Search PubMed⌕ Search

Biomedical subjects

Z Zhao

Publications and source records attributed to Z Zhao.

At least 307 records · Page 17Linked to original sources
PubMed1995

[Mutagenicity and anti-mutagenicity assay of airborne suspended particles in Shijiazhuang city].

Samples of airborne suspended particles collected from five air monitoring sites in Shijiazhuang City in 1993 were analyzed with rapid synchronous mutagenicity and anti-mutagenicity tests. It revealed airborne suspended particles collected had direct and indirect mutagenicity, but no anti-mutagenicity, and there was seasonal difference in their mutagenicity, which showed a decreasing trend with an order of winter, spring, summer and autumn. Mutagenicity related positively to air concentrations of total suspended particles and sulfur dioxide, inversely to those of ozone, and did not related to those of nitrogen oxide and carbon monoxide.

Air Pollutants↗
PubMed1995

Serological survey of nasopharyngeal carcinoma in 21 cities of south China.

This paper reports the results of serological survey of 318,912 persons for nasopharyngeal carcinoma (NPC) in 21 cities and counties of south China. There were 8,441 persons with positive VCA-IgA antibody (single item positive) of EB virus (EBV), with a rate of 2.65%. In these VCA-IgA positive persons, 287 persons also had positive EA-IgA (double items positive) of EBV. The overall positive rate was 0.09%. 100 cases of NPC were found and 87 of them (87.0%) were in early stage. NPC found in the group with single item positive accounts for 1.19%, but the rate in the group with double items positive was 19.16% (55 cases). In NPC patients with double items positive, 49 cases were in early stage (89.1%). In 100 cases of NPC found, 45 cases appeared with negative EA-IgA, only with positive VCA-IgA, which indicated that for diagnosis of NPC, sensitivity of EA-IgA was lower than that of VCA-IgA, but its specificity was higher. Therefore, both can increase the detecting rate and early diagnosis rate of NPC. The age of people checked varied with different antibody positive rate and NPC detecting rate. The three items showed a positive correlation. The results are compatible with those of the prospective study for NPC in Wuzhou City, Guangxi, China. The method for NPC serological diagnosis can be extended and applied to raise the NPC detecting rate and early diagnosis rate at secondary prevention. And, it is further proved that there is a close relationship between NPC and EBV.

Adult↗
PubMed1995

[Comprehensive evaluation of protective measures in electric welding].

Protective effects of safety masks, eyewear, work clothes, gloves, periodically physical examination system, and ventilation and barriers at workplace, were evaluated by one-way analysis for handtorch welding, carbon dioxide gas-protective welding, and argon-arc welding operations, etc. in township and village enterprises and state-owned enterprises by interviewing managers in the departments of technology and work safety and field investigating. Based on the results of one-way analysis of protective measures, comprehensive evaluations of various enterprises were made with a fussy mathematical model. Both enterprises in township and village level and of state-owned were graded as A on a basis of the evaluation, which will be helpful to the better management of occupational health in the future.

Evaluation Studies as Topic↗
PubMed1995

Plasma membrane sialoglycoproteins of human corneal epithelium in culture.

A number of studies, using either rat or rabbit models, have focused on delineating the role of cell surface glycoconjugates in corneal epithelial cell migration and wound healing. We have recently identified the cell surface sialoglycoproteins of rabbit corneal epithelium and have shown that the levels of at least three membrane glycoproteins are markedly altered during cell migration. Because species-related differences may be present, it is important to select an appropriate animal model for studies designed to contribute to the understanding of the mechanism of human corneal wound healing. The purpose of this study was to identify the cell surface sialoglycoproteins of human corneal epithelium. Plasma membrane sialoglycoproteins of primary cultures of human corneal epithelium were labeled with NaB3H4 after oxidation by mild NaIO4 treatment. The labeled glycoproteins were analyzed by SDS-polyacrylamide gel electrophoresis and fluorography. Four different preparations of human corneal epithelial cell cultures were analyzed, and results were compared with those of rabbit corneal epithelium. Of the 11 radiolabeled sialoglycoproteins we identified recently in rabbit corneal epithelium, eight were also present in human corneal epithelium. These similarities in the electrophoretic patterns of the plasma membrane glycoproteins of the two species suggest that rabbit is most likely an appropriate animal model for studies designed to contribute to the understanding of the structure and function of cell surface glycoproteins of human corneal epithelium.

