PP2A is an essential protein phosphatase that regulates most cellular processes through the formation of holoenzymes containing distinct regulatory B‐subunits. Only a limited number of PP2A‐regulated phosphorylation sites are known. This hampers our understanding of the mechanisms of site‐specific dephosphorylation and of its tumor suppressor functions. Here, we develop phosphoproteomic strategies for global substrate identification of PP2A‐B56 and PP2A‐B55 holoenzymes. Strikingly, we find that B‐subunits directly affect the dephosphorylation site preference of the PP2A catalytic subunit, resulting in unique patterns of kinase opposition. For PP2A‐B56, these patterns are further modulated by affinity and position of B56 binding motifs. Our screens identify phosphorylation sites in the cancer target ADAM17 that are regulated through a conserved B56 binding site. Binding of PP2A‐B56 to ADAM17 protease decreases growth factor signaling and tumor development in mice. This work provides a roadmap for the identification of phosphatase substrates and reveals unexpected mechanisms governing PP2A dephosphorylation site specificity and tumor suppressor function.

中文翻译：

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PP2A调节亚基施加的位点特异性去磷酸化和激酶拮抗的机制。

PP2A是一种必不可少的蛋白磷酸酶，它通过形成含有独特调节B亚基的全酶来调节大多数细胞过程。仅已知数量有限的PP2A调节的磷酸化位点。这阻碍了我们对位点特异性去磷酸化机制及其肿瘤抑制功能的理解。在这里，我们开发了磷酸蛋白质组学策略来鉴定PP2A-B56和PP2A-B55全酶的整体底物。令人惊讶的是，我们发现B亚基直接影响PP2A催化亚基的去磷酸化位点偏好，从而导致独特的激酶对立模式。对于PP2A-B56，B56结合基序的亲和力和位置进一步调节了这些模式。我们的筛查确定了癌症靶点ADAM17中的磷酸化位点，该位点通过保守的B56结合位点进行调控。PP2A-B56与ADAM17蛋白酶的结合减少了小鼠中的生长因子信号传导和肿瘤发展。这项工作为磷酸酶底物的鉴定提供了路线图，并揭示了控制PP2A脱磷酸位点特异性和肿瘤抑制功能的意外机制。