Biomedical subjects

Charles Vinson

Publications and source records attributed to Charles Vinson.

At least 19 recordsLinked to original sources

PubMed2026

Age-related distribution of homologous recombination deficiency in advanced ovarian carcinoma: a large real-world French cohort.

OBJECTIVE: Tumor genetic testing for BRCA and homologous recombination repair is essential for guiding maintenance therapy in high-grade non-mucinous ovarian carcinomas. While clinical trials (PAOLA-1, PRIMA, ATHENA-MONO, PRIME) have reported homologous recombination deficiency rates of 44% to 67% in cohorts with a median age of 61, real-world data suggest age-related variations. We aimed to evaluate homologous recombination deficiency prevalence in a large French population and hypothesized a distribution pattern similar to the recent German findings published in 2022, in which older age correlated with lower homologous recombination deficiency rates. METHODS: We retrospectively analyzed advanced ovarian carcinoma cases referred to the Dijon Cancer Center from 191 care centers between 2022 and 2024 for Myriad MyChoice homologous recombination deficiency testing. Data collected included age, histologic type, homologous recombination deficiency status, homologous recombination proficiency status, and genomic instability scores. We compared the distribution of homologous recombination deficiency and HRP tumors in women <60 and ≥60 years using the χ2 test. RESULTS: In 1322 advanced ovarian carcinoma cases with a median age of 70.1 years, the overall rates were 35.3% homologous recombination deficiency and 64.7% homologous recombination proficiency. A sub-analysis of 1226 high-grade cases (median age 70.4; including high-grade serous carcinoma, clear-cell carcinoma, undifferentiated carcinomas, and carcinosarcoma) showed 36.5% homologous recombination deficiency and 63.5% homologous recombination proficiency. Notably, patients aged ≥60 years had a significantly higher likelihood of presenting with a homologous recombination proficiency tumor compared with those aged <60 years (65.8% vs 53.2%, p < .001). Among 42 clear-cell carcinoma cases, 97.6% exhibited homologous recombination proficiency status. CONCLUSIONS: In this large real-world cohort of advanced ovarian carcinoma, we observed a notably higher prevalence of homologous recombination proficiency tumors compared to the 4 clinical trials reported in the literature, with homologous recombination proficiency incidence increasing significantly with age. Given that older patients predominantly present with homologous recombination proficiency tumors, which are associated with poorer survival, treatment strategies should be adjusted to better address the specific needs of this demographic.

Humans↗

PubMed2007

Elevated blood pressure in transgenic lipoatrophic mice and altered vascular function.

The role of perivascular fat in the control of vascular function was studied using lipoatrophic A-ZIP/F1 transgenic mice. Only a small amount of brown fat was found around the aorta but not around mesenteric arteries. Blood pressure of A-ZIP/F1 mice became higher than wild-type (WT) mice from 10 weeks of age. The presence of perivascular fat reduced the contraction of WT aorta to phenylephrine and serotonin, whereas this effect was either absent or less prominent in A-ZIP/F1 aorta. In WT mice, transfer of solution incubated with aorta with fat to aorta with fat removed caused a relaxation response, but not in A-ZIP/F1 mice, indicating the release of a relaxation factor from perivascular fat in WT aorta. This factor was acting through the activation of calcium-dependent potassium channels. Perfusion of phenylephrine to the isolated mesenteric bed caused a higher increase in perfusion pressure in A-ZIP/F1 than in WT mice. Contractile response of aorta to angiotensin II (Ang II) was mediated by Ang II type 1 receptors and was higher in A-ZIP/F1 than in WT mice. Expression of Ang II type 1 receptors but not Ang II type 2 receptors was higher in aorta of A-ZIP/F1 than WT mice. Treatment with an Ang II type 1 receptor antagonist (TCV 116, 10 mg/kg per day) for 2 weeks normalized the blood pressure of A-ZIP/F1 mice. These results suggest that the absence of perivascular fat tissue, which enhances the contractile response of the blood vessels to agonists, and an upregulation of vascular Ang II type 1 receptors in A-ZIP/F1 mice, are some of the mechanisms underlying the blood pressure elevation in these lipoatrophic mice.

