DNA methylation signatures in cord blood associated with birthweight are enriched for dmCpGs previously associated with maternal hypertension or pre-eclampsia, smoking and folic acid intake

Many epidemiological studies have linked low birthweight to an increased risk of non-communicable diseases (NCDs) in later life, with epigenetic proceseses suggested as an underlying mechanism. Here, we sought to identify neonatal methylation changes associated with birthweight, at the individual CpG and genomic regional level, and whether the birthweight-associated methylation signatures were associated with specific maternal factors. Using the Illumina Human Methylation EPIC array, we assessed DNA methylation in the cord blood of 557 and 483 infants from the UK Pregnancies Better Eating and Activity Trial and Southampton Women's Survey, respectively. Adjusting for gestational age and other covariates, an epigenome-wide association study identified 2911 (FDR≤0.05) and 236 (Bonferroni corrected p ≤ 6.45×10-8) differentially methylated CpGs (dmCpGs), and 1230 differentially methylated regions (DMRs) (Stouffer ≤0.05) associated with birthweight. The top birthweight-associated dmCpG was located within the Homeobox Telomere-Binding Protein 1 (HMBOX1) gene with a 195 g (95%CI: -241, -149 g) decrease in birthweight per 10% increase in methylation, while the top DMR was located within the promoter of corticotropin-releasing hormone-binding protein (CRHBP). Furthermore, the birthweight-related dmCpGs were enriched for dmCpGs previously associated with gestational hypertension/pre-eclampsia (14.51%, p = 1.37×10-255), maternal smoking (7.71%, p = 1.50 x 10-57) and maternal plasma folate levels during pregnancy (0.33%, p = 0.029). The identification of birthweight-associated methylation markers, particularly those connected to specific pregnancy complications and exposures, may provide insights into the developmental pathways that affect birthweight and suggest surrogate markers to identify adverse prenatal exposures for stratifying for individuals at risk of later NCDs.

High maternal folic acid intake around conception alters mouse blastocyst lineage allocation and expression of key developmental regulatory genes

Folate, a cofactor for the supply of one-carbon groups, is required by epigenetic processes to regulate cell lineage determination during development. The intake of folic acid (FA), the synthetic form of folate, has increased significantly over the past decade, but the effects of high periconceptional FA intake on cell lineage determination in the early embryo remains unknown. Here, we investigated the effect of maternal high FA (HFA) intake on blastocyst development and expression of key regulatory genes. C57BL/6 adult female mice were fed either Control diet (1 mg FA) for 4 weeks before conception and during the preimplantation period (Con-Con); Control diet for 4 weeks preconception, followed by HFA (5 mg FA) diet during preimplantation (Con-HFA); or HFA diet for 4 weeks preconception and during preimplantation (HFA-HFA). At E3.5, blastocyst cell number, protein, and mRNA expression were measured. In HFA-HFA blastocysts, trophectoderm cell numbers and expression of CDX2, Oct-4, and Nanog were reduced compared with Con-Con blastocysts; Con-HFA blastocysts showed lower CDX2 and Oct-4 expression than Con-Con blastocysts. These findings suggest periconceptional HFA intake induces changes in key regulators of embryo morphogenesis with potential implications for subsequent development.

DNA methylation of amino acid transporter genes in the human placenta

INTRODUCTION

Placental transfer of amino acids via amino acid transporters is essential for fetal growth. Little is known about the epigenetic regulation of amino acid transporters in placenta. This study investigates the DNA methylation status of amino acid transporters and their expression across gestation in human placenta.

METHODS

BeWo cells were treated with 5-aza-2'-deoxycytidine to inhibit methylation and assess the effects on amino acid transporter gene expression. The DNA methylation levels of amino acid transporter genes in human placenta were determined across gestation using DNA methylation array data. Placental amino acid transporter gene expression across gestation was also analysed using data from publically available Gene Expression Omnibus data sets. The expression levels of these transporters at term were established using RNA sequencing data.

RESULTS

Inhibition of DNA methylation in BeWo cells demonstrated that expression of specific amino acid transporters can be inversely associated with DNA methylation. Amino acid transporters expressed in term placenta generally showed low levels of promoter DNA methylation. Transporters with little or no expression in term placenta tended to be more highly methylated at gene promoter regions. The transporter genes SLC1A2, SLC1A3, SLC1A4, SLC7A5, SLC7A11 and SLC7A10 had significant changes in enhancer DNA methylation across gestation, as well as gene expression changes across gestation.

CONCLUSION

This study implicates DNA methylation in the regulation of amino acid transporter gene expression. However, in human placenta, DNA methylation of these genes remains low across gestation and does not always play an obvious role in regulating gene expression, despite clear evidence for differential expression as gestation proceeds.

DNA methylation of Th2 lineage determination genes at birth is associated with allergic outcomes in childhood

BACKGROUND

There is now increasing evidence that asthma and atopy originate in part in utero, with disease risk being associated with the altered epigenetic regulation of genes.

