Alternate RNA splicing of murine nfkb1 generates a nuclear isoform of the p50 precursor NF-kappa B1 that can function as a transactivator of NF-kappa B-regulated transcription

TRAF6 Mediates Basal Activation of NF-κB Necessary for Hematopoietic Stem Cell Homeostasis

Basal nuclear factor κB (NF-κB) activation is required for hematopoietic stem cell (HSC) homeostasis in the absence of inflammation; however, the upstream mediators of basal NF-κB signaling are less well understood. Here, we describe TRAF6 as an essential regulator of HSC homeostasis through basal activation of NF-κB. Hematopoietic-specific deletion of Traf6 resulted in impaired HSC self-renewal and fitness. Gene expression, RNA splicing, and molecular analyses of Traf6-deficient hematopoietic stem/progenitor cells (HSPCs) revealed changes in adaptive immune signaling, innate immune signaling, and NF-κB signaling, indicating that signaling via TRAF6 in the absence of cytokine stimulation and/or infection is required for HSC function. In addition, we established that loss of IκB kinase beta (IKKβ)-mediated NF-κB activation is responsible for the major hematopoietic defects observed in Traf6-deficient HSPC as deletion of IKKβ similarly resulted in impaired HSC self-renewal and fitness. Taken together, TRAF6 is required for HSC homeostasis by maintaining a minimal threshold level of IKKβ/NF-κB signaling.

Transcriptional regulatory networks in human lung adenocarcinoma

Lung adenocarcinoma (AC) is the most common histological subtype of lung cancer worldwide and its absolute incidence is increasing markedly. Transcriptional regulation is one of the most fundamental processes in lung AC development. However, high-throughput functional analyses of multiple transcription factors and their target genes in lung AC are rare. Thus, the objective of our study was to interpret the mechanisms of human AC through the regulatory network using the GSE2514 microarray data. Our results identified the genes peroxisome proliferator activated receptor-γ (PPARG), CCAAT/enhancer binding protein β (CEBPB), ets variant 4 (ETV4), Friend leukemia virus integration 1 (FLI1), T-cell acute lymphocytic leukemia 1 (TAL1) and nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NFKB1) as hub nodes in the transcriptome network. Among these genes, it appears that: PPARG promotes the PPAR signaling pathway via the upregulation of lipoprotein lipase (LPL) expression, but suppresses the cell cycle pathway via downregulation of growth arrest and DNA-damage-inducible, γ (GADD45G) expression; ETV4 stimulates matrix metallopeptidase 9 (MMP9) expression to induce the bladder cancer pathway; FLI upregulates transforming growth factor, β receptor II (TGFBR2) expression to activate TGF-β signaling and upregulates cyclin D3 (CCND3) expression to promote the cell cycle pathway; NFKB1 upregulates interleukin 1, β (IL-1B) expression and initiates the prostate cancer pathway; CEBPB upregulates IL-6 expression and promotes pathways in cancer; and TAL1 promotes kinase insert domain receptor (KDR) expression to promote the TGF-β signaling pathway. This transcriptional regulation analysis may provide an improved understanding of the molecular mechanisms and potential therapeutic targets in the treatment of lung AC.

Alternative splicing in the NF-kappaB signaling pathway

Activation of transcription factor NF-kappaB can affect the expression of several hundred genes, many of which are involved in inflammation and immunity. The proper NF-kappaB transcriptional response is primarily regulated by post-translational modification of NF-kappaB signaling constituents. Herein, we review the accumulating evidence suggesting that alternative splicing of NF-kappaB signaling components is another means of controlling NF-kappaB signaling. Several alternative splicing events in both the tumor necrosis factor and Toll/interleukin-1 NF-kappaB signaling pathways can inhibit the NF-kappaB response, whereas others enhance NF-kappaB signaling. Alternative splicing of mRNAs encoding some NF-kappaB signaling components can be induced by prolonged exposure to an NF-kappaB-activating signal, such as lipopolysaccharide, suggesting a mechanism for negative feedback to dampen excessive NF-kappaB signaling. Moreover, some NF-kappaB alternative splicing events appear to be specific for certain diseases, and could serve as therapeutic targets or biomarkers.

