Thrombin activates a Y box-binding protein (DNA-binding protein B) in endothelial cells

Identification of YB-1 as a regulator of PTP1B expression: implications for regulation of insulin and cytokine signaling

Changes in expression of PTP1B, the prototypic protein tyrosine phosphatase, have been associated with various human diseases; however, the mechanisms by which PTP1B expression is regulated have not been defined. We have identified an enhancer sequence within the PTP1B promoter which serves as a binding site for the transcription factor Y box-binding protein-1 (YB-1). Overexpression of YB-1 resulted in increased levels of PTP1B. Furthermore, depletion of YB-1 protein, by expression of a specific antisense construct, led to an approximately 70% decrease in expression of PTP1B, but no change in the level of its closest relative, TC-PTP. Expression of antisense YB-1 resulted in increased sensitivity to insulin and enhanced signaling through the cytokine receptor gp130, which was suppressed by re-expression of PTP1B. Finally, we observed a correlation between the expression of PTP1B and that of YB-1 in cancer cell lines and an animal model of type II diabetes. Our data reveal an important role for YB-1 as a regulator of PTP1B expression, and further highlight PTP1B as a critical regulator of insulin- and cytokine-mediated signal transduction.

Autoantibody to DNA binding protein B as a novel serologic marker in systemic sclerosis

Systemic sclerosis is a systemic disease that is characterized by tissue fibrosis, small-vessel vasculopathy, and an autoimmune response associated with autoantibodies. We performed serological analysis of cDNA expression library (SEREX) to identify autoantibodies associated with systemic sclerosis. We identified 4 clones that react with sera of patients with SSc but not with those of healthy donors. These clones are phosphoglycerate mutase, centromere autoantigen C, U1 small nuclear ribonucleoprotein, and DNA binding protein B (dbpB). We chose to study autoantibody to DNA binding protein B. Immunoreactivity against recombinant dbpB was detected in 40.5% (15/37) of patients with SSc, 14.6% (6/41) of patents with systemic lupus erythematosus, 6.7% (1/15) of patients with rheumatoid arthritis, 0% (0/12) of patients with Sjogren syndrome, and 5.9% (1/17) of patients with polymyositis/dermatomyositis. The frequency of anti-dbpB was significantly higher in the SSc patients (15/37, 40.5%) compared to the healthy controls (3/41, 7.3%, p=0.0005 by chi(2) test). Eleven patients (11/20, 55%) with the diffuse cutaneous type of SSc had anti-dbpB and 4 patients (4/17, 23.5%) with the limited cutaneous type had anti-dbpB. The presence of anti-dbpB was significantly associated with the diffuse cutaneous type (p=0.00003 by chi(2) test). This is the first report to suggest that autoantibody to dbpB can be used as a serologic marker of systemic sclerosis.

Specificity of mammalian Y-box binding protein p50 in interaction with ss and ds DNA analyzed with generic oligonucleotide microchip

p50 protein is a member of the Y-box binding transcription factor family and is a counterpart of YB-1 protein. The generic microchip was used to analyze the sequence specificity of p50 binding to single (ss) and double-stranded (ds) oligodeoxyribonucleotides. The generic microchip contained 4,096 single-stranded octadeoxyribonucleotides in which all possible core 6-mers (4(6)=4,096) were flanked at their 3' and 5'-ends with degenerated nucleotides. The oligonucleotides were chemically immobilized within polyacrylamide gel pads fixed on a glass slide. The binding of p50 to the generic microchip was shown to be the most specific to ss GGGG motif and then to ss CACC and CATC motifs. GC-rich ds oligonucleotides of the generic microchip, and particularly those containing GGTG/CACC, GATG/CATC, and GTGG/CCAC heterogeneous motifs, were most efficiently destabilized due to interaction with p50. Gel-shift electrophoresis has shown that the protein exhibits much higher binding specificity to 24-mer oligoA-TGGGGG-oligoA containing G-rich 6-mer, in comparison with 24-mer oligoA-AAATAT-oligoA carrying A,T-rich 6-mer in full correspondence with the data obtained with the microchip. Studies of DNA-binding proteins using gel-immobilized ss and ds DNA fragments provide a unique possibility to detect low-affinity complexes of these proteins with short sequence motifs and assess the role of these motifs in sequence-specific interactions with long recognition sites.

Endothelial cell dynamics and complexity theory

OBJECTIVE

To apply complexity theory to understanding endothelial cell function in health and disease.

DATA SOURCES AND STUDY SELECTION

Published research and review articles in the English language related to complexity theory and endothelial cell biology.

