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Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 361 records · Page 20Linked to original sources
PubMed1995

Biphenotypic sarcomas with myogenic and neural differentiation express the Ewing's sarcoma EWS/FLI1 fusion gene.

Accurate diagnosis of primitive childhood sarcomas continues to be a formidable problem because these malignancies generally demonstrate very little morphological evidence of their tissue of origin. One of these tumor classes, the Ewing's sarcoma family of peripheral primitive neuroectodermal tumors (pPNETs), are thought to have a neural histogenesis based on evidence of neuroectodermal differentiation. Greater than 95% of pPNETs carry t(11;22) or t(21;22) chromosomal translocations which fuse the EWS gene from chromosome 22q12 in-frame with either FLI1 from chromosome 11q24 or ERG from chromosome 21q22. The pPNETs are considered to be histogenetically distinct from rhabdomyosarcomas, myogenic tumors lacking these EWS gene fusions and hypothesized to derive from immature skeletal muscle precursors. In the present study, we describe a unique set of childhood soft tissue sarcomas that show both neural and myogenic differentiation. These biphenotypic tumors express myogenic regulatory factors and muscle-specific antigens and also show neuroectodermal differentiation with ultrastructural evidence of neurosecretory granules and expression of neural-associated genes. Northern analysis and reverse transcriptase PCR reveal expression of EWS/FLI1 gene fusions in all biphenotypic sarcomas analyzed. Chimeric EWS/FLI1 transcripts and fusion proteins in these tumors are identical to those described for pPNETs. Our results provide evidence for a class of biphenotypic childhood sarcomas with myogenic and neural differentiation and suggest that these tumors may be related to the Ewing's sarcoma family of pPNETs.

Adolescent↗
PubMed1995

Analysis of the NF2 tumor-suppressor gene and of chromosome 22 deletions in gliomas.

Recurrent deletions of chromosome fragments observed in neoplasms are thought to participate in tumor development through the inactivation of tumor-suppressor genes. In gliomas, the most frequent deletions involve chromosome arms 9p, 10q, 17p, 19q and 22q. We have analysed deletions of chromosome 22 in gliomas by studying loss of heterozygosity (LOH) at 8 microsatellite loci. LOH for this chromosome fragment was observed in 17/70 (24%) cases, most of them encompassing the region which encodes the gene altered in neurofibromatosis 2 (NF2), an inherited disease which predisposes to tumors of the nervous system. To investigate the possible involvement of the NF2 tumor-suppressor gene in the tumorigenesis of gliomas, we searched for alterations in its genomic structure and in its mature transcript. Northern-blot and reverse transcriptase-PCR experiments showed that the NF2 transcript is expressed and does not demonstrate obvious structural alterations. Moreover, analysis, at the genomic level, of the 16 coding exons of the NF2 gene by denaturing gradient gel electrophoresis failed to detect any somatically acquired point mutations. Altogether, these data strongly suggest that, although gliomas demonstrate recurrent chromosome 22 deletions most frequently encompassing the NF2 region, the NF2 gene is not altered in these tumors.

Base Sequence↗
PubMed1995

Polymorphisms and probable lack of mutation in the WAF1-CIP1 gene in colorectal cancer.

