AP-1 and Oct-1 transcription factors down-regulate the expression of the human PIT1/GHF1 gene

Long-Distance Repression by Human Silencers: Chromatin Interactions and Phase Separation in Silencers

Three-dimensional genome organization represents an additional layer in the epigenetic regulation of gene expression. Active transcription controlled by enhancers or super-enhancers has been extensively studied. Enhancers or super-enhancers can recruit activators or co-activators to activate target gene expression through long-range chromatin interactions. Chromatin interactions and phase separation play important roles in terms of enhancer or super-enhancer functioning. Silencers are another major type of cis-regulatory element that can mediate gene regulation by turning off or reducing gene expression. However, compared to active transcription, silencer studies are still in their infancy. This review covers the current knowledge of human silencers, especially the roles of chromatin interactions and phase separation in silencers. This review also proposes future directions for human silencer studies.

Primate-specific stress-induced transcription factor POU2F1Z protects human neuronal cells from stress

The emergence of new primate-specific genes is an essential factor in human and primate brain development and functioning. POU2F1/Oct-1 is a transcription regulator in higher eukaryotes which is involved in the regulation of development, differentiation, stress response, and other processes. We have demonstrated that the Tigger2 transposon insertion into the POU2F1 gene which occurred in the primate lineage led to the formation of an additional exon (designated the Z-exon). Z-exon-containing primate-specific Oct-1Z transcript includes a short upstream ORF (uORF) located at its 5’-end and the main ORF encoding the Oct-1Z protein isoform (Pou2F1 isoform 3, P14859-3), which differs from other Oct-1 isoforms by its N-terminal peptide. The Oct-1Z-encoding transcript is expressed mainly in human brain cortex. Under normal conditions, the translation of the ORF coding for the Oct-1Z isoform is repressed by uORF. Under various stress conditions, uORF enables a strong increase in the translation of the Oct-1Z-encoding ORF. Increased Oct-1Z expression levels in differentiating human neuroblasts activate genes controlling stress response, neural cell differentiation, brain formation, and organogenesis. We have shown that the Oct-1Z isoform of the POU2F1/Oct-1 transcription factor is an example of a primate-specific genomic element contributing to brain development and cellular stress defense.

The Molecular Basis of Congenital Hypopituitarism and Related Disorders

CONTEXT

Congenital hypopituitarism (CH) is characterized by the presence of deficiencies in one or more of the 6 anterior pituitary (AP) hormones secreted from the 5 different specialized cell types of the AP. During human embryogenesis, hypothalamo-pituitary (HP) development is controlled by a complex spatio-temporal genetic cascade of transcription factors and signaling molecules within the hypothalamus and Rathke's pouch, the primordium of the AP.

EVIDENCE ACQUISITION

This mini-review discusses the genes and pathways involved in HP development and how mutations of these give rise to CH. This may present in the neonatal period or later on in childhood and may be associated with craniofacial midline structural abnormalities such as cleft lip/palate, visual impairment due to eye abnormalities such as optic nerve hypoplasia (ONH) and microphthalmia or anophthalmia, or midline forebrain neuroradiological defects including agenesis of the septum pellucidum or corpus callosum or the more severe holoprosencephaly.

EVIDENCE SYNTHESIS

Mutations give rise to an array of highly variable disorders ranging in severity. There are many known causative genes in HP developmental pathways that are routinely screened in CH patients; however, over the last 5 years this list has rapidly increased due to the identification of variants in new genes and pathways of interest by next-generation sequencing.

CONCLUSION

The majority of patients with these disorders do not have an identified molecular basis, often making management challenging. This mini-review aims to guide clinicians in making a genetic diagnosis based on patient phenotype, which in turn may impact on clinical management.

The regulatory interplay between Oct-1 isoforms contributes to hematopoiesis and the isoforms imbalance correlates with a malignant transformation of B cells

Oct-1(POU2F1) is a DNA-binding transcription regulator and its level being highly increased in many human cancers. Oct-1 is present in the human cells as a family of functionally different isoforms which are transcribed from alternative promoters. Here, we have demonstrated that expression patterns of Oct-1 isoforms change during differentiation of hematopoetic progenitor cells (CD34+) (HPCs) to the B (CD19+) and T (CD3+) cells. While Oct-1L is expressed at a high level in the CD34+ HPCs, its expression level drops dramatically during the T-cell differentiation, although remains nearly the same in B-cells. We have described the novel human Oct-1R isoform which is conserved in mammals and is B cell-specific. Oct-1R was found in B cells, but not in HPCs. Oct-1R is transcribed from the same promoter as Oct-1L, another lymphocyte-specific isoform. Overexpression of Oct-1R and Oct-1L in the Namalwa cells leads to the repression of many genes involved in B-lymphocyte differentiation and signal transduction. Thus these isoforms may regulate the particular stages of development of normal B cells and maintain their proper differentiation status. However the extremely high level of Oct-1L isoform observed in the B-lymphoblast tumor cell lines indicated that the excess of Oct-L seem likely to considerably decrease the differentiation ability of these cells. Oct-1 may serve as a therapeutic target for many tumors, but it should be noted that in a tumor the content of a certain isoform Oct-1, rather than the total Oct-1 protein, can be increased.

Genetic screening of regulatory regions of pituitary transcription factors in patients with idiopathic pituitary hormone deficiencies

PURPOSE

Mutation frequencies of PROP1, POU1F1 and HESX1 in patients with combined pituitary hormone deficiencies (CPHD) vary substantially between populations. They are low in sporadic CPHD patients in Western Europe. However, most clinicians still routinely send DNA of their CPHD patients for genetic screening of these pituitary transcription factors. Before we can recommend against screening of PROP1, POU1F1 and HESX1 as part of routine work-up for Western-European sporadic CPHD patients, it is crucial to rule out possible defects in regulatory regions of these genes, which could also disturb the complex process of pituitary organogenesis.

METHODS

The regulatory regions of PROP1, POU1F1 and HESX1 are not covered by Whole Exome Sequencing as they are largely located outside the coding regions. Therefore, we manually sequenced the regulatory regions, previously defined in the literature, of PROP1, POU1F1 and HESX1 among 88 Dutch patients with CPHD. We studied promoter SNPs in relation to phenotypic data.

RESULTS

We found six known SNPs in the PROP1 promoter. In the POU1F1 promoter, we found one new variant and two known SNPs. We did not find any variant in the HESX1 promoter.

CONCLUSION

Although the new POU1F1 variant might explain the phenotype of one patient, the general conclusion of this study is that variants in regulatory regions of PROP1, POU1F1 and HESX1 are rare in patients with sporadic CPHD in the Netherlands. We recommend that genetic screening of these pituitary transcription factors should no longer be part of routine work-up for Western-European, and especially Dutch, sporadic CPHD patients.

Different N-terminal isoforms of Oct-1 control expression of distinct sets of genes and their high levels in Namalwa Burkitt's lymphoma cells affect a wide range of cellular processes

Oct-1 transcription factor has various functions in gene regulation. Its expression level is increased in several types of cancer and is associated with poor survival prognosis. Here we identified distinct Oct-1 protein isoforms in human cells and compared gene expression patterns and functions for Oct-1A, Oct-1L, and Oct-1X isoforms that differ by their N-terminal sequences. The longest isoform, Oct-1A, is abundantly expressed and is the main Oct-1 isoform in most of human tissues. The Oct-1L and the weakly expressed Oct-1X regulate the majority of Oct-1A targets as well as additional sets of genes. Oct-1X controls genes involved in DNA replication, DNA repair, RNA processing, and cellular response to stress. The high level of Oct-1 isoforms upregulates genes related to cell cycle progression and activates proliferation both in Namalwa Burkitt's lymphoma cells and primary human fibroblasts. It downregulates expression of genes related to antigen processing and presentation, cytokine-cytokine receptor interaction, oxidative metabolism, and cell adhesion, thus facilitating pro-oncogenic processes.

