E3泛素连接酶UBR5调控O-GlcNAc糖基化在胰腺癌吉西他滨耐药中的作用及机制研究

吉西他滨耐药是导致胰腺癌预后不佳的主要原因，但机制尚不清楚。既往研究和我们已发表的研究均证实O-GlcNAc糖基化在肿瘤对化疗耐药发挥关键作用。我们前期蛋白芯片分析发现E3泛素连接酶UBR5在吉西他滨耐药胰腺癌细胞中高表达；降低UBR5可抑制耐药细胞中O-GlcNAc糖基化水平，且增加吉西他滨的敏感性；进一步探索发现O-GlcNAc糖基化水解酶OGA是UBR5潜在的底物蛋白。据此，我们推测：UBR5通过促进OGA经泛素蛋白酶体降解，进而增加 O-GlcNAc 糖基化水平，最终导致胰腺癌细胞吉西他滨耐药。为验证假设，本研究拟利用体内外实验研究UBR5通过调控O-GlcNAc糖基化在胰腺癌吉西他滨耐药中的作用，阐明UBR5调节O-GlcNAc糖基化的分子机制，并明确UBR5、OGA、O-GlcNAc糖基化作为评估胰腺癌患者吉西他滨疗效及预后的分子标记物，以期为逆转胰腺癌吉西他滨耐药提供新线索。

Gemcitabine resistance is the main reason for the poor prognosis of pancreatic cancer, but the mechanism has not been clarified. Previous studies by us and others have suggested that O-GlcNAcylation plays a key role in chemotherapy resistance of tumors. We have found in early studies through a protein chip that E3 ubiquitin ligase UBR5 was highly expressed in gemcitabine-resistant pancreatic cancer; and downregulating UBR5 effectively suppressed O-GlcNAcylation in the chemo-resistant cancer cells, which was associated with increased chemo-sensitivity; and further studies revealed that the O-GlcNAc hydrolase OGA is a potential substrate of UBR5. Based on these data, we speculated that UBR5 may increase O-GlcNAcylation by promoting degradation of the corresponding hydrolase OGA via the ubiquitin-proteasome pathway, thereby promoting gemcitabine resistance of pancreatic cancer cells. To verify this hypothesis, this study intends to clarify that UBR5 affects gemcitabine resistance of pancreatic cancer by regulating O-GlcNAcylation and the underlying mechanism, and evaluate the potential of UBR5, OGA, and O-GlcNAcylation as markers for efficacy and prognosis of pancreatic cancer patients treated with gemcitabine, so as to provide new clues to reverse gemcitabine resistance of pancreatic cancer.