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Biomedical subjects

L C Huang

Publications and source records attributed to L C Huang.

At least 19 recordsLinked to original sources
PubMed1995

Genetic instability as a consequence of inappropriate entry into and progression through S-phase.

The stability of the mammalian genome depends on the proper function of G1 and G2 cell cycle control mechanisms. Two tumor suppressors, p53 and retinoblastoma (Rb), play key roles in progression from G1 into S-phase. We address the mechanisms by which these proteins mediate a G1 arrest in response to DNA damage and limiting metabolic conditions. Gamma-irradiation induced a prolonged, p53-dependent G1 arrest associated with a long-term increase in the levels of the cdk-inhibitor p21WAFl/Cipl (p21). Microinjection of linear plasmid DNA also caused a G1 arrest. The p53-dependent arrest induced by inhibitors of UMP biosynthesis was reversible and occurred in the absence of detectable DNA damage. Both arrest mechanisms contribute to limiting the formation and propagation of damaged genomes. Cells containing mutant p53 but wild-type Rb do not generate methotrexate (Mtx) resistant variants. However, pre-treatment with DNA damaging agents prior to drug selection resulted in resistant clones containing amplified dihydrofolate reductase (DHFR) genes, suggesting that DNA breakage is a rate limiting step for gene amplification. The Mtx-induced arrest did not occur in cells with non-functional Rb. Rb acts as a negative regulator of the E2F transcription factors, and Rb-deficient primary mouse embryo fibroblasts (MEFs) produced elevated levels of mRNA and protein for key E2F target genes. Failure to prevent entry into S-phase in Rb-/- MEFs exposed to DNA-damaging or nutrient limiting conditions caused apoptosis and correlated with p53 induction. Taken together, these findings indicate a link between p53 and Rb function and suggest that their coordination insures correct entry into S-phase, minimizing the emergence of genetic variants.

Animals↗
PubMed1993

Vulvar neoplasia associated with other primary malignancies.

It is recognized that a significant number of patients with vulvar neoplasia have had previous, concurrent, or subsequent genital tract neoplasia. This has resulted in speculation that there may be a common etiology and, in particular, of the possibility of an infection element. Among 59 cases of vulvar cancer diagnosed at the National Taiwan University Hospital from 1976 to 1991, there were seven cases (12%) associated with other primary malignancies. Carcinoma of the cervix was the most frequent other primary cancer (6/7, 86%). The possible role of human papilloma virus infection in genital neoplasia is discussed.

Adult↗
PubMed1992

In vivo conversion of [3H]myoinositol to [3H]chiroinositol in rat tissues.

We report here the in vivo conversion of [3H]myoinositol to [3H]chiroinositol. After labeling intraperitoneally with [3H]myoinositol for 3 days to reach radioisotope equilibrium in urine, [3H]chiroinositol was isolated from tissues and purified after 6 N HCl hydrolysis by two sequential paper chromatographies and high performance liquid chromatography (HPLC). Percent conversion of [3H]myoinositol to [3H]chiroinositol was highest in urine (36%), liver (8.8%), muscle (8.8%), and blood (7.6%) with intestine, brain, kidney, spleen, and heart decreasing in percentage from 2.8 to 0.7%. Labeling of other inositol isomers including scyllo-, neo-, and epi-, and mucoinositol was minimal, approximately 0.06% of [3H]myoinositol. Glucose was unlabeled, but glucuronate, the product of myoinositol oxidation, was labeled up to 1.5% of the [3H] myoinositol. Acid hydrolysates of combined inositol-containing phospholipids contain significant labeled chiroinositol. [3H]Phosphatidylinositols and [3H]glycosylphosphatidylinositols were extracted from liver, muscle, and blood, isolated by thin layer chromatography, and inositols purified by HPLC after acid hydrolysis. Percent conversion of [3H]myoinositol to [3H] chiroinositol was highest in blood (60.4%) followed by muscle (7.7%) and liver (2.2%).

