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Y Mao

Publications and source records attributed to Y Mao.

At least 163 records · Page 9Linked to original sources
PubMed1999

Molecular characterization and analysis of the biosynthetic gene cluster for the antitumor antibiotic mitomycin C from Streptomyces lavendulae NRRL 2564.

BACKGROUND: The mitomycins are natural products that contain a variety of functional groups, including aminobenzoquinone- and aziridine-ring systems. Mitomycin C (MC) was the first recognized bioreductive alkylating agent, and has been widely used clinically for antitumor therapy. Precursor-feeding studies showed that MC is derived from 3-amino-5-hydroxybenzoic acid (AHBA), D-glucosamine, L-methionine and carbamoyl phosphate. A genetically linked AHBA biosynthetic gene and MC resistance genes were identified previously in the MC producer Streptomyces lavendulae NRRL 2564. We set out to identify other genes involved in MC biosynthesis. RESULTS: A cluster of 47 genes spanning 55 kilobases of S. lavendulae DNA governs MC biosynthesis. Fourteen of 22 disruption mutants did not express or overexpressed MC. Seven gene products probably assemble the AHBA intermediate through a variant of the shikimate pathway. The gene encoding the first presumed enzyme in AHBA biosynthesis is not, however, linked within the MC cluster. Candidate genes for mitosane nucleus formation and functionalization were identified. A putative MC translocase was identified that comprises a novel drug-binding and export system, which confers cellular self-protection on S. lavendulae. Two regulatory genes were also identified. CONCLUSIONS: The overall architecture of the MC biosynthetic gene cluster in S. lavendulae has been determined. Targeted manipulation of a putative MC pathway regulator led to a substantial increase in drug production. The cloned genes should help elucidate the molecular basis for creation of the mitosane ring system, as well efforts to engineer the biosynthesis of novel natural products.

Amino Acid Sequence↗
PubMed1999

Risk factors for prostate cancer: results from the Canadian National Enhanced Cancer Surveillance System. The Canadian Cancer Registries Epidemiology Research Group.

OBJECTIVES: To evaluate the relationship between prostate cancer and several potential lifestyle risk factors. METHODS: We analyzed data obtained from a population-based case-control study conducted in eight Canadian provinces. Risk estimates were generated by applying multivariate logistic regression methods to 1623 histologically confirmed prostate cancer cases and 1623 male controls aged 50-74. RESULTS: Cases were more likely to have a first-degree relative with a history of cancer, particularly prostate cancer (OR = 3.1, 95% CI = 1.8-5.4). Reduced risks of prostate cancer were observed among those of Indian descent (OR = 0.2, 95% CI = 0.1-0.5) or any Asian descent (OR = 0.3, 95% CI = 0.2-0.6) relative to those of western European descent. Total fat consumption, tomato and energy intake, were not associated with prostate cancer. The risk of prostate cancer was inversely related to the number of cigarettes smoked daily (p = 0.06) and cigarette pack-years (p < 0.01), while no association was observed between the total number of smoking years or the number of years since smoking cessation. Anthropometric measures and moderate and strenuous levels of leisure time physical activity were not strongly related to prostate cancer. In contrast, strenuous occupational activities at younger ages appeared protective. CONCLUSIONS: Our analyses are limited by the absence of data related to tumor severity and screening history. Further studies are needed to investigate the relationship between behavioral risk factors and prostate cancer screening practices.

Aged↗
PubMed1999

Ovarian cancer histology-specific incidence trends in Canada 1969-1993: age-period-cohort analyses.

This study examined histology-specific incidence trends of ovarian cancer in Canada, 1969-1993. The impact of age, period and cohort effects on these trends were studied by means of age-period-cohort analysis. Age-standardized incidence rates of serous, endometrioid, clear cell and germ cell tumours increased significantly and the rates of sex cord-stromal and other classified epithelial ovarian tumours decreased considerably. The rates of mucinous and NOS/unclassified tumours remained unchanged. Cohort effect has a major impact on incidence trends of serous, endometrioid, germ cell, sex cord-stromal and other classified epithelial ovarian tumours but no meaningful impact on trends of mucinous, clear cell, or NOS/unclassified ovarian tumours. Various cohort patterns by histology subtypes were observed: the risk of developing serious tumours increased markedly among birth cohorts of 1895-1930, stabilized thereafter and decreased among young cohorts of 1950-1960; the risk of germ cell tumours increased significantly among young cohorts of 1965-1980; and the risk of sex cord-stromal tumours dropped constantly among cohorts 1910-1950. Various period patterns by histology subtypes observed in this study suggested changes in histology classification criteria over the period. Further studies need to consider the various etiologies and the classification criteria changes according to histology subtypes.

