Androgen receptor splicing variant 7 (ARv7) promotes DNA damage response in prostate cancer cells

In the treatment of patients with locally advanced prostate cancer (PCa), androgen deprivation therapy (ADT) significantly enhances the efficacy of radiotherapy by weakening the DNA damage response (DDR) pathway. Recently, several studies have suggested that androgen receptor splicing variants (ARvs) may mediate a compensatory DDR pathway when canonical androgen receptor (AR) signaling is inhibited, thus contributing to the resistance of some patients to this combinational treatment. However, the specific roles of certain ARvs as well as the detailed mechanism of how ARvs regulate the DDR are not well understood. Here, we demonstrated that AR splicing variant 7 (ARv7), which is the most abundant form of ARvs, significantly promotes the DDR of PCa cells under severe DNA damage independent of its parental AR by using the ionizing radiation (IR) and doxorubicin (Dox)-treated cell models. Mechanistically, ARv7 is sufficient to upregulate both the homologous recombination (HR) and the nonhomologous end joining (NHEJ) pathways by forming a positive regulatory loop with poly ADP-ribose polymerase 1 (PARP1). Moreover, the presence of ARv7 impairs the synergistic effect between AR antagonists and poly ADP-ribose polymerase (PARP) inhibitor, which has been recently shown to be a promising future treatment strategy for metastatic castration resistant prostate cancer (mCRPC). Combined, our data indicate that constitutively active ARv7 not only contributes to radioresistance after ADT, but may also serve as a potential predictive biomarker for assessing the efficacy of novel PARP inhibitor-based therapy in PCa.