Insights into Homologous Recombination, a Critical DNA Repair Process, Have Implications for Cancer

DNA repair process
Image: Rad51 paralogs bound to the end of a Rad51 filament.

Work led by Francis Crick Institute scientists has improved our understanding of homologous recombination – an essential process for repairing broken DNA that could otherwise lead to cancer.

Simon Boulton of the Crick explains: “Our work provides mechanistic insight into homologous recombination, which is an essential mechanism for the repair of double-stranded breaks in DNA and damaged replication forks. Failure to carry out homologous recombination is associated with cancer predisposition.”

Last year Dr Boulton’s team published a paper in Cell describing the biochemical function of an important family of tumour suppressor proteins called Rad51 paralogs. When they’re mutated in humans, these proteins cause hereditary breast and ovarian cancer and Fanconi anemia – a genetic disease that causes bone marrow failure and cancer in most sufferers, among other problems.

In their 2016 paper, the researchers extended their study of Rad51 paralogs using cutting-edge science to show precisely how the proteins modulate Rad51-DNA filaments to repair breaks.

Specifically, the team used a technique called stopped-flow kinetic measurements to study the formation and stability of Rad51 filaments and a method called single-molecule fluorescence resonance energy transfer (FRET) to monitor changes in filament length and flexibility. Collaborator Eric Greene of Columbia University Medical Center in New York pioneered DNA curtain technology, which allowed the scientists to watch what happened to Rad51 filaments when molecules of Rad51 paralogs were present.

Together the results revealed that the Rad51 paralogs keep Rad51 bound to DNA strands by capping the ends of the Rad51-DNA filaments and keeping them stable.

The next step for researchers is carrying out structural studies of the process.

Dr Boulton says: “Targeting this process with small molecules that interfere with it could provide a way to prevent homologous recombination and thus sensitise cells to agents that damage DNA. This might be something we could exploit in cancer treatments – it could provide a way to stop DNA repair in cancerous cells and therefore stop these growing and replicating.”

The paper, A Polar and Nucleotide-Dependent Mechanism of Action for RAD51 Paralogs in RAD51 Filament Remodeling, is published in Molecular Cell.