Interaction of TFAP2C with the estrogen receptor-alpha promoter is controlled by chromatin structure

Structural basis for specific DNA sequence motif recognition by the TFAP2 transcription factors

The TFAP2 family regulates gene expression during differentiation, development, and organogenesis, and includes five homologs in humans. They all possess a highly conserved DNA binding domain (DBD) followed by a helix-span-helix (HSH) domain. The DBD-HSH tandem domain specifically binds to a GCC(N3)GGC consensus sequence, but the precise recognition mechanisms remain unclear. Here, we found that TFAP2 preferred binding to the GCC(N3)GGC sequence, and the pseudo-palindromic GCC and GGC motifs and the length of the central spacer between the two motifs determined their binding specificity. Structural studies revealed that the two flat amphipathic α-helical HSH domains of TFAP2A stacked with each other to form a dimer via hydrophobic interactions, while the stabilized loops from both DBD domains inserted into two neighboring major grooves of the DNA duplex to form base-specific interactions. This specific DNA binding mechanism controlled the length of the central spacer and determined the DNA sequence specificity of TFAP2. Mutations of the TFAP2 proteins are implicated in various diseases. We illustrated that reduction or disruption of the DNA binding ability of the TFAP2 proteins is the primary cause of TFAP2 mutation-associated diseases. Thus, our findings also offer valuable insights into the pathogenesis of disease-associated mutations in TFAP2 proteins.

Crucial role of the transcription factors family activator protein 2 in cancer: current clue and views

The transcription factor family activator protein 2 (TFAP2) is vital for regulating both embryonic and oncogenic development. The TFAP2 family consists of five DNA-binding proteins, including TFAP2A, TFAP2B, TFAP2C, TFAP2D and TFAP2E. The importance of TFAP2 in tumor biology is becoming more widely recognized. While TFAP2D is not well studied, here, we mainly focus on the other four TFAP2 members. As a transcription factor, TFAP2 regulates the downstream targets directly by binding to their regulatory region. In addition, the regulation of downstream targets by epigenetic modification, posttranslational regulation, and interaction with noncoding RNA have also been identified. According to the pathways in which the downstream targets are involved in, the regulatory effects of TFAP2 on tumorigenesis are generally summarized as follows: stemness and EMT, interaction between TFAP2 and tumor microenvironment, cell cycle and DNA damage repair, ER- and ERBB2-related signaling pathway, ferroptosis and therapeutic response. Moreover, the factors that affect TFAP2 expression in oncogenesis are also summarized. Here, we review and discuss the most recent studies on TFAP2 and its effects on carcinogenesis and regulatory mechanisms.

Roles of activator protein-2 gamma in breast cancer: A narrative review (SANRA)

Activator protein-2 gamma (AP-2γ) is a crucial transcription factor involved in breast cancer development. Abnormal expression and activity of AP-2γ have also been identified as important markers of malignancy. In the last decade, the importance of AP-2γ in breast cancer progression has been widely studied. In this review, we summarize the current knowledge on the regulatory roles of AP-2γ in breast cancer oncogenesis and progression and its potential as a diagnostic biomarker and drug target in breast cancer treatment.

To Be or Not to Be a Germ Cell: The Extragonadal Germ Cell Tumor Paradigm

In the human embryo, the genetic program that orchestrates germ cell specification involves the activation of epigenetic and transcriptional mechanisms that make the germline a unique cell population continuously poised between germness and pluripotency. Germ cell tumors, neoplasias originating from fetal or neonatal germ cells, maintain such dichotomy and can adopt either pluripotent features (embryonal carcinomas) or germness features (seminomas) with a wide range of phenotypes in between these histotypes. Here, we review the basic concepts of cell specification, migration and gonadal colonization of human primordial germ cells (hPGCs) highlighting the analogies of transcriptional/epigenetic programs between these two cell types.

Interaction of transcription factor AP-2 gamma with proto-oncogene PELP1 promotes tumorigenesis by enhancing RET signaling

