CCAAT/enhancer-binding proteins are mediators in the protein kinase A-dependent activation of the decidual prolactin promoter

Immunomodulatory role of decidual prolactin on the human fetal membranes and placenta

The close interaction between fetal and maternal cells during pregnancy requires multiple immune-endocrine mechanisms to provide the fetus with a tolerogenic environment and protection against any infectious challenge. The fetal membranes and placenta create a hyperprolactinemic milieu in which prolactin (PRL) synthesized by the maternal decidua is transported through the amnion-chorion and accumulated into the amniotic cavity, where the fetus is bedded in high concentrations during pregnancy. PRL is a pleiotropic immune-neuroendocrine hormone with multiple immunomodulatory functions mainly related to reproduction. However, the biological role of PRL at the maternal-fetal interface has yet to be fully elucidated. In this review, we have summarized the current information on the multiple effects of PRL, focusing on its immunological effects and biological significance for the immune privilege of the maternal-fetal interface.

Transcriptional coactivator PGC-1α contributes to decidualization by forming a histone-modifying complex with C/EBPβ and p300

We previously reported that CCAAT/enhancer-binding protein beta (C/EBPβ) is the pioneer factor inducing transcription enhancer mark H3K27 acetylation (H3K27ac) in the promoter and enhancer regions of genes encoding insulin-like growth factor–binding protein-1 (IGFBP-1) and prolactin (PRL) and that this contributes to decidualization of human endometrial stromal cells (ESCs). Peroxisome proliferator–activated receptor gamma coactivator 1-alpha (PGC-1α; PPARGC1A) is a transcriptional coactivator known to regulate H3K27ac. However, although PGC-1α is expressed in ESCs, the potential role of PGC-1α in mediating decidualization is unclear. Here, we investigated the involvement of PGC-1α in the regulation of decidualization. We incubated ESCs with cAMP to induce decidualization and knocked down PPARGC1A to inhibit cAMP-induced expression of IGFBP-1 and PRL. We found cAMP increased the recruitment of PGC-1α and p300 to C/EBPβ-binding sites in the promoter and enhancer regions of IGFBP-1 and PRL, corresponding with increases in H3K27ac. Moreover, PGC-1α knockdown inhibited these increases, suggesting PGC-1α forms a histone-modifying complex with C/EBPβ and p300 at these regions. To further investigate the regulation of PGC-1α, we focused on C/EBPβ upstream of PGC-1α. We found cAMP increased C/EBPβ recruitment to the novel enhancer regions of PPARGC1A. Deletion of these enhancers decreased PGC-1α expression, indicating that C/EBPβ upregulates PGC-1α expression by binding to novel enhancer regions. In conclusion, PGC-1α is upregulated by C/EBPβ recruitment to novel enhancers and contributes to decidualization by forming a histone-modifying complex with C/EBPβ and p300, thereby inducing epigenomic changes in the promoters and enhancers of IGFBP-1 and PRL.

Relaxed constraint and functional divergence of the progesterone receptor (PGR) in the human stem-lineage

The steroid hormone progesterone, acting through the progesterone receptor (PR), a ligand-activated DNA-binding transcription factor, plays an essential role in regulating nearly every aspect of female reproductive biology. While many reproductive traits regulated by PR are conserved in mammals, Catarrhine primates evolved several derived traits including spontaneous decidualization, menstruation, and a divergent (and unknown) parturition signal, suggesting that PR may also have evolved divergent functions in Catarrhines. There is conflicting evidence, however, whether the progesterone receptor gene (PGR) was positively selected in the human lineage. Here we show that PGR evolved rapidly in the human stem-lineage (as well as other Catarrhine primates), which likely reflects an episode of relaxed selection intensity rather than positive selection. Coincident with the episode of relaxed selection intensity, ancestral sequence resurrection and functional tests indicate that the major human PR isoforms (PR-A and PR-B) evolved divergent functions in the human stem-lineage. These results suggest that the regulation of progesterone signaling by PR-A and PR-B may also have diverged in the human lineage and that non-human animal models of progesterone signaling may not faithfully recapitulate human biology.

Exchange protein directly activated by cAMP (EPAC) promotes transcriptional activation of the decidual prolactin gene via CCAAT/enhancer-binding protein in human endometrial stromal cells

Protein kinase A (PKA) signalling accompanies elevated intracellular cAMP levels during endometrial stromal cell (ESC) decidualisation. Exchange protein directly activated by cAMP (EPAC), an alternate mediator of cAMP signalling, promotes PKA analogue-induced decidualisation; however, the precise mechanism by which EPAC and PKA co-operatively stimulate decidualisation has not been characterised. To examine the role of CCAAT/enhancer-binding protein (C/EBP) in EPAC- and PKA-mediated decidualisation of primary human ESCs, a reporter plasmid containing the 332bp region upstream from the transcription initiation site of the decidual prolactin (dPRL) gene was generated and the promoter activity was evaluated using a luciferase assay. The dPRL promoter activity was increased by treatment of transfected ESCs with the PKA-selective cAMP analogue N6-phenyl-cAMP (Phe) and enhanced further by co-treatment with the EPAC-selective cAMP analogue 8-(4-chlorophenyltio)-2'-O-methyl cAMP (CPT). Treatment with forskolin, an adenylyl cyclase activator, had a similar effect on reporter activity. Site-directed mutagenesis of the C/EBPβ- and/or C/EBPδ-binding site in the dPRL promoter abolished Phe/CPT-mediated elevation of the reporter activity. EPAC2 knockdown markedly reduced Phe-stimulated C/EBPβ and C/EBPδ mRNA levels, as well as forkhead box O1 (FOXO1) protein levels. These results suggest that EPAC signalling enhances PKA-mediated dPRL expression in ESCs by acting on C/EBP response elements in the promoter region of the gene.

Crosstalk between human endometrial stromal cells and decidual NK cells promotes decidualization in vitro by upregulating IL‑25

Embryo implantation is essential for a successful pregnancy, and leads to the decidualization of endometrial stromal cells (ESCs) in the secretory phase of the menstrual cycle. It has previously been demonstrated that decidual stromal cells (DSCs) co‑express interleukin (IL)‑25/IL‑17RB and that IL‑25 further promotes the proliferation of DSCs via activating c‑Jun n‑terminal kinase and protein kinase B signals, therefore the present study primarily focused on the role of IL‑25 in the process of decidualization in vitro. It was demonstrated that the expression of IL‑25/IL‑17RB in ESCs was decreased compared with DSCs. In addition, following decidualization, the expression levels of IL‑25/IL‑17RB in ESCs were significantly elevated. Recombinant human (rh) IL‑25 promoted the decidualization of ESCs in the presence of 8‑bromoadenosine 3',5'‑cyclic monophosphate sodium salt and 6α‑methyl17α‑acetoxyprogesterone, which was partially inhibited by anti‑human IL‑25 neutralizing antibody (anti‑IL‑25) or anti‑IL‑17RB. In addition, decidual natural killer (dNK) cells not only secreted IL‑25, however also further accelerated the decidualization in vitro. Therefore, these findings indicated that ESCs differentiate into DSCs in the presence of ovarian hormones, resulting in the upregulation of IL‑25/IL‑17RB expression in ESCs. Furthermore, IL‑25 secreted by ESCs and dNK cells further facilitates the decidualization of ESCs, which may form a positive feedback mechanism at the maternal‑fetal interface and thus contribute to the establishment and maintenance of normal pregnancy.

