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Biomedical subjects

Y Chu

Publications and source records attributed to Y Chu.

12 recordsLinked to original sources
PubMed1992

Ellipticine increases the superhelical density of intracellular SV40 DNA by intercalation.

We investigated the in vivo effect of ellipticine, a mammalian topoisomeraseII(topoII) inhibitor, on SV40 DNA topology. In contrast to epipodophyllotoxins, ellipticine did not cause significant double stranded cleavage of intracellular SV40 DNA. Furthermore, ellipticine reduced cleavage induced by epipodophyllotoxins, VP16 and VM26. Unexpectedly, ellipticine dramatically increased the superhelical density of a fraction of intracellular SV40 DNA. Several lines of evidence suggest that the formation of this highly supercoiled DNA species (Ih form DNA) is not due to the inhibition of topoII per se, but is the result of intercalation by ellipticine in a subfraction of the intracellular SV40 chromatin followed by the fixation of DNA linking number by a topoisomerase activity. Based on the linking number change and the known unwinding angle of ellipticine, the intercalation density was calculated as one ellipticine molecule per 10-20 bp in the Ih DNA. This result suggests the existence of different populations of intracellular SV40 chromatin with respect to the accessibility to ellipticine intercalation.

Cell Line↗
PubMed1992

Developmental study of chondroitin-6-sulphate in normal and dystrophic rat retina.

The RCS rat is a widely studied model of human retinal dystrophies including retinitis pigmentosa. Chondroitin-6-sulphate (C6S) in the interphotoreceptor matrix was localised immunocytochemically in both the normal congenic and dystrophic strains of the RCS rat up to 65 days postnatally. From postnatal days 5 to 15 the distribution of C6S in both strains was similar, being localised in the interstices of developing inner and outer segments and adjacent to the RPE surface. In the normal rats, the distribution of C6S did not change with age. In the RCS rats, however, at postnatal days 20 to 35 staining was observed as a dense band at the junction of inner and outer segments and no staining was observed adjacent to the surface of the RPE. At postnatal day 45 onwards there was a decrease and a complete absence of C6S staining in these rats. This change in the pattern of staining correlated with the morphological observation of the progressive degeneration of photoreceptor cells suggesting that C6S may be important in photoreceptor degeneration in the RCS rat.

Aging↗
PubMed1992

Persistent infection of human adenovirus type 5 in human monocyte cell lines.

Adenovirus infection of human monocyte hybridoma cell lines and the fusion partner U937 was investigated. Adenovirus adsorbed poorly to these cells as well as primary human alveolar macrophages. The virus-binding experiments showed a 100-fold reduction in apparent viral binding to these cells compared to the permissive HeLa cells. Adsorption of adenovirus to these cells could be enhanced by preincubation of adenovirus with its antiserum. Following entry into the cells amplification of adenovirus DNA was detected starting at 2 days postinfection but few mature virus particles were produced. The infected cultures survived the infection and continued to grow for more than a year. In these chronically infected cultures, linear adenovirus DNA persisted up to 200 copies per cell and a small amount of mature virus was produced. Infectious center assay and cell cloning experiments showed that the majority of the cells in the chronically infected cultures harbor adenovirus genome. These results indicate that restriction of replication of human adenovirus type 5 at the late phase results in persistent infection of U937 and the human monocyte hybridoma cell lines.

Adenoviruses, Human↗
PubMed1992

The effect of IH764-3 on fibroblast proliferation and function.

The effect of IH764-3, a potent component isolated from Salvia miltiorrhiza, on the proliferation and function of cultured fibroblasts was studied. It was found that the fibroblast growth curve had a dose-dependent relationship with IH764-3 concentration. The incorporation of 3H-TdR and 3H-proline into fibroblasts was significantly inhibited by IH764-3, and calmodulin, fibronectin and thrombospondin contents in the test group were obviously lower than those in the control group. Flow cytometry showed that in the IH764-3-treated group, the percentage of cells in G0/G1 phase was higher than that in the control. Electron microscopic observation (TEM and SEM) showed that in the treated group, collagen secretion was decreased. All of these results indicate that IH764-3 exerts a direct inhibitory effect on fibroblast proliferation and affects their ability to synthesize collagen.

Animals↗
PubMed1991

A rapid method for screening vaccinia virus recombinants.

A rapid and small-scale method for screening vaccinia virus recombinants employing micrococcal nuclease is described. This protocol utilizes the differential sensitivity of cellular and viral DNA to the nuclease, which can be selectively activated by addition of Ca2+ and inactivated by elimination of Ca2+. Two to five micrograms of viral DNA can be obtained from one infected L cell plate (50 mm) after overnight incubation.

