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Wilfried Ellmeier

Publications and source records attributed to Wilfried Ellmeier.

15 recordsLinked to original sources
PubMed2006

The role of BTB domain-containing zinc finger proteins in T cell development and function.

Cell fate specifications during T lymphocyte differentiation result from the orchestrated expression of developmentally regulated genes. Furthermore, epigenetic processes that result in a heritable chromatin structure are required for the maintenance of gene expression programs within cells. More and more is known about the basic mechanisms of T cell development and their diversification into various peripheral T cell subsets. Recent research has begun to provide insight into the interactive network of transcription factors as critical regulators of T lymphocyte differentiation. In the past years several members of the BTB domain-containing family of zinc finger proteins (BTB-ZF) have been described to be important for the development and function of hematopoietic cells, and also to contribute to malignant hematopoiesis. This review will provide a brief overview about the role of BTB-ZF proteins during thymocyte development and T cell function.

Amino Acid Sequence↗
PubMed2006

Down-regulation of RXRalpha expression is essential for neutrophil development from granulocyte/monocyte progenitors.

Neutrophil granulocytes (Gs) represent highly abundant and short-lived leukocytes that are constantly regenerated from a small pool of myeloid committed progenitors. Nuclear receptor (NR) family members are ligand-activated transcription factors that play key roles in cellular proliferation and differentiation processes including myelopoiesis. Retinoid X receptor alpha (RXRalpha) represents the predominant NR types I and II homo- and heterodimerization partner in myeloid cells. Here we show that human myeloid progenitors express RXRalpha protein at sustained high levels during macrophage colony-stimulating factor (M-CSF)-induced monopoiesis. In sharp contrast, RXRalpha is down-regulated during G-CSF-dependent late-stage neutrophil differentiation from myeloid progenitors. Down-regulation of RXRalpha is critically required for neutrophil development since ectopic RXRalpha inhibited granulopoiesis by impairing proliferation and differentiation. Moreover, ectopic RXRalpha was sufficient to redirect G-CSF-dependent granulocyte differentiation to the monocyte lineage and to promote M-CSF-induced monopoiesis. Functional genetic interference with RXRalpha signaling in hematopoietic progenitor/stem cells using a dominant-negative RXRalpha promoted the generation of late-stage granulocytes in human cultures in vitro and in reconstituted mice in vivo. Therefore, our data suggest that RXRalpha down-regulation is a critical requirement for the generation of neutrophil granulocytes.

Animals↗
PubMed2006

Negative regulation of CD8 expression via Cd8 enhancer-mediated recruitment of the zinc finger protein MAZR.

Coreceptor expression is tightly regulated during thymocyte development. Deletion of specific Cd8 enhancers leads to variegated expression of CD8alphabeta heterodimers in double-positive thymocytes. Here we show CD8 variegation is correlated with an epigenetic 'off' state, linking Cd8 enhancer function with chromatin remodeling of the adjacent genes Cd8a and Cd8b1 (Cd8). The zinc finger protein MAZR bound the Cd8 enhancer and interacted with the nuclear receptor corepressor N-CoR complex in double-negative thymocytes. MAZR was downregulated in double-positive and CD8 single-positive thymocytes. 'Enforced' expression of MAZR led to impaired Cd8 activation and variegated CD8 expression. Our results demonstrate epigenetic control of the Cd8 loci and identify MAZR as an important regulator of Cd8 expression.

Animals↗
PubMed2005

CD8 T cell sensory adaptation dependent on TCR avidity for self-antigens.

