Phosphorylation and O-linked glycosylation of Elf-1 leads to its translocation to the nucleus and binding to the promoter of the TCR zeta-chain

Combining Selective Enrichment and a Boosting Approach to Globally and Site-Specifically Characterize Protein Co-translational O-GlcNAcylation

Protein O-GlcNAcylation plays extremely important roles in mammalian cells, regulating signal transduction and gene expression. This modification can happen during protein translation, and systematic and site-specific analysis of protein co-translational O-GlcNAcylation can advance our understanding of this important modification. However, it is extraordinarily challenging because normally O-GlcNAcylated proteins are very low abundant and the abundances of co-translational ones are even much lower. Here, we developed a method integrating selective enrichment, a boosting approach, and multiplexed proteomics to globally and site-specifically characterize protein co-translational O-GlcNAcylation. The boosting approach using the TMT labeling dramatically enhances the detection of co-translational glycopeptides with low abundance when enriched O-GlcNAcylated peptides from cells with a much longer labeling time was used as a boosting sample. More than 180 co-translational O-GlcNAcylated proteins were site-specifically identified. Further analyses revealed that among co-translational glycoproteins, those related to DNA binding and transcription are highly overrepresented using the total identified O-GlcNAcylated proteins in the same cells as the background. Compared with the glycosylation sites on all glycoproteins, co-translational sites have different local structures and adjacent amino acid residues. Overall, an integrative method was developed to identify protein co-translational O-GlcNAcylation, which is very useful to advance our understanding of this important modification.

ETS transcription factors: Multifaceted players from cancer progression to tumor immunity

The E26 transformation specific (ETS) family comprises 28 transcription factors, the majority of which are involved in tumor initiation and development. Serving as a group of functionally heterogeneous gene regulators, ETS factors possess a structurally conserved DNA-binding domain. As one of the most prominent families of transcription factors that control diverse cellular functions, ETS activation is modulated by multiple intracellular signaling pathways and post-translational modifications. Disturbances in ETS activity often lead to abnormal changes in oncogenicity, including cancer cell survival, growth, proliferation, metastasis, genetic instability, cell metabolism, and tumor immunity. This review systematically addresses the basics and advances in studying ETS factors, from their tumor relevance to clinical translational utility, with a particular focus on elucidating the role of ETS family in tumor immunity, aiming to decipher the vital role and clinical potential of regulation of ETS factors in the cancer field.

Bladder Cancer-Derived Small Extracellular Vesicles Promote Tumor Angiogenesis by Inducing HBP-Related Metabolic Reprogramming and SerRS O-GlcNAcylation in Endothelial Cells

A malformed tumour vascular network provokes the nutrient-deprived tumour microenvironment (TME), which conversely activates endothelial cell (EC) functions and stimulates neovascularization. Emerging evidence suggests that the flexible metabolic adaptability of tumour cells helps to establish a metabolic symbiosis among various cell subpopulations in the fluctuating TME. In this study, the authors propose a novel metabolic link between bladder cancer (BCa) cells and ECs in the nutrient-scarce TME, in which BCa-secreted glutamine-fructose-6-phosphate aminotransferase 1 (GFAT1) via small extracellular vesicles (sEVs) reprograms glucose metabolism by increasing hexosamine biosynthesis pathway flux in ECs and thus enhances O-GlcNAcylation. Moreover, seryl-tRNA synthetase (SerRS) O-GlcNAcylation at serine 101 in ECs promotes its degradation by ubiquitination and impeded importin α5-mediated nuclear translocation. Intranuclear SerRS attenuates vascular endothelial growth factor transcription by competitively binding to the GC-rich region of the proximal promotor. Additionally, GFAT1 knockout in tumour cells blocks SerRS O-GlcNAcylation in ECs and attenuates angiogenesis both in vitro and in vivo. However, administration of GFAT1-overexpressing BCa cells-derived sEVs increase the angiogenetic activity in the ECs of GFAT1-knockout mice. In summary, this study suggests that inhibiting sEV-mediated GFAT1 secretion from BCa cells and targeting SerRS O-GlcNAcylation in ECs may serve as novel strategies for BCa antiangiogenetic therapy.

Myeloid-derived suppressor cells and the pathogenesis of human immunodeficiency virus infection

There are several mechanisms by which human immunodeficiency virus (HIV) can mediate immune dysfunction and exhaustion during the course of infection. Chronic immune activation, after HIV infection, seems to be a key driving force of such unwanted consequences, which in turn worsens the pathological status. In such cases, the immune system is programmed to initiate responses that counteract unwanted immune activation, for example through the expansion of myeloid-derived suppressor cells (MDSCs). Although the expansion of immune suppressor cells in the setting of systemic chronic immune activation, in theory, is expected to contain immune activation, HIV infection is still associated with a remarkably high level of biomarkers of immune activation. Paradoxically, the expansion of immune suppressor cells during HIV infection can suppress potent anti-viral immune responses, which in turn contribute to viral persistence and disease progression. This indicates that HIV hijacks not only immune activation but also the immune regulatory responses to its advantage. In this work, we aim to pave the way to comprehend how such unwanted expansion of MDSCs could participate in the pathology of acute/primary and chronic HIV infection in humans, as well as simian immunodeficiency virus infection in rhesus macaques, according to the available literature.

Post-translational modifications in T cells in systemic erythematosus lupus

Systemic erythematosus lupus (SLE) is a classic autoimmune disease characterized by multiple autoantibodies and immune-mediated tissue damage. The aetiology of this disease is still unclear. A new drug, belimumab, which acts against the B-lymphocyte stimulator (BLyS), can effectively improve the condition of SLE patients, but it cannot resolve all SLE symptoms. The discovery of novel, precise therapeutic targets is urgently needed. It is well known that abnormal T-cell function is one of the most crucial factors contributing to the pathogenesis of SLE. Protein post-translational modifications (PTMs), including phosphorylation, glycosylation, acetylation, methylation, ubiquitination and SUMOylation have been emphasized for their roles in activating protein activity, maintaining structural stability, regulating protein-protein interactions and mediating signalling pathways, in addition to other biological functions. Summarizing the latest data in this area, this review focuses on the potential roles of diverse PTMs in regulating T-cell function and signalling pathways in SLE pathogenesis, with the goal of identifying new targets for SLE therapy.

Lipopolysaccharide Induces GFAT2 Expression to Promote O-Linked β-N-Acetylglucosaminylation and Attenuate Inflammation in Macrophages

Glycosylation with O-linked β-N-acetylglucosamine (O-GlcNAcylation) is a reversible posttranslational modification that regulates the activity of intracellular proteins according to glucose availability and its metabolism through the hexosamine biosynthesis pathway. This modification has been involved in the regulation of various immune cell types, including macrophages. However, little is known concerning the mechanisms that regulate the protein O-GlcNAcylation level in these cells. In the present work, we demonstrate that LPS treatment induces a marked increase in protein O-GlcNAcylation in RAW264.7 cells, bone marrow-derived and peritoneal mouse macrophages, as well as human monocyte-derived macrophages. Targeted deletion of OGT in macrophages resulted in an increased effect of LPS on NOS2 expression and cytokine production, suggesting that O-GlcNAcylation may restrain inflammatory processes induced by LPS. The effect of LPS on protein O-GlcNAcylation in macrophages was associated with an increased expression and activity of glutamine fructose 6-phosphate amidotransferase (GFAT), the enzyme that catalyzes the rate-limiting step of the hexosamine biosynthesis pathway. More specifically, we observed that LPS potently stimulated GFAT2 isoform mRNA and protein expression. Genetic or pharmacological inhibition of FoxO1 impaired the LPS effect on GFAT2 expression, suggesting a FoxO1-dependent mechanism. We conclude that GFAT2 should be considered a new LPS-inducible gene involved in regulation of protein O-GlcNAcylation, which permits limited exacerbation of inflammation upon macrophage activation.

