Liver glucokinase can be activated by peroxisome proliferator-activated receptor-gamma

Thiazolidinediones (TZDs), synthetic ligands of peroxisome proliferator-activated receptor (PPAR)-gamma, are known to decrease hepatic glucose production and increase glycogen synthesis in diabetic animals. Recently it was reported that glucokinase (GK) expression was increased by TZDs in the liver of diabetic ZDF rats. However, the mechanism whereby TZDs increase GK expression is not yet studied. We have assumed that liver type glucokinase (LGK) induction by TZDs could be achieved by direct transcriptional activation. Thus, we have dissected the LGK promoter to explore the presence of a PPAR response element (PPRE) in the promoter. From this study, we were able to localize a PPRE in the -116/-104 region of the rat LGK gene. The PPAR-gamma/retinoid X receptor-alpha heterodimer was bound to the element and activated the LGK promoter. The LGK promoter lacking the PPRE or having mutations in the PPRE could not be activated by PPAR-gamma. Furthermore, troglitazone increased endogenous GK mRNA in primary hepatocytes. These results indicate that PPAR-gamma can directly activate GK expression in liver and may contribute to improving glucose homeostasis in type 2 diabetes.ope

Hepatitis B virus X protein modulates peroxisome proliferator-activated receptor γ through protein–protein interaction

Ligand activation of peroxisome proliferator-activated receptor γ (PPARγ) has been reported to induce growth inhibition and apoptosis in various cancers including hepatocellular carcinoma (HCC). However, the effect of hepatitis B virus X protein (HBx) on PPARγ activation has not been characterized in hepatitis B virus (HBV)-associated HCC. Herein, we demonstrated that HBx counteracted growth inhibition caused by PPARγ ligand in HBx-associated HCC cells. We found that HBx bound to DNA binding domain of PPARγ and HBx/PPARγ interaction blocked nuclear localization and binding to recognition site of PPARγ. HBx significantly suppressed a PPARγ-mediated transactivation. These results suggest that HBx modulates PPARγ function through protein–protein interaction.ope

The functional relationship between co-repressor N-CoR and SMRT in mediating transcriptional repression by thyroid hormone receptor alpha.

A central issue in mediating repression by nuclear hormone receptors is the distinct or redundant function between co-repressors N-CoR (nuclear receptor co-repressor) and SMRT (silencing mediator of retinoid and thyroid hormone receptor). To address the functional relationship between SMRT and N-CoR in TR (thyroid hormone receptor)-mediated repression, we have identified multiple TR target genes, including BCL3 (B-cell lymphoma 3-encoded protein), Spot14 (thyroid hormone-inducible hepatic protein), FAS (fatty acid synthase), and ADRB2 (beta-adrenergic receptor 2). We demonstrated that siRNA (small interfering RNA) treatment against either N-CoR or SMRT is sufficient for the de-repression of multiple TR target genes. By the combination of sequence mining and physical association as determined by ChIP (chromatin immunoprecipitation) assays, we mapped the putative TREs (thyroid hormone response elements) in BCL3, Spot14, FAS and ADRB2 genes. Our data clearly show that SMRT and N-CoR are independently recruited to various TR target genes. We also present evidence that overexpression of N-CoR can restore repression of endogenous genes after knocking down SMRT. Finally, unliganded, co-repressor-free TR is defective in repression and interacts with a co-activator, p300. Collectively, these results suggest that both SMRT and N-CoR are limited in cells and that knocking down either of them results in co-repressor-free TR and consequently de-repression of TR target genes.ope

Identification and characterization of peroxisome proliferator response element in the mouse GLUT2 promoter

In the present study, we show that the expression of type 2 glucose transporter isoform (GLUT2) could be regulated by PPAR-γ in the liver. Rosiglitazone, PPAR-γ agonist, activated the GLUT2 mRNA level in the primary cultured hepatocytes and Alexander cells, when these cells were transfected with PPAR-γ/RXR-α. We have localized the peroxisome proliferator response element in the mouse GLUT2 promoter by serial deletion studies and site-directed mutagenesis. Chromatin immunoprecipitation assay using ob/ob mice also showed that PPAR-γ rather than PPAR-α binds to the -197/-184 region of GLUT2 promoter. Taken together, liver GLUT2 may be a direct target of PPAR-γ ligand contributing to glucose transport into liver in a condition when PAPR-γ expression is increased as in type 2 diabetes or in severe obesity.ope

