Antoccia, A. | Search bioRxiv

bioRxiv2021

TRF1 poly(ADP-ribosyl)ation by PARP1 allows proper telomere replication through helicase recruitment in non-ALT cells

Telomeres are nucleoprotein structures at eukaryotic chromosome termini. Their stability is preserved by a six-protein complex named shelterin. Among these, TRF1 binds telomere duplex and assists DNA replication with mechanisms only partly clarified. Poly (ADP-ribose) polymerase 1 (PARP1) is a chromatin associated enzyme which adds poly (ADP-ribose) polymers (PARs) to acceptor proteins by covalent hetero-modification. Here we found that TRF1 is covalently PARylated by PARP1 during DNA synthesis. PARP1 downregulation perturbs bromodeoxyuridine incorporation at telomeres in S-phase, triggering replication-dependent DNA damage and telomere fragility. PARylated TRF1 recruits WRN and BLM helicases in S-phase in a PARP1-dependent manner, probably through non-covalent PAR binding to solve secondary structures during telomere replication. ALT telomeres are less affected by PARP1 downregulation and are less sensitive to PARP inhibitors. This work unveils an unprecedented role for PARP1 as a "surveillant" of telomere replication, in absence of exogenous DNA insults, which orchestrates protein dynamics at proceeding replication fork.

molecular biology↗

bioRxiv2021

Intra-epithelial non-canonical Activin A signalling safeguards prostate progenitor quiescence

The healthy prostate is a relatively quiescent tissue. Yet, prostate epithelium overgrowth is a common condition during ageing, associated with urinary dysfunction and tumorigenesis. For over thirty years, TGF-{beta} ligands have been known to induce cytostasis in a large variety of epithelia, but the intracellular pathway mediating this signal in the prostate, as well as its relevance for quiescence, have remained elusive. Here, using mouse prostate organoids to model epithelial progenitors, we found that intra-epithelial non-canonical Activin A signalling inhibited cell proliferation in a Smad-independent manner. Mechanistically, Activin A triggered Tak1 and p38 MAPK activity, leading to p16 and p21 nuclear import. Spontaneous evasion from this quiescent state occurred upon prolonged culture, due to reduced Activin A secretion, a condition associated with DNA replication stress and aneuploidy. Organoids capable to escape quiescence in vitro were also able to implant with increased frequency into immunocompetent mice. Our study demonstrates that non-canonical Activin A signalling safeguards epithelial quiescence in the healthy prostate, with potential implications for the understanding of cancer initiation, and the development of therapies targeting quiescent tumour progenitors.

cancer biology↗