Department of Metabolic Medicine, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, 565-0871 Suita, Japan.
J Biol Chem. 2013 Jul 26;288(30):21648-58. doi: 10.1074/jbc.M113.481424. Epub 2013 Jun 17.
The transcription factor MafA is a key regulator of insulin gene expression and maturation of islet β cells. Despite its importance, the regulatory mechanism of MafA gene expression is still unclear. To identify the transcriptional regulators of MafA, we examined various transcription factors, which are potentially involved in β cell differentiation. An adenovirus-mediated overexpression study clearly demonstrated that Onecut1 suppresses the promoter activity of MafA through the Foxa2-binding cis-element on the MafA enhancer region (named area A). However, ChIP analysis showed that Foxa2 but not Onecut1 could directly bind to area A. Furthermore, overexpression of Onecut1 inhibited the binding of Foxa2 onto area A upon ChIP analysis. Importantly, insertion of a mutation in the Foxa2-binding site of area A significantly decreased the promoter activity of MafA. These findings suggest that Onecut1 suppresses MafA gene expression through the Foxa2-binding site. In the mouse pancreas, MafA expression was first detected at the latest stage of β cell differentiation and was scarcely observed in Onecut1-positive cells during pancreas development. In addition, Onecut1 expression was significantly increased in the islets of diabetic db/db mice, whereas MafA expression was markedly decreased. The improved glucose levels of db/db mice with insulin injections significantly reduced Onecut1 expression and rescued the reduction of MafA expression. These in vivo experiments also suggest that Onecut1 is a negative regulator of MafA gene expression. This study implicates the novel role of Onecut1 in the control of normal β cell differentiation and its involvement in β cell dysfunction under diabetic conditions by suppressing MafA gene expression.
转录因子 MafA 是胰岛素基因表达和胰岛 β 细胞成熟的关键调节因子。尽管它很重要，但 MafA 基因表达的调节机制仍不清楚。为了鉴定 MafA 的转录调节因子，我们研究了各种潜在参与 β 细胞分化的转录因子。腺病毒介导的过表达研究清楚地表明，Onecut1 通过 MafA 增强子区域（命名为区域 A）上的 Foxa2 结合顺式元件抑制 MafA 的启动子活性。然而，ChIP 分析表明，Foxa2 而不是 Onecut1 可以直接结合到区域 A。此外，过表达 Onecut1 抑制了 ChIP 分析中 Foxa2 结合到区域 A 的结合。重要的是，在 Foxa2 结合位点插入突变显著降低了 MafA 的启动子活性。这些发现表明，Onecut1 通过 Foxa2 结合位点抑制 MafA 基因表达。在小鼠胰腺中，MafA 表达在 β 细胞分化的最晚阶段首次被检测到，并且在胰腺发育过程中在 Onecut1 阳性细胞中几乎观察不到。此外，在糖尿病 db/db 小鼠的胰岛中，Onecut1 表达显著增加，而 MafA 表达明显减少。用胰岛素注射治疗 db/db 小鼠可显著改善血糖水平，同时降低 Onecut1 表达并挽救 MafA 表达的降低。这些体内实验还表明，Onecut1 是 MafA 基因表达的负调节因子。这项研究暗示了 Onecut1 在正常 β 细胞分化的控制中的新作用及其在糖尿病条件下通过抑制 MafA 基因表达参与 β 细胞功能障碍的作用。
