Replication fork remodeling: a double-edged sword in genome stability and cancer therapy
  • Massimo Lopes
  • SLS Colloquia / 05.18.2017. 04:00 pm / Room N104, Bldg 110.
Abstract

Combining standard molecular and cell biology methods with specialized single-molecule analysis of replication intermediates in vivo, we have recently reported the identification of fork reversal - i.e. the conversion of replication forks into four way junctions (reversed forks) - as a frequent, evolutionary conserved, protective response to a variety of sources of replication stress, including cancer chemotherapeutic drugs, oncogene activation and DNA sequences prone to form secondary structures. This remodeling of fork architecture appears to protect normal and cancer cells from chromosomal breakage and represents a promising target to potentiate anticancer treatments (Neelsen and Lopes, 2015). However, the cellular factors driving reversed fork formation, stability and restart are only beginning to be uncovered.

 

Our in vivo investigations have recently identified PCNA polyubiquitination and the DNA translocase ZRANB3 as crucial mediators of replication fork remodeling upon replication stress, linking fork reversal to a long-known, but yet-elusive mechanism of error-free DNA damage tolerance. Although this evidence further supports replication fork reversal as a physiological protective response to replication stress in human cells, we have also identified reversed replication forks as essential “entry points” for the clinically-relevant fork degradation, recently reported to mediate chemosensitivity of BRCA2-defective tumor cells. Different lines of evidence suggest that fork reversal can expose unprotected replication forks to unscheduled nucleolytic degradation and elucidate the complex interplay of different homologous recombination factors in replication fork remodeling and stability. I will summarize key published evidence on replication fork remodeling and then focus my presentation on these recent, yet-unpublished observations, which inspire much of the ongoing work in the lab.