Negative regulation of transactivation function but not DNA binding of NF-kappaB and AP-1 by IkappaBbeta1 in breast cancer cells.
The transcription factor NF-kappaB regulates the expression of genes involved in cancer cell invasion, metastasis, angiogenesis, and resistance to chemotherapy. In normal cells NF-kappaB is maintained in the cytoplasm by protein-protein interaction with inhibitor IkappaBs. In contrast, in cancer cells a substantial amount of NF-kappaB is in the nucleus and constitutively activates target genes. To understand the mechanisms of constitutive NF-kappaB activation, we have analyzed the function of IkappaBalpha and IkappaBbeta in breast cancer cells. In most cases, constitutive NF-kappaB DNA binding correlated with reduced levels of either IkappaBalpha or IkappaBbeta isoforms. Overexpression of IkappaBalpha but not IkappaBbeta1 resulted in reduced constitutive DNA binding of NF-kappaB in MDA-MB-231 cells. Unexpectedly, IkappaBbeta1 overexpression moderately increased 12-O-tetradecanoylphorbol-13-acetate- and interleukin-1-inducible NF-kappaB DNA binding. 12-O-Tetradecanoylphorbol-13-acetate- and interleukin-1-induced transactivation by NF-kappaB, however, was lower in IkappaBbeta1-overexpressing cells. Mutants of IkappaBbeta1 lacking the C-terminal casein kinase II phosphorylation sites, which form a stable complex with DNA bound NF-kappaB without inhibiting its transactivation in other cell types, repressed the transactivation by NF-kappaB in MDA-MB-231 cells. Consistent with the results of transient transfections, the expression of urokinase plasminogen activator, an NF-kappaB target gene, was reduced in IkappaBbeta1-overexpressing cells. These results suggest that depending on the cell type, IkappaBbeta1 represses the expression of NF-kappaB-regulated genes by inhibiting either DNA binding or transactivation function of NF-kappaB.
Newton
T R
TR
Department of Surgery, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
Patel
N M
NM
Bhat-Nakshatri
P
P
Stauss
C R
CR
Goulet
R J
RJ
Nakshatri
H
H
D001943:Breast Neoplasms / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000378:metabolism; D005260:Female; D006801:Humans; D020672:I-kappa B Proteins; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism
D004268:DNA-Binding Proteins; C083487:I kappa B beta protein; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D018808:Transcription Factor AP-1; D000072000:NF-KappaB Inhibitor alpha; D004815:Epidermal Growth Factor; D004247:DNA; D014568:Urokinase-Type Plasminogen Activator