Negative regulation of transactivation function but not DNA binding of NF-κB and AP-1 by IκBβ1 in breast cancer cells

Thomas R. Newton, Nikhil M. Patel, Poornima Bhat-Nakshatri, Carmen R. Stauss, Robert J. Goulet, Harikrishna Nakshatri

Research output: Contribution to journalArticle

59 Citations (Scopus)

Abstract

The 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.

Original languageEnglish
Pages (from-to)18827-18835
Number of pages9
JournalJournal of Biological Chemistry
Volume274
Issue number26
DOIs
StatePublished - Jun 25 1999

Fingerprint

Transcription Factor AP-1
Transcriptional Activation
Cells
Breast Neoplasms
Genes
DNA
Interleukin-1
Acetates
Casein Kinase II
Phosphorylation
Chemotherapy
Plasminogen Activators
Urokinase-Type Plasminogen Activator
Tetradecanoylphorbol Acetate
Protein Isoforms
Proteins
Transcription Factors
Chemical activation
Transfection
Neoplasms

ASJC Scopus subject areas

  • Biochemistry

Cite this

Negative regulation of transactivation function but not DNA binding of NF-κB and AP-1 by IκBβ1 in breast cancer cells. / Newton, Thomas R.; Patel, Nikhil M.; Bhat-Nakshatri, Poornima; Stauss, Carmen R.; Goulet, Robert J.; Nakshatri, Harikrishna.

In: Journal of Biological Chemistry, Vol. 274, No. 26, 25.06.1999, p. 18827-18835.

Research output: Contribution to journalArticle

Newton, Thomas R. ; Patel, Nikhil M. ; Bhat-Nakshatri, Poornima ; Stauss, Carmen R. ; Goulet, Robert J. ; Nakshatri, Harikrishna. / Negative regulation of transactivation function but not DNA binding of NF-κB and AP-1 by IκBβ1 in breast cancer cells. In: Journal of Biological Chemistry. 1999 ; Vol. 274, No. 26. pp. 18827-18835.
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AB - The 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.

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