• Biomedical Science Letters
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• v.11 no.2
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• pp.165-173
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• 2005

A potent demethylating agent, 5-Azacytidine (5-AzaC) has been widely used as in many studies on DNA methylation, regulation of gene expression, and cancer biology. The mechanisms of the demethylating activity were known to be formation of complex between DNA and DNA methyltransferase (MTase), which depletes cellular MTase activity. However, 5-AzaC can also induce hypermethylation of a transgene in a transgenic cell line, G12 cells and it was explained as a result of defense mechanisms to inactivate foreign gene(s) somehow. This finding evoked the question that whether the phenomenon of hypermethylation induced by 5-AzaC is limited to the transgene or it can be occurred in endogenous gene(s). In order to answer the question, mutagenicity test of 5-AzaC and molecular characterization of mutants obtained from the test were performed using an endogenous gene, thymidine kinase (tk) in Chinese hamster V79 cells. When V79 and V79-J3 subclone cells were treated with 1, 2.5 ,5, $10{\mu}M$ of 5-AzaC for 48 hours, their maximum mutant frequencies were revealed as $6\times10^{-3}\;at\;5{\mu}M$(350-fold induction over background) and $8\times10^{-3}\;at\;2.5{\mu}M$ (l,800-fold induction over background) respectively. Since the induction rates were too high to be induced by true mutations, many trifluorothymidine (TFT)-resistant $(TFT^R)$ cells were subjected to Northern blot analysis to check the presence of tk transcripts. Surprisingly, all clones tested possessed the transcripts in a similar level, that implicates the $TFT^R$ phenotype induced by 5-AzaC has not given rise to hypermethylation of the gene in spite of unusually high mutation frequency. In addition, it has shown that the TK activity in the pool of 5-AzaC-induced $TFT^R$ cells has about a half of that in spontaneously-induced $TFT^R$ cells or in non-selected parental V79-J3 cells. This result suggests that the mechanism(s) underlying the TFT-resistance between spontaneously occurred and 5-AzaC-induced cells may be different. These findings have shown that the $TFT^R$ phenotype induced by 5-AzaC has not given rise to hypermethylation of the tk gene, and 5-AzaC may be induced by one or combined pathways among many drug resistance mechanisms. The exact mechanisms for the 5-AzaC-induced $TFT^R$ phenotype remain to elucidate.

• Journal of Life Science
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• v.13 no.6
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• pp.849-855
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• 2003

Nitric oxide (NO) plays an important role as a signaling molecule in the proliferation of placenta trophoblasts. In this study, we investigated the effect of NO on the activation of phospholipase C (PLC) in BeWo cells, choriocar-cinoma cell line. Sodium nitroprusside (SNP), an agent to produce NO spontaneously in cells, alone increased $［^3H］$ thymidine incorporation of BeWo cells, indicating NO stimulates proliferation of the cells. NO-induced proliferation of BeWo cells was blocked by U73122, an inhibitor of PLC, suggesting that NO-induced PLC activation is involved in the cell proliferation. NO also stimulated extracellular signal-regulated kinase (ERK) in BeWo cells, indicated by increased phosphorylation of ERK1/2 in Western blotting using anti-phospho-ERK1/2 antibody. NO-induced phos-phorylation of ERK1/2 was not abrogated by U73122. $PLC\gamma_1$l but not$PLC\gamma_2$ was tyrosine phosphorylated by SNP in immunoprecipitation assay using anti-$PLC\gamma_1$/$PLC\gamma_2$ antibodies, and SNP-induced phosphorylation of $PLC\gamma_1$ was abrogated by pre-treatment of cells with genistein and PD98059, indicating that NO induced-phosphorylation of $PLC\gamma_1$ is mediated by ERK. These results suggest that NO stimulates the proliferation of BeWo cells through ERK and $PLC\gamma_1$.

