Specific expression of the human CD4 gene in mature CD4+ CD8- and immature CD4+ CD8+ T cells and in macrophages of transgenic mice

A conserved element in the first intron of Cd4 has a lineage specific, TCR signal-responsive, canonical enhancer function that matches the timing of cell surface CD4 upregulation required to prevent lineage choice error

Introduction

The regulation of Cd4 expression during T-cell development and immune responses is essential for proper lineage commitment and function in the periphery. However, the mechanisms of genetic and epigenetic regulation are complex, and their interplay not entirely understood. Previously, we demonstrated the need for CD4 upregulation during positive selection to ensure faithful commitment of MHC-II-restricted T cells to the CD4 lineage. In this study, we investigate whether a conserved region, here called NCE, that is proximal to the Cd4 silencer and contains E4m has the required developmental-stage-specific canonical enhancer function and TCR responsiveness to mediate the CD4 upregulation required to prevent lineage errors.

Methods

To investigate the role of NCE, transient transfection of reporter plasmids was performed in thymoma cell lines arrested at the double-positive (DP, CD4+CD8+) and intermediate (INT, CD4+CD8lo) stages of development. CRISPR/Cas9-mediated deletion of the coreNCE/E4m region was carried out in these cell lines to assess its impact on CD4 surface expression, re-expression rates, and TCR signaling responsiveness. To avoid developmental alterations from direct manipulation of the endogenous Cd4 locus in vivo, BAC-transgenic reporter mice were generated with the locus modified to express EGFP in the presence or absence of NCE. EGFP mRNA levels were measured via RT-qPCR, and EGFP fluorescence was analyzed in post-selection thymocytes.

Results

Our in vitro experiments demonstrate that NCE by itself can function as an enhancer at the INT, but not the DP stage of development. Furthermore, CRISPR/Cas9-mediated deletion of coreNCE/E4m resulted in reduced CD4 surface levels, slower re-expression rates, and reduced TCR signaling responsiveness in INT cells, but not in DP cells. In vivo, NCE-sufficient transgenic mice exhibited upregulation of Cd4 reporter EGFP mRNA levels at the INT stage and a corresponding upregulation of EGFP fluorescence, whereas NCE-deficient mice showed a significant loss of Cd4 reporter EGFP mRNA and no detectable EGFP production in any post-selection thymocytes.

Discussion

This study demonstrates that the canonical enhancer function of coreNCE/E4m is essential for CD4 upregulation following positive selection. The NCE region, with its developmental-stage-specific activity and its known epigenetic regulatory capabilities, ensures faithful lineage commitment to the CD4 lineage.

Epigenetic propagation of CD4 expression is established by the Cd4 proximal enhancer in helper T cells

The stability of a lineage program (cellular memory) is dependent on mechanisms that epigenetically maintain active or repressed states of gene expression (transcriptional memory). Although epigenetic silencing of genes has been clearly demonstrated from yeast to mammals, heritable maintenance of active transcription has been less clearly defined. To investigate the potential role of active transcriptional memory during lineage diversification, we employed targeted mutation of a positive-acting cis element in the Cd4 locus to determine the impact on CD4 expression and the differentiation of CD4(+) helper T cells in mice. We show that the proximal enhancer (E4(P)) of Cd4 is essential for CD4 expression in immature CD4(+)8(+) thymocytes. Furthermore, its loss resulted in reduced and unstable expression of CD4 in mature T cells. However, if the enhancer was deleted after cells had already committed to the helper T-cell lineage, CD4 expression remained high and was stable upon cell division. "Active" histone modifications, once initiated by E4(P), were also propagated independently of the enhancer. Thus, E4(P) is responsible for establishing an epigenetically inherited active Cd4 locus in the helper T-cell lineage. To our knowledge, this is the first genetic demonstration of active transcriptional memory in mammalian cells.

