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  • Title: Role of Smad proteins in the regulation of NF-kappaB by TGF-beta in colon cancer cells.
    Author: Grau AM, Datta PK, Zi J, Halder SK, Beauchamp RD.
    Journal: Cell Signal; 2006 Jul; 18(7):1041-50. PubMed ID: 16288847.
    Abstract:
    Nuclear factor kappa B (NF-kappaB) has been implicated in cancer cell survival. We explored the role of the TGF-beta pathway in the regulation of NF-kappaB in colon cancer cells. TGF-beta-1 treatment of the colon adenocarcinoma cell line FET-1, results in an early increase in IkappaB-alpha phosphorylation that precedes NF-kappaB nuclear translocation and DNA binding activity. Activation of the TGF-beta type I receptor is required for the TGF-beta-mediated activation of NF-kappaB. No activation of NF-kappaB is observed in a Smad4 null cell line, SW480, even though TGF-beta does result in IkappaB-alpha phosphorylation in these cells. Smad4 restores the TGF-beta-1-mediated NF-kappaB activation in SW480 cells. TGF-beta-1 treatment fails to activate NF-kappaB or phosphorylate IkappaB-alpha in FET-1 cells expressing the inhibitory Smad, Smad7. Taken together, these results suggest a role for Smad4 in the transcriptional activation of NF-kappaB, and a direct effect of Smad 7 inhibiting IkappaB-alpha phosphorylation rather than through the well-established inhibition of Smad2/3 phosphorylation with subsequent inhibition of the TGF-beta pathway.
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