Gain-of-function p53R175H blocks apoptosis in a precursor model of ovarian high-grade serous carcinoma

Ovarian high-grade serous carcinoma (HGSC) is a highly lethal malignancy for which early detection is a challenge and treatment of late-stage disease is ineffective. HGSC initiation involves exfoliation of fallopian tube epithelial (FTE) cells which form multicellular clusters called spheroids that colonize and invade the ovary. HGSC contains universal mutation of the tumour suppressor gene TP53. However, not all TP53 mutations are the same, as specific p53 missense mutants contain gain-of-function (GOF) properties that drive tumour formation. Additionally, the role of GOF p53 in spheroid-mediated spread is poorly understood. In this study, we developed and characterized an in vitro model of HGSC based on mutation of TP53 in mouse oviductal epithelial cells (OVE). We discovered increased bulk spheroid survival and increased anchorage-independent growth in OVE cells expressing the missense mutant p53R175H compared to OVE parental and Trp53ko cells. Transcriptomic analysis on spheroids identified decreased apoptosis signaling due to p53R175H. Further assessment of the apoptosis pathway demonstrated decreased expression of intrinsic and extrinsic apoptosis signaling molecules due to Trp53 deletion and p53R175H, but Caspase-3 activation was only decreased in spheroids with p53R175H. These results highlight this model as a useful tool for discovering early HGSC transformation mechanisms and uncover a potential anti-apoptosis GOF mechanism of p53R175H.

TBX3 promotes progression of pre-invasive breast cancer cells by inducing EMT and directly up-regulating SLUG

The acquisition of cellular invasiveness by breast epithelial cells and subsequent transition from ductal carcinoma in situ (DCIS) to invasive breast cancer is a critical step in breast cancer progression. Little is known about the molecular dynamics governing this transition. We have previously shown that overexpression of the transcriptional regulator TBX3 in DCIS‐like cells increases survival, growth, and invasiveness. To explore this mechanism further and assess direct transcriptional targets of TBX3 in a high‐resolution, isoform‐specific context, we conducted genome‐wide chromatin‐immunoprecipitation (ChIP) arrays coupled with transcriptomic analysis. We show that TBX3 regulates several epithelial–mesenchymal transition (EMT)‐related genes, including SLUG and TWIST1. Importantly, we demonstrate that TBX3 is a direct regulator of SLUG expression, and SLUG expression is required for TBX3‐induced migration and invasion. Assessing TBX3 by immunohistochemistry in early‐stage (stage 0 and stage I) breast cancers revealed high expression in low‐grade lesions. Within a second independent early‐stage non‐high‐grade cohort, we observed an association between TBX3 level in the DCIS and size of the invasive focus. Additionally, there was a positive correlation between TBX3 and SLUG, and TBX3 and TWIST1 in the invasive carcinoma. Pathway analysis revealed altered expression of several proteases and their inhibitors, consistent with the ability to degrade basement membrane in vivo. These findings strongly suggest the involvement of TBX3 in the promotion of invasiveness and progression of early‐stage pre‐invasive breast cancer to invasive carcinoma through the low‐grade molecular pathway. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Regulation of Active DNA Demethylation through RAR-Mediated Recruitment of a TET/TDG Complex

Retinoic acid (RA) plays important roles in development, growth, and homeostasis through regulation of the nuclear receptors for RA (RARs). Herein, we identify Hypermethylated in Cancer 1 (Hic1) as an RA-inducible gene. HIC1 encodes a tumor suppressor, which is often silenced by promoter hypermethylation in cancer. Treatment of cells with an RAR agonist causes a rapid recruitment of an RAR/RXR complex consisting of TDG, the lysine acetyltransferase CBP, and TET 1/2 to the Hic1 promoter. Complex binding coincides with a transient accumulation of 5fC/5caC and concomitant upregulation of Hic1 expression, both of which are TDG dependent. Furthermore, conditional deletion of Tdg in vivo is associated with Hic1 silencing and DNA hypermethylation of the Hic1 promoter. These findings suggest that the catalytic and scaffolding activities of TDG are essential for RA-dependent gene expression and provide important insights into the mechanisms underlying targeting of TET-TDG complexes.

Genome-wide analysis reveals a role for TDG in estrogen receptor-mediated enhancer RNA transcription and 3-dimensional reorganization

Background

The estrogen receptor (ER) is a ligand-dependant transcription factor expressed in many breast cancers and is the target of many endocrine-based cancer therapies. Genome-wide studies have shown that the ER binds to gene-specific enhancer regions in response to β-estradiol (E2) which undergo transcription producing noncoding enhancer RNA (eRNA). While eRNAs are important for transcriptional activation of neighboring genes, the mechanism remains poorly understood.

Results

Using ChIP-Seq we generate a global profile of thymine DNA glycosylase (TDG), an ER coactivator that plays an essential role in DNA demethylation, in response to E2 in the MCF7 breast cancer cell line. Remarkably, we found that in response to E2 TDG localized to enhancers which also recruit ERα, RNA Pol II and other coregulators and which are marked by histone modifications indicative of active enhancers. Importantly, depletion of TDG inhibits E2-mediated transcription of eRNAs and transcription of ER-target genes. Functionally, we find that TDG both sensitizes MCF7 cells to tamoxifen-mediated cytostasis and increases migration and invasion of MCF7 cells.

Conclusions

Taken together we find that TDG plays a central role in mediating transcription at a subset of enhancers and governs how MCF7 cells respond to both estrogenic and anti-estrogenic compounds and may be an effective therapeutic target.

Electronic supplementary material

The online version of this article (10.1186/s13072-018-0176-2) contains supplementary material, which is available to authorized users.

Human papillomavirus dysregulates the cellular apparatus controlling the methylation status of H3K27 in different human cancers to consistently alter gene expression regardless of tissue of origin

High-risk human papillomaviruses (HPV) cause cancer at multiple distinct anatomical locations. Regardless of the tissue of origin, most HPV positive (HPV+) cancers show highly upregulated expression of the p16 product of the cyclin-dependent kinase inhibitor 2A (CDKN2A) gene. Paradoxically, HPV+ tumor cells require continuous expression of this tumor suppressor for survival. Thus, restoration of normal p16 regulation has potential therapeutic value against HPV induced cancers. Normally, p16 transcription is tightly controlled at the epigenetic level via polycomb repressive complex-mediated tri-methylation of histone 3 lysine 27 (H3K27me3). Although a mechanism by which HPV induces p16 has been proposed based on tissue culture models, it has not been extensively validated in human tumors. In this study, we used data from over 800 human cervical and head and neck tumors from The Cancer Genome Atlas (TCGA) to test this model. We determined the impact of HPV status on expression from the CDKN2A locus, the adjacent CDKN2B locus, and transcript levels of key epigenetic regulators of these loci. As expected, HPV+ tumors from both anatomical sites exhibited high levels of p16. Furthermore, HPV+ tumors expressed higher levels of KDM6A, which demethylates H3K27me3. CpG methylation of the CDKN2A locus was also consistently altered in HPV+ tumors. This data validates previous tissue culture studies and identifies remarkable similarities between the effects of HPV on gene expression and DNA methylation in both cervical and oral tumors in large human cohorts. Furthermore, these results support a model whereby HPV-mediated dysregulation of CDKN2A transcription requires KDM6A, a potentially druggable target.