RESUMEN
Adiponectin is exclusively expressed in differentiated adipocytes and plays an important role in regulating energy homeostasis, including the glucose and lipid metabolism associated with increased insulin sensitivity. However, the control of adiponectin gene expression in adipocytes is poorly understood. We show here that levels of adiponectin mRNA and protein are reduced in the white adipose tissue of ob/ob and db/db mice and that there is a concomitant reduction of the adipocyte determination- and differentiation-dependent factor 1 (ADD1)/sterol regulatory element-binding protein 1c (SREBP1c) transcription factor. To determine whether ADD1/SREBP1c regulates adiponectin gene expression, we isolated and characterized the mouse adiponectin promoter. Analysis of the adiponectin promoter revealed putative binding sites for the adipogenic transcription factors ADD1/SREBP1c, peroxisomal proliferator-activated receptor gamma and CCAAT enhancer-binding proteins. DNase I footprinting and chromatin immunoprecipitation analyses revealed that ADD1/SREBP1c binds in vitro and in vivo to the proximal promoter containing sterol regulatory element (SRE) motifs. A luciferase reporter containing the promoter was transactivated by ADD1/SREBP1c, and introduction of SRE mutations into the construct abolished transactivation. Adenoviral overexpression of ADD1/SREBP1c also elevated adiponectin mRNA and protein levels in 3T3-L1 adipocytes. Furthermore, insulin stimulated adiponectin mRNA expression in adipocytes and augmented transactivation of the adiponectin promoter by ADD1/SREBP1c. Taken together, these data indicate that ADD1/SREBP1c controls adiponectin gene expression in differentiated adipocytes.
Asunto(s)
Adipocitos/metabolismo , Proteínas Potenciadoras de Unión a CCAAT/fisiología , Proteínas de Unión al ADN/fisiología , Regulación de la Expresión Génica , Péptidos y Proteínas de Señalización Intercelular , Biosíntesis de Proteínas , Células 3T3-L1 , Adenoviridae/genética , Adiponectina , Secuencias de Aminoácidos , Animales , Sitios de Unión , Northern Blotting , Western Blotting , Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Diferenciación Celular , Línea Celular , Cromatina/metabolismo , Clonación Molecular , Proteínas de Unión al ADN/metabolismo , Desoxirribonucleasa I/metabolismo , Luciferasas/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Obesos , Ratones Transgénicos , Modelos Genéticos , Pruebas de Precipitina , Regiones Promotoras Genéticas , Unión Proteica , Proteínas/metabolismo , ARN Mensajero/metabolismo , Ratas , Receptores Citoplasmáticos y Nucleares/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Proteína 1 de Unión a los Elementos Reguladores de Esteroles , Factores de Transcripción/metabolismo , TransfecciónRESUMEN
Recent studies with murine models propose that resistin would be a possible mediator to link between obesity and insulin resistance. Although it has been reported that resistin is highly expressed and secreted by adipocytes, transcription factors that are involved in resistin gene expression have not been well characterized. To investigate the molecular mechanisms of resistin gene expression, we cloned and characterized the human resistin promoter. Sequence analysis of the resistin promoter revealed several putative binding sites for adipogenic transcription factors including adipocyte determination- and differentiation-dependent factor 1 (ADD1)/sterol regulatory element binding protein 1c (SREBP1c) and CCAAT enhancer binding protein-alpha (C/EBP alpha). EMSA and chromatin immunoprecipitation assays demonstrated that ADD1/SREBP1c binds to the human resistin promoter in vitro and in vivo. Expression of ADD1/SREBP1c transactivated the luciferase reporter gene activity, the promoter region of which contains a human resistin promoter in a sterol regulatory element (SRE)-dependent manner. Furthermore, ectopic expression of ADD1/SREBP1c by adenovirus significantly increased the expression of resistin mRNA in adipocytes. Human resistin promoter was also activated by C/EBP alpha expression, although ectopic expression of both transcription factors did not show any synergistic effects on the activation of resistin promoter. Together, these data suggest that ADD1/SREBP1c and C/EBP alpha may play discrete roles in the regulation of the resistin gene expression.