Early growth response-1 is required for CD154 transcription

The impact of Nucleofection® on the activation state of primary human CD4 T cells

Gene transfer into primary human CD4 T lymphocytes is a critical tool in studying the mechanism of T cell-dependent immune responses and human immunodeficiency virus-1 (HIV-1) infection. Nucleofection® is an electroporation technique that allows efficient gene transfer into primary human CD4 T cells that are notoriously resistant to traditional electroporation. Despite its popularity in immunological research, careful characterization of its impact on the physiology of CD4 T cells has not been documented. Herein, using freshly-isolated primary human CD4 T cells, we examine the effects of Nucleofection® on CD4 T cell morphology, intracellular calcium levels, cell surface activation markers, and transcriptional activity. We find that immediately after Nucleofection®, CD4 T cells undergo dramatic morphological changes characterized by wrinkled and dilated plasma membranes before recovering 1h later. The intracellular calcium level also increases after Nucleofection®, peaking after 1h before recovering 8h post transfection. Moreover, Nucleofection® leads to increased expression of T cell activation markers, CD154 and CD69, for more than 24h, and enhances the activation effects of phytohemagglutinin (PHA) stimulation. In addition, transcriptional activity is increased in the first 24h after Nucleofection®, even in the absence of exogenous stimuli. Therefore, Nucleofection® significantly alters the activation state of primary human CD4 T cells. The effect of transferred gene products on CD4 T cell function by Nucleofection® should be assessed after sufficient resting time post transfection or analyzed in light of the activation caveats mentioned above.

IL-15 prolongs CD154 expression on human CD4 T cells via STAT5 binding to the CD154 transcriptional promoter

Activation-induced CD154 expression on CD4 T cells is prolonged in systemic lupus erythematosus, but the mechanism(s) for its dysregulation are unknown. The studies reported herein demonstrate that interleukin-15 (IL-15) is capable of prolonging CD154 expression on phytohemagglutinin (PHA)-activated CD4 T cells. As IL-15 signals through signal transducer and activator of transcription 5 (STAT5), predicted STAT5 binding sites in the human CD154 transcriptional promoter were identified, and STAT5 binding to the proximal CD154 promoter in vitro and in vivo following primary CD4 T-cell activation was demonstrated. Moreover, overexpression of wild-type STAT5 in primary human CD4 T cells augmented CD154 transcription, whereas overexpression of a dominant-negative (DN) STAT5 protein inhibited CD154 transcription. Mutation of the most proximal STAT5 binding site in the CD154 promoter resulted in diminished DNA binding and reduced CD154 transcriptional activity. Interestingly, STAT5-specific small interfering RNA inhibited CD154 surface expression at 48 but not 24 h after T-cell activation. Thus, these findings provide some of the first evidence to support a possible mechanistic link to explain how the overexpression of IL-15 observed in lupus patients may be involved in the prolonged expression of CD154 that has also been observed on lupus CD4 T cells.

Early growth response-1 (EGR-1) and nuclear factor of activated T cells (NFAT) cooperate to mediate CD40L expression in megakaryocytes and platelets

Increasing evidence implicates circulating platelets as mediators of chronic inflammatory and autoimmune diseases via the expression and release of CD40L, an important modulator of inflammation and adaptive immune responses traditionally associated with activated T cells. Emerging evidence suggests that platelet CD40L is dynamically regulated in several chronic inflammatory and autoimmune diseases and may mediate progression and secondary pathology associated with those disease states. The present study identifies NFATc2 as a key transcriptional modulator of CD40L expression in megakaryocytes and inflammatory activity of platelets. Furthermore, the current data show that EGR-1, a member of the early growth response family of zinc finger transcription factors, modulates NFATc2-dependent regulation of CD40L expression in megakaryocytes. Our novel demonstration that in vivo biochemical or genetic inhibition of NFATc2 activity in megakaryocyte diminishes platelet CD40L implicates the NFATc2/EGR-1 axis as a key regulatory pathway of inflammatory and immunomodulatory activity in platelets and represents a target for the development of therapeutics for the potential treatment of chronic inflammatory and autoimmune diseases.