Hmgn1 acts downstream of C/EBPβ to regulate the decidualization of uterine stromal cells in mice

Although Hmgn1 is involved in the regulation of gene expression and cellular differentiation, its physiological roles on the differentiation of uterine stromal cells during decidualization still remain unknown. Here we showed that Hmgn1 mRNA was highly expressed in the decidua on days 6-8 of pregnancy. Simultaneously, increased expression of Hmgn1 was also observed in the artificial and in vitro induced decidualization models. Hmgn1 induced the proliferation of uterine stromal cells and expression of Ccna1, Ccnb1, Ccnb2 and Cdk1 in the absence of estrogen and progesterone. Overexpression of Hmgn1 could enhance the expression of Prl8a2 and Prl3c1 which were 2 well-known differentiation markers for decidualization, whereas inhibition of Hmgn1 with specific siRNA could reduce their expression. Further studies found that Hmgn1 could mediate the effects of C/EBPβ on the expression of Prl8a2 and Prl3c1 during in vitro decidualization. In the uterine stromal cells, cAMP analog 8-Br-cAMP could stimulate the expression of Hmgn1 via C/EBPβ. Moreover, siRNA-mediated down-regulation of Hmgn1 could attenuate the effects of cAMP on the differentiation of uterine stromal cells. During in vitro decidualization, Hmgn1 might act downstream of C/EBPβ to regulate the expression of Cox-2, mPGES-1 and Vegf. Progesterone could up-regulate the expression of Hmgn1 in the ovariectomized mouse uterus, uterine epithelial cells and stromal cells. Knockdown of C/EBPβ with siRNA alleviated the up-regulation of progesterone on Hmgn1 expression. Collectively, Hmgn1 may play an important role during mouse decidualization.

The Transcriptomic Evolution of Mammalian Pregnancy: Gene Expression Innovations in Endometrial Stromal Fibroblasts

The endometrial stromal fibroblast (ESF) is a cell type present in the uterine lining of therian mammals. In the stem lineage of eutherian mammals, ESF acquired the ability to differentiate into decidual cells in order to allow embryo implantation. We call the latter cell type "neo-ESF" in contrast to "paleo-ESF" which is homologous to eutherian ESF but is not able to decidualize. In this study, we compare the transcriptomes of ESF from six therian species: Opossum (Monodelphis domestica; paleo-ESF), mink, rat, rabbit, human (all neo-ESF), and cow (secondarily nondecidualizing neo-ESF). We find evidence for strong stabilizing selection on transcriptome composition suggesting that the expression of approximately 5,600 genes is maintained by natural selection. The evolution of neo-ESF from paleo-ESF involved the following gene expression changes: Loss of expression of genes related to inflammation and immune response, lower expression of genes opposing tissue invasion, increased markers for proliferation as well as the recruitment of FOXM1, a key gene transiently expressed during decidualization. Signaling pathways also evolve rapidly and continue to evolve within eutherian lineages. In the bovine lineage, where invasiveness and decidualization were secondarily lost, we see a re-expression of genes found in opossum, most prominently WISP2, and a loss of gene expression related to angiogenesis. The data from this and previous studies support a scenario, where the proinflammatory paleo-ESF was reprogrammed to express anti-inflammatory genes in response to the inflammatory stimulus coming from the implanting conceptus and thus paving the way for extended, trans-cyclic gestation.

Identification of target genes for a prolactin family paralog in mouse decidua

Prolactin family 8, subfamily a, member 2 (PRL8A2; also called decidual prolactin-related protein; dPRP) is a member of the expanded prolactin family. PRL8A2 is expressed in the uterine decidua and contributes to pregnancy-dependent adaptations to hypoxia. The purpose of this study was to identify gene targets for PRL8A2 action within the uteroplacental compartment. Affymetrix DNA microarray analysis was performed for RNA samples from WT and Prl8a2 null tissues. Validation of the DNA microarray was performed using quantitative RT-PCR. Nine genes were confirmed with decreased expression in Prl8a2 null tissues (e.g., Klk7, Rimklb, Arhgef6, Calm4, Sprr2h, Prl4a1, Ccl27, Lipg, and Htra3). These include potential decidual, endothelial and trophoblast cell targets positively regulated by PRL8A2. A significant upregulation of Derl3, Herpud1, Creld2, Hsp90b1, Ddit3 and Hspa5 was identified in Prl8a2 null tissues, reflecting an increased endoplasmic reticulum (ER) stress response. ER stress genes were prominently expressed in the uterine decidua. We propose that PRL8A2 is a mediator of progesterone-dependent modulation of intrauterine responses to physiological stressors.

Orphan nuclear receptor NR4A2 induces transcription of the immunomodulatory peptide hormone prolactin

Background

Nuclear receptor 4A2 (NR4A2) is an orphan nuclear receptor and constitutively active transcription factor expressed at elevated levels in inflamed joint tissues from patients with arthritis. Inflammatory mediators rapidly and potently induce NR4A2 expression in resident joint cells and infiltrating immune cells. This receptor promotes synovial hyperplasia by increasing proliferation of synoviocytes and inducing transcription of matrix degrading enzymes and pro-inflammatory mediators. In order to further elucidate the molecular mechanisms of NR4A2, we conducted a gene expression screen to identify novel transcriptional targets of NR4A2 that may contribute to arthritis progression.

Methods

NR4A2 was over-expressed in human synoviocytes by lentiviral transduction and gene expression changes were measured using qPCR arrays specific for inflammation, proliferation, adhesion, and migration pathways. Subsequent analysis focused on the most potently induced gene prolactin (PRL). Messenger RNA levels of PRL and PRL receptor (PRL-R) were measured by RT-qPCR and protein levels were measured by ELISA. PRL promoter studies were conducted in synoviocytes transiently transfected with NR4A2 and PRL reporter constructs. Molecular responses to PRL in synoviocytes were addressed using qPCR arrays specific for JAK/STAT signaling pathways.

Results

PRL was the most potently induced gene on the qPCR arrays, exhibiting a 68-fold increase in response to ectopic NR4A2. This gene encodes an immunomodulatory peptide hormone with roles in autoimmune diseases and inflammation. Induction of PRL mRNA and secreted protein by NR4A2 was confirmed in subsequent experiments, with increases of 300-fold and 18-fold respectively. Depletion of endogenous NR4A receptors with shRNA reduced basal and PGE₂-induced PRL levels by 95%. At the transcriptional level, NR4A2 requires a functional DNA binding domain to transactivate the distal PRL promoter. Deletional analysis indicates that NR4A2 targets a region of the distal PRL promoter spanning −270 to -32 bp. In synoviocytes, recombinant PRL regulates several genes involved in inflammation, proliferation, and cell survival, suggesting that NR4A2 induced PRL may also impact these pathways and contribute to arthritis progression.

Conclusions

These results provide the first evidence for transcriptional regulation of the immunomodulatory peptide hormone PRL by NR4A2 in synoviocytes, and highlight a novel molecular pathway in inflammatory arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-015-0059-2) contains supplementary material, which is available to authorized users.

Cyclic decidualization of the human endometrium in reproductive health and failure

Decidualization denotes the transformation of endometrial stromal fibroblasts into specialized secretory decidual cells that provide a nutritive and immunoprivileged matrix essential for embryo implantation and placental development. In contrast to most mammals, decidualization of the human endometrium does not require embryo implantation. Instead, this process is driven by the postovulatory rise in progesterone levels and increasing local cAMP production. In response to falling progesterone levels, spontaneous decidualization causes menstrual shedding and cyclic regeneration of the endometrium. A growing body of evidence indicates that the shift from embryonic to maternal control of the decidual process represents a pivotal evolutionary adaptation to the challenge posed by invasive and chromosomally diverse human embryos. This concept is predicated on the ability of decidualizing stromal cells to respond to individual embryos in a manner that either promotes implantation and further development or facilitates early rejection. Furthermore, menstruation and cyclic regeneration involves stem cell recruitment and renders the endometrium intrinsically capable of adapting its decidual response to maximize reproductive success. Here we review the endocrine, paracrine, and autocrine cues that tightly govern this differentiation process. In response to activation of various signaling pathways and genome-wide chromatin remodeling, evolutionarily conserved transcriptional factors gain access to the decidua-specific regulatory circuitry. Once initiated, the decidual process is poised to transit through distinct phenotypic phases that underpin endometrial receptivity, embryo selection, and, ultimately, resolution of pregnancy. We discuss how disorders that subvert the programming, initiation, or progression of decidualization compromise reproductive health and predispose for pregnancy failure.

