Activating transcription factor-2 mediates transcriptional regulation of gluconeogenic gene PEPCK by retinoic acid

All-Trans Retinoic Acid Induces TGF-β2 in Intestinal Epithelial Cells via RhoA- and p38α MAPK-Mediated Activation of the Transcription Factor ATF2

Objective

We have shown previously that preterm infants are at risk of necrotizing enterocolitis (NEC), an inflammatory bowel necrosis typically seen in infants born prior to 32 weeks’ gestation, because of the developmental deficiency of transforming growth factor (TGF)-β₂ in the intestine. The present study was designed to investigate all-trans retinoic acid (atRA) as an inducer of TGF-β₂ in intestinal epithelial cells (IECs) and to elucidate the involved signaling mechanisms.

Methods

AtRA effects on intestinal epithelium were investigated using IEC6 cells. TGF-β₂ expression was measured using reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) and Western blots. Signaling pathways were investigated using Western blots, transiently-transfected/transduced cells, kinase arrays, chromatin immunoprecipitation, and selective small molecule inhibitors.

Results

AtRA-treatment of IEC6 cells selectively increased TGF-β₂ mRNA and protein expression in a time- and dose-dependent fashion, and increased the activity of the TGF-β₂ promoter. AtRA effects were mediated via RhoA GTPase, Rho-associated, coiled-coil-containing protein kinase 1 (ROCK1), p38α MAPK, and activating transcription factor (ATF)-2. AtRA increased phospho-ATF2 binding to the TGF-β₂ promoter and increased histone H2B acetylation in the TGF-β₂ nucleosome, which is typically associated with transcriptional activation.

Conclusions

AtRA induces TGF-β₂ expression in IECs via RhoA- and p38α MAPK-mediated activation of the transcription factor ATF2. Further studies are needed to investigate the role of atRA as a protective/therapeutic agent in gut mucosal inflammation.

Vitamin a supplementation, serum lipids, liver enzymes and C-reactive protein concentrations in obese women of reproductive age

Background

High-dose vitamin A influences glucose and lipid profile; however, the possible effects of moderate doses (25,000 IU/d) are conflicting. We aimed to compare the effect of vitamin A supplementation on several anthropometric and biochemical variables between obese and non-obese women.

Methods

This study was performed on 84 women among whom 56 were obese (body mass index [BMI] 30-35 kg/m2) and 28 were non-obese (BMI 18.5-24.9 kg/m2). Obese women were randomly divided into two groups: one group received 25,000 IU/d retinyl palmitate and another group received placebo. The third group was age-matched non-obese women who received 25,000 IU/d retinyl palmitate. At baseline and four months after intervention, fasting blood glucose (FBG), lipid profile, C-reactive protein (CRP) and liver enzymes were evaluated.

Results

Baseline concentrations of serum FBG and triglyceride in the obese vitamin A-treated group were significantly higher compared with the other groups (P = 0.004 and 0.007, respectively). A significant increase in serum FBG (P = 0.026), total cholesterol (TC) (P = 0.004) and low-density lipoprotein cholesterol (LDL-C) (P = 0.016) in the non-obese group and a significant decrease in serum high-density lipoprotein cholesterol (HDL-C) (P = 0.001) in the obese group was observed. Serum CRP increased significantly in the obese vitamin A-treated group (P = 0.03) and serum aspartate transaminase increased significantly in the obese and non-obese groups after vitamin A supplementation (P = 0.008 and 0.001, respectively).

Conclusions

Treatment with 25,000 IU/d vitamin A induced a mild elevation in serum lipids, CRP and liver enzymes in obese and non-obese women. Considering the other information about possible side-effects of excess vitamin A, use of vitamin A in this dose and duration should be considered with caution.

