RXRα and LXR activate two promoters in placenta- and tumor-specific expression of PLAC1

Investigation of Expression Profile of Placenta-specific 1 (PLAC1) in Acute Myeloid and Lymphoid Leukemias

Background

Placenta-specific 1 (PLAC1) is one of the cancer-testis-placenta antigens that has no expression in normal tissue except placenta trophoblast and testicular germ cells, but is overexpressed in a variety of solid tumors. There is a lack of studies on the expression of PLAC1 in leukemia. We investigated expression of PLAC1 in Acute Myeloid Leukemia (AML) and Acute Lymphoblastic Leukemia (ALL).

Methods

In this study, we investigated expression pattern of PLAC1 gene in peripheral blood and bone marrow mononuclear cells of newly-diagnosed patients with AML (n=31) and ALL (n=31) using quantitative real-time PCR. Normal subjects (n=17) were considered as control. The PLAC1 protein expression in the samples were also detected using western blotting.

Results

Our data demonstrated that PLAC1 transcripts had 2.7 and 2.9 fold-change increase in AML and ALL, respectively, compared to normal samples. PLAC1 transcript expression was totally negative in all studied normal subjects. Level of PLAC1 mRNA expression in ALL statistically increased compared to normal samples (p=0.038). However, relative mRNA expression of PLAC1 in AML was not significant in comparison to normal subjects (p=0.848). Furthermore, relative mRNA expression of PLAC1 in AML subtypes was not statistically significant (p=0.756). PLAC1 gene expression showed no difference in demographical clinical and para-clinical parameters. Western blotting confirmed expression of PLAC1 in the ALL and AML samples.

Conclusion

Considering PLAC1 expression profile in acute leukemia, PLAC1 could be a potential marker in leukemia which needs complementary studies in the future.

Placenta-specific protein 1 (PLAC1) expression is significantly down-regulated in preeclampsia via a hypoxia-mediated mechanism

OBJECTIVE

Examine a mechanism of PLAC1 regulation and its potential role in preeclampsia (PE).

MATERIALS AND METHODS

Placental tissue samples and detailed clinical information were obtained through the University of Iowa Maternal Fetal Tissue Bank (IRB# 200910784) from gestational and maternal age-matched control (n = 17) and PE affected pregnancies (n = 12). PLAC1 and PLAC1 promoter-specific expression was measured using quantitative polymerase chain reaction (qPCR) and differences were assessed via the standard ΔΔCt method. In addition, the role of hypoxia in PLAC1 transcription was investigated through the exposure of HTR8/SVneo human trophoblast cells to the hypoxia mimic dimethyloxaloylglycine (DMOG).

RESULTS

PLAC1 expression is seen to be 8.9-fold lower in human placentas affected by preeclampsia in comparison with controls (p < .05). Further, this decrease is paralleled by a significantly lower expression of the P2 or proximal PLAC1 promoter (p < .05). Expression of mediator complex subunit 1 (MED1), a known hypoxia-sensitive transcription coactivator and PLAC1 effector, is significantly correlated with PLAC 1 expression (r2 = 0.607, p < .001). These data suggest that PLAC1 expression is significantly down-regulated in preeclampsia at least in part via a MED1 hypoxia-mediated mechanism.

CONCLUSIONS

We confirm that PLAC1 transcription is suppressed in the placentae of women affected by preeclampsia. We further demonstrate that this suppression is driven through the P2 or proximal PLAC1 promoter. This demonstration led to the identification of the MED1-TRAP cofactor complex as the hypoxia-sensitive driver.

