Phosphatidylinositol 3 kinase modulation of trophoblast cell differentiation
© Kent et al; licensee BioMed Central Ltd. 2010
Received: 10 May 2010
Accepted: 14 September 2010
Published: 14 September 2010
The trophoblast lineage arises as the first differentiation event during embryogenesis. Trophoblast giant cells are one of several end-stage products of trophoblast cell differentiation in rodents. These cells are located at the maternal-fetal interface and are capable of invasive and endocrine functions, which are necessary for successful pregnancy. Rcho-1 trophoblast stem cells can be effectively used as a model for investigating trophoblast cell differentiation. In this report, we evaluated the role of the phosphatidylinositol 3-kinase (PI3K) signaling pathway in the regulation of trophoblast cell differentiation. Transcript profiles from trophoblast stem cells, differentiated trophoblast cells, and differentiated trophoblast cells following disruption of PI3K signaling were generated and characterized.
Prominent changes in gene expression accompanied the differentiation of trophoblast stem cells. PI3K modulated the expression of a subset of trophoblast cell differentiation-dependent genes. Among the PI3K-responsive genes were those encoding proteins contributing to the invasive and endocrine phenotypes of trophoblast giant cells.
Genes have been identified with differential expression patterns associated with trophoblast stem cells and trophoblast cell differentiation; a subset of these genes are regulated by PI3K signaling, including those impacting the differentiated trophoblast giant cell phenotype.
Hemochorial placental development is a complex process involving multiple signaling pathways. Effectively two placental compartments are established. One compartment contains trophoblast cells specialized for interactions with the maternal environment, while the other contains trophoblast cells directed toward the bidirectional transport of nutrients and wastes between the mother and the fetus. Trophoblast cells of the rat and mouse have the capacity to differentiate along a multi-lineage pathway. Cell lineages directed toward the maternal environment, include trophoblast giant cells, spongiotrophoblast, glycogen cells, and invasive trophoblast cells; whereas syncytial trophoblast regulate maternal-fetal nutrient and waste delivery [1–3]. Each lineage possesses specialized functions necessary for a normal pregnancy.
Trophoblast giant cells are the first trophoblast lineage to differentiate . Trophoblast giant cells are located at the maternal-fetal interface and have several functions. They produce steroid and peptide hormones  and have the ability to invade into the uterine vasculature [5, 6].
The phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT), pathway is involved in trophoblast cell development . Upon differentiation of trophoblast cells, PI3K is activated leading to the phosphorylation and constitutive activation of AKT . Inhibition of PI3K disrupts AKT activation and interferes with trophoblast cell differentiation [7, 8]. The predominant isoform of AKT in developing trophoblast giant cells is AKT1 [7, 9]. Mice possessing a null mutation at the Akt1 locus exhibit defects in placental development . Their placentas are smaller and accumulate less glycogen than wild-type mice.
In this report, we utilize Rcho-1 rat trophoblast stem cells as an in vitro model to gain a better understanding of trophoblast cell differentiation. Rcho-1 trophoblast cells are remarkable in that they can be maintained in a stem cell state or induced to differentiate along the trophoblast giant cell lineage [10–13]. This in vitro system represents an excellent model for investigating regulatory pathways controlling trophoblast giant cell differentiation. In order to gain new insights about trophoblast cell differentiation we performed genome wide screens for transcripts expressed in trophoblast stem cells, differentiating trophoblast cells, and differentiating trophoblast cells with disrupted PI3K signaling. Genes selected for further analyses exhibited high levels of expression, prominent differences among the experimental groups, and/or encoded proteins with actions potentially relevant to trophoblast biology. Expression patterns of a subset of genes identified from the array were verified by northern analysis and/or quantitative RT-PCR (qRT-PCR). In vivo placental expression patterns of the selected genes identified from the gene profiles were also determined. 'Trophoblast stem cell-associated', 'differentiation-associated', and 'PI3K-regulated' genes were identified. A subset of the 'differentiation-associated' genes is regulated by the PI3K signaling pathway and may contribute to the trophoblast cell phenotype.
Reagents and cDNA generation
All reagents were purchased from Sigma-Aldrich (St. Louis, MO) unless otherwise noted. cDNAs to selected transcripts were obtained from Invitrogen (Carlsbad, CA), American Type Culture Collection (ATCC, Rockville, MD), or cloned using TOPO TA cloning kit (Invitrogen). Other cDNAs were gifts from the following investigators: Atp1a1, Dr. Gustavo Blanco, University of Kansas Medical Center (Kansas City, KS); Cyp11a1, Dr. JoAnne Richards, Baylor College of Medicine (Houston, TX); Mmp9, Dr. Ruth Muschel, University of Pennsylvania (Philadelphia, PA), and Prl4a1, Dr. Mary Lynn Duckworth, University of Manitoba (Winnipeg, Manitboa, Canada). Additional file 1: Supplemental Table S1 includes information on the source of cDNAs and primer sequences used for the generation of cDNAs and for qRT-PCR.
Animals and tissue collection
Holtzman Sprague-Dawley rats were obtained from Harlan Laboratories (Indianapolis, IN). Animals were housed in an environmentally controlled facility with lights on from 0600-2000 h and were allowed free access to food and water. Timed pregnancies were generated by cohabitation of female and male animals. The presence of a copulatory plug or sperm in the vaginal smear was designated d0.5 of pregnancy. Rat placental tissues were collected on gestation d11.5 and d18.5. At d11.5 of gestation, the placenta contains a mixture of proliferating and differentiating trophoblast cells, while at gestation d18.5, the placenta is fully mature and comprised of differentiated trophoblast cells. D11.5 tissue samples contained all trophoblast present within the placentation site, whereas d18.5 tissue samples were restricted to the junctional zone. Placentation site dissections were performed as previously described . Tissues for histological analysis were frozen in dry-ice cooled heptane and stored at -80°C. Tissue samples for RNA extraction were frozen in liquid nitrogen and stored at -80°C. The University of Kansas Animal Care and Use Committee approved protocols for the care and use of animals.
Maintenance of Rcho-1 trophoblast stem cells
Rcho-1 trophoblast stem cells were maintained at subconfluent conditions in Stem Medium [RPMI-1640 culture medium (Cellgro, Herndon, VA) supplemented with 20% fetal bovine serum (FBS; Atlanta Biologicals, Norcross, GA) 50 μM 2-mercaptoethanol, 1 mM sodium pyruvate (Cellgro), 100 μM penicillin, and 100 U/ml streptomycin (Cellgro)] as previously reported [13, 15]. Differentiation was induced by growing cells to near confluence in FBS-supplemented culture medium and then replacing the medium with Differentiation Medium [NCTC-135 medium (Sigma-Aldrich) supplemented with 1% horse serum (HS; Atlanta Biologicals), 50 μM 2-mercaptoethanol, 1 mM sodium pyruvate, 10 mM HEPES, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (Fisher, Pittsburgh, PA), 38 mM sodium bicarbonate (Fisher), 100 μM penicillin and 100 U/ml streptomycin (Cellgro)]. High cell density and the absence of sufficient growth stimulatory factors (removal of FBS) facilitate trophoblast giant cell formation [12, 13]. Trypsin (0.25%)-ethylenediamine tetraacetic acid (EDTA, 0.1% in Hank's Balanced Salt Solution, Cellgro) was used to passage the cells. Cells in the stem cell condition were grown in Stem Medium and collected 24 h after subculture to restrict the accumulation of spontaneously differentiating cells. Cells in the differentiation condition were grown for eight days in Differentiation Medium prior to harvesting unless otherwise noted. RNA samples were extracted using TRIzol (Invitrogen) according to the manufacturer's instructions.
