The response to Poly (ADP-ribose) polymerase inhibitors (PARPi) is dictated by  homologous recombination (HR) DNA repair mechanisms and the abundance of lesions  that trap PARP enzymes on chromatin. It remains unclear, however, if the established  role of PARP in promoting chromatin accessibility impacts viability in these settings.  Using a CRISPR based screen, we identify the PAR-binding Snf2-like ATPase, ALC1 as  a key determinant of PARPi toxicity in HR-deficient cells. ALC1 loss reduced viability  of BRCA mutant cells and enhanced their sensitivity to PARPi by up to 250-fold, while  overcoming several known resistance mechanisms. ALC1 loss was not epistatic to other  repair pathways that execute the PARPi response. Instead, ALC1 deficiency reduced  chromatin accessibility concomitant with a decrease in the association of repair factors.  This resulted in an accumulation of replication associated DNA damage and a reliance on  HR. These findings establish PAR-dependent chromatin remodeling as a mechanistically  distinct aspect of PARPi responses, implicating ALC1 inhibition as a new approach to  overcome therapeutic resistance in HR-deficient cancers. SOURCE: Zhendong Cao (shi.pennlab@gmail.com) - Junwei Shi university of pennsylvania

Pluto Bioinformatics

GSE149104: ALC1 and PARP activities coordinate chromatin accessibility and viability in homologous recombination deficient cells (RNA-seq)