Holmqvist Per-Henrik, Belikov Sergey, Zaret Kenneth S, Wrange Orjan
Department of Cell and Molecular Biology, The Medical Nobel Institute, Box 285, Karolinska Institutet, SE-17177 Stockholm, Sweden.
Exp Cell Res. 2005 Apr 1;304(2):593-603. doi: 10.1016/j.yexcr.2004.12.002. Epub 2004 Dec 30.
Novel binding sites for the forkhead transcription factor family member Forkhead box A (FoxA), previously referred to as Hepatocyte Nuclear Factor 3 (HNF3), were found within the mouse mammary tumor virus long terminal repeat (MMTV LTR). The effect of FoxA1 on MMTV LTR chromatin structure, and expression was evaluated in Xenopus laevis oocytes. Mutagenesis of either of the two main FoxA binding sites showed that the distal site, -232/-221, conferred FoxA1-dependent partial inhibition of glucocorticoid receptor (GR) driven MMTV transcription. The proximal FoxA binding segment consisted of two individual FoxA sites at -57/-46 and -45/-34, respectively, that mediated an increased basal MMTV transcription. FoxA1 binding altered the chromatin structure of both the inactive- and the hormone-activated MMTV LTR. Hydroxyl radical foot printing revealed FoxA1-mediated changes in the nucleosome arrangement. Micrococcal nuclease digestion showed the hormone-dependent sub-nucleosome complex, containing approximately 120 bp of DNA, to be expanded by FoxA1 binding to the proximal segment into a larger complex containing approximately 200 bp. The potential function of the FoxA1-mediated expression of the MMTV provirus for maintenance of expression in different tissues is discussed.
在小鼠乳腺肿瘤病毒长末端重复序列（MMTV LTR）中发现了叉头转录因子家族成员叉头框A（FoxA，以前称为肝细胞核因子3，即HNF3）的新结合位点。在非洲爪蟾卵母细胞中评估了FoxA1对MMTV LTR染色质结构和表达的影响。对两个主要FoxA结合位点中的任何一个进行诱变表明，远端位点-232/-221赋予了FoxA1依赖性的糖皮质激素受体（GR）驱动的MMTV转录的部分抑制作用。近端FoxA结合片段分别由位于-57/-46和-45/-34的两个单独的FoxA位点组成，它们介导了基础MMTV转录的增加。FoxA1结合改变了非活性和激素激活的MMTV LTR的染色质结构。羟基自由基足迹揭示了FoxA1介导的核小体排列变化。微球菌核酸酶消化表明，含有约120 bp DNA的激素依赖性亚核小体复合物通过FoxA1与近端片段结合而扩展为含有约200 bp的更大复合物。讨论了FoxA1介导的MMTV前病毒表达在不同组织中维持表达的潜在功能。
