Selective activation of trophoblast-specific PLAC1 in breast cancer by CCAAT/enhancer-binding protein beta (C/EBPbeta) isoform 2

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.

Analysis of core genes for colorectal cancer prognosis based on immune and stromal scores

Background

Colorectal cancer (CRC) is one of the most common malignancies.An early diagnosis and an accurate prognosis are major focuses of CRC research. Tumor microenvironment cells and the extent of infiltrating immune and stromal cells contribute significantly to the tumor prognosis.

Methods

Immune and stromal scores were calculated based on the ESTIMATE algorithm using the sample expression profile of the The Cancer Genome Atlas (TCGA) database. GSE102479 was used as the validation database. Differentially expressed genes whose expression was significantly associated with the prognosis of CRC patients were identified based on the immune matrix score. Survival analysis was conducted on the union of the differentially expressed genes. A protein–protein interaction (PPI) network was constructed using the STRING database to identify the closely connected modules. To conduct functional enrichment analysis of the relevant genes, GO and KEGG pathway analyses were performed with Cluster Profiler. Pivot analysis of the ncRNAs and TFs was performed by using the RAID2.0 database and TRRUST v2 database. TF-mRNA regulatory relationships were analyzed in the TRRUST V2 database. Hubgene targeting relationships were screened in the TargetScan, miRTarBase and miRDB databases. The SNV data of the hub genes were analyzed by using the R maftools package. A ROC curve was drawn based on the TCGA database. The proportion of immune cells was estimated using CIBERSORT and the LM22 feature matrix.

Results

The results showed that the matrix score was significantly correlated with colorectal cancer stage T. A total of 789 differentially expressed genes and 121 survival-related prognostic genes were identified. The PPI network showed that 22 core genes were related to the CRC prognosis. Furthermore, four ncRNAs that regulated the core prognosis genes, 11 TFs with regulatory effects on the core prognosis genes, and two drugs, quercetin and pseudoephedrine, that have regulatory effects on colorectal cancer were also identified.

Conclusions

We obtained a list of tumor microenvironment-related genes for CRC patients. These genes could be useful for determining the prognosis of CRC patients. To confirm the function of these genes, additional experiments are necessary.

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.

Placenta-specific protein 1 promotes cell proliferation via the AKT/GSK-3β/cyclin D1 signaling pathway in gastric cancer

Gastric cancer is a malignant tumor with a poor prognosis. Therefore, it is important to search for molecules that play a vital role in the development, diagnosis, and treatment of this disease. Placenta-specific 1 (PLAC1) is one of the cancer-testis antigens; it plays an important role in both placental development and tumorigenesis. However, the role of PLAC1 in gastric cancer has not been fully investigated, and its underlying mechanism needs further study. We first explored the expression and clinical relevance of PLAC1 in gastric cancer and performed gene set enrichment analysis of PLAC1-related genes using online databases. Subsequently, we studied the function and mechanism of PLAC1 in gastric cancer cells through in vitro experiments. Our results showed that PLAC1 is highly expressed in gastric cancer, is associated with poor prognosis, and can promote gastric cancer cell proliferation through the AKT/GSK-3β/cyclin D1 signaling pathway. Moreover, we discovered that AKTi attenuates the effect of PLAC1. Our study further revealed the role and mechanism of PLAC1 in gastric cancer and suggested that this antigen might be a useful molecular marker for gastric cancer diagnosis, prognosis, and treatment.

Placenta-specific protein 1 enhances liver metastatic potential and is associated with the PI3K/AKT/NF-κB signaling pathway in colorectal cancer

To better explore the underlying mechanism of liver metastatic formation by placenta-specific protein 1 (PLAC1) in human colorectal cancer, we investigated the proliferation, invasion and angiogenic capabilities of human colorectal cancer cells with different liver metastatic potentials as well as the mechanism of action of PLAC1 in the metastatic process. The expression of PLAC1 was detected by reverse transcriptase PCR, western blot, and real-time PCR. The effect of PLAC1 on metastatic potential was determined by proliferation, invasion, and angiogenesis assays, including an in-vitro coculture system consisting of cancer cells and vascular endothelial cells that were used to detect the relationship between cancer cells and angiogenesis. In addition, we also determined PLAC1 downstream targets that preferentially contribute to the metastatic process. PLAC1 was expressed in HT-29, WiDr, and CaCo-2 colorectal cancer cells but not in Colo320 colorectal cancer cells. PLAC1 not only enhanced significantly the proliferation of CoLo320 and human umbilical vein endothelial cells (HUVECs) but also promoted the invasion of CoLo320 cells. The angiogenesis of HUVECs was enhanced by PLAC1 in a dose-dependent manner. In cocultured systems, angiogenesis was significantly increased by coculture with HT-29 cells. In addition, PLAC1 could promote angiogenesis in coculture with HT-29 cells. Furthermore, PLAC1-enhanced metastatic potential of colorectal cancer cells was dependent on the activation of the PI3K/Akt/NF-κB pathway. The activation of PI3K/Akt/NF-κB signaling by PLAC1 may be critical for metastasis of colorectal cancer cells. According to our results, we suggest that modification of PLAC1 function might be a promising new therapeutic approach to inhibit the aggressive spread of colorectal cancer.

