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J Biol Chem. 2006 Apr 14;281(15):10316-26. Epub 2006 Feb 2.

Persistent interleukin-1beta signaling causes long term activation of NFkappaB in a promoter-specific manner in human glial cells.

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  • 1UCD School of Biomolecular and Biomedical Science, Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland.


Nuclear factor-kappaB (NFkappaB) is an inducible transcription factor that plays a key role in regulating the expression of a wide range of immune and inflammatory response genes. The activity of NFkappaB is controlled at multiple levels, including cytoplasmic retention with inhibitor of kappaB (IkappaB) proteins in the basal state. Persistent activation of the transcription factor is seen in numerous chronic inflammatory disease states, and we have previously demonstrated sustained activation of NFkappaB in human glial cells upon stimulation with interleukin (IL)-1beta. In these cells, NFkappaB retains DNA binding activity for up to 72 h despite the presence of resynthesized IkappaBalpha and in the absence of IkappaBbeta. Here we characterized the apparent inability of newly synthesized IkappaBalpha to terminate activation of NFkappaB in glial cells. We showed unexpectedly that newly synthesized IkappaBalpha can enter the nucleus, interact with the NFkappaB subunit p65, and export it to the cytoplasm. However, in vitro analysis of enzyme activity demonstrates that IL-1beta causes the long term activation of the IkappaB kinase complex leading to chronic phosphorylation of the newly synthesized IkappaBalpha signal response domain and persistent activation of NFkappaB. Such sustained activation of NFkappaB is dependent on the continuous presence and activity of IL-1beta. Interestingly, the sustained nature of NFkappaB activity is promoter type-specific. Chromatin immunoprecipitation studies revealed that p65 is detected at the promoters of both intercellular adhesion molecule-1 and IL-8 1 h following IL-1beta stimulation but is only found at the latter at 24 h. The functional significance of this finding is indicated by the transient induction of intercellular adhesion molecule-1 mRNA, but more sustained induction of IL-8 expression, by IL-1beta. These studies thus demonstrated that persistent IL-1 signaling causes sustained activation of NFkappaB in a promoter-specific manner in human glial cells, leading to prolonged induction of selective pro-inflammatory genes. This is likely to make a key contribution to chronic inflammatory conditions of the brain.

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