title: FLT3 ligand causes autocrine signaling in acute myeloid leukemia cells.
abstract: The FLT3 receptor tyrosine kinase is highly expressed in most acute leukemias and frequently mutated in acute myeloid leukemia (AML). The mutated form of the receptor is constitutively activated and known to play an important role in AML, but the activation state of the overexpressed wild-type (wt) receptor is, at present, unknown. In this study, we examined the activation state of the wild-type receptor in AML. We found that the wild-type receptor was constitutively phosphorylated/activated in 8 of 12 primary AML samples and 4 of 13 leukemia cell lines. To explain why wtFLT3 is often activated, we investigated the expression of its ligand, FL, by these same cells. Coexpression of FL with FLT3 was a universal finding in both primary AML samples and leukemic-derived cell lines. To further prove that autocrine signaling was accounting for the activation, we showed that conditioned media but not fresh media was able to activate FLT3. In addition, an antibody that blocks binding of ligand to the receptor blocks FLT3 activation. Finally, depletion of FL from conditioned media is able to block the activation of FLT3. Taken together, these findings represent strong evidence that wtFLT3 is often constitutively activated in AML and thus, like its mutated form, might contribute to the altered signaling that characterizes leukemogenesis.
authors.affiliation: Johns Hopkins University School of Medicine, Oncology, Pediatrica, Baltimore, MD 21231-1000, USA.
authors.forename: Rui
authors.initials: R
authors.lastname: Zheng
authors.forename: Mark
authors.initials: M
authors.lastname: Levis
authors.forename: Obdulio
authors.initials: O
authors.lastname: Piloto
authors.forename: Patrick
authors.initials: P
authors.lastname: Brown
authors.forename: Brenda R
authors.initials: BR
authors.lastname: Baldwin
authors.forename: Norbert C
authors.initials: NC
authors.lastname: Gorin
authors.forename: Miloslav
authors.initials: M
authors.lastname: Beran
authors.forename: Zhenping
authors.initials: Z
authors.lastname: Zhu
authors.forename: Dale
authors.initials: D
authors.lastname: Ludwig
authors.forename: Dan
authors.initials: D
authors.lastname: Hicklin
authors.forename: Larry
authors.initials: L
authors.lastname: Witte
authors.forename: Yiwen
authors.initials: Y
authors.lastname: Li
authors.forename: Donald
authors.initials: D
authors.lastname: Small
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D017077:Culture Media, Conditioned; D004273:DNA, Neoplasm / Q000235:genetics; D004789:Enzyme Activation; D006801:Humans; D007938:Leukemia / Q000235:genetics / Q000378:metabolism; D015470:Leukemia, Myeloid, Acute / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D008223:Lymphoma / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051941:fms-Like Tyrosine Kinase 3
chemical_list: D017077:Culture Media, Conditioned; D004273:DNA, Neoplasm; D008024:Ligands; 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