Biomedical subjects

Kyung Chan Park

Publications and source records attributed to Kyung Chan Park.

10 recordsLinked to original sources

PubMed2006

Novel candidate targets of Wnt/beta-catenin signaling in hepatoma cells.

The activity of beta-catenin/TCF, the key component of Wnt signaling pathway, is frequently deregulated in HCC, resulting in the activation of genes whose dysregulation has significant consequences on tumor development. Therefore, identifying the target genes of Wnt signaling is important for understanding beta-catenin-mediated carcinogenesis. We analyzed the transcriptome profile of human hepatoma cell lines using cDNA microarrays representing 15,127 unique, liver-enriched gene loci to identify the target genes of beta-catenin-mediated transcription (p<0.005). This analysis yielded 130 potential Wnt-associated classifier genes, and we found 33 of them contain consensus TCF-binding sites in presumptive transcriptional regulatory sequences. These genes were, then, tested for their Wnt-dependence of expression in experimental models of Wnt activation. Genes such as RPL29, NEDD4L, FUT8, LYZ, STMN2, STARD7 and KIAA0998 were proven to be up-regulated upon Wnt/beta-catenin activation. Gene ontology analysis of the 33 candidate genes indicated the presence of functional categories relevant to Wnt pathway such as cell growth, proliferation, adhesion and signal transduction. In conclusion, we identified a number of candidate Wnt/beta-catenin target genes that can be useful for studying the role of altered Wnt signaling in liver cancer development, and showed that some of them might be direct targets of Wnt signaling in hepatoma cells.

Carcinoma, Hepatocellular↗

PubMed2006

STMN2 is a novel target of beta-catenin/TCF-mediated transcription in human hepatoma cells.

The activity of beta-catenin/TCF, the key component of Wnt signaling pathway, is frequently deregulated in human cancers, resulting in the activation of genes whose dysregulation has significant consequences on tumor development. Therefore, identifying the target genes of Wnt signaling is important for understanding beta-catenin-mediated carcinogenesis. Here, we report STMN2, a gene implicated in the regulation of microtubule dynamics, as a novel target of beta-catenin-mediated transcription. STMN2 was up-regulated in hepatoma and cirrhotic liver tissues compared to normal liver and also in cell lines where beta-catenin/TCF is constitutively activated. Transient activation of beta-catenin/TCF either by transfection of a constitutively active form of beta-catenin or by LiCl treatment induced the STMN2 mRNA expression in PLC/PRF/5 cells. Of the four members of STMN gene family, only STMN2 showed a Wnt-dependent expression pattern. Through promoter mapping and chromatin immunoprecipitation assays, we found that STMN2 is a direct target of beta-catenin/TCF-mediated transcription and that the TCF binding site at -1713 of STMN2 promoter is critical for beta-catenin/TCF-dependent expression regulation. siRNA-mediated knock-down of STMN2 expression indicated that STMN2 is required for maintaining the anchorage-independent growth state of beta-catenin/TCF-activated hepatoma cells. Our results suggest that STMN2 might be a novel player of beta-catenin/TCF-mediated carcinogenesis in the liver.

Carcinoma, Hepatocellular↗

PubMed2005

Reversal of silver sulfadiazine-impaired wound healing by epidermal growth factor.

Silver sulfadiazine (Ag-SD) is a useful antibacterial agent for wound treatment. However, recent findings indicate that the compound delays the wound-healing process. That delay may be reversed by treatment with growth factors. The purpose of this study, was to evaluate the cyto-protective effect of epidermal growth factor (EGF) against Ag-SD treated keratinocytes and to investigate the reversibility of the impaired wound-healing process by the co-supplementation of EGF. Four types of drug-loaded collagen sponge dressings with different concentrations of Ag-SD, EGF and Ag-SD + EGF were prepared. An immortalized keratinocyte, HaCaT cells, were cultured in 35-mm Petri-dish using Dulbecco's Modified Eagle's Minimal Essential Medium (DMEM) with 10% FBS. Cultures were treated with the samples submerged, and viabilities of cultures were evaluated using MTT assay. The wound heal efficacy was evaluated in a partial thickness burn mouse model. Cells treated with EGF showed a cyto-protective effect on 1% Ag-SD treated cells with significant increase in viable cell numbers at concentrations ranging from 1 to 50 microg/ml. The cytotoxicity of Ag-SD impaired wound healing, while the addition of EGF could reverse the impairment. This evidence suggests that EGF is a useful agent in the retardation of wound healing caused by Ag-SD. Therefore, a drug delivery system containing both EGF and Ag-SD, such as that used in the study, may be clinically relevant.

