The different inhibitory domains of the Oct-2 transcription factor have distinct functional activities

The Oct-2 POU family transcription factor contains three distinct regions whose deletion reduces its ability to inhibit transcription via its octamer binding site. Here we show that only one of these inhibitory domains is capable of also inhibiting the activity of activating molecules bound at adjacent sites upstream of a TATA box-containing promoter whereas the other two regions are inactive in this assay. None of the three regions is able to achieve this effect when located upstream of the same promoter containing an initiator motif. The mechanisms of action of these domains and their role in the functioning of the Oct-2 factor are discussed.

Coordinate induction of the three neurofilament genes by the Brn-3a transcription factor

The POU domain transcription factor Brn-3a is able to stimulate neurite outgrowth when overexpressed in the neuronal ND7 cell line, whereas the closely related Brn-3b factor does not have this effect. We show that Brn-3a overexpression also enhances the expression of the three neurofilament genes at both the mRNA and protein levels, whereas Brn-3b overexpression has no effect. In addition Brn-3a activates the three neurofilament gene promoters in co-transfection assays in both neuronal and non-neuronal cells. As observed for enhanced neurite outgrowth, the stimulation of neurofilament gene expression and activation of the neurofilament gene promoters is observed with the isolated POU domain of Brn-3a. A single amino acid change in the POU homeodomain of Brn-3a to the equivalent amino acid in Brn-3b abolishes its ability to activate the neurofilament promoters, whereas the reciprocal change converts Brn-3b to an activator of these promoters.

A single residue within the homeodomain of the Brn-3 POU family transcription factors determines whether they activate or repress the SNAP-25 promoter

The closely related POU family transcription factors Brn-3a and Brn-3b differ in their effect on a number of different neuronally expressed promoters such as that of the gene encoding the synaptic vesicle component SNAP-25. Thus Brn-3a activates these promoters whilst Brn-3b represses both their basal activity and their activation by Brn-3a. We show here that alterations of a single amino acid at position 22 in the POU-homeodomain from the isoleucine found in Brn-3b to the valine found at the equivalent position in Brn-3a converts Brn-3b from a repressor to an activator of the SNAP-25 gene promoter. The converse mutation in Brn-3a abolishes its ability to activate the SNAP-25 gene promoter and allows it to repress the basal activity of the promoter and its activation by wild type Brn-3a. This is the first time that a single amino acid change has been shown to convert an activator of a naturally occurring promoter to a repressor and vice versa. These results are discussed in terms of the critical role of position 22 in the POU homeodomain in the protein-protein interactions of POU proteins.

Therapeutic monitoring, the concentration-effect relationship and impact on the clinical efficacy of antibiotic agents

Therapeutic monitoring is now technically feasible for a wide variety of antibiotic agents and data are accumulating on the relationship of blood levels and clinical efficacy. For each antibiotic a therapeutic range and dosage regimen can be based theoretically on its known pharmacokinetics, pharmacodynamics in vitro, and also use in animal and human treatment studies. Antibiotics can be characterised into types by their mechanism of kill, as either concentration-dependent (for which achieving a large post-dose concentration to MIC ratio appears important) or concentration-independent/time-dependent (where efficacy is related to maintain the overall concentration above the MIC). Hopefully, concentration-controlled trials will be performed when new antibiotics are introduced, to determine a therapeutic range which correlates with clinical efficacy, and so enable monitoring to lead to a more rational approach to antibiotic administration.

