Progesterone induction of the 11beta-hydroxysteroid dehydrogenase type 2 promoter in breast cancer cells involves coordinated recruitment of STAT5A and progesterone receptor to a distal enhancer and polymerase tracking

Antiprogestins for breast cancer treatment: We are almost ready

The development of antiprogestins was initially a gynecological purpose. However, since mifepristone was developed, its application for breast cancer treatment was immediately proposed. Later, new compounds with lower antiglucocorticoid and antiandrogenic effects were developed to be applied to different pathologies, including breast cancer. We describe herein the studies performed in the breast cancer field with special focus on those reported in recent years, ranging from preclinical biological models to those carried out in patients. We highlight the potential use of antiprogestins in breast cancer prevention in women with BRCA1 mutations, and their use for breast cancer treatment, emphasizing the need to elucidate which patients will respond. In this sense, the PR isoform ratio has emerged as a possible tool to predict antiprogestin responsiveness. The effects of combined treatments of antiprogestins together with other drugs currently used in the clinic, such as tamoxifen, CDK4/CDK6 inhibitors or pembrolizumab in preclinical models is discussed since it is in this scenario that antiprogestins will be probably introduced. Finally, we explain how transcriptomic or proteomic studies, that were carried out in different luminal breast cancer models and in breast cancer samples that responded or were predicted to respond to the antiprogestin therapy, show a decrease in proliferative pathways. Deregulated pathways intrinsic of each model are discussed, as well as how these analyses may contribute to a better understanding of the mechanisms involved.

Age-associated genes in human mammary gland drive human breast cancer progression

Background

Aging is a comorbidity of breast cancer suggesting that aging-associated transcriptome changes may promote breast cancer progression. However, the mechanism underlying the age effect on breast cancer remains poorly understood.

Method

We analyzed transcriptomics of the matched normal breast tissues from the 82 breast cancer patients in The Cancer Genome Atlas (TCGA) dataset with linear regression for genes with age-associated expression that are not associated with menopause. We also analyzed differentially expressed genes between the paired tumor and non-tumor breast tissues in TCGA for the identification of age and breast cancer (ABC)-associated genes. A few of these genes were selected for further investigation of their malignancy-regulating activities with in vitro and in vivo assays.

Results

We identified 148 upregulated and 189 downregulated genes during aging. Overlapping of tumor-associated genes between normal and tumor tissues with age-dependent genes resulted in 14 upregulated and 24 downregulated genes that were both age and breast cancer associated. These genes are predictive in relapse-free survival, indicative of their potential tumor promoting or suppressive functions, respectively. Knockdown of two upregulated genes (DYNLT3 and P4HA3) or overexpression of the downregulated ALX4 significantly reduced breast cancer cell proliferation, migration, and clonogenicity. Moreover, knockdown of P4HA3 reduced growth and metastasis whereas overexpression of ALX4 inhibited the growth of xenografted breast cancer cells in mice.

Conclusion

Our study suggests that transcriptome alterations during aging may contribute to breast tumorigenesis. DYNLT3, P4HA3, and ALX4 play significant roles in breast cancer progression.

Tributyltin and triphenyltin induce 11β-hydroxysteroid dehydrogenase 2 expression and activity through activation of retinoid X receptor α

Exposure to the environmental pollutants organotins is of toxicological concern for the marine ecosystem and sensitive human populations, including pregnant women and their unborn children. Using a placenta cell model, we investigated whether organotins at nanomolar concentrations affect the expression and activity of 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2). 11β-HSD2 represents a placental barrier controlling access of maternal glucocorticoids to the fetus. The organotins tributyltin (TBT) and triphenyltin (TPT) induced 11β-HSD2 expression and activity in JEG-3 placenta cells, an effect confirmed at the mRNA level in primary human trophoblast cells. Inhibition/knock-down of retinoid X receptor alpha (RXRα) in JEG-3 cells reduced the effect of organotins on 11β-HSD2 activity, mRNA and protein levels, revealing involvement of RXRα. Experiments using RNA and protein synthesis inhibitors indicated that the effect of organotins on 11β-HSD2 expression was direct and caused by increased transcription. Induction of placental 11β-HSD2 activity by TBT, TPT and other endocrine disrupting chemicals acting as RXRα agonists may affect placental barrier function by altering the expression of glucocorticoid-dependent genes and resulting in decreased availability of active glucocorticoids for the fetus, disturbing development and increasing the risk for metabolic and cardiovascular complications in later life.

Molecular mechanisms underlying progesterone receptor action in breast cancer: Insights into cell proliferation and stem cell regulation

The ovarian steroid hormone progesterone and its nuclear receptor, the Progesterone Receptor (PR), play an essential role in the regulation of cell proliferation and differentiation in the mammary gland. In addition, experimental and clinical evidence demonstrate their critical role in controlling mammary gland tumorigenesis and breast cancer development. When bound to its ligand, the main action of PR is as a transcription factor, which regulates the expression of target genes networks. PR also activates signal transduction pathways through a rapid or non-genomic mechanism in breast cancer cells, an event that is fully integrated with its genomic effects. This review summarizes the molecular mechanisms of the ligand-activated PR actions that drive epithelial cell proliferation and the regulation of the stem cell population in the normal breast and in breast cancer.

