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Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 127 records · Page 7Linked to original sources
PubMed2000

Lack of somatic mutation in the coding sequence of SIAH1 in tumors hemizygous for this candidate tumor suppressor gene.

The human homolog of the Drosophila seven in absentia gene (SIAH1) may play an important role in apoptosis and tumor suppression. Transcription of SIAH1 is up-regulated in non-tumorigenic clonal populations of cells derived from 2 different tumorigenic parental cell lines. Intracellular SIAH1 mRNA concentration increases in intestinal cells as they migrate from the bottom of the crypt to the lumen, where they undergo apoptosis. Finally, SIAH1 is located on chromosome 16q12-q13, a region that is frequently deleted in a large variety of human tumors. These observations suggest SIAH1 as a candidate tumor suppressor gene that may be inactivated during tumorigenesis. To test this hypothesis, a search for mutation in the coding sequence of this gene was initiated in tumors exhibiting loss of heterozygosity (LOH) at 16q12-q13. No difference was found in 12 hepatocellular carcinomas, 19 breast carcinomas, 9 prostate carcinomas, 7 colon carcinomas and 5 human cell lines derived from colon cancer. One silent sequence variant (C to T transition at amino acid 270) was observed in the FET colon carcinoma cell line. It was subsequently found once in a group of 100 unrelated individuals from the CEPH families. A rapid real-time quantitative RT-PCR fluorescent method shows that SIAH1 remained transcriptionally active in the 6 colon cancer-derived cell lines, and the expression is comparable to the normal colon tissue. Taken together, these observations suggest that although many tumors may have lost one SIAH1 allele, the second allele would not be the site of frequent somatic mutations and may even remain functional.

Alleles↗
PubMed2000

The human T-cell transcription factor-4 gene: structure, extensive characterization of alternative splicings, and mutational analysis in colorectal cancer cell lines.

The human T cell transcription factor-4 (hTCF-4) interacts functionally with beta-catenin in the Wnt signaling pathway, which regulates many developmental processes. Moreover, inappropriate reactivation of this pathway attributable to APC or beta-catenin mutations has been described in colorectal cancers. Because only the human TCF-4 cDNA sequence was known, we determined its genomic structure. A total of 17 exons, of which 5 were alternative, were identified. Moreover, four alternative splice sites were observed either experimentally or in silico by a BLAST approach in expressed sequence tag databases. The alternative use of three consecutive exons localized in the 3' part of the hTCF-4 gene changes the reading frames used in the last exon, leading to the synthesis of a number of hTCF-4 isoforms with short, medium, or long-size COOH-terminal ends. We next screened the entire hTCF-4 gene for mutations in a series of 24 colorectal cancer cell lines by denaturing gradient gel electrophoresis and/or direct sequencing. Besides an already described deletion of an A in an (A)9 coding repeat in four cases, we found DNA variants in eight cases for a total of 12 variants, of which 8 were coding. These include one frameshift mutation in the beta-catenin binding domain (exon 1), and one missense mutation in exon 4. In the remaining six cases, nonsense or frameshift mutations were localized in the 3' part of the gene. These latter alterations have as a common consequence to decrease the proportion of the long COOH-terminal hTCF-4 isoform, which contains two binding domains for c-terminal binding protein, a protein implicated in the repression of the TCF family transcriptional activity. Thus, loss of the TCF-4 capacity to interact with COOH-terminal binding protein could be an important event during colorectal carcinogenesis by modifying Wnt signaling.

Alternative Splicing↗
PubMed2000

Conditional biallelic Nf2 mutation in the mouse promotes manifestations of human neurofibromatosis type 2.

