NF-κB was first described as a B-cell-specific transcription factor that binds the κB site in the Ig κ light chain enhancer. Soon after, NF-κB activity was found to be inducible in all cell types and ...it is now known that members of the NF-κB/Rel family regulate many genes involved in immune and inflammatory responses. Until recently, only a single NF-κB signaling pathway was known, whereby NF-κB activity is stimulated by proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1), as well as by pathogen-associated molecular patterns (PAMPs). However, two years ago, a second pathway leading to NF-κB activation was discovered. This pathway, now known as the alternative pathway, is activated by certain members of the TNF cytokine family but not by TNF-alpha itself. Recent results strongly suggest that the classical and alternative pathways to NF-κB activation have distinct regulatory functions, one that is mostly involved in innate immunity and the other in adaptive immunity.
The role of reactive oxygen intermediates (ROIs) in nuclear factor-kappaB (NF-κB) activation remains a matter of controversy. We have studied whether ROIs played any role in NF-κB induction by ...interleukin-1β (IL-1β) in different cell types. Our studies indicated three different pathways. IL-1β stimulation of lymphoid cells generates ROIs, which are required for IκB-α degradation and NF-κB activation. The source of these ROIs is the 5-lipoxygenase (5-LOX) enzyme. In monocytic cells, ROIs are also produced in response to IL-1β and necessary for NF-κB induction, but their source appears to be the NADPH oxidase complex. Finally, epithelial cells do not generate ROIs after IL-1β stimulation, but do rapidly activate NF-κB. Interestingly, transfection of epithelial cells with the 5-LOX and 5-LOX activating protein expression vectors restored ROI production and ROI-dependent NF-κB activation in response to IL-1β. Our data thus indicate that ROIs are cell type-specific second messengers for NF-κB induction by IL-1β.
In most cells trans-activating NF-kappaB induces many inflammatory proteins as well as its own inhibitor, IkappaB-alpha, thus assuring a transient response upon stimulation. However, ...NF-kappaB-dependent inflammatory gene expression is persistent in asthmatic bronchi, even after allergen eviction. In the present report we used bronchial brushing samples (BBSs) from heaves-affected horses (a spontaneous model of asthma) to elucidate the mechanisms by which NF-kappaB activity is maintained in asthmatic airways. NF-kappaB activity was high in granulocytic and nongranulocytic BBS cells. However, NF-kappaB activity highly correlated to granulocyte percentage and was only abrogated after granulocytic death in cultured BBSs. Before granulocytic death, NF-kappaB activity was suppressed by simultaneous addition of neutralizing anti-IL-1beta and anti-TNF-alpha Abs to the medium of cultured BBSs. Surprisingly, IkappaB-beta, whose expression is not regulated by NF-kappaB, unlike IkappaB-alpha, was the most prominent NF-kappaB inhibitor found in BBSs. The amounts of IkappaB-beta were low in BBSs obtained from diseased horses, but drastically increased after addition of the neutralizing anti-IL-1beta and anti-TNF-alpha Abs. These results indicate that sustained NF-kappaB activation in asthmatic bronchi is driven by granulocytes and is mediated by IL-1beta and TNF-alpha. Moreover, an imbalance between high levels of IL-1beta- and TNF-alpha-mediated IkappaB-beta degradation and low levels of IkappaB-beta synthesis is likely to be the mechanism preventing NF-kappaB deactivation in asthmatic airways before granulocytic death.
...-inducing kinase (NIK)-mediated IKKα phosphorylation activates the alternative ... pathway, which is characterized by nuclear translocation of p52:Re1B heterodimers. This alternative pathway is ...initiated by a select few receptors, including ..., BAFF-R, and CD40. Although NIK, IKKα, and p52 are all critical regulators of LT-βR signaling in stromal cells during humoral immune responses, lymphocytes require NIK, but not p52, for optimal Ig production. This disparity suggests that NIK possesses critical cell-type-specific functions that do not depend on ... Here we use mice bearing targeted mutations of the TKKα activation loop ... (...) to address the B cell-intrinsic functions of NIK-IKKα signaling in vivo. We find that ...B cells mount normal primary antibody responses but do not enter germinal centers. This defect likely derives from ineffective early T-B cell collaboration and leads to impaired generation of humoral memory and relatively short-lived, low-affinity antibody production. Our findings contrast with those obtained by using p52... B cells, which mount normal Ig responses, and alymphoplasia (NIK mutant) B cells, which produce very little primary 1g. Thus, the NIK-IKKα-p52 axis is not as linear and exclusive as previous studies suggest, and IKKa possesses critical ...-independent functions in B cells. (ProQuest-CSA LLC: ... denotes formulae/symbols omitted.)
