Loss of cytoplasmic actin filaments raises nuclear actin levels to drive INO80C-dependent chromosome fragmentation

• Published in: Nature communications 2024-11, Vol.15 (1), p.9910-22, Article 9910
• Main Authors: Hurst, Verena, Gerhold, Christian B., Tarashev, Cleo V. D., Challa, Kiran, Seeber, Andrew, Yamazaki, Shota, Knapp, Britta, Helliwell, Stephen B., Bodenmiller, Bernd, Harata, Masahiko, Shimada, Kenji, Gasser, Susan M.
• Format: Article
• Language: English
• Subjects: 13/1; 14/34; 42/41; 45; 45/22; 45/29; 45/44; 49; 631/208; 631/337; 631/337/1427; 631/45; 631/80; 82/58; Ablation; Actin; Actin Cytoskeleton - metabolism; Actins - metabolism; Base excision repair; Biodegradation; Bleomycin; Cell Nucleus - metabolism; Chromosomes; Chromosomes, Fungal - genetics; Chromosomes, Fungal - metabolism; Cytoplasm - metabolism; Degradation; Deoxyribonucleic acid; DNA; DNA damage; DNA polymerase; DNA Repair; DNA-directed DNA polymerase; Filaments; Fragmentation; Humanities and Social Sciences; Kinases; Lesions; multidisciplinary; Nuclear Proteins; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Science; Science (multidisciplinary); Wiskott-Aldrich syndrome; Yeast; Yeasts
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-54141-0

Loss of cytosolic actin filaments upon TORC2 inhibition triggers chromosome fragmentation in yeast, which results from altered base excision repair of Zeocin-induced lesions. To find the link between TORC2 kinase and this yeast chromosome shattering (YCS) we performed phosphoproteomics. YCS-relevant phospho-targets included plasma membrane-associated regulators of actin polymerization, such as Las17, the yeast Wiscott-Aldrich Syndrome protein. Induced degradation of Las17 was sufficient to trigger YCS in presence of Zeocin, bypassing TORC2 inhibition. In yeast, Las17 does not act directly at damage, but instead its loss, like TORC2 inhibition, raises nuclear actin levels. Nuclear actin, in complex with Arp4, forms an essential subunit of several nucleosome remodeler complexes, including INO80C, which facilitates DNA polymerase elongation. Here we show that the genetic ablation of INO80C activity leads to partial YCS resistance, suggesting that elevated levels of nuclear G-actin may stimulate INO80C to increase DNA polymerase processivity and convert single-strand lesions into double-strand breaks. Here the authors reveal that TORC2 inhibition and the rapid degradation of Las17/WASP elevates G-actin levels in the yeast nucleus which are responsible for altered long-patch base excision repair of clustered lesions, generating massive chromosome fragmentation.