RESUMEN
Fatty acid synthase (Fasn) is a key component of energy metabolism that is dynamically induced by food intake. Although extensive studies have revealed a number of transcription factors involved in the fasting/refeeding transition of Fasn expression in hepatocytes, much less evidence is available for adipocytes. Using the in vivo Ad-luc analytical system, we identified the inverted CCAAT element (ICE) around -100 nucleotides in the Fasn promoter as a critical cis-element for the refeeding response in adipocytes. Electrophoretic mobility shift assays and chromatin immunoprecipitation show that nuclear factor Y (NF-Y) binds to ICE specifically in refeeding states. Notably, the NF-Y binding to ICE is differently regulated between adipocytes and hepatocytes. These findings provide insights into the specific mechanisms controlling energy metabolism in adipocytes.
Asunto(s)
Adipocitos/metabolismo , Factor de Unión a CCAAT/metabolismo , Ácido Graso Sintasas/metabolismo , Conducta Alimentaria , Células 3T3-L1 , Adenoviridae/genética , Adipocitos/citología , Tejido Adiposo Blanco/metabolismo , Animales , Secuencia de Bases , Factor de Unión a CCAAT/genética , Inmunoprecipitación de Cromatina , Ensayo de Cambio de Movilidad Electroforética , Ácido Graso Sintasas/genética , Regulación de la Expresión Génica , Immunoblotting , Hígado/metabolismo , Luciferasas/genética , Luciferasas/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos ICR , Mutación , Regiones Promotoras Genéticas/genética , Unión Proteica , Elementos de Respuesta/genética , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
Hepatic lipogenesis is nutritionally regulated (i.e., downregulated during fasting and upregulated during the postprandial state) as an adaptation to the nutritional environment. While alterations in the expression level of the transcription factor SREBP-1c are known to be critical for nutritionally regulated lipogenesis, upstream mechanisms governing Srebf1 expression remain unclear. Here, we show that the fasting-induced transcription factor KLF15, a key regulator of gluconeogenesis, forms a complex with LXR/RXR, specifically on the Srebf1 promoter. This complex recruits the corepressor RIP140 instead of the coactivator SRC1, resulting in reduced Srebf1 and thus downstream lipogenic enzyme expression during the early and euglycemic period of fasting prior to hypoglycemia and PKA activation. Through this mechanism, KLF15 overexpression specifically ameliorates hypertriglyceridemia without affecting LXR-mediated cholesterol metabolism. These findings reveal a key molecular link between glucose and lipid metabolism and have therapeutic implications for the treatment of hyperlipidemia.
Asunto(s)
Proteínas de Unión al ADN/genética , Genoma , Gluconeogénesis/genética , Hepatocitos/metabolismo , Lipogénesis/genética , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/genética , Factores de Transcripción/genética , Animales , Proteínas Quinasas Dependientes de AMP Cíclico/genética , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Proteínas de Unión al ADN/metabolismo , Ayuno , Genes Reporteros , Hepatocitos/citología , Factores de Transcripción de Tipo Kruppel , Hígado/citología , Hígado/metabolismo , Receptores X del Hígado/genética , Receptores X del Hígado/metabolismo , Luciferasas/genética , Luciferasas/metabolismo , Masculino , Ratones , Ratones Endogámicos ICR , Ratones Noqueados , Co-Represor 1 de Receptor Nuclear/genética , Co-Represor 1 de Receptor Nuclear/metabolismo , Cultivo Primario de Células , Regiones Promotoras Genéticas , Unión Proteica , Receptores X Retinoide/genética , Receptores X Retinoide/metabolismo , Transducción de Señal , Proteína 1 de Unión a los Elementos Reguladores de Esteroles/metabolismo , Factores de Transcripción/metabolismo , Activación TranscripcionalRESUMEN
Fatty acid elongase 5 (ELOVL5) is an enzyme involved in the synthesis of polyunsaturated fatty acids. Sterol Regulatory Element-binding Protein (SREBP)-1 activates ELOVL5 and increases polyunsaturated fatty acid synthesis, which in turn negatively affects SREBP-1 expression. Thus, ELOVL5 has been established as an SREBP-1 target gene and an important component of the negative feedback loop of de novo lipogenesis. However, the human ELOVL5 promoter/enhancer has not been fully analyzed and the location of SREBP biding sites around the ELOVL5 gene has yet to be defined. Here we performed a detailed promoter/enhancer analysis of human ELOVL5 gene, and identified two new SREBP binding sites, one in the 10 kb upstream region and one in the exon 1. These two SRE motifs are conserved among mammals and the mechanism found in the present study by which SREBP activates ELOVL5 is considered to be common in mammals. Through these findings, we clarified the molecular mechanism how SREBP activates ELOVL5, an important regulator of de novo lipogenesis.
