DDX5, also known as p68, was first identified as a 68 kDa nuclear protein with similarity to translation initiation factor eIF-4A. DDX5 is a member of the DEAD box family of putative RNA helicases, defined by the presence of a conserved DEAD motif that appears to function primarily in the regulation of RNA secondary structure. DDX5 exhibits ATP-dependent RNA helicase activity and has been identified as a critical subunit of the DROSHA complex that regulates miRNA and rRNA processing. DDX may also regulate mRNA splicing and has been shown to interact with HDAC1, where it can regulate promoter-specific transcription. DDX5 interacts with a diverse group of proteins, including Runx2, p53, Smad3, CBP, and p300, suggesting an important role for DDX5 in a multitude of developmental processes. Notably, DDX5 may be involved in growth factor-induced epithelial mesechymal transition. Phosphorylation of DDX5 at Tyr593 following PDGF stimulation was shown to displace Axin from β-catenin; this prevented phosphorylation of β-catenin by GSK-3β, leading to Wnt-independent nuclear translocation of β-catenin and increased transcription of c-Myc, cyclin D1, and Snai1.
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