PLAC1 is essential for FGF7/FGFRIIIb-induced Akt-mediated cancer cell proliferation

PLAC1 (placenta enriched 1) is a mammalian trophoblast-specific protein. Aberrant expression of PLAC1 is observed in various human cancers, where it is involved in the motility, migration, and invasion of tumor cells, which are associated with the phosphoinositide 3-kinase (PI3K)/AKT pathway. We previously demonstrated that AKT activation mediates the downstream effects of PLAC1; however, the molecular mechanisms of PLAC1-induced AKT-mediated tumor-related processes are unclear. We studied human choriocarcinoma and breast cancer cell lines to explore the localization and receptor-ligand interactions, as well as the downstream effects of PLAC1. We show secretion and adherence of PLAC1 to the extracellular matrix, where it forms a trimeric complex with fibroblast growth factor 7 (FGF7) and its receptor, FGF receptor 2 IIIb (FGFR2IIIb). We further show that PLAC1 signaling via FGFR2IIIb activates AKT phosphorylation in cancer cell lines. As the FGF pathway is of major interest in anticancer therapeutic strategies, these data further promote PLAC1 as a promising anticancer drug target.

Involvement of the Endocrine-Disrupting Chemical Bisphenol A (BPA) in Human Placentation

Background: Endocrine-disrupting chemicals (EDCs) are environmental chemicals/toxicants that humans are exposed to, interfering with the action of multiple hormones. Bisphenol A (BPA) is classified as an EDC with xenoestrogenic activity with potentially adverse effects in reproduction. Currently, a significant knowledge gap remains regarding the complete spectrum of BPA-induced effects on the human placenta. As such, the present study examined the effects of physiologically relevant doses of BPA in vitro. Methods: qRT-PCR, Western blotting, immunofluorescence, ELISA, microarray analyses, and bioinformatics have been employed to study the effects of BPA using nonsyncytialised (non-ST) and syncytialised (ST) BeWo cells. Results: Treatment with 3 nM BPA led to an increase in cell number and altered the phosphorylation status of p38, an effect mediated primarily via the membrane-bound estrogen receptor (GPR30). Nonbiased microarray analysis identified 1195 and 477 genes that were differentially regulated in non-ST BeWo cells, whereas in ST BeWo cells, 309 and 158 genes had altered expression when treated with 3 and 10 nM, respectively. Enriched pathway analyses in non-ST BeWo identified a leptin and insulin overlap (3 nM), methylation pathways (10 nM), and differentiation of white and brown adipocytes (common). In the ST model, most significantly enriched were the nuclear factor erythroid 2-related factor 2 (NRF2) pathway (3 nM) and mir-124 predicted interactions with cell cycle and differentiation (10 nM). Conclusion: Collectively, our data offer a new insight regarding BPA effects at the placental level, and provide a potential link with metabolic changes that can have an impact on the developing fetus.

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.

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.

PLAC1-specific TCR-engineered T cells mediate antigen-specific antitumor effects in breast cancer

