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Young-Kook Kim

Publications and source records attributed to Young-Kook Kim.

10 recordsLinked to original sources
PubMed2006

The role of PACT in the RNA silencing pathway.

Small RNA-mediated gene silencing (RNA silencing) has emerged as a major regulatory pathway in eukaryotes. Identification of the key factors involved in this pathway has been a subject of rigorous investigation in recent years. In humans, small RNAs are generated by Dicer and assembled into the effector complex known as RNA-induced silencing complex (RISC) by multiple factors including hAgo2, the mRNA-targeting endonuclease, and TRBP (HIV-1 TAR RNA-binding protein), a dsRNA-binding protein that interacts with both Dicer and hAgo2. Here we describe an additional dsRNA-binding protein known as PACT, which is significant in RNA silencing. PACT is associated with an approximately 500 kDa complex that contains Dicer, hAgo2, and TRBP. The interaction with Dicer involves the third dsRNA-binding domain (dsRBD) of PACT and the N-terminal region of Dicer containing the helicase motif. Like TRBP, PACT is not required for the pre-microRNA (miRNA) cleavage reaction step. However, the depletion of PACT strongly affects the accumulation of mature miRNA in vivo and moderately reduces the efficiency of small interfering RNA-induced RNA interference. Our study indicates that, unlike other RNase III type proteins, human Dicer may employ two different dsRBD-containing proteins that facilitate RISC assembly.

Argonaute Proteins↗
PubMed2005

Dimeric sesquiterpenoids isolated from Chloranthus japonicus inhibited the expression of cell adhesion molecules.

In the search for cell adhesion inhibitors from natural sources, three active compounds were isolated from Chloranthus japonicus Sieb. (Chloranthaceae) roots. The compounds were identified as dimeric sesquiterpenoids of shizukaol B (1), cycloshizukaol A (2) and shizukaol F (3). These compounds inhibited PMA-induced homotypic aggregation of HL-60 cells without cytotoxicity with MIC values of 34.1 nM (1), 0.9 microM (2) and 27.3 nM (3), respectively. Although 1-3 did not affect the direct binding of LFA-1 to ICAM-1, these compounds markedly inhibited ICAM-1 expression in HL-60 cells in a dose-dependent fashion. On the other hand, when HUVEC were pretreated with 1-3 and stimulated with TNF-alpha, adhesion of THP-1 cells to HUVEC decreased in dose-dependent manner with IC(50) values of 54.6 nM, 1.2 microM and 34.1 nM, respectively. In fact, 1 inhibited TNF-alpha-induced surface expression of the ICAM-1, VCAM-1 and E-selectin in HUVEC with IC(50) values of 5.4 nM, 13.6 microM and 95.6 nM, respectively. The present findings suggest that 1-3 prevent monocyte adhesion to HUVEC through the inhibition of cell adhesion molecules expression stimulated by TNF-alpha.

Animals↗
PubMed2005

Manassantin A and B isolated from Saururus chinensis inhibit TNF-alpha-induced cell adhesion molecule expression of human umbilical vein endothelial cells.

Leukocyte adhesion to the vascular endothelium is a critical initiating step in inflammation and atherosclerosis. We have herein studied the effect of manassantin A (1) and B (2), dineolignans, on interaction of THP-1 monocytic cells and human umbilical vein endothelial cells (HUVEC) and expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin in HUVEC. When HUVEC were pretreated with 1 and 2 followed by stimulation with TNF-alpha, adhesion of THP-1 cells to HUVEC decreased in dose-dependent manner with IC50 values of 5 ng/mL and 7 ng/mL, respectively, without cytotoxicity. Also, 1 and 2 inhibited TNF-alpha-induced up-regulation of ICAM-1, VCAM-1 and E-selectin. The present findings suggest that 1 and 2 prevent monocyte adhesion to HUVEC through the inhibition of ICAM-1, VCAM-1 and E-selectin expression stimulated by TNF-alpha, and may imply their usefulness for the prevention of atherosclerosis relevant to endothelial activation.

Cell Adhesion Molecules↗
PubMed2004

The Drosha-DGCR8 complex in primary microRNA processing.

