Targeting of p300 to the interleukin-2 promoter via CREB-Rel cross-talk during mitogen and oncogenic molecular signaling in activated T-cells

In this report, we explore the mechanisms of targeting of p300 to the interleukin-2 (IL-2) promoter in response to mitogenic and oncogenic molecular signals. Recruitment of p300 by cAMP-responsive element-binding protein-Rel cross-talk at the composite CD28 response element (CD28RE)-TRE element of the IL-2 promoter is essential for promoter inducibility during T-cell activation, and CD28RE-TRE is the exclusive target of the human T-cell lymphotropic virus type I oncoprotein Tax. The intrinsic histone acetyltransferase activity of p300 is dispensable for activation of the IL-2 promoter, and the N-terminal 743 residues contain the minimal structural requirements for synergistic transactivation of the CD28RE-TRE, the IL-2 promoter, and endogenous IL-2 gene expression. Mutational analysis of p300 reveals differential structural requirements for the N-terminal p300 module by individual cis-elements within the IL-2 promoter. These findings provide evidence that p300 assembles at the IL-2 promoter to form an enhanceosome-like signal transduction target that is centrally integrated at the CD28RE-TRE element of the IL-2 promoter through specific protein module-targeted associations in activated T-cells.     

Defining the involvement of p38alpha MAPK in the production of anti- and proinflammatory cytokines using an SB 203580-resistant form of the kinase

Despite its lack of specificity, the inhibitor SB 203580 has been widely used to implicate p38 mitogen-activated protein kinase (MAPK) in the synthesis of many cytokines. Here we show unequivocally that the production of interleukin (IL)-1beta, IL-6, IL-10, and tumor necrosis factor alpha (TNFalpha) requires p38 MAPK activity by demonstrating that the inhibitory effects of SB 203580 were reversed by expression of an SB 203580-resistant form of p38alpha (SBR-p38alpha) that fails to bind to SB 203580. This strategy established the requirement for p38 activity for the lipopolysaccharide-stimulated production of IL-10, IL-1beta, and IL-6 by the monocytic cell WEHI 274 and the production of IL-6 and TNFalpha stimulated by ligation of the Fc-gamma receptor of the mast cell MC/9. Expression of SBR-p38alpha in primary macrophages abrogated the ability of SB 203580 to inhibit the lipopolysaccharide-stimulated production of TNFalpha but not of IL-10. Expression of SBR-p38alpha in primary T lymphocytes abrogated the ability of SB 203580 to inhibit the production of interferon-gamma induced by co-ligation of CD3 and CD28 but not the production of interferon-gamma or IL-10 induced by IL-12. These results suggest that the levels of p38 MAPK activity required for maximal cytokine production vary with different cytokines and stimuli.     

p38 alpha mitogen-activated protein kinase is activated by CD28-mediated signaling and is required for IL-4 production by human CD4+CD45RO+ T cells and Th2 effector cells.

T cell proliferation and cytokine production usually require stimulation via both the TCR/CD3 complex and the CD28 costimulatory receptor. Using purified human CD4+ peripheral blood T cells, we show that CD28 stimulation alone activates p38 alpha mitogen-activated protein kinase (p38 alpha). Cell proliferation induced by CD28 stimulation alone, a response attributed to CD4+CD45RO+ memory T cells, was blocked by the highly specific p38 inhibitors SB 203580 (IC50 = 10-80 nM) and RWJ 67657 (IC50 = 0.5-4 nM). In contrast, proliferation induced by anti-CD3 plus anti-CD28 mAbs was not blocked. Inhibitors of p38 also blocked CD4+ T cell production of IL-4 (SB 203580 IC50 = 20-100 nM), but not IL-2, in response to CD3 and CD28 stimulation. IL-5, TNF-alpha, and IFN-gamma production were also inhibited, but to a lesser degree than IL-4. IL-4 production was attributed to CD4+CD45RO+ T cells, and its induction was suppressed by p38 inhibitors at the mRNA level. In polarized Th1 and Th2 cell lines, SB 203580 strongly inhibited IL-4 production by Th2 cells (IC50 = 10-80 nM), but only partially inhibited IFN-gamma and IL-2 production by Th1 cells (<50% inhibition at 1 microM). In both Th1 and Th2 cells, CD28 signaling activated p38 alpha and was required for cytokine production. These results show that p38 alpha plays an important role in some, but not all, CD28-dependent cellular responses. Its preferential involvement in IL-4 production by CD4+CD45RO+ T cells and Th2 effector cells suggests that p38 alpha may be important in the generation of Th2-type responses in humans.     

A specific inhibitor of the p38 mitogen activated protein kinase affects differentially the production of various cytokines by activated human T cells: dependence on CD28 signaling and preferential inhibition of IL-10 production

Cytokine production upon T cell activation results from the integration of multiple signaling pathways from TCR/CD3 and from costimulatory molecules such as CD28. Among these pathways, the possible role of p38 mitogen activated protein kinase (MAPK) is the least understood. Here, we used a highly specific p38 MAPK inhibitor, the SB203580 compound, to examine the role of this enzyme in the induction of various cytokines in human T cells stimulated with anti-CD3 and anti-CD28 mAb together or in combination with PMA. Cytokine induction was monitored by ELISA and at the mRNA level. While SB203580 had little effect on IL-2 production and proliferation, it significantly reduced the production of several other cytokines. The secretion of IL-4, IL-5, IL-13, and TNF-alpha was inhibited by 20-50% with modes of T cell activation involving the CD28 pathway, whereas their mRNA expression was little affected. In contrast, IFN-gamma induction via CD28/PMA or CD3/CD28, but not CD3/PMA, was markedly diminished both at the protein and at the mRNA levels. Most interestingly, SB203580 also suppressed IL-10 secretion and mRNA induction via CD28-dependent activation by 75-85% (IC50 approximately 0.2 microM). Subset analysis suggested that this inhibition did not reflect a differential effect on T cell subsets. Therefore, p38 MAPK activity appears to contribute to cytokine production, mostly via CD28-dependent signaling. Moreover, IL-10 seems to rely more on this activity than other cytokines for its induction in T cells.     