A significant proportion of estrogen receptor-positive (ER+) breast cancer (BC) initially responds to endocrine therapy but eventually evolves into therapy-resistant BC. Transcription factor AP-2 gamma (TFAP2C) is a known regulator of ER activity, and high expression of TFAP2C is associated with a decreased response to endocrine therapies. PELP1 is a nuclear receptor coregulator, commonly overexpressed in BC, and its levels are correlated with poorer survival. In this study, we identified PELP1 as a novel interacting protein of TFAP2C. RNA-seq analysis of PELP1 knockdown BC cells followed by transcription factor motif prediction pointed to TFAP2C being enriched in PELP1-regulated genes. Gene set enrichment analysis (GSEA) revealed that the TFAP2C-PELP1 axis induced a subset of common genes. Reporter gene assays confirmed PELP1 functions as a coactivator of TFAP2C. Mechanistic studies showed that PELP1-mediated changes in histone methylation contributed to increased expression of the TFAP2C target gene RET. Furthermore, the TFAP2C-PELP1 axis promoted the activation of the RET signaling pathway, which contributed to downstream activation of AKT and ERK pathways in ER+ BC cells. Concomitantly, knockdown of PELP1 attenuated these effects mediated by TFAP2C. Overexpression of TFAP2C contributed to increased cell proliferation and therapy resistance in ER+ BC models, while knockdown of PELP1 mitigated these effects. Utilizing ZR75-TFAP2C xenografts with or without PELP1 knockdown, we provided genetic evidence that endogenous PELP1 is essential for TFAP2C-driven BC progression in vivo. Collectively, our studies demonstrated that PELP1 plays a critical role in TFAP2C transcriptional and tumorigenic functions in BC and blocking the PELP1-TFAP2C axis could have utility for treating therapy resistance.

Upregulation of the transcription factor TFAP2D is associated with aggressive tumor phenotype in prostate cancer lacking the TMPRSS2:ERG fusion

Background

TFAP2D is a transcription factor important for modulating gene expression in embryogenesis. Its expression and prognostic role in prostate cancer has not been evaluated.

Methods

Therefore, a tissue microarray containing 17,747 prostate cancer specimens with associated pathological, clinical, and molecular data was analyzed by immunohistochemistry to assess the role of TFAP2D.

Results

TFAP2D expression was typically increased in prostate cancer as compared to adjacent non-neoplastic glands. TFAP2D staining was considered negative in 24.3% and positive in 75.7% of 13,545 interpretable cancers. TFAP2D staining was significantly linked to advanced tumor stage, high classical and quantitative Gleason grade, lymph node metastasis, and a positive surgical margin (p ≤ 0.0045). TFAP2D positivity was more common in ERG fusion positive (88.7%) than in ERG negative cancers (66.8%; p < 0.0001). Subset analyses in 3776 cancers with and 4722 cancers without TMPRSS2:ERG fusion revealed that associations with tumor phenotype and patient outcome were largely driven by the subset of ERG negative tumors. Multivariate analysis did not identify TFAP2D protein expression levels as a robust independent prognostic parameter. Positive TFAP2D immunostaining was significantly associated with 10 of 11 previously analyzed chromosomal deletions in ERG negative cancers (p ≤ 0.0244 each) indicating that elevated TFAP2D expression parallels genomic instability in prostate cancer.

Conclusion

These data demonstrate that TFAP2D protein overexpression is linked to prostate cancer progression and genomic instability in ERG negative prostate cancers.

Histone methyltransferases regulate the transcriptional expression of ERα and the proliferation of tamoxifen-resistant breast cancer cells

Purpose

Although tamoxifen remains the frontline treatment for ERα-positive breast cancers, resistance to this drug limits its clinical efficacy. Most tamoxifen-resistant patients retain ERα expression which may support growth and progression of breast cancers. Therefore, we investigated epigenetic regulation of ERα that may provide a rationale for targeting ERα in these patients.

Methods

Expression levels of the mixed-lineage leukemia (MLL) family of proteins in tamoxifen-resistant breast cancer cells and publicly available breast cancer patient data sets were analyzed. Histone methylation levels in ERα promoter regions were assessed using chromatin immunoprecipitation. Expression levels of ERα and its target gene were analyzed using western blotting and real-time qPCR. Cell-cycle was analyzed by flow cytometry.

Results

The expression of MLL3 and SET-domain-containing 1A (SET1A) were increased in tamoxifen-resistant breast cancers. An MLL3 chromatin immunoprecipitation-sequencing data analysis and chromatin immunoprecipitation experiments for MLL3 and SET1A suggested that these proteins bound to enhancer or intron regions of the ESR1 gene and regulated histone H3K4 methylation status. Depletion of MLL3 or SET1A downregulated the expression level of ERα and inhibited the growth of tamoxifen-resistant breast cancer cells. Additional treatment with fulvestrant resulted in a synergistic reduction of ERα levels and the growth of the cells.

Conclusions

The enhanced expression of MLL3 and SET1A in tamoxifen-resistant breast cancer cells supported the ERα-dependent growth of these cells by increasing ERα expression. Our results suggest that targeting these histone methyltransferases might provide an attractive strategy to overcome endocrine resistance.

Electronic supplementary material

The online version of this article (10.1007/s10549-019-05517-0) contains supplementary material, which is available to authorized users.

