Daple-FLT3 gene fusion activates and localizes through a distinct mechanism from FLT3-ITD

Gene fusions are stable protein products often occurring from chromosomal rearrangements. These chimeric proteins typically contain distinct molecular entities from each parent gene, and thus, create a product with altered or aberrant function. Gene fusions are frequently found in cancers, including Leukemia. Here, we characterize the kinase activity and subcellular distribution of the Daple-FLT3 (CCDC88C-FLT3) fusion oncoprotein-a rare, but recurrent gene fusion found in patients with hematological malignancies. The protein contains the FLT3 kinase domain and is activated without ligand stimulation. This leads to activation in STAT5a, AKT, and MAPK signaling, which can be modulated by the tyrosine kinase inhibitor (TKIs) sorafenib and to the most specific FLT3 inhibitor quizartinib. The fusions localize to the pericentrosomal space, a unique subcellular localization pattern that is different compared to the well-known FLT3-ITD mutation. We further demonstrate that localization and maximal kinase activation is dependent on the Daple coiled-coil domain. These findings provide evidence that targeting Daple-FLT3 outside of its kinase domain (i.e. the coiled-coil region) may be a complementary approach with TKI therapy.