Autophagosomal IkappaB alpha degradation plays a role in the long term control of tumor necrosis factor-alpha-induced nuclear factor-kappaB (NF-kappaB) activity

Transcription factor NF-kappaB is persistently activated in many chronic inflammatory diseases and cancers. The short term regulation of NF-kappaB 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-kappaB activity for up to 48 h in intestinal epithelial cells. Results show that NF-kappaB remained persistently activated up to 48 h after TNF-alpha and that the long term activation of NF-kappaB was accompanied by a biphasic degradation of IkappaBalpha. The first phase of IkappaBalpha 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 IkappaBalpha co-localized with autophagosomal vesicles. Pharmacological or genetic blockade of autophagosome formation or the inhibition of lysosomal proteases decreased TNF-alpha-induced degradation of IkappaBalpha and lowered NF-kappaB target gene expression. Together, these findings indicate a role of autophagy in the control of long term NF-kappaB activity. Because abnormalities in autophagy have been linked to ineffective innate immunity, we propose that alterations in NF-kappaB may mediate this effect.Transcription factor NF-kappaB is persistently activated in many chronic inflammatory diseases and cancers. The short term regulation of NF-kappaB 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-kappaB activity for up to 48 h in intestinal epithelial cells. Results show that NF-kappaB remained persistently activated up to 48 h after TNF-alpha and that the long term activation of NF-kappaB was accompanied by a biphasic degradation of IkappaBalpha. The first phase of IkappaBalpha 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 IkappaBalpha co-localized with autophagosomal vesicles. Pharmacological or genetic blockade of autophagosome formation or the inhibition of lysosomal proteases decreased TNF-alpha-induced degradation of IkappaBalpha and lowered NF-kappaB target gene expression. Together, these findings indicate a role of autophagy in the control of long term NF-kappaB activity. Because abnormalities in autophagy have been linked to ineffective innate immunity, we propose that alterations in NF-kappaB may mediate this effect.