Nutrient regulation of signaling and transcription

In the early 1980s, while using purified glycosyltransferases to probe glycan structures on surfaces of living cells in the murine immune system, we discovered a novel form of serine/threonine protein glycosylation (O-linked β-GlcNAc; O-GlcNAc) that occurs on thousands of proteins within the nucleus, cytoplasm, and mitochondria. Prior to this discovery, it was dogma that protein glycosylation was restricted to the luminal compartments of the secretory pathway and on extracellular domains of membrane and secretory proteins. Work in the last 3 decades from several laboratories has shown that O-GlcNAc cycling serves as a nutrient sensor to regulate signaling, transcription, mitochondrial activity, and cytoskeletal functions. O-GlcNAc also has extensive cross-talk with phosphorylation, not only at the same or proximal sites on polypeptides, but also by regulating each other's enzymes that catalyze cycling of the modifications. O-GlcNAc is generally not elongated or modified. It cycles on and off polypeptides in a time scale similar to phosphorylation, and both the enzyme that adds O-GlcNAc, the O-GlcNAc transferase (OGT), and the enzyme that removes O-GlcNAc, O-GlcNAcase (OGA), are highly conserved from C. elegans to humans. Both O-GlcNAc cycling enzymes are essential in mammals and plants. Due to O-GlcNAc's fundamental roles as a nutrient and stress sensor, it plays an important role in the etiologies of chronic diseases of aging, including diabetes, cancer, and neurodegenerative disease. This review will present an overview of our current understanding of O-GlcNAc's regulation, functions, and roles in chronic diseases of aging.

O-GlcNAc Modification During Pregnancy: Focus on Placental Environment

Successful placentation is a key event for fetal development, which commences following embryo implantation into the uterine wall, eliciting decidualization, placentation, and remodeling of blood vessels to provide physiological exchange between embryo-fetus and mother. Several signaling pathways are recruited to modulate such important processes and specific proteins that regulate placental function are a target for the glycosylation with O-linked β-N-acetylglucosamine (O-GlcNAc), or O-GlcNAcylation. This is a reversible post-translational modification on nuclear and cytoplasmic proteins, mainly controlled by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). O-GlcNAcylation has been implicated as a modulator of proteins, both in physiological and pathological conditions and, more recently, O-GlcNAc has also been shown to be an important modulator in placental tissue. In this mini-review, the interplay between O-GlcNAcylation of proteins and placental function will be addressed, discussing the possible implications of this post-translational modification through placental development and pregnancy.

O-GlcNAc: a novel regulator of immunometabolism

The rapidly expanding field of immunometabolism focuses on how metabolism controls the function of immune cells. CD4⁺ T cells are essential for the adaptive immune response leading to the eradication of specific pathogens. However, when T cells are inappropriately over-active, they can drive autoimmunity, allergic disease, and chronic inflammation. The mechanisms by which metabolic changes influence function in CD4⁺ T cells are not fully understood. The post-translational protein modification, O-GlcNAc (O-linked β-N-acetylglucosamine), dynamically cycles on and off of intracellular proteins as cells respond to their environment and flux through metabolic pathways changes. As the rate of O-GlcNAc cycling fluctuates, protein function, stability, and/or localization can be affected. Thus, O-GlcNAc is critically poised at the nexus of cellular metabolism and function. This review highlights the intra- and extracellular metabolic factors that influence CD4⁺ T cell activation and differentiation and how O-GlcNAc regulates these processes. We also propose areas of future research that may illuminate O-GlcNAc's role in the plasticity and pathogenicity of CD4⁺ T cells and uncover new potential therapeutic targets.

Green Tea Polyphenol EGCG Upregulates Tollip Expression by Suppressing Elf-1 Expression

TLR signaling is critical to innate immune system regulation; however, aberrant TLR signaling is involved in several diseases, including insulin resistance, Alzheimer's disease, and tumor metastasis. Moreover, a recent study found that TLR-4 signaling pathway inhibition might be a target for the suppression of chronic inflammatory disorders. In this article, we show that the green tea polyphenol epigallocatechin-3-O-gallate (EGCG) increases the expression of Toll interacting protein, a strong inhibitor of TLR4 signaling, by suppressing the expression of E74-like ETS transcription factor 1 (Elf-1). A mechanistic study revealed that EGCG suppressed Elf-1 expression via protein phosphatase 2A/cyclic GMP (cGMP)-dependent mechanisms. We also confirmed that orally administered EGCG and a cGMP inducer upregulated Toll interacting protein expression, increased intracellular levels of cGMP in macrophages, and suppressed Elf-1 expression. These data support EGCG and a cGMP inducer as potential candidate suppressors of TLR4 signaling.

O-GlcNAc cycling and the regulation of nucleocytoplasmic dynamics

The dynamic carbohydrate post-translational modification (PTM) O-linked β-N-acetyl glucosamine (O-GlcNAc) is found on thousands of proteins throughout the nucleus and cytoplasm, and rivals phosphorylation in terms of the number of substrates and pathways influenced. O-GlcNAc is highly conserved and essential in most organisms, with disruption of O-GlcNAc cycling linked to diseases ranging from cancer to neurodegeneration. Nuclear pore proteins were the first identified O-GlcNAc-modified substrates, generating intense and ongoing interest in understanding the role of O-GlcNAc cycling in nuclear pore complex structure and function. Recent advances in detecting and altering O-GlcNAcylation levels have provided insights into many mechanisms by which O-GlcNAcylation influences the nucleocytoplasmic localization and stability of protein targets. The emerging view is that the multifunctional enzymes of O-GlcNAc cycling are critical nutrient-sensing components of a complex network of signaling cascades involving multiple PTMs. Furthermore, O-GlcNAc plays a role in maintaining the structural integrity of the nuclear pore and regulating its function as the gatekeeper of nucleocytoplasmic trafficking.

The antiproliferative ELF2 isoform, ELF2B, induces apoptosis in vitro and perturbs early lymphocytic development in vivo

Background

ELF2 (E74-like factor 2) also known as NERF (new Ets-related factor), a member of the Ets family of transcription factors, regulates genes important in B and T cell development, cell cycle progression, and angiogenesis. Conserved ELF2 isoforms, ELF2A, and ELF2B, arising from alternative promoter usage can exert opposing effects on target gene expression. ELF2A activates, whilst ELF2B represses, gene expression, and the balance of expression between these isoforms may be important in maintaining normal cellular function.

Methods

We compared the function of ELF2 isoforms ELF2A and ELF2B with other ELF subfamily proteins ELF1 and ELF4 in primary and cancer cell lines using proliferation, colony-forming, cell cycle, and apoptosis assays. We further examined the role of ELF2 isoforms in haemopoietic development using a Rag1^-/-murine bone marrow reconstitution model.

Results

ELF2B overexpression significantly reduced cell proliferation and clonogenic capacity, minimally disrupted cell cycle kinetics, and induced apoptosis. In contrast, ELF2A overexpression only marginally reduced clonogenic capacity with little effect on proliferation, cell cycle progression, or apoptosis. Deletion of the N-terminal 19 amino acids unique to ELF2B abrogated the antiproliferative and proapoptotic functions of ELF2B thereby confirming its crucial role. Mice expressing Elf2a or Elf2b in haemopoietic cells variously displayed perturbations in the pre-B cell stage and multiple stages of T cell development. Mature B cells, T cells, and myeloid cells in steady state were unaffected, suggesting that the main role of ELF2 is restricted to the early development of B and T cells and that compensatory mechanisms exist. No differences in B and T cell development were observed between ELF2 isoforms.

Conclusions

We conclude that ELF2 isoforms are important regulators of cellular proliferation, cell cycle progression, and apoptosis. In respect to this, ELF2B acts in a dominant negative fashion compared to ELF2A and as a putative tumour suppressor gene. Given that these cellular processes are critical during haemopoiesis, we propose that the regulatory interplay between ELF2 isoforms contributes substantially to early B and T cell development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0446-7) contains supplementary material, which is available to authorized users.

Expression of transmembrane protein 26 (TMEM26) in breast cancer and its association with drug response

We have previously shown that stromal cells desensitize breast cancer cells to the anti-estrogen fulvestrant and, along with it, downregulate the expression of TMEM26 (transmembrane protein 26). In an effort to study the function and regulation of TMEM26 in breast cancer cells, we found that breast cancer cells express non-glycosylated and N-glycosylated isoforms of the TMEM26 protein and demonstrate that N-glycosylation is important for its retention at the plasma membrane. Fulvestrant induced significant changes in expression and in the N-glycosylation status of TMEM26. In primary breast cancer, TMEM26 protein expression was higher in ERα (estrogen receptor α)/PR (progesterone receptor)-positive cancers. These data suggest that ERα is a major regulator of TMEM26. Significant changes in TMEM26 expression and N-glycosylation were also found, when MCF-7 and T47D cells acquired fulvestrant resistance. Furthermore, patients who received aromatase inhibitor treatment tend to have a higher risk of recurrence when tumoral TMEM26 protein expression is low. In addition, TMEM26 negatively regulates the expression of integrin β1, an important factor involved in endocrine resistance. Data obtained by spheroid formation assays confirmed that TMEM26 and integrin β1 can have opposite effects in breast cancer cells. These data are consistent with the hypothesis that, in ERα-positive breast cancer, TMEM26 may function as a tumor suppressor by impeding the acquisition of endocrine resistance. In contrast, in ERα-negative breast cancer, particularly triple-negative cancer, high TMEM26 expression was found to be associated with a higher risk of recurrence. This implies that TMEM26 has different functions in ERα-positive and -negative breast cancer.

The hematopoietic regulator, ELF-1, enhances the transcriptional response to Interferon-β of the OAS1 anti-viral gene

Interferon (IFN) therapy is effective in treating cancers, haematological and virus induced diseases. The classical Jak/Stat pathway of IFN signal transduction leading to changes in transcriptional activity is well established but alone does not explain the whole spectrum of cellular responses to IFN. Gene promoters contain cis-acting sequences that allow precise and contextual binding of transcription factors, which control gene expression. Using the transcriptional response to IFN as a starting point we report a high frequency of tandem GGAA motifs in the proximal promoters of Interferon stimulated genes, suggesting a key regulatory action. Utilizing the well-characterized anti-viral gene, OAS1, as an example Interferon stimulated gene promoter containing such a duplicated GGAA motif, we have demonstrated a regulatory role of this promoter in response to IFN by mutation analysis. Furthermore, we identified ELF-1 as a direct binding factor at this motif. Additionally, recruitment of RB1 and SP1 factors to the promoter following IFN stimulation is shown. ELF-1 overexpression enhanced and knockdown of ELF-1 inhibited full activation of OAS1 by IFN stimulation. Collectively, ELF-1 binds an important duplicated GGAA cis-acting element at the OAS1 promoter and in cooperation with RB1 and SP1 recruitment contributes to regulation in response to IFN stimulation.

In HIV-positive patients, myeloid-derived suppressor cells induce T-cell anergy by suppressing CD3ζ expression through ELF-1 inhibition

OBJECTIVE

During HIV infection, a down-modulation of CD3ζ was found on T cells, contributing to T-cell anergy. In this work, we studied the correlation between myeloid-derived suppressor cells (MDSC) frequency and T-cell CD3ζ expression. Moreover, we investigated the mechanisms of CD3ζ decrease exploited by MDSC.

DESIGN AND METHOD

CD3ζ expression and MDSC frequency were evaluated by flow cytometry on peripheral blood mononuclear cells from 105 HIV-positive (HIV+) patients. The role of MDSC in the modulation of the HIV-specific T-cell response was evaluated. The level of CD3ζ mRNA and ELF-1 protein were analysed by real-time-PCR and western blot, respectively.

RESULTS

We found that granulocytic-MDSC (Gr-MDSC) were expanded in HIV+ patients compared with healthy donors; in particular, in cART-treated individuals a higher Gr-MDSC frequency was observed in patients with a CD4 T-cell count below 400 cells/μl. We found an inverse correlation between the percentage of Gr-MDSC and CD3ζ level. Moreover, in-vitro MDSC depletion induced the up-regulation of CD3ζ in T cells, restoring the functionality of αβ, but not γδ T cells. The in-vitro effect of isolated MDSC on CD3ζ expression was found cell contact-dependent, and was not mediated by previously described molecules. CD3ζ down-modulation corresponds to the decrease of its mRNA induced by silencing the transcription factor ELF-1.

CONCLUSION

Our data provide new knowledge on mechanisms used by Gr-MDSC in immune-modulation and on their role in the immune reconstitution during antiviral treatments.

Lead poisoning influences TCR-related gene expression patterns in peripheral blood T-lymphocytes of exposed workers

Previous studies have shown that occupational lead (Pb) exposure might influence human T-lymphocyte function, including such as changes in T-cell receptor (TCR) Vβ and Vγ repertoire and in expression of the TCRζ gene. Thus, the study here further investigated expression of TCRζ-related factors and the FcεRIγ gene (whose product has a functional role complementary to the TCRζ chain) and the Elf-1 gene whose product is involved in regulation of TCR expression. Quantitative real-time RT-PCR was used to measure expression of TCRζ, FcεRIγ, and Elf-1 genes in peripheral blood mononuclear cells (PBMC) isolated from 17 Pb-exposed workers. Samples were collected before and after the workers had undergone chelation therapy regimens. Twenty-three healthy individuals served as controls. The results showed that TCRζ, FcεRIγ, and Elf-1 gene expression in Pb-exposed workers before chelation therapy was significantly lower than in PBMC from healthy individuals. After chelation therapy, expression of TCRζ appeared to trend toward normal levels; in comparison, lower expressions of FcεRIγ and Elf-1 persisted. In conclusion, the previously-documented impairment of T-lymphocyte functions and T- lymphocyte-mediated immune responses seen previously in response to occupational Pb exposure might be attributable, in part, to effects on TCR signaling pathways - including those related to TCRζ and FcεRIγ - and to any down-regulation of membrane TCRζ expression/activity that might be associated with Pb-induced effects on Elf-1 expression.

