Abstract
Prolactin (PRL) serves a critical role in breast cancer progression via activation of its cognate receptor. These studies reveal up-regulation of PRLR gene expression by PRL in absence of estradiol in MCF-7 and T47D breast cancer cells. PRL/PRLR via activation of STAT5 that binds a GAS-element in the PRLR gene and the participation of ERα stimulates PRLR transcription/expression. PRL/PRLR induces phosphorylation of ERα through the JAK2/PI3K/MAPK/ERK and JAK2/HER2 activated pathways. The increased recruitment of phospho-ERα, induced by PRL to Sp1 and C/EBPβ at PRLR promoter sites is essential for PRL-induced PRLR transcription. This recruitment is prevented by blockade of PRL expression using RNA interference or ERα phosphorylation using specific inhibitors of PI3K and ERK. Direct evidence is provided for local actions of PRL, independent of estradiol, in the up-regulation of PRLR transcription/expression by an activation-loop between STAT5 and the phospho-ERα/Sp1/C/EBPβ complex with requisite participation of signaling mechanisms. PRL's central role in the up-regulation of PRLR maximizes the action of the endogenous hormone. This study offers mechanistically rational basis for invasiveness fueled by prolactin in refractory states to adjuvant therapies in breast cancer.
Publication types
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Research Support, N.I.H., Intramural
MeSH terms
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Binding Sites / genetics
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Breast Neoplasms / genetics
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Breast Neoplasms / pathology
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CCAAT-Enhancer-Binding Protein-beta / genetics
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CCAAT-Enhancer-Binding Protein-beta / metabolism
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Cell Line, Tumor
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Enzyme Activation
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Estradiol / metabolism
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Estrogen Receptor alpha / genetics*
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Estrogen Receptor alpha / metabolism
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Extracellular Signal-Regulated MAP Kinases / antagonists & inhibitors
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Extracellular Signal-Regulated MAP Kinases / genetics
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Female
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Humans
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MAP Kinase Signaling System
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MCF-7 Cells
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Neoplasm Invasiveness / pathology
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Phosphatidylinositol 3-Kinases / genetics
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Phosphoinositide-3 Kinase Inhibitors
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Phosphorylation
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Prolactin / biosynthesis
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Prolactin / genetics*
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Promoter Regions, Genetic / genetics
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RNA Interference
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RNA, Small Interfering
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Receptors, Prolactin / genetics
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Receptors, Prolactin / metabolism*
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STAT5 Transcription Factor / genetics*
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Sp1 Transcription Factor / genetics
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Sp1 Transcription Factor / metabolism
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Transcription, Genetic / genetics
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Tumor Suppressor Proteins / genetics*
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Up-Regulation
Substances
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CCAAT-Enhancer-Binding Protein-beta
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CEBPB protein, human
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Estrogen Receptor alpha
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Phosphoinositide-3 Kinase Inhibitors
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RNA, Small Interfering
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Receptors, Prolactin
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STAT5 Transcription Factor
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STAT5A protein, human
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STAT5B protein, human
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Sp1 Transcription Factor
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SP1 protein, human
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Tumor Suppressor Proteins
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Estradiol
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Prolactin
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Extracellular Signal-Regulated MAP Kinases