Open AccessAutocrine Tumor Necrosis Factor Alpha Links Endoplasmic Reticulum Stress to the Membrane Death Receptor Pathway through IRE1α-Mediated NF-κB Activation and Down-Regulation of TRAF2 Expression
Author(s) -
Ping Hu,
Zhang Han,
Anthony D. Couvillon,
Randal J. Kaufman,
John H. Exton
Publication year - 2006
Publication title -
molecular and cellular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.14
H-Index - 327
eISSN - 1067-8824
pISSN - 0270-7306
DOI - 10.1128/mcb.26.8.3071-3084.2006
Subject(s) - unfolded protein response , traf2 , microbiology and biotechnology , biology , endoplasmic reticulum , programmed cell death , signal transduction , tumor necrosis factor alpha , apoptosis , tumor necrosis factor receptor 1 , cancer research , immunology , biochemistry , tumor necrosis factor receptor
NF-κB is critical for determining cellular sensitivity to apoptotic stimuli by regulating both mitochondrial and death receptor apoptotic pathways. The endoplasmic reticulum (ER) emerges as a new apoptotic signaling initiator. However, the mechanism by which ER stress activates NF-κB and its role in regulation of ER stress-induced cell death are largely unclear. Here, we report that, in response to ER stress, IKK forms a complex with IRE1α through the adapter protein TRAF2. ER stress-induced NF-κB activation is impaired in IRE1α knockdown cells and IRE1α−/− MEFs. We found, however, that inhibiting NF-κB significantly decreased ER stress-induced cell death in a caspase-8-dependent manner. Gene expression analysis revealed that ER stress-induced expression of tumor necrosis factor alpha (TNF-α) was IRE1α and NF-κB dependent. Blocking TNF receptor 1 signaling significantly inhibited ER stress-induced cell death. Further studies suggest that ER stress induces down-regulation of TRAF2 expression, which impairs TNF-α-induced activation of NF-κB and c-Jun N-terminal kinase and turns TNF-α from a weak to a powerful apoptosis inducer. Thus, ER stress induces two signals, namely TNF-α induction and TRAF2 down-regulation. They work in concert to amplify ER-initiated apoptotic signaling through the membrane death receptor.