Deltex1 is a target of the transcription factor NFAT that promotes T cell anergy.

The molecular process underlying T cell anergy is incompletely understood. Deltex1 (DTX1) is a Notch target with unknown physiological function. Here we show that Dtx1 was a transcription target of nuclear factor of activated T cells (NFAT) and participated in T cell anergy. DTX1 protein was upregulated during T cell anergy, and transgenic expression of Dtx1 attenuated T cell activation. DTX1 inhibited T cell activation by both E3-dependent and E3-independent mechanisms. In addition, DTX1 suppressed T cell activation in the absence of its Notch-binding domain. Importantly, DTX1 regulated the expression of two anergy-associated molecules, growth arrest and DNA-damage-inducible 45 beta (Gadd45 beta) and Cbl-b. DTX1 interacted with early growth response 2 (Egr-2) for optimum expression of Cbl-b. Furthermore, deficiency of DTX1 augmented T cell activation, conferred resistance to anergy induction, enhanced autoantibody generation, and increased inflammation. DTX1 therefore represents a component downstream of calcium-NFAT signaling that regulates T cell anergy.

Cellular FLIP Inhibits Myeloid Cell Activation by Suppressing Selective Innate Signaling.

Cellular FLIP (c-FLIP) specifically inhibits caspase-8 and suppresses death receptor-induced apoptosis. c-FLIP has also been reported to transmit activation signals. In this study, we report a novel function of c-FLIP involving inhibition of myeloid cell activation through antagonizing the selective innate signaling pathway. We found that conditional knockout of c-FLIP in dendritic cells (DCs) led to neutrophilia and splenomegaly. Peripheral DC populations, including CD11b(+) conventional DCs (cDCs), CD8(+) cDCs, and plasmacytoid DCs, were not affected by c-FLIP deficiency. We also found that c-FLIP knockout cDCs, plasmacytoid DCs, and bone marrow-derived DCs (BMDCs) displayed enhanced production of TNF-α, IL-2, or G-CSF in response to stimulation of TLR4, TLR2, and dectin-1. Consistent with the ability of c-FLIP to inhibit the activation of p38 MAPK, the enhanced activation of c-FLIP-deficient BMDCs could be partly linked to an elevated activation of p38 MAPK after engagement of innate receptors. Increased activation was also found in c-FLIP(+/-) macrophages. Additionally, the increased activation in c-FLIP-deficient DCs was independent of caspase-8. Our results reveal a novel inhibitory role of c-FLIP in myeloid cell activation and demonstrate the unexpected anti-inflammatory activity of c-FLIP. Additionally, our observations suggest that cancer therapy targeting c-FLIP downregulation may facilitate DC activation and increase T cell immunity.

Deltex1 promotes protein kinase Cθ degradation and sustains Casitas B-lineage lymphoma expression.

The generation of T cell anergy is associated with upregulation of ubiquitin E3 ligases including Casitas B-lineage lymphoma (Cbl-b), Itch, gene related to anergy in lymphocyte, and deltex1 (DTX1). These E3 ligases attenuate T cell activation by targeting to signaling molecules. For example, Cbl-b and Itch promote the degradation of protein kinase Cθ (PKCθ) and phospholipase C-γ1 (PLC-γ1) in anergic Th1 cells. How these anergy-associated E3 ligases coordinate during T cell anergy remains largely unknown. In the current study, we found that PKCθ and PLC-γ1 are also downregulated by DTX1. DTX1 interacted with PKCθ and PLC-γ1 and stimulated the degradation of PKCθ and PLC-γ1. T cell anergy-induced proteolysis of PKCθ was prevented in Dtx1(-/-) T cells, supporting the essential role of DTX1 in PKCθ downregulation. Similar to Cbl-b and Itch, DTX1 promoted monoubiquitination of PKCθ. Proteasome inhibitor did not inhibit DTX1-directed PKCθ degradation, but instead DTX1 directed the relocalization of PKCθ into the lysosomal pathway. In addition, DTX1 interacted with Cbl-b and increased the protein levels of Cbl-b. We further demonstrated the possibility that, through the downregulation of PKCθ, DTX1 prevented PKCθ-induced Cbl-b degradation and increased Cbl-b protein stability. Our results suggest the coordination between E3 ligases during T cell anergy; DTX1 acts with Cbl-b to assure a more extensive silencing of PKCθ, whereas DTX1-mediated PKCθ degradation further stabilizes Cbl-b.

A CSF-1R-blocking antibody/IL-10 fusion protein increases anti-tumor immunity by effectuating tumor-resident CD8+ T cells.

Strategies to increase intratumoral concentrations of an anticancer agent are desirable to optimize its therapeutic potential when said agent is efficacious primarily within a tumor but also have significant systemic side effects. Here, we generate a bifunctional protein by fusing interleukin-10 (IL-10) to a colony-stimulating factor-1 receptor (CSF-1R)-blocking antibody. The fusion protein demonstrates significant antitumor activity in multiple cancer models, especially head and neck cancer. Moreover, this bifunctional protein not only leads to the anticipated reduction in tumor-associated macrophages but also triggers proliferation, activation, and metabolic reprogramming of CD8+ T cells. Furthermore, it extends the clonotype diversity of tumor-infiltrated T cells and shifts the tumor microenvironment (TME) to an immune-active state. This study suggests an efficient strategy for designing immunotherapeutic agents by fusing a potent immunostimulatory molecule to an antibody targeting TME-enriched factors.

Deltex1 antagonizes HIF-1α and sustains the stability of regulatory T cells in vivo.

Application of regulatory T cells (Tregs) in transplantation, autoimmunity and allergy has been extensively explored, but how Foxp3 and Treg stability is regulated in vivo is incompletely understood. Here, we identify a requirement for Deltex1 (DTX1), a contributor to T-cell anergy and Foxp3 protein level maintenance in vivo. Dtx1(-/-) Tregs are as effective as WT Tregs in the inhibition of CD4(+)CD25(-) T-cell activation in vitro. However, the suppressive ability of Dtx1(-/-) Tregs is greatly impaired in vivo. We find that Foxp3 expression is diminished when Dtx1(-/-) Tregs are co-transferred with effector T cells in vivo. DTX1 promotes the degradation of HIF-1α. Knockout of HIF-1α restores the Foxp3 stability and rescues the defective suppressive activity in Dtx1(-/-) Treg cells in vivo. Our results suggest that DTX1 exerts another level of control on Treg stability in vivo by sustaining the expression of Foxp3 protein in Tregs.

Notch inhibits apoptosis by direct interference with XIAP ubiquitination and degradation.

The physiological activity of Notch is a function of its ability to increase survival in many cell types. Several pathways have been shown to contribute to the survival effect of Notch, but the exact mechanism of Notch action is not completely understood. Here we identified that the regulation of cell survival by Notch intracellular domain could partly be attributed to a selective increase of X-linked inhibitor of apoptosis protein (XIAP). We further found that Notch intracellular domain inhibited the degradation of XIAP during apoptosis. The transactivation domain of Notch interacted directly with the RING region of XIAP to block the binding of E2 and prevent the in vivo and in vitro ubiquitination of XIAP. This antiapoptotic activity of Notch was abolished when XIAP was knocked down. Our results reveal a novel mechanism for Notch-selective suppression of apoptosis through an increase in the stability of a key antiapoptotic protein, XIAP.