The C/ebp-Atf response element (CARE) location reveals two distinct Atf4-dependent, elongation-mediated mechanisms for transcriptional induction of aminoacyl-tRNA synthetase genes in response to amino acid limitation

The response to amino acid (AA) limitation of the entire aminoacyl-tRNA synthetase (ARS) gene family revealed that 16/20 of the genes encoding cytoplasmic-localized enzymes are transcriptionally induced by activating transcription factor 4 (Atf4) via C/ebp-Atf-Response-Element (CARE) enhancers. In contrast, only 4/19 of the genes encoding mitochondrial-localized ARSs were weakly induced. Most of the activated genes have a functional CARE near the transcription start site (TSS), but for others the CARE is downstream. Regardless of the location of CARE enhancer, for all ARS genes there was constitutive association of RNA polymerase II (Pol II) and the general transcription machinery near the TSS. However, for those genes with a downstream CARE, Atf4, C/ebp-homology protein (Chop), Pol II and TATA-binding protein exhibited enhanced recruitment to the CARE during AA limitation. Increased Atf4 binding regulated the association of elongation factors at both the promoter and the enhancer regions, and inhibition of cyclin-dependent kinase 9 (CDK9), that regulates these elongation factors, blocked induction of the AA-responsive ARS genes. Protein pull-down assays indicated that Atf4 directly interacts with CDK9 and its associated protein cyclin T1. The results demonstrate that AA availability modulates the ARS gene family through modulation of transcription elongation.

Heregulin Co-opts PR Transcriptional Action Via Stat3 Role As a Coregulator to Drive Cancer Growth

Accumulated findings have demonstrated the presence of bidirectional interactions between progesterone receptor (PR) and the ErbB family of receptor tyrosine kinases signaling pathways in breast cancer. We previously revealed signal transducer and activator of transcription 3 (Stat3) as a nodal convergence point between said signaling pathways proving that Stat3 is activated by one of the ErbBs' ligands, heregulin (HRG)β1 via ErbB2 and through the co-option of PR as a signaling molecule. Here, we found that HRGβ1 induced Stat3 recruitment to the promoters of the progestin-regulated cell cycle modulators Bcl-XL and p21(CIP1) and also stimulated Stat3 binding to the mouse mammary tumor virus promoter, which carries consensus progesterone response elements. Interestingly, HRGβ1-activated Stat3 displayed differential functions on PR activity depending on the promoter bound. Indeed, Stat3 was required for PR binding in bcl-X, p21(CIP1), and c-myc promoters while exerting a PR coactivator function on the mouse mammary tumor virus promoter. Stat3 also proved to be necessary for HRGβ1-induced in vivo tumor growth. Our results endow Stat3 a novel function as a coregulator of HRGβ1-activated PR to promote breast cancer growth. These findings underscore the importance of understanding the complex interactions between PR and other regulatory factors, such as Stat3, that contribute to determine the context-dependent transcriptional actions of PR.

Transcriptional complexity and roles of Fra-1/AP-1 at the uPA/Plau locus in aggressive breast cancer

Plau codes for the urokinase-type plasminogen activator (uPA), critical in cancer metastasis. While the mechanisms driving its overexpression in tumorigenic processes are unknown, it is regulated by the AP-1 transcriptional complex in diverse situations. The AP-1 component Fra-1 being overexpressed in aggressive breast cancers, we have addressed its role in the overexpression of Plau in the highly metastatic breast cancer model cell line MDA-MB231 using ChIP, pharmacological and RNAi approaches. Plau transcription appears controlled by 2 AP-1 enhancers located -1.9 (ABR-1.9) and -4.1 kb (ABR-4.1) upstream of the transcription start site (TSS) of the uPA-coding mRNA, Plau-001, that bind Fra-1. Surprisingly, RNA Pol II is not recruited only at the Plau-001 TSS but also upstream in the ABR-1.9 and ABR-4.1 region. Most Pol II molecules transcribe short and unstable RNAs while tracking down toward the TSS, where there are converted into Plau-001 mRNA-productive species. Moreover, a minority of Pol II molecules transcribes a low abundance mRNA of unknown function called Plau-004 from the ABR-1.9 domain, whose expression is tempered by Fra-1. Thus, we unveil a heretofore-unsuspected transcriptional complexity at Plau in a reference metastatic breast cancer cell line with pleiotropic effects for Fra-1, providing novel information on AP-1 transcriptional action.

Post-translational modifications of the progesterone receptors

Progesterone plays a key role in the development, differentiation and maintenance of female reproductive tissues and has multiple non-reproductive neural functions. Depending on the cell and tissue, the hormonal environment, growth conditions and the developmental stage, progesterone can either stimulate cell growth or inhibit it while promoting differentiation. Progesterone receptors (PRs) belong to the steroid hormone receptor superfamily of ligand-dependent transcription factors. PR proteins are subject to extensive post-translational modifications that include phosphorylation, acetylation, ubiquitination and SUMOylation. The interplay among these modifications is complex with alteration of the receptors by one factor influencing the impact of another. Control over these modifications is species-, tissue- and cell-specific. They in turn regulate multiple functions including PR stability, their subcellular localization, protein-protein interactions and transcriptional activity. These complexities may explain how tissue- and gene-specific differences in regulation are achieved in the same organism, by the same receptor protein and hormone. Here we review current knowledge of PR post-translational modifications and discuss how these may influence receptor function focusing on human breast cancer cells. There is much left to be learned. However, our understanding of this may help to identify therapeutic agents that target PR activity in tissue-specific, even gene-specific ways.

