• Molecular & Cellular Toxicology
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• 제4권4호
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• pp.348-354
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• 2008

Bisphenol A (BPA), an environmental endocrine disrupter, enters the human body continuously in food and drink. Young children are likely to be more vulnerable than adults to chemical exposure due to the immaturities of their organ systems, rapid physical development, and higher ventilation, metabolic rates, and activity levels. The direct effect of BPA on peripheral tissue might also be of importance to the development of insulin resistance. However, the influence that BPA has on insulin signaling molecules in skeletal muscle has not been previously investigated. In this study, we examined the effect of BPA on fasting blood glucose (FBG) in post-weaned Wistar rats and on insulin signaling proteins in C2C12 skeletal muscle cells. Subsequently, we investigated the effects of BPA on insulin-mediated Akt phosphorylation in C2C12 myotubes. In rats, BPA treatment (0.1-1,000 ng/mL for 24 hours) resulted in the increase of FBG and plasma insulin levels, and reduced insulin-mediated Akt phosphorylation. Furthermore, the mRNA expression of insulin receptor (IR) was decreased after 24 hours of BPA treatment in C2C12 cells in a dose-dependent manner, whereas the mRNA levels of other insulin signaling proteins, including insulin receptor substrate-1 (IRS-1) and 5'-AMP-dependent protein kinase (AMPK), were unaffected. Treatment with BPA increased GLUT4 expression and protein tyrosine phosphatase 1B (PTP1B) activity in C2C12 myotubes, but not in protein levels. We conclude that exposure to BPA can induce insulin resistance by decreasing IR gene expression, which is followed by a decrease in insulin- mediated Akt activation and increased PTP1B activity.

• Journal of Ginseng Research
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• 제40권4호
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• pp.351-358
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• 2016

Background: This study was designed to investigate whether ginsenoside Rb1 (Rb1) and compound K (CK) ameliorated insulin resistance by suppressing endoplasmic reticulum (ER) stress-induced inflammation in adipose tissue. Methods: To induce ER stress, epididymal adipose tissue from mice or differentiated 3T3 adipocytes were exposed to high glucose. The effects of Rb1 and CK on reactive oxygen species production, ER stress, TXNIP/NLRP3 inflammasome activation, inflammation, insulin signaling activation, and glucose uptake were detected by western blot, emzyme-linked immunosorbent assay, or fluorometry. Results: Rb1 and CK suppressed ER stress by dephosphorylation of $IRE1{\alpha}$ and PERK, thereby reducing TXNIP-associated NLRP3 inflammasome activation in adipose tissue. As a result, Rb1 and CK inhibited IL-$1{\beta}$ maturation and downstream inflammatory factor IL-6 secretion. Inflammatory molecules induced insulin resistance by upregulating phosphorylation of insulin receptor substrate-1 at serine residues and impairing insulin PI3K/Akt signaling, leading to decreased glucose uptake by adipocytes. Rb1 and CK reversed these changes by inhibiting ER stress-induced inflammation and ameliorating insulin resistance, thereby improving the insulin IRS-1/PI3K/Akt-signaling pathway in adipose tissue. Conclusion: Rb1 and CK inhibited inflammation and improved insulin signaling in adipose tissue by suppressing ER stress-associated NLRP3 inflammation activation. These findings offered novel insight into the mechanism by which Rb1 and CK ameliorate insulin resistance in adipose tissue.

• Molecules and Cells
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• 제38권4호
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• pp.356-361
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• 2015

Mitochondrial dysfunction is associated with insulin resistance and diabetes. We previously showed that retinoid X receptor ${\alpha}$ ($RXR{\alpha}$) played an important role in transcriptional regulation of oxidative phosphorylation (OXPHOS) genes in cells with mitochondrial dysfunction caused by mitochondrial DNA mutation. In this study, we investigated whether mitochondrial dysfunction induced by incubation with OXPHOS inhibitors affects insulin receptor substrate 1 (IRS1) mRNA and protein levels and whether $RXR{\alpha}$ activation or overexpression can restore IRS1 expression. Both IRS1 and $RXR{\alpha}$ protein levels were significantly reduced when C2C12 myotubes were treated with the OXPHOS complex inhibitors, rotenone and antimycin A. The addition of $RXR{\alpha}$ agonists, 9-cis retinoic acid (9cRA) and LG1506, increased IRS1 transcription and protein levels and restored mitochondrial function, which ultimately improved insulin signaling. $RXR{\alpha}$ overexpression also increased IRS1 transcription and mitochondrial function. Because $RXR{\alpha}$ overexpression, knock-down, or activation by LG1506 regulated IRS1 transcription mostly independently of mitochondrial function, it is likely that $RXR{\alpha}$ directly regulates IRS1 transcription. Consistent with the hypothesis, we showed that $RXR{\alpha}$ bound to the IRS1 promoter as a heterodimer with peroxisome proliferator-activated receptor ${\delta}$ ($PPAR{\delta}$). These results suggest that $RXR{\alpha}$ overexpression or activation alleviates insulin resistance by increasing IRS1 expression.