Inhibition of PI3K
LY294002 (Calbiochem, La Jolla, CA) was used to inhibit PI3K . For chronic treatment experiments, Rcho-1 trophoblast stem cells were grown to near confluence and then shifted to Differentiation Medium containing vehicle (0.1% final concentration of dimethyl sulfoxide, DMSO) or Differentiation Medium supplemented with LY294002 (10 μM). This LY294002 treatment regimen was based on our earlier report, which effectively disrupts PI3K signaling in Rcho-1 trophoblast cells . Cells were harvested after eight days of treatment. For acute inhibition of PI3K, cells were cultured for 6-12 days in Differentiation Medium and then shifted to Differentiation Medium containing vehicle (0.1% DMSO) or LY294002 (10 μM) for 48 h. Culture medium was replaced daily.
Affymetrix 230 2.0 DNA microarray chips (Affymetrix, Santa Clara, CA) were probed with cDNAs generated from Rcho-1 trophoblast cells grown under stem or differentiation conditions with chronic exposure to LY294002 or vehicle. Each treatment group was repeated in triplicate. RNA samples were hybridized to the Affymetrix 230 2.0 DNA microarray chip using the GeneChip® Hybridization Oven 640 (Affymetrix). Washing and staining of hybridized chips were conducted using the GeneChip® Fluidics Station 450 (Affymetrix). Chips were scanned using the Affymetrix GeneChip® Scanner 3000 (Affymetrix) with autoloader by the KUMC Biotechnology Support Facility. Hybridization signals were normalized with internal controls using the Mas5 algorithm in Expression Console (Affymetrix) and fold change computed. Significant differences were determined by paired two-tailed Student t-tests. Microarray data was processed for functional analysis using Ingenuity Pathway Analysis (Redwood City, CA). Expression of genes in Rcho-1 trophoblast stem cells and mouse trophoblast stem cells was compared using the "Compare Lists of Genes" program (http://elegans.uky.edu/MA/progs/Compare.html; Dr. James Lund, University of Kentucky, personal communication). Only genes annotated identically by Affymterix in both rat and mouse chips were included. Mouse trophoblast stem cell array data were downloaded from the Gene Expression Omnibus (GEO) database http://www.ncbi.nlm.nih.gov/geo/. TS 3.5 d0 (GSM325436) was compared to TS 3.5 d6 (GSM325442) . Probe sets included in the analysis were restricted to those changing at least 1.5 fold between group comparisons with signal strengths of ≥ 800 for the maximal value.
Northern blotting analysis was performed as previously described . Total RNA (20 μg) was separated in 1% formaldehyde-agarose gels and transferred to nitrocellulose membranes (Schleicher & Schuell Bioscience, Keene, NH). cDNA inserts were obtained by enzymatic digestion and labeled with [32P] (NEN Life Science Products, Boston, MA) using Prime-it II random primer labeling kits (Stratagene, La Jolla, CA). See Additional file 1: Supplemental Table S1 for information on cDNAs. Probes were incubated with the blots at 42°C overnight and washed with 2XSSPE/0.1XSDS at 42°C twice for 25 min and 1XSSPE/0.1XSDS at 50°C for 35 min. Blots were then exposed to x-ray film at -80°C. Glyceraldehyde-3-phosphate dehydrogenase (Gapdh) was used to assess RNA integrity and as a loading control.
cDNAs were reverse transcribed (RT) from RNA using reagents from Promega (Madison, WI) according to the manufacturer's instructions. SYBR GREEN PCR Master Mix (Applied Biosystems, Foster City, CA) was used in the PCR reaction. Reactions were run using a 7500 Real-Time PCR System (Applied Biosystems). Conditions included an initial holding stage (50°C for 2 min and 95°C for 10 min) and 40 cycles (95°C for 15 s and 60°C for 1 min) followed by a dissociation stage (95°C for 15 s, 60°C for 1 min, and then 95°C for 15 s). Primers are listed in Additional file 1: Supplemental Table S1. Expression of 18 S ribosomal RNA was used as an internal control. At least four replicates were run for each condition. Samples were normalized to the control sample for each gene. Statistical comparisons of two means were evaluated with Student's t-test.
In situ hybridization
mRNAs were localized in placental tissues using nonradioactive in situ hybridization as previously described [3, 19]. Ten μm cryosections were prepared and stored at -80°C until used. Plasmids containing cDNAs were used as templates to synthesize sense and antisense digoxigenin-labeled riboprobes according to the manufacturer's instructions (Roche Molecular Biochemicals, Indianapolis, IN). Information on the cDNAs for probe generation is presented in Additional file 1: Supplemental Table S1. Tissue sections were air dried and fixed in ice cold 4% paraformaldehyde in PBS. Prehybridization, hybridization, and detection of alkaline phosphatase-conjugated anti-digoxigenin were performed as previously reported [3, 19]. Images were captured using a Leica MZFLIII stereomicroscope equipped with a Leica CCD camera (Leica Microsystems GmbH, Welzlar, Germany).
Rcho-1 trophoblast stem cells were cultured on chamber slides under stem, differentiation, or differentiation conditions with chronic exposure to LY294002. Cells were fixed in ice-cold 4% paraformaldehyde. Actin filaments were visualized using rhodamine-conjugated phalloidin (Molecular Probes, Eugene, OR). Nuclei were stained with 4,6'-diamidino-2-phenylindole (DAPI, Molecular Probes). Bright field and fluorescence images were captured using either Leica MZFLIII stereomicroscope or DMI 4000 microscopes equipped with CCD cameras (Leica).
Analysis of DNA content
DNA content was estimated by flow cytometry . Cells were trypsinized and fixed in 70% ethanol and then stained with propidium iodine and analyzed using a BDLSRIII flow cytometer (BD Biosciences, San Jose, CA).
Steroid hormone measurements
Steroid radioimmunoassays (RIAs) were performed as previously reported . Androstenedione and progesterone concentrations were measured in Rcho-1 trophoblast cell conditioned medium with 125I-labelled RIA kits (Diagnostic Products, Los Angeles, CA) and normalized to cellular DNA content. DNA samples were obtained by lysis of cells with digestion buffer containing proteinase K. Samples were then incubated at 37°C overnight and diluted 10X with water. DNA content was then measured with the PicoGreen® dsDNA Quantitation Kit (Molecular Probes) according to the manufacturer's instructions. Statistical comparisons of two means were evaluated with Student's t-test.