OBJECTIVE AND METHODS

To determine the relationship between variations in DNA methylation at birth and the development of allergic disease, we examined the methylation status of CpG loci within the promoter regions of Th1/2 lineage commitment genes (GATA3, IL-4, IL-4R, STAT4 and TBET) in umbilical cord DNA at birth in a cohort of infants from the Southampton Women's Survey (n = 696) who were later assessed for asthma, atopic eczema and atopy.

RESULTS

We found that higher methylation of GATA3 CpGs -2211/-2209 at birth was associated with a reduced risk of asthma at ages 3 (median ratio [median methylation in asthma group/median methylation in non-asthma group] = 0.74, P = .006) and 6-7 (median ratio 0.90, P = .048) years. Furthermore, we demonstrated that the GATA3 CpG loci associated with later risk of asthma lie within a NF-κB binding site and that methylation here blocks transcription factor binding to the GATA3 promoter in the human Jurkat T-cell line. Associations between umbilical cord methylation of CpG loci within IL-4R with atopic eczema at 12 months (median ratio 1.02, P = .028), and TBET with atopy (median ratio 0.98, P = .017) at 6-7 years of age were also observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Our findings provide further evidence of a developmental contribution to the risk of later allergic disorders and suggest that involvement of epigenetic mechanisms in childhood asthma is already demonstrable at birth.

Genome-wide methylation analysis identifies differentially methylated CpG loci associated with severe obesity in childhood

Childhood obesity is a major public health issue. Here we investigated whether differential DNA methylation was associated with childhood obesity. We studied DNA methylation profiles in whole blood from 78 obese children (mean BMI Z-score: 2.6) and 71 age- and sex-matched controls (mean BMI Z-score: 0.1). DNA samples from obese and control groups were pooled and analyzed using the Infinium HumanMethylation450 BeadChip array. Comparison of the methylation profiles between obese and control subjects revealed 129 differentially methylated CpG (DMCpG) loci associated with 80 unique genes that had a greater than 10% difference in methylation (P-value < 0.05). The top pathways enriched among the DMCpGs included developmental processes, immune system regulation, regulation of cell signaling, and small GTPase-mediated signal transduction. The associations between the methylation of selected DMCpGs with childhood obesity were validated using sodium bisulfite pyrosequencing across loci within the FYN, PIWIL4, and TAOK3 genes in individual subjects. Three CpG loci within FYN were hypermethylated in obese individuals (all P < 0.01), while obesity was associated with lower methylation of CpG loci within PIWIL4 (P = 0.003) and TAOK3 (P = 0.001). After building logistic regression models, we determined that a 1% increase in methylation in TAOK3, multiplicatively decreased the odds of being obese by 0.91 (95% CI: 0.86 – 0.97), and an increase of 1% methylation in FYN CpG3, multiplicatively increased the odds of being obese by 1.03 (95% CI: 0.99 – 1.07). In conclusion, these findings provide evidence that childhood obesity is associated with specific DNA methylation changes in whole blood, which may have utility as biomarkers of obesity risk.

Child health, developmental plasticity, and epigenetic programming

Plasticity in developmental programming has evolved in order to provide the best chances of survival and reproductive success to the organism under changing environments. Environmental conditions that are experienced in early life can profoundly influence human biology and long-term health. Developmental origins of health and disease and life-history transitions are purported to use placental, nutritional, and endocrine cues for setting long-term biological, mental, and behavioral strategies in response to local ecological and/or social conditions. The window of developmental plasticity extends from preconception to early childhood and involves epigenetic responses to environmental changes, which exert their effects during life-history phase transitions. These epigenetic responses influence development, cell- and tissue-specific gene expression, and sexual dimorphism, and, in exceptional cases, could be transmitted transgenerationally. Translational epigenetic research in child health is a reiterative process that ranges from research in the basic sciences, preclinical research, and pediatric clinical research. Identifying the epigenetic consequences of fetal programming creates potential applications in clinical practice: the development of epigenetic biomarkers for early diagnosis of disease, the ability to identify susceptible individuals at risk for adult diseases, and the development of novel preventive and curative measures that are based on diet and/or novel epigenetic drugs.

Sex, but not maternal protein or folic acid intake, determines the fatty acid composition of hepatic phospholipids, but not of triacylglycerol, in adult rats

The aim of the study was to investigate whether the protein and folic acid content of the maternal diet and the sex of the offspring alter the polyunsaturated fatty acid content of hepatic phospholipids and triacylglycerol (TAG). Pregnant rats were fed diets containing 18% or 9% protein with either 1 or 5mg/kg folic acid. Maternal diet did not alter hepatic lipid composition in the adult offspring. Data from each maternal dietary group were combined and reanalysed. The proportion of 18:0, 20:4n-6 and 22:6n-3 in liver phospholipids was higher in females than in males, while hepatic TAG composition did not differ between sexes. Delta5 Desaturase expression was higher in females than in males. Neither Delta5 nor Delta6 desaturase expression was related to polyunsaturated fatty acid concentrations. These results suggest that sex differences in liver phospholipid fatty acid composition may reflect primary differences in the specificity of phospholipid biosynthesis.

