A Novel Member of the I B Family, Human I B- , Inhibits Transactivation of p65 and Its DNA Binding

Institute of Molecular Medicine, Heinrich-Heine-University, D-40225 Düsseldorf, Germany.
Journal of Biological Chemistry (Impact Factor: 4.57). 06/2006; 281(18):12645-54. DOI: 10.1074/jbc.M511956200
Source: PubMed


A novel member of the IkappaB family, human IkappaB-zeta, was identified by a differential screening approach of apoptosis-sensitive and -resistant tumor cells. The protein consists of 6 ankyrin repeats at its COOH terminus and shares about 30% identity with other IkappaB members. IkappaB-zeta associates with both the p65 and p50 subunit of NF-kappaB and inhibits the transcriptional activity as well as the DNA binding of the transcription factor. Interestingly, IkappaB-zeta is localized in the nucleus where it aggregates in matrix-associated deacetylase bodies, indicating that IkappaB-zeta regulates nuclear NF-kappaB activity rather than its nuclear translocation from the cytoplasm. IkappaB-zeta expression itself was regulated by NF-kappaB, suggesting that its activity is controlled in a negative feedback loop. Unlike classical IkappaB proteins, IkappaB-zeta was not degraded upon cell stimulation. Treatment with tumor necrosis factor-alpha, interleukin-1beta, and lipopolysaccharide induced a strong induction of IkappaB-zeta transcripts. Expression of IkappaB-zeta was detected in different tissues including lung, liver, and in leukocytes but not in the brain. Suppression of endogenous IkappaB-zeta by RNA interference rendered cells more resistant to apoptosis, whereas overexpression of IkappaB-zeta was sufficient to induce cell death. Our results, therefore, suggest that IkappaB-zeta functions as an additional regulator of NF-kappaB activity and, hence, provides another control level for the activation of NF-kappaB-dependent target genes.