Increased level of Oct-1 protein in tumor cells modulates cellular response to anticancer drugs

The effect of overexpression of Oct-1 protein isoforms on the cell response to two anticancer drugs camptothecin and dexamethasone was studied. The effect of Oct-1 isoforms on regulated gene transcription was estimated by the difference in the level of mRNA in Burkitt's lymphoma cells (Namalwa line) untransfected and stably transfected with Oct-1 isoforms. The response to anticancer drugs of the Oct-1 target genes involved in the development of apoptosis depended, firstly, on the type of drug, secondly, on the concentration of Oct-1 in cells. and, thirdly, on the Oct-1 isoform with which these cells were transfected.

Elevated OCT1 participates in colon tumorigenesis and independently predicts poor prognoses of colorectal cancer patients

Octamer transcription factor 1 (OCT1) was found to influence the genesis and progression of numerous cancers except for colorectal cancer (CRC). This study tried to explore the role of OCT1 in CRC and clarify the association between its expression and patients' clinical outcome. Transcriptional and post-transcriptional expression of OCT1 was detected in CRC cancerous tissues and paired normal mucosae by real-time PCR as well as immunohistochemistry. Moreover, the effect of OCT1 knockdown on CRC cell proliferation was investigated both in vitro and in vivo using Cell Counting Kit-8 assay, colony-forming assay, and mouse tumorigenicity assay. Expression of OCT1 was found to be elevated in CRC. Suppression of OCT1 significantly inhibited CRC cell proliferation both in vitro and in vivo. Furthermore, upregulated level of OCT1 was significantly associated with N stage, M stage, and American Joint Committee on Cancer (AJCC) stage (P = 0.027, 0.014, and 0.002, respectively) as well as differential degree (P = 0.022). By using multivariate Cox hazard model, OCT1 was also shown to be a factor independently predicting overall survival (OS; P = 0.013, hazard ratio = 2.747, 95 % confidence interval 1.125 to 3.715) and disease-free survival (DFS; P = 0.004, hazard ratio = 2.756, 95 % confidence interval 1.191 to 4.589) for CRC patients. Our data indicate that OCT1 carries weight in colorectal carcinogenesis and functions as a novel prognostic indicator and a promising target of anti-cancer therapy for CRC.

New alternative promoter in regulation of the Oct-1 human gene transcription

For the first time, the presence of a new alternative promoter in the gene of the oct-1 transcription factor from which a previously unknown mRNA isoform Oct-1X, with 5'-terminus different from the previously described isoforms, was demonstrated. The nucleotide sequence of the Oct-1X cDNA was determined and the presence of a long open reading frame which starts with the first ATG codon of the second exon was demonstrated. A protein shortened on its N-terminus is assumed to be the product of a new mRNA isoform. Expression of the new isoform was studied in various human cell lines; the results indicate the ubiquitous nature of the Oct-1X expression. Therefore, in the work, the third alternative promoter of human oct-1 gene (earlier, a ubiquitous promoter U and an inducible tissue-specific promoter L were described) contributing to the fine regulation of mRNA isoform synthesis and formation of structural and functional diversity of Oct-1 protein isoforms in cells was revealed.

Inactivation of transcription factor pit-1 to target tumoral somatolactotroph cells

The treatment of growth hormone (GH)- and prolactin (PRL)-secreting tumors resistant to current therapeutic molecules (somatostatin and dopamine analogues) remains challenging. To target these tumors specifically, we chose to inactivate a gene coding for a crucial factor in cell proliferation and hormonal regulation, specifically expressed in pituitary, by using a dominant-negative form of this gene involved in human pituitary deficiencies: transcription factor Pit-1 (POU1F1) mutated on arginine 271 to tryptophan (R271W). After lentiviral transfer, the effect of R271W was studied in vitro on human tumoral somatotroph and lactotroph cells and on the murine mammosomatotroph cell line GH4C1 and in vivo on GH4C1 subcutaneous xenografts in nude mice. R271W induced a decrease in GH and PRL hypersecretion by controlling the transcription of the corresponding hormones. This mutant decreased cell viability by an apoptotic mechanism and in vivo blocked the tumoral growth and GH secretion of xenografts obtained after transplantation of GH4C1 expressing mutant R271W. The strategy of using a dominant-negative form of a main factor controlling cell proliferation and hormonal secretion, and exclusively expressed in pituitary, seems promising for the gene therapy of human pituitary tumors and may be translated to other types of tumors maintaining some differentiation features.

PIT1 upregulation by HMGA proteins has a role in pituitary tumorigenesis

We have previously demonstrated that HMGA1B and HMGA2 overexpression in mice induces the development of GH and prolactin (PRL) pituitary adenomas mainly by increasing E2F1 transcriptional activity. Interestingly, these adenomas showed very high expression levels of PIT1, a transcriptional factor that regulates the gene expression of Gh, Prl, Ghrhr and Pit1 itself, playing a key role in pituitary gland development and physiology. Therefore, the aim of our study was to identify the role of Pit1 overexpression in pituitary tumour development induced by HMGA1B and HMGA2. First, we demonstrated that HMGA1B and HMGA2 directly interact with both PIT1 and its gene promoter in vivo, and that these proteins positively regulate Pit1 promoter activity, also co-operating with PIT1 itself. Subsequently, we showed, by colony-forming assays on two different pituitary adenoma cell lines, GH3 and αT3, that Pit1 overexpression increases pituitary cell proliferation. Finally, the expression analysis of HMGA1, HMGA2 and PIT1 in human pituitary adenomas of different histological types revealed a direct correlation between PIT1 and HMGA expression levels. Taken together, our data indicate a role of Pit1 upregulation by HMGA proteins in pituitary tumours.

Brn2 is a transcription factor regulating keratinocyte differentiation with a possible role in the pathogenesis of lichen planus

Terminal differentiation of skin keratinocytes is a vertically directed multi-step process that is tightly controlled by the sequential expression of a variety of genes. In this study, we investigated the role of the POU domain-containing transcription factor Brn2 in keratinocyte differentiation. Immunohistochemical analysis showed that Brn2 is expressed primarily in the upper granular layer. Consistent with its epidermal localization, Brn2 expression was highly induced at 14 days after calcium treatment of cultured normal human epidermal keratinocytes. When Brn2 was overexpressed by adenoviral transduction, Brn2 led to increased expression of the differentiation-related genes involucrin, filaggrin, and loricrin in addition to inhibition of their proliferation. Chromatin immunoprecipitation demonstrated that Brn2 bound to the promoter regions of these differentiation-related genes. We injected the purified Brn2 adenovirus into rat skin, which led to a thickened epidermis with increased amounts of differentiation related markers. The histopathologic features of adenovirus-Brn2 injected skin tissues looked similar to the features of lichen planus, a human skin disease showing chronic inflammation and well-differentiated epidermal changes. Moreover, Brn2 is shown to be expressed in almost all cell nuclei of the thickened epidermis of lichen planus, and Brn2 also attracts T lymphocytes. Our results demonstrate that Brn2 is probably a transcriptional factor playing an important role in keratinocyte differentiation and probably also in the pathogenesis of lichen planus lesions.

A far-upstream Oct-1 motif regulates cytokine-induced transcription of the human inducible nitric oxide synthase gene

Transcriptional regulation of the human inducible nitric oxide synthase (hiNOS) gene is highly complex and requires an orchestrated flow of positive and negative transcription factors that bind to specific cis-acting upstream response elements. Very little specific information exists about the far-upstream region of the hiNOS gene. Oct-1 protein belongs to the Pit-Oct-Unc domain transcription factor family and is constitutively expressed in all dividing cells. It is essential for proliferation, differentiation, and other key cell processes. However, the role of Oct-1 in regulating hiNOS gene expression has not been reported. In this work, the octamer sequence 5'-ATGCAAAT-3' at -10.2 kb in the hiNOS promoter was identified as high-affinity Oct-1 binding by electrophoretic mobility shift assay in vitro and chromatin immunoprecipitation assay in vivo. Mutation of Oct-1 motif at -10.2 kb in the hiNOS promoter decreased cytokine-induced hiNOS promoter activity by 40%. Cytokine-induced hiNOS promoter activity was also significantly reduced by Oct-1 small interfering RNA targeting. Overexpression of Oct-1 increased cytokine-induced hiNOS protein expression in primary human hepatocytes. Furthermore, the Oct-1 motif at -10.2 kb of the hiNOS promoter conferred increased transcriptional activity to the heterologous thymidine kinase promoter irrespective of cytokine induction. Taken together, this work identifies a far-upstream functional Oct-1 enhancer motif at -10.2 kb in the hiNOS promoter that regulates cytokine-induced hiNOS gene transcription and further underscores tight control mechanisms regulating the expression of the hiNOS gene.

