Ubiquitous and lymphocyte-specific factors are involved in the induction of the mouse interleukin 2 gene in T lymphocytes

CD28 Costimulation Augments IL-2 Secretion of Activated Lamina Propria T Cells by Increasing mRNA Stability Without Enhancing IL-2 Gene Transactivation

The pathways leading to activation in lamina propria (LP) T cells are different from peripheral T cells. LP T cells exhibit enhanced IL-2 secretion when activated through the CD2 pathway. Coligation of CD28 leads to synergistic enhancement of IL-2 secretion. Previous studies have characterized the CD28 augmentation of TCR-mediated signaling in peripheral blood T cells through transcriptional activation of an IL-2 promoter CD28 response element (CD28RE), along with enhanced mRNA stability. This study characterized molecular events involved in CD28 costimulation of IL-2 production in LP mononuclear cells (LPMC). LPMC exhibited increased IL-2 production in response to CD28 costimulation, compared with cells activated through CD2 alone. IL-2 secretion was paralleled by increased expression of IL-2 mRNA, resulting from enhanced IL-2 mRNA stability. In contrast to transcriptional activation in PBMC, EMSA revealed that CD28 coligation of CD2-activated LPMC does not result in increased binding of trans-factors to the CD28RE, nor did Western blots detect changes in I-κBα or I-κBβ levels following CD28 coligation. Furthermore, CD28 coligation fails to enhance IL-2 promoter-reporter or RE/AP construct expression in CD2-activated LPMC. The results reported herein indicate that the molecular mechanisms involved in CD28 cosignaling and regulation of IL-2 secretion in LP T cells are unique to that compartment and differ from those seen in peripheral blood T cells. These observations suggest a biological significance for different mechanisms of IL-2 activation in initiation and maintenance of the cytokine repertoire found in the mucosa.

Recognition of NFATp/AP-1 composite elements within genes induced upon the activation of immune cells

Composite elements are regulatory modules of promoters or enhancers that consist of binding sites of two different but synergizing transcription factors. A well-studied example is nuclear factors of activated T-cell (NFAT) sites which are composite elements of a NFATp/c and an activating protein 1 (AP-1) binding site. We have developed a computational approach to identify potential NFAT target genes which (a) comprises an improved method to scan for individual NFAT composite elements; (b) considers positional effects relative to transcription start sites; and (c) involves cluster analysis of potential NFAT composite elements. All three steps progressively helpX?ed to discriminate T-cell-specific promoter sequences against other functional regions (coding and intronic sequences) of the same genes, against promoters of muscle-specific genes or against random sequences. Using this approach, we identified potential NFAT composite elements in promoters of cytokine genes and their receptors as well as in promoters of genes for AP-1 family members, Ca2+-binding proteins and some other components of the regulatory network operating in activated T-cells and other immune cells. The method developed can be adapted to characterize and identify other composite elements as well. The program for recognition NFAT composite elements is available through the World Wide Web (http://compel.bionet.nsc.ru/FunSite/CompelScan. html and http://transfac.gbf.de/dbsearch/funsitep/s _comp.html).

Interaction of hematopoietic progenitor kinase 1 with adapter proteins Crk and CrkL leads to synergistic activation of c-Jun N-terminal kinase

Hematopoietic progenitor kinase 1 (HPK1), a mammalian Ste20-related protein kinase, is an upstream activator of c-Jun N-terminal kinase (JNK). In order to further characterize the HPK1-mediated JNK signaling cascade, we searched for HPK1-interacting proteins that could regulate HPK1. We found that HPK1 interacted with Crk and CrkL adaptor proteins in vitro and in vivo and that the proline-rich motifs within HPK1 were involved in the differential interaction of HPK1 with the Crk proteins and Grb2. Crk and CrkL not only activated HPK1 but also synergized with HPK1 in the activation of JNK. The HPK1 mutant (HPK1-PR), which encodes the proline-rich region alone, blocked JNK activation by Crk and CrkL. Dominant-negative mutants of HPK1 downstream effectors, including MEKK1, TAK1, and SEK1, also inhibited Crk-induced JNK activation. These results suggest that the Crk proteins serve as upstream regulators of HPK1. We further observed that the HPK1 mutant HPK1-KD(M46), which encodes the kinase domain with a point mutation at lysine-46, and HPK1-PR blocked interleukin-2 (IL-2) induction in Jurkat T cells, suggesting that HPK1 signaling plays a critical role in IL-2 induction. Interestingly, HPK1 phosphorylated Crk and CrkL, mainly on serine and threonine residues in vitro. Taken together, our findings demonstrate the functional interaction of HPK1 with Crk and CrkL, reveal the downstream pathways of Crk- and CrkL-induced JNK activation, and highlight a potential role of HPK1 in T-cell activation.

The roles of nuclear factor of activated T cells and ying-yang 1 in activation-induced expression of the interferon-gamma promoter in T cells

Nuclear factor of activated T cells (NFAT) plays an important role in expression of many cytokine genes including interleukin-2 and interleukin-4. However, its role in interferon-gamma (IFN-gamma) expression is not well understood. In the current studies, two strong NFAT-binding sites in the IFN-gamma promoter were identified by DNase I footprint analysis at positions -280 to -270 and -163 to -155. NFATp bound independently to both sites and was required for the formation of a composite element with AP-1 spanning position -163 to -147. In Jurkat T cells and primary lymphocytes, activation-induced expression of IFN-gamma reporter constructs containing point mutations in either NFAT site or the AP-1 component of the composite site was decreased by approximately 40-65%. Despite elimination of both strong NFAT-binding sites, the IFN-gamma promoter remained completely sensitive to inhibition by cyclosporin. This suggests that other elements in the IFN-gamma promoter, such as the IFN-gamma proximal element, are sufficient for cyclosporin sensitivity of this gene. Ying-Yang 1 (YY1), a potential inhibitor of IFN-gamma expression, binds to sites located between the two NFAT sites. Mutation of the YY1 sites alone had little effect on IFN-gamma promoter activity. However, mutation of both the NFAT and YY1-binding sites abolished activation-induced expression in primary murine splenocytes but not in Jurkat T cells. This suggests that under some conditions, YY1 may play a positive role in activation-induced transcription of IFN-gamma.

