Browsing by Author "Newton, Thomas R."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Negative Regulation of Transactivation Function but Not DNA Binding of NF-κB and AP-1 by IκBβ1 in Breast Cancer Cells
    (1999-06-25) Newton, Thomas R.; Patel, Nikhil M.; Bhat-Nakshatri, Poornima; Stauss, Carmen R.; Goulet, Robert J.; Nakshatri, Harikrishna
    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.
  • Thumbnail Image
    Item
    NF-κB activation and interleukin 6 production in fibroblasts by estrogen receptor-negative breast cancer cell-derived interleukin 1α
    (National Academy of Sciences, 1998-06-09) Bhat-Nakshatri, Poornima; Newton, Thomas R.; Goulet, Robert; Nakshatri, Harikrishna
    Several angiogenic factors and extracellular matrix-degrading enzymes that promote invasion and metastasis of cancer are produced by stromal fibroblasts that surround cancer cells. The expression of genes that code for some of these proteins is regulated by the transcription factor NF-κB. In this report, we demonstrate that conditioned medium (CM) from estrogen receptor (ER)-negative but not ER-positive breast cancer cells induces NF-κB in fibroblasts. In contrast, CM from both ER-positive and ER-negative breast cancer cells induces NF-κB in macrophages and endothelial cells. NF-κB activation in fibroblasts was accompanied by induction of interleukin 6 (IL-6) and urokinase plasminogen activator (uPA), both of which promote angiogenesis and metastasis. A survey of cytokines known for their ability to induce NF-κB identified IL-1α as the factor responsible for NF-κB activation in fibroblasts. Analysis of primary breast carcinomas revealed the presence of IL-1α transcripts in majority of lymph node-positive breast cancers. These results along with the known role of IL-1α and IL-6 in osteoclast formation provide insight into the mechanism of metastasis and hypercalcemia in advanced breast cancers.