Animals↗
PubMed1991

Specific binding and internalization of monoclonal antibody HI98-daunorubicin conjugate by human leukemic cells (HL60).

McAb-HI98 has been proved to bind specifically to HL60 cells. In this study, we further observed the specific binding of HI98-Daunorubicin (DNR) conjugate to HL60 cells, the transmembranal transport of HI98-DNR and the process of internalization by immunoelectron microscopy. After HL60 cells were incubated with HI98-DNR-Au, gold particles were first found on the surface membranes of HL60 cells, and then inside the cells. Internalization was found to occur through the formation of endocytic vesicles. Results indicate that the immunoconjugate selectively binds to target cells and enters the cells specifically and rapidly, thus enhancing intracellular drug concentration.

Antibodies, Monoclonal↗
PubMed1990

P1 nuclease defines a subpopulation of active SV40 chromatin--a new nuclease hypersensitivity assay.

Under exhaustive digestion conditions P1 nuclease was found to cleave a subpopulation of intracellular SV40 chromatin only once. The major P1 cleavage site in SV40 DNA was mapped at the origin of DNA replication, and the two minor sites at the SV40 enhancers. The P1-sensitive SV40 chromatin subpopulation was found to have higher superhelical density than the bulk of the intracellular SV40 chromatin. Furthermore, pulse labeled SV40 DNA which had higher superhelical density than that of the steady state viral DNA (S.S. Chen and M.T.Hsu, J. Virol 51:14-19, 1984) was also found to be preferentially cleaved by P1 nuclease. These results are consistent with a supercoil-dependent alteration of chromatin conformation near the regulatory region of the viral genome that can be recognized by P1 nuclease. Since P1 nuclease cleaves the subpopulation of SV40 chromatin only once without further degradation, this nuclease can be used as a general tool to define viral or cellular chromatin fraction with altered chromatin conformation and to map nuclease hypersensitive sites. Preliminary studies indicate that P1 makes limited double stranded cleavages in cellular chromatin to generate large DNA fragments.

Animals↗
PubMed1989

Monocyte function in chickens with hereditary muscular dystrophy.

Monocyte functions of Storrs strain muscular dystrophic (MD) chickens and Storrs control strain were compared. After short-term in vitro culture of monocytes, cells taken from Storrs MD chickens had a significantly lower incidence of cells capable of phagocytizing sheep red blood cells than did cells cultured from the control strain. In contrast, no difference was found in the ability of MD vs. control strain blood mononuclear cells to undergo in vitro chemotaxis in response to a bacterial culture supernatant. The study also revealed a distinct peripheral blood leukocyte profile of young MD chickens: elevated percentages and absolute numbers of granulocytes. The total leukocyte count in MD chickens was not significantly different from that of normal chickens. These findings extend previous observations concerning altered reticuloendothelial system function in MD strain chickens.

Animals↗
PubMed1988

The chicken macrophage response to carbohydrate-based irritants: temporal changes in peritoneal cell populations.

Temporal changes in the recruitment and functional activation of Cornell K strain chicken peritoneal macrophages elicited by starch and dextrans were determined. During a 72-hr period following intraperitoneal injection, Sephadex (cross-linked dextran) elicited a gradually increasing number of peritoneal exudate cells (PECs) which contained greater than or equal to 78% macrophages in the adherent cell population. In contrast, starch tended to elicit higher numbers of PECs early in the stimulation process, with heterophils comprising a major proportion of the adherent cells. Later in the time course, macrophages were the predominant adherent cell type. Comparisons of PEC recruitment using Sephadex vs. low molecular weight dextrans demonstrated that the low-molecular weight dextrans elicited fewer PECs than did Sephadex; unlike Sephadex, however, the low molecular weight dextrans generated a significant peak of heterophil infiltration that was similar, although delayed, to that produced with starch. Sephadex-stimulated peritoneal macrophages exhibited time-dependent functional acquisitions for 1) the phagocytosis of sheep erythrocytes, 2) the engulfment of opsonized sheep erythrocytes, and 3) opsonin-erythrocyte rosetting. Acquisition of phagocytic activity for uncoated vs. opsonized erythrocytes occurred under very different rates during the time course. The results suggest that both the nature of the irritant and the time point of cell harvest can be appropriately selected to provide the particular cell population and functional status desired for subsequent in vitro analyses.

Animals↗