Im Hogune, Grass Jeffrey A, Christensen Heather M, Perkins Andrew, Bresnick Emery H
Department of Pharmacology, Molecular and Cellular Pharmacology Program, University of Wisconsin Medical School, 383 Medical Science Center, 1300 University Avenue, Madison, Wisconsin 53706, USA.
Biochemistry. 2002 Dec 24;41(51):15152-60. doi: 10.1021/bi026786q.
The murine beta-globin locus in adult erythroid cells is characterized by a broad pattern of erythroid-specific histone acetylation. The embryonic beta-globin genes Ey and betaH1 are located in a approximately 30 kb central subdomain characterized by low-level histone acetylation, while the fetal/adult genes betamajor and betaminor and the upstream locus control region reside in hyperacetylated chromatin. Histone deacetylase (HDAC) inhibitors induce H4 acetylation at the Ey promoter [Forsberg, E. C., Downs, K. M., Christensen, H. M., Im, H., Nuzzi, P. A., and Bresnick, E. H. (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 14494-14499], indicating that HDACs maintain low-level H4 acetylation at this site. Since little is known about the establishment of broad histone modification patterns, we asked whether this mechanism applies only to the promoter or to the entire subdomain. We show that the HDAC inhibitor trichostatin A induces H4 hyperacetylation at multiple sites within the subdomain in erythroid cells. The hematopoietic factors p45/NF-E2, GATA-1, and erythroid kruppel-like factor (EKLF), which function through cis elements of the beta-globin locus, were not required for induction of H4 hyperacetylation. Analysis of chromatin structure within the subdomain revealed low accessibility to restriction endonucleases and nearly complete CpG dinucleotide methylation. Induction of H4 hyperacetylation did not restore hallmark features of transcriptionally active chromatin. We propose that an HDAC-dependent surveillance mechanism counteracts constitutive histone acetyltransferase (HAT) access, thereby maintaining low-level H4 acetylation throughout the subdomain.
成年红细胞中的小鼠β-珠蛋白基因座的特征是具有广泛的红细胞特异性组蛋白乙酰化模式。胚胎β-珠蛋白基因Ey和βH1位于一个约30 kb的中央亚结构域，其特征是低水平的组蛋白乙酰化，而胎儿/成人基因βmaj和βmin以及上游基因座控制区则位于高度乙酰化的染色质中。组蛋白脱乙酰酶（HDAC）抑制剂可诱导Ey启动子处的H4乙酰化[Forsberg, E. C., Downs, K. M., Christensen, H. M., Im, H., Nuzzi, P. A., and Bresnick, E. H. (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 14494 - 14499]，这表明HDAC维持了该位点的低水平H4乙酰化。由于对广泛的组蛋白修饰模式的建立了解甚少，我们询问这种机制是否仅适用于启动子还是整个亚结构域。我们发现HDAC抑制剂曲古抑菌素A可诱导红细胞中亚结构域内多个位点的H4高乙酰化。通过β-珠蛋白基因座的顺式元件发挥作用的造血因子p45/NF-E2、GATA-1和红细胞类krüppel样因子（EKLF）对于诱导H4高乙酰化并非必需。对亚结构域内染色质结构的分析显示，对限制性内切酶的可及性较低，且CpG二核苷酸几乎完全甲基化。H4高乙酰化的诱导并未恢复转录活性染色质的标志性特征。我们提出一种依赖HDAC的监测机制可抵消组成型组蛋白乙酰转移酶（HAT）的作用，从而在整个亚结构域维持低水平的H4乙酰化。
