• BMB Reports
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• v.34 no.6
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• pp.517-525
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• 2001

Six renaturable protein kinases that utilize the myelin basic protein (MBP) as a substrate were activated during prolonged exposure of cardiac myocytes to okadaic acid (OA). We characterized the substrate preference and activation of these kinases, with particular emphasis on 3 novel kinases-MBPK-55, MBPK-62 and MBPK-87. The transcription factors c-Jun, Elk, ATF2, and c-Fos that are used to assess mitogen-activated protein kinase activation were all poor substrates for these three kinases. MAPKAPK2 was also not phosphorylated. In contrast, Histone IIIS was phosphorylated by MBPK-55 and MBPK-62. These protein kinases were activated in cultured cardiac fibroblasts, H9c2 cardiac myoblasts, and Cos cells. High concentrations (0.5 to $1\;{\mu}M$) of OA were essential for the activation of the protein kinases in all of the cell types examined, whereas calyculin A [an inhibitor of protein phosphatase 1 (PP1) and PP2A], cyclosporin A (a PP2B inhibitor), and an inactive OA analog all failed to activate these kinases. The high dose of okadaic acid that is required for kinase activation was also required for phosphatase inhibition, as assessed by immunoblotting whole cell lysates with anti-phosphothreonine antibodies. A variety of chemical inhibitors, including PD98059 (MEK-specific), genistein (tyrosine kinase-specific) and Bisindolylmaleimide I (protein kinase C-specific), failed to inhibit the OA activation of these kinases. Thus, MBPK-55 and MBPK-62 are also Histone IIIS kinases that are widely expressed and specifically activated upon exposure to high OA concentrations.

• Journal of Life Science
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• v.21 no.2
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• pp.242-250
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• 2011

Although insulin-like growth factor-I (IGF-I) and androgen receptor (AR) coactivators are well known effectors of skeletal muscle, the molecular mechanism by which signaling pathways integrating AR coactivators and IGF-I in skeletal muscle cells has not been previously examined. In this study, the effects of IGF-I treatment on the gene expression of AR coactivators in the absence of AR ligands and the roles of the p38 MAPK and ERK1/2 signaling pathways in IGF-I-induced AR coactivators induction were examined. C2C12 cells were treated with 250 ng/ml of IGF-I in the presence or absence of specific inhibitors p38 MAPK (SB203580) or ERK1/2 (PD98059). Treatment of C2C12 cells with IGF-I resulted in increased in GRIP-1, SRC-1, and ARA70 protein expression. The levels of GRIP-1, SRC-1, and ARA70 mRNA were also significantly increased after 5min of IGF-I treatment. IGF-I-induced AR coactivator proteins were significantly blocked by pharmacological inhibitors of p38 MAPK and ERK1/2 pathways. However, there was no significant effect of those inhibitors on IGF-I-induced mRNA level of AR coactivators, suggesting that AR coactivators are post-transcriptionally regulated by IGF-I. Furthermore, the present results suggest that IGF-I stimulates the expression of AR coactivators by cooperative activation of the p38 MAPK and ERK1/2 pathways in C2C12 mouse skeletal muscle cells.

• Biomolecules & Therapeutics
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• v.32 no.1
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• pp.115-122
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• 2024

Heat shock protein (HSP) 90 is expressed in most living organisms, and several client proteins of HSP90 are necessary for cancer cell survival and growth. Previously, we found that HSP90 was cleaved by histone deacetylase (HDAC) inhibitors and proteasome inhibitors, and the cleavage of HSP90 contributes to their cytotoxicity in K562 leukemia cells. In this study, we first established mouse xenograft models with K562 cells expressing the wild-type or cleavage-resistant mutant HSP90β and found that the suppression of tumor growth by the HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) was interrupted by the mutation inhibiting the HSP90 cleavage in vivo. Next, we investigated the possible function of thioredoxin interacting protein (TXNIP) in the HSP90 cleavage induced by SAHA. TXNIP is a negative regulator for thioredoxin, an antioxidant protein. SAHA transcriptionally induced the expression of TXNIP in K562 cells. HSP90 cleavage was induced by SAHA also in the thymocytes of normal mice and suppressed by an anti-oxidant and pan-caspase inhibitor. When the thymocytes from the TXNIP knockout mice and their wild-type littermate control mice were treated with SAHA, the HSP90 cleavage was detected in the thymocytes of the littermate controls but suppressed in those of the TXNIP knockout mice suggesting the requirement of TXNIP for HSP90 cleavage. We additionally found that HSP90 cleavage was induced by actinomycin D, β-mercaptoethanol, and p38 MAPK inhibitor PD169316 suggesting its prevalence. Taken together, we suggest that HSP90 cleavage occurs also in vivo and contributes to the anti-cancer activity of various drugs in a TXNIP-dependent manner.

