Transcriptional regulation of hemoglobin switching in chicken embryos

mRNA Cap Methyltransferase, RNMT-RAM, Promotes RNA Pol II-Dependent Transcription

mRNA cap addition occurs early during RNA Pol II-dependent transcription, facilitating pre-mRNA processing and translation. We report that the mammalian mRNA cap methyltransferase, RNMT-RAM, promotes RNA Pol II transcription independent of mRNA capping and translation. In cells, sublethal suppression of RNMT-RAM reduces RNA Pol II occupancy, net mRNA synthesis, and pre-mRNA levels. Conversely, expression of RNMT-RAM increases transcription independent of cap methyltransferase activity. In isolated nuclei, recombinant RNMT-RAM stimulates transcriptional output; this requires the RAM RNA binding domain. RNMT-RAM interacts with nascent transcripts along their entire length and with transcription-associated factors including the RNA Pol II subunits SPT4, SPT6, and PAFc. Suppression of RNMT-RAM inhibits transcriptional markers including histone H2BK120 ubiquitination, H3K4 and H3K36 methylation, RNA Pol II CTD S5 and S2 phosphorylation, and PAFc recruitment. These findings suggest that multiple interactions among RNMT-RAM, RNA Pol II factors, and RNA along the transcription unit stimulate transcription.

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mRNA cap methyltransferase, RNMT-RAM, promotes RNA Pol II-dependent transcription

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RNMT-RAM-dependent transcription is independent of mRNA cap methylation

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RNMT-RAM binds to the entire length of pre-mRNA and to transcription-associated proteins

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Significant loss of RNA Pol II gene occupancy is observed on RNMT-RAM suppression

Mature microRNAs identified in highly purified nuclei from HCT116 colon cancer cells

MicroRNAs (miRNAs) have emerged as one of the major regulatory mechanisms of gene expression. A major function of miRNAs involves the post-transcriptional regulation of target mRNAs, which is reported to occur primarily in the cytoplasm. However, there is a significant amount of evidence demonstrating the existence of small non-coding RNAs, including small-interfering RNA (siRNA), miRNA, and Piwi-interacting RNA (piRNA) in the nucleus. In order to elucidate the potential subcellular localizations and functions of miRNAs, we have identified numerous miRNAs that are present in isolated nuclei from human colon cancer HCT116 cells. MicroRNA profiles were compared between cytoplasmic and nuclear fractions of the HCT116 cell line on the basis of multiple microarray analyses. MicroRNA species showing significant existence in isolated and highly purified populations of nuclei were selected and further tested with RT-PCR. The nuclear localization of the mature form of miRNAs was verified again by control RT-PCR excluding the detection of premature forms of miRNA, such as pri-miRNA or pre-miRNA. The elevated levels of representative miRNAs identified in purified nuclei were confirmed by Northern blot analysis, supporting the notion that significant numbers of mature miRNAs exist not only in the cytoplasm but also in the nucleus. These results will likely provide a basis for further studies concerning the intracellular trafficking and nuclear location of miRNAs.

Advances in the understanding of haemoglobin switching

The study of haemoglobin switching has represented a focus in haematology due in large part to the clinical relevance of the fetal to adult haemoglobin switch for developing targeted approaches to ameliorate the severity of the beta-haemoglobinopathies. Additionally, the process by which this switch occurs represents an important paradigm for developmental gene regulation. In this review, we provide an overview of both the embryonic primitive to definitive switch in haemoglobin expression, as well as the fetal to adult switch that is unique to humans and old world monkeys. We discuss the nature of these switches and models of their regulation. The factors that have been suggested to regulate this process are then discussed. With the increased understanding and discovery of molecular regulators of haemoglobin switching, such as BCL11A, new avenues of research may lead ultimately to novel therapeutic, mechanism-based approaches to fetal haemoglobin reactivation in patients.

Identification of newly transcribed RNA

Newly transcribed RNA can be identified using the nuclear runoff transcription assay. In this assay, isolated nuclei, free of membranes and cytoplasmic debris, are used in an in vitro transcription reaction in the presence of (32)P-labeled UTP. The labeled RNA can then be hybridized to cDNAs immobilized on nitrocellulose. This unit describes three methods for isolating suitable nuclei by detergent lysis, Dounce homogenization, and centrifugation on a sucrose gradient. Two Support Protocols describe the preparation of nitrocellulose filter strips containing double-stranded and single-stranded DNAs, which are used to detect the presence of specific transcripts in the nuclear runoff transcription assay.

The role of the epigenetic signal, DNA methylation, in gene regulation during erythroid development

The sequence complexity of the known vertebrate genomes alone is insufficient to account for the diversity between individuals of a species. Although our knowledge of vertebrate biology has evolved substantially with the growing compilation of sequenced genomes, understanding the temporal and spatial regulation of genes remains fundamental to fully exploiting this information. The importance of epigenetic factors in gene regulation was first hypothesized decades ago when biologists posited that methylation of DNA could heritably alter gene expression [Holliday and Pugh, 1975. Science 187(4173), 226-232; Riggs, 1975. Cytogenet. and Cell Genet.14(1), 9-25; Scarano et al., 1967. Proc. Natl. Acad. Sci. USA 57(5), 1394-1400)]. It was subsequently shown that vertebrate DNA methylation, almost exclusively at the 5' position of cytosine in the dinucleotide CpG, played a role in a number of processes including embryonic development, genetic imprinting, cell differentiation, and tumorigenesis. At the time of this writing, a large and growing list of genes is known to exhibit DNA methylation-dependent regulation, and we understand in some detail the mechanisms employed by cells in using methylation as a regulatory modality. In this context, we revisit one of the original systems in which the role of DNA methylation in vertebrate gene regulation during development was described and studied: erythroid cells. We briefly review the recent advances in our understanding of DNA methylation and, in particular, its regulatory role in red blood cells during differentiation and development. We also address DNA methylation as a component of erythroid chromatin architecture, and the interdependence of CpG methylation and histone modification.

EM703, the new derivative of erythromycin, inhibits transcription of type I collagen in normal and scleroderma fibroblasts

BACKGROUND

Excessive accumulation of collagen in the skin and internal organs in systemic sclerosis (SSc) is considered to result from enhanced transcription of collagen in fibroblasts. Macrolides have been reported to show various pharmacological activities. Recently, it was reported that EM703, a new derivative of erythromycin, improved bleomycin-induced pulmonary fibrosis in mice.

OBJECTIVE

Therefore, we attempted to examine the effects of EM703 on the type I collagen synthetic activity in normal and SSc dermal fibroblasts.

METHODS

Normal and SSc dermal fibroblasts were cultured with various concentrations of Erythromycin A or EM703 for 48h. Amount of type I collagen in the culture medium was measured with ELISA with anti-type I collagen antibody. Type I collagen mRNA levels were measured by northern blots analysis and type I collagen transcription and regulation of the human COL1A1 promoter activity were examined by transient transfection and luciferase assay. Electrophoretic gel mobility shift assay was also performed for measurement of binding activities of DNA binding factors to the COL1A1 promoter.

RESULTS

We found that EM703 reduced collagen production and the mRNA levels of alpha1(I) collagen in a dose-dependent manner in the normal fibroblasts. The transcription of COL1A1 was downregulated as detected by the luciferase assay. The downregulation was also detected using DNA containing various short lengths of the COL1A1 promoter region. EM703 did not inhibit COL1A1 transcription when the luciferase assay was performed using DNA containing the COL1A1 promoter with a short substitution mutation of the CCAAT box. Decreased production of type I collagen at the transcriptional level was also found in SSc fibroblasts treated with EM703.

CONCLUSION

These results suggest that EM703 inhibits the transcription of type I collagen in both normal and SSc fibroblasts, and that the transcription is inhibited through the CCAAT box of the COL1A1 promoter.

