Biology subjects

Panagopoulos, A.

Publications and source records attributed to Panagopoulos, A..

3 recordsLinked to original sources

bioRxiv2025

THE NSL COMPLEX PROMOTES NEURAL DEVELOPMENT BY PREVENTING R-LOOP INDUCED REPLICATION STRESS

Early neuronal development relies on the proliferation of neural progenitor cells, making this developmental stage particularly vulnerable to DNA replication impediments. Here, we identify a non-canonical role for the non-specific lethal (NSL) complex in safeguarding DNA replication during neurodevelopment. The NSL complex, which acetylates histone 4 at gene promoters and is mutated in Koolen-de Vries syndrome (KdVS), prevents unscheduled R-loop accumulation at weakly transcribed promoters that are typically devoid of R-loops. Single-cell sequencing reveals that loss of NSL causes replisome stalling and delayed S-phase progression. Neural organoids derived from KdVS patients exhibit impaired DNA replication, developmental abnormalities, and reduced synapse formation, driven entirely by unscheduled R-loop accumulation. These findings reveal that faithful DNA replication is critical for early neurodevelopment.

genomics↗

bioRxiv2021

53BP1 mediated recruitment of RASSF1A at ribosomal DNA breaks facilitates local ATM signal amplification

DNA lesions occur across the genome and constitute a threat to cell viability; however, damage at specific genomic loci has a disproportionally greater impact on the overall genome stability. The ribosomal RNA gene repeats (rDNA) are emerging fragile sites due to repetitive nature, clustering and high transcriptional activity. Notably, recent progress in understanding how the rDNA damage response is organized has highlighted the key role of adaptor proteins in the response. Here we identify that the scaffold and tumor suppressor, RASSF1A is recruited at sites of damage and particularly enriched at rDNA breaks. Employing targeted nucleolar DNA damage, we find that RASSF1A recruitment requires ATM activity and depends on the 53BP1. At sites of damage RASSF1A facilitates local ATM signal establishment and rDNA break repair. RASSF1A silencing, a common epigenetic event during malignant transformation, results in persistent breaks, rDNA copy number alterations and decreased cell viability. Moreover, meta-analysis of a lung adenocarcinoma cohort showed that epigenetic silencing of the scaffold leads in rDNA copy number discrepancies. Overall, we present evidence that RASSF1A acts as a DNA repair factor and offer mechanistic insight in how the nucleolar DNA damage response is organized.

cell biology↗

bioRxiv2018

Direct binding of Cdt2 to PCNA is important for targeting the CRL4Cdt2 E3 ligase activity to Cdt1

The CRL4Cdt2 ubiquitin ligase complex is an essential regulator of cell-cycle progression and genome stability, ubiquitinating substrates such as p21, Set8 and Cdt1, via a display of substrate degrons on PCNA. Here, we examine the hierarchy of the ligase and substrate recruitment kinetics onto PCNA at sites of DNA replication. We demonstrate that the C-terminal end of Cdt2 bears a PCNA interaction protein motif (PIP box, Cdt2PIP), which is necessary and sufficient for binding of Cdt2 to PCNA. Cdt2PIP binds PCNA directly with high affinity, two orders of magnitude tighter than the PIP box of Cdt1. X-ray crystallographic structures of PCNA bound to Cdt2PIP and Cdt1PIP show that the peptides occupy all three binding sites of the trimeric PCNA ring. Mutating Cdt2PIP weakens the interaction with PCNA, rendering CRL4Cdt2 less effective in Cdt1 ubiquitination and leading to defects in Cdt1 degradation. The molecular mechanism we present suggests a new paradigm for bringing substrates to the CRL4-type ligase, where the substrate receptor and substrates bind to a common multivalent docking platform to enable subsequent ubiquitination.\n\nSummary blurbThe C-terminal end of Cdt2 contains a PIP-box for binding to PCNA to promote CRL4Cdt2 function, creating a new paradigm, where the substrate receptor and substrates bind to a common multivalent docking platform for ubiquitination.

molecular biology↗