title: Src family tyrosine kinases are activated by Flt3 and are involved in the proliferative effects of leukemia-associated Flt3 mutations.
abstract: OBJECTIVE
  The hematopoietic growth factor receptor, Fms-like tyrosine kinase-3 (Flt3), modulates survival and proliferation of myeloid and B-cell precursors. Activating mutations of Flt3 are the most common molecular abnormalities in acute myeloid leukemia (AML) and have an apparent role in leukemogenesis. However, signaling pathways mediating Flt3 effects are incompletely understood. The role of Src kinases is unknown, although some, such as Lyn, have also been linked to leukemogenesis. This study examines the role of Src kinases in Flt3 signaling and the oncogenic effects of leukemia-associated Flt3 mutations.
  
  
  METHODS
  We examined the activation and functional roles of Src kinases in human leukemic myeloid cell lines expressing wild-type Flt3 or a constitutively active mutant, and in cells stably transduced with human wild-type or mutant Flt3.
  
  
  RESULTS
  Flt3 ligand stimulation of wild-type Flt3 increased phosphorylation of Src kinase Lyn. Constitutive Lyn phosphorylation and activation was found in cells expressing constitutively active Flt3 mutants. Src kinases are implicated in downregulation of closely related receptors, but Src inhibitors had no effect on ligand-stimulated Flt3 degradation, or on the rapid degradation of an Flt3 mutant. However, growth-factor-independent proliferation resulting from mutant Flt3 expression did depend on the activity of Src kinases.
  
  
  CONCLUSIONS
  Our studies reveal for the first time the involvement of Src kinases in Flt3 signaling, with activation of Lyn by constitutively active Flt3 mutants as well as ligand-stimulated wild-type receptor, and show that Src kinase inhibitors block proliferative effects of Flt3 mutants found in AML. Thus, Src kinases may represent targets for inhibitor therapy in Flt3-related AML.
authors.affiliation: Department of Pathology, University of Pittsburgh Medical School, Pittsburgh, PA 15261, USA. robinsonlj@msx.upmc.edu
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Robinson
authors.forename: Jia
authors.initials: J
authors.lastname: Xue
authors.forename: Seth J
authors.initials: SJ
authors.lastname: Corey
mesh_terms: D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D006801:Humans; D007951:Leukemia, Myeloid / Q000209:etiology / Q000235:genetics* / Q000473:pathology; D008565:Membrane Proteins / Q000494:pharmacology; D009154:Mutation; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D051941:fms-Like Tyrosine Kinase 3; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; C084881:flt3 ligand protein; C497970:FLT3 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D051941:fms-Like Tyrosine Kinase 3; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases