Heterogeneous nuclear ribonucleoprotein A1 binds to the transcription-regulatory region of mouse hepatitis virus RNA

A cellular protein, previously described as p35/38, binds to the complementary (-)-strand of the leader RNA and intergenic (IG) sequence of mouse hepatitis virus (MHV) RNA. The extent of the binding of this protein to IG sites correlates with the efficiency of the subgenomic mRNA transcription from that IG site, suggesting that it is a requisite transcription factor. We have purified this protein and determined by partial peptide sequencing that it is heterogeneous nuclear ribonucleoprotein (hnRNP) A1, an abundant, primarily nuclear protein. hnRNP A1 shuttles between the nucleus and cytoplasm and plays a role in the regulation of alternative RNA splicing. The MHV(-)-strand leader and IG sequences conform to the consensus binding motifs of hnRNP A1. Recombinant hnRNP A1 bound to these two RNA regions in vitro in a sequence-specific manner. During MHV infection, hnRNP A1 relocalizes from the nucleus to the cytoplasm, where viral replication occurs. These data suggest that hnRNP A1 is a cellular factor that regulates the RNA-dependent RNA transcription of the virus.

Phospholipid peroxidation induces cytosolic phospholipase A2 activity: membrane effects versus enzyme phosphorylation

Cytosolic phospholipase A2 (cPLA2) is a signal-responsive enzyme that is highly selective to the nature of phospholipid substrates. A mechanism for cPLA2 activity regulation through a signal transduction pathway has been proposed and this signaling appears to be influenced by oxidants. Oxidant-mediated signaling of PLA2 may serve as an alternative mechanism for enzyme regulation; however, the manner of regulation has yet to be delineated. In this report we demonstrate that there is a direct effect of membrane oxidation on cPLA2 phosphorylation and activity. A simple in vitro system consisting of purified cPLA2 and phospholipid vesicles was used to facilitate protein kinase C (PKC) activity and provide substrates for cPLA2. Using these vesicles we found that the activity of cPLA2 was enhanced twofold when the vesicles contained as little as 5 mol% phosphatidylcholine hydroperoxides (PLPCOOH). The order of hydrolytic preference for fatty acyl species was 20:4 > 18:2 > 18:1 > 16:0, and the presence of PLPCOOH stimulated hydrolysis largely of phosphatidylcholine containing 20:4. The Ca2+ concentrations required for stimulated hydrolytic activity were also twofold lower for oxidized compared to unoxidized vesicles. Using phospholipid micelles as substrates, PKC-mediated phosphorylation of cPLA2 increased hydrolytic activity 71% compared to preparations lacking PKC. Using phospholipid vesicles as substrates, PKC-mediated phosphorylation resulted in an 85% increase in cPLA2 activity compared to preparations without PKC. PKC-mediated phosphorylation of cPLA2, therefore, stimulates catalytic activity toward membrane phospholipids and the extent of activation is enhanced directly by peroxidation of membrane phospholipids and involves a peroxide-induced stimulation of cPLA2 phosphorylation.

Ictal single photon emission computed tomography in occipital lobe seizures

PURPOSE

Ictal single photon emission computed tomography (SPECT) has been evaluated as an adjunctive localizing technique in temporal lobe epilepsies and, to a lesser degree, in some extratemporal epilepsies. The purpose of this study was to determine whether occipital lobe seizures are associated with distinctive ictal cerebral blood perfusion (rCP) patterns.

METHODS

SPECT was used with the tracer 99mTc HMPAO to image ictal rCP in 6 patients in whom clinical, EEG, and imaging data indicated occipital lobe seizures.

RESULTS

Two patterns of rCP were seen. Four patients had hyperperfusion that was restricted to the occipital lobe, and two patients had hyperperfusion of the occipital lobe and the ipsilateral mesial temporal lobe, with hypoperfusion of the lateral temporal lobe. The latter 2 patients had clinical and surface EEG evidence of temporal lobe involvement in the seizure discharge.

CONCLUSIONS

Ictal rCP patterns in occipital lobe seizures are distinct from those in temporal lobe seizures and may vary according to whether or not ipsilateral temporal lobe structures are involved in the ictal discharge.

