Upstream stimulating factors: highly versatile stress-responsive transcription factors

A role of DNA-PK for the metabolic gene regulation in response to insulin

Fatty acid synthase (FAS) is a central enzyme in lipogenesis and transcriptionally activated in response to feeding and insulin signaling. The transcription factor USF is required for the activation of FAS transcription, and we show here that USF phosphorylation by DNA-PK, which is dephosphorylated by PP1 in response to feeding, triggers a switch-like mechanism. Under fasting conditions, USF-1 is deacetylated by HDAC9, causing promoter inactivation. In contrast, feeding induces the recruitment of DNA-PK to USF-1 and its phosphorylation, which then allows recruitment of P/CAF, resulting in USF-1 acetylation and FAS promoter activation. DNA break/repair components associated with USF induce transient DNA breaks during FAS activation. In DNA-PK-deficient SCID mice, feeding-induced USF-1 phosphorylation/acetylation, DNA breaks, and FAS activation leading to lipogenesis are impaired, resulting in decreased triglyceride levels. Our study demonstrates that a kinase central to the DNA damage response mediates metabolic gene activation.

Identification and analysis of differentially expressed genes in immune tissues of Atlantic cod stimulated with formalin-killed, atypical Aeromonas salmonicida

Physiological changes, elicited in animal immune tissues by exposure to pathogens, may be studied using functional genomics approaches. We created and characterized reciprocal suppression subtractive hybridization (SSH) cDNA libraries to identify differentially expressed genes in spleen and head kidney tissues of Atlantic cod (Gadus morhua) challenged with intraperitoneal injections of formalin-killed, atypical Aeromonas salmonicida. Of 4,154 ESTs from four cDNA libraries, 10 genes with immune-relevant functional annotations were selected for QPCR studies using individual fish templates to assess biological variability. Genes confirmed by QPCR as upregulated by A. salmonicida included interleukin-1 beta, interleukin-8, a small inducible cytokine, interferon regulatory factor 1 (IRF1), ferritin heavy subunit, cathelicidin, and hepcidin. This study is the first large-scale discovery of bacteria-responsive genes in cod and the first to demonstrate upregulation of IRF1 in fish immune tissues as a result of bacterial antigen stimulation. Given the importance of IRF1 in vertebrate immune responses to viral and bacterial pathogens, the full-length cDNA sequence of Atlantic cod IRF1 was obtained and compared with putative orthologous sequences from other organisms. Functional annotations of assembled SSH library ESTs showed that bacterial antigen stimulation caused changes in many biological processes including chemotaxis, regulation of apoptosis, antimicrobial peptide production, and iron homeostasis. Moreover, differences in spleen and head kidney gene expression responses to the bacterial antigens pointed to a potential role for the cod spleen in blood-borne pathogen clearance. Our data show that Atlantic cod immune tissue responses to bacterial antigens are similar to those seen in other fish species and higher vertebrates.

Activation of hepatic lipase expression by oleic acid: possible involvement of USF1

Polyunsaturated fatty acids affect gene expression mainly through peroxisome proliferator-activated receptors (PPARs) and sterol regulatory element binding proteins (SREBPs), but how monounsaturated fatty acids affect gene expression is poorly understood. In HepG2 cells, oleate supplementation has been shown to increase secretion of hepatic lipase (HL). We hypothesized that oleate affects HL gene expression at the transcriptional level. To test this, we studied the effect of oleate on HL promoter activity using HepG2 cells and the proximal HL promoter region (700 bp). Oleate increased HL expression and promoter activity 1.3-2.1 fold and reduced SREBP activity by 50%. Downregulation of SREBP activity by incubation with cholesterol+25-hydroxycholesterol had no effect on HL promoter activity. Overexpression of SREBP2, but not SREBP1, reduced HL promoter activity, which was effected mainly through the USF1 binding site at -307/-312. Oleate increased the nuclear abundance of USF1 protein 2.7 ± 0.6 fold, while USF1 levels were reduced by SREBP2 overexpression. We conclude that oleate increases HL gene expression via USF1. USF1 may be an additional fatty acid sensor in liver cells.

Structure and activity of the human growth hormone receptor (hGHR) gene V2 promoter

Human GH (hGH) has important effects on growth as well as carbohydrate, fat, and protein metabolism. These actions require the presence of normal levels of a functional hGH receptor (hGHR) on the surface of target cells. hGHR gene expression is characterized by the use of several 5'-noncoding exons and alternative splicing, resulting in the generation of multiple mRNA isoforms. The hGHR V2 transcript is predominant in most tissues, including human fat. However, factors regulating its ubiquitous expression have remained unidentified. The present study was aimed at characterizing the mechanisms regulating hGHR V2 transcription. Two major V2 transcriptional start sites were identified by primer extension assays. The V2 proximal promoter is TATA-less, with several characteristics of a housekeeping gene promoter. Transient transfection analyses of 2.6 kb of the 5'-flanking region of V2 confirmed its promoter activity in multiple primate cell lines. Similar promoter activity patterns were observed in human SGBS preadipocytes and mature adipocytes but with much higher V2 promoter activity in mature adipocytes, suggesting that changes in the availability of specific factors during adipocyte differentiation play a role in V2 promoter regulation. Serial deletion and mutation analyses revealed that transcription of hGHR V2 in different cell types, including adipocytes, is determined by a core promoter and distinct inhibitory and activation domains in the 5'-promoter region as well as within the V2 exon. Our data suggest that V2 transcription is the result of a complex interplay involving multiple factors, to ensure appropriate expression of hGHR in different hGH target cells.

Upstream stimulatory factors are involved in the P1 promoter directed transcription of the A beta H-J-J locus

BACKGROUND

Alternative splicing of the locus A beta H-J-J generates functionally distinct proteins: the enzyme aspartyl (asparaginyl) beta-hydroxylase (AAH), truncated homologs of AAH with a role in calcium homeostasis humbug and junctate and a structural protein of the sarcoplasmic reticulum membranes junctin. AAH and humbug are over expressed in a broad range of malignant neoplasms. We have previously reported that this locus contains two promoters, P1 and P2. While AAH and humbug are expressed in most tissues under the regulation of the P1 promoter, AAH, junctin and junctate are predominantly expressed in excitable tissues under the control of the P2 promoter. We previously demonstrated that Sp transcription factors positively regulate the P1 promoter.

RESULTS

In the present study, we extended the functional characterization of the P1 promoter of the A beta H-J-J locus. We demonstrated by quantitative Real-time RT-PCR that mRNAs from the P1 promoter are actively transcribed in all the human cell lines analysed. To investigate the transcription mechanism we transiently transfected HeLa cells with sequentially deleted reporter constructs containing different regions of the -661/+81 P1 nucleotide sequence. Our results showed that (i) this promoter fragment is a powerful activator of the reporter gene in HeLa cell line, (ii) the region spanning 512 bp upstream of the transcription start site exhibits maximal level of transcriptional activity, (iii) progressive deletions from -512 gradually reduce reporter expression. The region responsible for maximal transcription contains an E-box site; we characterized the molecular interactions between USF1/2 with this E-box element by electrophoretic mobility shift assay and supershift analysis. In addition, our USF1 and USF2 chromatin immunoprecipitation results demonstrate that these transcription factors bind the P1 promoter in vivo. A functional role of USF1/USF2 in upregulating P1-directed transcription was demonstrated by analysis of the effects of (i) in vitro mutagenesis of the P1/E-box binding site, (ii) RNA interference targeting USF1 transcripts.

CONCLUSION

Our results suggest that USF factors positively regulate the core of P1 promoter, and, together with our previously data, we can conclude that both Sp and USF DNA interaction and transcription activity are involved in the P1 promoter dependent expression of AAH and humbug.

