Diffuse large B-cell lymphoma (DLBCL) is a genetically heterogeneous disease and this variation can often be used to explain the response of individual patients to chemotherapy. One cancer therapeutic approach currently in clinical trials uses histone deacetylase inhibitors (HDACi's) as monotherapy or in combination with other agents. METHODOLOGY/PRINCIPAL FINDINGS: We have used a variety of cell-based and molecular/biochemical assays to show that two pan-HDAC inhibitors, trichostatin A and vorinostat, induce apoptosis in seven of eight human DLBCL cell lines. Consistent with previous reports implicating the BCL-2 family in regulating HDACi-induced apoptosis, ectopic over-expression of anti-apoptotic proteins BCL-2 and BCL-XL or pro-apoptotic protein BIM in these cell lines conferred further resistance or sensitivity, respectively, to HDACi treatment. Additionally, BCL-2 family antgonist ABT-737 increased the sensitivity of several DLBCL cell lines to vorinostat-induced apoptosis, including one cell line (SUDHL6) that is resistant to vorinostat alone. Moreover, two variants of the HDACi-sensitive SUDHL4 cell line that have decreased sensitivity to vorinostat showed up-regulation of BCL-2 family anti-apoptotic proteins such as BCL-XL and MCL-1, as well as decreased sensitivity to ABT-737. These results suggest that the regulation and overall balance of anti- to pro-apoptotic BCL-2 family protein expression is important in defining the sensitivity of DLBCL to HDACi-induced apoptosis. However, the sensitivity of DLBCL cell lines to HDACi treatment does not correlate with expression of any individual BCL-2 family member. CONCLUSIONS/SIGNIFICANCE: These studies indicate that the sensitivity of DLBCL to treatment with HDACi's is dependent on the complex regulation of BCL-2 family members and that BCL-2 antagonists may enhance the response of a subset of DLBCL patients to HDACi treatment.

Bcl-XL, but not Bcl-2, can protect human B-lymphoma cell lines from parthenolide-induced apoptosis.

In this report, we investigated the effects of the natural product parthenolide on human B-lymphoma cell lines. We show that parthenolide inhibited NF-κB transcription factor c-Rel (REL). In addition, the sensitivity of several human B-lymphoma cell lines to parthenolide-induced apoptosis inversely correlated with their levels of anti-apoptosis protein Bcl-X(L). Furthermore, ectopic expression of Bcl-X(L) (but not Bcl-2) in two B-lymphoma cell lines decreased their sensitivity to parthenolide-induced apoptosis. Finally, over-expression of a transforming mutant of REL, which increased expression of endogenous Bcl-X(L), decreased the sensitivity of BJAB B-lymphoma cells to parthenolide-induced apoptosis. These results demonstrate that the NF-κB target gene products Bcl-X(L) and Bcl-2 can play different roles in protecting B-lymphoma cells from chemical-induced apoptosis.

The c-Rel Transcription Factor in Development and Disease.

c-Rel is a member of the nuclear factor κB (NF-κB) transcription factor family. Unlike other NF-κB proteins that are expressed in a variety of cell types, high levels of c-Rel expression are found primarily in B and T cells, with many c-Rel target genes involved in lymphoid cell growth and survival. In addition to c-Rel playing a major role in mammalian B and T cell function, the human c-rel gene (REL) is a susceptibility locus for certain autoimmune diseases such as arthritis, psoriasis, and celiac disease. The REL locus is also frequently altered (amplified, mutated, rearranged), and expression of REL is increased in a variety of B and T cell malignancies and, to a lesser extent, in other cancer types. Thus, agents that modulate REL activity may have therapeutic benefits for certain human cancers and chronic inflammatory diseases.

A rearranged EP300 gene in the human B-cell lymphoma cell line RC-K8 encodes a disabled transcriptional co-activator that contributes to cell growth and oncogenicity.

Human diffuse large B-cell lymphoma cell line RC-K8 has an altered EP300 locus that encodes a C-terminally truncated histone acetyltransferase (HAT) protein (p300ΔC). We now show that p300ΔC contains 1047N-terminal amino acids of p300 fused to 25 amino acids encoded by sequences from chromosome 6. Over-expressed p300ΔC localized to nuclear subdomains and interacted with transcription factor REL. p300ΔC did not function as a co-activator for REL-directed transactivation, and blocked the ability of wild-type p300 to enhance transcriptional activation by REL. Knock down of p300ΔC in RC-K8 cells reduced their growth in both liquid culture and soft agar. Truncations of p300 were not found in eight other B-lymphoma cell lines. These results suggest that p300ΔC contributes to the oncogenic state of RC-K8 cells by acting as a defective co-activator.

