Wnt/β-Catenin Signaling Pathway Is a Direct Enhancer of Thyroid Transcription Factor-1 in Human Papillary Thyroid Carcinoma Cells

The Wnt/β-catenin signaling pathway is involved in the normal development of thyroid gland, but its disregulation provokes the appearance of several types of cancers, including papillary thyroid carcinomas (PTC) which are the most common thyroid tumours. The follow-up of PTC patients is based on the monitoring of serum thyroglobulin levels which is regulated by the thyroid transcription factor 1 (TTF-1): a tissue-specific transcription factor essential for the differentiation of the thyroid. We investigated whether the Wnt/β-catenin pathway might regulate TTF-1 expression in a human PTC model and examined the molecular mechanisms underlying this regulation. Immunofluorescence analysis, real time RT-PCR and Western blot studies revealed that TTF-1 as well as the major Wnt pathway components are co-expressed in TPC-1 cells and human PTC tumours. Knocking-down the Wnt/β-catenin components by siRNAs inhibited both TTF-1 transcript and protein expression, while mimicking the activation of Wnt signaling by lithium chloride induced TTF-1 gene and protein expression. Functional promoter studies and ChIP analysis showed that the Wnt/β-catenin pathway exerts its effect by means of the binding of β-catenin to TCF/LEF transcription factors on the level of an active TCF/LEF response element at [−798, −792 bp] in TTF-1 promoter. In conclusion, we demonstrated that the Wnt/β-catenin pathway is a direct and forward driver of the TTF-1 expression. The localization of TCF-4 and TTF-1 in the same area of PTC tissues might be of clinical relevance, and justifies further examination of these factors in the papillary thyroid cancers follow-up

The Influence of cis-Regulatory Elements on DNA Methylation Fidelity

It is now established that, as compared to normal cells, the cancer cell genome has an overall inverse distribution of DNA methylation (“methylome”), i.e., predominant hypomethylation and localized hypermethylation, within “CpG islands” (CGIs). Moreover, although cancer cells have reduced methylation “fidelity” and genomic instability, accurate maintenance of aberrant methylomes that underlie malignant phenotypes remains necessary. However, the mechanism(s) of cancer methylome maintenance remains largely unknown. Here, we assessed CGI methylation patterns propagated over 1, 3, and 5 divisions of A2780 ovarian cancer cells, concurrent with exposure to the DNA cross-linking chemotherapeutic cisplatin, and observed cell generation-successive increases in total hyper- and hypo-methylated CGIs. Empirical Bayesian modeling revealed five distinct modes of methylation propagation: (1) heritable (i.e., unchanged) high- methylation (1186 probe loci in CGI microarray); (2) heritable (i.e., unchanged) low-methylation (286 loci); (3) stochastic hypermethylation (i.e., progressively increased, 243 loci); (4) stochastic hypomethylation (i.e., progressively decreased, 247 loci); and (5) considerable “random” methylation (582 loci). These results support a “stochastic model” of DNA methylation equilibrium deriving from the efficiency of two distinct processes, methylation maintenance and de novo methylation. A role for cis-regulatory elements in methylation fidelity was also demonstrated by highly significant (p<2.2×10−5) enrichment of transcription factor binding sites in CGI probe loci showing heritably high (118 elements) and low (47 elements) methylation, and also in loci demonstrating stochastic hyper-(30 elements) and hypo-(31 elements) methylation. Notably, loci having “random” methylation heritability displayed nearly no enrichment. These results demonstrate an influence of cis-regulatory elements on the nonrandom propagation of both strictly heritable and stochastically heritable CGIs

Stat4 limits DNA methyltransferase recruitment and DNA methylation of the IL-18Rα gene during Th1 differentiation

Stat4 is required for Th1 development, although how a transiently activated factor generates heritable patterns of gene expression is still unclear. We examined the regulation of IL-18Rα expression to define a mechanism for Stat4-dependent genetic programming of a Th1-associated gene. Although Stat4 binds the Il18r1 promoter following IL-12 stimulation and transiently increases acetylated histones H3 and H4, patterns of histone acetylation alone in Th1 cells may not be sufficient to explain cell-type-specific patterns of gene expression. The level of DNA methylation and recruitment of Dnmt3a to Il18r1 inversely correlate with IL-18Rα expression, and blocking DNA methylation increases IL-18Rα expression. Moreover, there was decreased Il18r1–Dnmt3a association and DNA methylation following transient trichostatin A-induced histone hyperacetylation in Stat4−/−Th1 cultures. Increased association of Dnmt3a and the Dnmt3a cofactor Dnmt3L with the promoters of several Stat4-dependent genes was found in Stat4−/− Th1 cultures, providing a general mechanism for Stat4-dependent gene programming. These data support a mechanism wherein the transient hyperacetylation induced by Stat4 prevents the recruitment of DNA methyltransferases and the subsequent repression of the Il18r1 locus