Adaptation of the T cell activation threshold may be one mechanism to control autoreactivity. To investigate its occurrence in vivo, we engineered a transgenic mouse model with increased TCR-dependent excitability by expressing a Zap70 gain-of-function mutant (ZAP-YEEI) in postselection CD8 thymocytes and T cells. Increased basal phosphorylation of the Zap70 substrate linker for activation of T cells was detected in ZAP-YEEI-bearing CD8 T cells. However, these cells were not activated, but had reduced levels of TCR and CD5. Moreover, they produced lower cytokine amounts and showed faster dephosphorylation of linker for activation of T cells and ERK upon activation. Normal TCR levels and cytokine production were restored by culturing cells in the absence of TCR/spMHC interaction, demonstrating dynamic tuning of peripheral T cell responses. The effect of avidity for self-ligand(s) on this sensory adaptation was studied by expressing ZAP-YEEI in P14 or HY TCR transgenic backgrounds. Unexpectedly, double-transgenic animals expressed ZAP-YEEI prematurely in double-positive thymocytes, but no overt alteration of selection processes was observed. Instead, modifications of TCR and CD5 expression due to ZAP-YEEI suggested that signal tuning occurred during thymic maturation. Importantly, although P14 x ZAP-YEEI peripheral CD8 T cells were reduced in number and showed lower Ag-induced cytokine production and limited lymphopenia-driven proliferation, the peripheral survival/expansion and Ag responsiveness of HY x ZAP-YEEI cells were enhanced. Our data provide support for central and peripheral sensory T cell adaptation induced as a function of TCR avidity for self-ligands and signaling level. This may contribute to buffer excessive autoreactivity while optimizing TCR repertoire usage.

Adoptive Transfer↗
PubMed2005

Functional and molecular analysis of the double-positive stage-specific CD8 enhancer E8III during thymocyte development.

Several developmental stage-, subset-, and lineage-specific Cd8 cis-regulatory regions have been identified. These include the E8(III) enhancer, which directs expression in double-positive (DP) thymocytes, and E8(II), which is active in DP cells and CD8(+) T cells. Using a transgenic reporter expression assay, we identified a 285-bp core fragment of the E8(III) enhancer that retains activity in DP thymocytes. In vitro characterization of the core enhancer revealed five regulatory elements that are required for full enhancer activity, suggesting that multiple factors contribute to the developmental stage-specific activity. Furthermore, deletion of E8(III) in the mouse germline showed that this enhancer is required for nonvariegated expression of CD8 in DP thymocytes when E8(II) is also deleted. These results indicate that E8(III) is one of the cis-elements that contribute to the activation of the Cd8a and Cd8b gene complex during T cell development.

Animals↗
PubMed2005

Modulation of coreceptor transcription during positive selection dictates lineage fate independently of TCR/coreceptor specificity.

For developing T cells, coreceptor choice is matched to T cell antigen receptor (TCR) MHC specificity during positive selection in the thymus, but the mechanism remains uncertain. Here, we document that TCR-mediated positive selection signals inactivate the immature CD8(III) enhancer in double positive (DP) thymocytes, explaining in part the cessation of CD8 coreceptor transcription that occurs during positive selection. More importantly, by placing CD4 protein expression under the control of CD8 transcriptional regulatory elements, we demonstrate that cessation of CD4 coreceptor transcription during positive selection results in precisely the same lineage fate as cessation of CD8 coreceptor transcription. That is, MHC-II-signaled DP thymocytes differentiated into CD8-lineage cytotoxic T cells, despite the MHC-II specificity and CD4 dependence of their TCRs. This study demonstrates that termination of coreceptor transcription during positive selection promotes CD8-lineage fate, regardless of TCR specificity or coreceptor protein identity.

Animals↗
PubMed2004

Sustained correction of B-cell development and function in a murine model of X-linked agammaglobulinemia (XLA) using retroviral-mediated gene transfer.

