Expression analysis of Akirin-2, NFκB-p65 and β-catenin proteins in imatinib resistance of chronic myeloid leukemia.

OBJECTIVE: Chronic myleoid leukemia (CML) is a myeloproliferative disorder characterized with the constitutive activation of Bcr-Abl tyrosine kinase which is a target for imatinib, the first line treatment option for CML. Constitutive activation of NFκB and β-catenin signaling promotes cellular proliferation and survival and resistance to Imatinib therapy in CML. Akirin-2 is a nuclear protein which is required for NFκB dependent gene expression as a cofactor and has been linked to Wnt/beta-catenin pathway. The purpose of this study is to examine Akirin-2, NFκB and β-catenin in imatinib resistance of CML and to test if any direct physical protein-protein interaction exists between NFkB and both β-catenin and Akirin-2.

METHODS: RT-PCR and western blot were performed to determine Akirin-2, NFκB-p65 and β-catenin gene and protein expressions, Co-immunoprecipitation and chromatin immunoprecipitation analysis were carried out to detect the direct physical interactions and binding of NFκB-p65 and β-catenin proteins to MDR1 promoter region, respectively.

RESULTS: β-catenin and NFκB-p65 proteins bound to DNA promoter regions of MDR1 in imatinib-sensitive and resistant CML cells, whereas any direct protein-protein interaction could not be found between NFκB-p65 and Akirin-2 or β-catenin proteins. Nuclear β-catenin and NFκB-p65 levels increased in imatinib resistance. Moreover, increased Akirin-2 protein accumulation in the nucleus was shown for the first time in imatinib resistant CML cells.

DISCUSSION: We show for the first time that Akirin-2 can be a novel biomarker in imatinib resistance. Targeting Akirin-2, NFκB and β-catenin genes may provide an opportunity to overcome imatinib resistance in CML.