High-density lipoproteins: A promising tool against cancer

High-density lipoproteins (HDL) are well known for their protective role against the development and progression of atherosclerosis. Atheroprotection is mainly due to the key role of HDL within the reverse cholesterol transport, and to their ability to exert a series of antioxidant and anti-inflammatory activities. Through the same mechanisms HDL could also affect cancer cell proliferation and tumor progression. Many types of cancers share common alterations of cellular metabolism, including lipid metabolism. In this context, not only fatty acids but also cholesterol and its metabolites play a key role. HDL were shown to reduce cancer cell content of cholesterol, overall rewiring cholesterol homeostasis. In addition, HDL reduce oxidative stress and the levels of pro-inflammatory molecules in cancer cells and in the tumor microenvironment (TME). Here, HDL can also help in reverting tumor immune escape and in inhibiting angiogenesis. Interestingly, HDL are good candidates for drug delivery, targeting antineoplastic agents to the tumor mass mainly through their binding to the scavenger receptor BI. Since they could affect cancer development and progression per se, HDL-based drug delivery systems may render cancer cells more sensitive to antitumor agents and reduce the development of drug resistance.

The Synthetic Curcumin Analog HO-3867 Rescues Suppression of PLAC1 Expression in Ovarian Cancer Cells

Elevated expression of placenta-specific protein 1 (PLAC1) is associated with the increased proliferation and invasiveness of a variety of human cancers, including ovarian cancer. Recent studies have shown that the tumor suppressor p53 directly suppresses PLAC1 transcription. However, mutations in p53 lead to the loss of PLAC1 transcriptional suppression. Small molecules that structurally convert mutant p53 proteins to wild-type conformations are emerging. Our objective was to determine whether the restoration of the wild-type function of mutated p53 could rescue PLAC1 transcriptional suppression in tumors harboring certain TP53 mutations. Ovarian cancer cells OVCAR3 and ES-2, both harboring TP53 missense mutations, were treated with the p53 reactivator HO-3867. Treatment with HO-3867 successfully rescued PLAC1 transcriptional suppression. In addition, cell proliferation was inhibited and cell death through apoptosis was increased in both cell lines. We conclude that the use of HO-3867 as an adjuvant to conventional therapeutics in ovarian cancers harboring TP53 missense mutations could improve patient outcomes. Validation of this conclusion must, however, come from an appropriately designed clinical trial.

PLAC1 affects cell to cell communication by interacting with the desmosome complex

INTRODUCTION

X-linked PLAC1 is highly expressed in placenta during embryogenesis, and when ablated in mice, causes aberrant placental cell layer organization. It is also highly expressed in many types of cancer cell-lines. Although it has been shown that it promotes AKT phosphorylation in cancer cells, the exact mechanism by which it influences placental layer differentiation is unclear.

METHODS

To investigate the mechanism of action of PLAC1 we did cell fractionation and immunoprecipitation of the protein and Mass Spectrometry analysis to identify its interaction partners. The associated proteins were directly tested for interactions by co-transfection with PLAC1 and immunoprecipitation. Mutations in the ZP-N domain of PLAC1 were introduced to assess its involvement in the interactions.

RESULTS

We provide evidence that Desmoglein-2 (DSG2), a component of the membrane-associated desmosomal complex, directly interacts with PLAC1. Mutations of cysteines in ZP-N domain disrupt the interaction between PLAC1 and DSG-2.

DISCUSSION

Because desmosomes are responsible for establishing lateral cell-cell junctions, we suggest that direct interaction with the lateral junction protein complex may be implicated in the PLAC1 effects on cell-cell interactions, and thereby on the layer structure of the placenta.

PLAC1: biology and potential application in cancer immunotherapy

The emergence of immunotherapy has revolutionized medical oncology with unprecedented advances in cancer treatment over the past two decades. However, a major obstacle in cancer immunotherapy is identifying appropriate tumor-specific antigens to make targeted therapy achievable with fewer normal cells being impaired. The similarity between placentation and tumor development and growth has inspired many investigators to discover antigens for effective immunotherapy of cancers. Placenta-specific 1 (PLAC1) is one of the recently discovered placental antigens with limited normal tissue expression and fundamental roles in placental function and development. There is a growing body of evidence showing that PLAC1 is frequently activated in a wide variety of cancer types and promotes cancer progression. Based on the restricted expression of PLAC1 in testis, placenta and a wide variety of cancers, we have designated this molecule with new terminology, cancer-testis-placenta (CTP) antigen, a feature that PLAC1 shares with many other cancer testis antigens. Recent reports from our lab provide compelling evidence on the preferential expression of PLAC1 in prostate cancer and its potential utility in prostate cancer immunotherapy. PLAC1 may be regarded as a potential CTP antigen for targeted cancer immunotherapy based on the available data on its promoting function in cancer development and also its expression in cancers of different histological origin. In this review, we will summarize current data on PLAC1 with emphasis on its association with cancer development and immunotherapy.

