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The Human Leucocyte Antigen (HLA) locus and other DNA sequence variants identified in Genome-Wide Association (GWA) studies explain around 50% of the heritability of celiac disease (CD). However, the pathogenesis of CD could be driven by other layers of genomic information independent from sequence variation, such as DNA methylation, and it is possible that allele-specific methylation explains part of the SNP associations. Since the DNA methylation landscape is expected to be different among cell types, we analyzed the methylome of the epithelial and immune cell populations of duodenal biopsies in CD patients and controls separately. We found a cell type-specific methylation signature that includes genes mapping to the HLA region, namely TAP1 and HLA-B. We also performed Immunochip SNP genotyping of the same samples and interrogated the expression of some of the affected genes. Our analysis revealed that the epithelial methylome is characterized by the loss of CpG island (CGI) boundaries, often associated to altered gene expression, and by the increased variability of the methylation across the samples. The overlap between differentially methylated positions (DMPs) and CD-associated SNPs or variants contributing to methylation quantitative trait loci (mQTLs) is minimal. In contrast, there is a notable enrichment of mQTLs among the most significant CD-associated SNPs. Our results support the notion that DNA methylation alterations constitute a genotype-independent event and confirm its role in the HLA region (apart from the well-known, DQ allele-specific effect). Finally, we find that a fraction of the CD-associated variants could exert its phenotypic effect through DNA methylation.

MicroRNAs (miRNAs) are small regulatory non-coding RNAs with a diversity of cellular functions, and are frequently dysregulated in cancer. Using a novel computational method (ActMir) that we recently developed, the "activity" of miRNA hsa-miR-500a was implicated in estrogen receptor (ER) positive breast cancer; however its targets and functional impact remain poorly understood. Here, we performed an extensive gene expression analysis in ER+ breast cancer cell lines, to reveal the targets of miR-500a-5p after experimental modulation of its levels. We found that among mRNAs targeted by miR-500a-5p there was enrichment in oxidative stress response genes. Moreover, in vitro exposure to oxidative stress using H 2 O 2 induces miR-500a-5p overexpression and downregulation of the oxidative stress targets TXNRD1 and NFE2L2. Finally, expression of several of the identified miR-500a-5p targets related to oxidative stress, including TXNRD1, was associated with ER+ breast cancer survival in multiple datasets. Overall, we identify miR-500a-5p as an oxidative stress response miRNA whose activity may define breast cancer progression and survival.

The information on candidate cancer driver alterations available from public databases is often descriptive and of limited mechanistic insight, which poses difficulties for reliable distinction between true driver and passenger events. To address this challenge, we performed in-depth analysis of whole-exome sequencing data from cell lines generated by a barrier bypass-clonal expansion (BBCE) protocol. The employed strategy is based on carcinogen-driven immortalization of primary mouse embryonic fibroblasts and recapitulates early steps of cell transformation. Among the mutated genes were almost 200 COSMIC Cancer Gene Census genes, many of which were recurrently affected in the set of 25 immortalized cell lines. The alterations affected pathways regulating DNA damage response and repair, transcription and chromatin structure, cell cycle and cell death, as well as developmental pathways. The functional impact of the mutations was strongly supported by the manifestation of several known cancer hotspot mutations among the identified alterations. We identified a new set of genes encoding subunits of the BAF chromatin remodeling complex that exhibited Ras-mediated dependence on PRC2 histone methyltransferase activity, a finding that is similar to what has been observed for other BAF subunits in cancer cells. Among the affected BAF complex subunits, we determined Smarcd2 and Smarcc1 as putative driver candidates not yet fully identified by large-scale cancer genome sequencing projects. In addition, Ep400 displayed characteristics of a driver gene in that it showed a mutually exclusive mutation pattern when compared with mutations in the Trrap subunit of the TIP60 complex, both in the cell line panel and in a human tumor data set. We propose that the information generated by deep sequencing of the BBCE cell lines coupled with phenotypic analysis of the mutant cells can yield mechanistic insights into driver events relevant to human cancer development.

Epstein-Barr virus (EBV) was identified as the first human virus to be associated with a human malignancy, Burkitt's lymphoma (BL), a pediatric cancer endemic in sub-Saharan Africa. The exact mechanism of how EBV contributes to the process of lymphomagenesis is not fully understood. Recent studies have highlighted a genetic difference between endemic (EBV+) and sporadic (EBV-) BL, with the endemic variant showing a lower somatic mutation load, which suggests the involvement of an alternative virally-driven process of transformation in the pathogenesis of endemic BL. We tested the hypothesis that a global change in DNA methylation may be induced by infection with EBV, possibly thereby accounting for the lower mutation load observed in endemic BL. Our comparative analysis of the methylation profiles of a panel of BL derived cell lines, naturally infected or not with EBV, revealed that the presence of the virus is associated with a specific pattern of DNA methylation resulting in altered expression of cellular genes with a known or potential role in lymphomagenesis. These included ID3, a gene often found to be mutated in sporadic BL. In summary this study provides evidence that EBV may contribute to the pathogenesis of BL through an epigenetic mechanism.

The heat shock response is characterized by the transcriptional activation of both hsp genes and noncoding and repeated satellite III DNA sequences located at pericentric heterochromatin. Both events are under the control of Heat Shock Factor I (HSF1). Here we show that under heat shock, HSF1 recruits major cellular acetyltransferases, GCN5, TIP60 and p300 to pericentric heterochromatin leading to a targeted hyperacetylation of pericentric chromatin. Redistribution of histone acetylation toward pericentric region in turn directs the recruitment of Bromodomain and Extra-Terminal (BET) proteins BRD2, BRD3, BRD4, which are required for satellite III transcription by RNAP II. Altogether we uncover here a critical role for HSF1 in stressed cells relying on the restricted use of histone acetylation signaling over pericentric heterochromatin (HC).