Minireview: Extrapituitary prolactin: an update on the distribution, regulation, and functions

Prolactin (PRL) is an important hormone with many diverse functions. Although it is predominantly produced by lactrotrophs of the pituitary there are a number of other organs, cells, and tissues in which PRL is expressed and secreted. The impact of this extrapituitary PRL (ePRL) on localized metabolism and cellular functions is gaining widespread attention. In 1996, a comprehensive review on ePRL was published. However, since this time, there have been a number of advancements in ePRL research. This includes a greater understanding of the components of the control elements located within the superdistal promoter of the ePRL gene. Furthermore, several new sites of ePRL have been discovered, each under unique control by a range of transcription factors and elements. The functional role of ePRL at each of the expression sites also varies widely leading to gender and site bias. This review aims to provide an update to the research conducted on ePRL since the 1996 review. The focus is on new data concerning the sites of ePRL expression, its regulation, and its function within the organs in which it is expressed.

Reproductive actions of prolactin mediated through short and long receptor isoforms

Prolactin (PRL) is a polypeptide hormone with a wide range of physiological functions, and is critical for female reproduction. PRL exerts its action by binding to membrane bound receptor isoforms broadly classified as the long form and the short form receptors. Both receptor isoforms are highly expressed in the ovary as well as in the uterus. Although signaling through the long form is believed to be more predominant, it remains unclear whether activation of this isoform alone is sufficient to support reproductive functions or whether both types of receptor are required. The generation of transgenic mice selectively expressing either the short or the long form of PRL receptor has provided insight into the differential signaling mechanisms and physiological functions of these receptors. This review describes the essential finding that both long and short receptor isoforms are crucial for ovarian functions and female fertility, and highlights novel mechanisms of action for these receptors.

The role of exchange protein directly activated by cyclic AMP 2-mediated calreticulin expression in the decidualization of human endometrial stromal cells

Decidualization of human endometrial stromal cells (ESCs) accompanied by the production of prolactin (PRL) and IGF-binding protein (IGFBP) 1 and rounded-cell morphology is indispensable for the establishment and maintenance of pregnancy. Protein kinase A (PKA)-mediated cAMP signaling is known to be crucial for decidualization. We previously reported that activation of a cAMP mediator, called Exchange protein directly activated by cAMP (EPAC) promotes cAMP analog- or ovarian steroid-induced decidualization in cultured human ESCs. In addition, small interfering RNA-mediated knock-down of the EPAC subtypes, EPAC1 or EPAC2, or knock-down of Rap1, a downstream factor of EPAC signaling, blocked functional and morphological decidualization of ESCs. However, factors downstream of EPAC2 other than Rap1 have not been determined. The present study was undertaken to identify additional downstream targets of EPAC2 associated with decidualization. Using proteomic analysis, we identified calreticulin (CRT) as a potential target of EPAC2. Knock-down of CRT expression in cultured ESCs significantly inhibited PKA-selective cAMP analog- or PKA-selective cAMP analog plus EPAC-selective cAMP analog-induced PRL and IGFBP1 expression. Furthermore, CRT knock-down suppressed the ovarian steroid-stimulated PRL and IGFBP1 expression and morphological differentiation, and silencing of EPAC2 or CRT significantly increased senescence-associated β-galactosidase activity with enhanced p21 expression and decreased p53 expression. These results suggest that EPAC2 and CRT are associated with cellular senescence in ESCs. In conclusion, we demonstrate here that EPAC2-mediated CRT expression is essential for the functional and morphological differentiation of ESCs into decidual cells. Furthermore, both EPAC2 and CRT might prevent ESCs from undergoing abnormal cellular senescence during decidualization.

Extracellular signal-regulated kinase 1/2 signaling pathway is required for endometrial decidualization in mice and human

Decidualization is a crucial change required for successful embryo implantation and the maintenance of pregnancy. During this process, endometrial stromal cells differentiate into decidual cells in response to the ovarian steroid hormones of early pregnancy. Extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) are known to regulate cell proliferation and apoptosis in multiple cell types, including uterine endometrial cells. Aberrant activation of ERK1/2 has recently been implicated in the pathological processes of endometriosis and endometrial cancer. However, the function of ERK1/2 signaling during implantation and decidualization is still unknown. To determine the role and regulation of ERK1/2 signaling during implantation and decidualization, we examine ERK1/2 signaling in the mouse uterus during early pregnancy using immunostaining and qPCR. Interestingly, levels of phospho-ERK1/2 were highest within decidual cells located at the implantation sites. Expression levels of ERK1/2 target genes were also significantly higher at implantation sites, when compared to either inter-implantation sites. To determine if ERK1/2 signaling is also important during human endometrial decidualization, we examined levels of phospho-ERK1/2 in cultured human endometrial stromal cells during in vitro decidualization. Following treatment with a well-established decidualization-inducing steroidogenic cocktail, levels of phospho-ERK1/2 were markedly increased. Treatment with the ERK1/2 inhibitor, U0126, significantly decreased the expression of the known decidualization marker genes, IGFBP1 and PRL as well as inhibited the induction of known ERK1/2 target genes; FOS, MSK1, STAT1, and STAT3. Interestingly, the phosphorylation level of CCAAT/ enhancer binding protein β (C/EBPβ), a protein previously shown to be critical for decidualization, was significantly reduced in this model. These results suggest that ERK1/2 signaling is required for successful decidualization in mice as well as human endometrial stromal cells and implicates C/EBPβ as a downstream target of ERK1/2.

CCAAT enhancer binding protein δ plays an essential role in memory consolidation and reconsolidation

A newly formed memory is temporarily fragile and becomes stable through a process known as consolidation. Stable memories may again become fragile if retrieved or reactivated, and undergo a process of reconsolidation to persist and strengthen. Both consolidation and reconsolidation require an initial phase of transcription and translation that lasts for several hours. The identification of the critical players of this gene expression is key for understanding long-term memory formation and persistence. In rats, the consolidation of inhibitory avoidance (IA) memory requires gene expression in both the hippocampus and amygdala, two brain regions that process contextual/spatial and emotional information, respectively; IA reconsolidation requires de novo gene expression in the amygdala. Here we report that, after IA learning, the levels of the transcription factor CCAAT enhancer binding protein δ (C/EBPδ) are significantly increased in both the hippocampus and amygdala. These increases are essential for long-term memory consolidation, as their blockade via antisense oligodeoxynucleotide-mediated knockdown leads to memory impairment. Furthermore, C/EBPδ is upregulated and required in the amygdala for IA memory reconsolidation. C/EBPδ is found in nuclear, somatic, and dendritic compartments, and a dendritic localization of C/EBPδ mRNA in hippocampal neuronal cultures suggests that this transcription factor may be translated at synapses. Finally, the induction of long-term potentiation at CA3-CA1 synapses by tetanic stimuli in acute slices, a cellular model of long-term memory, leads to an accumulation of C/EBPδ in the nucleus. We conclude that the transcription factor C/EBPδ plays a critical role in memory consolidation and reconsolidation.

Krüppel-like factor 12 negatively regulates human endometrial stromal cell decidualization

Members of the KLFs family of transcription factors play roles in maternal endometrium development during embryo implantation. However, the specific role of KLF12 in endometrium development has not yet been described. In this study, we showed that KLF12 expression in human endometrial stromal cells (HESCs) was significantly decreased after decidualization stimulated by 8-Br-cAMP and medroxyprogesterone acetate (MPA). The adenovirus-mediated overexpression of KLF12 in HESCs significantly repressed the expression and secretion of decidualization biomarker genes and their products decidual prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP-1) induced by 8-Br-cAMP and MPA. Moreover, CHIP and luciferase reporter assays demonstrated that KLF12 bound to a CAGTGGG element within the decidual prolactin promoter and decreased decidual PRL promoter (dPRL/-2000Luc) activation in a sequence-specific manner. Taken together, these findings suggest KLF12 is a negative regulator of human endometrial stromal cell decidualization.