Impairment of alveolar macrophage transcription in idiopathic pulmonary fibrosis

RATIONALE

Alveolar macrophages are inflammatory cells that may contribute to the pathogenesis of idiopathic pulmonary fibrosis (IPF), which is characterized by excessive alveolar aggregation of cells and extracellular matrix proteins.

OBJECTIVES

To identify potential molecular mechanisms of IPF.

METHODS

To examine large-scale gene expression, messenger RNA isolated from alveolar macrophages and peripheral blood mononuclear cells from subjects with IPF and normal volunteers was hybridized to cDNA filters.

MEASUREMENTS AND MAIN RESULTS

We showed that in IPF there is global down-regulation of gene expression in alveolar macrophages but not in blood monocytes. Nuclear run-on and pulse-chase studies showed that alveolar macrophages had significantly reduced transcription (p < 0.01). No significant difference in RNA degradation was found between subjects with IPF and normal volunteers. Western blot analyses revealed that concentrations of transcription factor II-H, a general transcription factor, were significantly lower in alveolar macrophages from subjects with IPF than in those from normal volunteers (p = 0.012).

CONCLUSIONS

Impaired transcription in IPF is associated with decreased concentrations of transcription factor II-H in alveolar macrophages and may alter the intraalveolar milieu in IPF.

Arrest of transcription following anoxic exposure in a marine mollusc

The intertidal marine snail, Littorina littorea, is an anoxia tolerant species that endures long-term oxygen deprivation using a suite of compensatory metabolic adaptations that includes overall metabolic rate depression. Nuclear run-off assays were used to quantify the relative rates of mRNA transcription in nuclear extracts from hepatopancreas of aerobic and anoxic snails. Total [(32)P]-UTP incorporation into RNA by nuclei from 48 h anoxic snails ranged from 42 to 50% of that observed for nuclei from normoxic snails. When this data is transformed with respect to incubation time, the rate of [(32)P]-UTP incorporation by nuclei from 48 h anoxic snails showed a decrease of 68% as compared with the normoxic level. Examination of selected expressed sequence tags also showed an overall decrease in mRNA transcription levels in samples derived from anoxic nuclei as compared with normoxic nuclei. Control of ribosomal translation was also examined by assessing the levels of the eukaryotic initiation factors eIF-2alpha and eIF-4E and the eukaryotic elongation factor-1gamma (eEF-1gamma). Levels of eIF-4E and eEF-1gamma did not change between aerobic and anoxic states, but the amount of phosphorylated inactive eIF-2alpha rose strongly under anoxic conditions indicating that control of this factor is key to suppressing protein translation in anoxic snails. Since gene transcription is an ATP expensive process in cells, suppression of transcription to minimum levels provides substantial energy savings for the hepatopancreas, and the organism as a whole, under anoxic conditions.

MBD2 is a critical component of a methyl cytosine-binding protein complex isolated from primary erythroid cells

The chicken embryonic beta-type globin gene, rho, is a member of a small group of vertebrate genes whose developmentally regulated expression is mediated by DNA methylation. Previously, we have shown that a methyl cytosine-binding complex binds to the methylated rho-globin gene in vitro. We have now chromatographically purified and characterized this complex from adult chicken primary erythroid cells. Four components of the MeCP1 transcriptional repression complex were identified: MBD2, RBAP48, HDAC2, and MTA1. These 4 proteins, as well as the zinc-finger protein p66 and the chromatin remodeling factor Mi2, were found to coelute by gel-filtration analysis and pull-down assays. We conclude that these 6 proteins are components of the MeCPC. In adult erythrocytes, significant enrichment for MBD2 is seen at the inactive rho-globin gene by chromatin immunoprecipitation assay, whereas no enrichment is observed at the active beta(A)-globin gene, demonstrating MBD2 binds to the methylated and transcriptionally silent rho-globin gene in vivo. Knock-down of MBD2 resulted in up-regulation of a methylated rho-gene construct in mouse erythroleukemic (MEL)-rho cells. These results represent the first purification of a MeCP1-like complex from a primary cell source and provide support for a role for MBD2 in developmental gene regulation.

Chronic ethanol consumption upregulates the cytosolic and plasma membrane sialidase genes, but down regulates lysosomal membrane sialidase gene in rat liver

We have previously shown that chronic ethanol feeding stimulates liver cytosolic sialidase (CS) and plasma membrane sialidase (PMS), whereas it decreases lysosomal membrane sialidase (LMS) activities with concomitant alterations in their relative synthetic rate in rat. To understand the molecular mechanism(s) for these changes, we have evaluated the effect of ethanol administration in male Wistar rats as a function of increasing dietary ethanol concentration after 8 weeks of pair-feeding on (i) the expression of CS, PMS, and LMS genes by real-time quantitative polymerase chain reaction method; (ii) their relative transcription rates by nuclear run-on assay; and (iii) the actual amount of these sialidase proteins in the liver fractions of the respective groups by Western blot method. We have demonstrated that the animals fed with 10.6%, 20.8%, and 36% of total calories as ethanol showed a 20% (P<.05), 34% (P<.01), and 69% (P<.01) increase in CS mRNA level, and 22% (P<.05), 26% (P<.01), and 47% (P<.01) increase in PMS mRNA level, but a decrease in LMS mRNA level by 35% (P<.05), 50% (P<.01), and 80% (P<.01), respectively, as compared to controls. Western blot analyses of CS, PMS, and LMS in the liver subfractions showed that changes in protein levels of CS, LMS, and PMS were consistent with the corresponding changes in the respective mRNA levels. Thus, the upregulation of CS and PMS, but not LMS which is down regulated by chronic ethanol, may account for the appearance of asialoconjugates in alcoholics.

Thyroid hormone receptor β1 gene expression is increased by Dexamethasone at transcriptional level in rat liver

Triiodothyronine (T3) exerts most of its effect through nuclear thyroid hormone receptors (TR) which bind mainly as heterodimers with retinoid-X receptors (RXR) to thyroid hormone response elements (TRE) in target genes. It is well known that the synergistic interaction of T3 and glucocorticoids has a role on the synthesis of growth hormone in rat pituitary cell lines and in the T3-induced metamorphosis in amphibians. Glucocorticoids increased mRNAs of T3-regulated hepatic genes. Our laboratory reported increased specific metabolic actions of T3 in rat liver by Dexamethasone (Dex) through a mechanism involving an up-regulation of the maximal binding capacity of TR. In this study we further explored the participation of TR in the molecular mechanism of the Dex-induced increase on liver T3-specific metabolic action. Dex administration to adrenalectomized rats induced an increase of liver TRbeta1 protein and mRNA. Nuclear run-on assay revealed that Dex up-regulated the TR gene transcriptional rate. Transfection assay in COS-7 cells indicated that Dex increased the transcriptional activity of the TRbeta1 promoter. Electrophoretic mobility shift assay demonstrated that Dex induced the binding of additional proteins related to or neighboring the DNA sequence of a glucocorticoid receptor (GR) binding (GRE) half-site in the TRbeta1 promoter. Evidences for an interaction of GR on the TRbeta1 promoter have been obtained. Moreover, the specificity of the GR binding to GRE was determined not only by the GRE DNA sequence, but also by the interaction of the GR with other transacting factors bound to sequences flanking the GRE.

Lysophosphatidic acid induces early growth response gene 1 expression in vascular smooth muscle cells: CRE and SRE mediate the transcription

OBJECTIVE

Lysophosphatidic acid (LPA), one component of oxidized low-density lipoprotein, is a potent bioactive phospholipid. Early growth response gene-1 (Egr-1), an important transcription factor, regulates expression of an array of genes involved in vascular diseases. Whether and how LPA regulates the transcriptional machinery of Egr-1 gene is unknown and is addressed in this study.