A novel dysfunctional LHX4 mutation with high phenotypical variability in patients with hypopituitarism

CONTEXT

LHX4 is a LIM homeodomain transcription factor involved in pituitary ontogenesis. Only a few heterozygous LHX4 mutations have been reported to be responsible for congenital pituitary hormone deficiency.

SUBJECTS AND METHODS

A total of 136 patients with congenital hypopituitarism associated with malformations of brain structures, pituitary stalk, or posterior pituitary gland was screened for LHX4 mutations.

RESULTS

Three novel allelic variants that cause predicted changes in the protein sequence of LHX4 (2.3%) were found (p.Thr99fs, p.Thr90Met, and p.Gly370Ser). On the basis of functional studies, p.Thr99fs mutation was responsible for the patients' phenotype, whereas p.Thr90Met and p.Gly370Ser were likely polymorphisms. Patients bearing the heterozygous p.Thr99fs mutation had variable phenotypes: two brothers presented somato-lactotroph and thyrotroph deficiencies, with pituitary hypoplasia and poorly developed sella turcica; the youngest brother (propositus) also had corpus callosum hypoplasia and ectopic neurohypophysis; their father only had somatotroph deficiency and delayed puberty with pituitary hyperplasia. Functional studies showed that the mutation induced a complete loss of transcriptional activity on POU1F1 promoter and a lack of DNA binding. Cotransfection of p.Thr99fs mutant and wild-type LHX4 failed to evidence any dominant negative effect, suggesting a mechanism of haploinsufficiency. We also identified prolactin and GH promoters as potential target genes of LHX4 and found that the p.Thr99fs mutant was also unable to transactivate these promoters.

CONCLUSIONS

The present report describes three new exonic LHX4 allelic variants with at least one being responsible for congenital hypopituitarism. It also extends the phenotypical heterogeneity associated with LHX4 mutations, which includes variable anterior pituitary hormone deficits, as well as pituitary and extrapituitary abnormalities.

Modular changes of cis-regulatory elements from two functional Pit1 genes in the duplicated genome of Cyprinus carpio

The pituitary-specific transcription factor Pit1 is involved in its own regulation and in a network of transcriptional regulation of hypothalamo-hypophyseal factors including prolactin (PRL) and growth hormone (GH). In the ectotherm teleost Cyprinus carpio, Pit1 plays an important role in regulation of the adaptive response to seasonal environmental changes. Two Pit1 genes exist in carp, a tetraploid vertebrate and transcripts of both genes were detected by RT-PCR analysis. Powerful comparative analyses of the 5'-flanking regions revealed copy specific changes comprising modular functional units in the naturally evolved promoters. These include the precise replacement of four nucleotides around the transcription start site embedded in completely conserved regions extending upstream of the TATA-box, an additional transcription factor binding site in the 5'-UTR of gene-I and, instead, duplication of a 9 bp element in gene-II. Binding of nuclear factors was assessed by electro mobility shift assays using extracts from rat pituitary cells and carp pituitary. Binding was confirmed at one conserved Pit1, one conserved CREB and one consensus MTF1. Interestingly, two functional Pit1 sites and one putative MTF1 binding site are unique to the Pit1 gene-I. In situ hybridization experiments revealed that the expression of gene-I in winter carp was significantly stronger than that of gene-II. Our data suggest that the specific control elements identified in the proximal regulatory region are physiologically relevant for the function of the duplicated Pit1 genes in carp and highlight modular changes in the architecture of two Pit1 genes that evolved for at least 12 MYA in the same organism.

Preventing polyglutamine-induced activation of c-Jun delays neuronal dysfunction in a mouse model of SCA7 retinopathy

We have approached the role of cellular stress in neurodegenerative diseases caused by polyglutamine expansion (polyQ) in the context of Spinocerebellar ataxia type 7 (SCA7) that includes retinal degeneration. Using the R7E mouse, in which polyQ-ataxin-7 is specifically over-expressed in rod photoreceptors, we previously showed that rod dysfunction correlated to moderate and prolonged activation of the JNK/c-Jun stress pathway. SCA7 retinopathy was also associated with reduced expression of rod-specific genes, including the transcription factor Nrl, which is essential for rod differentiation and function. Here, we report that R7E retinopathy is improved upon breeding with the JunAA knock-in mice, in which JNK-mediated activation of c-Jun is compromised. Expression of Nrl and its downstream targets, which are involved in phototranduction, are partially restored in the JunAA-R7E mice. We further show that c-Jun can directly repress the transcription of Nrl. Our studies suggest that polyQ-induced cellular stress leads to repression of genes necessary for neuronal fate and function.

Autoregulation of Oct-1 gene expression is mediated by two octa-sites in alternative promoter

Transcription of the oct-1 gene is regulated by two alternative promoters: U promoter and L promoter located upstream of the exons 1U and 1L, respectively. The L promoter contains two octamer sequences of opposite orientation: proximal (ATTTGCAT) and distal (ATGCAAAT), showing high affinity toward the Oct proteins. Binding of the Oct-1 protein to the octa-sites located in the L promoter region has been confirmed in footprinting experiments. Dual luciferase assay using wild-type and mutated promoters have indicated that mutations in the proximal octa-site resulted in significant transcription enhancement both in myeloma cell line NS/0 and in fibroblast cell line 3T3 (about twofold and fivefold, respectively), whereas mutations in the distal site decreased the promoter activity (about 10% and 40%, respectively). Mutations in both octa-sites enhanced the effect and increased transcription to about fourfold in myeloma cell line NS/0 and about sixfold in fibroblast cell line 3T3. These results demonstrate that transcription of the oct-1 gene may be autoregulated by two octa-sites within the L promoter. Different function and interactive tissue-specific effect of distal and proximal octamer sequences can be suggested.

Activin inhibits the human Pit-1 gene promoter through the p38 kinase pathway in a Smad-independent manner

The pituitary transcription factor Pit-1 regulates hormonal production from the anterior pituitary gland. However, the mechanisms by which Pit-1 gene expression is regulated in humans are poorly understood. Activin, a member of the TGFbeta superfamily, acts as a negative regulator of cell growth and prolactin gene expression in lactotrope cells. In this study, we show that activin negatively regulates the human Pit-1 gene promoter. We defined a 117-bp element within the Pit-1 promoter that is sufficient to relay these inhibitory effects. We further investigated the signaling pathways that mediate activin-induced inhibition of Pit-1 gene promoter in pituitary lactotrope cells. We found that the activin effects on Pit-1 gene regulation are Smad independent and require the p38 MAPK pathway. Specifically, blocking p38 kinase activity reverses activin-mediated inhibition of the Pit-1 gene promoter. Together, our results highlight the p38 MAPK pathway as a key regulator of activin function in pituitary lactotrope cells and further emphasizes the critical role played by activin in regulating hormonal production in the pituitary gland.

The Transcription Factor PLA-1/SKN-1A is Expressed in Human Placenta and Regulates the Placental Lactogen-3 Gene Expression

Here we report the selective expression of two POU transcription factor genes, PLA-1 and OCT-1, in human placenta and choriocarcinoma cell lines JAR, JEG-3 and BeWo. Pla-1 protein binds to a POU-consensus DNA sequence in the human placental lactogen-3 (PL-3) promoter and it is capable of trans-activating its transcription up to 18-fold. Other tissue-specific or ubiquitous POU transcription factors such as Pit-1/GHF-1 or Oct-1 showed none or low levels of trans-activation of the PL-3 promoter. In addition, we identified an unique and highly charged region in the N-terminal portion of Pla-1 protein required for full trans-activation of the PL-3 promoter.