Regulation of aldosterone synthase by activator transcription factor/cAMP response element-binding protein family members

Aldosterone synthesis is regulated by angiotensin II (Ang II) and K(+) acting in the adrenal zona glomerulosa, in part through the regulation of aldosterone synthase (CYP11B2). Here, we analyzed the role of cAMP response element (CRE)-binding proteins (CREBs) in the regulation of CYP11B2. Expression analysis of activator transcription factor (ATF)/CREB family members, namely the ATF1 and ATF2, the CREB, and the CRE modulator, in H295R cells and normal human adrenal tissue was performed using quantitative real-time PCR. Ang II-induced phosphorylation of ATF/CREB members was analyzed by Western blot analysis, and their subsequent binding to the CYP11B2 promoter using chromatin immunoprecipitation assay. Aldosterone production and CYP11B2 expression were measured in small interfering RNA-transfected cells to knockdown the expression of ATF/CREB members. CYP11B2 promoter activity was measured in H295R cells cotransfected with NURR1 (NR4A2) alone or with constitutively active vectors for ATF/CREB members. Ang II induced phosphorylation of ATF1, ATF2, and CRE modulator in a time-dependent manner. Based on chromatin immunoprecipitation analysis, there was an increased association of these proteins with the CYP11B2 promoter after Ang II and K(+) treatment. Phosphorylated ATF/CREB members also bound the CYP11B2 promoter. Knockdown of ATF/CREB members reduced Ang II and K(+) induction of adrenal cell CYP11B2 mRNA expression and aldosterone production. The constitutively active ATF/CREB vectors increased the promoter activity of CYP11B2 and had a synergistic effect with NURR1. In summary, these results suggest that ATF/CREB and NGFI-B family members play a crucial role in the transcriptional regulation of CYP11B2 and adrenal cell capacity to produce aldosterone.

The role of ATF-2 family transcription factors in adipocyte differentiation: antiobesity effects of p38 inhibitors

ATF-2 is a member of the ATF/CREB family of transcription factors and is activated by stress-activated protein kinases, such as p38. To analyze the physiological role of ATF-2 family transcription factors, we have generated mice with mutations in Atf-2 and Cre-bpa, an Atf-2-related gene. The trans-heterozygotes of both mutants were lean and had reduced white adipose tissue (WAT). ATF-2 and CRE-BPa were required for bone morphogenetic protein 2 (BMP-2)-and p38-dependent induction of peroxisome proliferator-activated receptor gamma2 (PPARgamma2), a key transcription factor mediating adipocyte differentiation. Since stored fat supplies have been recognized as a possible target for antiobesity treatments, we tested whether inhibition of the p38-ATF-2 pathway suppresses adipocyte differentiation and leads to reduced WAT by treating mice with a p38 inhibitor for long periods of time. High-fat diet (HFD)-induced obesity was significantly reduced in mice fed the p38 inhibitor. Furthermore, the p38 inhibitor alleviated HFD-induced insulin resistance. In p38 inhibitor-treated mice, macrophage infiltration into WAT was reduced and the tumor necrosis factor alpha (TNF-alpha) levels were lower than control mice. Thus, p38 inhibitors may provide a novel antiobesity treatment.

Proteomic screen defines the hepatocyte nuclear factor 1alpha-binding partners and identifies HMGB1 as a new cofactor of HNF1alpha

Hepatocyte nuclear factor (HNF)-1α is one of the liver-enriched transcription factors involved in many tissue-specific expressions of hepatic genes. The molecular mechanisms for determining HNF1α-mediated transactivation have not been explained fully. To identify unknown proteins that interact with HNF1α, we developed a co-IP-MS strategy to search HNF1α interactions, and high mobility group protein-B1 (HMGB1), a chromosomal protein, was identified as a novel HNF1α-interacting protein. In vitro glutathione S-transferase pull-down and in vivo co-immunoprecipitation studies confirmed an interaction between HMGB1 and HNF1α. The protein–protein interaction was mediated through the HMG box domains of HMGB1 and the homeodomain of HNF1α. Furthermore, electrophoretic mobility shift assay and chromatin-immunoprecipitation assay demonstrated that HMGB1 was recruited to endogenous HNF1α-responsive promoters and enhanced HNF1α binding to its cognate DNA sequences. Moreover, luciferase reporter analyses showed that HMGB1 potentiated the transcriptional activities of HNF1α in cultured cells, and downregulation of HMGB1 by RNA interference specifically affected the HNF1α-dependent gene expression in HepG2 cell. Taken together, these findings raise the intriguing possibility that HMGB1 is a new cofactor of HNF1α and participates in HNF1α-mediated transcription regulation through protein–protein interaction.

