YAP/O-GlcNAc正反馈通路调控RNF8蛋白稳定性介导高糖水平诱导肝癌细胞耐药机制

Diabetes is a key risk factor of liver cancer, but mechanism remain unclear. YAP is oncoprotein which drives turmorigenesis of liver cells, O-GlcNAc of target protein may mediate the regulation of cell function by cell metabolism. In our previous work, we firstly found that Thr241 of YAP protein may be O-GlcNAcylated which promote the stability of YAP, YAP conversely enhances the global O-GlcNAc level in HCC cells, giving rise to a positive cycle promoting “vicious metabolism” in liver cancer cells. Recently our results suggested that the enhanced “vicious metabolism” in liver cancer may facilitate DNA damage repair process by promoting RNF8 O-GlcNAc through inhibition of ubiquination-induced degradation, increasing the drug-resistance. Our project will highlight the mechanism by which YAP/O-GlcNAc regulates DNA damage repair in liver cancer, providing a firm base for cancer treatment.

糖尿病是肝癌发生的重要危险因素之一，但机制不明。YAP是驱动肝癌发生发展的重要因素，O-GlcNAc是针对蛋白的一种单糖修饰方式，在肿瘤细胞中介导能量代谢对细胞功能的调控。前期研究中我们首次发现，高糖环境中YAP的Thr241位点发生O-GlcNAc修饰而增加YAP稳定性， YAP又能提高肝癌细胞整体O-GlcNAc修饰水平，二者构成正反馈的“邪恶轴心”，异化肿瘤细胞内的能量代谢方式，满足肿瘤快速增殖与转移过程中对能量物质的不断需求，提供肿瘤发展的“后勤保障”，另一方面又能够通过对DNA损伤修复的关键蛋白（如RNF8）进行O-GlcNAc修饰增加其稳定性，提高DNA损伤修复能力，增强肿瘤对放化疗作用的耐受能力。本课题拟通过体内外研究，进一步明确高糖诱导下YAP/ O-GlcNAc正反馈通路调控肝癌细胞中DNA损伤修复的机制，为糖尿病相关肝癌的临床治疗提供新的突破点。

我们首次发现，高糖环境中YAP的Thr241位点发生O-GlcNAc修饰而增加YAP稳定性，YAP又能提高肝癌细胞整体O-GlcNAc修饰水平，进而对损伤修复的关键蛋白RNF8进行O-GlcNAc修饰增加其稳定性。有趣的是，我们发现RNF8在化疗耐药肝癌细胞中表达上调，通过基因敲除或化学抑制RNF8可增强DNA损伤和凋亡激活并伴有XRCC1降解以逆转化疗耐药。E3连接酶Trim25可催化XRCC1的多泛素化并促进其蛋白酶体依赖性降解。RNF8可与XRCC1结合并去乙酰化其赖氨酸，防止发生β-Trcp依赖的泛素化降解。本项目们描述了RNF8通过去乙酰化和稳定XRCC1给肝癌细胞带来化疗耐药性。因此，靶向RNF8可能是一种管理肝癌和其他癌症化疗耐药的新策略。