BARX2 and estrogen receptor-alpha (ESR1) coordinately regulate the production of alternatively spliced ESR1 isoforms and control breast cancer cell growth and invasion

The estrogen receptor-alpha gene (ESR1) was previously identified as a direct target of the homeobox transcription factor BARX2 in MCF7 cells. Here, we show that BARX2 and ESR1 proteins bind to different ESR1 gene promoters and regulate the expression of alternatively spliced mRNAs that encode 66 and 46 kDa ESR1 protein isoforms. BARX2 increases the expression of both ESR1 isoforms; however, it has a greater effect on the 46 kDa isoform, leading to an increased ratio between the 46 and 66 kDa proteins. BARX2 also influences estrogen-dependent processes such as anchorage-independent growth and modulates the expression of the estrogen-responsive genes SOX5, RBM15, Dynein and Mortalin. In addition, BARX2 expression promotes cellular invasion and increases the expression of active matrix metalloproteinase-9 (MMP9). BARX2 also increases the expression of the tissue inhibitor of metalloproteinase (TIMP) genes, TIMP1 and TIMP3, in cooperation with estrogen signaling. Overall, these data indicate that BARX2 and ESR1 may coordinately regulate cell growth, survival and invasion pathways that are critical to breast cancer progression.

Prx1 controls vascular smooth muscle cell proliferation and tenascin-C expression and is upregulated with Prx2 in pulmonary vascular disease

Prx1 and Prx2 are homeobox transcription factors expressed during vasculogenesis. To begin to elucidate how Prx1 and Prx2 are regulated and function in the adult vasculature, in situ hybridization studies were performed. Prx1 and Prx2 mRNAs were not detected in normal adult rat pulmonary arteries; however, both genes were induced with vascular disease, colocalizing to sites of tenascin-C (TN-C) expression. Because catabolism of the extracellular matrix (ECM) is a critical step in the development of vascular disease, we investigated whether changes in vascular smooth muscle cell (SMC)-ECM interactions regulate Prx1 and Prx2. A10 SMCs cultured on native type I collagen showed low levels of Prx1 and Prx2 mRNA expression, whereas cells cultured on denatured collagen showed higher levels of expression of both genes. At a functional level, transfection of SMCs with a Prx1 expression plasmid significantly increased their growth. Because TN-C also promotes SMC growth and its expression is also upregulated by denatured collagen, we tested and thereafter showed that Prx1 expression significantly enhances TN-C gene promoter activity 20-fold. Similar experiments conducted with truncated Prx1 proteins showed that the N-terminal portion and the homeodomain of Prx1 were necessary to induce the bulk of TN-C promoter activity. These findings support the hypothesis that Prx genes are regulated by changes in SMC adhesion and play key morphoregulatory roles during the development and progression of pulmonary vascular disease in adults.

The homeodomain protein Barx2 contains activator and repressor domains and interacts with members of the CREB family

Barx1 and Barx2 are homeodomain proteins originally identified using regulatory elements of genes encoding certain cell adhesion molecules (CAMs). In the present study, we characterize regions of Barx2 that bind to regulatory elements of genes encoding three CAMs, L1, neuron-glia CAM (Ng-CAM), and neural CAM (N-CAM), and identify domains of Barx2 that regulate N-CAM transcription. The homeodomain of Barx2 was sufficient for binding to homeodomain binding sites (HBS) from all three CAM genes. The presence of a 17-amino acid Barx basic region resulted in a 2-fold decrease in binding to HBS sequences from the Ng-CAM and L1 genes, whereas it led to a 6.5-fold increase in binding to the HBS from the N-CAM promoter. Thus, the Barx basic region influences the strength and specificity of Barx2 binding to DNA. In co-transfection experiments, Barx2 repressed N-CAM promoter activity. A 24-residue N-terminal region of Barx2 was essential for repression. When this region was absent, Barx2 activated the N-CAM promoter. A 63-residue C-terminal domain was required for this activation. In GST pull-down experiments, Barx2 bound to proteins of the CREB family, CREB1 and ATF2. Overall, these findings provide a framework for understanding developmental and physiological contexts that influence repressor or activator functions of Barx2.