Placenta-specific 1 (PLAC1), a novel cancer-testis antigen (CTA), is expressed in a number of different human malignancies. It is frequently produced in breast cancer, serving a function in tumorigenesis. Adoptive immunotherapy using T cell receptor (TCR)-engineered T cells against CTA mediates objective tumor regression; however, to the best of our knowledge, targeting PLAC1 using engineered T cells has not yet been attempted. In the present study, the cDNAs encoding TCRα- and β-chains specific for human leukocyte antigen (HLA)-A*0201-restricted PLAC1 were cloned from a cytotoxic T-lymphocyte, generated by in vitro by the stimulation of CD8+ T cells using autologous HLA-A2+ dendritic cells loaded with a PLAC1-specific peptide (p28-36, VLCSIDWFM). The TCRα/β-chains were linked by a 2A peptide linker (TCRα-Thosea asigna virus-TCRβ), and the constructs were cloned into the lentiviral vector, followed by transduction into human cytotoxic (CD8+) T cells. The efficiency of transduction was up to 25.16%, as detected by PLAC1 multimers. TCR-transduced CD8+ T cells, co-cultured with human non-metastatic breast cancer MCF-7 cells (PLAC1+, HLA-A2+) and triple-negative breast cancer MDAMB-231 cells (PLAC1+, HLA-A2+), produced interferon γ and tumor necrosis factor α, suggesting TCR activation. Furthermore, the PLAC1 TCR-transduced CD8+ T cells efficiently and specifically identified and annihilated the HLA-A2+/PLAC1+ breast cancer cell lines in a lactate dehydrogenase activity assay. Western blot analysis demonstrated that TCR transduction stimulated the production of mitogen-activated protein kinase signaling molecules, extracellular signal-regulated kinases 1/2 and nuclear factor-κB, through phosphoinositide 3-kinase γ-mediated phosphorylation of protein kinase B in CD8+ T cells. Xenograft mouse assays revealed that PLAC1 TCR-transduced CD8+T cells significantly delayed the tumor progression in mice-bearing breast cancer compared with normal saline or negative control-transduced groups. In conclusion, a novel HLA-A2-restricted and PLAC1-specific TCR was identified. The present study demonstrated PLAC1 to be a potential target for breast cancer treatment; and the usage of PLAC1-specific TCR-engineered T cells may be a novel strategy for PLAC1-positive breast cancer treatment.

PLAC1 as a serum biomarker for breast cancer

Placental-specific protein 1 (PLAC1) is an X-linked trophoblast gene that is re-expressed in several malignancies, including breast cancer, and is therefore a potential biomarker to follow disease onset and progression. Sera from 117 preoperative/pretreatment breast cancer patients and 51 control subjects, including those with fibrocystic disease, were analyzed for the presence of PLAC1 protein as well as its expression by IHC in tumor biopsies in a subset of subjects. Serum PLAC1 levels exceeded the mean plus one standard deviation (mean+SD) of the level in control subjects in 67% of subjects with ductal carcinoma in situ (DCIS), 67% with HER2⁺ tumors, 73% with triple-negative cancer and 73% with ER⁺/PR⁺ tumors. Greater sensitivity was achieved using the mean+2 SD of control PLAC1 serum values, where the false positive rate was 3% and was exceeded by 38%, 40%, 60% and 43% of subjects with DCIS, HER2⁺, TNBC and ER⁺/PR⁺/HER2^- tumors. PLAC1 was detected in 97% of tumor biopsies, but did not correlate quantitatively with serum levels. There was no significant correlation of serum PLAC1 levels with race, age at diagnosis, body mass index (BMI) or the presence of metastatic disease. It remains to be determined whether PLAC1 serum levels can serve as a diagnostic biomarker for the presence or recurrence of disease post-surgery and/or therapy.

Placenta-specific protein 1 promotes cell proliferation and invasion in non-small cell lung cancer

Pulmonary carcinoma-associated proteins have emerged as crucial players in governing fundamental biological processes such as cell proliferation, apoptosis and metastasis in human cancers. Placenta-specific protein 1 (PLAC1) is a cancer-related protein, which is activated and upregulated in a variety of malignant tissues, including prostate cancer, gastric adenocarcinoma, colorectal, epithelial ovarian and breast cancer. However, its biological role and clinical significance in non-small cell lung cancer (NSCLC) development and progression are still unknown. In the present study, we found that PLAC1 was significantly upregulated in NSCLC tissues, and its expression level was associated with advanced pathological stage and it was also correlated with shorter progression-free survival of lung cancer patients. Furthermore, knockdown of PLAC1 expression by siRNA inhibited cell proliferation, induced apoptosis and impaired invasive ability in NSCLC cells partly via regulation of epithelial-mesenchymal transition (EMT)-related protein expression. Our findings present that increased PLAC1 could be identified as a negative prognostic biomarker in NSCLC and regulate cell proliferation and invasion. Thus, we conclusively demonstrated that PLAC1 plays a key role in NSCLC development and progression, which may provide novel insights on the function of tumor-related gene-driven tumorigenesis.