Adolescent↗
PubMed1999

Bench testing of nebulizers: a comparison of three methods.

Although nebulizers can vary widely in performance, there is no uniformly accepted method for bench testing these devices. In the present study, we compared three bench methods of measuring the performance of three commercial jet nebulizers (Whisper Jet [WJ; Marquest Medical, Englewood, CO], Sidestream [SS; Marquest Medical], and Vixone [VO; Westmed, Tucson, AZ] to assess the impact of the method of testing on reported nebulizer performance. Each nebulizer was charged with 3 mL of albuterol mixed with a radiotracer (technetium [99mTc]), and the radioactivity captured on a paper filter was expressed as a percentage of the nebulizer charge (% delivered). The nebulizers were tested with and without duplication of spontaneous respiration by a piston pump (spontaneous respiration and standing cloud methods, respectively). The nebulizers were also tested using a model of mechanical ventilation (mechanical ventilation method). For all three devices, the addition of the standardized breathing pattern significantly reduced the % delivered with all three nebulizers compared with the standing cloud method. For the standing cloud method, the presence of the T-piece/mouth-piece significantly reduced the % delivered with the WJ but not with the other two devices. The mechanical ventilation method had the lowest % delivered for all three devices. The magnitude of the differences between nebulizers varied with duration of treatment. The findings of this study emphasize the importance of bench testing that duplicates intended clinical usage, because significant differences in nebulizer performance may be manifested under certain clinical conditions but not under others.

Administration, Inhalation↗
PubMed1999

Expression of tumor necrosis factor-alpha and intercellular adhesion molecule-1 after focal cerebral ischemia in interleukin-1beta converting enzyme deficient mice.

Interleukin-1beta (IL-1beta) is expressed after cerebral ischemia and blocking its action reduces subsequent ischemic brain injury. However, the mechanisms by which IL-1beta affects ischemic brain are not understood. To investigate the role of IL- 1beta in regulation of tumor necrosis factor-alpha (TNF-alpha) and intercellular adhesion molecule-1 (ICAM-1) during focal cerebral ischemia, the authors studied mutant mice deficient in the IL-1 converting enzyme (ICE) gene (ICE knockout [KO] mice). Ninety-four adult male ICE KO and wild-type mice underwent 3, 6, 12, and 24 hours of permanent middle cerebral artery occlusion using the suture method. Expression of TNF-alpha and ICAM-1 protein in ischemic brain was examined using immunohistochemistry and Western blot analysis. Neither ICE KO nor wild-type mice had significant differences in CBF and body temperature measurements during the ischemic procedure. TNF-alpha expression increased in the ipsilateral hemisphere after 3 hours of occlusion, peaked at 12 hours and decreased at 24 hours of ischemia in both ICE KO and wild-type mice. ICAM-1 immunohistochemistry showed that the number of ICAM-1-positive vessels in the ischemic hemisphere was reduced in ICE KO mice (P < .05). Western blot analysis showed that ICAM-1 protein expression was significantly attenuated in the ipsilateral hemisphere in the ICE KO mice, which paralleled the immunohistochemistry results. The authors' results indicate that TNF-alpha expression is increased in both ICE KO and wild-type mice suggesting that TNF-alpha expression is not related to or upregulated by IL-1beta . ICAM-1 expression is significantly reduced in the ICE KO mice suggesting that IL-1beta plays an important role in the upregulation of adhesion molecules during focal cerebral ischemia.

Animals↗
PubMed1999

Overexpression of a dominant-negative allele of SEC4 inhibits growth and protein secretion in Candida albicans.

Candida albicans SEC4 was cloned by complementing the Saccharomyces cerevisiae sec4-8 mutation, and its deduced protein product (Sec4p) was 63% identical to S. cerevisiae Sec4p. One chromosomal SEC4 allele in C. albicans CAI4 was readily disrupted by homologous gene targeting, but efforts to disrupt the second allele yielded no viable null mutants. Although this suggested that C. albicans SEC4 was essential, it provided no information about this gene's functions. Therefore, we constructed a mutant sec4 allele encoding an amino acid substitution (Ser-28-->Asn) analogous to the Ser-17-->Asn substitution in a trans-dominant inhibitor of mammalian Ras protein. GAL1-regulated expression plasmids carrying the mutant sec4 allele (pS28N) had minimal effects in glucose-incubated C. albicans transformants, but six of nine transformants tested grew very slowly in galactose. Incubation of pS28N transformants in galactose also inhibited secretion of aspartyl protease (Sap) and caused 90-nm secretory vesicles to accumulate intracellularly, and plasmid curing restored growth and Sap secretion to wild-type levels. These results imply that C. albicans SEC4 is required for growth and protein secretion and that it functions at a later step in the protein secretion pathway than formation of post-Golgi secretory vesicles. They also demonstrate the feasibility of using inducible dominant-negative alleles to define the functions of essential genes in C. albicans.