PPARγ Expression Is Diminished in Macrophages of Recurrent Miscarriage Placentas

PPARγ belongs to the group of nuclear receptors which is expressed in the trophoblast and together with other factors is responsible for the maintenance of pregnancy. Apart from that PPARγ is also a main factor for macrophage polarization. The aim of this study was to investigate the combined expression pattern and frequency of PPARγ under physiological circumstances and in spontaneous and recurrent miscarriages in the trophoblast and in maternal macrophages of the decidua. Human placental tissues of the first trimester (15 physiologic pregnancies, 15 spontaneous abortion and 16 recurrent miscarriage placentas) were analyzed for expression of the nuclear receptor PPARγ. Expression changes were evaluated by immunohistochemistry and real time PCR (RT-PCR) in trophoblast and in maternal macrophages of the decidua. Maternal macrophages were identified by double immunofluorescence using cluster of differentiation 68 (CD68) as marker for macrophages and further characterized regarding their M1/M2 polarization status. The intermediate villous trophoblast revealed a significantly lower PPARγ expression in spontaneous and recurrent abortion. Maternal macrophages express PPARγ. Their number is significantly enhanced in the decidua of spontaneous miscarriages whereas in recurrent miscarriages maternal macrophages seem to express PPARγ only in very few cases. PPARγ is associated with an M2 polarization state that is common for decidual macrophages. The lack of PPARγ in recurrent miscarriage decidual macrophages seems to be associated with a specific inflammatory response against the fetus.

Plac1 Is a Key Regulator of the Inflammatory Response and Immune Tolerance In Mammary Tumorigenesis

Plac1 is an X-linked trophoblast gene expressed at high levels in the placenta, but not in adult somatic tissues other than the testis. Plac1 however is re-expressed in several solid tumors and in most human cancer cell lines. To explore the role of Plac1 in cancer progression, Plac1 was reduced by RNA interference in EO771 mammary carcinoma cells. EO771 "knockdown" (KD) resulted in 50% reduction in proliferation in vitro and impaired tumor growth in syngeneic mice; however, tumor growth in SCID mice was equivalent to tumor cells expressing a non-silencing control RNA, suggesting that Plac1 regulated adaptive immunity. Gene expression profiling of Plac1 KD cells indicated reduction in several inflammatory and immune factors, including Cxcl1, Ccl5, Ly6a/Sca-1, Ly6c and Lif. Treatment of mice engrafted with wild-type EO771 cells with a Cxcr2 antagonist impaired tumor growth, reduced myeloid-derived suppressor cells and regulatory T cells, while increasing macrophages, dendritic cells, NK cells and the penetration of CD8+ T cells into the tumor bed. Cxcl1 KD phenocopied the effects of Plac1 KD on tumor growth, and overexpression of Cxcl1 partially rescued Plac1 KD cells. These results reveal that Plac1 modulates a tolerogenic tumor microenvironment in part by modulating the chemokine axis.

Placenta-Specific Protein 1 Expression in Human Papillomavirus 16/18-Positive Cervical Cancers Is Associated With Tumor Histology

OBJECTIVE

Expression of the trophoblast-specific gene placenta-specific protein 1 (PLAC1) has been detected in a wide variety of cancers. However, to date, PLAC1 expression has not been shown in cervical cancer. We have carried out a preliminary study that shows for the first time that PLAC1 is expressed in cervical cancers.

METHODS

A total of 16 primary cervical tumors were obtained from patients shown to be human papillomavirus (HPV) 16/18 positive. Total cellular RNA, genomic DNA, and total protein were purified from each tumor. These materials were then used to determine PLAC1 expression, TP53 mutation status, and p53 expression.