Interleukin 2-mediated uncoupling of T cell receptor alpha/beta from CD3 signaling

T cell activation and clonal expansion is the result of the coordinated functions of the receptors for antigen and interleukin (IL)-2. The protein tyrosine kinase p56(lck) is critical for the generation of signals emanating from the T cell antigen receptor (TCR) and has also been demonstrated to play a role in IL-2 receptor signaling. We demonstrate that an IL-2-dependent, antigen-specific CD4(+) T cell clone is not responsive to anti-TCR induced growth when propagated in IL-2, but remains responsive to both antigen and CD3epsilon-specific monoclonal antibody. Survival of this IL-2-dependent clone in the absence of IL-2 was supported by overexpression of exogenous Bcl-xL. Culture of this clonal variant in the absence of IL-2 rendered it susceptible to anti-TCR-induced signaling, and correlated with the presence of kinase-active Lck associated with the plasma membrane. The same phenotype is observed in primary, resting CD4(+) T cells. Furthermore, the presence of kinase active Lck associated with the plasma membrane correlates with the presence of ZAP 70-pp21zeta complexes in both primary T cells and T cell clones in circumstances of responsive anti-TCR signaling. The results presented demonstrate that IL-2 signal transduction results in the functional uncoupling of the TCR complex through altering the subcellular distribution of kinase-active Lck.

A p56lck-independent pathway of CD2 signaling involves Jun kinase

The p56 Src family non-receptor tyrosine kinase has been shown to be critical for T lymphocyte differentiation and activation. Hence in the absence of p56, T cell receptor triggered activation does not occur. We now provide evidence for a CD2-based signaling pathway which, in contrast to that of the T cell receptor, is independent of p56. CD2-mediated interleukin-2 production occurs via activation of Jun kinase in cell lines lacking p56. Jun kinase then facilitates the binding of c-Jun/c-Fos heterodimers to the AP-1 consensus site and the subsequent transcriptional activity of the interleukin-2 promoter. These data elucidate differences between TCR and CD2 signaling pathways in the same T cells.

Differential gene expression in apoptosis: identification of ribosomal protein 23K, a cell proliferation inhibitor

Gene expression during the camptothecin-induced apoptotic death of human leukemic U937 cells and mouse T-cell hybridoma QW4.1 cells was studied by the mRNA differential display technique. Ten clones were confirmed to be differentially expressed, nine of which encoded novel sequences. One clone, U3.2, was induced approximately 10-fold in camptothecin-treated cells and was found to be identical to a highly basic 23-kDa human protein which contains basic leucine zipper-like motifs and has recently been identified as the human homologue of the rat ribosomal protein L13a. Northern blot analysis revealed a major mRNA of approximately 0.9 kb and a minor mRNA of approximately 1.3 kb. Overexpression of a full-length 23K cDNA, tagged with a FLAG sequence, in COS-7 cells revealed a predominantly nucleolar localization and the absence of any 23K protein from the cytoplasm. Subsequent transfection studies, using antisense phosphorothioate-modified oligonucleotides, revealed that inhibition of 23K expression results in an increased cell proliferation and greater sensitivity of U937 cells to the effects of camptothecin-induced cell death. Upregulation of 23K expression using a cDNA construct resulted in a decrease in cell proliferation and growth arrest, suggesting a role for 23K protein as a proliferation checkpoint following a cellular insult.

Inhibition of CD28/CD3-Mediated Costimulation of Naive and Memory Human T Lymphocytes by Intracellular Incorporation of Polyclonal Antibodies Specific for the Activator Protein-1 Transcriptional Complex

A number of indirect methods have been utilized in demonstrating activator protein-1 transcription factor function in IL-2 promoter activity. However, there has been no direct demonstration that activator protein-1 is involved in CD28-dependent costimulation of IL-2 gene transcription in freshly isolated naive and memory human T lymphocytes. To address this issue, the method of scrape loading was applied to purified peripheral blood T lymphocytes. Since scrape loading relies on adherent cells, peripheral blood human T (PB-T) cells were immobilized on the nonspecific cell attachment factor poly-l-lysine. Cells scraped off poly-l-lysine in the presence of Ig FITC efficiently incorporated Ig, with relatively uniform fluorescence. T cells retained their physical parameters as measured by forward and side light scatter, and functional activity as measured by costimulation of proliferation and IL-2 production after being scraped off this substrate. CD28/CD3-costimulated T cells produced intracellular IL-2 from all subsets measured (CD4+, CD4−, CD45RO+, and CD45RO−). IL-2 production and intracellular accumulation in nonscraped PB-T cells activated with CD28/CD3 coligation were skewed favoring CD45RO+ and CD4+ subsets, as was IL-2 production in scraped PB-T cells. The intracellular incorporation of Abs specific for c-Fos and c-Jun family members by scrape loading inhibited the production and intracellular accumulation of IL-2 within 6 h of costimulation with PMA/ionomycin, or costimulation by CD28 and CD3 ligation. Scrape loading thus provides an efficient mechanism for intracellular incorporation of macromolecules, and the first direct evidence that c-Fos and c-Jun are involved in transcription of the IL-2 gene within its correct chromosomal context, in resting human T lymphocyte subpopulations.

Chromatin remodeling of the interleukin-2 gene: distinct alterations in the proximal versus distal enhancer regions

Known transcription factor-DNA interactions in the minimal enhancer of the murine interleukin-2 gene (IL-2) do not easily explain the T cell specificity of IL-2 regulation. To seek additional determinants of cell type specificity, in vivo methodologies were employed to examine chromatin structure 5' and 3' of the 300 bp IL-2 proximal promoter/enhancer region. Restriction enzyme accessibility revealed that until stimulation the IL-2 proximal promoter/enhancer exists in a closed conformation in resting T and non-T cells alike. Within this promoter region, DMS and DNase I genomic footprinting also showed no tissue-specific differences prior to stimulation. However, DNase I footprinting of the distal -600 to -300 bp region revealed multiple tissue-specific and stimulation-independent DNase I hypersensitive sites. Gel shift assays detected T cell-specific complexes binding within this region, which include TCF/LEF or HMG family and probable Oct family components. Upon stimulation, new DNase I hypersensitive sites appeared in both the proximal and distal enhancer regions, implying that there may be a functional interaction between these two domains. These studies indicate that a region outside the established IL-2 minimal enhancer may serve as a stable nucleation site for tissue-specific factors and as a potential initiation site for activation-dependent chromatin remodeling.

