POLYCYSTIN MODULATION OF GLUCOCORTICOID RECEPTOR ACTIVITY

描述：(直接取自应用程序)多囊肾通常被描述为分化异常。我们的长期目标是了解PKD1的突变是如何导致这种异常分化状态并导致肾功能丧失的。多囊蛋白-1是PKD1基因的蛋白产物，被认为是一种质膜受体，介导信号转导事件，从而调节与获得和/或维持肾上皮细胞终末分化状态相关的基因表达。其中一个基因家族的肾脏表达与分化表型有关，并且已被证明在囊性肾脏中表达异常，这就是编码外源代谢谷胱甘肽S转移酶的基因。我们新的初步数据表明，在稳定表达的肾上皮细胞系中，膜导向的多囊蛋白融合蛋白可以增强内源性GST-Ya基因在糖皮质激素(GC)诱导下的表达。GCs参与细胞生长和分化的调节。糖皮质激素的大部分作用是由配体激活的糖皮质激素受体(GR)介导的，GR是一种转录调节因子，其活性受到磷酸化的影响。多囊藻毒素激活JNK和抑制GSK-3，这两个已知的磷酸化GR的激酶加在一起，这些数据表明，多囊藻毒素可以调节信号转导通路，调节GR的活性，从而导致GC诱导的GST-Ya基因表达的增强。多囊蛋白介导的信号通路和GC反应通路之间的串扰可能代表了多囊蛋白影响肾上皮细胞分化状态的一般机制，并可能被证明与多囊肾病相关的一些致病机制特别相关。本项目将利用GST-Ya基因启动子及其GC诱导的表达作为一个模型系统来确定多囊藻毒素在调节GR调节功能中的作用。这一目标将通过以下具体目标来实现：1)确定多囊藻毒素调节GC诱导的GST-Ya基因表达的核机制(S)；2)确定多囊藻毒素表达对GR活性的影响(S)；以及3)确定多囊藻毒素调节GR功能和GC诱导的GST-Ya基因表达所涉及的信号转导途径和下游效应因子。该项目有望对多囊藻毒素影响肾小管分化和防止PKD肾功能丧失的机制有新的认识。

Description: (Taken directly from the application) Polycystic kidneys are generally described as abnormally differentiated. Our long term goal is to understand how mutations in PKD1 result in this abnormally differentiated state and lead to the loss of renal function. Polycystin-1, the protein product of the PKD1 gene, is thought to be a plasma membrane receptor that mediates signal transduction events and thereby regulates gene expression associated with the acquisition and/or maintenance of the terminally differentiated state of renal epithelial cells. One family of genes whose renal expression is associated with a differentiated phenotype and whose expression has been shown to be aberrant in cystic kidneys is that encoding the xenobiotic-metabolizing glutathione S-transferase (GST) enzymes. Our new preliminary data demonstrates that the glucocorticoid (GC)-inducible expression of the endogenous GST-Ya gene is enhanced by expression of a membrane-directed polycystin fusion protein in a stably transfected renal epithelial cell line. GCs are involved in the regulation of cell growth and differentiation. Most of the effects of GCs are mediated by the ligand-activated glucocorticoid receptor (GR) that functions as a transcriptional regulator whose activity is affected by phosphorylation. Polycystin activates JNK and inhibits GSK-3, two kinases known to phosphorylate GR Taken together, these data suggest that polycystin could regulate signal transduction pathways that modulate the activity of GR and thereby result in augmentation of the GC-induced expression of the GST-Ya gene. Cross-talk between polycystin-mediated signaling pathways and the GC response pathway may represent a general mechanism by which polycystin influences the differentiated state of renal epithelial cells and may prove to be particularly relevant to some of the pathogenetic mechanisms associated with polycystic kidney disease. This project will utilize the GST-Ya gene promoter and its GC-induced expression as a model system in which to determine the role of polycystin in modulating GR-regulated functions. This objective will be addressed by the following Specific Aims: 1) determine the nuclear mechanism(s) by which polycystin modulates GC-induced GST-Ya gene expression; 2) determine the effect(s) of polycystin expression on GR activity; and 3) determine the signal transduction pathways and downstream effectors involved in polycystin modulation of GR function and GC-induced GST-Ya gene expression. This project is anticipated to lead to new insight into the mechanisms by which polycystin affects renal tubular differentiation and prevents the loss of renal function in PKD.