Rémy Bosselut

GATA3 controls Foxp3+ regulatory T cell fate during inflammation in mice

Tregs not only keep immune responses to autoantigens in check, but also restrain those directed toward pathogens and the commensal microbiota. Control of peripheral immune homeostasis by Tregs relies on their capacity to accumulate at inflamed sites and appropriately adapt to their local environment. To date, the factors involved in the control of these aspects of Treg physiology remain poorly understood. Here, we show that the canonical Th2 transcription factor GATA3 is selectively expressed in Tregs residing in barrier sites including the gastrointestinal tract and the skin. GATA3 expression in both murine and human Tregs was induced upon TCR and IL-2 stimulation. Although GATA3 was not required to sustain Treg homeostasis and function at steady state, GATA3 played a cardinal role in Treg physiology during inflammation. Indeed, the intrinsic expression of GATA3 by Tregs was required for their ability to accumulate at inflamed sites and to maintain high levels of Foxp3 expression in various polarized or inflammatory settings. Furthermore, our data indicate that GATA3 limits Treg polarization toward an effector T cell phenotype and acquisition of effector cytokines in inflamed tissues. Overall, our work reveals what we believe to be a new facet in the complex role of GATA3 in T cells and highlights what may be a fundamental role in controlling Treg physiology during inflammation.

The zinc finger protein cKrox directs CD4 lineage differentiation during intrathymic T cell positive selection.

The genetic programs directing CD4 or CD8 T cell differentiation in the thymus remain poorly understood. While analyzing gene expression during intrathymic T cell selection, we found that Zfp67, encoding the zinc finger transcription factor cKrox, was upregulated during the differentiation of CD4+ but not CD8+ T cells. Expression of a cKrox transgene impaired CD8 T cell development and caused major histocompatibility complex class I–restricted thymocytes to differentiate into CD4+ T cells with helper properties rather than into cytotoxic CD8+ T cells, as normally found. CD4 lineage differentiation mediated by cKrox required its N-terminal BTB (bric-a-brac, tramtrack, broad complex) domain. These findings identify cKrox as a chief CD4 differentiation factor during positive selection.

Decision checkpoints in the thymus

The development of T cells in the thymus involves several differentiation and proliferation events, during which hematopoietic precursors give rise to T cells ready to respond to antigen stimulation and undergo effector differentiation. This review addresses signaling and transcriptional checkpoints that control the intrathymic journey of T cell precursors. We focus on the divergence of αβ and γδ lineage cells and the elaboration of the αβ T cell repertoire, with special emphasis on the emergence of transcriptional programs that direct lineage decisions.

Characterization of Spi-B, a transcription factor related to the putative oncoprotein Spi-1/PU.1.

We have cloned a human cDNA from a new gene, spi-B, on the basis of its homology with the DNA-binding domain of the Spi-1/PU.1 putative oncogene product. spi-B codes for a protein of 262 amino acids presenting 43% overall identity with Spi-1. Its highly basic carboxy-terminal region exhibits 34% sequence identity with the DNA-binding domain of the Ets-1 protein. We showed that the Spi-B protein is able to bind the purine-rich sequence (PU box) recognized by Spi-1/PU.1 and to activate transcription of a reporter plasmid containing PU boxes. Chromosome in situ hybridization allowed us to map spi-B to the 19q13.3-19q13.4 region of the human genome. spi-B, like spi-1, was found to be expressed in various murine and human hematopoietic cell lines except T lymphoid cell lines.

Synergistic activation of the HTLV1 LTR Ets-responsive region by transcription factors Ets1 and Sp1.

Ets1 is the prototype of a family of transcriptional activators whose activity depends on the binding to specific DNA sequences characterized by an invariant GGA core sequence. We have previously demonstrated that transcriptional activation by Ets1 of the long terminal repeat (LTR) of human T cell lymphotropic virus type 1 is strictly dependent on the binding of Ets1 to two sites, ERE‐A and ERE‐B, localized in a 44 bp long Ets‐responsive region (ERR1). We report here that the activity of ERR1 as an efficient Ets1 response element in HeLa cells also depends on the integrity of an Sp1 binding site localized immediately upstream of ERE‐A. The response to Ets1 of an element restricted to the SP1/ERE‐A binding sites is also strictly dependent on both the Ets1 and Sp1 binding sites. In vitro, Sp1 and Ets1 are shown to cooperate to form a ternary complex with the SP1/ERE‐A element. Reconstitution experiments in Drosophila melanogaster Schneider cells show that Ets1 and Sp1 act synergistically to activate transcription from either the ERR1 or the SP1/ERE‐A elements and that synergy requires the binding of both Sp1 and Ets1 to their cognate sites. SP1/ERE‐A elements are found in the enhancer/promoter region of several cellular genes, suggesting that synergy between Ets1 and Sp1 is not restricted to the ERR1 region of the HTLV1 LTR. These results strengthen the notion that Ets1 as well as other members of the Ets family usually function as components of larger transcription complexes to regulate the activity of a variety of viral and cellular genes.