Identification of genes associated with trophoblast differentiation
Trophoblast stem-associated genes
Approximately half of the genes differentially expressed between the stem cell- and differentiated cell-states were specific to the stem cell state, termed 'trophoblast stem cell-associated' genes. Additional file 2: Supplemental Table S2 shows an abbreviated list of 'trophoblast stem cell-associated' genes. Genes listed in this table are those with arbitrary expression signal strengths ≥ 800 in the stem cell condition and displaying a significantly higher level of expression in the stem cell state versus the differentiated state (≥ 1.5 fold; P ≤ 0.05). We used Ingenuity Pathway Analysis software to investigate 'trophoblast stem cell-associated' genes. Of the 1720 probe sets listed in Additional file 2: Supplemental Table S2, 584 genes were annotated by Ingenuity Pathway Analysis software. Functions associated with the annotated 'trophoblast stem cell-associated' genes included cellular growth and proliferation (35%), cell cycle (32%), and cellular assembly and organization (15%), (Fig. 1B; Additional file 3: Supplemental Table S3). Not surprisingly, the analysis indicates that a large percentage of 'trophoblast stem cell-associated' genes have functions that correlate with the proliferative phenotype of these cells.
Trophoblast stem cell associated genes
GenBank Accession No.
Fold Change S/D
Fold Change D/D+LY
Fatty acid binding protein 3
Fatty acid binding
Pleckstrin homology-like domain, family A, member 2
Inhibitor of DNA binding 2
Sphingosine-1-phosphate receptor 1
Cell cycle regulator
Protection from oxidative stress
Aurora kinase B
Kruppel-like factor 5
Inhibitor of DNA binding 1
Solute carrier family 16 (monocarboxylic acid transporters), member 3
Special AT-rich sequence binding protein 1
Cell cycle regulator
Macrophage migration inhibitory factor
Ccn1, Ccna, Cyca
Cell cycle regulator
ATPase, Na+/K+ transporting, alpha 1 polypeptide
Phosphoglycerate mutase 1
Fatty acid binding protein 5, epidermal
Fatty acid binding
Trophoblast differentiation-associated genes
The second collection of genes exhibiting changes in mRNA expression is upregulated in association with differentiation and referred to as 'differentiation-associated' genes (Additional file 4: Supplemental Table S4). Genes listed in this table are those with arbitrary expression signal strengths ≥ 800 in the differentiated cell condition and displaying a significantly higher level of expression in the differentiated cell state versus the stem cell state (≥ 1.5 fold; P ≤ 0.05). Of the 1585 probe sets listed in Additional file 4: Supplemental Table S4, 537 genes were annotated by Ingenuity Pathway Analysis software. Functions associated with the annotated 'differentiation-associated' genes included cellular growth and proliferation (45%), cell survival (43%), gene expression (32%), cellular movement (27%), and lipid metabolism (6%) (Fig. 1B; Additional file 3: Supplemental Table S3). Many of the genes associated with the cellular growth and proliferation classification encode growth factors, cytokines, and peptide hormones (e.g. Igf2, Grn, members of the prolactin, PRL, family, etc); and represent features of the endocrine phenotype of trophoblast giant cells. Genes linked to cell movement and lipid metabolism, include those encoding proteins contributing to the invasive and steroid hormone producing phenotypes of trophoblast giant cells.
Trophoblast differentiation associated genes
GenBank Accession No.
Fold Change D/S
Fold Change D/D+LY
Keratin complex 1, acidic, gene 19
Carcinoembryonic antigen gene family 4
Secretory protein, unknown function
Carcinoembryonic antigen-related cell adhesion molecule 3
Cell adhesion molecule
Cytochrome P450, family 11, subfamily a, polypeptide 1
Prolactin family 4, subfamily a, member 1
Spleen protein 1 precursor
Solute carrier family 28 (sodium-coupled nucleoside transporter), member 2
Extracellular matrix protein
H19 fetal liver mRNA
Cytochrome P450, family 17, subfamily a, polypeptide 1
Hydroxysteroid (17-beta) dehydrogenase 2
CEA-related cell adhesion molecule 10
Cell adhesion molecule
Differentaly expressed X chromosome EST 1
Dif EST 1
Prolactin family 3, subfamily b, member 1
CD47 antigen (Rh-related antigen, integrin-associated signal transducer)
Sema domain, transmembrane domain (TM), and cytoplasmic domain, (semaphorin) 6D
Differentaly expressed X chromosom EST 2
Dif EST 2
Serine (or cysteine) peptidase inhibitor, clade E, member 1
blood coagulation, angiogenesis
Extracellular matrix protein 1
DNA-damage inducible transcript 3
Melanoma antigen, family D, 1
Apoptosis, cell cycle, transcription
Cbp/p300-interacting transactivator, with Glu/Asp-rich carboxy-terminal domain, 2
Mrg1, Msg2, p35srj
Hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1
Fos-like antigen 1
Putative cysteine protease
Insulin-like growth factor 2
Ligand, growth factor
Tribbles homolog 3 (Drosophila)
Trb3, Ifld2, Nipk
High mobility group box transcription factor 1
Lysosomal aspartic endopeptidase
Matrix metallopeptidase 9
Extracellular matrix remodeling
Fas ligand (TNF superfamily, member 6)
Reproductive homeobox on X chromosome, 9
Gep, Pcdgf, Pgrn
Ligand, growth factor
Cell surface glycoprotein
Phosphatidylinositol 3-kinase, catalytic, beta polypeptide
Inositol lipid kinase
Kruppel-like factor 2 (lung)
Tissue factor pathway inhibitor
Kunitz family serine protease inhibitor
Nuclear factor, erythroid derived 2, like 2
PI3K signaling and trophoblast differentiation
PI3K signaling: negatively regulated genes
The 'negatively regulated' PI3K dependent genes are diverse in their expression patterns (Additional file 5: Supplemental Table S5). Some are 'trophoblast stem cell-associated' genes, others are 'differentiation-associated' genes, while still others were not affected by differentiation state. Genes listed in Additional file 5: Supplemental Table S5 are those with arbitrary expression signal strengths ≥ 800 in the differentiated cell condition and displaying a significantly lower level of expression in the differentiated cell state versus the differentiated cell state treated with the PI3K inhibitor (≥ 1.5 fold; P ≤ 0.05). Of the 257 probe sets listed in Additional file 5: Supplemental Table S5, 99 genes were annotated by Ingenuity Pathway Analysis software. Functions associated with the annotated 'negatively regulated' genes included cell survival (45%), cellular assembly and organization (35%), cellular growth and proliferation (35%), cellular movement (31%), and lipid metabolism (16%) (Fig. 6B; Additional file 3: Supplemental Table S3). These functions overlap with those observed for both the 'trophoblast stem cell associated' and 'differentiation-associated' gene profiles (Fig. 1). Of the sixteen validated 'trophoblast stem cell-associated' genes only Id2 was regulated by PI3K signaling (Fig 6D). Klf2 and Rhob expression was not affected by differentiation state but was negatively regulated by PI3K (Fig. 6D).