Inhibition of neuronal process outgrowth and neuronal specific gene activation by the Brn-3b transcription factor

The differentiation of the ND7 neuronal cell line to a nondividing phenotype bearing numerous neurite processes is accompanied by a dramatic increase in the levels of the activating POU family transcription factor Brn-3a and a corresponding fall in the levels of the closely related inhibitory factor Brn-3b. We have previously shown that the artificial overexpression of Brn-3a in these cells can induce neurite outgrowth and the activation of genes encoding synaptic vesicle proteins in the absence of a differentiation-inducing stimulus. Here we show that overexpression of Brn-3b can reduce process outgrowth and synaptic vesicle gene expression following exposure to a stimulus which would normally induce differentiation. These inhibitory effects are abolished by altering a single amino acid in the POU homeodomain of Brn-3b to its equivalent in Brn-3a. The converse mutation in Brn-3a allows it to inhibit process outgrowth in response to a differentiation-inducing stimulus. Hence a single amino acid difference results in these closely related factors having opposite effects and allows the balance between them to regulate differentiation.

The Brn-3a transcription factor induces neuronal process outgrowth and the coordinate expression of genes encoding synaptic proteins

The Brn-3a POU family transcription factor is expressed only in posmitotic neurons in the central nervous system and identifies the first differentiated neurons to appear in the midbrain, hindbrain, and spinal cord during development. This factor is also induced when undifferentiated proliferating ND7 cells cease dividing and differentiate to a mature neuronal-like phenotype bearing numerous neurite processes. We show that overexpression of Brn-3a in undifferentiated ND7 cells induces a mature neuronal phenotype characterized by process outgrowth and the induction of genes encoding synaptic proteins, although the cells continue to proliferate. In contrast, the closely related factors Brn-3b and Brn-3c do not have this effect. Although the N-terminal activation domain of Brn-3a is required for maximum induction of neurite outgrowth and gene expression, these effects are primarily dependent on the DNA binding POU domain, which also acts as an activation domain. Overexpression of the isolated POU domain of Brn-3a is sufficient to induce neurite outgrowth, while the ability of full-length Brn-3a to do so is abolished by mutating a single amino acid in the Brn-3a POU homeodomain to its equivalent in Brn-3b. Thus, Brn-3a appears to play a critical role in the specification of the mature neuronal phenotype, acting by stimulating the expression of genes whose products are required for process outgrowth and synapse formation.

Differential regulation of genes encoding synaptic proteins by members of the Brn-3 subfamily of POU transcription factors

The three members of the Brn-3 subfamily of POU transcription factors have distinct effects on target gene expression. We show that the promoter of the gene encoding the presynaptic nerve terminal protein SNAP-25 resembles previously characterised target genes in being activated by Brn-3a and Brn-3c, but being repressed by Brn-3b. Unlike other target genes, however, the SNAP-25 promoter can be activated by either the N- or C-terminal activation domains of Brn-3a. In contrast to the SNAP-25 gene, the gene encoding the synaptic vesicle protein synapsin 1 is activated by all the Brn-3 factors, the first gene for which this activation pattern has been reported Interestingly, however, similar activation by all three Brn-3 factors can be observed if the SNAP-25 promoter is truncated by removal of sequences from -2200 to -288 relative to the transcriptional start site. Moreover, a region of the SNAP-25 promoter from -283 to -126 can render a heterologous promoter responsive to activation by all three Brn-3 factors. Differences in promoter structure may thus result in differences in the response to different Brn-3 factors, thus allowing these factors to produce diverse activation patterns of neuronally expressed genes, such as those encoding different synaptic proteins.

Differential regulation of the two neuronal nitric-oxide synthase gene promoters by the Oct-2 transcription factor

The Oct-2 transcription factor has been shown previously to repress both the cellular tyrosine hydroxylase and the herpes simplex virus immediate-early genes in neuronal cells. Here we identify the gene encoding the neuronal nitric-oxide synthase (nNOS) as the first example of a gene activated in neuronal cells by Oct-2. The levels of the nNOS mRNA and protein are greatly reduced in neuronal cell lines in which Oct-2 levels have been reduced by an antisense method, although these cells have enhanced levels of tyrosine hydroxylase. Moreover, the nNOS gene regulatory region is activated by Oct-2 expression vectors upon cotransfection into both neuronal and non-neuronal cells, and this response is dependent upon a 20-amino acid region within the COOH-terminal activation domain of Oct-2. Of the two closely linked promoters that drive nNOS gene expression, only the downstream 5.1 promoter is activated by Oct-2, whereas the 5.2 promoter is unaffected. These effects are discussed in terms of the potential role of Oct-2 in regulating nNOS expression in the nervous system.

