A Renal Epithelial Urea Sensor

描述（由申请人提供）：由于肾浓缩机制，体内肾髓质细胞暴露于极高浓度的强效变性剂尿素。这些细胞通过其响应和耐受这种恶劣环境的分子机制对于理解肾水和尿素稳态以及理解和潜在增强在不同病理生理学背景下对代谢应激的抵抗力具有意义。本申请人已经表明，肾上皮细胞独特且特异地表现出对外源性尿素的一系列信号传导应答，其具有促有丝分裂和应激信号传导的特征，并且其包括受体酪氨酸激酶的效应物的活化。最重要的假设是尿素有利地调节有丝分裂（即，细胞保护）和以肾上皮细胞特异性方式的细胞凋亡，并且尿素的这种作用是通过G蛋白偶联受体依赖性EGF受体家族成员的反式激活间接实现的，所述G蛋白偶联受体依赖性反式激活经由肝素结合表皮生长因子的激活（胞外域脱落）实现。在目的I中，尿素增加肾上皮细胞中D-细胞周期蛋白表达的机制将通过药理学、生物化学和分子生物学方法的组合作为尿素诱导的促增殖信号传导的相关性进行研究。在目的II中，将研究尿素保护肾上皮细胞免受高渗性促凋亡作用的机制，并关注先前被尿素激活的假定细胞保护信号中间体的作用。在目的III中，根据我们最新的初步数据，将评估肝素结合表皮生长因子（HB-EGF）胞外结构域脱落在尿素应激分子表型获得方面的作用。此外，将在异源表达模型中检查这些和尿素信号传导的相关信号传导元件的充分性。

DESCRIPTION (provided by applicant): Cells of the renal medulla in vivo are exposed to extraordinarily high concentrations of the potent denaturant urea as a consequence of the renal concentrating mechanism. The molecular mechanism through which these cells respond to and tolerate this harsh environment has implications for the understanding of renal water and urea homeostasis, and for the understanding of and potential enhancement of resistance to metabolic stress in diverse pathophysiological contexts. The applicant has shown that renal epithelial cells uniquely and specifically exhibit a series of signaling responses to exogenous urea that has features of both mitogenic and stress signaling, and which includes activation of effectors of a receptor tyrosine kinase. The overarching hypothesis is that urea favorably regulates the balance between mitogenesis (i.e., cytoprotection) and apoptosis in a renal epithelial cell-specific fashion, and that this effect of urea is achieved indirectly through G-protein-coupled receptor-dependent transactivation of an EGF receptor family member via activation (ectodomain shedding) of heparin-binding epidermal growth factor. In Aim I, the mechanism through which urea increases D-cyclin expression in renal epithelial cells will be investigated as a correlate of urea-inducible pro-proliferative signaling, through a combination of pharmacological, biochemical, and molecular biological approaches. In Aim II, the mechanism through which urea protects from the pro-apoptotic effect of hypertonicity in renal epithelial cells will be investigated, with attention to the role of putative cytoprotective signaling intermediates previously shown to be activated by urea. In Aim III, in light of our newest preliminary data, the role of ectodomain shedding of heparin-binding epidermal growth factor (HB-EGF) will be assessed with respect to the acquisition of the urea-stressed molecular phenotype. In addition, the sufficiency of these and related signaling elements for urea signaling will be examined in models of heterologous expression.