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Biomedical subjects

E H Chu

Publications and source records attributed to E H Chu.

17 recordsLinked to original sources
PubMed1992

Similarity of spontaneous germinal and in vitro somatic cell mutation rates in humans: implications for carcinogenesis and for the role of exogenous factors in "spontaneous" germinal mutagenesis.

The rate of spontaneous mutation resulting in electrophoretic variants per cell generation in a human lymphoblastoid cell line, on the basis of experiments described in this paper, is found to be 7.2 x 10(-8) per locus. A review of similar data on electrophoretic variants resulting from spontaneous mutation in the human germ line leads to an estimate of 3.3 x 10(-8) per locus per cell generation. It is argued that the similarity of these two estimates, despite an average cell generation time of 18.5 hr for the cultured somatic cells but about 26 days in the germ line, suggests that spontaneous mutation involving nucleotide substitutions is much more dependent on cell generation than on time. This finding permits the inference that environmental (exogenous) variables make a relatively small contribution to the rate of this type of human germinal spontaneous mutation. While in vitro somatic-cell mutation rates, such as derived in this study, provide a basis for modeling the contribution of nucleotide substitutions in multihit/clonal theories of carcinogenesis, it is also argued that the complex of events involved in carcinogenesis, including chromosomal rearrangements and mitotic recombination, could have very different individual probabilities. Estimates for the rates of these other types of mutation are needed to provide a better understanding of the manner in which multiple mutations accumulate in malignant cells.

Alleles↗
PubMed1979

Effects of DNA damaging agents on cultured fibroblasts derived from patients with Cockayne syndrome.

The cytotoxic action of physical and chemical agents on 10 skin fibroblast strains in culture derived from individuals with Cockayne's syndrome was measured in terms of colony-forming ability. As compared to fibroblasts from normal donors, all Cockayne cell strains tested exhibited a significantly increased sensitivity to UV light and a normal sensitivity to X-rays. Cells from two sets of parents of unrelated Cockayne children showed an intermediate level of UV sensitivity. There was no effect of 0.5 mM caffeine on UV survival in normal and two Cockayne strains tested, indicating that postreplicational repair in Cockayne cells as measured by caffeine sensitivity was probably normal. Sensitivity of normal and Cockayne cells to the chemical carcinogens and mutagens 4NQO, N-AcO-AAF, ICR-170 and EMS was also compared. An increased sensitivity of Cockayne cells to 4NQO or N-AcO-AAF, but not the ICR-170 or EMS, was observed. However, unlike the intermediate UV sensitivity, the cell strains from two parents of Cockayne patients showed the same sensitivity to N-AcO-AAF or 4NQO as fibroblasts from normal individuals. Quantiation of damage to the DNA after 20 J . m-2 UV irradiation indicates normal levels of [3H] thymidine incorporation in the Cockayne cells, in contrast to UV-irradiated xeroderma pigmentosum cells (XP 12BE) in which there was a very low level of repari synthesis. Moreover, we have shown previously that excision of UV-induced pyrimidine dimers in 2 of the 10 Cockayne cell strains was normal.

Carcinogens↗
PubMed1979

Interaction of wild-type and variant mouse 3T3 cells with lectins from Bandeiraea simplicifolia seeds.

An isolectin (BS I-B4) derived from Bandeiraea simplicifolia seeds and specific for terminal alpha-D-galactopyranosyl groups was found to be cytotoxic to Swiss 3T3 mouse cells. After mutagenesis and selection with BS I-B4, a variant clonal cell line resistant to both this isolectin and the alpha-D- and beta-D-galactose-binding lectin abrin was isolated. The parental cell line showed homogeneous and noninteracting binding sites for BS I-B4, whereas the variant cells exhibited a curved plot with a reduced number of binding regions. Another lectin, BS II, which is derived from the same seeds by specific for terminal N-acetyl-D-glucosaminyl groups, was cytotoxic to the variant but not the parental cells. These results suggest a possible lesion in the biosynthesis of cell surface structures resulting in the exposure of subterminal N-acetyl-D-glucosaminyl moieties in the variant line.

