Renin gene expression is partly mediated by intracellular cAMP in juxtaglomerular (JG) cells. We have identified a novel cAMP responsive element in the promoter of the mouse renin gene and have termed this element CNRE. We have demonstrated that a nuclear hormone receptor family member, LXR alpha (LXR), binds to this sequence, increases basal renin expression and mediates the cAMP-dependent induction. Furthermore, the c-myc gene, which also contains the CNRE element, is similarly regulated. We postulate that LXR plays a central role in renin regulation. Through its interactions with its specific cis element (the CNRE) in the renin and c-myc promoters, LXR coordinately increases renin gene expression (regulating JG cell phenotype) and induces cell growth and differentiation (regulating JG cell number), thereby contributing to JG cell hyperplasia. This unifying hypothesis may provide a potential explanation for the observation that the JG cell can undergo hyperplasia while maintaining a highly specialized renin-producing phenotype To test this hypothesis, we will address the following questions: 1. Are LXR and renin co-localized and co-expressed in vivo? We will co-localize LXR and renin gene expression in kidneys by immunohistochemistry, in situ hybridization and by analysis of FACS-sorted cells expressing a renin promoter-GFP construct. 2. What are the consequences of JG-directed overexpression of LXR? We will construct a vector expressing LXR under the control the renin gene promoter. We hypothesize that this will result in a positive feedback overexpression of LXR and renin and may result in a model of JG cell hyperplasia with high renin hypertension. 3. What are the consequences of disruption of LXR? We will examine the consequences of disruption of the LXR gene on renin expression. 4. What are the consequences of disruption of the CNRE in the renin gene? We will disrupt the CNRE element (LXR binding site) and examine the consequences on renin gene expression. 5. What is the role of the LXR-c-myc pathway in JG cell hyperplasia? We will examine the status of c-myc expression in JG cells under different conditions (Aims 1-3) and will examine the consequences of JG cell specific c-myc gene disruption. Taken together, this grant will define the role of LXR in renin regulation and JG hyperplasia. ? ?
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