CSK controls retinoic acid receptor (RAR) signaling: a RAR-c-SRC signaling axis is required for neuritogenic differentiation

Herein, we report the first evidence that c-SRC is required for retinoic acid (RA) receptor (RAR) signaling, an observation that suggests a new paradigm for this family of nuclear hormone receptors. We observed that CSK negatively regulates RAR functions required for neuritogenic differentiation. CSK overexpression inhibited RA-mediated neurite outgrowth, a result which correlated with the inhibition of the SFK c-SRC. Consistent with an extranuclear effect of CSK on RAR signaling and neurite outgrowth, CSK overexpression blocked the downstream activation of RAC1. The conversion of GDP-RAC1 to GTP-RAC1 parallels the activation of c-SRC as early as 15 min following all-trans-retinoic acid treatment in LA-N-5 cells. The cytoplasmic colocalization of c-SRC and RARgamma was confirmed by immunofluorescence staining and confocal microscopy. A direct and ligand-dependent binding of RAR with SRC was observed by surface plasmon resonance, and coimmunoprecipitation studies confirmed the in vivo binding of RARgamma to c-SRC. Deletion of a proline-rich domain within RARgamma abrogated this interaction in vivo. CSK blocked the RAR-RA-dependent activation of SRC and neurite outgrowth in LA-N-5 cells. The results suggest that transcriptional signaling events mediated by RA-RAR are necessary but not sufficient to mediate complex differentiation in neuronal cells. We have elucidated a nongenomic extranuclear signal mediated by the RAR-SRC interaction that is negatively regulated by CSK and is required for RA-induced neuronal differentiation.

ATF-2 regulates fat metabolism in Drosophila

ATF-2 is a member of the ATF/CREB family of transcription factors that is activated by stress-activated protein kinases such as p38. To analyze the physiological role of Drosophila ATF-2 (dATF-2), we generated dATF-2 knockdown flies using RNA interference. Reduced dATF-2 in the fat body, the fly equivalent of the mammalian liver and adipose tissue, decreased survival under starvation conditions. This was due to smaller triglyceride reserves of dATF-2 knockdown flies than control flies. Among multiple genes that control triglyceride levels, expression of the Drosophila PEPCK (dPEPCK) gene was strikingly reduced in dATF-2 knockdown flies. PEPCK is a key enzyme for both gluconeogenesis and glyceroneogenesis, which is a pathway required for triglyceride synthesis via glycerol-3-phosphate. Although the blood sugar level in dATF-2 knockdown flies was almost same as that in control flies, the activity of glyceroneogenesis was reduced in the fat bodies of dATF-2 knockdown flies. Thus, reduced glyceroneogenesis may at least partly contribute to decreased triglyceride stores in the dATF-2 knockdown flies. Furthermore we showed that dATF-2 positively regulated dPEPCK gene transcription via several CRE half-sites in the PEPCK promoter. Thus, dATF-2 is critical for regulation of fat metabolism.

Effects of retinoid therapy on insulin sensitivity, lipid profile and circulating adipocytokines

OBJECTIVE

In vitro and in vivo models indicate that all-trans retinoic acids influence glucose and lipid metabolism. We aimed to evaluate the effects of chronic treatment with acitretin, an all-trans retinoic acid, on glucose metabolism, lipid profile and adiponectin and resistin levels.

DESIGN

Ten normoglycemic, normolipemic patients affected with psoriasis vulgaris were studied before and after 1 and 3 months of oral treatment with 35 microg of acitretin.

METHODS

Glucose metabolism, lipid profile, and adiponectin and resistin levels were evaluated in basal conditions and after acitretin treatment. Ten healthy subjects matched for age, body mass index (BMI) and insulin sensitivity were studied as controls.

RESULTS

One-month acitretin treatment reduced psoriasis activity, insulin sensitivity, evaluated as QUICKI values (0.364 +/- 0.034 versus 0.329 +/- 0.051; P < 0.05) and HOMA-IR index (1.53 +/- 0.73 versus 2.59 +/- 1.41; P < 0.05), and high-density lipoprotein (HDL)-cholesterol levels (45.2 +/- 11.7 versus 39.4 +/- 10.4 mg/dl; P = 0.01). The impairment in glucose and lipid homeostasis was transient and not associated to BMI variations. Adiponectin levels did not change during the treatment, while resistin levels, which were higher in untreated patients than in controls (9.4 +/- 4.4 versus 6.2 +/- 2.1 ng/ml; P = 0.05), fell within the normal range after 1 and 3 months of therapy. The normalization of resistin levels occurred without significant changes in circulating tumor necrosis factor alpha (TNFalpha) levels, which persisted elevated throughout the treatment.