RESULTS

The PLAC1 expression was demonstrated in all 16 primary cervical tumors. The highest levels of expression were found in the more aggressive squamous and adenosquamous histologic types compared with adenocarcinomas. Moreover, the proportion of total PLAC1 message coming from the P1 promoter, also termed the distal or cancer promoter, was significantly greater in the more aggressive squamous and adenosquamous histologic types compared with adenocarcinomas. Finally, in spite of all 16 tumors being HPV-16/18 positive, 3 of 8 squamous cell cancers and 2 of 5 adenocarcinomas expressed wild-type p53 protein. Consistent with the recently shown suppression of the PLAC1P1 promoter by wild-type p53, these p53 positive tumors displayed among the lowest P1-specific PLAC1 expression levels.

CONCLUSIONS

The PLAC1 expression has been demonstrated for the first time in cervical cancers. This preliminary study has further revealed a complex relationship between PLAC1 expression, cervical cancer histologic type, p53, and HPV type that requires further investigation.

p53 mutation status is a primary determinant of placenta-specific protein 1 expression in serous ovarian cancers

Placenta-specific protein 1 (PLAC1) expression is co-opted in numerous human cancers. As a consequence of PLAC1 expression, tumor cells exhibit enhanced proliferation and invasiveness. This characteristic is associated with increased aggressiveness and worse patient outcomes. Recently, the presence of the tumor suppressor p53 was shown in vitro to inhibit PLAC1 transcription by compromising the P1, or distal/cancer, promoter. We sought to determine if this phenomenon occurs in primary patient tumors as well. Furthermore, we wanted to know if p53 mutation influenced PLAC1 expression as compared with wild-type. We chose to study serous ovarian tumors as they are well known to have a high rate of p53 mutation. We report herein that the phenomenon of PLAC1 transcription repression does occur in serous ovarian carcinomas but only when TP53 is wild-type. We find that mutant or absent p53 protein de-represses PLAC1 transcription. We further propose that the inability of mutant p53 to repress PLAC1 transcription is due to the fact that the altered TP53 protein is unable to occupy a putative p53 binding site in the PLAC1 P1 promoter thus allowing transcription to occur. Finally, we show that PLAC1 transcript number is significantly negatively correlated with patient survival in our samples. Thus, we suggest that characterizing tumors for TP53 mutation status, p53 protein status and PLAC1 transcription could be used to predict likely prognosis and inform treatment options in patients diagnosed with serous ovarian cancer.

Molecular dynamics of Dkk4 modulates Wnt action and regulates meibomian gland development

Secreted Dickkopf (Dkk) proteins are major Wnt pathway modulators during organ development. Dkk1 has been widely studied and acts as a general Wnt inhibitor. However, the molecular function of other Dkks remains largely unknown. Here, we show that Dkk4 selectively inhibits a subset of Wnts, but is further inactivated by proteolytic cleavage. Meibomian gland (MG) formation is employed as a model where Dkk4 and its Wnt targets are expressed. Skin-specific expression of Dkk4 arrests MG growth at early germ phase, which is similar to that observed in Eda-ablated Tabby mice. Consistent with transient Dkk4 action, intact Dkk4 inhibits MG extension but the cleaved form progressively increases during MG development with a concomitant upswing in Wnt activity. Furthermore, both Dkk4 and its receptor (and Wnt co-receptor) Lrp6 are direct Eda targets during MG induction. In cell and organotypic cultures, Dkk4 inhibition is eliminated by elevation of Lrp6. Also, Lrp6 upregulation restores MG formation in Tabby mice. Thus, the dynamic state of Dkk4 itself and its interaction with Lrp6 modulates Wnt function during MG development, with a novel limitation of Dkk4 action by proteolytic cleavage.