Regulation of basal core promoter activity of human organic cation transporter 1 (OCT1/SLC22A1)

Human organic cation transporter 1 (OCT1/SLC22A1) plays important roles in the hepatic uptake of cationic drugs. The functional characteristics of this transporter have been well evaluated, but molecular information regarding transcriptional regulation is limited. In the present study, therefore, we examined the gene regulation of OCT1 gene focusing on basal core expression. An approximately 2.5-kb fragment of the OCT1 promoter region was isolated, and promoter activity was measured by luciferase assay in the human liver cell lines Huh7 and HepG2. Deletion analysis suggested that the region spanning -141/-69 was essential for the basal core transcriptional activity and that this region contained the sequence of a cognate E-box (CACGTG). The E-box is known to be bound by the basal transcription factors, upstream stimulating factors (USFs), and the functional involvements of USF1 and USF2 were confirmed by a transactivation effect, a mutational analysis of the E-box, and an electrophoretic mobility shift assay. The transactivation effect of USFs on the OCT1 promoter was further stimulated by hepatocyte nuclear factor 4alpha, a liver-enriched transcription factor. There were no polymorphisms in the proximal promoter region (about 400 bp) of OCT1 gene (n = 109). These findings indicated that both USF1 and USF2 bind to an E-box sequence located in the OCT1 core promoter region and are required for the basal gene expression of this transporter.

Activation of renal renin-angiotensin system in upstream stimulatory factor 2 transgenic mice

Previously we demonstrated that upstream stimulatory factor 2 (USF2) transgenic (Tg) mice developed nephropathy including albuminuria and glomerular hypertrophy, accompanied by increased transforming growth factor (TGF)-beta and fibronectin accumulation in the glomeruli. However, the mechanisms by which overexpression of USF2 induces kidney injury are unknown. USF has been shown to regulate renin expression. Moreover, the renin-angiotensin system (RAS) plays important roles in renal diseases. Therefore, in the present studies the effects of USF2 on the regulation of RAS in the kidney as well as in mesangial cells from USF2 (Tg) mice were examined. The role of USF2-mediated regulation of RAS in TGF-beta production in mesangial cells was also determined. Our data demonstrate that USF2 (Tg) mice exhibit increased renin and angiotensin (ANG) II levels in the kidney. In contrast, renal expression of other components of RAS such as renin receptor, angiotensinogen, angiotensin-converting enzyme (ACE), ACE2, angiotensin type 1a (AT(1a)) receptor, and AT(2) receptor was not altered in USF2 (Tg) mice. Similarly, mesangial cells isolated from USF2 (Tg) mice had increased renin and ANG II levels. Mesangial cells overexpressing USF2 also had increased TGF-beta production, which was blocked by small interfering RNA-mediated renin gene knockdown or RAS blockade (enalapril or losartan). Collectively, these results suggest that USF2 promotes renal renin expression and stimulates ANG II generation, leading to activation of the intrarenal RAS. In addition, renin-dependent ANG II generation mediates the effect of USF2 on TGF-beta production in mesangial cells, which may contribute to the development of nephropathy in USF2 (Tg) mice.

Upstream stimulatory factor 2 is implicated in the progression of biliary atresia by regulation of hepcidin expression

BACKGROUND

Hepcidin is downregulated during the progression of biliary atresia (BA), but the mechanism is still unknown.

METHODS

We analyzed single nucleotide polymorphism of rs7251432 and 916145 within hepcidin and its upstream, USF2 gene, respectively, in 52 patients of BA and 96 healthy controls. Liver tissues were obtained from 10 patients with early and late stage of BA, 10 patients with choledochal cyst, and 4 normal controls to study upstream stimulatory factor 2 (USF2) messenger RNA (mRNA) and protein expressions. Chromatin immunoprecipitation assay and USF2-specific short interference RNA (siRNA) were used in human HepG2 cells to show that USF2 can regulate hepcidin expression.

RESULTS

C and CC allele frequencies of rs916145 of USF2 were significantly higher in patients with BA than in healthy controls. There was also significantly higher USF2 protein nuclear translocation in the early stage of BA than in the late stage, which was compatible with higher hepcidin mRNA expression in the early stage of BA. Chromatin immunoprecipitation assay demonstrated physiologic bindings of USF2 to the hepcidin promoter in HepG2 cells. USF2 siRNA also significantly knocked down hepcidin mRNA expression.

CONCLUSION

The study demonstrates that C allele of rs916145 in USF2 gene has more frequency for developing BA, and decreased USF2 protein nuclear translocation might partly play a role in the decreased hepcidin expression in the cholestatic liver injury of the late stage of BA.

Glucose increases hepatic lipase expression in HepG2 liver cells through upregulation of upstream stimulatory factors 1 and 2

AIMS/HYPOTHESIS

Elevated hepatic lipase (HL, also known as LIPC) expression is a key factor in the development of the atherogenic lipid profile in type 2 diabetes and insulin resistance. Recently, genetic screens revealed a possible association of type 2 diabetes and familial combined hyperlipidaemia with the USF1 gene. Therefore, we investigated the role of upstream stimulatory factors (USFs) in the regulation of HL.

METHODS

Levels of USF1, USF2 and HL were measured in HepG2 cells cultured in normal- or high-glucose medium (4.5 and 22.5 mmol/l, respectively) and in livers of streptozotocin-treated rats.

RESULTS

Nuclear extracts of cells cultured in high glucose contained 2.5 +/- 0.5-fold more USF1 and 1.4 +/- 0.2-fold more USF2 protein than cells cultured in normal glucose (mean +/- SD, n = 3). This coincided with higher DNA binding of nuclear proteins to the USF consensus DNA binding site. Secretion of HL (2.9 +/- 0.5-fold), abundance of HL mRNA (1.5 +/- 0.2-fold) and HL (-685/+13) promoter activity (1.8 +/- 0.3-fold) increased in parallel. In chromatin immunoprecipitation assays, the proximal HL promoter region was immunoprecipitated with anti-USF1 and anti-USF2 antibodies. Co-transfection with USF1 or USF2 cDNA stimulated HL promoter activity 6- to 16-fold. USF and glucose responsiveness were significantly reduced by removal of the -310E-box from the HL promoter. Silencing of the USF1 gene by RNA interference reduced glucose responsiveness of the HL (-685/+13) promoter region by 50%. The hyperglycaemia in streptozotocin-treated rats was associated with similar increases in USF abundance in rat liver nuclei, but not with increased binding of USF to the rat Hl promoter region.

CONCLUSIONS/INTERPRETATION

Glucose increases HL expression in HepG2 cells via elevation of USF1 and USF2. This mechanism may contribute to the development of the dyslipidaemia that is typical of type 2 diabetes.

Locus control region mediated regulation of adult beta-globin gene expression

Many genes residing in gene clusters and expressed in a differentiation or developmental-stage specific manner are regulated by locus control regions (LCRs). These complex genetic regulatory elements are often composed of several DNAse I hypersensitive sites (HS sites) that function together to regulate the expression of several cis-linked genes. Particularly well characterized is the LCR associated with the beta-globin gene locus. The beta-globin LCR consists of five HS sites that are located upstream of the beta-like globin genes. Recent data demonstrate that the LCR is required for the association of the beta-globin gene locus with transcription foci or factories. The observation that RNA polymerase II associates with the LCR in erythroid progenitor or hematopoietic stem cells which do not express the globin genes suggests that the LCR is always in an accessible chromatin configuration during differentiation of erythroid cells. We propose that erythroid specific factors together with ubiquitous proteins mediate a change in chromatin configuration that juxtaposes the globin genes and the LCR. The proximity then facilitates the transfer of activities from the LCR to the globin genes. In this article we will discuss recent observations regarding beta-globin locus activation with a particular emphasis on LCR mediated activation of adult beta-globin gene expression.

Role of upstream stimulating factors in the transcriptional regulation of the neuron-specific K-Cl cotransporter KCC2

The neuron-specific K-Cl cotransporter (KCC2) maintains a low intracellular Cl(-) concentration in neurons and is necessary for fast hyperpolarizing responses to GABA and glycine. The mammalian KCC2 gene (alias Slc12a5) generates two neuron-specific isoforms by using alternative promoters and first exons. Expression of the major isoform, KCC2b, is strongly upregulated during neuronal maturation, and is modulated by neuronal activity, trauma, and neurotrophic factors. In the present study, we have focused on the regulatory influence of the upstream stimulating factors USF1 and USF2 via an E-box control element in the KCC2b promoter (E-boxKCC2b). Electrophoretic mobility shift assay in cell lines and chromatin immunoprecipitation in neurons demonstrated binding of endogenous USF1 and USF2 to the E-box(KCC2b) element. Mutation of the E-boxKCC2b site resulted in reduced KCC2b promoter activity in cell lines and cortical neurons. Overexpression of a dominant-negative form of USF confirmed the involvement of endogenous USF proteins in the regulation of the KCC2b gene. The results suggest that binding of USF proteins to the E-boxKCC2b may contribute to the upregulation of KCC2b gene expression in developing brain.

