Search PubMed⌕ Search

Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 415 records · Page 23Linked to original sources
PubMed1994

TP53 gene mutations and p53 protein immunoreactivity in malignant and premalignant Barrett's esophagus.

BACKGROUND/AIMS: Limited data are available regarding TP53 gene alterations in Barrett's esophagus. This study was undertaken to characterize TP53 mutations and p53 protein immunoreactivity in cancers and preinvasive lesions of Barrett's esophageal mucosa. METHODS: Seventeen Barrett's adenocarcinomas were examined by polymerase chain reaction amplification, denaturant gradient gel electrophoresis, and sequencing for the presence of TP53 mutations in exons 5-8. In 9 cases, Barrett's epithelium adjacent to the cancer was investigated. p53 protein immunoreactivity was studied with PAb 1801. RESULTS: Sixteen mutations were found in 15 adenocarcinomas, including 10 missense, 3 nonsense, 1 frameshift, and 2 mutations located within consensus splice donor and acceptor sequences. All nucleotide substitutions were transitions. Eight of the 12 transitions involving a GC base pair occurred within the context of a CpG dinucleotide. p53 immunostaining was present in all 10 cases with missense mutations and in 1 case without a detectable mutation. The surrounding Barrett's mucosa showed TP53 mutations identical to that observed in the carcinoma in only 3 of 5 specimens showing high-grade dysplasia. CONCLUSIONS: TP53 gene mutations and p53 protein immunostaining are present in a majority of Barrett's adenocarcinomas. Our results suggest that these mutations are involved at an early stage during malignant transformation of Barrett's esophagus.

Adenocarcinoma↗
PubMed1994

Interphase molecular cytogenetics of Ewing's sarcoma and peripheral neuroepithelioma t(11;22) with flanking and overlapping cosmid probes.

The translocation, t(11;22)(q24;q12), recurrently observed in Ewing's sarcoma and in peripheral neuroepithelioma has been recently cloned. The analysis of a series of ES/PNE has revealed that the chromosome 22 breakpoints are clustered in a small region of 7 kb, called EWSR1, and that those on chromosome 11 are spread over a larger region of 40-50 kb, called EWSR2. Cosmids from loci flanking or overlapping these two regions have been obtained. We demonstrate here that fluorescence in situ hybridization (FISH) with these cosmids allows the localization of the two breakpoints with a 10-kb resolution and leads to a rapid and reliable ES/PNE diagnosis.

Cell Line↗
PubMed1994

Experience of the early use of technetium 99 bone scintigraphy in wrist injury.

In a retrospective study, patients with suspected scaphoid fracture had an average of three sets of scaphoid radiographs prior to scintigraphy. Scans were performed an average of 3 months after injury and many were inconclusive because of disuse changes. A prospective analysis of early scintigraphy in 35 cases over 18 months was carried out. Scans were performed at an average of 15.5 days after injury in selected cases. Patients had an average of 1.28 sets of negative radiographs prior to scanning. There were no false negative scans and in 13 with focal uptake a wrist fracture was demonstrated. Diffuse uptake was thought to be indicative of ligamentous damage or reflex sympathetic dystrophy. Early scintigraphy was found to be a sensitive, reliable and cost-effective examination in cases of suspected significant wrist injury.

Adolescent↗
PubMed1994

Association of p53 mutations with short survival in colorectal cancer.

BACKGROUND/AIMS: Mutations in p53, a tumor suppressor gene located on chromosome 17p, are the most frequent genetic alterations found in human cancers. Increased intracellular concentration of p53, which is frequently but not systematically related to p53 mutation, has been proposed to be associated with poor prognosis in some tumor types. In colorectal cancer, this significance is still a matter of debate. To directly investigate the relationship between prognosis and p53 mutation, this study screened a series of 85 colorectal carcinomas for mutations in exons 5-8 of this gene. METHODS: Polymerase chain reaction-amplified products from tumor DNA were analyzed by denaturing gradient gel electrophoresis and direct DNA sequencing. RESULTS: Forty-four tumors were found to be mutated (52%). A strong correlation between the presence of a mutation and short survival was observed (P = 0.003). When tumors were classified according to their histological stage, a multivariate Cox model analysis showed that p53 mutation, rather than 17p allelic loss (previously proposed to convey prognostic information), was retained as the only independent prognostic factor (relative risk, 2.25; 95% confidence interval, 1.06-4.80; P < 0.029). CONCLUSIONS: Combined with staging, direct monitoring of p53 mutation improves prognostic accuracy for colorectal cancer.