Construction of a homodimeric dihydrofolate reductase-thymidylate synthase bifunctional enzyme

A gene encoding a bifunctional homodimeric dihydrofolate reductase-thymidylate synthase (DHFR-TS) was constructed by destroying the stop codon of Escherichia coli dihydrofolate reductase (DHFR) and joining the coding sequences of the monofunctional enzymes by a five amino acid linker. The protein was designed to mimic features of active site proximity and electrostatics in the protozoan DHFR-TSs which are believed to be important in channeling of the DHFR substrate, H2folate, to TS. The genetically engineered catalytically active homodimeric bifunctional DHFR-TS was expressed, purified and characterized. The component activities of the purified bifunctional enzyme had kinetic properties similar to those of the monofunctional TS and DHFR, but unlike the authentic bifunctional enzymes from protozoa this enzyme did not kinetically channel dihydrofolate from DHFR to TS.

Diagnostic findings in the 1992 epornitic of neurotropic velogenic Newcastle disease in double-crested cormorants from the upper midwestern United States

Neurotropic velogenic Newcastle disease (NVND) occurred in juvenile double-crested cormorants, Phalacrocorax auritus, simultaneously in nesting colonies in Minnesota, North Dakota, South Dakota, and Nebraska and in Lakes Michigan, Superior, Huron, and Ontario during the summer of 1992. Mortality as high as 80%-90% was estimated in some of the nesting colonies. Clinical signs observed in 4- to 6-wk-old cormorants included torticollis, tremors, ataxia, curled toes, and paresis or weakness of legs, wings or both, which was sometimes unilateral. No significant mortality or unusual clinical signs were seen in adult cormorants. Necropsy of 88 cormorants yielded no consistent gross observations. Microscopic lesions in the brain and spinal cord were consistently present in all cormorants from which Newcastle disease virus (NDV) was isolated. Characteristic brain lesions provided rapid identification of new suspect sites of NVND. Lesions were also present in the heart, kidney, proventriculus, spleen, and pancreas but were less consistent or nonspecific. NDV was isolated at the National Wildlife Health Center from 27 of 93 cormorants tested. Virus was most frequently isolated from intestine or brain tissue of cormorants submitted within the first 4 wk of the epornitic. Sera collected from cormorants with neurologic signs were consistently positive for NDV antibody. The NDV isolate from cormorants was characterized as NVND virus at the National Veterinary Services Laboratories, Ames, Iowa. The NVND virus was also identified as the cause of neurologic disease in a North Dakota turkey flock during the summer of 1992. Although no virus was isolated from cormorants tested after the first month of submission, brain and spinal cord lesions characteristic of NVND were observed in cormorants from affected sites for 2 mo, at which time nesting colonies dispersed and no more submissions were received. Risk to susceptible populations of both wild avian species and domestic poultry makes early recognition and confirmation of NVND in wild birds a priority.

Ictal cerebral blood flow in seizures originating in the posterolateral cortex

In selecting patients for epilepsy surgery, it is important to distinguish mesial temporal seizures from seizures originating in the posterolateral cortex. We studied ictal cerebral perfusion in five patients with complex partial seizures with clear posterior EEG ictal onsets and clinical seizures semiology suggesting seizure origin in the posterolateral cortex.

METHODS

Ictal SPECT was performed during video EEG monitoring using 99mTc-HMPAO as a cerebral perfusion tracer and a rotating gamma camera to acquire images.

RESULTS

Three patterns of ictal hyperperfusion were seen: pattern A = temporoparieto-occipital junction extending into the lateral temporal cortex, involving the mesial temporal cortex and basal ganglia to a lesser degree and a small area of hyperperfusion in the contralateral parietal cortex (two patients); pattern B = pattern A but with no hyperperfusion of the mesial temporal cortex (one patient); and pattern C = localized hyperperfusion in the area of the temporoparieto-occipital junction (two patients).

CONCLUSION

Our results suggest distinct patterns of ictal perfusion in seizures with posterolateral ictal EEG onsets. Ictal SPECT may be useful in distinguishing such seizures.

