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Biomedical subjects

B M Kwon

Publications and source records attributed to B M Kwon.

At least 19 recordsLinked to original sources
PubMed2001

5,6-Diphenylpyridazine derivatives as acyl-CoA:cholesterol acyltransferase inhibitors.

Alkyl-5,6-diphenylpyridazine derivatives combining several main features of ACAT inhibitors, such as a long alkyl side chain linked to a heterocycle and the o-diphenyl system, were synthesized and tested. Moreover, modeling studies on representative terms were performed. Some compounds displayed ACAT inhibition in the micromolar range, both on the enzyme isolated from rat liver microsomes and in cell-free homogenate of murine macrophages.

Animals↗
PubMed2001

The neuron restrictive silencer factor can act as an activator for dynamin I gene promoter activity in neuronal cells.

The neuron restrictive silencer element (NRSE) has been identified in several neuronal genes and confers neuron specificity by silencing transcription in nonneuronal cells. We have previously reported that Sp1 and an NF-kappaB-like element (NE-1) are required for the promoter activity of mouse dynamin I gene. In the present study, we found that the upstream regulatory region of the dynamin I promoter has an NRSE-like sequence and showed that neuron restrictive silencer factor (NRSF) binds to this element in neuronal cells as well as in nonneuronal cells. We also showed that NRSF activates the promoter activity of dynamin I gene in neuronal cells. From the results in this study, we suggest that NRSE might be involved in the neuron restriction of dynamin I expression, and NRSF could act as an activator for promoter activity of dynamin I gene in neuronal cells.

Animals↗
PubMed2001

Negative regulation of YY1 transcription factor on the dynamin I gene promoter.

Dynamin I is highly expressed in brain and plays a critical role in clathrin-mediated endocytosis and synaptic vesicle recycling. To elucidate the molecular mechanism by which expression of dynamin I is tissue-specifically regulated, we previously cloned and characterized the promoter of the mouse dynamin I gene and suggested that there is a negative regulatory element in this promoter region. In the present study, we showed that YY1 binds to this negative regulatory element located at -111 to -107 by using the EMSA and supershift analyses. Cotransfection experiment using an YY1 expression vector revealed that YY1 exerts a repressive role on the dynamin I gene promoter activity. These results demonstrate that transcription factor YY1 negatively regulates dynamin I expression via binding to the negative regulatory element.

Animals↗
PubMed2001

Increased GTP-binding to dynamin II does not stimulate receptor-mediated endocytosis.

Regarding the molecular mechanism of dynamin in receptor-mediated endocytosis, GTPase activity of dynamin has been thought to have a critical role in endocytic vesicle internalization. However, a recent report suggested that GTP-binding to dynamin itself activates the dynamin to recruit molecular machinery necessary for endocytosis. In this study, to investigate the role of GTP binding to dynamin II, we generated two mutant dynamin II constructs: G38V and K44E. G38V, its GTP binding site might be mainly occupied by GTP caused by reduced GTPase activity, and K44E mutant, its GTP binding site might be vacant, caused by its decreased affinity for GTP and GDP. From the analysis of the ratio of GTP vs GDP bound to dynamin, we confirmed these properties. To test the effect of these mutant dynamins on endocytosis, we performed flow cytometry and confocal immunofluorescence analysis and found that these two mutants have inhibitory effect on transferrin-induced endocytosis. Whereas fluorescent transferrin was completely internalized in wild-type (WT) dynamin II expressing cells, no intracellular accumulation of fluorescent transferrin was found in the cells overexpressing K44E and G38V mutant. Interestingly, the amount of GTP bound to K44E was increased when endocytosis was induced than that bound to WT. The present results suggested that the GTPase activity of dynamin II is required for formation of endocytic vesicle and GTP-binding to dynamin II per se is not sufficient for stimulating endocytosis.

3T3 Cells↗
PubMed2001

Grb2 dominantly associates with dynamin II in human hepatocellular carcinoma HepG2 cells.

The two SH3 domains and one SH2 domain containing adaptor protein Grb2 is an essential element of the Ras signaling pathway in multiple systems. The SH2 domain of Grb2 recognizes and interacts with phosphotyrosine residues on activated tyrosine kinases, whereas the SH3 domains bind to several proline-rich domain-containing proteins such as Sos1. To define the difference in Grb2-associated proteins in hepatocarcinoma cells, we performed coprecipitation analysis using recombinant GST-Grb2 fusion proteins and found that several protein components (p170, p125, p100, and p80) differently associated with GST-Grb2 proteins in human Chang liver and hepatocarcinoma HepG2 cells. Sos1 and p80 proteins dominantly bind to Grb2 fusion proteins in Chang liver, whereas p100 remarkably associate with Grb2 in HepG2 cells. Also GST-Grb2 SH2 proteins exclusively bound to the p46(Shc), p52(Shc), and p66(Shc) are important adaptors of the Ras pathway in HepG2 cells. The p100 protein has been identified as dynamin II. We observed that the N-SH3 and C-SH3 domains of Grb2 fusion proteins coprecipitated with dynamin II besides Sos1. These results suggest that dynamin II may be a functional molecule involved in Grb2-mediated signaling pathway on Ras activation for tumor progression and differentiation of hepatocarcinoma cells.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Characterization of the mouse dynamin I gene promoter and identification of sequences that direct expression in neuronal cells.