METHOD AND RESULTS

We found that LPA markedly induces Egr-1 mRNA and protein in aortic smooth muscle cells (SMCs). RNA stability and nuclear run-on assays reveal that LPA-induced Egr-1 gene expression is controlled at the transcriptional level. Reporter gene analyses have shown that the -141 to +20 nt region of the Egr-1 promoter contains regulatory elements. Electrophoretic mobility shift assays reveal that the DNA-binding activities of both CREB and SRF to the CRE and SRE motifs of the Egr-1 promoter are markedly elevated in response to LPA. The increased binding activity depends on the phosphorylation of CREB and SRF. Luciferase assays of a series of deleted or mutated Egr-1 promoter-reporter gene constructs, along with dominant negative CREB transfection analysis revealed that the 2 CRE sites and the 2 proximal SRE sites in the Egr-1 promoter are required for maximal LPA-induced Egr-1 gene expression.

CONCLUSIONS

Our data reveal that LPA regulates Egr-1 expression via transcription factors CREB and SRF. These results establish a novel role for CREB in mediating LPA-induced gene expression. Our results imply that elevated LPA levels may, through activation of Egr-1, which regulates an array of atherogenic genes, exacerbate atheromatous lesions.

Ras activation is associated with vitamin D receptor mRNA instability in HC11 mammary cells

HC11, a spontaneously immortalized murine mammary lineage maintains features of normal cells while HC11 H-ras transformed cells (HC11 ras) are tumorigenic. Ras transformation is associated with a lower Vitamin D receptor (VDR) mRNA content. Our goal was to investigate the mechanism underlying VDR mRNA differences between these cells. Although the VDR transcriptional rate measured by run-on assays did not differ between the cells, our data suggested a pos transcriptional mechanism involving higher VDR mRNA degradation in HC11 ras cells which was not due to mutations in its 3'-UTR region since sequences of mRNA obtained from HC11 and HC11 ras cells were identical. Treatment of HC11 ras cells with a farnesyltransferase inhibitor, which prevents ras activation, causing an enhancement of VDR mRNA levels, indicating an association between the ras signaling pathway and VDR mRNA instability. The present work suggests that the decreased mRNA levels in HC11 ras cells might in part be due to an early loss of stability.

Negative regulation of gamma-globin gene expression by cyclic AMP-dependent pathway in erythroid cells

OBJECTIVE

Fetal hemoglobin inducers such as hemin, butyrate, and hydroxyurea stimulate gamma-globin gene expression by activating the cyclic GMP (cGMP)-dependent pathway. Although cGMP activates the cyclic AMP (cAMP)-dependent pathway by suppressing cGMP-inhibited phosphodiesterase 3 (PDE3), the effects of the cAMP-dependent pathway on gamma-globin gene expression are unknown.

MATERIALS AND METHODS

The cAMP-dependent pathway was activated in K562 cells using the adenylate cyclase activator forskolin. Expression of gamma-globin mRNA was examined by primer extension, and transcriptional activity of the gamma-globin gene promoter was determined by reporter gene assays.

RESULTS

PDE3 was expressed in K562 cells at a high level. The cAMP-dependent pathway was found to be activated in K562 cells in which the cGMP-dependent pathway was activated by hemin. Activation of the cAMP-dependent pathway by forskolin inhibited hemin-induced expression of gamma-globin mRNA and decreased transcriptional activity of the gamma-globin gene promoter. The levels of phosphorylation of mitogen-activated protein kinases (MAPKs) were not affected by the cAMP-dependent pathway.

CONCLUSIONS

These results suggested that the cAMP-dependent pathway, which is independent of MAPK pathways, plays a negative role in gamma-globin gene expression in K562 cells. cAMP and cGMP may have differential roles in the regulation of gamma-globin gene expression in erythroid cells.

Lysophosphatidic acid induction of tissue factor expression in aortic smooth muscle cells

OBJECTIVE

Tissue factor (TF), the initiator of the coagulation cascade, is expressed by cells in atherosclerotic lesions. Lysophosphatidic acid (LPA) is a component of oxidized lipoproteins and an agent released by activated platelets. The present study investigated whether and how TF expression is regulated by LPA.

METHODS AND RESULTS

Northern blotting, Western blotting, and TF activity assays demonstrated that LPA markedly induced TF mRNA, protein, and activity in vascular smooth muscle cells. LPA-induced TF expression is primarily controlled at the transcriptional level. Phosphorylation of mitogen-activated protein kinase kinase (MEK) and extracellular signaling-regulated kinases (ERK1/2) was rapidly and markedly induced by LPA. MEK inhibitors U0126 and PD98059 blocked both ERK activation and the increase in TF mRNA. In contrast, the specific p38 MAP kinase inhibitor SB203580 had no effect on LPA-induced TF mRNA increase. The Galpha(i) protein inhibitor, pertussis toxin, abolished LPA-induced phosphorylation of MEKs and ERKs, as well as the induction of TF mRNA.

CONCLUSIONS

Our data demonstrate that a Galpha(i) protein and activation of MEKs and ERKs mediate LPA-induced TF expression. Our data suggest that elevated LPA could be a thrombogenic risk factor by upregulating TF expression. These results may have important implications in vascular remodeling and vascular diseases.

Differential modulation of liver and pituitary triiodothyronine and 9-cis retinoid acid receptors by insulin-like growth factor I in rats

Triiodothyronine (T(3)) exerts most of its effects through nuclear thyroid hormone receptors (TRs) that bind mainly as heterodimers with retinoid-X receptors (RXRs) to thyroid hormone response elements in target genes. It is well known that T(3) activates the growth hormone (GH)-insulin-like growth factor I (IGF-I) axis in rats. In turn, IGF-I inhibits the T(3)-induced GH production in cell cultures. The impact of IGF-I on T(3) action has only been partially explored. We have presented evidence that IGF-I feeds back to limit specific metabolic actions of T(3) in rat liver through a downregulation of nuclear TR number and its mRNA expression. We have also found that IGF-I injected to rats inhibited pituitary GH production. In this study we aimed at exploring whether the IGF-I-induced feedback loop on T(3)-action in the liver also operates in the pituitary gland. The mechanism of the liver TR mRNA reduction induced by IGF-I was also studied. We evaluated the effect of recombinant human (rh) IGF-I administration (240 microg/100 g of body weight subcutaneously every 12 hours for 48 hours) to adult male Wistar rats on TR and RXR proteins (Western blot) from pituitary, liver, brain, and thyroid and TR mRNA (Northern blot) from pituitary and liver. The transcriptional rate of liver TR gene (run-on assay) was also determined. In pituitary, TR protein and TR mRNA isoforms were reduced by rhIGF-I. No changes in TR proteins in brain and thyroid were observed. Nuclear run-on assay revealed that IGF-I reduced the TR gene transcriptional rate in liver. A significant increase in RXR proteins in liver and pituitary without changes in thyroid and brain was induced by IGF-I. In conclusion, these results indicate that in pituitary, IGF-I downregulates TR expression, similarly as previously found in liver. A reduced transcriptional rate of TR gene is implicated in the IGF-I effect on the liver. The increase in RXR protein levels may be also involved in the expression of T(3) specific actions in liver and pituitary.

