Augmentation of signal transducer and activation of transcription (STAT)6 and STAT3 expression in stimulated B and T cells

Constitutive Phosphorylation of STAT3 by the CK2-BLNK-CD5 Complex

In chronic lymphocytic leukemia (CLL), STAT3 is constitutively phosphorylated on serine 727 and plays a role in the pathobiology of CLL. However, what induces constitutive phosphorylation of STAT3 is currently unknown. Mass spectrometry was used to identify casein kinase 2 (CK2), a serine/threonine kinase that coimmunoprecipitated with serine phosphorylated STAT3 (pSTAT3). Furthermore, activated CK2 incubated with recombinant STAT3 induced phosphorylation of STAT3 on serine 727. Although STAT3 and CK2 are present in normal B- and T cells, STAT3 is not constitutively phosphorylated in these cells. Further study found that CD5 and BLNK coexpressed in CLL, but not in normal B- or T cells, are required for STAT3 phosphorylation. To elucidate the relationship of CD5 and BLNK to CK2 and STAT3, STAT3 was immunoprecipitated from CLL cells, and CK2, CD5, and BLNK were detected in the immunoprecipitate. Conversely, STAT3, CD5, and BLNK were in the immunoprecipitate of CLL cells immunoprecipitated with CK2 antibodies. Furthermore, siRNA knockdown of CD5 or BLNK, or treatment with CD5-neutralizing antibodies significantly reduced the levels of serine pSTAT3 in CLL cells. Finally, confocal microscopy determined that CD5 is cell membrane bound, and fractionation studies revealed that the CK2/CD5/BLNK/STAT3 complex remains in the cytoplasm, whereas serine pSTAT3 is shuttled to the nucleus.Implications: These data show that the cellular proteins CK2, CD5, and BLNK are required for constitutive phosphorylation of STAT3 in CLL. Whether this protein complex phosphorylates other proteins or inhibiting its activity would have clinical benefit in patients has yet to be determined. Mol Cancer Res; 15(5); 610-8. ©2017 AACR.

The Flavonoid 7,4'-Dihydroxyflavone Inhibits MUC5AC Gene Expression, Production, and Secretion via Regulation of NF-κB, STAT6, and HDAC2

Mucus overproduction is a significant component of the pathophysiology of obstructive lung diseases. Currently, there are only a few medications available that inhibit mucus production. Previous studies showed that glycyrrhizin, a triterpenoid in Glycyrrhiza uralensis inhibits mucin 5AC (MUC5AC) mRNA and protein expression. Other potential mucus production inhibitory compounds contained within in G. uralensis have not been fully investigated. The aim of the present study was to determine if the G. uralensis flavonoid 7,4'-dihydroxyflavone (7,4'-DHF) inhibits MUC5AC gene expression, mucus production, and secretion, and if so, to elucidate the mechanism of this inhibition. 7,4'-Dihydroxyflavone significantly decreased phorbol 12-myristate 13-acetate-stimulated NCI-H292 human airway epithelial cell MUC5AC gene expression and mucus production, at a 28-fold lower concentration than glycyrrhizin (The half maximal inhibitory concentration IC50 value of 1.4 μM vs 38 μM, respectively); 7,4'-DHF also inhibited MUC5AC mucus secretion. Inhibition was associated with the suppression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), signal transducer and activator of transcription 6 (STAT6) activation, and enhanced histone deacetylase 2 (HDAC2) expression. In a murine model of asthma, 7,4'-DHF-treated mice exhibited a marked reduction in MUC5AC secretion in the bronchoalveolar lavage fluid compared with control mice. These findings, together with previous findings linking NF-κB, STAT6, and HDAC2 modulation to the control of MUC5AC expression, demonstrate that 7,4'-DHF is a newly identified component of G. uralensis that regulates MUC5AC expression and secretion via regulation of NF-κB, STAT6, and HDAC2.