PI3K signaling: positively regulated genes
PI3K regulation of trophoblast steroidogenesis
Organization of the hemochorial placenta is the result of signaling pathways directing the expansion and differentiation of trophoblast stem cell and progenitor cell populations. This decision-making culminates in the systematic activation and inactivation of gene networks within trophoblast cell populations and elaboration of specific functions that facilitate redirection of resources from the mother to the fetus. In this report, we utilized the Rcho-1 trophoblast stem cell model and induced differentiation through increased cell density and removal of growth stimuli. The growth factor deprivation may also lead to activation of stress pathways, which have been shown to influence trophoblast differentiation . Using this strategy, we have identified genes associated with trophoblast stem cell expansion, differentiation, and those impacted by the PI3K signaling pathway.
Trophoblast stem cell-associated genes
Stem cells possess the potential to proliferate and to differentiate. Several genes implicated in maintenance of the trophoblast stem cell state were identified in Rcho-1 trophoblast stem cells and are similarly present in mouse trophoblast stem cells. These include an assortment of genes implicated as cell cycle regulators in numerous cell types and also genes that have been more specifically shown to have a role in the specification and maintenance of trophoblast stem cells (e.g. Cdx2, Eomes, Id1, Id2) [23–25].
Phlda2 displayed one of the most striking differences in its expression profile in stem versus differentiated cells. It was high in stem cells and virtually undetectable following differentiation, which is also found in mouse trophoblast stem cells. Phlda2 is intriguing for a number of reasons. Phlda2 is an imprinted gene exhibiting maternal allele-specific expression in extraembryonic and embryonic structures and in postnatal tissues, including the kidney [26, 27]. In the mouse, disruption of the Phlda2 gene leads to placental overgrowth, while overexpression of Phlda2 results in placental growth restriction [28–30]. Given that PHLDA2 restrains placental growth it seems counter-intuitive that it would be abundantly expressed in stem cell populations. Insights will likely be forthcoming when more is learned about the cellular actions of PHLDA2. The activities of PHLDA2 may be linked to its pleckstrin homology domain and ability to bind phosphoinositides and could include an intracellular signal transduction function .
Some differences in the behavior of mouse trophoblast stem cells and Rcho-1 trophoblast stem cells are noteworthy. Elf5, a member of the ETS transcription factor family and a player in the derivation and maintenance of mouse trophoblast stem cells [32–34] is not among the 'trophoblast stem cell-associated' genes of the Rcho-1 trophoblast stem cell model. This may relate to differences in the requirements for exogenous factors to maintain trophoblast stem cell populations. Mouse trophoblast stem cells are dependent upon fibroblast growth factor-4 (FGF4)/FGF receptor 2 signaling , whereas maintenance of Rcho-1 trophoblast stem cells does not require FGF4 . Evidence indicates that ELF5 may be a downstream effector of FGF4 signaling needed to sustain activation of Cdx2 and Eomes genes and the trophoblast stem cell state . The requirement for Elf5 must in some way be circumvented in Rcho-1 trophoblast stem cell maintenance. In addition to Rcho-1 trophoblast stem cells other recently derived trophoblast cell lines from the rat and common vole also grow in the absence of exogenous FGF4 [36, 37]. These observations do not reflect a fundamental species difference in the regulation of trophoblast stem cells. FGF4-dependent trophoblast stem cell lines can be established from the rat blastocyst (K. Asanoma and M.J. Soares, unpublished data). Instead, the FGF4 independence of the trophoblast stem cell populations is probably the consequence of genetic and/or epigenetic modifications and in vitro selection.
Several 'trophoblast stem cell-associated genes' were not shared with mouse trophoblast stem cells. Among these genes were Mif and S1pr1. Mif encodes a pro-inflammatory cytokine implicated in the regulation of angiogenesis , the migration and adhesion of monocytes , and modulation of uterine natural killer cell cytolytic activity . S1pr1 encodes a Gi protein-coupled receptor for sphingosine 1-phosphate (S1P). S1P has been implicated in a range of functions, including controlling cell proliferation and differentiation . In human trophoblast, S1P inhibits differentiation . Activation of some of the 'trophoblast stem cell-associated' genes may represent a developmental progression beyond the trophoblast stem cell state exhibited by mouse trophoblast stem cells or alternatively may provide Rcho-1 cells with their tumorigenic features [18, 43].
Trophoblast differentiation-associated genes
'Differentiation-associated' genes possess a broader range of functions than noted for the 'trophoblast stem cell-associated' gene cluster. Many of these genes are characteristic of the trophoblast giant cell phenotype. The trophoblast giant cell is conspicuous in its location at the maternal-fetal interface and its functions are in large part directed toward uterine structures and in facilitating maternal adaptations to pregnancy. These functions include endocrine activities (PRL family and steroidogenesis) and intrauterine invasion and modulation of the maternal vasculature and immune cells (Il17f, Tfpi, Cgm4, Ecm1, Cd47, Fn, Lgmn, Mmp9, Grn, Igf2).
Among the 'differentiation-associated' genes was a subgroup of genes encoding transcriptional regulators (Hbp1, Ddit3, Rhox9, Nrf2, Fosl1, Junb, Cited2). Mouse mutagenesis experimentation has implicated a few of these genes (Fosl1, Junb, Cited2) as regulators of placental development [44–46]. However, the specific roles of FOSL1, JUNB. CITED2, and the other transcriptional regulators in the regulation of trophoblast differentiation are yet to be determined. Some may participate in the regulation or maintenance of the differentiated trophoblast cell phenotype.
There is a connection between the 'differentiation-associated' genes and the PI3K/AKT signaling pathway. As trophoblast stem cells differentiate, the PI3K/AKT signaling pathway becomes constitutively activated . IGF2 and GRN are candidate autocrine activators of the PI3K/AKT signaling pathway [47, 48]. Trb3 and Msn were also classified as 'differentiation-associated' genes. They encode proteins with potential roles downstream of PI3K/AKT signaling pathway [49, 50].
PI3K signaling-sensitive genes
PI3K regulates the phenotype of differentiating trophoblast cells . Endoreduplication and/or survival of trophoblast giant cells are influenced by PI3K signaling. An active PI3K pathway favors trophoblast giant cells with lower ploidy levels. These cells may be more motile and phenotypically resemble midgestation trophoblast lining uterine spiral arteries . PI3K signaling also possesses dramatic effects on gene expression patterns.
Overall, the functions of the PI3K-sensitive genes are biologically less diverse. Most interestingly, they include genes encoding proteins potentially impacting trophoblast invasion (Mmp9, ; Igf2, [53–55]; Serpine1, [56–58]), directed to the maternal uterine environment influencing immune and vascular cells (Cgm4, Faslg, Prl4a1, Adm, Il17f), and also regulating androgen biosynthesis (Hsd3b1, Cyp17a1).
