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Submitted on August 8, 2007
Accepted on January 22, 2008
Department of Medicine and Committee on Cancer Biology, University of Chicago, Chicago, Illinois, USA
* To whom correspondence should be addressed. E-mail: sdconzen{at}uchicago.edu.
The glucocorticoid receptor (GR) and its ligand, cortisol, play a central role in human physiology. The exact mechanisms by which GR activation regulates these processes are the subject of intensive investigation. We and others have shown that GR activation can indirectly downregulate specific genes via SGK-1-mediated inhibition of forkhead box O3a (FOXO3a) transcriptional activity. We previously used gene expression microarrays, together with bioinformatic analyses to identify putative FOXO3a target genes in breast epithelial cells. In this paper, we refine our analysis through the use of FOXO3a Chromatin Immunoprecipitation microarrays (ChIP-chip). ChIP-chip results reveal urokinase plasminogen activator (uPA) as a putative novel target of FOXO3a in breast epithelial and breast cancer cell lines. We further show that uPA downregulation following glucocorticoid treatment requires SGK-1-mediated inactivation of FOXO3a activity. Chromatin immunoprecipitation (ChIP) and luciferase assays confirm that FOXO3a can both occupy and transactivate the uPA promoter. Our data suggest that inactivation of FOXO3a following GR activation is an important mechanism contributing to glucocorticoid-mediated repression of uPA gene expression in breast epithelial and cancer cells.
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