Search PubMed⌕ Search

Biomedical subjects

Y Kang

Publications and source records attributed to Y Kang.

At least 73 records · Page 4Linked to original sources
PubMed2000

Establishment and characterization of 5-fluorouracil-resistant gastric cancer cells.

Two 5-fluorouracil (5-FU)-resistant cell lines from a Korean gastric cancer cell line were established by incubation of the cells with increasing concentration of 5-FU, and the resultant cell lines showed an over 800-fold increased resistance to 5-FU. To identify the mechanism of 5-FU resistance, the expressions of genes involved in 5-FU metabolism were examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Expressions of orotate phosphoribosyltransferase (OPRT), thymidine phosphorylase (TP), and uridine phosphorylase (UP) were significantly downregulated in these cell lines, resulting in low incorporation of 5-FU into nucleic acids. In contrast, an increased expression of thymidine kinase (TK) was observed in 5-FU-resistant cells. These results strongly indicate that blocking of 5-FU incorporation into nucleic acids and TK overexpression may play a major role in 5-FU resistance in these cells. Interestingly, these cell lines showed cross-resistance to paclitaxel, cisplatin, and doxorubicin, suggesting that other factors such as HSP27 and Mn-SOD could be also involved in the mechanism of multidrug resistance in these cell lines.

Antimetabolites, Antineoplastic↗
PubMed2000

Cellular and molecular mechanism for Kilham rat virus-induced autoimmune diabetes in DR-BB rats.

Kilham rat virus (KRV) causes autoimmune diabetes in diabetes-resistant BioBreeding (DR-BB) rats; however, the mechanism by which KRV induces autoimmune diabetes without the direct infection of beta cells is not well understood. We first asked whether molecular mimicry, such as a common epitope between a KRV-specific peptide and a beta cell autoantigen, is involved in the initiation of KRV-induced autoimmune diabetes in DR-BB rats. We found that KRV peptide-specific T cells generated in DR-BB rats infected with recombinant vaccinia virus expressing KRV-specific structural and nonstructural proteins could not induce diabetes, indicating that molecular mimicry is not the mechanism by which KRV induces autoimmune diabetes. Alternatively, we asked whether KRV infection of DR-BB rats could disrupt the finely tuned immune balance and activate autoreactive T cells that are cytotoxic to beta cells, resulting in T cell-mediated autoimmune diabetes. We found that both Th1-like CD45RC+CD4+ and cytotoxic CD8+ T cells were up-regulated, whereas Th2-like CD45RC-CD4+ T cells were down-regulated, and that isolated and activated CD45RC+CD4+ and CD8+ T cells from KRV-infected DR-BB rats induced autoimmune diabetes in young diabetes-prone BioBreeding (DP-BB) rats. We conclude that KRV-induced autoimmune diabetes in DR-BB rats is not due to molecular mimicry, but is due to a breakdown of the finely tuned immune balance of Th1-like CD45RC+CD4+ and Th2-like CD45RC-CD4+ T cells, resulting in the selective activation of beta cell-cytotoxic effector T cells.

Acute Disease↗
PubMed2000

Enhanced tumorigenesis and reduced transforming growth factor-beta type II receptor in lung tumors from mice with reduced gene dosage of transforming growth factor-beta1.

