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Biomedical subjects

H Y Wu

Publications and source records attributed to H Y Wu.

At least 19 recordsLinked to original sources
PubMed1992

Interlocking of plasmid DNAs due to Lac repressor-operator interaction.

The presence of a single lac repressor binding sequence on plasmid DNAs is shown to mediate the formation of interlocked dimers in E. coli. The presence of both homo- and hetero-interlocked dimers suggests that the lac repressor complex can bring together randomly two plasmid DNA molecules to facilitate gyrase-mediated interlocking. The exclusive formation of multiply intertwined dimers also suggest that the lac repressor complex may bind simultaneously to a pair of replicated daughter plasmid molecules prior to their segregation. The formation of interlocked plasmid DNAs can be indicative of interaction between two DNA bound proteins in vivo.

Base Sequence↗
PubMed1992

Identification of a DNA supercoiling activity in Saccharomyces cerevisiae.

A relaxed plasmid DNA is shown to become positively supercoiled in cell extracts from top1 strains of Saccharomyces cerevisiae. This positive supercoiling activity is dependent on the presence of bacterial DNA topoisomerase I and ATP (or dATP), and the positive supercoils generated in this reaction are not constrained by protein(s). Non-hydrolyzable ATP analogs cannot substitute for ATP in this supercoiling reaction, and the supercoiling activity is not due to RNA synthesis. The presence of an ARS sequence in the DNA does not alter the activity. Furthermore, this activity is equally active against UV irradiated or intact DNA. Extracts prepared from rad50 and rad52 mutant cells exhibited the same activity. Partial purification of this activity suggests that a protein factor with a native molecular weight of approximately 150 kDa is primarily responsible for the activity. The possibility that this supercoiling activity may be due to tracking of a protein along the intact duplex DNA is discussed.

Adenosine Triphosphate↗
PubMed1992

The structure of the Mental Health Inventory among Chinese in Taiwan.

This study attempted to ascertain the construct validity and external validity of the Mental Health Inventory in a Chinese population in Taiwan and contrast these results with results obtained from studies of several U.S. populations. In particular, a series of measurement models were specified and evaluated to address the issues of reliability and validity. Data were collected from personal interviews of a probability sample of 1,194 Chinese respondents 14 years of age and older in four townships in southwest Taiwan. The Mental Health Inventory was found to involve two major components: positive well-being and psychological distress. As a hierarchical structure, each component consists of one second-order and two or three first-order factors. The relationships between well-being and distress can be characterized as substantially independent and modestly bipolar depending on the level and specification.

Adolescent↗
PubMed1992

Serum antibody responses to Streptococcus mutans antigens in humans systemically infected with oral streptococci.

Sera from patients with subacute bacterial endocarditis (SBE) due to Streptococcus mutans or other oral streptococci and from normal subjects were assayed by enzyme-linked immunosorbent assay for antibodies to defined S. mutans antigens. Antibodies of IgG and IgA isotypes to Ag I/II and Ag III were greatly elevated in S. mutans-SBE sera, and the IgA antibodies in 3 sera included both polymeric and monomeric forms. Elevated IgM and IgG anti-lipoteichoic acid and IgG and IgA anti-serotype c polysaccharide antibodies were also found. The sera of 4 of 6 patients infected with other oral streptococci also displayed antibodies to S. mutans Ag I/II. Sera of 3 patients infected with Streptococcus mitis or Streptococcus oralis, but none of the S. mutans-infected cases, showed elevated antibodies to human heart sarcolemma, and all SBE sera had elevated rheumatoid factor. These results suggest that the known surface protein antigens of S. mutans are immunodominant in humans, and are not likely to be heart cross-reactive.

Antibodies, Bacterial↗
PubMed1992

Antibody-secreting cell responses in the mouse liver.