Lysine methylation of progesterone receptor at activation function 1 regulates both ligand-independent activity and ligand sensitivity of the receptor

Progesterone receptor (PR) exists in two isoforms, PRA and PRB, and both contain activation functions AF-1 and AF-2. It is believed that AF-1 is primarily responsible for the ligand-independent activity, whereas AF-2 mediates ligand-dependent PR activation. Although more than a dozen post-translational modifications of PR have been reported, no post-translational modification on AF-1 or AF-2 has been reported. Using LC-MS/MS-based proteomic analysis, this study revealed AF-1 monomethylation at Lys-464. Mutational analysis revealed the remarkable importance of Lys-464 in regulating PR activity. Single point mutation K464Q or K464A led to ligand-independent PR gel upshift similar to the ligand-induced gel upshift. This upshift was associated with increases in both ligand-dependent and ligand-independent PR phosphorylation and PR activity due to the hyperactivation of AF-1. In contrast, mutation of Lys-464 to the bulkier phenylalanine to mimic the effect of methylation caused a drastic decrease in PR activity. Importantly, PR-K464Q also showed heightened ligand sensitivity, and this was associated with increases in its functional interaction with transcription co-regulators NCoR1 and SRC-1. These results suggest that monomethylation of PR at Lys-464 probably has a repressive effect on AF-1 activity and ligand sensitivity.

Acetylation at lysine 183 of progesterone receptor by p300 accelerates DNA binding kinetics and transactivation of direct target genes

The identification of lysine acetylation of steroid hormone receptors has previously been based on the presence of consensus motif (K/R)XKK. This study reports the discovery by mass spectrometry of a novel progesterone receptor acetylation site at Lys-183 that is not in the consensus motif. In vivo acetylation and mutagenesis experiments revealed that Lys-183 is a primary site of progesterone receptor (PR) acetylation. Lys-183 acetylation is enhanced by p300 overexpression and abrogated by p300 gene silencing, suggesting that p300 is the major acetyltransferase for Lys-183 acetylation. Furthermore, p300-mediated Lys-183 acetylation is associated with heightened PR activity. Accordingly, the acetylation-mimicking mutant PRB-K183Q exhibited accelerated DNA binding kinetics and greater activity compared with the wild-type PRB on genes containing progesterone response element. In contrast, Lys-183 acetylation had no influence on PR tethering effect on the nuclear factor κ-light chain enhancer of activated B cells (NFκB). Additionally, increases of Lys-183 acetylation by p300 overexpression or inhibition of deacetylation resulted in increases of Ser-294 phosphorylation levels. In conclusion, PR acetylation at Lys-183 by p300 potentiates PR activity through accelerated binding of its direct target genes without affecting PR tethering on other transcription factors. The effect may be mediated by enhancing Ser-294 phosphorylation.

Progesterone receptor and Stat5 signaling cross talk through RANKL in mammary epithelial cells

Progesterone (P4) stimulates proliferation of the mammary epithelium by a mechanism that involves paracrine signaling mediated from progesterone receptor (PR)-positive to neighboring PR-negative cells. Here we used a primary mouse mammary epithelial cell (MEC) culture system to define the molecular mechanism by which P4 regulates the expression of target gene effectors of proliferation including the paracrine factor receptor and activator of nuclear factor κB ligand (RANKL). MECs from adult virgin mice grown and embedded in three-dimensional basement-membrane medium resemble mammary ducts in vivo structurally and with respect to other properties including a heterogeneous pattern of PR expression, P4 induction of RANKL and other target genes in a PR-dependent manner, and a proliferative response to progestin. RANKL was demonstrated to have multiple functional P4-responsive enhancers that bind PR in a hormone-dependent manner as detected by chromatin immunoprecipitation assay. P4 also stimulated recruitment of signal transducer and activator of transcription (Stat)5a to RANKL enhancers through an apparent tethering with PR. Analysis of primary MECs from Stat5a knockout mice revealed that P4 induction of RANKL and a broad range of other PR target genes required Stat5a, as did P4-stimulated cell proliferation. In the absence of Stat5a, PR binding was lost at selective RANKL enhancers but was retained with others, suggesting that Stat5a acts to facilitate PR DNA binding at selective sites and to function as a coactivator with DNA-bound PR at others. These results show that RANKL is a direct PR target gene and that Stat5a has a novel role as a cofactor in PR-mediated transcriptional signaling in the mammary gland.

Synthesis and antiprogestational properties of novel 17-fluorinated steroids

Progesterone receptor (PR) plays a key role in reproductive functions, and compounds that inhibit progesterone action (antiprogestins) have potential use in the treatment of estrogen- and progesterone-dependent diseases, including uterine leiomyomas and breast cancer. In the present study, we chemically synthesized novel 17-fluorinated steroids and evaluated the cytotoxicity profiles of these compounds in T47D breast cancer cells compared to the activity of known antiprogestins, including ZK230 211, RU-486, CDB2914, CDB4124 and ORG33628. We analyzed in vitro receptor-binding assays and PR-transactivation assays to establish the antiprogestational activity of these molecules. The representative antiprogestin EC304 was found to inhibit in vitro tumorigenicity in a dose-dependent fashion in T47D cells by a colony formation assay at 1 and 10nM concentrations. The potent in vivo antiprogestational activity of EC304 was also demonstrated in an antinidation assay for the interruption of early pregnancy in rats. The strong antiprogestational activity and absence of antiglucocorticoid activity in EC compounds may demonstrate their utility in the treatment of leiomyoma, endometriosis and breast cancer.

