Bagui Tapan K, Cui Dongming, Roy Sangita, Mohapatra Subhra, Shor Audrey C, Ma Le, Pledger W Jackson
Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, FL 33612, USA.
Cell Cycle. 2009 Jan 1;8(1):115-24. doi: 10.4161/cc.8.1.7527.
How mitogens reduce the abundance of the cell cycle inhibitor p27(Kip1) is an important question, and regulation of p27(Kip1) translation and turnover has been described. Here we show that platelet-derived growth factor (PDGF) reduces the activity of the p27(Kip1) promoter and the abundance of the p27(Kip1) transcript in density-arrested mouse fibroblasts. Inhibition of p27(Kip1) gene expression by PDGF required protein synthesis and histone deacetylase activity but not Akt or ERK activity. PDGF increased the expression of c-Myc in the absence but not presence of a histone deacetylase inhibitor, and c-Myc inhibited p27(Kip1) promoter activity when ectopically expressed in fibroblasts. c-Myc targeted the same region of the p27(Kip1) promoter as did PDGF (deletion analysis) and interacted with this region in vivo (chromatin immunoprecipitation assay). Collectively, these findings suggest that c-Myc mediates the inhibitory effects of PDGF on the p27(Kip1) promoter. We also demonstrate reductions in p27(Kip1) mRNA abundance in primary splenocytes exposed to concanavalin A and in T cells exposed to interleukin-2 (IL-2). In contrast to PDGF in fibroblasts, IL-2 required Akt activity for maximal reductions in p27(Kip1) promoter activity and mRNA abundance in T cells. Thus, mitogens repress p27(Kip1) gene transcription in multiple systems and by multiple mechanisms.
有丝分裂原如何降低细胞周期抑制剂p27（Kip1）的丰度是一个重要问题，并且p27（Kip1）的翻译和周转调控已有相关描述。在此我们表明，血小板衍生生长因子（PDGF）降低了处于密度抑制状态的小鼠成纤维细胞中p27（Kip1）启动子的活性以及p27（Kip1）转录本的丰度。PDGF对p27（Kip1）基因表达的抑制需要蛋白质合成和组蛋白去乙酰化酶活性，但不需要Akt或ERK活性。在不存在组蛋白去乙酰化酶抑制剂的情况下，PDGF增加了c-Myc的表达，而当在成纤维细胞中异位表达时，c-Myc抑制p27（Kip1）启动子活性。c-Myc靶向p27（Kip1）启动子的区域与PDGF相同（缺失分析），并且在体内与该区域相互作用（染色质免疫沉淀测定）。总的来说，这些发现表明c-Myc介导了PDGF对p27（Kip1）启动子的抑制作用。我们还证明，暴露于伴刀豆球蛋白A的原代脾细胞以及暴露于白细胞介素-2（IL-2）的T细胞中p27（Kip1）mRNA丰度降低。与成纤维细胞中的PDGF不同，IL-2在T细胞中最大程度降低p27（Kip1）启动子活性和mRNA丰度需要Akt活性。因此，有丝分裂原在多个系统中通过多种机制抑制p27（Kip1）基因转录。