A transcription factor map as revealed by a genome-wide gene expression analysis of whole-blood mRNA transcriptome in multiple sclerosis

Background

Several lines of evidence suggest that transcription factors are involved in the pathogenesis of Multiple Sclerosis (MS) but complete mapping of the whole network has been elusive. One of the reasons is that there are several clinical subtypes of MS and transcription factors that may be involved in one subtype may not be in others. We investigate the possibility that this network could be mapped using microarray technologies and contemporary bioinformatics methods on a dataset derived from whole blood in 99 untreated MS patients (36 Relapse Remitting MS, 43 Primary Progressive MS, and 20 Secondary Progressive MS) and 45 age-matched healthy controls.

Methodology/Principal Findings

We have used two different analytical methodologies: a non-standard differential expression analysis and a differential co-expression analysis, which have converged on a significant number of regulatory motifs that are statistically overrepresented in genes that are either differentially expressed (or differentially co-expressed) in cases and controls (e.g., V$KROX_Q6, p-value <3.31E-6; V$CREBP1_Q2, p-value <9.93E-6, V$YY1_02, p-value <1.65E-5).

Conclusions/Significance

Our analysis uncovered a network of transcription factors that potentially dysregulate several genes in MS or one or more of its disease subtypes. The most significant transcription factor motifs were for the Early Growth Response EGR/KROX family, ATF2, YY1 (Yin and Yang 1), E2F-1/DP-1 and E2F-4/DP-2 heterodimers, SOX5, and CREB and ATF families. These transcription factors are involved in early T-lymphocyte specification and commitment as well as in oligodendrocyte dedifferentiation and development, both pathways that have significant biological plausibility in MS causation.

Intermedilysin induces EGR-1 expression through calcineurin/NFAT pathway in human cholangiocellular carcinoma cells

Intermedilysin (ILY) is a cholesterol-dependent cytolysin produced by Streptococcus intermedius, which is associated with human brain and liver abscesses. Although intrahepatic bile duct cells play a valuable role in the pathogenesis of liver abscess, the molecular mechanism of ILY-treated intrahepatic bile duct cells remains unknown. In this study, we report that ILY induced a nuclear accumulation of intracellular calcium ([Ca(2+)]i) in human cholangiocellular cells HuCCT1. We also demonstrate that 10 ng/ml ILY induced NFAT1 dephosphorylation and its nuclear translocation in HuCCT1 cells. In contrast to the result that ILY induced NF-κB translocation in human hepatic HepG2 cells, ILY did not affect NF-κB localization in HuCCT1 cells. Dephosphorylation and nuclear translocation of NFAT1 caused by ILY were prevented by [Ca(2+)]i calcium chelator, BAPTA/AM, and calcineurin inhibitors, cyclosporine A and tacrolimus. ILY induced early growth response-1 (EGR-1) expression and it was inhibited by the pre-treatment with cyclosporine A, indicating that the calcineurin/NFAT pathway was involved in EGR-1 expression in response to ILY. ILY-induced calcineurin/NFAT1 activation and sequential EGR-1 expression might be related to the pathogenesis of S. intermedius in human bile duct cells.

EGR-2 is not required for in vivo CD4 T cell mediated immune responses

Background

The zinc finger transcription factor EGR-2 has been shown to play an important role in the induction of T cell anergy and the regulation of peripheral T cell tolerance. In vitro, a prior study has show that T cells deficient in EGR-2 are hyperproliferative to IL-2 and produce elevated levels of the effector cytokine IFN-γ. EGR-2 deficient mice have increased levels of CD44^high T cells in peripheral lymphoid organs, and with age, develop autoimmune-like features.

Principal Findings

Here we show that despite increased numbers of cells bearing an activated CD44^highCD62L^low phenotype, T cells from young healthy EGR-2 deficient mice have normal proliferative and cytokine responses, and the mice themselves mount normal immune responses against minor histocompatibility antigens, and the pathogens Toxoplasma gondii and lymphocytic choriomeningitis virus.