Intracellular angiotensin II increases the long isoform of PDGF mRNA in rat hepatoma cells

Our recent published studies suggest that angiotensin II (AII), generated and retained intracellularly, enhances growth of H4-II-E-C3 rat hepatoma cells, an average of 33%. Proliferation conferred by introduction of a plasmid [ Ang(-S)Exp/pSVL ] encoding a signal sequence-depleted angiotensinogen [Ang(-S)Exp] into these cells (which we have shown possess ACE and renin mRNAs) is mediated, at least in part, by enhanced PDGF-A chain mRNA production and protein secretion. The mitogenic effect is inhibited by losartan suggesting that it involves AII interaction with an AT(1)-like receptor. Introduction of anti-AII antibodies into the medium of these transfected cells has no effect upon growth of the cells, suggesting that AII is retained by the cells and that intracellular AII is growth stimulatory. In the present study, we sought to further characterize the intracellular localization and mode of action of Ang(-S)Exp. Consistent with our expectations, we now show that a fusion product of Ang(-S)Exp with green fluorescent protein [Ang(-S)Exp/EGFP], generated from an expression plasmid, is abundant and primarily cytoplasmic. Wild-type angiotensinogen/EGFP, in contrast, is only detectable following a cold-block (which acts to enhance folding-kinetics and slow secretion) and is largely restricted to the secretory pathway. We further show, using semi-quantitative RT/PCR that the long isoform of PDGF mRNA is elevated in Ang(-S)Exp transfected cells and in AII-treated naive cells but not in losartan-treated Ang(-S)Exp transfected cells. We identify C-terminal amidation recognition sites within the long-form protein (that are not present in the short-form) and show that these cells possess PAM (amidating enzyme precursor) and carboxypeptidase E mRNAs (the corresponding proteins of which are sufficient for amidation). Inhibitors of amidation inhibit growth of naive and Ang(-S)Cntr/ pSVL -transfected cells (2.6-fold for phenylbutenoic acid and 3.5-fold for disulfiram treatment) but more profoundly inhibit growth of Ang(-S)Exp/pSVL -transfected cells (6.7-fold for phenylbutenoic acid and 13-fold for disulfiram). In conclusion, these data confirm that signal sequence-depleted Ang(-S)Exp is retained within cells and is largely cytoplasmic. Because C-terminal amidation is absolutely required for full biological potency of a number of peptide hormones (including oxytocin, gastrin and calcitonin), we postulate that growth effects of both intracellular AII and exogenous AII can be conferred by PDGF long-form, possibly through an amidation-dependent mechanism.

NF-kappaB induced by IL-1beta inhibits elastin transcription and myofibroblast phenotype

Interleukin (IL)-1beta released after lung injury regulates the production of extracellular matrix components. We found that IL-1beta treatment reduced the rate of elastin gene transcription by 74% in neonatal rat lung fibroblasts. Deletion analysis of the rat elastin promoter detected a cis-acting element located at -118 to -102 bp that strongly bound Sp1 and Sp3 but not nuclear factor (NF)-kappaB. This element mediated IL-1beta-induced inhibition of the elastin promoter. IL-1beta treatment did not affect the level of Sp1 but did induce translocation of the p65 subunit of NF-kappaB. Overexpression of p65 decreased elastin promoter activity and markedly reduced elastin mRNA. Immunoprecipitation studies indicated an interaction between the p65 subunit and Sp1 protein. Microarray analysis of mRNA isolated after overexpression of p65 or treatment with IL-1beta revealed downregulation of alpha-smooth muscle actin and calponin mRNAs. Expression of these genes is associated with the myofibroblast phenotype. These results indicate that IL-1beta activates the nuclear localization of NF-kappaB that subsequently interacts with Sp1 to downregulate elastin transcription and expression of the myofibroblast phenotype.

Ubiquitin (UbC) expression in muscle cells is increased by glucocorticoids through a mechanism involving Sp1 and MEK1

The muscle protein catabolism present in rats with insulin-dependent diabetes and other catabolic conditions is generally associated with increased glucocorticoid production and mRNAs encoding components of the ubiquitin-proteasome system. The mechanisms that increase ubiquitin (UbC) expression have not been identified. We studied the regulation of UbC expression in L6 muscle cells because dexamethasone stimulates the transcription of this gene and others encoding components of the ubiquitin-proteasome pathway. Results of in vivo genomic DNA footprinting experiments indicate that a protein(s) binds to Sp1 sites approximately 50 bp upstream from the UbC transcription start site; dexamethasone changes the methylation pattern at these sites. Sp1 binds to DNA probes corresponding to the rat or human UbC promoter, and treating cells with dexamethasone increases this binding. Deletion and mutation analyses of the rat and human UbC promoters are consistent with an important role of Sp1 in UbC induction by glucocorticoids. Dexamethasone-induced ubiquitin expression is blocked by mithramycin, an inhibitor of Sp1 binding. UO126, a pharmacologic inhibitor of MEK1, also blocks UbC transcriptional activation by dexamethasone; L6 cells transfected to express constitutively active MEK1 exhibit increased UbC promoter activity. Thus, glucocorticoids increase UbC expression in muscle cells by a novel transcriptional mechanism involving Sp1 and MEK1.

Methylation of promoter proximal-transcribed sequences of an embryonic globin gene inhibits transcription in primary erythroid cells and promotes formation of a cell type-specific methyl cytosine binding complex

The methylation pattern of a 248-base pair proximal transcribed region (rho248) of the avian embryonic rho-globin gene was found to correlate inversely with stage-specific expression in avian erythroid cells. In vitro methylation of the rho248 segment alone (in the absence of promoter methylation) resulted in a 5-fold inhibition of transcription in a transient transfection assay in primary erythroid cells in which the transfected gene is packaged into nucleosomal chromatin. This effect was observed if the rho248 segment was positioned adjacent to the promoter but not when it was located 2.7 kilobases downstream. Fully methylated but not unmethylated rho248 formed a novel cell type-specific methyl cytosine-binding protein complex (MeCPC) that contained methyl binding domain protein-2 (MBD-2) and histone deacetylase 1 proteins but differed from MeCP-1. The histone deacetylase inhibitor trichostatin A failed to relieve methylation-mediated repression of transcription from the rho-gene promoter, supporting the notion of the dominance of methylation over histone deacetylation in silencing through CpG-rich sequences at this locus. These data demonstrate that site-specific methylation of a vertebrate gene 5'-transcribed region alone at the exact CpGs that are methylated in vivo can suppress transcription in homologous primary cells and facilitate binding to a cell type-specific MeCPC.

De novo methylation of an embryonic globin gene during normal development is strand specific and spreads from the proximal transcribed region

The recently discovered de novo methyltransferases DNMT3a and DNMT3b have been shown to be critical to embryonic development. However, at a single gene level, little is known about how the methylation pattern is established during development. The avian embryonic rho-globin gene promoter is completely unmethylated in 4-day-old chicken embryonic erythroid cells, where it is expressed at a high level, and completely methylated in adult erythroid cells, where it is silent. The methylation pattern of the rho-globin gene promoter, proximal transcribed region, and distal transcribed region on both DNA strands was examined during development in chicken erythroid cells. It was found that de novo methylation targets the CpG-dense proximal transcribed region on the coding (top) strand initially, followed by spreading into the 3' region and into the promoter region. Methylation of the template (bottom) strand lags behind that of the coding strand, and complete methylation of both strands occurs only after the gene has been silenced. The results of the study indicate that establishment of the de novo methylation pattern involves strand-specificity and methylation spreading.

Apigenin decreases expression of the myofibroblast phenotype

We investigated the effect of the dietary flavonoid apigenin on myofibroblast function. We report that in myofibroblasts treated with apigenin, proliferation and basal levels of alpha1(I) collagen and alpha-smooth muscle actin mRNAs were markedly reduced. Apigenin also attenuated the transforming growth factor-beta-stimulated increases of alpha1(I) collagen and alpha-smooth muscle actin mRNAs. Characterization of the apigenin effects indicates that apigenin reduces both the stability of the alpha1(I) collagen mRNA and the rate of transcription of the alpha1(I) collagen gene through a cycloheximide-sensitive pathway. Western blot analyses indicate that Akt activity is reduced in apigenin-treated myofibroblasts.