• BMB Reports
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• v.28 no.3
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• pp.216-220
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• 1995

cDNA for human cholesteryl ester transfer protein (CETP), a potent atherogenic plasma protein that redistributes the neutral lipids among lipoproteins, was expressed in recombinant vaccinia virus-infected cells (CV-1). Two insertion vectors regulated by different promoters were constructed. The vectors were introduced into human thymidine kinase-negative ($TK^-$) 1438 cells infected with wild-type vaccinia virus (WR strain). Recombinant viruses were selected with 5-bromodeoxyuridine (BUdR) and X-gal and identified with DNA dot blot analysis (vSC11-CETP and vTM1-CETP). The CETP cDNA insert in the recombinant vaccinia virus genome was identified by Southern blot analysis. Transcription of CETP cDNA in CV-1 cells infected with recombinant vaccinia virus was monitored by Northern blot analysis using the CETP cDNA as a probe. Positive signals were detected at 1.8 kb in cells infected with vSC11-CETP and at 2.3 kb in cells infected with vTM1-CETP. The recombinant vaccinia virus-infected CV-1 cells were shown to produce functional CETP when the culture medium was subjected to the CETP assay.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1997.04a
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• pp.81-81
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• 1997

We previously demonstrated an enhancer-like positive regulatory element within a 259-bp sequence (-2352 to-2094 bp) of the human CYP1A2 gene in HepG2 cells. Three protein binding sites were identified by DNase I footprint analyses within the 259-bp sequence: protected region A PRA ( -2283 to-2243 bp), PRB (-2218 to-2187 bp), and PRC (-2124 to-2098 bp) (I. Chung and E. Bresnick, Mol. Pharmacol. 47, 677-685, 1995). In the present study, the functional significance of those protected regions was examined. Transfection experiments with deletion and substitution mutants defined the PRB and PRC as containing positive and negative regulatory elements, respectively. Human breast carcinoma MCF-7 cells were cotransfected with a hepatocyte nuclear factor-1 (HNF-1) expression vector and CYP1A2 promoter-or thymidine kinase promoter-luciferase remoter gene constructs. HNF-1, which contributes to the liver specificity of genes, enhanced reporter gene activity in a PRC sequence-dependent manner. These results suggested that PRC could exist bound to a repressor which was displaceable by other transcription factors such as HNF-1. Results obtained by transfection of HepG2 hepatoma cells with various PRB substitution mutant-luciferase gene fusion constructs indicated that the entire sequence of PRB was necessary for promoter activity. Consequently, the regulation of CYP1A3 expression is very complex, requiring a number of both positive and negative regulatory factors.

• Molecular & Cellular Toxicology
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• v.2 no.4
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• pp.244-250
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• 2006

The detection of many synthetic chemicals used in industry that may pose a genetic hazard in our environment is of great concern at present. Since these substances are not limited to the original products, and enter the environment, they have become widespread environmental pollutants, thus leading to a variety of chemicals that possibly threaten the public health. In this respect, to regulate and to evaluate the chemical hazard will be important to environment and human health. The genotoxicity of 3 synthetic chemicals was evaluated in L5178Y $tk^{+/-}$ mouse lymphoma cells in vitro. 9H-carbazole (CAS No. 86-74-8) did not induce significant mutation frequencies both in the presence and absence of metabolic activation system. 1, 3-Dichloro-2-propanol (CAS No. 96-23-1) revealed a significant increase of mutation frequencies in the range of $625-373\;{\mu}g/mL$ in the absence of metabolic activation system and $157-79\;{\mu}g/mL$ in the presence of metabolic activation system. And also, fenpropathrin (CAS No. 64257-84-7) appeared the positive results only in the absence of metabolic activation system. Through the results of MLA tk assay with 3 synthetic chemicals in L5178Y cells in vitro, we may provide the important clues on the genotoxic potentials of these 3 chemicals.

