Title : Wnt-DP103-GSK3? Cascade Promotes Wnt/?-catenin Signaling in Parental and Stem Cells from Triple Negative Breast Cancer
Breast cancer is a principal cause of death in women globally and a diverse malignancy. Despite recent advances in breast cancer therapeutics, mortality of highly metastatic triple negative breast cancer (TNBC) subtype remains high; due to their lack hormone receptors expression for targeted therapy. Therefore, there is a pressing need to identify new prognostic markers and therapeutic targets for this group of breast cancers. Aberrant activation of Wnt/β-catenin signaling has been associated with breast cancers, where 40% of total breast cancers have elevated β-catenin levels and/or Wnt activity. Herein, we identify DEAD-box RNA helicase DP103 as a novel driver of Wnt/β-catenin pathway in TNBC. The link between DP103 and Wnt/beta-catenin signaling was further validated using in vivo Zebrafish models, where disruption in DDX20 gene splicing mechanisms resulted in severe early embryonic developmental defects such as reduced brain size, tail defects, lack of melanophores formation and cardiac deformities, which phenocopies loss of Wnt/beta-catenin signaling during gastrulation. Interestingly, we also show DP103 drives breast cancer stem cell (CSC) formation, a process regulated by the Wnt/beta-catenin pathway. Depletion of DP103 led to a marked reduction in the percentage of CSC-enriched mammospheres with reduced tumor-initiating ability. Mechanistically, we show DP103’s role in driving Wnt/beta-catenin pathway is independent of caesin kinase I activity but highly dependent on GSK3β activity. More interestingly, from molecular docking data, we found DP103 protein must be phosphorylated at threonine residue 552, when it interacts with GSK3β. Surprisingly, induction of Wnt/β-catenin signaling also significantly increased DP103 expression, indicating a possible positive feedback loop. Collectively, our data suggest a novel regulatory role of DP103 in the Wnt/β-catenin signaling pathway in parental and CSC derived TNBC - a study which has attracted Pharma company, Rexahn Pharmaceuticals Inc., USA to further develop their Phase I Wnt drug with our group here in Singapore.