The ability of the inhibitory domain of the POU family transcription factor Oct-2 to interfere with promoter activation by different classes of activation domains is dependent upon the nature of the basal promoter elements

The Oct-2 transcription factor contains an inhibitory domain which is able to repress transcription following DNA binding. Here we show that within the neuronally expressed Oct-2.5 form, the inhibitory domain can strongly inhibit activation by transcription factor activation domains which are either composed predominantly of acidic residues or contain the HOB motif, whereas it has a weaker effect or no effect on proline-rich activation domains and on a glutamine-rich domain. In contrast, the isolated inhibitory domain of Oct-2 can efficiently repress all types of activation domains. This effect is observed however, only on TATA box-containing promoters and not on promoters containing an initiator motif. This widespread inhibition of different activation domains and its dependence on the nature of the basal promoter elements indicate that the inhibitory domain is likely to act by contacting a common downstream target of activation domains within the basal transcriptional complex bound at the TATA box rather than quenching specific activation domains by direct interaction. These effects are discussed in terms of the functional role of the inhibitory domain within Oct-2.5 and the mechanism by which it acts.

A single amino acid change converts an inhibitory transcription factor into an activator

The closely related POU family transcription factors Brn-3a and Brn-3b differ in their functional activity with Brn-3a activating several target promoters, which are repressed by Brn-3b. Brn-3b also prevents promoter activation by Brn-3a. Here we have altered a single isoleucine residue in the POU homeodomain of Brn-3b to the valine residue found at the equivalent position in Brn-3a. This change not only abolishes the ability of Brn-3b to repress basal and Brn-3a-stimulated promoter activity but also converts it to an activator of similar potency to Brn-3a. Hence a single amino acid difference determines the difference between an activator and a repressor in the Brn-3 family.

The different activities of the two activation domains of the Brn-3a transcription factor are dependent on the context of the binding site

The POU (Pit-Oct-Unc) family transcription factor Brn-3a contains two distinct activation domains, one at the N terminus of the molecule and one at the C terminus coincident with the DNA binding domain. These different activation domains have been shown previously to differ in their ability to activate an artificial test promoter containing a Brn-3a binding site and the naturally occurring alpha-internexin gene promoter. Here we identify the target site for Brn-3a in the alpha-internexin gene promoter and show that it can confer responsiveness to Brn-3a on a heterologous promoter. One of the single-stranded DNA sequences derived from either this novel Brn-3a binding site or from the previously characterized site in the test promoter are shown to bind Brn-3a preferentially compared with the complementary single strand or the corresponding double-stranded sequence. The pattern of responsiveness of these two sequences when cloned upstream of the same test promoter and co-transfected with constructs encoding various portions of Brn-3a indicates that the activity of the two Brn-3a activation domains is dependent upon differences in the context of the target sequence in each promoter rather than on differences in the target sequence itself.

The incidence and epidemiology of beta-lactam resistance in Haemophilus influenzae