Regulation of decidualization in human endometrial stromal cells through exchange protein directly activated by cyclic AMP (Epac)

INTRODUCTION

Human endometrial stromal cells (ESCs) undergo differentiation during the decidualization process. Decidualization is characterized by their enhanced production of IGF binding protein-1 (IGFBP-1), prolactin (PRL), and the forkhead transcriptional factor FOXO1, and transformation into more rounded cells, during the secretory phase of the menstrual cycle and subsequent pregnancy. Protein kinase A (PKA)-mediated cAMP signaling is crucial for this process. The present study was undertaken to examine the involvement of a mediator of cAMP signaling, exchange protein directly activated by cAMP (Epac), in decidualization of cultured ESCs.

RESULTS

Treatment of ESCs with the Epac-selective cAMP analog 8-CPT-2-OMe-cAMP (CPT) had no effect on IGFBP-1, PRL, and FOXO1 mRNA expression. However, CPT potentiated IGFBP-1 and PRL expression stimulated by the PKA-selective cAMP analog N(6)-Phe-cAMP (Phe) and activated Rap1, a downstream regulator of Epac signaling. Knock-down of Epac1, Epac2, or Rap1 significantly inhibited the Phe- or Phe/CPT-induced increase in IGFBP-1 and PRL expression, as well as Rap1 activation. Furthermore, CPT enhanced IGFBP-1 and PRL expression and the morphological differentiation induced by ovarian steroids, whereas Epac1, Epac2, or Rap1 knock-down suppressed these events.

CONCLUSION

These data provide evidence for the involvement of the Epac/Rap1 signaling pathway in cAMP-mediated decidualization of human ESCs.

Regulation of human endometrial stromal proliferation and differentiation by C/EBPβ involves cyclin E-cdk2 and STAT3

During each menstrual cycle, the human uterus undergoes a unique transformation, known as decidualization, which involves endometrial stromal proliferation and differentiation. During this process, the stromal cells are transformed into decidual cells, which produce factors that prepare the uterus for potential embryo implantation. We previously identified the transcription factor CCAAT/enhancer-binding protein (C/EBP)β as a regulator of endometrial stromal proliferation and differentiation in mice. In this study, we addressed the role of C/EBPβ in human endometrial decidualization. Using small interfering RNA targeted to C/EBPβ mRNA, we demonstrated that C/EBPβ controls the proliferation of primary human endometrial stromal cells (HESCs) by regulating the expression of several key cell cycle-regulatory factors during the G(1)-S phase transition. Additionally, loss of C/EBPβ expression blocked the differentiation of HESCs in response to estrogen, progesterone, and cyclic AMP. Gene expression profiling of normal and C/EBPβ-deficient HESCs revealed that the receptor for the cytokine IL-11 and its downstream signal transducer signal transducer and activator of transcription 3 (STAT3) are targets of regulation by C/EBPβ. Chromatin immunoprecipitation analysis indicated that C/EBPβ controls the expression of STAT3 gene by directly interacting with a distinct regulatory sequence in its 5'-flanking region. Attenuation of STAT3 mRNA expression in HESCs resulted in markedly reduced differentiation of these cells, indicating an important role for STAT3 in decidualization. Gene expression profiling, using STAT3-deficient HESCs, showed an extensive overlap of pathways downstream of STAT3 and C/EBPβ during stromal cell differentiation. Collectively, these findings revealed a novel functional link between C/EBPβ and STAT3 that is a critical regulator of endometrial differentiation in women.

Regulatory evolution through divergence of a phosphoswitch in the transcription factor CEBPB

There is an emerging consensus that gene regulation evolves through changes in cis-regulatory elements and transcription factors. Although it is clear how nucleotide substitutions in cis-regulatory elements affect gene expression, it is not clear how amino-acid substitutions in transcription factors influence gene regulation. Here we show that amino-acid changes in the transcription factor CCAAT/enhancer binding protein-β (CEBPB, also known as C/EBP-β) in the stem-lineage of placental mammals changed the way it responds to cyclic AMP/protein kinase A (cAMP/PKA) signalling. By functionally analysing resurrected ancestral proteins, we identify three amino-acid substitutions in an internal regulatory domain of CEBPB that are responsible for the novel function. These amino-acid substitutions reorganize the location of key phosphorylation sites, introducing a new site and removing two ancestral sites, reversing the response of CEBPB to GSK-3β-mediated phosphorylation from repression to activation. We conclude that changing the response of transcription factors to signalling pathways can be an important mechanism of gene regulatory evolution.

Down-regulation of the histone methyltransferase EZH2 contributes to the epigenetic programming of decidualizing human endometrial stromal cells

Differentiation of human endometrial stromal cells (HESC) into decidual cells represents a highly coordinated process essential for embryo implantation. We show that decidualizing HESC down-regulate the histone methyltransferase enhancer of Zeste homolog 2 (EZH2), resulting in declining levels of trimethylation of histone 3 on lysine 27 (H3K27me3) at the proximal promoters of key decidual marker genes PRL and IGFBP1. Loss of H3K27me3 was associated with a reciprocal enrichment in acetylation of the same lysine residue, indicating active remodeling from repressive to transcriptionally permissive chromatin. Chromatin immunoprecipitation coupled with DNA microarray analysis demonstrated that decidualization triggers genome-wide changes in H3K27me3 distribution that only partly overlap those observed upon EZH2 knockdown in undifferentiated HESC. Gene ontology revealed that gain of the repressive H3K27me3 mark in response to decidualization and upon EZH2 knockdown in undifferentiated cells was enriched at the promoter regions of genes involved in transcriptional regulation and growth/cell proliferation, respectively. However, loss of the H3K27me3 mark (indicating increased chromatin accessibility) in decidualizing cells and upon EZH2 knockdown occurred at selective loci enriched for genes functionally implicated in responses to stimulus. In agreement, EZH2 knockdown in undifferentiated HESC was sufficient to augment the induction of decidual marker genes in response to cyclic AMP and progesterone signaling. Thus, loss of EZH2-dependent methyltransferase activity in the endometrium is integral to the process of chromatin remodeling that enables the transition from a proliferative to a decidual phenotype in response to differentiation cues.

Regulation of FoxO transcription factors by acetylation and protein-protein interactions

The forkhead box O transcription factors convert a variety of external stimuli, including growth factors, nutrients, and oxidative stress, into diverse biological responses through modulation of specific gene expression. Forkhead box O regulation is principally achieved by two distinct mechanisms: post-translational modifications and protein-protein interactions. Among several modifications of forkhead box O factors, we focus on reversible acetylation, describing past research and current advances. In the latter part of this review, we also provide an overview of forkhead box O-binding partners that control the transcriptional activity of forkhead box O factors. These two layers of regulation mostly overlap and thereby enable a more precise fine-tuning of forkhead box O functions involved in metabolism, longevity, and tumor suppression. This article is part of a Special Issue entitled: PI3K-AKT-FoxO axis in cancer and aging.

NADPH oxidase-derived reactive oxygen species mediate decidualization of human endometrial stromal cells in response to cyclic AMP signaling

Differentiation of human endometrial stromal cells into specialized decidual cells is critical for embryo implantation and survival of the conceptus. Initiation of this differentiation process is strictly dependent on elevated cAMP levels, but the signal intermediates that control the expression of decidual marker genes, such as prolactin (PRL) and IGFBP1, remain poorly characterized. Here we show that cAMP-dependent decidualization can be attenuated or enhanced upon treatment of primary cultures with a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor (diphenylen iodonium) or activator (apocynin), respectively. Time-course analysis demonstrated that cAMP enhances endogenous reactive oxygen species production, apparent after 12 h of stimulation, which coincides with a dramatic increase in decidual PRL and IGFBP1 expression. Knockdown of the Rho GTPase RAC1, which disables activation of the NADPH oxidase homologs NADPH oxidase (NOX)-1, NOX-2, and NOX-3, had no effect on PRL or IGFBP1 expression. In contrast, silencing of NOX-4, or its cofactor p22(PHOX), inhibited the expression of both decidual markers. Finally, we show that the NOX-4/p22(PHOX) complex regulates the DNA-binding activity of CCAAT/enhancer binding protein-β, a key regulator of human endometrial stromal cell differentiation. Thus, NOX-4 activation and reactive oxygen species signaling play an integral role in initiating the endometrial decidual response in preparation of pregnancy.