TFAP2C regulates carbonic anhydrase XII in human breast cancer

The expression of carbonic anhydrase XII (CA12) is associated with the expression of estrogen receptor alpha (ERα) in breast cancer and is linked to a good prognosis with a lower risk of metastasis. Transcription Factor Activator Protein 2γ (TFAP2C, AP-2γ) governs luminal breast cancer phenotype through direct and indirect regulation of ERα and ERα-associated genes, GATA3, FOXA1, EGFR, CDH1, DSP, KRT7, FBP1, MYB, RET, KRT8, MUC1, and ERBB2-genes which are responsible for the luminal signature in breast cancer. Herein, utilizing chromatin immunoprecipitation and direct sequencing (ChIP-seq), we show that CA12 is regulated by AP-2γ through binding with its promoter region in luminal breast cancer cell lines and indirectly through a distal estrogen-responsive region in ERα-positive cell lines by upregulation of ERα. CA12 is transcriptionally silenced in basal breast cancer cell lines through histone deacetylation and CpG methylation of the promoter region and can be re-activated with Trichostatin A (histone deacetylase inhibitor) and/or 5-aza-dC (an inhibitor of DNA methylation). Strong concordance in co-expression of CA12 and ESR1 (R² = 0.1128, p = 0486) and TFAP2C (R² = 0.1823, p = 0.0105) was found using a panel of primary breast tumor samples (n = 35), supporting a synergetic role of AP-2γ and ERα in activation of CA12. Our results highlight the essential role of AP-2γ in maintaining the luminal breast cancer phenotype and provide evidence that epigenetic mechanisms silence luminal gene expression in the basal phenotype. Additional studies to decipher mechanisms that drive epigenetic silencing of AP-2γ target genes are a critical area for further research.

Uncovering pseudotemporal trajectories with covariates from single cell and bulk expression data

Pseudotime algorithms can be employed to extract latent temporal information from cross-sectional data sets allowing dynamic biological processes to be studied in situations where the collection of time series data is challenging or prohibitive. Computational techniques have arisen from single-cell ‘omics and cancer modelling where pseudotime can be used to learn about cellular differentiation or tumour progression. However, methods to date typically implicitly assume homogeneous genetic, phenotypic or environmental backgrounds, which becomes limiting as data sets grow in size and complexity. We describe a novel statistical framework that learns how pseudotime trajectories can be modulated through covariates that encode such factors. We apply this model to both single-cell and bulk gene expression data sets and show that the approach can recover known and novel covariate-pseudotime interaction effects. This hybrid regression-latent variable model framework extends pseudotemporal modelling from its most prevalent area of single cell genomics to wider applications.

Cross-sectional omic data often have non-homogeneous genetic, phenotypic, or environmental backgrounds. Here, the authors develop a statistical framework to infer pseudotime trajectories in the presence of such factors as well as their interactions in both single-cell and bulk gene expression analysis

Identification of a Wells-Dawson polyoxometalate-based AP-2γ inhibitor with pro-apoptotic activity

AP-2 gamma (AP-2γ) is a transcription factor that plays pivotal roles in breast cancer biology. To search for small molecule inhibitors of AP-2γ, we performed a high-throughput fluorescence anisotropy screen and identified a polyoxometalate compound with Wells-Dawson structure K₆[P₂Mo₁₈O₆₂] (Dawson-POM) that blocks the DNA-binding activity of AP-2γ. We showed that this blocking activity is due to the direct binding of Dawson-POM to AP-2γ. We also provided evidence to show that Dawson-POM decreases AP-2γ-dependent transcription similar to silencing the gene. Finally, we demonstrated that Dawson-POM contains anti-proliferative and pro-apoptotic effects in breast cancer cells. In summary, we identified the first small molecule inhibitor of AP-2γ and showed Dawson-POM-mediated inhibition of AP-2γ as a potential avenue for cancer therapy.

A novel HER2 gene body enhancer contributes to HER2 expression

The transcriptional regulation of the human epidermal growth factor receptor-2 (HER2) contributes to an enhanced HER2 expression in HER2-positive breast cancers with HER2 gene amplification and HER2-low or HER2-negative breast cancers following radiotherapy or endocrine therapy, and this drives tumorigenesis and the resistance to therapy. Epigenetic mechanisms are critical for transcription regulation, however, such mechanisms in the transcription regulation of HER2 are limited to the involvement of tri-methylated histone 3 lysine 4 (H3K4me3) and acetylated histone 3 lysine 9 (H3K9ac) at the HER2 promoter region. Here, we report the identification of a novel enhancer in the HER2 3’ gene body, which we have termed HER2 gene body enhancer (HGE). The HGE starts from the 3’ end of intron 19 and extends into intron 22, possesses enhancer histone modification marks in specific cells and enhances the transcriptional activity of the HER2 promoters. We also found that TFAP2C, a known regulator of HER2, binds to HGE and is required for its enhancer function and that DNA methylation in the HGE region inhibits the histone modifications characterizing enhancer and is inversely correlated with HER2 expression in breast cancer samples. The identification of this novel enhancer sheds a light on the roles of epigenetic mechanisms in HER2 transcription, in both HER2-positive breast cancer samples and individuals with HER2-low or HER2-negative breast cancers undergoing radiotherapy or endocrine therapy.