Chromatin Immunoprecipitation Assay to Identify Genomic Binding Sites of Regulatory Factors

DNA-protein interactions are vital to fundamental cellular events including transcription, replication, DNA repair, and recombination. Thus, their study holds the key to our understanding of mechanisms underlying normal development and homeostasis as well as disease. Transcriptional regulation is a highly complex process that involves recruitment of numerous factors resulting in formation of multi-protein complexes at gene promoters to regulate gene expression. The studied proteins can be, for example, transcription factors, epigenetic regulators, co-activators, co-repressors, or ligand-activated nuclear receptors as estrogen receptor-α (ERα) bound either directly to the DNA or indirectly by interaction with other DNA-bound factors. Chromatin immunoprecipitation (ChIP) assay is a powerful method to study interactions of proteins and a specific genomic DNA region. Recruitment of ERα to promoters of estrogen-dependent genes is a common mechanism to activate or enhance gene transcription in breast cancer thus promoting tumor progression. In this chapter, we demonstrate a stepwise protocol for ChIP assay using binding of ERα to its genomic targets after stimulation with 17β-estradiol (E2) in breast cancer cells as an example.

Glyco-genes change expression in cancer through aberrant methylation

BACKGROUND

Most eukaryotic proteins are modified by covalent addition of glycan molecules that considerably influence their function. Aberrant glycosylation is profoundly involved in malignant transformation, tumor progression and metastasis. Some glycan structures are tumor-specific and reflect disturbed glycan biosynthesis pathways.

METHODS

We analyzed DNA methylation and expression of 86 glyco-genes in melanoma, hepatocellular, breast and cervical cancers using data from publicly available databases. We also analyzed methylation datasets without the available matching expression data for glyco-genes in lung cancer, and progression of melanoma into lymph node and brain metastases.

RESULTS

Ten glyco-genes (GALNT3, GALNT6, GALNT7, GALNT14, MGAT3, MAN1A1, MAN1C1, ST3GAL2, ST6GAL1, ST8SIA3) showing changes in both methylation and expression in the same type of cancer belong to GalNAc transferases, GlcNAc transferases, mannosidases and sialyltransferases, which is in line with changes in glycan structures already reported in the same type of tumors. Some of those genes were additionally identified as potentially valuable for disease prognosis. The MGAT5B gene, so far identified as specifically expressed in brain, emerged as a novel candidate gene that is epigenetically dysregulated in different cancers other than brain cancer. We also report for the first time aberrant expression of the GALNT and MAN genes in cancer by aberrant promoter methylation.

CONCLUSIONS

Aberrant expression of glyco-genes due to aberrant promoter methylation could be a way leading to characteristic glycosylation profiles commonly described in cancer.

GENERAL SIGNIFICANCE

Methylation status in promoters of candidate glyco-genes might serve as prognostic markers for specific tumors and point to potential novel targets for epigenetic drugs. This article is part of a Special Issue entitled "Glycans in personalised medicine" Guest Editor: Professor Gordan Lauc.

C/EBPβ's role in determining Ras-induced senescence or transformation

Introduction of activated Ras into normal cells leads to senescence, a tumor suppressive mechanism, whereas expression of this oncogene in many immortalized cell lines leads to transformation. Studying the signaling differences in cells that undergo Ras-induced senescence versus Ras transformation may shed light on potential therapeutic targets in the treatment of cancer. C/EBPβ is a transcription factor necessary for both Ras-induced senescence and Ras transformation. Three isoforms of this transcription factor exist due to alternative translation initation at three in frame ATGs. C/EBPβ1 is the isoform responsible for oncogene-induced senescence, and this isoform is degraded by the proteosome during Ras transformation. Phosphorylation of C/EBPβ1 on Thr235 by Cdk2 is necessary, but not sufficient, for degradation of C/EBPβ1. Proteasomal degradation of C/EBPβ1 may represent a mechanism to evade senescence. In contrast, C/EBPβ2 is expressed in breast cancer cells and is involved in proliferation, supporting a role for this isoform in Ras transformation. We propose here that one potential signaling difference in Ras-induced senescence versus Ras transformation is that Ras signals through different C/EBPβ isoforms (C/EBPβ1 versus C/EBPβ2) during these processes.

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.

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.

