Response Element Binding Protein Transcription Research Articles

TRAF3 as a powerful and multitalented regulator of lymphocyte functions.

This review summarizes the current state of knowledge regarding the roles of the signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 in regulating the functions of B and T lymphocytes. In B lymphocytes, TNFR-associated factor 3 inhibits signaling by TNFR superfamily receptors, Toll-like receptors, and interleukin-6R. In contrast, signaling to B cells by the virally encoded oncogenic protein latent membrane protein 1 is promoted by TNFR-associated factor 3. An important B cell-specific role for TNFR-associated factor 3 is the inhibition of homeostatic survival, directly relevant to the common occurrence of TNFR-associated factor 3 mutations in human B cell malignancies. TNFR-associated factor 3 was recently found to be a resident nuclear protein in B cells, where it interacts with and inhibits gene expression mediated by the cAMP response element-binding protein transcription complex, including expression of the prosurvival protein myeloid leukemia cell differentiation protein 1. In T lymphocytes, TNFR-associated factor 3 is required for normal signaling by the T cell antigen receptor, while inhibiting signaling by the interleukin-2 receptor. Cytoplasmic TNFR -associated factor 3 restrains nuclear factor-κB2 activation in both T and B cells. Clinical implications and future directions for the study of this context-dependent signaling regulator are discussed.

Regulation of Sertoli-Germ Cell Adhesion and Sperm Release by FSH and Nonclassical Testosterone Signaling

Testosterone and FSH act in synergy to produce the factors required to maximize the production of spermatozoa and male fertility. However, the molecular mechanisms by which these hormones support spermatogenesis are not well established. Recently, we identified a nonclassical mechanism of testosterone signaling in cultured rat Sertoli cells. We found that testosterone binding to the androgen receptor recruits and activates Src tyrosine kinase. Src then causes the activation of the epidermal growth factor receptor, which results in the phosphorylation and activation of the ERK MAPK and the cAMP response element-binding protein transcription factor. In this report, we find that FSH inhibits testosterone-mediated activation of ERK and the MAPK pathway in Sertoli cells via the protein kinase A-mediated inhibition of Raf kinase. In addition, FSH, as well as inhibitors of Src and ERK kinase activity, reduced germ cell attachment to Sertoli cells in culture. Using pathway-specific androgen receptor mutants we found that the nonclassical pathway is required for testosterone-mediated increases in germ cell attachment to Sertoli cells. Studies of seminiferous tubule explants determined that Src kinase, but not ERK kinase, activity is required for the release of sperm from seminiferous tubule explants. These findings suggest the nonclassical testosterone-signaling pathway acts via Src and ERK kinases to facilitate the adhesion of immature germ cells to Sertoli cells and through Src to permit the release of mature spermatozoa. In contrast, FSH acts to limit testosterone-mediated ERK kinase activity and germ cell attachment.

Reduction of liver fructokinase expression and improved hepatic inflammation and metabolism in liquid fructose-fed rats after atorvastatin treatment

Consumption of beverages that contain fructose favors the increasing prevalence of metabolic syndrome alterations in humans, including non-alcoholic fatty liver disease (NAFLD). Although the only effective treatment for NAFLD is caloric restriction and weight loss, existing data show that atorvastatin, a hydroxymethyl-glutaryl-CoA reductase inhibitor, can be used safely in patients with NAFLD and improves hepatic histology. To gain further insight into the molecular mechanisms of atorvastatin's therapeutic effect on NAFLD, we used an experimental model that mimics human consumption of fructose-sweetened beverages. Control, fructose (10% w/v solution) and fructose + atorvastatin (30 mg/kg/day) Sprague–Dawley rats were sacrificed after 14 days. Plasma and liver tissue samples were obtained to determine plasma analytes, liver histology, and the expression of liver proteins that are related to fatty acid synthesis and catabolism, and inflammatory processes. Fructose supplementation induced hypertriglyceridemia and hyperleptinemia, hepatic steatosis and necroinflammation, increased the expression of genes related to fatty acid synthesis and decreased fatty acid β-oxidation activity. Atorvastatin treatment completely abolished histological signs of necroinflammation, reducing the hepatic expression of metallothionein-1 and nuclear factor kappa B binding. Furthermore, atorvastatin reduced plasma (× 0.74) and liver triglyceride (× 0.62) concentrations, decreased the liver expression of carbohydrate response element binding protein transcription factor (×0.45) and its target genes, and increased the hepatic activity of the fatty acid β-oxidation system (× 1.15). These effects may be related to the fact that atorvastatin decreased the expression of fructokinase (× 0.6) in livers of fructose-supplemented rats, reducing the metabolic burden on the liver that is imposed by continuous fructose ingestion.

