YAP-TEAD诱导FOXM1上调在肝母细胞瘤形成中的机制研究

Hepatoblastoma (HB) is the most common hepatic malignancies in children, which has been seriously threatening children's life and health. Unfortunately, to date, its pathogenesis is still unclear. Recently studies revealed that Yes-associated protein (YAP) is activated in ~80% of human HB samples, and this activated YAP has been found to be associated with poor prognostic. These demonstrated that YAP is a pivotal and powerful oncogene in HB, however, the molecular mechanism by which YAP functions to promote HB development remains unknown..YAP induced tumorigenesis by regulating cell cycle related factors, increasing incidence of polyploidy and chromosome instability. As an important cell cycle regulator, Forkhead box M1 (FOXM1) was regulated by the complex of YAP-TEAD..Based on the above researches, our study is going to discuss the interplay and mechanism of YAP-TEAD and FOXM1 in the HB tumorigenesis. Firstly we will demonstrate that YAP induced HB tumorigenesis is TEAD dependent, meanwhile study will screen the major isoform of TEAD in HB. Further exploration will focused on interplay of YAP-TEAD and FOXM1 in HB. Our studies will prove YAP-TEAD regulates cell cycle and increases incidence of polyploidy in the development of HB by acting directly to the promoter of FOXM1. Inhibiting the function of FOXM1 can decrease the incidence of cell polyploidy, in hence delaying HB development. Therefore, targeting YAP-TEAD or FOXM1 may represent an effective treatment option for HB.

肝母细胞瘤（HB）是儿童最常见的肝脏恶性肿瘤。近期研究发现YAP在绝大多数HB病例中被激活，且YAP高表达常提示预后欠佳，说明YAP是HB形成中一个强有力的致癌因子，但其作用机制仍不明确。.研究发现YAP促进肿瘤形成的一个机制为调控细胞周期相关因子的表达，使多倍体细胞比率及染色体不稳定性发生率增加。FOXM1作为一个重要的细胞周期调控因子，受YAP-TEAD复合体的调控。.因此，本研究拟在HB中研究YAP-TEAD与FOXM1相互作用，促进肿瘤形成的机制。首先证实YAP诱导HB形成中需TEAD协助，并筛选出在HB中起主要作用的TEAD亚型。进一步机制研究将验证YAP-TEAD通过直接上调FOXM1的表达，调控细胞周期，增加多倍体细胞比率，促进肿瘤形成。而抑制FOXM1可降低多倍体细胞的发生率、抑制HB形成。拟通过该研究证实靶向YAP-TEAD或FOXM1为HB可能的治疗方向。

前期研究发现，YAP活化可诱导肝母细胞瘤(Hepatoblastoma, HB) 的形成，且与HB的恶性程度相关。作为转录共激活因子，YAP需依赖DNA结合转录因子来共同调控下游靶基因的表达。但近年来也有研究发现YAP可以以转录非依赖的形式，来发挥直接调控作用。YAP作为诱导HB形成的一个重要的致癌因子，其发挥促癌作用是否需其他DNA结合转录因子的协同帮助尚不明确。.本研究通过高压尾静脉共转染活化形式的YAP及β-catenin质粒进行HB小鼠造模，选择HepG2及Hep293TT细胞为HB研究细胞系，经细胞及动物实验证明：在HB形成中，过表达显性失活突变形式的TEAD（dnTEAD2）于HB 细胞及小鼠，干扰TEAD的功能，可阻碍YAP诱导的HB形成，说明YAP需与TEAD结合调控下游因子转录表达；在小鼠体内共转染TEAD2VP16及β-catenin，可诱导HB的形成，且诱导形成的肿瘤类型类似于YAP与β-catenin共转染形成的肿瘤类型；进一步进行实验研究在YAP诱导的HB中起主要作用的TEAD亚型。RT-qPCR结果显示TEAD4在人及小鼠HB标本中表达水平均明显上调；应用siRNA分别敲除 TEAD1-4，只有敲除TEAD4才可明显抑制YAP-TEAD的靶基因的表达，同时可致HB细胞的增殖能力减弱，而凋亡比率增加。在HB细胞中过表达TEAD4后则可促进肿瘤细胞增殖，抑制其凋亡。进一步研究发现FOXM1在HB中表达上调，YAP-TEAD可通过上调FOXM1的表达促进肿瘤形成。.上述研究结果证实TEAD是YAP发挥促癌作用中一个重要的协同因子，TEAD4是HB形成中辅助YAP转录调控的主要亚型。YAP-TEAD通过上调FOXM1的表达促进HB的形成。.该研究结果可为YAP-TEAD诱导HB形成机制提供研究基础，并为后续靶向药物治疗提供可能的研究方向。