REGγ regulates ERα degradation via ubiquitin-proteasome pathway in breast cancer

REGγ is a proteasome coactivator which regulates proteolytic activity in eukaryotic cells. Abundant lines of evidence have showed that REGγ is over expressed in a number of human carcinomas. However, its precise role in the pathogenesis of cancer is still unclear. In this study, by examining 200 human breast cancer specimens, we demonstrated that REGγ was highly expressed in breast cancers, and the expression of REGγ was positively correlated with breast cancer patient estrogen receptor alpha (ERα) status. Moreover, the expression of REGγ was found positively associated with poor clinical features and low survival rates in ERα positive breast cancer patients. Further cell culture studies using MCF7 and BT474 breast cancer cell lines showed that cell proliferation, motility, and invasion capacities were decreased significantly by REGγ knockdown. Lastly, we demonstrated that REGγ indirectly regulates the degradation of ERα protein via ubiquitin-proteasome pathway. In conclusion, our findings provide the evidence that REGγ expression was positively correlated with ERα status and poor clinical prognosis in ERα positive breast cancer patients. As well, we disclose a new connection between the two molecules that are both highly expressed in most breast cancer cases.

The many faces of estrogen signaling

Estrogens have long been known as important regulators of the female reproductive functions; however, our understanding of the role estrogens play in the human body has changed significantly over the past years. It is now commonly accepted that estrogens and androgens have important functions in both female and male physiology and pathology. This is in part due to the local synthesis and action of estrogens that broadens the role of estrogen signaling beyond that of the endocrine system. Furthermore, there are several different mechanisms through which the three estrogen receptors (ERs), ERα, ERβ and G protein-coupled estrogen receptor 1 (GPER1) are able to regulate target gene transcription. ERα and ERβ are mostly associated with the direct and indirect genomic signaling pathways that result in target gene expression. Membrane-bound GPER1 is on the other hand responsible for the rapid non-genomic actions of estrogens that activate various protein-kinase cascades. Estrogen signaling is also tightly connected with another important regulatory entity, i.e. epigenetic mechanisms. Posttranslational histone modifications, microRNAs (miRNAs) and DNA methylation have been shown to influence gene expression of ERs as well as being regulated by estrogen signaling. Moreover, several coregulators of estrogen signaling also exhibit chromatin-modifying activities further underlining the importance of epigenetic mechanisms in estrogen signaling. This review wishes to highlight the newer aspects of estrogen signaling that exceed its classical endocrine regulatory role, especially emphasizing its tight intertwinement with epigenetic mechanisms.

Differential regulation of estrogen receptor α expression in breast cancer cells by metastasis-associated protein 1

Metastasis-associated protein 1 (MTA1) is a component of the nucleosome remodeling and histone deacetylase (HDAC) complex, which plays an important role in progression of breast cancer. Although MTA1 is known as a repressor of the transactivation function of estrogen receptor α (ERα), its involvement in the epigenetic control of transcription of the ERα gene ESR1 has not been studied. Here, we show that silencing of MTA1 reduced the level of expression of ERα in ERα-positive cells but increased it in ERα-negative cells. In both MCF7 and MDA-MB-231, MTA1 was recruited to the region +146 to +461 bp downstream of the transcription start site of ESR1 (ERpro315). Proteomics analysis of the MTA1 complex that was pulled down by an oligonucleotide encoding ERpro315 revealed that the transcription factor AP-2γ (TFAP2C) and the IFN-γ-inducible protein 16 (IFI16) were components of the complex. Interestingly, in MCF7, TFAP2C activated the reporter encoding ERpro315 and the level of ERα mRNA. By contrast, in MDA-MB-231, IFI16 repressed the promoter activity and silencing of MTA1 increased expression of ERα. Importantly, class II HDACs are involved in the MTA1-mediated differential regulation of ERα. Finally, an MDA-MB-231-derived cell line that stably expressed shIFI16 or shMTA1 was more susceptible to tamoxifen-induced growth inhibition in in vitro and in vivo experiments. Taken together, our findings suggest that the MTA1-TFAP2C or the MTA1-IFI16 complex may contribute to the epigenetic regulation of ESR1 expression in breast cancer and may determine the chemosensitivity of tumors to tamoxifen therapy in patients with breast cancer.