Consecutive isolates of Haemophilus influenzae were collected by the Public Health Laboratory, Bath between 1 June 1992 and 31 May 1993. Of 379 apparently distinct isolates, 216 originated from the respiratory tract, 102 from eyes and 61 from other sites. The minimum inhibitory concentrations of amoxycillin, amoxycillin/clavulanate, cefaclor, cefuroxime, cefotaxime and cefpodoxime were determined for each isolate. Forty strains (10.6%) were beta-lactamase producers. MIC50 and MIC90 values and the range of MICs were determined for all isolates. The overall resistance rates were: amoxycillin (MIC > 1.0 mg/L), 22.7%; amoxycillin/clavulanate (MIC > 1.0 mg/L), 14.8%; cefuroxime (MIC > 1.0 mg/L), 18.5%, (MIC > 4.0 mg/L), 5.5%; cefaclor (MIC > 8 mg/L), 15.6%; cefpodoxime (MIC > 1.0 mg/L), 0.3%; cefotaxime (MIC > 1.0 mg/L), 0%. Twenty non-beta-lactamase producing but beta-lactam resistant strains (cefuroxime MIC > 4.0 mg/L) were matched with 20 susceptible strains on the basis of patient age, sex, and specimen type. The strains were characterised by outer-membrane protein (OMP), random amplified polymorphic DNA (RAPD) and ribotyping patterns. Eleven of the 20 resistant strains were indistinguishable by the methods used, suggesting spread of a single beta-lactam resistant, non-beta-lactamase producing clone. The distribution of resistant strains within the local community was plotted geographically.

Alternative splicing of the Brn-3a and Brn-3b transcription factor RNAs is regulated in neuronal cells

The closely related and functionally antagonistic POU family transcription factors Brn-3a and Brn-3b are encoded by two distinct genes that are expressed primarily in neuronal cells. In addition, however, the primary transcript of each of these genes is alternatively spliced to produce two distinct mRNAs encoding long and short isoforms that differ at the N-terminus of the protein. We show that this process is regulated so that different proportions of the mRNAs encoding the long and short forms of either Brn-3a or Brn-3b are produced in different rat tissues. Similarly, the ratio of each of these forms can be modulated by specific stimuli in both a neuronal cell line and primary neurons. The significance of these effects is discussed in relation to the functional differences between the two forms of each factor.

The ability of POU family transcription factors to activate or repress gene expression is dependent on the spacing and context of their specific response elements

The different forms of the Oct-2 and Brn-3 POU family transcription factors can have distinct effects on their target promoters involving both the activation and repression of gene expression. To investigate the requirements for these effects we have altered both the context and spacing of the two TAATGARAT binding sites for these factors within the herpes simplex virus immediate-early 3 gene promoter. We show that the activation of this promoter by Brn-3a and its repression by Brn-3b is dependent on the correct spacing of these binding sites. In contrast, repression of the promoter by Oct-2.4 and Oct-2.5 is dependent on both the spacing and context of these sites with the requirements for repression by Oct-2.4 or Oct-2.5 being different. These effects are discussed in the context of the mechanisms by which POU factors activate or repress their target genes.

Direct evidence that the POU family transcription factor Oct-2 represses the cellular tyrosine hydroxylase gene in neuronal cells

The POU family transcription factor Oct-2 was originally identified in B lymphocytes but has been shown to be expressed in neuronal cells, although it is absent in most other cell types. Cotransfection of Oct-2 expression vectors into nonneuronal cells with a tyrosine hydroxylase promoter/reporter plasmid suggests that Oct-2 can repress this promoter in this artificial situation. Here we report that reduction of endogenous Oct-2 levels in a neuronal cell line by an antisense approach results in an increase in endogenous tyrosine hydroxylase levels. In contrast, the level of the neuronal marker protein PGP9.5 remains unchanged in the antisense lines whereas that of the neuronal nitric oxide synthase decreases. Hence, the tyrosine hydroxylase gene is a natural target for repression by Oct-2 in neuronal cells. The significance of this effect is discussed in terms of the processes that regulate tyrosine hydroxylase gene expression and the role of Oct-2 in neuronal cells.