Activation of the CD2 Pathway in Lamina Propria T Cells Up-Regulates Functionally Active AP-1 Binding to the IL-2 Promoter, Resulting in Messenger RNA Transcription and IL-2 Secretion

The aim of this study was to identify molecular mechanisms involved in transcriptional regulation of IL-2 expression following CD2 and CD3 activation in lamina propria (LP) T cells. Studies used T cells from normal, ulcerative colitis, and Crohn’s disease mucosa and freshly isolated PBMC, PBMC stimulated with IL-2 alone, and PBMC stimulated with IL-2 and cocultured with B cell lines (LP-like T cells). Electrophoretic mobility shift assays were performed with nuclear extracts from cells activated with either anti-CD2 or anti-CD3 Abs. CD2 signaling in LPMC and LP-like T cells led to a pattern of sustained up-regulation of AP-1-binding complexes, whereas CD3 activation resulted in only transient up-regulation. While the pattern of regulation of AP-1 binding observed in normal, uninflamed, or inflamed Crohn’s disease LPMC is similar, differences in intensity of AP-1 binding were observed. Activation of LP-like T cells mimics the up-regulation of AP-1 with a kinetic profile similar to that observed with freshly isolated LPMC from Crohn’s disease-inflamed tissue. The AP-1 complex formed following CD2 activation is composed of jun/fos heterodimers. The CD2-enhanced responsiveness is reflected in functional analysis experiments utilizing transfection of both multimeric-TRE or IL-2 promoter-luciferase constructs directly into normal, ulcerative colitis, or Crohn’s disease LPMC. Our data suggest that activation of LP T cells from normal, ulcerative colitis, or Crohn’s disease mucosa through the CD2 pathway leads to induction of AP-1 complexes that bind to the IL-2 promoter, and may play a pivotal role in modulating IL-2 production in the gut.

Inhibitors of calcineurin block expression of cyclins A and E induced by fibroblast growth factor in Swiss 3T3 fibroblasts

In Swiss 3T3 fibroblasts, growth factor-stimulated progression from G1 to S phase involves activation of the Ca2+/calmodulin-dependent serine/threonine-specific protein phosphatase 2B (calcineurin). Here we report that both cobalt and the calcium chelator EGTA, inhibitors of calcium uptake, as well as cyclosporin A and FK-506, specific inhibitors of calcineurin function, abolished fibroblast growth factor (FGF)-induced expression of cyclins A and E, but not cyclin D1. At 0.1 microM concentration cyclosporin A completely blocked FGF-induced expression of cyclins E and A and it inhibited FGF-stimulated DNA synthesis by 40%; full inhibition of DNA synthesis required 10 microM cyclosporin A. PD 98059, an inhibitor of mitogen-activated protein (MAP) kinase kinase, and hemicholinium-3, an inhibitor of FGF-induced MAP kinase activity, did not inhibit the stimulatory effect of FGF on the expression of cyclin E. On the other hand, the inhibitory effect of 0.1 microM cyclosporin A on FGF-stimulated DNA synthesis was additive with that of hemicholinium-3, suggesting that the two inhibitors acted by different mechanisms. The inhibitors of calcineurin and calcium uptake also completely blocked the stimulatory effects of lysophosphatidic acid on the expression of cyclins E and A, but not cyclin D1. The results suggest that FGF- or lysophosphatidic acid-induced transcription of cyclin A and cyclin E genes is mediated by calcineurin involving a MAP kinase-independent mechanism and that increased expression of cyclins A and E is required for the maximal stimulatory effects of these mitogens on DNA synthesis.

Bruton's tyrosine kinase-mediated interleukin-2 gene activation in mast cells. Dependence on the c-Jun N-terminal kinase activation pathway

Cross-linking of the high affinity IgE receptor (FcepsilonRI) on mast cells induces secretion of cytokines, including interleukin (IL)-2, through transcriptional activation of cytokine genes. Previously, defects in the gene coding for Bruton's tyrosine kinase (Btk) were shown to result in defective cytokine production in mast cells, and thereby mice carrying btk mutations exhibited diminished anaphylactic reactions in response to IgE and antigen. In this study, we provide evidence that the transcription factors involved in the IL-2 gene expression in T cells are also required for maximal activation of the IL-2 gene in FcepsilonRI-stimulated mast cells. Among them, AP-1 (Jun/Fos) and NF-AT were identified as candidate transcription factors that are regulated by Btk. Consistent with our previous data indicating that Btk regulates stress-activated protein kinases, c-Jun N-terminal kinase (JNK), c-Jun and other JNK-regulatable transcription factors are activated by FcepsilonRI cross-linking in a Btk-dependent manner. Further, FcepsilonRI-induced IL-2 gene activation is dependent on c-Jun and a component, SEK1, of its upstream activation pathway. Collectively, these data demonstrate that Btk regulates the transcription of the IL-2 gene through the JNK-regulatable transcription factors in FcepsilonRI-stimulated mast cells.

Cloning and characterization of the promoter for the human complement factor I (C3b/C4b inactivator) gene

Complement factor I is a serine proteinase that regulates the classical and alternative pathways of complement by cleaving C3b and C4b and preventing the assembly of C3 and C5 convertase enzymes. In order to understand the regulation of factor I gene expression in liver cells, 4kb of the 5' flanking region of the gene was cloned, and the 1474-bp 3'-end was sequenced and shown to contain a number of transcription factor consensus sequences. A major and two minor transcription start sites were identified, respectively, at 152, 178, and 198bp upstream of the translation start site by primer extension analysis. The transcriptional activity of the 1474-bp fragment was analyzed by fusion of 5' deletion constructs to a cat-encoding gene expression vector and transient transfections into Hep G2 cells. A 273-bp fragment located at -112 to +161 relative to the major transcription start site was sufficient for promoter activity. The 3' fragment spanning +3 to +161 and containing a TATA-like element did not demonstrate promoter activity, suggesting that the core promoter resides in a 115-bp sequence located between -112 and +3. This region contains an Inr-like element overlapping the major cap site and a CTF-NF1 element, two potential CCAAT boxes and an AP-2 element partially overlapping an Sp-1 site. Thus, factor I promoter may belong to the TATA-less Inr-driven class II promoters whose transcription is regulated by Sp-1. The transcriptional activity of the 1474-bp 5' flanking fragment was upregulated by PMA, IL-6 and TNF-alpha, suggesting that factor I may be an acute phase reactant.

