Glucocorticoid receptor activation signals through forkhead transcription factor 3a in breast cancer cells.
Activation of the glucocorticoid receptor (GR) plays a critical role in the stress response of virtually all cell types. Despite recent advances in large-scale genomic and proteomic data acquisition, identification of physiologically relevant molecular events downstream of nuclear hormone receptor activation remains challenging. By analyzing gene expression changes 30 min after dexamethasone (Dex) treatment, we previously found that immediate induction of serum and glucocorticoid-regulated kinase-1 (SGK-1) expression is required for GR-mediated mammary epithelial cell survival signaling. We now report that activation of the GR mediates Forkhead transcription factor 3a (FOXO3a) phosphorylation and inactivation in mammary epithelial cells. GR-mediated induction of SGK-1 expression is required for FOXO3a inactivation; additional growth factor stimulation is not required. To further explore the gene expression changes that occur downstream of GR-mediated FOXO3a inactivation, we analyzed temporal gene expression data and selected GR-down-regulated genes containing core FOXO3a binding motifs in their proximal promoters. This approach revealed several previously unrecognized transcriptional target genes of FOXO3a, including IGF binding protein-3 (IGFBP-3). Endogenous IGFBP-3 expression was confirmed to be dependent on the GR-SGK-1-FOXO3a signaling pathway. Moreover, GR activation decreased FOXO3a-induced apoptosis in SK-BR-3 breast cancer cells. Collectively, our data suggest that GR-mediated FOXO3a inactivation is an important mechanism contributing to glucocorticoid-mediated mammary epithelial cell survival.
Wu
Wei
W
Department of Medicine and Committee on Cancer Biology, MC 2115, University of Chicago, Chicago, Illinois 60637, USA.
Zou
Min
M
Brickley
Deanna R
DR
Pew
Travis
T
Conzen
Suzanne D
SD
D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D019295:Computational Biology; D017931:DNA Primers; D005260:Female; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism; D008156:Luciferases; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D000099184:Serum-Glucocorticoid Regulated Kinases
D017931:DNA Primers; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D017874:Immediate-Early Proteins; D018972:Insulin-Like Growth Factor Binding Protein 3; D008156:Luciferases; D017346:Protein Serine-Threonine Kinases; D011965:Receptors, Glucocorticoid; D000099184:Serum-Glucocorticoid Regulated Kinases; C499517:FOXO3 protein, human