Synthetic promoter elements obtained by nucleotide sequence variation and selection for activity

Eukaryotic transcriptional regulation in different cells involves large numbers and arrangements of cis and trans elements. To survey the number of cis regulatory elements that are active in different contexts, we have devised a high-throughput selection procedure permitting synthesis of active cis motifs that enhance the activity of a minimal promoter. This synthetic promoter construction method (SPCM) was used to identify >100 DNA sequences that showed increased promoter activity in the neuroblastoma cell line Neuro2A. After determining DNA sequences of selected synthetic promoters, database searches for known elements revealed a predominance of eight motifs: AP2, CEBP, GRE, Ebox, ETS, CREB, AP1, and SP1/MAZ. The most active of the selected synthetic promoters contain composites of a number of these motifs. Assays of DNA binding and promoter activity of three exemplary motifs (ETS, CREB, and SP1/MAZ) were used to prove the effectiveness of SPCM in uncovering active sequences. Up to 10% of 133 selected active sequences had no match in currently available databases, raising the possibility that new motifs and transcriptional regulatory proteins to which they bind may be revealed by SPCM. The method may find uses in constructing databases of active cis motifs, in diagnostics, and in gene therapy.

Knockout of REST/NRSF shows that the protein is a potent repressor of neuronally expressed genes in non-neural tissues

The protein repressor element 1 silencing transcription factor/neuron restrictive silencer factor (REST/NRSF) is a negative regulator of neuronal genes that contain a particular DNA sequence, the neuron restrictive silencer element (NRSE). REST is expressed ubiquitously in non-neural tissues but is down-regulated in neural precursors and turned off in postmitotic neurons, suggesting that it can act both to prevent extraneural expression of certain genes and to delay the differentiation of neuronal subtypes. In a recent paper, Chen et al.(1) describe the production of a null mutant for REST in mice and the mosaic inactivation of REST function in chicken embryos. Knockout of REST led to malformations in several non-neural tissues, as well as apoptosis and embryonic lethality in mice. In addition, the expression of several REST target genes was derepressed in non-neural tissues and in neural progenitors in both mouse and chicken embryos. These studies clearly demonstrate that active repression of tissue-specific genes is required for proper tissue differentiation during embryonic development.

A binding site for homeodomain and Pax proteins is necessary for L1 cell adhesion molecule gene expression by Pax-6 and bone morphogenetic proteins

The cell adhesion molecule L1 regulates axonal guidance and fasciculation during development. We previously identified the regulatory region of the L1 gene and showed that it was sufficient for establishing the neural pattern of L1 expression in transgenic mice. In the present study, we characterize a DNA element within this region called the HPD that contains binding motifs for both homeodomain and Pax proteins and responds to signals from bone morphogenetic proteins (BMPs). An ATTA sequence within the core of the HPD was required for binding to the homeodomain protein Barx2 while a separate paired domain recognition motif was necessary for binding to Pax-6. In cellular transfection experiments, L1-luciferase reporter constructs containing the HPD were activated an average of 4-fold by Pax-6 in N2A cells and 5-fold by BMP-2 and BMP-4 in Ng108 cells. Both of these responses were eliminated on deletion of the HPD from L1 constructs. In transgenic mice, deletion of the HPD from an L1-lacZ reporter resulted in a loss of beta-galactosidase expression in the telencephalon and mesencephalon. Collectively, our experiments indicate that the HPD regulates L1 expression in neural tissues via homeodomain and Pax proteins and is likely to be a target of BMP signaling during development.

Determinants of UDP glucuronosyltransferase membrane association and residency in the endoplasmic reticulum

The UDP glucuronosyltransferases (UGT)2 are a family of enzymes which detoxify small hydrophobic compounds in mammalian cells. It is believed that UGTs are type I endoplasmic reticulum (ER) resident membrane proteins with a single membrane spanning domain near the carboxyl-terminus. The determinants of endoplasmic reticulum subcellular localization and membrane association for the UDP glucuronosyltransferase, UGT2B1, were examined. The construction and analysis of truncated and chimeric forms of UGT2B1 demonstrated that the protein contains regions of membrane interaction in the amino-terminal half of the lumenal domain in addition to the carboxyl-terminal transmembrane domain. UGT2B1 also remained resident in the ER in the absence of the cytosolic tail and transmembrane domain. Construction and analysis of an active, truncated form of UGT2B1 indicated that the cytosolically located dilysine motif, which is a putative ER membrane targeting signal, may be redundant for residency of UGT in the ER.

