Figure 8.

The roles of HP1 for BRCA1 function and the choice between HR and NHEJ repair. HP1 is a chromatin-associated protein, but the distribution of HP1 on chromatin is not even. Irradiation partially removes HP1 from chromatin, but the remaining HP1 molecules have active roles in recruiting BRCA1 to the damaged DNA sites. HP1 facilitates BRCA1 recruitment to chromatin after DNA damage, thereby activating G₂/M cell cycle arrest and error-free HR repair. However, if the chromatin is HP1- or BRCA1-deficient, 53BP1 should be recruited resulting in error-prone NHEJ repair of the DNA damage. The loss of both the G₂/M checkpoint control and HR repair pathway may increase the likelihood of apoptosis.