Casein kinase 2 (CK2) increases survivin expression via enhanced β-catenin–T cell factor/lymphoid enhancer binding factor-dependent transcription

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Abstract
Increased expression of casein kinase 2 (CK2) is associated with hyperproliferation and suppression of apoptosis in cancer. Mutations in the tumor suppressor APC (adenomatous polyposis coli) are frequent in colon cancer and often augment beta-catenin-T cell factor (Tcf)/lymphoid enhancer binding factor (Lef)-dependent transcription of genes such as c-myc and cyclin-D1. CK2 has also been implicated recently in the regulation of beta-catenin stability. To identify mechanisms by which CK2 promotes survival, effects of the specific CK2 inhibitors 4,5,6,7-tetrabromobenzotriazole (TBB) and 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole were assessed. TBB and 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole significantly decreased proliferation and increased apoptosis of HT29(US) colon cancer cells. RT-PCR and immunoblot analysis revealed that both inhibitors decreased survivin mRNA and protein levels in HT29(US) cells. Similar effects were observed with TBB in human DLD-1 and SW-480 colorectal cells as well as ZR-75 breast cancer cells and HEK-293T embryonic kidney cells. Expression of GFP-CK2alpha in HEK-293T cells resulted in beta-catenin-Tcf/Lef-dependent up-regulation of survivin and increased resistance to anticancer drugs. Augmented beta-catenin-Tcf/Lef-dependent transcription and resistance to apoptosis observed upon GFP-CK2alpha expression were abolished by TBB. Alternatively, HEK-293T cells expressing GFP-survivin were resistant to TBB-induced apoptosis. Finally, siRNA-mediated down-regulation of CK2alpha in HEK-293T cells coincided with reduced beta-catenin and survivin levels. Taken together, these results suggest that CK2 kinase activity promotes survival by increasing survivin expression via beta-catenin-Tcf/Lef-mediated transcription. Hence, selective CK2 inhibition or down-regulation in tumors may provide an attractive opportunity for the development of novel cancer therapies.