Activation function 1 of progesterone receptor is required for progesterone antagonism of oestrogen action in the uterus.

BACKGROUND: Progesterone receptor (PGR) is a master regulator of uterine function through antagonistic and synergistic interplays with oestrogen receptors. PGR action is primarily mediated by activation functions AF1 and AF2, but their physiological significance is unknown. RESULTS: We report the first study of AF1 function in mice. The AF1 mutant mice are infertile with impaired implantation and decidualization. This is associated with a delay in the cessation of epithelial proliferation and in the initiation of stromal proliferation at preimplantation. Despite tissue selective effect on PGR target genes, AF1 mutations caused global loss of the antioestrogenic activity of progesterone in both pregnant and ovariectomized models. Importantly, the study provides evidence that PGR can exert an antioestrogenic effect by genomic inhibition of Esr1 and Greb1 expression. ChIP-Seq data mining reveals intermingled PGR and ESR1 binding on Esr1 and Greb1 gene enhancers. Chromatin conformation analysis shows reduced interactions in these genes' loci in the mutant, coinciding with their upregulations. CONCLUSION: AF1 mediates genomic inhibition of ESR1 action globally whilst it also has tissue-selective effect on PGR target genes.

High Levels of Progesterone Receptor B in MCF-7 Cells Enable Radical Anti-Tumoral and Anti-Estrogenic Effect of Progestin.

The widely reported conflicting effects of progestin on breast cancer suggest that the progesterone receptor (PR) has dual functions depending on the cellular context. Cell models that enable PR to fully express anti-tumoral properties are valuable for the understanding of molecular determinant(s) of the anti-tumoral property. This study evaluated whether the expression of high levels of PR in MCF-7 cells enabled a strong anti-tumoral response to progestin. MCF-7 cells were engineered to overexpress PRB by stable transfection. A single dose of Promegestone (R5020) induced an irreversible cell growth arrest and senescence-associated secretory phenotype in MCF-7 cells with PRB overexpression (MCF-7PRB cells) but had no effect on MCF-7 cells with PRA overexpression. The growth-arresting effect was associated with downregulations of cyclin A2 and B1, CDK2, and CDK4 despite an initial upregulation of cyclin A2 and B1. R5020 also induced an evident activation of Nuclear Factor κB (NF-κB) and upregulation of interleukins IL-1α, IL-1ß, and IL-8. Although R5020 caused a significant increase of CD24+CD44+ cell population, R5020-treated MCF-7PRB cells were unable to form tumorspheres and underwent massive apoptosis, which is paradoxically associated with marked downregulations of the pro-apoptotic proteins BID, BAX, PARP, and Caspases 7 and 8, as well as diminution of anti-apoptotic protein BCL-2. Importantly, R5020-activated PRB abolished the effect of estrogen. This intense anti-estrogenic effect was mediated by marked downregulation of ERα and pioneer factor FOXA1, leading to diminished chromatin-associated ERα and FOXA1 and estrogen-induced target gene expression. In conclusion, high levels of agonist-activated PRB in breast cancer cells can be strongly anti-tumoral and anti-estrogenic despite the initial unproductive cell cycle acceleration. Repression of ERα and FOXA1 expression is a major mechanism for the strong anti-estrogenic effect.

Activation function 1 of progesterone receptor is required for mammary development and regulation of RANKL during pregnancy.

Progesterone receptor (PGR) is a member of the nuclear receptor superfamily of transcription factors. It is critical for mammary stem cells expansion, mammary ductal branching and alveologenesis. The transcriptional activity of PGR is mainly mediated by activation functions AF1 and AF2. Although the discovery of AF1 and AF2 propelled the understanding of the mechanism of gene regulation by nuclear receptors, their physiological roles are still poorly understood. This is largely due to the lack of suitable genetic models. The present study reports gain or loss of AF1 function mutant mouse models in the study of mammary development. The gain of function mutant AF1_QQQ exhibits hyperactivity while the loss of function mutant AF1_FFF shows hypoactivity on mammary development. However, the involvement of AF1 is context dependent. Whereas the AF1_FFF mutation causes significant impairment in mammary development during pregnancy or in response to estrogen and progesterone, it has no effect on mammary development in nulliparous mice. Furthermore, Rankl, but not Wnt4 and Areg is a major target gene of AF1. In conclusion, PGR AF1 is a pivotal ligand-dependent activation domain critical for mammary development during pregnancy and it exerts gene specific effect on PGR regulated genes.