Key Laboratory of Systems Biomedicine (Ministry of Education), Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
Key Laboratory of Systems Biomedicine (Ministry of Education), Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; SCSB (China)-AIST (Japan) Joint Medical Glycomics Laboratory, Shanghai, China.
Biochim Biophys Acta Gen Subj. 2019 May;1863(5):870-882. doi: 10.1016/j.bbagen.2019.01.009. Epub 2019 Feb 21.
Mucin-type O-glycosylation plays important roles in various biological processes. It is initiated by a family of 20 conserved UDP-GalNAc: polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts). Unlike most ppGalNAc-Ts localized to the Golgi apparatus, ppGalNAc-T18 is predominantly distributed on the endoplasmic reticulum (ER) and exhibits no ppGalNAc-T catalytic activity in vitro. Herein, we found that ppGalNAc-T18 silencing in cells decreased O-glycosylation levels and activated ER stress leading to apoptosis. After treatment with chemical chaperone 4-phenylbutyric acid (PBA) or forced expression of ppGalNAc-T18 in the ppGalNAc-T18 knockdown cell, these defects could be significantly alleviated, suggesting that ppGalNAc-T18 is important for ER homeostasis and protein O-glycosylation. Furthermore, we found that ppGalNAc-T18 exerts its functions in O-glycosylation and ER stress via a non-catalytic mechanism. These results reveal a novel molecular role of ppGalNAc-Ts that the ER-localized ppGalNAc-T18 could regulate the O-glycosylation and ER homeostasis in a non-catalytic manner.
粘蛋白型 O-糖基化在各种生物过程中发挥着重要作用。它由一系列 20 个保守的 UDP-GalNAc:多肽 N-乙酰半乳糖胺基转移酶 (ppGalNAc-Ts) 启动。与大多数定位于高尔基体的 ppGalNAc-Ts 不同，ppGalNAc-T18 主要分布在内质网 (ER) 上，体外没有 ppGalNAc-T 催化活性。在此，我们发现细胞中 ppGalNAc-T18 的沉默降低了 O-糖基化水平并激活了内质网应激导致细胞凋亡。用化学伴侣 4-苯基丁酸 (PBA) 处理或在 ppGalNAc-T18 敲低细胞中强制表达 ppGalNAc-T18 后，这些缺陷可显著缓解，表明 ppGalNAc-T18 对 ER 稳态和蛋白质 O-糖基化很重要。此外，我们发现 ppGalNAc-T18 通过非催化机制在 O-糖基化和内质网应激中发挥作用。这些结果揭示了 ppGalNAc-Ts 的一个新的分子作用，即 ER 定位的 ppGalNAc-T18 可以以非催化方式调节 O-糖基化和 ER 稳态。
