DHX15 promotes prostate cancer progression by stimulating Siah2-mediated ubiquitination of androgen receptor

Androgen receptor (AR) activation is critical for prostate cancer (PCa) development and progression, including castration resistance. The nuclear export signal of AR (NES^AR) has an important role in AR intracellular trafficking and proteasome-dependent degradation. Here, we identified the RNA helicase DHX15 as a novel AR co-activator using a yeast mutagenesis screen and revealed that DHX15 regulates AR activity by modulating E3 ligase Siah2-mediated AR ubiquitination independent of its ATPase activity. DHX15 and Siah2 form a complex with AR, through NES^AR. DHX15 stabilized Siah2 and enhanced its E3 ubiquitin-ligase activity, resulting in AR activation. Importantly, DHX15 was upregulated in PCa specimens and its expression was correlated with Gleason scores and prostate-specific antigen recurrence. Furthermore, DHX15 immunostaining correlated with Siah2. Finally, DHX15 knockdown inhibited the growth of C4-2 prostate tumor xenografts in mice. Collectively, our data argue that DHX15 enhances AR transcriptional activity and contributes to PCa progression through Siah2.