Structural Basis for EPC1-Mediated Recruitment of MBTD1 into the NuA4/TIP60 Acetyltransferase Complex

A Boolean network model of the double-strand break repair pathway choice

Double strand break (DSB) repair is critical to maintaining the integrity of the genome. DSB repair deficiency underlies multiple pathologies, including cancer, chromosome instability syndromes, and, potentially, neurodevelopmental defects. DSB repair is mainly handled by two pathways: highly accurate homologous recombination (HR), which requires a sister chromatid for template-based repair, limited to S/G2 phases of the cell cycle, and canonical non-homologous end joining (c-NHEJ), available throughout the cell cycle in which minimum homology is sufficient for highly efficient yet error-prone repair. Some circumstances, such as cancer, require alternative highly mutagenic DSB repair pathways like microhomology-mediated end-joining (MMEJ) and single-strand annealing (SSA), which are triggered to attend to DNA damage. These non-canonical repair alternatives are emerging as prominent drivers of resistance in drug-based tumor therapies. Multiple DSB repair options require tight inter-pathway regulation to prevent unscheduled activities. In addition to this complexity, epigenetic modifications of the histones surrounding the DSB region are emerging as critical regulators of the DSB repair pathway choice. Modeling approaches to understanding DSBs repair pathway choice are advantageous to perform simulations and generate predictions on previously uncharacterized aspects of DSBs response. In this work, we present a Boolean network model of the DSB repair pathway choice that incorporates the knowledge, into a dynamic system, of the inter-pathways regulation involved in DSB repair, i.e., HR, c-NHEJ, SSA, and MMEJ. Our model recapitulates the well-characterized HR activity observed in wild-type cells in response to DSBs. It also recovers clinically relevant behaviors of BRCA1/FANCS mutants, and their corresponding drug resistance mechanisms ascribed to DNA repair gain-of-function pathogenic variants. Since epigenetic modifiers are dynamic and possible druggable targets, we incorporated them into our model to better characterize their involvement in DSB repair. Our model predicted that loss of the TIP60 complex and its corresponding histone acetylation activity leads to activation of SSA in response to DSBs. Our experimental validation showed that TIP60 effectively prevents activation of RAD52, a key SSA executor, and confirms the suitable use of Boolean network modeling for understanding DNA DSB repair.

Expanding the molecular spectrum of gene fusions in endometrial stromal sarcoma: Novel subunits of the chromatin remodeling complexes PRC2 and NuA4/TIP60 as alternative fusion partners

Endometrial stromal sarcomas (ESS) are morphologically and molecularly heterogeneous. We report novel gene fusions (EPC1::EED, EPC1::EZH2, ING3::PHF1) identified by targeted RNA sequencing in five cases. The ING3::PHF1-fusion positive ESS presented in a 58-year-old female as extrauterine mesocolonic, ovarian masses, and displayed large, monomorphic ovoid-to-epithelioid cells arranged in solid sheets. The patient remained alive with disease 13 months after surgery. The three ESS with EPC1::EED occurred in the uterine corpus in patients with a median age of 58 years (range 27-62 years). One tumor showed a uniform epithelioid nested morphology, while the other two were composed of monomorphic spindle cells in fascicles with elevated mitotic figures, focal tumor cell necrosis, and lymphovascular invasion. At a median follow-up of 20 months, two patients developed local recurrence, including one with concomitant distant metastasis, while one patient remained free of disease. All three patients were alive at the last follow-up. The EPC1::EZH2-fusion positive ESS presented in a 52-year-old female in the uterus, and displayed uniform spindled cells arranged in short fascicles, with focally elevated mitotic activity but without necrosis. The patient remained free of disease 3 months after surgery. All cases were diffusely positive for CD10; four diffusely express estrogen and progesterone receptors. Our study expands the molecular spectrum of EPC1 and PHF1-related gene fusions in ESS to include additional novel subunits of the PRC2 and/or NuA4/TIP60 complexes. These cases displayed a monomorphic epithelioid or spindled phenotype, spanning low-grade and high-grade cytomorphology, all expressing CD10 and commonly ER and PR, and are prone to local and/or distant spread.

