Instituto de Biomedicina de Valencia (Consejo Superior de Investigaciones Científicas), Valencia, Spain.
J Biol Chem. 2010 Apr 16;285(16):11765-74. doi: 10.1074/jbc.M109.067447. Epub 2010 Feb 9.
Insulin-induced gene 2 (INSIG2) and its homolog INSIG1 encode closely related endoplasmic reticulum proteins that regulate the proteolytic activation of sterol regulatory element-binding proteins, transcription factors that activate the synthesis of cholesterol and fatty acids in animal cells. Several studies have been carried out to identify INSIG2 genetic variants associated with metabolic diseases. However, few data have been published regarding the regulation of INSIG2 gene expression. Two Insig2 transcripts have been described in rodents through the use of different promoters that produce different noncoding first exons that splice into a common second exon. Herein we report the cloning and characterization of the human INSIG2 promoter and the detection of an INSIG2-specific transcript homologous to the Insig2b mouse variant in human liver. Deletion analyses on 3 kb of 5'-flanking DNA of the human INSIG2 gene revealed the functional importance of a 350-bp region upstream of the transcription start site. Mutated analyses, chromatin immunoprecipitation assays, and RNA interference analyses unveiled the significance of an Ets-consensus motif in the proximal region and the interaction of the Ets family member SAP1a (serum response factor (SRF) accessory protein-1a) with this region of the human INSIG2 promoter. Moreover, our findings suggest that insulin activated the human INSIG2 promoter in a process mediated by phosphorylated SAP1a. Overall, these results map the functional elements in the human INSIG2 promoter sequence and suggest an unexpected regulation of INSIG2 gene expression in human liver.
胰岛素诱导基因 2（INSIG2）及其同源物 INSIG1 编码密切相关的内质网蛋白，调节固醇调节元件结合蛋白的蛋白水解激活，固醇调节元件结合蛋白是激活动物细胞胆固醇和脂肪酸合成的转录因子。已经进行了几项研究来鉴定与代谢疾病相关的 INSIG2 遗传变异。然而，关于 INSIG2 基因表达的调控，发表的数据很少。通过使用不同的启动子，在啮齿动物中已经描述了两种 Insig2 转录物，这些启动子产生不同的非编码第一个外显子，拼接成一个共同的第二个外显子。在此，我们报告了人 INSIG2 启动子的克隆和特征，并在人肝中检测到与 Insig2b 小鼠变体同源的 INSIG2 特异性转录本。对人 INSIG2 基因 3'端 5'-侧翼 DNA 的 3kb 缺失分析显示，转录起始位点上游 350bp 区域的功能重要性。突变分析、染色质免疫沉淀分析和 RNA 干扰分析揭示了近端区域 Ets 一致基序和 Ets 家族成员 SAP1a（血清反应因子（SRF）辅助蛋白-1a）与该区域的相互作用在人 INSIG2 启动子中的重要性。此外，我们的研究结果表明，胰岛素通过磷酸化 SAP1a 介导的过程激活了人 INSIG2 启动子。总之，这些结果确定了人 INSIG2 启动子序列中的功能元件，并提示人肝中 INSIG2 基因表达的意外调控。
