RESUMEN
Cholesterol 7alpha-hydroxylase (CYP7A1) regulates the balance between cholesterol supply and metabolism by catalyzing the rate-limiting step of bile acid biosynthesis. The transcriptional activity of CYP7A1 is tightly controlled by various nuclear receptors. A forkhead transcription factor O1 (FOXO1) plays a critical role in metabolism, and insulin inactivates FOXO1 through Akt-dependent phosphorylation and nuclear exclusion. We investigated the role of insulin-Akt-FOXO1 signaling pathway in CYP7A1 transcriptional regulation since we found putative insulin-response elements, FOXO1 binding sequences, in both rat and human CYP7A1 promoters. However, ectopic expression of FOXO1 increased the rat CYP7A1-, but mildly reduced human CYP7A1-promoter activities in a dose-dependent manner. Similarly to bile acids, insulin treatment increased small heterodimer partner (SHP) mRNA rapidly and transiently, leading to the suppression of CYP7A1 transcription in both human and rodents. Chromatin immunoprecipitation showed that FOXO1 directly bound to rat CYP1A1 promoter in the absence of insulin. FOXO1 binding to the rat promoter was diminished by insulin treatment as well as by expression of SHP. Our results suggest that the stimulation of insulin- signaling pathway of Akt-FOXO1 and SHP expression may regulate cholesterol/bile acid metabolisms in liver, linking carbohydrate and cholesterol metabolic pathways. A prolonged exposure of insulin in hyperinsulinemic insulin resistance or diabetic status represses CYP7A1 transcription and bile acid biosynthesis through SHP induction and FOXO1 inactivation, leading to impairment of the hepatic cholesterol/bile acid metabolisms.
Asunto(s)
Animales , Humanos , Ratones , Ratas , Ácidos y Sales Biliares/metabolismo , Colesterol/metabolismo , Colesterol 7-alfa-Hidroxilasa/genética , Factores de Transcripción Forkhead/genética , Regulación de la Expresión Génica/efectos de los fármacos , Glucosa/metabolismo , Células Hep G2 , Insulina/farmacología , Metabolismo de los Lípidos/efectos de los fármacos , Hígado/metabolismo , Ratones Endogámicos C57BL , Mutagénesis Sitio-Dirigida , Proteínas del Tejido Nervioso/genética , Unión Proteica/efectos de los fármacos , Proteínas Proto-Oncogénicas c-akt/metabolismo , Receptores Citoplasmáticos y Nucleares/genética , Eliminación de Secuencia/genética , Transducción de Señal/efectos de los fármacos , Activación Transcripcional/efectos de los fármacosRESUMEN
Cholesterol 7alpha-hydroxylase (CYP7A1) regulates the balance between cholesterol supply and metabolism by catalyzing the rate-limiting step of bile acid biosynthesis. The transcriptional activity of CYP7A1 is tightly controlled by various nuclear receptors. A forkhead transcription factor O1 (FOXO1) plays a critical role in metabolism, and insulin inactivates FOXO1 through Akt-dependent phosphorylation and nuclear exclusion. We investigated the role of insulin-Akt-FOXO1 signaling pathway in CYP7A1 transcriptional regulation since we found putative insulin-response elements, FOXO1 binding sequences, in both rat and human CYP7A1 promoters. However, ectopic expression of FOXO1 increased the rat CYP7A1-, but mildly reduced human CYP7A1-promoter activities in a dose-dependent manner. Similarly to bile acids, insulin treatment increased small heterodimer partner (SHP) mRNA rapidly and transiently, leading to the suppression of CYP7A1 transcription in both human and rodents. Chromatin immunoprecipitation showed that FOXO1 directly bound to rat CYP1A1 promoter in the absence of insulin. FOXO1 binding to the rat promoter was diminished by insulin treatment as well as by expression of SHP. Our results suggest that the stimulation of insulin- signaling pathway of Akt-FOXO1 and SHP expression may regulate cholesterol/bile acid metabolisms in liver, linking carbohydrate and cholesterol metabolic pathways. A prolonged exposure of insulin in hyperinsulinemic insulin resistance or diabetic status represses CYP7A1 transcription and bile acid biosynthesis through SHP induction and FOXO1 inactivation, leading to impairment of the hepatic cholesterol/bile acid metabolisms.
