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

Production and characterization of a panel of anti-mouse placenta-specific protein 1 (plac1) monoclonal antibodies

Placenta-Specific Protein 1 (PLAC1) is essential for normal placental and embryonic development. It is widely expressed in various types of cancer cells. We produced a panel of anti-mouse plac1 monoclonal antibodies (mAbs) with different applications. Two recombinant proteins were produced containing either the extracellular domain (ED) plus tetanus toxin P2, P30, pan-DR epitope (PADRE), and KDEL3 (main plac1) or ED plus KDEL3 (control plac1). Recombinant proteins were used for immunization and screening. Positive clones were selected by ELISA and flow cytometry. Purified mAbs were tested by ELISA, WB, flow cytometry, immunohistochemistry (IHC), and immunofluorescent (IF). A combination of bioinformatics tools was used to predict the target epitope(s) of the mAbs. Eight anti-mouse plac1 mAbs (all IgG1/κ1) were generated, all reacting with high affinity in ELISA. Seven clones recognized plac1 in both reduced and non-reduced Western blots, while one only recognized the non-reduced form. Cross-inhibition ELISA revealed that all mAbs recognized overlapping epitopes with a shared motif except for 5C9. Four clones reacted with the native antigen in flow cytometry, but none were functional in IF or IHC staining. The produced multifunctional mAbs can be used to investigate different aspects of PLAC1 biology in reproduction and cancer.

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.

The potential value of cancer-testis antigens in ovarian cancer: Prognostic markers and targets for immunotherapy

BACKGROUND

Tumor immunotherapy has become an important adjuvant therapy after surgery, radiotherapy, and chemotherapy. In recent years, the role of tumor-associated antigen (TAA) in tumor immunotherapy has become increasingly prominent. Cancer-testis antigen (CTA) is a kind of TAA that is highly restricted in a variety of tumors and can induce an immune response.

AIMS

This review article aimed to evaluate the role of CTA on the progression of ovarian cancer, its diagnostic efficacy, and the potential for immunotherapy.

METHODS

We analyzed publications and outlined a comprehensive of overview the regulatory mechanism, immunogenicity, clinical expression significance, tumorigenesis, and application prospects of CTA in ovarian cancer, with a particular focus on recent progress in CTA-based immunotherapy.

RESULTS

The expression of CTA affects the occurrence, development, and prognosis of ovarian cancer and is closely related to tumor immunity.

CONCLUSION

CTA can be used as a biomarker for the diagnosis and prognosis evaluation of ovarian cancer and is an ideal target for antitumor immunotherapy. These findings provide novel insights on CTA in the improvement of diagnosis and treatment for ovarian cancer. The successes, current challenges and future prospects were also discussed to portray its significant potential.

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.

Leveraging epigenetics to enhance the efficacy of cancer-testis antigen: a potential candidate for immunotherapy

Ovarian cancer is the most lethal gynecological malignancy in women. The phenotype is characterized by delayed diagnosis, recurrence and drug resistance. Inherent immunogenicity potential, oncogenic function and expression of cancer-testis/germline antigen (CTA) in ovarian cancer render them a potential candidate for immunotherapy. Revolutionary clinical findings indicate that tumor antigen-mediated T-cell and dendritic cell-based immunotherapeutic approaches provide an excellent strategy for targeting tumors. Currently, dendritic cell vaccination for the treatment of B-cell lymphoma and CTA-based T-cell receptor transduced T-cell therapy involving MAGE-A4 and NY-ESO-1 are well documented and shown to be effective. This review highlighted the mechanical aspects of epigenetic drugs that can elicit a CTA-based humoral and cellular immune response and implicate T-cell and dendritic cell-based immunotherapeutic approaches.

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.

Mutated p53 in HGSC-From a Common Mutation to a Target for Therapy

Simple Summary

Ovarian high-grade serous cancer (HGSC), the most common and the deadliest subtype of epithelial ovarian cancer, is characterized by frequent mutations in the TP53 tumor suppressor gene, encoding for the p53 protein in nearly 100% of cases. This makes p53 the focus of many studies trying to understand its role in HGSC. The aim of our review paper is to provide updates on the latest findings related to the role of mutant p53 in HGSC. This includes the clinical outcomes of TP53 mutations in HGSC, upstream regulators and downstream effectors of p53, its function in the earliest stages of HGSC development and in the interplay between the tumor cells and their microenvironment. We summarize with the likelihood of p53 mutants to serve as biomarkers for early diagnosis and as targets for therapy in HGSC.