In vivo regulation of follicle-stimulating hormone receptor by the transcription factors upstream stimulatory factor 1 and upstream stimulatory factor 2 is cell specific

Pituitary FSH promotes pubertal timing and normal gametogenesis by binding its receptor (FSHR) located on Sertoli and granulosa cells of the testis and ovary, respectively. Studies on Fshr transcription provide substantial evidence that upstream stimulatory factor (USF) 1 and USF2, basic helix-loop-helix leucine zipper proteins, regulate Fshr through an E-box within its promoter. However, despite the strong in vitro support for USF1 and USF2 in Fshr regulation, there is currently no in vivo corroborating evidence. In the present study, chromatin immunoprecipitation demonstrated specific binding of USF1 and USF2 to the Fshr promoter in both Sertoli and granulosa cells, in vivo. Control cells lacking Fshr expression showed no USF-Fshr promoter binding, thus correlating USF-promoter binding to gene activity. Evaluation of Fshr expression in Usf1 and Usf2 null mice further explored USF's role in Fshr transcription. Loss of either gene significantly reduced ovarian Fshr levels, whereas testis levels were unaltered. Chromatin immunoprecipitation analysis of USF-Fshr promoter binding in Usf-null mice indicated differences in the composition of promoter-bound USF dimers in granulosa and Sertoli cells. Promoter-bound USF dimer levels declined in granulosa cells from both null mice, despite increased USF2 levels in Usf1-null ovaries. However, compensatory increases in promoter-bound USF homodimers were evident in Usf-null Sertoli cells. In summary, this study provides the first in vivo evidence that USF1 and USF2 bind the Fshr promoter and revealed differences between Sertoli and granulosa cells in compensatory responses to USF loss and the USF dimeric composition required for Fshr transcription.

Enhancement of prostaglandin D(2) production through cyclooxygenase-2 and lipocalin-type prostaglandin D synthase by upstream stimulatory factor 1 in human brain-derived TE671 cells under serum starvation

We found that prostaglandin (PG) D(2) production was induced through transcriptional activation of cyclooxygenase (COX)-2 and lipocalin-type PGD synthase (L-PGDS) genes under serum-starved conditions in human brain-derived TE671 cells. Analysis of promoter and intron regions of the human L-PGDS gene demonstrated that an atypical E-box within intron 4 mediated serum starvation-induced up-regulation of L-PGDS gene expression. The results of electrophoretic mobility shift assay and chromatin immunoprecipitation assay showed that upstream stimulatory factor (USF) 1 bound to this atypical E-box. USF1 gene expression was also enhanced during serum starvation in TE671 cells through activation of p38 mitogen activated protein kinase, and the efficiency of the binding of USF1 to the atypical E-box was clearly increased by serum starvation. Administration of USF1 siRNA suppressed both L-PGDS and COX-2 gene expression and PGD(2) production. Moreover, NS-398, a COX-2 inhibitor and AT-56, an L-PGDS inhibitor, suppressed PGD(2) production in TE671 cells cultured under the serum-starved condition. These results indicate that PGD(2) production stimulated by serum starvation is mediated by both COX-2 and L-PGDS through enhancement of USF1 in TE671 cells.

USF1/2 transcription factor DNA-binding activity is induced during rat Sertoli cell differentiation

Each Sertoli cell can support a finite number of developing germ cells. During development of the testis, the cessation of Sertoli cell proliferation and the onset of differentiation determine the final number of Sertoli cells and, hence, the number of sperm that can be produced. We hypothesize that the transition from proliferation to differentiation is facilitated by E-box transcription factors that induce the expression of differentiation-promoting genes. The relative activities of E-box proteins were studied in primary Sertoli cells isolated from 5-, 11-, and 20-day-old rats, representing proliferating, differentiating, and differentiated cells, respectively. E-box DNA-binding activity is almost undetectable 5 days after birth but peaks with initiation of differentiation 11 days after birth and remains elevated. Upstream stimulatory factors 1 and 2 (USF1 and USF2) were found to be the predominant E-box proteins present within DNA-protein complexes formed after incubating E-box-containing probes with nuclear extracts from developing Sertoli cells. The known potentiator of Sertoli cell differentiation, thyroxine, increases USF DNA-binding activity in Sertoli cells before differentiation (5-day-old Sertoli cells) but not after differentiation is initiated (11- and 20-day-old Sertoli cells). The developmental-specific increase in USF1 and USF2 DNA-binding activity may facilitate the switch from proliferation to differentiation and, thus, determine the ultimate number of Sertoli cells present within the testes and the upper limit of fertility.

Chromatin profiling across the human tumour necrosis factor gene locus reveals a complex, cell type-specific landscape with novel regulatory elements

The TNF locus on chromosome 6p21 encodes a family of proteins with key roles in the immune response whose dysregulation leads to severe disease. Transcriptional regulation is important, with cell type and stimulus-specific enhancer complexes involving the proximal TNF promoter. We show how quantitative chromatin profiling across a 34 kb region spanning the TNF locus has allowed us to identify a number of novel DNase hypersensitive sites and characterize more distant regulatory elements. We demonstrate DNase hypersensitive sites corresponding to the lymphotoxin alpha (LTA) and tumour necrosis factor (TNF) promoter regions, a CpG island in exon 4 of lymphotoxin beta (LTB), the 3′ end of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor-like 1 (NFKBIL1) and 3.4 kb upstream of LTA. These sites co-localize to highly conserved DNA sequences and show evidence of cell type specificity when lymphoblastoid, Jurkat, U937, HeLa and HEK293T cell lines are analysed using Southern blotting. For Jurkat T cells, we define histone modifications across the locus. Peaks of acetylated histone H3 and H4, together with tri-methyl K4 of histone H3, correspond to hypersensitive sites, notably in exon 4 of LTB. We provide evidence of a functional role for an intergenic DNase I hypersensitive site distal to LTA in Jurkat cells based on reporter gene analysis, with evidence of recruitment of upstream stimulatory factors (USF) transcription factors.

Expressional changes in the intracellular melanogenesis pathways and their possible role in the pathogenesis of vitiligo

BACKGROUND

Main pathway in human melanocytes through which signal from the melanocortin system reaches the melanogenesis enzymes is cAMP/PKA pathway and it is modulated by Wnt and MAPK pathways. In our previous study we established significant increase of melanocortin receptor expression in unaffected skin of vitiligo patients compared to healthy subjects.

OBJECTIVE

The aim of this study was to assess the gene expression profile of the intracellular signalling pathways linking melanocortin system with enzymes involved in melanogenesis.

METHODS

Using QRT-PCR method, mRNA expression levels of eight genes related to signal transduction from the melanocortin system to melanogenesis enzymes was measured in lesional and non-lesional skin of vitiligo patients and in the skin of healthy control subjects. Following genes were analyzed in the study: MITF, CREB1, p38, USF1, PIK3CB (PI3K), RPS6KB1, LEF1 and BCL2.

RESULTS

The mRNA levels of MITF, LEF1, p38, PIK3CB and RPS6KB1 were decreased in lesional skin of vitiligo patients compared to skin of healthy control subjects. We also found increased expression of USF1 and BCL2 in non-lesional skin of vitiligo patients compared to skin of healthy control subjects. mRNA levels of MITF and BCL2 were decreased in lesional skin of vitiligo patients compared to non-lesional skin of vitiligo patients.

CONCLUSIONS

Present study indicates increased expression of the genes of the intracellular melanogenesis pathway in the non-lesional skin of vitiligo patients. This finding suggests activation of melanogenesis pathway in the non-lesional skin of vitiligo.