Dynamin I is expressed at high levels in brain and its expression is regulated during the developmental stages of brain. To elucidate the molecular mechanism by which the expression is tissue-specifically regulated, we cloned the 5'-flanking region of the mouse dynamin I gene and determined the nucleotide sequence of 1036 bases upstream from the translation start site. Transient transfection studies with a chloramphenicol acetyltransferase reporter gene in neuroblastoma NS20Y and Lewis lung cells demonstrated that the 5'-flanking region has a cell-type-specific promoter activity. Deletion analyses demonstrated that the minimal promoter activity was detected in the proximal region 195 bp upstream of the translation initiation codon (-90 to +105). The minimal promoter was embedded in a GC-rich region (75% GC content), in which an Sp1-binding motif and a nuclear factor (NF)-kappa B-like element (NE-1) were found, but it lacked TATA and CAAT boxes. Mutational analysis and electrophoretic mobility-shift assay analysis revealed that Sp1 binds to the Sp1 site and that this element is critical for the promoter activity of the dynamin I gene. We found that the NE-1 sequence is required for the expression of the dynamin I gene but NEBP (NE-1-binding protein), which binds to the NE-1 sequence, is not NF-kappa B. We also found that one base in the NE-1 sequence (the underlined G residue in GGGATTCGCGGA) is critical for binding specificity to discriminate between NEBP and NF-kappa B. By UV cross-linking analysis, we found that NEBP is an approx. 104 kDa nuclear protein.

Animals↗
PubMed2000

Natural and synthetic analogues of actinomycin D as Grb2-SH2 domain blockers.

Natural analogues (D, C2, and VII) of actinomycin inhibit Grb2 SH2 domain binding with phosphopeptide-derived from Shc in vitro and in intracellular system. To study structure-activity relationships, 13 actinomycin analogues were synthesized and we found that the inhibition activity depended on the substituents of cyclic peptide groups in actinomycin and two analogues with Tyr residue are the most potent inhibitors with IC50 value of 0.5 and 0.8 microM, respectively.

Adaptor Proteins, Signal Transducing↗
PubMed2000

8-O-Methylsclerotiorinamine, antagonist of the Grb2-SH2 domain, isolated from Penicillium multicolor.

A new secondary metabolite, 8-O-methylsclerotiorinamine (1), was isolated from a strain of Penicillium multicolor, and its structure was established using NMR spectroscopy and chemical evidence. The metabolite inhibited significantly the binding between the Grb2-SH2 domain and the phosphopeptide derived from the Shc protein and also blocked the protein-protein interactions of Grb2-Shc in cell-based experiments, with IC(50) values of 5.3 and 50 microM, respectively.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Chaetoatrosin A, a novel chitin synthase II inhibitor produced by Chaetomium atrobrunneum F449.

Chaetoatrosin A, a novel chitin synthase II inhibitor, was isolated from the culture broth of fungus F449, which was identified as Chaetomium atrobrunneum F449. Chaetoatrosin A was purified by solvent partition, silica gel, ODS, preparative TLC, and Sephadex LH-20 column chromatographies, consecutively. The structure of chaetoatrosin A was assigned as 1,8-dihydroxy-3(2-hydroxypropionyl)-6-methoxynaphthalene on the basis of various spectroscopic analyses including UV, IR, mass spectral, and NMR. Its molecular weight and formula were found to be 262 and C14H14O5, respectively. ,Chaetoatrosin A inhibited chitin synthase II by 50% at the concentration of 104 microg/ml in an enzyme assay system. This compound showed antifungal activities against Rhizoctonia solani, Pyricularia oryzae, Botrytis cinerea, Cryptococcus neoformans and Trichophyton mentagrophytes.

Antifungal Agents↗
PubMed2000

cis-fumagillin, a new methionine aminopeptidase (type 2) inhibitor produced by Penicillium sp. F2757.

