PubMed Health⌕ Search

Biomedical subjects

G C Li

Publications and source records attributed to G C Li.

At least 19 recordsLinked to original sources
PubMed2005

A preliminary assessment of consumer's exposure to pesticide residues in fisheries products.

The fisheries products in this study comprise fish, bivalve, crustacean and cephalopod collected from different types of markets in Taiwan between the years 2001 and 2003. A total of 91 pesticide residues belonging to four major pesticide groups were tested and analyzed. The test results show that 65.40% of fish, 93.55% of shellfish, 84.92% of crustacean and 98.33% of cephalopod samples contain no detectable residues. There are only two kinds (organochlorine and organophosphate) of totally six pesticides (DDTs, dieldrin, chlorpyrifos, fenitrotion, fenthion and prothion) that have been detected from the fisheries products in this study. For there were pesticides present in the fish products, consumption of fisheries product there was no zero risk. But the exposure of consumer did not exceed the acceptable daily intakes (ADI). For male, there was the highest risk in exposure to dieldrin, which the percentage of ADI was 93.56%. This study also suggests that a yearly monitoring program for organophosphate pesticide residues in fish is necessity.

Animals↗
PubMed2002

Allotype imbalance or microsatellite mutation in low-grade soft tissue sarcomas of the extremities in adults.

The ability to repair DNA double-strand breaks is essential to maintain chromosomal stability. Virtually all soft tissue sarcomas contain chromosomal instabilities, including clonal aberrations and cytogenetic aberrations. However, the relevance of DNA-dependent protein kinase (DNA-PK) in the pathogenesis of soft tissue sarcoma has not been clarified. The main aim of this work is to compare the prognostic impact of genotypic imbalance in low-grade soft tissue sarcomas of the extremities, and to correlate this with the translational level of DNA-PK. This study investigated 28 adult low-grade malignant spindle cell tumours of the extremities, predominantly fibrosarcomas, for loss of heterozygosity (LOH) and microsatellite mutation on flanking regions of each DNA-PK subunit, with identical immunophenotypes. Twelve different polymorphic markers flanking the specific loci of three subunits comprise the genetic map of DNA-PK, at 22q13, 2q35, and 8q11. Translational activity was also analysed by western blot and conventional immunohistochemistry. The overall sarcoma 5-year survival rate was 61.7%. LOH was identified in the specific coding region of DNA-PK in 39.29% for the DNA-PK catalytic subunit (cs), 17.86% for Ku70, and only 7.14% for Ku80. A positive LOH for DNA-PKcs was shown to be a significant factor for poor survival (log rank test p = 0.0160). Immunoreactivity and immunoblot results correlated with the loss of DNA-PKcs allotype in soft tissue sarcoma (Fisher's exact test p = 0.0037). Ku70 and DNA-PKcs were almost identical in terms of immunoreactivity. In conclusion, whereas microsatellite mutation seems an uncommon event during the evolution of low-grade fibrosarcoma of the extremities in adults, the loss of DNA-PKcs defines a biologically more aggressive subset.

Adolescent↗
PubMed2001

DNA-PKcs is critical for telomere capping.

The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is critical for DNA repair via the nonhomologous end joining pathway. Previously, it was reported that bone marrow cells and spontaneously transformed fibroblasts from SCID (severe combined immunodeficiency) mice have defects in telomere maintenance. The genetically defective SCID mouse arose spontaneously from its parental strain CB17. One known genomic alteration in SCID mice is a truncation of the extreme carboxyl terminus of DNA-PKcs, but other as yet unidentified alterations may also exist. We have used a defined system, the DNA-PKcs knockout mouse, to investigate specifically the role DNA-PKcs specifically plays in telomere maintenance. We report that primary mouse embryonic fibroblasts (MEFs) and primary cultured kidney cells from 6-8 month-old DNA-PKcs-deficient mice accumulate a large number of telomere fusions, yet still retain wild-type telomere length. Thus, the phenotype of this defect separates the two-telomere related phenotypes, capping, and length maintenance. DNA-PKcs-deficient MEFs also exhibit elevated levels of chromosome fragments and breaks, which correlate with increased telomere fusions. Based on the high levels of telomere fusions observed in DNA-PKcs deficient cells, we conclude that DNA-PKcs plays an important capping role at the mammalian telomere.