Chromosomes are dynamic structures that must be reversibly condensed and unfolded to accommodate mitotic division and chromosome segregation. Histone modifications are involved in the striking chromatin reconfiguration taking place during mitosis. However, the mechanisms that regulate activity and function of histone-modifying factors as cells enter and exit mitosis are poorly understood. Here, we show that the anaphase-promoting complex or cyclosome (APC/C) is involved in the mitotic turnover of TRRAP (TRansformation/tRanscription domain-Associated Protein), a common component of histone acetyltransferase (HAT) complexes, and that the pre-mitotic degradation of TRRAP is mediated by the APC/C ubiquitin ligase activators Cdc20 and Cdh1. Ectopic expression of both Cdh1 and Cdc20 reduced the levels of coexpressed TRRAP protein and induced its ubiquitination. TRRAP overexpression or stabilization induces multiple mitotic defects, including lagging chromosomes, chromosome bridges and multipolar spindles. In addition, lack of sister chromatid cohesion and impaired chromosome condensation were found after TRRAP overexpression or stabilization. By using a truncated form of TRRAP, we show that mitotic delay is associated with a global histone H4 hyperacetylation induced by TRRAP overexpression. These results demonstrate that the chromatin modifier TRRAP is targeted for destruction in a cell cycle-dependent fashion. They also suggest that degradation of TRRAP by the APC/C is necessary for a proper condensation of chromatin and proper chromosome segregation. Chromatin compaction mediated by histone modifiers may represent a fundamental arm for APC/C orchestration of the mitotic machinery.

Germline alterations of the tumour suppressor TP53 gene are detected approximately in 25% of the families suggestive of Li-Fraumeni syndrome (LFS), characterised by a genetic predisposition to a wide tumour spectrum, including soft-tissue sarcomas, osteosarcomas, premenopausal breast cancers, brain tumours, adrenocortical tumours, plexus choroid tumours, leukaemia and lung cancer. The aim of this study was to determine the contribution of germline copy number variations (CNVs) to LFS in families without detectable TP53 mutation. Using a custom-designed high-resolution array CGH, we evaluated the presence of rare germline CNVs in 64 patients fulfilling the Chompret criteria for LFS, but without any detectable TP53 alteration. In 15 unrelated patients, we detected 20 new CNVs absent in 600 controls. Remarkably, in four patients who had developed each brain tumour, the detected CNV overlap the KDM1A, MTA3, TRRAP or SIRT3 genes encoding p53 partners involved in histone methylation or acetylation. Focused analysis of SIRT3 showed that the CNV encompassing SIRT3 leads to SIRT3 overexpression, and that in vitro SIRT3 overexpression prevents apoptosis, increases G2/M and results in a hypermethylation of numerous genes. This study supports the causal role of germline alterations of genes involved in chromatin remodelling in genetic predisposition to cancer and, in particular, to brain tumours.

Chromatin modifications at core histones including acetylation, methylation, phosphorylation and ubiquitination play an important role in diverse biological processes. Acetylation of specific lysine residues within the N terminus tails of core histones is arguably the most studied histone modification; however, its precise roles in different cellular processes and how it is disrupted in human diseases remain poorly understood. In the last decade, a number of histone acetyltransferases (HATs) enzymes responsible for histone acetylation, has been identified and functional studies have begun to unravel their biological functions. The activity of many HATs is dependent on HAT complexes, the multiprotein assemblies that contain one HAT catalytic subunit, adapter proteins, several other molecules of unknown function and a large protein called TRansformation/tRanscription domain-Associated Protein (TRRAP). As a common component of many HAT complexes, TRRAP appears to be responsible for the recruitment of these complexes to chromatin during transcription, replication and DNA repair. Recent studies have shed new light on the role of TRRAP in HAT complexes as well as mechanisms by which it mediates diverse cellular processes. Thus, TRRAP appears to be responsible for a concerted and context-dependent recruitment of HATs and coordination of distinct chromatin-based processes, suggesting that its deregulation may contribute to diseases. In this review, we summarize recent developments in our understanding of the function of TRRAP and TRRAP-containing HAT complexes in normal cellular processes and speculate on the mechanism underlying abnormal events that may lead to human diseases such as cancer.

As a component of chromatin-modifying complexes with histone acetyltransferase (HAT) activity, TRRAP has been shown to be involved in various cellular processes including gene transcription and oncogenic transformation. Inactivation of Trrap, the murine ortholog of TRRAP, in mice revealed its function in development and cell cycle progression. However, the underlying mechanism is unknown. Here, we show that the loss of Trrap in mammalian cells leads to chromosome missegregation, mitotic exit failure and compromised mitotic checkpoint. These mitotic checkpoint defects are caused by defective Trrap-mediated transcription of the mitotic checkpoint proteins Mad1 and Mad2. The mode of regulation by Trrap involves acetylation of histones H4 and H3 at the gene promoter of these mitotic players. Trrap associated with the HAT Tip60 and PCAF at the Mad1 and Mad2 promoters in a cell cycle-dependent manner and Trrap depletion abolished recruitment of these HATs. Finally, ectopic expression of Mad1 and Mad2 fully restores the mitotic checkpoint in Trrap-deficient cells. These results demonstrate that Trrap controls the mitotic checkpoint integrity by specifically regulating Mad1 and Mad2 genes.