IL-10 down-regulates costimulatory molecules on Mycobacterium tuberculosis-pulsed macrophages and impairs the lytic activity of CD4 and CD8 CTL in tuberculosis patients

Activation of T cells requires both TCR-specific ligation and costimulation through accessory molecules during T cell priming. IFNgamma is a key cytokine responsible for macrophage activation during Mycobacterium tuberculosis (Mtb) infection while IL-10 is associated with suppression of cell mediated immunity in intracellular infection. In this paper we evaluated the role of IFNgamma and IL-10 on the function of cytotoxic T cells (CTL) and on the modulation of costimulatory molecules in healthy controls and patients with active tuberculosis (TB). gamma-irradiated-Mtb (i-Mtb) induced IL-10 production from CD14(+) cells from TB patients. Moreover, CD3(+) T cells of patients with advanced disease also produced IL-10 after i-Mtb stimulation. In healthy donors, IL-10 decreased the lytic activity of CD4(+) and CD8(+) T cells whereas it increased gammadelta-mediated cytotoxicity. Furthermore, we found that the presence of IL-10 induced a loss of the alternative processing pathways of antigen presentation along with a down-regulation of the expression of costimulatory molecule expression on monocytes and macrophages from healthy individuals. Conversely, neutralization of endogenous IL-10 or addition of IFNgamma to either effector or target cells from TB patients induced a strong lytic activity mediated by CD8(+) CTL together with an up-regulation of CD54 and CD86 expression on target cells. Moreover, we observed that macrophages from TB patients could use alternative pathways for i-Mtb presentation. Taken together, our results demonstrate that the presence of IL-10 during Mtb infection might contribute to mycobacteria persistence inside host macrophages through a mechanism that involved inhibition of MHC-restricted cytotoxicity against infected macrophages.

IL-4-dependent CD86 expression requires JAK/STAT6 activation and is negatively regulated by PKCdelta

CD86 expression is up-regulated in activated monocytes and macrophages by a mechanism that is not clearly defined. Here, we report that IL-4-dependent CD86 expression requires activation of ERK1/2 and JAK/STAT6 but is negatively regulated by PKCdelta. PMA differentiated U937 monocytic cells when stimulated with IL-4 increased CD11b and CD86 expression by 52- and 98-fold, respectively. PMA+IL-4 treatment also induced a synergistic enhancement of ERK1/2 activation when compared to the effects of PMA and IL-4 alone. Use of the mitogen or extracellular kinase (MEK) inhibitor, PD98059, completely blocked up-regulation of CD11b and CD86 demonstrating the importance of MEK-activated ERK1/2. JAK inhibition with WHI-P154-abrogated IL-4-dependent CD11b and CD86 up-regulation and inhibited STAT6 tyrosine phosphorylation. Importantly, CD11b and CD86 expression were not reliant on IL-4-dependent activation of phosphatidylinositol 3'-kinase (PI 3-kinase). Blockade of PKCdelta activation with rottlerin prevented CD11b expression but lead to a 75- and 213-fold increase in PMA and PMA+IL-4-dependent CD86 expression, respectively. As anticipated, increasing PKCdelta activity with anti-sense reduction of CD45 increased CD11b expression and reduced CD86 expression. Likewise, rottlerin prevented nuclear localization of activated PKCdelta. We conclude from these data that IL-4-dependent CD11b expression relies predominantly on enhanced activation of ERK1/2, while IL-4-dependent CD86 expression utilizes the JAK/STAT6 pathway.

Signal transducer and activator of transcription 6 haplotypes and asthma in the Indian population

In this paper, we report for the first time the results of an investigation on the association of signal transducer and activator of transcription 6 (STAT6) with asthma in the Indian population. A novel polymorphic CA-repeat in the proximal promoter region [R1] and a previously identified CA-repeat in the 5'-untranslated region [R3] were genotyped, and haplotypes [R1_R3] were generated using PHASE software. The 16 repeat allele at the R1 locus was positively associated (P = 0.01) with asthma. The 15 and 16 repeat alleles at the R3 locus were positively (P < 10(-4)) and negatively (P < 10(-5)) associated with asthma, respectively. Further, the 17_15 (P = 0.0031) and 16_15 (P = 0.001) haplotypes were found to be positively associated with asthma, whereas 17_14, 24_16, and 23_16 were negatively associated (P < 10(-5)). It appears that the R3 and R1 loci together play a bigger role in asthma than either of them alone, and the R3 locus has a larger effect than the R1 locus. Although alleles at the R1 locus appeared to be associated with total serum immunoglobulin E level, the genotypes showed no association, and the R3 locus showed no effect. As no exonic variants of STAT6 are known as yet, repeat polymorphisms in the regulatory regions and their haplotypes could be important in deciphering the genetic role of STAT6 in asthma and atopy.