Adult AIDS-like disease in a novel inducible human immunodeficiency virus type 1 Nef transgenic mouse model: CD4+ T-cell activation is Nef dependent and can occur in the absence of lymphophenia

CD4C/HIV(nef) transgenic (Tg) mice express Nef in CD4+ T cells and in the cells of the macrophage/monocyte/dendritic lineage, and they develop an AIDS-like disease similar to human AIDS. In these mice, Nef is constitutively expressed throughout life. To rule out the contribution of any developmental defects caused by early expression of Nef, we generated inducible human immunodeficiency virus type 1 (HIV-1) Nef Tg mice by using the tetracycline-inducible system. Faithful expression of the Nef transgene was induced in (CD4C/rtTA x TRE/HIV(Nef)) or (CD4C/rtTA2S-M2 x TRE/HIV(Nef)) double-Tg mice upon doxycycline (DOX) treatment in drinking water. Long-term treatment of these mice with DOX also led to loss, apoptosis, and activation of CD4+ T cells, this latter phenotype being observed even with low levels of Nef. These phenotypes could be transferred by bone marrow (BM) transplantation, indicating a hematopoietic cell autonomous effect. In addition, in mixed Tg:non-Tg BM chimeras, only Tg and not non-Tg CD4+ T cells exhibited an effector/memory phenotype in the absence of lymphopenia. Finally, the DOX-induced double-Tg mice developed nonlymphoid organ diseases similar to those of CD4C/HIV(Nef) Tg mice and of humans infected with HIV-1. These results show for the first time that adult mice are susceptible to the detrimental action of Nef and that Nef-mediated T-cell activation can be independent of lymphopenia. These Tg mice represent a unique model which is likely to be instrumental for understanding the cellular and molecular pathways of Nef action as well as the main characteristics of immune reconstitution following DOX withdrawal.

Selective expression of human immunodeficiency virus Nef in specific immune cell populations of transgenic mice is associated with distinct AIDS-like phenotypes

We previously reported that CD4C/human immunodeficiency virus (HIV)(Nef) transgenic (Tg) mice, expressing Nef in CD4(+) T cells and cells of the macrophage/dendritic cell (DC) lineage, develop a severe AIDS-like disease, characterized by depletion of CD4(+) T cells, as well as lung, heart, and kidney diseases. In order to determine the contribution of distinct populations of hematopoietic cells to the development of this AIDS-like disease, five additional Tg strains expressing Nef through restricted cell-specific regulatory elements were generated. These Tg strains express Nef in CD4(+) T cells, DCs, and macrophages (CD4E/HIV(Nef)); in CD4(+) T cells and DCs (mCD4/HIV(Nef) and CD4F/HIV(Nef)); in macrophages and DCs (CD68/HIV(Nef)); or mainly in DCs (CD11c/HIV(Nef)). None of these Tg strains developed significant lung and kidney diseases, suggesting the existence of as-yet-unidentified Nef-expressing cell subset(s) that are responsible for inducing organ disease in CD4C/HIV(Nef) Tg mice. Mice from all five strains developed persistent oral carriage of Candida albicans, suggesting an impaired immune function. Only strains expressing Nef in CD4(+) T cells showed CD4(+) T-cell depletion, activation, and apoptosis. These results demonstrate that expression of Nef in CD4(+) T cells is the primary determinant of their depletion. Therefore, the pattern of Nef expression in specific cell population(s) largely determines the nature of the resulting pathological changes.

Rapid evolution by positive Darwinian selection in T-cell antigen CD4 in primates

CD4, an integral membrane glycoprotein, plays a critical role in the immune response and in the life cycle of simian and human immunodeficiency virus (SIV and HIV). Pairwise comparisons of orthologous human and mouse genes show that CD4 is evolving much faster than the majority of mammalian genes. The acceleration is too great to be attributed to a simple relaxation of the action of purifying selection alone. Here we show that the selective pressure acting on CD4 is highly variable between regions in the protein and identify codon sites under strong positive selection. We reconstruct the coding sequences for ancestral primate CD4s and model tertiary structures of all ancestral and extant sequences. Structural mapping of positively selected sites shows they distribute on the surface of the D1 domain of CD4, where the exogenous SIV gp120 protein binds. Moreover, structural models of the ancestral sequences show substantially larger variation in the interfacial electrostatic charge on CD4 and in the surface complementary between CD4 and gp120 in CD4 lineages from primates with natural SIV infections than those without. Thus, positive selection on CD4 among primates may reflect forces driven by SIV infection and could provide a link between changes in sequence and structure of CD4 during evolution and the interaction with the immunodeficiency virus.

