Search PubMed⌕ Search

Biomedical subjects

M Ramsden

Publications and source records attributed to M Ramsden.

31 records · Page 2Linked to original sources
PubMed1988

Isolation and characterization of the 5' flanking region of the mouse c-Harvey-ras gene.

The complete 5' flanking region of the murine c-Ha-ras gene was cloned and sequenced. An untranslated exon (-1) was identified and the promoter region of the gene located. Like the rat and human homologues, the murine promoter is GC rich and contains several GC boxes together with a CAAT element, but lacks a TATA box, an arrangement similar to that found in many housekeeping genes. From primer extension studies, the gene was shown to have three transcriptional start sites, whose positions differ from those previously found for the human gene. No alterations in these start sites were detected between the normal gene and activated Ha-ras genes from mouse skin tumors. A region of strong homology between mouse, rat, and human Ha-ras genes exists within the large intron separating exon (-1) from the first coding exon. In addition, from chloramphenicol acetyltransferase assays, the upstream region has promoter activity which appears to be enhanced by the inclusion of sequences within this intron.

Animals↗
PubMed1986

v-ras genes from Harvey and BALB murine sarcoma viruses can act as initiators of two-stage mouse skin carcinogenesis.

Activated Harvey murine sarcoma virus ras genes were introduced into epidermal cells in vivo by direct application of retroviruses to mouse skin. Subsequent treatment with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) induced benign papillomas, some of which progressed to invasive carcinomas. Initiation with virus was irreversible for at least 4 months, since TPA treatment after this latency period produced papillomas within 4 weeks. Analysis of viral integration sites showed that carcinomas are clonal in origin. Both papillomas and carcinomas express virus-specific ras mRNA and the viral form of ras P21 protein. The results show that activated ras genes can replace chemical carcinogens in initiation of mouse skin carcinogenesis. This system presents a novel approach to in vivo analysis of the biological role of oncogenes in epithelial tumorigenesis.

Animals↗
PubMed1985

Differential methylation of the c-H-ras gene in normal mouse cells and during skin tumour progression.

We have previously shown that the mouse c-H-ras gene acquires transforming activity in chemically induced skin tumours. We have now investigated the pattern of DNA methylation at HpaII and XhoI sites around the c-H-ras locus in various tissues and stages of epidermal tumour progression. The results of this study suggest a correlation between the methylation state of the c-H-ras gene and its susceptibility to oncogenic conversion by a point-mutation. The locus is substantially undermethylated in normal epidermis in comparison with NIH/3T3 fibroblasts. Intermediate levels of methylation were observed in the other tissues investigated. The undermethylation at HpaII sites in epidermal DNA persists through the morphologically distinct phases of hyperplasia, benign papilloma and malignant carcinoma. Methylation at a specific XhoI site close to the c-H-ras gene is significantly reduced with respect to normal epidermis in some, but not all epidermal tumours. The methylation state of the c-H-ras locus in specific tumours is stably maintained following transfection of these DNAs into NIH/3T3 cells and selection of transformed foci. Demethylation of the locus is not essential in vitro for the transforming activity of DNA from epidermal tumours. The significance of changes in the methylation pattern of the c-H-ras gene in different tissues and during tumour progression is discussed.

Animals↗
PubMed1985

Impaired release of a T-cell specific suppressor factor in rheumatoid arthritis.

Peripheral blood T cells from patients with rheumatoid arthritis (RA) and scleroderma (PSS) were assessed for their ability to release T-cell-specific suppressor activity (TRSA) upon incubation with a suppressor activating factor (SAF) derived from a human lymphoblastoid cell line (CEM). T cells from 11/20 (55%) RA patients exhibited impaired TRSA release in contrast to 1/12 (8%) of PSS patients. RA patients demonstrating impaired TRSA release exhibited more active arthritis than patients demonstrating normal TRSA release.

Adult↗
PubMed1985

Lung inflammation in scleroderma: clinical, radiographic, physiologic and cytopathological features.

Twenty-five patients with systemic sclerosis were studied by chest radiography, lung function, esophageal motility, gallium-67 (67Ga) lung scanning and bronchoalveolar lavage (BAL). Alveolar inflammation, as defined by an elevation of proportional BAL lymphocyte or neutrophil counts, or increased thoracic uptake of 67Ga was found in 16 patients. An NIH gallium index greater than 65 index units identified a subgroup of patients with a significantly higher proportional BAL lymphocyte count (13.7 +/- 8.5 vs 5.6 +/- 3.1, p less than 0.0005). The presence of an abnormal chest radiograph correlated with physiologic evidence of lung restriction (p less than 0.01), and an elevation of proportional BAL lymphocyte count (15.5 +/- 8.2 vs 6.6 +/- 5.1, p less than 0.01). Eight patients receiving oral penicillamine therapy had significantly lower BAL lymphocyte counts compared to untreated patients (4.7 +/- 3.6 vs 11.3 +/- 7.7, p less than 0.05). We suggest that alveolar inflammation in scleroderma is characterized by lymphocyte accumulation and increased thoracic uptake of gallium.