Chickenpox immunisation in New Zealand

PREVENTION

The appropriate use of varicella vaccine, effective in the prevention of chickenpox, has been considered by a Ministry of Health Working Party in 1996 and 1997, including discussion at a workshop held in Wellington, 26-27 June 1996. The introduction of varicella vaccine into the routine childhood immunisation schedule was not supported at this stage. The use of the only varicella vaccine for which the Minister of Health has given consent for distribution in New Zealand, Varilrix (SmithKline Beecham Limited), in healthy children aged nine months to 13 years inclusive, was supported. Consent has not been given for the use of Varilrix in immunocompromised people or in adults. This report discusses other groups that could be candidates for vaccination, such as children with deteriorating renal function and susceptible health care workers who regularly come into contact with especially vulnerable patients. In these cases, the vaccine would need to be administered on a named patient basis. The use of Varilrix in immunocompromised people was not supported.

SURVEILLANCE

Enhanced surveillance of chickenpox and zoster are required in New Zealand. Adverse reactions to Varilrix should be carefully monitored.

OUTBREAK CONTROL

There are insufficient data at present to support the use of Varilrix in outbreak control. The frequency, cost and current management of nosocomial outbreaks should be ascertained. This information may also assist in the decision whether to incorporate a varicella vaccine into the routine childhood immunisation schedule in the future.

Structure and function of uridine diphosphate glucuronosyltransferases

1. The uridine diphosphate (UDP)-glucuronosyltransferases (UGT) are a family of enzymes that catalyse the covalent addition of glucuronic acid to a wide range of lipophilic chemicals. They play a major role in the detoxification of many exogenous and endogenous compounds by generating products that are more polar and, thus, more readily excreted in bile or urine. 2. Inherited deficiencies in UGT forms are deleterious, as exemplified by the debilitating effects of hyperbilirubinaemia and neurotoxicity in subjects with mutations in the enzyme that converts bilirubin to its more polar glucuronide. 3. The UGT protein can be conceptually divided into two domains with the amino-terminal half of the protein demonstrating greater sequence divergence between isoforms. This region apparently determines aglycone specificity. The aglycone binding site is presumed to be a 'loose' fit, as many structurally diverse substrates can be bound by the same UGT isoform. The carboxyl-terminal half, which is more conserved in sequence between different isoforms, is believed to contain a binding site for the cosubstrate UDP glucuronic acid (UDPGA). 4. Uridine diphosphate glucuronosyltransferase is localized to the endoplasmic reticulum (ER) and spans the membrane with a type I topology. The putative transmembrane domain is located near the carboxyl terminus of the protein such that only a small portion of the protein resides in the cytosol. This cytosolic tail is believed to contain an ER-targeting signal. The major portion of the protein is located in the ER lumen, including the proposed substrate-binding domains and the catalytic site. 5. The microsomal membrane impedes the access of UDPGA to the active site, resulting in latency of UGT activity in intact ER-derived microsomes. Active transport of UDPGA is believed to occur in hepatocytes, but the transport system has not been fully characterized. Uridine diphosphate glucuronosyltransferase activity is also highly lipid dependent and the enzyme may contain regions of membrane association in addition to the transmembrane domain.

UDP-glucuronosyltransferase, the role of the amino terminus in dimerization

UDP-glucuronosyltransferases (UGTs) comprise an important enzyme system in mammals that is involved in detoxification of a variety of small hydrophobic compounds of both endogenous and exogenous origin. Some evidence suggests that these enzymes may function as oligomers; however, little is known about the domain of interaction or the mechanism of oligomerization. In this work, evidence for a functional dimerization between UGTs is provided by studies on mutated forms of UGT2B1. When two inactive forms of UGT2B1 were co-expressed in cell culture, catalytic activity was restored, indicating that UGT2B1 forms functional dimers. To delineate the dimerization domain, inactive fusion proteins containing the amino- or carboxyl-terminal domains of UGT2B1 were generated and expressed with active UGT2B1. Expression of a fusion protein containing only the amino-terminal half of UGT2B1 with active UGT2B1 caused a reduction in UGT2B1 catalytic activity. This reduction in activity was not observed when UGT2B1 was co-expressed with a fusion protein containing only the carboxyl-terminal half of UGT2B1, strongly suggesting that the amino-terminal domain is involved in dimerization. Truncation of the immediate amino terminus of UGT2B1 abolished UGT2B1 activity and dimer formation. Activity was also abolished by an L4R substitution in this region of the mature protein, which is highly conserved in the UGT family. These results indicate that UGTs can interact through their amino-terminal domains to form catalytically active dimers. Possible mechanisms resulting in the formation and stabilization of the UGT2B1 dimer are discussed.