Primary human immunodeficiency virus type 1 nef alleles show major differences in pathogenicity in transgenic mice

We previously reported that the human immunodeficiency virus type 1 NL4-3 Nef is necessary and sufficient to induce a severe AIDS-like disease in transgenic (Tg) mice when the protein is expressed under the regulatory sequences of the human CD4 gene. We have now assayed additional Nef alleles (SF2, JR-CSF, YU10x, and NL4-3 [T71R] Nef alleles), including some from long-term nonprogressors (AD-93, 032an, and 039nm alleles) in the same Tg system and compared their pathogenicities. All these Nef alleles downregulated cell surface CD4 in human cells in vitro and also, with the exception of Nef(YU10x), in Tg CD4(+) T cells. Depletion of double-positive and single-positive thymocytes occurred with all alleles but was less pronounced in Nef(YU10x) Tg mice. A loss of peripheral CD4(+) T cells was observed with all alleles but was minimal in Nef(YU10x) Tg mice. In Nef(032an) and Nef(SF2) Tg mice, T-cell loss was severe despite lower levels of Tg expression, suggesting a higher virulence of these alleles. All Nef alleles except the Nef(YU10x) and Nef(NL4-3(T71R)) alleles induced an enhanced activated memory (CD25(+) CD69(+) CD44(high) CD45RB(low) CD62L(low)) and apoptotic phenotype. Also, all could interact with and/or activate PAK2 except the Nef(JR-CSF) allele. Organ (lung and kidney) diseases were present in Nef(NL4-3(T71R)), Nef(032an), Nef(039nm), and Nef(SF2) Tg mice, despite very low levels of Tg expression for the last strain. However, no organ disease or minimal organ disease developed in Nef(YU10x) and Nef(AD-93) Tg mice and Nef(JR-CSF) Tg mice, respectively, despite high levels of Tg expression. Our data show that important differences in the pathogenicities of various Nef alleles can be scored in Tg mice. Interestingly, our results also revealed that some phenotypes can segregate independently, such as CD4(+) T-cell depletion and activation, as well as severe depletion of thymic CD4(+) T cells and peripheral CD4(+) T cells. Therefore, expression of Nef alleles in Tg mice under the CD4C regulatory elements represents a novel assay for measuring their pathogenicity. Because of the very high similarity of this murine AIDS-like disease to human AIDS, this assay may have a predictive value regarding the behavior of Nef in infected humans.

The Nef-mediated AIDS-like disease of CD4C/human immunodeficiency virus transgenic mice is associated with increased Fas/FasL expression on T cells and T-cell death but is not prevented in Fas-, FasL-, tumor necrosis factor receptor 1-, or interleukin-1beta-converting enzyme-deficient or Bcl2-expressing transgenic mice

CD4(+)- and CD8(+)-T-cell death is a frequent immunological dysfunction associated with the development of human AIDS. We studied a murine model of AIDS, the CD4C/HIV transgenic (Tg) mouse model, to assess the importance of the apoptotic pathway in human immunodeficiency virus type 1 (HIV-1) pathogenesis. In these Tg mice, Nef is the major determinant of the disease and is expressed in immature and mature CD4(+) T cells and in cells of the macrophage/myeloid lineage. We report here a novel AIDS-like phenotype: enhanced death, most likely by apoptosis (as assessed by 7-aminoactinomycin D and annexin V/propidium iodide staining), of Tg thymic and peripheral CD4(+) and CD8(+) T cells. The Tg CD4(+) and CD8(+) T cells were also more susceptible to cell death after activation in vitro in mixed lymph node (LN) cultures. However, activation-induced cell death was not higher in Tg than in non-Tg-purified CD4(+) T cells. In addition, expression of Fas and FasL, assessed by flow cytometry, was increased in CD4(+) and CD8(+) T cells from Tg mice compared to that of non-Tg littermates. Despite the enhanced expression of Fas and FasL on Tg CD4(+) and CD8(+) T cells, Fas (lpr/lpr) and FasL (gld/gld) mutant CD4C/HIV Tg mice developed an AIDS-like disease indistinguishable from lpr/+ and gld/+ CD4C/HIV Tg mice, including loss of CD4(+) T cells. Similarly, CD4C/HIV Tg mice homozygous for mutations of two other genes implicated in cell death (interleukin-1beta-converting enzyme [ICE], tumor necrosis factor receptor 1 [TNFR-1]) developed similar AIDS-like disease as their respective heterozygous controls. Moreover, the double-Tg mice from a cross between the Bcl2/Wehi25 and CD4C/HIV Tg mice showed no major protection against disease. These results represent genetic evidence for the dispensable role of Fas, FasL, ICE, and TNFR-1 on the development of both T-cell loss and organ disease of these Tg mice. They also provide compelling evidence on the lack of protection by Bcl2 against Tg CD4(+)-T-cell death. In view of the high resemblance between numerous phenotypes observed in the CD4C/HIV Tg mice and in human AIDS, our findings are likely to be relevant for the human disease.