Anti-Bacterial Agents↗

PubMed2004

Dictyostelium PAKc is required for proper chemotaxis.

We have identified a new Dictyostelium p21-activated protein kinase, PAKc, that we demonstrate to be required for proper chemotaxis. PAKc contains a Rac-GTPase binding (CRIB) and autoinhibitory domain, a PAK-related kinase domain, an N-terminal phosphatidylinositol binding domain, and a C-terminal extension related to the Gbetagamma binding domain of Saccharomyces cerevisiae Ste20, the latter two domains being required for PAKc transient localization to the plasma membrane. In response to chemoattractant stimulation, PAKc kinase activity is rapidly and transiently activated, with activity levels peaking at approximately 10 s. pakc null cells exhibit a loss of polarity and produce multiple lateral pseudopodia when placed in a chemoattractant gradient. PAKc preferentially binds the Dictyostelium Rac protein RacB, and point mutations in the conserved CRIB that abrogate this binding result in misregulated kinase activation and chemotaxis defects. We also demonstrate that a null mutation lacking the PAK family member myosin I heavy chain kinase (MIHCK) shows mild chemotaxis defects, including the formation of lateral pseudopodia. A null strain lacking both PAKc and the PAK family member MIHCK exhibits severe loss of cell movement, suggesting that PAKc and MIHCK may cooperate to regulate a common chemotaxis pathway.

Actins↗

PubMed2004

Rac regulation of chemotaxis and morphogenesis in Dictyostelium.

Chemotaxis requires localized F-actin polymerization at the site of the plasma membrane closest to the chemoattractant source, a process controlled by Rac/Cdc42 GTPases. We identify Dictyostelium RacB as an essential mediator of this process. RacB is activated upon chemoattractant stimulation, exhibiting biphasic kinetics paralleling F-actin polymerization. racB null cells have strong chemotaxis and morphogenesis defects and a severely reduced chemoattractant-mediated F-actin polymerization and PAKc activation. RacB activation is partly controlled by the PI3K pathway. pi3k1/2 null cells and wild-type cells treated with LY294002 exhibit a significantly reduced second peak of RacB activation, which is linked to pseudopod extension, whereas a PTEN hypomorph exhibits elevated RacB activation. We identify a RacGEF, RacGEF1, which has specificity for RacB in vitro. racgef1 null cells exhibit reduced RacB activation and cells expressing mutant RacGEF1 proteins display chemotaxis and morphogenesis defects. RacGEF1 localizes to sites of F-actin polymerization. Inhibition of this localization reduces RacB activation, suggesting a feedback loop from RacB via F-actin polymerization to RacGEF1. Our findings provide a critical linkage between chemoattractant stimulation, F-actin polymerization, and chemotaxis in Dictyostelium.

Actins↗

PubMed2004

Selective COX-2 inhibitor, NS-398, inhibits the replicative senescence of cultured dermal fibroblasts.

Cyclooxygenase 2 (COX-2) is known to be increased in aged cells. Recent studies suggest that the increased expression of COX-2 may be involved in the pathogenesis of age-associated diseases such as rheumatoid arthritis and cancer. We investigated the role of COX-2 in cell cycle arrest and collagen deficiency during the aging process. Using the replicative senescence model of dermal fibroblasts, we demonstrated the increased expression of COX-2 and increased PGE(2) levels associated with replicative senescence. Replicative senescent cells showed a decreased ability to induce cell proliferation, probably due to the increased expression of the p53 protein and the decreased expression of the PCNA protein, and also showed increased expression of MMP-1, and decreased expression of tissue inhibitor of metalloproteinase-1 (TIMP-1) and procollagen. The selective COX-2 inhibitor, NS-398, can inhibit the senescence-associated increases of COX-2, PGE(2), p53 and MMP-1 expression, and the senescence-associated decreases of PCNA, TIMP-1 and procollagen expression. These results suggest that the increased level of COX-2 and higher level of PGE(2) in aged cells may play an important role in cellular senescence, and that selective COX-2 inhibitors may be useful for the intervention of skin aging.

