Abstract
Glucocorticoid receptor (GR) activation has recently been shown to inhibit apoptosis in breast epithelial cells. We have previously described a group of genes that is rapidly up-regulated in these cells following dexamethasone (Dex) treatment. In an effort to dissect the mechanisms of GR-mediated breast epithelial cell survival, we now examine the molecular events downstream of GR activation. Here we show that GR activation leads to both the rapid induction of MAPK phosphatase-1 (MKP-1) mRNA and its sustained expression. Induction of the MKP-1 protein in the MCF10A-Myc and MDA-MB-231 breast epithelial cell lines was also seen. Paclitaxel treatment resulted in MAPK activation and apoptosis of MDA-MB-231 breast cancer cells, and both processes were inhibited by Dex pretreatment. Furthermore, induction of MKP-1 correlated with the inhibition of extracellular signal-regulated kinase (ERK1/2) and c-Jun N-terminal kinase (JNK) activity, whereas p38 activity was minimally affected. Blocking Dex-induced MKP-1 induction using small interfering RNA increased ERK1/2 and JNK phosphorylation and decreased cell survival. ERK1/2 and JNK inactivation was associated with Ets-like transcription factor-1 (ELK-1) dephosphorylation. To explore the gene expression changes that occur downstream of ELK-1 dephosphorylation, we used a combination of temporal gene expression data and promoter element analyses. This approach revealed a previously unrecognized transcriptional target of ELK-1, the human tissue plasminogen activator (tPA). We verified the predicted ELK-1--> tPA transcriptional regulatory relationship using a luciferase reporter assay. We conclude that GR-mediated MAPK inactivation contributes to cell survival and that the potential transcriptional targets of this inhibition can be identified from large scale gene array analysis.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Motifs
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Antineoplastic Agents, Phytogenic / pharmacology
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Apoptosis
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Blotting, Northern
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Blotting, Western
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Breast / metabolism
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Cell Cycle Proteins / metabolism
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Cell Cycle Proteins / physiology*
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Cell Line, Tumor
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Cell Survival
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DNA-Binding Proteins / biosynthesis
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Down-Regulation
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Dual Specificity Phosphatase 1
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Enzyme Activation
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Gene Expression Regulation, Neoplastic
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Genes, Reporter
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Humans
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Immediate-Early Proteins / metabolism
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Immediate-Early Proteins / physiology*
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JNK Mitogen-Activated Protein Kinases / biosynthesis
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JNK Mitogen-Activated Protein Kinases / metabolism
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Luciferases / metabolism
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MAP Kinase Kinase 4
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MAP Kinase Signaling System*
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Mitogen-Activated Protein Kinase 1 / biosynthesis
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Mitogen-Activated Protein Kinase 3 / biosynthesis
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Mitogen-Activated Protein Kinase Kinases / metabolism
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Mitogen-Activated Protein Kinases / metabolism*
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Models, Biological
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Oligonucleotide Array Sequence Analysis
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Paclitaxel / pharmacology*
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Phosphoprotein Phosphatases / metabolism
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Phosphoprotein Phosphatases / physiology*
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Phosphorylation
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Protein Binding
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Protein Phosphatase 1
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Protein Tyrosine Phosphatases / metabolism
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Protein Tyrosine Phosphatases / physiology*
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Proto-Oncogene Proteins / biosynthesis
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RNA, Messenger / metabolism
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RNA, Small Interfering / metabolism
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Receptors, Glucocorticoid / metabolism*
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Reverse Transcriptase Polymerase Chain Reaction
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Time Factors
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Tissue Plasminogen Activator / metabolism
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Transcription Factors / biosynthesis
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Transcription, Genetic
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Transfection
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ets-Domain Protein Elk-1
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p38 Mitogen-Activated Protein Kinases / metabolism
Substances
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Antineoplastic Agents, Phytogenic
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Cell Cycle Proteins
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DNA-Binding Proteins
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ELK1 protein, human
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Immediate-Early Proteins
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Proto-Oncogene Proteins
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RNA, Messenger
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RNA, Small Interfering
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Receptors, Glucocorticoid
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Transcription Factors
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ets-Domain Protein Elk-1
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Luciferases
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JNK Mitogen-Activated Protein Kinases
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases
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p38 Mitogen-Activated Protein Kinases
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MAP Kinase Kinase 4
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Mitogen-Activated Protein Kinase Kinases
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Phosphoprotein Phosphatases
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Protein Phosphatase 1
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DUSP1 protein, human
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Dual Specificity Phosphatase 1
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Protein Tyrosine Phosphatases
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Tissue Plasminogen Activator
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Paclitaxel