OCT-1 is over-expressed in intestinal metaplasia and intestinal gastric carcinomas and binds to, but does not transactivate, CDX2 in gastric cells

Intestinal metaplasia (IM) is a preneoplastic lesion of the stomach in which there is transdifferentiation of the gastric mucosa to an intestinal phenotype. The caudal-related homeobox gene CDX2 encodes an intestine-specific transcription factor crucial for the regulation of proliferation and differentiation of intestinal cells. In addition, CDX2 is involved in the induction of IM in the stomach. The aim of this study was to access the putative involvement of OCT-1 in the induction of CDX2 expression de novo in gastric mucosa leading to the onset of IM. OCT-1 protein expression was evaluated by immunohistochemistry in 31 biopsies with chronic gastritis, 15 biopsies with foci of IM and adjacent gastric mucosa and 42 gastric carcinomas. Furthermore, we evaluated OCT-1 binding by electrophoretic mobility shift assay and activation of the CDX2 promoter by co-transfecting a CDX2 promoter/reporter construct with an OCT-1 expression vector in two gastric carcinoma cell lines, GP220 and MKN45. Our results show that OCT-1 is expressed in chronic gastritis, particularly when it is adjacent to IM and is expressed in 87% of IM foci. Furthermore, 74% of the gastric carcinomas were positive for OCT-1 and a strong association was observed between OCT-1 expression and intestinal-type carcinoma. We identified that OCT-1 binds to the CDX2 promoter, although we could not see a transactivation effect in gastric carcinoma cell lines. In conclusion, we observed increased OCT-1 expression in IM and in intestinal gastric carcinomas and identified the capacity of OCT-1 to bind to the CDX2 promoter, although we could not demonstrate a direct effect of OCT-1 in the transactivation of CDX2.

Promoter cloning and characterisation of the transcriptional regulation of the human thyrostimulin A2 subunit

The novel heterodimeric glycoprotein hormone thyrostimulin consists of two unique subunits, A2 and B5. To understand its yet unknown transcriptional regulation, we characterised the 3.1-kb immediate 5'-flanking region of the human A2 gene localised on chromosome 11q13. In transient transfection assays this sequence exhibited promoter activity, which could be confined to nucleotides -506 to -347 relative to the ATG start codon. Interestingly, this minimal promoter appeared to be non-tissue-specific. Deletional, mutational and gel shift analyses revealed regulatory elements that are essential for the regulation of the A2 gene expression. Another noteworthy feature of this gene is the presence of silencer elements upstream and downstream of the promoter. To surmise, our results provide an initial step toward a detailed analysis of the underlying molecular mechanisms of the human thyrostimulin gene expression.

The vitamin D receptor represses transcription of the pituitary transcription factor Pit-1 gene without involvement of the retinoid X receptor

Pituitary transcription factor-1 (Pit-1) plays a key role in cell differentiation during organogenesis of the anterior pituitary, and as a transcriptional activator for the pituitary GH and prolactin genes. However, Pit-1 is also expressed in nonpituitary cell types and tissues. In breast tumors, Pit-1 mRNA and protein levels are increased with respect to normal breast, and in MCF-7 human breast adenocarcinoma cells, Pit-1 increases GH secretion and cell proliferation. We report here that 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] administration to MCF-7 cells induces a significant decrease in Pit-1 mRNA and protein levels. By deletion analyses, we mapped a region (located between -147 and -171 bp from the transcription start site of the Pit-1 gene) that is sufficient for the repressive response to 1,25-(OH)2D3. Gel mobility shift and chromatin immunoprecipitation assays confirmed the direct interaction between the vitamin D receptor (VDR) as homodimer (without the retinoid X receptor), and the Pit-1 promoter, supporting the view that Pit-1 is a direct transcriptional target of VDR. Our data also indicate that recruitment of histone deacetylase 1 is involved in this repressive effect. This ligand-dependent Pit-1 gene inhibition by VDR in the absence of the retinoid X receptor seems to indicate a new mechanism of transcriptional repression by 1,25-(OH)2D3.

Determination of transcription factors and their possible roles in the regulation of Pax3 gene expression in the mouse B16 F1 melanoma cell line

The objective of this study was to determine which transcription factors regulate the expression of the Pax3 gene in the mouse B16 F1 melanoma cell line. The results showed that the -14 kilobase pair (kbp) Pax3 promoter, but not the -1.6 kbp Pax3 promoter, promoted Pax3 gene expression in B16 cells. Comparison of the sequence of the -14 kbp human Pax3 promoter with mouse Pax3 promoters indicated that homology sequences were located between -6.9 and -5.8 kbp, and also that the 1.1 kbp fragment (between -6.9 and -5.8 kbp), linked -1.6 kbp proximal to the Pax3 promoter [plasmid PGPax3PIV (N6.9/5.8) delta SST Lacz], could mimic the functions of plasmid PGPax3 -14(N-1.6) Lacz. Mutations of the core binding elements of either Pax3 site I or II or both sites I and II reduced significantly the beta-galactosidase (beta-gal) activity in the cells. However, mutations of the core binding sequences of site A or B increased significantly the beta-gal activity in the cells. Biochemistry analysis demonstrated that POU transcription factors (Oct-1 and Brn-2) bind to the specific binding elements of both sites I and II to stimulate Pax3 gene expression, whereas the TALE homeodomain-containing proteins (Pbx and Prep1) bind with the core binding sequences of sites A and B to repress the expression of the Pax3 gene in B16 cells.

Silencing of Fshr occurs through a conserved, hypersensitive site in the first intron

Expression of the FSH receptor (Fshr) is restricted to testicular Sertoli cells and ovarian granulosa cells, thereby limiting the direct targets of FSH action to these somatic cells of the gonads. Earlier studies indicate that transcription of Fshr in the gonads requires elements outside the gene's immediate 5' flanking sequence. To help uncover candidate regulatory sequences, comparative genomics and deoxyribonuclease I hypersensitivity mapping were employed. A total of 156 evolutionarily conserved sequences were found, and partial deoxyribonuclease I hypersensitivity mapping across 45 kb of 5' flanking sequence and the first intron identified four hypersensitive sites, DHS1-4. Notably, DHS1 and DHS2 localized to conserved sites in the promoter region and exon 1 and correlated with the active state of the gene. DHS3 also corresponded to a conserved site (site 7) but was more pronounced in nonexpressing myoid cells, suggesting a role in gene silencing. Transient transfection analysis of DHS3 confirmed its role in gene silencing, a function that was promoter, cell type, and position dependent. Protein-DNA binding studies on DHS3 revealed that octamer transcription factor 1 (OCT-1) and GATA-4 bound site 7, in vitro, and transient transfection analysis showed that their binding sites were required for silencing activity. Furthermore, chromatin immunoprecipitation revealed that OCT-1 bound to site 7 in the endogenous gene, but only in myoid cells. In contrast, GATA-1 bound site 7 predominantly in Sertoli cells, suggesting that it attenuates silencer activity. The findings reveal that OCT-1 binds within DHS3 to silence Fshr transcription and implicate members of the GATA family in the modulation of this activity.