Research resource: progesterone receptor targetome underlying mammary gland branching morphogenesis

Progesterone (P4)-activated progesterone receptors (PRs) play an essential role in driving pregnancy-associated mammary ductal side-branching morphogenesis and alveologenesis. However, the global cistromic and transcriptome responses that are required to elicit P4-dependent branching morphogenesis have not been elucidated. By combining chromatin immunoprecipitation followed by deep sequencing to identify genome-wide PR-binding sites in PR-positive luminal epithelial cells with global gene expression signatures acutely regulated by PRs in the mammary gland, we have identified a mammary epithelial PR targetome associated with active P4-dependent branching morphogenesis in vivo. We demonstrate that P4-induced side-branching is initiated by epithelial cell rearrangement into a multilayered epithelium that sprouts laterally from quiescent ducts via a mechanism requiring P4-dependent activation of Rac-GTPase signaling. We identify effectors of Rac-GTPases as direct transcriptional targets of PRs, and we demonstrate that disruption of the P4-activated Rac-GTPase signaling axis is sufficient to eliminate P4-dependent side-branching. Our data reveal that the molecular mediators of P4-dependent ductal side-branching overlap with those implicated in breast cancer.

A Common Docking Domain in Progesterone Receptor-B links DUSP6 and CK2 signaling to proliferative transcriptional programs in breast cancer cells

Progesterone receptors (PR) are transcription factors relevant to breast cancer biology. Herein, we describe an N-terminal common docking (CD) domain in PR-B, a motif first described in mitogen-activated protein kinases. Binding studies revealed PR-B interacts with dual-specificity phosphatase 6 (DUSP6) via the CD domain. Mutation of the PR-B CD domain (mCD) attenuated cell cycle progression and expression of PR-B target genes (including STAT5A and Wnt1); mCD PR-B failed to undergo phosphorylation on Ser81, a ck2-dependent site required for expression of these genes. PR-B Ser81 phosphorylation was dependent on binding with DUSP6 and required for recruitment of a transcriptional complex consisting of PR-B, DUSP6 and ck2 to an enhancer region upstream of the Wnt1 promoter. STAT5 was present at this site in the absence or presence of progestin. Furthermore, phospho-Ser81 PR-B was recruited to the STAT5A gene upon progestin treatment, suggestive of a feed-forward mechanism. Inhibition of JAK/STAT-signaling blocked progestin-induced STAT5A and Wnt1 expression. Our studies show that DUSP6 serves as a scaffold for ck2-dependent PR-B Ser81 phosphorylation and subsequent PR-B-specific gene selection in coordination with STAT5. Coregulation of select target genes by PR-B and STAT5 is likely a global mechanism required for growth promoting programs relevant to mammary stem cell biology and cancer.

Expression of CCT6A mRNA in chicken granulosa cells is regulated by progesterone

CCT6A, the zeta subunit of the chaperonin containing TCP1 complex, is the only cytosolic chaperonin in eukaryotes and is estimated to assist in the folding of multiple proteins including actin, tubulin, cyclin E, myosin, transducin and the Von Hippel Lindau tumor suppressor. In this study, we examined the expression of CCT6A and progesterone receptor (PGR) mRNA in various tissues of chickens and the regulation of CCT6A and PGR mRNA in ovarian granulosa cells. Northern blot analysis revealed that CCT6A had one transcript and was highly expressed in the ovary tissues from chickens at both the sexually immature and mature stages. CCT6A mRNA expression was increased maximally from pre-hierarchy follicles to F5 follicles and subsequently declined in pre-ovulatory and post-ovulatory follicles. The expression of PGR mRNA exhibited the similar pattern to CCT6A. In granulosa cells isolated from pre-ovulatory follicles, follicle-stimulating hormone (FSH) inhibited the expression of CCT6A mRNA, whereas progesterone activated CCT6A and suppressed PGR expression in a time-dependent manner. We further investigated the regulation of CCT6A transcription by progesterone by constructing various progressive deletions and mutants and identified the core promoter element of CCT6A and the binding region of progesterone, which is located from -2056 to -2051. Taken together, our results indicate that CCT6A likely plays an important role in follicle growth, and in granulosa cells, progesterone activates CCT6A transcription via a progesterone response element (PRE) located in the distal promoter of CCT6A.

