FLT3 and FLT3-ITD phosphorylate and inactivate the cyclin-dependent kinase inhibitor p27 ^Kip1 in acute myeloid leukemia

Abstract

P27Kip1 (p27) can prevent cell proliferation by inactivating cyclin-dependent kinases. This function is impaired upon phosphorylation of p27 at tyrosine residue 88. We observed that FLT3 and FLT3-ITD can directly bind and selectively phosphorylate p27 on this residue. Inhibition of FLT3-ITD in cell lines strongly reduced p27 tyrosine 88 phosphorylation and resulted in increased p27 levels and cell cycle arrest. Subsequent analysis revealed the presence of tyrosine 88 phosphorylated p27 in primary patient samples. Inhibition of FLT3 kinase activity with AC220 significantly reduced p27 tyrosine 88 phosphorylation in cells isolated from FLT3 wild type expressing acute myeloid leukemia (AML) patients. In FLT3-ITD positive AML patients, p27 tyrosine 88 phosphorylation was reduced in 5 out of 9 subjects, but, surprisingly, was increased in 4 patients. This indicated that other tyrosine kinases such as Src family kinases might contribute to p27 tyrosine 88 phosphorylation in FLT3-ITD positive AML cells. In fact, incubation with the Src family kinase inhibitor dasatinib could decrease p27 tyrosine 88 phosphorylation in these patient samples, indicating that p27 phosphorylated on tyrosine 88 may be a therapeutic marker for the treatment of AML patients with tyrosine kinase inhibitors.

Role of alternative polyadenylation dynamics in acute myeloid leukaemia at single-cell resolution

“…For instance, the down-regulated CDKN1B gene encoding P27 preferred using distal poly(A) site in 'Monocytes' in the AML027 pre-transplant (host) sample. P27 is an inhibitor of cell cycle progression, and FLT3 and FLT3-ITD can phosphorylate tyrosine residue 88 of P27, which impairs the function of cell proliferation prevention through inactivation of cyclin-dependent kinases in AML cells [43,44]. These findings are consistent with the main characteristic of AML that haematopoietic precursors are blocked from differentiating into mature myeloid cells, and further confirm the high involvement of APA in leukemic cells.…”

MEK inhibition enhances the response to tyrosine kinase inhibitors in acute myeloid leukemia

“…As FLT3 -WT and FLT3 mutants 46 are sensitive to midostaurin, and the receptor is activated in almost all types of AML 4,9,47,48 , we would propose the extended use of its combination with trametinib, even in FLT3 -WT patients. In this context, we demonstrate for the first time that ERK was also activated after sustained TKI treatment.…”

CDK6 Inhibition: A Novel Approach in AML Management

“…As PIM kinases phosphorylate and stabilize FLT3 [96], the combined inhibition of CDK6-PIM1-FLT3 interrupts a vicious cycle and feed-forward loop. The same feed-forward loop may explain why leukemic cells with FLT3-ITD alleles have a selective advantage which results in the expansion of FLT3-mutated clones: FLT3 together with PIM1 impairs expression of the CDK inhibitor p27 Kip by direct phosphorylation and/or by transcriptional repression; this promotes CDK6 kinase activity which in turn induces the transcription and activity of FLT3 and PIM1 [97,98] (Figure 4). Subsequent work extended these findings in FLT3-D835Y + cells and revealed additional transcriptional targets of CDK6 that are required for the viability and expansion of FLT3-mutant cells.…”