Structural Motifs of Importance for the Constitutive Activity of the Orphan 7TM Receptor EBI2: Analysis of Receptor Activation in the Absence of an Agonist

The Epstein-Barr induced receptor 2 (EBI2) is a lymphocyte-expressed orphan seven transmembrane-spanning (7TM) receptor that signals constitutively through Galphai, as shown, for instance by guanosine 5'-O-(3-thio)triphosphate incorporation. Two regions of importance for the constitutive activity were identified by a systematic mutational analysis of 29 residues in EBI2. The cAMP response element-binding protein transcription factor was used as a measure of receptor activity and was correlated to the receptor surface expression. PheVI:13 (Phe257), and the neighboring CysVI:12 (Cys256), in the conserved CW/FxP motif in TM 6, acted as negative regulators as Ala substitutions at these positions increased the constitutive activity 5.7- and 2.3-fold, respectively, compared with EBI2 wild type (wt). In contrast, ArgII:20 (Arg87) in TM-2 acted as a positive regulator, as substitution to Ala, but not to Lys, decreased the constitutive activity more than 7-fold compared with wt EBI2. IleIII:03 (Ile106) is located only 4 A from ArgII:20, and a favorable electrostatic interaction with ArgII:20 was created by introduction of Glu in III:03, given that the activity increased to 4.4-fold of that wt EBI2. It is noteworthy that swapping these charges by introduction of Glu in II:20 and Arg in III:03 resulted in a 2.7-fold increase compared with wt EBI2, thereby rescuing the two signaling-deficient single mutations, which exhibited a 3.8- to 4.5-fold decrease in constitutive activity. The uncovering of these molecular mechanisms for EBI2 activation is important from a drug development point of view, in that it may facilitate the rational design and development of small-molecule inverse agonists against EBI2 of putative importance as antiviral- or immune modulatory therapy.

Isolation and Characterization of a Cold-Induced DREB Gene from Aloe Vera L.

A new cold-induced dehydration-responsive element-binding (DREB) gene encoding an AP2/ethylene response element binding protein transcription factor was isolated from Aloe vera L. by rapid amplification of complementary DNA ends (RACE). The deduced protein contained a putative acidic activation domain and an AP2 DNA binding domain of 64 amino acids. The expression analysis showed that the transcripts accumulated rapidly under cold stress and peaked at 12 h, then decreased to the original level. Yeast one-hybrid analysis indicated that Aloe DREB1 can bind to DRE cis-elements and activate the expressions of reporter genes, but the binding and activation abilities were weak. Aloe DREB1 localized in nucleus, although it lacks typical nuclear localization signal. These results implied that Aloe DREB1 might function as a transcription activator involved in the regulation of cold-responsive genes via signal transduction pathway dependent or independent of the DREB transcription factor.

Signaling Pathways Involved in Cyclooxygenase-2 Induction by Hepatocyte Growth Factor in Non–Small-Cell Lung Cancer

Many studies have suggested a role for the hepatocyte growth factor (HGF)/c-Met pathway in tumorigenesis. Some actions of HGF are believed to be mediated by cyclooxygenase-2 (COX-2), resulting in the production of prostaglandin E2 (PGE(2)). We examined four c-Met-positive non-small-cell lung cancer (NSCLC) cell lines for effects of HGF on COX-2. HGF increased COX-2 protein expression 3-fold over basal levels. Induction of COX-2 occurred through both the extracellular signal-regulated kinase 1/2 and p38 pathways. HGF treatment caused activation of the activator protein-1, CCAAT/enhancer-binding protein, and cAMP response element-binding protein transcription factors, and COX-2 induction was blocked by actinomycin D. The half-life of COX-2 mRNA was also increased by HGF. HGF stimulation resulted in a 4-fold increase in PGE(2) secretion, and treatment of NSCLC cells with exogenous PGE(2) significantly increased cell proliferation. The addition of PGE(2) to NSCLC cells also led to rapid phosphorylation of c-Met in the absence of HGF, which was blocked by epidermal growth factor receptor (EGFR) inhibition. EGFR ligands were released in response to PGE(2). This suggests that secretion of PGE(2) induced by HGF/c-Met pathway activation can further activate the c-Met pathway via EGFR in a reinforcing loop that is independent of HGF. HGF and PGE(2) each significantly stimulated invasion in NSCLC cells. Cells transiently transfected with c-Met antisense plasmid showed a significant decrease in HGF- or PGE(2)-induced invasion. PGE(2)-induced invasion was EGFR-dependent, confirming a link between PGE(2), EGFR, and c-Met. Targeting of both the HGF/c-Met and PGE(2) pathways with a neutralizing antibody to HGF and celecoxib resulted in enhanced anti-invasion effects in response to HGF.