Download full-text


Available from: Reiner Jänicke, Jan 29, 2015
  • Source
    • "NFKBIZ encodes a novel member of the IκB family, IκB zeta. IκB zeta associates with both the p65 and p50 subunits of NF-κB and inhibits the transcriptional activity and DNA binding of NF-κB [12]. USP2 is a ubiquitin-specific protease which is required for the phosphorylation of IκB and functions as an additional positive regulator of TNF-α-induced NF-κB signaling [13]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Apolipoprotein O (apoO) is a new member of the apolipoprotein family. However, data on its physiological functions are limited and inconsistent. Using a microarray expression analysis, this study explored the function of apoO in liver cells. HepG2 cells were treated either with oleic acid or tumor necrosis factor-alpha for 24 h. mRNA and protein expression of apoO were assessed by quantitative real-time PCR (qRT-PCR) and Western blot respectively. An efficient lentiviral siRNA vector targeting the human apoO gene was designed and constructed. The gene expression profile of HepG2 human hepatocellular carcinoma cells transfected with the apoO silencing vector was investigated using a whole-genome oligonucleotide microarray. The expression levels of some altered genes were validated using qRT-PCR. ApoO expression in HepG2 cells was dramatically affected by lipid and inflammatory stimuli. A total of 282 differentially expressed genes in apoO-silenced HepG2 cells were identified by microarray analysis. These genes included those participating in fatty acid metabolism, such as ACSL4, RGS16, CROT and CYP4F11, and genes participating in the inflammatory response, such as NFKBIZ, TNFSF15, USP2, IL-17, CCL23, NOTCH2, APH-1B and N2N. The gene Uncoupling protein 2 (UCP2), which is involved in both these metabolic pathways, demonstrated significant changes in mRNA level after transfection. It is likely that apoO participates in fatty acid metabolism and the inflammatory response in HepG2 cells, and UCP2 may act as a mediator between lipid metabolism and inflammation in apoO-silenced HepG2 cells.
    Lipids in Health and Disease 12/2013; 12(1):186. DOI:10.1186/1476-511X-12-186 · 2.22 Impact Factor
  • Source
    • "Their main interaction partners are p50 and p52 within the NF-κB pathway [32,36,62,78,87]. The observed interaction of overexpressed human IκBζ with p65 and interaction studies using GST-IκBNS and in vitro translated REL proteins suggest, that atypical IκB proteins can also bind to the other NF-κB subunits [73,78]. However, these interactions might be cell type specific and could depend on specific stimuli or posttranslational modifications of IκBs and REL proteins as well. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Nuclear factor κB (NF-κB) controls a multitude of physiological processes such as cell differentiation, cytokine expression, survival and proliferation. Since NF-κB governs embryogenesis, tissue homeostasis and the functions of innate and adaptive immune cells it represents one of the most important and versatile signaling networks known. Its activity is regulated via the inhibitors of NF-κB signaling, the IκB proteins. Classical IκBs, like the prototypical protein IκBα, sequester NF-κB transcription factors in the cytoplasm by masking of their nuclear localization signals (NLS). Thus, binding of NF-κB to the DNA is inhibited. The accessibility of the NLS is controlled via the degradation of IκBα. Phosphorylation of the conserved serine residues 32 and 36 leads to polyubiquitination and subsequent proteasomal degradation. This process marks the central event of canonical NF-κB activation. Once their NLS is accessible, NF-κB transcription factors translocate into the nucleus, bind to the DNA and regulate the transcription of their respective target genes. Several studies described a distinct group of atypical IκB proteins, referred to as the BCL-3 subfamily. Those atypical IκBs show entirely different sub-cellular localizations, activation kinetics and an unexpected functional diversity. First of all, their interaction with NF-κB transcription factors takes place in the nucleus in contrast to classical IκBs, whose binding to NF-κB predominantly occurs in the cytoplasm. Secondly, atypical IκBs are strongly induced after NF-κB activation, for example by LPS and IL-1β stimulation or triggering of B cell and T cell antigen receptors, but are not degraded in the first place like their conventional relatives. Finally, the interaction of atypical IκBs with DNA-associated NF-κB transcription factors can further enhance or diminish their transcriptional activity. Thus, they do not exclusively act as inhibitors of NF-κB activity. The capacity to modulate NF-κB transcription either positively or negatively, represents their most important and unique mechanistic difference to classical IκBs. Several reports revealed the importance of atypical IκB proteins for immune homeostasis and the severe consequences following their loss of function. This review summarizes insights into the physiological processes regulated by this protein class and the relevance of atypical IκB functioning.
    Cell Communication and Signaling 04/2013; 11(1). DOI:10.1186/1478-811X-11-23 · 3.38 Impact Factor
  • Source
    • "These proteins are able to inactivate NF-kB by trapping it within the cytoplasm, thus preventing its nuclear translocation [30]. Unlike the other IkB proteins, NFKBIZ is able to inhibit NF-kB activity without affecting its nuclear translocation, instead it inhibits the DNA-binding of NF-kB [31]. NFKBIZ is also known to activate IL6 transcription whilst decreasing transcription of TNF in response to LPS [32] and may also be involved in the induction of inflammatory genes activated through the TLR/IL-1 signaling pathways [33]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Sheep scab, caused by infestation with the ectoparasitic mite Psoroptes ovis, results in the rapid development of cutaneous inflammation and leads to the crusted skin lesions characteristic of the disease. We described previously the global host transcriptional response to infestation with P. ovis, elucidating elements of the inflammatory processes which lead to the development of a rapid and profound immune response. However, the mechanisms by which this response is instigated remain unclear. To identify novel methods of intervention a better understanding of the early events involved in triggering the immune response is essential. The objective of this study was to gain a clearer understanding of the mechanisms and signaling pathways involved in the instigation of the immediate pro-inflammatory response. Through a combination of transcription factor binding site enrichment and pathway analysis we identified key roles for a number of transcription factors in the instigation of cutaneous inflammation. In particular, defined roles were elucidated for the transcription factors NF-kB and AP-1 in the orchestration of the early pro-inflammatory response, with these factors being implicated in the activation of a suite of inflammatory mediators. Interrogation of the host temporal response to P. ovis infestation has enabled the further identification of the mechanisms underlying the development of the immediate host pro-inflammatory response. This response involves key regulatory roles for the transcription factors NF-kB and AP-1. Pathway analysis demonstrated that the activation of these transcription factors may be triggered following a host LPS-type response, potentially involving TLR4-signalling and also lead to the intriguing possibility that this could be triggered by a P. ovis allergen.
    PLoS ONE 09/2011; 6(9):e24402. DOI:10.1371/journal.pone.0024402 · 3.23 Impact Factor
Show more