Aged↗
PubMed1994

Evidence for the complete inactivation of the NF2 gene in the majority of sporadic meningiomas.

Meningiomas are common central nervous system tumours which present usually in the 4th and 5th decades of life. Loss of constitutional heterozygosity on chromosome 22 in 60% of sporadic meningiomas has implied the involvement of a tumour suppressor gene. The neurofibromatosis type 2 gene (NF2), a prime candidate for involvement in meningioma, was screened for point mutations. After examining eight of the 16 known NF2 exons in 151 meningiomas, 24 inactivating mutations were characterized. Significantly, these aberrations were exclusively detected in tumours which lost the other chromosome 22 allele. These results provide strong evidence that the suppressor gene on chromosome 22, frequently inactivated in meningioma, is the NF2 gene, and suggest that another gene is involved in the development of 40% of meningiomas.

Adult↗
PubMed1994

pp60c-src enhances the acetylcholine receptor-dependent catecholamine release in vaccinia virus-infected bovine adrenal chromaffin cells.

Secretion of catecholamines by adrenal chromaffin cells is a highly regulated process that involves serine/threonine and tyrosine phosphorylations. The nonreceptor tyrosine kinase pp60c-src is expressed at high levels and localized to plasma membranes and secretory vesicle membranes in these cells, suggesting an interaction of this enzyme with components of the secretory process. To test the hypothesis that pp60c-src is involved in exocytosis, we transiently expressed exogenous c-src cDNA using a vaccinia virus vector in primary cultures of bovine adrenomedullary chromaffin cells. Chromaffin cells infected with a c-src recombinant virus restored the diminished secretory activity accompanying infection by wild type virus alone or a control recombinant virus. The level of enhanced catecholamine release correlated directly with the time and level of exogenous c-src expression. These results could not be attributed to differences in cytopathic effects of wild type versus recombinant viruses as assessed by cell viability assays, nor to differences in norepinephrine uptake or basal release, suggesting that pp60c-src is involved in stimulus-secretion coupling in infected cells. Surprisingly, exogenous expression of an enzymatically inactive mutant c-src also restored catecholamine release, indicating that regions of the introduced c-src protein other than the kinase domain may affect catecholamine release. Secretory activity was elevated by both forms of c-src in response to either nicotine or carbachol (which activate the nicotinic and the nicotinic/muscarinic receptors, respectively). In contrast, release of catecholamines upon membrane depolarization (as elicited by 55 mM K+) or by treatment with the calcium ionophore A23187 was unaffected by either vaccinia infection or increased levels of pp60c-src. These results suggest that pp60c-src affects secretory processes in vaccinia-infected cells that are activated through ligand-gated, but not voltage-gated, ion channels.

Adrenal Glands↗
PubMed1994

The neurofibromatosis type 2 gene is inactivated in schwannomas.

Schwannomas are tumors arising from schwann cells surrounding peripheral nerves. Although most schwannomas are sporadic, they are seen in approximately 90% of individuals with neurofibromatosis type 2 (NF2), an autosomal dominantly inherited disease with an incidence of 1:40000 live births. The NF2 gene has recently been isolated on chromosome 22 and encodes a putative membrane organizing protein named schwannomin. It is believed to act as a tumor suppressor gene based on the high frequency of loss of heterozygosity (LOH) on this autosome in both sporadic and NF2 associated schwannomas and meningiomas and the identification of inactivating mutation in NF2 patients. In this study we examined 61 schwannomas including 48 sporadic schwannomas (46 of which are vestibular schwannomas) and 12 schwannomas obtained from NF2 patients, for mutations in 10 of the 16 coding exons of the NF2 gene. Twelve inactivating mutations were identified, 8 in sporadic tumours and 4 in tumors from people with NF2. These results support the hypothesis that loss of function of schwannomin is a frequent and fundamental event in the genesis of schwannomas.

