Description: Dendritic cell (DC) maturation is characterized by upregulation of cell-surface MHC class II (MHC-II) and costimulatory molecules, and production of a variety of cytokines that can shape both innate and adaptive immunity. Paradoxically, transcription of the MHC-II genes, as well as its activator, CIITA, is rapidly silenced during DC maturation. The mechanisms that control CIITA/MHC-II expression and silencing have not been fully understood. We report in this article that the tumor suppressor tuberous sclerosis complex 1 (TSC1) is a critical regulator of DC function for both innate and adaptive immunity. Its deficiency in DCs results in increased mammalian target of rapamycin (mTOR) complex 1 but decreased mTORC2 signaling, altered cytokine production, impaired CIITA/MHC-II expression, and defective Ag presentation to CD4 T cells after TLR4 stimulation. We demonstrate further that IFN regulatory factor 4 can directly bind to CIITA promoters, and decreased IFN regulatory factor 4 expression is partially responsible for decreased CIITA/MHC-II expression in TSC1-deficient DCs. Moreover, we identify that CIITA/MHC-II silencing during DC maturation requires mTOR complex 1 activity. Together, our data reveal unexpected roles of TSC1/mTOR that control multifaceted functions of DCs.

Description: Thymic epithelial cells (TECs) play important roles in T cell generation. Mechanisms that control TEC development and function are still not well defined. The mammalian or mechanistic target of rapamycin complex (mTORC)2 signals to regulate cell survival, nutrient uptake, and metabolism. We report in the present study that mice with TEC-specific ablation of Rictor, a critical and unique adaptor molecule in mTORC2, display thymic atrophy, which accompanies decreased TEC numbers in the medulla. Moreover, generation of multiple T cell lineages, including conventional TCRαβ T cells, regulatory T cells, invariant NKT cells, and TCR T cells, was reduced in TEC-specific Rictor-deficient mice. Our data demonstrate that mTORC2 in TECs is important for normal thymopoiesis and efficient T cell generation.

Description: Development of effective immune therapies for cancer patients requires better understanding of hurdles that prevent the generation of effective antitumor immune responses. Administration of α-galactosylceramide (α-GalCer) in animals enhances antitumor immunity via activation of the invariant NKT ( i NKT) cells. However, repeated injections of α-GalCer result in long-term unresponsiveness or anergy of i NKT cells, severely limiting its efficacy in tumor eradication. The mechanisms leading to i NKT cell anergy remain poorly understood. We report in this study that the tuberous sclerosis 1 (TSC1), a negative regulator of mTOR signaling, plays a crucial role in i NKT cell anergy. Deficiency of TSC1 in i NKT cells results in resistance to α-GalCer–induced anergy, manifested by increased expansion of and cytokine production by i NKT cells in response to secondary Ag stimulation. It is correlated with impaired upregulation of programmed death-1, Egr2, and Grail. Moreover, TSC1-deficient i NKT cells display enhanced antitumor immunity in a melanoma lung metastasis model. Our data suggest targeting TSC1/2 as a strategy for boosting antitumor immune therapy.

Description: T cell development and activation are usually accompanied by expansion and production of numerous proteins that require active translation. The eukaryotic translation initiation factor 4E (eIF4E) binds to the 5' cap structure of mRNA and is critical for cap-dependent translational initiation. It has been hypothesized that MAPK-interacting kinase 1 and 2 (Mnk1/2) promote cap-dependent translation by phosphorylating eIF4E at serine 209 (S209). Pharmacologic studies using inhibitors have suggested that Mnk1/2 have important roles in T cells. However, genetic evidence supporting such conclusions is lacking. Moreover, the signaling pathways that regulate Mnk1/2 in T cells remain unclear. We demonstrate that TCR engagement activates Mnk1/2 in primary T cells. Such activation is dependent on Ras-Erk1/2 signaling and is inhibited by diacylglycerol kinases α and . Mnk1/2 double deficiency in mice abolishes TCR-induced eIF4E S209 phosphorylation, indicating their absolute requirement for eIF4E S209 phosphorylation. However, Mnk1/2 double deficiency does not affect the development of conventional αβ T cells, regulatory T cells, or NKT cells. Furthermore, T cell activation, in vivo primary and memory CD8 T cell responses to microbial infection, and NKT cell cytokine production were not obviously altered by Mnk1/2 deficiency. Although Mnk1/2 deficiency causes decreased IL-17 and IFN- production by CD4 T cells following immunization of mice with myelin oligodendrocyte glycoprotein peptide in complete Freund’s adjuvant, correlating with milder experimental autoimmune encephalomyelitis scores, it does not affect Th cell differentiation in vitro. Together, these data suggest that Mnk1/2 has a minimal role in T cell development and activation but may regulate non–T cell lineages to control Th1 and Th17 differentiation in vivo.