Adipose Tissue, Brown↗

PubMed2007

Interleukin-1beta and tetradecanoylphorbol acetate-induced biosynthesis of tumor necrosis factor alpha in human hepatoma cells involves the transcription factors ATF2 and c-Jun and stress-activated protein kinases.

The proinflammatory cytokine tumor necrosis factor (TNF) alpha is mainly produced in cells from the monocyte/macrophage lineage. TNFalpha is also a key signaling molecule in the liver functioning as an important physiological and pathogenic mediator. In hepatocytes or human hepatoma cells TNFalpha is expressed at extremely low levels but TNFalpha biosynthesis can be induced by interleukin (IL)-1beta or 12-O-tetradecanoylphorbol-13-acetate (TPA). Here, we show that IL-1beta and TPA stimulated TNFalpha gene transcription in hepatoma cells mediated by a composite TPA-responsive element/cAMP response element. Both IL-1beta and TPA triggered phosphorylation and activation of the basic region leucine zipper transcription factors c-Jun and ATF2 and expression of dominant-negative mutants of c-Jun and ATF2-reduced TNFalpha promoter activity and secretion of TNFalpha. Expression of the nuclear dual-specific MAP kinase phosphatase-1 (MKP-1) blocked TNFalpha promoter activity and TNFalpha secretion following IL-1beta or TPA stimulation, indicating that MKP-1 functions as a nuclear shut-of-device of IL-1beta and TPA-induced TNFalpha expression.

Activating Transcription Factor 2↗

PubMed2007

5'UTR of the neurogenic bHLH Nex1/MATH-2/NeuroD6 gene is regulated by two distinct promoters through CRE and C/EBP binding sites.

Expression of the bHLH transcription factor Nex1/MATH-2/NeuroD6, a member of the NeuroD subfamily, parallels overt neuronal differentiation and synaptogenesis during brain development. Our previous studies have shown that Nex1 is a critical effector of the NGF pathway and promotes neuronal differentiation and survival of PC12 cells in the absence of growth factors. In this study, we investigated the transcriptional regulation of the Nex1 gene during NGF-induced neuronal differentiation. We found that Nex1 expression is under the control of two conserved promoters, Nex1-P1 and Nex1-P2, located in two distinct non-coding exons. Both promoters are TATA-less with multiple transcription start sites, and are activated on NGF or cAMP exposure. Luciferase-reporter assays showed that the Nex1-P2 promoter activity is stronger than the Nex1-P1 promoter activity, which supports the previously reported differential expression levels of Nex1 transcripts throughout brain development. Using a combination of DNaseI footprinting, EMSA assays, and site-directed mutagenesis, we identified the essential regulatory elements within the first 2 kb of the Nex1 5'UTR. The Nex1-P1 promoter is mainly regulated by a conserved CRE element, whereas the Nex1-P2 promoter is under the control of a conserved C/EBP binding site. Overexpression of wild-type C/EBPbeta resulted in increased Nex1-P2 promoter activity in NGF-differentiated PC12 cells. The fact that Nex1 is a target gene of C/EBPbeta provides new insight into the C/EBP transcriptional cascade known to promote neurogenesis, while repressing gliogenesis.

5' Untranslated Regions↗

PubMed2006

Stability of 100 homo and heterotypic coiled-coil a-a' pairs for ten amino acids (A, L, I, V, N, K, S, T, E, and R).

We present the thermal stability monitored by circular dichroism (CD) spectroscopy at 222 nm of 100 heterodimers that contain all possible coiled-coil a-a' pairs for 10 amino acids (I, V, L, N, A, K S, T, E, and R). This includes the stability of 36 heterodimers for 6 amino acids (I, V, L, N, A, and K) previously described and 64 new heterodimers including the 4 amino acids (S, T, E, and R). We have calculated a double mutant alanine thermodynamic cycle to determine a-a' pair coupling energies to evaluate which a-a' pairs encourage specific dimerization partners. The four new homotypic a-a' pairs (T-T, S-S, R-R, E-E) are repulsive relative to A-A and have destabilizing coupling energies. Among the 90 heterotypic a-a' pairs, the stabilizing coupling energies contain lysine or arginine paired with either an aliphatic or a polar amino acid. The range in coupling energies for each amino acid reveals its potential to regulate dimerization specificity. The a-a' pairs containing isoleucine and asparagine have the greatest range in coupling energies and thus contribute dramatically to dimerization specificity, which is to encourage homodimerization. In contrast, the a-a' pairs containing charged amino acids (K, R, and E) show the least range in coupling energies and promiscuously encourage heterodimerization.

