María Moriel-Carretero, CRBM

Sterols define the fate of DNA intermediates during replicative stress

Kseniya Samardak1, Chantal Cazevieille2, María Moriel-Carretero1

1Centre de Recherche en Biologie Cellulaire de Montpellier (CRBM), University of Montpellier, France

2Institut des Neurosciences de Montpellier (INM), France

Genome stability studies primarily focus on protein–DNA interactions. In contrast, lipid contribution remains largely unexplored despite their close proximity to genomic DNA, i.e. the nuclear envelope.

We evidenced, in response to DNA Double Strand Breaks, the function of lipid droplets (LD)- dynamic organelles storing neutral lipids. By selectively storing sterols away from the nuclear envelope, a compensatory accumulation of a phosphoinositide results at the Golgi membrane that titrates the upstream kinase of the DNA Damage Response ATMTel1, in the end allowing signalling extinction and DNA repair completion.

Beyond DNA breaks, accurate DNA replication is essential for genome integrity and faithful genetic inheritance, yet it remains unexplored if related responses occur during difficulties in DNA duplication (termed replicative stress, RS). To study this, we provoked RS in S. cerevisiae by the AID-mediated depletion of Pol31, one essential subunit of DNA polymerase δ.  We established that the effect of this manipulation is to accumulate single-stranded DNA (ssDNA) in the parental strands that is transferred to the daughter strands by fork reversal. This event is accompanied by an initial accumulation of sterol-rich LD in the nucleus (nLD) followed by a robust LD formation in the cytoplasm (cLD). Preventing the transition from nLD to cLD, which sustains sterol proximity to the genome, counters fork reversal, leaving a dramatic accumulation of ssDNA in the parental strands. Mechanistically, sterol moieties (recently shown in vitro to bind chromatin) appear to mask lysine 79 of Histone 3, competing against its methylation - an epigenetic mark that contributes to Rad9 enrichment at damaged DNA. The decreased recruitment of Rad9 leaves free way to excessive nuclease-mediated resection at the initial ssDNA gaps. Our work establishes that RS elicits sterol mobilization from the nuclear envelope, and that their timely removal from the nucleoplasm is key to warrant accurate DNA processing. Beyond, these findings establish the intimate crosstalk between genome stability and lipid metabolic pathways, a discovery with a myriad of therapeutic implications.

Contact : B. Mollereau & A. Piazza