Involvement of nuclear factor-kappa B in platelet-activating factor-mediated tumor necrosis factor-alpha expression

Tumor necrosis factor (TNF)-alpha and platelet-activating factor (PAF) are important mediators of inflammatory reactions, and their release is controlled by a positive feedback network. However, the regulatory mechanisms underlying the interaction of these two molecules are unknown. Within 10 min of the injection of lipopolysaccharide (LPS) into C57BL/6 mice, effects inducible by PAF such as anaphylactic shock-like symptoms, disseminated intravascular coagulation, and hemorrhage in renal medullae were observed, and all these pathological changes were prevented by the PAF antagonist, BN 50739. The plasma level of PAF after LPS injection reached a peak at 5 min. TNF-alpha gene expression was evident 20 min after LPS injection and was maximal at 40 min, and the level of serum TNF-alpha reached a peak at 1 h. Pretreatment with BN 50739 inhibited LPS-induced TNF-alpha gene expression and protein synthesis in a dose-dependent manner. Injection of PAF or treatment of the macrophage cell line, J774A.1, with PAF activated the transcription factor, nuclear factor (NF)-kappa B, which is essential for inducible TNF-alpha transcription. The activation of NF-kappa B by PAF preceded the LPS-mediated TNF-alpha gene expression. Pretreatment with BN 50739 inhibited LPS-induced mobilization of NF-kappa B in a dose-dependent manner in vivo as well as in vitro. These data suggest that PAF, which is released immediately or shortly after LPS injection, induces the expression of TNF-alpha through the activation of NF-kappa B.

T cell clonal anergy

Recent experiments have elucidated two molecular mechanisms that may account for the failure of anergic T cell clones to initiate IL-2 gene transcription following TCR stimulation. First, a block has been identified in the ERK and JNK mitogen-activated protein kinase pathways; the block results from a failure to activate p21ras. It leads to reduced induction of c-Fos and JunB proteins and to a failure to form and phosphorylate the activator protein (AP)-1 heterodimers required for IL-2 gene transcriptional activation. Second, repressor molecules (Nil-2-a and a molecule related to AP-1) have been characterized that dominantly inhibit IL-2 gene transcription.

Constitutive binding of the transcription factor interleukin-2 (IL-2) enhancer binding factor to the IL-2 promoter

A positive regulatory element in the interleukin-2 (IL-2) promoter, designated the antigen receptor response element-2, is essential for the induction of IL-2 gene expression upon the binding of an inducible multiprotein complex of proteins known as nuclear factor of activated T cells. In the current study, we demonstrated that the winged-helix transcription factor IL-2 enhancer binding factor (ILF) is constitutively expressed in both resting and activated Jurkat cells and binds to two adjacent sequence motifs immediately downstream of the binding site for NFAT. One of these elements has a high degree of homology with consensus binding sites for a variety of winged-helix DNA binding proteins, and the second site functions to modulate ILF binding. Mutagenesis of each of the two sequence elements required for ILF binding decreased IL-2 promoter activity when assayed in transfection assays. Although ILF bound constitutively to the IL-2 promoter, it was not detected as a component of the NFAT complex. These results suggest that important regulatory sequences in the IL-2 promoter are bound by ILF and that this binding may be involved in the control of IL-2 gene expression.

Overexpression of mitogen-activated protein kinase kinase kinase reversed cAMP inhibition of NF-kappaB in T cells

cAMP inhibits T cell activation by acting as an antagonist for selective kinases and transcriptional factors. We have recently demonstrated that cAMP inhibited c-Jun N-terminal kinase (JNK) but left the mitogen-activated protein (MAP) kinase cascade almost unaffected in T lymphocytes. In accordance with recent reports, we also observed a selective suppression of nuclear factor NF-kappaB activation by cAMP. The possible link between the JNK cascade and NF-kappaB activation was demonstrated by the fact that the active form of MAP kinase kinase kinase (deltaMEKK), a constitutive activator of JNK, induced NF-kappaB but not AP-1, Oct, and NF-AT in T cells. In contrast, the induction of MAP kinase kinase (MEK)-MAP kinase did not stimulate NF-kappaB activity. The specific activation of NF-kappaB by a single MEKK-JNK cascade was thus unusual, given that the activation of other transcriptional elements in T cells requires at least two signal pathways. This was further confirmed by the fact that cAMP inhibition of NF-kappaB activation was reversed by overexpression of deltaMEKK.

Tyrosine phosphorylation of I kappa B-alpha activates NF-kappa B without proteolytic degradation of I kappa B-alpha

The transcription factor NF-kappa B regulates genes participating in immune and inflammatory responses. In T lymphocytes, NF-kappa B is sequestered in the cytosol by the inhibitor I kappa B-alpha and released after serine phosphorylation of I kappa B-alpha that regulates its ubiquitin-dependent degradation. We report an alternative mechanism of NF-kappa B activation. Stimulation of Jurkat T cells with the protein tyrosine phosphatase inhibitor and T cell activator pervanadate led to NF-kappa B activation through tyrosine phosphorylation but not degradation of I kappa B-alpha. Pervanadate-induced I kappa B-alpha phosphorylation and NF-kappa B activation required expression of the T cell tyrosine kinase p56ick. Reoxygenation of hypoxic cells appeared as a physiological effector of I kappa B-alpha tyrosine phosphorylation. Tyrosine phosphorylation of I kappa B-alpha represents a proteolysis-independent mechanism of NF-kappa B activation that directly couples NF-kappa B to cellular tyrosine kinase.

The effect of age on the expression of interleukin-2

Interleukin-2 (IL-2) is a growth promoting cytokine that has received a great deal of attention over the past decade with respect to aging and cancer. It is produced primarily by helper T cells and regulates the growth and function of various cells that are involved in cellular and humoral immunity. The expression of IL-2 has been found to decrease with age in humans and rodents. The decline in IL-2 production has been shown to parallel the age-related decrease in immunologic function. Several studies indicate that treatment of lymphocytes from old subjects with exogenous IL-2 or infusion of IL-2 into old animals partially or completely restores some of the immune functions that decline with age. The age-related decline in IL-2 production has been shown to arise from a decline in IL-2 transcription, and a recent study suggests that the transcription factor NFAT (nuclear factor of activated T cells) may play a role in the decline in IL-2 transcription.

Repression of interleukin-2 and interleukin-4 promoters by tumor suppressor protein p53

Interleukin 2 (IL-2) and interleukin 4 (IL-4) secreted by activated but not by resting mature T cells are pleiotropic cytokines affecting growth and differentiation of diverse cell types, such as T cells, B cells, and mast cells. There is little information about the molecular basis for the constitutive repression of IL-2 and IL-4 gene expression in unstimulated T cells. We investigated the possibility that wild-type (wt) p53, a nuclear tumor suppressor protein, might serve to repress IL-2 and IL-4 gene expression in murine E14 T lymphoma and in human Jurkat cells. We transiently cotransfected these cells with constitutive simian virus 40 (SV 40) early promoter expression plasmids overproducing wt or mutant murine p53 and with appropriate luciferase (luc) reporter plasmids containing the promoter elements of murine IL-2 and IL-4 genes to evaluate the effect of various p53 species on these promoters. Murine wt p53 derived from pSG5p53cD strongly repressed the IL-2 and IL-4 promoters in both cell lines induced by the phorbol ester TPA and the Ca2+ ionophore ionomycin but not, however, in uninduced cells. In similar transient transfection experiments with lymphoma cells, overexpression of deletion mutant species of murine p53 revealed that the N-terminal and C-terminal domains are crucial for inhibition of both IL-2 and IL-4 gene expression. These parts of p53 comprise the transactivation domain at the amino terminal side, which has previously also been shown to interact with the TATA-box binding-protein TBP and the carboxy-terminal oligomerization domain. Additionally, it was shown that a previously described inhibitory protein, the high-mobility-group protein HMG-I/Y, does not functionally interact with p53. Cotransfection of expression plasmids for both p53 and HMG-I/Y did not alter the extent of inhibition by the individual proteins. These data suggest that p53 can downmodulate both IL-2 and IL-4 gene expression and that both the transactivation and oligomerization domains of the tumor suppressor protein are essential for this transcriptional repression.