Labor and inflammation increase the expression of oxytocin receptor in human amnion

The oxytocin/oxytocin receptor (OXT/OXTR) system plays an important role in the regulation of parturition. The amnion is a major source of prostaglandins and inflammatory cytokine synthesis, which increase both before and during labor. Amnion is a noncontractile tissue; therefore, the role played by OXT/OXTR in this tissue will be fundamentally different from the role played in myometrial contractions. In the present study, we demonstrate increased OXTR mRNA and protein concentrations in human amnion epithelial cells associated with the onset of labor. We show that incubation of primary human amnion epithelial cells with IL1B results in a rapid, transient up-regulation of OXTR mRNA expression, which peaks in prelabor samples after 6 h. Incubation of prelabor amnion epithelial cells with OXT results in a marked increase of prostaglandin E(2) synthesis, and we demonstrate that OXT activates the extracellular signal-regulated protein kinase signal transduction pathway to stimulate up-regulation of cyclo-oxygenase 2 in human amnion epithelial cells. The increased ability of human amnion to produce prostaglandins in response to OXT treatment suggests a complementary role for the OXT/OXTR system in the activation of human amnion and the onset of labor.

HoxA-11 and FOXO1A cooperate to regulate decidual prolactin expression: towards inferring the core transcriptional regulators of decidual genes

During the menstrual cycle, the ovarian steroid hormones estrogen and progesterone control a dramatic transcriptional reprogramming of endometrial stromal cells (ESCs) leading to a receptive state for blastocyst implantation and the establishment of pregnancy. A key marker gene of this decidualization process is the prolactin gene. Several transcriptional regulators have been identified that are essential for decidualization of ESCs, including the Hox genes HoxA-10 and HoxA-11, and the forkhead box gene FOXO1A. While previous studies have identified downstream target genes for HoxA-10 and FOXO1A, the role of HoxA-11 in decidualization has not been investigated. Here, we show that HoxA-11 is required for prolactin expression in decidualized ESC. While HoxA-11 alone is a repressor on the decidual prolactin promoter, it turns into an activator when combined with FOXO1A. Conversely, HoxA-10, which has been previously shown to associate with FOXO1A to upregulate decidual IGFBP-1 expression, is unable to upregulate PRL expression when co-expressed with FOXO1A. By co-immunoprecipitation and chromatin immunoprecipitation, we demonstrate physical association of HoxA-11 and FOXO1A, and binding of both factors to an enhancer region (−395 to −148 relative to the PRL transcriptional start site) of the decidual prolactin promoter. Because FOXO1A is induced upon decidualization, it serves to assemble a decidual-specific transcriptional complex including HoxA-11. These data highlight cooperativity between numerous transcription factors to upregulate PRL in differentiating ESC, and suggest that this core set of transcription factors physically and functionally interact to drive the expression of a gene battery upregulated in differentiated ESC. In addition, the functional non-equivalence of HoxA-11 and HoxA-10 with respect to PRL regulation suggests that these transcription factors regulate distinct sets of target genes during decidualization.

Cyclic regulation of transcription factor C/EBP beta in human endometrium

BACKGROUND

The transcription factor CCAAT/enhancer-binding protein (C/EBP) beta is a critical mediator of murine endometrial function during embryo implantation. Our objective is to characterize changes in C/EBP beta mRNA abundance and protein localization over the normal human menstrual cycle.

METHODS

Fifty normally cycling volunteers without reproductive disorders were randomized to undergo endometrial sampling on a specific cycle day, with secretory phase samples timed using urinary LH surge. Samples were assessed for relative C/EBP beta mRNA expression using quantitative real-time RT-PCR and for C/EBP beta protein localization using immunohistochemistry. The semiquantitative histologic scoring (HSCORE) system was used to compare staining intensity in each tissue compartment between each cycle phase.

RESULTS

C/EBP beta mRNA expression by whole endometrium peaks in the late secretory phase and is significantly higher than that in the proliferative and mid-secretory phases. A marked increase in nuclear C/EBP beta protein immunostaining is seen in stromal cells beginning about cycle day 20, coincident with the start of endometrial receptivity. This increased staining continues for the remainder of the cycle.

CONCLUSION

In the normal human menstrual cycle, C/EBP beta mRNA and protein expression also change, with increased nuclear immunostaining in the mid-secretory phase, suggesting a possible role for C/EBP beta in human endometrial receptivity.

Relaxin physiology in the female reproductive tract during pregnancy

The characteristic functions of relaxin are associated with female reproductive tract physiology. These include the regulation of biochemical processes involved in remodeling the extracellular matrix of the cervix and vagina during pregnancy and rupture of the fetal membranes at term. Such modifications enable the young to move unimpeded through the birth canal and prevent dystocia. However, relaxin's physiological actions are not limited to late gestation. New functions for this peptide hormone in implantation and placentation are also emerging. Relaxin promotes uterine and placental growth and influences vascular development and proliferation in the endometrium. This chapter provides an overview of the current literature on relaxin physiology in the uterus, cervix and vagina of pregnant females and the impact on fetal health. It also outlines the potential mechanisms of relaxin action, particularly in the cervical extracellular matrix and uterine endometrium.

Systematic expression analysis and antibody screening do not support the existence of naturally occurring progesterone receptor (PR)-C, PR-M, or other truncated PR isoforms

Functional progesterone withdrawal associated with human parturition has been ascribed to various mechanisms modulating the function of the classical progesterone receptors (PRs), B and A, in utero. These include up-regulation of the inhibitory PR-C isoform, described as a 60-kDa protein occurring from translation initiation at codon 595. Our initial attempts to detect PR-C yielded uninterpretable results. To systematically validate antibodies for immunodetection of PR isoforms, we generated expression vectors for PR variants originating from putative start codons AUG-289, -301, -595, -632, and -692 in addition to those for PR-B and PR-A, and for alternative splice variants PR-T, PR-S, and PR-M. All constructs were subjected to in vitro and in vivo translation and immunoblotting with a panel of 13 PR antibodies. Antibodies raised against full-length PR were generally not capable of detecting N-terminally truncated forms, whereas C-terminal antibodies did not or only weakly reacted with PR-B and PR-A but produced prominent nonspecific signals. Thus, immunodetection of N-terminally truncated PR isoforms is prone to artifacts. Proteins of about 64 kDa were expressed from PR-289 and -301, but no corresponding endogenous forms were observed. PR-T, PR-S, and PR-M cDNAs yielded no detectable translation products. No protein was translated from AUG-595 in our PR-C expression vector unless a Kozak sequence was introduced, and the product was not 60 but 38 kDa in size. Thus, the 60-kDa protein called PR-C does not originate from AUG-595 and is not a naturally occurring PR isoform.

Molecular and cellular mechanisms for differentiation and regeneration of the uterine endometrium

The human endometrium undergoes cyclical changes including proliferation, differentiation, tissue breakdown, and shedding (menstruation) throughout a woman's reproductive life. The postovulatory rise in ovarian progesterone induces profound remodeling and differentiation of the estradiol-primed endometrium. This change, termed decidualization, is crucial for embryo implantation and maintenance of the pregnancy. To date, activation and crosstalk of cAMP- and progesterone-mediated signaling pathways have emerged as key cellular events to drive integrated changes at both the transcriptome and the proteome levels. This results in the induction and maintenance of the decidual phenotype and function. Our recent series of studies highlights the critical role of SRC kinase activation (v-src sarcoma viral oncogene homolog) and STAT5 (signal transducer and activator of transcription 5) phosphorylation in decidualization. After separation of the functional layer of the differentiated endometrium that follows progesterone withdrawal, i.e., menstruation, the basal layer of the endometrium, under the influence of estradiol, regrows and initiates a unique form of angiogenesis and regenerates a new functional layer. The molecular and cellular mechanisms for this process remain elusive, mainly because of difficulties in reproducing menstrual tissue breakdown, shedding, and subsequent tissue regeneration in vitro. We have recently developed a "humanized" mouse model in which a functional human endometrium is reconstituted. It may be used as an in vivo experimental tool for the study of endometrial angiogenesis and regeneration. This model may also be used to identify and test new therapeutic strategies for endometriosis, endometrial cancer, implantation failure, and infertility related to endometrial dysfunction.

