PRC2: an epigenetic multiprotein complex with a key role in the development of rhabdomyosarcoma carcinogenesis

RASGRP1 targeted by H3K27me3 regulates myoblast proliferation and differentiation in mice and pigs

Skeletal muscle is not only the largest organ in the body that is responsible for locomotion and exercise but also crucial for maintaining the body's energy metabolism and endocrine secretion. The trimethylation of histone H3 lysine 27 (H3K27me3) is one of the most important histone modifications that participates in muscle development regulation by repressing the transcription of genes. Previous studies indicate that the RASGRP1 gene is regulated by H3K27me3 in embryonic muscle development in pigs, but its function and regulatory role in myogenesis are still unclear. In this study, we verify the crucial role of H3K27me3 in RASGRP1 regulation. The gain/loss function of RASGRP1 in myogenesis regulation is performed using mouse myoblast C2C12 cells and primarily isolated porcine skeletal muscle satellite cells (PSCs). The results of qPCR, western blot analysis, EdU staining, CCK-8 assay and immunofluorescence staining show that overexpression of RASGRP1 promotes cell proliferation and differentiation in both skeletal muscle cell models, while knockdown of RASGRP1 leads to the opposite results. These findings indicate that RASGRP1 plays an important regulatory role in myogenesis in both mice and pigs.

Insights into the molecular roles of FOXR2 in the pathology of primary pediatric brain tumors

Forkhead box gene R2 (FOXR2) belongs to the family of FOX genes which codes for highly conserved transcription factors (TFs) with critical roles in biological processes ranging from development to organogenesis to metabolic and immune regulation to cellular homeostasis. A number of FOX genes are associated with cancer development and progression and poor prognosis. A growing body of evidence suggests that FOXR2 is an oncogene. Studies suggested important roles for FOXR2 in cancer cell growth, metastasis, and drug resistance. Recent studies showed that FOXR2 is overexpressed by a subset of newly identified entities of embryonal tumors. This review discusses the role(s) FOXR2 plays in the pathology of pediatric brain cancers and its potential as a therapeutic target.

Novel insights of EZH2-mediated epigenetic modifications in degenerative musculoskeletal diseases

Degenerative musculoskeletal diseases (Osteoporosis, Osteoarthritis, Degenerative Spinal Disease and Sarcopenia) are pathological conditions that affect the function and pain of tissues such as bone, cartilage, and muscles, and are closely associated with ageing and long-term degeneration. Enhancer of zeste homolog 2 (EZH2), an important epigenetic regulator, regulates gene expression mainly through the PRC2-dependent trimethylation of histone H3 at lysine 27 (H3K27me3). Increasing evidence suggests that EZH2 is involved in several biological processes closely related to degenerative musculoskeletal diseases, such as osteogenic-adipogenic differentiation of bone marrow mesenchymal stem cells, osteoclast activation, chondrocyte functional status, and satellite cell proliferation and differentiation, mainly through epigenetic regulation (H3K27me3). Therefore, the synthesis and elucidation of the role of EZH2 in degenerative musculoskeletal diseases have attracted increasing attention. In addition, although EZH2 inhibitors have been approved for clinical use, whether they can be repurposed for the treatment of degenerative musculoskeletal diseases needs to be considered. Here, we reviewed the role of EZH2 in the development of degenerative musculoskeletal diseases and brought forward prospects of its pharmacological inhibitors in the improvement of the treatment of the diseases.

Genomic and Epigenetic Changes Drive Aberrant Skeletal Muscle Differentiation in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS), the most common soft-tissue sarcoma in children and adolescents, represents an aberrant form of skeletal muscle differentiation. Both skeletal muscle development, as well as regeneration of adult skeletal muscle are governed by members of the myogenic family of regulatory transcription factors (MRFs), which are deployed in a highly controlled, multi-step, bidirectional process. Many aspects of this complex process are deregulated in RMS and contribute to tumorigenesis. Interconnected loops of super-enhancers, called core regulatory circuitries (CRCs), define aberrant muscle differentiation in RMS cells. The transcriptional regulation of MRF expression/activity takes a central role in the CRCs active in skeletal muscle and RMS. In PAX3::FOXO1 fusion-positive (PF+) RMS, CRCs maintain expression of the disease-driving fusion oncogene. Recent single-cell studies have revealed hierarchically organized subsets of cells within the RMS cell pool, which recapitulate developmental myogenesis and appear to drive malignancy. There is a large interest in exploiting the causes of aberrant muscle development in RMS to allow for terminal differentiation as a therapeutic strategy, for example, by interrupting MEK/ERK signaling or by interfering with the epigenetic machinery controlling CRCs. In this review, we provide an overview of the genetic and epigenetic framework of abnormal muscle differentiation in RMS, as it provides insights into fundamental mechanisms of RMS malignancy, its remarkable phenotypic diversity and, ultimately, opportunities for therapeutic intervention.

