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Type: Journal article
Title: Activation of protein phosphatase 2A in FLT3+ acute myeloid leukemia cells enhances the cytotoxicity of FLT3 tyrosine kinase inhibitors
Author: Smith, A.M.
Dun, M.D.
Lee, E.M.
Harrison, C.
Kahl, R.
Flanagan, H.
Panicker, N.
Mashkani, B.
Don, A.S.
Morris, J.
Toop, H.
Lock, R.B.
Powell, J.A.
Thomas, D.
Guthridge, M.A.
Moore, A.
Ashman, L.K.
Skelding, K.A.
Enjeti, A.
Verrills, N.M.
Citation: Oncotarget, 2016; 7(30):47465-47478
Publisher: Impact journals
Issue Date: 2016
ISSN: 1949-2553
Statement of
Amanda M. Smith, Matthew D. Dun, Erwin M. Lee, Celeste Harrison, Richard Kahl, Hayley Flanagan, Nikita Panicker, Baratali Mashkani, Anthony S. Don, Jonathan Morris, Hamish Toop, Richard B. Lock, Jason A. Powell, Daniel Thomas, Mark A. Guthridge, Andrew Moore, Leonie K. Ashman, Kathryn A. Skelding, Anoop Enjeti, Nicole M. Verrills
Abstract: Constitutive activation of the receptor tyrosine kinase Fms-like tyrosine kinase 3 (FLT3), via co-expression of its ligand or by genetic mutation, is common in acute myeloid leukemia (AML). In this study we show that FLT3 activation inhibits the activity of the tumor suppressor, protein phosphatase 2A (PP2A). Using BaF3 cells transduced with wildtype or mutant FLT3, we show that FLT3-induced PP2A inhibition sensitizes cells to the pharmacological PP2A activators, FTY720 and AAL(S). FTY720 and AAL(S) induced cell death and inhibited colony formation of FLT3 activated cells. Furthermore, PP2A activators reduced the phosphorylation of ERK and AKT, downstream targets shared by both FLT3 and PP2A, in FLT3/ITD+ BaF3 and MV4-11 cell lines. PP2A activity was lower in primary human bone marrow derived AML blasts compared to normal bone marrow, with blasts from FLT3-ITD patients displaying lower PP2A activity than WT-FLT3 blasts. Reduced PP2A activity was associated with hyperphosphorylation of the PP2A catalytic subunit, and reduced expression of PP2A structural and regulatory subunits. AML patient blasts were also sensitive to cell death induced by FTY720 and AAL(S), but these compounds had minimal effect on normal CD34+ bone marrow derived monocytes. Finally, PP2A activating compounds displayed synergistic effects when used in combination with tyrosine kinase inhibitors in FLT3-ITD+ cells. A combination of Sorafenib and FTY720 was also synergistic in the presence of a protective stromal microenvironment. Thus combining a PP2A activating compound and a FLT3 inhibitor may be a novel therapeutic approach for treating AML.
Keywords: PP2A; FTY720; AML; FLT3; tyrosine kinase inhibitor
Rights: Copyright status unknown
DOI: 10.18632/oncotarget.10167
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