YB-1 guanidinylation in systemic lupus erythematosus: Studies on molecular mechanisms, functional properties and its potential as biomarker

系统性红斑狼疮（SLE）是一种自身免疫性疾病，几乎可以影响每个器官系统。特别是肾脏受累的患者（狼疮肾炎，LN）仍然显示出很高的发病率和死亡率。我们自己的研究结果表明，受体蛋白Notch-3在LN患者肾小球和狼疮易感小鼠肾脏中的表达显著增加。Notch-3信号通过膜结合（规范）和可溶性配体（包括Y-box结合蛋白(YB)-1）激活。通过质谱分析，我们在SLE患者血清中高度保守的YB-1冷休克区域（YB-1- 2g）的两个赖氨酸残基上检测到特异性胍苷化。这些修饰尤其存在于活动性SLE患者中，尤其是LN患者，并诱导Notch-3显著激活。我们证明了Notch-3在狼疮发展过程中的激活具有许多保护作用，而遗传的Notch-3缺失会加重狼疮的几种表现。本研究旨在分析YB-1胍基化的分子机制和改变的功能后果，并阐明这种修饰是否影响Noch-3信号传导。此外，我们还研究了胍基化的潜在（酶促）机制及其抗原潜能，并将在更大的SLE患者队列中加强我们关于YB-1-2G存在与疾病活动性指数（SLEDAI/BILAG）关联的关键结果。

Systemic lupus erythematosus (SLE) is an autoimmune disease that may virtually affect every organ system. Particularly patients with renal involvement (lupus nephritis, LN) still display a high morbidity and mortality. Our own results demonstrate that expression of receptor protein Notch-3 is significantly increased in glomeruli from LN patients and in kidneys from lupus-prone mice. Notch-3 signalling is activated through membrane-bound (canonical) and soluble ligands including Y-box binding protein (YB)-1. By mass spectrometry, we detected a specific guadinylation at two lysine residues within the highly conserved cold shock domain of YB-1 (YB-1-2G) in sera obtained from SLE patients. These modifications were particularly present in active SLE patients and specifically in LN patients and induced a prominent Notch-3 activation. We demonstrated that Notch-3 activation during lupus development confers a number of protective effects whereas genetic Notch-3 depletion aggravates several lupus manifestations. With the present proposal, we aim to analyze molecular mechanisms and changed functional consequences of YB-1 guadinylation and to clarify whether this modification affects Noch-3 signalling. Furthermore, the underlying (enzymatic) mechanisms of guanidinylation and their antigen potential are investigated and we will strengthen our pivotal results on the association of YB-1-2G presence and disease activity indices (SLEDAI/BILAG) in larger cohorts of SLE patients.