The proteasome inhibitor bortezomib induces an inhibitory chromatin environment at a distal enhancer of the estrogen receptor-α gene

Expression of the estrogen receptor-α (ERα) gene, ESR1, is a clinical biomarker used to predict therapeutic outcome of breast cancer. Hence, there is significant interest in understanding the mechanisms regulating ESR1 gene expression. Proteasome activity is increased in cancer and we previously showed that proteasome inhibition leads to loss of ESR1 gene expression in breast cancer cells. Expression of ESR1 mRNA in breast cancer cells is controlled predominantly through a proximal promoter within ∼400 base pair (bp) of the transcription start site (TSS). Here, we show that loss of ESR1 gene expression induced by the proteasome inhibitor bortezomib is associated with inactivation of a distal enhancer located 150 kilobases (kb) from the TSS. Chromatin immunoprecipitation assays reveal several bortezomib-induced changes at the distal site including decreased occupancy of three critical transcription factors, GATA3, FOXA1, and AP2γ. Bortezomib treatment also resulted in decreased histone H3 and H4 acetylation and decreased occupancy of histone acetyltransferase, p300. These data suggest a mechanism to explain proteasome inhibitor-induced loss of ESR1 mRNA expression that highlights the importance of the chromatin environment at the −150 kb distal enhancer in regulation of basal expression of ESR1 in breast cancer cells.

Human Melanoma cells over-express extracellular matrix 1 (ECM1) which is regulated by TFAP2C

Extracellular matrix 1 (ECM1) is over-expressed in multiple epithelial malignancies. However, knowledge regarding the expression of ECM1 in melanomas and the mechanisms of ECM1 regulation is limited. In this study, we found that ECM1 is over-expressed in several melanoma cell lines, when compared to primary melanocytes, and furthermore, that ECM1 expression paralleled that of TFAP2C levels in multiple cell lines. Knockdown of TFAP2C in the A375 cell line with siRNA led to a reduction in ECM1 expression, and upregulation of TFAP2C with adenoviral vectors in the WM793 cell line resulted in ECM1 upregulation. Utilizing 5’ RACE to identify transcription start sites (TSS) and luciferase reporter assays in the ECM1-overexpressing A375 cell line, we identified the minimal promoter region of human ECM1 and demonstrate that an approximately 100bp fragment upstream of the TSS containing a TATA box and binding sites for AP1, SP1 and Ets is sufficient for promoter activity. Chromatin immunoprecipitation and direct sequencing (ChIP-seq) for TFAP2C in the A375 cell line identified an AP2 regulatory region in the promoter of the ECM1 gene. Gelshift assays further confirmed binding of TFAP2C to this site. ECM1 knockdown reduces melanoma cell attachment and is consistent with findings that ECM1 overexpression has been associated with a poor prognosis. Our investigations show an as yet unrecognized role for TFAP2C in melanoma via its regulation of ECM1.

High TFAP2C/low CD44 expression is associated with an increased rate of pathologic complete response following neoadjuvant chemotherapy in breast cancer

BACKGROUND

In luminal breast cancer cell lines, TFAP2C regulates expression of key genes in the estrogen receptor-associated cluster and represses basal-associated genes including CD44. We examined the effect of TFAP2C overexpression in a basal cell line and characterized the expression of TFAP2C and CD44 in breast cancer specimens to determine if expression was associated with clinical response.

METHODS

MDA-MB-231 breast cancer cells were treated with a TFAP2C-containing plasmid and evaluated for effects on CD44 expression. Pretreatment biopsy cores from patients receiving neoadjuvant chemotherapy for breast cancer were evaluated for TFAP2A, p53, TFAP2C, and CD44 expression by immunohistochemistry.

RESULTS

Overexpression of TFAP2C in MDA-MB-231 cells resulted in decreased expression of CD44 mRNA and protein, P < 0.05. A pathologic complete response (pCR) following neoadjuvant chemotherapy was achieved in 17% of patients (4/23). Average expression for TFAP2C by immunohistochemistry in patients with a pCR was 93%, compared with 46% in patients with residual disease, P = 0.016; and in tumors that stained at ≥80% for TFAP2C, 4 of 9 (44%) achieved pCR, compared with 0 of 14 below 80%, P = 0.01. Additionally, in tumors that stained ≤80% for CD44, 4 of 10 (40%) achieved pCR, compared with 0 of 13 >80%, P = 0.02. In tumors that stained high for TFAP2C (≥80%) and low for CD44 (≤80%), 4 of 7 (57%) achieved pCR, compared with 0 of 16 in all other groups (P = 0.004).

CONCLUSIONS

TFAP2C repressed CD44 expression in basal-derived breast cancer. In primary breast cancer specimens, high TFAP2C and low CD44 expression were associated with pCR after neoadjuvant chemotherapy and could be predictive of tumors that have improved response to neoadjuvant chemotherapy.

Epigenetic regulation of estrogen signaling in breast cancer

Estrogen signaling is mediated by ERα and ERβ in hormone dependent, breast cancer (BC). Over the last decade the implication of epigenetic pathways in BC tumorigenesis has emerged: cancer-related epigenetic modifications are implicated in both gene expression regulation, and chromosomal instability. In this review, the epigenetic-mediated estrogen signaling, controlling both ER level and ER-targeted gene expression in BC, are discussed: (1) ER silencing is frequently observed in BC and is often associated with epigenetic regulations while chemical epigenetic modulators restore ER expression and increase response to treatment;(2) ER-targeted gene expression is tightly regulated by co-recruitment of ER and both coactivators/corepressors including HATs, HDACs, HMTs, Dnmts and Polycomb proteins.

