Early growth response gene-2 (Egr-2) regulates the development of B and T cells

The study was supported by Arthritis Research UK. Copyright @ 2011 Li et al.BACKGROUND: Understanding of how transcription factors are involved in lymphocyte development still remains a challenge. It has been shown that Egr-2 deficiency results in impaired NKT cell development and defective positive selection of T cells. Here we investigated the development of T, B and NKT cells in Egr-2 transgenic mice and the roles in the regulation of distinct stages of B and T cell development. METHODS AND FINDINGS: The expression of Egr1, 2 and 3 were analysed at different stages of T and B cell development by RT-PCT and results showed that the expression was strictly regulated at different stages. Forced expression of Egr-2 in CD2+ lymphocytes resulted in a severe reduction of CD4+CD8+ (DP) cells in thymus and pro-B cells in bone marrow, which was associated with reduced expression of Notch1 in ISP thymocytes and Pax5 in pro-B cells, suggesting that retraction of Egr-2 at the ISP and pro-B cell stages is important for the activation of lineage differentiation programs. In contrast to reduction of DP and pro-B cells, Egr-2 enhanced the maturation of DP cells into single positive (SP) T and NKT cells in thymus, and immature B cells into mature B cells in bone marrow. CONCLUSIONS: Our results demonstrate that Egr-2 expressed in restricted stages of lymphocyte development plays a dynamic, but similar role for the development of T, NKT and B cells.This article is provided by the Brunel Open Access publishing fund

Enhanced Notch Activation Is Advantageous but Not Essential for T Cell Lymphomagenesis in Id1 Transgenic Mice

T cell lymphoblastic leukemia (T-ALL) is known to be associated with chromosomal abnormalities that lead to aberrant expression of a number of transcription factors such as TAL1, which dimerizes with basic helix-loop-helix (bHLH) E proteins and inhibits their function. Activated Notch receptors also efficiently induce T cell leukemogenesis in mouse models. Interestingly, gain-of-function mutations or cryptic transcription initiation of the Notch1 gene have been frequently found in both human and mouse T-ALL. However, the correlations between these alterations and overall Notch activities or leukemogenesis have not been thoroughly evaluated. Therefore, we made use of our collection of T cell lymphomas developed in transgenic mice expressing Id1, which like TAL1, inhibits E protein function. By comparing expression levels of Notch target genes in Id1-expressing tumors to those in tumors induced by a constitutively active form of Notch1, N1C, we were able to assess the overall activities of Notch pathways and conclude that the majority of Id1-expressing tumors had elevated Notch function to a varying degree. However, 26% of the Id1-expressing tumors had no evidence of enhanced Notch activation, but that did not delay the onset of tumorigenesis. Furthermore, we examined the genetic or epigenetic alterations thought to contribute to ligand-independent activation or protein stabilization of Notch1 and found that some of the Id1-expressing tumors acquired these changes, but they are not uniformly associated with elevated Notch activities in Id1 tumor samples. In contrast, N1C-expressing tumors do not harbor any PEST domain mutations nor exhibit intragenic transcription initiation. Taken together, it appears that Notch activation provides Id1-expressing tumor cells with selective advantages in growth and survival. However, this may not be absolutely essential for lymphomagenesis in Id1 transgenic mice and additional factors could also cooperate with Id1 to induce T cell lymphoma. Therefore, a broad approach is necessary in designing T-ALL therapy

The requirement for Notch signaling at the -selection checkpoint in vivo is absolute and independent of the pre-T cell receptor

Genetic inactivation of Notch signaling in CD4−CD8− double-negative (DN) thymocytes was previously shown to impair T cell receptor (TCR) gene rearrangement and to cause a partial block in CD4+CD8+ double-positive (DP) thymocyte development in mice. In contrast, in vitro cultures suggested that Notch was absolutely required for the generation of DP thymocytes independent of pre-TCR expression and activity. To resolve the respective role of Notch and the pre-TCR, we inhibited Notch-mediated transcriptional activation in vivo with a green fluorescent protein–tagged dominant-negative Mastermind-like 1 (DNMAML) that allowed us to track single cells incapable of Notch signaling. DNMAML expression in DN cells led to decreased production of DP thymocytes but only to a modest decrease in intracellular TCRβ expression. DNMAML attenuated the pre-TCR–associated increase in cell size and CD27 expression. TCRα or TCRαβ transgenes failed to rescue DNMAML-related defects. Intrathymic injections of DNMAML− or DNMAML+ DN thymocytes revealed a complete DN/DP transition block, with production of DNMAML+ DP thymocytes only from cells undergoing late Notch inactivation. These findings indicate that the Notch requirement during the β-selection checkpoint in vivo is absolute and independent of the pre-TCR, and it depends on transcriptional activation by Notch via the CSL/RBP-J–MAML complex

Costimulation of T-cell proliferation by anti-l-selectin antibody is associated with the reduction of a cdk inhibitor p27

In this study, we investigated the costimulatory activity of l-selectin in primary mouse T cells. Proliferation induced by immobilized anti-CD3 antibody was enhanced by immobilized anti-l-selectin antibody. In contrast to the anti-CD28 antibody, anti-l-selectin antibody did not enhance interleukin-2 (IL-2) expression. One of the cyclin-dependent kinase (cdk) inhibitors, p27, was reduced by costimulation with anti-l-selectin antibody, as with anti-CD28 antibody, suggesting that the enhancement of T-cell proliferation is the result of a reduced p27 level. Since anti-l-selectin antibody enhanced the activation of extracellular signal-regulated protein kinase (ERK) induced by anti-CD3 antibody, ERK plays an important role in signal integration during costimulation. These results suggest that the mechanism of T-cell costimulation is at least partially different between CD28 and l-selectin, although the two mechanisms share a common downstream event, a reduction of p27 level, as a critical biochemical event in the cell cycle progression of T cells