To elucidate the role of transforming growth factor-beta1 (TGF-beta1) and the TGF-beta type II receptor (TGF-beta RII) as tumor-suppressor genes in lung carcinogenesis, we mated C57BL/6 mice heterozygous (HT) for deletion of the TGF-beta1 gene with A/J mice to produce AJBL6 TGF-beta1 HT progeny and their wild-type (WT) littermates. Immunohistochemical staining, in situ hybridization, and northern blot analyses showed lower staining and hybridization for TGF-beta1 protein and mRNA, respectively, in the lungs of normal HT mice versus WT mice. Competitive reverse transcription-polymerase chain reaction (CRT-PCR) amplification showed the level of TGF-beta1 mRNA in the lungs of HT mice to be fourfold lower than the level in WT lung. When challenged with ethyl carbamate, lung adenomas were detected in 55% of HT mice by 4 mo but only in 25% of WT littermates at this time. Whereas all HT mice had adenomas by 6 mo, it was not until 10 mo before all WT mice had adenomas. After 12 mo, the average number of adenomas was fivefold higher in HT lungs than in WT lungs. Most dramatic was the appearance of lung carcinomas in HT mice 8 mo before they were visible in WT mice. Thus, the AJBL6 TGF-beta1 HT mouse provides an excellent model system to examine carcinogen-induced lung tumorigenesis by increasing progressive lesion incidence and multiplicity relative to their WT littermates. Immunohistochemical staining showed expression of the TGF-beta type I receptor (TGF-beta RI) at moderate to strong levels in lung adenomas and carcinomas in HT and WT mice. In contrast, whereas weak immunostaining for TGF-beta RII was detected in 67% of HT carcinomas at 12 mo, only 22% of WT carcinomas showed weak staining for this protein. Individual lung carcinomas showing reduced TGF-beta RII expression and adjacent normal bronchioles were excised from HT lungs using laser capture microdissection, and CRT-PCR amplification of the extracted RNA showed 12-fold less TGF-beta RII mRNA in these carcinomas compared with bronchioles. Decreasing TGF-beta RII mRNA levels occurred with increasing tumorigenesis in lung hyperplasias, adenomas, and carcinomas, with carcinomas having fourfold and sevenfold lower levels of TGF-beta RII mRNA than adenomas and hyperplasias, respectively. These data show enhanced ethyl carbamate-induced lung tumorigenesis in AJBL6 HT mice compared with WT mice, suggesting that both TGF-beta1 alleles are necessary for tumor-suppressor activity. Reduction of TGF-beta RII mRNA expression in progressive stages of lung tumorigenesis in HT mice suggests that loss of TGF-beta RII may play an important role in the promotion of lung carcinogenesis in mice with reduced TGF-beta1 gene dosage when challenged with carcinogen.

Animals↗
PubMed2000

Endogenous ecotropic murine leukemia viral (MuLV) envelope protein as a new autoantigen reactive with non-obese diabetic mice sera.

The identification and characterization of autoantigens associated with autoimmune IDDM (insulin dependent diabetes mellitus) would help to elucidate the pathogenic mechanism of this disease as well as to design antigen-based immunotherapy. Non-obese diabetic (NOD) mice have been used as the best model for studying the pathogenesis of human IDDM. To identify new autoantigens associated with IDDM, the lambda gt11-cDNA library from MIN6N8a, NOD-derived pancreatic beta cell line, was constructed and then candidate autoantigen clones were screened with prediabetic NOD sera. Nine positive clones were selected from 2x10(5)phage plaques. The nucleotide sequencing and homology searching showed that six of the nine positive clones had part of the endogenous ecotropic murine leukemia viral (MuLV) envelope gene. Nested deletion of this envelope gene revealed that the leucine zipper region in the transmembrane domain of MuLV envelope protein was the target epitope(s) reactive with prediabetic NOD mice sera. The prevalence of MuLV envelope protein-positive antibody in NOD mice was around 46%, while the non-NOD mice strains including BALB/c, ICR, C57BL/6, and SJL/J mice did not produce this envelope protein-reactive antibody. The expression of endogenous ecotropic MuLV envelope gene in NOD mouse pancreas was distinct in those with severe insulitis. However, both prediabetic and diabetic NOD mice did not show the MHC class II-restrictive cellular autoimmunity against our purified recombinant envelope protein. In this study, we showed that the endogenous ecotropic MuLV envelope protein was a new autoantigen reactive with the activated NOD humoral immune system.

Animals↗
PubMed2000

Overexpression of protein kinase C delta represses expression of proliferin in NIH3T3 cells that regulates cell proliferation.

Protein kinase C (PKC) delta is known to inhibit proliferation of many cell types. In this study we found that overexpression of PKCdelta reduced proliferation of NIH3T3 cells. To identify specific genes regulated by PKCdelta in regulation of cell proliferation, we used differential display-polymerase chain reaction in PKCdelta-overexpressing NIH3T3 cells and found that the expression of proliferin, a secreted protein known to stimulate cell proliferation, was significantly repressed. Transient transfection study indicated that the repression of proliferin expression was inversely proportional to the expression levels of PKCdelta. Addition of an anti-proliferin antibody to culture medium to neutralize the secreted proliferin decreased cell proliferation in a dose-dependent manner. Our results, therefore, suggest that overexpression of PKCdelta induces transcriptional repression of proliferin, thereby resulting in inhibition of cell proliferation.

