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

Identification of placenta-specific protein 1 (PLAC-1) expression on human PC-3 cell line-derived prostate cancer stem cells compared to the tumor parental cells

Placenta-specific protein 1 (PLAC-1) is a gene primarily expressed in the placenta and the testis. Interestingly, it is also found to be expressed in many solid tumors, and it is involved in malignant cell features. However, no evidence has been reported regarding the relationship between PLAC-1 and cancer stem cells (CSCs). In the current research, we explored the expression of the PLAC-1 molecule in prostate cancer stem cells (PCSCs) derived from the human PC-3 cell line. The enrichment of PCSCs was achieved using a three-dimensional cell culture technique known as the sphere-formation assay. To confirm the identity of PCSCs, we examined the expression of genes associated with stemness and pluripotency, such as SOX2, OCT4, Nanog, C-Myc, and KLF-4, as well as stem cell differentiation molecules like CD44 and CD133. These evaluations were conducted in both the PCSCs and the original tumor cells (parental cells) using real-time PCR and flow cytometry. Subsequently, we assessed the expression of the PLAC-1 molecule in both enriched cells and parental tumor cells at the gene and protein levels using the same techniques. The tumor cells from the PC-3 cell line formed spheroids with CSC characteristics in a non-adherent medium. The expression of SOX2, OCT4, Nanog, and C-Myc genes (p < 0.01), and the molecules CD44 and CD133 (p < 0.05) were significantly elevated in PCSCs compared to the parental cells. The expression of the PLAC-1 molecule in PCSCs showed a significant increase compared to the parental cells at both gene (p < 0.01) and protein (p < 0.001) levels. In conclusion, it was indicated for the first time that PLAC-1 is up-regulated in PCSCs derived from human PC-3 cell line. This study may propose PLAC-1 as a potential target in targeted therapies, which should be confirmed through further studies.

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.

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.

Baby Genomics: Tracing the Evolutionary Changes That Gave Rise to Placentation

It has long been challenging to uncover the molecular mechanisms behind striking morphological innovations such as mammalian pregnancy. We studied the power of a robust comparative orthology pipeline based on gene synteny to address such problems. We inferred orthology relations between human genes and genes from each of 43 other vertebrate genomes, resulting in ∼18,000 orthologous pairs for each genome comparison. By identifying genes that first appear coincident with origin of the placental mammals, we hypothesized that we would define a subset of the genome enriched for genes that played a role in placental evolution. We thus pinpointed orthologs that appeared before and after the divergence of eutherian mammals from marsupials. Reinforcing previous work, we found instead that much of the genetic toolkit of mammalian pregnancy evolved through the repurposing of preexisting genes to new roles. These genes acquired regulatory controls for their novel roles from a group of regulatory genes, many of which did in fact originate at the appearance of the eutherians. Thus, orthologs appearing at the origin of the eutherians are enriched in functions such as transcriptional regulation by Krüppel-associated box-zinc-finger proteins, innate immune responses, keratinization, and the melanoma-associated antigen protein class. Because the cellular mechanisms of invasive placentae are similar to those of metastatic cancers, we then used our orthology inferences to explore the association between placenta invasion and cancer metastasis. Again echoing previous work, we find that genes that are phylogenetically older are more likely to be implicated in cancer development.

Trophectoderm-Specific Knockdown of LIN28 Decreases Expression of Genes Necessary for Cell Proliferation and Reduces Elongation of Sheep Conceptus

LIN28 inhibits let-7 miRNA maturation which prevents cell differentiation and promotes proliferation. We hypothesized that the LIN28-let-7 axis regulates proliferation-associated genes in sheep trophectoderm in vivo. Day 9-hatched sheep blastocysts were incubated with lentiviral particles to deliver shRNA targeting LIN28 specifically to trophectoderm cells. At day 16, conceptus elongation was significantly reduced in LIN28A and LIN28B knockdowns. Let-7 miRNAs were significantly increased and IGF2BP1-3, HMGA1, ARID3B, and c-MYC were decreased in trophectoderm from knockdown conceptuses. Ovine trophoblast (OTR) cells derived from day 16 trophectoderm are a useful tool for in vitro experiments. Surprisingly, LIN28 was significantly reduced and let-7 miRNAs increased after only a few passages of OTR cells, suggesting these passaged cells represent a more differentiated phenotype. To create an OTR cell line more similar to day 16 trophectoderm we overexpressed LIN28A and LIN28B, which significantly decreased let-7 miRNAs and increased IGF2BP1-3, HMGA1, ARID3B, and c-MYC compared to control. This is the first study showing the role of the LIN28-let-7 axis in trophoblast proliferation and conceptus elongation in vivo. These results suggest that reduced LIN28 during early placental development can lead to reduced trophoblast proliferation and sheep conceptus elongation at a critical period for successful establishment of pregnancy.

Expression of Human Placenta-specific 1 (PLAC1) in CHO-K1 Cells

BACKGROUND

Placenta-specific 1 (PLAC1), as a new Cancer/Testis Antigen (CTA), is frequently expressed in a variety of cancers and localized to cytoplasm and plasma membrane. Surface expression of cancer target antigens is of great importance that enables antibody-mediated cancer immunotherapy. The aim of the current study was to express the intact human PLAC1 protein on plasma membrane of a eukaryotic cell as a model for future anti-PLAC1-based cancer immunotherapy.

METHODS

In the first approach, entire human PLAC1 gene including its own Signal Peptide (SP) was cloned into pIRES2-EGFP and LeGO-iG2 vectors and expressed in CHO-K1 cells. In the second approach, cytosolic and Signal-Anchor (SA) sequence of Transferrin Receptor Protein 1 (TFR1) were fused to extracellular portion of PLAC1 and expressed as above. Expression of PLAC1 was then assessed using Reverse Transcription Polymerase Chain Reaction (RT-PCR), Western Blot (WB), Immunocytochemistry (ICC), Immunofluorescence (IF) and Flow Cytometry (FC).

RESULTS

The first approach resulted in the expression of PLAC1 in submembranous but not in the surface of transfected CHO-K1 cells. Using the chimeric human PLAC1 construct, the same intracellular expression pattern was observed.

CONCLUSION

These results indicated that there are some yet unknown PLAC1 localization signals employed by cancer cells for surface expression of PLAC1.

Placenta specific protein-1 in recurrent pregnancy loss and in In Vitro Fertilisation failure: a prospective observational case-control study

Observations from studies have provided evidence that Placenta-specific protein1 (PLAC1) is important for the establishment and maintenance of pregnancy and suggest it as a potential biomarker for gestational pathologies. The aim of this study is to investigate whether maternal serum PLAC1 levels have any impact on etiopathogenesis of recurrent pregnancy loss (RPL) and repeated implantation failure after In Vitro Fertilisation (RIF). We conducted a prospective observational case-control study in a Research Hospital. Twenty-eight patients with RPL (group 1), 30 patients with unexplained infertility and RIF (group 2), 29 fertile patients (group 3) were included. The demographic features and serum PLAC1 levels were compared. There was a significant difference in PLAC1 levels between the groups (group 1 = 19.71 + 16.55 ng/ml; group 2 = 4.82 + 1.44 ng/ml; group 3 = 0.89 + 0.62 ng/ml, respectively) (p=.001). Positive correlation was found between serum PLAC1 levels and abortion rates (r = 0.64; p=.001), a negative correlation was found between serum PLAC1 levels and live birth rates (r = -0.69; p=.001). PLAC1 might have a negative effect on implantation in RPL and RIF. There may be a subgroup of PLAC with different bioactivity. There are no relevant studies conducted among these populations, further large-scale studies are needed to assess the molecular role of PLAC1 on implantation.IMPACT STATEMENTWhat is already known about this subject? PLAC1 (placenta-specific protein-1) gene is located on the X chromosome which encodes for a protein that is thought to be important for placental development although its role has not been clearly defined. Studies in the literature have provided evidence that PLAC1 has an important role in the establishment and maintenance of pregnancy and suggest it as a potential biomarker for gestational pathologies. Several reports over the past few years have demonstrated PLAC1 expression in a variety of human tumours including lung cancers, breast cancer, hepatocellular and colorectal cancers, gastric cancers and uterine cancers.What do the results of this study add? There have been no previous studies conducted among patients with recurrent pregnancy loss (RPL) or repeated implantation failure after In Vitro Fertilisation (RIF) that have searched for any association between PLAC1 levels and implantation failure. This study has demonstrated higher PLAC1 levels in infertile women with RIF and RPL for the first time; suggesting that it could have a negative effect on implantation in these populations. PLAC1 could be detected in the serum as a biomarker that is associated with RIF and RPL. What are the implications of these findings for clinical practice and/or further research? Defining the precise role of PLAC1 during implantation will provide new insight into understanding of poor reproductive outcomes such as RIF and RPL and help in developing treatment strategies. Further large-scale studies with more patients are needed to uncover the clinical value of PLAC1 as a biomarker to predict repeated implantation failure and RPL.