Upstream stimulatory factors, USF1 and USF2 are differentially expressed during Xenopus embryonic development

Upstream stimulatory factors (USF) 1 and 2 are members of the basic helix-loop-helix leucine zipper transcription factor family. They are considered to play critical roles in cell-cycle regulation and chromatin remodeling. Their gene expression patterns are considered ubiquitous but have not been fully investigated in terms of embryogenesis. We examined the expression of the genes encoding USF1 and USF2 in Xenopus laevis during embryonic development. Expression of both genes was first detected as maternal transcripts and was observed continuously throughout development. However, in situ hybridization analysis revealed that the two genes were expressed differentially. In the late blastula, both genes were expressed in the blastocoel roof and marginal zone. At the gastrula stage, USF2 was strongly expressed in the sensorial layer of the ectoderm and in the mesoderm, whereas USF1 expression was hardly detectable. From the neurula stage onward, expression of both genes was markedly enhanced in the neural tissues, neural crest, eye and otic vesicle. However, spatial expression of the genes within the neural tube differed in that the strongest USF1 signals were observed in the lateral region of the basal plate and the strongest USF2 ones in the dorsal region of the neural tube. Expression of the two genes occurred in different mesoderm derivatives at the tailbud stage (USF1, somite; USF2, pronephros and lateral plate mesoderm of the tail region). USF1 was expressed in the notochord of the early neurula, but was lost at the stage.

The canonical E-box motif: a target for glucocorticoid action that drives rhythmic mouse Pai-1 transcription in vitro

Circadian (approximately 24 h) control impinges on an array of diverse physiological processes in many organisms, ranging from plants to human. Disruption of the mammalian circadian clockwork can lead to severe chronic illnesses such as cardiovascular disease, cancer progression and metabolic disorders. Transcriptional regulation of plasminogen activator inhibitor 1 (PAI-1) is of particular importance because of its crucial role in these pathological conditions. Pai-1 expression is partly regulated by the circadian clock, although direct mechanisms on Pai-1 rhythmicity are unknown. In the present study, we have identified a conserved functional E-box cis-element in the distal part of the mouse Pai-1 gene that is necessary and sufficient to drive circadian expression in Pai-1 activity after dexamethasone synchronisation in vitro. Mutagenesis and in vitro transfection analysis indicated this E-box provides a cognate binding site for cross-talk between clock and hypoxia factors, thus providing a potential cooperation mechanism between circadian and stress pathways, which is conserved in the human Pai-1 gene. Together, these results suggest that the canonical E-box is a target for glucocorticoid action, thus providing the molecular interface between gene transcription and drug action. The mechanism described has global impact on diverse dynamic biological processes governed by the neuroendocrine axis and the circadian clockwork to control complex coordination of gene cascades and biology.

High glucose levels upregulate upstream stimulatory factor 2 gene transcription in mesangial cells

Previously, we demonstrated that upstream stimulatory factor 2 (USF2) mediates high glucose-induced thrombospondin1 (TSP1) gene expression and TGF-beta activity in glomerular mesangial cells and plays a role in diabetic renal complications. In the present studies, we further determined the molecular mechanisms by which high glucose levels regulate USF2 gene expression. In primary rat mesangial cells, we found that glucose treatment time and dose-dependently up-regulated USF2 expression (mRNA and protein). By using cycloheximide to block the de novo protein synthesis, similar rate of USF2 degradation was found under either normal glucose or high glucose conditions. USF2 mRNA stability was not altered by high glucose treatment. Furthermore, high glucose treatment stimulated USF2 gene promoter activity. By using the luciferase-promoter deletion assay, site-directed mutagenesis, and transactivation assay, we identified a glucose-responsive element in the USF2 gene promoter (-1,740 to -1,620, relative to the transcription start site) and demonstrated that glucose-induced USF2 expression is mediated through a cAMP-response element-binding protein (CREB)-dependent transactivation of the USF2 promoter. Furthermore, siRNA-mediated CREB knock down abolished glucose-induced USF2 expression. Taken together, these data indicate that high glucose levels up-regulate USF2 gene transcription in mesangial cells through CREB-dependent transactivation of the USF2 promoter.

Serial changes in expression of functionally clustered genes in progression of liver fibrosis in hepatitis C patients

AIM

To investigate the relationship of changes in expression of marker genes in functional categories or molecular networks comprising one functional category or multiple categories in progression of hepatic fibrosis in hepatitis C (HCV) patients.

METHODS

Marker genes were initially identified using DNA microarray data from a rat liver fibrosis model. The expression level of each fibrosis associated marker gene was analyzed using reverse transcription-polymerase chain reaction (RT-PCR) in clinical biopsy specimens from HCV-positive patients (n = 61). Analysis of changes in expression patterns and interactions of marker genes in functional categories was used to assess the biological mechanism of fibrosis.

RESULTS

The profile data showed several biological changes associated with progression of hepatic fibrosis. Clustered genes in functional categories showed sequential changes in expression. Several sets of clustered genes, including those related to the extracellular matrix (ECM), inflammation, lipid metabolism, steroid metabolism, and some transcription factors important for hepatic biology showed expression changes in the immediate early phase (F1/F2) of fibrosis. Genes associated with aromatic amino acid (AA) metabolism, sulfur-containing AA metabolism and insulin/ Wnt signaling showed expression changes in the middle phase (F2/F3), and some genes related to glucose metabolism showed altered expression in the late phase of fibrosis (F3/F4). Therefore, molecular networks showing serial changes in gene expression are present in liver fibrosis progression in hepatitis C patients.

CONCLUSION

Analysis of gene expression profiles from a perspective of functional categories or molecular networks provides an understanding of disease and suggests new diagnostic methods. Selected marker genes have potential utility for biological identification of advanced fibrosis.

Binding of upstream stimulatory factor 1 to the E-box regulates the 4G/5G polymorphism-dependent plasminogen activator inhibitor 1 expression in mast cells

BACKGROUND

Plasminogen activator inhibitor (PAI)-1 is a key regulator of the fibrinolytic system. PAI-1 levels are markedly elevated in the asthmatic airways. The 4G/5G polymorphism of the PAI-1 gene is associated with allergic asthma.

OBJECTIVE

To characterize the mechanisms of the 4G/5G-dependent PAI-1 expression in mast cells (MCs), a major source of PAI-1 and key effector cells in asthma.

METHODS

Transcription of PAI-1 was assessed by transiently transfecting human MC line (HMC-1) cells with the luciferase-tagged PAI-1 promoters containing the 4G or 5G allele (4G-PAI-1 or 5G-PAI-1 promoter). Upstream stimulatory factor (USF)-1 and the E-box interactions were studied by electrophoretic mobility shift assays and supershift assays. Expression of USF-1 was determined by Western blot analysis.

RESULTS

The 4G-PAI-1 promoter has higher promoter activity than the 5G-PAI-1 promoter in stimulated HMC-1 cells, and the E-box adjacent to the 4G/5G site (E-4G/5G) regulates the genotype-specific PAI-1 transcription. USF-1 binds to the E-4G with greater affinity than to the E-5G. USF-1 level is increased in HMC-1 cells after stimulation, and elevated USF-1 enhances PAI-1 transcription. Overexpression of wild-type USF-1 or dominant-negative USF remedies the 4G/5G-dependent PAI-1 transcription.

CONCLUSION

Binding of USF-1 to the E-4G/5G regulates the 4G/5G polymorphism-dependent PAI-1 expression in MCs.

Whole-genome maps of USF1 and USF2 binding and histone H3 acetylation reveal new aspects of promoter structure and candidate genes for common human disorders

Transcription factors and histone modifications are crucial regulators of gene expression that mutually influence each other. We present the DNA binding profiles of upstream stimulatory factors 1 and 2 (USF1, USF2) and acetylated histone H3 (H3ac) in a liver cell line for the whole human genome using ChIP-chip at a resolution of 35 base pairs. We determined that these three proteins bind mostly in proximity of protein coding genes transcription start sites (TSSs), and their bindings are positively correlated with gene expression levels. Based on the spatial and functional relationship between USFs and H3ac at protein coding gene promoters, we found similar promoter architecture for known genes and the novel and less-characterized transcripts human mRNAs and spliced ESTs. Furthermore, our analysis revealed a previously underestimated abundance of genes in a bidirectional conformation, where USFs are bound in between TSSs. After taking into account this promoter conformation, the results indicate that H3ac is mainly located downstream of TSS, and it is at this genomic location where it positively correlates with gene expression. Finally, USF1, which is associated to familial combined hyperlipidemia, was found to bind and potentially regulate nuclear mitochondrial genes as well as genes for lipid and cholesterol metabolism, frequently in collaboration with GA binding protein transcription factor alpha (GABPA, nuclear respiratory factor 2 [NRF-2]). This expands our understanding about the transcriptional control of metabolic processes and its alteration in metabolic disorders.