Steroid UDP glucuronosyltransferases: characterization and regulation

Under normal physiological conditions, glucuronidation generally terminates the biological activities of steroids and leads to their elimination in the bile and urine. This process is postulated to play a role in homeostasis by regulating the intracellular steady-state levels of these effector ligands. Indeed, the duration of response to specific steroid signals may be partly determined by the capacity of the cell or tissue to eliminate the steroids as unreactive glucuronides. Under pathophysiological conditions or during steroid therapies, glucuronidation may sometimes result in the formation of more biologically active or toxic metabolites as exemplified by the steroid D ring glucuronides. The degree of toxicity or biological effect in the cell exposed to these steroids will also depend on its complement of UGTs. To investigate these processes in more detail, the steroid specificities and distribution of individual UGTs in various target organs require elucidation. In this review, our current knowledge of the steroid specificities of various rat and human UGTs is described and preliminary investigations on the mechanisms governing tissue specificity are presented.

Mutational analysis of the carboxy-terminal region of UDP-glucuronosyltransferase 2B1

UDP-glucuronosyltransferases (UGTs) are membrane-bound glycoproteins that are resident in the endoplasmic reticulum with a type I topology. The roles of the membrane-spanning and membrane-proximal cytoplasmic domains in UGT activity were investigated. Site-directed and deletional mutagenesis techniques were used to generate truncated forms of the enzyme, forms with altered residues, or forms with heterologous tails appended to the carboxyl terminus. The presence of the transmembrane domain was a critical requirement for UGT activity whereas the cytoplasmic domain seemed to be a modulator of activity but was not essential. Truncation of the protein did not appear to lead to scavenging and degradation, although appending long heterologous tails to the cytoplasmic domain did seem to trigger proteolysis. Analysis of enzyme kinetic parameters and enzyme latency allowed us to discount substrate binding or substrate transport defects as the cause of ameliorated UGT activity in the mutants.

Central circuitry in the jellyfish Aglantha. II: The ring giant and carrier systems

1. The ring giant axon in the outer nerve ring of the jellyfish Aglantha digitale is a multinucleate syncytium 85 % of which is occupied by an electron-dense fluid-filled vacuole apparently in a Gibbs­Donnan equilibrium with the surrounding band of cytoplasmic cortex. Micropipette recordings show small (-15 to -25 mV) and large (-62 to -66 mV) resting potentials. Low values, obtained with a high proportion of the micropipette penetrations, are assumed to be from the central vacuole; high values from the cytoplasmic cortex. Background electrical activity includes rhythmic oscillations and synaptic potentials representing hair cell input caused by vibration. 2. After the ring giant axon has been cut, propagating action potentials evoked by stimulation are conducted past the cut and re-enter the axon on the far side. The system responsible (the carrier system) through-conducts at a velocity approximately 25 % of that of the ring giant axon and is probably composed of small neurones running in parallel with it. Numerous small neurones are seen by electron microscopy, some making one-way and some two-way synapses with the ring giant. 3. Despite their different conduction velocities, the two systems normally appear to fire in synchrony and at the velocity of the ring giant axon. We suggest that, once initiated, ring giant spikes propagate rapidly around the margin, firing the carrier neurones through serial synapses and giving them, in effect, the same high conduction velocity. Initiation of ring giant spikes can, however, require input from the carrier system. The spikes are frequently seen to be mounted on slow positive potentials representing summed carrier postsynaptic potentials. 4. The carrier system fires one-for-one with the giant axons of the tentacles and may mediate impulse traffic between the latter and the ring giant axon. We suggest that the carrier system may also provide the pathways from the ring giant to the motor giant axons used in escape swimming. 5. The findings show that the ring giant axon functions in close collaboration with the carrier system, increasing the latter's effective conduction velocity, and that interactions with other neuronal sub-systems are probably mediated exclusively by the carrier system.

