Suppression of the Pancreatic Duodenal Homeodomain Transcription Factor-1 (Pdx-1) Promoter by Sterol Regulatory Element-binding Protein-1c (SREBP-1c)
Suppression of the Pancreatic Duodenal Homeodomain Transcription Factor-1 (Pdx-1) Promoter by Sterol Regulatory Element-binding Protein-1c (SREBP-1c)
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DOI：
10.1074/jbc.m110.186221
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发表时间：
2011-08-12
影响因子：
4.8
通讯作者：
Shimano, Hitoshi
中科院分区：
文献类型：
--
作者：
Amemiya-Kudo, Michiyo;Oka, Junko;Shimano, Hitoshi
β细胞中固醇调节元件结合蛋白-1c（SREBP-1c）的过表达可导致胰岛素分泌受损和β细胞功能障碍，并与胰腺十二指肠同源结构域转录因子-1（PDX-1）的体外和体内表达减少相关。为了确定负责这种效应的分子机制，在β细胞和非β细胞系中分析了小鼠Pdx-1基因启动子（2.7 kb）。尽管没有明显的固醇调节元件结合蛋白结合位点，但Pdx-1启动子在β细胞中以剂量依赖性方式被SREBP-1c抑制。PDX-1激活了自己的启动子。近端区域的E-box（-104/-99 bp）被广泛表达的上游刺激因子（USF）占据，通过直接PDX-1.USF结合对PDX-1阳性自身调节环至关重要。这种正反馈激活是非β细胞中SREBP-1c抑制启动子的先决条件。SREBP-1c和PDX-1分别通过碱性螺旋-环-螺旋和同源框结构域直接相互作用。这种强大的SREBP-1c.PDX-1复合物干扰PDX-1.USF的形成并抑制PDX-1辅激活因子的募集。SREBP-1c还抑制PDX-1与Pdx-1启动子远端增强子区域中先前描述的PDX-1结合位点（-2721/-2646 bp）的结合。通过9-顺式维甲酸和22-羟基胆固醇激活肝脏X受体和类维生素A X受体，内源性上调INS-1细胞中的SREBP-1c，抑制PDX-1 mRNA和蛋白表达。相反，SREBP-1c RNAi恢复了Pdx-1 mRNA和蛋白水平。通过这些多种机制，SREBP-1c在脂毒性状态下诱导时，抑制PDX-1表达，从而抑制胰岛素表达和β细胞功能障碍。
Overexpression of sterol regulatory element-binding protein-1c (SREBP-1c) in beta cells causes impaired insulin secretion and beta cell dysfunction associated with diminished pancreatic duodenal homeodomain transcription factor-1 (PDX-1) expression in vitro and in vivo. To identify the molecular mechanism responsible for this effect, the mouse Pdx-1 gene promoter (2.7 kb) was analyzed in beta cell and non-beta cell lines. Despite no apparent sterol regulatory element-binding protein-binding sites, the Pdx-1 promoter was suppressed by SREBP-1c in beta cells in a dose-dependent manner. PDX-1 activated its own promoter. The E-box (-104/-99 bp) in the proximal region, occupied by ubiquitously expressed upstream stimulatory factors (USFs), was crucial for the PDX-1-positive autoregulatory loop through direct PDX-1.USF binding. This positive feedback activation was a prerequisite for SREBP-1c suppression of the promoter in non-beta cells. SREBP-1c and PDX-1 directly interact through basic helix-loop-helix and homeobox domains, respectively. This robust SREBP-1c.PDX-1 complex interferes with PDX-1.USF formation and inhibits the recruitment of PDX-1 coactivators. SREBP-1c also inhibits PDX-1 binding to the previously described PDX-1-binding site (-2721/-2646 bp) in the distal enhancer region of the Pdx-1 promoter. Endogenous up-regulation of SREBP-1c in INS-1 cells through the activation of liver X receptor and retinoid X receptor by 9-cis-retinoic acid and 22-hydroxycholesterol inhibited PDX-1 mRNA and protein expression. Conversely, SREBP-1c RNAi restored Pdx-1 mRNA and protein levels. Through these multiple mechanisms, SREBP-1c, when induced in a lipotoxic state, repressed PDX-1 expression contributing to the inhibition of insulin expression and beta cell dysfunction.