Molecular mechanisms of ETS transcription factor-mediated tumorigenesis

The E26 transformation-specific (ETS) family of transcription factors is critical for development, differentiation, proliferation and also has a role in apoptosis and tissue remodeling. Changes in expression of ETS proteins therefore have a significant impact on normal physiology of the cell. Transcriptional consequences of ETS protein deregulation by overexpression, gene fusion, and modulation by RAS/MAPK signaling are linked to alterations in normal cell functions, and lead to unlimited increased proliferation, sustained angiogenesis, invasion and metastasis. Existing data show that ETS proteins control pathways in epithelial cells as well as stromal compartments, and the crosstalk between the two is essential for normal development and cancer. In this review, we have focused on ETS factors with a known contribution in cancer development. Instead of focusing on a prototype, we address cancer associated ETS proteins and have highlighted the diverse mechanisms by which they affect carcinogenesis. Finally, we discuss strategies for ETS factor targeting as a potential means for cancer therapeutics.

The applied basic research of systemic lupus erythematosus based on the biological omics

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by the production of autoantibodies directed against nuclear self-antigens and circulating immune complexes. This results in damages to various organs or systems, including skin, joints, kidneys and the central nervous system. Clinical manifestations of SLE could be diverse, including glomerulonephritis, dermatitis, thrombosis, vasculitis, seizures and arthritis. The complicated pathogenesis and varied clinical symptoms of SLE pose great challenges in the diagnosis and monitoring of this disease. Unfortunately, the etiological factors and pathogenesis of SLE are still not completely understood. It is noteworthy that recent advances in our understanding of the biological omics and emerging technologies have been providing new tools in the analyses of SLE, such as genomics, epigenomics, transcriptomics, proteomics, metabolomics and so on. In this article, we summarize our current knowledge in this field for a better understanding of the pathogenesis, diagnosis and treatment for SLE.

Decreased O-GlcNAcylation of the key proteins in kinase and redox signalling pathways is a novel mechanism of the beneficial effect of α-lipoic acid in diabetic liver

The present study aimed to investigate the effects of the treatment with a-lipoic acid (LA), a naturally occurring compound possessing antioxidant activity, on liver oxidant stress in a rat model of streptozotocin (STZ)-induced diabetes by examining potential mechanistic points that influence changes in the expression of antioxidant enzymes such as catalase (CAT) and CuZn/Mn superoxide dismutase(s) (SOD). LA was administered for 4 weeks by daily intraperitoneal injections (10 mg/kg) to STZ-induced diabetic rats, starting from the last STZ treatment. LA administration practically normalised the activities of the indicators of hepatocellular injury, alanine and aspartate aminotransferases, and lowered oxidative stress, as observed by the thiobarbituric acid-reactive substance assay, restored the reduced glutathione:glutathione disulphide ratio and increased the protein sulfhydryl group content. The lower level of DNA damage detected by the comet assay revealed that LA reduced cytotoxic signalling, exerting a hepatoprotective effect. The LA-treated diabetic rats displayed restored specific enzymatic activities of CAT, CuZnSOD and MnSOD. Quantitative real-time PCR analysis showed that LA restored CAT gene expression to its physiological level and increased CuZnSOD gene expression, but the gene expression of MnSOD remained at the diabetic level. Although the amounts of CAT and CuZnSOD protein expression returned to the control levels, the protein expression of MnSOD was elevated. These results suggested that LA administration affected CAT and CuZnSOD expression mainly at the transcriptional level, and MnSOD expression at the post-transcriptional level. The observed LA-promoted decrease in the O-GlcNAcylation of extracellular signal-regulated kinase, protein 38 kinase, NF-kB, CCAAT/enhancer-binding protein and the antioxidative enzymes themselves in diabetic rats suggests that the regulatory mechanisms that supported the changes in antioxidative enzyme expression were also influenced by post-translational mechanisms.

Expression of ESE-3 isoforms in immunogenic and tolerogenic human monocyte-derived dendritic cells

Dendritic cells (DC) are the only hematopoietic cells expressing the epithelial specific Ets transcription factor ESE-3. Here we analyzed presence and quantity of isoforms ESE-3a, ESE-3b and ESE-3j in various immunogenic and tolerogenic human monocyte-derived DC (moDC) and blood DC populations using quantitative real time PCR and immunoblot analyses. ESE-3a and ESE-3b were detectable in all moDC populations with ESE-3b being the main transcript. ESE-3b expression was upregulated in immunogenic moDC and downregulated in tolerogenic moDC compared to immature moDC. ESE-3a had similar transcript levels in immature and immunogenic moDC and had very low levels in tolerogenic moDC. In blood DC populations only splice variant ESE-3b was detectable. ESE-3j was not detectable in any of the DC populations. These findings suggest that ESE-3b is the functionally most important ESE-3 isoform in DC.

DUSP4 deficiency enhances CD25 expression and CD4+ T-cell proliferation without impeding T-cell development

The differentiation and activation of T cells are critically modulated by MAP kinases, which are in turn feed-back regulated by dual-specificity phosphatases (DUSPs) to determine the duration and magnitude of MAP kinase activation. DUSP4 (also known as MKP2) is a MAP kinase-induced DUSP member that is dynamically expressed during thymocyte differentiation. We generated DUSP4-deficient mice to study the function of DUSP4 in T-cell development and activation. Our results show that thymocyte differentiation and activation-induced MAP kinase phosphorylation were comparable between DUSP4-deficient and WT mice. Interestingly, activated DUSP4(-/-) CD4(+) T cells were hyperproliferative while DUSP4(-/-) CD8(+) T cells proliferated normally. Further mechanistic studies suggested that the hyperproliferation of DUSP4(-/-) CD4(+) T cells resulted from enhanced CD25 expression and IL-2 signaling through increased STAT5 phosphorylation. Immunization of DUSP4(-/-) mice recapitulated the T-cell hyperproliferation phenotype in antigen recall responses, while the profile of Th1/Th2-polarized antibody production was not altered. Overall, these results suggest that other DUSPs may compensate for DUSP4 deficiency in T-cell development, MAP kinase regulation, and Th1/Th2-mediated antibody responses. More importantly, our data indicate that DUSP4 suppresses CD4(+) T-cell proliferation through novel regulations in STAT5 phosphorylation and IL-2 signaling.

A striking common O-linked N-acetylglucosaminyl moiety between cruzipain and myosin

Single units of O-linked N-acetylglucosamine (GlcNAc), usually components of nuclear and cytoplasmatic proteins, are present at the C-terminal domain of cruzipain (Cz), a lysosomal major antigen from Trypanosoma cruzi. On the other hand, antibodies directed against some self-antigens like myosin are associated with Chagas heart disease. The participation of O-GlcNAc moieties in the molecular antigenicity of Cz was determined using GlcNAc linked to aprotinin by ELISA. The immune cross-reactivity between Cz and myosin is mainly focused in the C-T domain. ELISA inhibition assays using rabbit sera specific for Cz and C-T in conjunction with immune-gold electron microscopy analysis of heart tissues from mice immunized with C-T confronted with polyclonal rabbit sera specific for Cz and C-T prior and after myosin adsorption provided evidence which indicates that O-GlcNAc moieties constitute a common epitope between Cz and either myosin or other cardiac O-GlcNAc-containing proteins, showing a new insight into the molecular immune pathogenesis of Chagas heart disease.