Amino Acid Sequence↗

PubMed2006

Elovl3: a model gene to dissect homeostatic links between the circadian clock and nutritional status.

The ELOVL3 protein is a very long-chain fatty acid elongase found in liver, skin, and brown adipose tissues. Circadian expression of the Elovl3 gene in the liver is perturbed in mutant CLOCK mice but persists in mice with severe hepatic dysfunction. A reliance on an intact clock, combined with the refractoriness to liver decompensation and the finding of a robust sexually dimorphic pattern of expression, evince a particularly complex mode of transcriptional control. The Elovl3 gene upstream region was repressed by RevErbalpha and activated by sterol-regulatory element binding protein-1 (SREBP1) transcription factors. We propose that the temporal coordination of RevErbalpha and SREBP1 activities integrates clock and nutrition signals to drive a subset of oscillatory transcripts in the liver. Proteolytic activation of SREBP1 is circadian in the liver, and because the cycle of SREBP1 activation was reversed after restricting meals to the inactive phase of the day, this factor could serve as an acute sensor of nutritional state. SREBP1 regulates many known lipogenic and cholesterogenic circadian genes; hence, our results could explain how feeding can override brain-derived entraining signals in the liver. This mechanism would permit a rapid adjustment in the sequence of key aspects of the absorptive and postabsorptive phases in the liver.

Acetyltransferases↗

PubMed2006

Susceptibility to induced and spontaneous carcinogenesis is increased in fatless A-ZIP/F-1 but not in obese ob/ob mice.

Obesity is typically associated with increased tumor susceptibility, whereas caloric restriction, a regimen resulting in leanness, inhibits carcinogenesis. The link between adiposity and malignancies suggests that adipose tissue may influence carcinogenesis. An adipose tissue hormone, leptin, could be procarcinogenic because it stimulates proliferation in various tissues and tumor cell lines. Leptin may contribute to the correlation between adiposity and malignancies as its levels are usually increased in obese subjects and reduced by caloric restriction. We hypothesized that leptin deficiency, despite obesity, would inhibit carcinogenesis in leptin-null ob/ob mice and tested this hypothesis in two models: (a) two-stage skin carcinogenesis initiated by 7,12-dimethylbenz(a)anthracene and promoted by phorbol 12-myristate 13-acetate (PMA) and (b) p53 deficiency. Contrary to a typical association between obesity and enhanced carcinogenesis, obese ob/ob mice developed induced skin papillomas and spontaneous p53-deficient malignancies, mostly lymphomas, similarly to their lean littermates. Surprisingly, lipodystrophic (ZIP) mice that had very little both adipose tissue and leptin were highly susceptible to carcinogenesis. Hyperphagia, hyperinsulinemia, and hyperglycemia are unlikely to have contributed significantly to the enhancement of carcinogenesis in ZIP mice because similarly hyperphagic, hyperinsulinemic, and hyperglycemic ob/ob mice had normal susceptibility to carcinogenesis. Our data suggest that, in contrast to a well-known correlation between obesity and cancer, the direct effect of adipose tissue may rather be protective.

Animals↗

PubMed2006

Activator protein-1 activity regulates epithelial tumor cell identity.