Animals↗
PubMed1995

[Research on the different blood types umbilical cord blood hematopoietic progenitors mixed culture in vitro].

Using single layer agar culture method, we make a study on culture of human hematopoietic progenitor cell from umbilical cord blood. The result showed the mean value of the granulocyte macrophage progenitor cells (CFU-GM) from twenty neonates cord blood was 95.6 +/- 36.5/10(6) MNC. We compared the mixed culture of two different blood types neonates cord blood hematopoietic progenitors with single sample and found little difference between them in number and growth characteristics. This may provide a theoretical basis for clinical transplantation of mixed human cord progenitor cells.

Blood Group Antigens↗
PubMed1995

[Serologic screening on nasopharyngeal cancer in 338,868 persons in 21 cities and counties of Guangxi Region, China].

Serological screening on nasopharyngeal cancer in 338,868 persons living in 21 cities and counties of Guangxi Zhuang Autonomous Region was carried out from January 1991 to September 1993. Results showed 9367 persons were positive for IgA antibodies to Epstein-Barr virus (EBV) capsid antigen, and 306 of them positive for IgA to EBV early antigen. One hundred and thirteen cases of nasopharyngeal cancer were detected in the former with 100 cases (88.5%) in the early stage, and 63 cases in the latter with 58 (92.1%) cases in the early stage. It suggested certain relationship existed between EBV and nasopharyngeal cancer, and serologic screening could be beneficial for secondary prevention of it.

Adult↗
PubMed1994

Insulin and glucagon modulate hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity by affecting immunoreactive protein levels.

The question of whether the effects of insulin and glucagon on hepatic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity are mediated largely by changes in the phosphorylation state of the enzyme or by changes in the quantity of enzyme protein was investigated by measuring enzyme protein and mRNA levels. If phosphorylation/dephosphorylation is responsible for the observed changes in HMG-CoA reductase activity, one would not expect to see changes in immunoreactive protein or mRNA levels in response to induction of diabetes, administration of insulin, or administration of insulin and glucagon. It was found that hepatic HMG-CoA reductase mRNA levels were decreased to 12% of control in diabetic rats. Immunoreactive protein was reduced to essentially undetectable levels. Administration of insulin restored both mRNA and immunoreactive protein levels. Glucagon blocked these effects. Enzyme activity changes were fully accounted for by changes in HMG-CoA reductase mRNA and immunoreactive protein. Fasting caused parallel falls in HMG-CoA reductase activity and immunoreactive protein levels with a lesser effect on mRNA levels. The insulin-mediated changes in HMG-CoA reductase gene expression correlated well with changes in blood glucose levels, indicating a physiological effect. Taken together, these results indicate that insulin and glucagon regulate HMG-CoA reductase gene expression largely at the level of enzyme protein through changes in mRNA concentrations.

Animals↗
PubMed1994

Thyroid hormone rapidly induces hepatic LDL receptor mRNA levels in hypophysectomized rats.

The effects of hypophysectomy and thyroid hormone treatment on the expression of the hepatic LDL receptor gene was studied in young male rats. Hypophysectomy lowered levels of LDL receptor mRNA and protein. It was found that increased levels of LDL receptor mRNA could be detected 30 min after giving hypophysectomized rats an intramuscular injection of 10 micrograms of L-triiodothyronine (T3) per 100 g of body weight. This dose of T3 also increased hepatic LDL receptor protein levels within 1 h. A T3 dose of only 0.25 microgram per 100 g increased LDL receptor mRNA levels more than threefold. The half-life of the hepatic LDL receptor mRNA was found to be about 30 min and was unaffected by T3. The data suggests that thyroid hormone acts physiologically to induce hepatic LDL receptor expression. This action may explain, in part, the hypocholesterolemic effect of the hormone.

Animals↗
PubMed1994

Analysis of nucleotide pools in human lymphoma cells by capillary electrophoresis.