Transcription of the Tollip gene is elevated in intestinal epithelial cells through impaired O-GlcNAcylation-dependent nuclear translocation of the negative regulator Elf-1

Intestinal epithelial cells (IECs) must be tolerant of the large number of commensal bacteria inhabiting the intestinal tract to avoid excessive inflammatory reactions. Toll-interacting protein (Tollip), a negative regulator of Toll-like receptor signaling, is known to be expressed at high levels in IECs, and to thereby contribute to the hyporesponsiveness of IECs to commensals. In this study, we analyzed the underlying mechanisms for elevated transcription of the Tollip gene in IECs using a human IEC line, Caco-2, and a human monocyte line, THP-1, as a control. Elf-1 was identified as a transcription factor that negatively regulates Tollip gene expression. The transcription factor Elf-1 was localized in the nucleus by O-linked N-acetylglucosamine (O-GlcNAc) modification, whereas the unmodified form was detected only in the cytoplasm. Comparison of Caco-2 and THP-1 cells revealed that O-GlcNAc modification of Elf-1 was significantly lower in IECs than in monocytes. Collectively, the results indicate that insufficient O-GlcNAc modification prevents Elf-1-mediated transcriptional repression and thereby upregulates Tollip gene expression in IECs.

ELF1 is associated with systemic lupus erythematosus in Asian populations

Systemic lupus erythematosus (SLE) is an autoimmune disease with a strong genetic involvement. The susceptibility genes identified so far can only explain a small proportion of disease heritability. Through a genome-wide association in a Hong Kong Chinese cohort and subsequent replication in two other Asian populations, with a total of 3164 patients and 4482 matched controls, we identified association of ELF1 (E74-like factor 1) with SLE (rs7329174, OR = 1.26, joint P= 1.47 × 10(-8)). ELF1 belongs to the ETS family of transcription factors and is known to be involved in T cell development and function. Database analysis revealed transcripts making use of three alternative exon1s for this gene. Near equivalent expression levels of distinct transcripts initiated from alternative exon1s were detected in peripheral blood mononuclear cells from both SLE patients and healthy controls. Although a direct association of rs7329174 with the three forms of transcripts for this gene was not detected, these findings support an important role of ELF1 in SLE susceptibility and suggest a potentially tight regulation for the expression of this gene.

Transcriptional regulation of Elf-1: locus-wide analysis reveals four distinct promoters, a tissue-specific enhancer, control by PU.1 and the importance of Elf-1 downregulation for erythroid maturation

Ets transcription factors play important roles during the development and maintenance of the haematopoietic system. One such factor, Elf-1 (E74-like factor 1) controls the expression of multiple essential haematopoietic regulators including Scl/Tal1, Lmo2 and PU.1. However, to integrate Elf-1 into the wider regulatory hierarchies controlling haematopoietic development and differentiation, regulatory elements as well as upstream regulators of Elf-1 need to be identified. Here, we have used locus-wide comparative genomic analysis coupled with chromatin immunoprecipitation (ChIP-chip) assays which resulted in the identification of five distinct regulatory regions directing expression of Elf-1. Further, ChIP-chip assays followed by functional validation demonstrated that the key haematopoietic transcription factor PU.1 is a major upstream regulator of Elf-1. Finally, overexpression studies in a well-characterized erythroid differentiation assay from primary murine fetal liver cells demonstrated that Elf-1 downregulation is necessary for terminal erythroid differentiation. Given the known activation of PU.1 by Elf-1 and our newly identified reciprocal activation of Elf-1 by PU.1, identification of an inhibitory role for Elf-1 has significant implications for our understanding of how PU.1 controls myeloid-erythroid differentiation. Our findings therefore not only represent the first report of Elf-1 regulation but also enhance our understanding of the wider regulatory networks that control haematopoiesis.

Modulation of transcription factor function by O-GlcNAc modification

O-linked beta-N-acetylglucosamine (O-GlcNAc) modification of nuclear and cytoplasmic proteins is important for many cellular processes, and the number of proteins that contain this modification is steadily increasing. This modification is dynamic and reversible, and in some cases competes for phosphorylation of the same residues. O-GlcNAc modification of proteins is regulated by cell cycle, nutrient metabolism, and other extracellular signals. Compared to protein phosphorylation, which is mediated by a large number of kinases, O-GlcNAc modification is catalyzed only by one enzyme called O-linked N-acetylglucosaminyl transferase or OGT. Removal of O-GlcNAc from proteins is catalyzed by the enzyme beta-N-acetylglucosaminidase (O-GlcNAcase or OGA). Altered O-linked GlcNAc modification levels contribute to the establishment of many diseases, such as cancer, diabetes, cardiovascular disease, and neurodegeneration. Many transcription factors have been shown to be modified by O-linked GlcNAc modification, which can influence their transcriptional activity, DNA binding, localization, stability, and interaction with other co-factors. This review focuses on modulation of transcription factor function by O-linked GlcNAc modification.

A review of post-translational modifications and subcellular localization of Ets transcription factors: possible connection with cancer and involvement in the hypoxic response

Post-translational modifications and subcellular localizations modulate transcription factors, generating a code that is deciphered into an activity. We describe our current understanding of these processes for Ets factors, which have recently been recognized for their importance in various biological processes. We present the global picture for the family, and then focus on particular aspects related to cancer and hypoxia. The analysis of Post-translational modification and cellular localization is only beginning to enter the age of "omic," high content, systems biology. Our snap-shots of particularly active fields point to the directions in which new techniques will be needed, in our search for a more complete description of regulatory pathways.

Effects of facial nerve axotomy on Th2- and Th1-associated chemokine expression in the facial motor nucleus of wild-type and presymptomatic mSOD1 mice

We have previously demonstrated a neuroprotective mechanism of facial motoneuron (FMN) survival after facial nerve axotomy that is dependent on CD4(+) Th2 cell interaction with peripheral antigen-presenting cells, as well as CNS resident microglia. To investigate this mechanism, we chose to study the Th2-associated chemokine, CCL11, and Th1-associated chemokine, CXCL11, in wild-type and presymptomatic mSOD1 mice after facial nerve axotomy. In this report, the results indicate that CCL11 is constitutively expressed in the uninjured facial motor nucleus, but CXCL11 is not expressed at all. Facial nerve axotomy induced a shift in CCL11 expression from FMN to astrocytes, whereas CXCL11 was induced in FMN. Differences in the number of CCL11- and CXCL11-expressing cells were observed between WT and mSOD1 mice after facial nerve axotomy.

O-GlcNAc inhibits interaction between Sp1 and Elf-1 transcription factors

The novel protein modification, O-linked N-acetylglucosamine (O-GlcNAc), plays an important role in various aspects of cell regulation. Although most of nuclear transcription regulatory factors are modified by O-GlcNAc, O-GlcNAc effects on transcription remain largely undefined yet. In this study, we show that O-GlcNAc inhibits a physical interaction between Sp1 and Elf-1 transcription factors, and negatively regulates transcription of placenta and embryonic expression oncofetal protein gene (Pem). These findings suggest that O-GlcNAc inhibits Sp1-mediated gene transcription possibly by interrupting Sp1 interaction with its cooperative factor.