To examine the consequences of inhibiting activator protein-1 (AP-1) transcription factors in skin, transgenic mice were generated, which use the tetracycline system to conditionally express A-FOS, a dominant negative that inhibits AP-1 DNA binding. Older mice develop mild alopecia and hyperplasia of sebaceous glands, particularly around the eyes. When A-FOS was expressed during chemical-induced skin carcinogenesis, mice do not develop characteristic benign and malignant squamous lesions but instead develop benign sebaceous adenomas containing a signature mutation in the H-ras proto-oncogene. Inhibiting AP-1 activity after tumor formation caused squamous tumors to transdifferentiate into sebaceous tumors. Furthermore, reactivating AP-1 in sebaceous tumors results in a reciprocal transdifferentiation into squamous tumors. In both cases of transdifferentiation, individual cells express molecular markers for both cell types, indicating individual tumor cells have the capacity to express multiple lineages. Molecular characterization of cultured keratinocytes and tumor material indicates that AP-1 regulates the balance between the wnt/beta-catenin and hedgehog signaling pathways that determine squamous and sebaceous lineages, respectively. Chromatin immunoprecipitation analysis indicates that c-Jun binds several wnt promoters, which are misregulated by A-FOS expression, suggesting that members of the wnt pathway can be a primary targets of AP-1 transcriptional regulation. Thus, AP-1 activity regulates tumor cell lineage and is essential to maintain the squamous tumor cell identity.

Adenocarcinoma, Sebaceous↗

PubMed2006

Accelerated tumor formation in a fatless mouse with type 2 diabetes and inflammation.

Epidemiologic studies show a positive association between obesity and cancer risk. In addition to increased body adiposity and secretion of fat-derived hormones, obesity is also linked to insulin resistance, type 2 diabetes, and chronic inflammation. We used the fatless A-ZIP/F-1 transgenic mouse to dissociate the relative role of each of these underlying factors in the development of cancer. These mice are unique in that they do not have white fat but do develop type 2 diabetes. In two cancer models, the classic two-stage skin carcinogenesis protocol and the C3(1)/T-Ag transgenic mouse mammary tumor model, A-ZIP/F-1 mice displayed higher tumor incidence, tumor multiplicity, and decreased tumor latency than wild-type mice. We examined circulating levels of adipokines, growth factors, and cytokines. As expected, adipokines (i.e., leptin, adiponectin, and resistin) were undetectable or found at very low levels in the blood of fatless mice. However, insulin, insulin-like growth factor-I, growth hormone, vascular endothelial growth factor, and proinflammatory Th2 cytokines, such as interleukin (IL)-1beta, IL-4, and IL-6, were elevated in A-ZIP/F-1 mice. Additionally, we examined multiple phosphorylated proteins (i.e., protein kinase B/Akt and ErbB2/HER-2 kinase) associated with cancer development. Results show that many of these phosphorylated proteins were activated specifically in the A-ZIP/F-1 skin but not in the wild-type skin. These findings suggest that adipokines are not required for the promotion of tumor development and thus contradict the epidemiologic data linking obesity to carcinogenesis. We postulate that insulin resistance and inflammation are responsible for the positive correlation with cancer observed in A-ZIP/F-1 mice.

Adiponectin↗

PubMed2006

Experimental identification of homodimerizing B-ZIP families in Homo sapiens.

B-ZIP transcription factors dimerization is mediated by a parallel coiled-coil termed the leucine zipper. We have evaluated the dimerization specificity of the seven coiled-coil B-ZIP proteins (ATF6, XBP, LZIP, NFIL3, TEF, CREB, and C/EBPalpha) with themselves and each other. To do this, we designed dominant negative proteins, termed A-ZIPs, that contain the leucine zipper dimerization domain of a B-ZIP protein and an acidic amphipathic N-terminal extension. The A-ZIPs heterodimerize with B-ZIP proteins in a leucine zipper-dependent manner. The acidic N-terminal extension is hypothesized to form an heterodimeric coiled-coil structure with the basic region, essentially zippering the leucine zipper into the basic region. We now present a new acidic extension design that stabilizes heterodimerization with B-ZIP proteins up to 11 kcal mol(-1). We have used these A-ZIP proteins in a competition EMSA to evaluate which A-ZIP can prevent DNA binding of which B-ZIP domain. Inhibition of DNA binding is interpreted to indicate that the A-ZIP is forming a heterodimer with the B-ZIP domain and thus prevents the B-ZIP from binding to DNA. All leucine zippers examined can homodimerize and two pairs (CREB & NFIL3 and ATF6 & XBP) can heterodimerize. We discuss these results with reference to the amino acid sequence of the leucine zipper region. These A-ZIP reagents may be of value in biological systems to inhibit the DNA binding and transcriptional potential of specific B-ZIP families.