Alleles↗
PubMed1999

Genetic localization and molecular characterization of two key genes (mitAB) required for biosynthesis of the antitumor antibiotic mitomycin C.

Mitomycin C (MC) is an antitumor antibiotic derived biosynthetically from 3-amino-5-hydroxybenzoic acid (AHBA), D-glucosamine, and carbamoyl phosphate. A gene (mitA) involved in synthesis of AHBA has been identified and found to be linked to the MC resistance locus, mrd, in Streptomyces lavendulae. Nucleotide sequence analysis showed that mitA encodes a 388-amino-acid protein that has 71% identity (80% similarity) with the rifamycin AHBA synthase from Amycolatopsis mediterranei, as well as with two additional AHBA synthases from related ansamycin antibiotic-producing microorganisms. Gene disruption and site-directed mutagenesis of the S. lavendulae chromosomal copy of mitA completely blocked the production of MC. The function of mitA was confirmed by complementation of an S. lavendulae strain containing a K191A mutation in MitA with AHBA. A second gene (mitB) encoding a 272-amino-acid protein (related to a group of glycosyltransferases) was identified immediately downstream of mitA that upon disruption resulted in abrogation of MC synthesis. This work has localized a cluster of key genes that mediate assembly of the unique mitosane class of natural products.

Amino Acid Sequence↗
PubMed1999

Mitomycin resistance in Streptomyces lavendulae includes a novel drug-binding-protein-dependent export system.

Sequence analysis of Streptomyces lavendulae NRRL 2564 chromosomal DNA adjacent to the mitomycin resistance locus mrd (encoding a previously described mitomycin-binding protein [P. Sheldon, D. A. Johnson, P. R. August, H.-W. Liu, and D. H. Sherman, J. Bacteriol. 179:1796-1804, 1997]) revealed a putative mitomycin C (MC) transport gene (mct) encoding a hydrophobic polypeptide that has significant amino acid sequence similarity with several actinomycete antibiotic export proteins. Disruption of mct by insertional inactivation resulted in an S. lavendulae mutant strain that was considerably more sensitive to MC. Expression of mct in Escherichia coli conferred a fivefold increase in cellular resistance to MC, led to the synthesis of a membrane-associated protein, and correlated with reduced intracellular accumulation of the drug. Coexpression of mct and mrd in E. coli resulted in a 150-fold increase in resistance, as well as reduced intracellular accumulation of MC. Taken together, these data provide evidence that MRD and Mct function as components of a novel drug export system specific to the mitomycins.

Amino Acid Sequence↗
PubMed1999

Endotoxin-induced inhibition of growth hormone receptor signaling in rat liver in vivo.

The bacterial lipopolysaccharide endotoxin induces a catabolic response characterized by resistance to multiple anabolic hormones. The objective of this study was to determine the effects of endotoxin on the GH signaling pathway in rat liver in vivo. After the iv injection of Escherichia coli endotoxin (1 mg/kg), there was a progressive decrease in liver STAT5 (signal transducer and activator of transcription-5) tyrosine phosphorylation in response to GH (40% decrease 6 h after endotoxin), which occurred in the absence of a change in abundance of the STAT5 protein. Endotoxin resulted in a rapid 40-fold increase in liver Janus family kinase-2 (JAK2) messenger RNA, followed by a 2-fold increase in JAK2 protein abundance. This was associated with a 50% decrease in phosphorylated/total JAK2 after GH stimulation. GH receptor abundance was unchanged, suggesting a postreceptor site of endotoxin-induced GH resistance. Rat complementary DNAs for three members of the suppressor of cytokine signaling gene family were cloned [cytokine-inducible sequence (CIS), suppressor of cytokine signaling-2 (SOCS-2), and SOCS-3] and, using these probes, messenger RNAs for SOCS-3 and CIS were shown to be increased 10- and 4-fold above control values, respectively, 2 h after endotoxin infusion. The finding of endotoxin inhibition of in vivo STAT5 tyrosine phosphorylation in response to a supramaximal dose of GH in the absence of a change in GH receptor abundance or total GH-stimulated JAK2 tyrosine phosphorylation provides the first demonstration of acquired postreceptor GH resistance. We hypothesize that this may occur through a specificity-spillover mechanism involving the induction of SOCS genes by cytokines released in response to endotoxin and subsequent SOCS inhibition of GH signaling.