• BMB Reports
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• v.42 no.6
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• pp.380-386
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• 2009

In neurodegenerative diseases, such as Alzheimer' and Parkinson', microglial cell activation is thought to contribute to CNS injury by producing neurotoxic compounds. Prothrombin and kringle-2 increase levels of NO and the mRNA expression of iNOS, IL-1$\beta$, and TNF-$\alpha$ in microglial cells. In contrast, the human prothrombin kringle-2 derived peptide NSA9 inhibits NO release and the production of pro-inflammatory cytokines such as IL-1$\beta$, TNF-$\alpha$, and IL-6 in LPS-activated EOC2 microglia. In this study, we investigated the anti-inflammatory effects of NSA9 in human prothrombin- and kringle-2-stimulated EOC2 microglia. Treatment with 20-100 ${\mu}M$ of NSA9 attenuated both prothrombin- and kringle-2-induced microglial activation. NO production induced by MAPKs and NF-$\kappa$B was similarly reduced by inhibitors of ERK (PD98059), p38 (SB203580), NF-$\kappa$B (N-acetylcysteine), and NSA9. These results suggest that NSA9 acts independently as an inhibitor of microglial activation and that its effects in EOC2 microglia are not influenced by the presence of kringle-2.

• Biomolecules & Therapeutics
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• v.24 no.6
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• pp.589-594
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• 2016

Insulin is a peptide hormone of the endocrine pancreas and exerts a wide variety of physiological actions in insulin sensitive tissues, such as regulation of glucose homeostasis, cell growth, differentiation, learning and memory. However, the role of insulin in osteoblast cells remains to be fully characterized. In this study, we demonstrated that the insulin (100 nM) has the ability to stimulate the phosphorylation of protein kinase B (Akt/PKB) and extracellular signal-regulated kinase (ERK) and the levels of inhibin-${\beta}E$ in the osteoblast-like UMR-106 cells. This insulin-stimulated activities were abolished by the PI3K and MEK1 inhibitors LY294002 and PD98059, respectively. This is the first report proving that insulin is a potential candidate that enables the actions of inhibin-${\beta}E$ subunit of the TGF-${\beta}$ family. The current investigation provides a foundation for the realization of insulin as a potential stimulator in survival signaling pathways in osteoblast-like UMR-106 cells.

• Molecules and Cells
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• v.26 no.5
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• pp.468-473
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• 2008

Low-density lipoprotein (LDL) induces cell proliferation in human aortic smooth muscle cells (hAoSMCs), which may be involved in atherogenesis and intimal hyperplasia. Recent studies have demonstrated that $Cl^-$ channels are related to vessel cell proliferation induced by a variety of stimuli. In this study, we investigated a potential role of $Cl^-$ channels in the signaling pathway of LDL effects on hAoSMC proliferation with a focus on the activation of Erk1/2-PI3K/Akt and the subsequent upregulation of Egr-1. $Cl^-$ channel blockers, DIDS, but neither NPPB nor Furosemide, completely abolished the LDL-induced DNA synthesis and cell proliferation. Moreover, DIDS, but not NPPB, significantly decreased LDL-stimulated $Cl^-$ concentration, as judged by flow cytometry analysis using MQAE as a $Cl^-$-detection dye. DIDS pretreatment completely abolished the activation of Erk1/2 and PI3K/Akt in a dose-dependent manner that is the hallmark of LDL activation, as judged by Western blot and proliferation assays. Moreover, pretreatment with DIDS ($Cl^-$ channel blockers) but not LY294002 (PI3K inhibitors) completely abolished the LDL-induced upregulation of Egr-1 to the same extent as PD98059 (MEK inhibitors to inhibit Erk), as judged by Western blot and luciferase reporter assays. This is the first report, to our knowledge, that DIDS-sensitive $Cl^-$-channels play a key role in the LDL-induced cell proliferation of hAoSMCs via the activation of Erk1/2 and PI3K/Akt and the upregulation of Egr-1.

• The Korean Journal of Physiology and Pharmacology
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• v.24 no.3
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• pp.267-276
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• 2020

T In the present study, we investigated the effect of oncogenic H-Ras on rat mdr1b expression in NIH3T3 cells. The constitutive expression of H-Ras^V12 was found to downregulate the mdr1b promoter activity and mdr1b mRNA expression. The doxorubicin-induced mdr1b promoter activity of the H-Ras^V12 expressing NIH3T3 cells was markedly lower than that of control NIH3T3 cells. Additionally, there is a positive correlation between the level of H-Ras^V12 expression and a sensitivity to doxorubicin toxicity. To examine the detailed mechanism of H-Ras^V12-mediated down-regulation of mdr1b expression, antioxidant N-acetylcysteine (NAC) and NADPH oxidase inhibitor diphenylene iodonium (DPI) were used. Pretreating cells with either NAC or DPI significantly enhanced the oncogenic H-Ras-mediated down-regulation of mdr1b expression and markedly prevented doxorubicin-induced cell death. Moreover, NAC and DPI treatment led to a decrease in ERK activity, and the ERK inhibitors PD98059 or U0126 enhanced the mdr1b-Luc activity of H-Ras^V12-NIH3T3 and reduced doxorubicin-induced apoptosis. These data suggest that Ras^V12 expression could downregulate mdr1b expression through intracellular reactive oxygen species (ROS) production, and ERK activation induced by ROS, is at least in part, contributed to the downregulation of mdr1b expression.

