Interaction of YAP1 with the Myb-MuvB (MMB) complex sustain proliferation in the postnatal heart

YAP, a major downstream effector of the Hippo signaling pathway, is an important regulator of cell proliferation. Previous studies have shown that YAP cooperates with the two transcription factors E2F and MYC to mediate G1 to S transition by regulating early cell cycle gene expression. On the other hand, the ability of YAP to regulate G2/M gene expression is dependent on the Myb-MuvB (MMB) complex, consisting of the evolutionary MuvB core complex of five proteins and the facultative subunit B-MYB, a transcription factor. We now carried out interaction studies and found that YAP directly binds to the B-MYB subunit of MMB. Disruption of the YAP/B-MYB interaction by overexpression of the YAP binding domain of B-MYB results in errors in cell division. We also show that YAP and MMB interact in vivo in the developing heart. Genome wide expression and binding studies revealed that YAP and MMB regulate an overlapping set of cell cycle genes in cardiomyocytes. Cardiac specific deletion of the LIN9 subunit of MMB prevents the upregulation of cell cycle genes and the increased proliferation of cardiomyocytes lacking the hippo-signaling component SAV1. Similarly, we find that proliferation of postnatal cardiomyocytes induced by constitutive active YAP depends on MMB. Our findings provide new insights in the mechanisms of cell cycle regulation by the Hippo pathway in cardiomyocytes and suggests that YAP and MMB interact to induce genes critical for cell cycle regulation. RNAseq analysis in the murine heart after Lin9 and Sav1 knockout. DNA binding of LIN9 was analyzed in E16 and P10 hearts using ChIPseq.Yes相关蛋白（YAP）是Hippo信号通路（Hippo signaling pathway）的主要下游效应因子，亦是细胞增殖的关键调控因子。既往研究显示，YAP可与两种转录因子E2F及MYC协同，通过调控细胞周期早期基因的表达，介导G1期向S期的转换。另一方面，YAP调控G2/M期基因表达的能力，依赖于由5种进化相关的MuvB核心复合物蛋白以及兼性亚基B-MYB（一种转录因子）构成的Myb-MuvB（MMB）复合物。本研究通过相互作用实验发现，YAP可直接结合MMB复合物的B-MYB亚基。通过过表达B-MYB的YAP结合结构域破坏YAP与B-MYB的相互作用，会导致细胞分裂出现异常。我们还证实，YAP与MMB复合物在发育中的心脏内可发生体内相互作用。全基因组表达与结合实验显示，YAP与MMB复合物在心肌细胞中调控一组重叠的细胞周期基因。心肌细胞特异性敲除MMB的LIN9亚基，可阻止细胞周期基因的上调以及缺失Hippo信号通路组分SAV1的心肌细胞增殖水平升高。类似地，我们发现组成型激活型YAP诱导的出生后心肌细胞增殖，同样依赖于MMB复合物。本研究结果为Hippo信号通路在心肌细胞中调控细胞周期的机制提供了新见解，并提示YAP与MMB复合物可相互作用，诱导对细胞周期调控至关重要的基因表达。本研究对敲除Lin9与Sav1的小鼠心脏开展了RNA测序（RNAseq）分析；并利用染色质免疫沉淀测序（ChIPseq），检测了胚胎期16天（E16）及出生后10天（P10）的小鼠心脏中LIN9的DNA结合能力。