Newton, Thomas R.Patel, Nikhil M.Bhat-Nakshatri, PoornimaStauss, Carmen R.Goulet, Robert J.Nakshatri, Harikrishna2019-04-162019-04-161999-06-25Newton, T. R., Patel, N. M., Bhat-Nakshatri, P., Stauss, C. R., Goulet, R. J., & Nakshatri, H. (1999). Negative Regulation of Transactivation Function but Not DNA Binding of NF-κB and AP-1 by IκBβ1 in Breast Cancer Cells. Journal of Biological Chemistry, 274(26), 18827–18835. https://doi.org/10.1074/jbc.274.26.188270021-9258, 1083-351Xhttps://hdl.handle.net/1805/18862The transcription factor NF-κB regulates the expression of genes involved in cancer cell invasion, metastasis, angiogenesis, and resistance to chemotherapy. In normal cells NF-κB is maintained in the cytoplasm by protein-protein interaction with inhibitor IκBs. In contrast, in cancer cells a substantial amount of NF-κB is in the nucleus and constitutively activates target genes. To understand the mechanisms of constitutive NF-κB activation, we have analyzed the function of IκBα and IκBβ in breast cancer cells. In most cases, constitutive NF-κB DNA binding correlated with reduced levels of either IκBα or IκBβ isoforms. Overexpression of IκBα but not IκBβ1 resulted in reduced constitutive DNA binding of NF-κB in MDA-MB-231 cells. Unexpectedly, IκBβ1 overexpression moderately increased 12-O-tetradecanoylphorbol-13-acetate- and interleukin-1-inducible NF-κB DNA binding. 12-O-Tetradecanoylphorbol-13-acetate- and interleukin-1-induced transactivation by NF-κB, however, was lower in IκBβ1-overexpressing cells. Mutants of IκBβ1 lacking the C-terminal casein kinase II phosphorylation sites, which form a stable complex with DNA bound NF-κB without inhibiting its transactivation in other cell types, repressed the transactivation by NF-κB in MDA-MB-231 cells. Consistent with the results of transient transfections, the expression of urokinase plasminogen activator, an NF-κB target gene, was reduced in IκBβ1-overexpressing cells. These results suggest that depending on the cell type, IκBβ1 represses the expression of NF-κB-regulated genes by inhibiting either DNA binding or transactivation function of NF-κB.en-USDNANF-κBbreast cancer cellsAP-1Article10.1074/jbc.274.26.18827