DATA EXTRACTION AND SYNTHESIS

The results of published studies have been used to generate a hypothesis of nonlinear dynamics in endothelial cell biology.

CONCLUSIONS

The endothelium displays nonlinear complexity. I propose a model in which healthy endothelium retains a broad range of responses and is therefore highly active, whereas dysfunctional endothelium becomes locked into a narrow range of responses, approaching a single steady state and eventual quiescence. These concepts lay a foundation for understanding the pathophysiology of endothelial cell dysfunction in the multiple organ dysfunction syndrome.

Functional interaction between JC virus late regulatory agnoprotein and cellular Y-box binding transcription factor, YB-1

Human polyomavirus JC virus (JCV) is a causative agent of progressive multifocal leukoencephalopathy which results from lytic infection of glial cells. Although significant progress has been made in understanding the regulation of JCV gene transcription, the mechanism(s) underlying the viral lytic cycle remains largely unknown. We recently reported that the JCV late auxiliary Agnoprotein may have a regulatory role in JCV gene transcription and replication. Here, we investigated its regulatory function in viral gene transcription through its physical and functional interaction with YB-1, a cellular transcription factor which contributes to JCV gene expression in glial cells. Time course studies revealed that Agnoprotein is first detected at day 3 postinfection and that its level increased during the late stage of the infection cycle. Agnoprotein is mainly localized to the cytoplasmic compartment of the infected cell, with high concentrations found in the perinuclear region. While the position of Agnoprotein throughout the infection cycle remained relatively unaltered, the subcellular distribution of YB-1 between the cytoplasm and nucleus changed. Results from coimmunoprecipitation and glutathione S-transferase pull-down experiments revealed that Agnoprotein physically interacts with YB-1 and that the amino-terminal region of Agnoprotein, between residues 1 and 36, is critical for this association. Further investigation of this interaction by functional assays demonstrated that Agnoprotein negatively regulates YB-1-mediated gene transcription and that the region corresponding to residues 1 to 36 of Agnoprotein is important for the observed regulatory event. Taken together, these data demonstrate that the interaction of the viral late regulatory Agnoprotein and cellular Y-box binding factor YB-1 modulates transcriptional activity of JCV promoters.

Thrombin stimulation of the vascular cell adhesion molecule-1 promoter in endothelial cells is mediated by tandem nuclear factor-kappa B and GATA motifs

The goal of this study was to delineate the transcriptional mechanisms underlying thrombin-mediated induction of vascular adhesion molecule-1 (VCAM-1). Treatment of human umbilical vein endothelial cells with thrombin resulted in a 3.3-fold increase in VCAM-1 promoter activity. The upstream promoter region of VCAM-1 contains a thrombin response element, two nuclear factor kappaB (NF-kappaB) motifs, and a tandem GATA motif. In transient transfection assays, mutation of the thrombin response element had no effect on thrombin induction. In contrast, mutation of either NF-kappaB site resulted in a complete loss of induction, whereas a mutation of the two GATA motifs resulted in a significant reduction in thrombin stimulation. In electrophoretic mobility shift assays, nuclear extracts from thrombin-treated endothelial cells displayed markedly increased binding to the tandem NF-kappaB and GATA motifs. The NF-kappaB complex was supershifted with anti-p65 antibodies, but not with antibodies to RelB, c-Rel, p50, or p52. The GATA complex was supershifted with antibodies to GATA-2, but not GATA-3 or GATA-6. A construct containing tandem copies of the VCAM-1 GATA motifs linked to a minimal thymidine kinase promoter was induced 2.4-fold by thrombin. Taken together, these results suggest that thrombin stimulation of VCAM-1 in endothelial cells is mediated by the coordinate action of NF-kappaB and GATA transcription factors.

Y box-binding factor promotes eosinophil survival by stabilizing granulocyte-macrophage colony-stimulating factor mRNA

Short-lived peripheral blood eosinophils are recruited to the lungs of asthmatics after allergen challenge, where they become long-lived effector cells central to disease pathophysiology. GM-CSF is an important cytokine which promotes eosinophil differentiation, function, and survival after transit into the lung. In human eosinophils, GM-CSF production is controlled by regulated mRNA stability mediated by the 3' untranslated region, AU-rich elements (ARE). We identified human Y box-binding factor 1 (YB-1) as a GM-CSF mRNA ARE-specific binding protein that is capable of enhancing GM-CSF-dependent survival of eosinophils. Using a transfection system that mimics GM-CSF metabolism in eosinophils, we have shown that transduced YB-1 stabilized GM-CSF mRNA in an ARE-dependent mechanism, causing increased GM-CSF production and enhanced in vitro survival. RNA EMSAs indicate that YB-1 interacts with the GM-CSF mRNA through its 3' untranslated region ARE. In addition, endogenous GM-CSF mRNA coimmunoprecipitates with endogenous YB-1 protein in activated eosinophils but not resting cells. Thus, we propose a model whereby activation of eosinophils leads to YB-1 binding to and stabilization of GM-CSF mRNA, ultimately resulting in GM-CSF release and prolonged eosinophil survival.

