Development of a detailed understanding of the regulation of renin gene expression, biosynthesis and secretion has been hampered by the lack of suitable cell culture models for the juxtaglomerular (JG) cell - the classical renal site of active renin release into the circulation. We have utilized the approach of transgene targeted oncogenesis to induce neoplasia in renin expressing cells of renal origin and have isolated and established a clonal cell line in in vitro culture. Preliminary studies suggest that this cell line has retained significant features characteristic of the differentiated state of its in vivo counterpart and thus should provide a unique resource with which to investigate important issues of renin gene expression. Most significantly, the 4.1 cell line exhibits high level expression of the endogenous renin gene (Ren 1c) as manifest in abundant renin. Moreover, exogenous renin genes introduced by transfection also exhibit high level expression. We thus propose to investigate the utility of these cells as an assay to define in detail the cis-acting DNA sequences pertinent to renal renin gene expression, and the transcriptional machinery which serves to give the JG cell its unique identity. We will also examine the utility of this cell line to assess mechanisms, and identify components, relevant to the targeting, processing and secretion of the renin polypeptide. It should be invaluable to assess and compare the results obtained with this cell line, which expresses its endogenous renin gene and is thought to be derived from a naturally occurring site of active renin generation, with those previously obtained from heterologous transfected cell systems. Finally, we propose to expand upon our current base to develop renal cell lines harboring conditional oncogenes and to develop representative cell lines from extra-renal sites. Cell lines obtained by conditional oncogenesis may afford opportunities for retention of increased differentiative character and thus provide refined tools for further analysis. Cell lines derived from other tissue sites or organ sites will provide important tools for more detailed analysis of the molecular basis for differential tissue specific expression of the murine renin genes.
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