Tumor necrosis factor-alpha-induced IKK phosphorylation of NF-kappaB p65 on serine 536 is mediated through the TRAF2, TRAF5, and TAK1 signaling pathway

The activation of NF-kappaB has been shown to be regulated by multiple phosphorylations of IkappaBs and the NF-kappaB p65 subunit. Here, we characterized the intracellular signaling pathway leading to phosphorylation of p65 on Ser-536 using a novel anti-phospho-p65 (Ser-536) antibody. The Ser-536 of endogenous p65 was rapidly phosphorylated in response to a wide variety of NF-kappaB stimulants including TNF-alpha in the cytoplasm and rapidly dephosphorylated in the nucleus. The TNF-alpha-but not IL-1beta-induced Ser-536 phosphorylation was severely impaired in murine embryonic fibroblasts derived from traf2-/-traf5-/- mice. Bay 11-7082, an inhibitor of IkappaB phosphorylation, inhibited the TNF-alpha-induced phosphorylation in vivo. In addition, overexpression of TGF-beta-activated kinase 1 (TAK1), IKKalpha and IKKbeta stimulated the phosphorylation, and their dominant negative mutants blocked the TNF-alpha-induced phosphorylation. Moreover, small interfering RNAs (siRNAs) against TAK1, IKKalpha and IKKbeta blocked the phosphorylation of endogenous p65. On the other hand, calyculin-A, a protein phosphatase inhibitor, blocked the dephosphorylation in the nucleus in vivo. These results indicate that similar signaling pathways were utilized for the phosphorylations of IkappaBalpha and p65, which further support the idea that both IkappaB and NF-kappaB are substrates for the IKK complex in the activation of NF-kappaB.     

Phosphorylation of serine 468 by GSK-3beta negatively regulates basal p65 NF-kappaB activity

The activity of NF-kappaB is controlled at several levels including the phosphorylation of the strongly transactivating p65 (RelA) subunit. However, the overall number of phosphorylation sites, the signaling pathways and protein kinases that target p65 NF-kappaB and the functional role of these phosphorylations are still being uncovered. Using a combination of peptide arrays with in vitro kinase assays we identify serine 468 as a novel phosphorylation site of p65 NF-kappaB. Serine 468 lies within a GSK-3beta consensus site, and recombinant GSK-3beta specifically phosphorylates a GST-p65-(354-551) fusion protein at Ser(468) in vitro. In intact cells, phosphorylation of endogenous Ser(468) of p65 is induced by the PP1/PP2A phosphatase inhibitor calyculin A and this effect is inhibited by the GSK-3beta inhibitor LiCl. Reconstitution of p65-deficient cells with a p65 protein where serine 468 was mutated to alanine revealed a negative regulatory role of serine 468 for NF-kappaB activation. Collectively our results suggest that a GSK-3beta-PP1-dependent mechanism regulates phosphorylation of p65 NF-kappaB at Ser(468) in unstimulated cells and thereby controls the basal activity of NF-kappaB.     

Bruton's tyrosine kinase is involved in p65-mediated transactivation and phosphorylation of p65 on serine 536 during NFkappaB activation by lipopolysaccharide

Bruton's tyrosine kinase (Btk) has recently been shown to participate in the induction of nuclear factor kappaB (NFkappaB)-dependent gene expression by the lipopolysaccharide (LPS) receptor Toll-like receptor-4 (TLR4). In this study we have examined the mechanism whereby Btk participates in this response. Treatment of the murine monocytic cell line Raw264.7 with LFM-A13, a specific Btk inhibitor, blocked LPS-induced NFkappaB-dependent reporter gene expression but not IkappaB alpha degradation. Transient transfection of HEK293 cells with Btk had no effect on NFkappaB-dependent reporter gene expression but strongly promoted transactivation of a reporter gene by a p65-Gal4 fusion protein. IkappaB alpha degradation activated by LPS was intact in macrophages from X-linked immunodeficiency (Xid) mice, which contain inactive Btk. Transfection of cells with a dominant negative form of Btk (BtkK430R) inhibited LPS-driven p65 mediated transactivation. Additionally LFM-A13 impaired phosphorylation of serine 536 on p65 induced by LPS in HEK293-TLR4 cells, and in Xid macrophages this response was impaired. This study therefore reveals a novel function for Btk. It is required for the signaling pathway activated by TLR4, which culminates in phosphorylation of p65 on serine 536 promoting transactivation by NFkappaB.     

Ultraviolet B-induced phosphorylation of histone H3 at serine 28 is mediated by MSK1.

