[Show abstract][Hide abstract] ABSTRACT: E3 ubiquitin ligase Cbl-b has emerged as a gatekeeper that controls the activation threshold of the T cell antigen receptor and maintains the balance between tolerance and autoimmunity. Here, we report that the loss of Cbl-b facilitates T helper 2 (Th2) and Th9 cell differentiation in vitro. In a mouse model of asthma, the absence of Cbl-b results in severe airway inflammation and stronger Th2 and Th9 responses. Mechanistically, Cbl-b selectively associates with Stat6 upon IL-4 ligation and targets Stat6 for ubiquitination and degradation. These processes are heightened in the presence of T cell receptor (TCR)/CD28 costimulation. Furthermore, we identify K108 and K398 as Stat6 ubiquitination sites. Intriguingly, introducing Stat6 deficiency into Cblb(-/-) mice abrogates hyper-Th2 responses but only partially attenuates Th9 responses. Therefore, our data reveal a function for Cbl-b in the regulation of Th2 and Th9 cell differentiation.
[Show abstract][Hide abstract] ABSTRACT: Gata5 is a transcription factor expressed in the lung, but whose physiological role is unknown. To test whether and how Gata5 regulates airway constrictor responsiveness, we studied Gata5-/-, Gata5+/-, and WT mice on the C57BL/6J background. Cholinergic airway constrictor responsiveness was assessed invasively in mice without and with induction of allergic airway inflammation through ovalbumin sensitization and aerosol exposure. Gata5 deficient mice displayed native airway constrictor hyperresponsiveness (AHR) in the absence of allergen-induced inflammation. Gata5 deficient mice retained their relatively greater constrictor responsiveness even in ovalbumin-induced experimental asthma. Gata5 deficiency did not alter the distribution of cell types in BAL fluid, but bronchial epithelial mucus metaplasia was more prominent in Gata5-/- mice after allergen challenge. Gene expression profiles revealed that apolipoprotein E was the fifth most down-regulated transcript in Gata5 deficient lungs, and quantitative RT-PCR and immunostaining confirmed reduced apoE expression in Gata5-/- mice. qRT-PCR also revealed increased IL-13 mRNA in the lungs of Gata5 deficient mice. These findings for the first time show that Gata5 regulates apoE and IL-13 expression in vivo and that its deletion causes AHR. Gata5 deficient mice exhibit an airway phenotype that closely resembles that previously reported for apoE-/- mice: Both exhibit cholinergic AHR in native and experimental asthma states, and there is excessive goblet cell metaplasia after allergen sensitization and challenge. The Gata5-deficient phenotype also shares features with that previously reported for IL-13-treated mice. Together, these results indicate that Gata5 deficiency induces AHR at least in part by blunting apoE and increasing IL-13 expression.
American Journal of Respiratory Cell and Molecular Biology 11/2013; · 4.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: E3 ubiquitin ligase Casitas-B-lineage lymphoma protein-b (Cbl-b) is critical for establishing the threshold for T cell activation and is essential for induction of T cell anergy. Recent studies suggest that Cbl-b is involved in the development of CD4(+)CD25(+) inducible regulatory T cells (iTregs). In this study, we report that the optimal induction of Foxp3 by naive CD4(+)CD25(-) T cells requires suboptimal TCR triggering. In the absence of Cbl-b, the TCR strength for optimal Foxp3 induction is downregulated in vitro. Using TCR-transgenic Rag(-/-) mice in combination with Cbl-b deficiency, we show that in vivo iTreg development is also controlled by Cbl-b via tuning the TCR strength. Furthermore, we show that Akt-2 but not Akt-1 regulates Foxp3 expression downstream of Cbl-b. Therefore, we demonstrate that Cbl-b regulates the fate of iTregs via controlling the threshold for T cell activation.
