尤物视频

Synopsis

Homologous recombination (HR) and nonhomologous end-joining (NHEJ) are two DNA double-strand break repair pathways that mutually antagonize to ensure faithful repair. 53BP1 and BRCA1 are DNA repair factors that promote NHEJ and HR, respectively. Defective HR caused by BRCA1 mutations is the leading cause of heritable breast and ovarian cancer. The same HR defect renders BRCA1-mutated tumors exquisitely sensitive to the DNA-damaging chemotherapy drug poly-ADP ribose polymerase 1 inhibitors (PARPi). Strikingly, 53BP1 loss de-represses HR in BRCA1-deficient cells and results in PARPi resistance. The molecular mechanisms underlying 53BP1 suppression of HR was unknown. 53BP1 is an oligomerizing protein that is recruited en masse to DNA double-strand breaks through chromatin interactions, where it is phosphorylated by a DNA repair kinase in its unstructured N-terminus. These phosphorylation sites recruit downstream effectors RIF1 and shieldin that are also critical determinants of PARPi sensitivity. We identified these phosphorylation motifs in 53BP1 and show that they are directly bound by RIF1. We then developed an AlphaFold2 pipeline to perform a comprehensive pairwise protein interaction screen within the 53BP1-RIF1-shieldin pathway to identify a bona fide novel interaction site between RIF1 and shieldin. These findings represent a key milestone in the quest to understand the molecular basis for 53BP1-BRCA1 antagonism.