Novel SAPK Activating Kinase in Renal Epithelial Stress

描述(由申请人提供)：继发于肾小管上皮细胞缺血性损伤的急性肾功能衰竭是患者发病率的主要原因。肾小管上皮细胞损伤导致细胞表型的显著变化，包括细胞形态的改变和遗传程序的诱导，这些遗传程序被认为是调节细胞对损伤的反应的关键。根据损伤的类型或程度，近端肾小管上皮细胞要么遭受亚致死性损伤并恢复，要么死亡并被取代。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质。应激激活蛋白激酶或c-jun氨基末端激酶(JNK)在包括肾脏缺血/再灌注损伤在内的多种细胞应激反应中迅速激活，参与细胞增殖、凋亡和发育的多种调控过程。我们已经从胚胎肾脏中鉴定、克隆并初步鉴定了被称为DLK的蛋白激酶。DLK是混合型谱系激酶家族(MLK)中的一种MAP激酶，可被细胞损伤激活，并能激活JNK。在肾脏中，DLK仅在近端肾小管上皮细胞中表达。鉴于这些观察，我们假设DLK代表信号通路的近端组件，该信号通路参与调节对近端肾小管上皮损伤的反应。部分地，MLK依赖的JNK信号可能通过调节Pax2的磷酸化和激活来影响肾小管损伤反应。转录因子Pax2是肾上皮形态发生的关键因子，在损伤后的近端肾小管上皮细胞中重新表达，并可能指导损伤后的肾小管再生。新的数据表明，Pax2的转录活性可能是由JNK介导的磷酸化调节的，可能是通过依赖MLK的JNK途径。本研究旨在研究DLK在其JNK信号复合体或模块中的基础生化和调节。通过使用生化方法的组合和新准备的DLK缺失小鼠的特征，该项目将开始研究DLK依赖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.