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Biomedical subjects

S A Bruce

Publications and source records attributed to S A Bruce.

49 records · Page 3Linked to original sources
PubMed1985

A comparative study on neoplastic transformation of human and Syrian hamster cells.

Three approaches have been taken to study simultaneously Syrian hamster cells and human cells in order to develop an extrapolation from the more established hamster system to human cells. On the Characterization of normal cells in comparison to tumor cells, human tumor cells and hamster tumor cells showed similarity in displaying anchorage independence, growth in suspension as micro tumor spheroids, and xenotumorigenicity in contrast to their respective normal cells; in addition, these tumor cells exhibited shorter population doubling time, higher saturation density, higher cloning efficiency, and higher fibrinolytic activity relative to their respective normal cell types. Other differences including ploidy change, contact inhibition on growth, serum requirement, and morphological transformation were also noted between human and hamster cells. On the application of microcarrier culture for a xenotumorigenicity test, the microcarrier technique seemed to have enhanced the sensitivity by reducing the number of inoculated tumor cells required for tumor formation. On the in vitro transformation of normal human and hamster cells, the highest efficiency of morphological transformation of hamster cells has been observed in the group treated with N-methyl-N'-nitro-N-nitrosoguanidine followed by griseofulvin which was employed to enhance the transformation by disturbing the chromosome apparatus. However, no evidence of transformation was observed in the treated human cells thus far.

Animals↗
PubMed1982

Hepatitis B virus core antigen: synthesis in Escherichia coli and application in diagnosis.

Fragments of hepatitis B virus DNA cloned in plasmid pBR322 carrying the gene for the viral core antigen have been placed under the control of the lac promoter of Escherichia coli. Several of the new recombinants direct higher levels of synthesis of the antigen, but the degree of enhancement varies with the different structures of the plasmids and hence the mRNAs produced. The antigen in crude bacterial lysates is a satisfactory diagnostic reagent for antibodies to the core antigen in serum samples.

Antibodies, Viral↗
PubMed1982

A qualitative and quantitative assay for cells lacking postconfluence inhibition of cell division: characterization of this phenotype in carcinogen-treated Syrian hamster embryo cells in culture.

We have developed a qualitative and quantitative assay system for detecting cells lacking postconfluence inhibition of cell division (contact insensitivity, CS-) in golden Syrian hamster embryo cells in culture by measuring the number of cells able to form colonies on a lethally irradiated, confluent monolayer of a contact-sensitive established cell line. A subpopulation in normal low-passage cultures of golden Syrian hamster embryo cells temporarily exhibits this CS- phenotype at very low frequency (approximately 4 x 10(-3)) but quickly loses the property within a few passages in vitro. This phenotype is invariably exhibited by various tumorigenic cell lines at very high frequency (7 to 50 x 10(-2)) and appears to correlate with the anchorage-independent growth phenotype. The temporal acquisition of the CS- phenotype by tertiary-passage golden Syrian hamster embryo cells following exposure to N-methyl-N'-nitro-N-nitrosoguanidine was examined. Cells with a stably heritable CS- phenotype are detected after approximately 20 posttreatment population doublings. In contrast, anchorage-independent cells are not detected until 35 to 95 posttreatment population doublings. These CS- cells appear to be preneoplastic cells, since clonally isolated CS- cells did not exhibit anchorage-independent growth until further passaging in vitro. The results suggest that acquisition of the CS- phenotype represents an early stage in neoplastic progression.

Animals↗
PubMed1981

Production of immunologically active surface antigens of hepatitis B virus by Escherichia coli.

Several plasmids have been constructed which direct the synthesis of hepatitis B virus surface antigens in Escherichia coli either as the native polypeptide or fused to other plasmid encoded polypeptides. When injected into rabbits, extracts from bacteria carrying some of these plasmids induced the synthesis of antibodies to the antigens even though the extracts did not give satisfactory positive results in radioimmunoassay for them. Either the NH2-terminal segment or the COOH-terminal segment of the surface antigens alone was sufficient to elicit the immune response, but antibodies against the two segments showed different specificities. The results emphasize the value of an in vivo assay for the presence of antigens in crude cell extracts and illustrate the feasibility of this type of screening with laboratory animals.

Antibody Specificity↗
PubMed1980

X-linked control of globin mRNA and hemoglobin production in erythroleukemia-lymphoma cell hybrids.

