Cyclin-dependent kinase (CDK)-activating phosphatases, CDC25A and CDC25B, are labile proteins, and their levels vary in a cell cycle-dependent manner. Immediate-early response IER5 protein negatively regulates the cellular CDC25B levels, and stress-induced IER5 expression potentiates G2/M arrest. IER5 binds to protein phosphatase PP2A and regulates the PP2A substrate specificity. We show that IER5 binds to CDC25B and assists PP2A to convert CDC25B to hypophosphorylated forms. Hypophosphorylation at Ser323 results in the dissociation of CDC25B from 14‐3-3 phospho-binding proteins. In IER5 expressing cells, CDC25B dissociated from 14‐3-3 is unstable but slightly activated, because 14‐3-3 inhibits CDC25B polyubiquitination and CDC25B binding to CDK1. The 14‐3-3 binding to CDC25A also impedes CDC25A degradation and CDC25A-CDK2 interaction. We propose that 14‐3-3 is an important regulator of CDC25A and CDC25B and that PP2A/IER5 controls the stability and activity of CDC25B through regulating the interaction of CDC25B and 14‐3-3.

细胞周期蛋白依赖性激酶（CDK）激活磷酸酶CDC25A和CDC25B是不稳定的蛋白质，其水平以细胞周期依赖性方式变化。立即早期反应IER5蛋白负调节细胞CDC25B水平，应激诱导的IER5表达增强G2 / M阻滞。IER5与蛋白质磷酸酶PP2A结合并调节PP2A底物特异性。我们表明，IER5绑定到CDC25B，并协助PP2A将CDC25B转换为次磷酸化形式。Ser323的低磷酸化导致CDC25B从14-3-3磷酸结合蛋白解离。在表达IER5的细胞中，从14-3-3解离的CDC25B不稳定，但被轻微激活，因为14-3-3抑制了CDC25B多聚泛素化和CDC25B与CDK1的结合。14-3-3与CDC25A的结合也阻碍了CDC25A的降解和CDC25A-CDK2的相互作用。