Animals↗
PubMed2001

Rb-associated protein 46 (RbAp46) suppresses the tumorigenicity of adenovirus-transformed human embryonic kidney 293 cells.

The retinoblastoma suppressor (Rb)-associated protein 46 (RbAp46) is a nuclear protein of the WD-repeat protein family and a component of the histone deacetylase complex that physically interacts with Rb. We demonstrated that RbAp46 is a gene up-regulated by the Wilms' tumor suppressor (WT1) and functions as a negative regulator of cell growth. Here we have investigated the ability of RbAp46 to inhibit malignant phenotype of adenovirus-transformed human embryonic kidney (HEK) 293 cells in tumorigenesis assays. We have found that expression of RbAp46 suppressed clonal growth of HEK 293 cells in soft agar and inhibited tumor growth of these cells in nude mice. Furthermore, expression of RbAp46 resulted in an increase of cells in the G2/M fraction of cell cycle and augmented apoptosis in serum-starved cells. The results suggest that high levels of RbAp46 expression inhibit the transformation of tumor cells through interfering with normal cell cycle and/or enhancing apoptotic cell death.

Adenoviridae↗
PubMed2001

Rb-associated protein 46 (RbAp46) inhibits transcriptional transactivation mediated by BRCA1.

The retinoblastoma suppressor (Rb)-associated protein 46 (RbAp46) is a member of the WD-repeat protein family and a component of the histone modifying and remodeling complexes. Previously, we demonstrated that RbAp46 is a potent growth inhibitor that can suppress the transformed phenotype of tumor cells. To explore the molecular mechanisms of RbAp46 function, we used RbAp46 as a bait in a yeast two-hybrid screening and found that RbAp46 interacts specifically with the C-terminal region of BRCA1 (the BRCT domain), a domain involved in the t transactivation activity of BRCA1. Coimmunoprecipitation assays demonstrated that the interaction of RbAp46 with BRCA1 requires the first two of the four Trp-Asp (WD)-repeats of RbAp46. We also showed that expression of RbAp46 represses the transactivation activity mediated by the BRCT/Gal4 fusion protein and inhibits the transactivation of the p21 promoter mediated by the full-length BRCA1. Interestingly, the association of BRCA1 and RbAp46 is disrupted in cells treated with DNA-damaging agents. These results suggest that RbAp46 may specifically interact with BRCA1 and modulate its transactivation activity in response to DNA damage.

BRCA1 Protein↗
PubMed2001

Cytotoxic mechanism of XK469: resistance of topoisomerase IIbeta knockout cells and inhibition of topoisomerase I.

Topoisomerase IIbeta knockout mouse cells (beta-/-) were found to have only slight resistance to m-AMSA, a dual topoisomerase IIalpha-IIbeta poison, as compared to wild-type cells (beta+/+) during 1 h or 3 day exposures to the drug. In contrast, the beta-/- cells were greater than threefold resistant to XK469, a selective topoisomerase IIbeta poison during three day drug exposures (beta+/+ IC(50) = 175 microM, beta-/- IC(50) = 581 microM). Short term (1 h) exposure to XK469 was not cytotoxic to either beta-/- or beta+/+ cells, suggesting that anticancer therapy with XK469 may be more efficacious if systemic levels can be prolonged. During studies on topoisomerase activity in nuclear extracts of the beta+/+ and beta-/- cells, we found evidence that XK469 is a weak topoisomerase I catalytic inhibitor. The high IC(50) for topoisomerase I inhibition (2 mM) suggests that topoisomerase I is not a significant target for XK469 cytotoxicity.