Laboratory indicators for monitoring HIV disease

Immunological monitoring of disease progression following HIV infection and seroconversion illness, latency and AIDS, not only helps in the basic investigation of the natural history of the viral infection in man, but also can assist in prognosis and treatment of AIDS-defining illnesses. However, outside clinical trials, these tests should be selected and used in clinical practice only if they are validated as relevant and effective. The absolute CD4+ T-helper lymphocyte count, measured by flow cytometry, has emerged as the best available investigation, but needs care in sampling due to diurnal and circadian rhythms, effects of age, pregnancy, therapy, intercurrent infections and technique. Sampling should provide a baseline and trends-monthly intervals initially, then quarterly in uncomplicated cases. Thresholds may be given for counts (e.g. 200/microliter) below which prophylaxis against pneumocystis pneumonia should be administered, and repeating persistently low counts (e.g. below 50/microliter) is seldom helpful in practice. Serum levels of beta-2 microglobulin, neopterin and immunoglobulins rarely add information. Physicians and laboratories should have testing guidelines based on clinical audit of best practice, based in turn on scientific understanding of the immunological processes involved.

Interactions of a transcriptional activator in the env gene of the mouse mammary tumor virus with activation-dependent, T cell-specific transacting factors

The mouse mammary tumor virus env gene contains a transcriptional activator (META) that can control transcription of the adjacent long terminal repeat region. Transcriptional control by META parallels that of several lymphokine genes, being specific to T cells, dependent on their activation, and inhibited by the immunosuppressive drug cyclosporine (CsA). DNase I footprinting indicated that nuclear factors from activated T lymphocytes bound a promoter-proximal site, META(P), and a promoter-distal site, META(D+), within the 400-base pair META region. Nuclear factors from unstimulated, but not from activated cells, bound a site, META(D-), adjacent to META(D+). META(D+) directed transcription of a linked luciferase gene, and gel shift analysis revealed binding of inducible, CsA-sensitive T cell factors, in parallel with transfection results. Authentic NFAT and NF-kappaB targets did not compete for the META(D+) binding factor(s). The SV40 core sequence competed for META(D+) binding factors, but META(D+) failed to compete for the complexes obtained with the SV40 probe. Our results, taken together, indicate that META(D+) is a novel transcriptional enhancer element that is similar in its cell-type specificity, activation dependence, and CsA sensitivity to the NFAT element. It may be relevant to the role of MMTV in expression of Mls antigens or the induction of T cell lymphomas.

Transcriptional regulation of the interleukin-2 gene in normal human peripheral blood T cells. Convergence of costimulatory signals and differences from transformed T cells

To study transcriptional regulation in normal human T cells, we have optimized conditions for transient transfection. Interleukin-2 (IL-2) promoter-reporter gene behavior closely parallels the endogenous gene in response to T cell receptor and costimulatory signals. As assessed with mutagenized promoters, the most important IL-2 cis-regulatory elements in normal T cells are the proximal AP-1 site and the NF- kappaB site. Both primary activation, with phytohemagglutinin or antibodies to CD3, and costimulation, provided by pairs of CD2 antibodies or B7-positive (B cells) or B7-negative (endothelial) accessory cells, are mediated through the same cis-elements. Interestingly, the nuclear factor of activated T cell sites are much less important in normal T cells than in Jurkat T cells. We conclude that IL-2 transcriptional regulation differs in tumor cell lines compared with normal T cells and that different costimulatory signals converge on the same cis-elements in the IL-2 promoter.

Effect of staphylococcal enterotoxin B-induced anergy on cytokine gene expression: anergy-sensitive and resistant mRNA expression

We examined the effect of staphylococccal enterotoxin B (SEB)-induced anergy on expression of six different cytokine genes in T cells restimulated with SEB in vitro. We found that although IL-2, IL-3, and IL-4 mRNA levels are substantially reduced in anergic T cells, mRNAs for IL-6, IL-10, IFN-gamma, and TNF-alpha are expressed normally. Thus, there appeared both anergy-sensitive and resistant cytokine mRNA expression in restimulated anergic T cells. The same pattern of cytokine mRNA responses was observed in anergic CD4+ T cells, indicating that the preferential induction of anergy in Th1-like cells is not evident in this in vivo model. Employing TCR V beta 8.2 transgenic mice in which almost all T cells become anergic, we found that the TCR/CD3 complex can transduce both anergy-sensitive and resistant signals. Furthermore, a series of experiments using FK506, A23187, and PMA suggests that signals between TCR and activation of calcineurin and protein kinase C may be blocked in anergic T cells. This is supported by our gel mobility shift assays indicating that calcineurin and/or PMA-inducible NF-ATp, OAP40, and AP-1, but not calcineurin-independent Oct-2, are repressed in anergic spleen T cells upon restimulation with SEB. Taken together, these results suggest that, among signals elicited by stimulation of TCR with SEB, a Ca2+/calcineurin-NF-ATp pathway and other signals, including protein kinase C, are repressed in anergic T cells upstream of their activation, which are essential for the cytokine mRNA expression of the anergy-sensitive type but are dispensible for those of the anergy-resistant type.

Immunosuppression by glucocorticoids: inhibition of NF-kappa B activity through induction of I kappa B synthesis

Glucocorticoids are among the most potent anti-inflammatory and immunosuppressive agents. They inhibit synthesis of almost all known cytokines and of several cell surface molecules required for immune function, but the mechanism underlying this activity has been unclear. Here it is shown that glucocorticoids are potent inhibitors of nuclear factor kappa B (NF-kappa B) activation in mice and cultured cells. This inhibition is mediated by induction of the I kappa B alpha inhibitory protein, which traps activated NF-kappa B in inactive cytoplasmic complexes. Because NF-kappa B activates many immunoregulatory genes in response to pro-inflammatory stimuli, the inhibition of its activity can be a major component of the anti-inflammatory activity of glucocorticoids.