Description: T (T) cells belong to a distinct T cell lineage that performs immune functions different from αβ T (αβT) cells. Previous studies established that Erk1/2 MAPKs are critical for positive selection of αβT cells. Additional evidence suggests that increased Erk1/2 activity promotes T cell generation. RasGRP1, a guanine nucleotide-releasing factor for Ras, plays an important role in positive selection of αβT cells by activating the Ras–Erk1/2 pathway. In this article, we demonstrate that RasGRP1 is critical for TCR-induced Erk1/2 activation in T cells, but it exerts different roles for T cell generation and activation. Deficiency of RasGRP1 does not obviously affect T cell numbers in the thymus, but it leads to increased T cells, particularly CD4 – CD8 + T cells, in the peripheral lymphoid organs. The virtually unhindered T cell development in the RasGRP1 –/– thymus proved to be cell intrinsic, whereas the increase in CD8 + T cells is caused by non–cell-intrinsic mechanisms. Our data provide genetic evidence that decreased Erk1/2 activation in the absence of RasGRP1 is compatible with T cell generation. Although RasGRP1 is dispensable for T cell generation, RasGRP1-deficient T cells are defective in proliferation following TCR stimulation. Additionally, RasGRP1-deficient T cells are impaired to produce IL-17 but not IFN. Together, these observations revealed that RasGRP1 plays differential roles for and αβ T cell development but is critical for T cell proliferation and production of IL-17.

Description: Tumors use a wide array of immunosuppressive strategies, such as reducing the longevity and survival of dendritic cells (DCs), to diminish immune responses and limit the effect of immunotherapy. In this study, we found that tumors upregulate the expression of multiple microRNAs (miRNAs), such as miR-16-1, miR-22, miR-155, and miR-503. These tumor-associated miRNAs influenced the survival and longevity of DCs by affecting the expression of multiple molecules that are associated with apoptotic signaling pathways. Specifically, miR-22 targeted YWHAZ to interrupt the PI3K/Akt and MAPK signaling pathways, and miR-503 downregulated Bcl2 expression. The result of the increased expression of miR-22 and miR-503 in the tumor-associated DCs was their reduced survival and longevity. Thus, tumor-associated miRNAs can target multiple intracellular signaling molecules to cause the apoptosis of DCs in the tumor environment. Use of miR-22 and miR-503 as inhibitors may therefore represent a new strategy to improve DC-based immunotherapies against tumors.

Description: Activation of the transcription factor NF-B is critical for cytokine production and T cell survival after TCR engagement. The effects of persistent NF-B activity on T cell function and survival are poorly understood. In this study, using a murine model that expresses a constitutively active form of inhibitor of NF-B kinase β (caIKKβ) in a T cell-specific manner, we demonstrate that chronic inhibitor of NF-B kinase β signaling promotes T cell apoptosis, attenuates responsiveness to TCR-mediated stimulation in vitro, and impairs T cell responses to bacterial infection in vivo. caIKKβ T cells showed increased Fas ligand expression and caspase-8 activation, and blocking Fas/Fas ligand interactions enhanced cell survival. T cell unresponsiveness was associated with defects in TCR proximal signaling and elevated levels of B lymphocyte-induced maturation protein 1, a transcriptional repressor that promotes T cell exhaustion. caIKKβ T cells also showed a defect in IL-2 production, and addition of exogenous IL-2 enhanced their survival and proliferation. Conditional deletion of B lymphocyte-induced maturation protein 1 partially rescued the sensitivity of caIKKβ T cells to TCR triggering. Furthermore, adoptively transferred caIKKβ T cells showed diminished expansion and increased contraction in response to infection with Listeria monocytogenes expressing a cognate Ag. Despite their functional defects, caIKKβ T cells readily produced proinflammatory cytokines, and mice developed autoimmunity. In contrast to NF-B’s critical role in T cell activation and survival, our study demonstrates that persistent IKK–NF-B signaling is sufficient to impair both T cell function and survival.