Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada M5G 2M9.
ACS Chem Biol. 2009 Dec 18;4(12):1017-27. doi: 10.1021/cb900190u.
FOXO3a is a transcription factor belonging to the forkhead box O-Class (FOXO) subfamily, and it regulates metabolism, cell-cycle arrest, cell differentiation, and apoptosis through activating or suppressing gene transcription. FOXO3a contains a well-folded DNA-binding forkhead (FH) domain, but a large portion of the remaining protein sequence (75% of the total) is predicted to comprise intrinsically disordered regions (IDRs). Within the IDRs, there are three conserved regions (CR1-CR3), and it has been shown that CR3 (residues D610-N650) is a transactivation domain that recruits the coactivator histone acetyltransferase (HAT) CBP/p300, through binding to its KIX domain. In a previous study, we determined the solution structure of the FH domain and identified an intramolecular interaction between FH and CR3 domains of FOXO3a. Here we illustrate that the KIX domain of CBP interacts with the central core region (L620-A635) of CR3, which also internally interacts with the FH domain. In this heterotypic interplay, FH prevents CR3 from binding to KIX; however, upon binding to the Forkhead response element (FRE) DNA, the FH domain releases the CR3 domain, allowing it to interact with KIX. While previous studies have shown that the transactivation domains of c-Myb and MLL bind to distinct sites on KIX, our results indicate that FOXO3a CR3 has an ability to bind to both of these sites. These results suggest a model of FOXO3a-dependent coactivator recruitment in which the dynamic interplay between KIX and FH domains for binding to CR3 plays a key regulatory role in gene transcription activation.
FOXO3a 是一种转录因子，属于叉头框 O 类（FOXO）亚家族，通过激活或抑制基因转录来调节代谢、细胞周期停滞、细胞分化和细胞凋亡。FOXO3a 包含一个结构良好的 DNA 结合叉头（FH）结构域，但其余大部分蛋白质序列（总蛋白的 75%）预计由固有无序区域（IDRs）组成。在 IDRs 中，有三个保守区域（CR1-CR3），已经表明 CR3（残基 D610-N650）是一个转录激活结构域，通过与 KIX 结构域结合，招募共激活因子组蛋白乙酰转移酶（HAT）CBP/p300。在之前的一项研究中，我们确定了 FH 结构域的溶液结构，并鉴定了 FOXO3a 的 FH 和 CR3 结构域之间的分子内相互作用。在这里，我们说明 CBP 的 KIX 结构域与 CR3 的中央核心区域（L620-A635）相互作用，该区域也与 FH 结构域内部相互作用。在这种异型相互作用中，FH 阻止 CR3 与 KIX 结合；然而，当结合 Forkhead 反应元件（FRE）DNA 时，FH 结构域释放 CR3 结构域，使其能够与 KIX 相互作用。虽然之前的研究表明，c-Myb 和 MLL 的转录激活结构域结合在 KIX 上的不同位点，但我们的结果表明，FOXO3a CR3 具有结合这两个位点的能力。这些结果表明了一种 FOXO3a 依赖性共激活因子募集模型，其中 KIX 和 FH 结构域与 CR3 结合的动态相互作用在基因转录激活中起着关键的调节作用。
