The development ofimatinib (IM),a selective tyrosine kinase inhibitor for treatment of chronic myeloid leukemia (CML),is the first molecularly targeted therapy for the human malignancies.However,early relapses and IM-resistant disease remain significant problems.Thus alternative drug targets need to be identified.One candidate target is Ahi-1/AHI-1 (Abelson helper integration site-1),a recently discovered oncogene.The Ahi-1/AHI-1 protein contains one SH3 domain,seven WD40 repeats and multiple SH3 binding sites,indicating a regulatory role in signaling transduction.It is highly deregulated in leukemic stem cells from patients with CML.We have recently identified a novel AHI-1-BCR-ABL-JAK2 complex that mediates leukemic cell transformation and plays a key role in the IM response/resistance of primary CML stem/progenitor cells.To further understand the molecular mechanism ofAhi-1 s involvement in the biological activities and identify which domain ofAhi-1 is essential for the JAK2-BCR-ABL interaction,full length Ahi-1 and several mutant forms,including SH3 deletion (Ahi-1SH3△) and N-terminal deletion (Ahi-lN-ter△),were generated,and stably transduced into a BCR-ABL inducible BaF3 cell line,in which the level of expression of P210BCR-ABL can be down-regulated by exposure to doxycycline (Dox).