USF1 Gene Variants, Cardiovascular Risk, and Mortality in European Americans

Objective— A common haplotype of the upstream transcription factor 1 gene ( USF1 ) has been associated with decreased susceptibility to familial combined hyperlipidemia (FCHL) and, paradoxically, with increased risk of cardiovascular disease (CVD) and all-cause mortality.

Methods and Results— We assessed associations between USF1 tagSNPs, CVD risk factors, and aging-related phenotypes using data from 2 large population-based cohorts, Coronary Artery Risk Development in Young Adults (CARDIA) and the Cardiovascular Health Study (CHS), comprising younger and older adults, respectively. In CARDIA, each additional copy of the FCHL low-risk allele was associated with 2.4 mg/dL lower levels of LDL cholesterol ( P =0.01) and decreased risk of subclinical atherosclerosis as assessed by coronary artery calcium (odds ratio 0.79; 95%CI 0.63 to 0.98). Whereas there was little association between USF1 genotype and metabolic or CVD traits in older adults from CHS, the USF1 low-risk dyslipidemia allele was associated with higher plasma C-reactive protein and interleukin (IL)-6 levels and with increased risk of mortality, particularly attributable to noncardiovascular causes.

Conclusions— There appears to be a complex and possibly age-dependent relationship between USF1 genotype, atherosclerosis phenotypes, and CVD risk. USF1 may influence mortality through pathways distinct from atherosclerosis. Alternatively, linkage disequilibrium with neighboring polymorphisms in other genes such as F11R may be responsible for the observed USF1 genotype–phenotype associations in older adults.

Mechanisms of melanogenesis inhibition by 2,5-dimethyl-4-hydroxy-3(2H)-furanone

BACKGROUND

Increased production and accumulation of melanin is characteristic of a large number of skin diseases, including acquired hyperpigmentation such as melasma, postinflammatory melanoderma and solar lentigo. Thus, there is a increasing need for the development of depigmenting agents.

OBJECTIVES

To evaluate the depigmenting capacity of 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) and to elucidate the mechanisms by which it inhibits alpha-melanocyte-stimulating hormone (alpha-MSH)-induced melanogenesis in B16 melanoma cells in vitro.

METHODS

Several experiments were performed in B16 melanoma cells. We studied melanin content, tyrosinase activity and cAMP production, and performed cAMP response element (CRE) luciferase reporter assay and Western blots for proteins involved in melanogenesis.

RESULTS

The melanin content and tyrosinase activity induced by alpha-MSH were inhibited significantly by DMHF. To clarify the mechanism of the depigmenting property of DMHF, we examined the involvement of DMHF in cAMP signalling induced by alpha-MSH. In CRE luciferase reporter assay, CRE reporter activation induced by alpha-MSH was inhibited by DMHF. Additionally, although DMHF did not inhibit cAMP production by alpha-MSH, both CRE binding protein (CREB) phosphorylation and the reduction of glycogen synthase kinase-3beta phosphorylation by alpha-MSH were blocked by DMHF. These data suggest that DMHF inhibits the downstream step of cAMP production induced by alpha-MSH, consequently inhibiting melanogenesis. This suggestion was further confirmed by the fact that the increased production levels of microphthalmia-associated transcription factor, tyrosinase and tyrosinase-related protein-1 induced by alpha-MSH were all reduced by DMHF in B16 melanoma cells.

CONCLUSIONS

Our study shows that DMHF inhibits alpha-MSH-induced melanogenesis by suppressing CREB phosphorylation, which is induced by protein kinase A, and suggests that DMHF may be an effective inhibitor of hyperpigmentation.

Mechanisms regulating human FMO3 transcription

Flavin-containing monooxygenases (FMOs) are important oxidative drug metabolizing enzymes. FMO3 is the primary human adult liver FMO enzyme, but is developmentally regulated. FMO3 promoter characterization using in vitro DNA binding assays with HepG2 cell and fetal and adult liver nuclear protein, as well as FMO3/reporter construct transient expression in HepG2 cells, provided evidence for specific mechanisms contributing to both developmental and constitutive adult regulation. NFY, USF1, an unidentified GC box binding protein, and YY1 appear to play major roles regulating constitutive FMO3 transcription, while Pbx(2) as a heterodimer with an unidentified Hox isoform also may contribute to FMO3 developmental expression.

Rosmarinic acid induces melanogenesis through protein kinase A activation signaling

Melanogenesis is a physiological process that results in the synthesis of melanin pigments, which play a crucial protective role against skin photocarcinogenesis. In order to determine the effects of rosmarinic acid on melanogenesis and elucidate the molecular events of melanogenesis induced by rosmarinic acid, several experiments were performed in B16 melanoma cells. In this study, we showed that the melanin content and tyrosinase expression were increased by rosmarinic acid in a concentration-dependent manner. In addition, after the melanin content was increased by rosmarinic acid, it was reduced by H-89 and KT 5720, protein kinase A (PKA) inhibitors, but not by SB203580, a p38(mapk) inhibitor, or Ro-32-0432, a PKC inhibitor, which suggests the involvement of PKA in rosmarinic acid-induced melanogenesis. Consistent with this, rosmarinic acid induced the phosphorylation of CRE-binding protein (CREB), but had no effect on the phosphorylation of p38(mapk) or the inhibition of Akt phosphorylation. Additionally, rosmarinic acid induced the activation of cAMP response element (CRE) without having any effect on cAMP production, which suggests that rosmarinic acid-induced melanogenesis is mediated by PKA, which occurs downstream of cAMP production. This result was further confirmed by the fact that rosmarinic acid-induced phosphorylation of CREB was inhibited by H-89, but not by PD98059, a MEK1 inhibitor, or by LY294002, a phosphatidylinositol-3-kinase (PI3K) inhibitor. Rosmarinic acid-induced expression of tyrosinase protein was attenuated by H-89. Based on these results, we report for the first time that rosmarinic acid induces melanogenesis through PKA activation signaling.

Cyclin D1 is transcriptionally down-regulated by ZO-2 via an E box and the transcription factor c-Myc

Recent reports have indicated the participation of tight junction (TJ) proteins in the regulation of gene expression and cell proliferation. Here, we have studied the role of zona occludens (ZO)-2, a TJ peripheral protein, in the regulation of cyclin D1 transcription. We found that ZO-2 down-regulates cyclin D1 transcription in a dose-dependent manner. To understand how ZO-2 represses cyclin D1 promoter activity, we used deletion analyses and found that ZO-2 negatively regulates cyclin D1 transcription via an E box and that it diminishes cell proliferation. Because ZO-2 does not associate directly with DNA, electrophoretic mobility shift assay and chromatin immunoprecipitation (ChIP) assay were used to identify the transcription factors mediating the ZO-2-repressive effect. c-Myc was found to bind the E box present in the cyclin D1 promoter, and the overexpression of c-Myc augmented the inhibition generated by ZO-2 transfection. The presence of ZO-2 and c-Myc in the same complex was further demonstrated by immunoprecipitation. ChIP and reporter gene assays using histone deacetylases (HDACs) inhibitors demonstrated that HDACs are necessary for ZO-2 repression and that HDAC1 is recruited to the E box. We conclude that ZO-2 down-regulates cyclin D1 transcription by interacting with the c-Myc/E box element and by recruiting HDAC1.

Overexpression of upstream stimulatory factor 2 accelerates diabetic kidney injury

Diabetic nephropathy is the most common cause of end-stage renal failure in the United States. Hyperglycemia is an important factor in the pathogenesis of diabetic nephropathy. Hyperglycemia upregulates the expression of transforming growth factor-beta (TGF-beta), which stimulates extracellular matrix deposition in the kidney, contributing to the development of diabetic nephropathy. Our previous studies demonstrated that the transcription factor, upstream stimulatory factor 2 (USF2), was upregulated by high glucose, which bound to an 18-bp sequence in the thrombospondin 1 (TSP1) gene promoter and regulated high glucose-induced TSP1 expression and TGF-beta activity in mesangial cells, suggesting that USF2 might play a role in the development of diabetic nephropathy. In the present studies, we examined the effect of overexpression of USF2 on the development of diabetic nephropathy. Type 1 diabetes was induced in USF2 transgenic mice [USF2 (Tg)] and their wild-type littermates (WT) by injection of streptozotocin. Four groups of mice were studied: control WT, control USF2 (Tg), diabetic WT, and diabetic USF2 (Tg). Mice were killed after 15 wk of diabetes onset. At the end of studies, control USF2 (Tg) mice ( approximately 6 mo old) exhibited increased urinary albumin excretion. These mice also exhibited glomerular hypertrophy, accompanied by increased TSP1, active TGF-beta, fibronectin accumulation in the glomeruli compared with control WT littermates. Type 1 diabetes onset further augmented the urinary albumin excretion and glomerular hypertrophy in the USF2 (Tg) mice. These findings suggest that overexpression of USF2 accelerates the development of diabetic nephropathy.