Transcriptional regulation of the GPX1 gene by TFAP2C and aberrant CpG methylation in human breast cancer

The complexity of gene regulation has created obstacles to defining mechanisms that establish the patterns of gene expression characteristic of the different clinical phenotypes of breast cancer. TFAP2C is a transcription factor that has a critical role in the regulation of both estrogen receptor-alpha (ERα) and c-ErbB2/HER2 (Her2). Herein, we performed chromatin immunoprecipitation and direct sequencing (ChIP-seq) for TFAP2C in four breast cancer cell lines. Comparing the genomic binding sites for TFAP2C, we identified that glutathione peroxidase (GPX1) is regulated by TFAP2C through an AP-2 regulatory region in the promoter of the GPX1 gene. Knockdown of TFAP2C, but not the related factor TFAP2A, resulted in an abrogation of GPX1 expression. Selenium-dependent GPX activity correlated with endogenous GPX1 expression and overexpression of exogenous GPX1 induced GPX activity and significantly increased resistance to tert-butyl hydroperoxide. Methylation of the CpG island encompassing the AP-2 regulatory region was identified in cell lines where TFAP2C failed to bind the GPX1 promoter and GPX1 expression was unresponsive to TFAP2C. Furthermore, in cell lines where GPX1 promoter methylation was associated with gene silencing, treatment with 5'-aza-2-deoxycytidine (5'-aza-dC) (an inhibitor of DNA methylation) allowed TFAP2C to bind to the GPX1 promoter resulting in the activation of GPX1 RNA and protein expression. Methylation of the GPX1 promoter was identified in ∼20% of primary breast cancers and a highly significant correlation between the TFAP2C and GPX1 expression was confirmed when considering only those tumors with an unmethylated promoter, whereas the related factor, TFAP2A, failed to demonstrate a correlation. The results demonstrate that TFAP2C regulates the expression of GPX1, which influences the redox state and sensitivity to oxidative stress induced by peroxides. Given the established role of GPX1 in breast cancer, the results provide an important mechanism for TFAP2C to further influence oncogenesis and progression of breast carcinoma cells.

Expression of the RET proto-oncogene is regulated by TFAP2C in breast cancer independent of the estrogen receptor

BACKGROUND

The RET proto-oncogene is expressed as part of the estrogen receptor (ER) cluster in breast cancer. We sought to determine if TFAP2C regulates Ret expression directly or indirectly through ER.

METHODS

Chromatin immunoprecipitation sequencing (ChIP-Seq) and gel-shift assay were used to identify TFAP2C binding sites in the RET promoter in four breast cancer cell lines. Ret mRNA and protein levels were evaluated in ER-positive and ER-negative breast cancer cell lines after knockdown of TFAP2C. Luciferase expression assay was performed to assess expression from two of the identified sites.

RESULTS

ChIP-Seq identified five main binding peaks for TFAP2C in the RET promoter at -101.5 kb, -50.7 kb, -32.5 kb, +5.0 kb, and +33.6 from the RET transcriptional start site. Binding at three of the AP-2 sites was conserved across all four cell lines, whereas the RET -101.5 and RET +33.6 sites were each found to be unbound by TFAP2C in one cell line. A TFAP2C consensus element was confirmed for all five sites. Knockdown of TFAP2C by siRNA in ER-positive MCF-7 cells resulted in significant down regulation of Ret mRNA compared to nontargeting (NT) siRNA (0.09 vs. 1.0, P < 0.001). Knockdown of TFAP2C in ER-negative MDA-MB-453 cells also led to a significant reduction in Ret mRNA compared to NT siRNA (0.16 vs. 1.0, P < 0.001). In MCF-7 cells, knockdown of TFAP2C abrogated Ret protein expression (0.02 vs. 1.0, P < 0.001) before reduction in ER.

CONCLUSIONS

TFAP2C regulates expression of the RET proto-oncogene through five AP-2 regulatory sites in the RET promoter. Regulation of Ret by TFAP2C occurs independently of ER expression in breast carcinoma.