Conclusions

Our results indicate that EGR-2 is not required to mount normal acute in vivo immune responses against foreign antigens, and suggest instead that it may serve to regulate the response to chronic antigenic exposure, such as that which occurs to autoantigens.

Prolonged expression of CD154 on CD4 T cells from pediatric lupus patients correlates with increased CD154 transcription, increased nuclear factor of activated T cell activity, and glomerulonephritis

OBJECTIVE

To assess CD154 expression in patients with pediatric systemic lupus erythematosus (SLE) and to explore a transcriptional mechanism that may explain dysregulated expression of CD154.

METHODS

Cell surface CD154 expression (pre- and postactivation) in peripheral blood CD4 T cells from 29 children with lupus and 29 controls matched for age, sex, and ethnicity was examined by flow cytometry. CD154 expression was correlated with clinical features, laboratory parameters, and treatments received. Increased CD154 expression on CD4 T cells from the SLE patients was correlated with CD154 message and transcription rates by real-time reverse transcription-polymerase chain reaction (RT-PCR) and nuclear run-on assays, respectively. Nuclear factor of activated T cell (NF-AT) transcription activity and mRNA levels in CD4 T cells from SLE patients were explored by reporter gene analysis and real-time RT-PCR, respectively.

RESULTS

CD154 surface protein levels were increased 1.44-fold in CD4 T cells from SLE patients as compared with controls in cells evaluated 1 day postactivation ex vivo. This increase correlated clinically with the presence of nephritis and an elevated erythrocyte sedimentation rate. Increased CD154 protein levels also correlated with increased CD154 mRNA levels and with CD154 transcription rates, particularly at later time points following T cell activation. Reporter gene analyses revealed a trend for increased NF-AT, but decreased activator protein 1 and similar NF-kappaB, activity in CD4 T cells from SLE patients as compared with controls. Moreover, NF-AT1 and, in particular, NF-AT2 mRNA levels were notably increased in CD4 T cells from SLE patients as compared with controls.

CONCLUSION

Following activation, cell surface CD154 is increased on CD4 T cells from pediatric lupus patients as compared with controls, and this increase correlates with the presence of nephritis, increased CD154 transcription rates, and increased NF-AT activity. These results suggest that NF-AT/calcineurin inhibitors, such as tacrolimus and cyclosporine, may be beneficial in the treatment of lupus nephritis.

Early growth response transcription factors and the modulation of immune response: implications towards autoimmunity

Early Growth Response (EGR) zinc finger transcription factors are induced under diverse mitogenic signals on different cell types such as lymphocytes. Their genetic expression does not require de novo protein synthesis, which suggests its role as immediate response mediators between cell surface receptor signaling and gene expression regulation. EGR factors are involved in modulating the immune response, by means of the induction of differentiation of lymphocyte precursors, activation of T and B cells, as well as their involvement in central and peripheral tolerance. The maturation state, particularly for B cells, and signaling through the T or B cell receptors seems to be quite relevant for the induction of the expression of these transcription factors. EGR-1 functions as a positive regulatory factor for B and T cells mediated by transcriptional regulation of key cytokines and costimulatory molecules, and its interaction with NFAT. On the opposite, EGR-2 and 3 act as negative regulators involved in anergy induction and apoptosis. EGR-2 and 3 deficiency has been related to the development of lupus like disease in murine models. The deficiency of these transcription factors has been associated to deficient Cbl-b expression, a resistant to anergy phenotype, and expansion of effector and activated T cells.

