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J C Barrett

Publications and source records attributed to J C Barrett.

At least 361 records · Page 20Linked to original sources
PubMed1981

Diethylstilbestrol induces neoplastic transformation without measurable gene mutation at two loci.

The frequency with which diethylstilbestrol induces neoplastic transformation and somatic mutation was measured concomitantly in Syrian hamster embryo cells. While diethylstilbestrol was as active as benzo[a]pyrene in inducing transformation, it failed to induce mutations at two conventionally studied loci. These results suggest that diethylstilbestrol may transform cells in the absence of gene mutations.

Animals↗
PubMed1981

Comparison between mutagenesis in normal and transformed Syrian hamster fibroblasts: difference in the temporal order of HPRT gene replication.

A highly tumorigenic subdiploid cell line, BP6T, derived in our laboratory from Syrian hamster embryo (SHE) cells, is amenable to studies of somatic mutation in vitro. Cellular and biochemical characterization of clonally derived BP6T cells resistant to 6-thioguanine (TGr) or ouabain (Quar) demonstrated these mutants to be similar qualitatively to mutants of SHE cells characterized previously (Barrett et al., 1978). BP6T TGr mutants resistant to 6-thioguanine are cross-resistant to 8-azaguanine, lack HPRT activity, exhibit a low frequency of reversion and arise spontaneously at a rate of approximately 5 X 10(-7) mutants per cell per generation. BP6T Ouar mutants were shown to be highly resistant to ouabain-mediated inhibition of 86Rb influx, indicating an alteration in the Na+/K+ ATPase. These studies on the BP6T cell line provide the experimental basis for a comparative study of the mutagenic responses of normal, diploid SHE cells versus those of related, but transformed aneuploid cells. Highly synchronized cultures of these 2 cells were mutagenized by pulse treatment with BrdU during different periods of S phase, followed immediately by near-UV irradiation. The induced mutation frequencies so obtained provided information about the temporal order of replication of genes encoding HPRT and Na+/K+ ATPase in both SHE and BP6T cells. The temporal pattern of replication of Na+/K+ ATPase gene loci is similar in both cell types, but the temporal order of replication of the HPRT gene is significantly different between SHE and BP6T cells (mid-late S phase, versus early S phase, resp.). This observed difference emphasizes the caution required in the study of mutagenesis and DNA replication using transformed, aneuploid cells under the assumption that the underlying mechanisms are the same for normal, diploid cells.

Animals↗
PubMed1981

Induction of gene mutation in and cell transformation of mammalian cells by modified purines: 2-aminopurine and 6-N-hydroxylaminopurine.

2-Aminopurine, a classical mutagen in prokaryotic systems, is inactive as a carcinogen in two animal species. To determine the basis for this discrepancy in the correlation between carcinogenesis and mutagenesis, the ability of 2-aminopurine to induce somatic mutation and neoplastic transformation concomitantly in the same cellular system was examined. 6-N-hydroxylaminopurine, a related modified purine that is a mutagen and a carcinogen, was also studied. 2-Aminopurine was a mutagen in Syrian hamster embryo cells, but its activity was very weak. The maximum induced mutation frequency with either of two mutational markers was only 7 X 10(-6) mutants per surviving cell. 2-Aminopurine also induced morphological transformation of the cells under the same conditions, but the frequency was only approximately 0.04% per surviving colony. Neoplastic transformation of the cells after 2-aminopurine treatment was not observed in these experiments. These results indicate that 2-aminopurine is, at best, a weak transforming agent. The lack of carcinogenic activity in vivo with 2-aminopurine is consistent with these observations. In contrast to the results with 2-aminopurine, 6-N-hydroxylaminopurine was a very effective mutagen in these cells (up to 10(-3) mutants per survivor) and induced morphological transformation of the cells in a dose-dependent manner. Furthermore, neoplastic transformation was induced by this nucleic acid base analog. The correlation of mutagenic activity with transforming ability of these two modified purines supports a relationship between mutagenesis and carcinogenesis. However, relative to other carcinogens, there is a quantitative difference in the ability of 6-N-hydroxylaminopurine to induce cell transformation and mutation. For example, in benzo[a]pyrene-treated cultures, the ratio of the frequency of induced morphological transformation to that of somatic mutation was approximately 100, whereas for 6-N-hydroxylaminopurine-treated cultures, the ratio of transformation to mutation was only 3-12.5. This indicates that 6-N-hydroxylaminopurine is less potent than benzo[a]pyrene in inducing transformation when compared at equal mutagenic potency. This is consistent with our hypothesis that cell transformation, and possibly cancer, occurs predominantly as the result of a mutation at the chromosome level rather than a gene mutation.

2-Aminopurine↗
PubMed1981

Hyperplasia of Syrian hamster epidermis induced by single but not multiple treatments with 12-O-tetradecanoylphorbol-13-acetate.

Treatment of initiated hamster skin with 12-O-tetradecanoylphorbol-13-acetate does not promote the formation of papillomas and carcinomas as it does in the classic two-stage epidermal carcinogenesis model in many strains of mice. We have begun to examine the basis of this species specificity to TPA. We have found that, although hamster and mouse epidermis respond to a single exposure of TPA with a comparable degree of hyperplasia, they differ in their response to multiple treatments. In contrast to the reported potentiation of hyperplasia of mouse skin following two or more treatments with TPA, hamster skin is capable of adapting to multiple exposures to the promoter. Weekly TPA treatments of hamster skin result in hyperplasia of 4 to 6 nucleated cell layers after the first treatment, reduced hyperplasia after the second treatment, and no hyperplasia after 4 weeks of treatment. Decreasing the time interval between treatments accelerates the adaptation process. This adaptation phenomenon should be useful in studying the mechanism of TPA action by examining TPA effects in adapted and nonadapted tissues from the same species.

