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. C4-2 cells stably expressing ARv7 and 22Rv-1 cells with ARv7 depletion were generated by puromycin selection. Then total RNA was extracted to assess the differentially expressed genes after ARv7 levels changes.

在局部晚期前列腺癌（prostate cancer, PCa）患者的治疗中，雄激素剥夺疗法（androgen deprivation therapy, ADT）可通过削弱DNA损伤应答（DNA damage response, DDR）通路显著提升放疗疗效。近期多项研究表明，当经典雄激素受体（androgen receptor, AR）信号通路受到抑制时，雄激素受体剪接变异体（androgen receptor splicing variants, ARvs）可能介导代偿性DNA损伤应答通路，进而导致部分患者对该联合治疗产生耐药性。然而，部分ARvs的具体功能以及ARvs调控DNA损伤应答的详细机制仍未被完全阐明。本研究通过电离辐射（ionizing radiation, IR）和多柔比星（doxorubicin, Dox）处理的细胞模型，证实了丰度最高的ARvs形式——雄激素受体剪接变异体7（androgen receptor splicing variant 7, ARv7）可在不依赖亲本AR的情况下，显著促进严重DNA损伤下前列腺癌细胞的DNA损伤应答。从机制上来说，ARv7可与多聚ADP核糖聚合酶1（poly ADP-ribose polymerase 1, PARP1）形成正向调控环路，从而同时上调同源重组（homologous recombination, HR）与非同源末端连接（nonhomologous end joining, NHEJ）通路。此外，ARv7的存在会削弱雄激素受体拮抗剂与多聚ADP核糖聚合酶（poly ADP-ribose polymerase, PARP）抑制剂之间的协同作用——而该协同疗法近期被证实是治疗转移性去势抵抗性前列腺癌（metastatic castration resistant prostate cancer, mCRPC）的潜在新兴策略。综合来看，本研究数据表明，组成型激活的ARv7不仅会加剧雄激素剥夺疗法后的放射抵抗，还可作为潜在的预测生物标志物，用于评估基于新型PARP抑制剂的前列腺癌治疗方案的疗效。本研究通过嘌呤霉素筛选，构建了稳定表达ARv7的C4-2细胞系以及敲低ARv7的22Rv-1细胞系。随后提取总RNA，以分析ARv7水平变化后差异表达的基因。