Upstream stimulating factor-1 mediates the E-box-dependent transcriptional repression of the plasminogen activator inhibitor-1 gene in human mast cells

Plasminogen activator inhibitor (PAI)-1 promotes development of asthma. PAI-1 mRNA and protein are markedly induced in activated mast cells (MCs), a major effector cell type in asthma. However, regulatory mechanisms of PAI-1 transcription in MCs are unknown. We present first evidence that PAI-1 is transcriptionally regulated in human MCs (hMCs). In addition to three enhancer regions, we demonstrated that the E-box at -566 bp to -561 bp is the negative regulatory element, and the specific and constitutive binding of the upstream stimulating factor-1 to this E-box is the key mechanism of the negative regulation of PAI-1 expression in hMCs.

Transcriptional regulation of the distal promoter of the rat pyruvate carboxylase gene by hepatocyte nuclear factor 3beta/Foxa2 and upstream stimulatory factors in insulinoma cells

PC (pyruvate carboxylase) plays a crucial role in intermediary metabolism including glucose-induced insulin secretion in pancreatic islets. In the present study, we identified two regions of the 1.2 kb distal promoter, the -803/-795 site and the -408/-403 E-box upstream of the transcription start site, as the important cis-acting elements for transcriptional activation of the luciferase reporter gene. Site-directed mutagenesis of either one of these sites in the context of this 1.2 kb promoter fragment, followed by transient transfections in the insulinoma cell line, INS-1, abolished reporter activity by approx. 50%. However, disruption of either the -803/-795 or the -408/-403 site did not affect reporter gene activity in NIH 3T3 cells, suggesting that this promoter fragment is subjected to cell-specific regulation. The nuclear proteins that bound to these -803/-795 and -408/-403 sites were identified by gel retardation assays as HNF3beta (hepatocyte nuclear factor 3beta)/Foxa2 (forkhead/winged helix transcription factor box2) and USFs (upstream stimulatory factors), USF1 and USF2, respectively. Chromatin immunoprecipitation assays using antisera against HNF3beta/Foxa2, USF1 and USF2 demonstrated that endogenous HNF3beta/Foxa2 binds to the -803/-795 Foxa2 site, and USF1 and USF2 bind to the -408/-403 E-box respectively in vivo, consistent with the gel retardation assay results. Although there are weak binding sites located at regions -904 and -572 for PDX1 (pancreatic duodenal homeobox-1), a transcription factor that controls expression of beta-cell-specific genes, it did not appear to regulate PC expression in INS-1 cells in the context of the 1.2 kb promoter fragment. The results presented here show that Foxa2 and USFs regulate the distal promoter of the rat PC gene in a cell-specific manner.

Upstream stimulatory factor regulates constitutive expression and hormonal suppression of the 90K (Mac-2BP) protein

We previously reported that hormones important for the normal growth and function of FRTL-5 rat thyroid cells, TSH, or its cAMP signal plus insulin or IGF-I, could transcriptionally suppress constitutive and gamma-interferon (IFN)-increased synthesis of the 90K protein (also known as Mac-2BP). Here we cloned the 5'-flanking region of the rat 90K gene and identified a minimal promoter containing an interferon response element and a consensus E-box or upstream stimulator factor (USF) binding site, which are highly conserved in both the human and murine genes. We show that suppression of constitutive and gamma-IFN-increased 90K gene expression by TSH/cAMP plus insulin/IGF-I depends on the ability of the hormones to decrease the binding of USF to the E-box, located upstream of the interferon response element. This site is required for the constitutive expression of the 90K gene. Transfection with USF1 and USF2 cDNAs increases constitutive promoter activity, attenuates the ability of TSH/cAMP plus insulin/IGF-I to decrease constitutive or gamma-IFN-increased 90K gene expression but does not abrogate the ability of gamma-IFN itself to increase 90K gene expression.

The tyrosinase enhancer is activated by Sox10 and Mitf in mouse melanocytes

The terminal differentiation of melanocytes is associated with the transcriptional activation of genes responsible for pigment production such as tyrosinase. Pigment cell-specific transcription factors, such as Mitf, as well as specific proximal and distal regulatory elements (DRE) are implicated in the tight control of tyrosinase expression during development and adulthood. Proper tyrosinase expression in melanocytes depends upon the presence of a DRE that is located at -15 kb and provides enhancer activity via a central element termed core-enhancer. In this report, we show that the transcription factors Sox10, Mitf and USF-1 are able to activate the core-enhancer in luciferase reporter assays. Comparative sequence analysis identified evolutionarily motifs resembling Sox10 binding sites that were required for full enhancer activity in melanoma cells and in tyrosinase::lacZ transgenic mice. Sox10 was able to bind the DRE in vitro and mutation of the conserved motifs abolished the enhancer transactivation mediated by Sox10. In addition, two highly conserved CAGCTG E-box motifs were identified that were also required for enhancer activity and for transactivation by Mitf. The results suggest that Sox10 directly, and Mitf, most likely indirectly, activate the tyrosinase enhancer, underlining the contribution of Sox10 to tyrosinase gene regulation in melanocytes.

Diosgenin inhibits melanogenesis through the activation of phosphatidylinositol-3-kinase pathway (PI3K) signaling

An increased level of melanin is characteristic of a large number of skin diseases, including acquired hyperpigmentation conditions such as melasma, post inflammatory melanoderma, and solar lentigo. Thus, there is an increasing need for the development of depigmenting agents. In order to evaluate the depigmenting capacity of diosgenin and elucidate its mechanism of action, several experiments were performed in B16 melanoma cells. Melanin content and Western blots for proteins that are involved in melanogenesis were assessed in this study. The melanin content was significantly inhibited by diosgenin. To clarify the mechanism of the depigmenting property of diosgenin, we examined the involvement of diosgenin in the phosphatidylinositol-3-kinase (PI3K) pathway. In this study, diosgenin inhibited the reduction of Akt and GSK 3beta phosphorylation induced by LY294,002, a PI3K inhibitor. In accordance with this result, production levels of MITF (microphthalmia-associated transcription factor) and tyrosinase were increased by diosgenin. These data suggest that diosgenin inhibits melanogenesis through the activation of the PI3K pathway. This suggestion was further confirmed by the fact that the increased production level of melanin by LY294,002 was reduced by diosgenin in B16 melanoma cells. Our study shows that diosgenin inhibits melanogenesis by activating the PI3K pathway, and also suggests that diosgenin may be an effective inhibitor of hyperpigmentation.

Cooperative activation of lipocalin-type prostaglandin D synthase gene expression by activator protein-2beta in proximal promoter and upstream stimulatory factor 1 within intron 4 in human brain-derived TE671 cells

We investigated the activation mechanism of gene expression of lipocalin-type prostaglandin D synthase (L-PGDS) in human brain-derived TE671 cells. Reporter analyses of constructs carrying various lengths of the promoter region and intron 1 to 6, or 3'-untranslated region of the human L-PGDS gene demonstrated that one atypical E-box (aE-box) at +2569 in intron 4 was critical for transactivation of the gene. The aE-box inside the intron 4 functioned as an enhancer element in both directions and in a cell-type specific manner in TE671 cells. Yeast one-hybrid screening revealed that upstream stimulatory factor (USF) 1 bound to the aE-box. Expression of exogenous USF1 induced the endogenous L-PGDS expression in TE671 cells, whereas administration of USF1 siRNA suppressed L-PGDS expression. Binding of USF1 to the aE-box was confirmed by performing electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Furthermore, USF1-mediated transcriptional activation was dependent upon activator protein (AP)-2beta binding to the AP-2 element at position -98 in the proximal promoter region of human L-PGDS gene. These results indicate that L-PGDS gene expression in TE671 cells was activated by USF1 through the aE-box within intron 4 and cooperatively by AP-2beta in the promoter in a cell-type-specific manner.

