PREPROEGF, PROTGF, AND EGF RECEPTOR IN RENAL EPITHELIA

极化肾小管上皮细胞单层形成选择性 动态平衡的根本障碍，部分是通过结构性和 质膜的功能极性。膜蛋白与 通过以下方式将专门的功能定位于顶端或基底侧面 对信号进行内在分类。这项提案的总体目标是 理解三种相关血浆的生物发生和极化分选 膜蛋白在肾脏发生和肾小管中的重要作用 细胞增殖：多肽生长的膜结合前体 表皮生长因子(PreproEGF)，表达于上皮细胞顶面 粗大的Henle(Talh)升支和远端卷曲的细胞 小管；结构相关多肽的膜结合前体， 转化生长因子α(ProTGFpha)，它似乎是 在集合管细胞的顶膜上表达；细胞 表皮生长因子和转化生长因子α受体(EGFR)，发现于基底外侧 大多数肾小管段的表面。配体的不对称局域化 受体可能有助于解释为什么肾上皮细胞正常 除肾小管损伤时外，在体内处于静止状态。PreproEGF、TGFAlpha和 EGFR表面的极性也可能影响肾脏的器官发生，因为它们的 在发育过程中，表达受到严格的调控。它最近一直在 表明某些膜蛋白的表面极性发生了一定的变化 病理生理条件。例如，有报道称，EGFR 慢性阻塞性肺疾病患者囊性上皮细胞的极性部分反转 常染色体显性遗传多囊肾病(ADPKD)。如果是真的，那么 EGF/TGFpha信号转导可能受到不对称的深刻影响 ADPKD上皮细胞中其他细胞成分的表达 这取决于EGFR的表达位置。这项建议的具体目的 将描绘新合成的前EGF的细胞内运输， 肾小管上皮细胞中的原转化生长因子α和表皮生长因子受体；鉴定固有的 肾小管中前原EGF、原转化生长因子α和EGFR的信号分选 上皮细胞；并确定调控的翻译后效应 丝氨酸/苏氨酸磷酸化对肾小管上皮细胞EGFR转运的影响 细胞，重点是内吞后分选途径。

Monolayers of polarized kidney tubule epithelial cells form a selective barrier fundamental to homeostasis, achieved in part by structural and functional polarity of the plasma membrane. Membrane proteins with specialized functions are targeted to apical or basolateral surfaces by intrinsic sorting signals. The overall goal of this proposal is to understand the biogenesis and polarized sorting of three related plasma membrane proteins that play important roles in renal genesis and tubular cell proliferation: the membrane-bound precursor of the polypeptide growth factor EGF (preproEGF), which is expressed on apical surfaces of epithelial cells in the thick ascending limb of Henle (TALH) and distal convoluted tubule; the membrane-bound precursor of a structurally related polypeptide, transforming growth factor alpha (proTGFalpha), which appears to be expressed on apical membranes of collecting tubule cells; and the cellular receptor for EGF and TGFalpha (EGFR), which is found on basolateral surfaces of most renal tubule segments. Asymmetric localization of ligand and receptor may help explain why renal epithelial cells are normally quiescent in vivo except during tubular damage. PreproEGF, TGFalpha, and EGFR surface polarity may also influence kidney organogenesis, since their expression is tightly regulated during development. It has recently been shown that surface polarity of some membrane proteins is altered in certain pathophysiological conditions. There are reports, for example, that EGFR polarity is partially reversed in cystic epithelia from patients with autosomal dominant polycystic kidney disease (ADPKD). If true, then EGF/TGFalpha signalling could be profoundly influenced by asymmetric expression of other cellular components in ADPKD epithelial cells, depending on where EGFR is expressed. The specific aims of this proposal will delineate intracellular trafficking of newly synthesized preproEGF, proTGFalpha, and EGFR in renal tubular epithelial cells; identify intrinsic sorting signals for preproEGF, proTGFalpha and EGFR in renal tubular epithelial cells; and determine the effect of regulated posttranslational Ser/Thr phosphorylation on EGFR trafficking in renal tubular epithelial cells, with an emphasis on post-endocytotic sorting pathways.