LIN28-let-7 axis regulates genes in immortalized human trophoblast cells by targeting the ARID3B-complex

Abnormal placental development is one of the main etiological factors for intrauterine growth restriction (IUGR). Here, we show that LIN28A and LIN28B are significantly lower and lethal-7 (let-7) microRNAs (miRNAs) significantly higher in term human IUGR vs. normal placentas. We hypothesize that let-7 miRNAs regulate genes with known importance for human placental development [high-mobility group AT-hook 1 (HMGA1), transcriptional regulator Myc-like (c-myc), vascular endothelial growth factor A (VEGF-A), and Wnt family member 1 (WNT1)] by targeting the AT-rich interacting domain (ARID)-3B complex. ACH-3P cells with LIN28A and LIN28B knockout (DKOs) significantly increased let-7 miRNAs, leading to significantly decreased ARID3A, ARID3B, and lysine demethylase 4C (KDM4C). Similarly, Sw.71 cells overexpressing LIN28A and LIN28B (DKIs) significantly decreased let-7 miRNAs, leading to significantly increased ARID3A, ARID3B, and KDM4C. In ACH-3P cells, ARID3A, ARID3B, and KDM4C make a triprotein complex [triprotein complex comprising ARID3A, ARID3B, and KDM4C (ARID3B-complex)] that binds the promoter regions of HMGA1, c-MYC, VEGF-A, and WNT1. ARID3B knockout in ACH-3P cells disrupted the ARID3B-complex, leading to a significant decrease in HMGA1, c-MYC, VEGF-A, and WNT1. DKOs had a significant reduction, whereas DKIs had a significant increase in HMGA1, c-MYC, VEGF-A, and WNT1, potentially due to regulation by the ARID3B-complex. This is the first study showing regulation of let-7 targets in immortalized human trophoblast cells by the ARID3B-complex.-Ali, A., Anthony, R. V., Bouma, G. J., Winger, Q. A. LIN28-let-7 axis regulates genes in immortalized human trophoblast cells by targeting the ARID3B-complex.

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.

Long-term effect of pregnancy-related factors on the development of endometrial neoplasia: A nationwide retrospective cohort study

Objective

By identifying pregnancy-related risk factors for endometrial neoplasia, women’s risk of developing this disease after childbirth can be predicted and high-risk women can be screened for early detection.

Methods

Study data from women who gave birth in Korea in 2007 were collected from the Korea National Health Insurance (KNHI) claims database between 2007 and 2015. The adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the development of endometrial neoplasia were estimated by multivariate Cox proportional hazards models.