Phosphatidylinositol 3-kinase-dependent stabilization of alpha1(I) collagen mRNA in human lung fibroblasts

We investigated the role of phosphatidylinositol 3-kinase (PI3K) in the expression of alpha1(I) collagen mRNA. We report that the basal level of alpha1(I) collagen mRNA was reduced when PI3K activity was inhibited by either LY-294002 or wortmannin. These PI3K inhibitors also blocked increases of alpha1(I) collagen mRNA levels after the addition of transforming growth factor-beta. The effect of PI3K inhibition was abolished by the removal of the inhibitor or by the addition of cycloheximide. Inhibition of PI3K activity decreased the stability of the alpha1(I) collagen mRNA with no change in the rate of transcription of the alpha1(I) collagen gene as assessed by Northern blotting with actinomycin D-treated fibroblasts and nuclear run-on assays. Expression of a truncated alpha1(I) collagen minigene driven by a cytomegalovirus promoter in murine fibroblasts was decreased by LY-294002 treatment. These data indicate that PI3K activation results in increased stabilization of alpha1(I) collagen mRNA. In vivo, the PI3K activity in fibroblasts may regulate basal levels of alpha1(I) collagen mRNA expression.

Thrombin regulates insulin-like growth factor-1 receptor transcription in vascular smooth muscle: characterization of the signaling pathway

We have previously demonstrated that thrombin upregulation of insulin-like growth factor-1 receptor (IGF-1R) is essential for thrombin-induced mitogenic signaling. To characterize the mechanisms involved, we studied transcription of the IGF-1R gene in rat aortic smooth muscle cells. Thrombin markedly increased IGF-1R mRNA levels, peaking at 3 hours (112+/-7% above control). This effect was mimicked by the hexapeptide SFFLRN (that functions as a tethered ligand) and was blocked by the thrombin inhibitor hirudin. Nuclear run-on assays indicated that thrombin stimulated IGF-1R gene transcription by 2.1-fold, and this was confirmed with the use of actinomycin D. Thrombin-mediated upregulation of IGF-1R mRNA and protein levels was protein kinase C independent but was completely inhibited by the protein tyrosine kinase inhibitor genistein and by the antioxidants N-acetyl-L-cysteine and pyrrolidinedithiocarbamate, suggesting the involvement of reactive oxygen species. The thrombin-induced increase in IGF-1R mRNA was inhibitable by diphenyleneiodonium chloride but not by other inhibitors of cellular oxidase systems, suggesting that NAD(P)H oxidase was necessary for the increase. Furthermore, inhibitors of the epidermal growth factor receptor kinase, Janus kinase-2 kinase, and Src kinase did not block the effect. Thus, thrombin transcriptionally regulates the IGF-1R gene via a redox-sensitive protein tyrosine kinase-dependent pathway that does not require protein kinase C activation. In view of our prior data indicating that IGF-1R density is a critical determinant of vascular smooth muscle cell growth, our findings have particular relevance to understanding mechanisms whereby growth factors such as thrombin regulate vascular proliferation in vivo.

Estradiol down regulates expression of vasoactive intestinal polypeptide receptor type-1 in breast cancer cell lines

Three breast carcinoma cell lines were tested for 17beta-estradiol (E(2)) mediated regulation of vasoactive intestinal polypeptide receptor type-1 (VPAC(1)) expression. In all three, E(2) was found to down-regulate the mRNA level. We studied T47D cells in more details and found a 25 and 70% decrease in the VPAC(1) mRNA level upon 7 and 48 h of E(2) treatment, respectively. The number of vasoactive intestinal polypeptide (VIP) binding sites was reduced 66% upon treatment with E(2) for 72 h. After cycloheximide pretreatment, the E(2) mediated mRNA reduction was attenuated from 50% to 25% after 24 h suggesting the effect to be at least partly independent of protein synthesis. Experiments with the transcriptional inhibitor actinomycin D showed that E(2) did not influence the VPAC(1) mRNA half-life while nuclear run-on experiments indicated that E(2) decreased the VPAC(1) transcription rate. Two antiestrogens: ICI 182780 (ICI) and 4-hydroxy-tamoxifen (4-OHT) mediated a concentration dependent inhibition of E(2)'s effect on the mRNA level. Transient transfection with reporter-gene constructs containing various portions of the VPAC(1) 5'-flanking sequence revealed the most proximal 100 bp to be essential for the basal transcriptional activity. However, E(2) did not influence the expression of the reporter gene using up to 3250 bp of the VPAC(1) 5'-flariking region.

IL-1beta induces eotaxin gene transcription in A549 airway epithelial cells through NF-kappaB

Eotaxin is an asthma-related C-C chemokine that is produced in response to interleukin-1beta (IL-1beta). We detected an increase in newly transcribed eotaxin mRNA in IL-1beta-stimulated airway epithelial cells. Transient transfection assays using promoter-reporter constructs identified a region as essential for IL-1beta-induced increases in eotaxin transcription. Using site-directed mutagenesis, we found that a nuclear factor-kappaB (NF-kappaB) site located 46 bp upstream from the transcriptional start site was both necessary and sufficient for IL-1beta induction of reporter construct activity. Electrophoretic mobility shift assay demonstrated that IL-1beta-stimulated airway epithelial cells produced p50 and p65 protein that bound this site in a sequence-specific manner. The functional importance of the NF-kappaB site was demonstrated by coexpression experiments in which increasing doses of p65 expression vector were directly associated with reporter activity exclusively in constructs with an intact NF-kappaB site (r(2) = 0.97, P = 0.002). Moreover, IL-1beta-induced increases in eotaxin mRNA expression are inhibited by inhibitors of NF-kappaB. Our findings implicate NF-kappaB and its binding sequence in IL-1beta-induced transcriptional activation of the eotaxin gene.

Tools for evaluating ubiquitin (UbC) gene expression: characterization of the rat UbC promoter and use of an unique 3' mRNA sequence

UbC is one of three members of the ubiquitin gene family. We have cloned the rat UbC promoter and used primer extension analysis to map the UbC site of transcription initiation to 63 bp upstream of the putative first intron. We used a rat UbC promoter-luciferase reporter minigene to transfect H9c2 cardiomyocytes, HepG2 hepatocytes, CaCo2 colon cells, NIH3T3 fibroblasts or L6 myocytes and found the rat UbC promoter has constitutive activity. We also showed that dexamethasone stimulated the UbC promoter in L6 myocytes. Finally, we showed that a UbC-specific sequence at the 3' end of the rat UbC mRNA transcript can be used to selectively and quantitatively measure UbC: (1) mRNA using a RNase protection assay, and (2) transcription using a nuclear run-off assay to measure the rate of transcription of the UbC gene. These findings will be useful in studying the regulation of the UbC gene.

Deregulation of glucose transporter 1 and glycolytic gene expression by c-Myc

Unlike normal mammalian cells, which use oxygen to generate energy, cancer cells rely on glycolysis for energy and are therefore less dependent on oxygen. We previously observed that the c-Myc oncogenic transcription factor regulates lactate dehydrogenase A and induces lactate overproduction. We, therefore, sought to determine whether c-Myc controls other genes regulating glucose metabolism. In Rat1a fibroblasts and murine livers overexpressing c-Myc, the mRNA levels of the glucose transporter GLUT1, phosphoglucose isomerase, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and enolase were elevated. c-Myc directly transactivates genes encoding GLUT1, phosphofructokinase, and enolase and increases glucose uptake in Rat1 fibroblasts. Nuclear run-on studies confirmed that the GLUT1 transcriptional rate is elevated by c-Myc. Our findings suggest that overexpression of the c-Myc oncoprotein deregulates glycolysis through the activation of several components of the glucose metabolic pathway.

