Biology subjects

Baranello, L.

Publications and source records attributed to Baranello, L..

7 recordsLinked to original sources

bioRxiv2025

Localised activity of reverse gyrase at gene regulatory elements

DNA topoisomerases are essential enzymes found in all cells, where they regulate DNA supercoiling. Reverse gyrase (RG) is a unique type of topoisomerase that introduces positive supercoils into DNA and appears exclusively in hyperthermophiles where it was proposed to play a key, yet still elusive, role. Here, we investigate RG activity in the hyperthermophilic archaeon Thermococcus kodakarensis at 85{degrees}C, its optimal growth temperature, using genetics and functional genomics assays. Deletion of RG led to a loss of positive supercoiling in plasmid DNA and the reduced dynamic range of transcription, without affecting histone occupancy. To investigate the effects of RG loss on the topology of chromosomal DNA, we established a psoralen photobinding assay (TMP-seq) in T. kodakarensis under native growth conditions. TMP enrichment patterns were consistent with the twin-domain model of transcription and further revealed that promoters of expressed transcription units are, on average, underwound. TMP-seq profiles in an RG deletion strain revealed that promoters are hotspots for RG activity, consistent with RG acting on hyper-negatively supercoiled substrates. We propose that RG acts not as a global modulator of supercoiling, but as a local genome guardian, selectively stabilising vulnerable regulatory regions to ensure a delicate balance between DNA accessibility and integrity under extremely high temperatures.

microbiology↗

bioRxiv2025

MYC modulates TOP2A diffusion to promote substrate detection and activity

Topoisomerases alleviate DNA supercoiling by cleaving and resealing DNA strands. Previously, we showed that the oncoprotein MYC recruits and stimulates topoisomerases to remove DNA entanglements generated by oncogenic transcription. Understanding this mechanism may suggest methods to inhibit MYC-driven topoisomerase activation, targeting tumor-specific transcription. Here, we demonstrate that the essential topoisomerase TOP2A in human cells exists in a dynamic equilibrium between sequestration in the nucleolus, substrate searching in transcription hubs, and active engagement on chromatin. This equilibrium is highly responsive to changes in DNA topology, allowing cells to regulate TOP2A levels. Using single molecule tracking, we show that MYC accelerates TOP2A diffusion in cells. We explain this phenotype by demonstrating that MYC limits TOP2A self-interaction in vitro, while decreasing the size of TOP2A complexes in cells. By increasing TOP2A diffusion, MYC promotes substrate binding and increases TOP2A engagement on chromatin genome-wide, revealing the mechanism underlying MYC stimulation of TOP2A activity.

cell biology↗

bioRxiv2024

Epigenetic control of Topoisomerase 1 activity presents a cancer vulnerability

DNA transactions introduce torsional constraints that pose an inherent risk to genome integrity. While topoisomerase 1 (TOP1) activity is essential for removing DNA supercoiling, aberrant stabilization of TOP1:DNA cleavage complexes (TOP1ccs) can result in cytotoxic DNA lesions. What protects genomic hot spots of topological stress from aberrant TOP1 activity remains unknown. Here, we identify chromatin context as an essential means to coordinate TOP1cc resolution. Through its ability to bind poly(ADP-ribose) (PAR), a protein modification required for TOP1cc repair, the histone variant macroH2A1.1 establishes a TOP1-permissive chromatin environment, while the alternatively spliced macroH2A1.2 isoform is unable to bind PAR or protect from TOP1ccs. By visualizing transcription-induced topological stress in single cells, we find that macroH2A1.1 facilitates PAR-dependent recruitment of the TOP1cc repair effector XRCC1 to protect from ssDNA damage. Impaired macroH2A1.1 splicing, a frequent cancer feature, was predictive of increased sensitivity to TOP1 poisons in a pharmaco-genomic screen in breast cancer cells, and macroH2A1.1 inactivation mirrored this effect. Consistent with this, low macroH2A1.1 expression correlated with improved survival in cancer patients treated with TOP1 inhibitors. We propose that macroH2A1 alternative splicing serves as an epigenetic modulator of TOP1-associated genome maintenance and a potential cancer vulnerability.

molecular biology↗

bioRxiv2023

Co-inhibition of topoisomerase 1 and BRD4-mediated pause release selectively kills pancreatic cancer via readthrough transcription

Pancreatic carcinoma is one of the most lethal cancers and the absence of efficient therapeutic strategies results in poor prognosis. Transcriptional dysregulation due to alterations in KRAS and MYC impacts initiation, development, and survival of this tumor type. Using patient-derived xenografts of pancreatic carcinoma driven by KRAS and MYC oncogenic transcription, we show that co-inhibition of Topoisomerase 1 (TOP1) and bromodomain containing protein 4 (BRD4) synergistically induce tumor regression through targeting promoter pause-release, a rate-limiting step in transcription elongation. By comparing the nascent transcriptome with the recruitment of elongation and termination factors along genes, we found that co-inhibition of TOP1 and BRD4, while globally impairing RNA production, disturbs recruitment of proteins involved in termination. Thus, RNA polymerases continue transcribing downstream of genes for hundreds of kilobases leading to readthrough transcription. This pervasive transcription also occurs during replication, perturbing replisome progression and leading to DNA damage. The synergistic effect of TOP1 and BRD4 inhibition is specific for cancer cells leaving normal cells unharmed, highlighting the sensitivity of the tumor to these transcriptional defects. This preclinical study provides a mechanistic understanding of the benefit of combining TOP1 and BRD4 inhibitors to treat pancreatic carcinomas addicted to oncogenic drivers of high transcription and replication. One Sentence SummaryTOP1 and BRD4 inhibitors synergize to selectively kill pancreatic cancer in vivo via readthrough transcription without emergence of drug resistance

cancer biology↗

bioRxiv2021

The Epstein-Barr virus ubiquitin deconjugase BPLF1 regulates the activity of Topoisomerase II during virus replication