Base Sequence↗
PubMed1994

Human alveolar macrophage mediated vasodilation and the role of arginine compounds.

To determine whether human alveolar macrophages (AM) generate a compound similar to the endothelium-derived relaxing factor, we studied the effect of AM on the isometric response of the pre-contracted rat aorta preparation in the presence and absence of L-arginine or N-substituted L-arginine compounds. Addition of AM to the pre-contracted aorta preparation was ineffective even in the presence of millimolar concentrations of L-arginine. But, AM in the presence of the substituted L-arginine, N alpha-benzoyl L-arginine ethyl ester, significantly increased vasodilation. The enhanced relaxation was associated with an increase in vascular cyclic guanosine 3,5'-monophosphate formation. Hemoglobin and N omega-nitro L-arginine methyl ester are inhibitors of the endothelium-dependent relaxation, and both attenuated the vasodilation elicited by AM. Human AM were found to metabolize N alpha-benzoyl L-arginine ethyl ester to a citrulline derivative. No such metabolism was observed with L-arginine. A specific, high-pressure liquid chromatographic assay for guanidines revealed that the lack of effect of external L-arginine is not due to the presence of an excess amount of endogenous L-arginine in AM. These results demonstrate that nonactivated human AM, unlike rodent macrophages, possess an enzyme system(s) that metabolize(s) arginine derivatives but not L-arginine to a vasodilator, and this vasodilator has properties similar to that of endothelium-derived relaxing factor. This human AM-derived vasodilator may have an important role in regulating airway smooth muscle function.

Adult↗
PubMed1994

Advances in the genetics and molecular biology of colorectal tumors.

Fascinating progress has been made in the past 2 years in our understanding of the genetic alterations associated with colorectal cancer predisposition and development. First, the genotype-phenotype relationship of the cancer susceptibility syndrome associated with familial adenomatous polyposis has been shown to depend on mutation type. Second, hereditary nonpolyposis colorectal cancer syndromes have been recognized as being frequently associated with a defect in the DNA mismatch-repair pathway. A gene on chromosome 2 called hMSH2, which demonstrates homology with the bacterial repair gene MutS, has been shown to be altered in some families with hereditary nonpolyposis colorectal cancer. A defect on chromosome 3 may act by impairing the same pathway. Genotyping of particular loci, termed microsatellite, provides an easy identification of tumors deficient in mismatch repair. Third, the mechanisms by which the inactivation of tumor-suppressor genes such as p53 and APC may contribute to the tumorigenic process have begun to be elucidated. These different discoveries will have important impacts in the prevention and management of colorectal carcinoma, one of the most frequent human cancers.

Adenomatous Polyposis Coli↗
PubMed1994

Muscle- and pneumatic-powered counterpulsating LVADs: a pilot study.

There is a worldwide interest in supporting the failing heart with a skeletal muscle by either wrapping it around the natural heart (dynamic cardiomyoplasty) or by constructing a skeletal muscle ventricle (SMV) used for counterpulsation. Conventional cardiomyoplasty in many clinics carries an operative mortality rate of 15-20% partly because it requires 6 weeks to train the muscle to contract continually. A flexible, pear-shaped blood pump with an inflatable air chamber was designed and made around which a muscle can be wrapped. The advantage of our design is that it can also be driven by pneumatic power, immediately supporting the circulation of a seriously ill patient while that patient is still on the operating table. After a period of time to allow for revascularization and the subsequent training of the muscle, the external pneumatic power can be gradually discontinued. Then the assisted patient becomes tether-free. If, at any time, the muscle power fails, the pneumatic-powered mechanism can be reactivated. In the preferred approach, the blood pump is connected to the aorta for diastolic counterpulsation. A muscle can either be wrapped around the blood pump directly, or around one of two separate muscle pouches connected to the blood pump. To facilitate surgery, a large pouch is inserted under the musculus latissimus dorsi, which is connected to a blood pump. When stimulated, the muscle will contract over the pouch compressing it and providing power to the blood pump. If it is found that the pressure generated in the pouch cannot meet the aortic blood pressure, it can be augmented by using a pressure amplifier.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Studies on the mechanism of spasmolytic activity of (O-methyl-)-N-(2,6-dihydroxybenzoyl)tyramine, a constituent of Aniba riparia (Nees) Mez. (Lauraceae), in rat uterus, rabbit aorta and guinea-pig alveolar leucocytes.