Regulation of cellular processes by PPARgamma ligands in neuroblastoma cells is modulated by the level of retinoblastoma protein expression

Neuroblastoma is a childhood cancer, which spontaneously regresses. This has led to a search for agents that mimic this process. We show that both natural and synthetic ligands of PPARgamma (peroxisome-proliferator-activated receptor gamma) inhibit the growth of neuroblastoma cells in vitro. The degree of PPAR activation was attenuated however in the presence of the retinoblastoma protein. Addition of trichostatin A, a histone deacetylase inhibitor, abolished retinoblastoma protein repression of PPAR activity. Moreover, enhanced growth inhibition was observed when neuroblastoma cells were treated with a PPARgamma ligand and a histone deacetylase inhibitor, suggesting a combination therapy to treat neuroblastoma might prove more effective than using either agent alone.

Nerve growth factor induces the expression of the LIM homeodomain transcription factor Isl-1 with the kinetics of an immediate early gene in adult rat dorsal root ganglion

LIM-homeodomain genes encode a major class of transcription factors which play a critical role in regulating tissue specific gene expression. In this report, we have shown that three members of the LIM-homeodomain gene family - Isl-1, Rlim and Lim-3 are expressed in adult rat sensory neurons. Furthermore, we show that the addition of nerve growth factor (NGF) to cultures of primary dorsal root ganglion neurons leads to the induction of Isl-1, Rlim and Lim-3 mRNA expression. The increase in Isl-1 mRNA levels upon NGF addition was rapid and occurred even in the presence of cycloheximide. These findings place Isl-1 as a novel member of the immediate early class of genes. In contrast, Rlim and Lim-3mRNA induction by NGF required protein synthesis. The role of LIM-homeodomain genes in mediating responses to NGF in adult sensory neurons is discussed.

Effect of fatty acid supplementation on growth and differentiation of human IMR-32 neuroblastoma cells in vitro

Polyunsaturated fatty acids play a critical role in the structure and function of the developing nervous system. It has been proposed that fatty acids may effect a variety of biologic processes through the activation of the peroxisome proliferator activated receptors (PPARs)-ligand activated transcription factors. In this report, we demonstrate that fatty acids can inhibit the proliferation of the human neuronal cell line IMR-32. The fatty acids linoleate, alpha-linoleate, arachidonate, docosahexaenoate, and oleate all inhibited [(3)H]thymidine incorporation of IMR-32 cells after 72 h. Fatty acid supplementation also led to the morphologic differentiation of the IMR-32 cells. Linoleate and arachidonate, fatty acids of the n-6 series, induced the most extensive differentiation. Furthermore, the addition of fatty acids to IMR-32 cells led to PPAR activation, suggesting that PPAR activation may be an important event in fatty acid modulation of IMR-32 cell growth. In support of this hypothesis, clofibric acid, a specific ligand of PPARalpha, also inhibited IMR-32 cell proliferation and strongly induced PPAR activation. Together these results suggest that fatty acids may play an important role in the development of neuronal precursor cells and that activation of the PPARs may be one pathway by which fatty acids modulate the growth and differentiation of neuronal precursor cells.

Induction of antisense Pax-3 expression leads to the rapid morphological differentiation of neuronal cells and an altered response to the mitogenic growth factor bFGF

Mutations within the Pax-3 gene lead to a range of developmental abnormalities in both humans and mice. In this report, we have investigated the role that Pax-3 plays in neuronal cell development by specifically downregulating Pax-3 expression within a neuronal cell line. This was achieved by stably transfecting the neuronal cell line ND7 with an expression vector in which antisense Pax-3 RNA was produced under the control of the inducible MMTV promoter. In the stable transfectants, we found that the addition of dexamethasone led to the induction of antisense Pax-3 RNA and a rapid downregulation in endogenous Pax-3 protein expression. The decrease in endogenous Pax-3 protein expression corresponded with a dramatic change in the morphology of the cell: the normally rounded ND7 cells exhibited increased cell to substrate adhesion, extended long neurite processes and expressed genes such as snap-25 that are characteristic of a mature neuron. The morphological differentiation induced by a reduction in Pax-3 expression was followed 24–48 hours later by a cessation in cell proliferation. Interestingly the morphological differentiation and cessation in cell proliferation inducted in the cell lines lacking Pax-3 could be reversed by the addition of the mitogenic growth factor EGF but not by bFGF, whose receptor was downregulated in these cells. These results suggest that the expression of Pax-3 is essential to maintain the undifferentiated phenotype of these immature neuronal cells, and in its absence the cells acquire many of the characteristics of a mature neuronal cell. The slow onset of cell cycle arrest in the cells lacking Pax-3 argues against this transcription factor playing a direct role in the regulation of neuronal cell proliferation.

The DNA binding activity of the paired box transcription factor Pax-3 is rapidly downregulated during neuronal cell differentiation

Mutations in the murine Pax-3 gene lead to a range of developmental abnormalities including deficiencies in sensory and sympathetic neurones. We have investigated Pax-3 expression during neuronal differentiation and show levels of Pax-3 DNA binding decrease upon cell cycle arrest and morphological differentiation. The fall in Pax-3 DNA binding occurs within 1 h of the induction of differentiation and is mediated in part by a decrease in Pax-3 mRNA. This decrease in Pax-3 binding activity precedes any changes in cell proliferation or morphology, suggesting that the downregulation of this transcription factor may be an important prerequisite for the differentiation of neuronal progenitor cells.