Animals↗
PubMed2001

Dissipation of epoxiconazole in the paddy field under subtropical conditions of Taiwan.

The environmental fate and distribution of fungicide epoxiconazole were studied by a rice paddy field model ecosystem. One week before the head-sprouting stage, rice plant was treated separately once with OPUS (tradename of epoxiconazole) 12% SC 2.1 kg ha(-1) and 1.4 kg ha(-1), respectively. Soil, water and rice plant were sampled seven days intervals nine times after application. The bioconcentration factor of epoxiconazole on mosquito fish in the ecosystem was also determined, based on the amounts of epoxiconazole content both in fish and water. This was initiated one day after the fungicide treatment, and continued for four days. In addition, the residue of epoxiconazole in rice grains was analyzed after harvest. After harvest, both planted water spinach (Ipomoea aquatica Forsk) and edible amaranth (Amaranthus mangostanüs L.) were analyzed. The results showed that epoxiconazole degraded in the local environment under the experimental conditions described. The degradation equations were in accordance with the first order kinetics. The DT50 of soil, field water and rice plant were 20-69 days, 11-20 days and 14-39 days, respectively. The bioconcentration factors of epoxiconazole on mosquito fish were 12.9 and 10.6 from 2.1 kg ha(-1) and 1.4 kg ha(-1) treatment, respectively. Residues of epoxiconazole in both rice and harvest vegetables were non-detectable. This indicates that epoxiconazole applied to rice at the recommended rates and application frequencies will not accumulate on rice grain and successive cropping vegetables.

Amaranthus↗
PubMed2001

[Cloning and expression of human anti-colonic cancer single-chain Fv fragment].

We report a new strategy for the generation of human anticolon cancer monoclonal antibodies based on the molecular cloning and expression of immunoglobulin variable region cDNAs derived from peripheral blood mononuclear cells (PBMC) that were transformed by EBV. The immortalized B cells secreting tumor-specific antibodies were identified by HRT-18 cell ELISA and cloned by limiting dilution. Heavy- and light-chain VH-CH1 (gamma) and V kappa-C kappa cDNAs were rescued from ELISA-positive cells wells by RT-PCR. VH and V kappa were amplified by 2nd PCR and linked them together by 3rd PCR assembly with the use of a (Gly4Ser)3 linker. The ScFv cDNAs were then cloned into the fUSE 5 vector and displayed on phage. Phage clones were selected on HRT-18 cells and normal human PBMC. ELISA tested phage clones randomly picked after each panning step. > 80% of the clones showed a strong ELISA reaction, demonstrating the effectiveness of the panning procedure for selecting anticolon cancer antibodies. This approach offers an effective method by combining in vitro immunization, B-cell expansion for enrichment of specific B-lymphocytes, PCR gene cloning and phage display to make high-affinity human anticolon cancer monoclonal antibody molecules.

Antibodies, Monoclonal↗
PubMed2000

ATM is required for IkappaB kinase (IKKk) activation in response to DNA double strand breaks.

Following challenge with proinflammatory stimuli or generation of DNA double strand breaks (DSBs), transcription factor NF-kappaB translocates from the cytoplasm to the nucleus to activate expression of target genes. In addition, NF-kappaB plays a key role in protecting cells from proapoptotic stimuli, including DSBs. Patients suffering from the genetic disorder ataxia-telangiectasia, caused by mutations in the ATM gene, are highly sensitive to inducers of DSBs, such as ionizing radiation. Similar hypersensitivity is displayed by cell lines derived from ataxia-telangiectasia patients or Atm knockout mice. The ATM protein, a member of the phosphatidylinositol 3-kinase (PI3K)-like family, is a multifunctional protein kinase whose activity is stimulated by DSBs. As both ATM and NF-kappaB deficiencies result in increased sensitivity to DSBs, we examined the role of ATM in NF-kappaB activation. We report that ATM is essential for NF-kappaB activation in response to DSBs but not proinflammatory stimuli, and this activity is mediated via the IkappaB kinase complex. DNA-dependent protein kinase, another member of the PI3K-like family, PI3K itself, and c-Abl, a nuclear tyrosine kinase, are not required for this response.