Asunto(s)
Animales , Humanos , Ratones , Ratas , Ácidos y Sales Biliares/metabolismo , Colesterol/metabolismo , Colesterol 7-alfa-Hidroxilasa/genética , Factores de Transcripción Forkhead/genética , Regulación de la Expresión Génica/efectos de los fármacos , Glucosa/metabolismo , Células Hep G2 , Insulina/farmacología , Metabolismo de los Lípidos/efectos de los fármacos , Hígado/metabolismo , Ratones Endogámicos C57BL , Mutagénesis Sitio-Dirigida , Proteínas del Tejido Nervioso/genética , Unión Proteica/efectos de los fármacos , Proteínas Proto-Oncogénicas c-akt/metabolismo , Receptores Citoplasmáticos y Nucleares/genética , Eliminación de Secuencia/genética , Transducción de Señal/efectos de los fármacos , Activación Transcripcional/efectos de los fármacosRESUMEN
Angiotensin II is a major effector molecule in the development of cardiovascular disease. In vascular smooth muscle cells (VSMCs), angiotensin II promotes cellular proliferation and extracellular matrix accumulation through the upregulation of plasminogen activator inhibitor-1 (PAI-1) expression. Previously, we demonstrated that small heterodimer partner (SHP) represses PAI-1 expression in the liver through the inhibition of TGF-beta signaling pathways. Here, we investigated whether SHP inhibited angiotensin II-stimulated PAI-1 expression in VSMCs. Adenovirus-mediated overexpression of SHP (Ad-SHP) in VSMCs inhibited angiotensin II- and TGF-beta-stimulated PAI-1 expression. Ad-SHP also inhibited angiotensin II-, TGF-beta- and Smad3-stimulated PAI-1 promoter activity, and angiotensin II-stimulated AP-1 activity. The level of PAI-1 expression was significantly higher in VSMCs of SHP-/- mice than wild type mice. Moreover, loss of SHP increased PAI-1 mRNA expression after angiotensin II treatment. These results suggest that SHP inhibits PAI-1 expression in VSMCs through the suppression of TGF-beta/Smad3 and AP-1 activity. Thus, agents that target the induction of SHP expression in VSMCs might help prevent the development and progression of atherosclerosis.
Asunto(s)
Animales , Humanos , Ratones , Ratas , Adenoviridae/genética , Angiotensina II/farmacología , Northern Blotting , Células Cultivadas , Ensayo de Cambio de Movilidad Electroforética , Vectores Genéticos/genética , Músculo Liso Vascular/citología , Miocitos del Músculo Liso/efectos de los fármacos , Inhibidor 1 de Activador Plasminogénico/genética , Regiones Promotoras Genéticas/genética , Receptores Citoplasmáticos y Nucleares/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Proteína smad3/genética , Factor de Crecimiento Transformador beta/farmacologíaRESUMEN
Small heterodimer partner (SHP) is an atypical member of nuclear receptor superfamily that lacks a DNA-binding domain. In previous study, we showed that SHP, c-jun, p65 of NF-kappaB subunits, and p21WAF1 expression was increased during monocytic differentiaton with the exposure of human leukemia cells to a differentiation agent, PMA. In this study, c-Jun and p65 were shown to mediate the transcriptional activation of the SHP promoter. In addition, SHP induced the cell cycle regulatory protein levels and cooperatively increased an induction of p21WAF1 expression with p65. Furthermore, SHP protected differentiated cells from etoposide-induced cellular apoptosis through the induction and cytoplasmic sequestration of p21WAF1. Complex formation between SHP and p21WAF1 was demonstrated by means of coimmunoprecipitation. These results suggest that SHP prolongs a cellular survival of differentiating monocytes through the transcriptional regulation of target genes of cell survival and differentiation.