Activation of mitogen- and stress-activated kinase 1 is required for proliferation of breast cancer cells in response to estrogens or progestins

Growth of breast cancers is often dependent on ovarian steroid hormones making the tumors responsive to antagonists of hormone receptors. However, eventually the tumors become hormone independent, raising the need to identify downstream targets for the inhibition of tumor growth. One possibility is to focus on the signaling mechanisms used by ovarian steroid hormones to induce breast cancer cell proliferation. Here we report that the mitogen- and stress-activated kinase 1 (MSK1) could be a potential druggable target. Using the breast cancer cell line T47D, we show that estrogens (E2) and progestins activate MSK1, which forms a complex with the corresponding hormone receptor. Inhibition of MSK1 activity with H89 or its depletion by MSK1 short hairpin RNAs (shRNAs) specifically abrogates cell proliferation in response to E2 or progestins without affecting serum-induced cell proliferation. MSK1 activity is required for the transition from the G1- to the S-phase of the cell cycle and inhibition of MSK1 compromises both estradiol- and progestin-dependent induction of cell cycle genes. ChIP-seq experiments identified binding of MSK1 to progesterone receptor-binding sites associated with hormone-responsive genes. MSK1 recruitment to epigenetically defined enhancer regions supports the need of MSK1 as a chromatin remodeler in hormone-dependent regulation of gene transcription. In agreement with this interpretation, expression of a histone H3 mutated at S10 eliminates the hormonal effect on cell proliferation and on induction of relevant target genes. Finally, we show that E2- or progestin-dependent growth of T47D cells xenografted in immunodefficient mice is inhibited by depletion of MSK1, indicating that our findings are not restricted to cultured cells, and that MSK1 plays an important role for hormone-dependent breast cancer growth in a more physiological context.

The biology of progesterone receptor in the normal mammary gland and in breast cancer

This paper reviews work on progesterone and the progesterone receptor (PR) in the mouse mammary gland that has been used extensively as an experimental model. Studies have led to the concept that progesterone controls proliferation and morphogenesis of the luminal epithelium in a tightly orchestrated manner at distinct stages of development by paracrine signaling pathways, including receptor activator of nuclear factor κB ligand (RANKL) as a major paracrine factor. Progesterone also drives expansion of stem cells by paracrine signals to generate progenitors required for alveologenesis. During mid-to-late pregnancy, progesterone has another role to suppress secretory activation until parturition mediated in part by crosstalk between PR and prolactin/Stat5 signaling to inhibit induction of milk protein gene expression, and by inhibiting tight junction closure. In models of hormone-dependent mouse mammary tumors, the progesterone/PR signaling axis enhances pre-neoplastic progression by a switch from a paracrine to an autocrine mode of proliferation and dysregulation of the RANKL signaling pathway. Limited experiments with normal human breast show that progesterone/PR signaling also stimulates epithelial cell proliferation by a paracrine mechanism; however, the signaling pathways and whether RANKL is a major mediator remains unknown. Work with human breast cancer cell lines, patient tumor samples and clinical studies indicates that progesterone is a risk factor for breast cancer and that alteration in progesterone/PR signaling pathways contributes to early stage human breast cancer progression. However, loss of PR expression in primary tumors is associated with a less differentiated more invasive phenotype and worse prognosis, suggesting that PR may limit later stages of tumor progression.

Progesterone receptors, their isoforms and progesterone regulated transcription

This review discusses mechanisms by which progesterone receptors (PR) regulate transcription. We examine available data in different species and tissues regarding: (1) regulation of PR levels; and (2) expression profiling of progestin-regulated genes by total PRs, or their PRA and PRB isoforms. (3) We address current views about the composition of progesterone response elements, and postulate that PR monomers acting through "half-site" elements are common, entailing cooperativity with neighboring DNA-bound transcription factors. (4) We summarize transcription data for multiple progestin-regulated promoters as directed by total PR, or PRA vs. PRB. We conclude that current models and methods used to study PR function are problematical, and recommend that future work employ cells and receptors appropriate to the species, focusing on analyses of the effects of endogenous receptors targeting endogenous genes in native chromatin.

Impact of chromatin structure on PR signaling: transition from local to global analysis

The progesterone receptor (PR) interacts with chromatin in a highly dynamic manner that requires ongoing chromatin remodeling, interaction with chaparones and activity of the proteasome. Here we discuss dynamic interaction of steroid receptor with chromatin, with special attention not only to PR but also to the glucocorticoid receptor (GR), as these receptors share many similarities regarding interaction with, and remodeling of, chromatin. Both receptors can bind nucleosomal DNA and have accordingly been described as pioneering factors. However recent genomic approaches (ChIP-seq and DHS-seq) show that a large fraction of receptor binding events occur at pre-accessible chromatin. Thus factors which generate and maintain accessible chromatin during development, and in fully differentiated tissue, contribute a major fraction of receptor tissue specificity. In addition, chromosome conformation capture techniques suggest that steroid receptors preferentially sequester within distinct nuclear hubs. We will integrate dynamic studies from single cells and genomic studies from cell populations, and discuss how genomic approaches have reshaped our current understanding of mechanisms that control steroid receptor interaction with chromatin.

Progestins activate 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) in breast cancer cells

PFKFB (6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase) catalyses the synthesis and degradation of Fru-2,6-P2 (fructose-2,6-bisphosphate), a key modulator of glycolysis and gluconeogenesis. The PFKFB3 gene is extensively involved in cell proliferation owing to its key role in carbohydrate metabolism. In the present study we analyse its mechanism of regulation by progestins in breast cancer cells. We report that exposure of T47D cells to synthetic progestins (ORG2058 or norgestrel) leads to a rapid increase in Fru-2,6-P2 concentration. Our Western blot results are compatible with a short-term activation due to PFKFB3 isoenzyme phosphorylation and a long-term sustained action due to increased PFKFB3 protein levels. Transient transfection of T47D cells with deleted gene promoter constructs allowed us to identify a PRE (progesterone-response element) to which PR (progesterone receptor) binds and thus transactivates PFKFB3 gene transcription. PR expression in the PR-negative cell line MDA-MB-231 induces endogenous PFKFB3 expression in response to norgestrel. Direct binding of PR to the PRE box (-3490 nt) was confirmed by ChIP (chromatin immunoprecipiation) experiments. A dual mechanism affecting PFKFB3 protein and gene regulation operates in order to assure glycolysis in breast cancer cells. An immediate early response through the ERK (extracellular-signal-regulated kinase)/RSK (ribosomal S6 kinase) pathway leading to phosphorylation of PFKFB3 on Ser461 is followed by activation of mRNA transcription via cis-acting sequences on the PFKFB3 promoter.