CD14-dependent modulation of NF-κB alternative splicing in the lung after burn injury

Nuclear factor kappa-B (NF-kappaB), a key downstream player of the LPS signaling pathway, has been shown to undergo alternative splicing in in vitro studies. In this study, we examined the effect of injury and the role of CD14 on NF-kappaB alternative splicing using a murine burn model. CD14 knockout and respective wild-type mice were sacrificed after 18% total body surface area burn. RT-PCR and subsequent sequencing analysis revealed that injury induced multiple novel splicing variants of relA, relB, and NF-kappaB2 in the lungs of CD14 knockout but not wild-type mice. These novel variants resulted either from exon skipping, alternative usage of splicing signals, or intron retention. All but one variant resulted in a frameshift leading to premature termination of translation. These splicing variants encoded for proteins that lacked the domains essential for NF-kappaB transcription factor functions. Two NF-kappaB2 variants acquired only minor changes in their C-terminus that might affect their post-translational cleavage into active isoforms. These results suggest that alternative splicing may be one of the mechanisms by which NF-kappaB activity in the lungs can be regulated after injury. Furthermore, the CD14-mediated LPS signaling pathway may play a role in the regulation of NF-kappaB alternative splicing in the lungs after injury.

Stronger correlation of bcl-3 than bcl-2, bcl-xL, costimulation, or antioxidants with adjuvant-induced T cell survival

A set of signals separate from those needed for T cell activation and clonal expansion acts to sustain a T cell response once it has begun. Immunologic adjuvants can initiate these signals in a process we designate adjuvant-induced survival (AIS). Here, the natural adjuvant LPS was used in a super-antigen model of AIS to understand which factors are needed to sustain T cell survival after activation. Flow cytometric stains for antiapoptotic Bcl-2 and Bcl-xL showed that neither factor was well correlated with AIS, although both were increased transiently upon T cell activation. T cells protected via AIS showed no increased ability to resist death caused by reactive oxygen species, and cellular division was not accelerated as might be expected if AIS were to operate through co-stimulatory pathways. Finally, microarray analyses were performed that showed increased expression of Bcl-3, an NFkappaB/IkappaB factor, was correlated with AIS. It is proposed that T cell survival during productive immune responses occurs by successive activities of Bcl-2, Bcl-xL and Bcl-3, with Bcl-3 requiring innate immune responses to adjuvants for its expression.

Angiotensin II induces gene transcription through cell-type-dependent effects on the nuclear factor-kappaB (NF-kappaB) transcription factor

The vasopressor octapeptide, angiotensin II (Ang II), exerts homeostatic responses in cardiovascular tissues, including the heart, blood vessel wall, adrenal cortex and liver (a major source of circulating plasma proteins). One of the effects of Ang II is to induce expression of regulatory, structural and cytokine genes that play important roles in long-term control of blood pressure, vascular remodeling, cardiac hypertrophy and inflammation. The identification of nuclear signaling pathways and target transcription factors has provide important insight into cellular responses and the spectrum of genes controlled by Ang II. Here we will review how Ang II activates the transcription factors, Activator Protein 1 (AP-1), Signal Transducer and Activator of Transcription (STATs), and Nuclear Factor-kappaB (NF-kappaB). NF-kappaB is of particular interest because it is an important mediator of resynthesis of the Ang II precursor, angiotensinogen AGT. Through this positive feedback loop, long-term changes in the activity of the renin angiotensin system occur. Although NF-kappaB is ubiquitously expressed, surprisingly the mechanism for Ang II-inducible NF-kappaB regulation differs between aortic smooth muscle cells (VSMCs) and hepatocytes. In VSMC, Ang II induces nuclear translocation of cytoplasmic transactivatory NF-kappaB proteins through proteolysis of its inhibitor, IkappaB. By contrast, in hepatocytes, Ang II induces large nuclear isoforms of NF-kappaB1 to bind DNA through a mechanism independent of changes in IkappaB turnover. NF-kappaB activation depends upon the activity of DAG-sensitive PKC isoforms and ROS signaling pathway. These observations indicate that significant differences exist in Ang II signaling depending upon cell-type involved and suggest the possibility that tissue-selective modulation of Ang II effects is possible in the cardiovascular system.

Angiotensin II induces nuclear factor (NF)-kappaB1 isoforms to bind the angiotensinogen gene acute-phase response element: a stimulus-specific pathway for NF-kappaB activation

The vasopressor angiotensin II (AII) activates transcriptional expression of its precursor, angiotensinogen. This biological "positive feedback loop" occurs through an angiotensin receptor-coupled pathway that activates a multihormone-responsive enhancer of the angiotensinogen promoter, termed the acute-phase response element (APRE). Previously, we showed that the APRE is a cytokine [tumor necrosis factor-alpha (TNFalpha)]- inducible enhancer by binding the heterodimeric nuclear factor-kappaB (NF-kappaB) complex Rel A x NF-kappaB1. Here, we compare the mechanism for NF-kappaB activation by the AII agonist, Sar1 AII, with TNFalpha in HepG2 hepatocytes. Although Sar1 AII and TNFalpha both rapidly activate APRE-driven transcription within 3 h of treatment, the pattern of inducible NF-kappaB binding activity in electrophoretic mobility shift assay is distinct. In contrast to the TNFalpha mechanism, which strongly induces Rel A x NF-kappaB1 binding, Sar1 AII selectively activates a heterogenous pattern of NF-kappaB1 binding. Using a two-step microaffinity DNA binding assay, we observe that Sar1 AII recruits 50-, 56-, and 96-kDa NF-kappaB1 isoforms to bind the APRE. Binding of all three NF-kappaB1 isoforms occurs independently of changes in their nuclear abundance or proteolysis of cytoplasmic IkappaB inhibitors. Phorbol ester-sensitive protein kinase C (PKC) isoforms are required because PKC down-regulation completely blocks AII-inducible transcription and inducible NF-kappaB1 binding. We conclude that AII stimulates the NF-kappaB transcription factor pathway by activating latent DNA-binding activity of NF-kappaB subunits through a phorbol ester-sensitive (PKC-dependent) mechanism.

