• Proceedings of the Korea Environmental Mutagen Society Conference
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• 2002.11a
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• pp.142-142
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• 2002

• Toxicological Research
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• v.21 no.3
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• pp.195-208
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• 2005

Diabetes is a major cause of morbidity and mortality, and associated with a high risk of atherosclerosis, and liver, kidney, nerve and tissue damage. Defective insulin secretion in pancreas and/or insulin resistance in peripheral tissues is a central component of diabetes. It is well established that, regardless of the degree of muscle insulin resistance, glucose levels in diabetic and non-diabetic individuals are determined by the rate of hepatic glucose production. Moreover recently studies using liver-specific insulin receptor knockout mice show the paramount role of the liver in insulin resistance and diabetes. Insulin exerts a multifaceted and highly integrated series of actions via its intracellular signaling systems. The first major section of this review defines the major insulin-mediated signaling pathways including phosphatidylinositol 3-kinase and mitogen activated protein kinases. The second major section of the review presents a summary and evaluation of methods for determination of the role and function of signaling pathways, including methods for determination of kinase phosphorylation, the use of pharmacological inhibitors of kinase and dominant-negative kinase constructs, and the application of new RNA interference methods.

• The Journal of Korean Society for Radiation Therapy
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• v.14 no.1
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• pp.165-174
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• 2002

Vascular endothelial growth factor (VEGF) has been identified as a peptide growth factor specific for vascular endothelial cells. In this study, we examined the effect of VEGF on radiation induced apoptosis and receptor/second messenger signal transduction pathway for VEGF effect in human umbilical vein endothelial cells (HUVECs). VEGF was found to protect HUVECs against the lethal effects of ionizing radiation by inhibiting the apoptosis induced in these cells by radiation exposure. VEGF (1-30 ng/ml) dose dependently inhibited apoptosis by irradiation. Pre-treatment with Flt-1 and Flk-l/KDR receptor blocked the VEGF-in duced antiapoptotic effect. Phosphatidylinositol 3'-kinase (PI3-kinase) specific inhibitor, Wortman in and LY294002, blocked the VEGF-induced antiapoptotic effect. These data suggest that VEGF may play an important role in survival of HUVECs due to the prevention of apoptotic cell death caused by some stresses such as ionizing radiation.

• Biomedical Science Letters
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• v.15 no.4
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• pp.349-353
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• 2009

Lysophosphatidic Acid (LPA) is a bioactive lysophospholipid that is a potent signaling molecule able to provoke a variety of cellular responses in many cell types such as differentiation, inflammation and apoptosis. In this study, we have investigated the effect of LPA on Nitric oxide (NO)-induced apoptosis in rabbit articular chondrocytes. LPA dramatically reduced NO induced apoptosis of chondrocytes determined by phase contrast microscope and MTT assay. When chondrocytes alone treated with LPA, LPA induced phosphorylation of p70S6kinase, a serine/threonine kinase that acts downstream of phosphatidylinositol 3,4,5-trisphosphate (PIP3) and phosphoinositide-dependent kinase-1 (PDK-1) in the PI3 kinase pathway, dose-dependently detected by Western blot analysis. Phosphorylation of p70S6k with LPA was reduced expression of p53 in NO-induced apoptosis of chondrocytes. Also, inhibition of p70S6kinase with rapamycin was enhanced expression of p53 in chondrocytes. Our findings collectively suggest that LPA regulates NO induced apoptosis through p70S6kinase pathway in rabbit articular chondrocytes.

• Molecules and Cells
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• v.25 no.3
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• pp.397-406
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• 2008

Computational modeling of signal transduction is currently attracting much attention as it can promote the understanding of complex signal transduction mechanisms. Although several mathematical models have been used to examine signaling pathways, little attention has been given to crosstalk mechanisms. In this study, an attempt was made to develop a computational model for the pathways involving growth-factor-mediated mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3'-kinase/protein kinase B (PI3K/Akt). In addition, the dynamics of the protein activities were analyzed based on a set of kinetic data. The simulation approach integrates the information on several levels and predicts systems behavior. The in-silico analysis conducted revealed that the Raf and Akt pathways act independently.

• Journal of Life Science
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• v.25 no.9
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• pp.976-983
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• 2015

Achyranthoside C dimethyl ester (ACDE) is an oleanolic acid glycoside from Achyranthes japonica which has been used in traditional medicine for the treatment of edema and arthritis. In this study, we investigated the anti-inflammatory effects of ACDE in RAW264.7 macrophages. ACDE significantly induced heme oxygenase-1 (HO-1) gene expression in RAW264.7 cells, while ACDE improved LPS-induced toxicity of cells. And ACDE induced nuclear translocation of nuclear factor E2-related factor 2 (Nrf2), a transcription factor that regulates HO-1 expression. Further study demonstrated that ACDE-induced expression of HO-1 was inhibited by inhibitors of phosphatidylinositol 3-kinase (PI-3K) (LY294002), c-Jun kinase (JNK) (SP600125), extracellular signal regulated kinase (ERK) (PD98059) and p38 kinase (SB203580). Moreover, ACDE phosphorylated Akt, JNK, ERK, and p38 MAPK. In addition, ACDE inhibited LPS-induced NO secretion as well as inducible NO synthase (iNOS) expression in a dose-dependent manner. The inhibitory effects of ACDE on iNOS expression were abrogated by small interfering RNA (siRNA)-mediated knock-down of HO-1. Therefore, these results suggest that ACDE suppresses the production of pro-inflammatory mediator such as NO by inducing HO-1 expression via PI-3K/Akt/MAPK-Nrf2 signaling pathway. These findings could help us to understand the active principle included in the roots of A. japonica and the molecular mechanisms underlying anti-inflammatory action of ACDE.