Avian reovirus-induced syncytium formation is independent of infectious progeny virus production and enhances the rate, but is not essential, for virus-induced cytopathology and virus egress

The nonenveloped avian reoviruses represent a distinct antigenic subgroup of orthoreoviruses. Unlike their mammalian counterparts, the avian reoviruses exhibit the unusual property of inducing rapid and extensive syncytium formation in cell cultures, a cytopathic effect more commonly associated with enveloped virus replication. While the syncytium-inducing capability of avian reovirus has been known for quite some time, the relationship between cell fusion and the virus replication cycle has not been determined. The conservation of the syncytial phenotype among all field isolates of avian reovirus suggests that avian reovirus-induced syncytium formation either reflects an essential step in the virus replication cycle involving intracellular membrane interactions or that cell fusion contributes to enhanced virus replication in infected animals. In order to distinguish between these possibilities, we have examined several aspects of virus replication in the presence of inhibitors of syncytium formation. Inhibitors of intracellular vesicle transport and O-linked glycosylation eliminated or markedly reduced syncytium formation with little effect on the rate or extent of virus macromolecular synthesis and infectious progeny virus production. Moreover, syncytium formation was not required for virus-induced cytopathology or virus egress but did significantly enhance the rate of both of these processes. The data indicate that, unlike the syncytium-inducing enveloped viruses, the membrane interactions and protein trafficking required for avian reovirus-induced syncytium formation do not reflect the sequelae of an essential step in the virus replication cycle. These results suggest that the conservation of the avian reovirus syncytial phenotype may reflect a fortuitous aspect of virus replication which confers advantages associated with the rapid spread of the virus within an infected host.

Autoantigens interact with cis-acting elements of rubella virus RNA

Rubella virus (RV) infections in adult women can be associated with acute and chronic arthritic symptoms. In many autoimmune individuals, antibodies are found targeting endogenous proteins, called autoantigens, contained in ribonucleoprotein complexes (RNPs). In order to understand the molecular mechanisms involved in the RV-associated pathology, we investigated the nature of cellular factors binding RV RNA and whether such RNPs were recognized by antibodies in infected individuals. Previously, we noted that cellular proteins associated with the RV 5'(+) stem-loop (SL) RNA are recognized by serum with Ro reactivity. To better understand the nature of the autoantigens binding RV cis-acting elements, serum samples from individuals with various autoimmune diseases were tested for their ability to immunoprecipitate RNPs containing labeled RV RNAs. A subset of serum samples recognizing autoantigen La, or Ro and La, immunoprecipitated both the RV 5'(+)SL and 3'(+)SL RNA-protein complexes. Autoantigens binding the RV 5'(+)SL and 3'(+)SL RNAs differed in molecular mass, specificities for respective RNA binding substrates, and sensitivity to alkaline phosphatase treatment. The La autoantigen was found to interact with the RV 5'(+)SL RNA as determined by immunological techniques and binding reactions with mixtures containing recombinant La protein. To test whether there is a correlation between La binding to an RV RNA element and the appearance of an anti-La response, we measured anti-La titers in RV-infected individuals. Significant anti-La activity was detected in approximately one-third of RV-infected individuals 2 years postinfection.

The low pH-dependent entry of avian reovirus is accompanied by two specific cleavages of the major outer capsid protein mu 2C

Avian reoviruses are capable of inducing rapid and extensive syncytium formation, a process that occurs preferentially under conditions of neutral or alkaline pH. In order to ascertain whether the membrane fusion-inducing capability of avian reovirus confers a pH-independent entry mechanism on the virus, virus entry was investigated using internalization assays and several lysomotropic agents that inhibit endosomal acidification. The ability of avian reovirus to infect cells was severely restricted under all conditions that prevented endosomal acidification. The decreased infection efficiency in the presence of the lysomotropic agents correlated with an inhibition in the proteolytic processing of the major outer capsid protein mu 2C. The importance, with respect to virus infection, of the low pH-dependent cleavage of the avian reovirus mu 2C protein was confirmed by demonstrating that infectious subviral particles, generated by proteolytic processing in vitro, were capable of efficiently infecting cells in the presence of the lysomotropic agents. These results indicated that avian reovirus entry-specific membrane interactions are largely dependent on an endosome-mediated proteolytic processing of the virus particle, suggesting that the syncytium-inducing properly of the sigma 3 protein is not sufficient to promote virus uptake. Furthermore, avian reovirus internalization was associated with two distinct cleavages of the major outer capsid protein mu 2C, unlike the entry-specific processing of the analagous mammalian reovirus major outer capsid protein mu 1C. The mu 2C cleavages occured sequentially and appeared to involve distinct cleavage specificities. Moreover, the second cleavage event was observed to be both virus strain- and cell type-independent, suggesting that the cleavage is both specific and biologically significant.

