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Biomedical subjects

A Balmain

Publications and source records attributed to A Balmain.

At least 91 records · Page 5Linked to original sources
PubMed1989

Chemical induction of oncogene mutations and growth factor activity in mouse skin carcinogenesis.

The goal of understanding the molecular basis of human tumor development has been greatly facilitated by the use of animal model systems in which the etiology of tumor development can be carefully controlled. Environmental chemicals, either naturally occurring or artificially produced, are thought to make a major contribution to the human tumor burden. Many of the concepts of multistage carcinogenesis have been developed and refined using the mouse skin model system and the work described in this article has been carried out in an attempt to analyze the molecular changes that are associated with the initiation of tumor development, the selection of initiated cells to form papillomas, or the progression of premalignant tumors to carcinoma. We have analyzed a number of skin tumors induced in mice by a two-stage initiation and promotion protocol and have detected a high frequency of c-ras oncogene mutations in this system. The mutation found in each case correlates well with the known reactivity of the carcinogens used. It has also been shown that where ras activation occurs this represents an early event in the tumor model system. Transforming growth factor beta is induced in mouse skin by tumor promoter treatment and may therefore play a role in the selection of initiated cells to form papillomas. Additional events, some of which involve the loss of normal ras alleles and possibly tumor suppressor genes, appear to take place at a later stage of carcinogenesis.

Animals↗
PubMed1988

Localized production of TGF-beta mRNA in tumour promoter-stimulated mouse epidermis.

Tumour promoters induce a wide spectrum of morphological and biochemical alterations when applied to mouse epidermis in vivo. These include the induction of RNA, DNA and protein synthesis during discrete phases of proliferation and differentiation. This constitutes an ideal model for studying molecular events underlying the disruption of epidermal homeostasis by TPA, and its subsequent re-establishment. Transforming growth factor-beta (TGF-beta) can induce either growth stimulation, inhibition, or differentiation, depending on the target cell. A function has been proposed for TGF-beta in wound healing and in tumour promotion, but the main source of TGF-beta is generally thought to be platelets, macrophages or lymphocytes, and a direct role for this growth factor in regulating tissue homeostasis in vivo has not been demonstrated. We show here that when the tumour promoter 12-tetradecanoyl-phorbol-13-acetate (TPA) is applied to the skin of mice, very high levels of TGF-beta messenger RNA are induced in the epidermal cells. In situ hybridization techniques show that the main site of TGF-beta synthesis is in the suprabasal differentiating epidermal cells. These results suggest that TGF-beta may be a natural regulator of epidermal homeostasis which is important in tumour promotion.

Animals↗
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↗
PubMed1988

Molecular analysis of chemical carcinogenesis in the skin.

The goal of understanding the molecular basis of human tumour development has been greatly facilitated by the use of animal model systems in which the aetiology of tumour development can be carefully controlled. Environmental chemicals, either naturally occurring or artificially produced, are thought to make a major contribution to the human tumour burden. The process of carcinogenesis can be divided operationally into the stages of initiation, promotion and progression and many different classes of chemical agents can act at one or more of these stages. Many of the concepts of multistage carcinogenesis have been developed and refined using the mouse skin model system and most of the work to be described in this article has been carried out in an attempt to analyse the molecular changes which are associated with the initiation of tumour development, the selection of initiated cells to form papillomas or the progression of premalignant tumours to carcinomas.

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

Immunocytochemical demonstration of p21 ras family oncogene product in normal mucosa and in premalignant and malignant tumours of the colorectum.

Study of the distribution of the p21 ras oncogene product as demonstrated by monoclonal antibody Y13-259 shows this protein to be apparently present in all epithelial populations of both premalignant and malignant tumours and throughout the normal foetal and adult epithelial crypt population in the colorectum. Metastatic tumour in liver shows a similar staining pattern which is less intense however than in the surrounding normal hepatocytes. Our results suggest that the presence of this protein is a widespread feature of normal cellular metabolism in certain cell types and is not restricted to those actively involved in cellular proliferation. It appears, furthermore, that neither cells at different stages of carcinogenesis nor those representing variants of a malignant phenotype can be identified using this particular antibody.

Antibodies, Monoclonal↗
PubMed1983

Induction of granulocyte-macrophage colony-stimulating activity in mouse skin by inflammatory agents and tumor promoters.

The granulocyte-macrophage colony stimulating activity (GM-CSA) was assayed in acetic acid extracts of skin from mice which were topically treated with inflammatory and tumor-promoting diterpene esters. Extremely large increases in GM-CSA were found in skin treated with the strongly tumor-promoting 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and the weakly promoting mezerein, while only a very slight increase was found with the non-promoting 4-O-methyl-TPA (4-OMe-TPA). Untreated areas of skin had very little GM-CSA. In the treated skins, the elevated GM-CSA was noted within a few hours and lasted for greater than 24 h after treatment. Although the levels of GM-CSA induced in the skin correspond to the degree of inflammation elicited by the respective treatments, the leukocytes in the acute inflammatory infiltrate did not appear to be responsible for the increased GM-CSA. Both epidermis and dermis had increased GM-CSA following TPA treatment of skin. Treatment of fibroblast and epithelial continuous cell lines with diterpene esters resulted in a similar pattern of GM-CSA induction in their supernatant media as that noted in the skin extracts. A large majority of the colonies stimulated by the diterpene-ester induced GM-CSA were composed of only macrophages. The results demonstrate that the topical administration of an inflammatory diterpene ester results in a rapid, marked yet local GM-CSA induction in the skin of treated mice. This indirect action in which diterpene esters induce in certain cells a growth regulatory factor for other types of cells may be an important element in carcinogenesis.

Animals↗
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↗
PubMed1982

Cloning and characterisation of the abundant cytoplasmic 7S RNA from mouse cells.

A cDNA library has been prepared from mouse embryo small RNAs and screened for the presence of clones complementary to the highly abundant cytoplasmic 7S RNA. One clone (pA6) was selected which hybridized exclusively with 7S RNA on a Northern blot prepared from cytoplasmic RNA run on high resolution polyacrylamide/urea gels. Sequence analysis of this clone has shown that at least 65 nucleotides at the 5' end of 7S RNA are extensively homologous with the highly repeated mouse B1 family. Heterologous hybridisations between the cloned mouse 7S sequence and RNAs prepared from rat, human and chick cells have shown that the non-B1 part of the 7S RNA molecule has been highly conserved during recent eucaryotic evolution. There are multiple copies of 7S RNA genes in the genomes of mouse, human, rat and chick cells, but substantial differences exist in copy number and genomic organisation in these organisms.

Animals↗