The Role of HB-EGF in Renal Epithelial Cell Injury

越来越多的证据表明，EGF受体（EGFR; HER1）激活在急性肾损伤后恢复中的作用。通过EGFR和HER4发出信号的肝素结合表皮生长因子（HB-EGF）在哺乳动物肾脏中对急性损伤的反应中表达增加。可溶性HB-EGF的前体是膜相关HB-EGF （proHB-EGF）。我们假设在肾上皮细胞中，proHB-EGF介导的细胞功能不同于可溶性HB-EGF。我们认为，proHBEGF通过以下途径帮助维持上皮细胞的极性、完整性和分化：1)通过EGFR和/或HER4传递近肽信号；2)作为促进细胞间相互作用的膜相关元件和细胞骨架元件（四联蛋白、整合蛋白和糖蛋白）的支架。因此，proHB-EGF的裂解可能通过释放可溶性HB-EGF（可作为自分泌和旁分泌生长因子）以及破坏proHB-EGF和相关蛋白的细胞-细胞、细胞- ecm和细胞骨架相互作用（易使上皮细胞运动、增殖和去分化）导致细胞活化。特异性目的1将研究proHBEGF激活近肽在上皮细胞-细胞相互作用中的作用。特异性目标#2将确定proHBEGF与四联蛋白-整合素网和含硫酸肝素糖蛋白相互作用在细胞-基质和细胞-细胞相互作用中的作用。特异性目的#3将研究proHB-EGF保护肾上皮细胞免受凋亡的机制。对于Specific Aims #1-3，我们将利用proHB-EGF分子的突变和嵌合体来区分EGFR激活、肝素结合、四跨蛋白相互作用和细胞质蛋白相互作用。Specific Aim #4将利用表达固定HB-EGF的小鼠与表达靶向肾单元片段特异性Cre重组酶的小鼠的杂交，以及在近端肾单元过表达HB-EGF的转基因小鼠，来研究HB-EGF表达改变对肾脏对急性和进行性损伤的反应的影响。

There is increasing evidence for a role for EGF receptor (EGFR; HER1) activation in recovery from acute renal injury. Expression of heparin-binding epidermal growth factor (HB-EGF), which signals through EGFR as well as HER4, increases in the mammalian kidney in response to acute injury. The precursor for soluble HB-EGF is membrane-associated HB-EGF (proHB-EGF). We hypothesize that in renal epithelial cells, proHB-EGF mediates different cellular functions than soluble HB-EGF. We propose that proHBEGF helps to maintain epithelial cell polarity, integrity and differentiation by: 1) juxtacrine signaling through EGFR and/or HER4; and 2) serving as a scaffold for membrane-associated and cytoskeletal elements (tetraspanins, integrins and glycoproteins) that promote cell-cell interactions. Therefore, cleavage of proHB-EGF may lead to cell activation by release of soluble HB-EGF that can serve as an autocrine and paracrine growth factor as well as by disruption of cell-cell, cell-ECM and cytoskeletal interactions of proHB-EGF and associated proteins that predispose the epithelial cells to motility, proliferation and dedifferentiation. Specific Aim #1 will study the role of juxtacrine activation by proHBEGF in mediation of epithelial cell-cell interactions. Specific Aim #2 will determine the role of proHBEGF's interactions with the tetraspanin-integrin web and with heparin sulfate-containing glycoproteins in mediation of cell-matrix and cell-cell interactions. Specific Aim #3 will investigate the mechanisms by which proHB-EGF protects renal epithelial cells against apoptosis. For Specific Aims #1-3, we will utilize mutations and chimeras of the proHB-EGF molecule that will discriminate among EGFR activation, heparin binding, tetraspanin interaction and cytosolic protein interactions. Specific Aim #4 will utilize crosses of mice expressing floxed HB-EGF with mice expressing targeted nephron segment specific Cre recombinase, as well as transgenic mice overexpressing HB-EGF in proximal nephron, to examine the effects of altered HB-EGF expression on kidney responses to acute and progressive injury.