A Renal Epithelial Urea Sensor

描述（由申请人提供）：体内肾髓质细胞暴露于异常高浓度的强效变性尿素中，这是肾浓缩机制的结果。这些细胞对这种恶劣环境作出反应和耐受的分子机制，对理解肾脏水和尿素稳态，以及在不同病理生理背景下对代谢应激的抵抗和潜在增强具有重要意义。申请人已经证明肾上皮细胞对外源性尿素表现出独特和特异性的一系列信号反应，这些信号反应具有有丝分裂和应激信号的特征，包括受体酪氨酸激酶效应物的激活。总的假设是，尿素以肾上皮细胞特异性的方式有利地调节有丝分裂（即细胞保护）和凋亡之间的平衡，尿素的这种作用是通过激活（胞外结构域脱落）肝素结合表皮生长因子，通过g蛋白偶联受体依赖的EGF受体家族成员的反激活间接实现的。在Aim I中，尿素增加肾上皮细胞中D-cyclin表达的机制将通过药理学、生化和分子生物学方法的结合，作为尿素诱导的促增殖信号的相关研究。在Aim II中，尿素保护肾上皮细胞免受高渗性促凋亡作用的机制将被研究，并关注先前被证明由尿素激活的假定的细胞保护信号中间体的作用。在Aim 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）的外域脱落在尿素应激分子表型获得方面的作用。此外，这些和相关信号元件在尿素信号传导中的充分性将在异源表达模型中进行检验。

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.