Zhang Peng, Wang Shuting, Wang Sai, Qiao Jing, Zhang Lei, Zhang Zhe, Chen Zhengjun
Key Laboratory of Systems Biology, Institute of Biochemistry and Cell Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; University of Chinese Academy of Sciences, Beijing, China.
State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences , Shanghai, China.
Cell Discov. 2016 Jul 5;2:16021. doi: 10.1038/celldisc.2016.21. eCollection 2016.
Partitioning-defective 3 (Par3), a key component of the evolutionarily conserved polarity PAR complex (Par3/Par6/aPKC), controls cell polarity and contributes to cell migration, proliferation and tumor development. Emerging evidence indicates that cell polarity proteins function as upstream modulators that regulate the Hippo pathway. However, little is known about Par3's involvement in the Hippo pathway. Here, we find Par3 and YAP dynamically co-localize in different subcellular compartments; that is, the membrane, cytoplasm and nucleus, in a cell-density-dependent manner. Interestingly, Par3 knockdown promotes YAP phosphorylation, leading to a significant impairment of YAP nuclear translocation at low cell density, but not at high density, in MDCK cells. Furthermore, via its third PDZ domain, Par3 directly binds to the PDZ-binding motif of YAP. The interaction is required for regulating YAP phosphorylation and nuclear localization. Mechanistically, Par3, as a scaffold protein, associates with LATS1 and protein phosphatase 1, α subunit (PP1A) in the cytoplasm and nucleus. Par3 promotes the dephosphorylation of LATS1 and YAP, thus enhancing YAP activation and cell proliferation. Strikingly, we also find that under the condition of PP1A knockdown, Par3 expression promotes YAP hyperphosphorylation, leading to the suppression of YAP activity and its downstream targets. Par3 expression results in differential effects on YAP phosphorylation and activation in different tumor cell lines. These findings indicate that Par3 may have a dual role in regulating the activation of the Hippo pathway, in a manner possibly dependent on cellular context or cell type in response to cell-cell contact and cell polarity signals.
分区缺陷蛋白3（Par3）是进化上保守的极性PAR复合物（Par3/Par6/aPKC）的关键组成部分，它控制细胞极性，并参与细胞迁移、增殖和肿瘤发展。新出现的证据表明，细胞极性蛋白作为上游调节因子调控Hippo信号通路。然而，关于Par3在Hippo信号通路中的作用知之甚少。在此，我们发现Par3和YAP在不同亚细胞区室（即细胞膜、细胞质和细胞核）中以细胞密度依赖的方式动态共定位。有趣的是，在MDCK细胞中，敲低Par3会促进YAP磷酸化，导致在低细胞密度而非高细胞密度时YAP核转位显著受损。此外，Par3通过其第三个PDZ结构域直接与YAP的PDZ结合基序结合。这种相互作用是调节YAP磷酸化和核定位所必需的。从机制上讲，Par3作为一种支架蛋白，在细胞质和细胞核中与LATS1和蛋白磷酸酶1α亚基（PP1A）结合。Par3促进LATS1和YAP的去磷酸化，从而增强YAP的激活和细胞增殖。引人注目的是，我们还发现，在敲低PP1A的条件下，Par3的表达促进YAP过度磷酸化，导致YAP活性及其下游靶点受到抑制。Par3的表达在不同肿瘤细胞系中对YAP磷酸化和激活产生不同影响。这些发现表明，Par3可能在调节Hippo信号通路的激活中具有双重作用，其方式可能取决于细胞环境或细胞类型，以响应细胞间接触和细胞极性信号。