Glucocorticoids induce proteasome C3 subunit expression in L6 muscle cells by opposing the suppression of its transcription by NF-kappa B

Muscle wasting in catabolic conditions results from activation of the ubiquitin-proteasome proteolytic pathway by a process that requires glucocorticoids and is generally associated with increased levels of mRNAs encoding components of this proteolytic system. In L6 muscle cells, dexamethasone stimulates proteolysis and increases the amount of the proteasome C3 subunit protein by augmenting its transcription. Transfection studies with human C3 promoter-luciferase reporter genes and electrophoretic mobility shift assays revealed that a NF-kappaB.protein complex containing Rel A is abundant in L6 muscle cell nuclei. Glucocorticoids stimulate C3 subunit expression by antagonizing the interaction of this NF-kappaB protein with an NF-kappaB response element in the C3 subunit promoter region. Dexamethasone also increased the cytosolic amounts of the NF-kappaB p65 subunit and the IkappaBalpha inhibitor proteins in L6 cells. Incubation of L6 cells with a cytokine mixture not only increased the amount of activated NF-kappaB but also decreased C3 promoter activity and lowered endogenous C3 subunit mRNA. Thus, NF-kappaB is a repressor of C3 proteasome subunit transcription in muscle cells, and glucocorticoids stimulate C3 subunit expression by opposing this suppressor action.

Pituitary adelylate cyclase-activating peptide is an activator of vasoactive intestinal polypeptide gene transcription in human neuroblastoma cells

In many ganglia, the neuropeptide pituitary adenylate cyclase-activating peptide (PACAP) innervates nerve cell bodies containing the homologous neuropeptide vasoactive intestinal polypeptide (VIP). We therefore investigated whether PACAP affected the VIP gene expression and elucidated the molecular mechanisms using the human neuroblastoma cell line NB-1. A concentration dependent induction of the VIP mRNA level was found upon PACAP stimulation. Five nM PACAP mediated transient elevation of the VIP mRNA being evident after 2 h, the maximal 65-fold induction was reached after 6-8 h and hereafter the level decreased rapidly. In cell extracts, the concentration of immunoreactive VIP was elevated four-fold upon PACAP stimulation for 8 h, and it remained elevated during the next 40 h. In conditioned medium, a stable 20-fold VIP increase was seen after 8-24 h. Experiments with the translational inhibitor cycloheximide showed a direct effect of PACAP on the VIP mRNA level, and nuclear run-on assays revealed a three- to four-fold enhancement of the VIP gene transcription rate after PACAP stimulation. The VIP mRNA induction was abolished by transcriptional inhibition with the actinomycin D, and PACAP did not seem to mediate any changes in the VIP mRNA half-life. However, the VIP mRNA level seemed very stable during the transcriptional cessation. Reporter gene constructs were used to evaluate involvement of the VIP CRE site in the PACAP mediated induction of the VIP gene transcription. Mutation of the CRE site did not abolish the induction suggesting it to be of minor if any importance for the induction. In conclusion, the PACAP mediated induction of the VIP gene expression suggests that PACAP released from nerve terminals could influence the function of VIP'ergic neurons in target tissues.

Connecting transcription to messenger RNA processing

The production of messenger RNA by gene transcription requires at least three RNA-processing mechanisms: capping, splicing and polyadenylation. All three reactions occur in intimate association with the elongating polymerase complex through the C terminus of the largest subunit of RNA polymerase II. The processing of mRNA is therefore orchestrated to act on the nascent RNA as soon as it emerges from the polymerase complex.

The interferon regulatory factors 1 and 2 bind to a segment of the human c-myb first intron: possible role in the regulation of c-myb expression

The preferential expression of the protooncogene c-myb in hematopoietic cells is in part regulated by a mechanism of transcriptional block in the first intron. By electrophoresis mobility shift assays using probes corresponding to different segments of the putative human c-myb intron 1 transcription pause region and nuclear extracts from myeloid leukemia HL 60 and fibroblast WI 38 cells, we detected a HL-60-specific DNA-protein complex with a 123-bp fragment containing binding sites for the interferon regulatory factors (IRFs) nuclear proteins. Formation of the DNA-protein complex was abrogated by competition with an oligomer containing the wild-type, but not the mutated, IRF binding site and the complex was specifically supershifted by the anti-IRF-1 or the anti-IRF-2 antibody. Moreover, in vitro translated IRF-1 or IRF-2 protein did interact with the 123-bp c-myb intron 1 fragment. Upon TPA-induced differentiation, c-myb expression was readily down-modulated in parental HL 60 cells, but not in cells transfected with an antisense IRF-1 plasmid. Moreover, chloramphenicol acetyltransferase activity driven by a c-myb promoter containing the entire intron 1 was suppressed upon IRF-1, but not IRF-2 expression. Together, these results are consistent with the existence of a functional relationship between IRF-1 and c-myb in which IRF-1 negatively regulates c-myb expression at the transcriptional level by a mechanism that may depend on the interaction of IRF-1 with a segment of the c-myb gene implicated in transcription pausing.

Transcriptional and post-transcriptional regulation of monocyte chemoattractant protein-3 gene expression in human endothelial cells by phorbol ester and cAMP signalling

Monocyte chemoattractant protein-3 (MCP-3) is one of the most broadly active chemokines, potentially inducing chemotaxis of all leucocytic cells. In the present study, we examined the regulation of MCP-3 mRNA and protein production in endothelial cells by protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA) and cAMP signalling. On stimulation of endothelial cells with 10 nM PMA, MCP-3 mRNA increased to 300-fold the basal level at 3 hr and rapidly declined to 0.2-fold the basal level at 24 hr. PMA-induced MCP-3 mRNA and protein production of human endothelial cells were partially inhibited by pretreatment with the adenylate cyclase activator, forskolin, or membrane-permeable cAMP derivative. The PMA-induced MCP-3 mRNA increase was almost abrogated when cells were pretreated with cycloheximide (CHX). Forskolin inhibited the transcription of PMA-induced MCP-3 gene expression. Following PMA stimulation for 3 hr, subsequent addition of actinomycin D suppressed the rapid decay of PMA-induced MCP-3 mRNA. These results suggest that PMA induces the transcriptional activation of the MCP-3 gene through de novo protein synthesis and the rapid decay of PMA-induced MCP-3 mRNA through de novo synthesis of adenosine/uridine (AU)-rich element binding proteins and cAMP signalling inhibits the PMA-induced transcriptional activation of the MCP-3 gene expression.

Depression of nuclear transcription and extension of mRNA half-life under anoxia in Artemia franciscana embryos

Transcriptional activity, as assessed by nuclear run-on assays, was constant during 10 h of normoxic development for embryos of the brine shrimp Artemia franciscana. Exposure of embryos to only 4 h of anoxia resulted in a 79.3+/−1 % decrease in levels of in-vivo-initiated transcripts, and transcription was depressed by 88. 2+/−0.7 % compared with normoxic controls after 24 h of anoxia (means +/− s.e.m., N=3). Initiation of transcription was fully restored after 1 h of normoxic recovery. Artificially lowering the intracellular pH of aerobic embryos to the value reflective of anoxia (pH 6.7) showed that acidification alone explained over half the transcriptional arrest. Initiation of transcription was not rescued by application of 80 % carbon monoxide under anoxia, which suggests that heme-based oxygen sensing is not involved in this global arrest. When these transcriptional data are combined with the finding that mRNA levels are unchanged for at least 6 h of anoxia, it is clear that the half-life of mRNA is extended at least 8.5-fold compared with that in aerobic embryos. In contrast to the activation of compensatory mechanisms to cope with anoxia that occurs in mammalian cells, A. franciscana embryos enter a metabolically depressed state in which gene expression and mRNA turnover are cellular costs apparently not compatible with survival and in which extended tolerance supercedes the requirement for continued metabolic function.