Immunopathogenesis of oropharyngeal candidiasis in human immunodeficiency virus infection

Oropharyngeal and esophageal candidiases remain significant causes of morbidity in human immunodeficiency virus (HIV)-infected patients, despite the dramatic ability of antiretroviral therapy to reconstitute immunity. Notable advances have been achieved in understanding, at the molecular level, the relationships between the progression of HIV infection, the acquisition, maintenance, and clonality of oral candidal populations, and the emergence of antifungal resistance. However, the critical immunological defects which are responsible for the onset and maintenance of mucosal candidiasis in patients with HIV infection have not been elucidated. The devastating impact of HIV infection on mucosal Langerhans' cell and CD4(+) cell populations is most probably central to the pathogenesis of mucosal candidiasis in HIV-infected patients. However, these defects may be partly compensated by preserved host defense mechanisms (calprotectin, keratinocytes, CD8(+) T cells, and phagocytes) which, individually or together, may limit Candida albicans proliferation to the superficial mucosa. The availability of CD4C/HIV transgenic mice expressing HIV-1 in immune cells has provided the opportunity to devise a novel model of mucosal candidiasis that closely mimics the clinical and pathological features of candidal infection in human HIV infection. These transgenic mice allow, for the first time, a precise cause-and-effect analysis of the immunopathogenesis of mucosal candidiasis in HIV infection under controlled conditions in a small laboratory animal.

Cardiac disease in transgenic mice expressing human immunodeficiency virus-1 nef in cells of the immune system

We previously reported that a severe acquired immune deficiency syndrome-like disease develops in transgenic (Tg) mice expressing the human immunodeficiency virus-1 in its natural target cells: immature and mature CD4(+) T cells and cells of the macrophage/dendritic lineage. Here, we show that these mice also develop cardiac disease, characterized most prominently by a focal myocytolysis, occasionally by myocarditis and by deposition of endogenous immunoglobulin on cardiomyocytes. Microfil perfusion demonstrated widespread coronary arteriospasm and echocardiographic analysis revealed depressed cardiac function in Tg mice. A higher (but still modest) level of cardiomyocyte apoptosis was detected in Tg as compared to non-Tg hearts. Tg expression was detected in some of the infiltrating mononuclear cells, but not in cardiomyocytes or in cells of the heart vessels, suggesting a human immunodeficiency virus-1-induced disease process mediated by cells of the immune system. The similarity of the heart disease observed in these Tg mice to that observed in acquired immune deficiency syndrome patients suggests a common pathogenesis.