Animals↗
PubMed1999

Have diagnostic practices contributed to trends in leukemia incidence and mortality among Canadians?

OBJECTIVE: To outline the patterns and temporal trends in leukemia, regarding incidence and mortality, in Canada since 1970. DESIGN: A descriptive analysis of trends in incidence and mortality by age, sex, time period and leukemia subtype, using change-point modelling and log-linear regression. SETTING: Data from all provincial and territorial cancer registries. MAIN OUTCOME MEASURE: Incidence and mortality rate per population of 100,000. RESULTS: The overall age-adjusted incidence rates for all males and females increased from 12.3 and 7.3 per 100,000 in 1970-1972 to 14.6 and 9.0 in 1979-1981, then decreased to 13.2 and 8.3 in 1991-1993, respectively. The overall age-adjusted mortality rates decreased from 9.1 and 5.7 per population of 100,000 in 1970-1972 to 8.3 and 4.8 in 1993-1995 for males and females, respectively. The incidence of acute leukemias decreased between 1970 and 1993. A sharp increase in the incidence of chronic leukemias from 1978 to 1980 was observed in the older age group. Mortality rates also showed a small increase from 1979 to 1989 in seniors. CONCLUSION: The increase in the incidence of chronic leukemias among older subjects was probably due to improvements in diagnosis and changes in registration practices, whereas the decrease in the incidence of acute leukemias was probably a real change attributable to environmental factors. Further investigation is needed to clarify whether and to what extent diagnostic practices contributed to the increased detection of chronic leukemias among elderly Canadians.

Adolescent↗
PubMed1999

Epidemiology of contralateral breast cancer.

Two to 11% of women diagnosed with breast cancer will develop contralateral breast cancer in their lifetime. Women with a first primary are at a 2-6-fold increased risk of developing contralateral breast cancer compared with the risk in the general population of women developing a first primary cancer. The incidence rate of contralateral breast cancer varies from four to eight per 1000 person-years. To assess the risk factors associated with the development of contralateral breast cancer among women with a first primary breast cancer, the epidemiological literature concerning these factors was reviewed and summarized. Studies have shown that a family history of breast cancer, an early age at initial diagnosis, and a lobular histology of the first primary breast cancer increase the risk of developing contralateral breast cancer. Although chemotherapy and tamoxifen therapy may reduce this risk, there are inconsistent results regarding the effects of radiotherapy and the effects of reproductive, environmental and other factors. Additional analytical studies addressing all potential risk factors associated with the development of contralateral breast cancer are necessary in view of the increasing incidence and survival of women with a first primary.

Breast Neoplasms↗
PubMed1999

Effects of the configuration of a multi-epitope chimeric malaria DNA vaccine on its antigenicity to mice.

OBJECTIVE: Four B and Th cell epitopes were selected from conservative domain of Plasmodium falciparum antigens to construct two groups of chimeric malaria DNA vaccines with different configurations and their antigenicities were studied. METHODS: The partially synthesized oligonucleotide was annealed, PCR amplified and cloned into a mammalian cell expression vector. By using a pair of isocaudamers on the vector, different single copies of B epitopes were multiplied and were tenderly stringed into two groups of chimeric DNA vaccine with different configurations. BALB/c mice were immunized with these DNA plasmids by either intramuscular or intradermal injections. RESULTS: The antisera from the immunized mice tested by ELISA showed that only the configuration which had a single copy of universal T helper cell epitope, CS. T3, located at the C terminal of the multi-copy B cell epitopes induced a high antibody response. The T helper cell epitope at any other position of the peptide, or the double T helper cell epitopes configured with the B cell epitopes did not enhance antibody response, and some configurations even decreased the humoral response to a B cell epitope. CONCLUSION: This study demonstrated that both combination and configuration of the epitope may affect the antigenicity of a chimeric multiple antigen.

Animals↗
PubMed1999

[Flow cytometry for testing chemosensitivity of malignant bone tumors].

