Biology subjects

Friskes, A.

Publications and source records attributed to Friskes, A..

5 recordsLinked to original sources

bioRxiv2025

Visualizing homology search in living cells

Homologous recombination (HR) is a DNA repair process that requires a homologous sequence for the repair of DNA double-stranded breaks. The search for homology is the rate limiting step for HR, but the dynamics of homology search in vivo are currently poorly understood. This is largely due to a lack of tools to visualize homology search in action in living human cells. Here, we show that RAD51 and MND1, two proteins operating in homology search, become visible in long filamentous structures several hours after double-stranded break formation. Using GFP-MND1 we can visualize these filaments in living human cells and find that they are highly dynamic, explore the nuclear space, and can resolve over time. We show that the resolution of these filaments depends on RAD54L, known for its role in RAD51-driven homology search and strand-invasion. In addition, we find that loss of cohesin also inhibits the resolution of these filaments, in accordance with a role for cohesin in HR. Thus, our data suggest that these filaments are visible intermediates of an active DNA repair process, and that MND1-GFP can be used as a tool to study the dynamics of homology search in living human cells.

cell biology↗

bioRxiv2024

Centriole structural integrity defects are a crucial feature of Hydrolethalus Syndrome

Hydrolethalus Syndrome (HLS) is a lethal, autosomal recessive ciliopathy caused by the mutation of the conserved centriole protein HYLS1. However, how HYLS1 facilitates the centriole-based templating of cilia is poorly understood. Here, we show that mice harboring the HYLS1 disease mutation die shortly after birth and exhibit developmental defects that recapitulate several manifestations of the human disease. These phenotypes arise from tissue-specific defects in cilia assembly and function caused by a loss of centriole integrity. We show that HYLS1 is recruited to the centriole by CEP120 and functions to recruit centriole inner scaffold proteins that stabilize the centriolar microtubule wall. The HLS mutation disrupts the interaction of HYLS1 with CEP120 leading to HYLS1 displacement and degeneration of the centriole distal end. We propose that tissue-specific defects in centriole integrity caused by the HYLS1 mutation prevent ciliogenesis and drive HLS phenotypes.

cell biology↗

bioRxiv2023

Paradoxical activation of oncogenic signaling as a cancer treatment strategy

Cancer homeostasis depends on a balance between activated oncogenic pathways driving tumorigenesis and engagement of stress-response programs that counteract the inherent toxicity of such aberrant signaling. While inhibition of oncogenic signaling pathways has been explored extensively, there is increasing evidence that overactivation of the same pathways can also disrupt cancer homeostasis and cause lethality. We show here that inhibition of Protein Phosphatase 2A (PP2A) hyperactivates multiple oncogenic pathways and engages stress responses in colon cancer cells. Genetic and compound screens identify combined inhibition of PP2A and WEE1 as synergistic in multiple cancer models by collapsing DNA replication and triggering premature mitosis followed by cell death. This combination also suppressed the growth of patient-derived tumors in vivo. Remarkably, acquired resistance to this drug combination suppressed the ability of colon cancer cells to form tumors in vivo. Our data suggest that paradoxical activation of oncogenic signaling can result in tumor suppressive resistance.

cancer biology↗

bioRxiv2022

MND1 enables repair of two-ended DNA double-strand breaks

Faithful and timely repair of DNA double-strand breaks (DSBs) is fundamental for the maintenance of genomic integrity. Here, we demonstrate that the meiotic recombination co-factor MND1 facilitates the repair of DSBs in somatic cells. We show that MND1 localizes to DSBs, where it stimulates DNA repair through homologous recombination (HR). Importantly, MND1 is not involved in the response to replication-associated DSBs, implying that it is dispensable for HR-mediated repair of one-ended DSBs. Instead, we find that MND1 specifically plays a role in the response to two-ended DSBs that are induced by IR or various chemotherapeutic drugs, specifically in G2. MND1 localization to DSBs is dependent on resection of the DNA ends, and seemingly occurs through direct binding of MND1 to RAD51-coated ssDNA. Importantly, the lack of MND1-driven HR repair directly potentiates the toxicity of IR-induced damage, which could open new possibilities for therapeutic intervention, specifically in HR-proficient tumors.

cell biology↗

bioRxiv2021

Perturbations in 3D genome organization can promote acquired drug resistance

Acquired drug resistance is a major problem in the treatment of cancer. hTERT-immortalized, untransformed RPE-1 (RPE) cells can acquire resistance to taxol by derepressing the ABCB1 gene, encoding for the multidrug transporter P-gP. Here we have investigated how the ABCB1 gene is derepressed. We show that activation of the ABCB1 gene is associated with reduced DNA methylation, reduced H3K9 trimethylation and increased H3K27 acetylation at the ABCB1 promoter. In addition, we find that the ABCB1 locus has moved away from the nuclear lamina in the taxol-resistant cells. This raises the question which of these alterations were causal to derepression. Directly modifying DNA methylation or H3K27 methylation had neither significant effect on ABCB1 expression, nor did it promote drug resistance. In contrast, the disruption of Lamin B Receptor (LBR), a component of the nuclear lamina involved in genome organization, did promote the acquisition of a taxol-resistant phenotype in a subset of cells. Using CRISPRa-mediated gene activation, we could further substantiate a model in which disruption of lamina association renders the ABCB1 gene permissive to derepression. Based on these data we propose a model in which nuclear lamina dissociation of a repressed gene allows for its activation, implying that deregulation of the 3D genome topology could play an important role in tumor evolution and the acquisition of drug resistance.

molecular biology↗