Detailed analysis of gene expression during development of T cell lineages in the thymus

Effects of dietary Glycyrrhiza polysaccharide on growth, serum biochemistry, immunity, and egg laying in quail

This study was conducted to evaluate the effects of dietary supplementation with Glycyrrhiza polysaccharide (GCP) on growth performance, serum biochemistry, immunity, and egg laying in female quail. 300 1-day-old female quail were sorted into four dietary treatments with five replicate cages of 15 birds each. The basic diet in the four treatment groups was supplemented with 0, 500, 1000 and 1500 mg/kg GCP, and the experiment continued for 80 days. Results showed that dietary supplementation with GCP significantly (p < 0.05) increased average daily gain in a dose-dependent fashion, and decreased (p < 0.05) the feed-to-gain ratio and mortality. The relative weights of the thymus and bursa of Fabricius increased (p < 0.05) linearly with increasing dose of GCP from 0 to 1500 mg/kg on day 20. GCP birds showed higher serum levels of protein, glucose, immunoglobulin A and immunoglobulin M, but lower serum triglycerides (p < 0.05) on day 50. GCP increased (p < 0.05) average laying rate and average egg weight linearly from days 60 to 80, whereas feed to egg ratio was decreased (p < 0.05). Taken together, these results revealed that GCP could improve growth performance, serum biochemistry, immunity, and egg laying in female quail. Therefore, GCP may be a potential replacement for antibiotic growth promoters in poultry.

Role of the COP9 Signalosome (CSN) in Cardiovascular Diseases

The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) is an evolutionarily conserved multi-protein complex, consisting of eight subunits termed CSN1-CSN8. The main biochemical function of the CSN is the control of protein degradation via the ubiquitin-proteasome-system through regulation of cullin-RING E3-ligase (CRL) activity by deNEDDylation of cullins, but the CSN also serves as a docking platform for signaling proteins. The catalytic deNEDDylase (isopeptidase) activity of the complex is executed by CSN5, but only efficiently occurs in the three-dimensional architectural context of the complex. Due to its positioning in a central cellular pathway connected to cell responses such as cell-cycle, proliferation, and signaling, the CSN has been implicated in several human diseases, with most evidence available for a role in cancer. However, emerging evidence also suggests that the CSN is involved in inflammation and cardiovascular diseases. This is both due to its role in controlling CRLs, regulating components of key inflammatory pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and complex-independent interactions of subunits such as CSN5 with inflammatory proteins. In this case, we summarize and discuss studies suggesting that the CSN may have a key role in cardiovascular diseases such as atherosclerosis and heart failure. We discuss the implicated molecular mechanisms ranging from inflammatory NF-κB signaling to proteotoxicity and necrosis, covering disease-relevant cell types such as myeloid and endothelial cells or cardiomyocytes. While the CSN is considered to be disease-exacerbating in most cancer entities, the cardiovascular studies suggest potent protective activities in the vasculature and heart. The underlying mechanisms and potential therapeutic avenues will be critically discussed.

Unexpected role of clathrin adaptor AP-1 in MHC-dependent positive selection of T cells

Trafficking of transmembrane receptors to a specific intracellular compartment is conducted by adaptor molecules that bind to target motifs within the cytoplasmic domains of cargo proteins. We generated mice containing a lymphoid-specific deficiency of AP-1 using RNAi knockdown technology. Inhibition of AP-1 expression in thymocytes blocks progression from double-positive immature thymocytes, resulting in complete absence of CD4(+) single-positive thymocytes and severe reduction of CD3(+)CD8(+) single-positive thymocytes. Analysis of the contribution of AP-1 deficiency on the interaction between mature CD4(+) T cells and antigen-presenting cells revealed that AP-1 is essential to efficient immune synapse formation and associated T cell activation, suggesting a possible mechanism of AP-1 function in thymocyte development.

Lack of reproducible growth inhibition by Schlafen1 and Schlafen2 in vitro

The Schlafen gene family has been implicated in lymphoid and myeloid maturation and differentiation as well as inflammation. However, little is known about the functions of this gene family except that anti-proliferative activities, particularly for Schlafen1, the prototype member of the family, have been reported. This was shown mainly by ectopic expression of Schlafen1 in murine fibroblasts resulting in growth inhibition and a G1 cell cycle arrest apparently via repression of Cyclin D1 expression. However, we have been unable to reproduce these findings. Schlafen1 and Schlafen2 failed to inhibit cell proliferation, cause G1 cell cycle arrest, or affect Cyclin D1 level in murine fibroblasts. This was regardless of whether overexpression was constitutive, induced or from transient transfections. Moreover, in our hands, Schlafen1 and -2 do not appear to regulate the activity of Cyclin D1 promoter. Importantly, we also showed that Schlafen1 and -2 do not play anti-proliferative roles in more physiologically-relevant myeloid cell lines. We therefore suggest that Schlafen1 and Schlafen2 might not have obligatory anti-proliferative activities, at least in vitro, and that efforts to explore their functions should be directed to other aspects, such as haemopoietic development and immune response.