H3K27me3 Protein Is a Promising Predictive Biomarker of Patients’ Survival and Chemoradioresistance in Human Nasopharyngeal Carcinoma

Trimethylation of lysine 27 on histone H3 (H3K27me3) is an epigenetic change which plays a critical role in tumor development and/or progression. However, the molecular status of H3K27me3 and its clinicopathologic/prognostic significance in nasopharyngeal carcinoma (NPC) have not been elucidated. In this study, the methods of Western blotting and immunohistochemistry (IHC) were utilized to examine the expression of H3K27me3 protein in NPC tissues and nonneoplastic nasopharyngeal epithelial tissues. Receiver operating characteristic (ROC) curve analysis was used to determine the cutpoint for H3K27me3 high expression. High expression of H3K27me3 could be observed in 127/209 (60.8%) of NPCs and in 8/50 (16.0%) normal nasopharyngeal epithelial tissues (P < 0.001). Further correlation analysis demonstrated that high expression of H3K27me3 was positively associated with tumor later T classification, tumor metastasis, advanced clinical stage and chemoradioresistance (P < 0.05). Moreover, high expression of H3K27me3 was closely associated with NPC patient shortened survival time as evidenced by univariate and multivariate analysis (P < 0.05). Consequently, a new clinicopathologic prognostic model with three poor prognostic factors (H3K27me3 expression, distant metastasis and treatment regimen) was constructed. The model could stratify risk significantly (low, intermediate and high) for overall survival and progression-free survival (P < 0.0001). These findings provide evidence that H3K27me3 expression, as examined by IHC, has the potential to be used as an immunomarker to predict NPC chemoradiotherapy response and patient prognosis. The combined clinicopathologic prognostic model may become a useful tool for identifying NPC patients with different clinical outcomes

Multivalent epigenetic marks confer microenvironment-responsive epigenetic plasticity to ovarian cancer cells

“Epigenetic plasticity” refers to the capability of mammalian cells to alter their differentiation status via chromatin remodeling-associated alterations in gene expression. While epigenetic plasticity has been best associated with lineage commitment of embryonic stem cells, recent studies have demonstrated chromatin remodeling even in terminally differentiated normal cells and advanced-stage melanoma and breast cancer cells, in context-dependent responses to alterations in their microenvironment. In the current study, we extend this attribute of epigenetic plasticity to aggressive ovarian cancer cells, by using an integrative approach to associate cellular phenotypes with chromatin modifications (“ChIP-chip”) and mRNA and microRNA expression. While we identified numerous gene promoters possessing the well-known “bivalent mark” of H3K27me3/H3K4me2, we also report 14 distinct, lesser known bi-, tri- and tetravalent combinations of activating and repressive chromatin modifications, in platinum-resistant CP 70 ovarian cancer cells. The vast majority (>90%) of all the histone marks studied localized to regions within 2,000 bp of transcription start sites, supporting a role in gene regulation. Upon a simple alteration in the microenvironment, transition from two- to three-dimensional culture, an increase (17–38%) in repressive-only marked promoters was observed, concomitant with a decrease (31–21%) in multivalent (i.e., juxtaposed permissive and repressive histone marked) promoters. Like embryonic/tissue stem and other (non-ovarian) carcinoma cells, ovarian cancer cell epigenetic plasticity reflects an inherent transcriptional flexibility for context-responsive alterations in phenotype. It is possible that this plasticity could be therapeutically exploited for the management of this lethal gynecologic malignancy

TYRO3 as a molecular target for growth inhibition and apoptosis induction in bladder cancer

International audienceBACKGROUND: Muscle-invasive bladder cancer (MIBC) is an aggressive neoplasm with poor prognosis, lacking effective therapeutic targets. Oncogenic dependency on members of the TAM tyrosine kinase receptor family (TYRO3, AXL, MERTK) has been reported in several cancer types, but their role in bladder cancer has never been explored.METHODS: TAM receptor expression was evaluated in two series of human bladder tumours by gene expression (TCGA and CIT series), immunohistochemistry and western blotting analyses (CIT series). The role of the different TAM receptors was assessed by loss-of-function experiments and pharmaceutical inhibition in vitro and in vivo.RESULTS: We reported a significantly higher expression of TYRO3, but not AXL or MERTK, in both non-MIBCs and MIBCs, compared to normal urothelium. Loss-of-function experiments identified a TYRO3-dependency of bladder carcinoma-derived cells both in vitro and in a mouse xenograft model, whereas AXL and MERTK depletion had only a minor impact on cell viability. Accordingly, TYRO3-dependent bladder tumour cells were sensitive to pharmacological treatment with two pan-TAM inhibitors. Finally, growth inhibition upon TYRO3 depletion relies on cell cycle inhibition and apoptosis associated with induction of tumour-suppressive signals.CONCLUSIONS: Our results provide a preclinical proof of concept for TYRO3 as a potential therapeutic target in bladder cancer