Animals↗
PubMed1981

Inhibition of terminal differentiation of hamster epidermal cells in culture by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate.

The effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the terminal differentiation of hamster epidermal cells in culture was studied. Epidermal cells were isolated from 1-day-old Syrian hamsters by separating the epidermis from the dermis by cold trypsin treatment. A large number of cells were isolated by this procedure without contamination with dermal fibroblasts. When grown in culture, the epidermal cells divided rapidly, stratified, and differentiated as measured by elaboration of abundant keratin-like amorphous material, red staining with rhodanile blue (which is characteristic of cornifying epithelium), and formation of cornified envelopes. These structures were measured by electron microscopy and quantitation of detergent-insoluble cell ghosts. TPA markedly inhibited this differentiation of the hamster epidermal cells in culture. When grown in the presence of TPA (5 to 1000 ng/ml) for three or more days, the epidermal cell monolayers failed to stain positively with rhodanile blue, and the cell stratification and production of keratin-like material was reduced. The differentiation of the epidermal cells was quantitated by measuring the percentage of cells with cornified envelopes; TPA reduced by up to 70% the number of these terminally differentiated cells. Phorbol didecanoate also inhibited the differentiation of hamster epidermal cells in culture, while phorbol was inactive. The effect of TPA was reversible. When TPA was removed from the media, the cells rapidly differentiated to the same extent as did untreated cells. TPA also stimulated DNA synthesis of the epidermal cells, especially after 10 days in culture when the vast number of cells in control cultures had ceased DNA synthesis. These results are discussed in view of the fact that TPA has not been demonstrated to promote epidermal carcinogenesis in Syrian hamsters.

Animals↗
PubMed1980

Prostaglandin and thromboxane production by fibroblasts and vascular endothelial cells.

We have compared the production of prostaglandins in fibroblast-like cells and endothelial cells in culture. Of the fibroblasts studied 10T1/2, SHE, BP6T and KD produce significant amounts of PGI2, PGE2 and PGF2F2 under optimal culture conditions, but only 3T3 and BHK produce TXA2 in addition to PGI2. The adult bovine aortic endothelial cells (ABAE) and fetal bovine heart endothelium (FBHE) synthesise PGI2 but not TXA2, either from endogenous or exogenous substrates. Both cultured endothelial cells and fibroblasts apparently lack 15-hydroxyprostaglandin dehydrogenase pathway and the ability to convert 6-Keto PGF1 alpha into 6-Keto PGE1. PGI2 production by ABAE was 3-5 times that of FBHE, about twice that of SHE cells and 6-8 times that of 10T1/2 or BP6T cells. Supernatants or media obtained from these cells inhibited aggregation of human platelet-rich plasma, a known biological effect of PGI2. This effect was abolished when cell monolayers were preincubated with indomethacin or tranylcypromine. RIA and chromatographic data of 6-Keto PGF1 alpha from these experiments confirmed that the inhibition of platelet aggregation was due to the formation of PGI2. The production of all prostanoids by endothelial cells or fibroflasts was significantly higher during the exponential phase of growth as compared to confluent monolayers. We propose that fibroblasts 10T1/2 or SHE can serve as useful experimental models for the study of metabolism and transport of PGI2 and/or TXA2 in cells of nonendothelial nature.

Animals↗
PubMed1980

A preneoplastic stage in the spontaneous neoplastic transformation of syrian hamster embryo cells in culture.

Spontaneous neoplastic transformation of Syrian hamster embryo cells in culture occurs in at least two steps. An intermediate stage is represented by an aneuploid cell line which is preneoplastic. These cells differ from the diploid cells by a number of properties, including their ability to become neoplastic in vivo when injected while attached to a substrate. These results support a multistep process for neoplastic transformation of cells in vitro and caution against considering aneuploid cell lines as "normal" cells.

Aneuploidy↗
PubMed1979

Effects of the venom of the green mamba, Dendroaspis angusticeps on skeletal muscle and neuromuscular transmission.

1 The venom of the green mamba, Dendroaspis angusticeps, was tested for effects on neuromuscular transmission and skeletal muscle contractility in isolated phrenic nerve-hemidiaphragm preparations of the rat and mouse, chick biventer cervicis muscle preparations and in aneural cultures of embryonic chick skeletal muscle. 2 The venom (10 to 40 micrograms/ml) augmented the responses to indirect but not direct stimulation. As the venom did not have anticholinesterase activity and did not increase receptor sensitivity, it is likely that the venom enhanced release of acetylcholine. 3 Higher concentrations of venom (40 to 80 micrograms/ml) inhibited acetylcholine receptor sensitivity. 4 Prolonged exposure to the higher concentrations of venom produced a failure of muscle contractility. Signs of muscle degeneration were seen in skeletal muscle cultures.

Animals↗
PubMed1979

Correlation of in vitro growth properties and tumorigenicity of Syrian hamster cell lines.

Several in vitro phenotypic characteristics frequently associated with neoplastic cells were examined in a series of spontaneous and benzo(a)pyrene-induced Syrian hamster clonal cell lines which differed in their degree of tumorigenicity. Nonparametric statistical analysis demonstrated cloning efficiency in semisolid agar, enhanced fibrinolytic activity, decreased serum requirement for growth, decreased organization of intracellular actin, and increased cloning efficiency in liquid medium to be correlated with tumorigenicity. These correlations were not only qualitative but also quantitative. This suggests that the factors determining the degree of tumorigenicity of a cell can be cellular growth properties.

Actins↗