Characterization of the Basal promoter element of human organic cation transporter 2 gene

Human organic cation transporter 2 (hOCT2; SLC22A2) is abundantly expressed in the kidney, and it plays important roles in the renal tubular secretion of cationic drugs. Although the transport characteristics of hOCT2 have been studied extensively, there is no information available for the transcriptional regulation of hOCT2. The present study was undertaken to identify the cis-element and trans-factor for basal expression of hOCT2. The transcription start site was located 385 nucleotides above the translation start site by using 5'-rapid amplification of cDNA ends. An approximately 4-kilobase fragment of the hOCT2 promoter region was isolated and the promoter activities were measured in the renal epithelial cell line LLC-PK1. A deletion analysis suggested that the region spanning -91 to -58 base pairs was essential for basal transcriptional activity. This region lacked a TATA-box but contained a CCAAT box and an E-box. Electrophoretic mobility shift assays showed that specific DNA/protein complexes were present in the E-box but not in the CCAAT box, and supershift assays revealed that upstream stimulatory factor 1 (USF-1), which belongs to the basic helix-loop-helix-leucine zipper family of transcription factors, bound to the E-box. Mutation of the E-box resulted in a decrease in hOCT2 promoter activity, and overexpression of USF-1 enhanced the hOCT2 promoter activity in a dose-dependent manner. This article reports the first characterization of the hOCT2 promoter and shows that USF-1 functions as a basal transcriptional regulator of the hOCT2 gene via the E-box.

Cloning and expression analysis of myogenin from flounder (Paralichthys olivaceus) and promoter analysis of muscle-specific expression

Myogenin is a bHLH transcription factor of the MyoD family. It plays a crucial role in myoblast differentiation and maturation. We report here the isolation of flounder myogenin gene and the characterization of its expression patterns. Sequence analysis indicated that flounder myogenin shared a similar structure and the conserved bHLH domain with other vertebrate myogenin genes. Flounder myogenin gene contains 3 exons and 2 introns. Sequence alignment and phylogenetic showed that flounder myogenin was more homologous with halibut (Hippoglossus hippoglossus) myogenin and striped bass (Morone saxatilis) myogenin. Whole-mount embryo in situ hybridization revealed that flounder myogenin was first detected in the medial region of somites that give rise to slow muscles, and expanded later to the lateral region of the somite that become fast muscles. The levels of myogenin transcripts dropped significantly in matured somites at the trunk region. Its expression could only be detected in the caudal somites, which was consistent with the timing of somite maturation. Transient expression analysis showed that the 546 bp flounder myogenin promoter was sufficient to direct muscle-specific GFP expression in zebrafish embryos.

Ebola virus-like particle-induced activation of NF-kappaB and Erk signaling in human dendritic cells requires the glycoprotein mucin domain

Dendritic cells (DCs), important early targets of Ebola virus (EBOV) infection in vivo, are activated by Ebola virus-like particles (VLPs). To better understand this phenomenon, we have systematically assessed the response of DCs to VLPs of different compositions. VLPs containing the viral matrix protein (VP40) and the viral glycoprotein (GP), were found to induce a proinflammatory response highly similar to a prototypical DC activator, LPS. This response included the production of several proinflammatory cytokines, activation of numerous transcription factors including NF-kappaB, the functional importance of which was demonstrated by employing inhibitors of NF-kappaB activation, and activation of ERK1/2 MAP kinase. In contrast, VLPs constituted with a mutant GP lacking the heavily glycosylated mucin domain showed impaired NF-kappaB and Erk activation and induced less DC cytokine production. We conclude that the GP mucin domain is required for VLPs to stimulate human dendritic cells through NF-kappaB and MAPK signaling pathways.

Aryl hydrocarbon receptor nuclear translocator and upstream stimulatory factor regulate Cytochrome P450 2a5 transcription through a common E-box site

The aryl hydrocarbon receptor nuclear translocator (ARNT) belongs to the basic-helix-loop-helix (bHLH) transcription factors and regulates several genes as heterodimers with other bHLH proteins. ARNT is also able to homodimerize, but no mammalian target genes for the homodimer have been shown. We identified a palindromic E-box element in the 5' regulatory region of the murine cytochrome P450 (Cyp) 2a5 gene that was found to be important for Cyp2a5 transcription in primary hepatocytes, and was found by chromatin immunoprecipitation assays to interact with ARNT. Electrophoretic mobility-shift assay experiments with in vitro translated ARNT showed binding without heterodimerization partner, indicating binding as a homodimer. Transfection studies in wild-type and ARNT-deficient Hepa-1 cells revealed that ARNT expression is necessary for full activity of the Cyp2a5 promoter. In the liver-specific Arnt-null mouse line, the level of hepatic CYP2A5 mRNA was decreased significantly. Co-transfection studies with an ARNT expression vector lacking the transactivation domain (TAD) demonstrated that the ARNT TAD is needed for Cyp2a5 activation, which suggests that ARNT transactivates Cyp2a5 as a homodimer. In primary hepatocytes, the mRNA levels of both CYP2A5 and ARNT splice variant 1 were increased during cultivation. Upstream stimulatory factors 1 and 2a were also able to bind to the same E-box as ARNT, indicating that there may be competition for DNA binding between these factors. Indeed, the upstream stimulatory factors activated the Cyp2a5 promoter through the E-box only in the presence of hepatocyte nuclear factor-4alpha, while ARNT transactivation was independent of hepatocyte nuclear factor-4alpha. In conclusion, these results indicate that ARNT controls Cyp2a5 transcription and thus, for the first time, suggest active involvement of the ARNT homodimer in mammalian gene regulation.

Characterization of the promoter of the gene encoding human tripeptidyl-peptidase II and identification of upstream silencer elements

Tripeptidyl-peptidase II (TPP II) is one of the many proteases involved in the important process of intracellular proteolysis. The widespread distribution and broad substrate specificity suggest that TPP II is encoded by a "house-keeping gene". However, both TPP II protein and mRNA levels vary in different cells. To investigate whether these variations are due to regulation on a genetic level, the promoter of the TPP2 gene has previously been identified. The promoter contains two inverted CCAAT-boxes and an E-box. By means of reporter assays and electrophoretic mobility shift assays the promoter has now been further characterized. It could be concluded that USF-1 (upstream stimulatory factor-1) binds to the E-box in the promoter. The transcription factors NF-Y and USF-1 are present in protein-DNA complexes of different sizes. Mutation of the E-box had no effect, indicating that only binding of NF-Y to the two CCAAT-boxes was important for activation of transcription. However, this does not exclude the possibility that USF-1 can play an important role in transcription in other types of cells. Furthermore, the region upstream of the promoter was investigated due to its ability to inhibit transcription. Several silencer elements were identified and we also showed that Oct-1 binds to one of these elements. Thus, this investigation reveals that TPP II expression could be regulated through both positive and negative regulatory elements. Further studies are required to establish the involvement of different genetic elements, and how the interplay between different transcription factors will affect the transcriptional rate in vivo.

Mitf regulation of Dia1 controls melanoma proliferation and invasiveness

It is widely held that cells with metastatic properties such as invasiveness and expression of matrix metalloproteinases arise through the stepwise accumulation of genetic lesions arising from genetic instability and "clonal evolution." By contrast, we show here that in melanomas invasiveness can be regulated epigenetically by the microphthalmia-associated transcription factor, Mitf, via regulation of the DIAPH1 gene encoding the diaphanous-related formin Dia1 that promotes actin polymerization and coordinates the actin cytoskeleton and microtubule networks at the cell periphery. Low Mitf levels lead to down-regulation of Dia1, reorganization of the actin cytoskeleton, and increased ROCK-dependent invasiveness, whereas increased Mitf expression leads to decreased invasiveness. Significantly the regulation of Dia1 by Mitf also controls p27(Kip1)-degradation such that reduced Mitf levels lead to a p27(Kip1)-dependent G1 arrest. Thus Mitf, via regulation of Dia1, can both inhibit invasiveness and promote proliferation. The results imply variations in the repertoire of environmental cues that determine Mitf activity will dictate the differentiation, proliferative, and invasive/migratory potential of melanoma cells through a dynamic epigenetic mechanism.

