Abstract LB-071: Kub5-Hera/RPRD1B controls CDK1 regulation and synthetic lethality to PARP1 inhibition

Abstract

Abstract Aberrant CDK1 regulation induces impulsive proliferation as well as genomic and chromosomal instability in cancer cells. However, the mechanism of how CDK1 is regulated at the transcriptional level, especially under pathological conditions (e.g. cancer), remains elusive. Here, we show that Kub5-Hera (K-H), a known transcription termination factor, plays a novel role in promoting CDK1 transcription to mediate DNA repair and cellular response to PARP1 inhibition in various cancer cell lines. At the molecular level, we demonstrate via luciferase reporter assays and mutagenesis studies that K-H binds the phospho-Serine 2-containing C-terminal domain (CTD) of RNA Pol II, which is then recruited to the cell-cycle homology region (CHR) of the CDK1 promoter to efficiently stimulate CDK1 transcription. Mechanistically, the loss of K-H concomitantly reduces CDK1 mRNA/protein expression levels, which consequently compromises homologous recombination (HR)-mediated DNA repair due to the lack of BRCA1 phosphorylation for efficient function. Intriguingly, loss of K-H stimulates PARP1 activity needed for cancer cell survival. Genetic and pharmacological ablation of PARP1 activity in BRCA-proficient cells 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 attenuated RNAPII binding. The mechanistic insights gained from this study should lay foundation toward promising new tumor biology-based targets (i.e., K-H as a novel therapeutic target) and innovative strategies to reduce normal tissue toxicity, increase tumor control, and expand the use of PARP1 inhibitors (e.g., Rucaparib) against BRCA-proficient cancers with aberrant K-H loss. Citation Format: Edward A. Motea, Farjana Fattah, Ling Xiao, Luc Girard, Amy Rommel, Julio Morales, Praveen Patidar, Andrew Porter, John Minna, David Boothman. Kub5-Hera/RPRD1B controls CDK1 regulation and synthetic lethality to PARP1 inhibition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-071. doi:10.1158/1538-7445.AM2015-LB-071