The Role of HB-EGF in Renal Epithelial Cell Injury

越来越多的证据表明，EGF受体(EGFR；HER1)的激活在急性肾损伤的恢复中发挥了作用。肝素结合的表皮生长因子(HB-EGF)通过EGFR和HER4在哺乳动物肾脏中表达，作为对急性损伤的反应。可溶性HB-EGF的前体为膜相关HB-EGF(proHB-EGF)。我们推测，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的旁分泌信号；2)作为促进细胞-细胞相互作用的膜相关和细胞骨架元件(四环素、整合素和糖蛋白)的支架。因此，ProHB-EGF的切割可能通过释放可作为自分泌和旁分泌生长因子的可溶性HB-EGF，以及通过破坏ProHB-EGF及其相关蛋白的细胞-细胞、细胞-ECM和细胞骨架相互作用而导致细胞激活，从而使上皮细胞易于运动、增殖和去分化。具体目标#1将研究前HBEGF激活旁分泌在调节上皮细胞-细胞相互作用中的作用。具体目标#2将确定ProHBEGF与四环素整合素网络和含硫酸肝素糖蛋白的相互作用在调节细胞-基质和细胞-细胞相互作用中的作用。具体目标#3将研究proHB-EGF保护肾上皮细胞免于凋亡的机制。对于特定的目标#1-3，我们将利用前HB-EGF分子的突变和嵌合体来区分EGFR激活、肝素结合、Tetraspanin相互作用和胞浆蛋白相互作用。特定目的#4将利用表达FLOXED HB-EGF的小鼠与表达靶向肾单位片段特异性Cre重组酶的小鼠以及在近端肾单位过表达HB-EGF的转基因小鼠杂交，以检测HB-EGF表达的改变对急性和进行性肾脏损伤反应的影响。

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.