Acetylglucosamine↗
PubMed1978

Inverse relationship between galactokinase activity and 2-deoxygalactose resistance in Chinese hamster ovary cells.

Galactokinase activity is reduced in 12 independent clones of Chinese hamster ovary cells resistant to 2-deoxygalactose. The frequency of resistant colonies is increased with chemical mutagens. The resistant phenotype is stable in the absence of selection. There is an inverse correlation between the levels of galactokinase activity and the cloning efficiency in deoxygalactose. Cells with high resistance have 1% or less of the enzyme activity observed in the parental cells; while cells with low resistance have 10-30% galactokinase activity. Studies with tetraploid hybrid cells reveal that resistance to deoxygalactose is a recessive trait and that cells with high resistance do not complement those with low resistance. In cell lines with low resistance, the Km for galactose, Ki for deoxygalactose, Km for ATP, and thermolability were not significantly altered compared to sensitive parental cells. Although the possibility of mutation at the structural gene locus has not been ruled out, the reduced enzyme activity may also be due to mutation at a regulatory site which affects the number of galactokinase molecules per cell.

Animals↗
PubMed1977

Regional chromosomal localization of the human gene for galactose-1-phosphate uridyltransferase.

In the progeny of somatic cell hybrids formed by fusion of human lymphocytes and Chinese hamster mutant cells, a single human chromosome A2 was selectively retained when grown in appropriate medium. Spontaneous breakage of this chromosome in different hybrid subclones led to the assignment of the gene for galactose-1-phosphate uridyltransferase to the centromeric region of this chromosome (2q11 leads to 2q14). This gene is shown to be syntenic to the previously mapped genes for acid phosphatase 1 and malate dehydrogenase 1.

Acid Phosphatase↗
PubMed1977

Partial trisomy of the long arm of human chromosome 1 as demostrated by in situ hybridization with 5S ribosomal RNA.

In a newborn boy with multiple malformations, a tandem duplication was detected at the distal end of the long arm of one human chromosome 1. The Giemsa bands, 1q31 to 1q43--44, were repeated serially. Since 5S rRNA genes are located at 1q42--43, in situ hybridization of 125I 5S rRNA with fixed chromosome preparations was used to confirm the chromosomal duplication. The infant exhibited numerous developmental and clinical abnormalities as might be expected with an abnormality of chromosome structure relating to a ribosome component.

Chromosomes, Human, 1-3↗
PubMed1977

Chromosomes of lemuriformes. II. Chromosome polymorphism in Lemur fulvus collaris (E. Geoffroy 1812).

Two previously unreported diploid numbers, 2N = 50 and 2N = 51, from five individual Lemur fulvus collaris are described. In both chromosome complements, the nombre fondamental is 64. The 2N = 50 complement is composed of 7 pairs of bi-armed chromosomes, 17 pairs of acrocentric chromosomes with small short arms, and acrocentric sex chromosomes. The 2N = 51 complement is identical with these exceptions: Only one member equivalent to bi-armed pair 6 of L.f. collaris (2N = 50) is present, and two extra acrocentrics are found in the 2N = 51 complement. G-banding analyses suggest that these chromosomes are a heteromorphic pair of the Robertsonian type. This conculsion is supported by evidence from studies of meiotic pairing relationships of the three chromosomes and the complements of hybrids resulting from interspecific matings. Comparison of the 2N = 50 and 2N = 51 complements with a published 2N = 48 complement suggests that these new karyotypes do not provide a lineal link between the 2N = 52 and 2N = 48 karyotypes (Rumpler, Y., and R. Albignac 1969 C.R. Soc. Biol., 163: 1989-1992).

Animals↗
PubMed1977

Mutational approaches to the study of carcinogenesis.

A number of circumstantial lines of evidence are consistent with the somatic mutation theory of carcinogenesis, but there has been a paucity of experimental data that either support or contradict the genetic theory. In this paper, we summarize the predictions, the recent experimental approaches, and the problems involved in testing the theory. Results are presented that define the conditions and demonstrate the existence of two-stage processes of mutagenesis and carcinogenesis in vitro. We conclude that mutagenesis is responsible for the initiation of carcinogenesis and an epigenetic mechanism is responsible for its promotion. Carcinogenic agents can induce a stable transformation of a cell by either mutation or epigenetic alteration in gene expression. This conclusion has led us to propose a new integrative theory of carcinogenesis, encompassing the tenets of four main theories: (1) the mutation and epigenetic basis for carcinogenesis, (2) the two-stage theory of carcinogenesis, (3) a general theory of carcinogenesis, and (4) the somatic deletion mutation theory of carcinogenesis.