To elucidate the origins of biliary IgA antibodies, we investigated the isotype and specificity of antibody-secreting cells (ASC) in the liver in comparison with the spleen and intestinal lamina propria of mice immunized by peroral or parenteral routes. The profile of specific IgM, IgG1, IgG2a, and IgA ASC in the liver resembled that of the spleen rather than the lamina propria, regardless of the route of immunization. Peroral immunization increased the proportion of specific IgA ASC in all three organs. However, liver mononuclear cells (MNC) contained a higher proportion of total IgA-secreting cells than spleen cells. After immunization, the number and proportion of B220+ B cells were increased in the liver but not in the spleen. Although the predominant isotype of Ig and specific antibody in bile in response to immunization by either route was IgA, IgM and IgG were clearly detectable. However, specific activities of biliary antibodies relative to total Ig isotype were generally higher than in serum. The predominance of IgA-secreting cells in the liver and the large amount of IgA secreted in the bile resemble the situation at other secretory sites of the mucosal immune system. However, specific antibody-secreting cells appear to accumulate in the liver promptly after immunization, regardless of isotype, and contribute locally produced antibodies to the bile.

Administration, Oral↗
PubMed1991

DNA looping alters local DNA conformation during transcription.

The effect of protein-mediated DNA looping on local DNA conformation during active transcription was studied using the lac repressor-operator system. Our results suggest that lac repressor-mediated DNA looping within a plasmid DNA molecule containing two lac repressor binding sequences in vivo effectively separates plasmid DNA into two topological domains. Supercoils generated by transcription within each topological domain can be rapidly removed by DNA topoisomerase I.

Base Sequence↗
PubMed1991

Evidence in favor of the mechanical (intrauterine torsion) theory over the endocrinopathy (cryptorchidism) theory in the pathogenesis of testicular agenesis.

There are 2 competing theories regarding the pathogenesis of testicular agenesis--the endocrinopathy/cryptorchidism and the mechanical/intrauterine torsion theories. We compare the number of Leydig cells, total number of germ cells and the transformation of adult dark spermatogonia into primary spermatocytes in semithin sections of testicular biopsies from 59 contralateral descended testes of patients with testicular agenesis with those in the contralateral descended testes from 250 patients with unilateral cryptorchidism. The contralateral descended testes from boys with testicular agenesis demonstrated higher numbers of Leydig cells, higher numbers of total germ cells and a higher rate of transformation of adult dark spermatogonia into primary spermatocytes than did the contralateral descended testes from the patients with unilateral cryptorchidism. These findings favor the mechanical/intrauterine torsion theory over the endocrinopathy/cryptorchidism theory in the pathogenesis of testicular agenesis.

Biopsy↗
PubMed1991

Distribution, persistence, and recall of serum and salivary antibody responses to peroral immunization with protein antigen I/II of Streptococcus mutans coupled to the cholera toxin B subunit.

After peroral immunization of mice with surface protein antigen (Ag) I/II of Streptococcus mutans conjugated to the cholera toxin B (CTB) subunit, cells actively secreting immunoglobulin A (IgA) antibodies specific for Ag I/II, but not for CT, were induced in the salivary glands; salivary IgA anti-Ag I/II antibodies and total salivary IgA were also elevated. The development of large numbers of IgA and IgG antibody-secreting cells in the mesenteric lymph nodes and spleen and high levels of serum IgA and IgG antibodies to Ag I/II and CT demonstrated that a response to both antigens occurred. At least two to three intragastric doses of 15 micrograms or more of Ag I/II-CTB conjugate, plus free CT as an adjuvant, were needed to induce the salivary IgA anti-Ag I/II response, which peaked at about 35 days and persisted at lower levels for 5 to 6 months. A single booster intragastric immunization did not induce enhanced salivary IgA anti-Ag I/II antibodies relative to the primary response, but serum IgA and IgG antibodies to both Ag I/II and CT showed evidence of marked anamnestic responses. The results indicated that relatively long-term mucosal IgA antibody responses could be induced by peroral immunization with small quantities of a CTB-conjugated protein. However, additional factors governed the distribution of cells secreting antibodies of different specificities, or capable of mounting anamnestic responses, between different compartments of the mucosal and circulatory immune systems.

Adjuvants, Immunologic↗
PubMed1991

Role of nitrosamides in the high risk for gastric cancer in China.