Serum growth factor regulation of the paired-box transcription factor Pax-3 in neuronal cells

Mutations in the murine Pax (paired-box)-3 gene results in a number of developmental abnormalities including a deficiency in sensory neurons. To determine the role that Pax-3 plays in neuronal cell development, we have studied the expression of Pax-3 in the ND7 neuronal cell line. Upon serum starvation, Pax-3 mRNA expression fell rapidly. Within 2 h of the removal of serum a 2-3-fold decrease in Pax-3 expression was observed and by 6 h Pax-3 mRNA expression was undetectable. Interestingly this decrease in Pax-3 expression could be reversed by the addition of serum growth factors. This rise in Pax-3 expression upon growth factor addition, was followed by an increase in cell proliferation and a reduction in neurite outgrowth, suggesting that Pax-3 may play a role in mediating cellular responses to these factors in neuronal cells.

Activation of the herpes simplex virus immediate-early gene promoters by neuronally expressed POU family transcription factors

Herpes simplex virus immediate-early (IE) promoters contain the TAATGARAT motif which acts as a target site for the cellular POU family transcription factors Oct-1 and Oct-2. Here we show that other members of the POU family that are expressed in sensory neurons can also affect IE promoter activity. In particular, two members of the Brn-3 family of POU proteins Brn-3a and Brn-3c can activate the IE-1 and IE-3 promoters when co-transfected into fibroblasts and neuronal cells whereas a third member Brn-3b represses IE promoter activity. In contrast, Brn-3 proteins cannot overcome the inhibitory effect of neuronal Oct-2 on IE promoter activity in co-transfections nor do they prevent transactivation of the IE promoters by the Oct-1-Vmw65 complex. The potential regulation of the IE promoters by several different neuronally expressed POU proteins during the initiation, maintenance and re-activation of latent infection in sensory neurons is discussed.

Activation of the alpha-internexin promoter by the Brn-3a transcription factor is dependent on the N-terminal region of the protein

The Brn-3a, Brn-3b, and Brn-3c proteins are closely related POU (Pit-Oct-Unc) family transcription factors which are expressed predominantly in neuronal cells. We have identified the alpha-internexin gene as the first reported, neuronally expressed, target gene whose promoter activity is modulated by these factors. Both the Brn-3a and Brn-3c factors can activate the alpha-internexin promoter while Brn-3b represses it and can prevent activation by Brn-3a. Using chimeric constructs containing different regions of Brn-3a or Brn-3b, we show that activation of the alpha-internexin promoter requires the N-terminal region of Brn-3a. In contrast the activation by Brn-3a but not Brn-3b of an artificial promoter containing a synthetic Brn-3 binding site can be shown using the same constructs to be dependent on the POU domain of Brn-3a. Moreover, the isolated POU domain of Brn-3a can activate this artificial promoter but not the alpha-internexin promoter. Hence Brn-3a contains two distinct transactivation domains, at the N terminus and within the POU domain, whose effect is dependent upon the target promoter. The relationship of gene transactivation by Brn-3a to its ability to transform primary cells which is also dependent on the N-terminal region of the protein is discussed.

The levels of the antagonistic POU family transcription factors Brn-3a and Brn-3b in neuronal cells are regulated in opposite directions by serum growth factors

The Brn-3a and Brn-3b proteins are closely related POU family transcription factors with generally antagonistic effects on gene expression. We show that transfer of ND7 neuronal cells to medium containing either no foetal calf serum or low concentrations of serum results in a rise in Brn-3a mRNA levels and a fall in Brn-3b mRNA levels, although the precise serum dependence of these two effects differ. These effects can be reversed by addition of specific growth factors to the medium lacking serum, although not all growth factor treatments which suppress the rise in Brn-3a can reverse the fall in Brn-3b levels. These effects do not correlate with the effects of each treatment on cellular proliferation indicating that they are not simply a consequence of changes in proliferation. Interestingly however, treatments which produce a rise in Brn-3a levels also induce the outgrowth of neuritic processes. Hence the expression of a functionally antagonistic pair of POU factors is regulated in opposite directions by treatments with serum growth factors and this is likely to represent one means by which such growth factors modulate the gene expression patterns and ultimately the behaviour of neuronal cells.

Regulated splicing of the Oct-2 transcription factor RNA in neuronal cells

The primary RNA transcript derived from the gene encoding the Oct-2 transcription factor is alternatively spliced to yield a number of different mRNAs which encode different isoforms of this protein. The mRNAs encoding two such isoforms Oct-2c and mini Oct-2 were originally detected in neuronal cells. We show here that the mRNAs encoding these forms also occur in other tissues with the proportion of the mini Oct-2 mRNA being much higher in the spleen than in the brain. However, the levels of the mini Oct-2 mRNA increase in neuronal cell lines in response to differentiation-inducing stimuli and decrease upon exposure to growth factors. Hence the splicing of the Oct-2 transcript can be regulated in both a tissue specific manner and in neuronal cells in response to specific stimuli. The significance of this effect is discussed in terms of the differing ability of different forms of Oct-2 to activate or inhibit gene expression.