Hemizygosity for the NF2 gene in humans causes a syndromic susceptibility to schwannoma development. However, Nf2 hemizygous mice do not develop schwannomas but mainly osteosarcomas. In the tumors of both species, the second Nf2 allele is inactivated. We report that conditional homozygous Nf2 knockout mice with Cre-mediated excision of Nf2 exon 2 in Schwann cells showed characteristics of neurofibromatosis type 2. These included schwannomas, Schwann cell hyperplasia, cataract, and osseous metaplasia. Thus, the tumor suppressor function of Nf2, here revealed in murine Schwann cells, was concealed in hemizygous Nf2 mice because of insufficient rate of second allele inactivation in this cell compartment. The finding of this conserved function documents the relevance of the present approach to model the human disease.

Alleles↗
PubMed2000

Proliferation, but not growth, blocked by conditional deletion of 40S ribosomal protein S6.

Because ribosome biogenesis plays an essential role in cell proliferation, control mechanisms may have evolved to recognize lesions in this critical anabolic process. To test this possibility, we conditionally deleted the gene encoding 40S ribosomal protein S6 in the liver of adult mice. Unexpectedly, livers from fasted animals deficient in S6 grew in response to nutrients even though biogenesis of 40S ribosomes was abolished. However, liver cells failed to proliferate or induce cyclin E expression after partial hepatectomy, despite formation of active cyclin D-CDK4 complexes. These results imply that abrogation of 40S ribosome biogenesis may induce a checkpoint control that prevents cell cycle progression.

Animals↗
PubMed2000

Effect of geological processes on coal quality and utilization potential: review with examples from western Canada.

This review article compares the elemental and radionuclide concentrations in coals from western Canada, the vast majority of which are used for power generation in Alberta. The coals range in age from lower Cretaceous to middle Eocene, and in rank from subbituminous to high volatile bituminous. Some of the coals were deposited in deltaic lagoonal to marine settings while others formed under lacustrine conditions in intermontane graben settings or in alluvial plains. The role of source rock (provenance), depositional environment, tectonic regime and hydrologic conditions on elemental concentration and distribution will be discussed, with specific examples from western Canada. In addition, the effect of natural weathering, igneous intrusion and self-burning (spontaneous combustion) on the enrichment and/or depletion of elements will be presented. The emphasis throughout this review article will be on the fate of elements of environmental concern and interest (e.g. As, Ba, B, Cl, Co, Cr, Cu, Mn, Mo, Se, Th, U, V and Zn) and of radionuclides of the U and Th series upon coal utilization. This article is also intended for those not familiar with the geological or environmental sciences, particularly as related to fossil fuel utilization.

Alberta↗
PubMed2000

Identification of insulin-induced sites of ribosomal protein S6 phosphorylation in Drosophila melanogaster.

Insulin treatment of Drosophila melanogaster Kc 167 cells induces the multiple phosphorylation of a Drosophila ribosomal protein, as judged by its decreased electrophoretic mobility on two-dimensional polyacrylamide gels. The extent to which insulin induces this response is potentiated by cycloheximide and blocked by pretreatment with rapamycin. Isolation and mass spectrometric analysis revealed that the multiply phosphorylated protein was the larger of two Drosophila melanogaster orthologues of mammalian 40S ribosomal protein S6, termed here DS6A. Proteolytic cleavage of DS6A derived from stimulated Kc 167 cells with the endoproteinase Lys-C released a number of peptides, one of which contained all the putative phosphorylation sites. Conversion of phosphoserines to dehydroalanines with Ba(OH)(2) showed that the sites of phosphorylation reside at the carboxy terminus of DS6A. The sites of phosphorylation were identified by Edman degradation after conversion of the phosphoserine residues to S-ethylcysteine as Ser(233), Ser(235), Ser(239), Ser(242), and Ser(245). Finally, phosphopeptide mapping of individual phosphoderivatives, isolated from two-dimensional polyacrylamide gels, indicated that DS6A phosphorylation, in analogy to mammalian S6 phosphorylation, appears to proceed in an ordered fashion. The importance of these observations in cell growth and development is discussed.

Amino Acid Sequence↗
PubMed2000

Estimation of the contact rate in a seasonal SEIR model: application to chickenpox incidence in France.