• The Korean Journal of Nuclear Medicine
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• v.38 no.2
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• pp.175-179
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• 2004

Molecular nuclear cardiac imaging has included Tc-99m Annexin imaging to visualize myocardial apoptosis, but is now usually associated with gene therapy and cell-based therapy. Cardiac gene therapy was not successful so far but cardiac reporter gene imaging was made possible using HSV-TK (herpes simplex virus thymidine kinase) and F-18 FHBG (fluoro-hydroxymethylbutyl guanine) or I-124 FIAU (fluoro-deoxyiodo-arabino-furanosyluracil). Gene delivery was performed by needic injection with or without catheter guidance. Tk expression did not last longer than 2 weeks in myocardium. Cell-based therapy of ischemic heart or failing heart looks promising, but biodistribution and differentiation of transplanted cells are not known. Reporter genes can be transfected to the stem/progenitor cells and cells containing these genes can be transplanted to the recipients using catheter-based purging or injection. Repeated imaging should be available and if promoter are varied to let express reporter transgenes, cellular (trans)differentiation can be studied. NIS (sodium iodide symporter) or D2R receptor genes are promising in this aspect.

• BMB Reports
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• v.36 no.4
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• pp.379-386
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• 2003

A mutant herpes simplex virus 1, mtHSV, was constructed by inserting the E. coli beta-galactosidase gene into the loci of icp34.5, the apoptosis-inhibiting gene of HSV. The mtHSV replicated in and lysed U251 (human glioma cells), EJ (human bladder cells), and S-180 (mice sarcoma cells), but not Wish (human amnion cells) cells. With its intact tk (thymidine kinase) gene, mtHSV exhibited susceptibility to acyclovir (ACV), which provided an approach to control viral replication. An in vivo test with mtHSV was conducted in immune-competent mice bearing sarcoma S-180 tumors, which were treated with a single intratumoral injection of mtHSV or PBS. Tumor dimensions then were measured at serial time points, and the tumor volumes were calculated. Sarcoma growth was significantly inhibited with prolonged time and reduced tumor volume. There was microscopic evidence of necrosis of tumors in treated mice, whereas no damage was found in other organs. Immunohistochemical staining revealed that virus replication was exclusively confined to the treated tumor cells. HSV-1 DNA was detected in tumors, but not in the other organs by a polymerase chain reaction analysis. From these experiments, we concluded that mtHSV should be a safe and promising oncolytic agent for cancer treatment.

• Archives of Pharmacal Research
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• v.24 no.4
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• pp.323-326
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• 2001

Previous studies have demonstrated that CW252053, a quinazoline antifolate, exhibits potent inhibitory activity against thymidylate synthase (TS) as well as cytotoxic activity against tumor cell lines in vitro. In this studys, we evaluated the in vivo antitumor efficacy of CW252053 in the mouse tumor model. Female B6D2F$_1$ mice were injected with LY3.7. 2C TK-/- (thymidine kinase deficient mouse Iymphoma) cells into the gastrocnemius muscle. Then, CW252053 was administered twice daily by intraperitoneal injection for 10 days, and tumor growth was monitored daily by leg diameter measurement. All animals in the vehicle, 5-FU, and low dose (30mgmg/kg CW252053 treated groups died between days 12 and 23 because of the tumor burden. In contrast, dosing with 60 mg/kg of CW252053 produced a cure rat against tumor growth of 37.5% and a survival rate of 50%. Even more significantly, a higher dose of CW252053 (120 mg/kg) elicited both a 100% cure rate and a 100% survival rate at the termination of the study, confirming that this compound has very potent in vivo antitumor activity against tumor growth. During the experimental period of this study no signs of toxicity were observed even at the high CW252053 dosage rate of 120 mg/kg.

• Reproductive and Developmental Biology
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• v.28 no.4
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• pp.211-219
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• 2004