3T3 Cells↗
PubMed2000

Ipsilesional versus contralesional neglect depends on attentional demands.

Right hemisphere injuries often produce contralesional hemispatial neglect (CN). In contrast to CN, some patients with right hemisphere damage can also show so-called ipsilesional neglect (IN). Previous reports found that patients tend to show IN on line bisection tasks but CN on other tasks such as target cancellation. To learn why these two tasks induce different spatial biases in patients with right hemisphere injury, conventional (i.e. solid) line bisection was compared with two novel bisection tasks consisting of horizontally aligned strings of characters. The subjects' task was to mark a target character that was at or closest to the true midpoint of the simulated line. Four of the 5 patients showed a dissociation whereby IN occurred for solid lines while CN was observed on character lines. The two patients assessed with an antisaccade paradigm showed a "visual grasp" for leftward stimuli. The present results suggest that neglect on line bisection may reflect two opposing forces, an approach behavior or "visual grasp" toward left hemispace and an attentional bias toward right hemispace.

Adult↗
PubMed2000

P(2Y) purinoceptor subtypes recruit different mek activators in astrocytes.

Extracellular ATP can function as a glial trophic factor as well as a neuronal transmitter. In astrocytes, mitogenic signalling by ATP is mediated by metabotropic P(2Y) receptors that are linked to the extracellular signal regulated protein kinase (Erk) cascade, but the types of P(2Y) receptors expressed in astrocytes have not been defined and it is not known whether all P(2Y) receptor subtypes are coupled to Erk by identical or distinct signalling pathways. We found that the P(2Y) receptor agonists ATP, ADP, UTP and 2-methylthioATP (2MeSATP) activated Erk and its upstream activator MAP/Erk kinase (Mek). cRaf-1, the first kinase in the Erk cascade, was activated by 2MeSATP, ADP and UTP but, surprisingly, cRaf-1 was not stimulated by ATP. Furthermore, ATP did not activate B-Raf, the major isoform of Raf in the brain, nor other Mek activators such as Mek kinase 1 (MekK1) and MekK2/3. Reverse transcriptase-polymerase chain reaction (RT - PCR) studies using primer pairs for cloned rat P(2Y) receptors revealed that rat cortical astrocytes express P(2Y(1)), a receptor subtype stimulated by ATP and ADP and their 2MeS analogues, as well as P(2Y(2)) and P(2Y(4)), subtypes in rats for which ATP and UTP are equipotent. Transcripts for P(2Y(6)), a pyrimidine-preferring receptor, were not detected. ATP did not increase cyclic AMP levels, suggesting that P(2Y(11)), an ATP-preferring receptor, is not expressed or is not linked to adenylyl cyclase in rat cortical astrocytes. These signal transduction and RT - PCR experiments reveal differences in the activation of cRaf-1 by P(2Y) receptor agonists that are inconsistent with properties of the P(2Y(1)), P(2Y(2)) and P(2Y(4)) receptors shown to be expressed in astrocytes, i.e. ATP=UTP; ATP=2MeSATP, ADP. This suggests that the properties of the native P(2Y) receptors coupled to the Erk cascade differ from the recombinant P(2Y) receptors or that astrocytes express novel purine-preferring and pyrimidine-preferring receptors coupled to the ERK cascade.

Adenosine Diphosphate↗
PubMed2000

SRL1: a new locus specific to the phyB-signaling pathway in Arabidopsis.