Capillary electrophoresis is applied to determine nucleotide pool levels in human Burkitt lymphoma cells. The analysis was performed on a 65 cm x 50 microns I.D. Ucon-coated column with on-column UV detector. The method requires only nanoliters of sample and a simple sample preparation procedure. Over 12 nucleotides were separated and quantitated with high resolution and reproducibility. The whole capillary electrophoretic separation time was only 35 min. These results demonstrate that capillary electrophoresis provides a useful and easy way to analyze nucleotide pools in cells.

Adenine Nucleotides↗
PubMed1994

Thyroid hormone rapidly increases cholesterol 7 alpha-hydroxylase mRNA levels in hypophysectomized rats.

The induction of hepatic cholesterol 7 alpha-hydroxylase mRNA by triiodothyronine was investigated in hypophysectomized rats. These rats exhibited markedly decreased levels of cholesterol 7 alpha-hydroxylase mRNA compared to normal controls. An increase in this mRNA could be detected within 30 min after giving triiodothyronine. A triiodothyronine dose of 0.25 microgram per 100 g of body weight, which produces 50% occupancy of hepatic nuclear thyroid hormone receptors, caused significant increases in hydroxylase mRNA levels. The half-life of cholesterol 7 alpha-hydroxylase mRNA was about 30 min and was not affected by thyroid hormone. Administration of the protein synthesis inhibitor, cycloheximide, after triiodothyronine caused superinduction. Hepatic HMG-CoA reductase mRNA levels, which are also low in livers from hypophysectomized rats, were unaffected by these doses of hormone within the 2 h time-frame examined in these studies. The results suggest that thyroid hormone may exert a primary affect on the expression of the hepatic cholesterol 7 alpha-hydroxylase gene. This could explain, in part, the hypocholesterolemic effect of thyroid hormone.

Animals↗
PubMed1994

Verapamil-reversing concentrations induce blood flow changes that could counteract in vivo the MDR-1-modulating effects.

BACKGROUND: Intraarterial hepatic (IAH) administration of verapamil should achieve mdr-1-reversing concentrations with reduced cardiac toxicity. The authors have explored the tolerance of its IAH administration and its effects on doxorubicin pharmacodymamics. METHODS: Verapamil was given to rabbits by intravenous or IAH administration, and its effects on heart rates were compared. Doxorubicin then was given intravenously either with IAH verapamil or with an IAH control perfusion, and tumor and liver drug concentrations were determined. Hepatic blood flow changes were studied by the administration of 99mTc-albumin macroaggregates (99mTc-MAA) under verapamil IAH perfusions. RESULTS: Compared with the intravenous route, IAH administration of verapamil was not toxic, and cardiac effects were reduced significantly. Its effect on doxorubicin distribution was detrimental, because the tumor-liver doxorubicin concentration ratios were lower in the verapamil group (0.23 vs. 3.37; P < 0.05). Tumor doxorubicin concentrations were lower when verapamil was coinfused (43 vs. 573 ng/100 mg tissue; P < 0.05). In normal liver tissue, increased amounts of doxorubicin and metabolites were observed. The verapamil IAH perfusions with 99mTc-MAA confirmed a differential action on tumor and normal vessels; the distribution of radionuclide was diverted away from the tumor bed significantly when verapamil was administered (tumor-to-liver ratio of 25.3 control rabbits vs. 5.99 rabbits who received verapamil; P < 0.05). CONCLUSIONS: Reversing the concentrations of verapamil provoked changes in the distribution of the liver blood flow. The hemodynamic effects of verapamil regional perfusions could counteract in vivo its potential mdr-1-reversing properties.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Phosphorylation and identification of a major tyrosine phosphorylation site in protein tyrosine phosphatase 1C.