In somatic cell hybrids formed by the fusion of mouse erythroleukemic cells with cultured mouse lymphoma cells, retention of the X chromosome donated by the lymphoma parent is correlated with inhibition of hemoglobin accumulation in response to dimethyl sulfoxide. The inhibition of hemoglobin production was due to an inhibition of globin mRNA accumulation. Heme can partially overcome the effects of the lymphoma X chromosome and induce globin mRNA and hemoglobin accumulation in the dimethylsulfoxide-treated hybrid cells. The data suggests that the X chromosome contributed by the lymphoma cells inhibits hemoglobin production by inhibiting both inducible globin mRNA accumulation as well as inducible heme biosynthesis, most likely at a step after the formation of delta-aminolevulinic acid. The properties of erythroleukemia x lymphoma cell hybrids are compared with those of a series of erythroleukemia x bone marrow cell hybrids. The data indicate the possibility of multiply loci on the X chromosome capable of regulating the expression of erythroid characteristics.

Aminolevulinic Acid↗
PubMed1978

Negative control of hemoglobin production in somatic cell hybrids due to heme deficiency.

In somatic cell hybrids formed by the fusion of mouse erythroleukemic cells with mouse primary bone marrow cells, retention of the X chromosome contributed by the bone marrow parent is correlated with inhibition of hemoglobin accumulation in response to dimethyl sulfoxide. The inhibition of hemoglobin accumulation is not due to the absence of globin mRNA. Dimethyl sulfoxide-treated hybrid cells accumulate polyribosomal globin mRNA to levels comparable to those of the parental erythroleukemic cells under the same conditions. Heme, or its precursor delta-aminolevulinc acid, can overcome the effects of the bone marrow X chromosome and induce hemoglobin accumulation in the dimethyl sulfoxide-treated hybrid cells. The data suggest that the X chromosome contributed by the bone marrow cells inhibits hemoglobin production by inhibiting inducible heme biosynthesis, most probably at the step catalyzed by delta-aminolevulinic acid synthetase (EC 2.3.1.37).

Aminolevulinic Acid↗
PubMed1976

Isolation and characterization of two sequence-specific endonucleases from Anabaena variabilis.

Two endonucleases, AvaI and AvaII, were isolated from Anabaena variabilis on the basis of their ability to make a limited number of breaks at specific points in bacteriophage lambda DNA. Neither enzyme has cofactor requirements beyond Mg2+. Endonuclease AvaI makes eight breaks in the phage lambda chromosome at which the 5'-terminal sequence is pPy-C-G-N. AvaII endonuclease cuts phage lambda DNA more extensively, yielding fragments with the 5'-terminal sequence G-T-C-N or G-A-C-N. Neither enzyme generates cohesive ends.

Bacteria↗
PubMed1970

Suppression of malignancy and differentiation in melanotic melanoma cells.

Tumorigenicity of mouse melanoma cells is reduced or lost upon growth in vitro in 1 to 3 mug/ml of 5-bromodeoxyuridine (BUdR). The rate of growth is very little affected by these concentrations. The morphology of the cells is altered, such that the cells grow in a flattened, often fibroblastic monolayer, showing contact inhibition, instead of the rounded, multilayered mounds characteristic of the line. Melanotic cells lose their pigment-producing ability within one week. These effects are reversible and the inclusion of thymidine with BUdR prevents their occurrence. The reduction in tumorigenicity, the effects on cell morphology, and the suppression of pigmentation occur in clones derived from single cells growing in BUdR as well as in mass populations. These clones appear capable of indefinite growth in vitro in BUdR with altered morphology. The suppression of cytodifferentiation in these melanoma cells and in embryonic cells, coupled with the modification of malignancy, leads to the hypothesis that both differentiation and malignancy are regulated by similar cellular mechanisms. These effects of BUdR offer promise of a powerful tool to probe these regulatory mechanisms.

Animals↗
PubMed1969

Hybridization of two biochemically marked human cell lines.

A hybrid cell line of clonal origin has been obtained by cocultivation of two biochemically marked human cell strains. One parental line is diploid and derived from a male infant with orotic aciduria, a rare autosomal recessive disease. This line has deficient activity for the final two enzymes in the biosynthetic pathway leading to uridylic acid and possesses the B electrophoretic type of glucose-6-phosphate dehydrogenase. The other parental line (D98/AH-2) is heteroploid, is resistant to 8-azahypoxanthine, and has deficient inosinic acid pyrophosphorylase activity. It displays the A(+) variant of glucose-6-phosphate dehydrogenase. The A(+) and B types of this dehydrogenase are known to be determined by allelic, sex-linked, Mendelian genes. The cloned hybrid cells exhibit genetic traits of both parents: (1) Their modal chromosome number is approximately the sum of those of the two parental lines; (2) they have levels of activity for both enzymes affected by the gene for orotic aciduria which are intermediate between those of the two parental lines; (3) they have higher activity than the D98/AH parent for inosinic acid pyrophosphorylase; (4) they have both A(+) and B isozyme bands of glucose-6-phosphate dehydrogenase. These hybrid cells represent the first known example of a cloned line of mammalian origin in which two X-linked allelic genes function.

Carboxy-Lyases↗