WAF1/CIP1, a gene up-regulated by p53 encodes an inhibitor of cyclin-dependent kinases. Induction of WAF1/CIP1 in cells with intact p53 is believed to be instrumental in cell cycle arrest and apoptosis caused by DNA damage. In a model system, WAF1/CIP1 has been shown to have tumor suppressive activity. It is not known however whether WAF1/CIP1 is mutated in human primary tumors. Cells from colorectal cancer have been shown to acquire a series of genetic alterations, including frequent p53 mutations. Thus colorectal tumors, particularly those without identified p53 mutations, are good candidate to search for putative WAF1/CIP1 mutations. DNA extracted from 45 tumors, (including 28 tumors for which p53 mutations had previously been searched for and not found) were PCR amplified for exon 2 of WAF1/CIP1. A search for point mutations was performed in each amplified product using a denaturing gradient gel electrophoresis (DGGE) technique which enables the efficient screening of codons 9 to 139 (i.e. 80% of the WAF1/CIP1 coding sequence). Two different DNA variants were identified and shown to be present in constitutional DNAs of the corresponding patients. The first variant, a C to A transversion at codon 31, changes a serine for an arginine and was detected in eight tumors (18% of the cases). The second variant, detected in a single case (2%) is a silent A to T transversion at the third base of codon 91. DNA extracted from 70 unrelated members from the Centre d'Etude du Polymorphisme Humain (CEPH) was screened for these polymorphisms. The ser/arg polymorphism of codon 31 was detected in seven cases (10%) thus suggesting that it is not associated with a marked colorectal cancer predisposition. The polymorphism on codon 91 was not detected. Two additional variants (arginine to histidine at position 67 and threonine to methionine at position 80) were observed once each in the CEPH family members. Somatic mutation of the WAF1/CIP1 gene was not observed, indicating that, unless there are hot spots for mutations outside the screened region, this gene is not a frequent site of point mutation in colorectal cancer.

Base Sequence↗
PubMed1995

Internally quenched fluorogenic substrate for furin.

A new substrate for furin, Abz-Arg-Val-Lys-Arg-Gly-Leu-Ala-Tyr(NO2)-Asp-OH, has been synthesized and characterized. The peptide is an internally quenched fluorogenic substrate. The kinetic parameters are Km = 3.8 microM, kcat = 29.3 s-1, and kcat/KM = 7,710,000 M-1 s-1. The substrate is efficiently cleaved by furin; its kcat/KM value is over 2000-fold higher than that of the commonly used substrate Boc-Arg-Val-Arg-Arg-AMC.

Amino Acid Sequence↗
PubMed1995

Molecular analysis of genetic changes in ependymomas.

Ependymomas are glial cell-derived tumors. They are, in contrast to other gliomas (astrocytomas, oligodendrogliomas, and oligoastrocytomas), ill-defined with respect to the genes and chromosomal segments important in their tumorigenesis. In this study, we extensively screened 17 ependymomas for genetic changes characteristic of other gliomas. Allelic loss was detected on chromosome arm 22q in three tumors; on chromosome 10 in two tumors; on chromosome arm 17p in two tumors; and on chromosome arms 6q, 9p, 13q, and 19q, each in one tumor. No allelic losses were found on chromosome arms 1p and 16q. None of the tumors had EGFR gene amplification. In each case, the chromosomal segment affected by the deletion included the region known to harbor a tumor suppressor gene important in glioma tumorigenesis. We conclude that ependymomas resemble the other glial neoplasms with respect to type and location of the chromosomal changes involved. Given the relatively infrequent occurrence of these genetic changes, ependymomas should be considered genetically as low-grade gliomas.

Adolescent↗
PubMed1995

Clinical review of adult granulosa cell tumors of the ovary.

Granulosa cell tumors are uncommon neoplasms that are characterized by their long natural history and for their tendency to recur years after an apparent clinical cure. As such they are difficult tumors to study. In the majority of cases, the initial therapy is surgical although the extent of the necessary procedure remains controversial. The role for any adjuvant therapy after complete resection remains to be established. In patients with advanced disease, combination chemotherapy consisting of cisplatinum/vinblastine/bleomycin has the highest identified response rates. In patients with recurrent or metastatic disease therapy is palliative and has not yet been standardized. Treatments therefore need to be individualized.

Female↗
PubMed1995

Regulation of p70s6k/p85s6k and its role in the cell cycle.

Two to three-fold increases in the rate of protein synthesis are required both to enter the G1 phase of the cell cycle from G0 and to proceed to S phase in response to growth factors and mitogens. This increase is in part regulated via multiple phosphorylation of the 40S ribosomal protein S6 by the mitogen-stimulated p70s6k/p85s6k. At the protein synthesis level this event appears to be involved in specifically increasing the efficiency of translation of a family of essential mRNAs containing a polypyrimidine tract at their 5' transcriptional start site. The activation of p70s6k/p85s6k and maintenance of its activity throughout G1 is controlled via multiple phosphorylation events mediated by a complex signalling network acting on distinct sets of phosphorylation sites.