N-terminal tail phosphorylation of histone H3 plays an important role in gene expression, chromatin remodeling, and chromosome condensation. Phosphorylation of histone H3 at serine 10 was shown to be mediated by RSK2, mitogen- and stress-activated protein kinase-1 (MSK1), and mitogen-activated protein kinases depending on the specific stimulation or stress. Our previous study showed that mitogen-activated protein kinases MAP kinases are involved in ultraviolet B-induced phosphorylation of histone H3 at serine 28 (Zhong, S., Zhong, Z., Jansen, J., Goto, H., Inagaki, M., and Dong, Z., J. Biol. Chem. 276, 12932-12937). However, downstream effectors of MAP kinases remain to be identified. Here, we report that H89, a selective inhibitor of the nucleosomal response, totally inhibits ultraviolet B-induced phosphorylation of histone H3 at serine 28. H89 blocks MSK1 activity but does not inhibit ultraviolet B-induced activation of MAP kinases p70/85(S6K), p90(RSK), Akt, and protein kinase A. Furthermore, MSK1 markedly phosphorylated serine 28 of histone H3 and chromatin in vitro. Transfection experiments showed that an N-terminal mutant MSK1 or a C-terminal mutant MSK1 markedly blocked MSK1 activity. Compared with wild-type MSK1, cells transfected with N-terminal or C-terminal mutant MSK1 strongly blocked ultraviolet B-induced phosphorylation of histone H3 at serine 28 in vivo. These data illustrate that MSK1 mediates ultraviolet B-induced phosphorylation of histone H3 at serine 28.     

Role of B7-CD28/CTLA-4 costimulation and NF-kappa B in allergen-induced T cell chemotaxis by IL-16 and RANTES

The mechanisms that cause T cell recruitment into inflamed airways of asthmatic individuals are poorly understood. It has been shown previously that both natural exposure to allergen and challenge in the laboratory induce T cell accumulation in the bronchial mucosa of sensitized asthmatics. To study the mechanisms involved in this process, we have used an explant model in which bronchial biopsies taken from mild atopic asthmatic volunteers during fiberoptic bronchoscopy were stimulated in culture for 24 h by the common aeroallergen house dust mite (Dermatophagoides pteronyssinus (Der p)). Analysis of culture supernatants showed that stimulation with Der p significantly enhanced both the generation of T cell chemotactic activity by the mucosal tissue, as assayed in microchemotaxis chambers, and the production of IL-16 and RANTES. Neutralization experiments showed that IL-16 contributed more to the chemotactic activity than RANTES. The fusion protein CTLA-4-Ig, blocking B7:CD28 costimulation, and dexamethasone both significantly reduced the ex vivo production of chemotactic activity and release of IL-16 and RANTES. The proteasome inhibitor Cbz-Ile-Glu(OtBu)-Ala-leucinal also had a significant inhibitory effect on T cell chemotactic activity and IL-16 but not RANTES generation, indicating a role for nuclear factor NF kappa B activation. These results indicate that allergen stimulates cells within the bronchial mucosa to increase IL-16 and RANTES release, both of which contribute to T cell accumulation in asthmatic airways. The allergen-induced chemotactic activity is dependent on cell activation via CD28 and involves, at least partly, NF-kappa B.     

Active repression of antiapoptotic gene expression by RelA(p65) NF-kappa B

With the emerging role of NF-kappa B in cancer it is important that its responses to stimuli relevant to tumor progression and therapy are understood. Here, we demonstrate that NF-kappa B induced by cytotoxic stimuli, such as ultraviolet light (UV-C) and the chemotherapeutic drugs daunorubicin/doxorubicin, is functionally distinct to that seen with the inflammatory cytokine TNF and is an active repressor of antiapoptotic gene expression. Surprisingly, these effects are mediated by the RelA(p65) NF-kappa B subunit. Furthermore, UV-C and daunorubicin inhibit TNF-induced NF-kappa B transactivation, indicating that this is a dominant effect. Consistent with this, mechanistic studies reveal that UV-C and daunorubicin induce the association of RelA with histone deacetylases. RelA can therefore be both an activator and repressor of its target genes, dependent upon the manner in which it is induced. This has important implications for the role of NF-kappa B in tumorigenesis and the use of NF-kappa B inhibitors in cancer therapy.     

Reactive oxygen species-induced phosphorylation of p53 on serine 20 is mediated in part by polo-like kinase-3.

Upon exposure of cells to hydrogen peroxide (H(2)O(2)) phosphorylation of p53 was rapidly induced in human fibroblast GM00637, and this phosphorylation occurred on serine 9, serine 15, serine 20, but not on serine 392. In addition, H(2)O(2)-induced phosphorylation of p53 was followed by induction of p21, suggesting functional activation of p53. Induction of phosphorylation of p53 on multiple serine residues by H(2)O(2) was caffeine-sensitive and blocked in ATM(-/-) cells. Polo-like kinase-3 (Plk3) activity was also activated upon H(2)O(2) treatment, and this activation was ATM-dependent. Recombinant His(6)-Plk3 phosphorylated glutathione S-transferase (GST)-p53 fusion protein but not GST alone. When phoshorylated in vitro by His(6)-Plk3, but not by the kinase-defective mutant His6-Plk3(K52R), GST-p53 was recognized by an antibody specifically to serine 20-phosphorylated p53, indicating that serine 20 is an in vitro target of Plk3. Also serine 20-phosphorylated p53 was coimmunoprecipitated with Plk3 in cells treated with H(2)O(2). Furthermore, although H(2)O(2) strongly induced serine 15 phosphorylation of p53, it failed to induce serine 20 phosphorylation in Plk3-dificient Daudi cells. Ectopic expression of a Plk3 dominant negative mutant, Plk3(K52R), in GM00637 cells suppressed H(2)O(2)-induced serine 20 phosphorylation. Taken together, our studies strongly suggest that the oxidative stress-induced activation of p53 is at least in part mediated by Plk3.