CD40 contributes to lethality in acute sepsis: in vivo role for CD40 in innate immunity

Sepsis induces an early inflammatory cascade initiated by the innate immune response. This often results in the development of multisystem organ failure. We examined the role of CD40, a costimulatory molecule that is integral in adaptive immunity, by using a murine model of polymicrobial sepsis. CD40 knockout (KO) mice had delayed death and improved survival after cecal ligation and puncture (CLP). In addition, they had less remote organ injury as manifested by reduced pulmonary capillary leakage. The improvements in survival and remote organ dysfunction in CD40 KO mice were associated with reduced interleukin-6 (IL-6) and IL-10 levels in serum and bronchoalveolar lavage fluid compared to the levels in wild-type (WT) controls. Furthermore, in contrast to WT mice, CD40 KO mice had no induction of the Th1 cytokines IL-12 and gamma interferon in serum or lungs after CLP. The alterations in cytokine production in CD40 KO mice were associated with similar changes in transcription factor activity. After CLP, CD40 KO mice had attenuated activation of nuclear factor kappaB and signal transducer and activator of transcription 3 in both the lung and the liver. Finally, WT mice had increased expression of CD40 on their alveolar macrophages. These data highlight the importance of CD40 activation in the innate immune response during polymicrobial sepsis and the subsequent development of remote organ dysfunction.

Overactivation of IL-4-induced activator protein-1 in atopic dermatitis

Atopic dermatitis is regarded as mediated by Th2-type immunity. In fact, it frequently coincides with the elevation of immunoglobulin (Ig)-E in patients' sera. Due to the pivotal role of interleukin (IL)-4 in regulation of IgE, we hypothesized if atopic dermatitis represents a hyper-reactive condition in response to IL-4 when it coincides the higher serum level of IgE. To address this possibility, peripheral blood mononuclear cells (PBMC) isolated from patients with atopic dermatitis with the high serum IgE level, from those with psoriasis or from healthy volunteers were stimulated with recombinant IL-4 and analyzed for activation of transcription factors including activator protein (AP)-1 or signal transducers and activators of transcription (STAT)-6 by employing electrophoretic mobility shift assays. Although no significant difference between atopy patients and other groups was observed in the STAT-6 binding activity in IL-4-stimulated PBMC, it over-activated the binding of AP-1 in PBMC of the patients with atopic dermatitis. The AP-1 binding was interfered by the use of an antibody directed against JunB. This is the indication that IL-4-overactivated AP-1 is composed of JunB. Furthermore, semi-quantitative RT-PCR analyses revealed marked down-modulation of a Th1 cytokine, interferon (IFN)-gamma, in IL-4-stimulated PBMC derived from atopy patients, but not that from healthy individuals. Together, our present study indicates that AP-1 is over-activated by IL-4 in PBMC of the atopic patients with the higher IgE level, thereby implying that IL-4-induced over-activation of AP-1 might be one of pathogenic factors in atopic dermatitis.

Stat6-deficient mice develop airway hyperresponsiveness and peribronchial fibrosis during chronic fungal asthma

Signal transducer and activator of transcription 6 (Stat6) is critical for Th2-mediated responses during allergic airway disease. To investigate the role of Stat6 in fungus-induced airway hyperresponsiveness and remodeling, Stat6-deficient (Stat6-/-) and Stat6-wildtype (Stat6+/+) mice were sensitized to Aspergillus fumigatus and airway disease was subsequently assessed in both groups at days 21, 30, 38, and 44 after an intratracheal challenge with live A. fumigatus conidia. At all times after conidia, histological analysis revealed an absence of goblet cell hyperplasia and markedly diminished peribronchial inflammation in Stat6-/- mice in contrast to Stat6+/+ mice. Airway hyperresponsiveness and peribronchial fibrosis in Stat6-/- mice were significantly reduced at day 21 after conidia compared with Stat6+/+ mice, but both groups exhibited significant, similar increases in these parameters at all subsequent times after conidia. In separate experiments, IL-13-responsive cells in Stat6-/- mice were targeted via the daily intranasal administration of 200 ng of IL-13-PE38QQR (IL13-PE), comprised of human IL-13 and a derivative of Pseudomonas exotoxin, from days 38 to 44 after the conidia challenge. IL13-PE treatment abolished airway hyperresponsiveness, but not peribronchial fibrosis in Stat6-/- mice. Taken together, these data demonstrate that the chronic development of airway hyperresponsiveness during fungal asthma is IL-13-dependent but Stat6-independent.