FOXP3 inhibits activation-induced NFAT2 expression in T cells thereby limiting effector cytokine expression

The forkhead DNA-binding protein FOXP3 is critical for the development and suppressive function of CD4(+)CD25(+) regulatory T cells (T(REG)), which play a key role in maintaining self-tolerance. Functionally, FOXP3 is capable of repressing transcription of cytokine genes regulated by NFAT. Various mechanisms have been proposed by which FOXP3 mediates these effects. Using novel cell lines that inducibly express either wild-type or mutant FOXP3, we have identified NFAT2 as an early target of FOXP3-mediated transcriptional repression. NFAT2 is typically expressed at low levels in resting T cells, but is up-regulated by NFAT1 upon cellular activation. We demonstrate that transcription from the NFAT2 promoter is significantly suppressed by FOXP3, and NFAT2 protein expression is markedly diminished in activated CD4(+)CD25(+)FOXP3(+) T(REG) compared with CD4(+)CD25(-)FOXP3(-) T cells. Chromatin immunoprecipitation experiments indicate that FOXP3 competes with NFAT1 for binding to the endogenous NFAT2 promoter. This antagonism of NFAT2 activity by FOXP3 is important for the anergic phenotype of T(REG), as ectopic expression of NFAT2 from a retroviral LTR partially restores expression of IL-2 in FOXP3(+) T(REG). These data suggest that FOXP3 functions not only to suppress the first wave of NFAT-mediated transcriptional responses, but may also affect sustained NFAT-mediated inflammatory gene expression through suppression of inducible NFAT2 transcription.

T-bet expression is regulated by EGR1-mediated signaling in activated T cells

T-bet is a Th1-specific transcription factor that is directly involved in three important pathways for Th1 cell differentiation, namely TCR signaling, and the IFN-gamma-STAT1 and IL-12-STAT4 pathways. A recent study also showed that T-bet plays a vital role in innate immunity. However, the molecular mechanism responsible for transcriptional activation of T-bet during T cell development is not yet known. Here, we characterize the essential human T-bet promoter elements and show that binding of EGR1 to this promoter induces T-bet transcription. Notably, overexpression of EGR1 transactivates and, synergistically in concert with TCR signaling, induces T-bet expression in activated T cells. In contrast, depletion of EGR1 significantly decreases T-bet induction. Finally, we report a positive correlation between EGR1 and T-bet expression during T helper cell differentiation. Collectively, these findings provide molecular insight into T-bet transcription and suggest that EGR1 is an upstream regulator of T-bet induction.

A T-cell-specific CD154 transcriptional enhancer located just upstream of the promoter

CD154 (CD40-ligand) is a critical immune regulator. CD154 expression is tightly regulated and largely restricted to activated CD4 T cells. Using DNase I hypersensitivity site (HSS) mapping, we identified two novel HSS mapping to the human CD154 promoter element and just upstream. Both HSS were activation independent and CD4 T-cell specific. Approximately 350 bp of DNA sequence flanking the upstream HSS site was highly conserved between mouse and man, and was rich in binding sites for GATA and NFAT proteins. Gel shift and chromatin immunoprecipitation assays demonstrated both NFAT1 and the Th2 factor, GATA-3, bound this enhancer element in vitro and in vivo, respectively. A PstI/XbaI 345 bp fragment of this region acted as a transcriptional enhancer of the CD154 promoter in primary human CD4 T cells. Overexpression of repressor of GATA and a dominant negative GATA-3 protein independently inhibited transcription, whereas overexpression of wild-type GATA-3 enhanced transcriptional activity, by this element in primary CD4 T cells. Moreover, more interleukin-4-producing CD4 T cells expressed CD154 following activation than interferon-gamma-producing CD4 T cells. Thus, we identified a novel T-cell-specific, GATA-3 responsive, CD154 transcriptional enhancer, which may contribute to increased propensity of Th2 cells to express CD154.