Glycobiology in the cytosol: the bitter side of a sweet world

Progress in glycobiology has undergone explosive growth over the past decade with more of the researchers now realizing the importance of glycan chains in various inter- and intracellular processes. However, there is still an area of glycobiology awaiting exploration. This is especially the case for the field of "glycobiology in the cytosol" which remains rather poorly understood. Yet evidence is accumulating to demonstrate that the glycoconjugates and their recognition molecules (i.e. lectins) are often present in this subcellular compartment.

PP2A dephosphorylates Elf-1 and determines the expression of CD3zeta and FcRgamma in human systemic lupus erythematosus T cells

T cells from patients with systemic lupus erythematosus are characterized by decreased expression of CD3zeta-chain and increased expression of FcRgamma-chain, which becomes part of the CD3 complex and contributes to aberrant signaling. Elf-1 enhances the expression of CD3zeta, whereas it suppresses the expression of FcRgamma gene and lupus T cells have decreased amounts of DNA-binding 98 kDa form of Elf-1. We show that the aberrantly increased PP2A in lupus T cells dephosphorylates Elf-1 at Thr-231. Dephosphorylation results in limited expression and binding of the 98 kDa Elf-1 form to the CD3zeta and FcRgamma promoters. Suppression of the expression of the PP2A leads to increased expression of CD3zeta and decreased expression of FcRgamma genes and correction of the early signaling response. Therefore, PP2A serves as a central determinant of abnormal T cell function in human lupus and may represent an appropriate treatment target.

Oncogenic activation of the human Pygopus2 promoter by E74-like factor-1

Pygopus is a component of the T-cell factor/beta-catenin transcriptional complex essential for activation of Wnt target genes and is also required for cell regulation in the absence of Wnt signaling. Human Pygopus2 (hPygo2) is overexpressed in a high proportion of breast and epithelial ovarian malignant tumors and is required for the growth of several cell lines derived from these carcinomas. The mechanisms regulating hPygo2 gene activation, however, are unknown. Here, we have determined cis- and trans-interacting factors responsible for hPygo2 expression in cancer. The minimal region required for a maximal 109-fold activation of the hPygo2 promoter in MCF-7 breast cancer cells is 48 bp upstream of the start of transcription. Within 25 bp of the transcriptional start, there are two overlapping tandem Ets transcription factor-binding sites, which are critical for hPygo2 promoter activity. In vitro DNA pull-down assays and proteomic analyses identified the Ets family members Elk-1 and E74-like factor-1 (Elf-1) as potential hPygo2 promoter binding factors, whereas in vivo chromatin immunoprecipitation assays verified that only Elf-1 specifically bound to the hPygo2 promoter in MCF-7 cells. Modulation of elf-1 in MCF-7 cells by silencing via RNA interference or overexpression caused a corresponding decrease or increase, respectively, in hPygo2 promoter activity. Overexpression of Elf-1 in HeLa cells, in which Elf-1 is expressed at a lower level than in MCF-7 cells, caused a 4-fold increase in endogenous hPygo2 mRNA levels. These results provide new evidence that Elf-1 is involved in transcriptional activation of hPygo2. Like hPygo2, previous studies implicated Elf-1 in breast and ovarian cancer and our present findings suggest that the oncogenic requirement of hPygo2 is fulfilled, in part, by Elf-1.

Histone H1 is released from myonuclei and present in rimmed vacuoles with DNA in inclusion body myositis

To investigate myonuclear alterations in sporadic inclusion body myositis (s-IBM), we immuno-localized histones in muscles in 11 patients. The examination showed that vacuolar rims were frequently positive for histone H1. In triple-color fluorescence study, the H1-positive products were found on the inner side of an emerin-positive circle with DNA. Moreover, H1-positive materials appeared to be released into the cytoplasm in some vacuoles and myonuclei. The localization of H1 was different from phosphorylated Elk-1, which is a nuclear protein, but abnormally accumulated in the cytoplasm in s-IBM. The results strongly support the hypothesis that rimmed vacuoles are derived from the nucleus. The cytoplasmic H1-release suggests dysfunction of nuclear membranes in an early phase of the nuclear disintegration. We hypothesize that, in s-IBM muscles, compromised nuclear envelope may permit release of some nuclear components such as histone H1 and cannot facilitate the incorporation of others to the nucleus as in pElk-1.

Requirement for O-linked N-acetylglucosaminyltransferase in lymphocytes activation

The dynamic modification of nuclear and cytoplasmic proteins with O-linked beta-N-acetylglucosamine (O-GlcNAc) by the O-linked N-acetylglucosaminyltransferase (OGT) is a regulatory post-translational modification that is responsive to various stimuli. Here, we demonstrate that OGT is a central factor for T- and B-lymphocytes activation. SiRNA-mediated knockdown of OGT in T cells leads to an impaired activation of the transcription factors NFAT and NFkappaB. This results in a reduction of IL-2 production consistent with prevention of T-cell activation. OGT is also required for the early activation of B cells mediated by stimulation of the B-cell receptor. Mechanistically, we demonstrate that NFkappaB as well as NFAT are glycosylated with O-GlcNAc after direct binding to OGT. Moreover, kinetic experiments show that O-GlcNAc modification prominently increased shortly after activation of lymphoid cells and it might be required for nuclear translocation of the transcription factors NFkappaB and NFAT.

Elf-1 Binds to GGAA Elements on the FcRγ Promoter and Represses Its Expression

The Fc receptor (FcR) gamma-chain has been shown to be up-regulated in T cells when the TCR zeta-chain is decreased. We demonstrate that Elf-1, but not other Ets family transcription factors, bind to a cluster of GGAA sites located within the 200 bp upstream from the transcription initiation site of the FcRgamma promoter. Forced expression of Elf-1 results in the suppression of FcRgamma expression, whereas silencing its expression with small interfering RNA Elf-1 results in increased FcRgamma expression. Elf-1 represents the first transcription factor identified to be involved in the transcriptional regulation of FcRgamma, and cells that fail to express Elf-1, as is the case with human systemic lupus erythematosus T cells, will express FcRgamma-chain.

Decreased TCR zeta-chain expression in T cells from patients with acquired aplastic anaemia

In aplastic anaemia, T cells have a central role in the pathophysiology of bone marrow destruction. This study showed that T cells from patients with aplastic anaemia expressed decreased T-cell receptor (TCR) zeta-chain protein and mRNA levels compared to healthy controls. Patients with decreased TCR zeta-chain showed an abnormal response in intracellular calcium following stimulation through the TCR. We also observed an altered pattern of the transcription factors CREMalpha and Elf-1 that are implicated in zeta-chain transcription. We concluded that TCR zeta-chain expression was decreased in the majority of patients with aplastic anaemia, regardless of disease activity or treatment status.