The inhibitory domain in the Oct-2 transcription factor represses gene activity in a cell type-specific and promoter-independent manner

The Oct-2 transcription factor contains an N-terminal inhibitory domain which can act to inhibit promoter activity when linked to either its corresponding DNA-binding POU domain or the heterologous DNA binding domain of the yeast transcription factor GAL4. This inhibitory effect is independent of the number of DNA binding sites or their context in the target promoter. In contrast the effect is cell type-specific and can be relieved by over-expression of the isolated inhibitory domain in the absence of a DNA binding domain. These results suggest that the inhibitory domain acts by decreasing the activity of the basal transcriptional complex but that it operates indirectly by recruiting a second cell type-specific factor to the promoter which then interacts with the basal complex decreasing its activity.

Down regulation of the octamer binding protein Oct-1 during growth arrest and differentiation of a neuronal cell line

The octamer binding transcription/DNA replication factor Oct-1 is present in virtually all cell types including proliferating cell lines of neuronal origin but is not detectable in mature non-dividing neurons. Cell cycle arrest in G0/G1 and morphological differentiation of a neuronal cell line is accompanied by a decline in the level of Oct-1 DNA binding, although the level of DNA binding by another octamer binding protein, Oct-2 is unaltered. This effect is paralled by a decline in the level of the Oct-1 mRNA in the non-dividing cells. The decrease in Oct-1 levels occurs only with the production of a mature, non-dividing neuronal phenotype and not when the cells are arrested in late G1 and do not undergo morphological differentiation. The potential role of Oct-1 and other octamer binding proteins in gene regulation in neuronal cells and in their differentiation is discussed.

Repression of a herpes simplex virus immediate-early promoter by the Oct-2 transcription factor is dependent on an inhibitory region at the N terminus of the protein

The B-cell form of the Oct-2 transcription factor Oct 2.1 can activate the herpes simplex virus immediate-early gene 3 (IE3) promoter, whereas the neuronally expressed Oct 2.4 and 2.5 forms of the protein, which contain a different C terminus, can repress this promoter. Here we show that partial or full deletion of the C terminus of Oct 2.1 in the presence of an intact N terminus results in a protein which can strongly repress the IE3 promoter. In contrast, deletion of the entire N terminus or a short region within it leaving the C terminus intact results in a very strong activator. Deletion of both N and C termini leaving only the isolated POU domain generates only a very weak repressor. The N-terminal region defined in this way can repress a heterologous promoter when linked to the DNA-binding domain of the GAL4 factor, indicating that it can function as an independent inhibitory domain. These results indicate that a specific region within the N terminus common to Oct 2.1, 2.4, and 2.5 plays a critical role in the ability of neuronally expressed forms of Oct-2 to repress the IE3 promoter but can do so only when the C-terminal region of Oct 2.1 is altered or deleted.

The opposite and antagonistic effects of the closely related POU family transcription factors Brn-3a and Brn-3b on the activity of a target promoter are dependent on differences in the POU domain

The Brn-3a, Brn-3b, and Brn-3c POU family transcription factors are closely related to one another and are members of the group IV subfamily of POU factors. Here we show that despite this close relationship, the factors have different effects on the activity of a target promoter: Brn-3a and Brn-3c stimulate the promoter whereas Brn-3b represses it. Moreover, Brn-3b can antagonize the stimulatory effect of Brn-3a on promoter activity and can also inhibit promoter activation by the Oct-2.1 POU factor. The difference in the transactivation activities of Brn-3a and Brn-3b is dependent upon the C-terminal region containing the POU domain of the two proteins, since exchange of this domain between the two factors converts Brn-3a into a repressor and Brn-3b into an activator.

The DNA target site for the Brn-3 POU family transcription factors can confer responsiveness to cyclic AMP and removal of serum in neuronal cells

The POU factors Brn-3a and Brn-3b are closely related transcription factors which are expressed in neuronal cells. The levels of the transcripts encoding these factors are regulated in opposite directions in neuronal cells by specific cellular signalling pathways with dibutyryl cyclic AMP treatment and serum removal enhancing the level of Brn-3a and reducing the level of Brn-3b expression. This opposite expression pattern is paralleled by the ability of Brn-3a to specifically transactivate a target promoter bearing its DNA binding site whereas this promoter is repressed by Brn-3b. As predicted from these observations this target promoter is strongly activated by serum removal or addition of dibutyryl cyclic AMP. Therefore changes in Brn-3a and b expression can have a functional effect on promoter activity indicating that Brn-3a and Brn-3b can regulate gene expression via a specific binding site in response to the activation of specific cellular signalling pathways. The reasons for the differences in activity between these two related factors and their role in regulating gene activity in the nervous system are discussed.

