Activation Signal of Nuclear Factor-.KAPPA.B in Response to Endoplasmic Reticulum Stress is Transduced via IRE1 and Tumor Necrosis Factor Receptor-Associated Factor 2

Abstract

Secretory and membrane proteins are correctly folded and glycosylated in the endoplasmic reticulum (ER) by ER-resident molecular chaperones. The ER stores intracellular calcium and is a major signal-transducing organelle releasing calcium in the cytoplasm. Exposure of cells to various pharmacological agents that disturb ER functions, such as calcium depletion from the ER lumen, inhibition of glycosylation or reduction of disulfide bonds, and in physiological conditions, expression of mutant proteins or overexpression of some wild-type proteins by viral infection, leads to an accumulation of proteins in the ER lumen. Under these conditions called ER stress, two distinct signal transduction pathways, termed the unfolded protein response (UPR) and the ER-overload response (EOR), are activated to transduce the signal from the ER to the nucleus. 1,2)The UPR leads to an increase in the expression of ER stress-response genes, including ER chaperones and CHOP/GADD153. 3,4) This response is mediated by an ERtransmembrane molecule, IRE1 (a and b), whose cytosolic domain contains a Ser/Thr protein kinase and an endoribonuclease domain with its C-terminus.5,6) Accumulation of unfolded proteins in the ER lumen initiates oligomerization and trans-autophosphorylation of IRE1, resulting in activation of the kinase/RNase activities. Activated IRE1 then cleaves off the intron of XBP-1, a transcription factor that binds to the ER stress-response element (ERSE), to increase the transcription of target genes. 7-10)The EOR triggers the activation of nuclear factor-kB (NFkB) through accumulation of proteins in the ER.11) NF-kB is activated by a wide variety of stimuli such as cytokines, oxidant-free radicals, ultraviolet irradiation, and viral products. The activation of NF-kB induced by ER stress has been suggested to require the release of calcium from the ER through overloading of the ER with accumulated proteins and subsequent production of reactive oxygen species (ROS).12) On the other hand, production of GRP78/Bip, an ER chaperone, as the UPR was independent of the activation of NF-kB, since overexpression of NF-kB subunits fails to induce GRP78/Bip. 11) Therefore, the EOR appears to be distinguishable from the UPR.c-Jun N-terminal kinase (JNK) is also activated by ER stress. 13,14) This signaling pathway is mediated by the association of IRE1s with tumor necrosis factor-a (TNF-a) receptor-associated factor 2 (TRAF2).15) However, it has been unclear whether ER stress-induced NF-kB activation depends on the IRE1-TRAF2-mediated response. A signal initiated by TNF-a diverges from TRAF2 to two pathways leading to NF-kB and JNK signaling. 16,17) Thus, IRE1 seems to activate NF-kB through TRAF2, as well as JNK. We here show that ER stress-induced NF-kB activation is mediated by IRE1 and TRAF2, similar to the JNK activation. MATERIALS AND METHODS Expression Vector ConstructionHuman full-length IRE1a (the region corresponding to amino acids; 1-977) and DRN-IRE1a (a truncated form of the C-terminal RNase domain; 1-786) with a hemagglutin...

Cross-talk between the unfolded protein response and nuclear factor-κB signalling pathways regulates cytokine-mediated beta cell death in MIN6 cells and isolated mouse islets

“…Increased IκBα degradation is facilitated by enhanced proteasomal activity, which is highly dependent on the ERAD network. This is distinct from the previously reported mechanisms by which ER stress activates NFκB via the PERK-eIF2α pathway [36][37][38] or by IRE1-mediated activation of TNF receptorassociated factor 2 [39,40]. Interestingly, an increase in ER stress markers and NFκB target genes has been observed in islets of diabetic NOD mice in the prediabetic period [25], raising the possibility that interaction between the pathways is important in the development of type 1 diabetes.…”

Palmitate induces a pro-inflammatory response in human pancreatic islets that mimics CCL2 expression by beta cells in type 2 diabetes

“…Saturated NEFA are pro-inflammatory in several cell types [43,44] and also cause ER stress [10]. Because palmitate (but not oleate or high glucose) induces ER stress in human islets [10] and there is a crosstalk between ER stress and NF-κB pathways [45][46][47], we explored this mechanism further. We have previously shown that palmitate activates PERK, and also leads to ATF6 and IRE1 activation through depletion of ER Ca 2+ stores [10].…”

“…Ca 2+ efflux from the ER activates NF-κB through generation of reactive oxygen species [46] and release of a diffusible, still unknown, NF-κB activator [48]. IRE1 and TNF receptor-associated factor 2 (TRAF-2) can activate NF-κB [45], and stalled protein translation caused by eIF2α phosphorylation decreases IκBα protein availability, consequently activating NF-κB [49]. CPA, a canonical ER stressor, upregulates chemokines and cytokines and activates NF-κB in human islets with an effect comparable with that of palmitate (present data).…”

Enhanced intracellular replication of Salmonella enteritidis in HLA–B27–expressing human monocytic cells: Dependency on glutamic acid at position 45 in the B pocket of HLA–B27

“…ER stress has also been reported to activate NF-B (20). Although it was initially unclear how this might occur, recent studies implicate the IRE1/TRAF2 pathway (21). Some of the gene products induced or activated by the UPR are important in the regulation of inflammatory processes (e.g., XBP-1, CHOP, NF-B, and JNK).…”