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Haematologica 2019 Volume 104(12):2418-2428
Acute Myeloid Leukemia
FLT3-ITD cooperates with Rac1
to modulate the sensitivity of leukemic cells to chemotherapeutic agents via regulation of DNA repair pathways
Min Wu,1 Li Li,2 Max Hamaker,1 Donald Small2 and Amy S. Duffield1
1Department of Pathology and 2Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins Hospital, Baltimore, Maryland, USA
ABSTRACT
Acute myeloid leukemia (AML) is an aggressive hematologic neo- plasm, and patients with an internal tandem duplication (ITD) muta- tion of the FMS-like tyrosine kinase-3 (FLT3) receptor gene have a poor prognosis. FLT3-ITD interacts with DOCK2, a G effector protein that activates Rac1/2. Previously, we showed that knockdown of DOCK2 leads to decreased survival of FLT3-ITD leukemic cells. We further investigated the mechanisms by which Rac1/DOCK2 activity affects cell survival and chemotherapeutic response in FLT3-ITD leukemic cells. Exogenous expres- sion of FLT3-ITD led to increased Rac1 activity, reactive oxygen species, phosphorylated STAT5, DNA damage response factors and cytarabine resistance. Conversely, DOCK2 knockdown resulted in a decrease in these factors. Consistent with the reduction in DNA damage response factors, FLT3-ITD cells with DOCK2 knockdown exhibited significantly increased sensitivity to DNA damage response inhibitors. Moreover, in a mouse model of FLT3-ITD AML, animals treated with the CHK1 inhibitor MK8776 + cytarabine survived longer than those treated with cytarabine alone. These findings suggest that FLT3-ITD and Rac1 activity cooperative- ly modulate DNA repair activity, the addition of DNA damage response inhibitors to conventional chemotherapy may be useful in the treatment of FLT3-ITD AML, and inhibition of the Rac signaling pathways via DOCK2 may provide a novel and promising therapeutic target for FLT3-ITD AML.
Introduction
Acute myeloid leukemia (AML) is an aggressive hematologic neoplasm character- ized by clonal expansion of myeloid blasts. Over 30% of AML patients harbor acti- vating mutations in the FMS-like tyrosine kinase-3 (FLT3) gene, and those who carry an internal tandem duplication (ITD) mutation in the juxtamembrane domain have a particularly poor prognosis.1,2 FLT3 is a receptor tyrosine kinase that plays important roles in the survival, proliferation and differentiation of hematopoietic stem/progenitor cells.3-5 The FLT3-ITD mutation confers constitutive autophospho- rylation and activation of downstream signaling pathways, including PI-3- kinase/AKT, RAS/ERK and STAT5.2,6
FLT3 interacts with Dedicator of Cytokinesis 2 (DOCK2), which is a guanine nucleotide exchange factor for Rac1 and Rac2.7-10 Rac1 is widely expressed and plays key regulatory roles in various cellular functions, including actin cytoskeleton reorganization, cell proliferation, DNA damage response (DDR), angiogenesis and glucose uptake.11-16 Unlike Rac1, DOCK2 is expressed predominantly in hematopoi- etic tissues.10 DOCK2 is known to regulate several crucial processes, including lym- phocyte migration, activation and differentiation of T cells, cell-cell adhesion, and bone marrow homing of various immune cells.17-28 Patients with DOCK2 deficiency exhibit pleiotropic immune defects, often characterized by early-onset invasive bacterial and viral infections with T- and/or B-cell lymphopenia, as well as defective T-cell, B-cell, and natural killer-cell responses.29,30
We previously demonstrated that suppression of DOCK2 expression in FLT3-
Correspondence:
AMY S. DUFFIELD
aduffie1@jhmi.edu
Received: October 10, 2018. Accepted: April 9, 2019. Pre-published: April 11, 2019.
doi:10.3324/haematol.2018.208843
Check the online version for the most updated information on this article, online supplements, and information on authorship & disclosures: www.haematologica.org/content/104/12/2418
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