Abstract A51: The role of ATF6-mediate AP-1 signaling in promoting PARP inhibitor-resistant ovarian cancer

Abstract

Abstract The purpose of this study is to define the role of AP-1 mediated DNA repair in PARP inhibitor (PARPi)-resistant high-grade serous ovarian cancer (HGSOC). AP-1 is a dimeric transcription factor comprising Jun, Fos, and/or ATF proteins and its signaling is known to regulate multiple DNA repair genes, including PARP1. Wnt activation can promote AP-1 signaling and upregulates expression of AP-1 subunits. We previously published that hyperactive Wnt signaling in PARPi-resistant HGSOC cells promotes DNA repair and attenuates PARPi response. We therefore hypothesized that Wnt signaling drives PARPi resistance thorough increased AP1-signaling and subsequent enhanced DNA repair. We performed transcription factor analysis of RNA sequencing data from TP53/BRCA2-mutated olaparib-sensitive (PEO1) and -resistant (PEO1-OR) HGSOC cells. We observed increased AP-1 target genes in resistant cells and confirmed elevated AP-1 activity with a reporter assay. Quantitative PCR (qPCR) demonstrated that a majority of AP-1 subunits were upregulated in olaparib-resistant cells, namely JUN, ATF5, and ATF6. An shRNA screen was performed to determine which AP-1 subunits are necessary to convey olaparib resistance. Four out of five shRNAs targeting ATF6 effectively resensitized PARPi-resistant cells to olaparib. We confirmed that ATF6 protein was elevated in PEO1-OR cells. To further explore the role of ATF6 in AP-1 mediated PARPi resistance, ATF6 was stably knocked down in PEO1-OR cells. Colony formation assays confirmed that loss of ATF6 resensitized cells to olaparib. Knockdown of ATF6 also resulted in decreased transcription of PARP1, as measured by qPCR, and higher baseline levels of DNA damage, as measured by phosphorylated histone gamma-H2AX. Future studies will evaluate ATF6-dependent DNA repair in in vitro and in vivo models of PARPi-resistant HGSOC. In summary, these data indicate activation of AP-1 signaling through increased expression of ATF6 is promoting enhanced DNA repair capacity, which could be contributing to PARPi resistance. Thus, pharmacologic inhibition of AP-1 or ATF6 could provide a targetable approach to overcome resistance and improve patient outcomes. Citation Format: Alexandra N. McMellen, Benjamin G. Bitler. The role of ATF6-mediate AP-1 signaling in promoting PARP inhibitor-resistant ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A51.