Crosstalk between integrin αvβ3 and estrogen receptor-α is involved in thyroid hormone-induced proliferation in human lung carcinoma cells

A cell surface receptor for thyroid hormone that activates extracellular regulated kinase (ERK) 1/2 has been identified on integrin αvβ3. We have examined the actions of thyroid hormone initiated at the integrin on human NCI-H522 non-small cell lung carcinoma and NCI-H510A small cell lung cancer cells. At a physiologic total hormone concentration (10(-7) M), T(4) significantly increased proliferating cell nuclear antigen (PCNA) abundance in these cell lines, as did 3, 5, 3'-triiodo-L-thyronine (T(3)) at a supraphysiologic concentration. Neutralizing antibody to integrin αvβ3 and an integrin-binding Arg-Gly-Asp (RGD) peptide blocked thyroid hormone-induced PCNA expression. Tetraiodothyroacetic acid (tetrac) lacks thyroid hormone function but inhibits binding of T(4) and T(3) to the integrin receptor; tetrac eliminated thyroid hormone-induced lung cancer cell proliferation and ERK1/2 activation. In these estrogen receptor-α (ERα)-positive lung cancer cells, thyroid hormone (T(4)>T(3)) caused phosphorylation of ERα; the specific ERα antagonist ICI 182,780 blocked T(4)-induced, but not T(3)-induced ERK1/2 activation, as well as ERα phosphorylation, proliferating-cell nuclear antigen (PCNA) expression and hormone-dependent thymidine uptake by tumor cells. Thus, in ERα-positive human lung cancer cells, the proliferative action of thyroid hormone initiated at the plasma membrane is at least in part mediated by ERα. In summary, thyroid hormone may be one of several endogenous factors capable of supporting proliferation of lung cancer cells. Activity as an inhibitor of lung cancer cell proliferation induced at the integrin receptor makes tetrac a novel anti-proliferative agent.

Identification of primary gene targets of TFAP2C in hormone responsive breast carcinoma cells

The TFAP2C transcription factor is involved in mammary development, differentiation, and oncogenesis. Previous studies established a role for TFAP2C in the regulation of ESR1 (ERalpha) and ERBB2 (Her2) in breast carcinomas. However, the role of TFAP2C in different breast cancer phenotypes has not been examined in detail. To develop a more complete characterization of TFAP2C target genes, ChIP-seq with anti-TFAP2C antibody and expression arrays with TFAP2C knock down were analyzed in MCF-7 breast carcinoma cells. Genomic sequences common to the ChIP-seq data set defined the consensus sequence for TFAP2C chromatin binding as the nine base sequence SCCTSRGGS (S = G/C, r = A/G), which closely matches the previously defined optimal in vitro binding site. Comparing expression arrays before and after knock down of TFAP2C with ChIP-seq data demonstrated a conservative estimate that 8% of genes altered by TFAP2C expression are primary target genes and includes genes that are both induced and repressed by TFAP2C. A set of 447 primary target genes of TFAP2C was identified, which included ESR1 (ERalpha), FREM2, RET, FOXA1, WWOX, GREB1, MYC, and members of the retinoic acid response pathway. The identification of ESR1, WWOX, GREB1, and FOXA1 as primary targets confirmed the role of TFAP2C in hormone response. TFAP2C plays a critical role in gene regulation in hormone responsive breast cancer and its target genes are different than for the Her2 breast cancer phenotype.

Manipulating protein acetylation in breast cancer: a promising approach in combination with hormonal therapies?

Estrogens play an essential role in the normal physiology of the breast as well as in mammary tumorigenesis. Their effects are mediated by two nuclear estrogen receptors, ERα and β, which regulate transcription of specific genes by interacting with multiprotein complexes, including histone deacetylases (HDACs). During the past few years, HDACs have raised great interest as therapeutic targets in the field of cancer therapy. In breast cancer, several experimental arguments suggest that HDACs are involved at multiple levels in mammary tumorigenesis: their expression is deregulated in breast tumors; they interfere with ER signaling in intricate ways, restoring hormone sensitivity in models of estrogen resistance, and they clinically represent new potential targets for HDACs inhibitors (HDIs) in combination with hormonal therapies. In this paper, we will describe these different aspects and underline the clinical interest of HDIs in the context of breast cancer resistance to hormone therapies (HTs).

Loss of transcription factor AP-2gamma/TFAP2C impairs branching morphogenesis of the murine mammary gland

Extensive development of the mammary gland occurs during puberty, when rising levels of ovarian hormones induce the formation of highly proliferative terminal end buds (TEBs) at the tips of mammary ducts. TEBs consist of an outer layer of cap cells and of inner body cells. TEBs invade the adipose stroma and bifurcate while extending the ducts to generate an arborized ductal network. We show that in murine mammary glands transcription factor AP-2gamma is strongly expressed in the cap cell layer and in a subset of body cells of TEBs. To decipher AP-2gamma functions during mammary development we generated AP-2gamma-deficient mice. Their mammary glands displayed impaired ductal branching and elongation. Cellular proliferation within TEBs was reduced. Although estrogen receptor was expressed, exogenously administered ovarian hormones could not restore normal development. Therefore, AP-2gamma is functionally involved in branching morphogenesis of the mammary epithelium, possibly by controlling genetic processes downstream of ovarian hormones.