Dynamics of a simple regulatory switch

We consider the dynamics of a model toggle switch abstracted from the genetic interactions operative in a fungal stress response circuit. The switch transduces an external signal and propagates it forward by mediating the transport between compartments of two interacting gene products. The transport between compartments is assumed to be related to the degree of association between the interacting proteins, a fact for which there exists a wealth of biological evidence. The ubiquity and modularity of this cellular control mechanism warrants a detailed study of the dynamics entailed by various modelling assumptions. Specifically, we consider a general gate model in which both of the associating proteins are freely transportable between compartments. A more restrictive, but biologically supported model, is considered in which only one of the two proteins undergoes transport. Under the strong assumption that the disassociation of the interacting proteins is unidirectional we show that the qualitative dynamics of the two models are similar; that is they both converge to unique periodic orbits. From a biophysical perspective the assumption of unidirectional dissociation is unrealistic. We show that the same result holds for the more restrictive model when one weakens the assumption of unidirectional binding or disassociation. We speculate that this is not true for the more general model. This difference in dynamics may have important biological implications and certainly points to promising avenues of research.

Glucose mediates the translocation of NeuroD1 by O-linked glycosylation

O-Linked GlcNAc modification of nuclear and cytosolic proteins has been shown to regulate the function of many cellular proteins. Increased O-linked glycosylation, observed under chronic hyperglycemia conditions, has been implicated in the pathogenesis of diabetes. However, the exact role of O-GlcNAc modification in regulating glucose homeostasis remains to be established. We report here that the subcellular localization of the pancreatic beta cell-specific transcription factor NeuroD1 is regulated by O-linked glycosylation in the mouse insulinoma cell line MIN6. Under low glucose conditions, NeuroD1 is mainly in the cytosol. However, treatment of MIN6 cells with high glucose results in O-linked GlcNAc modification of NeuroD1 and its subsequent translocation into the nucleus. Consistent with these data, treatment of MIN6 cells with O-(2-acetamido-2-deoxy-d-glucopyranosylidene)-amino N-phenylcarbamate, an inhibitor of O-GlcNAcase, causes Neuro-D1 localization to the nucleus and induction of insulin gene expression even on low glucose. Furthermore, we demonstrate that NeuroD1 interacts with the O-GlcNAc transferase, OGT only at high concentrations of glucose and depletion of OGT by using small interfering RNA oligos interferes with the nuclear localization of NeuroD1 on high glucose. On low glucose NeuroD1 interacts with the O-GlcNAcase and becomes deglycosylated, which is likely to be important for export of Neuro-D1 into cytosol in the presence of low glucose. In summary, the presented data suggest that glucose regulates the subcellular localization of NeuroD1 in pancreatic beta cells via O-linked GlcNAc modification of NeuroD1 by OGT.

The effect of glucosamine concentration on the development and sex ratio of bovine embryos

Glucosamine is a component of hyaluronic acid and an alternative substrate to glucose for the extracellular matrix synthesis of COCs. Its addition to an IVM medium reduces the glucose consumption of bovine COCs. Glucosamine is also metabolized to UDP-N-acetyl glucosamine (UDP-GlcNAc) via the hexosamine biosynthesis pathway and is utilized for O-linked glycosylation by the X-linked enzyme, O-linked GlcNAc transferase (OGT). Moreover, the inactivation of the second X chromosome in female embryos is influential in producing the sex ratio bias observed in vitro when embryos are cultured in the presence of glucose above 2.5mM. Accordingly, the aim of this study is to examine whether the presence of glucosamine during maturation or embryo culture causes a sex ratio bias in bovine blastocysts. Glucosamine was added to the medium in three different embryo developmental periods: in vitro maturation, the one-cell to eight-cell stage (before the maternal-zygotic transition, MZT), and the eight-cell to blastocyst stage (after MZT). When glucosamine was added during in vitro maturation, the developmental competence of oocytes was severely compromised. However, the sex ratio of embryos was not influenced. When glucosamine was added to embryo culture medium during development from one-cell to eight-cell stage (before MZT), it affected neither the development nor the sex ratio of bovine embryos. Finally, when glucosamine was added after MZT, the development rate of embryos was severely decreased, and the sex ratio was skewed toward males. Moreover, an inhibitor of OGT, benzyl-2-acetamido-2-deoxy-alpha-D-galactopyranoside (BADGP), negated the effect of glucosamine on the sex ratio when it was added to embryo culture medium from the eight-cell to blastocyst stage (after MZT). These results suggest that, like glucose, the supplementation of glucosamine into the medium skewed the sex ratio to males and that OGT, an X-linked enzyme, was involved in this phenomenon. Moreover, this effect of glucosamine was limited only to when it was present in the embryo culture medium after MZT.

Cell signaling, the essential role of O-GlcNAc!

An increasing body of evidence points to a central regulatory role for glucose in mediating cellular processes and expands the role of glucose well beyond its traditional role(s) in energy metabolism. Recently, it has been recognized that one downstream effector produced from glucose is UDP-GlcNAc. Levels of UDP-GlcNAc, and the subsequent addition of O-linked beta-N-acetylglucosamine (O-GlcNAc) to Ser/Thr residues, is involved in regulating nuclear and cytoplasmic proteins in a manner analogous to protein phosphorylation. O-GlcNAc protein modification is essential for life in mammalian cells, highlighting the importance of this simple post-translational modification in basic cellular regulation. Recent research has highlighted key roles for O-GlcNAc serving as a nutrient sensor in regulating insulin signaling, the cell cycle, and calcium handling, as well as the cellular stress response.

The Cyclic AMP Response Element Modulator Regulates Transcription of the TCR ζ-Chain

Systemic lupus erythematosus T cells display decreased amounts of TCR zeta mRNA that results in part from limited binding of the transcriptional enhancer Elf-1 to the TCR zeta promoter. We have identified a new cis-binding site for the cAMP response element (CRE) modulator (CREM) on the TCR zeta promoter, centered on the -390 nucleotide. Transfection of T cells with an antisense CREM alpha plasmid reduced the binding of CREM to the TCR zeta promoter, as shown by chromatin and reporter chromatin immunoprecipitation assays, and enhanced the production of TCR zeta mRNA and protein. Mutagenesis of the -390 CRE site prevented the binding of CREM to the TCR zeta promoter. The mechanism of CREM-mediated repression appears to be chromatin dependent, because antisense CREM promotes the acetylation of histones on the TCR zeta promoter. Finally, we established an enhanced binding of CREM to the TCR zeta-chain promoter in systemic lupus erythematosus cells compared with control T cells. Our studies demonstrate that CREM alpha binds to the TCR zeta promoter and repress its activity.

C/EBPα functionally and physically interacts with GABP to activate the human myeloid IgA Fc receptor (FcαR, CD89) gene promoter

Human Fcα receptor (FcαR; CD89), the receptor for the crystallizable fragment (Fc) of immunoglobulin A (IgA), is expressed exclusively in myeloid cells, including granulocytes and monocytes/macrophages, and is considered to define a crucial role of these cells in immune and inflammatory responses. A 259-base pair fragment of the FCAR promoter is sufficient to direct myeloid expression of a reporter gene and contains functionally important binding sites for CCAAT/enhancer-binding protein α (C/EBPα) (CE1, CE2, and CE3) and an unidentified Ets-like nuclear protein. Here, we show that the Ets-binding site is bound by a heterodimer composed of GA-binding protein α (GABPα), an Ets-related factor, and GABPβ, a Notch-related protein. Cotransfection of GABP increased FCAR promoter activity 3.7-fold through the Ets-binding site. GABP and C/EBPα synergistically activated the FCAR promoter 280-fold. Consistent with these observations, in vitro binding analyses revealed a physical interaction between the GABPα subunit and C/EBPα. This is the first report demonstrating both physical and functional interactions between GABP and C/EBPα and will provide new insights into the molecular basis of myeloid gene expression. (Blood. 2005;106:2534-2542)

O-GlcNAc glycosylation: a signal for the nuclear transport of cytosolic proteins?