Egr-1 regulates expression of the glial scar component phosphacan in astrocytes after experimental stroke

Ischemic brain injury causes tissue damage and neuronal death. The deficits can often be permanent because adult neurons fail to regenerate. One barrier to neuronal regeneration is the formation of the glial scar, a repair mechanism that is otherwise necessary to seal off necrotic areas. The process of gliosis has been well described, but the mechanisms regulating the robust production of scar components after injury remain poorly understood. Here we show that the early growth response 1 transcriptional factor (Egr-1, also called Krox24, Zif268, and NGFI-A) is expressed in astrocytes in the ventricular wall, corpus callosum, and striatum of normal mouse brain. After experimental stroke caused by permanent occlusion of the middle cerebral artery, Egr-1 was expressed long term in reactive astrocytes that accumulate around the injury site. Gain- and loss-of-function studies in primary astrocytes indicated that Egr-1 regulates the transcription of chondroitin sulfate proteoglycans genes, the main extracellular matrix proteins of the glial scar. Egr-1 bound to a site within the phosphacan promoter and transactivated its expression. Egr-1-deficient mice accumulated lower levels of phosphacan RNA and protein than wild-type mice after stroke, but there were no measurable differences in neurite outgrowth toward the infarct area between the two groups. Our findings suggest that Egr-1 is an important component of the transcriptional network regulating genes involved in gliosis after ischemic injury.

Opposing regulation of T cell function by Egr-1/NAB2 and Egr-2/Egr-3

TCR-induced NF-AT activation leads to the up-regulation of multiple genes involved in T cell anergy. Since NF-AT is also involved in T cell activation, we have endeavored to dissect TCR-induced activating and inhibitory genetic programs. This approach revealed roles for the early growth response (Egr) family of transcription factors and the Egr coactivator/corepressor NGFI-A-binding protein (NAB)2 in regulating T cell function. TCR-induced Egr-1 and NAB2 enhance T cell function, while Egr-2 and Egr-3 inhibit T cell function. In this report, we demonstrate that Egr-2 and Egr-3 are induced by NF-AT in the absence of AP-1, while Egr-1 and NAB2 both require AP-1-mediated transcription. Our data suggest that Egr-3 is upstream of Egr-2, and that mechanistically Egr-2 and Egr-3 suppress Egr-1 and NAB2 expression. Functionally, T cells from Egr-2 and Egr-3 null mice are hyperresponsive while T cells from Egr-3 transgenic, overexpressing mice are hyporesponsive. Furthermore, an in vivo model of autoimmune pneumonitis reveals that T cells from Egr-3 null mice hasten death while Egr-3-overexpressing T cells cause less disease. Overall, our data suggest that just as the Egr/NAB network of genes control cell fate in other systems, TCR-induced Egr-1, 2, 3 and NAB2 control the fate of antigen recognition in T cells.

Transcription factors NFAT2 and Egr1 cooperatively regulate the maturation of T-lymphoma in vitro

We have demonstrated that transcription factors Egr1 and NFAT2 cooperate in regulation of the early stages of T-lymphocyte development, whereas the related factors Egr2 and Egr3 do not cooperate with NFAT2. Egr1 and NFAT2 are shown to cooperatively control gene expression of the regulatory factor Id3 and recombinase Rag2, whose functions are critical for T-lymphocyte differentiation. Thus, the concerted action of the transcription factors Egr1 and NFAT2 can play a crucial role in regulation of the T cell differentiation in vitro due to the cooperative regulation of Id3 and Rag2 gene expression.

Inhibitory effects and target genes of bone morphogenetic protein 6 in Jurkat TAg cells

Bone morphogenetic proteins (BMP) are multifunctional cytokines that belong to the TGF-beta superfamily. BMP have been shown to regulate haematopoietic stem cells, B lymphopoiesis and early thymocyte differentiation. In the present study we explored the role of BMP-6 in Jurkat TAg cells. BMP-6 rapidly induced phosphorylation of Smad1/5/8, p38 and ERK1/2, followed by a potent up-regulation of ID1, ID2 and ID3. ID1 and ID3 were also induced at the protein level. Genome-wide expression profiling of cells treated with BMP-6 compared to medium confirmed that ID1-ID3 were target genes of BMP-6 together with Noggin and Smad6. Furthermore, several genes involved in transcriptional regulation were also identified, including NFKBIA, HEY1, DLX2, KLF10 and early growth response 1. Stimulation with BMP-6 exerted an antiproliferative effect that was counteracted by inhibitor of DNA binding (Id)1 siRNA, indicating that Id1 is an important downstream mediator in Jurkat TAg cells. A subset of CD4(+) T cells were found to express the BMP receptors Alk-2 and Alk-3 (type I), in addition to BMPRII (type II). BMP-6 also induced phosphorylation of Smad1/5/8, followed by transcriptional increase in ID1-ID3 mRNA expression. However, we did not observe significant changes in Id protein expression in CD4(+) T cells. Altogether, the data indicate a role for BMP-6 in human T lineage cells.