This work was an attempt at analysing the seasonal pattern of varicella epidemics in France by fitting a susceptibles-exposed-infectives-recovered (SEIR) model with a periodic contact rate function to weekly chickenpox incidence data collected over the period 1991 to 1996. The contact rate was assumed to be either a continuous, or a piecewise constant, periodic function. Both assumptions gave a reasonable fit to the data and yielded estimates of the incubation and infectious periods that were consistent with values derived on clinical or serological grounds. Seasonal fluctuation of the estimated contact rate function was likely to reflect the impact of school holidays on chickenpox diffusion among schoolchildren.

Adolescent↗
PubMed2000

The differential regulation of group II(A) and group V low molecular weight phospholipases A(2) in cultured rat astrocytes.

In astrocytes, cytokines stimulate the release of secretory phospholipase A(2) (sPLA(2)) activity and group II(A) sPLA(2) expression. This paper reports that two sPLA(2) isoforms, group II(A) and group V, are in fact expressed by astrocytes. Our studies showed that tumor necrosis factor alpha (TNFalpha) enhanced the mRNA of both isoforms, but the time courses of enhancement differed; group V was induced much faster than group II(A). Moreover, TNFalpha stimulated both the NF-kappaB and mitogen-activated protein (MAP) kinase (extracellular signal-regulated kinase, c-Jun NH(2)-terminal kinase, and p38 MAP kinase) signaling pathways in astrocytes. Interestingly, PI 3-kinase activity also was enhanced by TNFalpha, and NF-kappaB pathway was involved in mediating its effect. Specific inhibitors were used to show that both extracellular signal-regulated kinase and p38 MAP kinase may contribute to the effect of TNFalpha and that blocking phosphatidylinositol 3-kinase activity fully reversed the effect of TNFalpha. Furthermore, in astrocytes, TNFalpha-induced release of sPLA(2) activity was partially reversed by thyroid hormone and almost abolished by growth factors. This phenomenon was accompanied by a less marked increase in both group II(A) and group V sPLA(2) mRNA. In the presence of growth factors, the increase in group V mRNA was inhibited early and transiently, in contrast to what was observed with group II(A), which was more persistently inhibited. Although a transcriptional effect of thyroid hormone or growth factors in astrocytes cannot be definitively excluded, both types of factor interfered with sPLA(2) expression in a manner suggesting the existence of regulation of post-transcriptional events.

Animals↗
PubMed2000

Characterization of the sialidase molecular defects in sialidosis patients suggests the structural organization of the lysosomal multienzyme complex.

Sialidosis is an autosomal recessive disease caused by the genetic deficiency of lysosomal sialidase, which catalyzes the hydrolysis of sialoglycoconjugates. The disease is associated with progressive impaired vision, macular cherry-red spots and myoclonus (sialidosis type I) or with skeletal dysplasia, Hurler-like phenotype, dysostosis multiplex, mental retardation and hepatosplenomegaly (sialidosis type II). We have analyzed the genomic DNA from nine sialidosis patients of multiple ethnic origin in order to find mutations responsible for the enzyme deficiency. The activity of the identified variants was studied by transgenic expression. One patient had a frameshift mutation (G623delG deletion), which introduced a stop codon, truncating 113 amino acids. All others had missense mutations: G679G-->A (Gly227Arg), C893C-->T (Ala298Val), G203G-->T (Gly68Val), A544A-->G (Ser182Gly) C808C-->T (Leu270Phe) and G982G-->A (Gly328Ser). We have modeled the three-dimensional structure of sialidase based on the atomic coordinates of the homologous bacterial sialidases, located the positions of mutations and estimated their potential effect. This analysis showed that five mutations are clustered in one region on the surface of the sialidase molecule. These mutations dramatically reduce the enzyme activity and cause a rapid intralysosomal degradation of the expressed protein. We hypothesize that this region may be involved in the interface of sialidase binding with lysosomal cathepsin A and/or beta-galactosidase in their high-molecular-weight complex required for the expression of sialidase activity in the lysosome.