Polyclonal hypergammaglobulinaemia in a case of B-cell chronic lymphocytic leukaemia: the result of IL-2 production by the proliferating monoclonal B cells?

SEQ DATA who developed polyclonal hypergammaglobulinaemia: 38.3 milligrams polyclonal IgG, 0.97 milligram IgA and 0.33 milligram IgM. Immunophenotyping showed a monoclonal lymphocytic population CD19+ CD5+ CD40+ CD23+, low sIg+ (95%), kappa type in the great majority (96%). RT-PCR of immunoglobulin genes gave evidence of monoclonal rearrangement of the IgM type. Our tests showed that IL-2 was produced when leukaemic B cells were stimulated with phorbol myristate acetate, ionomycin and lipopolysaccharide. In addition, transfections with the full IL-2 promoter or elements thereof revealed that IL-2 expression is inducible and mediated through the NF-kB-promoter element. Finally, the amount of IL-2 secreted by these cells is about 39 ng/ml/10(6) cells, which is remarkably high for non-T cells. These results suggest that the large amounts of polyclonal IgG seen in this case of B-CLL are secreted by normal B cells which are in turn stimulated by IL-2 produced by proliferating monoclonal (leukaemic) B cells. Under cyclosporin A treatment, immunoglobulin secretion and B cell count remained low.

Defective expression of early activation genes in cartilage-hair hypoplasia (CHH) with severe combined immunodeficiency (SCID)

Cartilage-hair hypoplasia (CHH) is an autosomal recessive disease of unknown etiology characterized by metaphyseal dysostosis, unpigmented hair, and defective cellular immunity. We studied peripheral blood mononuclear cells (PBMC) of a boy with CHH and combined immunodeficiency in an attempt to characterize further the immune defect in this disease. Stimulation of his PBMC with mitogens was associated with severely depressed IL-2 and interferon-gamma (IFN-gamma) synthesis and IL-2 receptor alpha-chain (IL-2R alpha) expression and resulted in poor lymphocyte proliferation that was only modestly upregulated by the addition of recombinant IL-2 (rIL-2). The defective proliferation and lymphokine synthesis were not corrected by the addition of phorbol myristate acetate (PMA) and ionomycin, agents that bypass receptor-mediated signalling, indicative of a distal abnormality. Importantly, the levels of mRNA encoding c-myc, IL-2R alpha, IL-2 and IFN-gamma were markedly decreased in patient lymphocytes stimulated with PMA+ionomycin as compared to control lymphocytes. The defect in the expression of these early activation genes was selective in that induction by mitogens of mRNA encoding other early activation gene products such as c-fos and c-jun was not impaired. These results suggest that the underlying defect in this patient and perhaps others with CHH may be an abnormality in a component of intracellular signalling pathways or in a trans-acting factor which regulates the expression of a selected number of early activation genes.

Cloning of the cDNA encoding human C/EBP gamma, a protein binding to the PRE-I enhancer element of the human interleukin-4 promoter

The positive regulatory element-I (PRE-I) is a strong enhancer element essential for expression of the human interleukin-4 (IL-4)-encoding gene. In order to identify transcription factors binding to PRE-I, we screened a cDNA expression library from human Jurkat T-cells. A cDNA encoding the human CCAAT/enhancer binding protein-gamma (hC/EBP gamma) was cloned. The deduced amino acid (aa) sequence of HC/EBP gamma contains 150 aa with high homology to mouse Ig/EBP-1 and rat C/EBP gamma. The mRNA of hC/EBP gamma is expressed at a high level in Jurkat T-cells in three forms generated via differential polyadenylation. DNA-binding experiments with recombinant protein produced in bacteria demonstrate that hC/EBP gamma binds to PRE-I, but not to unrelated DNA fragments. Our data also show that hC/EBP gamma may cooperate with Fos to bind PRE-I.

Only one of the two DNA-bound orientations of AP-1 found in solution cooperates with NFATp

BACKGROUND

The transcription factor AP-1 activates the expression of numerous genes in response to mitogenic stimuli. AP-1 regulates gene expression both through solitary binding to independent recognition sites and, in cooperation with various heterologous transcription factors, through targeting to composite response elements. The two subunits that make up the AP-1 heterodimer, Fos and Jun, possess identical residues at positions that make sequence-specific contacts to DNA. This degeneracy leaves the protein with no apparent way of orienting itself uniquely on DNA by differentially recognizing its two non-identical half-sites. Here, we have analyzed the orientation of the AP-1 basic-leucine-zipper (bZip) domain on a cognate site, both alone and in the cooperative complex formed together with the 'nuclear factor of activated T cells' (NFATp).

RESULTS

The results of affinity cleaving experiments demonstrate that, in solution, the AP-1 bZip binds DNA as a mixture of two orientational isomers. However, in the cooperative complex formed with NFATp on a composite response element, the AP-1 bZip adopts a single orientation, with Jun and Fos bound to the NFATp-proximal and NFATp-distal half-sites, respectively. Protein cross-linking experiments demonstrate that protein-protein contacts are responsible for this 'orientational locking'.

CONCLUSIONS

Our results demonstrate that, through protein-protein interactions, one protein can force another to adopt a single DNA-bound orientation. Thus, cooperative interactions between adjacent regulatory proteins can influence not only the energetics of their interactions with DNA, but also their precise geometric and stereochemical arrangement. Because orientational isomers present markedly different structures to the transcriptional apparatus, it seems likely that orientation will exert an effect on the ability to activate transcription.