Multiomics Integrative Analysis Identifying EPC1 as a Prognostic Biomarker in Head and Neck Squamous Cell Carcinoma

Background. Biomarker research in head and neck squamous cell carcinoma (HNSCC) is constantly revealing promising findings. An enhancer of polycomb homolog 1 (EPC1) was found to play a procancer role in nasopharyngeal carcinoma (NPC), but its role in HNSCC with strong heterogeneity is still unclear. Herein, we investigated the prognostic significance and related mechanisms of EPC1 in HNSCC. Methods. The Kaplan-Meier plotter was used to evaluate the prognostic significance of EPC1. Based on a range of published public databases, the multiomics expression of EPC1 in HNSCC was explored to investigate the mechanisms affecting prognosis. Results. According to the clinical data, high EPC1 expression in HNSCC was a predictor of patient prognosis (hazard ratio $\left(\text{HR}\right)=0.64$ ; 95% confidence interval (CI) 0.49-0.83; $P<0.01$ ). EPC1 expression varied among clinical subtypes and was related to key factors, such as TP53 and human papillomavirus (HPV) ( $P<0.05$ ). At the genetic level, EPC1 expression level may be associated with protein phosphorylation, cell adhesion, cancer-related pathways, etc. For the noncoding region, a competing endogenous RNA network was constructed, and 6 microRNAs and 12 long noncoding RNAs were identified. At the protein level, a protein-protein interaction (PPI) network related to EPC1 expression was constructed and found to be involved in HPV infection, endocrine resistance, and multiple cancer pathways. At the immune level, EPC1 expression was correlated with a variety of immune cells and immune molecules, which together constituted the immune microenvironments of tumors. Conclusion. High EPC1 expression may predict a better prognosis in HNSCC, as it is more frequently found in HNSCC with HPV infection. EPC1 may participate in the genomics, transcriptomics, proteomics, and immunomics of HNSCC, and the results can provide a reference for the development of targeted drugs and evaluation of patient prognosis.

Recurrent chromosomal translocations in sarcomas create a megacomplex that mislocalizes NuA4/TIP60 to Polycomb target loci

Chromosomal translocations frequently promote carcinogenesis by producing gain-of-function fusion proteins. Recent studies have identified highly recurrent chromosomal translocations in patients with endometrial stromal sarcomas (ESSs) and ossifying fibromyxoid tumors (OFMTs), leading to an in-frame fusion of PHF1 (PCL1) to six different subunits of the NuA4/TIP60 complex. While NuA4/TIP60 is a coactivator that acetylates chromatin and loads the H2A.Z histone variant, PHF1 is part of the Polycomb repressive complex 2 (PRC2) linked to transcriptional repression of key developmental genes through methylation of histone H3 on lysine 27. In this study, we characterize the fusion protein produced by the EPC1-PHF1 translocation. The chimeric protein assembles a megacomplex harboring both NuA4/TIP60 and PRC2 activities and leads to mislocalization of chromatin marks in the genome, in particular over an entire topologically associating domain including part of the HOXD cluster. This is linked to aberrant gene expression-most notably increased expression of PRC2 target genes. Furthermore, we show that JAZF1-implicated with a PRC2 component in the most frequent translocation in ESSs, JAZF1-SUZ12-is a potent transcription activator that physically associates with NuA4/TIP60, its fusion creating outcomes similar to those of EPC1-PHF1 Importantly, the specific increased expression of PRC2 targets/HOX genes was also confirmed with ESS patient samples. Altogether, these results indicate that most chromosomal translocations linked to these sarcomas use the same molecular oncogenic mechanism through a physical merge of NuA4/TIP60 and PRC2 complexes, leading to mislocalization of histone marks and aberrant Polycomb target gene expression.

