The small heat shock protein Hsp27 has been long demonstrated as a major driver of Castration Resistant Prostate Cancer (CRPC) progression via an androgen receptor-independent pathway. In the light of identification of its molecular mechanisms, we found that the RNA helicase protein DDX5 was an interactor of Hsp27 and DDX5 expression was regulated by Hsp27 through its cytoprotective function. We showed that DDX5 was overexpressed in a large collection of human samples in aggressive PCs, especially CRPC. Here, we described the protein-protein interaction network of DDX5 which were identified in four human prostate cell lines (PNT1A, LNCaP, DU-145 and PC-3) representing different disease stages using immunoaffinity purification and quantitative mass spectrometry. The DDX5 interactome in CRPC cells was enriched in several functions (DNA damage response, translation, transcription, RNA stability, and DNA conformation changes) involved in disease progression. Furthermore, we found a new critical function of DDX5 in DNA damage repair in CRPC and validated the interaction of DDX5 with the DNA repair complex Ku70/Ku86 which plays a pivotal role in the NHEJ process. We also showed that DDX5 overexpression conferred resistance to DNA damage poisoners (such as irradiation and cisplatin) in CRPC, a feature that could lead to genome maintenance, tumor progression and treatment resistance.