The Oct-2 transcription factor represses tyrosine hydroxylase expression via a heptamer TAATGARAT-like motif in the gene promoter

The tyrosine hydroxylase (TH) gene promoter contains adjacent octamer and heptamer motifs which act as target sites for octamer binding transcription factors. Mutation of the heptamer motif but not the octamer motif enhances TH promoter activity in neuronal cells expressing Oct-2 but not in non-expressing fibroblasts. Similarly addition of the heptamer motif to a minimal TH promoter represses gene expression in neuronal cells but not in fibroblasts. These effects can be reproduced by the artificial expression of neuronal isoforms of Oct-2 in fibroblasts which results in the repression of transfected TH promoters containing an intact heptamer motif but not those in which this motif has been mutated or deleted. The TH promoter thus represents the first example of a cellular promoter which is repressed by Oct-2. The significance of this effect is discussed in terms of the cell type specificity of the TH promoter and its induction by different physiological stimuli.

Inhibition of herpes simplex virus infection by ectopic expression of neuronal splice variants of the Oct-2 transcription factor

Herpes simplex virus (HSV) is capable of lytic replication in most cells, such replication in epithelial cells resulting in the mucocutaneous lesions observed following in vivo infection. In addition however, the virus also establishes asymptomatic latent infections in sensory neurons which serve as a reservoir for further cycles of peripheral lytic infections. These latent infections are dependent upon the inhibition of viral immediate-early (IE) gene expression via the octamer-related TAATGARAT motif in the IE promoters resulting in the failure of the viral lytic cycle. Here we show that the ectopic expression of neuronal isoforms of the octamer/TAATGARAT-binding transcription factor Oct-2 in permissive BHK cells represses IE gene expression following HSV infection and inhibits the viral lytic cycle whereas the B lymphocyte isoform of Oct-2 does not have this effect. These results suggest that the neuronal isoforms of Oct-2 play a critical role in rendering neuronal cells non-permissive for the viral lytic cycle thereby allowing the establishment of latent infection. Moreover, this is the first time that the ectopic expression of a cellular transcription factor has been shown to inhibit infection with any virus, raising the possibility of therapeutically inhibiting lytic viral infections by inducing such ectopic expression.

Functional interaction between different isoforms of the Oct-2 transcription factor expressed in neuronal cells

The predominant neuronal isoforms of the Oct-2 transcription factor, Oct 2.4 and Oct 2.5, repress the herpes simplex virus immediate-early promoter both in neuronal cells and in fibroblasts normally lacking Oct-2. In contrast, the predominant B lymphocyte form Oct 2.1, which is present at a lower level in neuronal cells, activates the immediate-early promoter in fibroblasts but represses it in neuronal cells. We show here that both Oct 2.4 and Oct 2.5 can functionally interact with Oct 2.1 and convert it from an activator into a repressor. Hence, the cell type-specific activity of Oct 2.1 results from the presence of Oct 2.4 and 2.5 in neuronal cells and their absence in other cell types. The significance of this effect is discussed in terms of the role of Oct-2 in the regulation of viral and cellular gene expression in neuronal cells.

Cell cycle arrest and morphological differentiation can occur in the absence of apoptosis in a neuronal cell line

Apoptotic cell death plays a critical role in the development of the nervous system. Although the apoptotic death of mature non-dividing neurons has been extensively studied, the mechanisms mediating the extensive cell death in areas of the developing brain where proliferating neuroblasts are differentiating into mature neurons have not been analyzed. We have previously shown that the cell cycle arrest of a proliferating neuronal cell line by transfer from medium containing 10% foetal calf serum (FCS) to serum-free medium results in the morphological differentiation of some cells and the death of others by apoptosis. Here we show that the effect of 10% FCS can be mimicked by medium containing either similar concentrations of newborn or adult bovine serum or 1% FCS all of which maintain cellular proliferation and inhibit differentiation and apoptosis. In contrast, the presence of 0.5% FCS in the medium effectively prevents apoptosis but does not allow cellular proliferation or inhibit morphological differentiation. Hence cell cycle arrest and differentiation can occur in the absence of apoptosis in cells of neuronal origin and the factors in serum responsible for modulating these processes are likely to be distinct.

The octamer binding protein Oct-2 inhibits transactivation of the herpes simplex virus immediate-early genes by the virion protein Vmw65

Transactivation by a complex of the cellular transcription factor Oct-1 and the virion protein Vmw65 is necessary for the high-level activity of the HSV immediate-early promoters during lytic infection. We show that this trans-activation can be inhibited by two forms of the Oct-2 transcription factor which are expressed at high levels in neuronal cells as well as by the isolated DNA binding, POU domain of Oct-2. The inhibition of Oct-1-Vmw65 DNA binding by these neuronal forms of Oct-2 is likely to play a critical role in the nonpermissivity of neuronal cells for the HSV lytic cycle and therefore in the establishment of latent infections.

