Kub5‐Hera deficiency compromises homologous recombination and enhances vulnerability to PARP inhibition in BRCA‐proficient breast cancers

Purpose Identification of novel factors that compromise homologous recombination (HR) is key toward innovative strategies to expand the use of poly(ADP‐ribose) polymerase (PARP) inhibitors beyond BRCA deficiency. Our lab discovered that partial loss of Kub5‐Hera (K‐H), a transcription termination factor, stimulates the formation of various BRCA‐related cancers in female mice that was accelerated by single exposure to ionizing radiation (IR, 1 Gy). Here, we investigated how K‐H functionally impacts homologous recombination (HR) and cellular response to PARP inhibition in a subset of BRCA‐proficient breast cancer cell lines Experimental Methods The functional impact of K‐H alterations in a subset of breast cancer cell lines were assessed by targeted gene silencing, bioinformatics, mutagenesis techniques, plasmid reporter assays, immunofluorescence, microarray/qPCR analyses, chromatin immunoprecipitation, colony formation assays, rescue experiments and Western blots. Results Kub5‐Hera promotes the expression of a critical DNA damage response and repair effector, cyclin dependent kinase 1 (CDK1), which phosphorylates BRCA1 for efficient repair of double‐strand breaks (DSBs). Mechanistically, we demonstrate that K‐H binds RNA Polymerase II (RNAPII) at the CDK1 promoter to efficiently enhance CDK1 transcription. K‐H depletion compromises HR, but upregulates poly(ADP‐ribose) polymerase 1 (PARP1) activity for cancer cell survival. Genetic and pharmacological ablation of PARP1 activity in a subset of BRCA‐proficient cell lines with aberrant K‐H reduction leads to synthetic lethality, which is reversed by re‐expression of wild‐type K‐H but not the mutant with reduced RNAPII binding. Conclusions K‐H deficiency promotes genomic instability and a state of “BRCAness” in a subset of breast cancers. These cells may have an exploitable addiction to PARP‐mediated DNA repair for survival that could greatly expand the use of PARP inhibitors beyond BRCA mutations. Collectively, these results suggest that aberrant K‐H alterations may impact overall cellular response and survival to DNA damage and have clinical implications in cancer. Support or Funding Information NIH R01 CA210489 (PI: David A. Boothman); Minority Supplement CURE Award CA139217‐05S1 and T32CA124334 to E.A. Motea This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .