Kramps Christoph, Strieder Verena, Sapetschnig Alexandra, Suske Guntram, Lutz Werner
Institute of Molecular Biology and Tumor Research, 35033 Marburg, Germany.
J Biol Chem. 2004 Feb 13;279(7):5110-7. doi: 10.1074/jbc.M304758200. Epub 2003 Nov 26.
Amplification of the MYCN gene, resulting in overexpression of MYCN, distinguishes a subset of neuroblastomas with poor prognosis. We recently identified MYCN as a target gene of the E2F transcription factors. Here we show that Sp1 and Sp3 cooperate with E2F-1 to activate the MYCN promoter. However, in a neuroblastoma cell line that does not express MYCN, overexpression of E2F-1 was not sufficient to activate the MYCN promoter even in the presence of trichostatin A and 5-aza-cytidine. This was because of a failure of E2F-1 to bind to the MYCN promoter in these cells, although access of E2F-1 to the inactive MYCN promoter was not blocked by a nucleosome. Differences in nucleosomal organization of the MYCN promoter in different cell lines did not correlate with gene activation per se but with the switch from basal to activated transcription. Binding of E2F and Sp1/Sp3 to the MYCN promoter in vivo correlated with acetylation of histones H3 and H4 and recruitment of RNA polymerase II and the protein acetyltransferase Tip60 but not with nucleosome remodeling. Our results define distinct chromatin states of the MYCN promoter, indicate that factors in addition to E2F and Sp1/Sp3 are required to activate MYCN in neuroblastomas, and provide evidence for a novel mechanism of controlling access of E2F to selected target genes.
MYCN基因的扩增导致MYCN的过表达，这区分出了一部分预后不良的神经母细胞瘤。我们最近将MYCN鉴定为E2F转录因子的一个靶基因。在此我们表明，Sp1和Sp3与E2F-1协同作用以激活MYCN启动子。然而，在一个不表达MYCN的神经母细胞瘤细胞系中，即使存在曲古抑菌素A和5-氮杂胞苷，E2F-1的过表达也不足以激活MYCN启动子。这是因为在这些细胞中E2F-1无法与MYCN启动子结合，尽管E2F-1接近无活性的MYCN启动子并未被核小体阻断。不同细胞系中MYCN启动子核小体组织的差异本身与基因激活并无关联，而是与从基础转录到激活转录的转变有关。E2F和Sp1/Sp3在体内与MYCN启动子的结合与组蛋白H3和H4的乙酰化以及RNA聚合酶II和蛋白质乙酰转移酶Tip60的募集相关，但与核小体重塑无关。我们的结果定义了MYCN启动子不同的染色质状态，表明在神经母细胞瘤中激活MYCN除了需要E2F和Sp1/Sp3外还需要其他因子，并为控制E2F接近选定靶基因的新机制提供了证据。