Oncogenic ZMYND11-MBTD1 fusion protein anchors the NuA4/TIP60 histone acetyltransferase complex to the coding region of active genes

A recurrent chromosomal translocation found in acute myeloid leukemia leads to an in-frame fusion of the transcription repressor ZMYND11 to MBTD1, a subunit of the NuA4/TIP60 histone acetyltransferase complex. To understand the abnormal molecular events that ZMYND11-MBTD1 expression can create, we perform a biochemical and functional characterization comparison to each individual fusion partner. ZMYND11-MBTD1 is stably incorporated into the endogenous NuA4/TIP60 complex, leading to its mislocalization on the body of genes normally bound by ZMYND11. This can be correlated to increased chromatin acetylation and altered gene transcription, most notably on the MYC oncogene, and alternative splicing. Importantly, ZMYND11-MBTD1 expression favors Myc-driven pluripotency during embryonic stem cell differentiation and self-renewal of hematopoietic stem/progenitor cells. Altogether, these results indicate that the ZMYND11-MBTD1 fusion functions primarily by mistargeting the NuA4/TIP60 complex to the body of genes, altering normal transcription of specific genes, likely driving oncogenesis in part through the Myc regulatory network.

Multifaceted regulation and functions of 53BP1 in NHEJ‑mediated DSB repair (Review)

The repair of DNA double-strand breaks (DSBs) is crucial for the preservation of genomic integrity and the maintenance of cellular homeostasis. Non-homologous DNA end joining (NHEJ) is the predominant repair mechanism for any type of DNA DSB during the majority of the cell cycle. NHEJ defects regulate tumor sensitivity to ionizing radiation and anti-neoplastic agents, resulting in immunodeficiencies and developmental abnormalities in malignant cells. p53-binding protein 1 (53BP1) is a key mediator involved in DSB repair, which functions to maintain a balance in the repair pathway choices and in preserving genomic stability. 53BP1 promotes DSB repair via NHEJ and antagonizes DNA end overhang resection. At present, novel lines of evidence have revealed the molecular mechanisms underlying the recruitment of 53BP1 and DNA break-responsive effectors to DSB sites, and the promotion of NHEJ-mediated DSB repair via 53BP1, while preventing homologous recombination. In the present review article, recent advances made in the elucidation of the structural and functional characteristics of 53BP1, the mechanisms of 53BP1 recruitment and interaction with the reshaping of the chromatin architecture around DSB sites, the post-transcriptional modifications of 53BP1, and the up- and downstream pathways of 53BP1 are discussed. The present review article also focuses on the application perspectives, current challenges and future directions of 53BP1 research.

New insights into the DNA repair pathway choice with NuA4/TIP60

In eukaryotic cells, DNA double-strand breaks (DSBs) can be repaired through two main pathways, non-homologous end-joining (NHEJ) or homologous recombination (HR). The selection of the repair pathway choice is governed by an antagonistic relationship between repair factors specific to each pathway, in a cell cycle-dependent manner. The molecular mechanisms of this decision implicate post-translational modifications of chromatin surrounding the break. Here, we discuss the recent advances regarding the function of the NuA4/TIP60 histone acetyltransferase/chromatin remodeling complex during DSBs repair. In particular, we emphasise the contribution of NuA4/TIP60 in repair pathway choice, in collaboration with the SAGA acetyltransferase complex, and how they regulate chromatin dynamics, modify non-histone substrates to allow DNA end resection and recombination.

LG-ESSs and HG-ESSs: underlying molecular alterations and potential therapeutic strategies

Endometrial stromal tumors (ESTs) include endometrial stromal nodule (ESN), low-grade endometrial stromal sarcoma (LG-ESS), high-grade endometrial stromal sarcoma (HG-ESS), and undifferentiated uterine sarcoma (UUS). Since these are rare tumor types, there is an unmet clinical need for the systematic therapy of advanced LG-ESS or HG-ESS. Cytogenetic and molecular advances in ESTs have shown that multiple recurrent gene fusions are present in a large proportion of LG-ESSs, and HG-ESSs are identified by the tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein epsilon (YWHAE)-family with sequence similarity 22 (FAM22) fusion. Recently, a group of ESSs harboring both zinc finger CCCH domain-containing protein 7B (ZC3H7B)-B-cell lymphoma 6 corepressor(BCOR) fusion and internal tandem duplication (ITD) of the BCOR gene have been provisionally classified as HG-ESSs. In this review, we firstly describe current knowledge about the molecular characteristics of recurrent aberrant proteins and their roles in the tumorigenesis of LG-ESSs and HG-ESSs. Next, we summarize the possibly shared signal pathways in the tumorigenesis of LG-ESSs and HG-ESSs, and list potentially actionable targets. Finally, based on the above discussion, we propose a few promising therapeutic strategies for LG-ESSs and HG-ESSs with recurrent gene alterations.