Control of progesterone receptor transcriptional synergy by SUMOylation and deSUMOylation

Background

Covalent modification of nuclear receptors by the Small Ubiquitin-like Modifier (SUMO) is dynamically regulated by competing conjugation/deconjugation steps that modulate their overall transcriptional activity. SUMO conjugation of progesterone receptors (PRs) at the N-terminal lysine (K) 388 residue of PR-B is hormone-dependent and suppresses PR-dependent transcription. Mutation of the SUMOylation motif promotes transcriptional synergy.

Results

The present studies address mechanisms underlying this transcriptional synergy by using SUMOylation deficient PR mutants and PR specifically deSUMOylated by Sentrin-specific proteases (SENPs). We show that deSUMOylation of a small pool of receptors by catalytically competent SENPs globally modulates the cooperativity-driven transcriptional synergy between PR observed on exogenous promoters containing at least two progesterone-response elements (PRE₂). This occurs in part by raising PR sensitivity to ligands. The C-terminal ligand binding domain of PR is required for the transcriptional stimulatory effects of N-terminal deSUMOylation, but neither a functional PR dimerization interface, nor a DNA binding domain exhibiting PR specificity, are required.

Conclusion

We conclude that direct and reversible SUMOylation of a minor PR protein subpopulation tightly controls the overall transcriptional activity of the receptors at complex synthetic promoters. Transcriptional synergism controlled by SENP-dependent PR deSUMOylation is dissociable from MAPK-catalyzed receptor phosphorylation, from SRC-1 coactivation and from recruitment of histone deacetylases to promoters. This will provide more information for targeting PR as a part of hormonal therapy of breast cancer. Taken together, these data demonstrate that the SUMOylation/deSUMOylation pathway is an interesting target for therapeutic treatment of breast cancer.

DHHC-7 and -21 are palmitoylacyltransferases for sex steroid receptors

Extranuclear sex steroid receptors require palmitoylation to traffic to the plasma membrane, where they activate signal transduction cascades. We identify DHHC-7 and -21 palmitoylacyltransferases as conserved enzymes for the three classes of sex steroid receptors.

Classical estrogen, progesterone, and androgen receptors (ERs, PRs, and ARs) localize outside the nucleus at the plasma membrane of target cells. From the membrane, the receptors signal to activate kinase cascades that are essential for the modulation of transcription and nongenomic functions in many target cells. ER, PR, and AR trafficking to the membrane requires receptor palmitoylation by palmitoylacyltransferase (PAT) protein(s). However, the identity of the steroid receptor PAT(s) is unknown. We identified the DHHC-7 and -21 proteins as conserved PATs for the sex steroid receptors. From DHHC-7 and -21 knockdown studies, the PATs are required for endogenous ER, PR, and AR palmitoylation, membrane trafficking, and rapid signal transduction in cancer cells. Thus the DHHC-7 and -21 proteins are novel targets to selectively inhibit membrane sex steroid receptor localization and function.

BRCA1 counteracts progesterone action by ubiquitination leading to progesterone receptor degradation and epigenetic silencing of target promoters

Germ-line mutations in the BRCA1 gene increase the risk of breast cancer in women, but the precise mechanistic basis for this connection remains uncertain. One popular hypothesis to explain breast tissue specificity postulates a link between BRCA1 and the action of the ovarian hormones estrogen and progesterone. Given the relevance of progesterone for normal mammary development and breast cancer formation, we searched for a functional relationship between BRCA1 and progesterone receptor (PR) in the PR-positive breast cancer cell line T47D. Here, we report that BRCA1 inhibits the transcriptional activity of PR by at least 2 mechanisms involving the E3 ubiquitin ligase activity of BRCA1. First, BRCA1 has a direct effect on the cellular level of PR and, hence, on the extent of PR recruitment to target promoters through the promotion of its ligand-independent and -dependent degradation. Through in vitro and in vivo assays, we found that BRCA1/BARD1 may be the main E3 ubiquitin ligase responsible for ubiquitination and degradation of PR in the absence of hormone. Second, after hormone treatment of cells, the BRCA1/BARD1 complex is recruited via interaction with PR to the hormone-responsive regions of PR target genes, affecting local levels of monoubiquitinated histone H2A and contributing to epigenetic silencing of these promoters. The connections between BRCA1/BARD1 and PR activity suggested by our findings may help explain why host mutations in BRCA1 exert a tissue specificity in preferentially elevating the risk of breast cancer.

