Department of Geriatrics, Geriatric Research, Education, and Clinical Center, South Texas Veterans Healthcare System, San Antonio, TX 78229, USA.
Carcinogenesis. 2010 Nov;31(11):2022-30. doi: 10.1093/carcin/bgq189. Epub 2010 Sep 13.
Tuberin (protein encodes by tuberous sclerosis complex 2, Tsc2) deficiency is associated with the decrease in the DNA repair enzyme 8-oxoG-DNA glycosylase (OGG1) in tumour kidney of tuberous sclerosis complex (TSC) patients. The purpose of this study was to elucidate the mechanisms by which tuberin regulates OGG1. The partial deficiency in tuberin expression that occurs in the renal proximal tubular cells and kidney cortex of the Eker rat is associated with decreased activator protein 4 (AP4) and OGG1 expression. A complete deficiency in tuberin is associated with loss of AP4 and OGG1 expression in kidney tumour from Eker rats and the accumulation of significant levels of 8-oxo-deoxyguanosine. Knockdown of tuberin expression in human renal epithelial cells (HEK293) with small interfering RNA (siRNA) also resulted in a marked decrease in the expression of AP4 and OGG1. In contrast, overexpression of tuberin in HEK293 cells increased the expression of AP4 and OGG1 proteins. Downregulation of AP4 expression using siRNA resulted in a significant decrease in the protein expression of OGG1. Immunoprecipitation studies show that AP4 is associated with tuberin in cells. Gel shift analysis and chromatin immunoprecipitation identified the transcription factor AP4 as a positive regulator of the OGG1 promoter. AP4 DNA-binding activity is significantly reduced in Tsc2(-/-) as compared with Tsc2(+/+) cells. Transcriptional activity of the OGG1 promoter is also decreased in tuberin-null cells compared with wild-type cells. These data indicate a novel role for tuberin in the regulation of OGG1 through the transcription factor AP4. This regulation may be important in the pathogenesis of kidney tumours in patients with TSC disease.
结节性硬化症患者的肿瘤肾脏中，抑瘤蛋白（由结节性硬化症复合物 2，Tsc2 编码的蛋白）缺乏与 DNA 修复酶 8-氧鸟嘌呤-DNA 糖基化酶（OGG1）的减少有关。本研究旨在阐明抑瘤蛋白调节 OGG1 的机制。Eker 大鼠的肾近端小管细胞和肾皮质中发生的抑瘤蛋白表达部分缺乏与激活蛋白 4（AP4）和 OGG1 表达减少有关。抑瘤蛋白完全缺乏与 Eker 大鼠肾脏肿瘤中 AP4 和 OGG1 表达的丧失以及 8-氧脱氧鸟苷的大量积累有关。用小干扰 RNA（siRNA）在人肾上皮细胞（HEK293）中敲低抑瘤蛋白表达也导致 AP4 和 OGG1 的表达明显下降。相比之下，HEK293 细胞中抑瘤蛋白的过表达增加了 AP4 和 OGG1 蛋白的表达。用 siRNA 下调 AP4 表达导致 OGG1 蛋白表达显著减少。免疫沉淀研究表明，AP4 与细胞中的抑瘤蛋白相关。凝胶移位分析和染色质免疫沉淀鉴定出转录因子 AP4 是 OGG1 启动子的正调节因子。与 Tsc2(+/+) 细胞相比，Tsc2(-/-) 细胞中的 AP4 DNA 结合活性显著降低。与野生型细胞相比，抑瘤蛋白缺失细胞中 OGG1 启动子的转录活性也降低。这些数据表明，抑瘤蛋白通过转录因子 AP4 对 OGG1 进行调节，这可能在 TSC 患者的肾脏肿瘤发病机制中很重要。