Animals↗
PubMed1992

Age trends in lung cancer.

To investigate the relationship between the stages of cancer development and the age trends in histologic type found at the time of disease diagnosis, we studied 1,669 patients with histologically proven lung cancer. These patients were examined at the National Taiwan University Hospital using Mantel-Haenszel Chi-square testing to determine a linear trend. These patients were divided into three age groups: group 1 (< 45 years), 141 patients (8%); group 2 (45-64 years), 946 patients (57%); group 3 (65 years or more), 582 patients (35%). The ratio of men to women was 1.4 in group 1, 2.5 in group 2 and 2.3 in group 3. In men, there was a significant trend for the proportion of squamous cell carcinoma to increase from 26% to 42% and that of adenocarcinoma to decrease from 52% to 34% as age increased. In women, an age trend for histologic type was not observed. There was also a significant trend for local-stage squamous cell carcinoma in men to increase from 18% in group 1 to 35% in group 2 and to 42% in group 3. In men, but not in women, local-stage large cell carcinoma increased from 20% in group 1 to 31% in group 2 and to 64% in group 3. However, the age-stage trend for other cell types was not significant in men.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenocarcinoma↗
PubMed1991

A bacterial model system for chromosomal targeting.

A system that permits efficient site-specific chromosomal targeting of foreign DNA on the Escherichia coli chromosome has been developed, using the FLP site-specific recombination system derived from the yeast 2 mu plasmid. The system demonstrates the feasibility of using site-specific recombination for this purpose, and provides a means to gather information on parameters that may affect chromosomal targeting to guide efforts to establish similar systems in higher eukaryotes. In this model system, the efficiency of integration of foreign DNA is affected by the location of the target site in the chromosome, and the structure of the recombination sites.

Base Sequence↗
PubMed1991

Insulin mediators are the signal transduction system responsible for insulin's actions on human placental steroidogenesis.

To test the hypothesis that insulin mediators serve as the signal transduction system for insulin's steroidogenic actions in human placental cytotrophoblasts, we examined the effects of two inositolglycan insulin mediators, the insulin pH 2.0 chiro-inositol mediator (IM-pH 2.0) and the insulin pH 1.3 myo-inositol mediator (IM-pH 1.3), on cytotrophoblastic steroidogenesis. When human cytotrophoblasts were incubated in medium supplemented with androstenedione for 24 h, treatment with IM-pH 2.0 or IM-pH 1.3 suppressed aromatase activity by 15% (P less than 0.05) and 49% (P less than 0.05), respectively, compared to insulin, which suppressed aromatase activity by 21% (P less than 0.05). When cytotrophoblasts were incubated in medium supplemented with pregnenolone for 24 h, treatment with IM-pH 2.0 or IM-pH 1.3 stimulated 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) activity by 145% (P less than 0.05) and 168% (P less than 0.05), respectively, compared to insulin, which stimulated 3 beta HSD activity by 63% (P less than 0.05). Suppression of aromatase activity and stimulation of 3 beta HSD activity by inositolglycan mediators were both concentration dependent. Moreover, preincubation of cytotrophoblasts with the antiinositolglycan antibody alpha IGP completely abolished insulin's ability to either inhibit aromatase or stimulate 3 beta HSD activity. These results indicate that insulin mediators mimic insulin's effects on cytotrophoblastic aromatase and 3 beta HSD activities and suggest that inositolglycan mediators are the signal transduction mechanism responsible for insulin's regulation of human placental steroid hormone biosynthesis.

3-Hydroxysteroid Dehydrogenases↗
PubMed1990

Anti-inositolglycan antibodies selectively block some of the actions of insulin in intact BC3H1 cells.

