Case Western Reserve University, Department of Biochemistry, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
J Virol. 2010 Apr;84(8):4050-9. doi: 10.1128/JVI.02131-09. Epub 2010 Jan 20.
Despite data suggesting that the adenovirus E1A protein of 243 amino acids creates an S-phase environment in quiescent cells by overcoming the nucleosomal repression of E2F-regulated genes, the precise mechanisms underlying E1A's ability in this process have not yet been defined at the biochemical level. In this study, we show by kinetic analysis that E1A, as opposed to an E1A mutant failing to bind p130, can temporally eliminate corepressor complexes consisting of p130-E2F4 and HDAC1/2-mSin3B from the promoters of E2F-regulated genes in quiescent cells. Once the complexes are removed, the di-methylation of H3K9 at these promoters becomes dramatically diminished, and this in turn allows for the acetylation of H3K9/14 and the recruitment of activating E2F family members, which is then followed by the transcriptional activity of the E2F-regulated genes. Remarkably, although an E1A mutant that can no longer bind to a histone acetyltransferase (PCAF) is as capable as wild-type E1A in eliminating corepressor complexes and methyl groups from the promoters of these genes, it cannot mediate the acetylation of H3K9/14 or induce their transcription. These findings suggest that corepressors as well as coactivators are acted upon by E1A to derepress E2F-regulated genes in quiescent cells. Thus, our results highlight for the first time a functional relationship between E1A and two transcriptional pathways of differing functions for transitioning cells out of quiescence and into S phase.
尽管有数据表明，243 个氨基酸组成的腺病毒 E1A 蛋白通过克服 E2F 调节基因的核小体抑制，在静止细胞中创造 S 期环境，但 E1A 在该过程中的精确机制在生化水平上尚未确定。在这项研究中，我们通过动力学分析表明，E1A 可以暂时从静止细胞中 E2F 调节基因的启动子中去除由 p130-E2F4 和 HDAC1/2-mSin3B 组成的核心抑制复合物，而不是结合 p130 的 E1A 突变体。一旦复合物被去除，这些启动子上的 H3K9 二甲基化显著减少，这反过来又允许 H3K9/14 的乙酰化和激活 E2F 家族成员的募集，随后是 E2F 调节基因的转录活性。值得注意的是，尽管不能再与组蛋白乙酰转移酶（PCAF）结合的 E1A 突变体在从这些基因的启动子中去除核心抑制复合物和甲基方面与野生型 E1A 一样有效，但它不能介导 H3K9/14 的乙酰化或诱导其转录。这些发现表明，E1A 作用于抑制物和共激活物以解除静止细胞中 E2F 调节基因的抑制。因此，我们的结果首次强调了 E1A 与两种不同功能的转录途径之间的功能关系，这两种转录途径使细胞从静止状态进入 S 期。