Pathology tissue-chromatin immunoprecipitation, coupled with high-throughput sequencing, allows the epigenetic profiling of patient samples

Epigenetic alterations in the pattern of DNA and histone modifications play a crucial role in cancer development. Analysis of patient samples, however, is hampered by technical limitations in the study of chromatin structure from pathology archives that usually consist of heavily fixed, paraffin-embedded material. Here, we present a methodology [pathology tissue-ChIP (PAT-ChIP)] to extract and immunoprecipitate chromatin from paraffin-embedded patient samples up to several years old. In a pairwise comparison with canonical ChIP, PAT-ChIP showed a high reproducibility of results for several histone marks and an identical ability to detect dynamic changes in chromatin structure upon pharmacological treatment. Finally, we showed that PAT-ChIP can be coupled with high-throughput sequencing (PAT-ChIP-Seq) for the genome-wide analysis of distinct chromatin modifications. PAT-ChIP therefore represents a versatile procedure and diagnostic tool for the analysis of epigenetic alterations in cancer and potentially other diseases.

Epigenetic control of the basal-like gene expression profile via Interleukin-6 in breast cancer cells

Background

Basal-like carcinoma are aggressive breast cancers that frequently carry p53 inactivating mutations, lack estrogen receptor-α (ERα) and express the cancer stem cell markers CD133 and CD44. These tumors also over-express Interleukin 6 (IL-6), a pro-inflammatory cytokine that stimulates the growth of breast cancer stem/progenitor cells.

Results

Here we show that p53 deficiency in breast cancer cells induces a loss of methylation at IL-6 proximal promoter region, which is maintained by an IL-6 autocrine loop. IL-6 also elicits the loss of methylation at the CD133 promoter region 1 and of CD44 proximal promoter, enhancing CD133 and CD44 gene transcription. In parallel, IL-6 induces the methylation of estrogen receptor (ERα) promoter and the loss of ERα mRNA expression. Finally, IL-6 induces the methylation of IL-6 distal promoter and of CD133 promoter region 2, which harbour putative repressor regions.

Conclusion

We conclude that IL-6, whose methylation-dependent autocrine loop is triggered by the inactivation of p53, induces an epigenetic reprogramming that drives breast carcinoma cells towards a basal-like/stem cell-like gene expression profile.

Epigenetic regulation on the 5'-proximal CpG island of human porcine endogenous retrovirus subgroup A receptor 2/GPR172B

Porcine endogenous retroviruses (PERVs) have been considered one of the major risks of xenotransplantation from pigs to humans. PERV-A efficiently utilizes human PERV-A receptor 2 (HuPAR-2)/GPR172B to infect human cells; however, there has been no study on the regulation mechanisms of HuPAR-2/GPR172B expression. In this study, we examined the expression of HuPAR-2/GPR172B from the standpoint of epigenetic regulation and discussed the risks of PERV-A infection in xenotransplantation. Quantitative real-time RT-PCR revealed that HuPAR-2 mRNA was preferentially expressed in placental tissue, whereas it was highly suppressed in BeWo cells (a human choriocarcinoma cell line) and HEK293 cells. A CpG island containing the HuPAR-2 transcription starting site was identified by in silico analysis. The DNA methylation ratio (the relative quantity of methylcytosine to total cytosine) and histone modification (H3K9me3) levels in the CpG island measured by bisulfite genomic sequencing and ChIP assay, respectively, were inversely correlated with the mRNA levels. Both HuPAR-2 mRNA and HuPAR-2 protein were up-regulated in HEK293 cells by inhibiting DNA methylation and histone deacetylation. Additionally, promoter/enhancer activities within the CpG island were suppressed by in vitro DNA methylation. Our results demonstrated that epigenetic modification regulates HuPAR-2 expression.

[Molecular mechanisms of regulation of estrogen receptor a expression level in breast cancer]

Estrogen receptor alpha (ERalpha) plays an important role in breast cancer development and progression and thus becomes a useful molecular target for breast cancer therapy. ERalpha is differentially expressed in breast cancer patients. Moreover, ERalpha expression levels may change at different stages of breast cancer even for the same patient. ERalpha expression is closely associated with the effect of endocrine therapy and prognosis. The mechanisms underlying ERalpha expression are complicated, because ERalpha expression is regulated at different levels, including chromatin, transcriptional, post- transcriptional, translational, and post-translational levels. Many proteins modulate the transcription of ERalpha gene at the chromatin and transcriptional levels through direct or indirect interaction with the ERa promoter. Some microRNAs decrease ERalpha levels possibly by induction of the degradation of ERalpha mRNA and/or repression of the mRNA translation. At the post-translational level, many proteins regulate ERalpha protein levels through ubiquitin-proteosome pathway. This review focuses on molecular mechanisms of regulation of ERalpha expression at different levels.