Autophagosomal IκBα Degradation Plays a Role in the Long Term Control of Tumor Necrosis Factor-α-induced Nuclear Factor-κB (NF-κB) Activity

Transcription factor NF-kappa B is persistently activated in many chronic inflammatory diseases and cancers. The short term regulation of NF-kappa B is well understood, but little is known about the mechanisms of its long term activation. We studied the effect of a single application of TNF-alpha on NF-kappa B activity for up to 48 h in intestinal epithelial cells. Results show that NF-kappa B remained persistently activated up to 48 h after TNF-alpha and that the long term activation of NF-kappa B was accompanied by a biphasic degradation of I kappa B alpha. The first phase of I kappa B alpha degradation was proteasome-dependent, but the second was not. Further investigation showed that TNF-alpha stimulated formation of autophagosomes in intestinal epithelial cells and that I kappa B alpha co-localized with autophagosomal vesicles. Pharmacological or genetic blockade of autophagosome formation or the inhibition of lysosomal proteases decreased TNF-alpha-induced degradation of I kappa B alpha and lowered NF-kappa B target gene expression. Together, these findings indicate a role of autophagy in the control of long term NF-kappa B activity. Because abnormalities in autophagy have been linked to ineffective innate immunity, we propose that alterations in NF-kappa B may mediate this effect.