Arthritis, Rheumatoid↗

PubMed2003

Deubiquitinating enzymes as cellular regulators.

Modification of proteins by the covalent attachment of ubiquitin is a key regulatory mechanism of many cellular processes including protein degradation by the 26S proteasome. Deubiquitination, reversal of this modification, must also regulate the fate and function of ubiquitin-conjugated proteins. Deubiquitinating enzymes catalyze the removal of ubiquitin from ubiquitin-conjugated substrate proteins as well as from its precursor proteins. Deubiquitinating enzymes occupy the largest family of enzymes in the ubiquitin system, implying their diverse function in regulation of the ubiquitin-mediated pathways. Here we explore the diversity of deubiquitinating enzymes and their emerging roles as cellular regulators.

Animals↗

PubMed2002

Antagonistic regulation of myogenesis by two deubiquitinating enzymes, UBP45 and UBP69.

Protein modification by ubiquitin is a dynamic and reversible process that is involved in the regulation of a variety of cellular processes. Here, we show that myogenic differentiation of embryonic muscle cells is antagonistically regulated by two deubiquitinating enzymes, UBP45 and UBP69, that are generated by alternative splicing. Both enzymes cleaved off ubiquitin from polyubiquitinated protein conjugates in vivo as well as from linear ubiquitin-protein fusions in vitro. In cultured myoblasts, the level of UBP69 mRNA markedly but transiently increased before membrane fusion, whereas that of UBP45 mRNA increased as the cells fused to form myotubes. Both myoblast fusion and accumulation of myosin heavy chain were dramatically stimulated by the stable expression of UBP69 but strongly attenuated by that of the catalytically inactive form of the protease, suggesting that the mutant enzyme acts dominant negatively on the function of the wild-type protease. In contrast, stable expression of UBP45 completely blocked both of the myogenic processes but that of inactive enzyme did not, indicating that the catalytic activity of the enzyme is essential for its inhibitory effects. These results indicate that differential expression of UBP45 and UBP69 is involved in the regulation of muscle cell differentiation.

Animals↗

PubMed1998

A Method for Assaying Deubiquitinating Enzymes.

A general method for the assay of deubiquitinating enzymes was described in detail using (125)I-labeled ubiquitin-fused alphaNH-MHISPPEPESEEEEEHYC (referred to as Ub-PESTc) as a substrate. Since the tyrosine residue in the PESTc portion of the fusion protein was almost exclusively radioiodinated under a mild labeling condition, such as using IODO-BEADS, the enzymes could be assayed directly by simple measurement of the radioactivity released into acid soluble products. Using this assay protocol, we could purify six deubiquitinating enzymes from chick skeletal muscle and yeast and compare their specific activities. Since the extracts of E. coli showed little or no activity against the substrate, the assay protocol should be useful for identification and purification of eukaryotic deubiquitinating enzymes cloned and expressed in the cells.

Journal Article↗

PubMedDate not supplied

Enhanced expression of cylooxygenase-2 by UV in aged human skin in vivo.

Prostaglandins (PGs) induced by UV may play important roles in UV-induced inflammation, photocarcinogenesis, and photoaging processes in human skin. The age-related PGE2 production and cyclooxygenase-2 (COX-2) expression in the human skin in vivo remain unclear. The purpose of this study was to examine the influence of aging on UV-induced PGE2 production and COX-2 expression in human skin in vivo. We found that aged human skin produces higher amounts of PGE2 than young skin, when exposed to UV. The inductions of COX-2 mRNA and protein by UV in aged skin were higher than those in the young skin, whereas COX-1 mRNA expression remained unchanged. Aged human macrophage expressed higher amounts of PGE2 and COX-2 protein constitutively, and also induced these species after LPS treatment more so than young cells. Our data suggest that skin aging may increase susceptibility to the development of skin cancer and photoaging, by enhanced PGE2 and COX-2 expression due to UV in human skin in vivo.

Adult↗