T to C Substitution at –175 or –173 of the γ-Globin Promoter Affects GATA-1 and Oct-1 Binding in Vitro Differently but Can Independently Reproduce the Hereditary Persistence of Fetal Hemoglobin Phenotype in Transgenic Mice

The T to C substitution at position -175 of the gamma-globin gene has been identified in some individuals with non-deletion hereditary persistence of fetal hemoglobin (HPFH). In this study, the HPFH phenotype was reestablished in transgenic mice carrying the mu'LCRAgamma(-175)psibetadeltabeta construct, which contained a 3.1-kb mu'LCR cassette linked to a 29-kb fragment from the Agamma-to beta-globin gene with the natural chromosome arrangement but with the -175 mutation, which provided evidence for this single mutation as the cause of this form of HPFH. The HPFH phenotype was also reproduced in transgenic mice carrying the mu'LCRAgamma(-173)psibetadeltabeta construct, in which the -175 T to C Agamma gene was substituted with the -173 T to C Agamma gene. In vitro experiments proved that the -175 mutation significantly reduced binding of Oct-1 but not GATA-1, whereas the -173 mutation dramatically decreased binding of GATA-1 but not Oct-1. These results suggest that abrogation of either GATA-1 or Oct-1 binding to this promoter region may result in the HPFH phenotype. An in vivo footprinting assay revealed that either the -175 mutation or the -173 mutation significantly decreased overall protein binding to this promoter region in adult erythrocytes of transgenic mice. We hypothesize that a multiprotein complex containing GATA-1, Oct-1, and other protein factors may contribute to the formation of a repressive chromatin structure that silences gamma-globin gene expression in normal adult erythrocytes. Both the -173 and -175 T to C substitutions may disrupt the complex assembly and result in the reactivation of the gamma-globin gene in adult erythrocytes.

Isolation and characterization of the 5'-flanking region of the growth hormone secretagogue receptor gene from black seabream Acanthopagrus schlegeli

Ghrelin, the recently discovered endogenous ligand for growth hormone secretagogue receptor (GHSR), is widely expressed and involved in regulating diverse physiological functions in addition to stimulation of growth hormone (GH) secretion. Previous studies have demonstrated the functional significance of the ghrelin/GHSR system, yet the transcriptional regulation of the ghrelin and GHSR genes are poorly understood. We have recently cloned the GHSR cDNA from the pituitary of black seabream Acanthopagrus schlegeli. In the present study, we have isolated a 2.1 kb 5'-flanking region of the GHSR gene from the same species and have investigated, for the first time, the transcriptional regulation of GHSR from a non-human species. The 5'-flanking region of the seabream GHSR gene was found to contain a number of unique putative transcription factor-binding sites different from the human counterpart. Functional characterization of the 5'-flanking region in several cell lines indicates that the region between -1423 and +19 contains sufficient elements for promoter function. Moreover, progressive 3'-deletion analysis suggests the presence of negative regulatory element(s) and essential cis-acting element(s) at -514/+19 and -928/-515, respectively. Furthermore, we have shown that the promoter activity is significantly enhanced by a GHSR agonist in a cell line stably expressing the seabream GHSR, and this stimulatory effect could be completely blocked by a GHSR antagonist. These results suggest that homologous up-regulation plays an important role in the transcriptional control of the teleostean GHSR gene. This is in big contrast to the human situation in which a homologous down-regulation of the GHSR gene transcription by its own ligand has been previously demonstrated.

The regulation of the Oct-1 gene transcription is mediated by two promoters

The ubiquitous transcription factor Oct-1 is a member of the POU domain family of regulatory proteins. Target genes controlled by Oct-1 include housekeeping genes, e.g. the genes encoding histon H2B or snRNAs, as well as tissue-specific genes, e.g. the genes encoding the light and heavy chains of immunoglobulines, some interleukins, and others. Oct-1 pre-mRNA may be spliced in several ways, resulting in production of several protein isoforms that may differ functionally. The 5'-end of the Oct-1 gene contains two exons-exon 1U and exon 1L that alternatively present in Oct-1 mRNA. We studied regulation of transcription of the Oct-1 gene using reporter gene assays of promoter-luciferase gene-constructs. It was shown that transcription of the Oct-1 gene is regulated by two promoters located upstream of the exon 1U and upstream of the exon 1L. The promoter located upstream of the exon 1U contains G/C-rich sequences and multiple Sp1 sites, while the promoter located upstream of the exon 1L contains A/T-rich motifs and autoregulation-related cis-elements: two octamer sites ATGCAAAT, two octamer related sites and multiple TAAT-core sites. Exons 1U and 1L in the human OTF-1 locus encoding the Oct-1 gene are located at the distance of 108 kbp. In the murine locus otf-1 the distance between exons 1U and 1L is 67 kbp. We suggest that the two promoters can differ functionally.

Human Oct-1L isoform has tissue-specific expression pattern similar to Oct-2

POU homeodomain proteins are important regulators of ubiquitous as well as tissue-specific transcription. Ubiquitously expressed Oct-1 and tissue-specific Oct-2 proteins are members of the POU family and contain very similar DNA-binding POU domains. While Oct-1 is ubiquitous, Oct-2 is predominantly expressed in B cells, in activated T cells and in nervous system. Oct-1 is involved in regulation of some houskeeping genes-histone H2B, snRNAs as well as in tissue-specific regulation of immunoglobuline gene transcription and of some other genes. Here we report that novel alternatively spliced product of the human Oct-1 gene encode Oct-1L isoform with tissue-specific expression pattern, similar to Oct-2. Oct-1L differ from ubiquitously expressed Oct-1A in 5'-terminal exon (exon 1L). Analysis of nucleotide sequences from Human Genome Data Bank has located exon 1L about 108 kbp downstream ubiquitously expressed exon 1U. Amino terminus of Oct-1L show extensive similarity to amino terminus of Oct-2. We suppose, that Oct-1L may has a specific role in gene expression in lymphoid tissues and brain.

Modulation of interferon expression by hepatitis C virus NS5A protein and human homeodomain protein PTX1

Hepatitis C virus (HCV) NS5A protein transcriptionally modulates a number of cellular genes. Since there is no evidence of binding of NS5A protein to DNA, it is likely to exert its activity in concert with cellular factor(s). In this study, we have identified a specific interaction of HCV NS5A with homeodomain protein PTX1 of human origin by a yeast two-hybrid interacting cloning system. The authenticity of this interaction was verified by mammalian two-hybrid assay, in vivo co-immunoprecipitation analysis, and from a colocalization study. Recently, murine PTX1 (mPTX1) has been shown to repress virus-induced murine interferonA4 promoter activity. Interferon-à alone or together with ribavirin is the only available therapy for HCV-infected patients. Therefore, we examined whether coexpression of NS5A and human PTX1 (hPTX1) proteins modulate human IFN-à promoter activity. An in vitro reporter assay by transfection of HepG2 cells with NS5A suggested an activation of IFN-à promoter to approximately 20-fold upon Newcastle disease virus (NDV) infection. Under similar experimental conditions, hPTX1-activated IFN-à prompter to approximately sevenfold, unlike mPTX1. However, cotransfection of NS5A and hPTX1 displayed a lower interferon promoter activity, probably for physical association between these two proteins. Subsequent study demonstrated that activation of IFN promoter by NS5A is associated with an increased expression of IRF-3. Further analysis revealed that ectopic expression of NS5A in HepG2 cells enhances endogenous IFN-à secretion and MxA expression upon induction with NDV. However, exogenous expression of hPTX1 did not significantly alter NS5A-mediated function in the stable transfectants. Taken together, these results suggested that the level of endogenous hPTX1 is not sufficient to block the function of NS5A for augmentation of virus-mediated IFN activity in HepG2 cells.

Oct-1 is involved in the transcriptional repression of the gonadotropin-releasing hormone receptor gene

Previous deletion analysis of the 5'-flanking region of human GnRH receptor (GnRHR) gene has revealed a powerful negative regulatory element (NRE) located between nucleotide -1017 and -771. In the present study, we demonstrated that this NRE could repress the homologous promoter, irrespective of its position and completely abolish the activity of a heterologous thymidine kinase promoter in an orientation-dependent manner. Progressive 3'-deletion analysis revealed that most of the silencing activity of the NRE resided in a putative octamer regulatory sequence (5'AAGCAAACT3'), which alone could repress the promoter activities by 69-90% in ovarian OVCAR-3, placental JEG-3, and gonadotrope-derived alphaT3-1 cells. Mutation of the AAAC residues of the octamer sequence completely removed its silencing activity. Interestingly, conversion of the octamer sequence into that of the rodent GnRHR promoter (5'AAGCAAAGT3') did not attenuate its silencing effect, indicating that the repressive role of the octamer sequence is evolutionarily conserved. EMSAs showed that common DNA-protein complexes of the same mobility were formed with nuclear extracts from the reproductive cells and gonadotropes, and a consensus octamer transcription factor-1 (Oct-1) binding sequence could dose dependently inhibit the complex formation. Antibody supershift and Southwestern blot assays confirmed that the protein binding to the octamer sequence was the ubiquitously expressed transcription factor Oct-1. Overexpression of Oct-1 augmented the silencing activity of the octamer sequence in alphaT3-1 cells. Taken together, our results clearly indicate a role of Oct-1 in the transcriptional repression of the human GnRHR gene.