Protein tyrosine phosphatase 1C (PTP1C) was the first member of the protein tyrosine phosphatase family demonstrated to contain the src homology 2 (SH2) domain. This enzyme is believed to play a role in regulating downstream signaling in hematopoietic cells since it was predominantly expressed in these cells. However, recent studies have revealed that the protein is expressed in other tissues as well. This report describes both the phosphorylation of PTP1C in non-hematopoietic cells treated with growth factors (in vivo) and incubation of purified PTP1C with a variety of protein kinases (in vitro). PTP1C was transiently phosphorylated in A431 and 293 cells and also when the purified enzyme was incubated with receptor protein tyrosine kinases. In vitro, the tyrosine-phosphorylated PTP1C underwent rapid auto-dephosphorylation, an effect which could be blocked by the addition of sodium vanadate. On the other hand, cells containing a PTP1C in which the catalytic site had been inactivated through mutagenesis, stably phosphorylated the phosphatase. These results suggested that PTP1C was responsible for its own auto-dephosphorylation. The sites of tyrosine phosphorylation were characterized from purified enzyme following treatment with insulin receptor kinase and from PTP1C expressed in 293 cells which had been stimulated with platelet-derived growth factor. Through the techniques of peptide mapping and microsequencing, Tyr538 was determined to be the major phosphorylation site. This result was confirmed in vivo through site-specific mutagenesis of PTP1C expressed in 293 cells; changing Tyr538 to Phe538 completely abolished tyrosine phosphorylation of the molecule. In addition, Tyr538 lies within the sequence ESEYGNI which can be correlated with the consensus sequence pYXNX associated with GRB2 binding. These results suggest that PTP1C plays a prominent role in growth factor receptor-mediated signal transduction within both hematopoietic cells and tissues of non-lymphoid origin.

Amino Acid Sequence↗
PubMed1994

Breakpoint cluster region gene product-related domain of n-chimaerin. Discrimination between Rac-binding and GTPase-activating residues by mutational analysis.

The breakpoint cluster region gene product (Bcr) is a GTPase-activating protein (GAP) for members of the Rho family, Cdc42Hs, and Rac1, as is the brain protein n-chimaerin. At least 15 proteins have sequence identity to the GAP domain (150 amino acid residues) of Bcr. The widespread occurrence of proteins that possess sequence identity to the Bcr-related GAP domain makes it especially important to understand its structure/function relationships. Amino acid sequence alignment of these proteins reveals three blocks of conservation in the GAP domain. Here, we present a mutational analysis of this domain using n-chimaerin sequences. Ten mutations were constructed (at least two in each of the blocks of conservation), expressed as glutathione S-transferase fusion proteins in Escherichia coli, and purified. Seven of the mutants, including deletions, still possessed GAP activity for Rac1. Three of the mutants had no Rac1-GAP activity but were still able to bind Rac1. IC50 values obtained from competition experiments suggest that n-chimaerin and the mutants with no GAP activity bound Rac1 with similar apparent binding constants. Thus, this mutant analysis allows discrimination between Rac1-binding and Rac1 GTPase- activating residues.

Amino Acid Sequence↗
PubMed1994

Dephosphorylation of insulin receptor substrate 1 by the tyrosine phosphatase PTP2C.

The phosphotyrosine (Tyr(P)) form of insulin receptor substrate 1 (IRS-1) is a key component in insulin signaling. Our previous study revealed that Tyr(P) IRS-1 binds to the widely distributed tyrosine phosphatase PTP2C through the src homology 2 (SH2) domains of the latter. In the present study, we examined the activity of this enzyme and of a truncated form lacking the SH2 domains (delta PTP2C) toward IRS-1 and also toward the cytoplasmic domain of the insulin receptor. Tyr(P) IRS-1 was prepared by phosphorylation of recombinant IRS-1 with recombinant cytoplasmic insulin receptor kinase (CIRK). PTP2C rapidly dephosphorylated Tyr(P) IRS-1; dephosphorylation by delta PTP2C was approximately one-third as fast. Other substrates, including Tyr(P) CIRK, were not dephosphorylated as rapidly by PTP2C; moreover, delta PTP2C was at least 10 times more active than PTP2C toward CIRK and other substrates. These results indicate that the binding of Tyr(P) residues on IRS-1 to the SH2 domain(s) of PTP2C enhances its activity toward IRS-1 and suggest that PTP2C is the phosphatase responsible for the dephosphorylation of IRS-1 in vivo. In addition, with the expectation that a PTP2C-resistant form of IRS-1 will be useful in investigations of IRS-1 function, we determined that IRS-1 can be thiophosphorylated with adenosine 5'-O-(3-thiotriphosphate) and CIRK and that this form of IRS-1 is resistant to PTP2C.