Central circuitry in the jellyfish Aglantha. I: The relay system

1. The relay system is an interneuronal pathway in the margin of the jellyfish Aglantha digitale. It excites a second interneuronal pathway, the carrier system, and is itself excited by pacemaker neurones concerned with slow swimming. It also excites a slow conduction pathway in the tentacles causing graded, tonic contractions of all the tentacles during slow swimming. 2. The pacemakers, the carrier system and the relay system all contribute to the production of excitatory postsynaptic potentials (EPSPs) in a giant axon that runs in the outer nerve ring (ring giant axon). These EPSPs may cause the latter to spike during slow swimming. If it does so, it will fire tentacle giant axons, producing twitch contractions of the tentacles. Such contractions probably help to contract the tentacles rapidly at the start of slow swimming. This is an unusual case of a giant axon that normally mediates escape behaviour being appropriated for use during a non-escape activity. 3. The relay system can conduct impulses on its own but their conduction velocity is greatly increased when preceded by either pacemaker or ring giant spikes. This phenomenon, termed the 'piggyback effect', may be due to extracellular field effects rather than to actions mediated by chemical or electrical synapses. 4. Recordings from the epithelial cells that ensheath the ring giant and outer nerve ring neurones show miniature synaptic potentials and other events that seem to reflect events in the nervous system, but no functions can be assigned to them. 5. There is no obvious counterpart to the relay system in medusae lacking escape circuitry.

Endogenous Na(+)-K+ (or NH4+)-2Cl- cotransport in Rana oocytes; anomalous effect of external NH4+ on pHi

1. In Rana oocytes, measurements with chloride-sensitive microelectrodes show that the mean intracellular chloride activity (34.8 +/- 6.3 mM, n = 79) is three times higher than that expected for the passive distribution of chloride ions across the outer membrane (12.4 mM, mean membrane potential -43 +/- 8.8 mV, n = 79). 2. Reuptake of chloride into oocytes depleted by prolonged exposure to chloride-free saline takes place against the electrochemical gradient. 3. Chloride reuptake does not take place in sodium-free solution or in a sodium-substituted potassium-free solution. It is inhibited by bumetanide (10(-5) M) in the bathing medium. 4. The overall stoichiometry of the transport mechanism deduced from simultaneous measurements of intracellular sodium and chloride using ion-selective electrodes is 1Na+:1K+:2Cl-. 5. Ammonium ions substitute for potassium on the cotransporter. 6. In oocytes smaller than 0.9 mm in diameter, exposure to external ammonium causes an alkaline shift in intracellular pH as the NH3 enters and takes up H+ to form NH4+. We propose that chloride-dependent NH4+ transport contributes to the accumulation of NH4+ and causes the 'postexposure' acidification as the intracellular NH4+ releases H+ to form NH3 which is then lost from the cell. 7. In larger oocytes ammonium exposure produces a rapid reduction in pHi which may be explained in part by cotransport-mediated uptake of NH4+. Evidence is also provided for a second chloride-dependent NH4+ transport mechanism and a chloride-independent process.

Rapidly activating hydrogen ion currents in perfused neurones of the snail, Lymnaea stagnalis

Cells from the circumoesophageal nerve ring of the pond snail Lymnaea stagnalis were internally perfused with solutions containing Cs aspartate, EGTA and pH buffers. Time-dependent, voltage-dependent 'residual' outward currents were observed at positive potentials. They were found to be carried largely by H+. The outward H+ currents were reduced by high internal pH, low external pH, external Cd2+ and 4-aminopyridine. External tetraethylammonium ions reduced the H+ currents but had a more effective blocking action on the K+ currents in these cells. All five agents reduced the maximum H+ conductance. In addition Cd2+, low external pH and high internal pH were found to shift the voltage dependence of the H+ current to more positive potentials. There was no significant difference between H+ currents recorded with the internal pCa2+ about 7 and those recorded with the internal pCa2+ near 5. It is likely that the H+ channel described here provides the basis for the increase in H+ permeability described by Thomas & Meech (1982) in depolarized Helix neurones. As judged by their sensitivity to different antagonists, H+ channels are unlike any other previously described channel. They are highly selective for protons and we suggest that their role in molluscan neurones is to compensate for the rapid intracellular acidification which is generated by trains of action potentials (Ahmed & Connor, 1980).