Progesterone Receptor Repression of Prolactin/Signal Transducer and Activator of Transcription 5-Mediated Transcription of the β-Casein Gene in Mammary Epithelial Cells

Department of Molecular & Cellular Biology, Baylor College of Medicine, Houston, Texas, United States
Molecular Endocrinology (Impact Factor: 4.02). 02/2007; 21(1):106-25. DOI: 10.1210/me.2006-0297
Source: PubMed


Prolactin (PRL) and glucocorticoids act synergistically to stimulate transcription of the beta-casein milk protein gene. Signal transducer and activator of transcription 5 (Stat5) mediates PRL-dependent trans-activation, and glucocorticoid potentiation occurs through cross talk between glucocorticoid receptor (GR) and Stat5 at the beta-casein promoter. In the mouse, progesterone withdrawal leads to terminal differentiation and secretory activation of the mammary gland at parturition, indicating progesterone's role in repressing milk protein gene expression during pregnancy. To investigate the mechanism of the inhibitory action of progesterone, experiments were performed with cell culture systems reconstituted to express progesterone receptor (PR), the PRL receptor/Stat5 signaling pathway, and GR, enabling evaluation of PR, GR, and Stat5 interactions at the beta-casein promoter. With COS-1, normal murine mammary gland, HC-11, and primary mammary epithelial cells, progestin-PR directly repressed the PRL receptor/Stat5a signaling pathway's mediation of PRL-induced beta-casein transcription. Progestin-PR also inhibited glucocorticoid-GR enhancement of PRL induced trans-activation of beta-casein. Inhibition depended on a functional PR DNA binding domain and specific PR-DNA interactions at the beta-casein promoter. Chromatin immunoprecipitation assays in HC-11 cells revealed recruitment of PR and Stat5a to the beta-casein promoter by progestin or PRL, respectively. Recruitment was disrupted by cotreatment with progestin and PRL, suggesting a mutual interference between activated PR and Stat5a. Without PRL, progestin-PR also recruited Stat5a to the beta-casein promoter, suggesting that recruitment of an unactivated form of Stat5a may contribute to inhibition of beta-casein by progesterone. These results define a negative cross talk between PR and Stat5a/GR that may contribute to the physiological role of progesterone to repress lactogenic hormone induction of the beta-casein gene in the mammary gland during pregnancy.

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Available from: Wolfgang Doppler, Jul 21, 2015
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    • "These findings also indicate that the interferon-gamma responsive elements identified within the RANKL promoter are essential for activation of the JAK2/STAT5A response [51] and potentially important for progestogen-dependent increases. Other studies have shown that nuclear phosphorylated STAT5A is co-localized with PGR and RANKL in cells after EPT [26], further suggesting that progestogen-dependent increases in RANKL transcription may be governed at the RANKL promoter, at least in part, by a complex of PGR and STAT5A, similar to that observed with the β-casein promoter [52]. Finally, EGFR ligands have been shown to strongly decrease OPG expression in an EGFR-dependent manner [27] and activate STAT5A in mammary tissue [53]. "
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    ABSTRACT: Menopausal hormone therapies vary widely in their effects on breast cancer risk, and the mechanisms underlying these differences are unclear. The primary goals of this study were to characterize the mammary gland transcriptional profile of estrogen+progestin therapy in comparison with estrogen-alone or tibolone and investigate pathways of cell proliferation in a postmenopausal primate model. Ovariectomized female cynomolgus macaque monkeys were randomized into the following groups: placebo (Con), oral conjugated equine estrogens (CEE), CEE with medroxyprogesterone acetate (MPA) (CEE+MPA), and tibolone given at a low or high dose (Lo or Hi Tib). All study treatment doses represented human clinical dose equivalents and were administered in the diet over a period of 2 years. Treatment with CEE+MPA had the greatest effect on global mRNA profiles and markers of mammary gland proliferation compared to CEE or tibolone treatment. Changes in the transcriptional patterns resulting from the addition of MPA to CEE were related to increased growth factors and decreased estrogen receptor (ER) signaling. Specific genes induced by CEE+MPA treatment included key members of prolactin receptor (PRLR)/signal transducer and activator of transcription 5 (STAT5), epidermal growth factor receptor (EGFR), and receptor activator of nuclear factor kappa B (RANK)/receptor activator of nuclear factor kappa B ligand (RANKL) pathways that were highly associated with breast tissue proliferation. In contrast, tibolone did not affect breast tissue proliferation but did elicit a mixed pattern of ER agonist activity. Our findings indicate that estrogen+progestin therapy results in a distinct molecular profile compared to estrogen-alone or tibolone therapy, including upregulation of key growth factor targets associated with mammary carcinogenesis in mouse models. These changes may contribute to the promotional effects of estrogen+progestin therapy on breast cancer risk.
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    • "Protein-protein interactions between STAT5 and other cellular proteins are able to modify STAT5 action. One class of protein-protein interactions in mammary epithelial cells is between STAT5 and the nuclear hormone receptors expressed in these cells, including ERα [43-45], progesterone receptor (PR) [46], and glucocorticoid receptor [7,47-50]. Other cellular proteins that have been shown to impact STAT5 activity include PI 3-kinase enhancer A (PIKE-A) [51], serine/threonine protein kinase Akt (AKT) [52], p21-activated kinase 1 (Pak1) [18], the transcription factor protooncogene v-Myb myeloblastosis viral oncogene homolog (avian) (c-Myb) [53], breast tumor kinase (Brk) [54], and caveolin [55]. "
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    ABSTRACT: STAT5 consists of two proteins, STAT5A/B, that impact mammary cell differentiation, proliferation, and survival. In normal development, STAT5 expression and activity are regulated by prolactin signaling with JAK2/ELF5, EGF signaling networks that include c-Src, and growth hormone, insulin growth factor, estrogen, and progesterone signaling pathways. In cancer, erythropoietin signaling can also regulate STAT5. Activation levels are influenced by AKT, caveolin, PIKE-A, Pak1, c-Myb, Brk, beta-integrin, dystroglycan, other STATs, and STAT pathway molecules JAK1, Shp2, and SOCS. TGF-β and PTPN9 can downregulate prolactin- and EGF-mediated STAT5 activation, respectively. IGF, AKT, RANKL, cyclin D1, BCL6, and HSP90A lie downstream of STAT5.
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    • "5.3. Genes regulated more strongly or only by PRA The b-casein promoter is induced by PRL and suppressed more strongly by PRA than PRB (Buser et al., 2007). Two PRE ½ sites flank a STAT5a response element in the promoter and P ligands recruit both PR and STAT5 to these sites. "
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