Early growth response 1 and NF-ATc1 act in concert to promote thymocyte development beyond the beta-selection checkpoint

Development of immature T cell precursors beyond the beta-selection checkpoint is regulated by signals transduced by the pre-TCR complex. The pre-TCR-induced differentiation program is orchestrated by a network of transcription factors that serve to integrate this signaling information. Among these transcription factors are those of the early growth response (Egr) and NF-AT families. In this study, we demonstrate that Egr1 and NF-ATc1 act together to promote development of T cell precursors beyond the beta-selection checkpoint to the CD8 immature single-positive and CD4+ CD8+ double-positive stages. Moreover, we find that Egr1 and NF-AT cooperatively induce the expression of inhibitor of DNA binding 3 (Id3), a regulatory factor known to play an important role in positive selection of thymocytes, but not previously demonstrated to be required for beta-selection. Importantly, we show in this study that Id3 deficiency abrogates the ability of ectopically expressed Egr1 to promote traversal of the beta-selection checkpoint. Id3 is presumably essential for traversal of the beta-selection checkpoint in this context because of the inability of other inhibitor of DNA binding family members to compensate, since transgenic Egr1 does not induce expression of inhibitor of DNA binding 1 (Id1) or 2 (Id2). Taken together, these data demonstrate that Id3 is a cooperatively induced target that is important for Egr-mediated promotion of development beyond the beta-selection checkpoint. Moreover, these data indicate that the ERK and calcium signaling pathways may converge during beta-selection through the concerted action of Egr1 and NF-ATc1, respectively.

Estrogen and CD4+ T cells

PURPOSE OF REVIEW

Many autoimmune rheumatic autoimmune disorders predominantly affect women. Sex hormones, in particular estrogen, can influence CD4 T-helper development and function. We highlight recent studies that begin to provide insights into the mechanisms by which estrogen modulates CD4 T-cell development and function, and thus potentially contribute to disease pathogenesis.

RECENT FINDINGS

High levels of estrogen can lead to thymic atrophy. Recent studies showed that this phenomenon results from effects of estrogen at multiple stages in early T-cell development. Estrogen is also known to affect mature CD4 T-cell function, and, in particular, their ability to produce selected cytokine profiles. The mechanisms by which estrogen can exert these effects were also recently explored and shown to include effects on expression of critical molecules known to be involved in these processes.

SUMMARY

Dissecting the molecular pathways employed by estrogen to modulate CD4 T cells will be critical in elucidating the manner by which estrogen exerts its effects on this compartment. Given that cell type specific differences underlie the ability of many hormonal therapies to exert tissue-specific estrogenic or antiestrogenic activities, this knowledge will be crucial to further exploitation of hormonal therapies in rheumatic autoimmune diseases.

Suppression of growth factor expression and human vascular smooth muscle cell growth by small interfering RNA targeting EGR-1

Smooth muscle cell (SMC) proliferation and migration are key processes that occur in the reparative response to injury after percutaneous coronary intervention and in failed bypass grafts for the treatment of atherosclerosis. In the present study, we generated novel synthetic small interfering RNA (siRNA) molecules targeting the coding region of human early growth response-1 (EGR-1) mRNA that attenuate the expression of EGR-1 and that of fibroblast growth factor-2 (FGF-2) and granulocyte-colony stimulating factor (G-CSF). These agents suppressed SMC proliferation in a dose-dependent and non-toxic manner and blocked SMC regrowth from the wound edge following mechanical injury in vitro. In contrast, the scrambled counterpart did not inhibit SMC proliferation, EGR-1 protein expression or SMC regrowth after injury. These findings demonstrate that EGR-1 siRNA can serve as inhibitors of SMC proliferation and wound repair suggesting that these agents may potentially be useful in the control of vascular proliferative disorders.