Androstadienes↗
PubMed2000

DNA-PKcs is required for activation of innate immunity by immunostimulatory DNA.

Bacterial DNA and related synthetic immunostimulatory oligodeoxyribonucleotides (ISS-ODN) stimulate innate immunity. However, the molecular recognition mechanism that initiates signaling in response to bacterial DNA and ISS-ODN has not been identified. Herein, we demonstrate that administration of bacterial DNA and ISS-ODN to mice lacking the catalytic subunit of DNA-PK (DNA-PKcs) and in vitro stimulation of BMDM from these mice result in defective induction of IL-6 and IL-12. Further analysis using BMDM of IKKbeta(-/-) revealed that both DNA-PKcs and IKKbeta are essential for normal cytokine production in response to ISS-ODN or bacterial DNA. ISS-ODN and bacterial DNA activate DNA-PK, which in turn contributes to activation of IKK and NF-kappaB. These results reveal a novel role of DNA-PKcs in innate immune responses and a link between DNA repair and innate immunity.

Androstadienes↗
PubMed2000

Ku acts in a unique way at the mammalian telomere to prevent end joining.

Telomeres are specialized DNA/protein structures that act as protective caps to prevent end fusion events and to distinguish the chromosome ends from double-strand breaks. We report that TRF1 and Ku form a complex at the telomere. The Ku and TRF1 complex is a specific high-affinity interaction, as demonstrated by several in vitro methods, and exists in human cells as determined by coimmunoprecipitation experiments. Ku does not bind telomeric DNA directly but localizes to telomeric repeats via its interaction with TRF1. Primary mouse embryonic fibroblasts that are deficient for Ku80 accumulated a large percentage of telomere fusions, establishing that Ku plays a critical role in telomere capping in mammalian cells. We propose that Ku localizes to internal regions of the telomere via a high-affinity interaction with TRF1. Therefore, Ku acts in a unique way at the telomere to prevent end joining.

Animals↗
PubMed2000

Signal joint formation is also impaired in DNA-dependent protein kinase catalytic subunit knockout cells.

The effort to elucidate the mechanism of V(D)J recombination has given rise to a dispute as to whether DNA-dependent protein kinase catalytic subunit (DNA-PKcs) contributes to signal joint formation (sjf). Observations reported to date are confusing. Analyses using DNA-PKcs-deficient cells could not conclude the requirement of DNA-PKcs for sjf, because sjf can be formed by end-joining activities which are diverse among cells other than those participating in V(D)J recombination. Here, we observed V(D)J recombination in DNA-PKcs knockout cells and showed that both signal and coding joint formation were clearly impaired in the cells. Subsequently, to directly demonstrate the requirement of DNA-PKcs for sjf, we introduced full-length cDNA of DNA-PKcs into the knockout cells. Furthermore, several mutant DNA-PKcs cDNA constructs designed from mutant cell lines (irs-20, V3, murine scid, and SX9) were also introduced into the cells to obtain further evidence indicating the involvement of DNA-PKcs in sjf. We found as a result that the full-length cDNA complemented the aberrant sjf and that the mutant cDNAs constructs also partially complemented it. Lastly, we looked at whether the kinase activity of DNA-PKcs is necessary for sjf and, as a result, demonstrated a close relationship between them. Our observations clearly indicate that the DNA-PKcs controls not only coding joint formation but also the sjf in V(D)J recombination through its kinase activity.

Animals↗
PubMed2000

[Study of monoclonal anti-idiotype antibody that bears the internal image of nasopharyngeal carcinoma associated antigen].