Activating Transcription Factor 2↗

PubMed2006

Up-regulation of tyrosine hydroxylase gene transcription by tetradecanoylphorbol acetate is mediated by the transcription factors Ets-like protein-1 (Elk-1) and Egr-1.

Tyrosine hydroxylase is the rate-limiting enzyme in the biosynthesis of catecholamines. Expression of the tyrosine hydroxylase gene is regulated at the transcriptional level by extracellular signalling molecules, including epidermal growth factor (EGF), nerve growth factor (NGF) and glucocorticoids. We have analysed the stimulation of tyrosine hydroxylase gene transcription by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) in noradrenergic locus coeruleus-like CATH.a cells and observed a striking enhancement of the transcriptional activation potential of the ternary complex factor Ets-like protein-1 (Elk-1), a key transcriptional regulator of serum response element-driven gene transcription. Likewise, TPA strongly up-regulated the biosynthesis of the transcription factor Egr-1 via distal serum response elements within the Egr-1 5'-flanking region. Subsequently, enhancement of the transcriptional activation potential of Egr-1 was observed. Overexpression of Egr-1 was sufficient to activate transcription of a tyrosine hydroxylase promoter/reporter gene, corroborating the view that the tyrosine hydroxylase gene is a target gene of Egr-1. Expression of dominant-negative mutants of Elk-1 or Egr-1 impaired TPA-induced stimulation of a tyrosine hydroxylase promoter/reporter gene transcription. In contrast, dominant-negative mutants of the transcription factors activating transcription factor (ATF)-2, ATF4, cAMP response element-binding protein, c-Jun and CCAAT/enhancer binding protein (C/EBP) did not change TPA-induced tyrosine hydroxylase promoter activity, indicating that these proteins are not part of the TPA-mediated signalling cascade directed towards the tyrosine hydroxylase gene.

Animals↗

PubMed2006

Deciphering B-ZIP transcription factor interactions in vitro and in vivo.

Over the last 15 years, numerous studies have addressed the structural rules that regulate dimerization stability and dimerization specificity of the leucine zipper, a dimeric parallel coiled-coil domain that can either homodimerize or heterodimerize. Initially, these studies were performed with a limited set of B-ZIP proteins, sequence-specific DNA binding proteins that dimerize using the leucine zipper domain to bind DNA. A global analysis of B-ZIP leucine zipper dimerization properties can be rationalized using a limited number of structural rules [J.R. Newman, A.E. Keating, Comprehensive identification of human bZIP interactions with coiled-coil arrays, Science 300 (2003) 2097-2101]. Today, however, access to the genomic sequences of many different organisms has made possible the annotation of all B-ZIP proteins from several species and has generated a bank of data that can be used to refine, and potentially expand, these rules. Already, a comparative analysis of the B-ZIP proteins from Arabidopsis thaliana and Homo sapiens has revealed that the same amino acids are used in different patterns to generate diverse B-ZIP dimerization patterns [C.D. Deppmann, A. Acharya, V. Rishi, B. Wobbes, S. Smeekens, E.J. Taparowsky, C. Vinson, Dimerization specificity of all 67 B-ZIP motifs in Arabidopsis thaliana: a comparison to Homo sapiens B-ZIP motifs, Nucleic Acids Res. 32 (2004) 3435-3445]. The challenge ahead is to investigate the biological significance of different B-ZIP protein-protein interactions. Gaining insight at this level will rely on ongoing investigations to (a) define the role of target DNA on modulating B-ZIP dimerization partners, (b) characterize the B-ZIP transcriptome in various cells and tissues through mRNA microarray analysis, (c) identify the genomic localization of B-ZIP binding at a genomic level using the chromatin immunoprecipitation assay, and (d) develop more sophisticated imaging technologies to visualize dimer dynamics in single cells and whole organisms. Studies of B-ZIP family leucine zipper dimerization and the regulatory mechanisms that control their biological activities could serve as a paradigm for deciphering the biophysical and biological parameters governing other well-characterized protein-protein interaction motifs. This review will focus on the dimerization specificity of coiled-coil proteins, particularly the human B-ZIP transcription family that consists of 53 proteins that use the leucine zipper coiled-coil as a dimerization motif.