Increased levels of NF-ATc2 differentially regulate CD154 and IL-2 genes in T cells from patients with systemic lupus erythematosus

T cells from patients with systemic lupus erythematosus (SLE) are characterized by heightened TCR-initiated free intracytoplasmic calcium responses. We demonstrate that activated T cells from SLE patients, but not from rheumatoid arthritis patients, displayed higher levels of the calcineurin-dependent transcription factor NF-ATc2 in the nucleus compared with control T cells. DNA NF-AT-binding activity was also increased, as was the amount of NF-ATc2 bound to the promoters of CD154 (CD40L) and IL-2 genes. Nevertheless, although high NF-ATc2 levels translated into higher CD154 transcription in SLE, IL-2 transcription was decreased. The absence of important transcriptional activators (AP-1, NF-kappaBeta) and the presence of transcriptional repressors (cAMP response element modulator) on the IL-2 promoter explain this dichotomous effect.

Estrogen does not regulate CD154 mRNA stability in systemic lupus erythematosus T cells

Previous studies in our laboratory showed a dose-dependent and hormone-specific increase in CD154 expression in T cells from females with systemic lupus erythematosus (SLE). This present study investigates if the estrogen-dependent increase in CD154 expression is due to stabilization of the messenger RNA. T cells from female SLE patients and controls were cultured for 18 h in serum-free medium without and with estradiol 17-beta (10(-7) M). T cells were either unstimulated (resting) or were activated by further culture on anti-CD3 coated plates. Actinomycin D (25 microg/mL) was added to parallel cultures to inhibit new messenger RNA synthesis. CD154 messenger RNA stability was assessed by reverse-transcription polymerase chain amplification. Resting SLE (n = 10, P = 0.88) and normal (n = 7, P = 0.65) T cells showed no significant differences in message stability in response to estradiol. CD154 messenger RNA was also not significantly stabilized in activated SLE (n = 10, P = 0.15) or activated normal (n = 6, P = 0.077) T cells in response to estradiol. These findings indicate that the estrogen-dependent increase in CD154 in SLE T cells is not due to stability of the mRNA. These data are consistent with the postulate that estradiol stimulates CD154 transcription in SLE T cells.

Deregulated expression of CD40 ligand in HTLV-I infection: distinct mechanisms of downregulation in HTLV-I-transformed cell lines and ATL patients

HTLV-I infection is associated with the development of adult T cell leukemia (ATL) and the neuroinflammatory disease HAM/TSP. There are quantitative and qualitative differences in the antiviral cytotoxic T cell (CTL) response in ATL and HAM/TSP although the underlying mechanisms are unclear. Here, we demonstrate that the HTLV-I Tax trans-activating protein is a transcriptional activator of CD40 ligand (CD40L), a critical regulator of dendritic cell maturation and adaptive immunity. Tax activates CD40L expression via a cyclosporin A insensitive pathway that is also independent of NF-kappaB. Although Tax upregulates CD40L gene expression, CD40L expression is absent in Tax-expressing HTLV-I-transformed cell lines via an epigenetic mechanism involving methylation. T lymphocytes cultured ex vivo from ATL patients, but not HAM/TSP or normal controls, exhibit a potent block in the induction of CD40L, but not CD69. However, the CD40L gene is not silenced by methylation in ATL patients, thus CD40L is downregulated by distinct mechanisms in HTLV-I-transformed cell lines and ATL patients.

