B-cell translocation gene 2 positively regulates GLP-1-stimulated insulin secretion via induction of PDX-1 in pancreatic beta-cells

Glucagon-like peptide-1 (GLP-1) is a potent glucoincretin hormone and an important agent for the treatment of type 2 diabetes. Here we demonstrate that B-cell translocation gene 2 (BTG2) is a crucial regulator in GLP-1-induced insulin gene expression and insulin secretion via upregulation of pancreatic duodenal homeobox-1 (PDX-1) in pancreatic beta-cells. GLP-1 treatment significantly increased BTG2, PDX-1 and insulin gene expression in pancreatic beta-cells. Notably, adenovirus-mediated overexpression of BTG2 significantly elevated insulin secretion, as well as insulin and PDX-1 gene expression. Physical interaction studies showed that BTG2 is associated with increased PDX-1 occupancy on the insulin gene promoter via a direct interaction with PDX-1. Exendin-4 (Ex-4), a GLP-1 agonist, and GLP-1 in pancreatic beta-cells increased insulin secretion through the BTG2-PDX-1-insulin pathway, which was blocked by endogenous BTG2 knockdown using a BTG2 small interfering RNA knockdown system. Finally, we revealed that Ex-4 and GLP-1 significantly elevated insulin secretion via upregulation of the BTG2-PDX-1 axis in pancreatic islets, and this phenomenon was abolished by endogenous BTG2 knockdown. Collectively, our current study provides a novel molecular mechanism by which GLP-1 positively regulates insulin gene expression via BTG2, suggesting that BTG2 has a key function in insulin secretion in pancreatic beta-cells.

Analysis of connective tissue growth factor promoter polymorphism in Thai children with biliary atresia.

OBJECTIVE: Connective tissue growth factor (CTGF) has been proposed to play a key role in the pathogenesis of hepatic fibrosis in biliary atresia (BA). The aim of the present study was to determine the single nucleotide polymorphism (SNP) in the promoter region of CTGF gene in a Thai population, and to investigate the possible role of CTGF promoter polymorphism in the susceptibility of BA. MATERIAL AND METHOD: Genomic DNA was obtained from 84 patients with BA and 142 healthy controls. The -447 G/C and -132 C/G in CTGF promoter were amplified and examined by amplification-refractory mutation system (ARMs) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis, respectively. The test of Hardy-Weinberg equilibrium (HWE) was performed using HWE program of SNPAnalyzer. Statistical analysis was carried out with SPSS and Epi Info. RESULT: According to the previous experiment, there were two SNPs, which were at position -447 and -132 on the promoter. However, there was only one SNP at the position -447 in the Thai population. No significant differences in genotype and allele frequency were observed between BA and controls or with BA subgroups. CONCLUSION: The present study demonstrated that CTGF polymorphism at -447 G/C was not associated with BA and the jaundice status of the postoperative BA patients.

Monocrotaline-induced pulmonary hypertension correlates with upregulation of connective tissue growth factor expression in the lung

Pulmonary hypertension (PH) is characterized by structural and functional changes in the lung including proliferation of vascular smooth muscle cells (VSMCs) and excessive collagen synthesis. Although connective tissue growth factor (CTGF) is known to promote cell proliferation, migration, adhesion, and extracellular matrix production in various tissues, studies on the role of CTGF in pulmonary hypertension have been limited. Here, we examined CTGF expression in the lung tissues of male Sprague Dawley rats treated with monocrotaline (MCT, 60 microgram/kg), a pneumotoxic agent known to induce PH in animals. Establishment of PH was verified by the significantly increased right ventricular systolic pressure and right ventricle/left ventricle weight ratio in the MCT-treated rats. Histological examination of the lung revealed profound muscular hypertrophy in the media of pulmonary artery and arterioles in MCT-treated group. Lung parenchyma, vein, and bronchiole did not appear to be affected. RT-PCR analysis of the lung tissue at 5 weeks indicated significantly increased expression of CTGF in the MCT-treated group. In situ hybridization studies also confirmed abundant CTGF mRNA expression in VSMCs of the arteries and arterioles, clustered pneumocytes, and infiltrated macrophages. Interestingly, CTGF mRNA was not detected in VSMCs of vein or bronchiole. In saline-injected control, basal expression of CTGF was seen in bronchial epithelial cells, alveolar lining cells, and endothelial cells. Taken together, our results suggest that CTGF upregulation in arterial VSMC of the lung might be important in the pathogenesis of pulmonary hypertension. Antagonizing the role of CTGF could thus be one of the potential approaches for the treatment of PH.

Implication of Egr-1 in trifluoperazine-induced growth inhibition in human U87MG glioma cells

The early growth response gene-1 (Egr-1) is a tumor suppressor which plays an important role in cell growth, differentiation and apoptosis. Egr-1 has been shown to be down-regulated in many types of tumor tissues. Trifluoperazine (TFP), a phenothiazine class of antipsychotics, restored serum-induced Egr-1 expression in several cancer cell lines. We investigated the effect of Egr-1 expression on the TFP-induced inhibition of cell growth. Ectopic expression of Egr-1 enhanced the TFP-induced antiproliferative activity and downregulated cyclin D1 level in U87MG glioma cells. Our results suggest that antipsychotics TFP exhibits antiproliferative activity through up-regulation of Egr-1.