Expression of simian immunodeficiency virus nef in immune cells of transgenic mice leads to a severe AIDS-like disease

In order to study the functions of simian immunodeficiency virus (SIV) Nef in vivo in a small-animal model, we constructed transgenic (Tg) mice expressing the SIV(mac)239 nef gene in the natural target cells of the virus under the control of the human CD4 gene promoter (CD4C). These CD4C/SHIV-nef(SIV) Tg mice develop a severe AIDS-like disease, with manifestations including premature death, failure to thrive or weight loss, wasting, thymic atrophy, an especially low number of peripheral CD8+ T cells as well as a low number of peripheral CD4+ T cells, diarrhea, splenomegaly, and kidney (interstitial nephritis, segmental glomerulosclerosis), lung (lymphocytic interstitial pneumonitis), and heart disease. In addition, these Tg mice fail to mount a class-switched antibody response after immunization with ovalbumin, they produce anti-DNA autoantibodies, and some of them develop Pneumocystis carinii lung infections. All these results suggest a generalized Nef-induced immunodeficiency. The low numbers of peripheral CD8+ and CD4+ T cells are likely to reflect a thymic defect and may be similar to the DiGeorge-like "thymic defect" immunophenotype described for a subgroup of human immunodeficiency virus type 1-infected children. Therefore, it appears that SIV Nef alone expressed in mice, in appropriate cell types and at sufficient levels, can elicit many of the phenotypes of simian and human AIDS. These Tg mice should be instrumental in studying the pathogenesis of SIV Nef-induced phenotypes.

The pathogenicity of human immunodeficiency virus (HIV) type 1 Nef in CD4C/HIV transgenic mice is abolished by mutation of its SH3-binding domain, and disease development is delayed in the absence of Hck

The human immunodeficiency virus type 1 (HIV-1) Nef protein is an important determinant of AIDS pathogenesis. We have previously reported that HIV-1 Nef is responsible for the induction of a severe AIDS-like disease in CD4C/HIV transgenic (Tg) mice. To understand the molecular mechanisms of this Nef-induced disease, we generated Tg mice expressing a mutated Nef protein in which the SH3 ligand-binding domain (P(72)XXP(75)XXP(78)) was mutated to A(72)XXA(75)XXQ(78). This mutation completely abolished the pathogenic potential of Nef, although a partial downregulation of the CD4 cell surface expression was still observed in these Tg mice. We also studied whether Hck, one of the effectors previously found to bind to this PXXP motif of Nef, was involved in disease development. Breeding of Tg mice expressing wild-type Nef on an hck(-/-) (knockout) background did not abolish any of the pathological phenotypes. However, the latency of disease development was prolonged. These data indicate that an intact PXXP domain is essential for inducing an AIDS-like disease in CD4C/HIV Tg mice and suggest that interaction of a cellular effector(s) with this domain is required for the induction of this multiorgan disease. Our findings indicate that Hck is an important, but not an essential, effector of Nef and suggest that another factor(s), yet to be identified, may be more critical for disease development.

Precise arrangement of factor-binding sites is required for murine CD4 promoter function

The control of CD4 expression is linked to the signaling events that mediate T-cell development and is directly dependent on the CD4 promoter. The CD4 promoter does not contain functionally redundant sites: all four factor-binding sites must be intact to achieve wild-type activity. Here we demonstrate that the precise position of three factor-binding sites relative to each other is essential for promoter activity, indicating that they function together as an inseparable cassette for assembly of the transcription initiation complex. Small changes in either phasing or distance between any two sites in this cassette leads to complete abrogation of promoter function. In addition, we demonstrate that one of the factors that bind the promoter cassette is not present in CD8 SP T(C) cells. Thus, this factor is a candidate for mediating the relative subclass specificity of CD4 promoter function in activated CD4 SP T(H) cells.

Distinct Stage-Specific cis-Active Transcriptional Mechanisms Control Expression of T Cell Coreceptor CD8α at Double- and Single-Positive Stages of Thymic Development

Developing thymocytes that give rise to CD8+ (cytotoxic) and CD4+ (helper) αβ-TCR T lymphocytes go through progressive stages of expression of coreceptors CD8 and CD4 from being negative for both (the double-negative stage), to coexpressing both (the double-positive (DP) stage), to a mutually exclusive sublineage-specific expression of one or the other (the single-positive (SP) stage). To delineate the mechanisms underlying regulation of CD8 during these developmental transitions, we have examined expression of a series of mouse CD8α gene constructs in developing T cells of conventional and CD8α “knock-out” transgenic mice. Our results indicate that cis-active transcriptional control sequences essential for stage- and sublineage-specific expression lie within a 5′ 40-kb segment of the CD8 locus, ∼12 kb upstream of the CD8α gene. Studies to characterize and sublocalize these cis sequences showed that a 17-kb 5′ subfragment is able to direct expression of the CD8α gene up to the CD3intermediate DP stage but not in more mature DP or SP cells. These results indicate that stage-specific expression of CD8α in developing T cells is mediated by the differential activity of multiple functionally distinct cis-active transcriptional control mechanisms. It will be important to determine the relationship of “switching” between these cis mechanisms and selection.

