Increased genomic instability and reshaping of tissue microenvironment underlie oncogenic properties of Arid1a mutations

ARID1A and Its Impact Across the Hallmarks of Cancer

ARID1A, a subunit of the SWI/SNF chromatin remodeling complex, has emerged as a pivotal tumor suppressor altered in a broad range of human malignancies. Its frequent inactivation across diverse cancer types has revealed pleiotropic roles that intersect multiple Hallmarks of Cancer. In this review, we integrate current knowledge on how ARID1A loss influences cellular processes including proliferative signaling, resistance to cell death, genomic instability, metabolic reprogramming, immune evasion, and more. We discuss the context-specific consequences of ARID1A deficiency, its cooperation with other oncogenic events, and its implications for therapeutic vulnerability-particularly in the realm of synthetic lethality and immune modulation. By mapping ARID1A's functional impact onto the established hallmarks framework, we highlight its centrality in cancer biology and underscore opportunities for biomarker-driven strategies and targeted interventions. Understanding ARID1A's multifaceted roles offers a compelling lens through which to explore chromatin dysregulation in cancer and guide translational advances.

Chromatin remodellers as therapeutic targets

Large-scale cancer genome sequencing studies have revealed that chromatin regulators are frequently mutated in cancer. In particular, more than 20% of cancers harbour mutations in genes that encode subunits of SWI/SNF (BAF) chromatin remodelling complexes. Additional links of SWI/SNF complexes to disease have emerged with the findings that some oncogenes drive transformation by co-opting SWI/SNF function and that germline mutations in select SWI/SNF subunits are the basis of several neurodevelopmental disorders. Other chromatin remodellers, including members of the ISWI, CHD and INO80/SWR complexes, have also been linked to cancer and developmental disorders. Consequently, therapeutic manipulation of SWI/SNF and other remodelling complexes has become of great interest, and drugs that target SWI/SNF subunits have entered clinical trials. Genome-wide perturbation screens in cancer cell lines with SWI/SNF mutations have identified additional synthetic lethal targets and led to further compounds in clinical trials, including one that has progressed to FDA approval. Here, we review the progress in understanding the structure and function of SWI/SNF and other chromatin remodelling complexes, mechanisms by which SWI/SNF mutations cause cancer and neurological diseases, vulnerabilities that arise because of these mutations and efforts to target SWI/SNF complexes and synthetic lethal targets for therapeutic benefit.

SpikeFlow: automated and flexible analysis of ChIP-Seq data with spike-in control

ChIP with reference exogenous genome (ChIP-Rx) is widely used to study histone modification changes across different biological conditions. A key step in the bioinformatics analysis of this data is calculating the normalization factors, which vary from the standard ChIP-seq pipelines. Choosing and applying the appropriate normalization method is crucial for interpreting the biological results. However, a comprehensive pipeline for complete ChIP-Rx data analysis is lacking. To address these challenges, we introduce SpikeFlow, an integrated Snakemake workflow that combines features from various existing tools to streamline ChIP-Rx data processing and enhance usability. SpikeFlow automates spike-in data scaling and provides multiple normalization options. It also performs peak calling and differential analysis with distinct modalities, enabling the detection of enrichment regions for histone modifications and transcription factor binding. Our workflow runs in-depth quality control at all the processing steps and generates an analysis report with tables and graphs to facilitate results interpretation. We validated the pipeline by performing a comparative analysis with DiffBind and SpikChIP, demonstrating robust performances in various biological models. By combining diverse functionalities into a single platform, SpikeFlow aims to simplify ChIP-Rx data analysis for the research community.

Arid1a Loss Enhances Disease Progression in a Murine Model of Osteosarcoma

Osteosarcoma is an aggressive bone malignancy, molecularly characterized by acquired genome complexity and frequent loss of TP53 and RB1. Obtaining a molecular understanding of the initiating mutations of osteosarcomagenesis has been challenged by the difficulty of parsing between passenger and driver mutations in genes. Here, a forward genetic screen in a genetic mouse model of osteosarcomagenesis initiated by Trp53 and Rb1 conditional loss in pre-osteoblasts identified that Arid1a loss contributes to OS progression. Arid1a is a member of the canonical BAF (SWI/SNF) complex and a known tumor suppressor gene in other cancers. We hypothesized that the loss of Arid1a increases the rate of tumor progression and metastasis. Phenotypic evaluation upon in vitro and in vivo deletion of Arid1a validated this hypothesis. Gene expression and pathway analysis revealed a correlation between Arid1a loss and genomic instability, and the subsequent dysregulation of genes involved in DNA DSB or SSB repair pathways. The most significant of these transcriptional changes was a concomitant decrease in DCLRE1C. Our findings suggest that Arid1a plays a role in genomic instability in aggressive osteosarcoma and a better understanding of this correlation can help with clinical prognoses and personalized patient care.

Endonucleosis mediates internalization of cytoplasm into the nucleus

Setd8 regulates transcription elongation, mitotic DNA condensation, DNA damage response and replication licensing. Here we show that, in mitogen-stimulated liver-specific Setd8-KO mice, most of the hepatocytes are eliminated by necrosis but a significant number of them survive via entering a stage exhibiting several senescence-related features. Setd8-deficient hepatocytes had enlarged nuclei, chromosomal hyperploidy and nuclear engulfments progressing to the formation of intranuclear vesicles surrounded by nuclear lamina. These vesicles contain glycogen, cytoplasmic proteins and even entire organelles. We term this process "endonucleosis". Intranuclear vesicles are absent in hepatocytes of Setd8/Atg5 knockout mice, suggesting that the process requires the function of the canonical autophagy machinery. Endonucleosis and hyperploidization are temporary, early events in the surviving Setd8-deficient cells. Larger vesicles break down into microvesicles over time and are eventually eliminated. The results reveal sequential events in cells with extensive DNA damage, which function as part of survival mechanisms to prevent necrotic death.