Selective inhibition against the yeast MetAP2 (methionine aminopeptidase type 2) was detected in the fermentation broth of a fungus F2757 that was later identified as Penicillium janczewskii. A new compound cis-fumagillin methyl ester (1) was isolated from the diazomethane treated fermentation extracts together with the known compound fumagillin methyl ester (2). The cis-fumagillin methyl ester, a stereoisomer of fumagillin methyl ester at the C2'-C3' position of the aliphatic side chain, selectively inhibited growth of the map1 mutant yeast strain (MetAP1 deletion strain) at a concentration as low as 1 ng. However, the wild type yeast w303 and the mutant map2 (MetAP2 deleted) strains were resistant up to 10 microg of the compound. In enzyme experiments, compound 1 inhibited the MetAP2 with an IC50 value of 6.3 nM, but it did not inhibit the MetAP1 (IC50 >200 microM). Compound 2 also inhibited the MetAP2 with an IC50 value of 9.2 nM and 105 microM against MetAP1.

Aminopeptidases↗
PubMed2000

Phellinsin A, a novel chitin synthases inhibitor produced by Phellinus sp. PL3.

Phellinsin A, a novel chitin synthases inhibitor was isolated from the cultured broth of fungus PL3, which was identified as Phellinus sp. PL3. Phellinsin A was purified by solvent partition, silica gel, ODS column chromatographies, and preparative HPLC, consecutively. The structure of phellinsin A was assigned as a phenolic compound on the basis of various spectroscopic analyses including UV, IR, Mass, and NMR. Its molecular weight and formula were found to be 358 and C18H14O8, respectively. Phellinsin A selectively inhibited chitin synthase I and II of Saccharomyces cerevisiae with an IC50 value of 76 and 28 microg/ml, respectively, in our cell free assay system. This compound showed antifungal activity against Colletotrichum lagenarium, Pyricularia oryzae, Rhizoctonia solani, Aspergillus fumigatus, and Trichophyton mentagrophytes.

Alternaria↗
PubMed1999

Actinomycin D as a novel SH2 domain ligand inhibits Shc/Grb2 interaction in B104-1-1 (neu*-transformed NIH3T3) and SAA (hEGFR-overexpressed NIH3T3) cells.

Actinomycins, a family of bicyclic chromopeptide lactones with strong antineoplastic activity, were screened as inhibitors of Shc/Grb2 interaction in in vitro assay systems. To investigate the effects of actinomycin D on Shc/Grb2 interaction in cell-based experiments, we used SAA (normal hEGFR-overexpressed NIH3T3) cells and B104-1-1 (neu*-transformed NIH3T3) cells, because a large number of the Shc/Grb2 complexes were detected. Associated protein complexes containing Shc were immunoprecipitated from actinomycin D-treated cell lysates with polyclonal anti-Shc antibody. Then the association with Grb2 was assessed by immunoblotting with monoclonal anti-Grb2 antibody. The result of the immunoblotting experiment revealed that actinomycin D inhibited Shc/Grb2 interaction in a dose-dependent manner in both B104-1-1 and EGF-stimulated SAA cells. The inhibition of Shc/Grb2 interaction by actinomycin D in B104-1-1 cells also reduced tyrosine phosphorylation of MAP kinase (Erk1/Erk2), one of the major components in the Ras-MAP kinase signaling pathway. These results suggest that actinomycin D could be a non-phosphorylated natural and cellular membrane-permeable SH2 domain antagonist.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Acyl-CoA: cholesterol acyltransferase inhibitory activity of ginseng sapogenins, produced from the ginseng saponins.

Ginseng sapogenins were produced from ginseng saponins, isolated from Korean ginseng roots. Ginseng saponins very mildly inhibited acyl-CoA:cholesterol acyltransferase (ACAT) in vitro, however, the sapogenins showed strong inhibitory activity on microsomal ACAT. Therefore, the sapogenins will be one of key ingredients of ginseng affected a lowering of the serum total cholesterol level.

Animals↗
PubMed1999

Inhibition of chitin synthase II by catechins from stem bark of Taxus cuspidata.

Two flavonoids, (+/-)-catechin and (-)-epicatechin, were isolated from the stem bark of Taxus cuspidata by monitoring chitin synthase II inhibitory activity. The compounds inhibit chitin synthase II with an IC50 of 15 and 29 micrograms/ml, respectively and appear to be selective for chitin synthase II. They did not inhibit chitin synthase III.

Catechin↗
PubMed1999

Inhibition of human tumor growth by 2'-hydroxy- and 2'-benzoyloxycinnamaldehydes.

2'-Hydroxycinnamaldehyde (HCA) was isolated from Cinnamomum cassia Blume (Lauraceae) and 2'-benzoyloxycinnamaldehyde (BCA) was prepared by the reaction of HCA and benzoyl chloride. HCA and BCA strongly inhibited in vitro growth of 29 kinds of human cancer cells and in vivo growth of SW-620 human tumor xenograft without the loss of body weight in nude mice. HCA prevented adherence of SW-620 cells to the culture surface but did not inhibit oncogenic K-Ras processing, implying its antitumor mechanisms at the cellular level.

Acrolein↗