Angiotensin II induces interleukin-6 transcription in vascular smooth muscle cells through pleiotropic activation of nuclear factor-kappa B transcription factors

Interleukin-6 (IL-6) is a multifunctional cytokine expressed by angiotensin II (Ang II)-stimulated vascular smooth muscle cells (VSMCs) that functions as an autocrine growth factor. In this study, we analyze the mechanism for Ang II-inducible IL-6 expression in quiescent rat VSMCs. Stimulation with the Ang II agonist Sar1 Ang II (100 nmol/L) induced transcriptional expression of IL-6 mRNA transcripts of 1.8 and 2.4 kb. In transient transfection assays of IL-6 promoter/luciferase reporter plasmids, Sar1 Ang II treatment induced IL-6 transcription in a manner completely dependent on the nuclear factor-kappaB (NF-kappaB) motif. Sar1 Ang II induced cytoplasmic-to-nuclear translocation of the NF-kappaB subunits Rel A and NF-kappaB1 with parallel changes in DNA-binding activity in a biphasic manner, which produced an early peak at 15 minutes followed by a nadir 1 to 6 hours later and a later peak at 24 hours. The early phase of NF-kappaB translocation was dependent on weak simultaneous proteolysis of the IkappaBalpha and beta inhibitors, whereas later translocation was associated with enhanced processing of the p105 precursor into the mature 50-kDa NF-kappaB1 form. Pretreatment with a potent inhibitor of IkappaBalpha proteolysis, TPCK, completely blocked Sar1 Ang IIAng II-induced NF-kappaB activation and induction of endogenous IL-6 gene expression, which indicated the essential role of NF-kappaB in mediating IL-6 expression. We conclude that Ang II is a pleiotropic regulator of the NF-kappaB transcription factor family and may be responsible for activating the expression of cytokine gene networks in VSMCs.

Role of NF-kappaB in immune and inflammatory responses in the gut

NF-kappaB is a pleiotropic transcription factor with key functions in the intestinal immune system. NF-kappaB family members control transcriptional activity of various promoters of proinflammatory cytokines, cell surface receptors, transcription factors, and adhesion molecules that are involved in intestinal inflammation. The perpetuated activation of NF-kappaB in patients with active inflammatory bowel disease suggests that regulation of NF-kappaB activity is a very attractive target for therapeutic intervention. Such strategies include antioxidants, proteasome inhibitors, inhibition of NF-kappaB by adenoviral I kappaB alpha expression vectors, and antisense DNA targeting of NF-kappaB. These approaches will hopefully permit the design of new treatment strategies for chronic intestinal inflammation.

The kappa B enhancer of the human interleukin-6 promoter is necessary and sufficient to confer an IL-1 beta and TNF-alpha response in transfected human cell lines: requirement for members of the C/EBP family for activity

The human interleukin-6 (IL-6) promoter contains two regulatory elements, a kappa B enhancer and a NFIL-6 (C/EBP beta) binding site, which have been reported to be essential for inducibility of the IL-6 gene. We show that the kappa B element alone is sufficient to confer inducibility on the IL-6 gene in cells treated with either IL-1 beta or TNF-alpha. Gel-retardation analysis of nuclear extracts from IL-1 beta or TNF-alpha-treated cells using specific antibodies has shown that at least five retarded complexes bind to the IL-6 kappa B element in addition to NF-kappa B. Furthermore, apart from p50 (NF-kappa B1) and p65 (RelA), no other members of the Rel family are present in these complexes. Comparative analysis with the kappa B enhancer of the immunoglobulin kappa chain gene shows that three of these complexes bind specifically to the IL-6 kappa B enhancer: a complex of p50/NFIL6, a p65 homodimer, and a non-Rel-related constitutive protein. Finally, transfection experiments, in which NF-kappa B subunits, NFIL-6, and NFIL-6 beta (C/EBP delta), were overexpressed in cells transfected with mutated IL-6 enhancer elements linked to a reporter gene show that interaction between members of the two families of factors is required for activation of the IL-6 gene in the absence of the NFIL-6 binding site. We conclude that the kappa B enhancer of the IL-6 promoter is the IL-1 beta and TNF-alpha responsive element and that its activity is dependent on the direct interaction of NF-kappa B with non-Rel transcription factors.

