Novel Role for PTEN in Regulating Non Homologous End‐Joining Factor 53BP1 to Suppress Replication Fork Instability (LB120)

Abstract

PTEN is one of the most frequently inactivated tumor suppressors with unresolved connections to DNA repair processes that prevent genomic instability. Using single molecule DNA spreading, we here show that PTEN suppresses replication fork instability by promoting efficient replication restart of stalled replication forks, a phenotype mirroring ATM and BLMs helicase functions. Moreover, we find that similar to BLMs, PTEN suppresses replication stress dependent DNA bridges. Previous studies show non‐homologous end‐joining (NHEJ) protein and ATM phosphorylation target 53BP1 in complex with BLMs at stalled fork, an interaction requiring phosphorylation of 53BP1. Yet, the role of 53BP1 at stalled forks remains ill‐defined. Strikingly, 53BP1 is highly phosphorylated in PTEN proficient cells upon replication stalling, but not in cells lacking PTEN. We further find 53BP1 to be readily recruited to nuclear foci upon replication stalling. Yet foci formation is compromised in PTEN defective cells, implying PTEN controls a function for 53BP1 when replication forks are stalling. Lastly, we reveal a direct requirement for 53BP1 in restarting stalled replication forks. These data reveal a surprising function for NHEJ factors controlled by PTEN to suppress replication fork stability and genomic instability.Grant Funding Source: Supported by 1K22CA175262‐01 (K.S.) and UO1CA164188 (H.W.)