Topoisomerases are essential for the replication of herpesviruses but the mechanisms by which the viruses hijack the cellular enzymes are largely unknown. We found that topoisomerase-II (TOP2) is a substrate of the Epstein-Barr virus (EBV) ubiquitin deconjugase BPLF1. BPLF1 selectively inhibited the ubiquitination of TOP2 following treatment with topoisomerase poisons, interacted with TOP2 and TOP2{beta} in co-immunoprecipitation and in vitro pull-down, stabilized Etoposide-trapped TOP2 cleavage complexes (TOP2cc) and promoted TOP2 SUMOylation, which halted the DNA-damage response and reduced Etoposide toxicity. Induction of the productive virus cycle promoted the accumulation of TOP2{beta}cc, enhanced TOP2{beta} SUMOylation, and reduced Etoposide toxicity in lymphoblastoid cell lines carrying recombinant EBV encoding the active enzyme. Attenuation of this phenotype upon expression of a catalytic mutant BPLF1-C61A impaired viral DNA synthesis and virus release. These findings highlight a previously unrecognized function of BPLF1 in promoting non-proteolytic pathways for TOP2cc debulking that favor cell survival and virus production.

microbiology↗

bioRxiv2020

Optimal and regulated transcription facilitates formation of damage-induced cohesion

The structural maintenance of chromosome (SMC) complex cohesin mediates sister chromatid cohesion established during replication, and damage-induced cohesion formed in response to DSBs post-replication. The translesion synthesis polymerase Pol{eta} is required for damage-induced cohesion through a hitherto unknown mechanism. Since Pol{eta} is functionally associated with transcription, and transcription triggers de novo cohesion in Schizosaccharomyces pombe, we hypothesized that transcription facilitates damage-induced cohesion in Saccharomyces cerevisiae. Here, we show dysregulated transcriptional profiles in Pol{eta}-depleted cells (rad30{Delta}), where genes involved in chromatin assembly and positive transcription regulation were downregulated. In addition, chromatin association of RNA polymerase II was reduced at promoters and coding regions in rad30{Delta} compared to WT cells, while occupancy of the H2A.Z variant (Htz1) at promoters was increased in rad30{Delta} cells. Perturbing histone exchange at promoters inactivated damage-induced cohesion, similarly to deletion of the RAD30 gene. Conversely, altering regulation of transcription elongation suppressed the deficient damage-induced cohesion in rad30{Delta} cells. These results indicate that Pol{eta} has an assisting role during the transcriptional process, which consecutively facilitates formation of damage-induced cohesion. This further suggests a potential linkage between regulation of transcription and formation of damage-induced cohesion after replication. Author SummaryThe cohesin complex dynamically associates with chromosomes and holds sister chromatids together through cohesion established during replication. This ensures faithful chromosome segregation at anaphase. In budding yeast, DNA double strand breaks trigger sister chromatid cohesion even after replication. This so-called damage-induced cohesion is formed both close to the breaks, and genome-wide on undamaged chromosomes. The translesion synthesis polymerase eta (Pol{eta}) is specifically required for genome wide damage-induced cohesion. Although Pol{eta} is well characterized for its function in bypassing ultraviolet-induced DNA lesions, its mechanistic role in damage-induced cohesion is unclear. Here, we show that transcriptional regulation is perturbed in the absence of Pol{eta}. We propose that Pol{eta} could aid in chromatin association of RNA polymerase II through phosphorylation of the Pol{eta}-S14 residue, a non-canonical role of Pol{eta} which further facilitates formation of damage-induced cohesion genome wide. In addition, we observe the need of replication-independent nucleosome assembly/histone exchange for formation of damage-induced cohesion. This together provides new insight into formation of damage-induced cohesion after replication, which will be interesting to further explore.

cell biology↗

bioRxiv2018

Spatial chromosome folding and active transcription drive DNA fragility and formation of oncogenic MLL translocations

How spatial chromosome organization influences genome integrity is still poorly understood. Here we show that DNA double-strand breaks (DSBs) mediated by topoisomerase 2 (TOP2) activities, are enriched at chromatin loop anchors with high transcriptional activity. Recurrent DSBs occur at CTCF/cohesin bound sites at the bases of chromatin loops and their frequency positively correlates with transcriptional output and directionality. The physiological relevance of this preferential positioning is indicated by the finding that genes recurrently translocating to drive leukemias, are highly transcribed and are enriched at loop anchors. These genes accumulate DSBs at recurrent hot spots that give rise to chromosomal fusions relying on the activity of both TOP2 isoforms and on transcriptional elongation. We propose that transcription and 3D chromosome folding jointly pose a threat to genomic stability, and are key contributors to the occurrence of genome rearrangements that drive cancer.

cell biology↗