Role of TNF receptor-associated factor 2 and p38 mitogen-activated protein kinase activation during 4-1BB-dependent immune response

4-1BB is a costimulatory member of the TNFR family, expressed on activated CD4(+) and CD8(+) T cells. Previous results showed that 4-1BB-mediated T cell costimulation is CD28-independent and involves recruitment of TNFR-associated factor 2 (TRAF2) and activation of the stress-activated protein kinase cascade. Here we describe a role for the p38 mitogen-activated protein kinase (MAPK) pathway in 4-1BB signaling. Aggregation of 4-1BB alone induces p38 activation in a T cell hybridoma, whereas, in normal T cells, p38 MAPK is activated synergistically by immobilized anti-CD3 plus immobilized 4-1BB ligand. 4-1BB-induced p38 MAPK activation is inhibited by the p38-specific inhibitor SB203580 in both a T cell hybridoma and in murine T cells. T cells from TRAF2 dominant-negative mice are impaired in 4-1BB-mediated p38 MAPK activation. A link between TRAF2 and the p38 cascade is provided by the MAPK kinase kinase, apoptosis-signal-regulating kinase 1. A T cell hybrid transfected with a kinase-dead apoptosis-signal-regulating kinase 1 fails to activate p38 MAPK in response to 4-1BB signaling. To assess the role of p38 activation in an immune response, T cells were stimulated in an MLR in the presence of SB203580. In a primary MLR, SB203580 blocked IL-2, IFN-gamma, and IL-4 secretion whether the costimulatory signal was delivered via 4-1BB or CD28. In contrast, following differentiation into Th1 or Th2 cells, p38 inhibition blocked IL-2 and IFN-gamma without affecting IL-4 secretion. Nevertheless, IL-4 secretion by Th2 cells remained costimulation-dependent. Thus, critical T cell signaling events diverge following Th1 vs Th2 differentiation.     

A critical role for p38 mitogen-activated protein kinase in the maturation of human blood-derived dendritic cells induced by lipopolysaccharide, TNF-alpha, and contact sensitizers

We investigated the involvement of mitogen-activated protein kinases (MAPKs) in the maturation of CD83(-) dendritic cells (DC) derived from human blood monocytes. Maturating agents such as LPS and TNF-alpha induced the phosphorylation of members of the three families of MAPK (extracellular signal-regulated kinase l/2, p46/54 c-Jun N-terminal kinase, and p38 MAPK). SB203580, an inhibitor of the p38 MAPK, but not the extracellular signal-regulated kinase l/2 pathway blocker PD98059, inhibited the up-regulation of CD1a, CD40, CD80, CD86, HLA-DR, and the DC maturation marker CD83 induced by LPS and TNF-alpha. In addition, SB203580 inhibited the enhancement of the allostimulatory capacity and partially prevented the down-regulation of FITC-dextran uptake induced by LPS and TNF-alpha. Likewise, SB203580 partially prevented the up-regulation of IL-1alpha, IL-1beta, IL-lRa, and TNF-alpha mRNA upon stimulation with LPS and TNF-alpha, as well as the release of bioactive TNF-alpha induced by LPS. DC maturation induced by the contact sensitizers 2,4-dinitrofluorobenzene and NiSO(4), as seen by the up-regulation of CD80, CD86, and CD83, was also coupled to the phosphorylation of p38 MAPK, and was inhibited by SB203580. The irritants SDS and benzalkonium chloride that do not induce DC maturation did not trigger p38 MAPK phosphorylation. Together, these data indicate that phosphorylation of p38 MAPK is critical for the maturation of immature DC. These results also suggest that p38 MAPK phosphorylation in DC may become useful for the identification of potential skin contact sensitizers.     

p38 mitogen-activated protein kinase regulates human T cell IL-5 synthesis.

Involvement of p38 mitogen-activated protein (MAP) kinase in human T cell cytokine synthesis was investigated. p38 MAP kinase was clearly induced in human Th cells activated through the TCR. SB203580, a highly selective inhibitor of p38 MAP kinase, inhibited the induction of p38 MAP kinase in human Th cells. Major T cell cytokines, IL-2, IL-4, IL-5, and IFN-gamma, were produced by Der f 2-specific Th clones upon stimulation through the TCR. IL-5 synthesis alone was significantly inhibited by SB203580 in a dose-dependent manner, whereas the production of IL-2, IL-4, and IFN-gamma was not affected. The proliferation of activated T cells was not affected. IL-5 synthesis of human Th clones induced upon stimulation with rIL-2, phorbol ester plus anti-CD28 mAb, and immobilized anti-CD3 mAb plus soluble anti-CD28 mAb was also suppressed by SB203580 in the same concentration response relationship. The results clearly indicated that IL-5 synthesis by human Th cells is dependent on p38 MAP kinase activity, and is regulated distinctly from IL-2, IL-4, and IFN-gamma synthesis. Selective control of IL-5 synthesis will provide a novel treatment devoid of generalized immune suppression for bronchial asthma and atopic dermatitis that are characterized by eosinophilic inflammation.