Cgm4 is one of the most abundant genes expressed by differentiating trophoblast cells. It encodes a member of the expanded pregnancy specific glycoprotein (PSG) family called PSG16. PSGs act on immune cells, potentially through CD9, to influence cytokine production [59–62]; they also target the vasculature and modulate endothelial cell function . The presence of Cd9 in differentiating trophoblast cells implies that PSGs may also possess autocrine/paracrine actions on trophoblast development, which may include regulating the trophoblast invasive phenotype .
FAS ligand (FASLG), PRL-like protein A (PLP-A; Prl4a1), adrenomedullin (ADM), and interleukin 17f (IL17F) are cytokines produced by differentiating trophoblast that are exquisitely sensitive to PI3K regulation. FASLG binds to the FAS receptor and can initiate cell death. Trophoblast derived FASLG has been implicated as a modulator of intraplacental immune cell trafficking [64, 65] and is hypothesized to be a key participant in uterine spiral arteriole remodeling [66, 67]. PLP-A targets natural killer cells and contributes to placentation site-specific adaptations to physiological stressors [3, 68, 69]. ADM may possess an autocrine role regulating trophoblast invasion  but also probably affects the uterine vasculature by regulating vessel diameter, permeability, and angiogenesis [71–73]. Insights about IL17F and its potential role at the placentation site are limited. IL17F is proinflammatory with prominent effects on immune and vascular cells [74–76]. Whether IL17F contributes to the organization of the hemochorial placentation site remains to be determined.
Key components of the enzymatic machinery required for trophoblast cell androgen biosynthesis are positively regulated by PI3K, including 17α hydroxylase (encoded by Cyp17a1). Trophoblast giant cells are sites of androstenedione biosynthesis [77, 78]. Androstenedione can serve as a prohormone for the biosynthesis of estrogens and more potent androgens, such as testosterone. Estrogens possess a vital luteotropic role essential for the maintenance of pregnancy . Differentiating rodent trophoblast cells also express 17β hydroxysteroid dehydrogenase type 2 (encoded by Hsd17b2), which is responsible for converting testosterone to less biologically potent androgens, thereby protecting the fetus from excessive androgen exposure [79, 80]. Thus, PI3K signaling has a vital role in determining the steroid hormone milieu at the maternal-fetal interface.
In summary, the PI3K signaling pathway regulates the differentiated trophoblast cell phenotype. Under the direction of the PI3K signaling pathway, trophoblast cells produce a battery of cytokines and hormones. These extracellular signals modulate intrauterine immune and inflammatory cells, regulate vascular remodeling, and collectively ensure a successful pregnancy.
Gene expression array data sets were generated by the KUMC-Microarray Facility, which is supported by the Kansas Intellectual and Developmental Disabilities Research Center (HD02528) and the Kansas IDeA Network of Biomedical Research Excellence (RR016475). We would also like to acknowledge Dr. Namita Sahgal for her contribution to preliminary studies relevant to this work and input during the early planning stages of this work.
This work was supported by grants from the National Institutes of Health (HD20676, HD39878, HD48861, HD49503) and the Hall Family Foundation.
- Soares MJ, Chapman BM, Rasmussen CA, Dai G, Kamei T, Orwig KE: Differentiation of trophoblast endocrine cells. Placenta. 1996, 17: 277-289. 10.1016/S0143-4004(96)90051-X.View ArticlePubMedGoogle Scholar
- Rossant J, Cross JC: Placental development: lessons from mouse mutants. Nat Rev Genet. 2001, 2: 538-548. 10.1038/35080570.View ArticlePubMedGoogle Scholar
- Ain R, Canham LN, Soares MJ: Gestation stage-dependent intrauterine trophoblast cell invasion in the rat and mouse: novel endocrine phenotype and regulation. Dev Biol. 2003, 260: 176-190. 10.1016/S0012-1606(03)00210-0.View ArticlePubMedGoogle Scholar
- Riley P, Anson-Cartwright L, Cross JC: The Hand1 bHLH transcription factor is essential for placentation and cardiac morphogenesis. Nat Genet. 1998, 18: 271-275. 10.1038/ng0398-271.View ArticlePubMedGoogle Scholar
- Adamson SL, Lu Y, Whiteley KJ, Holmyard D, Hemberger M, Pfarrer C, Cross JC: Interactions between trophoblast cells and the maternal and fetal circulation in the mouse placenta. Dev Biol. 2002, 250: 358-373.View ArticlePubMedGoogle Scholar
- Hemberger M, Nozaki T, Masutani M, Cross JC: Differential expression of angiogenic and vasodilatory factors by invasive trophoblast giant cells depending on depth of invasion. Dev Dyn. 2003, 227: 185-191. 10.1002/dvdy.10291.View ArticlePubMedGoogle Scholar
- Kamei T, Jones SR, Chapman BM, MCGonigle KL, Dai G, Soares MJ: The phosphatidylinositol 3-kinase/Akt signaling pathway modulates the endocrine differentiation of trophoblast cells. Mol Endocrinol. 2002, 16: 1469-1481. 10.1210/me.16.7.1469.View ArticlePubMedGoogle Scholar
- Nadra K, Anghel SI, Joye E, Tan NS, Basu-Modak S, Trono D, Wahli W, Desvergne B: Differentiation of trophoblast giant cells and their metabolic functions are dependent on peroxisome proliferator-activated receptorβ/δ. Mol Cell Biol. 2006, 26: 3266-3281. 10.1128/MCB.26.8.3266-3281.2006.PubMed CentralView ArticlePubMedGoogle Scholar
- Yang ZZ, Tschopp O, Hemmings-Mieszczak M, Feng J, Brodbeck D, Perentes E, Hemmings BA: Protein kinase B alpha/Akt1 regulates placental development and fetal growth. J Biol Chem. 2003, 278: 32124-32131. 10.1074/jbc.M302847200.View ArticlePubMedGoogle Scholar