MicroRNA-191, an estrogen-responsive microRNA, functions as an oncogenic regulator in human breast cancer

Estrogen- and microRNA-mediated gene regulation play a crucial role in breast cancer biology. However, a functional link between the two major players remains unclear. This study reveals miR-191 as an estrogen-inducible onco-miR in breast cancer, which promotes several hallmarks of cancer including enhanced cell proliferation, migration, chemoresistance and survival in tumor microenvironment. miR-191 is a direct estrogen receptor (ER) target and our results suggest existence of a positive regulatory feedback loop. We show miR-191 as critical mediator of estrogen-mediated cell proliferation. Investigations of mechanistic details of miR-191 functions identify several cancer-related genes like BDNF, CDK6 and SATB1 as miR-191 targets. miR-191 and SATB1 show inverse correlation of expression. miR-191-mediated enhanced cell proliferation and migration are partly dependent on targeted downregulation of SATB1. Further, functional validation of estrogen:miR-191:SATB1 link suggests a cascade initiated by estrogen that induces miR-191 in ER-dependent manner to target SATB1, a global chromatin remodeler, thereby contributing to estrogen-specific gene signature to regulate genes like ANXA1, PIWIL2, CASP4, ESR1/ESR2, PLAC1 and SOCS2 involved in breast cancer progression and migration. Overall, the identification of estrogen/ER/miR-191/SATB1 cascade seems to be a significant pathway in estrogen signaling in breast cancer with miR-191 as oncogenic player.

Circulating Anti-PLAC1 Antibodies during Pregnancy and in Women with Reproductive Failure: A Preliminary Analysis

The aims of this study were to determine the prevalence of anti-PLAC1 antibodies in normal pregnant women and in women with infertility or recurrent pregnancy loss (RPL). Secondary outcomes were the development of complications associated with anti-PLAC1 seropositivity and the rate of seroconversion during pregnancy. Sera from 103 healthy pregnant women and 45 women with unexplained infertility or RPL were analyzed by ELISA. The prevalence of anti-PLAC1 antibodies was 2% in healthy pregnant women and 4.5% in women with unexplained infertility or RPL (P=0.355). There was no detectable association of seropositivity with increased risk of pregnancy complications. Finally, 2% of women seroconverted during pregnancy. The prevalence of anti-PLAC1 antibodies in women with unexplained infertility or RPL is not significantly higher than the prevalence in normal pregnant women. However, the sample size in this study was too small. The exposure to the PLAC1 antigen during pregnancy can lead to the spontaneous development of antibodies.

Negative regulation of C/EBPbeta1 by sumoylation in breast cancer cells

Sumoylation is a post-translational modification that is oftentimes deregulated in diseases such as cancer. Transcription factors are frequent targets of sumoylation and modification by SUMO can affect subcellular localization, transcriptional activity, and stability of the target protein. C/EBPbeta1 is one such transcription factor that is modified by SUMO-2/3. Non-sumoylated C/EBPbeta1, p52-C/EBPbeta1, is expressed in normal mammary epithelial cells but not breast cancer cell lines and plays a role in oncogene-induced senescence, a tumor suppressive mechanism. Although p52-C/EBPbeta1 is not observed via immunoblot in breast cancer cell lines, higher molecular weight bands are observed when breast cancer cell lines are subjected to immunoblot analysis with a C/EBPbeta1-specific antibody. We show that exogenously expressed C/EBPbeta1 is sumoylated in breast cancer cells, and that the higher molecular weight bands we observe in anti-C/EBPbeta1 immunoblots of breast cancer cell lines is sumoylated C/EBPbeta1. Phosphorylation oftentimes enhances sumoylation, and phosphorylation cascades are activated in breast cancer cells. We demonstrate that phosphorylation of C/EBPbeta1Thr235 by Erk-2 enhances sumoylation of C/EBPbeta1 in vitro. In addition, sumoylated C/EBPbeta1 is phosphorylated on Thr235 and mutation of Thr235 to alanine leads to a decrease in sumoylation of C/EBPbeta1. Finally, using a C/EBPbeta1-SUMO fusion protein we show that constitutive sumoylation of C/EBPbeta1 completely blocks its capability to induce senescence in WI38 fibroblasts expressing hTERT. Thus, sumolylation of C/EBPbeta1 in breast cancer cells may be a mechanism to circumvent oncogene-induced senescence.