Adult↗
PubMed1983

Identification of a rapidly labelled 350K histidine-rich protein in neonatal mouse epidermis.

The major histidine-rich protein (HRP) found in the stratum corneum of neonatal mouse epidermis (band 2 protein, molecular weight 27,000) is a relatively late product of epidermal differentiation and incorporates labelled amino acids in vivo only after a 6-9 h lag period. A number of putative precursor HRPs in the 70-300 K molecular weight range were initially identified using short pulse labeling times and our previously described methods for isolation of epidermis and extraction of proteins. However, when steps were taken to minimise proteolysis during preparation, a single species of approximately 350 K molecular weight was the most strongly labelled protein following a 1 h in vivo pulse of [3H]-histidine. This protein was stable in sodium dodecyl sulphate dithiothreitol at 100 degrees C and in 4 M urea, suggesting a single covalently linked polypeptide. The kinetics of labelling and the localisation of the 350 K HRP in the lower granular layers suggest that it is a precursor of the stratum corneum HRP. The processing of the 350 K HRP to the stratum corneum species appears to involve a complex series of specific cleavage steps which give rise to a number of HRPs of intermediate molecular weight.

Animals↗
PubMed1973

Discrimination of a response-independent component in a multiple schedule.

Pigeons were trained to respond in non-differential reinforcement pre-discrimination training, with a multiple variable-interval 1-min variable-interval 1-min schedule. Each bird then received discrimination training with a multiple variable-interval 1-min variable-time 1-min schedule. Thus, discrimination training was between response-dependent (variable-interval) and response-independent (variable-time) schedules with the rate of reinforcement equated. In Experiment I, only three sessions of non-differential reinforcement preceded discrimination training and for half the birds, a 0 degrees line was correlated with the response-dependent schedule; for the remaining birds the 0 degrees line was correlated with the response-independent schedule. Post-discrimination gradients of excitatory stimulus control were obtained from the former group, while the latter group showed little evidence of post-discrimination stimulus control by the 0 degrees line. Differential responding to the variable-time schedule was not accompanied by behavioral contrast to the variable-interval schedule. In Experiment II, 20 sessions of non-differential reinforcement preceded discrimination training and the 0 degrees line was correlated with variable-time reinforcement for each bird. Differential responding to the 0 degrees line was accompanied by negative induction to the variable-interval schedule and by inhibitory stimulus control about the 0 degrees line during a post-discrimination generalization test.

Journal Article↗
PubMedDate not supplied

Activation of the mouse cellular Harvey-ras gene in chemically induced benign skin papillomas.

An important feature of the development of many human and animal tumours is the appearance of pre-malignant benign lesions, some of which undergo further changes during progression to malignancy. Many of the currently accepted concepts of multi-stage carcinogenesis have been developed using an experimental model based on the chemical induction of tumours in mouse skin. In this system, many of the premalignant papillomas which arise are promoter-dependent, and appear to regress if promoter treatment is interrupted, whereas others progress to form autonomous benign lesions and, in some cases, malignant carcinomas. Although the number and nature of the events leading to malignancy are not known, DNA transfection experiments have led to the identification of several genes which may be qualitatively altered in tumour cells (see ref. 6 for review). We have previously shown that DNA from transplantable mouse skin carcinomas induced by chemical carcinogens has the ability to transform NIH/3T3 cells, and that the gene responsible for the transformation is an activated form of the mouse cellular Harvey-ras gene (c-rasH). We have now investigated the stage of carcinogenesis at which the proto-oncogene acquires transforming activity. We demonstrate that primary papillomas induced by chemical carcinogens in two different mouse strains have an activated c-rasH gene. This constitutes the first report of a benign tumour which contains DNA with detectable transforming activity. In addition, steady-state levels of c-rasH gene transcripts are elevated in the papillomas as compared with normal epidermis.

Animals↗
PubMedDate not supplied

Carcinogen-specific mutation and amplification of Ha-ras during mouse skin carcinogenesis.

Cellular proto-oncogenes can be activated by both point mutations and chromosomal translocations, suggesting that there may be a direct link between exposure to agents which damage DNA and genetic change leading to malignancy. Several groups have therefore analysed mutations found in cellular oncogenes of tumours induced by particular physical or chemical carcinogens. Here, we have analysed the molecular changes at different stages of carcinogenesis in mouse skin tumours induced by initiating and promoting agents. Over 90% of tumours, including premalignant papillomas, initiated with dimethylbenzanthracene (DMBA) have a specific A----T transversion at the second nucleotide of codon 61 of the Harvey-ras (Ha-ras) gene. The frequency of this mutation was dependent on the initiating agent used, but not on the promoter, suggesting that the mutation occurs at the time of initiation. The mutation was heterozygous in most papillomas tested, but was homozygous or amplified in some carcinomas. The development of further chromosomal changes at the c-Ha-ras gene locus is therefore a common feature of tumour progression.

9,10-Dimethyl-1,2-benzanthracene↗