Role of POGLUT2 and POGLUT3 in regulating microfibril structure and function

蛋白质O-葡糖基转移酶2和3（POGLUT 2和POGLUT 3）将O-连接的葡萄糖添加到丝氨酸 含有推定共有序列的表皮生长因子样（EGF）重复序列中的残基 C3 xNTxGS（Y/F）xC 4，其中C3和C4是EGF重复序列中的第三和第四个保守半胱氨酸。数据库 研究表明，原纤维蛋白（FBN）和潜在的TGFβ结合蛋白（LTBP）具有大量的EGF， 重复与共识，而其他蛋白质只有一个或两个。FBN 1和FBN 2是主要的 细胞外基质中10-12 nm微纤维中的结构蛋白，在那里它们充当细胞外基质的支架。 弹性组织中的弹性蛋白，提供肺等组织功能所必需的弹性和回缩。微纤丝 也结合许多其他分子，包括LTBP，调节组织稳态。FBN 1突变 引起马凡氏综合征（MFS），可导致主动脉夹层/夹层，也可引起肺、骨生长， 和眼睛缺陷。小鼠中Fbn 1、Ltbp 1或Ltbp 4的消除导致围产期死亡，概括了几种 在MFS患者中观察到的表型。没有人知道EGF O-葡萄糖基化对细胞生长的影响。 FBN或LTBP功能。使用我们的糖蛋白质组质谱方法，我们证明了47个中的27个 从人真皮成纤维细胞培养物免疫纯化的FBN 1中的EGF重复序列用O-葡萄糖修饰。 在HEK 293 T细胞中表达的重组FBN 2、LTPB 1和LTBP 4中发现了相似水平的O-葡萄糖。 当POGLUT 2和P0 GLUT 3表达时，FBN 1的N-末端片段（EGF 1 -26）的分泌显著减少。 在HEK 293 T细胞中，POGLUT 3被敲除，这表明这些酶的修饰， 在内质网中，是有效折叠和分泌这些底物所必需的。的 这种O-葡萄糖修饰的重要性被我们最近的观察所强调， Poglut 2/Poglut 3双敲除（DKO）小鼠围产期死亡。幸存者有类似Fbn的异常， Ltbp科斯，包括肺缺损、小尺寸和并指。基于这些观察，我们假设 FBN和LTPB的O-葡糖基化对于功能性微纤维网络是必需的。我们预测 O-葡糖基化的丧失将减少这些蛋白质的分泌和/或破坏与微纤维的结合 相关蛋白，导致组织中的结构和/或信号缺陷。我们将检验这一假设 三个目标。目的1使用基于细胞的方法解决O-葡萄糖的损失如何影响POGLUT 2/3底物蛋白。 分泌测定、微纤维的超微结构分析和FBN 1-配体相互作用的分析。Aim 2测试 假定的POGLUT 2/3共有序列中的保守氨基酸是否是O-葡糖基化所必需的，以及 这些保守残基中的MFS突变是否通过O-葡萄糖的损失介导它们对FBN 1的影响。目的 图3使用小鼠肺发育模型检测POGLUT 2/3的缺失是否损害肺发育中的微纤维网络。 模型、组织学方法和遗传相互作用研究。结合起来，这些目标将提供分子 机制来解释O-葡萄糖如何影响微纤维网络的结构和功能。

Protein O-glucosyltransferases 2 and 3 (POGLUT2 and POGLUT3) add an O-linked glucose to a serine residue in Epidermal Growth factor-like (EGF) repeats containing the putative consensus sequence C3xNTxGS(Y/F)xC4, where C3 and C4 are the third and fourth conserved cysteine in the EGF repeat. Database searches reveal that the fibrillins (FBNs) and Latent TGFβ Binding Proteins (LTBPs) have numerous EGF repeats with the consensus, while other proteins only have one or two. FBN1 and FBN2 are the major structural proteins in the 10-12 nm microfibrils in extracellular matrix, where they serve as the scaffold for elastin in elastic tissues, providing elasticity and recoil essential for function of tissues such as lung. Microfibrils also bind a number of other molecules, including LTBPs, that regulate tissue homeostasis. Mutations in FBN1 cause Marfan Syndrome (MFS) that can result in aortic aneurism/dissection and also cause lung, bone-growth, and eye defects. Elimination of Fbn1, Ltbp1, or Ltbp4 in mice results in perinatal lethality, recapitulating several of the phenotypes seen in MFS patients. Nothing is known about the impact of EGF O-glucosylation on FBN or LTBP function. Using our glycoproteomic mass spectral methods, we demonstrated that 27 of the 47 EGF repeats in FBN1 immunopurified from human dermal fibroblast cultures are modified with O-glucose. Similar levels of O-glucose were found in recombinant FBN2, LTPB1, and LTBP4 expressed in HEK293T cells. Secretion of an N-terminal fragment (EGF1-26) of FBN1 was significantly reduced when POGLUT2 and POGLUT3 were knocked out in HEK293T cells, suggesting that modification by these enzymes, both localized in the endoplasmic reticulum, are required for efficient folding and secretion of these substrates. The importance of this O-glucose modification is underscored by our recent observation that the majority of our Poglut2/Poglut3 double knockout (DKO) mice die perinatally. Survivors have abnormalities similar to Fbn and Ltbp KOs including lung defects, small size, and syndactyly. Based on these observations, we hypothesize that O-glucosylation of FBNs and LTPBs is essential for a functional microfibril network. We predict that loss of O-glucosylation will reduce secretion of these proteins and/or disrupt binding to microfibril associated proteins, leading to structural and/or signaling defects in tissues. We will test this hypothesis in three Aims. Aim 1 addresses how loss of O-glucose affects POGLUT2/3 substrate proteins using cell-based secretion assays, ultrastructural analysis of microfibrils, and analysis of FBN1-ligand interactions. Aim 2 tests whether conserved amino acids in the putative POGLUT2/3 consensus are required for O-glucosylation, and whether MFS mutations in these conserved residues mediate their effects on FBN1 by loss of O-glucose. Aim 3 examines whether loss of POGLUT2/3 impairs the microfibril network in developing lungs using mouse models, histological approaches, and genetic interaction studies. Combined, these aims will provide molecular mechanisms to explain how O-glucose affects the structure and function of the microfibril network.