The Journal of Immunology 06/2013; · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Silencing of GATA5 gene expression as a result of promoter hypermethylation has been observed in lung, gastrointestinal and ovarian cancers. However, the regulation of GATA5 gene expression has been poorly understood. In the present study, we have demonstrated that an E (enhancer)-box in the GATA5 promoter (bp -118 to -113 in mice; bp -164 to -159 in humans) positively regulates GATA5 transcription by binding USF1 (upstream stimulatory factor 1). Using site-directed mutagenesis, EMSA (electrophoretic mobility-shift analysis) and affinity chromatography, we found that USF1 specifically binds to the E-box sequence (5'-CACGTG-3'), but not to a mutated E-box. CpG methylation of this E-box significantly diminished its binding of transcription factors. Mutation of the E-box within a GATA5 promoter fragment significantly decreased promoter activity in a luciferase reporter assay. Chromatin immunoprecipitation identified that USF1 physiologically interacts with the GATA5 promoter E-box in mouse intestinal mucosa, which has the highest GATA5 gene expression in mouse. Co-transfection with a USF1 expression plasmid significantly increased GATA5 promoter-driven luciferase transcription. Furthermore, real-time and RT (reverse transcription)-PCR analyses confirmed that overexpression of USF1 activates endogenous GATA5 gene expression in human bronchial epithelial cells. The present study provides the first evidence that USF1 activates GATA5 gene expression through the E-box motif and suggests a potential mechanism (disruption of the E-box) by which GATA5 promoter methylation reduces GATA5 expression in cancer.
[Show abstract][Hide abstract] ABSTRACT: E3 ubiquitin ligase Cbl-b plays a crucial role in T cell activation and tolerance induction. However, the molecular mechanism by which Cbl-b inhibits T cell activation remains unclear. Here, we report that Cbl-b does not inhibit PI3K but rather suppresses TCR/CD28-induced inactivation of Pten. The elevated Akt activity in Cbl-b(-/-) T cells is therefore due to heightened Pten inactivation. Suppression of Pten inactivation in T cells by Cbl-b is achieved by impeding the association of Pten with Nedd4, which targets Pten K13 for K63-linked polyubiquitination. Consistent with this finding, introducing Nedd4 deficiency into Cbl-b(-/-) mice abrogates hyper-T cell responses caused by the loss of Cbl-b. Hence, our data demonstrate that Cbl-b inhibits T cell activation by suppressing Pten inactivation independently of its ubiquitin ligase activity.
[Show abstract][Hide abstract] ABSTRACT: Program death-1 (PD-1) has been documented to negatively regulate immune responses. However, the cellular and molecular mechanisms for PD-1-mediated immune suppression have not been fully elucidated. In this study, we show that loss of PD-1 does not lead to defective induction of CD4(+) T cell anergy in vitro and in vivo. Rather, the absence of PD-1 inhibits the development of inducible CD4(+)Foxp3(+) regulatory T cells (iTregs) induced by TGF-β in vitro. In support of this finding, PD-1 deficiency impairs the generation of iTregs in vivo and leads to development of severe T cell-transfer-induced colitis. Mechanistically, defective iTreg generation in the absence of PD-1 was attributed to the heightened phosphorylation of Akt. Therefore, we first demonstrate that PD-1 controls peripheral T cell tolerance via an anergy-independent but iTreg-dependent mechanism.
[Show abstract][Hide abstract] ABSTRACT: CD40 is essential for optimal B cell activation. It has been shown that CD40 stimulation can augment BCR-induced B cell responses, but the molecular mechanism(s) by which CD40 regulates BCR signaling is poorly understood. In this report, we attempted to characterize the signaling synergy between BCR- and CD40-mediated pathways during B cell activation. We found that spleen tyrosine kinase (Syk) is involved in CD40 signaling, and is synergistically activated in B cells in response to BCR/CD40 costimulation. CD40 stimulation alone also activates B cell linker (BLNK), Bruton tyrosine kinase (Btk), and Vav-2 downstream of Syk, and significantly enhances BCR-induced formation of complex consisting of, Vav-2, Btk, BLNK, and phospholipase C-gamma2 (PLC-γ2) leading to activation of extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase, Akt, and NF-κB required for optimal B cell activation. Therefore, our data suggest that CD40 can strengthen BCR-signaling pathway and quantitatively modify BCR signaling during B cell activation.
