Roles of IKK kinases and protein kinase CK2 in activation of nuclear factor-kappa B in breast cancer

Nuclear factor-kappaB (NF-kappaB)/Rel transcription factors regulate genes that control cell proliferation, survival, and transformation. In normal br east epithelial cells, NF-kappaB/Rel proteins are mainly sequestered in the cytoplasm bound to one of the specific inhibitory I kappaB proteins, where as in breast cancers they are activated aberrantly. Human breast tumor cell lines, carcinogen-transformed mammary epithelial cells, and the majority o f primary human or rodent breast tumor tissue samples express constitutivel y high levels of nuclear NF-kappaB/Rel. To begin to understand the mechanis m of this aberrant NF-kappaB/Rel expression, in this study we measured the activity of the major kinases implicated in regulation of I kappaB stabilit y, namely IKK alpha, IKK beta, and protein kinase, CK2 (formerly casein kin ase II). Hs578T, D3-1, and BP-1 breast cancer cell lines displayed higher l evels of IKK alpha, IKK beta, and CK2 activity than untransformed MCF-10F m ammary epithelial cells. Inhibition of IKK activity upon expression of domi nant negative kinases or of CK2 activity by treatment with selective inhibi tors decreased NF-kappaB/Rel activity in breast canter cells. Inactivation of the I kappaB kinase complex in Hs578T cells via expression of a dominant negative IKK gamma /NF-kappaB essential modulator/IKK-associated protein 1 reduced soft agar colony growth. Thus, the aberrant expression of CK2 or I KK kinases promotes increased nuclear levels of NF-kappaB/Rel and transform ation of breast cancer cells. Furthermore, primary human breast cancer spec imens that displayed aberrant constitutive expression of NF-kappaB/Rel were found to exhibit increased CK2 and/or IKK kinase activity. These observati ons suggest these kinases play a similar role in an intracellular signaling pathway that leads to the elevated NF-kappaB/Rel levels seen in primary hu man mammary tumors and, therefore, represent potential therapeutic targets in the treatment of patients with breast cancer.