Interleukin-2 promoter activity in Epstein-Barr virus-transformed B lymphocytes is controlled by nuclear factor-chi B

The regulation of interleukin (IL)-2 gene expression has been investigated mainly in T lymphocytes, the predominant producers of IL-2. However, B cells can also synthesize IL-2. In the present study we analyzed the control of IL-2 promoter activity in Epstein-Barr virus (EBV)-transformed B cell clones which are capable of secreting IL-2 at a low level after stimulation with phorbol 12-myristate 13-acetate and the Ca2+ ionophore ionomycin. Transient transfections using reporter constructs with multiples of transcription factor binding sites from the IL-2 promoter [distal nuclear factor (NF)-AT, proximal NF-AT, AP-1/Octamer (UPS) or NF-chi B (TCEd) sites] were performed. In EBV-transformed B clones, the chi B site exerted the strongest inducible activity; the NF-AT binding sites showed either no or only weak activity compared to Jurkat T cells. An IL-2 promoter bearing a defective NF-chi B site was completely inactive in EBV-transformed B cells, while it still had activity in Jurkat T cells. In seven EBV-B cell clones or lines differing in their capacity to secrete IL-2, the activity of the IL-2 promoter correlated well with the status of IL-2 secretion. Similarly, a human immunodeficiency virus promoter, whose activity is controlled through chi B factors, was found to be active in the IL-2 producing EBV-B cells, but inactive in the non-IL-2-producing cells. Electrophoretic mobility shift assays using protein extracts from EBV-B cells and the IL-2 NF-chi B probe revealed the constitutive generation of chi B complexes in IL-2-secreting cells consisting mainly of heterodimeric p50/p65 complexes. A weaker chi B complex formation and faster-migrating complexes were detected in non-IL-2-secreting cells. These results demonstrate that the IL-2 NF-chi B site is indispensable for the activity of the IL-2 promoter in EBV-transformed B cells, whereas other transcription factors appear to be less important for IL-2 expression in these cells.

A direct physical association between ETS and AP-1 transcription factors in normal human T cells

The Ets and AP-1 families of transcription factors bind distinct DNA elements and subserve diverse functions in multiple lymphoid and nonlymphoid cell types. Functionally important Ets and AP-1 binding sites have been identified in a large number of enhancer elements, suggesting important cooperative interactions between these two families of transcription factors. In this report, we have demonstrated a direct physical interaction between Ets and AP-1 proteins both in vitro and in activated human T cells. This interaction is mediated by the binding of the basic domain of Jun to the Ets domain of Ets proteins. Jun, in association with Ets, is capable of interacting with Fos family members to form a trimolecular protein complex. The physical association between Ets-1 and AP-1 proteins is required for the transcriptional activity of enhancer elements containing adjacent Ets and AP-1 binding sites. We conclude that direct physical interactions between Ets and AP-1 transcription factors play an important role in regulating mammalian gene expression.

Definition of cis-regulatory elements of the mouse interleukin-5 gene promoter. Involvement of nuclear factor of activated T cell-related factors in interleukin-5 expression

We have previously reported that the promoter region of the mouse interleukin-5 (IL-5) gene, extending from a nucleotide position about -1,200 to +33 relative to the transcription initiation site, can mediate transcriptional stimulation by phorbol 12-myristate 13-acetate and dibutyryl cAMP (Bt2cAMP) in mouse thymoma EL-4 cells. Here, we describe identification of four cis-regulatory elements necessary for full activity of the IL-5 promoter, using deletion and mutation analyses. We designated these elements as IL-5A (-948 approximately -933), IL-5P (-117 approximately -92), IL-5C (-74 approximately -56), and IL-5CLE0 (-55 approximately -38). We found that IL-5P bears homology to the binding site for the nuclear factor of activated T cells (NF-AT) and interacted with protein factors in nuclear extracts prepared from EL-4 cells stimulated with phorbol 12-myristate 13-acetate and Bt2cAMP (designated NFIL-5P). NFIL-5P complex was inhibited in the presence of an excess NF-AT and AP1 oligonucleotides and super-shifted by antisera raised against NF-ATp, c-Fos, and c-Jun. It thus seems likely that an NF-AT-related factor is involved in the regulation of IL-5 gene transcription.

Coordinate and cooperative roles for NF-AT and AP-1 in the regulation of the murine IL-4 gene

The transcription factor NF-AT plays an essential role in the inducible transcription of several cytokine genes during T cell activation. The distal NF-AT site of the murine IL-2 promoter binds both NF-AT and AP-1 proteins, and thus represents a composite regulatory site that integrates Ca(2+)- and PKC-dependent signaling pathways in T cell activation. However, the individual contributions of the NF-AT and AP-1 components to promoter activity via this composite site have not been resolved, owing to the absence of a clearly defined AP-1 binding site, which, when mutated abolishes AP-1 binding. We describe here an apparently analogous NF-AT/AP-1 composite site in the murine IL-4 promoter, which can be mutated to selectively block the recruitment of each component. We show that the cooperative and coordinate involvement of both NF-AT and AP-1 is necessary for full activity of the NF-AT/AP-1 composite site, and, ultimately, the entire IL-4 promoter.

Regulation of interferon-gamma mRNA in a cytolytic T cell clone: Ca(2+)-induced transcription followed by mRNA stabilization through activation of protein kinase C or increase in cAMP

Activation pathways inducing the expression of the interferon (IFN)-gamma gene in a cytotoxic T lymphocyte (CTL) clone were studied for their effects on transcription and on mRNA stability. IFN-gamma was secreted by the CTL clone in response to the Ca2+ ionophore ionomycin when used in conjunction with either protein kinase C (PKC)-activating phorbol 12-myristate 13-acetate (PMA) or with agents increasing cAMP, including prostaglandin E2. We describe that ionomycin induced IFN-gamma gene transcription, which was totally inhibited in the presence of cyclosporin A (CSA), an immunosuppressant forming a calcineurin-inhibiting complex with cyclophilin. Ionomycin did not, however, permit accumulation of IFN-gamma mRNA. Activation of PKC by PMA or of cAMP-dependent protein kinase through increase in cAMP had no transcription-inducing effect, either alone or in conjunction with ionomycin, as measured in run on assays of the IFN-gamma gene. When transcription of the IFN-gamma gene, initiated in the presence of ionomycin and an agent increasing intracellular cAMP, was inhibited by CSA in the absence of PKC or cAMP-dependent protein kinase activation, the IFN-gamma mRNA was rapidly degraded (half-life = 30 min). When either PKC was activated or intracellular cAMP was increased at the time of inhibition with CSA, a stabilizing effect was observed on IFN-gamma mRNA, which led to an increase in secreted IFN-gamma. These effects were selective, they did not affect the rate of transcription of the actin gene, nor the accumulation of actin mRNA. These results show that (i) post-transcriptional events can be critical for IFN-gamma expression in activated lymphocytes, and (ii) specific stabilization of IFN-gamma mRNA can be mediated by activation of two different protein kinases involved in T cell activation.

Analysis of proteins that interact with the IL-2 regulatory region in patients with rheumatic diseases

In order to investigate transcriptional regulation of lymphokine genes in rheumatic diseases, peripheral blood mononuclear cells from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and systemic sclerosis (SSc) were analysed for expression of DNA-binding proteins. Nuclear extracts prepared from unstimulated and mitogen-activated cells were studied for their ability to bind to 32P-labelled oligonucleotides containing the AP-1, NF-AT, NF-B and CD28RC sites of the IL-2 promoter. Using gel mobility-shift assay, detection of protein binding to the AP-1 site was reduced in SLE compared with controls. NF-AT binding activity was enhanced in all groups of patients, and was associated with measures of disease activity in RA. In addition, SSc patients showed increased NF-kappa B binding activity. Altered patterns of DNA-binding proteins suggest disturbed intracellular signalling which may contribute to abnormal lymphokine production in rheumatic diseases.