• Biomolecules & Therapeutics
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• 제19권3호
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• pp.267-273
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• 2011

Syndecans are membrane-anchored proteoglycans and implicated in the pathogenesis of cancer progression and metastasis. Syndecans also play important roles in interacting with growth factors, extracellular matrix and other cell surface molecules such as IGF-1 receptor. In the present review, we discuss about the syndecan structure, their role in signaling with other receptors, in addition to its general biology. The emerging roles of syndecans in the pathophysiology of human diseases, especially insulin resistance, diabetes and cancer is discussed.

• 생명과학회지
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• 제24권9호
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• pp.1006-1011
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• 2014

인삼은 건강에 효과적인 약초라고 알려져 왔다. 인삼의 열매인 진생베리는 인삼의 주성분과 비슷한 ginsenoside, saponin, polyphenol, polyacetylene, alkaloid 등의 성분을 포함한다. 본 연구의 목적은 인삼과 같이 진생베리 열수 추출물(Ginseng berry water extract, GBE)이 당뇨와 연관된 세포 외 효소와 인슐린 신호전달 경로에 있는 분자의 발현에 어떤 효과를 가지고 있는지를 조사하였다. ${\alpha}$-Amylase와 ${\alpha}$-glucosidase는 섭취한 다당분자를 분해하여 포도당을 생성함으로 항당뇨 약물개발의 표적 효소이다. GBE에 의한 두 효소의 활성 억제능을 in vitro에서 측정하였으나 최고 $1,000{\mu}g/ml$ 농도에서도 효소활성 억제능이 나타나지 않았다. 인슐린 신호전달 경로의 영향을 확인하기 위해서 HepG2 세포에서 GBE에 의한 인슐린 신호전달 경로의 주요 단백질인 protein-tyrosine phosphatase 1B (PTP1B)와 Akt1의 발현수준 변화를 Western blot 방법으로 조사하였다. 이때 인슐린에 의한 이들 분자의 변화에 GBE가 영향을 주는 것으로 나타났다. PTP1B는 인슐린에 의해 증가된 발현량이 저농도의 GBE이 의해 더욱 증가하였으나, $200{\mu}g/ml$ 농도의 GBE에 의해서는 다소 감소하는 것으로 나타났다. 또한, Akt1도 인슐린에 의해 증가된 발현량이 GBE 농도에 따라 감소하는 것으로 나타났다.

• Asian Pacific Journal of Cancer Prevention
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• 제14권10호
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• pp.5675-5680
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• 2013

Background: Preexisting type 2 diabetes mellitus (T2DM) affects the prognosis and mortality of patients with some cancers. Insulin like growth factor (IGF) and insulin receptor (IR) signaling axes play important roles in both cancer and diabetes development. We aimed to explore the expression characteristics of proteins in IGF/IR axis in non-small cell lung cancer (NSCLC) cases with preexisting T2DM. Methods: Fifty-five NSCLC patients with preexisting T2DM were retrospectively included and matched by 55 NSCLC without diabetes at a 1:1 ratio. The expression of proteins in IGF/IR axis was detected by immunohistochemical staining. Clinicopathological data were collected to analyze their relationship with the protein expression. Results: Both IGF 1 receptor (IGF-1R) and insulin receptor substrate 2 (IRS-2) showed higher expression in the NSCLC with T2DM group, compared with those without T2DM. The high expression of IGF-1R and IRS-2 were found to be negatively associated with lymph node metastases and T staging in the T2DM group, respectively, and IRS-2 expression was also found more in the subgroup whose T2DM duration was more than 4 years. No difference was detected in the expression of IRS-1, IGF-1, IGF-2, IGFBP3, IR and mTOR between groups with or without T2DM. Conclusion: Our study found higher expression of IGF-1R and IRS-2 proteins in NSCLC patients with preexisting T2DM, and that there was an association with early stage NSCLC, which suggested that IGF signaling may play an important early event in development of NSCLC associated with diabetes.

• Fisheries and Aquatic Sciences
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• 제21권2호
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• pp.4.1-4.5
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• 2018

Insulin-like growth factors (IGFs), along with IGF-binding protein and IGF receptor, are well-known regulators in the growth and survival of vertebrates. In this study, we investigated the involvement of IGFs and protein variation during embryonic development of the olive flounder (Paralichthys olivaceus). Morphological stages were divided into six main developments as blastula, gastrula, cephalization, cranial regionalization, tail lift, and hatch. During embryonic development, protein variation was investigated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrospray ionization quadrupole time-of-flight mass spectrometry/mass spectrometry. In addition, the mechanism of signaling of IGF-I receptor was examined using immuno-blot analysis. We found marked changes in protein expression at four stages of embryonic development and identified proteins as belonging to the vitellogenin 2 family. As development progresses, expression of IGF-II, phosphotyrosine, and phospho-Akt increased, while expression of growth factor receptor-bound protein 2 (GRB2) and one of guanine-nucleotide-binding proteins (Ras) decreased. These results provide basic information on the IGF system in the embryonic development of the olive flounder.