Adolescent↗
PubMed2000

Membrane-associated GAIP is a phosphoprotein and can be phosphorylated by clathrin-coated vesicles.

GAIP (G alpha interacting protein) is a member of the RGS (regulators of G protein signaling) family and accelerates the turnover of GTP bound to Galphai, Galphaq, and Galpha13. There are two pools of GAIP-a soluble and a membrane-anchored pool. The membrane-anchored pool is found on clathrin-coated vesicles (CCVs) and pits in rat liver and AtT-20 pituitary cells. By treatment of a GAIP-enriched rat liver fraction with alkaline phosphatase, we found that membrane-bound GAIP is phosphorylated. By immunoprecipitation carried out on [(32)P]orthophosphate-labeled AtT-20 pituitary cells stably expressing GAIP, (32)P-labeling was associated exclusively with the membrane pool of GAIP. Phosphoamino acid analysis revealed that phosphorylation of GAIP occurred largely on serine residues. Recombinant GAIP could be phosphorylated at its N terminus with purified casein kinase 2 (CK2). It could also be phosphorylated by isolated CCVs in vitro. Phosphorylation was Mn(2+)-dependent, using both purified CK2 and CCVs. Ser-24 was identified as one of the phosphorylation sites. Our results establish that GAIP is phosphorylated and that only the membrane pool is phosphorylated, suggesting that GAIP can be regulated by phosphorylation events taking place at the level of clathrin-coated pits and vesicles.

Animals↗
PubMed2000

Dehydroepiandrosterone (DHEA), DHEA sulfate, and aging: contribution of the DHEAge Study to a sociobiomedical issue.

The secretion and the blood levels of the adrenal steroid dehydroepiandrosterone (DHEA) and its sulfate ester (DHEAS) decrease profoundly with age, and the question is posed whether administration of the steroid to compensate for the decline counteracts defects associated with aging. The commercial availability of DHEA outside the regular pharmaceutical-medical network in the United States creates a real public health problem that may be resolved only by appropriate long-term clinical trials in elderly men and women. Two hundred and eighty healthy individuals (women and men 60-79 years old) were given DHEA, 50 mg, or placebo, orally, daily for a year in a double-blind, placebo-controlled study. No potentially harmful accumulation of DHEAS and active steroids was recorded. Besides the reestablishment of a "young" concentration of DHEAS, a small increase of testosterone and estradiol was noted, particularly in women, and may be involved in the significantly demonstrated physiological-clinical manifestations here reported. Bone turnover improved selectively in women >70 years old, as assessed by the dual-energy x-ray absorptiometry (DEXA) technique and the decrease of osteoclastic activity. A significant increase in most libido parameters was also found in these older women. Improvement of the skin status was observed, particularly in women, in terms of hydration, epidermal thickness, sebum production, and pigmentation. A number of biological indices confirmed the lack of harmful consequences of this 50 mg/day DHEA administration over one year, also indicating that this kind of replacement therapy normalized some effects of aging, but does not create "supermen/women" (doping).

Absorptiometry, Photon↗
PubMed2000

Molecular characterization of germline NF2 gene rearrangements.

Neurofibromatosis type 2 (NF2) is an autosomal dominant disease that causes a predisposition to nervous system tumors. Deleterious point mutations have been found in about 55% of NF2 patients, and large genomic deletions account for approximately 33% of NF2 gene alterations. The majority of these deletions are larger than 50 kb, with a breakpoint usually lying outside the NF2 gene. We identified two cases of intragenic deletion with loss of 1.5 and 40 kb, respectively. In both cases, one boundary of the deletion was located in or at the proximity of an SVA sequence in NF2 intron 4. No sequence identity longer than 5 bases and no signal of specific recombination have been evidenced on either side of the deletion breakpoints. These observations are compatible with a nonhomologous recombination being responsible for the genomic deletions. In a third case, a paracentric inversion of chromosome 22 was found. This chromosomal rearrangement breaks the NF2 gene in two parts and carries the first NF2 exon in a juxta-centromeric position. The variability in position of the deletions and the observation of a new chromosomal rearrangement in the NF2 gene underscore the importance of FISH analysis in the molecular diagnosis of NF2.

