Poster Presentation 41st Lorne Genome Conference 2020

Molecular mechanisms of radiation-induced cell death (#250)

Radoslaw Szmyd 1 2 , Noa Lamm-shalem 1 , Eric Hau 2 3 4 , Harriet E Gee 2 3 , Tony Cesare 1
  1. Genome Integrity Unit, Children's Medical Research Institute, Sydney, NSW, Australia
  2. Sydney West Radiation Oncology Network (SWRON), Sydney, NSW, Australia
  3. Sydney Medical School, C24 - Westmead Hospital, University of Sydney, Sydney, NSW, Australia
  4. The Westmead Institute for Medical Research, Sydney, NSW, Australia

Radiotherapy is responsible for 40% of cancer cures but resistance remains a problem. Stereotactic ablative body radiotherapy (SABR) now enables cure with high radiation dosages in a small number of treatments. SABR has improved the median survival for oligometastatic disease and the response rate to immunotherapy. However, cell death mechanisms accompanying treatment with SABR dosages remain unknown.

Here we are investigating radiation-induced cell death primarily through long-duration live microscopy. We found that irradiation of asynchronous p53-compromised cancer cells with SABR equivalent dosages induce distinct waves of cell death dictated by cell cycle phase at the time of irradiation. Cells irradiated in S/G2 phase die in the immediately following mitosis, preceded by a pronounced S/G2 phase delay and significant increase in nuclear volume. Mitotic arrest depends on the cohesin antagonist WAPL, and mitotic lethality is induced by WAPL-dependent cohesion fatigue and signaled via BAX/BAK-mediated apoptosis. Conversely, the majority of irradiated G1 cells progress through S-phase faster (compared to S/G2 counterparts but not to untreated cells) and exhibit rather normal mitotic duration, but display numerous chromosome segregation errors including lagging chromosomes, DNA bridges and micronuclei. A pronounced induction of a proinflammatory response and autophagy follows radiation in a dose-dependent manner, and cells irradiated in G1 phase eventually die in a subsequent interphase. Inhibiting DNA-PKcs, which prevents non-homologous end joining (NHEJ), shunts G1 irradiated cells into the mitotic death pathway.

We hypothesize that radiation during DNA replication induces lethal replication defects culminating in mitotic death. While in G1 phase, DNA breaks are resolved by NHEJ, but aberrant repair confers chromosome segregation errors in the following mitosis, triggering intrinsic immune response activation. Preventing NHEJ enables passage of genomic damage into S-phase where replication stress ensues. We are working to clarify these pathways with a goal of improving radiation induced cell lethality.