Hippo/YAP信号通路在2型神经纤维瘤病发生中的作用机制研究

Neurofibromatosis type 2 (NF2) is an autosomal dominant genetic disease,which is progressive and multiple tumor syndrome caused by encoded protein Merlin function reduction or inactivation after NF2 gene mutaion. The specific mechanism of tumorigenesis is unclear.Hippo / YAP signaling pathway plays an important inhibitory effect on organ development and cell proliferation.Merlin is the key upstream regulatory protein of Hippo / YAP signaling pathway, which can activate the core kinase chain reaction in this pathway, and result in effector proteins phosphorylated YAP, thus making it lose the activity and it is not able to come into nucleus to play proliferation, inhibition of apoptosis.We can come into conclusion after comparing schwannoma of NF2 and normal nerve: 1) a significant increase in key kinases MST1/2 of oncology group Hippo/YAP signaling pathway and in mRNA of effector proteins YAP. 2) a significant increase in the expression of oncology group YAP in the nucleus. We speculate the reasons of NF2 are: Merlin function reduction or absence; core kinase chain reaction in Hippo/YAP signaling pathway is not able to happen effectively; its effector protein phosphorylation YAP reduces, but overexpression in the nucleus, causing abnormal transcription of downstream target genes. We intend to verify the speculation thourgh the different levels among NF2 tumor specimens, primary cultured tumor cells and nude mouse xenograft model in this project. The function of Hippo/YAP signaling pathway in NF2 disease and its possible mechanism would be clarified preliminarily.

2型神经纤维瘤病是常染色体显性遗传病，为NF2基因突变致其编码蛋白Merlin功能降低或失活引起的渐进性、多发性肿瘤综合征，发病机制不明。Hippo/YAP信号通路在器官发育、细胞增殖中发挥抑制作用，Merlin是其上游关键调控蛋白，通过激活该通路核心激酶链反应，致效应蛋白YAP磷酸化失去活性，不能进入核发挥促增殖、抑凋亡作用。我们对比NF2神经鞘瘤与正常神经发现：1. 肿瘤组Hippo/YAP信号通路的关键激酶MST1/2和效应蛋白YAP的mRNA显著增加；2. 肿瘤组YAP核内表达明显升高。我们推测“Merlin功能降低或缺失，Hippo/YAP通路核心激酶链反应不能有效进行，其效应蛋白YAP磷酸化减少而在核内过度表达，引起下游靶基因转录异常，参与NF2肿瘤形成”。本项目拟在NF2肿瘤标本、原代细胞及裸鼠移植瘤等水平验证该假设，阐明Hippo/YAP信号通路在NF2发生中的作用及机制。

前庭神经鞘瘤（Vestibular schwannoma）是起源于第八颅神经髓鞘的良性肿瘤，为颅内最常见的良性肿瘤之一。该肿瘤不仅可见于散发病例，也是2型神经纤维瘤病（neurofibromatosis type 2，NF2）的特征性表现。目前，前庭神经鞘瘤的治疗方法主要包括手术治疗和立体定向放射治疗，但这些治疗手段常常会引起听力丧失、面瘫等神经功能障碍。同时，由于NF2前庭神经鞘瘤呈双侧、渐进性生长，手术切除困难，术后易于复发，亟需新的治疗手段。随着近年来对Merlin蛋白功能的深入研究，发现Merlin蛋白作为Hippo通路的上游蛋白，可以调控Hippo通路的正常功能。我们通过一代测序、全基因组表达谱芯片、western blot及免疫组化等方法，对正常神经、散发前庭神经鞘瘤及NF2前庭神经鞘瘤进行DNA水平、RNA转录水平及蛋白表达分析。确定：Hippo通路在人前庭神经鞘瘤中存在明显的功能失调，并造成YAP蛋白激活并进入细胞核内，促进施旺细胞增殖。使用维替泊芬后，不仅能引起细胞内YAP的表达水平降低，而且可有效抑制肿瘤细胞的增殖能力。以上结果提示我们Hippo-YAP通路未来有望成为神经鞘瘤治疗的潜在靶点。