Base Sequence↗
PubMed2000

A protein-based therapeutic for human cytomegalovirus infection.

Current antiviral strategies target viral gene products. Although initially successful, their severe toxicity and susceptibility to circumvention by the generation of drug-resistant variants limit their usefulness. By contrast, the central role of the host cell serine endoprotease furin in the proteolytic activation of numerous pathogens points to the endoprotease as a strategic target for therapeutics. Herein, we show that the production of infectious human cytomegalovirus is dramatically reduced by exogenous addition of a bioengineered serpin, alpha(1)-PDX. This protein is a potent and selective furin inhibitor (K(i) = 0.6 nM) and is 10-fold more effective than currently used antiherpetic agents in cell-culture models. The requirement of furin for the processing of envelope glycoproteins from many pathogenic viruses and for the activation of several bacterial toxins suggests that selective inhibitors of furin have potential as broad-based anti-pathogens.

Blotting, Western↗
PubMed2000

Prostate stem cell antigen (PSCA) expression increases with high gleason score, advanced stage and bone metastasis in prostate cancer.

Prostate stem cell antigen (PSCA) is a recently defined homologue of the Thy-1/Ly-6 family of glycosylphosphatidylinositol (GPI)-anchored cell surface antigens. PSCA mRNA is expressed in the basal cells of normal prostate and in more than 80% of prostate cancers. The purpose of the present study was to examine PSCA protein expression in clinical specimens of human prostate cancer. Five monoclonal antibodies were raised against a PSCA-GST fusion protein and screened for their ability to recognize PSCA on the cell surface of human prostate cancer cells. Immunohistochemical analysis of PSCA expression was performed on paraffin-embedded sections from 25 normal tissues, 112 primary prostate cancers and nine prostate cancers metastatic to bone. The level of PSCA expression in prostate tumors was quantified and compared with expression in adjacent normal glands. The antibodies detect PSCA expression on the cell surface of normal and malignant prostate cells and distinguish three extracellular epitopes on PSCA. Prostate and transitional epithelium reacted strongly with PSCA. PSCA staining was also seen in placental trophoblasts, renal collecting ducts and neuroendocrine cells in the stomach and colon. All other normal tissues tested were negative. PSCA protein expression was identified in 105/112 (94%) primary prostate tumors and 9/9 (100%) bone metastases. The level of PSCA expression increased with higher Gleason score (P=0.016), higher tumor stage (P=0.010) and progression to androgen-independence (P=0. 021). Intense, homogeneous staining was seen in all nine bone metastases. PSCA is a cell surface protein with limited expression in extraprostatic normal tissues. PSCA expression correlates with tumor stage, grade and androgen independence and may have prognostic utility. Because expression on the surface of prostate cancer cells increases with tumor progression, PSCA may be a useful molecular target in advanced prostate cancer.

Antibodies, Monoclonal↗
PubMed2000

Early findings from a community-based, cluster-randomized, controlled oral cancer screening trial in Kerala, India. The Trivandrum Oral Cancer Screening Study Group.