The 4G/5G genetic polymorphism in the promoter of the plasminogen activator inhibitor-1 (PAI-1) gene is associated with differences in plasma PAI-1 activity but not with risk of myocardial infarction in the ECTIM study. Etude CasTemoins de I'nfarctus du Mycocarde

We have investigated the interrelationships of plasma PAI-1 activity, the PAI-1 4G/5G polymorphism and risk of myocardial infarction (MI) in the ECTIM study, a case-control study of MI based in Belfast, Lille, Strasbourg and Toulouse. Mean PAI-1 levels in cases were similar across all centres but in controls, levels in the French centres were significantly higher. Only in Belfast were PAIl1 levels higher in cases (11.7 AU/ml) than controls (10.5 AU/ml). The PAI-1 4G allele frequency was similar in cases and controls (0.55 and 0.54). In all groups, 4G homozygotes had the highest mean plasma PAI-1 level (4G4G vs 5G5G; cases overall: 14.2 vs 12.1AU/ml; controls overall: 15.0 vs 12.6AU/ml), with the heterozygotes generally intermediate. The data from Belfast are consistent with the literature implicating PAI-1 level as an MI risk factor. In ECTIM, the PAI-1 4G/5G polymorphism is not a genetic risk factor for MI but is associated with PAI-1 activity. Thus homozygosity for the 4G allele may predispose to elevated PAI-1 and impaired fibrinolysis, perhaps requiring interaction with other genetic or environmental factors to influence MI risk.

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 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.

Chronic active toxoplasmosis in an immunocompetent patient

We report the case of an apparently immunocompetent woman whose symptoms and signs have persisted for 8 years following a serologically and histologically confirmed diagnosis of toxoplasmosis. During this period she had two successful pregnancies despite persistently increased anti-toxoplasma IgM antibodies. Neither child is infected.

Two pathways of iron-catalyzed oxidation of bilirubin: effect of desferrioxamine and trolox, and comparison with microsomal oxidation

The bilirubin-degrading activity of liver microsomes from rats induced with 3-methylcholanthrene has been shown to be markedly stimulated by addition of 3,3',4,4',5,5'-hexabromobiphenyl, a polyhalogenated chemical which resembles in size and shape the most effective inducers of cytochrome P450IA1, but lacks the structural features necessary for it to be metabolised. The degradation of bilirubin by this microsomal system has been compared to oxidation by a chemical model system involving H2O2 and Fe-EDTA (ethylenediaminetetraacetic acid). In both systems bilirubin disappearance was accompanied by bleaching. However, when either desferrioxamine or Trolox were present in the chemical model system, the rate of bilirubin oxidation was greatly enhanced and, at the same time, bilirubin was largely or entirely converted to biliverdin, a pathway of oxidation which proceeds by dehydrogenation. In the presence of desferrioxamine, biliverdin was also further oxidised to an unidentified red pigment.

The two allele sequences of a common polymorphism in the promoter of the plasminogen activator inhibitor-1 (PAI-1) gene respond differently to interleukin-1 in HepG2 cells

We have detected a common (allele frequency 0.53/0.47) single base pair insertion/deletion polymorphism 675 base pairs upstream from the start of transcription of the plasminogen activator inhibitor-1 (PAI-1) gene, using the chemical cleavage mismatch analysis. "Band shift assays" suggest that the allele with the single base pair insertion contains an additional protein binding site which is not present in the del allele. Competition experiments confirmed that the binding was specific to the sequence of the ins allele and suggest that proteins bound to this site may be NF-kB-like proteins. Analysis of chloramphenicol acetyltransferase (CAT) mRNA produced by constructs containing the PAI-1 promoter (-805 to +83) showed that the deletion allele produced six times more mRNA than the insertion allele in response to interleukin-1 (p < 0.001). In a sample of 107 young patients with previous myocardial infarction and 95 healthy population-based subjects, the del allele was associated with increased PAI-1 levels, 21% higher than the sample mean in the del homozygotes (p < 0.05). This study also suggested that individuals homozygous for the del allele may have an altered response to the acute phase stimulus. Taken together these results suggest that the insertion/deletion polymorphism in the PAI-1 promoter is of functional importance in regulating the expression of the PAI-1 gene.