Gastric cancer is the leading cause of death from cancer in China. Samples of fish sauce, a traditional seasoning, were collected in the high-risk area for gastric cancer in the Fuzhou area, Fujian Province. When fish sauce samples were nitrosated at pH 2.0, direct mutagenicity and high contents of N-nitrosamide were detected (30.9-78.0 microM); the N-nitrosamide content of three samples of fish sauce made in Guangdong and purchased from a market outside Fujian were low (2.1-6.0 microns). When the nitrosated fish sauce extract was given to newborn rats by gavage, dysplasia and adenocarcinoma were induced in the glandular stomach in the 4th and 16th experimental week, respectively. N-Nitrosamides were also found in fasting gastric juice from patients with chronic gastritis in the high-risk area of Putian. The mean concentration of total N-nitrosamides in the extracts correlated with the severity of gastritis in the stomach. These findings indicate that N-nitrosamides may play an important role in causing gastric cancer in China.

Animals↗
PubMed1990

Transcriptional activation by wild-type but not transforming mutants of the p53 anti-oncogene.

The protein encoded by the wild-type p53 proto-oncogene has been shown to suppress transformation, whereas certain mutations that alter p53 become transformation competent. Fusion proteins between p53 and the GAL4 DNA binding domain were made to anchor p53 to a DNA target sequence and to allow measurement of transcriptional activation of a reporter plasmid. The wild-type p53 stimulated transcription in this assay, but two transforming mutations in p53 were unable to act as transcriptional activators. Therefore, p53 can activate transcription, and transformation-activating mutations result in a loss of function of the p53 protein. The inability of the p53 mutant proteins to activate transcription may enable them to be transformation competent.

Base Sequence↗
PubMed1990

Effects of transcription and translation on gyrase-mediated DNA cleavage in Escherichia coli.

Gyrase-mediated DNA cleavage on plasmid DNAs was measured in Escherichia coli treated with oxolinic acid. On pBR322 DNA, gyrase cleavage sites were concentrated in the region between the 3'-ends of the tetA and bla genes. The preferential cleavage in this region was dependent on RNA transcription and the divergent orientation of these two transcription units. The enhanced gyrase cleavage also required translation; chloramphenicol treatment or the insertion of a translation terminator within the 5'-proximal region of the tetA gene abolished the enhanced cleavage. We suggest that the enhanced gyrase cleavage may reflect the changes in local DNA supercoiling during RNA transcription as gyrase cleavage in vitro was shown to be sensitive to the supercoiling state of DNA. The effects of transcription and translation on gyrase cleavage can best be explained by the twin-supercoiled-domain model of transcription (Liu, L. F., and Wang, J. C. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7024-7027).

DNA Topoisomerases, Type II↗
PubMed1990

Immunological cross-reactivity between Streptococcus mutans and human heart tissue examined by cross-immunization experiments.

Hyperimmunization of rabbits with Streptococcus mutans or other related cariogenic streptococci sometimes induces serum antibodies that react with human heart muscle. To determine whether antigen I/II (AgI/II), a major surface protein antigen present in most human isolates of these organisms, was responsible for inducing cross-reactive antibodies, we tested it for antigenic similarity to heart components, exploiting the ability of immune systems to mount anamnestic responses to antigens previously encountered. Mice immunized with a strain of Streptococcus pyogenes type M6, known to be heart cross-reactive, or with intact S. mutans cells developed antibodies that could be detected on a human heart sarcolemmal preparation. However, mice immunized with AgI/II and boosted with sarcolemma were unable to develop significant antisarcolemmal antibodies attributable to prior sensitization by AgI/II. Similarly, AgI/II was unable to recall antisarcolemmal responses in mice previously immunized with sarcolemma. Nevertheless, strong immunoglobulin G antibody responses to AgI/II were detected at the single-cell level in spleens and as circulating antibodies in all mice immunized with AgI/II or AgI/II-bearing S. mutans. We conclude that the ability of S. mutans to induce heart-reactive antibodies is not due to antigenic similarity between AgI/II and components of human heart but may be caused by other cross-reactive antigens in the bacterial cells or by nonspecific stimulation of the immune system.

Animals↗
PubMed1990

Streptococcus mutans and the problem of heart cross-reactivity.