Short-term incubation of bovine placentome sections as a tool to study xenobiotic mechanism of action

Studies on the effects of various factors, including xenobiotics, on the maternal-fetal connections in the placenta are restricted by the lack of a simple and inexpensive research model. We used placentomes collected at a slaughterhouse to in vitro study the bovine sections contained integral maternal-fetal connections. The placentomes from cows (n=4/experiment, 120-150 days post coitum) were cut using a razor blade into 60-80 mg sections and incubated in either DMEM/Ham's F-12 or M-199 supplemented with FCS (2%, 5% or 10%), amniotic fluid (AF or inactive AF, 10% or 20%) or both. The sections (n=4/supplement) were incubated for 24 or 48 h in a water bath at 37.5°C in an atmosphere of 5% CO2 and 95% O2. The structure and secretory activity of placentome sections were maintained when incubated in DMEM/Ham's F-12 with 2% FCS and 10% AF. M-199 was less acidified than DMEM/Ham's F-12 during incubation, and thus, this medium was better able to maintain the integrity of the placenta and the secretion of estradiol, progesterone and oxytocin for 48 h. Moreover, we detected a decrease in the expression of placenta-specific 1 (PLAC1) mRNA (an indicator of trophoblast proliferation) and an increase in the levels of keratin 8 (KRT8; a marker of normal placental barrier function) and hypoxia induced factor 1α (HIF1α; a marker of hypoxia) mRNA. These results indicate the presence of adaptation and repair mechanisms and confirm the biological activity of the placentome sections. We propose the use of placentome sections as an in vitro model to study maternal-fetal connections in cows.

Role of placenta-specific protein 1 in trophoblast invasion and migration

Placenta-specific protein 1 (PLAC1), a placenta-specific gene, is known to be involved in the development of placenta in both humans and mice. However, the precise role of PLAC1 in placental trophoblast function remains unclear. In this study, the localization of PLAC1 in human placental tissues and its physiological significance in trophoblast invasion and migration are investigated by technical studies including real-time RT-PCR, in situ hybridization, immunohistochemistry, and functional studies by utilizing cell invasion and migration assays in the trophoblast cell line HTR8/SVneo as well as the primary inducing extravillous trophoblasts (EVTs). The results show that PLAC1 is mainly detected in the trophoblast columns and syncytiotrophoblast of the first-trimester human placental villi, as well as in the EVTs that invade into the maternal decidua. Knockdown of PLAC1 by RNA interference significantly suppresses the invasion and migration of HTR8/SVneo cells and shortens the distance of the outgrowth of the induced EVTs from the cytotrophoblast column of the explants. All the above data suggests that PLAC1 plays an important role in human placental trophoblast invasion and migration.

Placenta-specific protein 1: a potential key to many oncofetal-placental OB/GYN research questions

Placenta-specific protein 1 (PLAC1) is a secreted protein found in trophoblasts. Several reports implicate a central role for PLAC1 in establishment and maintenance of the placenta. In addition to placentae PLAC1 is expressed in a variety of solids including breast, endometrial, and ovarian cancers. In order to show that PLAC1 is potentially relevant to a number of research questions in OB/GYN, we report on PLAC1 expression in a selected panel that includes two choriocarcinoma cell lines, normal placental tissues, and endometrial and ovarian tumors. We report for the first time that PLAC1 is also expressed in human fetal tissues. PLAC1 is transcriptionally heterogeneous with one promoter (P1) generating two transcripts with alternately spliced 5' UTRs and the other promoter (P2) generating a third transcript. Placental tissues favor P2 transcripts, while P1 is favored in most of the other cells. Mechanisms determining multiple PLAC1 transcripts and promoter preferences are as yet unknown, but it is clear that this protein is likely to be important in a variety of phenomena relevant to both gynecologic oncology and maternal-fetal medicine.

NCOA3 is a selective co-activator of estrogen receptor α-mediated transactivation of PLAC1 in MCF-7 breast cancer cells

Background

The placenta-specific 1 (PLAC1) gene encodes a membrane-associated protein which is selectively expressed in the placental syncytiotrophoblast and in murine fetal tissues during embryonic development. In contrast to its transcriptional repression in all other adult normal tissues, PLAC1 is frequently activated and highly expressed in a variety of human cancers, in particular breast cancer, where it associates with estrogen receptor α (ERα) positivity. In a previous study, we showed that ERα-signaling in breast cancer cells transactivates PLAC1 expression in a non-classical pathway. As the members of the p160/nuclear receptor co-activator (NCOA) family, NCOA1, NCOA2 and NCOA3 are known to be overexpressed in breast cancer and essentially involved in estrogen-mediated cancer cell proliferation we asked if these proteins are involved in the ERα-mediated transactivation of PLAC1 in breast cancer cells.