The product of the c-ets-1 proto-oncogene and the related Ets2 protein act as transcriptional activators of the long terminal repeat of human T cell leukemia virus HTLV-1

The c‐ets‐1 proto‐oncogene and the related c‐ets‐2 gene encode related nuclear chromatin‐associated proteins which bind DNA in vitro. To investigate the possibility that Ets1 and Ets2 are transcriptional activators, we analyzed the ability of these proteins to trans‐activate promoter/enhancer sequences in transient co‐transfection experiments. A CAT construct driven by the long terminal repeat of the human T cell leukemia virus, HTLV‐1 was found to be trans‐activated by both Ets1 and Ets2 in NIH3T3 and HeLa cells. The increased levels of CAT activity were paralleled by increased levels of correctly initiated CAT mRNA. Mutant Ets1 proteins unable to accumulate in the nucleus were found to be inactive. An ets‐responsive sequence between positions −117 and −160 of the LTR was identified by analyses of a series of 5′ deletion mutants of the HTLV‐1 LTR and of dimerized versions of specific motifs of the LTR enhancer region. Using a gel shift binding assay, Ets1 was found to bind specifically to an oligonucleotide corresponding to region −117 to −160. This sequence, which also contributes to Tax1 responsiveness of the HTLV‐1 LTR, is characterized by the presence of four repeats of a pentanucleotide sequence of the type CC(T/A)CC. Competition experiments show that integrity of repeats 1 and 4 is important for Ets1 binding. These results show that Ets1 and Ets2 are sequence‐specific transcriptional activators. In view of the high level expression of Ets1 in lymphoid cells, Ets1 could be part of the transcription complex which mediates the response to Tax1 and the control of HTLV‐1 replication. More generally, Ets1 and Ets2 could regulate transcription of cellular genes.

Role of CD8β Domains in CD8 Coreceptor Function: Importance for MHC I Binding, Signaling, and Positive Selection of CD8+ T Cells in the Thymus

Abstract The contribution of the CD8β subunit to CD8 coreceptor function is poorly understood. We now demonstrate that the CD8β extracellular domain increases the avidity of CD8 binding to MHC I, and that the intracellular domain of CD8β enhances association with two intracellular molecules required for TCR signal transduction, Lck and LAT. By assessing CD8 + T cell differentiation in CD8β-deficient mice reconstituted with various transgenic CD8β chimeric molecules, we also demonstrate that the intracellular and extracellular domains of CD8β can contribute independently to CD8 + T cell development, but that both CD8β domains together are most efficient. Thus, this study identifies the molecular functions of the CD8β intracellular and extracellular domains and documents their contributions to CD8 + T cell development.

Duration of TCR signaling controls CD4-CD8 lineage differentiation in vivo

The duration of T cell receptor (TCR) signaling is thought to be important for thymocyte differentiation into the CD4 or CD8 lineage. However, the in vivo relevance of this hypothesis is unclear. Here we divided T cell positive selection into genetically separable developmental steps by confining TCR signal transduction to discrete thymocyte developmental windows. TCR signals confined to the double-positive thymocyte stage promoted CD8, but not CD4, lineage differentiation. Major histocompatibility complex (MHC) class II–restricted thymocytes were, instead, redirected into the CD8 lineage. These findings support the hypothesis that distinct kinetics of MHC class I– and MHC class II–induced TCR signals direct intrathymic developmental decisions.

CD4/CD8-lineage differentiation in the thymus: from nuclear effectors to membrane signals

During thymocyte development, immature thymocytes that express both CD4 and CD8 genes must choose either a helper CD4+ or cytotoxic CD8+ T-cell fate. Over the past two years, there have been some important advances regarding T-cell lineage choice, including the identification of transcription factors required for CD4 gene silencing by CD8-lineage cells (RUNX3) or for CD4+ T-cell differentiation (GATA3), and a better understanding of how T-cell receptor (TCR) signalling correlates CD4/CD8-lineage differentiation to MHC specificity. This review summarizes these recent advances and highlights potential links between TCR signals and nuclear effectors of lineage differentiation.

The Zinc Finger Transcription Factor Zbtb7b Represses CD8-Lineage Gene Expression in Peripheral CD4+ T Cells

How CD4-CD8 differentiation is maintained in mature T cells is largely unknown. The present study has examined the role in this process of the zinc finger protein Zbtb7b, a critical factor for the commitment of MHC II-restricted thymocytes to the CD4+ lineage. We showed that Zbtb7b acted in peripheral CD4+ T cells to suppress CD8-lineage gene expression, including that of CD8 and cytotoxic effector genes perforin and Granzyme B, and was important for the proper repression of interferon-gamma (IFN-gamma) during effector differentiation. The inappropriate expression of IFN-gamma by Zbtb7b-deficient CD4+ T cells required the activities of Eomesodermin and Runx transcription factors. Runx activity was needed for Granzyme B expression, indicating that Runx proteins control expression of the cytotoxic program. We conclude that a key function of Zbtb7b in the mature CD4+ T cell compartment is to repress CD8-lineage gene expression.