As part of an effort to isolate new Arabidopsis mutants specifically defective in responsiveness to red light, we identified srl1 (short hypocotyl in red light) by screening an EMS-mutagenized M2 population derived from a phytochrome B (phyB)-overexpressor line (ABO). The srl1 mutant shows enhanced responsiveness to continuous red but not far-red light, in both wild-type and ABO backgrounds, consistent with involvement in the phyB-signaling pathway but not that of phyA. The hypersensitive phenotype of srl1 is not due to overexpression of endogenous phyA or phyB, and the locus maps to the center of chromosome 2, distinct from any other known photomorphogenic mutants. srl1 seedlings display enhancement of several phyB-mediated responses, including shorter hypocotyls, more expanded cotyledons, shorter petioles and modestly higher levels of CAB gene expression under red light than the wild type. Double mutant analyses show that the hypersensitive phenotype of srl1 is completely phyB-dependent. The data suggest, therefore, that SRL1 may encode a negatively acting component specific to the phyB-signaling pathway.

Arabidopsis↗
PubMed2000

Transforming growth factor-beta 1 and its receptors in human lung cancer and mouse lung carcinogenesis.

The transforming growth factor-betas (TGF-beta s) are multifunctional proteins that inhibit the proliferation of many epithelial cells through a set of cell protein receptors that includes the TGF-beta type I (RI) and type II (RII) receptors. Loss of growth inhibition by TGF-beta is thought to contribute to the development of many types of tumors. In the present study, we have examined expression of the proteins and mRNAs for TGF-beta 1, TGF-beta RI, and TGF-beta RII in normal human lung, well-characterized non-small cell lung cancer (NSCLC) cell lines, and primary NSCLC specimens. Immunohistochemical staining for TGF-beta 1, TGF-beta RI, and TGF-beta RII using specific antibodies in normal human lung showed expression of the 3 proteins in the epithelium of bronchi and bronchioles as well as in alveoli. Differential expression of TGF-beta RI and TGF-beta RII proteins was detected in 5 NSCLC cell lines using Western blot analysis, with reduced levels in 3 cell lines. A panel of 45 formalin-fixed and paraffin-embedded NSCLC specimens showed positive immunostaining for TGF-beta 1, TGF-beta RI, and TGF-beta RII, with reduced TGF-beta RII in poorly differentiated adenocarcinomas and squamous cell carcinomas and some moderately differentiated adenocarcinomas. In situ hybridization studies conducted with specific riboprobes for TGF-beta 1, TGF-beta RI, and TGF-beta RII showed corresponding localization of expression of the mRNAs in the specimens that showed positive immunostaining for the proteins. To investigate the roles of TGF-beta 1, TGF-beta RI, and TGF-beta RII in chemically induced mouse lung tumorigenesis, we examined the expression of their proteins and mRNAs in 2 mouse model systems. Whereas expression of the proteins and mRNAs for TGF-beta 1 and TGF-beta RI was comparable in lung adenomas and bronchioles of A/J mice treated with benzo(alpha)pyrene, decreased immunostaining and hybridization for TGF-beta RII protein and mRNA was detected in 50% of lung adenomas in these mice. Interestingly, expression of TGF-beta 1 and the TGF-beta receptor proteins was similar to that of bronchioles in C57B1/6 mice and their littermates heterozygous for deletion of the TGF-beta 1 gene treated with diethylnitrosamine. These data show that reduced levels of expression of TGF-beta RII occur in some, but not all, human and mouse lung tumors. This suggests that different mechanisms of action, some of which may involve the TGF-beta signaling pathway, may contribute to the progression of lung tumorigenesis.

Adenoma↗
PubMed2000

Increased expression after X-irradiation of MUC1 in cultured human colon carcinoma HT-29 cells.

The effect of X-irradiation on production of MUC1 was studied with human colon carcinoma HT-29 cells. As evaluated by immunocytochemical staining, the percentages of MUC1-positive cells in cells at 4 days after 6 Gy irradiation and in unirradiated control cells were 52 +/- 3.5% (n = 6) and 26 +/- 2.8% (n = 6), respectively. Flow-cytometric analysis of living cells showed that MUC1 began to rise from day 1, reaching a plateau by day 4 after 6 Gy irradiation. Western blot analysis with monoclonal antibody MY.1E12 against glycosylated MUC1 (mature form) showed dose-dependent increases of two bands (500 and 390 kDa) corresponding to two polymorphic MUC1 alleles. Premature forms of MUC1 (350 and 240 kDa) were detectable with monoclonal antibody HMFG-2 only in irradiated cells, suggesting that new core protein synthesis had been induced. The transcriptional activity of the MUC1 gene was analyzed in terms of transient expression of MUC1-CAT reporter plasmids containing 5'-flanking sequences of the MUC1 gene fused to the bacterial chloramphenicol acetyltransferase (CAT) gene. The results of CAT assay indicate that enhanced expression of MUC1 in irradiated HT-29 cells was due to upregulation of MUC1 transcription, and required the upstream promoter.