Cutting Edge: TCR-induced NAB2 enhances T cell function by coactivating IL-2 transcription

TCR engagement leads to the up-regulation of genetic programs that can both activate and inhibit T cell function. The early growth receptor (Egr) proteins Egr-2 and Egr-3 have recently been identified as TCR-induced negative regulators of T cell function. NAB2 (NGFI-A-binding protein 2) is both a coactivator and a corepressor of Egr-mediated transcription and has been implicated in regulating Schwann cell myelination. In this report we demonstrate that NAB2 is induced by TCR engagement and that its expression is enhanced by the presence of costimulation. The overexpression of NAB2 enhanced IL-2 production while small interfering RNA to NAB2 markedly inhibited IL-2 expression. Mechanistically, we demonstrate that NAB2 enhances IL-2 transcription by acting as a coactivator for Egr-1. Indeed, chromatin immunoprecipitation analysis reveals that NAB2 is recruited to the Egr-1 binding site of the IL-2 promoter. Taken together, our findings identify NAB2 as a novel coactivator of T cell function.

Phylogenetic analysis of the promoter region of the CD40L gene in primates and other mammals

CD40L is a type II membrane protein comprised of 261 amino acids. CD40L plays a crucial role in the immune system where it is primarily expressed on activated T cells and triggers immunoglobulin class switching. The genetic disease X-linked hypergammaglobulinemia (HIGM1, XHIGM or XHIM) is caused by mutations in the CD40L gene. Individuals with HIGM1 are susceptible to recurrent infections to pathogens and a relationship has been shown to exist with malaria [Sabeti, P., Usen, S., Farhadian, S., Jallow, M., Doherty, T., Newport, M., Pinder, M., Ward, R., Kwiatkowski, D., 2002a. CD40L association with protection from severe malaria. Genes Immun. 3, 286-291]. In this paper, we phylogenetically examine the promoter region of CD40L in primates and other mammals via phylogenetic shadowing. This analysis revealed several regions of the CD40L promoter that were highly constrained and thereby inferred to be functional. These constrained regions confirmed many known regulatory sites. In addition, a novel, highly constrained upstream region was also identified which had an NF-AT recognition motif. These analyses also showed that the different mammal groups do not share an exactly similar set of promoter binding sites and taxon-specific promoters have evolved.

Update on the treatment of lupus nephritis

Lupus nephritis (LN) is a major cause of morbidity and mortality in patients with systemic lupus erythematosus. Although the use of aggressive immunosuppression has improved both patient and renal survival over the past several decades, the optimal treatment of LN remains challenging. Improved outcomes have come at the expense of significant adverse effects owing to therapy. Moreover with long-term survival, the chronic adverse effects of effective therapies including risk of malignancy, atherosclerosis, infertility, and bone disease all become more important. Finally, some patients fail to achieve remission with standard cytotoxic therapy and others relapse when therapy is reduced. For these reasons, recent clinical trials have attempted to define alternate treatment protocols that appear to be efficacious in achieving and maintaining remission, but with less toxicity than standard regimens. This paper discusses established and newer treatment options for patients with proliferative and membranous LN, with an emphasis on the results of these recent clinical trials. We also review the experimental and human data regarding some of the novel targeted forms of therapy that are under investigation and in different phases of clinical trials.

Transcription factors TFE3 and TFEB are critical for CD40 ligand expression and thymus-dependent humoral immunity

TFE3 and TFEB are broadly expressed transcription factors related to the transcription factor Mitf. Although they have been linked to cytokine signaling pathways in nonlymphoid cells, their function in T cells is unknown. TFE3-deficient mice are phenotypically normal, whereas TFEB deficiency causes early embryonic death. We now show that combined inactivation of TFE3 and TFEB in T cells resulted in a hyper-immunoglobulin M syndrome due to impaired expression of CD40 ligand by CD4(+) T cells. Native TFE3 and TFEB bound to multiple cognate sites in the promoter of the gene encoding CD40 ligand (Cd40lg), and maximum Cd40lg promoter activity and gene expression required TFE3 or TFEB. Thus, TFE3 and TFEB are direct, physiological and mutually redundant activators of Cd40lg expression in activated CD4(+) T cells critical for T cell-dependent antibody responses.