Adaptive changes in the transcription factor HoxA-11 are essential for the evolution of pregnancy in mammals

Evolutionary change in gene regulation can result from changes in cis-regulatory elements, leading to differences in the temporal and spatial expression of genes or in the coding region of transcription factors leading to novel functions or both. Although there is a growing body of evidence supporting the importance of cis-regulatory evolution, examples of protein-mediated evolution of novel developmental pathways have not been demonstrated. Here, we investigate the evolution of prolactin (PRL) expression in endometrial cells, which is essential for placentation/pregnancy in eutherian mammals and is a direct regulatory target of the transcription factor HoxA-11. Here, we show that (i) endometrial PRL expression is a derived feature of placental mammals, (ii) the PRL regulatory gene HoxA-11 experienced a period of strong positive selection in the stem-lineage of eutherian mammals, and (iii) only HoxA-11 proteins from placental mammals, including the reconstructed ancestral eutherian gene, are able to up-regulate PRL from the promoter used in endometrial cells. In contrast, HoxA-11 from the reconstructed therian ancestor, opossum, platypus, and chicken are unable to up-regulate PRL expression. These results demonstrate that the evolution of novel gene expression domains is not only mediated by the evolution of cis-regulatory elements but can also require evolutionary changes of transcription factor proteins themselves.

FOXO-binding partners: it takes two to tango

Modulation FOXO transcription factor activities can lead to a variety of cellular outputs resulting in changes in proliferation, apoptosis, differentiation and metabolic responses. Although FOXO proteins all contain an identical DNA-binding domain their cellular functions appear to be distinct, as exemplified by differences in the phenotype of Foxo1, Foxo3 and Foxo4 null mutant mice. While some of these differences may be attributable to the differential expression patterns of these transcription factors, many cells and tissues express several FOXO isoforms. Recently it has become clear that FOXO proteins can regulate transcriptional responses independently of direct DNA-binding. It has been demonstrated that FOXOs can associate with a variety of unrelated transcription factors, regulating activation or repression of diverse target genes. The complement of transcription factors expressed in a particular cell type is thus critical in determining the functional end point of FOXO activity. These interactions greatly expand the possibilities for FOXO-mediated regulation of transcriptional programmes. This review details currently described FOXO-binding partners and examines the role of these interactions in regulating cell fate decisions.

What can we learn from rodents about prolactin in humans?

Prolactin (PRL) is a 23-kDa protein hormone that binds to a single-span membrane receptor, a member of the cytokine receptor superfamily, and exerts its action via several interacting signaling pathways. PRL is a multifunctional hormone that affects multiple reproductive and metabolic functions and is also involved in tumorigenicity. In addition to being a classical pituitary hormone, PRL in humans is produced by many tissues throughout the body where it acts as a cytokine. The objective of this review is to compare and contrast multiple aspects of PRL, from structure to regulation, and from physiology to pathology in rats, mice, and humans. At each juncture, questions are raised whether, or to what extent, data from rodents are relevant to PRL homeostasis in humans. Most current knowledge on PRL has been obtained from studies with rats and, more recently, from the use of transgenic mice. Although this information is indispensable for understanding PRL in human health and disease, there is sufficient disparity in the control of the production, distribution, and physiological functions of PRL among these species to warrant careful and judicial extrapolation to humans.

Adipocyte prolactin: regulation of release and putative functions

Pituitary-derived prolactin (PRL) is a well-known regulator of the lactating mammary gland. However, the recent discovery that human adipose tissue produces PRL as well as expresses the PRL receptor (PRLR) highlights a previously unappreciated action of PRL as a cytokine involved in adipose tissue function. Biologically active PRL is secreted by all adipose tissue depots examined: breast, visceral and subcutaneous. The expression of adipose PRL is regulated by a non-pituitary, alternative superdistal promoter. PRL expression and release increases during early pre-adipocyte differentiation and is stimulated by cyclic AMP activators, including beta adrenergic receptor agonists. PRL release from subcutaneous adipose explants is attenuated during obesity, suggesting that adipose PRL production is altered by the metabolic state. Several lines of evidence indicate that PRL suppresses lipid storage as well as the release of adipokines such as adiponectin, interleukin-6 and possibly leptin. PRL has also been implicated in the regulation of adipogenesis. A newly developed PRL-secreting human adipocyte cell line, LS14, should allow comprehensive examination of the regulation and function of adipocyte-derived PRL. Collectively, these studies raise the prospect that PRL affects energy homeostasis through its action as an adipokine and is involved in the manifestation of insulin resistance.

Analysis on the promoter region of human decidual prolactin gene in the progesterone-induced decidualization and cAMP-induced decidualization of human endometrial stromal cells

PURPOSE

To elucidate the promoter region of human decidual prolactin (dPRL) gene in the human endometrial stromal cells (ESC).

METHODS

Various segments of the human dPRL promoter that direct the expression of the secreted alkaline phosphatase (SEAP) reporter gene were transfected into human ESC decidualized by estrogen (E) + progesterone (P) or cyclic AMP (cAMP) to identify E + P or cAMP responsive elements.

RESULTS

The region between nucleotides -2038 and -1605 relative to the transcriptional initiation site includes two activator protein-1 (AP-1) sites, which both provided maximal response to E + P or cAMP in decidualized cells. When either AP-1 site was mutated, response in the promoter activity to both E + P or cAMP response showed a decrease compared with control. The region between -310 and -285 that contains consensus-binding sequences for transcription factors of CCAAT/Enhancer-binding proteins (C/EBP) contributed to E + P and cAMP response in decidualized cells. Also, the 5'-flanking region that extends 79 base pairs upstream, including an imperfect cAMP response element (CRE), contributed to E + P and cAMP response. In cells treated with E + P or cAMP for 10 days, mutant of C/EBP-binding site showed an increase in promoter activity comparing to dPRL-2038. In contrast, treatment with PKI showed a decrease in promoter activity in cells treated with E + P or cAMP alone.

CONCLUSIONS

These results suggest that cAMP-induced region of the human dPRL promoter resides between -1862 and -1856, -1703 and -1697, -310 and -285, and that the sequences between -1862 and -1856, -1703 and -1697 of the promoter display E + P-induced promoter activity. Furthermore, the current study indicates that E + P or cAMP cooperatively regulate the dPRL gene transcription through some transcriptional factors such as C/EBP, CREB, and other cofactor(s), and that some repressor(s) or corepressor(s) may be involved in the C/EBP-binding site of the human dPRL promoter.

Prolactin in man: a tale of two promoters

The pituitary hormone prolactin (PRL) is best known for its role in the regulation of lactation. Recent evidence furthermore indicates PRL is required for normal reproduction in rodents. Here, we report on the insertion of two transposon-like DNA sequences in the human prolactin gene, which together function as an alternative promoter directing extrapituitary PRL expression. Indeed, the transposable elements contain transcription factor binding sites that have been shown to mediate PRL transcription in human uterine decidualised endometrial cells and lymphocytes. We hypothesize that the transposon insertion event has resulted in divergent (pituitary versus extrapituitary) expression of prolactin in primates, and in differential actions of pituitary versus extrapituitary prolactin in lactation versus pregnancy respectively. Importantly, the TE insertion might provide a context for some of the conflicting results obtained in studies of PRL function in mice and man.

