GSK3βlocalization in CML CP progenitors in response to GF stimulation and IM. Freshly isolated normal (A) and CML (B) CD34⁺CD38⁻ cells were cultured in the absence of serum and cytokines (−5GF) for 6 hours, and then exposed for 2 hours to a 5 GF cocktail (+5GF) in the absence (no drug) or presence of dasatinib (0.15μM) and/or IM (1μM), SB216763 (5μM) alone, or the combination of IM and SB216763. Each confocal image is representative of 3 immunofluorescence analyses of GSK3β using an anti-GSK3β Alexa Fluor 488–conjugated Ab (top panels). Overlap of GSK3β fluorescence signal and 4′,6-diamidino-2-phenylindole staining (bottom panels) is also shown (magnification, 60×). The depicted model illustrates that the shuttling of GSK3β in and out of the nucleus of normal cells is promoted by a GF-receptor engagement of SRC tyrosine kinases, because it is selectively inhibited by dasatinib but not imatinib. GSK3β is mislocalized to the cytoplasm of GF-stimulated CML cells and relocated to the nucleus after IM treatment, indicating a BCR-ABL kinase–dependent regulation.