| Abstract: |
The Wnt/β-catenin/Tcf and IκB/NF-κB cascades are independent pathways involved in cell cycle control, cellular differentiation, and inflammation. Constitutive Wnt/β-catenin signaling occurs in certain cancers from mutation of components of the pathway and from activating growth factor receptors, including RON and MET. The resulting accumulation of cytoplasmic and nuclear β-catenin interacts with the Tcf/LEF transcription factors to induce target genes. The IκB kinase complex (IKK) that phosphorylates IκB contains IKKα, IKKβ, and IKKγ. Here we show that the cyclin D1 gene functions as a point of convergence between the Wnt/β-catenin and IκB pathways in mitogenic signaling. Mitogenic induction of G1-S phase progression and cyclin D1 expression was PI3K dependent, and cyclin D1-/- cells showed reduced PI3K-dependent S-phase entry. PI3K-dependent induction of cyclin D1 was blocked by inhibitors of PI3K/Akt/IκB/IKKα or β-catenin signaling. A single Tcf site in the cyclin D1 promoter was required for induction by PI3K or IKKα. In IKKα-/- cells, mitogen-induced DNA synthesis, and expression of Tcf-responsive genes was reduced. Reintroduction of IKKα restored normal mitogen induction of cyclin D1 through a Tcf site. In IKKα-/- cells, β-catenin phosphorylation was decreased and purified IKKα was sufficient for phosphorylation of β-catenin through its N-terminus in vitro. Because IKKα but not IKKα induced cyclin D1 expression through Tcf activity, these studies indicate that the relative levels of IKKα and IKKβ may alter their substrate and signaling specificities to regulate mitogen-induced DNA synthesis through distinct mechanisms. |
| Keywords: |
signal transduction; protein kinase b; controlled study; protein expression; protein phosphorylation; unclassified drug; dna binding protein; human cell; promoter region; dna-binding proteins; nonhuman; flow cytometry; dna synthesis; protein function; animal cell; mouse; metabolism; cell cycle; cell cycle s phase; mitogenesis; protein binding; transcription factor; immunoglobulin enhancer binding protein; genetic transcription; protein interaction; cell differentiation; transcription, genetic; in vitro study; transfection; protein serine threonine kinase; phosphorylation; phosphatidylinositol 3 kinase; physiology; time; time factors; gene vector; animalia; genetic vectors; transcription factors; blotting, western; transcription regulation; amino terminal sequence; genetic transfection; protein purification; protein-serine-threonine kinases; transactivator protein; substrate specificity; western blotting; 1-phosphatidylinositol 3-kinase; glutathione transferase; reporter gene; cytoplasm; binding site; fluorescence microscopy; microscopy, fluorescence; binding sites; genes, reporter; serodiagnosis; trans-activators; cell nucleus; cyclin d1; enzyme specificity; beta catenin; wnt protein; cell separation; ctnnb1 protein, human; cell cycle g1 phase; g1 phase; s phase; t cell factor protein; i kappa b kinase; 2 morpholino 8 phenylchromone; wortmannin; cytoskeleton protein; lymphoid enhancer factor 1; lymphoid enhancer-binding factor 1; cytoskeletal proteins; i kappa b; growth factor receptor; i-kappa b kinase; 2 (2 amino 3 methoxyphenyl)chromone; promoter regions (genetics); 4 (4 fluorophenyl) 2 (4 methylsulfinylphenyl) 5 (4 pyridyl)imidazole; precipitin tests; humans; human; priority journal; article; chuk protein, human; ikbkb protein, human; ikbke protein, human
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