We prepared anti-idiotypic monoclonal antibodies (Ab2) against FC2 and HNL5 that recognized as nasopharyngeal cancer (NPC) associated antigens. These Ab2, which designated as 2H4 and 5D3, could inhibit the binding of FC2 or HNL5 to NPC cell lines. The anti-sera from the immunized mice that contained anti-anti-idiotype antibodies (Ab3) could compete with FC2 or HNL5 for binding with NPC cell by a competitive inhibition assay. When 2H4 or 5D3 immunized mice coupled with keyhole limpet hemocyanin(KLH), positive and specific delayed-type hypersensitivity (DTH) reaction occurred after the mice were stimulated by NPC cells. The proliferative response of the splenocytes was significantly higher in experimental groups than that in control groups. Therefore, it is suggested that the anti-idiotypic antibodies (Ab2) 2H4 and 5D3 are the Ab2 beta bearing the internal image of the epitope of NPC associated antigen, that either 2H4 or 5D3 expressing three dimensional shapes which resemble the structure of natural antigens can induce humoral and cellular immune response.

Animals↗
PubMed2000

The catalytic subunit of DNA-dependent protein kinase selectively regulates p53-dependent apoptosis but not cell-cycle arrest.

DNA damage induced by ionizing radiation (IR) activates p53, leading to the regulation of downstream pathways that control cell-cycle progression and apoptosis. However, the mechanisms for the IR-induced p53 activation and the differential activation of pathways downstream of p53 are unclear. Here we provide evidence that the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) serves as an upstream effector for p53 activation in response to IR, linking DNA damage to apoptosis. DNA-PKcs knockout (DNA-PKcs-/-) mice were exposed to whole-body IR, and the cell-cycle and apoptotic responses were examined in their thymuses. Our data show that IR induction of apoptosis and Bax expression, both mediated via p53, was significantly suppressed in the thymocytes of DNA-PKcs-/- mice. In contrast, IR-induced cell-cycle arrest and p21 expression were normal. Thus, DNA-PKcs deficiency selectively disrupts p53-dependent apoptosis but not cell-cycle arrest. We also confirmed previous findings that p21 induction was attenuated and cell-cycle arrest was defective in the thymoctyes of whole body-irradiated Atm-/- mice, but the apoptotic response was unperturbed. Taken together, our results support a model in which the upstream effectors DNA-PKcs and Atm selectively activate p53 to differentially regulate cell-cycle and apoptotic responses. Whereas Atm selects for cell-cycle arrest but not apoptosis, DNA-PKcs selects for apoptosis but not cell-cycle arrest.

Animals↗
PubMed1999

DNA double-strand break repair proteins are required to cap the ends of mammalian chromosomes.

Recent findings intriguingly place DNA double-strand break repair proteins at chromosome ends in yeast, where they help maintain normal telomere length and structure. In the present study, an essential telomere function, the ability to cap and thereby protect chromosomes from end-to-end fusions, was assessed in repair-deficient mouse cell lines. By using fluorescence in situ hybridization with a probe to telomeric DNA, spontaneously occurring chromosome aberrations were examined for telomere signal at the points of fusion, a clear indication of impaired end-capping. Telomeric fusions were not observed in any of the repair-proficient controls and occurred only rarely in a p53 null mutant. In striking contrast, chromosomal end fusions that retained telomeric sequence were observed in nontransformed DNA-PK(cs)-deficient cells, where they were a major source of chromosomal instability. Metacentric chromosomes created by telomeric fusion became even more abundant in these cells after spontaneous immortalization. Restoration of repair proficiency through transfection with a functional cDNA copy of the human DNA-PK(cs) gene reduced the number of fusions compared with a negative transfection control. Virally transformed cells derived from Ku70 and Ku80 knockout mice also displayed end-to-end fusions. These studies demonstrate that DNA double-strand break repair genes play a dual role in maintaining chromosomal stability in mammalian cells, the known role in repairing incidental DNA damage, as well as a new protective role in telomeric end-capping.

Animals↗