A Renal Epithelial Urea Sensor

描述(由申请人提供)：由于肾脏浓缩机制，活体肾髓质细胞暴露在极高浓度的强变性尿素中。这些细胞对这种恶劣环境的反应和耐受的分子机制对于理解肾脏水和尿素的动态平衡，以及在不同的病理生理环境下理解和潜在地增强对代谢应激的抵抗力具有重要意义。申请人已经证明，肾上皮细胞对外源尿素具有独特和特异的一系列信号反应，具有促有丝分裂和应激信号的特征，其中包括激活受体酪氨酸激酶的效应器。最重要的假设是，尿素以一种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，并且这种作用是通过G蛋白偶联受体依赖的反式激活EGF受体家族成员而间接实现的，该反式激活是通过肝素结合的表皮生长因子的激活(胞外区脱落)实现的。在目标I中，通过结合药理学、生化和分子生物学方法，将尿素增加肾上皮细胞D-细胞周期蛋白表达的机制作为尿素诱导的促增殖信号的相关性进行研究。在AIM II中，将研究尿素保护肾上皮细胞免受高张促凋亡作用的机制，重点关注先前被尿素激活的假定的细胞保护信号中间体的作用。在目标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)胞外结构域脱落在获得尿素应激分子表型方面的作用。此外，这些和相关的信号元件对于尿素信号的充分性将在异源表达的模型中被检验。

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.