NF-kappaB-inducing kinase (NIK)-mediated IKKalpha phosphorylation activates the alternative NF-kappaB pathway, which is characterized by nuclear translocation of p52:RelB heterodimers. This ...alternative pathway is initiated by a select few receptors, including LT-betaR, BAFF-R, and CD40. Although NIK, IKKalpha, and p52 are all critical regulators of LT-betaR signaling in stromal cells during humoral immune responses, lymphocytes require NIK, but not p52, for optimal Ig production. This disparity suggests that NIK possesses critical cell-type-specific functions that do not depend on NF-kappaB. Here we use mice bearing targeted mutations of the IKKalpha activation loop Ser(176/180) (IKKalpha(AA)) to address the B cell-intrinsic functions of NIK-IKKalpha signaling in vivo. We find that IKKalpha(AA) B cells mount normal primary antibody responses but do not enter germinal centers. This defect likely derives from ineffective early T-B cell collaboration and leads to impaired generation of humoral memory and relatively short-lived, low-affinity antibody production. Our findings contrast with those obtained by using p52(-/-) B cells, which mount normal Ig responses, and alymphoplasia (NIK mutant) B cells, which produce very little primary Ig. Thus, the NIK-IKKalpha-p52 axis is not as linear and exclusive as previous studies suggest, and IKKalpha possesses critical NF-kappaB-independent functions in B cells.
We previously demonstrated that IL-1 beta -mediated induction of the nuclear factor- Kappa B (NF- Kappa B) transcription factor proceeds through the production of reactive oxygen intermediates in ...lymphoid cells, while it occurs independently of any oxidative stress in epithelial transformed cells. Indeed, inhibition of receptor internalization as well as NH sub(4)Cl and chloroquine blocked IL-1 beta -mediated induction of NF- Kappa B in OVCAR-3 and in other epithelial cell lines but not in lymphoid cells, indicating that distinct pathways are involved. Conversely, while we observed phospholipase A2 activity in both cell types following IL-1 beta stimulation, specific inhibitors of this enzyme inhibited NF- Kappa B induction only in lymphoid cells. Moreover, expression of the 5-lipoxygenase (5-LOX) enzyme was not detected in epithelial cells, and inhibition of this enzyme blocked NF- Kappa B induction by IL-1 beta only in lymphoid cells. This study thus indicates that the activation of NF- Kappa B following IL-1 beta treatment involves the activation of phospholipase A2 and 5-LOX and the production of reactive oxygen intermediates (ROIs) in lymphoid cells, while in epithelial cells, another pathway predominates and could involve the acid sphingomyelinase. Moreover, arachidonic acid could induce NF- Kappa B in epithelial and lymphoid cells, but this activation involved the 5-LOX enzyme and the production of ROIs only in lymphoid cells. The inefficiency of the ROI pathway in epithelial cells is probably the consequence of both low ROI production due to undetectable expression of 5-LOX and rapid degradation of hydrogen peroxide due to high catalase activity.
Ceramide is a key component of intracellular stress responses. Evidence is provided for a novel mechanism of ceramide formation that mediates solar ultraviolet (UV) A radiation‐induced expression of ...the intercellular adhesion molecule (ICAM)‐1. Similarly to UVA radiation, ceramide stimulation of human keratinocytes induced ICAM‐1 mRNA expression and activated the ICAM‐1 promoter through transcription factor AP‐2. Ceramide‐activated AP‐2 and ceramide‐induced ICAM‐1 reporter gene activation were abrogated through deletion of the AP‐2 binding site. UVA radiation increased the level of ceramide in keratinocytes and inhibition of sphingomyelin synthesis prevented UVA radiation‐induced ICAM‐1 expression. Hitherto, two pathways have been identified for ceramide accumulation: hydrolysis from sphingomyelin through neutral and acid sphingomyelinases, and de novo synthesis by ceramide synthase. UVA radiation did not activate any of these enzymes. Ceramide generation in UVA‐irradiated cells, however, was inhibited by singlet oxygen quenchers and mimicked in unirradiated cells by a singlet oxygen‐generating system. In addition, UVA radiation and singlet oxygen both generated ceramide in protein‐free, sphingomyelin‐containing liposomes. This study indicates that singlet oxygen triggers a third, non‐enzymatic mechanism of ceramide formation.
The NF-κB transcription factor is ubiquitously expressed and controls the expression of a large number of genes. Experimental data clearly indicate that NF-κB is a major regulator of the inflammatory ...reaction by controlling the expression of pro-inflammatory molecules in response to cytokines, oxidative stress and infectious agents. We demonstrated that NF-κB activation by IL-1β follows three distinct cell-specific pathways. Moreover, our studies indicated that in one model of inflammatory diseases, horse recurrent airway obstruction (RAO), the extent of NF-κB basal activity correlates with pulmonary dysfunction. Another role of NF-κB activity protects cancer cells against apoptosis and could participate in the resistance to cancer treatment. However, we did not observe any increased cytotoxicity after treatment with anticancer drugs or TNF-α of cells expressing a NF-κB inhibitor. Therefore, we can conclude that the inhibition of apoptosis by NF-κB is likely to be cell type and stimulus-dependent. Further studies are required to determine whether NF-κB could be a target for anticancer treatments.
![The two NF-[kappa]B activat...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1471-4906/small "The two NF-[kappa]B activation pathways and their role in innate and adaptive immunity")
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