NF-kappaB down-regulates expression of the B-lymphoma marker CD10 through a miR-155/PU.1 pathway.

Cell-surface protein CD10 is a prognostic marker for diffuse large B-cell lymphoma (DLBCL), where high expression of CD10 is found in the germinal center B-cell (GCB) subtype and CD10 expression is low or absent in the activated B-cell (ABC) subtype. As compared with the GCB subtype, patients with ABC DLBCL have a poorer prognosis after standard treatment, and ABC tumor cells have higher NF-κB activity. Herein, we show that increased expression of the NF-κB target micro-RNA miR-155 is correlated with reduced expression of transcription factor PU.1 and CD10 in several B-lymphoma cell lines. Moreover, electromobility shift assays and luciferase reporter assays indicate that PU.1 can directly activate expression from the CD10 promoter. Expression of a DLBCL-derived mutant of the adaptor CARD11 (a constitutive activator of NF-κB) in the GCB-like human BJAB cell line or v-Rel in the chicken DT40 B-lymphoma cell line causes reduced expression of PU.1. The CARD11 mutant also causes a decrease in CD10 levels in BJAB cells. Similarly, overexpression of miR-155, which is known to down-regulate PU.1, leads to reduced expression of CD10 in BJAB cells. Finally, we show that CD10 expression is reduced in BJAB cells after treatment with the NF-κB inducer lipopolysaccharide (LPS). Additionally, miR-155 is induced by LPS treatment or expression of the CARD11 mutant in BJAB cells. These results point to an NF-κB-dependent mechanism for down-regulation of CD10 in B-cell lymphoma: namely, that increased NF-κB activity leads to increased miR-155, which results in decreased PU.1, and consequently reduced CD10 mRNA and protein.

Characterization of the core elements of the NF-κB signaling pathway of the sea anemone Nematostella vectensis.

The sea anemone Nematostella vectensis is the leading developmental and genomic model for the phylum Cnidaria, which includes anemones, hydras, jellyfish, and corals. In insects and vertebrates, the NF-κB pathway is required for cellular and organismal responses to various stresses, including pathogens and chemicals, as well as for several developmental processes. Herein, we have characterized proteins that comprise the core NF-κB pathway in Nematostella, including homologs of NF-κB, IκB, Bcl-3, and IκB kinase (IKK). We show that N. vectensis NF-κB (Nv-NF-κB) can bind to κB sites and activate transcription of reporter genes containing multimeric κB sites or the Nv-IκB promoter. Both Nv-IκB and Nv-Bcl-3 interact with Nv-NF-κB and block its ability to activate reporter gene expression. Nv-IKK is most similar to human IKKε/TBK kinases and, in vitro, can phosphorylate Ser47 of Nv-IκB. Nv-NF-κB is expressed in a subset of ectodermal cells in juvenile and adult Nematostella anemones. A bioinformatic analysis suggests that homologs of many mammalian NF-κB target genes are targets for Nv-NF-κB, including genes involved in apoptosis and responses to organic compounds and endogenous stimuli. These results indicate that NF-κB pathway proteins in Nematostella are similar to their vertebrate homologs, and these results also provide a framework for understanding the evolutionary origins of NF-κB signaling.

Inhibition of NF-κB signaling as a strategy in disease therapy.

As described extensively in this issue, NF-κB transcription factors regulate a number of important physiological processes, including inflammation and immune responses, cell growth and survival, and the expression of certain viral genes. Moreover, NF-κB activity is elevated in and contributes to the pathology of several human diseases, including many cancers and chronic inflammatory diseases. Therefore, there has been great interest in the characterization and development of methods to limit NF-κB signaling for pharmacological intervention. This article describes some of the approaches that have been employed to inhibit NF-κB using in vitro and in vivo experimental models. Moreover, some examples of the clinical use of NF-κB inhibitors are discussed, primarily for the treatment of two B-cell malignancies, multiple myeloma and diffuse large B-cell lymphoma. Finally, the rationale and strategies for inhibiting specific NF-κB subunit activity for disease therapy are discussed.