Abstract

Mutations in tumor suppressor gene TP53, encoding for the p53 protein, are the most ubiquitous genetic variation in human ovarian HGSC, the most prevalent and lethal histologic subtype of epithelial ovarian cancer (EOC). The majority of TP53 mutations are missense mutations, leading to loss of tumor suppressive function of p53 and gain of new oncogenic functions. This review presents the clinical relevance of TP53 mutations in HGSC, elaborating on several recently identified upstream regulators of mutant p53 that control its expression and downstream target genes that mediate its roles in the disease. TP53 mutations are the earliest genetic alterations during HGSC pathogenesis, and we summarize current information related to p53 function in the pathogenesis of HGSC. The role of p53 is cell autonomous, and in the interaction between cancer cells and its microenvironment. We discuss the reduction in p53 expression levels in tumor associated fibroblasts that promotes cancer progression, and the role of mutated p53 in the interaction between the tumor and its microenvironment. Lastly, we discuss the potential of TP53 mutations to serve as diagnostic biomarkers and detail some more advanced efforts to use mutated p53 as a therapeutic target in HGSC.

Characterization of a TP53 Somatic Variant of Unknown Function From an Ovarian Cancer Patient Using Organoid Culture and Computational Modeling

In our proof-of-concept study of 1 patient with stage IIIC carcinosarcoma of the ovary, we discovered a rare mutation in the tumor suppressor, TP53, that results in the deletion of N131. Immunofluorescence imaging of the organoid culture revealed hyperstaining of p53 protein. Computational modeling suggests this residue is important for maintaining protein conformation. Drug screening identified the combination of a proteasome inhibitor with a histone deacetylase inhibitor as the most effective treatment. These data provide evidence for the successful culture of a patient tumor and analysis of drug response ex vivo.

Expression of placenta-specific 1 and its potential for eliciting anti-tumor helper T-cell responses in head and neck squamous cell carcinoma

Placenta-specific 1 (PLAC1) is expressed primarily in placental trophoblasts but not in normal tissues and is a targetable candidate for cancer immunotherapy because it is a cancer testis antigen known to be up-regulated in various tumors. Although peptide epitopes capable of stimulating CD8 T cells have been previously described, there have been no reports of PLAC1 CD4 helper T lymphocyte (HTL) epitopes and the expression of this antigen in head and neck squamous cell carcinoma (HNSCC). Here, we show that PLAC1 is highly expressed in 74.5% of oropharyngeal and 51.9% of oral cavity tumors from HNSCC patients and in several HNSCC established cell lines. We also identified an HTL peptide epitope (PLAC1_31-50) capable of eliciting effective antigen-specific and tumor-reactive T cell responses. Notably, this peptide behaves as a promiscuous epitope capable of stimulating T cells in the context of more than one human leukocyte antigen (HLA)-DR allele and induces PLAC1-specific CD4 T cells that kill PLAC1-positive HNSCC cell lines in an HLA-DR-restricted manner. Furthermore, T-cells reactive to PLAC1_31-50 peptide were detected in the peripheral blood of HNSCC patients. These findings suggest that PLAC1 represents a potential target antigen for HTL based immunotherapy in HNSCC.

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.

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.

Cancer-testis antigens in ovarian cancer: implication for biomarkers and therapeutic targets

Ovarian cancer remains the most fatal gynecologic malignancy worldwide due to delayed diagnosis as well as recurrence and drug resistance. Thus, the development of new tumor-related molecules with high sensitivity and specificity to replace or supplement existing tools is urgently needed. Cancer-testis antigens (CTAs) are exclusively expressed in normal testis tissues but abundantly found in several types of cancers, including ovarian cancer. Numerous novel CTAs have been identified by high-throughput sequencing techniques, and some aberrantly expressed CTAs are associated with ovarian cancer initiation, clinical outcomes and chemotherapy resistance. More importantly, CTAs are immunogenic and may be novel targets for antigen-specific immunotherapy in ovarian cancer. In this review, we attempt to characterize the expression of candidate CTAs in ovarian cancer and their clinical significance as biomarkers, activation mechanisms, function in malignant phenotypes and applications in immunotherapy.

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.

Placental expression of PAPPA, PAPPA-2 and PLAC-1 in pregnacies is associated with FGR

Fetal growth restriction (FGR) is a gynecological disorder of varying etiology. In the present study, an expression analysis of pregnancy-associated plasma protein A (PAPPA), pregnancy-associated plasma protein A2 (PAPPA2) and placenta-specific-1 (PLAC-1) was conducted in pregnancies with FGR and control pregnancies. Placental tissues were collected from pregnancies with FGR (n=16) and control pregnancies (n=16) and the expression of the genes of interest was examined by qPCR. The mean expression levels of PAPPA and PAPPA2 were significantly lower (P<0.001) in placental tissues from FGR pregnancies compared with tissues from healthy subjects, whereas the opposite pattern was observed for PLAC-1 (P<0.001). PAPPA and PLAC-1 expression in FGR and control subjects correlated with birth weight (P<0.001). The findings suggest a possible pathophysiological link between the development of FGR and the expression of PAPPA, PAPPA2 and PLAC-1.