Doi Kuriko, Takeuchi Hiroto, Sakurai Hiroshi
Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, Japan.
FEBS J. 2023 Feb;290(3):745-762. doi: 10.1111/febs.16612. Epub 2022 Sep 12.
The retinoblastoma (RB) tumour suppressor protein regulates cell proliferation, motility, differentiation and apoptosis. The phosphorylation state of RB is modulated by kinases and phosphatases, and RB exhibits phosphorylation-sensitive interactions with E2F family transcription factors. Here, we characterize RB dephosphorylation by protein phosphatase 2A (PP2A). The growth factor-inducible immediate early response (IER) proteins IER2 and IER5 possess an adapter-like function in which IER proteins bind to both PP2A and its target proteins and enhance PP2A activity towards the proteins. IER2 interacts with RB and facilitates dephosphorylation of RB at T821/T826 by PP2A. In IER2 knockdown cells, elevated phosphorylation of RB resulted in reduced binding of RB to the promoters and derepression of cyclin D1 and p21. IER5 binds to both RB and RB-like 1 (p107/RBL1), enhances dephosphorylation of these proteins by PP2A and represses the expression of various cell cycle-related genes. However, IER2-regulated dephosphorylation at T821/T826 is not necessary for the repression function of RB in cell mobility-related gene expression. Our data identify PP2A adapter proteins as critical regulators of RB family proteins and suggest that the phosphorylation status of RB differentially affects gene expression.
视网膜母细胞瘤（RB）肿瘤抑制蛋白调节细胞增殖、运动、分化和凋亡。RB的磷酸化状态由激酶和磷酸酶调节，并且RB与E2F家族转录因子表现出磷酸化敏感性相互作用。在此，我们对蛋白磷酸酶2A（PP2A）介导的RB去磷酸化进行了表征。生长因子诱导的即时早期反应（IER）蛋白IER2和IER5具有类似衔接蛋白的功能，其中IER蛋白既与PP2A及其靶蛋白结合，并增强PP2A对这些蛋白的活性。IER2与RB相互作用，并促进PP2A介导的RB在T821/T826位点的去磷酸化。在IER2敲低的细胞中，RB磷酸化水平升高导致RB与启动子的结合减少，以及细胞周期蛋白D1和p21的去抑制。IER5与RB和类RB1（p107/RBL1）都结合，增强PP2A对这些蛋白的去磷酸化作用，并抑制各种细胞周期相关基因的表达。然而，IER2介导的T821/T826位点去磷酸化对于RB在细胞迁移相关基因表达中的抑制功能并非必需。我们的数据确定PP2A衔接蛋白是RB家族蛋白的关键调节因子，并表明RB的磷酸化状态对基因表达有不同影响。