We have studied the mechanism of generation of insulin mediators by using specific antibodies raised against the oligosaccharide anchor of membrane proteins. These antibodies (i) block the in vitro effects of purified insulin mediators and (ii) block the insulin-induced stimulation of pyruvate dehydrogenase in intact BC3H1 myocytes but not insulin-stimulated glucose uptake, generation of diacylglycerol, or generation of insulin mediators. When added to intact cells in the presence of insulin, these antibodies induce the accumulation of insulin mediator activity in the extracellular medium. We therefore conclude that these anti-inositolglycan antibodies block some of the effects of insulin by inhibiting the uptake of specific insulin mediators generated outside the cell.

Animals↗
PubMed1988

Rat liver insulin mediator which stimulates pyruvate dehydrogenase phosphate contains galactosamine and D-chiroinositol.

It has been established that insulin treatment of cells, isolated plasma membranes, or whole animals leads to the generation of low molecular weight mediators which serve as intermediates in the signalling pathway. At least two distinct classes of mediator have been described, based on differences in apparent molecular weight, isoelectric point and biological activity (Cheng, K., and Larner, J. (1985) Ann. Rev. Physiol. 45, 407-424). Recently, Saltiel's (Saltiel, A.R., and Cuatrecasas, P. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 5793-5797) and Mato's (Mato, J.M., Kelly, K.L., Abler, A., and Jarett, L. (1987) J. Biol. Chem. 262, 2131-2137) laboratories have described an insulin "modulator" which was apparently derived from glycosylphosphoinositol linker, similar to those known to anchor proteins to the external surface of the cell membrane (Low, M.G. (1987) Bioch. J. 244, 1-13). In this paper, we report that highly purified preparations of the insulin mediator which stimulates pyruvate dehydrogenase phosphatase contain mannose, galactosamine, and D-chiroinositol. These determinations are based upon analyses using paper chromatography and gas chromatography/mass spectroscopy. Nitrous acid deamination of the mediator resulted in release of inositol phosphate, indicating that the galactosamine and D-chiroinositol are linked. Although the presence of chiroinositol in modulator from H35 hepatoma cells has been recently reported (Mato, J.M., Kelly, K.L., Abler, A., Jarett, L., Corkey, B.E., Cashel, J.A., and Zopf, D. (1987) Bioch. Biophys. Res. Comm. 146, 764-770), the optical identity of the inositol remained unknown until the present report. Likewise, the presence of galactosamine rather than glucosamine in insulin mediator is a novel finding. These findings, coupled with those of Saltiel and Mato's groups, provide clear evidence for the existence of multiple forms of insulin mediators. Additionally, the results presented here afford further confirmation for the formation of insulin mediators from glycosyl-phosphoinositol linkers.

Animals↗
PubMed1988

Holliday intermediates and reaction by-products in FLP protein-promoted site-specific recombination.

Holliday structures are formed and resolved by FLP protein during site-specific recombination. These structures have been isolated and are visualized in both native and partially denatured states by electron microscopy. No single-strand breaks are found within the junction, indicating that the structure results from a reciprocal exchange of strands. These structures have properties consistent with being reaction intermediates. Double-strand cleavage products and "Y structures" are also detected and appear to be by-products of the reaction. The Y structures are three-armed branched molecules with a covalently closed junction located at the FLP recombination target site. Models are discussed, suggesting that both of these novel structures are made by aberrant cleavages during formation and resolution of the Holliday intermediate.

Bacterial Outer Membrane Proteins↗
PubMed1986

The function of Mg-ATP in interactions between the regulatory and catalytic subunits of type I cAMP-dependent protein kinase from rabbit skeletal muscle.

