Hmadcha A, Bedoya F J, Sobrino F, Pintado E
Departamento de Bioquímica Médica y Biología Molecular, Facultad de Medicina y Hospital Universitario Virgen Macarena, Universidad de Sevilla, 41009 Sevilla, Spain.
J Exp Med. 1999 Dec 6;190(11):1595-604. doi: 10.1084/jem.190.11.1595.
Interleukin (IL)-1beta is a pleiotropic cytokine implicated in a variety of activities, including damage of insulin-producing cells, brain injury, or neuromodulatory responses. Many of these effects are mediated by nitric oxide (NO) produced by the induction of NO synthase (iNOS) expression. We report here that IL-1beta provokes a marked repression of genes, such as fragile X mental retardation 1 (FMR1) and hypoxanthine phosphoribosyltransferase (HPRT), having a CpG island in their promoter region. This effect can be fully prevented by iNOS inhibitors and is dependent on DNA methylation. NO donors also cause FMR1 and HPRT gene silencing. NO-induced methylation of FMR1 CpG island can be reverted by demethylating agents which, in turn, produce the recovery of gene expression. The effects of IL-1beta and NO appear to be exerted through activation of DNA methyltransferase (DNA MeTase). Although exposure of the cells to NO does not increase DNA MeTase gene expression, the activity of the enzyme selectively increases when NO is applied directly on a nuclear protein extract. These findings reveal a previously unknown effect of IL-1beta and NO on gene expression, and demonstrate a novel pathway for gene silencing based on activation of DNA MeTase by NO and acute modification of CpG island methylation.
白细胞介素（IL）-1β是一种多效性细胞因子，参与多种活动，包括胰岛素生成细胞损伤、脑损伤或神经调节反应。其中许多效应是由诱导型一氧化氮合酶（iNOS）表达产生的一氧化氮（NO）介导的。我们在此报告，IL-1β可显著抑制启动子区域含有CpG岛的基因，如脆性X智力低下1基因（FMR1）和次黄嘌呤磷酸核糖转移酶基因（HPRT）。iNOS抑制剂可完全阻止这种效应，且该效应依赖于DNA甲基化。NO供体也会导致FMR1和HPRT基因沉默。去甲基化剂可逆转NO诱导的FMR1 CpG岛甲基化，进而使基因表达恢复。IL-1β和NO的作用似乎是通过激活DNA甲基转移酶（DNA MeTase）来实现的。虽然细胞暴露于NO不会增加DNA MeTase基因表达，但当直接将NO应用于核蛋白提取物时，该酶的活性会选择性增加。这些发现揭示了IL-1β和NO对基因表达的一种前所未知的作用，并证明了基于NO激活DNA MeTase和CpG岛甲基化的急性修饰而产生的一种新的基因沉默途径。