Inhibition of IL-12 production in human monocyte-derived macrophages by TNF

IL-12 is a pivotal cytokine that links the innate and adaptive immune responses. TNF-alpha also plays a key role in orchestrating inflammation and immunity. The reciprocal influence of these two inflammatory mediators on each other may have significant impact on the cytokine balance that shapes the type and extent of immune responses. To investigate the relationship between TNF-alpha and IL-12 production, we analyzed the effects of exposure of human monocyte-derived macrophages to TNF-alpha on LPS- or Staphylococcus aureus-induced IL-12 production in the presence or absence of IFN-gamma. TNF-alpha is a potent inhibitor of IL-12 p40 and p70 secretion from human macrophages induced by LPS or S. aureus. IL-10 is not responsible for the TNF-alpha-mediated inhibition of IL-12. TNF-alpha selectively inhibits IL-12 p40 steady-state mRNA, but not those of IL-12 p35, IL-1alpha, IL-1beta, or IL-6. Nuclear run-on analysis identified this specific inhibitory effect at the transcriptional level for IL-12 p40 without down-regulation of the IL-12 p35 gene. The major transcriptional factors identified to be involved in the regulation of IL-12 p40 gene expression by LPS and IFN-gamma, i.e., c-Rel, NF-kappaB p50 and p65, IFN regulatory factor-1, and ets-2, were not affected by TNF-alpha when examined by nuclear translocation and DNA binding. These data demonstrate a selective negative regulation on IL-12 by TNF-alpha, identifying a direct negative feedback mechanism for inflammation-induced suppression of IL-12 gene expression.

Regulation of connective tissue growth factor expression by prostaglandin E(2)

Transforming growth factor-beta (TGF-beta) stimulates alpha(1)(I) collagen mRNA synthesis in human lung fibroblasts through a mechanism that is partially sensitive to cycloheximide and that may involve synthesis of connective tissue growth factor (CTGF). Northern blot analyses indicate that TGF-beta stimulates time- and dose-dependent increases in CTGF mRNA. In TGF-beta-stimulated fibroblasts, maximal levels of CTGF mRNA (3.7-fold above baseline) occur at 6 h. The TGF-beta-stimulated increase in CTGF mRNA was not blocked by cycloheximide. Nuclear run-on analysis indicates that TGF-beta increases the CTGF transcription rate. The TGF-beta-stimulated increases in CTGF transcription and steady-state levels of CTGF mRNA are attenuated in prostaglandin E(2) (PGE(2))-treated fibroblasts. PGE(2) fails to attenuate luciferase activity induced by TGF-beta in fibroblasts transfected with the TGF-beta-responsive luciferase reporter construct p3TP-LUX. In amino acid-deprived fibroblasts, PGE(2) and insulin regulate alpha(1)(I) collagen mRNA levels without affecting CTGF mRNA levels. The data suggest that the regulation of alpha(1)(I) collagen mRNA levels by TGF-beta and PGE(2) may function through both CTGF-dependent and CTGF-independent mechanisms.

Native and oxidized low density lipoprotein induction of tissue factor gene expression in smooth muscle cells is mediated by both Egr-1 and Sp1

Tissue factor, in association with factor VIIa, initiates the coagulation cascade. We studied the influences of two pathophysiological stimuli, native (unmodified) and oxidized low density lipoprotein, on tissue factor gene expression in a cell important in vascular remodeling and vascular diseases, the smooth muscle cell. Our results demonstrated that both lipoproteins significantly induced tissue factor gene expression in rat aortic smooth muscle cells; oxidized low density lipoprotein was slightly more potent. Both lipoproteins increased tissue factor mRNA in a concentration- and time-dependent manner. Results from nuclear run-on assays and mRNA stability experiments indicated that increased tissue factor mRNA accumulation in response to the lipoproteins was principally controlled at the transcriptional level. By using lipid extracts of low density lipoprotein or methylation of the intact lipoprotein to block receptor recognition, we showed that this lipoprotein induced tissue factor mRNA via both receptor-independent and receptor-augmented pathways. Transfection studies using a series of deleted tissue factor promoters revealed that a -143- to +106-base pair region of the rat tissue factor promoter contained regulatory elements required for lipoprotein-mediated induction. Electrophoretic mobility shift assays showed that the binding activities of the transcription factor Egr-1, but not Sp1, were markedly elevated in response to these lipoproteins. Transfection of site-directed mutants of the tissue factor (TF) promoter demonstrated that not only Egr-1 but also Sp1 cis-acting elements in the TF (-143) promoter construct were necessary for optimal TF gene induction. Our data show for the first time that both low density lipoprotein and oxidized low density lipoprotein induce tissue factor gene expression in smooth muscle cells and that this tissue factor gene expression is mediated by both Egr-1 and Sp1 transcription factors.

Hypoxia downregulates tropoelastin gene expression in rat lung fibroblasts by pretranslational mechanisms

Elastolytic lung injury disrupts cell barriers, flooding alveoli and producing regional hypoxia. Abnormal O2 tensions may alter repair of damaged elastin fibers. To determine the effect of hypoxia on extravascular elastin formation, we isolated rat lung fibroblasts and cultured them under a variety of O2 conditions. Hypoxia downregulated tropoelastin mRNA in a dose- and time-related fashion while upregulating glyceraldehyde-3-phosphate dehydrogenase mRNA levels. The changes in tropoelastin gene expression were not due to cell toxicity as measured by chromium release and cell proliferation studies. Neither cycloheximide nor actinomycin D abrogated this effect. Hypoxia induced early decreases in tropoelastin mRNA stability; minor suppression of gene transcription occurred later. When returned to 21% O2, tropoelastin mRNA recovered to control levels in part by upregulating tropoelastin gene transcription. Taken together, these data indicate that hypoxia regulates tropoelastin gene expression and may alter repair of acutely injured lung.

Overexpression of urokinase-type plasminogen activator in pancreatic adenocarcinoma is regulated by constitutively activated RelA

The Rel/NF-kappaB transcription factors regulate the expression of many genes. The activity of RelA, a member of the Rel/NF-kappaB transcription factor family, is constitutively activated in the majority of pancreatic adenocarcinomas and cell lines. We report that the urokinase-type plasminogen activator (uPA), one of the critical proteases involved in tumor invasion and metastasis, is overexpressed in pancreatic tumor cells and its overexpression is induced by constitutive RelA activity. The uPA promoter contains an NF-kappaB binding site that directly mediates the induction of uPA expression by RelA. Expression of a dominant-negative IkappaBalpha mutant inhibits kappaB site-dependent transcriptional activation of a uPA promoter-CAT reporter gene. Treating the pancreatic tumor cell lines with the known NF-kappaB inhibitors, dexamethasone and n-tosylphenyalanine chloromethyl ketone (TPCK), abolishes constitutive RelA activity and uPA overexpression. These results show that uPA is one of the downstream target genes induced by constitutively activated RelA in human pancreatic tumor cells, and suggests that constitutive RelA activity may play a critical role in tumor invasion and metastasis. Inhibition of constitutive RelA in pancreatic tumor cells may reduce their invasive and metastatic potential.