Glucose-stimulated upregulation of GLUT2 gene is mediated by sterol response element-binding protein-1c in the hepatocytes

GLUT2 is mainly expressed in the liver, β-cells of the pancreas, and the basolateral membrane of kidney proximal tubules and plays an important role in glucose homeostasis in living organisms. The transcription of the GLUT2 gene is known to be upregulated in the liver during postprandial hyperglycemic states or in type 2 diabetes. However, a molecular mechanism by which glucose activates GLUT2 gene expression is not known. In this study, we report evidence that sterol response element–binding protein (SREBP)-1c plays a key role in glucose-stimulated GLUT2 gene expression. The GLUT2 promoter reporter is activated by SREBP-1c, and the activation is inhibited by a dominant-negative form of SREBP-1c (SREBP-1c DN). Adenoviral expression of SREBP-1c DN suppressed glucose-stimulated GLUT2 mRNA level in primary hepatocytes. An electrophoretic mobility shift assay and mutational analysis of the GLUT2 promoter revealed that SREBP-1c binds to the −84/−76 region of the GLUT2 promoter. Chromatin immunoprecipitation revealed that the binding of SREBP-1c to the −84/−76 region was increased by glucose concentration in a dose-dependent manner. These results indicate that SREBP-1c mediates glucose-stimulated GLUT2 gene expression in hepatocytes.ope

HDR 시스템에서 무선 채널 상태를 고려한 버스트 트래픽 수락제어 기법

학위논문(석사)--아주대학교 정보통신전문대학원 :정보통신공학과,2003Maste

정보비대칭성, 절세전략, 재무이익과 세무이익 차이 간의 관계

학위논문(석사)--서울대학교 대학원 :경영학과,2011.2. 정운오.Maste

Identification and functional characterization of the peroxisomal proliferator response element in rat GLUT2 promoter

We identified the peroxisomal proliferator response element (PPRE) in the +68/+89 region of the rat GLUT2 gene. To identify whether the putative PPRE in the GLUT2 gene (GLUT2-PPRE) is functional, GLUT2 promoter-luciferase reporter constructs were transfected into CV-1 cells. Promoter activities were increased by coexpression of peroxisomal proliferator-activated receptor (PPAR)-gamma, retinoid X receptor (RXR)-alpha, and treatment of their ligands; troglitazone and 9-cis retinoic acid potentiated the transactivational effects. Introduction of mutations in GLUT2-PPRE resulted in loss of transactivational effects of the PPAR-gamma/RXR-alpha heterodimer. Electrophoretic mobility shift assay using nuclear extracts of CV-1 cells, which were transfected with various combinations of PPARs or RXR-alpha expression plasmids, revealed that heterodimers of PPAR-gamma and RXR-alpha preferentially bound to GLUT2-PPRE. In HIT-T15 cells, promoter activity of the rat GLUT2 gene was increased by troglitazone and 9-cis retinoic acid, and mutations of GLUT2-PPRE resulted in reduction of promoter activity. In addition, we observed increased GLUT2 transcription by troglitazone and 9-cis retinoic acid in isolated rat primary islets. These results suggested that the GLUT2-PPRE is functional and plays a significant role in gene expression of GLUT2 in pancreatic beta-cells. This is the first report identifying PPRE in a gene involved in glucose homeostasis, linking the effect of troglitazone on the regulation of insulin secretion.restrictio

Peroxisomal proliferator activated receptor-γ upregulates the glucokinase gene expression in β cells