EZH2 W113C is a gain-of-function mutation in B cell lymphoma enabling both PRC2 methyltransferase activation and tazemetostat resistance

Polycomb Repressive Complex2 (PRC2) suppresses gene transcription by methylating lysine 27 of histone H3 (H3K27) and plays critical roles in embryonic development. Among the core PRC2 subunits, EZH2 is the catalytic subunit and EED allosterically activates EZH2 upon binding trimethylated H3K27 (H3K27me3). Activating mutations on Y641, A677, and A687 within the enzymatic SET domain of EZH2 have been associated with enhanced H3K27me3 and tumorigenicity of many cancers including B-cell lymphoma and melanoma. To tackle the critical residues outside the EZH2 SET domain, we examined EZH2 mutations in lymphoma from cancer genome databases and identified a novel gain-of-function (GoF) mutation W113C, which increases H3K27me3 in vitro and in vivo and promotes CDKN2A silencing to a similar level as the EZH2 Y641F. Different from other GoF mutations, this mutation is located in the SAL motif at the EZH2 N-terminus, which stabilizes the SET domain and facilitates substrate binding. This may explain how the W113C mutation increases PRC2 activity. Tazemetostat is an FDA-approved EZH2 binding inhibitor for follicular lymphoma treatment. Intriguingly, the W113C mutation leads to tazemetostat-resistance in cell and in vivo in both H3K27 methylation and tumor proliferation. Another class of allosteric PRC2 inhibitor binding EED overcomes the resistance, effectively decreases H3K27me3, and blocks tumor proliferation in cells expressing EZH2 W113C. As this mutation is originally identified from lymphoma samples, our results demonstrated its activating characteristic and the deleterious consequence, provide insights on PRC2 regulation, and support the continued exploration of treatment optimization for lymphoma patients.

Bromodomain Inhibitor JQ1 Provides Novel Insights and Perspectives in Rhabdomyosarcoma Treatment

Rhabdomyosarcoma (RMS) is the most common type of pediatric soft tissue sarcoma. It is classified into two main subtypes: embryonal (eRMS) and alveolar (aRMS). MYC family proteins are frequently highly expressed in RMS tumors, with the highest levels correlated with poor prognosis. A pharmacological approach to inhibit MYC in cancer cells is represented by Bromodomain and Extra-Terminal motif (BET) protein inhibitors. In this paper, we evaluated the effects of BET inhibitor (+)-JQ1 (JQ1) on the viability of aRMS and eRMS cells. Interestingly, we found that the drug sensitivity of RMS cell lines to JQ1 was directly proportional to the expression of MYC. JQ1 induces G1 arrest in cells with the highest steady-state levels of MYC, whereas apoptosis is associated with MYC downregulation. These findings suggest BET inhibition as an effective strategy for the treatment of RMS alone or in combination with other drugs.

Emerging Role and Mechanism of circRNAs in Pediatric Malignant Solid Tumors

Circular RNAs (circRNAs) are non-coding RNAs with covalent closed-loop structures and are widely distributed in eukaryotes, conserved and stable as well as tissue-specific. Malignant solid tumors pose a serious health risk to children and are one of the leading causes of pediatric mortality. Studies have shown that circRNAs play an important regulatory role in the development of childhood malignant solid tumors, hence are potential biomarkers and therapeutic targets for tumors. This paper reviews the biological characteristics and functions of circRNAs as well as the research progress related to childhood malignant solid tumors.

Epigenetic modulation in sensitizing metastatic sarcomas to therapies and overcoming resistance

Sarcomas are a class of rare malignancies of mesenchymal origin with a heterogeneous histological spectrum. They are classically associated with poor outcomes, especially once metastasized. A path to improving clinical outcomes may be made through modifying the epigenome, where a variety of sarcomas demonstrate changes that contribute to their oncogenic phenotypes. This Perspective article identifies and describes changes in the sarcoma genome, while discussing specific epigenetic changes and their effect on clinical outcomes. Clinical attempts at modulating epigenetics in sarcoma are reviewed, as well as potential implications of these studies. Epigenetic targets to reverse and delay chemotherapy resistance are discussed. Future directions with primary next steps are proposed to invigorate the current understanding of epigenetic biomarkers to enact targeted therapies to epigenetic phenotypes of sarcoma subtypes. Modifications to prior studies, as well as proposed clinical steps, are also addressed.