FLT3-ITD drives Ara-C resistance in leukemic cells via the induction of RUNX3

• FLT3-ITD induces RUNX3 expression in leukemic cells.
• The knockdown of RUNX3 expression sensitizes leukemic cells to Ara-C.
• The overexpression of RUNX3 per se confers enhanced resistance to Ara-C.

Internal tandem duplication (ITD) mutations of the FLT3 gene (FLT3-ITD) are well known to correlate with a poor prognosis in acute myeloid leukemia (AML). We previously reported that FLT3-ITD confers resistance to cytosine arabinoside (Ara-C), a key cytotoxic agent in AML treatments. In order to elucidate the detailed molecular mechanisms underlying the Ara-C resistance induced by FLT3-ITD, we performed a microarray gene expression analysis of the human leukemic cell line K562 transduced with FLT3-ITD (K562/FLT3-ITD) and identified RUNX3 as a downstream target of FLT3-ITD. The transcriptional induction of the RUNX3 expression by FLT3-ITD was noted on a Luciferase assay. The knockdown of the RUNX3 expression in the K562/FLT3-ITD cells increased the sensitivity to Ara-C, and the exogenous expression of RUNX3 per se resulted in the enhancement of Ara-C resistance in the K562 cells. A relationship between the FLT3-ITD-induced RUNX3 expression and Ara-C resistance was also observed in AML cells with an endogenous FLT3-ITD expression. Collectively, these findings demonstrate that RUNX3 is a prerequisite for Ara-C resistance via FLT3-ITD signaling.