Novel SAPK Activating Kinase in Renal Epithelial Stress

描述（由申请人提供）：继发于小管上皮缺血性损伤的急性肾功能衰竭是患者发病的主要原因。肾小管上皮细胞损伤会导致显著的细胞表型改变，包括形态学改变和基因程序的诱导，这些基因程序被认为是调节细胞对损伤反应的关键。根据损伤的类型或程度，近端小管上皮细胞要么维持亚致死损伤并恢复，要么死亡并被替换。研究调节这些反应的近端信号通路可以更好地理解这些损伤反应的复杂性。应激激活蛋白激酶或c-Jun n -末端激酶（JNK）在包括肾缺血/再灌注损伤在内的多种细胞应激下迅速激活，并参与调节细胞增殖、凋亡和发育等多种过程。我们从胚胎肾脏中克隆出一种蛋白激酶，叫做DLK。DLK是混合谱系激酶家族（MLK）的一种MAP激酶激酶，可被细胞损伤激活，并能激活JNK。在肾脏中，DLK仅在近端小管上皮中表达。鉴于这些观察结果，我们假设DLK代表了参与调节近端小管上皮损伤反应的信号通路的近端组成部分。在某种程度上，mlk依赖的JNK信号可能通过调节Pax2的磷酸化和激活来影响小管损伤反应。对肾上皮形态发生至关重要的转录因子Pax2在损伤后近端小管上皮中重新表达，并可能指导损伤后小管再生。新的数据表明，Pax2的转录活性可能通过mlk依赖的JNK途径受到JNK介导的磷酸化的调节。本研究主要旨在研究DLK在其JNK信号复合物或模块中的基本生物化学和调控。通过结合生化方法和表征新制备的DLK缺失小鼠，该项目将开始研究DLK依赖性信号在肾脏中的作用。

DESCRIPTION (provided by applicant): Acute renal failure secondary to tubular epithelial ischemic injury is a major cause of patient morbidity. Renal tubular epithelial cell injury results in dramatic cellular phenotypic changes including alterations in morphology and induction of genetic programs thought to be critical for regulating the cell's response to injury. Depending on the type or extent of injury, proximal tubular epithelial cells either sustain sublethal injury and recover, or die and are replaced. Investigating the proximal signaling pathways that regulate these responses should provide better understanding of the complex nature of these responses to injury. Stress activating protein kinases or c-Jun N-terminal kinases (JNK) are rapidly activated by multiple cellular stresses including renal ischemia/reperfusion injury and are implicated in regulating processes as diverse as cell proliferation, apoptosis, and development. We have identified, cloned from embryonic kidney, and initially characterized the protein kinase called DLK. DLK is a MAP kinase kinase kinase of the mixed lineage kinase family (MLK) that may be activated by cellular injury and is capable of activating JNK. In the kidney, DLK is uniquely expressed in the proximal tubular epithelium. Given these observations, we hypothesize that DLK represents a proximal component of a signaling pathway that participates in modulating the response to proximal tubular epithelial injury. In part, MLK-dependent JNK signaling might affect the tubular injury response by regulating Pax2 phosphorylation and activation. Critical for renal epithelial morphogenesis, the transcription factor Pax2 is re-expressed in proximal tubular epithelium following injury and may direct post-injury tubular regeneration. New data suggests that Pax2 transcriptional activity is regulated by JNK-mediated phosphorylation potentially via an MLK-dependent JNK pathway.This proposal seeks primarily to investigate the fundamental biochemistry and regulation of DLK within its JNK signaling complex or module. By using a combination of biochemical approaches and by characterizing a newly prepared DLK null mouse, this project will begin to investigate the role of DLK-dependent signaling in the kidney.