Antibodies, Monoclonal↗
PubMed2000

Analysis of cellular factors that mediate nuclear export of RNAs bearing the Mason-Pfizer monkey virus constitutive transport element.

There is now convincing evidence that the human Tap protein plays a critical role in mediating the nuclear export of mRNAs that contain the Mason-Pfizer monkey virus constitutive transport element (CTE) and significant evidence that Tap also participates in global poly(A)(+) RNA export. Previously, we had mapped carboxy-terminal sequences in Tap that serve as an essential nucleocytoplasmic shuttling domain, while others had defined an overlapping Tap sequence that can bind to the FG repeat domains of certain nucleoporins. Here, we demonstrate that these two biological activities are functionally correlated. Specifically, mutations in Tap that block nucleoporin binding also block both nucleocytoplasmic shuttling and the Tap-dependent nuclear export of CTE-containing RNAs. In contrast, mutations that do not inhibit nucleoporin binding also fail to affect Tap shuttling. Together, these data indicate that Tap belongs to a novel class of RNA export factors that can target bound RNA molecules directly to the nuclear pore without the assistance of an importin beta-like cofactor. In addition to nucleoporins, Tap has also been proposed to interact with a cellular cofactor termed p15. Although we were able to confirm that Tap can indeed bind p15 specifically both in vivo and in vitro, a mutation in Tap that blocked p15 binding only modestly inhibited CTE-dependent nuclear RNA export. However, p15 did significantly enhance the affinity of Tap for the CTE in vitro and readily formed a ternary complex with Tap on the CTE. This result suggests that p15 may play a significant role in the recruitment of the Tap nuclear export factor to target RNA molecules in vivo.

Amino Acid Sequence↗
PubMed2000

Retroviral gene therapy with an immunoglobulin-antigen fusion construct protects from experimental autoimmune uveitis.

Immunoglobulins can serve as tolerogenic carriers for antigens, and B cells can function as tolerogenic antigen-presenting cells. We used this principle to design a strategy for gene therapy of experimental autoimmune uveitis, a cell-mediated autoimmune disease model for human uveitis induced with the uveitogenic interphotoreceptor retinoid-binding protein (IRBP). A retroviral vector was constructed containing a major uveitogenic IRBP epitope in frame with mouse IgG1 heavy chain. This construct was used to transduce peripheral B cells, which were infused into syngeneic recipients. A single infusion of transduced cells, 10 days before uveitogenic challenge, protected mice from clinical disease induced with the epitope or with the native IRBP protein. Protected mice had reduced antigen-specific responses, but showed no evidence for a classic Th1/Th2 response shift or for generalized anergy. Protection was not transferable, arguing against a mechanism dependent on regulatory cells. Importantly, the treatment was protective when initiated 7 days after uveitogenic immunization or concurrently with adoptive transfer of primed uveitogenic T cells. We suggest that this form of gene therapy can induce epitope-specific protection not only in naive, but also in already primed recipients, thus providing a protocol for treatment of established autoimmunity.

Animals↗
PubMed2000

Defects in the differentiation and function of bone marrow-derived dendritic cells in non-obese diabetic mice.