Results

Data from 386,614 women were collected for this study. By 2015, 3,370 women from the initial cohort had been diagnosed with endometrial neoplasia secondary to delivery. Multivariate Cox proportional hazards regression revealed that preeclampsia (HR 1.55, 95% CI 1.29, 1.86), advanced maternal age (≥ 35; HR 1.52, 95% CI 1.39, 1.66), multifetal pregnancy (HR 1.81, 95% CI 1.46, 2.23), multiparity (HR 1.16, 95% CI 1.08, 1.24), cesarean section (HR 1.15, 95% CI 1.07, 1.23) and delivery of a large-for-gestational-age infant (HR 1.19, 95% CI 1.02, 1.39) were independent risk factors for future endometrial neoplasia. The risk for endometrial neoplasia increased as the number of risk factors increased (risk factors ≥3: HR 2.11, 95% CI 1.86–2.40).

Conclusion

This study showed that six pregnancy-related factors—advanced maternal age, multiparity, multifetal pregnancy, cesarean section, delivery of a large-for-gestational-age infant, and preeclampsia—are positively correlated with future development of endometrial neoplasia, including endometrial hyperplasia or cancer. Close observation and surveillance are warranted to enable early diagnosis of endometrial diseases, including endometrial cancer after pregnancy in high-risk women. However, due to unavailability of clinical information, many clinical/epidemiological factors can become confounders. Further research is needed on factors associated with the risk of endometrial neoplasia.

The miR-503 cluster is coordinately under-expressed in endometrial endometrioid adenocarcinoma and targets many oncogenes, cell cycle genes, DNA repair genes and chemotherapy response genes

Background

The miR-503 miRNA cluster, located at Xq23.1, is composed of six miRNAs; miR-424, miR-503, miR-542, miR-450a-1, miR-450a-2 and miR-450b. Numerous studies have focused on the relationship of one or two members of the cluster and various human cancers. Here, we suggest that the entire cluster as a single coordinately expressed polycistron transcribed from a single promoter in endometrial endometrioid adenocarcinoma (EEA).

Subjects and methods

A tissue panel composed of twenty histologically confirmed endometrial endometrioid adenocarcinomas (EEA) and four benign endometrium was assembled under informed consent. Expression of each member of the miR-503 cluster was determined by quantitative PCR and differences in expression between EEA and benign tissues were assessed via the standard ΔΔCt method. In addition, the role of promoter methylation status in miRNA expression was examined in Ishikawa H cells following exposure to the cytidine analog Decitabine.

Results

Expression of each member of the miR-503 cluster is significantly downregulated in EEA in our tumor sample. Both in our tumor sample and in The Cancer Genome Atlas (TCGA) there is evidence of highly correlated expression further supporting the idea that the miR-503 cluster is a polycistron. Looking at each member of the miR-503 cluster we were able to identify 55 unique experimentally validated target genes which include a substantial number of genes involved in carcinogenesis, DNA damage response, cell cycle regulation and chemotherapeutic response. We also found preliminary evidence that regulation of the miR-503 cluster is governed by methylation of the promoter in EEA.

Conclusion

The totality of the data presented here strongly suggest that the miR-503 cluster as a whole merits further investigation as an important potential therapeutic target in EEA.

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.

Placenta-specific protein 1 is conserved throughout the Placentalia under purifying selection

Placental mammals (Placentalia) are a very successful group that, today, comprise 94% of all mammalian species. Recent phylogenetic analyses, coupled with new, quite complete fossils, suggest that the crown orders were all established rapidly from a common ancestor just after the Cretaceous/Tertiary (K/T) boundary 65 million years ago. Extensive molecular and morphologic evidence has led to a description of the common ancestor of all Placentalia in which a two-horned uterus and a hemochorial placenta are present. Thus, the process of placentation in which the placenta invades and anchors to the uterine epithelium was already established. One factor that has been suggested as a crucial component of this process is placenta-specific protein 1 (PLAC1). A phylogenetic analysis of the PLAC1 protein in 25 placental mammal species, representing nine of the sixteen crown orders of the Placentalia, suggests that this protein was present in the placental common ancestor in the form we see it today, that it evolved in the Placentalia and has been subject to the effects of purifying selection since its appearance.