Myosin VB (MYO5B)突变促进胰腺导管腺癌上皮间质转换（EMT）的机制研究

Pancreatic ductal adenocarcinoma (PDAC) is the most lethal disease in the solid tumours. The currently used treatment and diagnosis manner in PDAC have shown limited effect, which results in a poor prognosis and extremely low 5-year survival rate (~6%). Thus understanding the molecular network of PDAC progression would bring insight into control of this malignancy. Interestingly, we have found that myosin VB (MYO5B) is downregulated in the tumour tissue of PDAC patients who showed earlier metastasis and significantly decreased survival compared to the patients having high MYO5B expression. MYO5B is a member of class V unconventional nonfilamous myosin. It was reported that mutations of MYO5B disrupted epithelial cell polarity, however, the mutations and function of MYO5B in cancer were not investigated. Here, we will investigate the genetic alteration, expression level, function and regulatory mechanism of MYO5B in the human and mouse PDAC models. Our preliminary data showed that the inactivating mutations of MYO5B were associated with its low expression level. Also, depletion of MYO5B converted the human PDAC cell lines prone to epithelial to mesenchymal transition (EMT). Moreover, MYO5B depletion mediated EMT exerted PDAC cell metastasis. It may interact with RPL26 and play a role in transporting TP53 mRNA to ribosome, then regulate TP53 translation and EMT signalling. In the further study, we will clarify the molecular mechanism(s) regulated by MYO5B in the PDAC EMT. Also, the orthotopic PDAC mouse model will be utilized to illustrate the outcome of MYO5B depletion in vivo. Our results would firstly shed light on the mechanism of MYO5B-regulated EMT in cancer, and provide novel targets for controlling PDAC progression.

胰腺导管腺癌（PDAC）是极为恶性的实体肿瘤，五年生存率仅6％，目前尚无有效治疗方法。上皮间质转化（EMT）通常会使细胞丧失极性，在胰腺癌中促进肿瘤转移和发展，研究EMT的分子机制将对控制胰腺癌起到积极作用。Myosin VB (MYO5B)属第五类非线性肌球蛋白家族，其突变可导致细胞极性改变，但MYO5B在恶性肿瘤中的突变及功能未知。本课题组前期发现约15%的PDAC患者携带MYO5B突变，突变患者的癌组织低表达MYO5B，其更早出现转移且显示总生存期显著短于未突变患者。MYO5B缺失促进PDAC细胞株发生EMT及转移，其可能通过结合RPL26参与TP53 mRNA转运至核糖体，进而调控TP53翻译及影响EMT。基于上述发现，本课题拟进一步明确MYO5B调控EMT的分子机理，并检测MYO5B缺失对肿瘤发展的体内作用，该研究成果将为控制胰腺癌的发展、转移提供新的治疗标靶和理论基础。

胰腺导管腺癌恶性程度高，治疗效果差，发现和发展新的针对胰腺癌的治疗方法和药物十分迫切。目前针对胰腺癌由基因突变引起的发病及进展机理仍不明确，虽然已开展了一些胰腺癌患者的二代基因测序工作，但对大多数被检测到的胰腺癌相关突变基因的功能不清楚。课题组在前期工作中对 34 名 PDAC 患者的癌组织和全血样本进行了全外显子测序，测序结果中发现约15%的PDAC患者拥有MYO5B突变，且3名患者的突变类型为失活突变、2名患者为错义突变。通过与患者临床预后数据进行比较分析，发现MYO5B基因突变的患者术后总生存期显著低于MYO5B未突变患者。为了明确 MYO5B 突变对其表达水平的影响，我们对突变患者和未突变患者的癌组织石蜡切片进行了IHC，发现MYO5B突变的癌组织中MYO5B的表达亦处于低水平，而未突变患者中则发现癌组织相对高表达 MYO5B。而且，我们发现在MYO5B表达低的胰腺癌患者中，病人发生转移的程度越高且时间越早。我们进一步通过体外细胞系的功能学实验，证实MYO5B对胰腺癌细胞的EMT通路有显著影响，并进一步通过对MYO5B的结合蛋白进行了质谱分析，发现MYO5B可结合核糖体蛋白RPL26，随后我们利用RPL26单抗对MYO5B的结合蛋白进行了孵育，证实了MYO5B可高效结合该核糖体蛋白。 经过一些列补救实验均证实MYO5B通过结合RPL26影响下游EMT 通路进而对胰腺癌的发生发展产生影响。目前正进一步研究干预靶点，将为胰腺癌的治疗提供新的思路。

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