The effects of adenosine 5'-triphosphate (ATP) and ATP analogs, P/sub 2y/ purinoceptor agonists, on growth of normal mouse mammary epithelial cells (NMuMG) were examined. Cells were plated onto 24 well plates in DMEM supplemented with 10 % fetal calf serum. After serum starvation for 24 hours, ATP, P/sub 2y/ purinoceptor agonists (AdoPP[NH]P, ATP-α-S, ATP-γ-S, β, γ-me-ATP and 2me-S-ATP), P/sub 2u/ purinoceptor agonist (UTP) and P/sub 2y/ purinoceptor antagonists (Reactive Blue 2, more selective to P/sub 2y/ receptor than PPADS; PPADS) were added. DNA synthesis was estimated as incorporation of 3H-thymidine into DNA (1 hour pulse with 1 μ Ci/ml, 18～19 hours after treatment). ATP, Adopp[NH]P, ATP-α-S or ATP-γ-S, significantly increased DNA synthesis at 1, 10 and 100 μM concentrations with dose-dependency (P<0.05), and the maximum responses of ATP and ATP analogs were shown at 100 μM concentration (P<0.05). The potency order of DNA synthesis was ATP≥ATP- γ -S>Adopp [NH]P>ATP-α-S. β, γ -me-ATP, 2me-S-ATP and UTP did not increase DNA synthesis. In autoradiographic analysis of percentage of S-phase cells, similar results were observed to those of DNA synthesis. Addition of 1, 10 or 100 μM Reactive Blue 2 or PPADS significantly decreased ATP (100 μM)-induced DNA synthesis, however, PPADS was less effective than Reactive Blue 2. In Elvax 40P implant experiment, ATP directly stimulated mammary endbud growth in situ suggesting the physiological regulator of ATP in mammary growth. ATP 100 μM rapidly increased MAPK activity, reaching a maximum at 5 min and then gradually decreasing to the base level in 30 min. ATP analogs, Adopp[NH]P and ATP-γ-S also increased MAPK activity, however, β, γ-me-ATP and 2me-S-ATP did not. The inhibitor of the upstream MAPK kinase (MEK), PD 98059 (25 μM), effectively reduced ATP (100 μM) or EGF(10 ng/ml, as positive control)-induced MAPK activity and DNA synthesis (P<0.05). These results indicate that ATP-induced DNA synthesis was prevented from the direct inhibition of MAPK kinase pathway. Overall results support the hypothesis that the stimulatory effects of normal mouse mammary epithelial growth by addition of ATP or ATP analogs are mediated through mammary tissue specific P/sub 2y/ purinoceptor subtype, and MAPK activation is necessary for the ATP-induced cell growth.

• Molecular & Cellular Toxicology
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• v.1 no.3
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• pp.179-188
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• 2005

To develop the novel anti-allergic drug, many sophoricoside derivatives were synthesized. Among these derivatives, JSH-II-3, VI-3, VII-3, VIII-3, VII-20 and VII-20 (sodium salt) were selected and subjected to high throughput toxicity screening (HTTS) because they revealed strong IL-5 inhibitory activity and limitation of quantity. Single cell gel electrophoresis (Comet) assay, mouse lymphoma thymidine kinase ($tk^{+/-}$) gene assay (MOLY), chromosomal aberration assay in mammalian cells and Ames reverse mutation assay in bacterial system were used as simplified, inexpensive, short-term in vitro screening tests in our laboratory. Through the primary screening using the comet assay, we could choose the first candidates of sophoricoside derivatives with no genotoxic potentials as JSH-VI-3, VII-3, VII-20 and VII-20 (sodium salt). Also JSH-VII-3, VII-20 and VII-20 (sodium salt) are non-mutagenic in MOLY assay, while JSH-II-3 is mutagenic at high concentration with the presence of metabolic activation system in both comet assay and MOLY assay. The selected derivatives (JSH-VI-3, VII-3, VII-20 and VII-20 (sodium salt) are not mutagenic in S. typhimurium TA98 and TA100 strains both in the presence and absence of metabolic activation. From results of chromosomal aberration assay, 6 h treatment of JSH-VI-3, VII-3 and VII-20 (sodium salt) were not revealed clastogenicity both in the presence and absence of S-9 mixture. Therefore, we suggests that JSH-VI-3, VII-3, VII-20 and VII-20 (sodium salt), as the optimal candidates with both no genotoxic potential and IL-5 inhibitory effects must be chosen. To process the development into new anti-inflammatory drug of these derivatives, further investigation will need.