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors increase the binding activity and nuclear level of Oct-1 in mononuclear cells

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are drugs very effective to decrease low-density lipoprotein (LDL) cholesterol. In addition, a number of studies suggest that statins have other beneficial clinical effects beyond cholesterol lowering. We recently reported that statins decrease nuclear factor kappa B (NF-kappaB) binding activity in monocytes and vascular smooth muscle cells. We now explored the effect of two different statins, simvastatin and atorvastatin, in the activation of the octamer transcription factor Oct-1 on the monocytic cell line THP-1. Oct-1 is a nuclear factor that represses the transcription of proinflammatory genes such as interleukin-8, CD11c/CD18, vascular cell adhesion molecule-1 (VCAM-1) and platelet endothelial cell adhesion molecule-1 (PECAM-1). Low concentrations of both statins increased Oct-1 DNA binding activity (electrophoretic mobility shift assay) that was resolved into two specific bands. The upper one was supershifted by preincubation of nuclear extracts with anti-Oct-1 antibody. The lower one was supershifted by preincubation of nuclear extracts with an anti-Oct-2 antibody, also partially competed with 100 mol/l excess of cold activator protein-1 (AP-1) and attenuated by anti-c-Jun antibody. Both statins increased Oct-1 and Oct-2 nuclear protein levels (Western blot). In contrast, neither had any effect on PMA-differentiated cells, suggesting a distinct sensitivity between circulating monocytes and resident tissular macrophages. In addition, statins did not increase Oct-lipoprotein lipase binding activity that contains an Oct-1 binding element. The mRNA expression of interleukin-8, a chemokine containing Oct sites in its promoter, was diminished by statin pretreatment. Our results indicate that simvastatin and atorvastatin increase the activity of the transcriptional repressor Oct-1 in mononuclear cells, and could thus contribute to decrease the activation of these cells. These data suggest a possible novel mechanism supporting a certain anti-inflammatory effect of these two 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors.

Human homeobox HOXA7 regulates keratinocyte transglutaminase type 1 and inhibits differentiation

Keratinocyte proliferation and differentiation result from expression of specific groups of genes regulated by unique combinations of transcription factors. To better understand these regulatory processes, we studied HOXA7 expression and its regulation of differentiation-specific keratinocyte genes. We isolated the homeobox transcription factor HOXA7 from keratinocytes through binding to a differentiation-dependent viral enhancer and analyzed its effect on endogenous differentiation-dependent genes, primarily transglutaminase 1. HOXA7 overexpression repressed transglutaminase 1-reporter activity. HOXA7 message markedly decreased, and transglutaminase RNA increased, upon phorbol ester-induced differentiation, in a protein kinase C-dependent manner. Overexpression of HOXA7 attenuated the transglutaminase 1 induction by phorbol ester, demonstrating that HOXA7 expression is inversely related to keratinocyte differentiation, and to transglutaminase 1 expression. Antisense HOXA7 expression activated transglutaminase 1, involucrin, and keratin 10 message and protein levels, demonstrating that endogenous HOXA7 down-regulates multiple differentiation-specific keratinocyte genes. In keeping with these observations, epidermal growth factor receptor activation stimulated HOXA7 expression. HOX genes function in groups, and we found that HOXA5 and HOXB7 were also down-regulated by phorbol ester. These results provide the first example of protein kinase C-mediated homeobox gene regulation in keratinocytes, and new evidence that HOXA7, potentially in conjunction with HOXA5 and HOXAB7, silences differentiation-specific genes during keratinocyte proliferation, that are then released from inhibition in response to differentiation signals.

Repression of virus-induced interferon A promoters by homeodomain transcription factor Ptx1

Interferon A (IFN-A) genes are differentially expressed after virus induction. The differential expression of individual IFN-A genes is modulated by substitutions in the proximal positive virus responsive element A (VRE-A) of their promoters and by the presence or absence of a distal negative regulatory element (DNRE). The functional feature of the DNRE is to specifically act by repression of VRE-A activity. With the use of the yeast one-hybrid system, we describe here the identification of a specific DNRE-binding protein, the pituitary homeobox 1 (Ptx1 or Pitx1). Ptx1 is detectable in different cell types that differentially express IFN-A genes, and the endogenous Ptx1 protein binds specifically to the DNRE. Upon virus induction, Ptx1 negatively regulates the transcription of DNRE-containing IFN-A promoters, and the C-terminal region, as well as the homeodomain of the Ptx1 protein, is required for this repression. After virus induction, the expression of the Ptx1 antisense RNA leads to a significant increase of endogenous IFN-A gene transcription and is able to modify the pattern of differential expression of individual IFN-A genes. These studies suggest that Ptx1 contributes to the differential transcriptional strength of the promoters of different IFN-A genes and that these genes may provide new targets for transcriptional regulation by a homeodomain transcription factor.

Oct-1 specifically binds the UEF4 site of the human AP1-regulated urokinase enhancer

The inducible urokinase enhancer contains three essential elements: a combined PEA3/AP1 and a downstream AP1 site, separated by a 74-bp DNA region called COM (cooperation mediator), that is required for the synergism between the three sites. The 5' half of COM (uCOM) forms four retarded complexes with HeLa or HepG2 nuclear proteins (UEF1-4). We now demonstrate that the UEF4 complex is the transcription factor Oct-1. Because of functional redundancy of the UEF sites, single mutations in UEF4 have no phenotype; we have changed UEF4 from a low to a high affinity binding site for Oct-1. In vitro, this mutation increases the DNA binding of Oct-1 and disturbs the binding of the Prep-Pbx complexes to the nearby UEF3 site. In vivo, this mutation reduces the basal transcriptional activity of the urokinase enhancer, while not affecting its phorbol ester inducibility. This is in keeping with the effect of the deletions of the COM region, which result in an increase in the basal level and, as a consequence, in the loss of 4beta-phorbol 12-myristate 13-acetate inducibility. Oct-1 therefore is not involved in the inducibility of the urokinase enhancer but only in determining its basal activity level.

Complex interactions between epidermal POU domain and activator protein 1 transcription factors regulate the expression of the profilaggrin gene in normal human epidermal keratinocytes

The human profilaggrin gene is expressed in the granular layer during the late stages of the epidermal differentiation. The proximal promoter region of the gene confers high levels of keratinocyte-specific transcription via interactions with c-Jun/c-Fos heterodimers. Here we provide evidence for another level of complexity in the regulation of the profilaggrin promoter activity. The POU domain proteins Oct1, Skn1a/i, and Oct6, which are abundantly expressed in the epidermal cells, act to both stimulate and repress transcription in a general and a cell type-specific mode. While binding to specific recognition elements within the promoter region, they exert their effects by either stimulating or antagonizing the c-Jun-dependent activity of the promoter. The response of the promoter to forced expression of the POU domain proteins reflects the effect of these transcription factors on the endogenous profilaggrin mRNA synthesis and suggests that the latter requires a fine balance in the amounts and the activities of the individual activator protein 1 and POU domain proteins.

