Updated in 4/7/2013 12:01:15 PM      Viewed: 153 times      (Journal Article)
Clinical cancer research : an official journal of the American Association for Cancer Research 9 (6): 2140-50 (2003)

Overexpression and constitutive activation of FLT3 induces STAT5 activation in primary acute myeloid leukemia blast cells

K Spiekermann , K Bagrintseva , R Schwab , K Schmieja , W Hiddemann
AbstractPURPOSE: Activating length mutations in the juxtamembrane domain (FLT3-LM) and mutations in the tyrosine kinase domain (FLT3-TKD) of FLT3 represent the most frequent genetic alterations in acute myeloid leukemia (AML). However, the functional role of active FLT3 mutants in primary AML blast cells is not well characterized.EXPERIMENTAL DESIGN: We analyzed the transforming potential and the signaling of FLT3-ITD mutants in Ba/F3 cells and in primary AML blasts.RESULTS: FLT3-ITD mutants induce an autophosphorylation of the receptor, interleukin 3-independent growth in Ba/F3 cells, and a strong STAT5 and mitogen-activated protein kinase (MAPK) activation. In contrast to the FLT3-ITD mutants, the ligand-stimulated FLT3-WT receptor was unable to transduce a fully proliferative response in Ba/F3 and monocytic OCI-AML5 cells. The ligand-stimulated FLT3-WT receptor activated AKT and MAPK, but not STAT5. In primary blast cells from 60 patients with AML, FLT3 was expressed in 91.9% of patients carrying a FLT3-LM/TKD mutation compared with 77.8% in FLT3-LM/TKD-negative patients. STAT3 and STAT5 were constitutively activated in 76 and 63% of patients, respectively. In accordance with the results in Ba/F3 cells, a high FLT3 expression and the presence of a FLT3-LM was strongly associated with the STAT5 but not with the STAT3 activation in primary AML blast cells. Moreover, the constitutive tyrosine phosphorylation of STAT5 was efficiently down-regulated by a FLT3 protein tyrosine kinase inhibitor in AML cells expressing an active FLT3 mutant.CONCLUSIONS: Active FLT3 receptor mutants have transforming potential in hematopoietic cells and induce a strong activation of STAT5 in primary AML cells. The FLT3-STAT5 pathway contributes to the malignant phenotype and represents a promising molecular therapeutic target structure in AML.
ISSN: 1078-0432