Crosstalk between FLT3/ITD mutation and the cellular morphogens

Abstract

FLT3 (fms-like tyrosine kinase 3), also known as FLK2 (fetal liver kinase 2) and STK1 (human stem cell kinase 1), belongs to the class III RTK (receptor tyrosine kinase) family and was originally cloned from hematopoietic progenitor cells. The gain-of-function mutation, FLT3/ITD (internal tandem duplication), occurs in 30% of AML (acute myeloid leukemia) and is associated with inferior clinical prognosis. TKI (tyrosine kinase inhibitor) including sorafenib and AC220 were effective in inducing remission. However, resistance to TKI was common, suggesting the targets are likely to be evolving and warrant further investigation. In this study, we made use of zebrafish embryo model to unveil the mechanism by which FLT3 mutations affect the hematopoiesis and morphogenesis in a whole organism level. Low dosage of FLT3/ITD mRNA (250pg per embryo) injection at 1-2 cell stage induced evident myeloid cells (pu.1 and l-plastin) expansion, but not affecting the erythroid cells (gata1) and hematopoietic progenitor cells (scl) at 18 hpf (hour post fertilization). Intriguingly, high dosage of FLT3/ITD mRNA (450-750pg per embryo) injection resulted in significant dorsalization phenotype (even axis duplication and double-head in a proportion of the embryos), and was effectively ameliorated by AC220 administration. FLT3/ITD embryos showed expanded and radial gsc (goosecoid) expression at shield stage (6 hpf), suggesting that the certain morphogens may be altered by FLT3/ITD. Morphogens regulating the DV (dorsal/ventral) and AP (anterior/posterior) development, such as WNT (wingless), BMP (bone morphogenetic protein), FGF (fibroblast growth factor), TGF-β (transforming growth factor beta), Hedgehog, Retinoic acid, etc., may be implicated in the FLT3 mutated AML and served as valuable therapeutic targets.