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

PLAC1 expression, first characterized as restricted to developing placenta among normal tissues, is also found in a wide range of tumors and transformed cell lines. To understand the basis for its unusual expression profile, we have analyzed the gene structure and its mode of transcription. We find that the gene has a hitherto unique feature, with two promoters, P1 and P2, separated by 105 kb. P2 has been described before. Here we define P1 and show that it and P2 are activated by RXRα in conjunction with LXRα or LXRβ. In placenta, P2 is the preferred promoter, whereas various tumor cell lines tend to express predominantly either one or the other promoter. Furthermore, when each promoter is fused to a luciferase reporter gene and transfected into cancer cell lines, the promoter corresponding to the more active endogenous promoter is preferentially transcribed. Joint expression of activating nuclear receptors can partially account for the restricted expression of PLAC1 in placenta, and may be co-opted for preferential P1 or P2 PLAC1 expression in various tumor cells.

Progesterone induces expression of the prolactin receptor gene through cooperative action of Sp1 and C/EBP

Prolactin (Prl) and progesterone (P) cooperate synergistically during mammary gland development and tumorigenesis. We hypothesized that one mechanism for these effects may be through mutual induction of receptors (R). EpH4 mouse mammary epithelial cells stably transfected with PR-A express elevated levels of PrlR mRNA and protein compared to control EpH4 cells that lack the PR. Likewise, T47D human breast cancer cells treated with P overexpress the PrlR and activate PrlR promoter III. PrlR promoter III does not contain a classical P response element but contains several binding sites for transcription proteins, including C/EBP, Sp1 and AP1, which may also interact with the PR. Using promoter deletion and site directed mutagenesis analyses as well as gel shift assays, cooperative activation of the C/EBP and adjacent Sp1A, but not the Sp1B or AP1, sites by P is shown to confer P responsiveness leading to increased PrlR transcription.

Regulation of C/EBPbeta1 by Ras in mammary epithelial cells and the role of C/EBPbeta1 in oncogene-induced senescence

Overexpression of Ras(V12) in MCF10A cells, an immortalized mammary epithelial cell line, leads to transformation of these cells. We demonstrate that this is accompanied by degradation of C/EBPbeta1. C/EBPbeta is a transcription factor in which three protein isoforms exist due to alternative translation at three in-frame methionines. When C/EBPbeta1 is expressed in MCF10A-Ras(V12) cells, immunoblot analysis reveals that C/EBPbeta1 is degraded in these cells. Treatment of the MCF10A-Ras(V12)-C/EBPbeta1 cells with the cdk inhibitor roscovitine leads to stabilization of C/EBPbeta1. It has been previously shown that cdk2 phosphorylates C/EBPbeta on Thr235. We demonstrate that mutation of Thr235 to alanine in C/EBPbeta1 is sufficient to restore the stability of C/EBPbeta1 expression in the MCF10A-Ras(V12) cells.

Overexpression of Ras(V12) in primary cells induces senescence rather than transformation, thus suppressing tumorigenesis. C/EBPbeta is required for Ras(V12)-induced senescence in primary mouse embryonic fibroblasts (MEFs). Upregulation of IL6 by C/EBPbeta has been shown to be necessary for oncogene-induced senescence, but the specific isoform of C/EBPbeta has not been investigated. We show that the C/EBPbeta1 isoform upregulates IL6 when introduced into normal fibroblasts. Additionally, we show that C/EBPbeta1 induces senescence. Taken together, degradation of C/EBPbeta1 by Ras activation may represent a mechanism to bypass OIS.

PLAC1 (Placenta-specific 1): a novel, X-linked gene with roles in reproductive and cancer biology

Placenta-specific 1 (PLAC1) is a recently described X-linked gene with expression restricted primarily to cells derived from trophoblast lineage during embryonic development. PLAC1 localizes to a region of the X chromosome thought to be important in placental development although its role in this process has not been defined. This review summarizes our current understanding of its expression, regulation, and function. PLAC1 is expressed throughout human pregnancy by the differentiated trophoblast and localizes to membranous structures in the syncytiotrophoblast, including the microvillous plasma membrane surface. Recent studies have demonstrated that PLAC1 is also expressed by a wide variety of human cancers. Studies of the PLAC1 promoter regions indicate that its expression in both normal placenta and cancer cells is driven by specific interactions involving a combination of transcription factors. Although functional insight into PLAC1 in the normal trophoblast is lacking, preliminary studies suggest that cancer-derived PLAC1 has the potential to promote tumor growth and function. In addition, it also appears to elicit a specific immunologic response that may influence survival in some cancer patients, suggesting that it may provide a therapeutic target for the treatment of some cancers. We also discuss a potential role for PLAC1 as a biomarker predictive of specific pregnancy complications, such as preeclampsia.