The interaction of interleukin-1␤ (IL-1␤) with its type 1 cell surface receptor initiates a cascade of intracellular reactions leading to the activation of transcription factors and the expression of target genes. One of the major transcription factors mediating IL-1␤ biological activities is NF-B (for reviews, see references 2, 3, and 22). This factor is sequestered in the cytoplasm by an inhibitor from the IB family. IL-1␤ cellular stimulation leads to a rapid phosphorylation and degradation of IB␣, the most common NF-B inhibitor. This reaction allows NF-B to translocate to the nucleus, to bind DNA, and to activate the transcription of specific genes (2, 55).Following its interaction with IL-1, the type 1 IL-1 receptor recruits the IL-1 receptor-associated kinase (IRAK) protein, which subsequently interacts with the TRAF6 adapter protein (15,16,30,61,62,65). TRAF6 is required for IL-1␤-induced NF-B activation, as demonstrated in 293 cells (16).However, the signaling pathways leading to NF-B activation from the IL-1␤ receptors are still controversial. It has been demonstrated that TRAF6 interacts with a MAP kinase kinase kinase (MAPKKK) known as NIK and that NIK is required for IL-1␤-or tumor necrosis factor alpha (TNF-␣)-dependent 56). Large (500 to 900 kDa) multimeric protein kinase complexes have been purified from HeLa cells and transmit the signal from the TNF receptor type 1 (TNFR-1) and type 1 IL-1 receptors to the NF-B/IB cytoplasmic complex (17,20,33,41). From these complexes three IB kinases, IKK-␣, IKK-␤, and IKK-␥, have been purified, and their genes were cloned (20,42,49,66). Other investigators have cloned IKK kinases by virtue of their association with the NIK protein kinase (47, 64). Moreover, inactivation of these kinases by dominant negative mutants suppresses IL-1␤ and TNF-␣ induction of NF-B. These studies indicate that the activated NIK kinase phosphorylates and activates the IKK protein kinases. IKK protein kinases can in turn phosphorylate the IB␣ protein on serines located at positions 32 and 36, a reaction which targets IB␣ for ubiquitination and rapid degradation by the proteasome (12,58,59). These reactions are extremely rapid, and the cellular IB␣ protein is completely degraded within minutes following TNF-␣ or IL-1␤ cell stimulation (4, 13).Despite this simplified linear receptor-TRAF-NIK-IKK axis for IB␣ phosphorylation and degradation, other intermediates might be involved in NF-B activation by TNF-␣ or IL-1␤. First, several components of the large signaling complex remain to be identified, as the three IKK protein kinases do not account for the molecular weight of the whole complex. Second, a large number of studies, some of them being a matter of controversy, have identified other intermediates which seem to be required for TNF-␣-or IL-1␤-mediated NF-B activation. These intermediates are Raf-1, MAP kinases, the PKC and / isoforms, Rho and Rac proteins, and ceramide or reactive oxygen intermediates (ROIs) (19,24,25,32,33,38,46,(50)(51)(52)(53)57). Such a large number of controver...

The NF-jB2/p100 and bcl-3 genes are involved in chromosomal translocations described in chronic lymphocytic leukemias (CLL) and non-Hodgkin's lymphomas, and nuclear factor kappaB (NF-jB) protects cancer cells against apoptosis. Therefore, we investigated whether this transcription factor could modulate the expression of the Bcl-2 antiapoptotic protein. Bcl-2 promoter analysis showed multiple putative NF-jB binding sites. Transfection assays of bcl-2 promoter constructs in HCT116 cells showed that NF-jB can indeed transactivate bcl-2. We identified a jB site located at position À180 that can only be bound and transactivated by p50 or p52 homodimers. As p50 and p52 homodimers are devoid of any transactivating domains, we showed that they can transactivate the bcl-2 promoter through association with Bcl-3. We also observed that stable overexpression of p100 and its processed product p52 can induce endogenous Bcl-2 expression in MCF7AZ breast cancer cells. Finally, we demonstrated that, in breast cancer and leukemic cells (CLL), high NF-jB2/p100 expression was associated with high Bcl-2 expression. Our data suggest that Bcl-2 could be an in vivo target gene for NF-jB2/p100.

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Asthma is a chronic inflammatory disease of the airways, in which many inflammatory genes are overexpressed. Transcription factor, nuclear factor-kappaB (NF-kappaB), which is thought to control the transcriptional initiation of inflammatory genes, has been poorly investigated in asthma. In the present report, bronchial cells (BCs), recovered by bronchial brushing in healthy and heaves-affected horses (i.e., an animal model of asthma), were assessed for NF-kappaB activity. Small amounts of active NF-kappaB were present in BCs of healthy horses, whereas high levels of NF-kappaB activity was found during crisis (i.e., acute airway obstruction) in all heaves-affected horses. Three weeks after the crisis, the level of NF-kappaB activity found in BCs of heaves-affected horses was highly correlated (p < 0.01) to the degree of residual lung dysfunction. Unexpectedly, active NF- kappaB complexes found in BCs of heaves-affected horses were mainly p65 homodimers, rather than classic p65-p50 heterodimers. At last, intercellular adhesion molecule-1 (ICAM-1) expression paralleled p65 homodimers activity in these cells. These results demonstrate that the kinetics of NF-kappaB activity is strongly related to the course of the disease and confirm the relevance of NF-kappaB as a putative target in asthma therapy. Moreover, uncommon p65 homodimers could transactivate, in BCs, a subset of genes, such as ICAM-1, characteristic of chronic airway inflammation.

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