Animals↗
PubMed1994

Protein-tyrosine-phosphatase 2C is phosphorylated and inhibited by 44-kDa mitogen-activated protein kinase.

Protein-tyrosine-phosphatase 2C (PTP2C, also named SHPTP2, SHPTP3, or PTP1D) is a cytosolic enzyme with two Src homology 2 domains. We have investigated its regulation by phosphorylation in PC12 rat pheochromocytoma cells. In untreated cells, PTP2C was phosphorylated predominantly on serine residues. A 5-min treatment with epidermal growth factor (EGF) induced an increase in phosphorylation on threonine and, to a lesser degree, on serine. After 45 min of exposure to EGF, PTP2C phosphorylation returned to basal levels. Using an in vitro kinase assay, we found that the 44-kDa mitogen-activated protein kinase, p44mapk, phosphorylated PTP2C on serine and threonine residues. This phosphorylation resulted in a pronounced inhibition of PTP2C enzyme activity measured with phosphorylated EGF receptors as substrate. Moreover, in intact PC12 cells, PTP2C was also inhibited following a short EGF treatment, but its activity returned to normal when the exposure to EGF was maintained for 45 min. The profile of this response to EGF can be inversely correlated to that of the stimulatory action of EGF on p44mapk. These data suggest that the EGF-induced regulation of PTP2C activity is mediated by p44mapk. These findings provide evidence for an additional role of the mitogen-activated protein kinase cascade--namely, the regulation of a PTP.

Animals↗
PubMed1994

Phorbol ester-induced expression, phosphorylation, and translocation of protein-tyrosine-phosphatase 1C in HL-60 cells.

PTP1C, a protein-tyrosine-phosphatase (PTP) containing two Src homology 2 domains, is expressed at high levels in HL-60 human promyelocytic leukemia cells. It represents 0.15% of total protein in a postnuclear extract and corresponds to approximately 70% of phosphatase activity measured with p-nitrophenyl phosphate at pH 5.0. Upon differentiation of HL-60 cells to macrophages induced by phorbol 12-myristate 13-acetate (PMA), the activity and expression levels of PTP1C increase 2- to 3-fold. Furthermore, PTP1C is phosphorylated on serine residues upon PMA treatment. While the enzyme localizes entirely in the cytosolic fraction in untreated cells, 30-40% is found in a particulate fraction following differentiation. Immunofluorescent staining of differentiated cells before and after digitonin treatment indicates that the bound enzyme localizes on the plasma membrane. The time courses of induction and translocation of PTP1C correlate with the differentiation process. The PMA-induced differentiation is inhibited by sodium orthovanadate, suggesting the PTPs are required for this process.

Biological Transport↗
PubMed1994

Complete primary structure of the sixth chain of human basement membrane collagen, alpha 6(IV). Isolation of the cDNAs for alpha 6(IV) and comparison with five other type IV collagen chains.

Basement membranes were previously believed to contain five distinct type IV collagen subunits. We have recently isolated part of the cDNA for a novel type IV collagen, alpha 6(IV), and shown that COL4A6, the gene encoding this new chain, is deleted in Alport syndrome-associated leiomyomatosis (Zhou, J., Mochizuki, T., Smeets, H., Antignac, C., Laurila, P., de Paepe, A., Tryggvason, K., and Reeders, S. T. (1993) Science 261, 1167-1169). Here, we describe the entire human alpha 6(IV) cDNA and show that the gene encodes a classical type IV collagen with homology throughout its length to all the other five chains. There is a 21-residue signal peptide, a 1417-residue collagenous domain interrupted at 25 points, and a 228-residue carboxyl-terminal non-collagenous domain. When the complete primary structure of this new chain was compared with all the other known chains, it became clear that alpha 6(IV) has the most resemblance to alpha 2(IV) and alpha 4(IV). The evolution of the six chains was deduced, allowing a new classification of the type IV collagen family. The alpha 6(IV) chain is a candidate gene for X-linked Alport syndrome; knowledge of the complete structure of the chain will permit us to screen systematically for mutations in patients and to generate recombinant proteins and synthetic peptides for further study of cell-matrix interactions involving the alpha 6(IV) chain.

Amino Acid Sequence↗