Interaction between FGFR-2, STAT5, and progesterone receptors in breast cancer

Fibroblast growth factor (FGF) receptor 2 (FGFR-2) polymorphisms have been associated with an increase in estrogen receptor and progesterone receptor (PR)-positive breast cancer risk; however, a clear mechanistic association between FGFR-2 and steroid hormone receptors remains elusive. In previous works, we have shown a cross talk between FGF2 and progestins in mouse mammary carcinomas. To investigate the mechanisms underlying these interactions and to validate our findings in a human setting, we have used T47D human breast cancer cells and human cancer tissue samples. We showed that medroxyprogesterone acetate (MPA) and FGF2 induced cell proliferation and activation of ERK, AKT, and STAT5 in T47D and in murine C4-HI cells. Nuclear interaction between PR, FGFR-2, and STAT5 after MPA and FGF2 treatment was also showed by confocal microscopy and immunoprecipitation. This effect was associated with increased transcription of PRE and/or GAS reporter genes, and of PR/STAT5-regulated genes and proteins. Two antiprogestins and the FGFR inhibitor PD173074, specifically blocked the effects induced by FGF2 or MPA respectively. The presence of PR/FGFR-2/STAT5 complexes bound to the PRE probe was corroborated by using NoShift transcription and chromatin immunoprecipitation of the MYC promoter. Additionally, we showed that T47D cells stably transfected with constitutively active FGFR-2 gave rise to invasive carcinomas when transplanted into NOD/SCID mice. Nuclear colocalization between PR and FGFR-2/STAT5 was also observed in human breast cancer tissues. This study represents the first demonstration of a nuclear interaction between FGFR-2 and STAT5, as PR coactivators at the DNA progesterone responsive elements, suggesting that FGFRs are valid therapeutic targets for human breast cancer treatment.

Minireview: role of kinases and chromatin remodeling in progesterone signaling to chromatin

Steroid hormones regulate gene expression by interaction of their receptors with hormone-responsive elements on DNA or with other transcription factors, but they can also activate cytoplasmic signaling cascades. Rapid activation of Erk by progestins via an interaction of the progesterone receptor (PR) with the estrogen receptor is critical for transcriptional activation of the mouse mammary tumor virus (MMTV) promoter and other progesterone target genes. Erk activation leads to the phosphorylation of PR, activation of mitogen- and stress-activated protein kinase 1, and the recruitment of a complex of the three activated proteins and of P300/CBP-associated factor (PCAF) to a single nucleosome, resulting in the phosphoacetylation of histone H3 and the displacement of heterochromatin protein 1γ. Hormone-dependent gene expression requires ATP-dependent chromatin remodeling complexes. Two switch/sucrose nonfermentable-like complexes, Brahma-related gene 1-associated factor (BAF) and polybromo-BAF are present in breast cancer cells, but only BAF is recruited to the MMTV promoter and cooperates with PCAF during activation of hormone-responsive promoters. PCAF acetylates histone H3 at K14, an epigenetic mark recognized by BAF subunits, thus anchoring the complex to chromatin. BAF catalyzes localized displacement of histones H2A and H2B, facilitating access of nuclear factor 1 and additional PR complexes to the hidden hormone-responsive elements on the MMTV promoter. The linker histone H1 is a structural component of chromatin generally regarded as a general repressor of transcription. However, it contributes to a better regulation of the MMTV promoter by favoring a more homogeneous nucleosome positioning, thus reducing basal transcription and actually enhancing hormone induced transcription. During transcriptional activation, H1 is phosphorylated and displaced from the promoter. The kinase cyclin-dependent kinase 2 is activated after progesterone treatment and could catalyze progesterone-induced phosphorylation of histone H1 by chromatin remodeling complexes. The initial steps of gene induction by progestins involve changes in the chromatin organization of target promoters that require the activation of several kinase signaling pathways initiated by membrane anchored PR. Because these pathways also respond to other external signals, they serve to integrate the hormonal response in the global context of the cellular environment.

Physiological changes in maternal cortisol do not alter expression of growth-related genes in the ovine placenta

OBJECTIVES

The aim of this study was to investigate the effect of cortisol on growth-related genes in the ovine placenta.

STUDY DESIGN

Ewes carrying singleton pregnancies were operated on between 112 and 116 days of gestation (115 ± 0.4, term = 147 days) and randomly assigned into three groups: six control animals, five ewes that were administered cortisol by continuous intravenous infusion (1 mg/kg/day, high cortisol), and five ewes that were adrenalectomized and replaced with 0.5-0.6 mg cortisol/kg/day and 3 μg aldosterone/kg/day to produce cortisol concentrations equivalent to pre-pregnancy values (low cortisol). At necropsy (130 ± 0.2 days of gestation), placental tissue was frozen and stored at -80 °C for mRNA analysis.

MAIN OUTCOME MEASURES

To assess potential molecular mechanisms by which cortisol alters placental structure and function and fetal growth.

RESULTS

Cortisol levels did not significantly affect 11β-hydroxysteroid dehydrogenase 1 and 2 enzymes, glucocorticoid receptor, mineralocorticoid receptor and angiotensin II receptor, type 1 (AT1R) expression levels. Gene expression levels of AT2R were increased in the high cortisol group for type B placentomes. There was little effect of cortisol on the insulin-like growth factor (IGF) axis. There was significantly more IGF-I mRNA in B versus A type and more IGFBP-2 mRNA in B and C type versus A type placentomes regardless of treatment (p < 0.05).

CONCLUSIONS

These data suggest that cortisol increases placental AT2R expression at high concentrations whereas it has little effect on the placental IGF axis.