Due to their high immunostimulatory ability as well as the critical role they play in the maintenance of self-tolerance, dendritic cells have been implicated in the pathogenesis of autoimmune diseases. The non-obese diabetic (NOD) mouse is an animal model of autoimmune type 1 diabetes, in which pancreatic beta cells are selectively destroyed mainly by T cell-mediated immune responses. To elucidate initiation mechanisms of beta cell-specific autoimmunity, we attempted to generate bone marrow-derived dendritic cells from NOD mice. However, our results showed low proliferative response of NOD bone marrow cells and some defects in the differentiation into the myeloid dendritic cells. NOD dendritic cells showed lower expressions of MHC class II, B7-1, B7-2 and CD40, compared with C57BL/6 dendritic cells. In mixed lymphocyte reactions, stimulatory activities of NOD dendritic cells were also weak. Treatment with LPS, INF-gamma and anti-CD40 stimulated NOD dendritic cells to produce IL-12p70. The amount of IL-12, however, appeared to be lower than that of C57BL/6. Results of the present study indicated that there may be some defects in the development of NOD dendritic cells in the bone marrow, which might have an impact on the breakdown of self tolerance.

Animals↗
PubMed2000

[Enantioselective pharmacokinetics of benproperine in healthy volunteers].

AIM: To investigate the enantioselective pharmacokinetic process of benproperine in healthy volunteers. METHODS: An enantiospecific HPLC method was developed and used to determine the plasma concentrations of each enantiomer. Six healthy Chinese male volunteers received an oral dose of 60 mg (+/-)-benproperine. The ratios of the enantiomers in plasma samples were measured on a chiral AGP column. The plasma concentration of each enantiomer was then calculated using the ratios of enantiomers and total concentration of the two enantiomers previously measured. RESULTS: The plasma levels of (-)-(S)-benproperine were always significantly higher than those of its antipode in six volunteers. The mean AUC0-t and Cmax values for (-)-(S)-benproperine were 2.18 and 2.12 times higher than those of (+)-(R)-benproperine. There was no significant difference between the T1/2 for both enantiomers, tested by paired t test (P > 0.05). Half an hour after administration of benproperine, the S/R ratio in plasma samples was as high as 3.8, and in 2 hours it drastically decreased to about 2.2, then kept on till 24 hours. CONCLUSION: Benproperine showed significant enantioselective pharmacokinetics in the human after an oral dose of the racemate.

Administration, Oral↗
PubMed2000

[IR spectra and structures of two trinuclear molybdenum cluster compounds coordinated by binary carboxylates].

Two trinuclear molybdenum cluster compounds coordinated by binary carboxylates compounds Mo3S4 (DTP)3(phthalate) (Py)(A) and Mo3S4 (DTP)3(malonate)(Py)(B) have been synthesized. IR absorption peaks of Mo3S4 core and the ligands are assigned with reference to those of Mo3S4(DTP)4(Py)(C). The assignment of stretching vibrations of carboxylate (COO-) for both (A) and (B) reveals much information corresponding to their molecular structures.

English Abstract↗
PubMed1999

Cdc2 and Cdk2 kinase activated by transforming growth factor-beta1 trigger apoptosis through the phosphorylation of retinoblastoma protein in FaO hepatoma cells.

The signaling pathway leading to TGF-beta1-induced apoptosis was investigated using a TGF-beta1-sensitive hepatoma cell line, FaO. Cell cycle analysis demonstrated that the accumulation of apoptotic cells was preceded by a progressive decrease of the cell population in the G(1) phase concomitant with a slight increase of the cell population in the G(2)/M phase in response to TGF-beta1. TGF-beta1 induced a transient increase in the expression of Cdc2, cyclin A, cyclin B, and cyclin D1 at an early phase of apoptosis. During TGF-beta1-induced apoptosis, the transient increase in cyclin-dependent kinase (Cdk) activities coincides with a dramatic increase in the hyperphosphorylated forms of RB. Treatment with roscovitine or olomoucine, inhibitors of Cdc2 and Cdk2, blocked TGF-beta1-induced apoptosis by inhibiting RB phosphorylation. Overexpression of Bcl-2 or adenovirus E1B 19K suppressed TGF-beta1-induced apoptosis by blocking the induction of Cdc2 mRNA and the subsequent activation of Cdc2 kinase, whereas activation of Cdk2 was not affected, suggesting that Cdc2 plays a more critical role in TGF-beta1-induced apoptosis. In conclusion, we present the evidence that Cdc2 and Cdk2 kinase activity transiently induced by TGF-beta1 phosphorylates RB as a physiological target in FaO cells and that RB hyperphosphorylation may trigger abrupt cell cycle progression, leading to irreversible cell death.

Animals↗