- Faria TN, Soares MJ: Trophoblast cell differentiation: establishment, characterization, and modulation of a rat trophoblast cell line expressing members of the placental prolactin family. Endocrinology. 1991, 129: 2895-2906. 10.1210/endo-129-6-2895.View ArticlePubMedGoogle Scholar
- Hamlin GP, Lu XJ, Roby KF, Soares MJ: Recapitulation of the pathway for trophoblast giant cell differentiation in vitro: stage-specific expression of members of the prolactin gene family. Endocrinology. 1994, 134: 2390-2396. 10.1210/en.134.6.2390.PubMedGoogle Scholar
- Yamamoto T, Roby KF, Kwok SC, Soares MJ: Transcriptional activation of cytochrome P450 side chain cleavage enzyme expression during trophoblast cell differentiation. J Biol Chem. 1994, 269: 6517-6523.PubMedGoogle Scholar
- Sahgal N, Canham LN, Soares MJ: Rcho-1 trophoblast cells: a model for studying trophoblast differentiation. Methods Mol Med. 2006, 121: 159-178.PubMedGoogle Scholar
- Ain R, Konno T, Canham LN, Soares MJ: Phenotypic analysis of the rat placenta. Methods Mol Med. 2006, 121: 295-313.PubMedGoogle Scholar
- Peters TJ, Chapman BM, Soares MJ: Trophoblast differentiation. An in vitro model for trophoblast giant cell development. Methods Mol Biol. 2000, 137: 301-311.PubMedGoogle Scholar
- Vlahos CJ, Matter WF, Hui KY, Brown RF: A specific inhibitor of phosphatidylinositol 3-kinase, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). J Biol Chem. 1994, 269: 5241-5248.PubMedGoogle Scholar
- Ralston A, Cox BJ, Nishioka N, Sasaki H, Chea E, Rugg-Gunn P, Guo G, Robson P, Draper JS, Rossant J: Gata3 regulates trophoblast development downstream of Tead4 and in parallel to Cdx2. Development. 2010, 137: 395-403. 10.1242/dev.038828.View ArticlePubMedGoogle Scholar
- Faria TN, Deb S, Kwok SC, Talamantes F, Soares MJ: Ontogeny of placental lactogen-I and placental lactogen-II expression in the developing rat placenta. Dev Biol. 1990, 141: 279-291. 10.1016/0012-1606(90)90384-U.View ArticlePubMedGoogle Scholar
- Wiemers DO, Ain R, Ohboshi S, Soares MJ: Migratory trophoblast cells express a newly identified member of the prolactin gene family. J Endocrinol. 2003, 179: 335-346. 10.1677/joe.0.1790335.View ArticlePubMedGoogle Scholar
- Quinn J, Kunath T, Rossant J: Mouse trophoblast stem cells. Methods Mol Med. 2006, 121: 125-148.PubMedGoogle Scholar
- Yamamoto T, Chapman BM, Johnson DC, Givens CR, Mellon SH, Soares MJ: Cytochrome P450 17 alpha-hydroxylase gene expression in differentiating rat trophoblast cells. J Endocrinol. 1996, 150: 161-168. 10.1677/joe.0.1500161.View ArticlePubMedGoogle Scholar
- Rappolee DA: Impact of transient stress and stress enzymes on development. Dev Biol. 2007, 304: 1-8. 10.1016/j.ydbio.2006.12.032.View ArticlePubMedGoogle Scholar
- Ralston A, Rossant J: Genetic regulation of stem cell origins in the mouse embryo. Clin Genet. 2005, 68: 106-112. 10.1111/j.1399-0004.2005.00478.x.View ArticlePubMedGoogle Scholar
- Simmons DG, Cross JC: Determinants of trophoblast lineage and cell subtype specification in the mouse placenta. Dev Biol. 2005, 284: 12-24. 10.1016/j.ydbio.2005.05.010.View ArticlePubMedGoogle Scholar
- Sasaki H: Mechanisms of trophectoderm fate specification in preimplantation mouse development. Dev Growth Differ. 2010, 52: 263-273. 10.1111/j.1440-169X.2009.01158.x.View ArticlePubMedGoogle Scholar
- Qian N, Frank D, O'Keefe D, Dao D, Zhao L, Yuan L, Wang Q, Keating M, Walsh C, Tycko B: The IPL gene on chromosome 11p15.5 is imprinted in humans and mice and is similar to TDAG51, implicated in Fas expression and apoptosis. Hum Mol Genet. 1997, 6: 2021-2029. 10.1093/hmg/6.12.2021.View ArticlePubMedGoogle Scholar
- Frank D, Mendelsohn CL, Ciccone E, Svensson K, Ohlsson R, Tycko B: A novel pleckstrin homology-related gene family defined by Ipl/Tssc3, TDAG51, and Tih1: tissue-specific expression, chromosomal location, and parental imprinting. Mamm Genome. 1999, 10: 1150-1159. 10.1007/s003359901182.View ArticlePubMedGoogle Scholar
- Frank D, Fortino W, Clark L, Musalo R, Wang W, Saxena A, Li CM, Reik W, Ludwig T, Tycko B: Placental overgrowth in mice lacking the imprinted gene Ipl. Proc Natl Acad Sci USA. 2002, 99: 7490-7495. 10.1073/pnas.122039999.PubMed CentralView ArticlePubMedGoogle Scholar
- Salas M, John R, Saxena A, Barton S, Frank D, Fitzpatrick G, Higgins MJ, Tycko B: Placental growth retardation due to loss of imprinting of Phlda2. Mech Dev. 2004, 121: 1199-1210. 10.1016/j.mod.2004.05.017.View ArticlePubMedGoogle Scholar
- Tunster SJ, Tycko B, John RM: The imprinted Phlda2 gene regulates extraembryonic energy stores. Mol Cell Biol. 2010, 30: 295-306. 10.1128/MCB.00662-09.PubMed CentralView ArticlePubMedGoogle Scholar
- Saxena A, Morozov P, Frank D, Musalo R, Lemmon MA, Skolnik EY, Tycko B: Phosphoinositide binding by the pleckstrin homology domains of Ipl and Tih1. J Biol Chem. 2002, 277: 49935-49944. 10.1074/jbc.M206497200.View ArticlePubMedGoogle Scholar
- Donnison M, Beaton A, Davey HW, Broadhurst R, L'Huillier P, Pfeffer PL: Loss of the extraembryonic ectoderm in Elf5 mutants leads to defects in embryonic patterning. Development. 2005, 132: 2299-2308. 10.1242/dev.01819.View ArticlePubMedGoogle Scholar
- Ng RK, Dean W, Dawson C, Lucifero D, Madeja Z, Reik W, Hemberger M: Epigenetic restriction of embryonic cell lineage fate by methylation of Elf5. Nat Cell Biol. 2008, 10: 1280-1290. 10.1038/ncb1786.PubMed CentralView ArticlePubMedGoogle Scholar
- Kuckenberg P, Buhl S, Woynecki T, van Fürden B, Tolkunova E, Seiffe F, Moser M, Tomilin A, Winterhager E, Schorle H: The transcription factor TCFAP2C/AP-2gamma cooperates with CDX2 to maintain trophectoderm formation. Mol Cell Biol. 2010, 30: 3310-3320. 10.1128/MCB.01215-09.PubMed CentralView ArticlePubMedGoogle Scholar
- Tanaka S, Kunath T, Hadjantonakis AK, Nagy A, Rossant J: Promotion of trophoblast stem cell proliferation by FGF4. Science. 1998, 282: 2072-2075. 10.1126/science.282.5396.2072.View ArticlePubMedGoogle Scholar