Dysregulation of miR-381-3p and miR-23b-3p in skeletal muscle could be a possible estimator of early post-mortem interval in rats

Background

The post-mortem interval (PMI) is the time elapsed since the dead of an individual until the body is found, which is relevant for forensic purposes. The miRNAs regulate the expression of some genes; and due to their small size, they can better support degradation, which makes them suitable for forensic analysis. In the present work, we evaluated the gene expression of miR-381-3p, miR-23b-3p, and miR-144-3p in skeletal muscle in a murine model at the early PMI.

Methods

We designed a rat model to evaluate the early PMI under controlled conditions. This model consisted in 25 rats divided into five groups of rats, that correspond to the 0, 3, 6, 12 and 24 hours of PMI. The 0 h-PMI was considered as the control group. Muscle samples were taken from each rat to analyze the expression of miR-381-3p, miR-23b-3p, and miR-144-3p by quantitative RT-PCR. The gene expression of each miRNA was expressed as Fold Change (FC) and compared among groups. To find the targets of these miRNAs and the pathways where they participate, we performed an in-silico analysis. From the gene targets of miR-381-3p identified in the silico analysis, the EPC1 gene was selected for gene expression analysis by quantitative RT-PCR in these samples. Also, to evaluate if miR-381-3p could predict the early PMI, a mixed effects model was calculated using its gene expression.

Results

An upregulation of miR-381-3p was found at 24 h-PMI compared with the control group of 0 h-PMI and (FC = 1.02 vs. FC = 1.96; p = 0.0079). This was the opposite for miR-23b-3p, which had a down-regulation at 24 h-PMI compared to 0 h-PMI (FC = 1.22 vs. FC = 0.13; p = 0.0079). Moreover, the gene expression of miR-381-3p increased throughout the first 24 h of PMI, contrary to miR-23b-3p. The targets of these two miRNAs, participate in biological pathways related to hypoxia, apoptosis, and RNA metabolism. The gene expression of EPC1 was found downregulated at 3 and 12 h of PMI, whereas it remained unchanged at 6 h and 24 h of PMI. Using a multivariate analysis, it was possible to predict the FC of miR-381-3p of all but 6 h-PMI analyzed PMIs.

Discussion

The present results suggest that miR-23b-3p and miR-381-3p participate at the early PMI, probably regulating the expression of some genes related to the autolysis process as EPC1 gene. Although the miR-381-3p gene expression is a potential estimator of PMI, further studies will be required to obtain better estimates.

ZMYND11-MBTD1 induces leukemogenesis through hijacking NuA4/TIP60 acetyltransferase complex and a PWWP-mediated chromatin association mechanism

Recurring chromosomal translocation t(10;17)(p15;q21) present in a subset of human acute myeloid leukemia (AML) patients creates an aberrant fusion gene termed ZMYND11-MBTD1 (ZM); however, its function remains undetermined. Here, we show that ZM confers primary murine hematopoietic stem/progenitor cells indefinite self-renewal capability ex vivo and causes AML in vivo. Genomics profilings reveal that ZM directly binds to and maintains high expression of pro-leukemic genes including Hoxa, Meis1, Myb, Myc and Sox4. Mechanistically, ZM recruits the NuA4/Tip60 histone acetyltransferase complex to cis-regulatory elements, sustaining an active chromatin state enriched in histone acetylation and devoid of repressive histone marks. Systematic mutagenesis of ZM demonstrates essential requirements of Tip60 interaction and an H3K36me3-binding PWWP (Pro-Trp-Trp-Pro) domain for oncogenesis. Inhibitor of histone acetylation-'reading' bromodomain proteins, which act downstream of ZM, is efficacious in treating ZM-induced AML. Collectively, this study demonstrates AML-causing effects of ZM, examines its gene-regulatory roles, and reports an attractive mechanism-guided therapeutic strategy.