Induction of prolactin expression and release in human preadipocytes by cAMP activating ligands

In addition to the pituitary, prolactin (PRL) in humans is produced at non-pituitary sites where it acts as a cytokine. We previously reported that PRL is expressed and released from breast adipose explants, raising the question as to the dynamics of its production and its regulation. Preadipocytes were isolated from breast adipose tissue obtained during breast reduction. PRL expression was transiently increased during early preadipocyte differentiation. Both isoproterenol, a beta-adrenergic receptor agonist, and PACAP, pituitary adenylate cyclase activating peptide, increased PRL expression, and release from preadipocytes. This stimulation was suppressed by several protein kinase inhibitors, suggesting involvement of multiple signaling pathways. Transfection of preadipocytes with a superdistal PRL promoter/luciferase reporter revealed two stimulatory domains and an inhibitory domain. These data establish the transcriptional regulation of adipocyte PRL by the superdistal PRL promoter, its transient expression during adipogenesis, and the stimulatory effect of catecholamines and PACAP.

Galectin-1 induces skeletal muscle differentiation in human fetal mesenchymal stem cells and increases muscle regeneration

Cell therapy for degenerative muscle diseases such as the muscular dystrophies requires a source of cells with the capacity to participate in the formation of new muscle fibers. We investigated the myogenic potential of human fetal mesenchymal stem cells (hfMSCs) using a variety of stimuli. The use of 5-azacytidine or steroids did not produce skeletal muscle differentiation, whereas myoblast-conditioned medium resulted in only 1%-2% of hfMSCs undergoing muscle differentiation. However, in the presence of galectin-1, 66.1% +/- 5.7% of hfMSCs, but not adult bone marrow-derived mesenchymal stem cells, assumed a muscle phenotype, forming long, multinucleated fibers expressing both desmin and sarcomeric myosin via activation of muscle regulatory factors. Continuous exposure to galectin-1 resulted in more efficient muscle differentiation than pulsed exposure (62.3% vs. 39.1%; p < .001). When transplanted into regenerating murine muscle, galectin-1-exposed hfMSCs formed fourfold more human muscle fibers than nonstimulated hfMSCs (p = .008), with similar results obtained in a scid/mdx dystrophic mouse model. These data suggest that hfMSCs readily undergo muscle differentiation in response to galectin-1 through a stepwise progression similar to that which occurs during embryonic myogenesis. The high degree of myogenic conversion achieved by this method has relevance for the development of therapies for muscular dystrophies.

Association of polymorphisms in the promoter region of chicken prolactin with egg production

Chicken prolactin (PRL) is a physiological candidate gene for egg production. The objective of the current research was to investigate the association of polymorphisms in the chicken PRL promoter region with egg production. Genotyping of 177 individuals from White Leghorn, Yangshan, Taihe Silkies, White Rock, and Nongdahe breeds for 6 single nucleotide polymorphisms (C-2402T, C-2161G, T-2101G, C-2062G, T-2054A, and G-2040A) and 1 24-bp indel (insertion-deletion) at the site of -358 of the chicken PRL gene revealed large breed differences in allelic frequencies for all but the T-2101G and T-2054A polymorphisms. An F2 population produced from Nongdahe x Taihe Silkies chickens consisted of 374 hens, which were recorded for egg production traits and genotyped for the above 7 polymorphisms. Marker-trait association analysis indicated that the 24-bp indel was associated with egg production (P < 0.01) and that H3 (C C T C T G) was the most advantageous haplotype for egg production.

Physical interaction and mutual transrepression between CCAAT/enhancer-binding protein beta and the p53 tumor suppressor

The tumor suppressor protein p53 is not only involved in defending cells against genotoxic insults but is also implicated in differentiation processes, a function that it shares with the CCAAT/enhancer-binding protein beta (C/EBPbeta). We previously reported an up-regulation of both factors in the cycle-dependent differentiation process of human endometrial stromal cells, termed decidualization. C/EBPbeta-mediated activation of a decidualization marker, the decidual prolactin promoter, was antagonized by p53. Here we report that C/EBPbeta in turn represses the transcriptional activity of p53. Competition for limiting amounts of coactivator CREB-binding protein/p300 was ruled out as the underlying mechanism of transrepression. Physical interaction between p53 and C/EBPbeta was demonstrated in vitro and in vivo and shown to depend on the C-terminal domains of both proteins. In gel shift experiments, C/EBPbeta reduced complex formation between p53 and its response element. Conversely, p53 strongly inhibited binding of endogenous C/EBPbeta from endometrial stromal cells to the C/EBP-responsive region in the decidual prolactin promoter. The observed negative cross-talk between p53 and C/EBPbeta is likely to impact expression of their respective target genes.

Ligand activated relaxin receptor increases the transcription of IGFBP-1 and prolactin in human decidual and endometrial stromal cells

The aim of this study was to investigate relaxin (RLX) receptor-mediated gene activation in human endometrium. We determined the promoter activities of insulin-like growth factor binding protein-1 (IGFBP-1) and prolactin (PRL) and identified sequence(s) that mediate RLX activated transcription in human decidual cells and endometrial stromal cells. In human decidual cells, the promoter activity of IGFBP-1 was increased significantly in cells incubated with RLX. In endometrial stromal cells, the RLX mediated activation was enhanced only when stromal cells were co-transfected with RLX-receptor (LGR7) expression vector and RLX alone had little effect (Mazella et al., 2004). Deletion and mutation analysis showed that the cAMP regulatory element (CRE, -263 to -259 bp) in the IGFBP-1 promoter was essential for the activation. In addition, RLX increased the phosphorylation of CRE binding protein (CREB to p-CREB) and p-CREB resided in the nucleus, indicating that RLX activates the protein kinase (PKA) system in decidual cells. Gel shift assay showed that nuclear extracts prepared from RLX treated decidual cells increased the binding to the CRE site of the IGFBP-1 promoter. RLX increased the PRL promoter activity mediated through the region containing multiple CCAAT/enhancer-binding proteins (C/EBP) binding sites that have been shown to mediate the PRL gene activation by cAMP analogue (Pohnke et al., 1999). RLX enhanced IGFBP-1 promoter activity was inhibited by cAMP dependent PKA inhibitor, H-89. PRL promoter activity was inhibited by both H-89 and U0126 indicating multiple signalling pathways are activated by RLX in endometrial cells for different target gene activation.

EGF stimulates Pit-1 independent transcription of the human prolactin pituitary promoter in human breast cancer SK-BR-3 cells through its proximal AP-1 response element

Normal and neoplastic human mammary gland cells are targets for the proliferative action of prolactin. These cells also synthesize prolactin, thereby inducing an autocrine/paracrine proliferative loop. We present the first extensive analysis of the transcriptional regulation of the human prolactin gene (hPRL) in human mammary tumor cells, SK-BR-3. We show that the pituitary promoter is functional in these cells in the absence of the pituitary-specific factor Pit-1. Expression of exogenous Pit-1 or epidermal growth factor (EGF) treatment stimulates the transfected hPRL pituitary promoter and the endogenous hPRL expression. EGF stimulation is mediated by increased synthesis of c-fos and c-jun, resulting in AP-1 binding to the proximal hPRL pituitary promoter. This regulation involves the EGF receptor, possibly ErbB2 that is highly expressed in SK-BR-3 cells, and a PI3K/JNK pathway. The stimulation of hPRL gene transcription by EGF in mammary cells may include hPRL in a complex regulatory network controlling growth of human mammary cells.

Cannabinoid receptor I activation markedly inhibits human decidualization

The role of cannabinoid receptor I (CBR-1) in the induction of decidualization was examined using decidual fibroblasts and human endometrial stromal cells as model systems. Decidual fibroblasts decidualized in vitro for 3 and 6 days in the presence of the CBR-1 agonist R(+)-WIN 55,212-2 mesylate (WIN, 0.1-10 microM) expressed less of the decidualization-specific markers prolactin, CBR-1, forkhead (FKHR), TIMP-3, laminin, endometrial bleeding associated factor (EBAF), decorin and insulin-like growth factor binding protein-1 (IGFBP-1) mRNA levels compared to control cells. The maximal decrease for each transcript was in the range of 50-99%. In contrast, cells exposed to the CBR-1 inhibitor AM-251 (1 microM) expressed about two-fold higher levels of the decidualization-specific marker gene mRNAs. The WIN-exposed cells showed a marked decrease in intracellular cAMP levels and a progressive, concentration-dependent increase in DNA fragmentation (TUNEL assay) and caspase 3 levels during decidualization compared to control cells. These studies strongly suggest that activation of CBR-1 inhibits human decidualization and stimulates apoptosis by a cAMP-dependent mechanism.

