FOXO1 represses peroxisome proliferator-activated receptor-γ1 and -γ2 gene promoters in primary adipocytes -: A novel paradigm to increase insulin sensitivity
FOXO1 represses peroxisome proliferator-activated receptor-γ1 and -γ2 gene promoters in primary adipocytes -: A novel paradigm to increase insulin sensitivity
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DOI：
10.1074/jbc.m600320200
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发表时间：
2006-07-21
影响因子：
4.8
通讯作者：
Karnieli, Eddy
中科院分区：
文献类型：
--
作者：
Armoni, Michal;Harel, Chava;Karnieli, Eddy
FOXO 1和过氧化物酶体增殖物激活受体-γ（PPAR-gamma）是调节胰岛素靶组织中葡萄糖代谢和胰岛素反应性的关键转录因子。我们已经表明，在原代大鼠脂肪细胞中，两种因子都调节胰岛素响应性GLUT 4基因的转录，并且在噻唑烷二酮结合后，从GLUT 4启动子上分离的PPAR γ 2上调GLUT 4基因表达，从而增加胰岛素敏感性（Armoni，M.，Kritz，N.，哈雷尔角，Bar-Yoseph，F.，陈洪，Quon，M. J.，Karnieli，E.（2003）J.Biol.Chem.278，30614-30623）。然而，调节PPAR γ基因转录的机制在很大程度上是未知的。我们研究了FOXO 1对原代大鼠脂肪细胞中人PPAR γ基因表达的影响，发现这两个基因都是内源性表达的。FOXO 1共表达剂量依赖性地抑制了来自PPAR γ 1或PPAR γ 2启动子报告基因的转录，抑制率为65%，而胰岛素（100 nM，20-24 h）部分或完全逆转了这种作用。磷酸化缺陷型FOXO 1突变体T24 A、S256 A、S319 A和T24 A/S256 A/S319 A在基础细胞或胰岛素刺激细胞中仍然抑制了PPAR γ 1启动子，并部分丧失了对PPAR γ 2启动子的作用。使用DNA结合缺陷型FOXO 1（H215 R）表明，该结构域对于FOXO 1抑制PPAR γ 2（而不是PPAR γ 1）启动子至关重要。进行性5 '-缺失和凝胶阻滞分析显示，这种抑制涉及FOXO 1与PPAR γ 2启动子的直接和特异性结合;染色质免疫沉淀分析证实这种结合发生在细胞中。我们提出了一种新的范例，以增加脂肪细胞中的胰岛素敏感性，其中FOXO 1抑制PPAR γ，后者是GLUT 4启动子的阻遏物，因此导致GLUT 4去阻遏/上调，从而增强细胞胰岛素敏感性。新发现的PPAR γ 2启动子上的FOXO 1结合位点可能作为2型糖尿病的治疗靶点。
FOXO1 and peroxisome proliferator-activated receptor-gamma (PPAR gamma) are crucial transcription factors that regulate glucose metabolism and insulin responsiveness in insulin target tissues. We have shown that, in primary rat adipocytes, both factors regulate transcription of the insulin-responsive GLUT4 gene and that PPAR gamma 2 detachment from the GLUT4 promoter upon thiazolidinedione binding up-regulates GLUT4 gene expression, thus increasing insulin sensitivity (Armoni, M., Kritz, N., Harel, C., Bar-Yoseph, F., Chen, H., Quon, M. J., and Karnieli, E. (2003) J. Biol. Chem. 278, 30614-30623). However, the mechanisms regulating PPAR gamma gene transcription are largely unknown. We studied the effects of FOXO1 on human PPAR gamma gene expression in primary rat adipocytes and found that both genes are endogenously expressed. FOXO1 coexpression dose-dependently repressed transcription from either the PPAR gamma 1 or PPAR gamma 2 promoter reporter by 65%, whereas insulin (100 nM, 20-24 h) either partially or completely reversed this effect. Phosphorylation-defective FOXO1 mutants T24A, S256A, S319A, and T24A/S256A/S319A still repressed the PPAR gamma 1 promoter and partially lost their effects on the PPAR gamma 2 promoter in either basal or insulin-stimulated cells. Use of DNA binding-defective FOXO1(H215R) indicated that this domain is crucial for FOXO1 repression of the PPAR gamma 2 (but not PPAR gamma 1) promoter. Progressive 5'-deletion and gel retardation analyses revealed that this repression involves direct and specific binding of FOXO1 to the PPAR gamma 2 promoter; chromatin immunoprecipitation analysis confirmed that this binding occurs in cellulo. We suggest a novel paradigm to increase insulin sensitivity in adipocytes in which FOXO1 repression of PPAR gamma, the latter being a repressor of the GLUT4 promoter, consequently leads to GLUT4 derepression/up-regulation, thus enhancing cellular insulin sensitivity. The newly identified FOXO1-binding site on the PPAR gamma 2 promoter may serve as a therapeutic target for type 2 diabetes.