An upstream Oct-1- and Oct-2-binding silencer governs B29 (Ig beta) gene expression

The B cell-specific B29 (Igbeta) gene is activated in the earliest B cell precursors and is expressed throughout B cell development. Tissue-specific expression of the murine B29 gene is controlled by a B cell-specific promoter whose activity is governed by a cassette of upstream transcriptional silencers. This study describes a potent new silencer that is located 5' of the previously identified B29 silencer elements, FROG and TOAD. Like these known elements, the new B29 silencer is not restricted to the B29 promoter. Nuclear proteins from all cell lines tested interacted with this A+T-rich sequence, which closely resembled a noncanonical octamer binding motif and also conformed to the consensus sequence for nuclear matrix attachment regions. Interaction of Oct-1 and Oct-2 with the B29 A+T-rich sequence was confirmed using octamer-specific Abs. Oct-1/Oct-2 binding was required for the inhibitory activity of this sequence because mutations that blocked Oct-1/Oct-2 binding also eliminated inhibition of the B29 promoter. This B29 A+T-rich sequence specifically interacted with isolated nuclear matrix proteins in vitro, suggesting that it may also function as a matrix attachment region element. Maintenance of the level of B29 gene expression through the interaction of the minimal promoter and the upstream silencer elements FROG, TOAD, and the A+T-rich Oct-1/Oct-2 binding motif may be essential for normal B cell development and/or function.

Far upstream sequences regulate the human prolactin promoter transcription

The human prolactin gene is mainly expressed in pituitary lactotrope cells, but transcription from an alternative, far upstream promoter was detected in lymphoid, placental and mammary cells. We describe the transcriptional activity in rat pituitary cells of the complete region separating the two promoters, using transient transfection experiments. A far upstream activating region was only functional in combination with the prolactin promoter. DNaseI protection experiments revealed, in addition to binding sites for the pituitary-specific factor Pit-1, sites (e.g. SD1) for several ubiquitous factors and one lymphoid-specific factor (SD4). A single copy of the ubiquitous site SD1 or the lymphoid-specific site SD4 was unable to activate transcription of a heterologous promoter in pituitary cells. However, SD1 activated transcription in nonpituitary cells and SD4 was functional specifically in lymphoid cells. Five copies of a distal site (D8) activated transcription in each cell type tested. Gel retardation experiments show that this site binds the specific factor C/EBP in liver and a distinct factor in other cell types. Our results suggest that different elements within this large region direct specific expression from each promoter via a complex interplay between cell-specific and ubiquitous transcription factors.

Binding of YY1 and Oct1 to a novel element that downregulates expression of IL-5 in human T cells

BACKGROUND

IL-5 controls development of eosinophilia and has been shown to be involved in the pathogenesis of allergic diseases. In both atopic and nonatopic asthma, elevated IL-5 has been detected in peripheral blood and the airways. IL-5 is produced mainly by activated T cells, and its expression is regulated at the transcriptional level.

OBJECTIVE

This study focuses on the functional analysis of the human IL-5 (hIL-5) promoter and characterization of cis -regulatory elements and transcription factors involved in the suppression of IL-5 transcription in T cells.

METHODS

Methods used in this study include DNase I footprint assays, electrophoretic mobility shift assays, and functional analysis by mammalian cell transfection involving deletion analysis and site-directed mutagenesis.

RESULTS

We identified 5 protein binding regions (BRs) located within the proximal hIL-5 promoter. Functional analysis indicates that the BRs are involved in control of hIL-5 promoter activity. Two of these regions, BR3 and BR4 located at positions -102 to -73, have not previously been described as regulators of IL-5 expression in T cells. We show that the BR3 sequence contains a novel negative regulatory element located at positions -90 to -79 of the hIL-5 promoter, which binds Oct1, octamer-like, and YY1 nuclear factors. Substitution mutations, which abolished binding of these proteins to the BR3 sequence, significantly increased hIL-5 promoter activity in activated T cells.

CONCLUSION

We suggest that Oct1, YY1, and octamer-like factors binding to the -90/-79 sequence within the proximal IL-5 promoter are involved in suppression of IL-5 transcription in T cells.

A possible mechanism of TPA-mediated downregulation of neurotrophin-3 gene expression in rat cultured vascular smooth muscle cells

We have previously reported that in cultured rat vascular smooth muscle cells (VSMCs), neurotrophin-3 (NT-3) gene expression was suppressed by TPA (12-O-tetradecanoyl phorbol-13-acetate), which induces an AP-1 transcription factor. In the present study, to clarify the mechanism for TPA-mediated downregulation of NT-3 gene expression, effects of cycloheximide and dexamethasone (Dex) on the TPA-mediated downregulation were examined in VSMCs. Pretreatment with cycloheximide, an inhibitor of protein synthesis, or simultaneous treatment with Dex, an inhibitor of AP-1, suppressed the TPA-mediated downregulation of NT-3 gene expression. Furthermore, co-transfection of c-fos and c-jun expression vectors into VSMCs resulted in decrease in the NT-3 gene expression. The present findings suggest that TPA-induced AP-1 de novo synthesis causes the downregulation of NT-3 gene expression in VSMCs.

The glucocorticoid receptor is tethered to DNA-bound Oct-1 at the mouse gonadotropin-releasing hormone distal negative glucocorticoid response element

An element required for glucocorticoid repression of mouse gonadotropin-releasing hormone (GnRH) gene transcription, the distal negative glucocorticoid response element (nGRE), is not bound directly by glucocorticoid receptors (GRs) but is recognized by Oct-1 present in GT1-7 cell nuclear extracts or by Oct-1 purified from HeLa cells. Furthermore, purified full-length GRs interact directly with purified Oct-1 bound to the distal nGRE. Increasing the extent of distal nGRE match to an Oct-1 consensus site not only increases the affinity of Oct-1 binding, but also alters the conformation of DNA-bound Oct-1 and the pattern of protein DNA complexes formed in vitro with GT1-7 cell nuclear extracts. In addition, the interaction of purified GR with DNA-bound Oct-1 is altered when Oct-1 is bound to the consensus Oct-1 site. Mutation of the distal nGRE to a consensus Oct-1 site is also associated with reduced glucocorticoid repression in transfected GT1-7 cells. Furthermore, repression of GnRH gene transcription by 12-O-tetradecanoylphorbol-13-acetate, which utilizes sequences that overlap with the nGRE, is reversed by this distal nGRE mutation leading to activation of GnRH gene transcription. Thus, changes in the assembly of multi-protein complexes at the distal nGRE can influence the regulation of GnRH gene transcription.

Protein kinase A-dependent derepression of the human prodynorphin gene via differential binding to an intragenic silencer element

Induction of the prodynorphin gene has been implicated in medium and long-term adaptation during memory acquisition and pain. By 5' deletion mapping and site-directed mutagenesis of the human prodynorphin promoter, we demonstrate that both basal transcription and protein kinase A (PKA)-induced transcription in NB69 and SK-N-MC human neuroblastoma cells are regulated by the GAGTCAAGG sequence centered at position +40 in the 5' untranslated region of the gene (named the DRE, for downstream regulatory element). The DRE repressed basal transcription in an orientation-independent and cell-specific manner when placed downstream from the heterologous thymidine kinase promoter. Southwestern blotting and UV cross-linking experiments with nuclear extracts from human neuroblastoma cells or human brain revealed a protein complex of approximately 110 kDa that specifically bound to the DRE. Forskolin treatment reduced binding to the DRE, and the time course paralleled that for an increase in prodynorphin gene expression. Our results suggest that under basal conditions, expression of the prodynorphin gene is repressed by occupancy of the DRE site. Upon PKA stimulation, binding to the DRE is reduced and transcription increases. We propose a model for human prodynorphin activation through PKA-dependent derepression at the DRE site.