The Y-box binding protein YB-1 suppresses collagen alpha 1(I) gene transcription via an evolutionarily conserved regulatory element in the proximal promoter

Appropriate expression of collagen type I, a major component of connective tissue matrices, is dependent on tight transcriptional control and a number of trans-activating and repressing factors have been characterized. Here we identify the Y-box binding protein-1 (YB-1) as a novel repressor of the collagen type alpha1(I) (COL1A1) gene. Collagen type I mRNA and protein levels decreased upon overexpression of YB-1 by transfection in NRK fibroblasts. The human, rat, and mouse COL1A1 promoter -220/+115 contains three putative Y-boxes, one of these sites, designated collagen Y-box element (CYE), includes a Y-box plus an adjacent 3' inverted repeat. DNase-I footprinting and Southwestern blotting with fibroblast nuclear extract demonstrated binding of several nuclear proteins across the CYE, one of which was identified as YB-1. Recombinant YB-1 bound the CYE sequence in gel shift assays with a preference for single-stranded templates. The entire sequence (-88/-48) was required for high affinity binding. Complex formation of endogenous YB-1 with the CYE was established by supershift studies. COL1A1 promoter-reporter constructs were suppressed up to 80% by cotransfection with YB-1 in a variety of cell types. In addition, CYE conferred YB-1 responsiveness on two heterologous promoters further demonstrating the importance of this repressor region. Mung bean nuclease sensitivity analysis suggested that repression is most likely exerted through changes in DNA conformation.

Thrombin induces the release of the Y-box protein dbpB from mRNA: a mechanism of transcriptional activation

We have recently demonstrated that thrombin induces expression of the platelet-derived growth factor B-chain gene in endothelial cells (EC) through activation of the Y-box binding protein DNA-binding protein B (dbpB). We now present evidence that dbpB is activated by a novel mechanism: proteolytic cleavage leading to release from mRNA, nuclear translocation, and induction of thrombin-responsive genes. Cytosolic, full-length dbpB (50 kDa) was rapidly cleaved to a 30-kDa species upon thrombin stimulation of EC. This truncated, "active" dbpB exhibited nuclear localization and binding affinity for the thrombin response element sequence, which is distinct from the Y-box sequence. Oligo(dT) affinity chromatography revealed that cytosolic dbpB from control EC, but not active dbpB from thrombin-treated EC, was bound to mRNA. Latent dbpB immunoprecipitated from cytosolic extracts of control EC was activated by ribonuclease treatment. Furthermore, when EC cytosolic extracts were subjected to Nycodenz gradient centrifugation, latent dbpB fractionated with mRNA, whereas active dbpB fractionated with free proteins. The cytosolic retention domain of dbpB, which we localized to the region 247-267, was proteolytically cleaved during its activation. In contrast to full-length dbpB, truncated dbpB stimulated platelet-derived growth factor B-chain and tissue factor promoter activity by over 5-fold when transiently cotransfected with reporter constructs. These results suggest a novel mode of transcription factor activation in which an agonist causes release from mRNA of a latent transcription factor leading to its transport to the nucleus and its regulation of target gene expression.

Cold shock domain factors activate the granulocyte-macrophage colony-stimulating factor promoter in stimulated Jurkat T cells

Cold shock domain (CSD) family members have been shown to play roles in either transcriptional activation or repression of many genes in various cell types. We have previously shown that CSD proteins dbpAv and dbpB (also known as YB-1) act to repress granulocyte-macrophage colony-stimulating factor transcription in human embryonic lung (HEL) fibroblasts via binding to single-stranded DNA regions across the promoter. Here we show that the same CSD factors are involved in granulocyte-macrophage colony-stimulating factor transcriptional activation in Jurkat T cells. Unlike the mechanisms of CSD repression in HEL fibroblasts, CSD-mediated activation in Jurkat T cells is not mediated through DNA binding but presumably through protein-protein interactions via the C terminus of the CSD protein with transcription factors such as RelA/NF-kappaB p65. We demonstrate that Jurkat T cells lack truncated CSD factor subtypes present in HEL fibroblasts, which raises the possibility that the cellular content of CSD proteins may determine their final role as activators or repressors of transcription.