• The Korean Journal of Physiology and Pharmacology
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• v.17 no.4
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• pp.307-314
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• 2013

Connective tissue growth factor (CTGF) is a potent pro-fibrotic factor, which is implicated in fibrosis through extracellular matrix (ECM) induction in diabetic cardiovascular complications. It is an important downstream mediator in the fibrotic action of transforming growth factor ${\beta}$ ($TGF{\beta}$) and is potentially induced by hyperglycemia in human vascular smooth muscle cells (VSMCs). Therefore, the goal of this study is to identify the signaling pathways of CTGF effects on ECM accumulation and cell proliferation in VSMCs under hyperglycemia. We found that high glucose stimulated the levels of CTGF mRNA and protein and followed by VSMC proliferation and ECM components accumulation such as collagen type 1, collagen type 3 and fibronectin. By depleting endogenous CTGF we showed that CTGF is indispensable for the cell proliferation and ECM components accumulation in high glucose-stimulated VSMCs. In addition, pretreatment with the MEK1/2 specific inhibitors, PD98059 or U0126 potently inhibited the CTGF production and ECM components accumulation in high glucose-stimulated VSMCs. Furthermore, knockdown with ERK1/2 MAPK siRNA resulted in significantly down regulated of CTGF production, ECM components accumulation and cell proliferation in high glucose-stimulated VSMCs. Finally, ERK1/2 signaling regulated Egr-1 protein expression and treatment with recombinant CTGF reversed the Egr-1 expression in high glucose-induced VSMCs. It is conceivable that ERK1/2 MAPK signaling pathway plays an important role in regulating CTGF expression and suggests that blockade of CTGF through ERK1/2 MAPK signaling may be beneficial for therapeutic target of diabetic cardiovascular complication such as atherosclerosis.

• The Korean Journal of Physiology and Pharmacology
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• v.17 no.2
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• pp.157-162
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• 2013

Insulin-like growth factor binding proteins (IGFBPs) are important components of insulin growth factor (IGF) signaling pathways. One of the binding proteins, IGFBP-5, enhances the actions of IGF-1, which include the enhanced proliferation of smooth muscle cells. In the present study, we examined the expression and the biological effects of IGFBP-5 in vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). The levels of IGFBP-5 mRNA and protein were found to be higher in the VSMC from SHR than in those from WKY. Treatment with recombinant IGFBP-5-stimulated VSMC proliferation in WKY to the levels observed in SHR. In the VSMCs of WKY, incubation with angiotensin (Ang) II or IGF-1 dose dependently increased IGFBP-5 protein levels. Transfection with IGFBP-5 siRNA reduced VSMC proliferation in SHR to the levels exhibited in WKY. In addition, recombinant IGFBP-5 significantly up-regulated ERK1/2 phosphorylation in the VSMCs of WKY as much as those of SHR. Concurrent treatment with the MEK1/2 inhibitors, PD98059 or U0126 completely inhibited recombinant IGFBP-5-induced VSMC proliferation in WKY, while concurrent treatment with the phosphatidylinositol-3 kinase inhibitor, LY294002, had no effect. Furthermore, knockdown with IGFBP-5 siRNA inhibited ERK1/2 phosphorylation in VSMC of SHR. These results suggest that IGFBP-5 plays a role in the regulation of VSMC proliferation via ERK1/2 MAPK signaling in hypertensive rats.

• Archives of Pharmacal Research
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• v.27 no.3
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• pp.324-333
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• 2004

To determine whether Insulin-like growth factor (IGF-I) treatment represents a potential means of enhancing the survival of cardiac muscle cells from adriamycin (ADR)-induced cell death, the present study examined the ability of IGF-I to prevent cell death. The study was performed utilising the embryonic, rat, cardiac muscle cell line, H9C2. Incubating cardiac muscle cells in the presence of adriamycin increased cell death, as determined by MTT assay and annexin V-positive cell number. The addition of 100 ng/mL IGF-I, in the presence of adriamycin, decreased apoptosis. The effect of IGF-I on phosphorylation of PI, a substrate of phosphatidylinositol 3-kinase (PI 3-kinase) or protein kinase B (AKT), was also examined in H9C2 cardiac muscle cells. IGF-I increased the phosphorylation of ERK 1 and 2 and $PKC{\;}{\zeta}{\;}kinase$. The use of inhibitors of PI 3-kinase (LY 294002), in the cell death assay, demonstrated partial abrogation of the protective effect of IGF-I. The MEK1 inhibitor-PD098059 and the PKC inhibitor-chelerythrine exhibited no effect on IGF-1-induced cell protection. In the regulatory subunit of PI3K-p85- dominant, negative plasmid-transfected cells, the IGF-1-induced protective effect was reversed. This data demonstrates that IGF-I protects cardiac muscle cells from ADR-induced cell death. Although IGF-I activates several signaling pathways that contribute to its protective effect in other cell types, only activation of PI 3-kinase contributes to this effect in H9C2 cardiac muscle cells.