• Molecules and Cells
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• 제28권5호
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• pp.495-499
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• 2009

Although insulin-like growth factor-I (IGF-I) and androgen receptor (AR) are well known effectors of skeletal muscle, the molecular mechanism by which signaling pathways integrating AR and IGF-I in skeletal muscle cells has not been previously examined. In this study, the role of PI3K/Akt on IGF-I-induced gene expression and activation of AR in skeletal muscle cells was investigated. C2C12 cells were treated with IGF-I in the absence or presence of inhibitors of PI3K/Akt pathway (LY294002 and Wortmannin). Inhibition of the PI3K/Akt pathway with LY294002 or Wortmannin led to a significant decrease in IGF-I-induced AR phosphorylation and total AR protein expression. Furthermore, IGF-I-induced AR mRNA and skeletal ${\alpha}-actin$ mRNA were blocked by LY294002 or Wortmannin. Confocal images showed that IGF-I-induced AR translocation from cytosol to nucleus was inhibited significantly in response to treatment with LY294002 or Wortmannin. The present results suggest that modulating effect of IGF-I on AR gene expression and activation in C2C12 mouse skeletal muscle cells is mediated at least in part by the PI3K/Akt pathway.

• Nutrition Research and Practice
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• 제7권6호
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• pp.439-445
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• 2013

It has been shown that dysregulation of IGF-1 signaling is associated with tumor incidence and progression, whereas blockade of the signaling can effectively inhibit carcinogenesis. Although several mechanisms of anticancer activity of quercetin were proposed, molecular targets of quercetin have not been identified yet. Hence, we assessed the effect of quercetin on IGF-1 signaling inhibition in BK5.IGF-1 transgenic (Tg) mice, which over-expresses IGF-1 in the skin epidermis. A quercetin diet (0.02% wt/wt) for 20 weeks remarkably delayed the incidence of skin tumor by 2 weeks and reduced tumor multiplicity by 35% in a 7,12-dimethylbenz(a)anthracene (DMBA)-tetradecanoyl phorbol-13-acetate (TPA) two stage mouse skin carcinogenesis protocol. Moreover, skin hyperplasia in Tg mice was significantly inhibited by a quercetin supplementation. Further analysis of the MT1/2 skin papilloma cell line showed that a quercetin treatment dose dependently suppressed IGF-1 induced phosphorylation of the IGF-1 receptor (IGF-1R), insulin receptor substrate (IRS)-1, Akt and S6K; however, had no effect on the phosphorylation of PTEN. Additionally, the quercetin treatment inhibited IGF-1 stimulated cell proliferation in a dose dependent manner. Taken together, these data suggest that quercetin has a potent anticancer activity through the inhibition of IGF-1 signaling.

• Asian-Australasian Journal of Animal Sciences
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• 제20권7호
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• pp.1030-1038
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• 2007

Results on localization of growth hormone receptor (GHR), interaction of growth hormone (GH) with receptor in buffalo adipose tissue and identification of activated signaling molecules in the action of GH are presented. Bovine GH (bGH) was labeled with fluorescein or biotin. Fluorescein-labelled bGH was used for localization of GHRs in buffalo adipocytes. The receptors were present on the cell surface. The affinity of binding of GH to its receptor was determined by designing an experiment in which buffalo adipose tissue explants, biotinylated GH and streptavidin-peroxidase conjugate were employed. The affinity constant was calculated to be $2{\times}10^8M^{-1}$. The receptor density on adipose tissue was found to be 1 femto mole per mg of tissue. Signalling molecules generated in the action of GH were tentatively identified by employing Western blot and enhanced chemiluminescence techniques using anti-phosphotyrosine antibody. Based on molecular weights of proteins reactive to anti-phosphotyrosine antibody, three signaling molecules viz. insulin receptor substrate, Janus activated kinase (Jak) and mitogen activated protein were tentatively identified. These signaling molecules appeared in a time (incubation time of explants with growth hormone) dependent way. The activation of Jak2 was confirmed by employing anti-Jak2 antibody in a Western blot. The activation of Jak2 occurred during 5 min incubation of buffalo adipose tissue explants with GH and incubation for an additional period, viz. 30 min. or 60 min., resulted in a drastic reduction in activation. The results suggest that Jak2 activation is an early event in the action of GH in buffalo adipose tissue.