Methods

Applying quantitative real-time RT-PCR (qRT-PCR), Western Blot analysis and chromatin immunoprecipitation, we analyzed the involvement of NCOA1, NCOA2, NCOA3 in the ERα-mediated transactivation of PLAC1 in the breast cancer cell lines MCF-7 and SK-BR-3. RNAi-mediated silencing of NCOA3, qRT-PCR, Western blot analysis and ERα activation assays were used to examine the role of NCOA3 in the ERα-mediated regulation of PLAC1 in further detail. Transcript expression of NCOA3 and PLAC1 in 48 human breast cancer samples was examined by qRT-PCR and statistical analysis was performed using Student’s t-test.

Results

We detected selective recruitment of NCOA3 but not NCOA1 or NCOA2 to the PLAC1 promoter only in ERα-positive MCF-7 cells but not in ERα-negative SK-BR-3 breast cancer cells. In addition, we demonstrate that silencing of NCOA3 results in a remarkable decrease of PLAC1 expression levels in MCF-7 cells which cannot be restored by treatment with estradiol (E₂). Moreover, significant higher transcript levels of PLAC1 were found only in ERα-positive human breast cancer samples which also show a NCOA3 overexpression.

Conclusions

In this study, we identified NCOA3 as a selective co-activator of ERα-mediated transactivation of PLAC1 in MCF-7 breast cancer cells. Our data introduce PLAC1 as novel target gene of NCOA3 in breast cancer, supporting the important role of both factors in breast cancer biology.

T antigen transformation reveals Tp53/RB-dependent route to PLAC1 transcription activation in primary fibroblasts

PLAC1 (placenta-specific 1) is a gene that is placenta specific and transcribed very little, if at all, in any somatic tissue. It is nevertheless expressed in many cancer cell lines. To understand how cancer cells may activate the gene in nonexpressing cells, we found that a model is provided by classical transformation of normal fibroblasts by SV40 T antigen. T antigen derepressed the PLAC1 P1 promoter, with Tp53 and RB exerting critical and opposing actions and nuclear receptors, retinoid X receptor and  liver X receptor, sharply increasing the level of expression.

PPARδ induces estrogen receptor-positive mammary neoplasia through an inflammatory and metabolic phenotype linked to mTOR activation

The peroxisome proliferator-activated receptor-δ (PPARδ) regulates a multitude of physiological processes associated with glucose and lipid metabolism, inflammation, and proliferation. One or more of these processes are potential risk factors for the ability of PPARδ agonists to promote tumorigenesis in the mammary gland. In this study, we describe a new transgenic mouse model in which activation of PPARδ in the mammary epithelium by endogenous or synthetic ligands resulted in progressive histopathologic changes that culminated in the appearance of estrogen receptor- and progesterone receptor-positive and ErbB2-negative infiltrating ductal carcinomas. Multiparous mice presented with mammary carcinomas after a latency of 12 months, and administration of the PPARδ ligand GW501516 reduced tumor latency to 5 months. Histopathologic changes occurred concurrently with an increase in an inflammatory, invasive, metabolic, and proliferative gene signature, including expression of the trophoblast gene, Plac1, beginning 1 week after GW501516 treatment, and remained elevated throughout tumorigenesis. The appearance of malignant changes correlated with a pronounced increase in phosphatidylcholine and lysophosphatidic acid metabolites, which coincided with activation of Akt and mTOR signaling that were attenuated by treatment with the mTOR inhibitor everolimus. Our findings are the first to show a direct role of PPARδ in the pathogenesis of mammary tumorigenesis, and suggest a rationale for therapeutic approaches to prevent and treat this disease.