The NF-kappa B and I kappa B proteins: new discoveries and insights

The transcription factor NF-kappa B has attracted widespread attention among researchers in many fields based on the following: its unusual and rapid regulation, the wide range of genes that it controls, its central role in immunological processes, the complexity of its subunits, and its apparent involvement in several diseases. A primary level of control for NF-kappa B is through interactions with an inhibitor protein called I kappa B. Recent evidence confirms the existence of multiple forms of I kappa B that appear to regulate NF-kappa B by distinct mechanisms. NF-kappa B can be activated by exposure of cells to LPS or inflammatory cytokines such as TNF or IL-1, viral infection or expression of certain viral gene products, UV irradiation, B or T cell activation, and by other physiological and nonphysiological stimuli. Activation of NF-kappa B to move into the nucleus is controlled by the targeted phosphorylation and subsequent degradation of I kappa B. Exciting new research has elaborated several important and unexpected findings that explain mechanisms involved in the activation of NF-kappa B. In the nucleus, NF-kappa B dimers bind to target DNA elements and activate transcription of genes encoding proteins involved with immune or inflammation responses and with cell growth control. Recent data provide evidence that NF-kappa B is constitutively active in several cell types, potentially playing unexpected roles in regulation of gene expression. In addition to advances in describing the mechanisms of NF-kappa B activation, excitement in NF-kappa B research has been generated by the first report of a crystal structure for one form of NF-kappa B, the first gene knockout studies for different forms of NF-kB and of I kappa B, and the implications for therapies of diseases thought to involve the inappropriate activation of NF-kappa B.

Phosphorylation of p105 PEST sequence via a redox-insensitive pathway up-regulates processing of p50 NF-kappaB

The p105 Rel protein has dual functions; it is the precursor of the p5O subunit of NF-kappaB, and it acts as an IkappaB-like inhibitor to retain other Rel subunits in the cytoplasm. We have investigated the posttranslational regulation of p105 following activation of Jurkat T cells and find that a rapid and sustained phosphorylation of p105 is induced. The inducible phosphorylation occurs on multiple serines in the C-terminal-most 150 amino acids of the molecule, a region rich in Pro, Glu, Ser, and Thr residues. Phosphorylation of p105 in Jurkat cells treated with phorbol 12-myristate 13-acetate/ionomycin or with okadaic acid, another activator of NF-kappaB, is correlated with an increase in proteolytic processing to p5O. Intact PEST sequences are required for the phorbol 12-myristate 13-acetate/ionomycin-induced p105 processing, as a 68-amino acid C-terminal deletion abolishes the response to stimulation. When compounds that block Ikappa B alpha phosphorylation and degradation were tested, the serine protease inhibitors L-1-tosylamido-2-phenylethyl chloromethyl ketone and 1-chloro-3-tosyl-amido-7-amino-2-heptanone blocked inducible p105 phosphorylation, but the antioxidants pyrrolidine dithiocarbamate and butylated hydroxyanisol did not. Thus, while regulation of the p105 IkappaB resembles that of lkappaBa, involving inducible serine phosphorylation and proteolysis of the inhibitory ankyrin repeat domain, it depends on a different, redox-insensitive, signaling pathway.

Regulation of NF-kappa B through the nuclear processing of p105 (NF-kappa B1) in Epstein-Barr virus-immortalized B cell lines

Transcription factors of the NF-kappa B/Rel family are retained in the cytoplasm as inactive complexes through association with I kappa B inhibitory proteins. Several NF-kappa B activators induce the proteolysis of I kappa B proteins, which results in the nuclear translocation and DNA binding of NF-kappa B complexes. Here, we report a novel mechanism of NF-kappa B regulation mediated by p105 (NF-kappa B1) precursor of p50 directly at the nuclear level. In Epstein-Barr virus-immortalized B cells, p105 was found in the nucleus, where it was complexed with p65. In concomitance with NF-kappa B activation, mitomycin C induced the processing of p105 to p50 in the nucleus, while it did not affect the steady-state protein levels of I kappa B alpha and p105 in the cytoplasm. Differently, phorbol 12-myristate 13-acetate induced a significant proteolysis of both I kappa B alpha and p105 in the cytoplasm, while it did not affect the protein level of p105 in the nucleus. These results suggest that in Epstein-Barr virus-positive B cell lines the nuclear processing of p105 can contribute to NF-kappa B activation in response to specific signaling molecules, such as DNA-damaging agents.