FLT3-ITD induces expression of Pim kinases through STAT5 to confer resistance to the PI3K/Akt pathway inhibitors on leukemic cells by enhancing the mTORC1/Mcl-1 pathway.

Keigo Okada,Ayako Nogami,Hiroki Akiyama,Yoshihiro Umezawa,Osamu Miura,Cheng Chen,Shinya Ishida

doi:10.18632/oncotarget.22926

Keigo Okada, Ayako Nogami + Show 5 more

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https://doi.org/10.18632/oncotarget.22926

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Journal: Oncotarget	Publication Date: Dec 4, 2017
Citations: 25	License type: cc-by

Affiliation: Tokyo Medical and Dental University

Abstract

FLT3-ITD is the most frequent tyrosine kinase mutation in acute myeloid leukemia (AML) associated with poor prognosis. We previously reported that activation of STAT5 confers resistance to PI3K/Akt inhibitors on the FLT3-ITD-positive AML cell line MV4-11 and 32D cells driven by FLT3-ITD (32D/ITD) but not by FLT3 mutated in the tyrosine kinase domain (32D/TKD). Here, we report the involvement of Pim kinases expressed through STAT5 activation in acquisition of this resistance. The specific pan-Pim kinase inhibitor AZD1208 as well as PIM447 in combination with the PI3K inhibitor GDC-0941 or the Akt inhibitor MK-2206 cooperatively downregulated the mTORC1/4EBP1 pathway, formation of the eIF4E/eIF4G complex, and Mcl-1 expression leading to activation of Bak and Bax to induce caspase-dependent apoptosis synergistically in these cells. These cooperative effects were enhanced or inhibited by knock down of mTOR or expression of its activated mutant, respectively. Overexpression of Mcl-1 conferred the resistance on 32D/ITD cells to combined inhibition of the PI3K/Akt pathway and Pim kinases, while the Mcl-1-specific BH3 mimetic A-1210477 conquered the resistance of MV4-11 cells to GDC-0941. Furthermore, overexpression of Pim-1 in 32D/TKD enhanced the mTORC1/Mcl-1 pathway and partially protected it from the PI3K/Akt inhibitors or the FLT3 inhibitor gilteritinib to confer the resistance to PI3K/Akt inhibitors. Finally, AZD1208 and GDC-0941 cooperatively inhibited the mTORC1/Mcl-1 pathway and reduced viable cell numbers of primary AML cells from some FLT3-ITD positive cases. Thus, Pim kinases may protect the mTORC1/4EBP1/Mcl-1 pathway to confer the resistance to the PI3K/Akt inhibitors on FLT3-ITD cells and represent promising therapeutic targets.

Highlights

FMS-like tyrosine kinase 3 (FLT3) is a receptortyrosine kinase expressed on hematopoietic progenitors and regulates early steps of hematopoietic progenitor cell proliferation, survival, and differentiation [1,2,3]
Inhibition of Pim kinases abrogates the resistance to PI3K/Akt pathway inhibitors conferred through robust STAT5 activation by FLT3-Internal tandem duplication (ITD)
To examine the possibility that Pim kinases mediate the resistance of FLT3-ITD-expressing cells to the PI3K/ Akt inhibitors, we examined the effects of AZD1208 on 32D cells driven by FLT3-ITD (32D/ITD) cells

Summary

Introduction

FMS-like tyrosine kinase 3 (FLT3) is a receptortyrosine kinase expressed on hematopoietic progenitors and regulates early steps of hematopoietic progenitor cell proliferation, survival, and differentiation [1,2,3]. MTORC1 plays a critical role in regulation of cap-dependent translation by phosphorylating 4EBP1 to release it from the mRNA m7-GTP cap-binding protein eIF4E, allowing its interaction with the scaffolding protein eIF4G to initiate the formation of the translationinitiating complex eIF4F. This mechanism is important for the translation of mRNAs containing long 5’-UTRs with a high G+C content, such as those for Mcl-1, c-Myc, and cyclin D1 [14,15,16]. We have previously found that FLT3ITD confers resistance to GDC-0941 and MK-2206 by protecting the mTOR pathway through the robust STAT5 activation to maintain the expression level of Mcl-1 [21]

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