Possible stage-specific function of NF-kappaB during pre-B cell differentiation

Dysregulated interleukin-8 secretion and NF-κB activity in human cystic fibrosis nasal epithelial cells

BACKGROUND

It is not clear whether cystic fibrosis (CF) airway inflammation is a consequence of bacterial infection or is intrinsically dysregulated. The aim of this study was to investigate IL-8 secretion and NF-kappaB activity in primary respiratory epithelial cells cultured from nasal polyps obtained from CF and non-CF subjects.

METHODS

NF-kappaB activity was studied by electrophoretic mobility-shift and quantitative colorimetric assays in nuclear extracts. Immunoreactive IL-8 levels were assessed by ELISA in cell culture supernatants. Both parameters were studied at baseline and following challenge with Pseudomonas aeruginosa or stimulation with pro-inflammatory cytokines.

RESULTS

Under basal conditions, CF cells presented a significant higher activity of NF-kappaB than non-CF cells (P=0.0004). P. aeruginosa challenge and IL-1beta/H2O2 co-stimulation caused four and two fold induction of NF-kappaB activity in non-CF and CF cells, respectively. IL-8 levels in unstimulated CF cells were significantly higher than in non-CF cells (P=0.0025). Upon incubation with P. aeruginosa and IL-1beta/H2O2, non-CF cells produced 6.3 times more IL-8 than unstimulated cells, whereas IL-8 secretion increased only of 1.4 times in CF cells.

CONCLUSIONS

CF respiratory epithelial cells exhibit a basal dysregulated production of IL-8 that partially correlates to enhanced NF-kappaB activity. Our data corroborate the hypothesis of a basal exaggerated inflammatory response in the CF respiratory epithelium.

Nuclear factor-kappa B is involved in the catecholaminergic suppression of immunocompetent cells

Catecholamines are known to exert a powerful impact on the immune system by downregulation of proliferation and differentiation, and induction of apoptosis. However, the mechanism for this regulatory route is still unclear. Therefore well established human monocytic cell-lines and nontransformed human monocytes, obtained from peripheral blood, were incubated with an optimal concentration of LPS and varying concentrations of the catecholamine dopamine. The proliferative response to LPS was determined by [3H]thymidine incorporation, and a significant suppressive effect by dopamine was obtained. LPS-induced binding of NF-kappa B to DNA, determined by electrophoretic mobility shift assay, was inhibited by extrinsic dopamine, leading to a decreased proliferation and cytokine expression. In contrast, the intracellular ceramide concentration was not affected by incubation of peripheral blood lymphocytes with dopamine. Our findings suggest that the NF-kappa B-I-kappa B transcription machinery may well be involved in the catecholaminergic regulation of the immune system, while the ceramide-SAPK/JNK cascade appears not to play a significant role in this suppression.

The role of NF-kappaB as a survival factor in environmental chemical-induced pre-B cell apoptosis

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous environmental chemicals that suppress the immune system at multiple levels, including at the level of B cell development in the bone marrow microenvironment. Specifically, PAH induce preB cell apoptosis in primary bone marrow cultures and in cocultures of an early preB cell line (BU-11) and a bone marrow stromal cell line (BMS2). Previous studies focused on the molecular mechanisms through which PAH induce stromal cells to deliver an apoptosis signal to adjacent preB cells. Apoptosis signaling within the preB cell itself was not investigated. Here, the role of NF-kappaB, a lymphocyte survival factor, in PAH-induced preB cell apoptosis was assessed. Analysis of DNA-binding proteins extracted from the nuclei of untreated BU-11 cells indicated DNA-binding complexes comprising NF-kappaB subunits p50, c-Rel, and/or Rel A. NF-kappaB down-regulation with previously described inhibitors induced BU-11 cell apoptosis, demonstrating that the default apoptosis pathway blocked by NF-kappaB is functional at this early stage in B cell development. Similarly, exposure of BU-11/BMS2 cocultures to 7,12-dimethylbenz[a]anthracene (DMBA), a prototypic PAH, down-regulated nuclear Rel A and c-Rel before overt apoptosis. Finally, ectopic expression of Rel A or c-Rel rescued BU-11 cells from DMBA-induced apoptosis. These results extend previous observations by demonstrating that 1) NF-kappaB is a survival factor at an earlier stage of B cell development than previously appreciated and 2) NF-kappaB down-regulation is likely to be part of the molecular mechanism resulting in PAH-induced preB cell apoptosis. These results suggest nonclonally restricted, PAH-mediated suppression of B lymphopoiesis.

Alterations in mitochondria and mtTFA in response to LPS-induced differentiation of B-cells

Stimulation of immune cells results in altered cell function and metabolism, which must be recognized by and coordinated with energy production from mitochondria. Mitochondria contain their own DNA genome encoding 13 polypeptides that combine with nuclear-derived subunits to create functional enzyme complexes of the electron transport chain. Therefore, coordination of mitochondrial and nuclear transcription is necessary to achieve a sustained elevation in mitochondrial ATP production. Pre-B-lymphocytes stimulated with lipopolysaccharide exhibit increased activity levels of the mitochondrial enzymes, succinate dehydrogenase and cytochrome c oxidase. Immunoblot analyses of purified mitochondria indicate an increase in the mitochondrial transcription factor (mtTFA) levels in mitochondria induced by cell stimulation. This increase is consistent with increased mtTFA production in the cytoplasm. In addition, mitochondrial protein extracts indicate an increase in protein binding to a mtTFA-DNA binding site from the mitochondrial genome, subsequent to cell stimulation. These results indicate that mitochondrial activity changes during B-lymphocyte stimulation, and mtTFA may contribute to the coordination of respiration with cellular energy demand.

2-Acetylaminofluorene suppresses immune response through the inhibition of nuclear factor-kappaB activation during the early stage of B cell development

2-Acetylaminofluorene (AAF), an arylamide carcinogen, has been known to inhibit humoral and cell-mediated immune response by lipopolysaccharide (LPS). In the current study we demonstrate that AAF induced the down-regulation of protein kinase C (PKC) that is a key enzyme in the pathways leading to LPS-induced B-cell proliferation, while having no inhibitory effect on intracellular cAMP in spleen cells. Additionally, to identify the mechanism of action of AAF during B-cell development, we determined the effects of AAF on LPS-induced nuclear factor-kappaB (NF-kappaB) activation in 70Z/3 murine pre-B cells, CH12 murine mature B cells and S194 murine plasmacytoma cells. LPS-induced NF-kappaB activation, which is dependent on PKC, was inhibited by pretreatment with AAF for 2 h in the nuclei of 70Z/3 murine pre-B cells by detection of NF-kappaB specific DNA-protein binding. Conversely, AAF barely inhibited the constitutive NF-kappaB binding activity in mature B-cells, S194 and CH12. To confirm the effect of AAF on NF-kappaB activation, a chloramphenicol acetyl transferase (CAT) expression vector containing multiple copies of the NF-kappaB element (pCAT(kappaB)(3)) was transiently transfected into 70Z/3 or S194 cells, and assessed for inducible CAT activity. AAF treatment of 70Z/3 cells resulted in a significant inhibition of CAT activity induced by LPS. However, AAF exhibited no inhibitory effect on constitutive CAT activity in mature B cells, S194, indicating that AAF no longer has suppressive effects on the immune response in differentiated B cells. Taken together, these results suggest that AAF may act to suppress immune response by blocking the activation of PKC and nuclear expression of NF-kappaB at the early stage of B cell development.