Minireview: Extranuclear steroid receptors: roles in modulation of cell functions

Steroid receptors existing outside the nucleus are increasingly being recognized in many organs and cell types, impacting the biology of bone, the heart and blood vessels, and the central nervous system. Some controversy exists as to the nature of the receptors at the plasma membrane. However, compelling evidence has been advanced that at least some classical steroid receptors mediate steroid ligand actions originating as signaling from the cell surface. Here I review the recent findings in this evolving field emphasizing the in vivo impact of these receptor pools with a focus on estrogen receptors.

Mutational analysis of progesterone receptor functional domains in stable cell lines delineates sets of genes regulated by different mechanisms

Steroid hormone receptors act directly in the nucleus on the chromatin organization and transcriptional activity of several promoters. Furthermore, they have an indirect effect on cytoplasmic signal transduction pathways, including MAPK, impacting ultimately on gene expression. We are interested in distinguishing between the two modes of action of progesterone receptor (PR) on the control of gene expression and cell proliferation. For this, we have stably expressed, in PR-negative breast cancer cells, tagged forms of the PR isoform B mutated at regions involved either in DNA binding (DNA-binding domain) or in its ability to interact with the estrogen receptor and to activate the c-Src/MAPK/Erk/Msk cascade (estrogen receptor-interacting domain). Both mutants impair PR-mediated activation of a well-understood model promoter in response to progestin, as well as hormone-induced cell proliferation. Additional mutants affecting transactivation activity of PR (activation function 2) or a zinc-finger implicated in dimerization (D-box) have also been tested. Microarrays and gene expression experiments on these cell lines define the subsets of hormone-responsive genes regulated by different modes of action of PR isoform B, as well as genes in which the nuclear and nongenomic pathways cooperate. Correlation between CCND1 expression in the different cell lines and their ability to support cell proliferation confirms CCND1 as a key controller gene.

Mechanisms underlying the control of progesterone receptor transcriptional activity by SUMOylation

Posttranslational modification by small ubiquitin-like modifier (SUMO) is a major regulator of transcription. We previously showed that progesterone receptors (PR) have a single consensus psiKXE SUMO-conjugation motif centered at Lys-388 in the N-terminal domain of PR-B and a homologous site of PR-A. SUMOylation of the PR is hormone-dependent and has a suppressive effect on transcription of an exogenous promoter. Here we show that repression of PR activity by SUMOylation at Lys-388 is uncoupled from phosphorylation, involves synergy between tandem progesterone response elements, and is associated with lowered ligand sensitivity and slowed ligand-dependent down-regulation. However, paradoxically, cellular overexpression of SUMO-1 increases PR transcriptional activity even if Lys-388 is mutated, suggesting that the receptors are activated indirectly by other SUMOylated proteins. One of these is the coactivator SRC-1, whose binding to PR and enhancement of agonist-dependent N-/C-terminal interactions is augmented by the presence of SUMO-1. Increased transcription due to SRC-1 is independent of PR SUMOylation based on assays with the Lys-388 mutants and the pure antiprogestin ZK98299, which blocks N-/C-terminal interactions. In summary, SUMOylation tightly regulates the transcriptional activity of PR by repressing the receptors directly while activating them indirectly through augmented SRC-1 coactivation.

Depletion of human histone H1 variants uncovers specific roles in gene expression and cell growth

At least six histone H1 variants exist in somatic mammalian cells that bind to the linker DNA and stabilize the nucleosome particle contributing to higher order chromatin compaction. In addition, H1 seems to be actively involved in the regulation of gene expression. However, it is not well known whether the different variants have distinct roles or if they regulate specific promoters. We have explored this by inducible shRNA-mediated knock-down of each of the H1 variants in a human breast cancer cell line. Rapid inhibition of each H1 variant was not compensated for by changes of expression of other variants. Microarray experiments have shown a different subset of genes to be altered in each H1 knock-down. Interestingly, H1.2 depletion caused specific effects such as a cell cycle G1-phase arrest, the repressed expression of a number of cell cycle genes, and decreased global nucleosome spacing. On its side, H1.4 depletion caused cell death in T47D cells, providing the first evidence of the essential role of an H1 variant for survival in a human cell type. Thus, specific phenotypes are observed in breast cancer cells depleted of individual histone H1 variants, supporting the theory that distinct roles exist for the linker histone variants.

Eukaryotic DNA is packaged into chromatin through its association with histone proteins. The linker histone H1 sits at the base of the nucleosome near the DNA entry and exit sites to stabilize two full turns of DNA. In particular, histone H1 participates in nucleosome spacing and formation of the higher-order chromatin structure. In addition, H1 seems to be actively involved in the regulation of gene expression. Histone H1 in mammals is a family of closely related, single-gene encoded proteins, including five somatic subtypes (from H1.1 to H1.5) and a terminally differentiated expressed isoform (H1.0). It is not well known whether the different variants have distinct roles or if they regulate specific promoters. We have explored this by inducible knock-down of each of the H1 variants in breast cancer cells. A different subset of genes is altered in each H1 knock-down, and depletion has different effects on cell survival. Interestingly, H1.2 and H1.4 depletion specifically caused arrest of cell proliferation. Concomitant with this, H1.2 depletion caused decreased global nucleosome spacing and repressed expression of a number of cell cycle genes. Thus, specific phenotypes are observed in breast cancer cells depleted of individual histone H1 variants.