Animals↗
PubMed1995

Recurrent and novel LDL receptor gene mutations causing heterozygous familial hypercholesterolemia in La Habana.

The molecular basis of familial hypercholesterolemia (FH) in three families of Spanish descent from La Habana was investigated by the candidate gene approach. The Arg3500Gln mutation of apolipoprotein B-100 was not found. Identification of low density lipoprotein receptor (LDLR) gene haplotypes segregating with FH guided the characterisation of three point mutations by automated sequencing. One, a Val408-->Met missense mutation, a founder mutation in Afrikaner FH patients, was recurrent, being associated with a distinct DNA haplotype. The other two, Glu256-->Lys and Val776-->Met missense mutations, were novel and modified highly conserved residues. These mutations were absent in normolipidemic subjects and were associated in heterozygous carriers with twice the cholesterol levels observed in non-carriers. Noticeably, cardiovascular complications were rarely observed in older heterozygotes, even in those with the Afrikaner FH-2 mutation. These findings confirm the molecular heterogeneity of LDLR gene mutations causing FH and the variability of their expression across different populations.

Adolescent↗
PubMed1995

Family with neurofibromatosis type 2 and autosomal dominant hearing loss: identification of carriers of the mutated NF2 gene.

A family is presented in which neurofibromatosis type 2 (NF2) and autosomal dominant hearing loss segregate in an apparently independent way. The presence of the latter condition caused anxiety in all family members at risk for NF2 in whom hearing loss became apparent. Previously, we identified a G-->A transition in the donor splice site of exon 5 of the NF2 gene in a family member with proven NF2. As expected, the mutation was present in two other family members who fulfilled the diagnostic criteria for NF2. Four out of five family members at risk for NF2 developed hearing loss. Two of these had the G-->A transition. The mutation was absent in the two other individuals with hearing loss and in the fifth family member without hearing loss or other clinical symptoms. In this family, the identification of the underlying NF2 gene mutation excluded NF2 as the cause of hearing loss in two potential carriers of the mutated gene. On the other hand, it enabled the identification of two carriers of the NF2 gene mutation who did not fulfill the diagnostic criteria for NF2. They will have to be monitored very carefully for the development of NF2-associated tumors. The consistent association within this family of a relatively mild clinical phenotype with the NF2 mutation, supports earlier suggestions that intrafamilial variability is small in NF2.

Adult↗
PubMed1995

Excess of deletions of maternal origin in the DiGeorge/velo-cardio-facial syndromes. A study of 22 new patients and review of the literature.

We have determined the parental origin of the deleted chromosome 22 in 29 cases of DiGeorge syndrome (DGS) using a CA-repeat mapping within the commonly deleted region, and in one other case by using a chromosome 22 short arm heteromorphism. The CA-repeat was informative in 21 out of 29 families studied and the deleted chromosome was of maternal origin in 16 cases (72%). When these data are pooled with recent results from the literature, 24 de novo DGS, velo-cardio-facial syndrome (VCFS) and isolated conotruncal cardiac disease deletions are found to be of maternal origin and 8 of paternal origin, yielding a chi 2 of 8 with a probability level lower than 0.01. These data, and review of the literature on familial DGS/VCFS and isolated conotruncal cardiopathies suggest that there is a strong tendency for the 22q11.2 deletions to be of maternal origin.

Chromosome Deletion↗
PubMed1995

Genotyping of a patient homozygous for a rare apolipoprotein E1 [Gly127-->Asp; Arg158-->Cys] (Weisgraber allele).

We examined the apolipoprotein E polymorphism of an obese patient presenting non-insulin-dependent diabetes, hypertension and moderate lipid disturbances. The apolipoprotein E genotyping carried out from leukocyte DNA using PCR amplification and restriction enzyme digestion demonstrated homozygosity for the rare apoE1[Gly127-->Asp; Arg158--> Cys] (Weisgraber allele). The nucleotide change results in a glycine to aspartic acid substitution at amino acid 127 in the apolipoprotein E2.