A unique transactivation sequence motif is found in the carboxyl-terminal domain of the single-strand-binding protein FBP

The far-upstream element-binding protein (FBP) is one of several recently described factors which bind to a single strand of DNA in the 5' region of the c-myc gene. Although cotransfection of FBP increases expression from a far-upstream element-bearing c-myc promoter reporter, the mechanism of this stimulation is heretofore unknown. Can a single-strand-binding protein function as a classical transactivator, or are these proteins restricted to stabilizing or altering the conformation of DNA in an architectural role? Using chimeric GAL4-FBP fusion proteins we have shown that the carboxyl-terminal region (residues 448 to 644) is a potent transcriptional activation domain. This region contains three copies of a unique amino acid sequence motif containing tyrosine diads. Analysis of deletion mutants demonstrated that a single tyrosine motif alone (residues 609 to 644) was capable of activating transcription. The activation property of the C-terminal domain is repressed by the N-terminal 107 amino acids of FBP. These results show that FBP contains a transactivation domain which can function alone, suggesting that FBP contributes directly to c-myc transcription while bound to a single-strand site. Furthermore, activation is mediated by a new motif which can be negatively regulated by a repression domain of FBP.

C-terminal trimerization, but not N-terminal trimerization, of the reovirus cell attachment protein Is a posttranslational and Hsp70/ATP-dependent process

The C-terminal globular head of the lollipop-shaped final sigma1 protein of reovirus is responsible for interaction with the host cell receptor. Like the N-terminal fibrous tail, it has its own trimerization domain. Whereas N-terminal trimerization (formation of a triple alpha-helical coiled coil) occurs at the level of polysomes (i.e. cotranslationally) and is ATP-independent, C-terminal trimerization is a posttranslational event that requires ATP. Coprecipitation experiments using anti-Hsp70 antibodies and truncated final sigma1 proteins synthesized in vitro revealed that only regions downstream of the N-terminal alpha-helical coiled coil were associated with Hsp70. Hsp70 was also found to be associated with nascent final sigma1 chains on polysomes as well as with immature postribosomal final sigma1 trimers (hydra-like intermediates with assembled N termini and unassembled C termini). These latter structures were true intermediates in the final sigma1 biogenetic pathway since they could be chased into mature final sigma1 trimers with the release of Hsp70. Thus, unlike N-terminal trimerization, C-terminal trimerization is Hsp70- and ATP-dependent. The involvement of two mechanistically distinct oligomerization events for the same molecule, one cotranslational and one posttranslational, may represent a common approach to the generation of oligomeric proteins in the cytosol.

HMPAO as a regional cerebral blood flow tracer at high flow levels

HMPAO is being used extensively to image rCBF during focal seizures in humans. It is, however, theoretically possible that back-diffusion of tracer causes retention to fall as flow rises at high levels.

METHODS

We used a double label 99mTc-HMPAO/14C-IAP autoradiographic technique to compare HMPAO retention and regional cerebral blood flow in penicillin induced focal seizures in rats.

RESULTS

Using this protocol, flows of up to 717 ml/100 g per min were observed. The same pattern of uptake was seen on IAP and HMPAO autoradiographs, with the exception of relatively high HMPAO uptake in the choroid plexus, in the fissures and, in one animal only, the supramammilary nucleus. Correlation of HMPAO retention and blood flow showed a linear relationship up to 200 ml/100 g per min all animals. HMPAO retention then showed a falloff in its rise with blood flow, but was still increasing, even at the highest flows seen. At 700 ml/100 g/min, HMPAO retention was 20% of that expected from a linear relationship.

CONCLUSION

HMPAO is a suitable tracer of rCBF at high flows and is unlikely to produce anomalous images in human focal seizures.

