One of the main challenges in the treatment of advanced prostate cancer (PCa) is the development of therapeutic resistance to androgen targeted therapies (ATT). Cell lineage plasticity is increasingly being implicated as a part of adaptive response to ATT, however, the mechanisms that drive this plasticity are not well understood. We have previously identified an RNA binding protein, Quaking (QKI), that regulates breast cancer cell plasticity through changes in alternative mRNA splicing. In PCa clinical samples, we find QKI levels increase upon ATT during PCa progression and is further elevated in castration resistant PCa (CRPC). In LNCaP cells, QKI is markedly upregulated by treatment with the ATT - Enzalutamide (ENZ) and modulates ENZ-induced changes in cell plasticity and alternative splicing. Furthermore, knockout of QKI in the ENZ-resistant LNCaP derived cell line MR42D re-sensitises these cells to ENZ. In highly metastatic PC-3 cells, QKI modulates hallmark features of metastasis including changes in cell morphology, migration, and invasion with concomitant changes in alternative splicing. CLIP-seq studies demonstrate direct binding of QKI to many mRNAs where it particularly directs alternative splicing of cytoskeletal protein encoding transcripts. These studies suggest a widespread QKI-regulated alternative splicing program which influences the development of resistance to ATT and metastatic PCa progression. Overall, findings from this project will pave the way for novel alternative splicing targeting therapies to treat resistant PCa.