[Show abstract][Hide abstract] ABSTRACT: Th cells that produce IL-17 (Th17 cells) are a distinct subset of Th cells implicated in several autoimmune diseases. Although CD28-B7 interaction has been shown to be involved in Th17 differentiation in vitro, the role of CTLA-4 in controlling Th17 development is completely unknown. We report in this paper that blocking the CTLA-4-B7 interaction potentiates Th17 cell differentiation in vitro and in vivo. Furthermore, blocking CTLA-4-B7 interaction in vivo confers the susceptibility of experimental autoimmune myocarditis to CD28(-/-) mice or increases the severity of experimental autoimmune myocarditis in wild-type mice. The enhanced disease susceptibility is mediated by heightened Th17 responses. With these results, we are the first to demonstrate that CTLA-4-B7 interaction inhibits Th17 differentiation in vitro and in vivo and suppresses Th17-mediated autoimmunity.
The Journal of Immunology 08/2010; 185(3):1375-8. · 5.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It has previously been shown that E3 ubiquitin ligase Casitas B-lineage lymphoma-b (Cbl-b) negatively regulates T-cell activation, but the molecular mechanism(s) underlying this inhibition is not completely defined. In this study, we report that the loss of Cbl-b selectively results in aberrant activation of NF-kappaB upon T-cell antigen receptor (TCR) ligation, which is mediated by phosphatidylinositol 3-kinase (PI3-K)/Akt and protein kinase C-theta (PKC-theta). TCR-induced hyperactivation of Akt in the absence of Cbl-b may potentiate the formation of caspase recruitment domain-containing membrane-associated guanylate kinase protein 1 (CARMA1)-B-cell lymphoma/leukemia 10 (Bcl10)-mucosa-associated lymphatic tissue 1(MALT1) (CBM) complex, which appears to be independent of PKC-theta. Cbl-b associates with PKC-theta upon TCR stimulation and regulates TCR-induced PKC-theta activation via Vav-1, which couples PKC-theta to PI3-K and allows it to be phosphorylated. PKC-theta then couples IkappaB kinases (IKKs) to the CBM complex, resulting in the activation of the IKK complex. Therefore, our data provide the first evidence to demonstrate that the down-regulation of TCR-induced NF-kappaB activation by Cbl-b is mediated coordinately by both Akt-dependent and PKC-theta-dependent signaling pathways in primary T cells.
Molecular and Cellular Biology 05/2008; 28(7):2470-80. · 5.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It has been documented that CD40 is essential for B cell function. Casitas-B-lineage lymphoma protein-b (Cbl-b), an adapter protein and ubiquitin ligase, has been shown to regulate the activation of T and B cells through their Ag receptors. In this study, we report that CD40-induced B cell proliferation is significantly augmented in mice lacking Cbl-b. Furthermore, Cbl-b(-/-) mice display enhanced thymus-dependent Ab responses and germinal center formation, whereas introduction of CD40 deficiency abolishes these effects. Hyper thymus-dependent humoral response in Cbl-b(-/-) mice is in part due to an intrinsic defect in B cells. Mechanistically, Cbl-b selectively down-modulates CD40-induced activation of NF-kappaB and JNK. Cbl-b associates with TNF receptor-associated factor 2 upon CD40 ligation, and inhibits the recruitment of TNF receptor-associated factor 2 to the CD40. Together, our data suggest that Cbl-b attenuates CD40-mediated NF-kappaB and JNK activation, thereby suppressing B cell responses.
The Journal of Immunology 11/2007; 179(7):4473-9. · 5.52 Impact Factor