• Proceedings of the Korean Biophysical Society Conference
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• 2003.06a
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• pp.29-29
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• 2003

Compartmentation of intracellular signaling pathways serves as an important mechanism conferring the specificity of G protein-coupled receptor (GPCR) signaling. In the heart, stimulation of $\beta$$_2$-adrenoceptor ($\beta$$_2$-AR), a prototypical GPCR, activates a tightly localized protein kinase A (PKA) signaling, which regulates substrates at cell surface membranes, bypassing cytosolic target proteins (eg, phospholamban). Although a concurrent activation of $\beta$$_2$-AR-coupled $G_{i}$ proteins has been implicated in the functional compartmentation of PKA signaling, the exact mechanism underlying the restriction of the $\beta$$_2$-AR-PKA pathway remains unclear. In the present study, we demonstrate that phosphatidylinositol 3-kinase (PI3K) plays an essential role in confining the $\beta$$_2$-AR-PKA signaling. Inhibition of PI3K with LY294002 or wortmannin enables $\beta$$_2$-AR-PKA signaling to reach intracellular substrates, as manifested by a robust increase in phosphorylation of phospholamban, and markedly enhances the receptor-mediated positive contractile and relaxant responses in cardiac myocytes. These potentiating effects of PI3K inhibitors are not accompanied by an increase in $\beta$$_2$-AR-induced cAMP formation. Blocking $G_{i}$ or $G_{$\square$$\square$}$ signaling with pertussis toxin or $\beta$ARK-ct, a peptide inhibitor of $G_{$\square$$\square$}$, completely prevents the potentiating effects induced by PI3K inhibition, indicating that the pathway responsible for the functional compartmentation of $\beta$$_2$-AR-PKA siglaling sequentially involves $G_{i}$, $G_{$\square$$\square$}$, and PI3K. Thus, PI3K constitutes a key downstream event of $\beta$$_2$-AR- $G_{i}$ signaling, which confines and negates the concurrent $\beta$$_2$-AR/Gs-mediated PKA signaling.gnaling.

• BMB Reports
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• v.44 no.3
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• pp.182-186
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• 2011

Exogenous stimuli such as nerve growth factor (NGF) exert their effects on neurite outgrowth via Trk neurotrophin receptors. TrkA receptors are known to be ubiquitinated via proteasome inhibition in the presence of NGF. However, the effect of proteasome inhibition on neurite outgrowth has not been studied extensively. To clarify these issues, we investigated signaling events in PC12 cells treated with NGF and the proteasome inhibitor MG132. We found that MG132 facilitated NGF-induced neurite outgrowth and potentiated the phosphorylation of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) and phosphatidylinositol-3-kinase (PI3K)/AKT pathways and TrkA receptors. MG132 stimulated internalization of surface TrkA receptor and stabilized intracellular TrkA receptor, and the $Ub^{K63}$ chain was found to be essential for stability. These results indicate that the ubiquitin-proteasome system potentiated neurite formation by regulating the stability of TrkA receptors.

• Biomedical Science Letters
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• v.15 no.1
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• pp.61-66
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• 2009

Leflunomide is an immunomodulatory agent used for the treatment of rheumatoid arthritis (RA). Leflunomide known as a regulator of iNOS synthesis which largely decreases NO production in diverse cell type. However, the effect of leflunomide on chondrocyte is still poorly understood. In our previous studies, we have shown that direct production of Nitric oxide (NO) by treating chondrocytes with NO donor, sodium nitroprusside (SNP), causes apoptosis via p38 mitogen-activated protein kinase in association with elevation of p53 protein level, caspase-3 activation. In this study, we characterized the molecular mechanism by which A77 1726 inhibit apoptosis. We found that A77 1726 inhibit NO-induced apoptosis as determined by MTT (Thiazolyl Blue Tetrazolium Bromide) assay and DNA fragmentation. The inhibition of apoptosis by A77 1726 was accompanied by increased PI-3 kinase and AKT activities. So, inhibition of phosphatidylinositol (PI)-3kinase with LY294002 rescued apoptosis. Triciribine, the specific inhibitor of AKT, also abolished anti-apoptotic effect. Our results indicate that A77 1726, the active metabolite of leflunomide, mediates NO-induced apoptosis in chondrocytes by modulating up-regulation of PI-3 kinase and AKT.

• Proceedings of the PSK Conference
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• 2003.10b
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• pp.144.1-144.1
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• 2003

We previously reported that the activation of p$21^{WAFl/Cip1}$ transcription by histone deacetylase inhibitor apicidin was mediated through Spl sites and pointed to the possible participation of protein kinase C (PKC). In this study, we investigated the role and identity of the specific isoforms of PKC involved and identified phosphatidylinositol 3-kinase (PI 3-kinase) as an upstream effector in HeLa cells. Using an isoform-specific pharmacological inhibitor of PKC, a PKC$\varepsilon$ dominant-negative mutant, and antisense oligonucleotide to inhibit PKC$\varepsilon$ specifically, (omitted)