Are you Woon Jae Chung?

Claim your profile

Publications (5)15.74 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Osteoclast differentiation is a multi-step process that involves cell proliferation, commitment, and fusion. Some adhesion molecules, including integrin alphavbeta3, have been shown to have roles in osteoclast fusion. In the course of studying with pharmacologic agents known to inhibit protein tyrosine kinases of the Src family, we found that radicicol increased cell fusion during receptor activator of nuclear factor kappaB ligand (RANKL)-driven differentiation of osteoclasts at concentrations far below the ones shown to inhibit its targets in previous studies. Treatments of low doses of radicicol to RAW 264.7 cells that undergo osteoclastic differentiation in the presence of RANKL enhanced the RANKL-induced gene expression of integrin beta3 without any effect on the expression of integrin alphav, which was constitutively high. The cell surface level of integrin alphavbeta3 complexes was consequently augmented by radicicol. In addition, sustained ERK and MEK activation was observed in cells treated with both radicicol and RANKL. More importantly, modulation of ERK activity by the MEK inhibitor U0126 or the gene transduction of a constitutively active form of MEK resulted in a suppression and increment, respectively, of integrin beta3 induction by RANKL. Our data indicate that sustained ERK activity is associated with integrin beta3 induction and subsequent cell surface expression of the alphavbeta3 integrin complex, which may contribute to cell fusion during RANKL-directed osteoclastogenesis.
    Experimental Cell Research 11/2003; 289(2):368-77. · 3.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: NF-kappaB that plays an important role in iNOS expression is one of the targets of various potential anti-inflammatory agents including resveratrol. Resveratrol contains a structural similarity with estrogen, and there has been speculation about resveratrol as estrogen agonist. In this study, the mechanism and structural requirements of resveratrol and related hydroxystilbenes for the inhibition of LPS-induced nitric oxide production were studied in macrophage cells (RAW 264.7 and J774) by comparing its effect on LPS-induced NF-kappaB translocation and nitric oxide production, and by considering the possibility of involvement of an estrogen receptor. LPS-induced nitric oxide production was inhibited only when cells were treated with resveratrol prior to stimulation with LPS, suggesting that resveratrol does not affect the enzyme itself. A higher concentration of resveratrol than needed for the inhibition of nitric oxide production was required for the inhibition of NF-kappaB mobilization or iNOS expression. Estrogen and diethylstilbesterol, an estrogen agonist, caused only weak inhibition of nitric oxide production, and the effects of resveratrol were not noticeably blocked by ICI-182780, an estrogen antagonist. Structure-activity analysis of resveratrol and nine hydroxystilbenes suggests that the structural balance between oxygen functional groups on the benzene rings is important for their activity. Our results suggest that resveratrol might act on other cellular targets as well as NF-kappaB at the initial stage of gene expression. Unique structural features of hydroxystilbenes are needed for suppression of nitric oxide production and it is unlikely that estrogen receptor is involved in it.
    Life Sciences 10/2002; 71(17):2071-82. · 2.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: It has been suggested that blood vessel formation is an important event coupled to bone formation. The expression of vascular endothelial growth factor (VEGF), a potent angiogenic factor, has been shown to be greatly stimulated in osteoblasts by hypoxic stimuli such as deprivation of oxygen and treatment with cobalt. In other cell types, hypoxia-inducible factor-1 (HIF-1) that binds hypoxia-response element (HRE) has been shown to mediate gene expression induced by hypoxic stimuli. In this study, we investigated the effects of hypoxic stimuli on HIF-1, HRE, and VEGF in osteoblastic cell lines. Exposure of these cells to hypoxia or cobalt resulted in a great increase in the protein level of HIF-1alpha and the gene expression of VEGF. Transforming growth factor-beta1, prostaglandin E2, dexamethasone, and 1,25-dihydroxyvitamin D3 that have been shown to regulate VEGF gene expression in osteoblasts had no effect on HIF-1alpha induction. Blocking the enzymatic activity of phosphatidylinositol 3-kinase, p38, MEK-1 did not have any effect on the cobalt-stimulated increase of HIF-1alpha in these cells. In contrast, N-acetylcysteine (NAC), a scavenger of reactive oxygen species, abolished the cobalt induction of HIF-1alpha and that of the VEGF and a HRE-driven reporter genes. However, the hypoxia responses were not affected by NAC. These findings suggest that hypoxia and cobalt can induce VEGF gene expression in osteoblasts by increasing the level of HIF-1alpha protein through different mechanisms.
    Cytokine 02/2002; 17(1):14-27. · 2.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Differentiated osteoclasts have a short life span. We tested various cytokines and growth factors for the effects on the survival of purified mature osteoclasts. In the absence of any added factors, osteoclasts exhibited the survival rate of less than 25% after a 24-h incubation. Among the tested factors, tumor necrosis factor-α (TNF-α) was found to increase the survival rate to ∼80%. The TNF-α-enhanced survival of osteoclasts appeared to be associated with reduction in apoptosis and suppression of caspase activation. The antiapoptotic signaling pathways involved in the TNF-α-induced osteoclast survival were investigated. TNF-α treatment increased the phosphorylation of Akt in osteoclasts, which was suppressed by a phosphatidylinositol 3-kinase inhibitor LY294002 and an Src family kinase-selective inhibitor PP1. These inhibitors also attenuated the TNF-α stimulation of osteoclast survival. In addition an increase in the phosphorylation of ERK was observed upon TNF-α stimulation. PD98059, a specific inhibitor of the ERK-activating kinase MEK-1, abolished the TNF-α-induced ERK phosphorylation and osteoclast survival, and in these responses the involvement of Grb2 and ceramide was observed. These results suggest that TNF-α promotes the survival of osteoclasts by engaging the phosphatidylinositol 3-kinase Akt and MEK/ERK signaling pathways.
    Journal of Biological Chemistry 12/2001; 276(52):49343-49349. · 4.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Although it has been suggested that some biological activities of platelet-activating factor (PAF) are mediated by, at least in part, reactive oxygen intermediates (ROI), the precise mechanisms underlying the interaction between the two remains to be elucidated. Antioxidants, such as -tocopherol acid succinate, N-acetyl-L-Cysteine, pyrrolidinedithiocarbamate failed to inhibit PAF-induced immediate systemic reactions such as lethality, symptoms of disseminated intravascular coagulation, and histological changes such as pulmonary edema and hemorrhage in renal medullae 10 min following PAF injection. In contrast, antioxidants significantly inhibited both the in vivo and in vitro PAF-induced NF-B activation and NF-B-dependent TNF- expression. The effects of the antioxidants were due to their inhibition of PAF-induced degradation of IB, a protein responsible for keeping NF-B in an inactive form. A protein tyrosine kinase and N-tosyl-L-phenylalanine chloromethyl ketone sensitive serine protease were involved in both PAFand H2O2-induced NF-B activation. Collectively, these data indicate that the PAF-induced NF-B activation is selectively mediated through the generation of ROI.
    Inflammation 09/2000; 24(5):385-398. · 2.46 Impact Factor