Brain Korea 21 Project for Medical Sciences/박사[한글] PPARγ의 합성 리간드인 Thiazolidinediones은 말초조직에서 인슐린 감수성을 향 상시키고, 췌장 베타세포에서 혈당에 의한 인슐린의 분비 조절을 향상시키는 것으로 알려져 있다. 본 연구에서는 췌장 베타 세포의 혈당 인지 과정에서 PPARγ의 역할을 규명하기 위하 여 혈당 인지 과정에 관여하고 있는 글루코키나제 유전자의 프로모터 부위를 분석하여 PPARγ에 의해 활성화되는 부위인 PPRE를 규명하였다. PPRE는 췌장형 글루코키나제 유전자 프로모터의 +47에서 +68 사이의 부위에 위치하며, PPARγ와 RXRα의 heterodimer가 이 부위에 결합하여 유전자 발현을 활성화시킨다. 그리고 luciferase reporter와 결합된 췌장형 글루코키나제 유전자의 프로모터에서 PPRE를 없애 거나 돌연변이를 유발시키면 PPARγ에 대한 반응성이 없어진다. Thiazolidinediones의 하나인 troglitazone는 췌장 베타 세포주에서 글루코키나제 유전자의 발현을 증가시키며, 제 2형 당뇨병의 동물 모델인 Zucker Diabetic Fatty 백서에서 내당능을 향상시키고, 췌장 베타 세포에서 글루코키나제 유전자의 발현을 회복시킨다. 본 연구결과는 PPARγ가 췌장 베타세포에서 혈당인지 기구의 유전자 발현 조절에 관여하여 베타 세포의 혈당 감수성을 향상시키는 것을 의미하고, 이러힌 작용은 PPARγ의 리간드가 인슐린비의존형 당뇨병 환자에서 췌장 베타세포의 기능 회복에 기여할 수 있음을 시사한다. -------------------- 핵심되는 말 : PPARγ, 글루코키나제, 베타세포, 포도당, 인슐린 [영문] Thiazolidinediones (TZDs), synthetic ligands of PPARγ, improve peripheral insulin sensitivity and glucose stimulated insulin secretion in pancreatic β cells. To explore the role of PPARγ in glucose sensing of β cells, we have dissected β cell specific glucokinase (βGK) promoter, which constitutes glucose sensing apparatus in pancreatic βcells, and identified a peroxisomal proliferator response element (PPRE) in the promoter. PPRE is located in the region between +47 and +68 of βGK gene. PPARγ/RXRα heterodimer bound to this element and activated βGK promoter. βGK promoter luciferase constructs lacking PPRE or having mutations in PPRE lost PPARγ responsiveness. Ligand scavenging dominant negative mutant of PPARγ inhibited the ligand dependent activation of βGK by PPARγ. Furthermore, troglitazone, a kind of TZDs, increased endogenous GK expression in β cell lines. Significantly, troglitazone treated diabetic ZDF rats restored glucose tolerance and GK expression of the pancreatic islets. These results indicated that PPARγ could regulate βGK expression in vivo and in vitro. Taken together with the GLUT2-PPRE, it is concluded that PPARγ regulates gene expression of glucose sensing apparatus and thereby improves glucose sensing ability of β cells, contributing to the restoration of β cell function in NIDDM subjects by troglitazone.prohibitio

Exogenous L-arginine ameliorates cisplatin-sensitivity in various cancer cells and alone induces apoptosis depending on the degree of endogenous Argininosuccinate synthetase expression

The association is well known between cisplatin-resistance and the loss of endogenous argininosuccinate synthetase (ASS1) expression in various cancer cells. Except for the on-target effect of cisplatin resistance related with epigenetic silencing of ASS1, other resistance mechanisms in cancer cells is currently unclear. ASS1 is a key enzyme and rate-limiting step in arginine synthesis, there is a possibility of the signaling alteration triggered by different ASS1 expression level or by cellular arginine availability. In other words, there is potential to ameliorate the cisplatin sensitivity via alteration of intracellular signaling or metabolic change driven by ASS1 itself or arginine. Given this circumstance, we aim to investigate how the ASS1 expression level and arginine supply effect on cisplatin-resistance and survival in cancer cells in terms of cellular signaling. We found not only exogenous arginine supply restores cisplatin-sensitivity in cancer cells but also arginine supply alone could negatively associate with cancer cell survival by alteration of certain signaling molecules according to ASS1 expression level.Docto