Pim-1 kinase phosphorylates and stabilizes 130 kDa FLT3 and promotes aberrant STAT5 signaling in acute myeloid leukemia with FLT3 internal tandem duplication

PLoS One. 2013 Sep 5;8(9):e74653. doi: 10.1371/journal.pone.0074653. eCollection 2013.


The type III receptor tyrosine kinase fms-like tyrosine kinase 3 (FLT3) is expressed on both normal hematopoietic stem cells and acute myeloid leukemia (AML) cells and regulates their proliferation. Internal tandem duplication (ITD) mutation of FLT3 is present in a third of AML cases, results in constitutive activation and aberrant signaling of FLT3, and is associated with adverse treatment outcomes. While wild-type (WT) FLT3 is predominantly a 150 kDa complex glycosylated cell surface protein, FLT3-ITD is partially retained in the endoplasmic reticulum as a 130 kDa underglycosylated species associated with the chaperones calnexin and heat shock protein (HSP) 90, and mediates aberrant STAT5 signaling, which upregulates the oncogenic serine/threonine kinase Pim-1. FLT3 contains a Pim-1 substrate consensus serine phosphorylation site, and we hypothesized that it might be a Pim-1 substrate. Pim-1 was indeed found to directly interact with and serine-phosphorylate FLT3. Pim-1 inhibition decreased the expression and half-life of 130 kDa FLT3, with partial abrogation by proteasome inhibition, in association with decreased FLT3 binding to calnexin and HSP90, and increased 150 kDa FLT3 expression and half-life, with abrogation by inhibition of glycosylation. These findings were consistent with Pim-1 stabilizing FLT3-ITD as a 130 kDa species associated with calnexin and HSP90 and inhibiting its glycosylation to form the 150 kDa species. Pim-1 knockdown effects were similar. Pim-1 inhibition also decreased phosphorylation of FLT3 at tyrosine 591 and of STAT5, and expression of Pim-1 itself, consistent with inhibition of the FLT3-ITD-STAT5 signaling pathway. Finally, Pim-1 inhibition synergized with FLT3 inhibition in inducing apoptosis of FLT3-ITD cells. This is, to our knowledge, the first demonstration of a role of Pim-1 in a positive feedback loop promoting aberrant signaling in malignant cells.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Calnexin / metabolism
  • Cell Line
  • Cell Proliferation
  • Endoplasmic Reticulum / metabolism
  • Glycosylation
  • Heat-Shock Proteins / metabolism
  • Humans
  • Leukemia, Myeloid, Acute / metabolism*
  • Mice
  • Mutation
  • Phosphorylation
  • Proteasome Endopeptidase Complex / metabolism
  • Proto-Oncogene Proteins c-pim-1 / metabolism*
  • STAT5 Transcription Factor / metabolism*
  • Serine / metabolism
  • Signal Transduction*
  • Tyrosine / metabolism
  • fms-Like Tyrosine Kinase 3 / metabolism*


  • Heat-Shock Proteins
  • STAT5 Transcription Factor
  • Calnexin
  • Tyrosine
  • Serine
  • FLT3 protein, human
  • fms-Like Tyrosine Kinase 3
  • Proto-Oncogene Proteins c-pim-1
  • Proteasome Endopeptidase Complex