RNase III proteins play key roles in microRNA (miRNA) biogenesis. The nuclear RNase III Drosha cleaves primary miRNAs (pri-miRNAs) to release hairpin-shaped pre-miRNAs that are subsequently cut by the cytoplasmic RNase III Dicer to generate mature miRNAs. While Dicer (class III) and other simple RNase III proteins (class I) have been studied intensively, the class II enzyme Drosha remains to be characterized. Here we dissected the action mechanism of human Drosha by generating mutants and by characterizing its new interacting partner, DGCR8. The basic action mechanism of Drosha was found to be similar to that of human Dicer; the RNase III domains A and B form an intramolecular dimer and cleave the 3' and 5' strands of the stem, respectively. Human Drosha fractionates at approximately 650 kDa, indicating that Drosha functions as a large complex. In this complex, Drosha interacts with DGCR8, which contains two double-stranded RNA (dsRNA)-binding domains. By RNAi and biochemical reconstitution, we show that DGCR8 may be an essential component of the pri-miRNA processing complex, along with Drosha. Based on these results, we propose a model for the action mechanism of class II RNase III proteins.

Blotting, Northern↗
PubMed2003

Mass-production of human ACAT-1 and ACAT-2 to screen isoform-specific inhibitor: a different substrate specificity and inhibitory regulation.

Recently, acyl-CoA:cholesterol acyltransferase was found to be present as two isoforms, ACAT-1 and ACAT-2, in mammalian tissues with different metabolic functions and tissue-specific locations. In this study, the isoforms were mass-produced individually from insect cells to establish a more sensitive and reliable screening method for specific inhibitors against each isoform. The expressed hACAT-1 and hACAT-2 appeared as a 50 kDa- and a 46 kDa-band on SDS-PAGE, respectively, from Hi5 cells and they preferred to exist in oligomeric form, from dimer to tetramer, during the purification process. They also exhibited an approximate 3.4 to 3.7-fold increase in activities when compared to rat liver microsomal fractions at the same protein concentration. Known ACAT inhibitors, pyripyropene A, oleic acid anilide, and diethyl pyrocarbonate, were tested to evaluate the inhibitory specificity and sensitivity of the expressed enzymes. Interestingly, pyripyropene A inhibited only the hACAT-2 fraction with IC(50)=0.64 microM but not the hACAT-1 fraction; whereas the fatty acid anilide did not show a significant difference in inhibitory activity with either hACAT-1 or hACAT-2. Furthermore, cholesterol was more rapidly utilized by hACAT-1, but hACAT-2 esterified other cholic acid derivatives more efficiently. These results suggest that the specificity of each substrate and inhibitor was highly different, depending on each isoform from the viewpoint of the regulatory site and the substrate binding site location.

Animals↗
PubMed2003

Inhibitory effects of manassantin A and B isolated from the roots of Saururus chinensis on PMA-induced ICAM-1 expression.

Cell adhesion inhibitors were isolated from the methanol extract of Saururus chinensis roots by bioactivity-guided fractionation. The active compounds were identified as manassantin A ( 1) and B ( 2), dineolignan compounds. Compounds 1 and 2 inhibited PMA-induced ICAM-1/LFA-1-mediated homotypic aggregation of the HL-60 cells without cytotoxicity with MIC values of 1.0 and 5.5 nM, respectively. Even though 1 and 2 did not affect the adhesion of ICAM-1 to LFA-1, these compounds inhibited PMA-induced ICAM-1 expression in HL-60 cells in a dose-dependent fashion. These results suggest that 1 and 2 inhibit cell aggregation through down-regulation of ICAM-1 expression.

Cell Aggregation↗
PubMed2002

Novel 3-arylamino- and 3-cycloalkylamino-5, 6-diphenyl-pyridazines active as ACAT inhibitors.

A new series of pyridazine derivatives, structurally related to the previously reported ACAT inhibitors 3-(cyclo)alkylamino-5, 6-diphenyl-pyridazines, were synthesized and tested for their inhibitory properties. Substitution of the 3-alkylamino chain with a phenylamino group maintains activity. In contrast, the presence of either substituents on the phenylamino group or aliphatic rings having more or less than six carbon atoms lowers it.

Animals↗
PubMed2002

Isolation of Acyl-CoA:cholesterol acyltransferase inhibitor from Persicaria vulgaris.

In the course of our search for Acyl-CoA:cholesterol acyltransferase (ACAT) inhibitors from natural sources, a new type of ACAT inhibitor was isolated from the methanol extract of Persicaria vulgaris. On the basis of spectral evidence, the structure of the active compound was identified as pheophorbide A. Pheophorbide A inhibited ACAT activity with an IC 50 value of 1.1 microg/ml in an enzyme assay using rat liver microsomes with a dose dependent fashion.

Animals↗