Mechanism of prostaglandin (PG)E2-induced prolactin expression in human T cells: cooperation of two PGE2 receptor subtypes, E-prostanoid (EP) 3 and EP4, via calcium- and cyclic adenosine 5'-monophosphate-mediated signaling pathways

We previously reported that prolactin gene expression in the T-leukemic cell line Jurkat is stimulated by PGE(2) and that cAMP acts synergistically with Ca(2+) or protein kinase C on the activation of the upstream prolactin promoter. Using the transcription inhibitor actinomycin D, we now show that PGE(2)-induced prolactin expression requires de novo prolactin mRNA synthesis and that PGE(2) does not influence prolactin mRNA stability. Furthermore, PGE(2)-induced prolactin expression was inhibited by protein kinase inhibitor fragment 14-22 and BAPTA-AM, which respectively, inhibit protein kinase A- and Ca(2+)-mediated signaling cascades. Using specific PGE(2) receptor agonists and antagonists, we show that PGE(2) induces prolactin expression through engagement of E-prostanoid (EP) 3 and EP4 receptors. We also found that PGE(2) induces an increase in intracellular cAMP concentration as well as intracellular calcium concentration via EP4 and EP3 receptors, respectively. In transient transfections, 3000 bp flanking the leukocyte prolactin promoter conferred a weak induction of the luciferase reporter gene by PGE(2) and cAMP, whereas cAMP in synergy with ionomycin strongly activated the promoter. Mutation of a C/EBP responsive element at -214 partially abolished the response of the leukocyte prolactin promoter to PGE(2), cAMP, and ionomycin plus cAMP.

CCAAT/enhancer binding protein delta (C/EBPdelta) expression and elevation in Alzheimer's disease

The CCAAT-enhancer binding protein (C/EBP) family of transcription factors, particularly C/EBPdelta, is well known to regulate or co-regulate a wide range of inflammatory mediators and mechanisms in the periphery, including interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). These cytokines, in turn, can induce C/EBPdelta expression and translocation to the nucleus as an active transcription factor. Because IL-1, IL-6, and TNF-alpha are increased in pathologically vulnerable regions of the Alzheimer's disease (AD) brain, we sought to determine if C/EBPdelta might be expressed in AD cortex. Immunohistochemistry of AD tissue sections revealed profuse C/EBPdelta staining of astrocytes, particularly reactive astrocytes surrounding amyloid beta peptide deposits. Substantially less immunoreactivity was observed in comparable sections from nondemented elderly control (ND) patients. These qualitative findings were consistent with quantitative Western blot densitometry results showing significant increases in C/EBPdelta in AD compared to ND cortex samples. Additional in vitro studies were pursued in order to characterize functional activity of C/EBPdelta in human elderly astrocytes. Consistent with a functionally active transcription factor, C/EBPdelta immunoreactivity predominated in the nucleus of cultured AD and ND astrocytes, and exhibited increases and nuclear localization, as determined by Western blots and electrophoretic mobility shifts after exposure to C/EBPdelta-inducing cytokines.

Immunoexpression of the relaxin receptor LGR7 in breast and uterine tissues of humans and primates

BACKGROUND

The receptor for the peptide hormone relaxin has recently been identified as the heptahelical G-protein coupled receptor, LGR7. In order to generate molecular tools with which to characterize both in vivo and in vitro expression of this receptor in human and primate tissues, specific monotypic antibodies have been generated and applied to a preliminary analysis of human and primate female reproductive tissues.

METHODS

Three peptide sequences were identified from the proposed open reading frame of the cloned LGR7 receptor gene, representing both extracellular and intracellular domains. Two to three rabbits were immunized for each epitope, and the resulting sera subjected to a systematic validation using cultured cells transiently transfected with a receptor-expressing gene construct, or appropriate control constructs.

RESULTS

Human and monkey (marmoset, macaque) endometrium showed consistent and specific immunostaining in the stromal cells close to glands. Staining appeared to be more intense in the luteal phase of the cycle. Weak immunostaining was also evident in the endometrial epithelial cells of the marmoset. A myoma in one patient exhibited strong immunostaining in the circumscribing connective tissue. Uterine expression was supported by RT-PCR results from cultured primary endometrial and myometrial cells. Human breast tissue (healthy and tumors) consistently indicated specific immunostaining in the interstitial connective (stromal) tissue within the glands, but not in epithelial or myoepithelial cells, except in some tumors, where a few epithelial and tumor cells also showed weak epitope expression.

CONCLUSIONS

Using validated monotypic antibodies recognizing different epitopes of the LGR7 receptor, and from different immunized animals, and in different primate species, a consistent pattern of LGR7 expression was observed in the stromal (connective tissue) cells of the endometrium and breast, consistent also with the known physiology of the relaxin hormone.

Calcium channel and NMDA receptor activities differentially regulate nuclear C/EBPbeta levels to control neuronal survival

Insulin-like growth factor-1 (IGF-1) promotes the survival of cerebellar granule neurons by enhancing calcium influx through L-type calcium channels, whereas NMDA receptor-mediated calcium influx can lead to excitotoxic death. Here we demonstrate that L and NMDA receptor channel activities differentially regulate the transcription factor C/EBPbeta to control neuronal survival. Specifically, we show that L channel-dependent calcium influx results in increased CaMKIV activity, which acts to decrease nuclear C/EBPbeta levels. Conversely, NMDA receptor-mediated influx rapidly elevates nuclear C/EBPbeta and induces excitotoxic death via activation of the calcium-dependent phosphatase, calcineurin. Moderate levels of AMPA receptor activity stimulate L channels to improve survival, whereas higher levels stimulate NMDA receptors and reduce neuronal survival, suggesting differential synaptic effects. Finally, N-type calcium channel activity reduces survival, potentially by increasing glutamate release. Together, these results show that the L-type calcium channel-dependent survival and NMDA receptor death pathways converge to regulate nuclear C/EBPbeta levels, which appears to be pivotal in these mechanisms.

Regulation of prolactin expression in leukemic cell lines and peripheral blood mononuclear cells

To address the role of different intracellular signals in prolactin (PRL) expression in leukocytes, we have investigated the effects of chlorophenylthio-cAMP (cptcAMP), phorbol myristate acetate (PMA) and ionomycin on the activation of the upstream PRL promoter in several leukemic cell lines. All three stimulators, alone or in synergism with each other, were able to modulate promoter activity, but their actions were cell-type dependent. In freshly isolated peripheral blood mononuclear cells (PBMC), PRL expression could only be stimulated by cptcAMP. The physiological importance of cAMP in the regulation of PRL expression in leukocytes is suggested by the finding that in PBMC, PRL expression is enhanced by prostaglandin-E(2) and the beta(2)-adrenergic agonist terbutaline, which both signal through cAMP.

Mechanisms of decidualization

The uterus is composed of heterogeneous cell types that undergo cyclic synchronized waves of proliferation and differentiation in response to the rise and fall of ovarian oestrogen and progesterone. The spatial and temporal diversity in cellular responses to ovarian hormones within a given endometrial cell compartment is thought to be effected by locally released factors. These endometrial polypeptides bind to specific cell surface receptors on target cells, resulting in activation of signal transduction pathways by way of coupling to GTP-binding proteins (G proteins), or through autophosphorylation in response to conformational changes induced by the binding of ligand. Within this paradigm, the highly complex and coordinated expression of decidua-specific genes by differentiating endometrial stroma cells during the late secretory phase of the menstrual cycle could be regarded as the result of the convergence of liganded steroid hormone receptors and specific activated cytoplasmatic signalling pathways.