- Grigor'eva EV, Shevchenko AI, Mazurok NA, Elisaphenko EA, Zhelezova AI, Shilov AG, Dyban PA, Dyban AP, Noniashvili EM, Slobodyanyuk SY, Nesterova TB, Brockdorff N, Zakian SM: FGF4 independent derivation of trophoblast stem cells from the common vole. PLoS ONE. 2009, 4: e7161-10.1371/journal.pone.0007161.PubMed CentralView ArticlePubMedGoogle Scholar
- Chuykin I, Lapidus I, Popova E, Vilianovich L, Mosienko V, Alenina N, Binas B, Chai G, Bader M, Krivokharchenko A: Characterization of trophoblast and extraembryonic endoderm cell lineages derived from rat preimplantation embryos. PLoS ONE. 2010, 5: e9794-10.1371/journal.pone.0009794.PubMed CentralView ArticlePubMedGoogle Scholar
- Amin MA, Volpert OV, Woods JM, Kumar P, Harlow LA, Koch AE: Migration inhibitory factor mediates angiogenesis via mitogen-activated protein kinase and phosphatidylinositol kinase. Circ Res. 2003, 93: 321-329. 10.1161/01.RES.0000087641.56024.DA.View ArticlePubMedGoogle Scholar
- Amin MA, Haas CS, Zhu K, Mansfield PJ, Kim MJ, Lackowski NP, Koch AE: Migration inhibitory factor up-regulates vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 via Src, PI3 kinase, and NFkappaB. Blood. 2006, 107: 2252-2261. 10.1182/blood-2005-05-2011.PubMed CentralView ArticlePubMedGoogle Scholar
- Arcuri F, Cintorino M, Carducci A, Papa S, Riparbelli MG, Mangioni S, Di Blasio AM, Tosi P, Viganò P: Human decidual natural killer cells as a source and target of macrophage migration inhibitory factor. Reproduction. 2006, 131: 175-182. 10.1530/rep.1.00857.View ArticlePubMedGoogle Scholar
- Skoura A, Hla T: Regulation of vascular physiology and pathology by the S1P2 receptor subtype. Cardiovasc Res. 2009, 82: 221-228. 10.1093/cvr/cvp088.PubMed CentralView ArticlePubMedGoogle Scholar
- Johnstone ED, Chan G, Sibley CP, Davidge ST, Lowen B, Guilbert LJ: Sphingosine-1-phosphate inhibition of placental trophoblast differentiation through a G(i)-coupled receptor response. J Lipid Res. 2005, 46: 1833-1839. 10.1194/jlr.M500095-JLR200.View ArticlePubMedGoogle Scholar
- Teshima A, Shimosato Y, Koide T, Kuroki M, Kikuchi Y, Aizawa M: Transplantable choriocarcinoma of rats induced by fetectomy and its biological activities. Gann. 1983, 74: 205-212.PubMedGoogle Scholar
- Schreiber M, Wang ZQ, Jochum W, Fetka I, Elliott C, Wagner EF: Placental vascularisation requires the AP-1 component fra1. Development. 2000, 127: 4937-4948.PubMedGoogle Scholar
- Schorpp-Kistner M, Wang ZQ, Angel P, Wagner EF: JunB is essential for mammalian placentation. EMBO J. 1999, 18: 934-48. 10.1093/emboj/18.4.934.PubMed CentralView ArticlePubMedGoogle Scholar
- Withington SL, Scott AN, Saunders DN, Lopes Floro K, Preis JI, Michalicek J, Maclean K, Sparrow DB, Barbera JP, Dunwoodie SL: Loss of Cited2 affects trophoblast formation and vascularization of the mouse placenta. Dev Biol. 2006, 294: 67-82. 10.1016/j.ydbio.2006.02.025.View ArticlePubMedGoogle Scholar
- Vincent AM, Feldman EL: Control of cell survival by IGF signaling pathways. Growth Horm IGF Res. 2002, 12: 193-197. 10.1016/S1096-6374(02)00017-5.View ArticlePubMedGoogle Scholar
- Ong CH, Bateman A: Progranulin (granulin-epithelin precursor, PC-cell derived growth factor, acrogranin) in proliferation and tumorigenesis. Histol Histopathol. 2003, 18: 1275-1288.PubMedGoogle Scholar
- Qi L, Heredia JE, Altarejos JY, Screaton R, Goebel N, Niessen S, Macleod IX, Liew CW, Kulkarni RN, Bain J, Newgard C, Nelson M, Evans RM, Yates J, Montminy M: TRB3 links the E3 ubiquitin ligase COP1 to lipid metabolism. Science. 2006, 312: 1763-1766. 10.1126/science.1123374.View ArticlePubMedGoogle Scholar
- Wu KL, Khan S, Lakhe-Reddy S, Jarad G, Mukherjee A, Obejero-Paz CA, Konieczkowski M, Sedor JR, Schelling JR: The NHE1 Na+/H+ exchanger recruits ezrin/radixin/moesin proteins to regulate Akt-dependent cell survival. J Biol Chem. 2004, 279: 26280-26286. 10.1074/jbc.M400814200.View ArticlePubMedGoogle Scholar
- Librach CL, Werb Z, Fitzgerald ML, Chiu K, Corwin NM, Esteves RA, Grobelny D, Galardy R, Damsky CH, Fisher SJ: 92-kD type IV collagenase mediates invasion of human cytotrophoblasts. J Cell Biol. 1991, 113: 437-449. 10.1083/jcb.113.2.437.View ArticlePubMedGoogle Scholar
- Peters TJ, Albieri A, Bevilacqua E, Chapman BM, Crane LH, Hamlin GP, Seiki M, Soares MJ: Differentiation-dependent expression of gelatinase B/matrix metalloproteinase-9 in trophoblast cells. Cell Tissue Res. 1999, 295: 287-296. 10.1007/s004410051235.View ArticlePubMedGoogle Scholar
- Irwin JC, Suen LF, Martina NA, Mark SP, Giudice LC: Role of the IGF system in trophoblast invasion and pre-eclampsia. Hum Reprod. 1999, 14 (Suppl 2): 90-96.View ArticlePubMedGoogle Scholar
- Aplin JD, Lacey H, Haigh T, Jones CJ, Chen CP, Westwood M: Growth factor-extracellular matrix synergy in the control of trophoblast invasion. Biochem Soc Trans. 2000, 28: 199-202.View ArticlePubMedGoogle Scholar
- Hiden U, Glitzner E, Hartmann M, Desoye G: Insulin and the IGF system in the human placenta of normal and diabetic pregnancies. J Anat. 2009, 215: 60-68. 10.1111/j.1469-7580.2008.01035.x.PubMed CentralView ArticlePubMedGoogle Scholar
- Graham CH: Effect of transforming growth factor-beta on the plasminogen activator system in cultured first trimester human cytotrophoblasts. Placenta. 1997, 18: 137-143. 10.1016/S0143-4004(97)90085-0.View ArticlePubMedGoogle Scholar
- Bauer S, Pollheimer J, Hartmann J, Husslein P, Aplin JD, Knöfler M: Tumor necrosis factor-alpha inhibits trophoblast migration through elevation of plasminogen activator inhibitor-1 in first-trimester villous explant cultures. J Clin Endocrinol Metab. 2004, 89: 812-822. 10.1210/jc.2003-031351.View ArticlePubMedGoogle Scholar