Amino Acid Motifs↗

PubMed2006

Math6 expression during kidney development and altered expression in a mouse model of glomerulosclerosis.

Math6 is a tissue-restricted member of the Atonal family of basic helix-loop-helix (bHLH) transcription factors and has been implicated in specification and differentiation of cell lineages in the brain. We identify here Math6 as a podocyte-expressed bHLH protein that was down-regulated in human immunodeficiency virus-associated nephropathy (HIVAN); a collapsing glomerulopathy characterized by podocyte dedifferentiation. Early in metanephric development, Math6 was expressed in metanephric mesenchyme but not ureteric bud-derived cells, with overall Math6 expression most abundant in the nephrogenic zone, including developing glomeruli. In adult kidney, Math6 expression was restricted to podocytes. In adult podocyte cell lines and kidneys from the transgenic mouse model of HIVAN, Math6 podocyte expression was reduced concurrent with previously reported reductions in Nephrin and Synaptopodin expression, suggesting a correlation between the loss of Math6 expression and typical podocyte terminal differentiation markers. These studies suggest that Math6 may participate in kidney development and may be a permissive factor for podocyte differentiation.

Amino Acid Sequence↗

PubMed2006

Comparative genomics of Drosophila and human core promoters.

BACKGROUND: The core promoter region plays a critical role in the regulation of eukaryotic gene expression. We have determined the non-random distribution of DNA sequences relative to the transcriptional start site in Drosophila melanogaster promoters to identify sequences that may be biologically significant. We compare these results with those obtained for human promoters. RESULTS: We determined the distribution of all 65,536 octamer (8-mers) DNA sequences in 10,914 Drosophila promoters and two sets of human promoters aligned relative to the transcriptional start site. In Drosophila, 298 8-mers have highly significant (p < or = 1 x 10(-16)) non-random distributions peaking within 100 base-pairs of the transcriptional start site. These sequences were grouped into 15 DNA motifs. Ten motifs, termed directional motifs, occur only on the positive strand while the remaining five motifs, termed non-directional motifs, occur on both strands. The only directional motifs to localize in human promoters are TATA, INR, and DPE. The directional motifs were further subdivided into those precisely positioned relative to the transcriptional start site and those that are positioned more loosely relative to the transcriptional start site. Similar numbers of non-directional motifs were identified in both species and most are different. The genes associated with all 15 DNA motifs, when they occur in the peak, are enriched in specific Gene Ontology categories and show a distinct mRNA expression pattern, suggesting that there is a core promoter code in Drosophila. CONCLUSION: Drosophila and human promoters use different DNA sequences to regulate gene expression, supporting the idea that evolution occurs by the modulation of gene regulation.

Animals↗

PubMed2005

Regulation of GTP cyclohydrolase I gene transcription by basic region leucine zipper transcription factors.

Tetrahydrobiopterin is an essential cofactor for the phenylalanine, tyrosine and tryptophan hydroxylases, and the family of nitric oxide synthases. The initial and rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin is GTP cyclohydrolase I. The proximal promoter of the human GTP cyclohydrolase I gene contains the sequence motif 5'-TGACGCGA-3', resembling a cAMP response element (CRE). The objective of this study was to analyze the regulation of GTP cyclohydrolase I gene transcription by basic region leucine zipper (bZIP) transcription factors. A constitutively active mutant of the cAMP response element binding (CREB) protein strongly stimulated GTP cyclohydrolase I promoter activity, indicating that the CRE in the context of the GTP cyclohydrolase I gene is functional. Likewise, GTP cyclohydrolase I promoter/luciferase gene transcription was stimulated following nuclear expression of the catalytic subunit of cAMP-dependent protein kinase. Constitutively active mutants of activating transcription factor 2 (ATF2) and c-Jun additionally stimulated GTP cyclohydrolase I promoter activity, but to a lesser extent than the constitutively active CREB mutant. The fact that stress-activated protein kinases target the GTP cyclohydrolase I gene was corroborated by expression experiments involving p38 and MEKK1 protein kinases. We conclude that signaling pathways involving either the cAMP-dependent protein kinase or stress-activated protein kinases converge to the GTP cyclohydrolase I gene. Hence, enzymatic reactions that require tetrahydrobiopterin as cofactor are therefore indirectly controlled by signaling cascades involving the signal-responsive transcription factors CREB, c-Jun, and ATF2.