X-linked agammaglobulinemia (XLA) is a human immunodeficiency caused by mutations in Bruton tyrosine kinase (Btk) and characterized by an arrest in early B-cell development, near absence of serum immunoglobulin, and recurrent bacterial infections. Using Btk- and Tec-deficient mice (BtkTec(-/-)) as a model for XLA, we determined if Btk gene therapy could correct this disorder. Bone marrow (BM) from 5-fluorouracil (5FU)-treated BtkTec(-/-) mice was transduced with a retroviral vector expressing human Btk and transplanted into BtkTec(-/-) recipients. Mice engrafted with transduced hematopoietic cells exhibited rescue of both primary and peripheral B-lineage development, recovery of peritoneal B1 B cells, and correction of serum immunoglobulin M (IgM) and IgG(3) levels. Gene transfer also restored T-independent type II immune responses, and B-cell antigen receptor (BCR) proliferative responses. B-cell progenitors derived from Btk-transduced stem cells exhibited higher levels of Btk expression than non-B cells; and marking studies demonstrated a selective advantage for Btk-transduced B-lineage cells. BM derived from primary recipients also rescued Btk-dependent function in secondary hosts that had received a transplant. Together, these data demonstrate that gene transfer into hematopoietic stem cells can reconstitute Btk-dependent B-cell development and function in vivo, and strongly support the feasibility of pursuing Btk gene transfer for XLA.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed2004

The role of Tec family kinases in myeloid cells.

Members of the Tec kinase family (Bmx, Btk, Itk, Rlk and Tec) are primarily expressed in the hematopoietic system and form, after the Src kinase family, the second largest class of non-receptor protein tyrosine kinases. During lymphocyte development and activation Tec kinases have important functions in signaling pathways downstream of the antigen receptors. Tec family kinases are also expressed in cells of the myeloid lineage. However, with the exception of mast cells and platelets, their biological role in the myeloid system is only poorly understood. This review summarizes the current knowledge about the function of Tec family kinases in hematopoietic cells of the myeloid lineage.

Blood Platelets↗
PubMed2004

CD8alphaalpha-mediated survival and differentiation of CD8 memory T cell precursors.

Memory T cells are long-lived antigen-experienced T cells that are generally accepted to be direct descendants of proliferating primary effector cells. However, the factors that permit selective survival of these T cells are not well established. We show that homodimeric alpha chains of the CD8 molecule (CD8alphaalpha) are transiently induced on a selected subset of CD8alphabeta+ T cells upon antigenic stimulation. These CD8alphaalpha molecules promote the survival and differentiation of activated lymphocytes into memory CD8 T cells. Thus, memory precursors can be identified among primary effector cells and are selected for survival and differentiation by CD8alphaalpha.

Animals↗
PubMed2004

Btk is required for an efficient response to erythropoietin and for SCF-controlled protection against TRAIL in erythroid progenitors.

Regulation of survival, expansion, and differentiation of erythroid progenitors requires the well-controlled activity of signaling pathways induced by erythropoietin (Epo) and stem cell factor (SCF). In addition to qualitative regulation of signaling pathways, quantitative control may be essential to control appropriate cell numbers in peripheral blood. We demonstrate that Bruton's tyrosine kinase (Btk) is able to associate with the Epo receptor (EpoR) and Jak2, and is a substrate of Jak2. Deficiency of Btk results in reduced and delayed phosphorylation of the EpoR, Jak2, and downstream signaling molecules such as Stat5 and PLCgamma1 as well as in decreased responsiveness to Epo. As a result, expansion of erythroid progenitors lacking Btk is impaired at limiting concentrations of Epo and SCF. In addition, we show that SCF induces Btk to interact with TNF-related apoptosis-inducing ligand (TRAIL)-receptor 1 and that lack of Btk results in increased sensitivity to TRAIL-induced apoptosis. Together, our results indicate that Btk is a novel, quantitative regulator of Epo/SCF-dependent expansion and survival in erythropoiesis.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed2003

Tec regulates platelet activation by GPVI in the absence of Btk.