Interictal temporal hypoperfusion is related to early-onset temporal lobe epilepsy

Previous studies of interictal regional cerebral blood flow (rCBF) in temporal lobe epilepsy have shown variable correlations with clinical measures. We used high spatial resolution hexamethyl propyleneamine oxime single photon emission computed tomography (HMPAO SPECT) in 80 consecutive patients with complex partial seizures (CPS), comparing results with those from a large series of normal subjects. Visual image analysis detected abnormalities of rCBF in 41 of 80 (51%; numeric analysis detected abnormalities in 38 of 80). Age at epilepsy onset was significantly younger in patients with temporal hypoperfusion (p = 0.002), and the frequency distribution of hypoperfusion versus age at epilepsy onset was reverse exponential. The results of numerical image analysis showed that degree of hypoperfusion did not vary with age at epilepsy onset. These data suggest a single insult operating early in life as a cause of temporal hypoperfusion, as has been shown for mesial temporal sclerosis (MTS). We could not demonstrate relationships with other clinical variables, including time since last seizure.

Gamma scintigraphy of the biodistribution of 123I-labelled N-(2-hydroxypropyl)methacrylamide copolymer-doxorubicin conjugates in mice with transplanted melanoma and mammary carcinoma

An N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin conjugate is currently under clinical evaluation as a new antitumour agent. It has been shown previously that such conjugates exhibit selective tumour accumulation. In this study HPMA copolymer doxorubicin conjugates of low (LMW) or high (HMW) molecular weight were synthesised (which had a weight average molecular weight (Mw) of 25,000 and 94,000 respectively) and additionally contained a small amount (1 mol%) of the comonomer methacryloyltyrosinamide to permit labelling with [123I or 125I]iodide. Gamma camera imaging using the 123I-labelled probes was used to follow time-dependent biodistribution after intraperitoneal (i.p.) or intravenous (i.v.) administration to mice bearing subcutaneously either B16F10 melanoma or a mammary carcinoma. Imaging showed more rapid clearance of LMW conjugate from the peritoneal cavity than HMW conjugate. The images of mice given the LMW conjugate revealed rapid urinary excretion of radioactivity after both i.p. and i.v. injection with an early high concentration of tracer in the bladder, and subsequently a very high concentration in the kidneys, which came to dominate the views. Dissection analysis 2 days after administration of the LMW conjugate revealed a kidney level of radioactivity corresponding to 25-40% dose/g tissue in mice bearing the two tumour models. Following administration of the HMW conjugate kidney accumulation at 2 days was less due to retention of the higher molecular weight polymer molecules in the circulation, and spleen and liver displayed the highest concentrations of radioactivity. The tumour accumulation of LMW and HMW conjugates was; mammary carcinoma 3.18 and 5.29% dose/g respectively; B16F10 melanoma 3.23 and 8.82 %dose/g although these levels of tracer enabled visualisation in the images of the mammary carcinoma with HMW conjugate at later time points. The smaller size of the B16F10 tumour masses did not permit clear visualisation.

Gamma scintigraphy of a 123I-labelled N-(2-hydroxypropyl)methacrylamide copolymer-doxorubicin conjugate containing galactosamine following intravenous administration to nude mice bearing hepatic human colon carcinoma

Polymer drug conjugates composed of N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymer covalently bound doxorubicin, and containing additionally galactosamine to facilitate hepatocyte-specific targeting (HPMA copolymer-dox-gal), were synthesised to contain a small amount (approximately 1 mol%) of the monomer methacryloyltyrosinamide to permit radioiodination with [123I]iodide. After intravenous administration to both normal mice and nude mice bearing hepatic human colon carcinoma, the biodistribution of the conjugate was monitored using the gamma camera, and also by dissection analysis. Efficient liver accumulation of HPMA copolymer-dox-gal was seen in the gamma camera images within 20 min, both in normal and tumour-bearing animals. Quantitatively liver uptake was approximately 40% dose administered/g liver. Images of the tumour-bearing animals showed clearly a much lower accumulation of HPMA copolymer-dox-gal in the colon carcinoma deposits within the liver (3-9% dose/g tumour), and this lack of uptake was verified by ex vivo imaging of the tumour-containing liver and also by dissection analysis. It can be concluded that 123I-labelled HPMA copolymer conjugates offer great potential as effective imaging agents and can be used for future non-invasive clinical studies. This nuclear imaging method will enable optimisation of the dosing schedule by identification of doses of HPMA copolymer-dox-gal that display receptor saturation (and hence diminished targeting efficiency). In addition this conjugate can provide negative images of liver-associated tumour deposits that do not express the asialoglycoprotein receptor.