Investigations of immune responses to Streptococcus mutans have fostered consideration of vaccination as a possible preventive measure against dental caries. However, the finding that hyperimmune rabbit antisera to S. mutans sometimes give immunofluorescent reactions on human heart raised concerns over safety, especially as most individuals display circulating antibodies to this common oral organism. Recent progress in elucidating the molecular mechanisms of the well-established immunological cross-reactivity between group A streptococci and human heart tissue and the structure of S. mutans antigens permits a re-evaluation of this problem. This review examines the evidence for heart cross-reactivity induced by S. mutans in relation to studies on group A streptococci and current understanding of autoimmunity. Although the mechanisms involved in this phenomenon need further clarification, it now appears that it cannot be ascribed to antigenic similarity between heart tissue and a high-molecular-weight surface protein antigen of S. mutans.

Antibody Formation↗
PubMed1989

Transcription-driven supercoiling of DNA: direct biochemical evidence from in vitro studies.

The translocation of an RNA polymerase elongation complex along double helical DNA has been proposed to generate positive supercoiling waves ahead of and negative supercoiling waves behind the transcription ensemble. This twin supercoiled domain model has been tested in vitro. In the presence of prokaryotic DNA topoisomerase I, which selectively removes negative supercoils, transcription from a single promoter results in rapid and extensive positive supercoiling of the DNA template. The accumulation of positive supercoils in the DNA template requires continued movement of the elongation complex as well as sizable nascent RNA chains. These in vitro results provide direct biochemical evidence supporting the twin supercoiled domain model of transcription. Furthermore, the magnitute of DNA supercoiling (torsional) waves generated by transcription is much greater than previously expected, suggesting that transcription is one of the principal factors affecting intracellular DNA supercoiling.

DNA Topoisomerases, Type I↗
PubMed1988

Proliferation-dependent regulation of DNA topoisomerase II in cultured human cells.

The intracellular level of DNA topoisomerase II appears to be reversibly regulated by serum concentration in cultured primary human skin fibroblasts (HSF). Upon serum starvation, the intracellular level of topoisomerase II in HSF, as monitored by immunoblotting with antitopoisomerase II antibodies, gradually decreased to a nondetectable level (less than 10(4) copies/cell) over a period of 72 h. Addition of 10% serum to the starved cells led to a gradual increase of the intracellular topoisomerase II to the original level (approximately 10(6) copies/cell) over a period of 24 h. The intracellular DNA topoisomerase II level in HSF is also sensitive to cell density; minimally a 7-fold decrease was observed when HSF were grown to saturation density in a constant serum concentration. Similarly, the intracellular levels of DNA topoisomerase II in other "nontransformed" cells such as mouse NIH 3T3 and 3T6 cells are also sensitive to both the serum concentration and the cell density. In contrast, topoisomerase II levels in transformed cells such as HeLa cells, L1210 cells, and SV40 T-antigen-transformed COS-1 cells are maintained at high levels (approximately 10(6) copies/cell) and are much less sensitive to growth conditions. The topoisomerase II level in HeLa cells synchronized by a double thymidine block remained relatively constant (less than 2-fold difference) throughout the late G1, S, G2, and M phases of the cell cycle. Our results suggest that the level of DNA topoisomerase II is primarily regulated in the G0-G1 phase of the cell cycle and is elevated to a high level (approximately 10(6) copies/cell) in proliferating cells. In contrast, the intracellular levels of DNA topoisomerase I in these cells were largely unaffected by these growth conditions either in HSF or in HeLa cells.

Cell Cycle↗
PubMed1988

Transcription generates positively and negatively supercoiled domains in the template.

We show that transcription of a DNA molecule inside a bacterium is accompanied by local and temporal supercoiling of the DNA template: as transcription proceeds, DNA in front of the transcription ensemble becomes positively supercoiled, and DNA behind the ensemble becomes negatively supercoiled. Because bacterial gyrase and topoisomerase I act differently on positively and negatively supercoiled DNA, the formation of twin supercoiled domains during transcription is manifested by a large increase or decrease in the linking number of an intracellular plasmid when bacterial DNA gyrase or topoisomerase I, respectively, is inhibited. Such changes in linking number are strongly dependent on transcription of the plasmid in cis and on the relative orientations of transcription units on the plasmid. These results indicate that the state of supercoiling of bacterial DNA is strongly modulated by transcription, and that DNA topoisomerases are normally involved in the elongation step of transcription.

DNA Topoisomerases, Type I↗