Animals↗
PubMed1977

Effect of phorbol myristate acetate on the recovery of spontaneous and ultraviolet light-induced 6-thioguanine and ouabain-resistant Chinese hamster cells.

12-0-Tetradecanoyl-phorbol-13-acetate (TPA) and phorbol were tested in Chinese hamster cells for their effects on mutagenesis (resistance to 6-thioguanine and to ouabain), DNA repair, and survival after ultraviolet (UV) irradiation. Recovery of 6-thioguanine- and ouabain-resistant colonies was significantly increased by TPA treatment and, to a lesser extent, by phorbol in UV-irradiated cells. Moreover, maximum enhancement of recoverable UV-induced 6-thioguanine- and ouabain-resistant mutants occurred when TPA was present after the mutation "expression" time and after the completion of DNA repair. This eenhancement effect, while persisting up to 18 days in the 6-thioguanine mutation system, was maximal when TPA was applied about 2 days after UV irradiation for the ouabain resistance mutation system. No significant decrease in cell survival was noted after post-UV treatment with TPA or phorbol, under conditions where there was a slight but nonspecific inhibition of unscheduled DNA repair synthesis. These results do not support the hypothesis that the tumor-promoting activity of TPA is due to its ability to inhibit "error-free" excision repair. The results are, however, consistent with a "two-stage" hypothesis of carcinogenesis which includes mutational and epigenetic mechanisms to explain the initiation and promotion phases.

Animals↗
PubMed1977

Cockayne syndrome: a cellular sensitivity to ultraviolet light.

Two unrelated children, a boy 2 1/2 years old and a girl 4 years old, were affected with the cachectic dwarfism of Cockayne syndrome. Fibroblast cultures derived from these patients exhibited increased sensitivity to ultraviolet (UV) light, but not to x-irradiation, as measured by colony-forming ability. In both Cockayne fibroblast cultures, the rate of removal of thymidine dimer from the irradiated cellular DNA was normal. This demonstration of a cellular defect in Cockayne cells suggests that there may be an enzymatic defect in the repair of UV light-induced damage.

Abnormalities, Multiple↗
PubMed1975

Mutant hamster cells exhibiting a pleiotropic effect on carbohydrate metabolism.

Sixty-seven galactose negative (Gal minus) clones were established from survivors after treatment of Chinese hamster lung (V79) cells with 5-bromodeoxyuridine and black light. The mutational origin of these clonal isolates was inferred on the basis of the previously demonstrated mutagenic action of the combined treatment, persistence of the Gal minus phenotype in cell progeny in the absence of selection, conditional lethality of three isolates, interallelic complementation, and assignment of a homologous human gene to chromosome A2. In contrast to the parental cells, Gal minus mutants could not utilize exogenous galactose, mannose, fructose, galactose 1-phosphate, glucose 1-phosphate, or glucose 6-phosphate. Permeation of galactose into mutant cells appeared unimpaired. In intra- and interspecific cell hybrids, the mutation causing the Gal minus phenotype behaved like a recessive character. The pleiotropic nutritional response was due not to deficiency of any one specific enzyme in the Leloir pathway but to significant reduction in activities of phosphoglucomutase, NADP-dependent isocitrate dehydrogenase, and perhaps other enzymes. In temperature-sensitive Gal minus mutants grown at permissive temperature or in complementing intra- and interspecific cell hybrids, the activities of these enzymes were restored to normal levels, accompanied by a regained ability to use the particular hexoses or hexose monophosphates. We postulate that the change from Gal + to Gal minus phenotype in hamster cells could be due to mutations at a regulatory gene locus, or at a yet unknown locus with enzymic defect that causes secondary metabolic imbalances.

Animals↗