Alleles↗
PubMed1995

A multiplex PCR assay for routine evaluation of deletion of the short arm of chromosome 1 in neuroblastoma.

Deletions of the short arm of chromosome 1 (1p) are frequent alterations in neuroblastoma. Although a consensus region of deletion has been mapped to chromosome subband 1p36, recent studies suggest that several distinct loci on this chromosome may be involved in neuroblastoma. Moreover, different patterns of deletion might be associated with different clinical and biological characteristics of the tumours. These findings emphasise the importance of assessing the localisation and the extent of the deletions in neuroblastoma. We developed a technique which allows analysis of loss of heterozygosity at multiple loci on 1p in a single step, making use of a multiplex PCR method. Primers specific for six microsatellite loci mapped in the different regions of interest on 1p were used for simultaneous amplification of DNA, and loss of heterozygosity was determined after separation of the alleles by denaturing polyacrylamide gel electrophoresis. This technique enables a simple analysis of the position and extent of 1p deletions, and can be used for routine evaluation of 1p status in neuroblastoma.

Chromosome Deletion↗
PubMed1995

Improving the acceptability of high-dose radiotherapy by reducing the duration of treatment: accelerated radiotherapy in high-grade glioma.

Radiotherapy, although clearly beneficial in patients with high-grade glioma, is largely palliative, and a protracted course of treatment may not be the most appropriate approach in the context of limited survival. We therefore assessed the feasibility, toxicity and survival results of a short accelerated radiotherapy regimen given twice daily over a period of 3 weeks. A total of 116 patients with high-grade glioma were treated with radiotherapy in a prospective study using an accelerated fractionation regimen. The total dose of 55 Gy was given in 32-36 fractions of 1.72-1.53 Gy, twice daily 5 days a week, with a minimum 6 h interval between fractions. Toxicity was assessed using Karnofsky performance status scale and in the later part of the study with the Barthel index. Survival data were compared with a control group treated with 60 Gy in 30 daily fractions in a previous MRC study, matched for known prognostic factors. The median survival of 116 patients treated with accelerated radiotherapy was 10 months. Survival comparison of accelerated patients with matched controls treated with conventional fractionation demonstrated a hazard ratio of 1.13 (95% confidence interval 0.85-1.51; P = 0.39). Early treatment toxicity was acceptable, with only seven patients developing transient decrease in performance status. The accelerated radiotherapy regimen was logistically feasible and acceptable to patients, carers and staff. Treatment time was reduced without apparent increase in early toxicity and there was no loss of survival benefit. The effectiveness and convenience of a short accelerated regimen makes this a suitable alternative to a 6 week course of radiotherapy in patients with high-grade glioma. However, a full randomised trial comparing conventional and accelerated radiotherapy may be required as proof of equivalence.

Actuarial Analysis↗
PubMed1995

Sensitive detection of occult Ewing's cells by the reverse transcriptase-polymerase chain reaction.

Recently, Ewing's tumours have been shown to carry specific hybrid transcripts resulting from the fusion of the EWS gene with FLI-1 or ERG genes. Based on the sensitivity and specificity of the detection of these alterations by the reverse transcriptase-polymerase chain reaction technique, we have developed an assay to search for small numbers of Ewing cells in various sites from patients with Ewing's tumour. This method enables the detection of fewer than one tumour cell per million blood mononuclear cells. A total of 28 primary sites and 51 peripheral samples from 36 patients were investigated. Tumour cells could be detected in 4/18 blood samples, 4/15 bone marrow aspirates and 2/18 peripheral stem cell harvests. EWS/FLI-1 and EWS/ERG transcripts being observed in eight and two cases respectively. The type of fusion transcript detected in peripheral site(s) was identical to that observed in the primary site. At diagnosis 5/16 patients (31%) demonstrated either circulating tumour cells or/and occult bone marrow metastasis. After induction therapy, tumour cells were detected in 3/21 patients. This highly sensitive method should be a relevant tool to allow a more accurate clinical assessment of the dissemination of Ewing's tumours.