Transactivation of the human papilloma virus 16 octamer motif by the octamer binding protein Oct-2 requires both the N and C terminal activation domains

The upstream regulatory region (URR) of the human papillomaviruses HPV16 and 18 contains a sequence with a seven out of eight base match to the consensus binding site for octamer binding transcription factors. This motif acts as a target for repression by the Oct-1 transcription factor and therefore inhibits promoter activity in non-cervical cells expressing only Oct-1. In contrast the HPV octamer motif activates promoter activity in cervical cells. Here we show that cervical cells express the activating form of the Oct-2 transcription factor, Oct 2.1 and that this factor can transactivate promoter activity via the HPV16 octamer. This effect is dependent upon both the N and C-terminal activation domains of Oct-2. The expression of specific octamer binding proteins such as Oct-2 in cervical cells thus allows the HPV16 motif to produce opposite effects on gene expression in cervical and non-cervical cells suggesting that it may play a role in the cervical specificity of URR driven gene expression.

Alternative splicing of the Oct-2 transcription factor RNA is differentially regulated in neuronal cells and B cells and results in protein isoforms with opposite effects on the activity of octamer/TAATGARAT-containing promoters

The RNA encoding the octamer-binding transcription factor Oct-2 is alternatively spliced in both neuronal cells and in B cells to yield multiple mRNAs encoding different isoforms of the protein. We show that, compared with B cells, neuronal cells overexpress the mRNAs encoding Oct 2.4 and 2.5 which differ from the other forms (Oct 2.1, 2.2, and 2.3) at the C terminus of the protein. When introduced into cells lacking endogenous Oct-2, the various Oct-2 isoforms have different effects on octamer-containing promoters. The Oct 2.1, 2.2, and 2.3 forms stimulate all octamer-containing promoters. However, the Oct 2.4 and 2.5 forms can repress some promoters and stimulate others, depending on the sequence of the octamer motif and its context within the promoter. In contrast, when introduced into neuronal cells which express a high endogenous level of the inhibitory Oct 2.4 and 2.5 forms, all the Oct-2 isoforms can repress octamer-mediated gene expression. The significance of these findings is discussed with regard to the known inhibitory effect of the octamer motif on viral and cellular gene expression in neuronal cells.

A novel POU family transcription factor is closely related to Brn-3 but has a distinct expression pattern in neuronal cells

The use of the polymerase chain reaction in conjunction with degenerate oligonucleotides has allowed the isolation of cDNA clones derived from each of the POU family transcription factors expressed in the proliferating ND7 neuronal cell line. In addition to the previously characterized Oct-1, Oct-2 and Brn-3 factors, ND7 cells have been shown by this means to express a novel POU factor. This factor is closely related to Brn-3 but differs at seven amino acids in the POU domain, one of which is located in a region which is critical for protein-protein interactions between different POU proteins. Like Brn-3, the novel factor is expressed at high levels in embryonic brain and declines in abundance during neuronal development. In contrast to Brn-3 however, it is absent in mature sensory neurons and its expression declines during the in vitro differentiation of ND7 cells to a non-dividing phenotype whilst Brn-3 expression increases. The significance of these distinct but overlapping expression patterns is discussed in terms of the possible role of these two factors in regulating neuronal gene expression.

Regulation of expression of the neuronal POU protein Oct-2 by nerve growth factor

POU proteins are a class of homeobox-containing transcription factors that regulate tissue-specific gene expression and influence cell differentiation and function. We have investigated the possible role of such factors in mediating the actions of nerve growth factor (NGF) on sensory neurons. NGF has been found to have differential effects on the levels of three POU protein transcription factors that are expressed in adult rat sensory neurons. A sensory neuron octamer-binding protein with the properties of the transcription factor Oct-2 is up-regulated 3-4-fold by NGF, as measured by mobility shift assays using nuclear extracts from adult rat dorsal root ganglion neurons grown in the presence or absence of NGF. Quantitation of Oct-2 mRNA by polymerase chain reaction amplification of RNA from such cells shows a parallel increase in Oct-2 mRNA levels. In contrast, the levels of mRNA encoding the ubiquitous POU protein Oct-1 or the neuron-specific POU protein Brn-3, also present in sensory neurons, are unaffected by NGF. These observations suggest a role for Oct-2 in mediating transcriptional effects induced by NGF. In particular, as Oct-2 is known to inhibit herpes simplex virus immediate-early gene expression in neuronal cells, these findings provide a mechanism for the known action of NGF in the maintenance of latent herpes virus infections in sensory neurons.

Interferon-alpha treatment of Daudi cells down-regulates the octamer binding transcription/DNA replication factors Oct-1 and Oct-2

Treatment of Daudi cells with alpha-interferon (alpha-IFN) results in a considerable decrease in the levels of the octamer-binding DNA replication/transcription factors Oct-1 and Oct-2 and specifically inhibits gene expression by octamer-containing promoters. The inhibitory effect on octamer-binding proteins also occurs after culturing cells with phorbol 12-myristate 13-acetate but it does not occur following alpha-IFN treatment of an alpha-IFN-resistant variant of the Daudi cell line or of HeLa cells. We discuss the potential role of the decreased levels of octamer-binding proteins in the inhibition of cell proliferation.

