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Ubiquitinated PCNA drives USP1 synthetic lethality in cancer


ABSTRACT: CRISPR Cas9-based functional genomics screening is a powerful approach for identifying and characterizing novel oncology drug targets. Here, we elucidate the synthetic lethal mechanism of deubiquitinating enzyme USP1 in cancers with underlying DNA damage vulnerabilities, specifically BRCA1/2 mutant tumors and a subset of BRCA1/2 wild-type (WT) tumors. In sensitive cells, pharmacological inhibition of USP1 leads to decreased DNA synthesis concomitant with the induction of S-phase-specific DNA damage. Genome-wide CRISPR-Cas9 screens identified RAD18 and UBE2K, which promote PCNA mono- and polyubiquitination respectively, as downstream mediators of USP1 dependency. The accumulation of mono- and polyubiquitinated PCNA following USP1 inhibition was associated with a reduction in total PCNA protein levels. Ectopic expression of WT and ubiquitin-dead K164R PCNA reversed USP1 inhibitor sensitivity. Our results demonstrate, for the first time, that USP1 dependency hinges on the aberrant processing of mono- and polyubiquitinated PCNA. Moreover, this mechanism of USP1 dependency extends beyond BRCA1/2 mutant tumors to a novel subset of BRCA1/2 WT cancer enriched in ovarian and lung lineages. We further show PARP and USP1 inhibition are strongly synergistic in BRCA1/2 mutant cell lines and xenograft models. We postulate USP1 dependency unveils a previously uncharacterized vulnerability linked to post-translational modifications of PCNA. Taken together, USP1 inhibition may represent a unique therapeutic strategy for BRCA1/2 mutant tumors and a subset of BRCA1/2 WT tumors.

ORGANISM(S): Homo sapiens

PROVIDER: GSE214121 | GEO | 2022/09/27

REPOSITORIES: GEO

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