Activating Transcription Factor 2↗

PubMed2005

Role of CCAAT/enhancer-binding protein, histone acetylation, and coactivator recruitment in the regulation of malic enzyme transcription by thyroid hormone.

In chick embryo hepatocytes, activation of malic enzyme gene transcription by triiodothyronine (T3) is mediated by a T3 response unit (T3RU) that contains five T3 response elements (T3REs) plus five accessory elements that enhance T3 responsiveness conferred by the T3REs. Results from in vitro binding assays indicate that one of the accessory elements (region F) binds CCAAT/enhancer-binding protein-alpha (C/EBPalpha). Here, we investigated the role of C/EBPalpha in the regulation of malic enzyme transcription by T3. Transfection analyses demonstrated that the stimulation of T3RE function by region F did not require the presence of additional malic enzyme gene promoter sequences. Expression of a dominant negative C/EBP inhibited the ability of region F to stimulate T3 responsiveness. In chromatin immunoprecipitation assays, C/EBPalpha and TR associated with the malic enzyme T3RU in the absence and presence of T3 with the extent of the association being greater in the presence of T3. These observations indicate that C/EBPalpha interacts with TR on the malic enzyme T3RU to enhance T3 regulation of malic enzyme gene transcription. T3 treatment increased the acetylation of histones, decreased the recruitment of nuclear receptor corepressor and increased the recruitment of steroid receptor coactivator-1, CREB binding protein, and the thyroid hormone associated protein/mediator complex at the malic enzyme T3RU. In contrast, T3 treatment had no effect on the acetylation of histones and the recruitment of corepressors and coactivators at the T3RU that mediates the T3 activation of acetyl-CoA carboxylase-alpha gene transcription. We propose that differences between the malic enzyme T3RU and the ACCalpha T3RU in the ability of T3 to modulate histone acetylation and coregulatory protein recruitment are due to differences in the composition of the nuclear receptor complexes that bind these regulatory regions.

Acetyl-CoA Carboxylase↗

PubMed2005

Glucose-induced lipogenesis in pancreatic beta-cells is dependent on SREBP-1.

High concentrations of glucose induce de novo fatty acid synthesis in pancreatic beta-cells and chronic exposure of elevated glucose and fatty acids synergize to induce accumulation of triglycerides, a phenomenon termed glucolipotoxicity. Here we investigate the role of sterol-regulatory element binding proteins in glucose-induced lipogenesis in the pancreatic beta-cell line INS-1E. We show that glucose induces SREBP-1c expression and SREBP-1 activity independent of insulin secretion and signaling. Using adenoviral expression of SREBP-1c and a SREBP-mutant we show that lipogenic gene expression, de novo fatty acid synthesis and lipid accumulation are induced primarily through sterol-regulatory elements (SREs) and not E-Boxes. Adenoviral expression of a dominant negative SREBP compromises glucose induction of some lipogenic genes and significantly reduces glucose-induction of de novo fatty acid synthesis. Thus, we demonstrate for the first time that SREBP activity is necessary for full glucose induction of de novo fatty acid synthesis in pancreatic beta-cells.

Adenoviridae↗

PubMed2005

A rationally designed small molecule that inhibits the HIF-1alpha-ARNT heterodimer from binding to DNA in vivo.

Modern drug development is focused on two steps: the identification of new molecular targets and the development of drugs that affect these targets. A molecular target can be an enzymatic activity or a macromolecular interface that is important in a disease pathway. Current drugs on the market are biased toward targeting cell surface receptors and intracellular enzymatic activities. However, macromolecular interfaces can also serve as potential molecular targets. A recent paper from Kaelin and Dervan's groups examined an underused molecular target-transcription factor DNA binding. To specifically disrupt transcriptional activation, they used a rationally designed small molecule that binds specifically in the minor groove of a DNA sequence that in vivo is bound by a bHLH heterodimer transcription factor.

Angiogenesis Inhibitors↗