OBJECTIVE: To study chemosensitivity and multidrug resistance of malignant bone tumors and to make an individual protocol of chemotherapy with sensitive antitumor agents. METHODS: Apoptosis induced by MTX, ADM, MMC, VP-16, VCR and CTX, and chemosensitivity in 32 fresh specimens of malignant bone tumors were analyzed by flow cytometry (FCM) and quantitative immunofluorescence. The expression of P-glycoprotein (P170) in the specimen and the relation between P170, multidrug resistance, and chemosensitivity were detected. RESULTS: The rate of apoptosis was significantly different in malignant bone tumor cells treated with different drugs: MTX (30.50 +/- 10.22)%, ADM (26.28 +/- 9.35)%, MMC (23.11 +/- 7.38)%, VP-16 (18.17 +/- 6.14)%, VCR (4.44 +/- 2.55)%, and CTX (1.22 +/- 0.59)%. The individual variation of cell apoptosis was prominent in the specimens of same pathological type treated with same agent. There was lower chemosensitivity in the malignant bone tumors with a high expression of P170. CONCLUSIONS: Chemosensitivity testing by flow cytometry is a simple, quick and sensitive assay. Quantitative analysis of expression of P170 could be used to predict multidrug resistance and its chemosensitivity of malignant bone tumors.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

[Development of plasmid-based transgenic mice carrying with target gene xylE].

OBJECTIVE: To develop a transgenic mouse model carrying with plasmid pUC118NX integrated into its genomic DNA for detecting mutagenesis. METHODS: DNA of plasmid UC118NX in target gene xy1E was injected microscopically into male protonucleus of 376 mouse spermatova, and 225 survival spermatova were transferred into the oviducts in both sides of 11 pseudopregnant female mice to develop their offspring. The genomic DNA in survival young mice were analyzed with polymerase chain reaction (PCR)-Southern blot, plasmid transformation test and endonuclease-digestion. RESULTS: Seven pseudopregnant mice got pregnant, and 29 offspring were delivered and 25 survived of which 18 were identified with positive for PCR-Southern blot (72%). The two stout male mice with intact integration of plasmid pUC118NX in their genome were finally chosen as founders to detect gene mutation in vivo and establish transgenic mouse lineages. CONCLUSION: Transgenic C57BL/6J mice integrated with plasmid pUC118NX into their genomic DNA have been successfully developed.

Animals↗
PubMed1999

[Studies on chemical constituents in the fruit of Canarium album Raeusch].

OBJECTIVE: To study the chemical constituents in the fruit of Canarium album. METHOD: Compounds were isolated by chromatography and elucidated on the basis of spectroscopic analysis. RESULT: The compounds obtained were determined as scoparone, scopoletin, (E)-3,3'-dihydroxy-4,4'-dimethoxystilbene and gallic acid. CONCLUSION: All the compounds, except gallic acid, were obtained from this plant for the first time.

Burseraceae↗
PubMed1999

[An analysis of DNA content in 405 cases of human tumor by flow cytometry].

This study was intended to evaluate the relationship between the DNA content of cell cycle and the histology in human tumors. We detected the DNA content in 405 cases of fresh human tumor tissue by means of flow cytometry and observed the histology of tumor with light microscopy. The occurrences of aneuploidy in 22 cases of benign tumor and 383 cases of malignant tumor were 27% and 52% respectively. There were differences in aneuploidy in different histologic types of tumor. The aneuploidy in adenocarcinoma was about 50%, that in sarcoma was more than 37%, and that in squamous carcinoma less than 17%. S > or = 10, G2/m > or = 10 or S > or = 20, G2/m > or = 5 were present in malignant tumors, but were not found in benign tumors. The results suggest that there is obvious difference in the occurrences of aneuploidy in benign and malignant tumors and in different histologic type of tumor(P < 0.05). Benign and malignant tumor may be distinguished when SPF and G2/m reach a higher level (P < 0.01).

Carcinoma, Squamous Cell↗
PubMed1999

[Cloning of mitomycin C resistance gene from Streptoverticillium caespitosum ATCC27422 and studying its function].

Streptoverticillium caespitosum is the major producer of anti-cancer drug mitomycin. It demonstrated that there exists a strong restriction system for the transformation of foreign DNA in this strain. Using the blocked mutant S-6 which is sensitive to mitomycin C (MC) and does not produce mitomycin as a recepient and plasmid pIJ699 as vector, the gene library of the strain ATCC27422 was constructed. A clone of mitomycin C resistance gene(mcr) was obtained by screening from this library. The mitomycin C resistance gene cloned on the 6.2 kb fragment of plasmid pLX5 could be expressed in the Strptonmyces lividans TK54. It was the first time to introduce successfully the plasmid pLX5 into the wild type strain ATCC27422 by electroporation technique. And the transformant's resistance to mitomycin C has risen greatly: the MIC has gone up from 200 micrograms/ml to more than 1000 micrograms/ml. The result of fermentation showed that the yield of mitomycin of ATCC27422 harboring plasmid pLX5 was more than the wild strain ATCC27422's. It suggested that there is some relationship between the level of the resistance to mitomycin C and its biosynthesis.

Antibiotics, Antineoplastic↗