Activation of the Mitf promoter by lipid-stimulated activation of p38-stress signalling to CREB

The microphthalmia-associated transcription factor Mitf plays a critical role in regulating many aspects of melanocyte biology. It is required for melanoblast and postnatal melanocyte survival, regulates proliferation, and activates genes associated with differentiation such as tyrosinase and related genes involved in melanogenesis. Identifying the signals that regulate Mitf expression is crucial if we are to understand how cells of the melanocyte lineage respond to environmental cues. Here we show that the Mitf promoter is induced by lipid signalling via the p38 stress-activated kinase pathway that is also activated by a wide range of receptors as well as UV irradiation. Signalling via p38 leads to increased phosphorylation and activation of cyclic adenosine monophosphate response element-binding (CREB) that binds and activates the Mitf promoter via the cyclic adenosine monophosphate (cAMP) response element. Moreover, we also show that activation of p38 mediated by lipids is potentiated by inhibition of the PI3kinase pathway but not by inhibition of protein kinase A (PKA). The results identify a mechanism in which stress signalling via p38 leads to activation of CREB, enhanced Mitf expression and consequently increased tyrosinase expression. The results are relevant for the regulation of melanocytes by Mitf, but also raise the possibility that lipid mediated activation of p38 signalling may represent a potential therapy for vitiligo.

Modulation of UVB-induced and basal cyclooxygenase-2 (COX-2) expression by apigenin in mouse keratinocytes: Role of USF transcription factors

Apigenin is a bioflavonoid with chemopreventive activity against UV- or chemically-induced mouse skin tumors. To further explore the mechanism of apigenin's chemopreventive activity, we determined whether apigenin inhibited UVB-mediated induction of cyclooxygenase-2 (COX-2) expression in mouse and human keratinocytes. Apigenin suppressed the UVB-induced increase in COX-2 protein and mRNA in mouse and human keratinocyte cell lines. UVB radiation of keratinocytes transfected with a mouse COX-2 promoter/luciferase reporter plasmid resulted in a threefold increase in transcription from the promoter, and apigenin inhibited the UV-induced promoter activity at doses of 5-50 microM. Transient transfections with COX-2 promoter deletion constructs and COX-2 promoter constructs containing mutations in specific enhancer elements indicated that the effects of UVB required intact Ebox and ATF/CRE response elements. Electrophoretic mobility shift assays with supershifting antibodies were used to identify USF-1, USF-2, and CREB as proteins binding to the ATF/CRE-Ebox responsive element of the COX-2 promoter. Keratinocytes co-transfected with the COX-2 luciferase reporter and a USF-2 expression vector, alone or in combination with a USF-1 expression vector, exhibited enhanced promoter activity in both UVB-irradiated and nonirradiated cultures. However, COX-2 promoter activity was inhibited in keratinocytes co-transfected with USF-1 alone. Finally, we present data showing that the suppressive effect of apigenin on COX-2 expression could be reversed by co-expression of USF-1 and USF-2. These results suggest that one pathway by which apigenin inhibits COX-2 expression is through modulation of USF transcriptional activity.

Xenopus cDNA microarray identification of genes with endodermal organ expression

The endoderm is classically defined as the innermost layer of three Metazoan germ layers. During organogenesis, the endoderm gives rise to the digestive and respiratory tracts as well as associated organs such as the liver, pancreas, and lung. At present, however, how the endoderm forms the variety of cell types of digestive and respiratory tracts as well as the budding organs is not well understood. In order to investigate the molecular basis and mechanism of organogenesis and to identify the endodermal organ-related marker genes, we carried out microarray analysis using Xenopus cDNA chips. To achieve this goal, we isolated the Xenopus gut endoderm from three different stages of Xenopus organogenesis, and separated each stage of gut endoderm into anterior and posterior regions. Competitive hybridization of cDNA between the anterior and posterior endoderm regions, to screen genes that specifically expressed in the major organs, revealed 915 candidates. We then selected 104 clones for in situ hybridization analysis. Here, we report the identification and expression patterns of the 104 Xenopus endodermal genes, which would serve as useful markers for studying endodermal organ development.

Isolation and Characterization of the Rat SND p102 Gene Promoter

In this work, we report the isolation and characterization of a 1,688-bp sequence corresponding to the promoter region of the rat endoplasmic reticulum (ER) cholesterol ester hydrolase gene, renamed as staphylococcal nuclease domain-containing protein of 102 kDa (SND p102) in GenBank database according to the structural properties and molecular weight of the protein. The transcription start site was located 216 bases upstream of the ATG start codon by RNA ligase mediated-rapid amplification of cDNA ends (RLM-RACE). Bioinformatic analysis of the isolated sequence revealed a lack of typical promoter TATA box and the presence of GC-rich motifs and CCAAT boxes recognized by Sp 1 and nuclear factor-Y among other putative binding sites for a number of transcription factors implicated in both basal and regulated processes. Electrophoretic mobility shift and supershift assays using nuclear extracts from human (HepG2) and rat (McA-RH7777) hepatoma cells demonstrated that nuclear factor-Y (NF-Y) transcription factor bound to the core sequences at (-257, -253), (-290, -286), and (-370, -366) upstream translation initiation site. The absence of TATA box and the location and reverse orientation of the CCAAT boxes in the promoter region strongly suggest a role for NF-Y in the regulation of transcription of SND p102 gene.

PAI-1 transcriptional regulation during the G0 --> G1 transition in human epidermal keratinocytes

Plasminogen activator inhibitor type-1 (PAI-1) is the major negative regulator of the plasmin-dependent pericellular proteolytic cascade. PAI-1 gene expression is normally growth state regulated but frequently elevated in chronic fibroproliferative and neoplastic diseases affecting both stromal restructuring and cellular migratory activities. Kinetic modeling of cell cycle transit in synchronized human keratinocytes (HaCaT cells) indicated that PAI-1 transcription occurred early after serum stimulation of quiescent (G0) cells and prior to entry into a cycling G1 condition. PAI-1 repression (in G0) was associated with upstream stimulatory factor-1 (USF-1) occupancy of two consensus E box motifs (5'-CACGTG-3') at the PE1 and PE2 domains in the PF1 region (nucleotides -794 to -532) of the PAI-1 promoter. Chromatin immunoprecipitation (ChIP) analysis established that the PE1 and PE2 site E boxes were occupied by USF-1 in quiescent cells and by USF-2 in serum-activated, PAI-1-expressing keratinocytes. This reciprocal and growth state-dependent residence of USF family members (USF-1 vs. USF-2) at PE1/PE2 region chromatin characterized the G0 --> G1 transition period and the transcriptional status of the PAI-1 gene. A consensus E box motif was required for USF/E box interactions, as a CG --> AT substitution at the two central nucleotides inhibited formation of USF/probe complexes. The 5' flanking sites (AAT or AGAC) in the PE2 segment were not necessary for USF binding. USF recognition of the PE1/PE2 region E box sites required phosphorylation with several potential involved residues, including T153, maping to the USF-specific region (USR). A T153A substitution in USF-1 did not repress serum-induced PAI-1 expression whereas the T153D mutant was an effective suppressor. As anticipated from the ChIP results, transfection of wild-type USF-2 failed to inhibit PAI-1 induction. Collectively, these data suggest that USF family members are important regulators of PAI-1 gene control during serum-stimulated recruitment of quiescent human epithelial cells into the growth cycle.

Melanocytes: the new Black

Melanocytes, pigment-producing cells residing primarily in the hair follicle, epidermis and eye, are responsible for skin hair and eye pigmentation. Pigmentation is achieved by the highly regulated manufacture of the pigment melanin in specialised organelles, melanosomes that are transported along dendritic processes before being transferred to growing hair, or keratinocytes where melanin protects from UV-induced DNA damage. Because loss of melanocytes gives a clear pigmentation phenotype yet is non-lethal, over 130 genes implicated in the development or function of this cell type have been identified to date, and in humans the loss of melanocytes or their ability to produce pigment, or transport or transfer melanosomes is associated with several diseases such as vitiligo, albinism and Hermansky-Pudlak syndrome. Importantly, the effective combination of genetics, cell and molecular biology possible with this cell type is attracting an increasing number of researchers focussed on understanding how cells coordinate survival, proliferation, differentiation and stem cell maintenance.