A sequence with homology to human HPFH-linked enhancer elements and to a family of G-protein linked membrane receptor genes is located downstream of the chicken beta-globin locus

We report 5805bp of novel sequence (GenBank/EMBL Accession No. AJ012570) from a region starting approx. 11.5kb downstream of the chicken beta-globin locus (map position approx. +30.8 to +36.6kb), which contains a 945bp open reading frame (map position approx. +33 to +33.9kb). This is predicted to encode a 315-residue protein containing seven hydrophobic helical regions and a 17 amino acid motif characteristic of the R7G family of G-protein coupled membrane-bound receptors. The open reading frame and some surrounding sequence also have significant homology with the breakpoint enhancer elements, which also contain open reading frames, implicated in the HPFH-1/2 and HPFH-6 deletional forms of the human syndrome, hereditary persistence of foetal haemoglobin (HPFH). The existence of similar sequences at similar distances downstream of the beta-globin genes in chickens and HPFH patients is intriguing.

IL-18 and CD28 Use Distinct Molecular Mechanisms to Enhance NK Cell Production of IL-12-Induced IFN-γ

NK cells play an important role in innate immune resistance, particularly through synthesis of the pro-inflammatory cytokine IFN-γ. This study compares the abilities of the cytokine IL-18 and the costimulatory cell surface molecule CD28 to enhance IL-12-driven IFN-γ production by NK cells. Studies with other cytokines (IL-1β, IL-6, TNF-α, IL-15) showed that IL-18 or anti-CD28 treatments were the most efficient inducers of IFN-γ when combined with IL-12. The ability of IL-18 to enhance IFN-γ was shown to be dependent on the presence of IL-12. Similarly, although anti-CD28 stimulation alone could enhance IFN-γ synthesis, this effect was significantly increased in the presence of IL-12. Although neither method of costimulation required de novo protein synthesis for their effects on IFN-γ mRNA expression, these molecules used distinct mechanisms. Specifically, nuclear run-on analysis revealed that IL-18 in combination with IL-12 enhanced the rate of transcription of the IFN-γ gene. Conversely, treatment with anti-CD28 plus IL-12 did not significantly up-regulate the rate of transcription of the IFN-γ gene, but stabilized IFN-γ mRNA expression within NK cells. These findings illustrate costimulatory pathways that result in potent IFN-γ responses by NK cells and show that although IL-18 and anti-CD28 can enhance the synthesis of IL-12-driven IFN-γ, they employ molecular mechanisms that are distinct from one another.

Suppression of metastasis-associated S100A4 gene expression by gamma-interferon in human colon adenocarcinoma cells

S100A4 belongs to the S100 subfamily of calcium-binding proteins and has been suggested to be directly involved in invasion and metastasis of rodent and human tumour cells. The present study demonstrates that interferon gamma (IFN-gamma), but not IFN-alpha and IFN-beta, down-regulates the S100A4 mRNA level in colon adenocarcinoma WiDr cells in time- and dose-dependent manners. The effect was not associated with any cytotoxicity and was specific for the S100A4 mRNA, since the levels of the S100A6 and GAPDH mRNAs were not significantly affected by the treatment. IFN-gamma also strongly suppressed the S100A4 mRNA expression in HT-29 cells, but weakly in Colo201 cells. Flow cytometric analysis revealed that the level of the IFN-gamma receptor expression in Colo201 cells was lower than that in WiDr and HT-29 cells, suggesting that the suppression of the S100A4 expression by IFN-gamma depends on the amount of cell surface IFN-gamma receptor protein. IFN-gamma had no effect on the transcription rate of the S100A4 gene but reduced the stability of the S100A4 mRNA. WiDr cells treated with IFN-gamma showed reduced motile ability, further supporting the assumption that the S100A4 gene product is involved in controlling cell motility.

E-selectin gene expression is induced synergistically with the coexistence of activated classic protein kinase C and signals elicited by interleukin-1beta but not tumor necrosis factor-alpha

We have examined the effect of protein kinase C (PKC) on the expression of the E-selectin and intercellular adhesion molecule-1 (ICAM-1) mRNAs in human umbilical vein endothelial cells. The lower classic PKC activity on pretreatment with phorbol ester (phorbol 12-myristate 13-acetate (PMA)) for 24 h markedly decreased IL-1beta-induced E-selectin mRNA expression in the presence of fetal calf serum and basic fibroblast growth factor, although the induction of ICAM-1 mRNA expression was only influenced a little by the PKC down-regulation. On the other hand, tumor necrosis factor-alpha (TNFalpha)-induced gene expression of these adhesion molecules was unaffected by such PKC modulation. The intracellular signals generated by interleukin (IL)-1beta and TNFalpha themselves are not mediated through classic PKC activation, because the response to neither stimulant was inhibited by the PKC down-regulation in the absence of fetal calf serum and basic fibroblast growth factor. Simultaneous treatment with IL-1beta and PMA synergistically induced E-selectin gene expression but not when TNFalpha was substituted for IL-1beta. ICAM-1 mRNA expression was only additively induced on the cotreatment. The synergistic effect on E-selectin mRNA induction was independent of de novo protein synthesis and mediated by elevated transcriptional activity. Promoter analysis of E-selectin indicated that the NF-ELAM1/activating transcription factor element is critical for the synergistic effect of the cotreatment with IL-1beta and PMA.

Epstein-Barr virus small RNA (EBER) genes: differential regulation during lytic viral replication

In every latently Epstein-Barr virus-infected cell the viral genes EBER-1 and EBER-2 are transcribed by polymerase III. In lytically infected cells in vivo the EBER genes could not be detected. However, in cell culture downregulation could not be confirmed, and hence the relevance of this shutdown to the replication of the virus was not clear. We assayed the transcriptional activity of the EBER genes by nuclear run-on assays with enriched lytically infected cells and demonstrated that EBER-1 and EBER-2 are differentially downregulated on the transcriptional level during the switch to lytic viral replication. This downregulation was an early event during the lytic replication of the virus.

Interferon inhibits the replication of HIV-1, SIV, and SHIV chimeric viruses by distinct mechanisms

Interferon (IFN) treatment of lentivirus-infected cells substantially reduces virus replication in vitro. Although the replication of both HIV-1 and simian immunodeficiency virus (SIV) is inhibited, IFN blocks the replication of these viruses at different stages of the viral life cycle. We previously demonstrated that in HIV-1-infected cells, IFN blocks a late step in viral replication, leading to a decrease in viral protein stability and a deregulation of polyprotein processing. In contrast, in SIV-infected cells, IFN blocks an early step in viral replication, between virus binding and reverse transcription. Thus, the viral gene products targeted by IFN may be different for each of these viruses. To attempt to define which viral proteins are targeted by the IFN response, we examined the effects of IFN on the replication of two SIV/HIV-1 (SHIV) chimeric viruses, SHIV-4(vpu+) and SHIV-4(vpu-) in 174 x CEM cells. These viruses were grown from constructs in which the SIVmac239 env, tat, and rev genes have been replaced with those HIV-1. The use of SHIV-4(vpu+) allowed us to examine whether vpu, which is unique to HIV-1, might contribute to the differential effects of IFN on HIV-1 and SIV replication. Surprisingly, we found that IFN inhibited SHIV replication differently than the replication of either HIV-1 or SIV. IFN treatment of SHIV-infected cells resulted in a decrease in the level of viral RNA expression but had no apparent effect on the integration of proviral DNA. Nuclear runoff transcription assays indicated that the reduction of SHIV RNA expression in IFN-treated cells was not due to alterations in RNA polymerase II-mediated transcription, suggesting that IFN may block SHIV replication by promoting the increased degradation of viral RNA. The presence of absence of the vpu gene did not alter the effects of IFN on SHIV replication, indicating that Vpu is not responsible for the differential effect of IFN on HIV-1 and SIV replication. Thus the response of SHIVs to antiviral agents such as IFN may be unique from either HIV-1 or SIV. This may be an important consideration when using SHIVs to evaluate anti-HIV-1 therapies in animal models of AIDS.