The Tec family kinase Btk plays an important role in the regulation of phospholipase C gamma 2 (PLC gamma 2) downstream of the collagen receptor glycoprotein VI (GPVI) in human platelets. Platelets also express a second member of this family, Tec; however, its function has not been analyzed. To address the role of Tec, we analyzed Btk-/-, Tec-/-, and Btk/Tec double-deficient (Btk-/-/Tec-/-) platelets. Tec-/- platelets exhibit a minor reduction in aggregation to threshold concentrations of collagen or the GPVI-specific agonist collagen-related peptide (CRP), whereas responses to higher concentrations are normal. Tyrosine phosphorylation of PLC gamma 2 by collagen and CRP is not altered in Tec-/- platelets. However, Btk-/-/Tec-/- platelets exhibit a greater reduction in PLC gamma 2 phosphorylation than is seen in the absence of Btk, thus revealing an important role for Tec in this situation. Furthermore, Btk-/-/Tec-/- platelets fail to undergo an increase in Ca2+, aggregation, secretion, and spreading in response to collagen or CRP, whereas they aggregate normally to adenosine diphosphate (ADP) and spread on fibrinogen. A residual GPVI signal exists in the Btk-/-/Tec-/- platelets as CRP synergizes with ADP to mediate aggregation. These results demonstrate an essential requirement for Tec and Btk in platelet activation by GPVI and reveal a functional role for Tec in the regulation of PLC gamma 2 in the absence of Btk.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed2002

Progress toward a human CD4/CCR5 transgenic rat model for de novo infection by human immunodeficiency virus type 1.

The development of a permissive small animal model for the study of human immunodeficiency virus type (HIV)-1 pathogenesis and the testing of antiviral strategies has been hampered by the inability of HIV-1 to infect primary rodent cells productively. In this study, we explored transgenic rats expressing the HIV-1 receptor complex as a susceptible host. Rats transgenic for human CD4 (hCD4) and the human chemokine receptor CCR5 (hCCR5) were generated that express the transgenes in CD4(+) T lymphocytes, macrophages, and microglia. In ex vivo cultures, CD4(+) T lymphocytes, macrophages, and microglia from hCD4/hCCR5 transgenic rats were highly susceptible to infection by HIV-1 R5 viruses leading to expression of abundant levels of early HIV-1 gene products comparable to those found in human reference cultures. Primary rat macrophages and microglia, but not lymphocytes, from double-transgenic rats could be productively infected by various recombinant and primary R5 strains of HIV-1. Moreover, after systemic challenge with HIV-1, lymphatic organs from hCD4/hCCR5 transgenic rats contained episomal 2-long terminal repeat (LTR) circles, integrated provirus, and early viral gene products, demonstrating susceptibility to HIV-1 in vivo. Transgenic rats also displayed a low-level plasma viremia early in infection. Thus, transgenic rats expressing the appropriate human receptor complex are promising candidates for a small animal model of HIV-1 infection.

Animals↗
PubMed2002

Combined deletion of CD8 locus cis-regulatory elements affects initiation but not maintenance of CD8 expression.

Developmental stage-, subset-, and lineage-specific CD8 enhancers have been identified recently by transgenic reporter analyses. Enhancer E8(II) (CIV-4,5) is active in both immature double-positive thymocytes (DP) and mature CD8 single-positive (SP) thymocytes and T cells, whereas E8(I) (CIII-1,2) directs expression only in mature cells. In mice lacking either E8(I) (CIII-1,2) or E8(II) (CIV-4,5), there was no effect on CD8 expression in DP thymocytes. However, deletion of both enhancers resulted in variegated expression of CD8, with appearance of CD4(+)CD8(-) SP thymocytes expressing surface markers characteristic of DP thymocytes. Consequently, fewer mature CD8(+) T cells developed from the reduced pool of DP cells. These results suggest that the initiation of CD8 expression is mediated by cis-regulatory elements that are distinct from any that may be involved in maintenance of expression.

Animals↗
PubMed2002

Chromatin and CD4, CD8A and CD8B gene expression during thymic differentiation.

The regulation of gene expression during thymocyte development provides an ideal experimental system to study lineage-commitment processes. In particular, expression of the CD4, CD8A and CD8B genes seems to correlate well with the cell-fate decisions that are taken by thymocytes, and elucidating the molecular mechanisms that underlie the differential expression of these genes could reveal key events in differentiation processes. Here, we review examples of how gene cis elements (such as promoters, enhancers and locus control regions) and trans elements (such as transcription factors, chromatin-remodelling complexes and histone-modification enzymes) come together to orchestrate a finely tuned sequence of events that results in the complex pattern of CD4, CD8A and CD8B gene expression that is observed during thymocyte development.

Animals↗