Internal tandem duplication of FLT3 (FLT3/ITD) induces increased ROS production, DNA damage, and misrepair: implications for poor prognosis in AML

Abstract

IntroductionAcute myeloid leukemia (AML) is an aggressive form of a malignant disorder of the hematopoietic system that shows increasing incidence with age and is characterized by highly proliferative blast cells. [1][2][3] Aberrant activity of tyrosine kinases has been shown to be present in various malignant diseases and AML is no exception. The FMS-like tyrosine kinase 3 (FLT3) gene in chromosome band 13q12 encodes a receptor tyrosine kinase that belongs to the same family as FMS, KIT, and the 2 genes encoding PDGFR␣ and ␤. [4][5][6][7] It is normally expressed by hematopoietic stem/progenitor cells (HSPCs) and as hematopoietic cells differentiate FLT3 expression is lost. [8][9][10][11] A large body of work has shown that FLT3 plays roles in survival, proliferation, and differentiation. Aside from its role in regulating normal hematopoiesis, FLT3 is also highly expressed in several hematologic malignancies. 7 Mutations in the receptor, in the form of internal tandem duplication (ITD) of the juxtamembrane domain and point mutations of the kinase domain, both result in constitutive activation. 7 These mutations occur in one third of AML patients making it one of the most commonly mutated genes in AML. 12,13 Patients with FLT3/ITD mutations have been demonstrated to have very poor prognosis. 5,14,15 However, the molecular basis by which FLT3/ITD mutations lead to aggressive disease and poor prognosis in AML is not yet clearly understood.The process of activation, internalization, and degradation of FLT3 occurs in a similar fashion to other members of the class III receptor-type tyrosine kinases (RTKs) family. 16 Binding of FLT3 ligand (FL) causes homodimerization, tyrosine kinase activation, receptor autophosphorylation, and initiation of downstream signaling cascades. 7 The FLT3 receptor kinase shares structural homology with other type III receptor kinases, such as KIT and FMS, with all 3 playing an important role in survival, proliferation, and differentiation of hematopoietic cells. 17 We and other investigators have shown that STAT5 is one of the principal pathways involved in mediating gene expression in response to constitutive receptor activation through mutation. FLT3 signaling results in activation of pathways through phosphorylation of STAT5, MAPK, AKT, VAV, CBL, and BAD. [18][19][20] Phosphorylation and activation of STAT5 by FLT3/ITD mutants are particularly strong compared with its phosphorylation in the wild-type FLT3 allele. 21 STAT5 tyrosine phosphorylation mediates STAT5 protein dimerization through a mechanism involving SH2 domains and N-terminal regions and results in translocation to the nucleus where it activates transcription of a number of genes. 22 However, recent data suggest that STAT5 may have other interacting partners. 23,24 For example, signal-transducing adapter proteins (STAPs) have been shown to constitutively interact with inactive STAT5 in the cytoplasm but dissociate when STAT5 is phosphorylated. 24 STAT5 is also phosphorylated on serine residues, possibly by the ERK1/2 prote...

Targeting MTHFD2 in acute myeloid leukemia

“…It will thus be important to test FLT3 inhibitors in combination with MTH FD2 suppression in future studies. Although the precise mechanism for increased sensitivity to MTH FD2 suppression in FLT3-ITD AML is uncertain, one might speculate that the increased production of reactive oxygen species by internal tandem duplications of FLT3 may render greater sensitivity (Sallmyr et al, 2008;Godfrey et al, 2012;Stanicka et al, 2015).…”

NADPH Oxidase-generated Hydrogen Peroxide Induces DNA Damage in Mutant FLT3-expressing Leukemia Cells

“…Constitutively activated FLT3-ITD kinase stimulates aberrant proliferative signaling pathways, including PI3K, RAS/ERK, and STAT5 pathways characterized by resistance to apoptosis, abnormal cell growth, and differentiation block (6 -10). It was also demonstrated that cells expressing the ITD-mutated FLT3 generate higher levels of ROS (11)(12)(13). ROS, for example, H 2 O 2 , are considered to play an important role in cancers, including leukemia (14,15).…”

“…Sallmyr et al (11) showed that FLT3-ITD-generated ROS are mediated by Rac1 GTPase, which is an essential component of the NOX complex. NOXs are one of the sources of ROS in cells.…”

Drug resistance in mutant FLT3-positive AML

“…Intracellular reactive oxygen species (ROS) have the potential to damage DNA, leading to direct oxidation or DNA strand breaks . Consistent with this model, FLT3-ITD has been shown to induce ROS production, as well as DNA damage and decreased fidelity of DNA repair (Sallmyr et al, 2008). Cells transformed by FLT3-ITD and other oncogenic tyrosine kinases are also associated with increased mutagenic single-strand annealing (SSA), a repair process that involves sequence repeats (Cramer et al, 2008;Fernandes et al, 2009).…”