Cytokine-induced stabilization of newly synthesized I(kappa)B-alpha.
NF-kappaB activation is triggered by the degradation of inhibitory proteins, such as I(kappa)B-alpha. I(kappa)B-alpha levels are only transiently lowered since one gene activated by NF-kappaB is I(kappa)B-alpha. We found that I(kappa)B-alpha was replenished rapidly in a human colon cell line (HT-29), even in the presence of degradation-inducing phosphorylation (at serine-32). This finding lead us to hypothesize that posttranscriptional mechanisms were also in place to facilitate I(kappa)B-alpha replenishment. Expression of I(kappa)B-alpha from the constitutive, non-NF-kappaB regulated cytomegalovirus promoter in HT-29 cells showed that TNF-alpha or IL-1beta treatment increased I(kappa)B-alpha levels in the absence of transcriptional activation. The TNF-alpha-induced increase in transgenic I(kappa)B-alpha appeared to result from the stabilization of newly synthesized I(kappa)B-alpha, since this increase was effectively preempted by a proteasome inhibitor (MG132) or by I(kappa)B-alpha stabilization through the deletion C-terminal destabilizing elements (without additive or synergistic effects). Analysis of a hepatoma cell line (Hepa 1-4C7) indicated that the I(kappa)B-alpha stabilization may be constitutive in these cells. NF-kappaB stimuli therefore appear to trigger negative feedback pathways in some cells that terminate a NF-kappaB response by increasing the stability of newly synthesized I(kappa)B-alpha.
Place
R F
RF
Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA.
Haspeslagh
D
D
Hubbard
A K
AK
Giardina
C
C
D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism*; D005246:Feedback; D019073:HT29 Cells; D006801:Humans; D020672:I-kappa B Proteins; D007375:Interleukin-1 / Q000494:pharmacology*; D000072000:NF-KappaB Inhibitor alpha; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D007375:Interleukin-1; C000606204:NFKBIA protein, human; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha