Novel SAPK Activating Kinase in Renal Epithelial Stress

描述（由申请方提供）：继发于肾小管上皮缺血性损伤的急性肾衰竭是患者发病的主要原因。肾小管上皮细胞损伤导致显著的细胞表型变化，包括形态学改变和被认为对调节细胞对损伤的反应至关重要的遗传程序的诱导。根据损伤的类型或程度，近端肾小管上皮细胞要么承受亚致死性损伤并恢复，要么死亡并被替换。研究调节这些反应的近端信号通路应该能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）被多种细胞应激（包括肾缺血/再灌注损伤）快速激活，并参与调节细胞增殖、凋亡和发育等多种过程。我们已经从胚胎肾中鉴定、克隆并初步表征了名为DLK的蛋白激酶。DLK是混合谱系激酶家族（MLK）的MAP激酶，其可以通过细胞损伤激活并且能够激活JNK。在肾脏中，DLK仅在近端肾小管上皮中表达。鉴于这些观察结果，我们假设DLK代表参与调节近端肾小管上皮损伤反应的信号通路的近端组分。MLK依赖的JNK信号通路可能通过调节Pax 2的磷酸化和激活来影响肾小管损伤反应。对于肾上皮形态发生至关重要的是，转录因子Pax 2在损伤后的近端肾小管上皮中重新表达，并可指导损伤后肾小管再生。新的研究结果表明，Pax 2的转录活性可能通过JNK介导的磷酸化作用，通过MLK依赖的JNK通路来调节，本研究主要探讨DLK在其JNK信号复合物或模块中的基本生物化学和调控。通过使用生物化学方法的组合和通过表征新制备的DLK缺失小鼠，该项目将开始研究DLK依赖性信号传导在肾脏中的作用。

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.