Wang Jiao, Okkeri Juha, Pavic Karolina, Wang Zhizhi, Kauko Otto, Halonen Tuuli, Sarek Grzegorz, Ojala Päivi M, Rao Zihe, Xu Wenqing, Westermarck Jukka
Department of Biological Structure, University of Washington, Seattle, WA, USA.
College of Life Sciences, Nankai University, Tianjin, China.
EMBO Rep. 2017 Mar;18(3):437-450. doi: 10.15252/embr.201642788. Epub 2017 Feb 7.
Protein phosphatase 2A (PP2A) is a critical human tumor suppressor. Cancerous inhibitor of PP2A (CIP2A) supports the activity of several critical cancer drivers (Akt, MYC, E2F1) and promotes malignancy in most cancer types via PP2A inhibition. However, the 3D structure of CIP2A has not been solved, and it remains enigmatic how it interacts with PP2A. Here, we show by yeast two-hybrid assays, and subsequent validation experiments, that CIP2A forms homodimers. The homodimerization of CIP2A is confirmed by solving the crystal structure of an N-terminal CIP2A fragment (amino acids 1-560) at 3.0 Å resolution, and by subsequent structure-based mutational analyses of the dimerization interface. We further describe that the CIP2A dimer interacts with the PP2A subunits B56α and B56γ. CIP2A binds to the B56 proteins via a conserved N-terminal region, and dimerization promotes B56 binding. Intriguingly, inhibition of either CIP2A dimerization or B56α/γ expression destabilizes CIP2A, indicating opportunities for controlled degradation. These results provide the first structure-function analysis of the interaction of CIP2A with PP2A/B56 and have direct implications for its targeting in cancer therapy.
蛋白磷酸酶2A（PP2A）是一种关键的人类肿瘤抑制因子。PP2A的癌性抑制剂（CIP2A）支持多种关键癌症驱动因子（Akt、MYC、E2F1）的活性，并通过抑制PP2A在大多数癌症类型中促进恶性肿瘤的发生。然而，CIP2A的三维结构尚未解析，其与PP2A的相互作用方式仍然是个谜。在此，我们通过酵母双杂交试验及后续验证实验表明，CIP2A形成同源二聚体。通过解析N端CIP2A片段（氨基酸1 - 560）的晶体结构（分辨率为3.0 Å）以及对二聚化界面进行基于结构的突变分析，证实了CIP2A的同源二聚化。我们进一步描述了CIP2A二聚体与PP2A亚基B56α和B56γ相互作用。CIP2A通过保守的N端区域与B56蛋白结合，二聚化促进了与B56的结合。有趣的是，抑制CIP2A二聚化或B56α/γ的表达会使CIP2A不稳定，这为可控降解提供了机会。这些结果首次对CIP2A与PP2A/B56的相互作用进行了结构 - 功能分析，并对其在癌症治疗中的靶向作用具有直接意义。