The oncoplacental gene placenta-specific protein 1 is highly expressed in endometrial tumors and cell lines

Placenta-specific protein 1 (PLAC1) is a small secreted protein expressed exclusively in trophoblast cells in the mammalian placenta. PLAC1 is expressed early in gestation and is maintained throughout. It is thought to function in trophoblast invasion of the uterine epithelium and, subsequently, to anchor the placenta to the epithelium. In recent years, evidence has accumulated that PLAC1 is also expressed in a variety of human solid tumors, notably in breast cancers. We demonstrate for the first time that PLAC1 is ubiquitously expressed in tumors originating in uterine epithelium. Further, we find that PLAC1 expression is significantly higher in the more advanced, more aggressive endometrial serous adenocarcinomas and carcinosarcomas relative to endometrioid adenocarcinomas by more than 6-fold and 16-fold, respectively. We also show that PLAC1 is simultaneously transcribed from two promoters but that, in all cases, the more distal P1 promoter dominates the more proximal P2 promoter. While the function of the two PLAC1 promoters and their regulation are as yet unknown, overall expression data suggest that PLAC1 may serve as a biomarker for endometrial cancer as well as a potential prognostic indicator.

PLAC1 Expression Decreases in Chorionic Villi in Response to Labor

PLAC1 (Placenta-Specific 1) is a recently described, trophoblast-expressed gene essential for normal placental development. The protein localizes to the microvillus membrane surface of the syncytiotrophoblast in direct proximity to the maternal compartment. Although its role has not been defined, increased circulating levels of human PLAC1 mRNA in maternal blood are associated with preeclampsia. Furthermore, PLAC1-null mice exhibit decreased viability in the peripartum period suggesting a role in pregnancy maintenance late in gestation. We examined PLAC1 gene expression in the human placenta during normal pregnancy and pregnancies associated with maternal diabetes and preeclampsia using quantitative, real time PCR (q-RT-PCR). Although there was no apparent difference in PLAC1 gene expression among human pregnancies complicated by diabetes or preeclampsia, an unexpected effect of labor was noted at term. PLAC1 expression in placentae delivered vaginally following induced or spontaneous labor was significantly reduced compared to placentae not exposed to labor making it one of only a few placental genes influenced by labor. The significance of this finding is unknown. Viewed in the context of its importance in placental development, however, these findings are consistent with a role for PLAC1 in the maintenance of the maternal-fetal interface.

Plac1 (placenta-specific 1) is essential for normal placental and embryonic development

Plac1 is a recently identified, X-linked gene whose expression is restricted primarily to cells of the trophoblast lineage. It localizes to a chromosomal locus previously implicated in placental growth. We therefore sought to determine if Plac1 is necessary for placental and embryonic development by examining a mutant mouse model. Plac1 ablation resulted in placentomegaly and mild intrauterine growth retardation (IUGR). At E16.5, knockout (KO) and heterozygous (Het) placentae of the Plac1-null allele inherited from the mother (X(m-) X) weighed approximately 100% more than wildtype (WT) placentae, whereas the corresponding embryos weighed 7-12% less. Histologically, Plac1 mutants exhibited an expanded spongiotrophoblast layer that invaded the labyrinth. By contrast, Het placentae that inherited the null allele from the father (XX(p-) ) exhibited normal growth and were histologically indistinguishable from WT placentae, consistent with paternal imprinting of Plac1. When examined across gestation, WT and X(m-) X placental weights peaked at E16.5 and decreased slightly thereafter. KO placentae (X(m-) X(p-) and X(m-) Y), however, continued to increase in weight after E16.5, consistent with a functional role for the paternal Plac1 allele. Subsequent analysis confirmed that the paternal allele partially escapes complete X-inactivation and thus contributes to placental growth regulation. Additionally, although male Plac1 KO mice can survive, they exhibit decreased viability as a consequence of events occurring late in gestation or shortly after birth. Thus, Plac1 is a paternally imprinted, X-linked gene essential for normal placental and embryonic development.