Sekido Takashi, Nishio Shin-Ichi, Ohkubo Yohsuke, Sekido Keiko, Kitahara Junichiro, Miyamoto Takahide, Komatsu Mitsuhisa
Division of Diabetes, Endocrinology and Metabolism, Department of Internal Medicine, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto, 390-8621, Japan.
Miyamoto Clinic, Matsumoto, 390-0841, Japan.
In Vitro Cell Dev Biol Anim. 2019 Apr;55(4):226-236. doi: 10.1007/s11626-019-00328-5. Epub 2019 Feb 21.
The mechanism whereby 17β-estradiol (E2) mediates insulin gene transcription has not been fully elucidated. In this study, exposure of hamster insulinoma (HIT-T15) cells to 5 × 10 to 1 × 10 M E2 led to a concentration-dependent decrease of insulin mRNA levels. Transient expression of the estrogen receptor (ER) in HIT-T15 cells revealed that estrogen receptor α (ERα) repressed transcription of the rat insulin II promoter in both ligand-dependent and ligand-independent manners. The N-terminal A/B domain of ERα was not required for either activity. However, the repression was absent with mutated ER lacking the DNA-binding domain. Moreover, introducing mutations in the D-box and P-box of the zinc finger of ER (C227S, C202L) also abolished the repression. Deletion of the insulin promoter region revealed that nucleotide positions - 238 to - 144 (relative to the transcriptional start site) were needed for ER repression of the rat insulin II gene. PDX1- and BETA2-binding sites were required for the repression, but an estrogen response element-like sequence or an AP1 site in the promoter was not involved. In conclusion, we found that estrogen repressed insulin mRNA expression in a beta cell line. In addition, the ER suppressed insulin gene transcription in a ligand-independent matter. These observations suggest ER may regulate insulin transcription by indirect genomic signaling.
17β-雌二醇（E2）介导胰岛素基因转录的机制尚未完全阐明。在本研究中，将仓鼠胰岛素瘤（HIT-T15）细胞暴露于5×10至1×10 M的E2中，导致胰岛素mRNA水平呈浓度依赖性下降。在HIT-T15细胞中瞬时表达雌激素受体（ER）表明，雌激素受体α（ERα）以配体依赖性和配体非依赖性方式抑制大鼠胰岛素II启动子的转录。ERα的N端A/B结构域对任何一种活性都不是必需的。然而，缺乏DNA结合结构域的突变型ER则不存在这种抑制作用。此外，在ER锌指的D框和P框中引入突变（C227S、C202L）也消除了这种抑制作用。胰岛素启动子区域的缺失表明，大鼠胰岛素II基因的ER抑制需要核苷酸位置-238至-144（相对于转录起始位点）。抑制作用需要PDX1和BETA2结合位点，但启动子中的雌激素反应元件样序列或AP1位点不参与其中。总之，我们发现雌激素在β细胞系中抑制胰岛素mRNA表达。此外，ER以配体非依赖性方式抑制胰岛素基因转录。这些观察结果表明，ER可能通过间接基因组信号传导调节胰岛素转录。