Subcellular localization of the Schlafen protein family

Although the first members of the Schlafen gene family were first described almost 10 years ago, the precise molecular/biochemical functions of the proteins they encode still remain largely unknown. Roles in cell growth, haematopoietic cell differentiation, and T cell development/maturation have, with some experimental support, been postulated, but none have been conclusively verified. Here, we have determined the subcellular localization of Schlafens 1, 2, 4, 5, 8, and 9, representing all three of the murine subgroups. We show that the proteins from subgroups I and II localize to the cytoplasm, while the longer forms in subgroup III localize exclusively to the nuclear compartment. We also demonstrate upregulation of Schlafen2 upon differentiation of haematopoietic cells and show this endogenous protein localizes to the cytoplasm. Thus, we propose the different subgroups of Schlafen proteins are likely to have functionally distinct roles, reflecting their differing localizations within the cell.

A Stat5b transgene is capable of inducing CD8+ lymphoblastic lymphoma in the absence of normal TCR/MHC signaling

Stat5 proteins are critical signaling molecules activated by many cytokines. Within the immune system, Stat5 plays important roles related to the development of thymocytes and proliferation of T cells. Stat5 has been implicated in malignant transformation, and moreover, the activated tyrosine phosphorylated form of Stat5 is frequently observed in human lymphomas. We previously demonstrated the oncogenic potential of Stat5, with thymic lymphoblastic lymphomas developing in a significant proportion of transgenic (TG) mice overexpressing Stat5a or Stat5b in lymphocytes. In addition, immunization or expression of a T-cell receptor (TCR) transgene augmented the rate of tumor formation. Here, we investigate the mechanism of Stat5-mediated lymphomagenesis by exploring the contributions of major histocompatibility complex (MHC)/TCR and pre-TCR signals. We present data demonstrating that Stat5b TG mice unexpectedly develop CD8(+) lymphoma even in the absence of either pre-TCR signaling or normal thymic selection. Indeed, acceleration of Stat5b transgene-mediated lymphoma occurred on TCRalpha(-/-) and pre-TCRalpha(-/-) backgrounds. In light of these data, we propose a model in which alterations in T-cell development at the double-negative/double-positive (DN/DP) stages cooperate with cytokine-mediated pathways in immature thymocytes to give rise to lymphoblastic T-cell lymphomas in Stat5b TG mice.

Receptor signals and nuclear events in CD4 and CD8 T cell lineage commitment

MHC specificity in positive selection is a major determinant in the CD4/CD8 T cell lineage decision. Previous studies support the view that quantitative differences in T cell receptor (TCR) signaling in immature CD4+CD8+ double positive thymocytes leads to an instructive bias in CD4/CD8 T cell lineage commitment that must be re-inforced in subsequent selection steps to ensure that MHC-restricted antigen recognition is linked to appropriate effector functions in mature T cells. Recent work has further defined the TCR signaling pathways involved in this process, but a major effort has been made to identify transcription factors and other regulators of CD4 and CD8 T cell lineage commitment. Methods and screens for detecting changes in gene expression, associated with TCR signaling in positive selection and lineage determination, are starting to provide a better understanding of these complex developmental processes.

Thymocyte stimulation by anti-TCR-beta, but not by anti-TCR-alpha, leads to induction of developmental transcription program

Anti-T cell receptor (aTCR) antibody (Ab) stimulation of T cells results in TCR down-modulation and T cell activation. Differences in the effect of anti-alpha-chain and beta-chain Ab have been reported on thymocytes. Anti-beta-chain Ab but not anti-alpha-chain reagents cause long-term TCR down-modulation. However, both types of Ab result in TCR cross-linking and activate early steps in signal transduction. In this study, we show that TCR internalization and calcium flux, hallmarks of T cell activation, are similar with aValpha and aVbeta treatment. Therefore, we have compared the gene expression profiles of preselection thymocytes stimulated with these reagents. We find that aValpha treatment does not cause any significant change in gene expression compared with control culture conditions. In contrast, aVbeta stimulation results in numerous changes in gene expression. The alterations of expression of genes known to be expressed in thymocytes are similar to changes caused by positive thymic selection, suggesting that the expression of some of the genes without known roles in thymocyte development and of novel genes whose expression is found to be altered may also be involved in this process.

Signaling by the kinase MINK is essential in the negative selection of autoreactive thymocytes

Signaling through the T cell antigen receptor leading to elimination (negative selection) or differentiation (positive selection) of developing thymocytes generates a self-tolerant T cell repertoire. Here we report that the serine-threonine kinase MINK selectively connects the T cell receptor to a signaling pathway that mediates negative but not positive selection. Analysis of this pathway suggested that the essential function of MINK in the elimination of self-reactive thymocytes may be associated with 'downstream' activation of Jun kinase and enhancement of expression of the proapoptotic molecule Bim.