Fyn Expression Potentiates Flt3-Itd-Induced Mitogenic Signaling In Acute Myeloid Leukemia

FYN is a non-receptor tyrosine kinase belonging to the SRC family of kinases. SRC family kinases are frequently over-expressed in human cancers, and play key roles in cancer cell invasion, metastasis, proliferation, survival and many other biological processes. SRC has long been recognized as an important oncogene; but little attention has been given to its other family members such as FYN. In this report, we have studied the role of FYN in FLT3 signaling with respect to acute myeloid leukemia (AML). FLT3 is a type III receptor tyrosine kinase which is found to be mutated in around 30% of AML cases. We observed that FYN displays a strong association with wild-type FLT3 as well as oncogenic FLT3-ITD. While association with wild-type FLT3 is dependent on ligand stimulation, it is constitutively associated with FLT3-ITD. In addition, a kinase-dead FLT3 mutant was unable to associate with FYN suggesting that FLT3 activation is required for association with FYN. A FYN SH2-domain mutant lacking a critical arginine residue was unable to associate with FLT3 indicating that FYN associates with FLT3 through its SH2 domain. A phopho-peptide fishing experiment identified multiple FYN binding sites in FLT3, which partially overlap with the known SRC binding sites but also differ from these sites. To understand the role of FYN in FLT3 signaling, we have generated Ba/F3-FLT3/FYN or Ba/F3-FLT3/empty vector cell lines. We observed that expression of FYN results in enhanced phosphorylation of AKT, ERK1/2 and p38 phosphorylation in response to ligand stimulation. Ba/F3-FLT3-ITD cells overexpressing FYN also showed higher STAT5 activation. Furthermore, FYN expression led to a significant increase in FLT3-ITD-dependent cell proliferation but did not alter apoptosis induced by cytokine starvation. Finally, we showed that FYN expression was deregulated in AML patient samples and that higher expression of FYN in combination with FLT3-ITD expression correlates with poor prognosis in AML. Taken together our data suggest that FYN cooperates with oncogenic FLT3-ITD which results in poor prognosis in AML and therefore inhibition of FYN in combination with FLT3 inhibition will most likely be beneficial for AML patients. Citation Format: Rohit A. Chougule, Julhash U. Kazi, Lars Ronnstrand. FYN expression potentiates FLT3-ITD-induced mitogenic signaling in acute myeloid leukemia. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1135.