Year 2004 marks the 20th anniversary of the discovery of O-linked N-acetylglucosamine (O-GlcNAc) by Gerald W. Hart. Despite interest for O-GlcNAc, the functions played by this single monosaccharide remain poorly understood, though numerous roles have been suggested, among which is the involvement of O-GlcNAc in the nuclear transport of cytosolic proteins. This idea was first sustained by studies on bovine serum albumin that showed that the protein could be actively carried to the nucleus when it was modified with sugars. In this paper, we will review data on this puzzling problem. We will first describe the well-established nuclear localisation signal (NLS)-dependent nuclear transport by presenting the different factors involved, and then, we will examine where and how O-GlcNAc could be involved in nuclear transport. Whereas it has been suggested that O-GlcNAc could interfere at two levels in the nuclear transport both by modifying proteins to be translocated to the nucleus and by modifying the nucleoporins of the nuclear pore complex, according to us, this second idea seems unlikely. Part of this study will also be dedicated to a relatively new concept in the nuclear transport: the role of the 70-kDa heat shock proteins (HSP70). The action of the chaperone in nuclear translocation was put forward 10 years ago, but new findings suggest that this mechanism could be linked to O-GlcNAc glycosylation.

Post-translational modifications influence transcription factor activity: a view from the ETS superfamily

Transcription factors provide nodes of information integration by serving as nuclear effectors of multiple signaling cascades, and thus elaborate layers of regulation, often involving post-translational modifications, modulating and coordinate activities. Such modifications can rapidly and reversibly regulate virtually all transcription factor functions, including subcellular localization, stability, interactions with cofactors, other post-translational modifications and transcriptional activities. Aside from analyses of the effects of serine/threonine phosphorylation, studies on post-translational modifications of transcription factors are only in the initial stages. In particular, the regulatory possibilities afforded by combinatorial usage of and competition between distinct modifications on an individual protein are immense, and with respect to large families of closely related transcription factors, offer the potential of conferring critical specificity. Here we will review the post-translational modifications known to regulate ETS transcriptional effectors and will discuss specific examples of how such modifications influence their activities to highlight emerging paradigms in transcriptional regulation.

Dissecting the molecular mechanisms of TCR zeta chain downregulation and T cell signaling abnormalities in human systemic lupus erythematosus

Abnormal expression of key signaling molecules and defective function of T lymphocytes play a significant role in the pathogenesis of systemic lupus erythematosus (SLE). Probing on altered expression of genes that may predispose to SLE revealed that the expression of TCR zeta chain is defective in the majority of SLE patients. Current research has been directed towards understanding the molecular basis of TCR zeta chain deficiency and dissecting the T cell signalling abnormalities in SLE T cells. Latest developments suggest that interplay of abnormal transcriptional factor expression, aberrant mRNA processing/editing, unbiquitination, proteolysis, and the effects of oxidative stress as well as changes in chromatin structure invariably contribute to TCR zeta chain deficiency in SLE T cells. On the other hand, multiple factors, including altered receptor structure, modulation of membrane clustering, lipid-raft distribution of signaling molecules, and defective signal silencing mechanisms, play a key role in delivering the increased TCR/CD3-mediated intracellular calcium response in SLE T cells.

Transcriptional regulation of interleukin 2 in SLE T cells

Interleukin-2 (IL-2) is a central cytokine required for the activation of T, B, and NK cells. It propagates the immune response and terminates it by promoting the activation induced cell death of T cells. IL-2 production is altered in T cells of patients with systemic lupus erythematosus (SLE). The consequence of reduced IL-2 production in SLE is decreased immune response to infectious agents. Decreased IL-2 production by SLE T cells is the result of transcriptional repression of the IL-2 gene. This article will review the defective transcription regulation of IL-2 in SLE T cells, which is the result of decreased expression of the enhancers NF-kappa B and AP1 and the increased expression of the transcriptional repressor CREM.

The tumor suppressor HIC1 (hypermethylated in cancer 1) is O-GlcNAc glycosylated

HIC1 (hypermethylated in cancer 1) is a transcriptional repressor containing five Krüppel-like C(2)H(2) zinc fingers and an N-terminal dimerization and autonomous repression domain called BTB/POZ. Here, we demonstrate that full-length HIC1 proteins are modified both in vivo and in vitro with O-linked N-acetylglucosamine (O-GlcNAc). This is a highly dynamic glycosylation found within the cytosolic and the nuclear compartments of eukaryotes. Analysis of [(3)H]Gal-labeled tryptic peptides indicates that HIC1 has three major sites for O-GlcNAc glycosylation. Using C-terminal deletion mutants, we have shown that O-GlcNAc modification of HIC1 proteins occurred preferentially in the DNA-binding domain. Nonglycosylated and glycosylated forms of full-length HIC1 proteins separated by wheat germ agglutinin affinity purification, displayed the same specific DNA-binding activity in electrophoretic mobility shift assays proving that the O-GlcNAc modification is not directly implicated in the specific DNA recognition of HIC1. Intriguingly, N-terminal truncated forms corresponding to BTB-POZ-deleted proteins exhibited a strikingly differential activity, as the glycosylated truncated forms are unable to bind DNA whereas the unglycosylated ones do. Electrophoretic mobility shift assays performed with separated pools of glycosylated and unglycosylated forms of a construct exhibiting only the DNA-binding domain and the C-terminal tail of HIC1 (residues 399-714) and supershift experiments with wheat germ agglutinin or RL-2, an antibody raised against O-GlcNAc residues, fully corroborated these results. Interestingly, these truncated proteins are O-GlcNAc modified in their C-terminal tail (residues 670-711) and not in the DNA-binding domain, as for the full-length proteins. Thus, the O-GlcNAc modification of HIC1 does not affect its specific DNA-binding activity and is highly sensitive to conformational effects, notably its dimerization through the BTB/POZ domain.

Alterations in lipid raft composition and dynamics contribute to abnormal T cell responses in systemic lupus erythematosus

In response to appropriate stimulation, T lymphocytes from systemic lupus erythematosus (SLE) patients exhibit increased and faster intracellular tyrosine phosphorylation and free calcium responses. We have explored whether the composition and dynamics of lipid rafts are responsible for the abnormal T cell responses in SLE. SLE T cells generate and possess higher amounts of ganglioside-containing lipid rafts and, unlike normal T cells, SLE T cell lipid rafts include FcRgamma and activated Syk kinase. IgM anti-CD3 Ab-mediated capping of TCR complexes occurs more rapidly in SLE T cells and concomitant with dramatic acceleration of actin polymerization kinetics. The significance of these findings is evident from the observation that cross-linking of lipid rafts evokes earlier and higher calcium responses in SLE T cells. Thus, we propose that alterations in the lipid raft signaling machinery represent an important mechanism that is responsible for the heightened and accelerated T cell responses in SLE.