The regulatory subunit of Type I cAMP-dependent protein kinase from rabbit skeletal muscle can bind [3H]cAMP to form the R-[3H]cAMP complex, and the slow phase of the enhanced exchange of free cAMP with [3H]cAMP from the R-[3H]cAMP complexes was studied under various conditions using the equilibrium isotope exchange technique. Results indicate that Mg-ATP and the catalytic subunit are absolutely required for the enhanced exchange reaction to occur, but phosphorylation of the regulatory subunit by Mg-ATP does not play a determining role in the slow rate of the dissociation/association of the Type I protein-kinase in the presence of cAMP and the catalytic subunit. We interpret the role of Mg-ATP as being one in which it may provide the structural attributes required for formation of a stabilized transient state of the cAMP-regulatory subunit-catalytic subunit ternary complex, an obligatory intermediate involved in the dissociation/association of Type I cAMP-dependent protein kinase.

Adenosine Triphosphate↗
PubMed1986

Biochemical and ultrastructural study of Leu M1 antigen in Reed-Sternberg cells: comparison with granulocytes and interdigitating reticulum cells.

A group of monoclonal antibodies was shown to react with glycoconjugates containing a sugar sequence--lacto-N-fucopentaose III (LNF-III)--in granulocytes and in some normal nonlymphoid cells. The antibodies including anti-Leu M1, anti-My-1, WGHS 29-1, 534F-8, and 538F-12 of the immunoglobulin M-type were used to study the biochemical properties of LNF-III antigens in granulocytes, interdigitating reticulum cells, and neoplastic cells of Hodgkin's disease. In contrast to the presence of an abundant LNF-III glycolipid in granulocytes, the Hodgkin's neoplastic cells had no LNF-III glycolipid or contained only minimal amounts; however, both LNF-III glycoconjugates isolated from Hodgkin's neoplastic cells and interdigitating reticulum cells appeared to be a similar, if not an identical, 150,000-molecular-weight glycoprotein. The neoplastic cells in Hodgkin's disease appeared to show a biochemical property more closely related to interdigitating reticulum cells than any other cells in the monocyte-granulocyte-histiocyte system.

Antibodies, Monoclonal↗
PubMed1985

Phosphorylation of the regulatory subunit of type I cyclic AMP-dependent protein kinase by its catalytic subunit.

The regulatory subunit (R) of Type I cAMP-dependent protein kinase from rabbit skeletal muscle can serve as a substrate for its catalytic subunit (C). The degree of phosphorylation depends on both the concentration of C and the the time of incubation. Moreover, the phosphorylation can be totally blocked by protein kinase inhibitors. In contrast, cAMP stimulates the phosphorylation of R using the holoenzyme. The purified holoenzyme isolated from rabbit skeletal muscle can be further fractionated into two fractions on DEAE Sephadex column. The first fraction eluted with low salt (50 mM NaCl) contains a much lower concentration of kinases than the second fraction eluted with high salt (100 mM NaCl), but the low salt kinase can be readily phosphorylated in the presence of MgATP. Our data thus implies that only a small fraction of Type I cAMP-dependent protein kinases in the skeletal muscle is present as the phosphorylatable species.

Animals↗
PubMed1983

Chemical cross-linking of cyclic AMP-dependent protein kinase and its dissimilar subunits.

Previous kinetic studies have demonstrated that the activation of cyclic AMP-dependent protein kinase by cyclic AMP involves the formation of a ternary complex of cyclic AMP, the regulatory subunit (R) and the catalytic subunit (C). It is suggested that only this ternary complex breaks down to liberate the enzymically active catalytic subunit. We have performed cross-linking experiments with the holoenzyme and its dissimilar subunits in the presence of MgATP and various concentrations of cyclic AMP. Results from these cross-linking studies indicate that regulatory subunits exist as dimers in the native form. Moreover, dissociation of the holoenzyme or the reconstituted enzyme is promoted by cyclic AMP, and the effect of MgATP is to stabilize the enzyme in the tetrameric form. The success in cross-linking the regulatory and the catalytic subunits of protein kinase with the lysine-specific bifunctional cross-linking reagent dimethyl suberimidate may be attributed to the presence of a large number of lysine residues in the enzyme.

Adenosine Triphosphate↗