Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan.
Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan.
Biochim Biophys Acta Gene Regul Mech. 2023 Sep;1866(3):194960. doi: 10.1016/j.bbagrm.2023.194960. Epub 2023 Jul 17.
The transcription factor E2F1 participates in cell cycle control through transcriptional activation of genes that promote S-phase entry. E2F1 is also linked to the expression of proapoptotic genes, and the loss of E2F1 activity facilitates tumor progression by reducing cellular apoptosis. Phosphorylation controlled by protein kinases and phosphatases is the major posttranslational modification and regulates the cellular levels and transactivator function of E2F1. Here, we characterize the regulatory roles of serine-375 (S375), one of the major phosphorylation sites of E2F1. Cyclin-dependent kinases such as CDK8 phosphorylate at S375 of E2F1, which is dephosphorylated by protein phosphatase 2A (PP2A) containing the B55 regulatory subunit. The PP2A adapter protein IER5 binds to both PP2A/B55 and E2F1 and assists dephosphorylation at S375 by PP2A. S375-dephosphorylated E2F1 exhibits higher DNA-binding affinity than the phosphorylated form. Although the promoter regions of proapoptotic genes are less occupied by E2F1 in cells, an increase in S375-dephosphorylated E2F1 induces preferential binding of E2F1 to the proapoptotic gene promoters and their expression. Our data identify PP2A/B55-IER5 as a critical regulator of E2F1 and suggest that the phosphorylation state of E2F1 is an important determinant for the expression of proapoptotic genes.
转录因子 E2F1 通过转录激活促进 S 期进入的基因参与细胞周期控制。E2F1 也与促凋亡基因的表达有关，E2F1 活性的丧失通过减少细胞凋亡促进肿瘤进展。蛋白激酶和磷酸酶控制的磷酸化是主要的翻译后修饰，调节 E2F1 的细胞水平和转录激活功能。在这里，我们描述了 E2F1 的一个主要磷酸化位点丝氨酸 375（S375）的调节作用。细胞周期蛋白依赖性激酶（如 CDK8）在 E2F1 的 S375 位点磷酸化，该位点被含有 B55 调节亚基的蛋白磷酸酶 2A（PP2A）去磷酸化。PP2A 衔接蛋白 IER5 结合 PP2A/B55 和 E2F1，并协助 PP2A 在 S375 处去磷酸化。与磷酸化形式相比，S375 去磷酸化的 E2F1 表现出更高的 DNA 结合亲和力。尽管促凋亡基因的启动子区域在细胞中被 E2F1 占据较少，但 S375 去磷酸化的 E2F1 增加会诱导 E2F1 优先结合促凋亡基因启动子并表达它们。我们的数据确定 PP2A/B55-IER5 是 E2F1 的关键调节因子，并表明 E2F1 的磷酸化状态是促凋亡基因表达的一个重要决定因素。