The mechanism of action of a nonspecific smooth muscle relaxant, (O-methyl-)-N-(2,6-dihydroxybenzoyl)tyramine (riparin), a constituent of Aniba riparia (Nees) Mez. (Lauraceae) was studied in relation to Ca2+ metabolism in smooth muscle tissues and in guinea-pig alveolar leucocytes. In rat depolarized uterus, riparin inhibited in a reversible and noncompetitive manner CaCl2-induced contraction, a response mediated through voltage-dependent Ca2+ channels. The pD2 value (mean +/- s.e.m.) for riparin was 4.98 +/- 0.06. When compared with sodium nitroprusside (IC50 2.5 microM), an antagonist of receptor-operated Ca2+ channels, riparin was ineffective in suppressing noradrenaline-induced sustained contractions of rabbit aortic strips. However, in the aorta, the compound inhibited intracellular calcium-dependent transient contractions of noradrenaline and riparin (IC50 10.1 microM) was approximately two and a half times more potent than procaine (IC50 25.5 microM) a known inhibitor. In guinea-pig alveolar leucocytes, riparin (IC50 3.2 microM) inhibited intracellular Ca2+ accumulation induced by the calcium ionophore A23187. The results suggest that the inhibition of Ca2+ influx and of Ca2+ release from intracellular stores contribute to the spasmolytic effects of riparin, which may not involve cyclic AMP generation as the levels of this nucleotide were not increased in alveolar macrophages treated with riparin (10-100 microM).

Animals↗
PubMed1994

Sequence specificity of furin, a proprotein-processing endoprotease, for the hemagglutinin of a virulent avian influenza virus.

The virulence of avian influenza viruses correlates with the sensitivity of their hemagglutinin (HA) to cellular proteases. Furin, a proprotein-processing subtilisin-related endoprotease, is a leading candidate for the enzyme that cleaves the HA of virulent avian viruses. We therefore compared the specificity of furin with those of proteases in a variety of cultured cells and in a rat Golgi fraction, using the HA cleavage mutants of a virulent avian influenza virus, A/Turkey/Ireland/1378/85 (H5N8). The results indicated similar sequence specificities among the endoproteases when purified furin was used. In experiments with the vaccinia virus expression system, overexpressed furin cleaved mutant HAs that were not recognized by the endogenous proteases, resulting in an apparent broader specificity of furin. These findings authenticate the proposed role of furin as an HA-activating protease in vivo and caution against the use of expression vectors to study protease sequence specificity.

Amino Acid Sequence↗
PubMed1994

DNA-binding and transcriptional activation properties of the EWS-FLI-1 fusion protein resulting from the t(11;22) translocation in Ewing sarcoma.

The 5' half of the EWS gene has recently been described to be fused to the 3' regions of genes encoding the DNA-binding domain of several transcriptional regulators, including ATF1, FLI-1, and ERG, in several human tumors. The most frequent occurrence of this situation results from the t(11;22)(q24;q12) chromosome translocation specific for Ewing sarcoma (ES) and related tumors which joins EWS sequences to the 3' half of FLI-1, which encodes a member of the Ets family of transcriptional regulators. We show here that this chimeric gene encodes an EWS-FLI-1 nuclear protein which binds DNA with the same sequence specificity as the wild-type parental FLI-1 protein. We further show that EWS-FLI-1 is an efficient sequence-specific transcriptional activator of model promoters containing FLI-1 (Ets)-binding sites, a property which is strictly dependent on the presence of its EWS domain. Comparison of the properties of the N-terminal activation domain of FLI-1 to those of the EWS domain of the fusion protein indicates that EWS-FLI-1 has altered transcriptional activation properties compared with FLI-1. These results suggest that EWS-FLI-1 contributes to the transformed phenotype of ES tumor cells by inducing the deregulated and/or unscheduled activation of genes normally responsive to FLI-1 or to other close members of the Ets family. ES and related tumors are characterized by an elevated level of c-myc expression. We show that EWS-FLI-1 is a transactivator of the c-myc promoter, suggesting that upregulation of c-myc expression is under control of EWS-FLI-1.

