Signal transducer and activator of transcription 3 activation is required for Asp816 mutant c-Kit–mediated cytokine-independent survival and proliferation in human leukemia cells

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Abstract
Activating mutations of c-kit at codon 816 (Asp816) have been implicated in a variety of malignancies, including acute myeloid leukemia (AML). The mutant c-Kit receptor confers cytokine-independent survival of leukemia cells and induces tumorigenicity. Changes in the signal transduction pathways responsible for Asp816 mutant c-Kit–mediated biologic effects are largely undefined. The results of this study show that Asp816 mutant c-Kit induces constitutive activation of signal transducer and activator of transcription 3 (STAT3) and STAT1, and up-regulates STAT3 downstream targets, Bcl-xL and c-myc. The phosphatidylinositol-3-kinase (PI-3K)/Akt pathway, but not the Ras-mediated mitogen-activated protein (MAP) kinase pathway, is also constitutively activated by Asp816 mutant c-Kit. Suppression of STAT3 activation by a dominant negative molecule in MO7e leukemia cells transduced with mutant c-kit inhibits stem cell factor (SCF)-independent survival and proliferation, accompanied by the down-regulation of Bcl-xL and c-myc. However, activated STAT3 does not appear to be the sole mediator that is responsible for the phenotypic changes induced by Asp816 mutant c-Kit, because expression of constitutively activated STAT3 in MO7e cells does not completely reconstitute cytokine independence. Activation of other signaling components by mutant c-Kit, such as those in the PI-3K/Akt pathway, is demonstrated and may also be needed for the mutant c-Kit–mediated biologic effects. The investigation of altered signal transduction pathways and the resulting functional consequences mediated by Asp816 mutant c-Kit should provide important information for the characterization of subsets of leukemia and potential molecular pathways for therapeutic targeting.