Transgenic mice expressing human immunodeficiency virus type 1 in immune cells develop a severe AIDS-like disease

We have constructed transgenic (Tg) mice expressing the entire human immunodeficiency virus type 1 (HIV-1) coding sequences in cells targeted by HIV-1 infection in humans. These Tg mice developed a severe AIDS-like disease leading to early death (< 1 month). They developed muscle wasting, severe atrophy and fibrosis of lymphoid organs, tubulointerstitial nephritis, and lymphoid interstitial pneumonitis. In addition the expression of RANTES was increased in various tissues of these Tg mice relative to that in the normal controls. Disease appearance was correlated with the levels of transgene expression. The numerous pathologies observed in these mice are remarkably similar to those observed in human AIDS and, more specifically, in pediatric AIDS.

Vascular bed-specific expression of an endothelial cell gene is programmed by the tissue microenvironment

The endothelium is morphologically and functionally adapted to meet the unique demands of the underlying tissue. At the present time, little is known about the molecular basis of endothelial cell diversity. As one approach to this problem, we have chosen to study the mechanisms that govern differential expression of the endothelial cell-restricted von Willebrand factor (vWF) gene. Transgenic mice were generated with a fragment of the vWF gene containing 2,182 bp of 5' flanking sequence, the first exon and first intron coupled to the LacZ reporter gene. In multiple independent lines of mice, beta-galactosidase expression was detected within endothelial cells in the brain, heart, and skeletal muscle. In isogeneic transplantation models, LacZ expression in host-derived auricular blood vessels was specifically induced by the microenvironment of the heart. In in vitro coculture assays, expression of both the transgene and the endogenous vWF gene in cardiac microvascular endothelial cells (CMEC) was upregulated in the presence of cardiac myocytes. In contrast, endothelial cell levels of thrombomodulin protein and mRNA were unchanged by the addition of ventricular myocytes. Moreover, CMEC expression of vWF was not influenced by the addition of 3T3 fibroblasts or mouse hepatocytes. Taken together, the results suggest that the vWF gene is regulated by vascular bed-specific pathways in response to signals derived from the local microenvironment.

Second-messenger regulation of receptor association with clathrin-coated pits: a novel and selective mechanism in the control of CD4 endocytosis

CD4, a member of the immunoglobulin superfamily, is not only expressed in T4 helper lymphocytes but also in myeloid cells. Receptor-mediated endocytosis plays a crucial role in the regulation of surface expression of adhesion molecules such as CD4. In T lymphocytes p56lck, a CD4-associated tyrosine kinase, prevents CD4 internalization, but in myeloid cells p56lck is not expressed and CD4 is constitutively internalized. In this study, we have investigated the role of cyclic AMP (cAMP) in the regulation of CD4 endocytosis in the myeloid cell line HL-60. Elevations of cellular cAMP were elicited by 1) cholera toxin, 2) pertussis toxin, 3) forskolin and IBMX, 4) NaF, or 5) the physiological receptor agonist prostaglandin E1. All five interventions led to an inhibition of CD4 internalization. Increased cAMP levels did not inhibit endocytosis per se, because internalization of insulin receptors and transferrin receptors and fluid phase endocytosis were either unchanged or slightly enhanced. The mechanism of cAMP inhibition was further analyzed at the ultrastructural level. CD4 internalization, followed either by quantitative electron microscopy autoradiography or by immunogold labeling, showed a rapid and temperature-dependent association of CD4 with clathrin-coated pits in control cells. This association was markedly inhibited in cells with elevated cAMP levels. Thus these findings suggest a second-messenger regulation of CD4 internalization through an inhibition of CD4 association with clathrin-coated pits in p56lck-negative cells.

A Myc-associated zinc finger protein binding site is one of four important functional regions in the CD4 promoter

The CD4 promoter plays an important role in the developmental control of CD4 transcription. In this report, we show that the minimal CD4 promoter has four factor binding sites, each of which is required for full function. Using biochemical and mutagenesis analyses, we determined that multiple nuclear factors bind to these independent sites. We determined that an initiator-like sequence present at the cap site and an Ets consensus sequence are required for full promoter function. We also demonstrate that the Myc-associated zinc finger protein (MAZ) appears to be the predominant factor binding to one of these sites. This last site closely resembles the ME1a1 G3AG4AG3 motif previously shown to be a critical element in the P2 promoter of the c-myc gene. We therefore believe that the MAZ transcription factor is also likely to play an important role in the control of developmental expression of the CD4 gene.

Human von Willebrand factor gene sequences target expression to a subpopulation of endothelial cells in transgenic mice

The present study was undertaken to define the 5' and 3' regulatory sequences of human von Willebrand factor gene that confer tissue-specific expression in vivo. Transgenic mice were generated bearing a chimeric construct that included 487 bp of 5' flanking sequence and the first exon fused in-frame to the Escherichia coli lacZ gene. In situ histochemical analyses in independent lines demonstrated that the von Willebrand factor promoter targeted expression of LacZ to a subpopulation of endothelial cells in the yolk sac and adult brain. LacZ activity was absent in the vascular beds of the spleen, lung, liver, kidney, testes, heart, and aorta, as well as in megakaryocytes. In contrast, in mice containing the lacZ gene targeted to the thrombomodulin locus, the 5-bromo-4-chloro-3-indolyl beta-D-galactopyranoside reaction product was detected throughout the vascular tree. These data highlight the existence of regional differences in endothelial cell gene regulation and suggest that the 733-bp von Willebrand factor promoter may be useful as a molecular marker to investigate endothelial cell diversity.

Elf-1 binds to a critical element in a second CD4 enhancer

The coordinated expression of CD4 and CD8 during T-cell development is tightly coupled with the maturation state of the T cell. Additionally, the mutually exclusive expression of these receptors in mature T cells is representative of the functional T-cell subclasses (CD4+ helper T cells versus CD8+ cytotoxic T cells). We have studied the regulation CD4 gene transcription during T-cell development in an attempt to gain an understanding of the molecular mechanisms involved in T-cell development and differentiation. Here we present the identification of a second transcriptional enhancer in the murine CD4 locus 24 kb upstream of the CD4 promoter. This enhancer is active in mature T cells and is especially active in CD4+ helper T cells. A number of nuclear proteins bind to elements in the minimal CD4 enhancer that includes consensus sites for AP-1, Sp1, Gata, and Ets transcription factor families. We find that the Ets consensus site is crucial for enhancer activity and that the recently identified Ets factor, Elf-1, which is expressed at high levels in T cells and involved in the regulation of several other T-cell-specific genes, is a dominant protein in T-cell nuclear extracts that binds to this site.

Elf-1 binds to a critical element in a second CD4 enhancer

The coordinated expression of CD4 and CD8 during T-cell development is tightly coupled with the maturation state of the T cell. Additionally, the mutually exclusive expression of these receptors in mature T cells is representative of the functional T-cell subclasses (CD4+ helper T cells versus CD8+ cytotoxic T cells). We have studied the regulation CD4 gene transcription during T-cell development in an attempt to gain an understanding of the molecular mechanisms involved in T-cell development and differentiation. Here we present the identification of a second transcriptional enhancer in the murine CD4 locus 24 kb upstream of the CD4 promoter. This enhancer is active in mature T cells and is especially active in CD4+ helper T cells. A number of nuclear proteins bind to elements in the minimal CD4 enhancer that includes consensus sites for AP-1, Sp1, Gata, and Ets transcription factor families. We find that the Ets consensus site is crucial for enhancer activity and that the recently identified Ets factor, Elf-1, which is expressed at high levels in T cells and involved in the regulation of several other T-cell-specific genes, is a dominant protein in T-cell nuclear extracts that binds to this site.