The octamer-binding protein Oct-2 represses HSV immediate-early genes in cell lines derived from latently infectable sensory neurons

Transcription of herpes simplex virus (HSV) immediate-early (IE) genes does not occur in sensory neurons latently infected with the virus or following infection of neuronal cell lines. In neuronal cell lines this inability results from the weak activity of the viral IE promoters, which is caused by a neuron-specific repressor factor that binds specifically to the TAATGARAT motif in these promoters and to related octamer elements. Cells expressing this repressor contain an additional octamer-binding protein that is absent from permissive cells. We identify this factor as the lymphocyte- and neuron-specific octamer-binding protein Oct-2 and show that Oct-2 mRNA is also present in dorsal root ganglion neurons, the natural site of HSV latency in vivo. Moreover, artificially elevated expression of Oct-2 can repress the IE promoter. The potential role of Oct-2 in the initiation and maintenance of in vivo latent infection with HSV is discussed.

The B-cell and neuronal forms of the octamer-binding protein Oct-2 differ in DNA-binding specificity and functional activity

B lymphocytes contain an octamer-binding transcription factor, Oct-2, that is absent in most other cell types and plays a critical role in the B-cell-specific transcription of the immunoglobulin genes. A neuronal form of this protein has also been detected in brain and neuronal cell lines by using a DNA mobility shift assay, and an Oct-2 mRNA is observed in these cells by Northern (RNA) blotting and in situ hybridization. We show that the neuronal form of Oct-2 differs from that found in B cells with respect to both DNA-binding specificity and functional activity. In particular, whereas the B-cell protein activates octamer-containing promoters, the neuronal protein inhibits octamer-mediated gene expression. The possible role of the neuronal form of Oct-2 in the regulation of neuronal gene expression and its relationship to B-cell Oct-2 are discussed.

Activity of herpes simplex virus type 1 latency-associated transcript (LAT) promoter in neuron-derived cells: evidence for neuron specificity and for a large LAT transcript

By using chloramphenicol acetyltransferase (CAT) assays in neuron-derived cell lines, we show here that promoter activity associated with the herpes simplex virus type 1 latency-associated transcript (LAT) had neuronal specificity. Promoter activity in these transient CAT assays coincided with a DNA region containing excellent RNA polymerase II promoter consensus sequences. Primer extension analysis in a LAT promoter-CAT plasmid construct placed the start of transcription about 28 nucleotides from the first T in the consensus TATA box sequence. Neuronal specificity of this promoter was suggested by examining the effect of sequences upstream of the promoter on CAT activity in neuronal versus nonneuronal cells. In nonneuronal cells, promoter activity was decreased 3- to 12-fold with the addition of upstream sequences. In contrast, in neuron-derived cells, the addition of upstream sequences did not decrease promoter activity. The LAT promoter predicted by our transient CAT assays was located over 660 nucleotides upstream from the 5' end of the previously mapped 2-kilobase (kb) LAT. This unusual location was explained by in situ and Northern (RNA) blot hybridization analyses that suggested that LAT transcription began near the promoter detected in our CAT assays, rather than near the 5' end of the 2-kb LAT. In situ hybridization with neurons from latently infected rabbits detected small amounts of LAT RNA within 30 nucleotides of the consensus TATA box sequence. This suggested that LAT transcription began near this TATA box. Northern blot hybridization of RNA from ganglia of latently infected rabbits revealed a faint 8.3-kb band of the same sense as LAT. We conclude that (i) the LAT promoter has neuronal specificity, (ii) the LAT promoter is located over 660 nucleotides upstream of the 5' end of the previously characterized stable 2-kb LAT, (iii) LAT transcription begins about 28 nucleotides from the first T of the consensus TATA box sequence and extends to near the first available polyadenylation site approximately 8.3 kb away, and (iv) this 8.3-kb RNA may be an unstable precursor of the more stable 2- and 1.3-kb LATs.

C-erbB2 mRNA expression in human breast tumours: comparison with c-erbB2 DNA amplification and correlation with prognosis

In this study, we have investigated the expression of the proto-oncogene c-erbB2 in a total of 70 human primary breast tumours. In agreement with other workers, we observed c-erbB2 gene amplification in 17.5% of the tumours studied. In addition, we carried out a comprehensive analysis of c-erbB2 mRNA expression in the tumours using RNase mapping and in situ hybridisation techniques. Our results indicated a more frequent (30%) overexpression of c-erbB2 mRNA, which was associated only with breast carcinomas of a ductal origin. Furthermore, analysis of the c-erbB2 mRNA gene locus in the same tumours demonstrated that enhanced c-erbB2 expression could occur in the presence or absence of gene amplification, suggesting that additional molecular mechanisms may result in overexpression of c-erbB2 mRNA in human mammary tumours. In situ hybridisation showed that elevated levels of c-erbB2 mRNA were specific to malignant cells within the breast tumour. Analysis of the association between c-erbB2 mRNA overexpression and clinicopathological factors revealed a significant correlation with poor tumour grade, but not with steroid receptor status or patient menopausal status. No significant correlation was observed between overexpression of c-erbB2 mRNA and early disease recurrence in our group of patients, although there was a definite trend towards poorer prognosis.