BACKGROUND: Oral cancer satisfies the criteria for a suitable disease for screening, and oral visual inspection is a suitable test for oral cancer screening. The efficacy of screening in reducing mortality from oral cancer has not yet been evaluated. The authors describe a cluster-randomized, controlled oral cancer screening trial in southern India and its early results. METHODS: Apparently healthy subjects age 35 years or older in 13 clusters called panchayaths were randomized to either an intervention group (n = 7) or a control group (n = 6). Subjects in the intervention group will receive 3 rounds of screening consisting of oral visual inspection by trained health workers at 3-year intervals. The first round of screening was carried out between October 1995 and May 1998. Participants were visited in their homes and interviewed for sociodemographic details, tobacco-smoking and alcohol-drinking habits, and personal medical history. Those with tobacco or alcohol habits were advised to stop those habits. Subjects in the intervention group were offered screening, and those with lesions suggestive of oral leukoplakia, submucous fibrosis, or oral cancer were referred for examination by physicians. Confirmed leukoplakias were excised whenever possible, others were kept on follow-up, and those with confirmed oral cancers were referred for treatment. Data on oral cancer incidence, stage distribution, survival, and mortality in the study groups are obtained by record linkage with the Trivandrum population-based cancer registry and municipal death registration systems. RESULTS: There were 59,894 eligible subjects in the intervention group and 54,707 in the control group; 31.4% of the former group reported no tobacco or alcohol habits, compared with 44.1% of the latter. The distribution of age, education, occupation, income, and socioeconomic status were similar in the two groups. Of 3585 subjects in the intervention group referred, 52.4% were examined by physicians; 36 subjects with oral cancers and 1310 with oral precancers were diagnosed. Of the 63 oral cancers recorded in the cancer registry, 47 were in the intervention group and 16 were in the control group, yielding incidence rates of 56.1 and 20.3 per 100,000 person-years in the intervention and control groups, respectively. The program sensitivity for detection of oral cancer was 76.6% and the specificity 76.2%; the positive predictive value was 1.0% for oral cancer. In the intervention group, 72.3% of the cases were in Stages I-II, as opposed to 12.5% in the control group. The 3-year case fatality rates were 14.9% (7 of 47 patients) in the intervention group and 56.3% (9 of 16 patients) in the control group. CONCLUSIONS: Though compliance with referral for confirmatory examination in the first round was lower than the 70% anticipated, intermediate end points, such as stage at diagnosis and case fatality, indicate that the trial is making fairly satisfactory progress.

Adult↗
PubMed2000

Coamplification of prostate stem cell antigen (PSCA) and MYC in locally advanced prostate cancer.

Gain of sequences on chromosome arm 8q is a common feature of prostate cancer that may correlate with metastatic and androgen-independent progression. The target gene(s) for this gain is not known, although MYC is amplified in a subset of advanced tumors and is one potential candidate. Prostate stem cell antigen (PSCA) is a prostate-specific cell surface protein that maps to chromosome region 8q24.2 and is overexpressed in prostate cancer. Our aim in this study was to test the hypothesis that PSCA overexpression may result from overrepresentation of chromosome arm 8q. Twenty locally advanced prostate cancers were analyzed by dual-probe fluorescence in situ hybridization (FISH) for alterations of MYC and PSCA. Extra copies of MYC were found in 12/20 (60%) tumors, including 5 (25%) with simple gain (no increase in MYC copy number relative to the chromosome 8 centromere) and 7 (35%) with an additional increase (AI or overrepresentation) in MYC copy number relative to the centromere. In the five cases with simple gain of MYC, there was a concomitant gain of PSCA. PSCA was overrepresented in 5/7 (71%) cases with AI of MYC. Immunohistochemical staining of the 20 tumors with monoclonal antibodies specific for PSCA showed a high degree of correlation between PSCA gene overrepresentation and protein overexpression. Four of 5 tumors with AI of PSCA overexpressed PSCA protein, compared with only 2/15 tumors with a normal PSCA copy number or simple gain of PSCA (P = 0.014). These results demonstrate that PSCA is co-overrepresented with MYC in a majority of cases, but may not be a necessary part of the 8q amplicon. PSCA protein overexpression can result from AI of PSCA and might be useful as a cell surface marker on prostate cancer cells with 8q overrepresentation. Genes Chromosomes Cancer 27:95-103, 2000.

Antigens, Neoplasm↗