PP2A-activating Drugs Enhance FLT3 Inhibitor Efficacy through AKT Inhibition–Dependent GSK-3β–Mediated c-Myc and Pim-1 Proteasomal Degradation
- 10 February 2021
- journal article
- research article
- Published by American Association for Cancer Research (AACR) in Molecular Cancer Therapeutics
- Vol. 20 (4), 676-690
- https://doi.org/10.1158/1535-7163.mct-20-0663
Abstract
Fms-like tyrosine like kinase 3 internal tandem duplication (FLT3-ITD) is present in acute myeloid leukemia (AML) in 30% of patients and is associated with short disease-free survival. FLT3 inhibitor efficacy is limited and transient but may be enhanced by multi-targeting of FLT3-ITD signaling pathways. FLT3-ITD drives both STAT5-dependent transcription of oncogenic Pim-1 kinase and inactivation of the tumor suppressor protein phosphatase 2A (PP2A), and FLT3-ITD, Pim-1 and PP2A all regulate the c-Myc oncogene. We studied mechanisms of action of co-treatment of FLT3-ITD-expressing cells with FLT3 inhibitors and PP2A-activating drug (PADs), which are in development. PADs, including FTY720 and DT-061, enhanced FLT3 inhibitor growth suppression and apoptosis induction in FLT3-ITD-expressing cell lines and primary AML cells in vitro and MV4-11 growth suppression in vivo. PAD and FLT3 inhibitor co-treatment independently downregulated c-Myc and Pim-1 protein through enhanced proteasomal degradation. c-Myc and Pim-1 downregulation was preceded by AKT inactivation, did not occur in cells expressing myristoylated (constitutively active) AKT1, and could be induced by AKT inhibition. AKT inactivation resulted in activation of GSK-3β, and GSK-3β inhibition blocked downregulation of both c-Myc and Pim-1 by PAD and FLT3 inhibitor co-treatment GSK-3β activation increased c-Myc proteasomal degradation through c-Myc phosphorylation on T58; infection with c-Myc with T58A substitution, preventing phosphorylation, blocked downregulation of c-Myc by PAD and FLT3 inhibitor co-treatment. GSK-3β also βphosphorylated Pim-1L/Pim-1S on S95/S4. Thus, PADs enhance efficacy of FLT3 inhibitors in FLT3-ITD-expressing cells through a novel mechanism involving AKT inhibition-dependent GSK-3β-mediated increased c-Myc and Pim-1 proteasomal degradation.Keywords
Other Versions
Funding Information
- Merit Review Award (BX002184)
- Department of Veterans Affairs Biomedical Laboratory Research and Development Service
- NIH NCI (RO1 CA163800)
- NIH NCI (R01 CA181654)
- NIH NCI (CA240993)
- NHLBI (HL144741R01)
This publication has 53 references indexed in Scilit:
- Pim-1 Kinase Phosphorylates and Stabilizes 130 kDa FLT3 and Promotes Aberrant STAT5 Signaling in Acute Myeloid Leukemia with FLT3 Internal Tandem DuplicationPLOS ONE, 2013
- Selective Akt Inhibitors Synergize with Tyrosine Kinase Inhibitors and Effectively Override Stroma-Associated Cytoprotection of Mutant FLT3-Positive AML CellsPLOS ONE, 2013
- Prognostic Relevance of Integrated Genetic Profiling in Acute Myeloid LeukemiaNew England Journal of Medicine, 2012
- A potential therapeutic target for FLT3-ITD AML: PIM1 kinaseLeukemia Research, 2012
- Pim kinase-dependent inhibition of c-Myc degradationOncogene, 2008
- Potentiation of antileukemic therapies by the dual PI3K/PDK-1 inhibitor, BAG956: effects on BCR-ABL– and mutant FLT3-expressing cellsBlood, 2008
- Constitutive Fms‐like tyrosine kinase 3 activation results in specific changes in gene expression in myeloid leukaemic cellsBritish Journal of Haematology, 2007
- Pim-1 is up-regulated by constitutively activated FLT3 and plays a role in FLT3-mediated cell survivalBlood, 2005
- Direct Repression of FLIP Expression by c-myc Is a Major Determinant of TRAIL SensitivityMolecular and Cellular Biology, 2004
- Protein Phosphatase 2A Regulates the Stability of Pim Protein KinasesJournal of Biological Chemistry, 2003