CONCLUSIONS

Treatment with a low dose of acitretin induced a mild, transient reduction of insulin sensitivity and HDL-cholesterol levels that was not related to modifications of adiponectin, resistin and TNFalpha levels. Although the role of resistin in humans remains elusive, the levels of this adipocytokine seem to be affected, at least in part, by retinoids.

Vitamin A status in mice affects the histone code of the phosphoenolpyruvate carboxykinase gene in liver

Vitamin A deficiency decreases hepatic phosphoenolpyruvate carboxykinase (PEPCK) gene expression in mice, and expression is restored with retinoic acid (RA) treatment in vivo. In the studies reported here, we examined changes in histone modification and coregulator association with the regulatory domains of the PEPCK gene in response to alterations in vitamin A status. We identified nuclear receptors that bind to retinoic acid response elements (RAREs) in the PEPCK promoter by electrophoretic mobility shift assay and verified these in vivo using chromatin immunoprecipitation in mouse liver. Hypothetically, nuclear receptors at PEPCK RAREs recruit specific coactivator molecules that contribute to the acetylation of core histones and/or serve as bridging molecules between nuclear receptors and basal transcription factors at the transcription start site. We identified 3 coactivator molecules, cAMP-response element binding protein (CBP), steroid receptor coactivator (SRC)-1, and peroxisome-proliferator activated receptor (PPAR)-gamma-coactivator (PGC)-1alpha, that bound in association with the PEPCK RAREs in vivo. Furthermore, there was differential binding of these coactivators in vitamin A-deficient mice. Related to this, specific lysine residues were acetylated on histones H3 and H4 at the 3 RAREs of the PEPCK promoter, consistent with the action of the above coactivators, and acetylation of certain lysines was significantly decreased with vitamin A deficiency. These results demonstrate the associated changes that occur in nuclear receptor binding, coactivator recruitment, and histone acetylation in response to vitamin A status, identified at specific RAREs in the PEPCK gene in vivo.

30 some years of heme oxygenase: from a "molecular wrecking ball" to a "mesmerizing" trigger of cellular events

In the beginning, the microsomal HO system was presumed to be made of one isozymes, now known as HO-1, which was cytP450-dependent; and, was thought to be of physiological significance solely in the context of catalysis of hemoglobin heme to bile pigments and CO. A succession of discoveries including characterization of the system as an independent mono-oxygenase, identification of a second form, called HO-2, free radical quenching activity of bile pigments, analogous function of CO in cell signaling to NO, and characterization of the system as HSP32 cognates has led to such an impressive expansion in the number of reports dealing with the HO system that surpass anyone's expectation. This review is a compilation of certain older findings and recent events that together ensure placement of the HO system in the mainstream research for decades to come.

Exploring the O-GlcNAc proteome: direct identification of O-GlcNAc-modified proteins from the brain

The covalent modification of intracellular proteins by O-linked beta-N-acetylglucosamine (O-GlcNAc) is emerging as a crucial regulatory posttranslational modification akin to phosphorylation. Numerous studies point to the significance of O-GlcNAc in cellular processes such as nutrient sensing, protein degradation, and gene expression. Despite its importance, the breadth and functional roles of O-GlcNAc are only beginning to be elucidated. Advances in our understanding will require the development of new strategies for the detection and study of O-GlcNAc-modified proteins in vivo. Herein we report the direct, high-throughput analysis of O-GlcNAc-glycosylated proteins from the mammalian brain. The proteins were identified by using a chemoenzymatic approach that exploits an engineered galactosyltransferase enzyme to selectively label O-GlcNAc proteins with a ketone-biotin tag. The tag permits enrichment of low-abundance O-GlcNAc species from complex mixtures and localization of the modification to short amino acid sequences. Using this approach, we discovered 25 O-GlcNAc-glycosylated proteins from the brain, including regulatory proteins associated with gene expression, neuronal signaling, and synaptic plasticity. The functional diversity represented by this set of proteins suggests an expanded role for O-GlcNAc in regulating neuronal function. Moreover, the chemoenzymatic strategy described here should prove valuable for identifying O-GlcNAc-modified proteins in various tissues and facilitate studies of the physiological significance of O-GlcNAc across the proteome.