Biology subjects

Tiusanen, V.

Publications and source records attributed to Tiusanen, V..

4 recordsLinked to original sources

bioRxiv2026

Mitochondrial dysfunction reshapes methyl-group allocation inskeletal muscle

Mitochondria are central metabolic organelles with functions extending beyond energy production to anabolic and folate-mediated one-carbon (1C) metabolism. One-carbon metabolism supports methylation reactions that modify diverse targets including metabolites, nucleic acids, and chromatin, and has emerged as a contributor to mitochondrial disease-related stress responses. Here, we report tissue-specific remodeling of methylation events in response to mtDNA replication defect, using the deletor mice carrying a dominant mutation in Twinkle, the replicative helicase of mtDNA, causing adult-onset mitochondrial myopathy (MM) in humans and mice. In affected skeletal muscle, deletors show a distinct methylation signature, with increased creatine synthesis and reduced phosphatidylcholine production, two major consumers of S-adenosylmethionine-derived methyl groups. We further observed tissue-specific upregulation of selected RNA methylation marks and redistribution of the repressive histone mark H3K9me3, indicating coordinated remodeling of metabolic and epigenetic methylation pathways. Our evidence shows that a mtDNA replication defect remodels muscle-specific methylation signature of phospholipids, histones and RNA, identifying methylation remodeling as a key component of MM pathogenesis.

molecular biology↗

bioRxiv2026

Classical enhancers couple cis-regulatory logic with transcriptional condensates and 3D genome architecture

Deciphering the regulatory logic of enhancers remains a central question in understanding cell- and tissue-specific gene expression in multicellular organisms. This is particularly pertinent at multipartite enhancer clusters such as super-enhancers, where multiple enhancers contribute to the expression of a single gene. Gene expression has been studied largely through sequence-dependent recruitment of transcription factors (TF) and co-activators, whereas 3D chromatin structure has been attributed to architectural proteins such as cohesion and CTCF1-3. However, the contribution of DNA sequence encoded in enhancers to shaping higher-order genome organization remains poorly understood. Here we show that classical enhancers, embedded within multipartite super-enhancer structures, act as determinant regulatory elements that initiate the gene regulatory cascade by linking DNA sequence recognition to 3D chromatin architecture. Classical enhancers are more evolutionarily conserved and display stronger regulatory activity than facilitator elements, which lack intrinsic enhancer activity but potentiate classical enhancer function. We show that classical enhancers are selectively bound by specific TFs with strong intrinsically disordered regions, such as NFE2L2 in liver cancer cells, capable of driving transcriptional condensate formation through phase separation. NFE2L2 depletion reduced enhancer activity and induced widespread chromatin reorganization, characterized by increased cohesin and CTCF occupancy at super-enhancer boundaries and beyond. This "cohesin clogging" impaired DNA loop extrusion, led to formation of smaller topologically associated domains, and weakened enhancer-promoter contacts. These findings highlight that sequence-specific TFs have multifaceted roles beyond transcriptional control, establishing a direct mechanistic link between enhancer sequence, TF binding, condensate formation, and 3D genome organization, with the regulatory logic being encoded in the DNA sequence itself.

genomics↗

bioRxiv2025

Oncogenic virus hijacks SOX18 pioneer function to enhance viral persistence

Kaposis sarcoma herpesvirus (KSHV) establishes lifelong oncogenic infection in lymphatic endothelial cells (LECs) by ensuring episomal maintenance of its genome via the viral protein LANA. Efficient viral genome maintenance typically involves host DNA replication and episome tethering, but the extent of cell-type-specific regulation remains unclear. Here, we identify that KSHV hijacks the pioneering function of the endothelial-specific transcription factor SOX18 to facilitate persistence of viral episomes. Upon infection, LANA co-opts SOX18 to recruit the SWI/SNF chromatin-remodeling complex via its ATPase subunit BRG1, enhancing chromatin accessibility and enabling efficient viral genome persistence. Disruption of SOX18 or BRG1--genetically or pharmacologically--leads to reduced episome load and attenuated hallmarks of virus infection. This work highlights how viruses can harness lineage-specific transcriptional regulators to establish persistent nuclear retention of their episome into the host genome.

molecular biology↗

bioRxiv2024

Cancer cell type-specific derepression of transposable elements by inhibition of chromatin modifier enzymes

The combination of immunotherapy and epigenetic therapy is emerging as a promising approach for cancer therapy. Epigenetic therapy can induce derepression of transposable elements (TEs) that play a major role in activation of immune response against cancer cells. However, the molecular mechanism of TE regulation by distinct chromatin modifier enzymes (CME) and in the context of p53 is still elusive. Here, we used epigenetic drugs to inhibit distinct CMEs in p53 wild-type and p53-mutant colorectal and esophageal cancer cells. We show that distinct TEs subfamilies are derepressed by inhibition of different CMEs in a cell-type specific manner with loss of p53 resulting in stronger TE derepression. We show that KAP1, a known repressor of TEs, associates with stronger derepression of specific TE subfamilies such as LTR12C, indicating that KAP1 also has an activating role in TE regulation in cancer cells upon co-inhibition of DNMT and HDAC. Co-inhibition of DNMT and HDAC activates immune response by inducing inverted repeat Alu expression, reducing ADAR1-mediated Alu RNA editing and inducing cell type-specific TE-chimeric transcript expression. Collectively, our study demonstrates that inhibition of different CMEs results in derepression of distinct TEs in cell type-specific manner and by utilizing distinct mechanistic pathways, providing insights for epigenetic therapies that could selectively enhance anti-tumor immunity in distinct cancer types.

cancer biology↗