Characterization of a novel syncytium-inducing baboon reovirus

A syncytium-inducing reovirus was recently isolated from brain homogenates of a baboon suffering from acute, progressive meningoencephalo myelitis. This baboon reovirus (BRV) was classified as a member of the genus Orthoreovirus, family Reoviridae, on the basis of the characteristic capsid morphology and genome and protein profiles. We have assessed the relationship between BRV and the other syncytium-inducing reoviruses in order to determine whether the emergence of this virus represents a host range or pathogenic alteration in a previously described isolate or the appearance of a novel entity. BRV was compared to representative members of the prototype mammalian reoviruses, avian reoviruses, and Nelson Bay virus on the basis of electropherotype, protein profile, and antigenic similarity as measured by immunoprecipitation using homologous and heterologous antisera. In spite of similarities between the genome and protein profiles of BRV and the other orthoreoviruses, migration-rate polymorphisms indicate that BRV has diverged extensively from the previously described syncytium-inducing orthoreoviruses. Most importantly, the limited epitope conservation suggests that BRV has existed in genetic isolation from other reoviruses for quite some time. We conclude that BRV represents a novel syncytium-inducing mammalian reovirus, which is of particular interest in view of its association with disease in nonhuman primates during natural infections and its unusual syncytial phenotype.

Effect of dietary salt restriction on renal sensitivity to vasopressin in man

1. We have previously described a progressive antidiuresis in response to low-dose vasopressin infusion during salt restriction in man, despite stable or even declining plasma vasopressin concentration. In the present study we examine the hypothesis that renal sensitivity to the antidiuretic effect of arginine vasopressin may be enhanced by salt restriction. 2. Extremely low-dose infusions of arginine vasopressin were given to normal subjects after equilibration to high (260 mmol/day) and low (20 mmol/day) sodium intakes. 3. Salt restriction increased the antidiuretic effect of arginine vasopressin (2 fmol min-1 kg-1 arginine vasopressin increased urine osmolality from 67.8 +/- 2.6 to 196.3 +/- 35.7 mosmol/l in the high-salt study and from 268.3 +/- 49 mosmol/l in the low-salt study; P < 0.05 between sodium intakes). Glomerular filtration rate, estimated from inulin clearance, was unchanged during arginine vasopressin infusion irrespective of salt intake (high salt 116.5 +/- 9.4 to 118.9 +/- 6.4 ml/min; low salt, 135.1 +/- 9.2 to 111.2 +/- 12.4 ml/min). Renal plasma flow, estimated from para-aminohippurate clearance, fell further during infusion of 2 fmol min-1 kg-1 arginine vasopressin in the low-salt study than in the high-salt study (low salt, from 555.7 +/- 22.7 to 298.3 +/- 27.6 ml/min; high salt, from 544.5 +/- 30.2 to 452.9 +/- 28.9 ml/min; P < 0.05 between sodium intakes).(ABSTRACT TRUNCATED AT 250 WORDS)

The chemotherapy of colon cancer

Despite extensive clinical trials, mortality from colon cancer has remained essentially unchanged since the 1950s. However, the increasing numbers of complete and partial responses seen in clinical trials suggest that colon cancer can be successfully treated by chemotherapy, but only if the antitumour selectivity can be increased by a substantial amount. This will be possible by the introduction of new drugs with more precise mechanisms of action, such as those acting specifically on signalling or cell cycle control pathways shown to be aberrant in colon cancer. Alternatively, the selectivity of present day agents may be increased considerably by the selective activation of prodrugs in tumours (ADEPT) or by targeting them to tumours using polymers. Other new approaches using vaccines or some form of gene therapy will potentiate present chemotherapy, while the introduction of positron emission tomography (PET) scanning will allow the rapid detection of agents with activity that would have been missed by conventional measurements of response.