Amino Acid Sequence↗
PubMed1994

Stochastic modeling of the hypothalamic pulse generator activity.

Luteinizing hormone (LH) is released by the pituitary in discrete pulses. In the monkey, the appearance of LH pulses in the plasma is invariably associated with sharp increases (i.e, volleys) in the frequency of the hypothalamic pulse generator electrical activity, so that continuous monitoring of this activity by telemetry provides a unique means to study the temporal structure of the mechanism generating the pulses. To assess whether the times of occurrence and durations of previous volleys exert significant influence on the timing of the next volley, we used a class of periodic counting process models that specify the stochastic intensity of the process as the product of two factors: 1) a periodic baseline intensity and 2) a stochastic regression function with covariates representing the influence of the past. This approach allows the characterization of circadian modulation and memory range of the process underlying hypothalamic pulse generator activity, as illustrated by fitting the model to experimental data from two ovariectomized rhesus monkeys.

Animals↗
PubMed1994

Mapping of 18 probes on human chromosome 18 using single- and double-color FISH.

Fluorescence in situ hybridization (FISH) techniques were applied to the mapping of 18 probes from chromosome 18, permitting seven new assignments: D18S16 (18p11.31), D18S12 (18p11.1), D18S1 (18q12.2), D18S13 (18q21.31), D18S18 (18q21.31), D18S14 (18q21.33), and D18S17 (18q23). In addition, the localization of D18S3 in 18p11.3 was confirmed and that of D18S6, previously mapped in 18p11, was changed to 18q21.13. Finally, a more accurate mapping for nine probes was proposed: D18S7 (18q12.2), D18S10 (18q12.2), D18S24 (18q21.13), D18S8 (18q21.13), GRP (18q21.31), BCL2 (18q21.33), D18S5 (18q22.1), D18S19 (18q22.1), and D18S11 (18q22.3). The ordering of probes located in close proximity was made possible by combined use of single-color FISH with direct assignment on banded chromosomes, chromosomal length measurements, and double-color FISH.

Chromosome Mapping↗
PubMed1994

Cloning of the entire FLI1 gene, disrupted by the Ewing's sarcoma translocation breakpoint on 11q24, in a yeast artificial chromosome.

FLI1 (Friend leukemia virus integration 1), a member of the Ets gene family, is disrupted on 11q24 by the Ewing's Sarcoma (ES) and Peripheral Neuroepithelioma (PNE) t(11;22)(q24;q12) translocation. ES and PNE are Primitive Neuroectodermal Tumors (PNETs) and the consistent translocation t(11;22)(q24;q12) can be used for differential diagnosis. In PNETs the 3' part of human FLI1 is translocated from 11q24 to 22q12, where it is juxtaposed to the 5' end of the Ewing's Sarcoma gene (EWS). A fusion transcript, resulting in a chimeric protein, is generated. Here, we present the isolation and detailed characterization of a 250-kb colinear YAC, B45C11, which encompasses the ES and PNE breakpoint on 11q24, as shown by FISSH on ES and PNE chromosomes and interphase nuclei. This YAC represents a new reagent for potential use in rapid differential diagnosis by FISSH on tumor biopsies and on paraffin embedded samples, particularly when DNA and/or RNA are not available for molecular analysis. YAC B45C11, which spans 250 kb of contiguous DNA around the ES and PNE breakpoint, contains the entire FLI1 gene. Three potential HpaII-tiny-fragment (HTF) islands are revealed within the YAC. One of these islands appears to be associated with the 5' end of FLI1, which extends over approximately 120 kb of DNA on 11q24. In addition, we demonstrate that YAC B45C11 contains other transcribed sequences in addition to FLI1, by "cross-species" Northern blot hybridizations, which suggests the presence of additional genes in the immediate vicinity of the ES breakpoint on 11q24.

Base Sequence↗