RESUMO
Intestinal epithelial cells undergo rapid turnover and exfoliation especially at the villus tips. This process is modulated by various nutrients especially fat. Apoptosis is one of the important regulatory mechanisms of this turnover. Therefore, identification of the factors that control epithelial cell apoptosis should help us understand the mechanism of intestinal mucosal turnover. Here, we report the identification of a novel small intestine-specific member of the Ly-6 family, intectin, by signal sequence trap method. Intectin mRNA expression was exclusively identified in the intestine and localized at the villus tips of intestinal mucosa, which is known to undergo apoptosis. Intectin mRNA expression was modulated by nutrition. Intestinal epithelial cells expressing intectin were more sensitive to palmitate-induced apoptosis, compared with control intestinal epithelial cells, and such effect was accompanied by increased activity of caspase-3. Intectin expression also reduced cell-cell adhesion of intestinal epithelial cells.
Assuntos
Apoptose , Células Epiteliais/metabolismo , Glicosilfosfatidilinositóis/química , Mucosa Intestinal/metabolismo , Glicoproteínas de Membrana/química , Glicoproteínas de Membrana/fisiologia , Sequência de Aminoácidos , Animais , Sequência de Bases , Northern Blotting , Western Blotting , Caspase 3 , Caspases/metabolismo , Membrana Celular/metabolismo , Clonagem Molecular , Citosol/metabolismo , DNA Complementar/metabolismo , Relação Dose-Resposta a Droga , Epitélio/metabolismo , Vetores Genéticos , Hibridização In Situ , Mucosa Intestinal/patologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Dados de Sequência Molecular , Ácido Palmítico/química , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Homologia de Sequência de Aminoácidos , Frações Subcelulares , Fatores de Tempo , Distribuição TecidualRESUMO
Adiponectin is a fat-derived hormone with antidiabetic and antiatherogenic properties. Hypoadiponectinemia seen in obesity is associated with insulin-resistant diabetes and atherosclerosis. Thiazolidinediones, peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists, have been shown to increase plasma adiponectin levels by the transcriptional induction in adipose tissues. However, the precise mechanism of such action is unknown. In this study, we have identified a functional PPAR-responsive element (PPRE) in human adiponectin promoter. PPAR-gamma/retinoid X receptor (RXR) heterodimer directly bound to the PPRE and increased the promoter activity in cells. In adipocytes, point mutation of the PPRE markedly reduced the basal transcriptional activity and completely blocked thiazolidinedione-induced transactivation of adiponectin promoter. We have also identified a responsive element of another orphan nuclear receptor, liver receptor homolog-1 (LRH-1), in adiponectin promoter. LRH-1 was expressed in 3T3-L1 cells and rat adipocytes. LRH-1 bound specifically to the identified responsive element (LRH-RE). LRH-1 augmented PPAR-gamma-induced transactivation of adiponectin promoter, and point mutation of the LRH-RE significantly decreased the basal and thiazolidinedione-induced activities of adiponectin promoter. Our results indicate that PPAR-gamma and LRH-1 play significant roles in the transcriptional activation of adiponectin gene via the PPRE and the LRH-RE in its promoter.