Base Sequence↗
PubMed1995

Yangambin: a new naturally-occurring platelet-activating factor receptor antagonist: binding and in vitro functional studies.

The effects of the furofuran lignan yangambin on rabbit platelet aggregation and binding of [3H]-PAF to rabbit platelet plasma membranes were studied. Log concentration-response curves to PAF were obtained in the presence or absence of increasing concentrations of yangambin. This lignan dose-dependently inhibited PAF-induced platelet aggregation in platelet-rich plasma (PRP) and shifted PAF curves to the right without decreasing the maximal response. The Schild plot constructed from these data showed a slope of 1.17 and a pA2 of 6.45. Moreover, yangambin at 10(-5) M did not inhibit the platelet aggregation induced by ADP (5 x 10(-7) M), collagen (0.1 microgram ml-1), or thrombin (0.05 U ml-1). Biochemical studies showed that [3H]-PAF labelled in a saturable manner a single class of binding sites on platelet membranes with a Kd of 1.25 +/- 0.24 nM and a maximal binding capacity (Bmax) of 14.9 +/- 2.4 pmol mg protein-1. Both unlabelled PAF and yangambin competitively displaced [3H]-PAF binding with an IC50 of 1.54 +/- 0.37 nM and 1.93 +/- 0.53 microM, respectively. The incubation of rabbit blood neutrophils with yangambin at 10(-5) M did not prevent PAF-induced in vitro chemotaxis in conditions where the PAF antagonist SR 27417 at 10(-5) M abolished the phenomenon. These results indicate that yangambin is an antagonist that selectively blocks PAF receptors on platelets.

Animals↗
PubMed1995

Yangambin: a new naturally-occurring platelet-activating factor receptor antagonist: in vivo pharmacological studies.

The pharmacological profile of a novel specific platelet-activating factor (PAF) receptor antagonist-yangambin-isolated from the Brazilian plant Ocotea duckei Vattimo (Lauraceae), was investigated in the pentobarbitone-anaesthetized rabbit. The i.v. administration of PAF (0.03-3.0 microgram kg-1) induced marked but reversible hypotensive effects and mild reductions in the heart rate. Both effects are independent of the respiratory conditions imposed on the animals. Moreover, PAF (3.0 microgram kg-1, i.v.) induced a reversible decrease of the circulating levels of platelets and of polymorphonuclear leukocytes. Pretreatment with yangambin (10 and 20 mg kg-1, i.v.) dose-dependently attenuated PAF-induced cardiovascular changes and thrombocytopaenia. Nevertheless, the neutropenic leukopaenia elicited by PAF (3.0 microgram kg-1, i.v.) was not prevented by yangambin whereas the reference PAF antagonists WEB 2086 (2 mg kg-1, i.v.) and SR 27417 (1 mg kg-1, i.v.) significantly inhibited the phenomenon. The hypotensive effects of acetylcholine, histamine, and 5-hydroxytryptamine were not affected by prior administration of yangambin. It is concluded that yangambin is a selective antagonist of the cardiovascular effects of PAF which could be useful in pathological states characterized by abnormal PAF release, such as anaphylactic and septic shocks. Furthermore, yangambin might discriminate a PAF receptor subtype present in the cardiovascular system and platelets from the one existing in polymorphonuclear leukocytes in the rabbit.

Animals↗
PubMed1995

Familial adenomatous polyposis: desmoid tumours and lack of ophthalmic lesions (CHRPE) associated with APC mutations beyond codon 1444.

An earlier study has shown that FAP patients with mutations in codons 136-302 of the APC gene do not develop congenital hypertrophy of the retinal pigment epithelium (CHRPE), whereas those with mutations in codons 463-1387 regularly do. Here we present data on 36 patients from 20 families with mutations in codons 1445-1578. These patients lack CHRPE. Furthermore, with the exception of three prepubertal children all patients with mutations in codons 1445-1578 developed desmoid tumours. This relationship between certain extracolonic manifestations and site of the APC mutation points to a specific role of the APC protein in different tissues.

Adenomatous Polyposis Coli↗