- Anteby EY, Greenfield C, Natanson-Yaron S, Goldman-Wohl D, Hamani Y, Khudyak V, Ariel I, Yagel S: Vascular endothelial growth factor, epidermal growth factor and fibroblast growth factor-4 and -10 stimulate trophoblast plasminogen activator system and metalloproteinase-9. Mol Hum Reprod. 2004, 10: 229-235. 10.1093/molehr/gah031.View ArticlePubMedGoogle Scholar
- Wessells J, Wessner D, Parsells R, White K, Finkenzeller D, Zimmermann W, Dveksler G: Pregnancy specific glycoprotein 18 induces IL-10 expression in murine macrophages. Eur J Immunol. 2000, 30: 1830-1840. 10.1002/1521-4141(200007)30:7<1830::AID-IMMU1830>3.0.CO;2-M.View ArticlePubMedGoogle Scholar
- Waterhouse R, Ha C, Dveksler GS: Murine CD9 is the receptor for pregnancy-specific glycoprotein 17. J Exp Med. 2002, 195: 277-282. 10.1084/jem.20011741.PubMed CentralView ArticlePubMedGoogle Scholar
- Ha CT, Waterhouse R, Wessells J, Wu JA, Dveksler GS: Binding of pregnancy-specific glycoprotein 17 to CD9 on macrophages induces secretion of IL-10, IL-6, PGE2, and TGF-beta1. J Leukoc Biol. 2005, 77: 948-957. 10.1189/jlb.0804453.View ArticlePubMedGoogle Scholar
- Wynne F, Ball M, McLellan AS, Dockery P, Zimmermann W, Moore T: Mouse pregnancy-specific glycoproteins: tissue-specific expression and evidence of association with maternal vasculature. Reproduction. 2006, 131: 721-732. 10.1530/rep.1.00869.View ArticlePubMedGoogle Scholar
- Park KR, Inoue T, Ueda M, Hirano T, Higuchi T, Konishi I, Fujiwara H, Fujii S: Anti-CD9 monoclonal antibody-stimulated invasion of endometrial cancer cell lines in vitro: possible inhibitory effect of CD9 in endometrial cancer invasion. Mol Hum Reprod. 2000, 6: 719-725. 10.1093/molehr/6.8.719.View ArticlePubMedGoogle Scholar
- Hunt JS, Vassmer D, Ferguson TA, Miller L: Fas ligand is positioned in mouse uterus and placenta to prevent trafficking of activated leukocytes between the mother and the conceptus. J Immunol. 1997, 158: 4122-4128.PubMedGoogle Scholar
- Abrahams VM, Straszewski-Chavez SL, Guller S, Mor G: First trimester trophoblast cells secrete Fas ligand which induces immune cell apoptosis. Mol Hum Reprod. 2004, 10: 55-63. 10.1093/molehr/gah006.View ArticlePubMedGoogle Scholar
- Ashton SV, Whitley GS, Dash PR, Wareing M, Crocker IP, Baker PN, Cartwright JE: Uterine spiral artery remodeling involves endothelial apoptosis induced by extravillous trophoblasts through Fas/Fasl interactions. Arterioscler Thromb Vasc Biol. 2005, 25: 102-108.PubMed CentralPubMedGoogle Scholar
- Harris LK, Keogh RJ, Wareing M, Baker PN, Cartwright JE, Aplin JD, Whitley GS: Invasive trophoblasts stimulate vascular smooth muscle cell apoptosis by a fas ligand-dependent mechanism. Am J Pathol. 2006, 169: 1863-1874. 10.2353/ajpath.2006.060265.PubMed CentralView ArticlePubMedGoogle Scholar
- Müller H, Liu B, Croy BA, Head JR, Hunt JS, Dai G, Soares MJ: Uterine natural killer cells are targets for a trophoblast cell-specific cytokine, prolactin-like protein A. Endocrinology. 1999, 140: 2711-2720. 10.1210/en.140.6.2711.PubMedGoogle Scholar
- Ain R, Dai G, Dunmore JH, Godwin AR, Soares MJ: A prolactin family paralog regulates reproductive adaptations to a physiological stressor. Proc Natl Acad Sci USA. 2004, 101: 16543-16548. 10.1073/pnas.0406185101.PubMed CentralView ArticlePubMedGoogle Scholar
- Zhang X, Green KE, Yallampalli C, Dong YL: Adrenomedullin Enhances Invasion by Trophoblast Cell Lines. Biol Reprod. 2005, 73: 619-626. 10.1095/biolreprod.105.040436.View ArticlePubMedGoogle Scholar
- Wilson C, Nikitenko LL, Sargent IL, Rees MCP: Adrenomedullin: multiple functions in human pregnancy. Angiogenesis. 2004, 7: 203-212. 10.1007/s10456-004-4183-5.View ArticlePubMedGoogle Scholar
- Kato J, Tsuruda T, Kita T, Kitamura K, Eto T: Adrenomedullin: a protective factor for blood vessels. Arterioscler Thromb Vasc Biol. 2005, 25: 2480-2487. 10.1161/01.ATV.0000184759.91369.f8.View ArticlePubMedGoogle Scholar
- Temmesfeld-Wollbrück B, Hocke AC, Suttorp N, Hippenstiel S: Adrenomedullin and endothelial barrier function. Thromb Haemost. 2007, 98: 944-951.PubMedGoogle Scholar
- Kolls JK, Lindén A: Interleukin-17 family members and inflammation. Immunity. 2004, 21: 467-476. 10.1016/j.immuni.2004.08.018.View ArticlePubMedGoogle Scholar
- Gaffen SL: An overview of IL-17 function and signaling. Cytokine. 2008, 43: 402-407. 10.1016/j.cyto.2008.07.017.PubMed CentralView ArticlePubMedGoogle Scholar
- Spolski R, Leonard WJ: Cytokine mediators of Th17 function. Eur J Immunol. 2009, 39: 658-661. 10.1002/eji.200839066.PubMed CentralView ArticlePubMedGoogle Scholar
- Soares MJ, Talamantes F: Midpregnancy elevation of serum androstenedione levels in the C3H/HeN mouse: placental origin. Endocrinology. 1983, 113: 1408-1412. 10.1210/endo-113-4-1408.View ArticlePubMedGoogle Scholar
- Gibori G, Khan I, Warshaw ML, McLean MP, Puryear TK, Nelson S, Durkee TJ, Azhar S, Steinschneider A, Rao MC: Placental-derived regulators and the complex control of luteal cell function. Recent Prog Horm Res. 1988, 44: 377-429.PubMedGoogle Scholar
- Labrie F, Simard J, Luu-The V, Pelletier G, Belghmi K, Bélanger A: Structure, regulation and role of 3 beta-hydroxysteroid dehydrogenase, 17 beta-hydroxysteroid dehydrogenase and aromatase enzymes in the formation of sex steroids in classical and peripheral intracrine tissues. Baillieres Clin Endocrinol Metab. 1994, 8: 451-474. 10.1016/S0950-351X(05)80261-7.View ArticlePubMedGoogle Scholar
- Labrie F, Luu-The V, Lin SX, Simard J, Labrie C: Role of 17 beta-hydroxysteroid dehydrogenases in sex steroid formation in peripheral intracrine tissues. Trends Endocrinol Metab. 2000, 11: 421-427. 10.1016/S1043-2760(00)00342-8.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.