A small molecule inhibitor of beta-catenin/CREB-binding protein transcription [corrected

Inherited and somatic mutations in the adenomatous polyposis coli occur in most colon cancers, leading to activation of beta-catenin-responsive genes. To identify small molecule antagonists of this pathway, we challenged transformed colorectal cells with a secondary structure-templated chemical library, looking for compounds that inhibit a beta-catenin-responsive reporter. We identified ICG-001, a small molecule that down-regulates beta-catenin/T cell factor signaling by specifically binding to cyclic AMP response element-binding protein. ICG-001 selectively induces apoptosis in transformed cells but not in normal colon cells, reduces in vitro growth of colon carcinoma cells, and is efficacious in the Min mouse and nude mouse xenograft models of colon cancer.

Testosterone activates mitogen-activated protein kinase and the cAMP response element binding protein transcription factor in Sertoli cells.

The androgen testosterone is essential for the Sertoli cell to support the maturation of male germ cells and the production of spermatozoa (spermatogenesis). In the classical view of androgen action, binding of androgen to the intracellular androgen receptor (AR) produces a conformational change in AR such that the receptor-steroid complex has high affinity for specific DNA regulatory elements and is able to stimulate gene transcription. Here, we demonstrate that testosterone can act by means of an alternative, rapid, and sustainable mechanism in Sertoli cells that is independent of AR-DNA interactions. Specifically, the addition of physiological levels of testosterone to Sertoli cells stimulates the mitogen-activated protein kinase signaling pathway and causes phosphorylation of the cAMP response element binding protein transcription factor on serine 133, a modification known to be required for Sertoli cells to support spermatogenesis. Androgen-mediated activation of mitogen-activated protein kinase and cAMP response element binding protein occurs within 1 min, extends for at least 12 h and requires AR. Furthermore, androgen induces endogenous cAMP response element binding protein-mediated transcription in Sertoli cells. These newly identified mechanisms of androgen action in Sertoli cells suggest new targets for developing male contraceptive agents.

Activation of the mouse heme oxygenase-1 gene by 15-deoxy-Delta(12,14)-prostaglandin J(2) is mediated by the stress response elements and transcription factor Nrf2.

The mechanism of heme oxygenase-1 (ho-1) gene activation by 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) was examined. 15d-PGJ(2) stimulated expression of HO-1 mRNA and protein and of a mouse ho-1 gene promoter/luciferase fusion construct (HO15luc) in a dose-dependent manner in mouse hepatoma (Hepa) cells. HO15luc expression was not effected by troglitazone, a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligand, but induction by 15d-PGJ(2) was abrogated by the antioxidant N-acetylcysteine. The primary 15d-PGJ(2) responsive sequences were localized to a 5' distal enhancer (E1) and identified as the stress-response element, previously shown to mediate ho-1 activation by several agents, including heme and heavy metals. Treatment of Hepa cells with 15d-PGJ(2) stimulated stress-response element-binding activity as judged by electrophoretic mobility shift assays. Antibody "supershift" experiments identified NF-E2 related factor 2 (Nrf2), but not Fos, Jun, or activating transcription factor/cyclic AMP response element binding protein transcription factors, within the 15d-PGJ(2)-induced complexes. Similarly, a dominant-negative mutant of Nrf2, but not of c-Jun or c-Fos, abrogated 15d-PGJ(2)-stimulated E1 transcription activity. Finally, prior induction of HO-1 in RAW264.7 mouse macrophages by 15d-PGJ(2) attenuated cell death caused by diesel exhaust particle extracts. These results demonstrate that induction of mouse HO-1 expression by 15d-PGJ(2) is independent of PPAR-gamma but dependent on oxidative stress, is regulated by the oxidative stress-activated transcription factor Nrf2, and provides cytoprotective activity.

CDNA-AFLP Reveals a Striking Overlap in Race-Specific Resistance and Wound Response Gene Expression Profiles

The tomato Cf-9 gene confers resistance to races of the fungal pathogen Cladosporium fulvum expressing the Avr9 gene. cDNA amplified fragment length polymorphism analysis was used to display transcripts whose expression is rapidly altered during the Avr9- and Cf-9-mediated defense response in tobacco cell cultures. Diphenyleneiodonium was used to abolish the production of active oxygen species during gene induction. Of 30,000 fragments inspected, 290 showed altered abundance, of which 263 were induced independently of active oxygen species. cDNA clones were obtained for 13 ACRE (for Avr9/Cf-9 rapidly elicited) genes. ACRE gene induction occurred in the presence of cycloheximide. Avr9 induced ACRE gene expression in leaves. Surprisingly, ACRE genes were also rapidly but transiently induced in leaves in response to other stresses. The amino acid sequences of some ACRE proteins are homologous to sequences of known proteins such as ethylene response element binding protein transcription factors, the N resistance protein, a calcium binding protein, 13-lipoxygenase, and a RING-H2 zinc finger protein. Rapid induction of ACRE genes suggests that they play a pivotal role during plant defense responses.