Protein kinase C is not a downstream effector of p21ras in activated T cells

The aim of this present study was to investigate the role of protein kinase C (PKC), downstream of p21ras, in activating interleukin-2 (IL-2) gene expression. It has been reported that PKC is an effector of p21ras in T cells. Data is presented, using the potent and selective PKC inhibitor Ro 31-8425 and transient expression of a constitutively active ras mutant, which clearly shows that PKC is not downstream of p21ras in the induction of NF-AT and AP-1 transcriptional activity and in the expression of IL-2 in human Jurkat T cells. Reporter gene experiments demonstrated that NF-kappa B transcriptional activity is not affected by expression of activated p21ras. The signaling pathways involving PKC activation, calcium mobilization and ras activation combine to provide the necessary components for production of IL-2 during T cell activation.

Hydrogen peroxide as a potent activator of T lymphocyte functions

During inflammatory processes infiltrating cells produce large amounts of reactive oxygen intermediates (ROI). Increasing evidence suggests that ROI besides being cytotoxic may act as important mediators influencing various cellular and immunological processes. In this study, we have investigated the effects of hydrogen peroxide on several aspects of lymphocyte activation. In ESb-L T lymphoma cells, micromolar concentrations of hydrogen peroxide rapidly induced activation of the transcription factor NF-kappa B, whereas DNA-binding activity of the transcription factor AP-1 was virtually not affected. In addition, hydrogen peroxide induced early gene expression of interleukin-2 (IL-2) and the IL-2 receptor alpha chain. The stimulation of IL-2 expression was found to be conferred by a kappa B-like cis-regulatory region within the IL-2 gene promoter. In contrast to these activating effects, addition of hydrogen peroxide was largely inhibitory on cell proliferation which is consistent with a general requirement of thiol compounds for lymphocyte proliferation. However, hydrogen peroxide significantly increased T cell proliferation when applied for a short period under reducing conditions. These data indicate that ROI may act as an important competence signal in T lymphocytes inducing early gene expression as well as cell proliferation.

Expression and biochemical characterization of human protein kinase C-theta

In this study, the recently identified human protein kinase C-theta (PKC-theta) isoform has been biochemically characterized in detail. An antiserum raised against the unique V3 domain of PKC-theta identified an 80-kDa protein in all human T-cell lines tested, in erythroleukemia K562 cells and in histiocytic lymphoma U-937 cells, but not in a B-lymphoma line (Raji) or in several melanoma, carcinoma, schwanoma or astrocytoma lines, confirming, at the protein level, its predominant expression in hematopoietic cell lines, in particular T cells. Immunoreactive PKC-theta was detected almost exclusively in the cytosolic compartment of unstimulated Jurkat T cells. Stimulation with phorbol ester, however, caused rapid translocation to the membrane. In order to compare the properties of PKC-theta with a representative member of the Ca(2+)-dependent PKC enzymes, full-length cDNAs encoding PKC-theta or PKC-alpha were transiently expressed in COS-1 cells, and recombinant enzymes were partially purified via a six-histidine peptide tag. The catalytic activity of these PKC enzymes was assayed against distinct substrates in the absence and presence of known PKC cofactors. Significant differences were found with respect to activation requirements and substrate preferences between PKC-theta and PKC-alpha. Both enzymes were stimulated by phospholipid and phorbol ester, and were active towards a PKC-derived substrate peptide corresponding to the pseudosubstrate site of PKC. In contrast to PKC-alpha, however, full activation of PKC-theta did not require Ca2+, and its basal activity towards histone H1 was not stimulated by lipid cofactors. Additionally, a myelin-basic-protein-(MBP)-derived peptide, which was readily phosphorylated by PKC-alpha, was a poor substrate for PKC-theta. Similar to PKC-alpha, transient PKC-theta overexpression in murine EL4 thymoma cells caused an approximately 2.5-fold increase in the phorbol-12-myristate-13-acetate-induced transcriptional activation of an interleukin-2 promoter-reporter gene construct. The unique expression and functional properties of PKC-theta suggest that it may play a specialized role in T-cell signaling pathways.

Glucocorticoids and the immune system in AIDS

Data reported in the literature show in the majority of cases an increased basal cortisol level in HIV-positive patients compared with controls, although the plasma concentration of cortisol in HIV-positive patients is generally within the physiological range. It is well known that pharmacological doses of glucocorticoids are immunosuppressive, but little is known about the effects of physiological concentrations of cortisol on the immune system. If a dialogue really exists between the HPA axis and the immune system, immune responses should be modulated by physiological concentrations of cortisol, as well as pathological levels of cortisol (high as in Cushing's syndrome or low as in Addison's disease), which are known to be associated with impaired immune system responses. We suggest that in HIV-positive patients, a chronic increase in the basal endogenous cortisol levels may provoke an imbalance in cytokine production, with a decrease in the production of type 1 and an increase in that of type 2. The type 1 to type 2 shift might be synergic with the increased cortisol levels in enhancing viral replication and apoptotic phenomena, and finally in causing the progression of HIV infection.

Binding of AP-1/CREB proteins and of MDBP to contiguous sites downstream of the human TGF-beta 1 gene

Transcription of the human gene encoding transforming growth factor beta 1 (TGF-beta 1), which is a key regulator of cell growth and differentiation, is inducible by phorbol esters. DNA sequences resembling phorbol ester response elements (TREs) are present upstream and downstream of this gene. TREs are recognized by proteins from the AP-1 family of transcription factors. We examined a 16 basepair (bp) sequence downstream of the TGF-beta 1 gene that contains three putative TREs. This sequence had been shown to stimulate reporter gene expression from a downstream location in response to phorbol ester treatment. Electrophoretic mobility shift assays suggest that minor proteins from the related AP-1 and CREB families of transcription factors bind to the overlapping TREs within the 16 bp element. A site beginning at the end of this 16 bp element matches the consensus sequence of a DNA-binding protein called MDBP and was shown to bind to this protein. When the intact MDBP site was present in a reporter gene construct in addition to the TREs, the phorbol ester-induced stimulation of reporter gene expression was no longer observed. This suggests that MDBP can counteract the stimulation of transcription by AP-1/CREB-like proteins binding to this downstream enhancer element.