Oct-1 Is Involved in the Transcriptional Repression of the von Willebrand Factor Gene Promoter

The negative regulation of transcription of the human von Willebrand factor (vWF) gene was investigated in human umbilical vein endothelial cells (HUVECs) and HeLa cells. A fragment spanning −89 to +244 nucleotides (nt), containing the first exon, is active in HUVECs only but not in HeLa cells. The activity of this promoter is sharply reduced by mutagenesis of the GATA binding site at +221. Extension of the upstream sequences from nt −89 to −142 and to −496 results in progressive reduction of the activity of the −89 to +244 promoter identifying a negative regulatory element between nt −142 and −89. A factor present in nuclear extracts from endothelial and nonendothelial cells binds to an AT-rich sequence located between nt −133 and −125. Mutagenesis of the AT-rich sequence interferes with nuclear protein binding and restores the activity of the −142 to +244 fragment to the level of the −89 to +244 promoter. Binding of the nuclear protein to the vWF AT-rich sequence in mobility shift assays is inhibited by competition with a consensus Oct-1 binding site and with a silencer octamer-like sequence from the vascular cell adhesion molecule-1 (VCAM-1) promoter. Subsequent supershift experiments identified Oct-1 as the transcription factor that binds to vWF and VCAM-1 silencer elements. These results indicate that Oct-1 acts as a transcriptional repressor of promoters of genes expressed in endothelial cells.

© 1998 by The American Society of Hematology.

Oct-1 Is Involved in the Transcriptional Repression of the von Willebrand Factor Gene Promoter

The negative regulation of transcription of the human von Willebrand factor (vWF) gene was investigated in human umbilical vein endothelial cells (HUVECs) and HeLa cells. A fragment spanning −89 to +244 nucleotides (nt), containing the first exon, is active in HUVECs only but not in HeLa cells. The activity of this promoter is sharply reduced by mutagenesis of the GATA binding site at +221. Extension of the upstream sequences from nt −89 to −142 and to −496 results in progressive reduction of the activity of the −89 to +244 promoter identifying a negative regulatory element between nt −142 and −89. A factor present in nuclear extracts from endothelial and nonendothelial cells binds to an AT-rich sequence located between nt −133 and −125. Mutagenesis of the AT-rich sequence interferes with nuclear protein binding and restores the activity of the −142 to +244 fragment to the level of the −89 to +244 promoter. Binding of the nuclear protein to the vWF AT-rich sequence in mobility shift assays is inhibited by competition with a consensus Oct-1 binding site and with a silencer octamer-like sequence from the vascular cell adhesion molecule-1 (VCAM-1) promoter. Subsequent supershift experiments identified Oct-1 as the transcription factor that binds to vWF and VCAM-1 silencer elements. These results indicate that Oct-1 acts as a transcriptional repressor of promoters of genes expressed in endothelial cells.

© 1998 by The American Society of Hematology.

Nuclear factor 1 regulates the distal silencer of the human PIT1/GHF1 gene

Here we report the characterization of 12 kb genomic DNA upstream of the human PIT1/GHF1 promoter. Different regions involved in the modulation of human PIT1/GHF1 gene expression were defined by transient transfection studies. Two regions, one proximal (-7.1/-2. 3) and one distal (-11.8/-10.9), presented an enhancer activity in pituitary cells when placed upstream of the SV40 promoter. The 0.9 kb distal region was analysed further and found to decrease the basal transcriptional activity of the human PIT1/GHF1 minimal promoter, indicating that this region behaves as a silencer for its own promoter. Three Pit-1/GHF-1-binding sites and two ubiquitous nuclear factor 1 (NF-1)-binding sites were identified by DNase I footprinting in the distal regulatory region. Deletion analysis indicated that NF-1 or NF-1-related protein(s) participate in the down-regulation of human PIT1/GHF1 gene expression by interacting with an NF-1-binding site within the distal regulatory region.

Autoregulation of eukaryotic transcription factors

The structures of several promoters regulating the expression of eukaryotic transcription factors have in recent years been examined. In many cases there is good evidence for autoregulation, in which a given factor binds to its own promoter and either activates or represses transcription. Autoregulation occurs in all eukaryotes and is an important component in controlling expression of basal, cell cycle specific, inducible response and cell type-specific factors. The basal factors are autoregulatory, being strictly necessary for their own expression, and as such must be epigenetically inherited. Autoregulation of stimulus response factors typically serves to amplify cellular signals transiently and also to attenuate the response whether or not a given inducer remains. Cell cycle-specific transcription factors are positively and negatively autoregulatory, but this frequently depends on interlocking circuits among family members. Autoregulation of cell type-specific factors results in a form of cellular memory that can contribute, or define, a determined state. Autoregulation of transcription factors provides a simple circuitry, useful in many cellular circumstances, that does not require the involvement of additional factors, which, in turn, would need to be subject to another hierarchy of regulation. Autoregulation additionally can provide a direct means to sense and control the cellular conce]ntration of a given factor. However, autoregulatory loops are often dependent on cellular pathways that create the circumstances under which autoregulation occurs.

Transcriptional regulation of interleukin-1beta gene by interleukin-1beta itself is mediated in part by Oct-1 in thymic stromal cells

Interleukin (IL)-1 is involved in many processes, including thymic development. However, control of IL-1 expression in thymic-derived stromal cells (TSC) has not been reported. We found that IL-1beta increased steady-state mRNA levels for IL-1alpha and IL-1beta in TSC-936 and TSC-2C4 cells; stability was not a major determinant of this effect. To study transcriptional regulation of IL-1beta, we functionally characterized 4 kilobase pairs of the 5'-flanking region and first intron of the bovine IL-1beta gene. The -470/+14 fragment was sufficient to confer maximal responsiveness to IL-1beta upon transfection into these cell lines. Progressive 5' deletions identified several IL-1beta-responsive regions, including -308 to -226, which we further characterized. Electrophoretic mobility shift and supershift analyses showed that IL-1beta induced the ability to form multiple protein complexes with -261/-226 and that one of these contained nuclear factor Oct-1. A competitor containing a mutated Oct consensus site failed to compete not only for this complex but others as well, suggesting that this sequence regulates binding of other proteins to this region. Functional analysis confirmed that this element was essential for maximal induction of transcription. These findings document a heretofore undescribed mechanism utilized by TSC for regulation of IL-1beta transcription by IL-1beta itself.

Oct-1 promoter region contains octamer sites and TAAT motifs recognized by Oct proteins

The 5'-upstream region (1.3 kb) of the gene encoding the POU domain transcription factor Oct-1 was cloned and sequenced. CAT reporter gene analysis of this region has detected a functionally active promoter. This region contains 24 TAAT-core sites, arranged in five clusters (four to six sites in one cluster); two octamer sites (ATGCAAAT) are located in the first and second clusters; in the second one the CCAAT-box adjacent to the octamer overlaps with the TAAT-core site. As shown by gel retardation assay, Oct-1, Oct-2, and some unknown proteins from myeloma cell line NS/0 interact with the TAAT-core sites of these clusters. The results suggest autoregulation of Oct-1 gene expression that may also be controlled by other POU proteins, homeodomain proteins and CCAAT trans-action factors.

Induction of tissue transglutaminase by dexamethasone: its correlation to receptor number and transglutaminase-mediated cell death in a series of malignant hamster fibrosarcomas

Treatment of the hamster fibrosarcoma cell lines (Met B, D and E) and BHK-21 hamster fibroblast cells with the glucocorticoid dexamethasone led to a powerful dose-dependent mRNA-synthesis-dependent increase in transglutaminase activity, which can be correlated with dexamethasone-responsive receptor numbers in each cell line. Increasing the number of dexamethasone-responsive receptors by transfection of cells with the HG1 glucocorticoid receptor protein caused an increase in transglutaminase activity that was proportional to the level of transfected receptor. In all experiments the levels of the tissue transglutaminase-mediated detergent-insoluble bodies was found to be comparable with increases in transglutaminase activity. Despite an increase in detergent-insoluble body formation, an increase in apoptosis as measured by DNA fragmentation was not found. Incubation of cells with the non-toxic competitive transglutaminase substrate fluorescein cadaverine led to the incorporation of this fluorescent amine into cellular proteins when cells were damaged after exposure to trypsin during cell passage. These cross-linked proteins containing fluorescein cadaverine were shown to be present in the detergent-insoluble bodies, indicating that the origin of these bodies is via activation of tissue transglutaminase after cell damage by trypsinization rather than apoptosis per se, since Met B cells expressing the bcl-2 cDNA were not protected from detergent-insoluble body formation. We describe a novel mechanism of cell death related to tissue transglutaminase expression and cell damage.