XBP-1 Couples Endoplasmic Reticulum Stress to Augmented IFN- Induction via a cis-Acting Enhancer in Macrophages

Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53792, USA.
The Journal of Immunology (Impact Factor: 4.92). 08/2010; 185(4):2324-30. DOI: 10.4049/jimmunol.0903052
Source: PubMed


Perturbation of the endoplasmic reticulum (ER) results in a conserved stress response called the unfolded protein response (UPR). Macrophages undergoing a UPR respond to LPS with log-fold increased production of IFN-beta, a cytokine with diverse roles in innate and adaptive immunity. In this study, we found that thapsigargin-induced ER stress augmented recruitment of IFN regulatory factor-3, CREB binding protein/p300, and transcriptional machinery to the murine ifnb1 promoter during LPS stimulation. Although full synergistic IFN-beta production requires X-box binding protein 1 (XBP-1), this UPR-regulated transcription factor did not appreciably bind the ifnb1 promoter. However, XBP-1 bound a conserved site 6.1 kb downstream of ifnb1, along with IFN regulatory factor-3 and CREB binding protein only during concomitant UPR and LPS stimulation. XBP-1 physically associates with p300, suggesting a mechanism of multimolecular assembly at the +6.1 kb site. Luciferase reporter assays provide evidence this +6 kb region functions as an XBP-1-dependent enhancer of ifnb1 promoter activity. Thus, this study identifies a novel role for a UPR-dependent transcription factor in the regulation of an inflammatory cytokine. Our findings have broader mechanistic implications for the pathogenesis of diseases involving ER stress and type I IFN, including viral infection, ischemia-reperfusion injury, protein misfolding, and inflammatory diseases.

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    • "Similar XBP1-dependent induction of IFN-␤ has also been observed in murine DCs treated with polyI:C (Hu et al., 2011). Notably, recent studies have identified putative XBP1 binding to the promoter/enhancer sequences of IL- 6, TNF-␣ and IFN-␤ (Martinon et al., 2010; Zeng et al., 2010). In terms of coronavirus infection, induction of IL-8 has been associated with ER stress and XBP1 splicing in cells infected with MHV or in cells over-expressing the MHV spike protein (Versteeg et al., 2007). "
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    ABSTRACT: Coronavirus replication is structurally and functionally associated with the endoplasmic reticulum (ER), a major site of protein synthesis, folding, modification and sorting in the eukaryotic cells. Disturbance of ER homeostasis may occur under various physiological or pathological conditions. In response to the ER stress, signaling pathways of the unfolded protein response (UPR) are activated. UPR is mediated by three ER transmembrane sensors, namely the PKR-like ER protein kinase (PERK), the inositol-requiring protein 1 (IRE1) and the activating transcriptional factor 6 (ATF6). UPR facilitates adaptation to ER stress by reversible translation attenuation, enhancement of ER protein folding capacity and activation of ER-associated degradation (ERAD). In cells under prolonged and irremediable ER stress, UPR can also trigger apoptotic cell death. Accumulating evidence has shown that coronavirus infection causes ER stress and induces UPR in the infected cells. UPR is closely associated with a number of major signaling pathways, including autophagy, apoptosis, the mitogen-activated protein (MAP) kinase pathways, innate immunity and pro-inflammatory response. Therefore, studies on the UPR are pivotal in elucidating the complicated issue of coronavirus-host interaction. In this paper, we present the up-to-date knowledge on coronavirus-induced UPR and discuss its potential involvement in regulation of innate immunity and apoptosis.
    Full-text · Article · Oct 2014 · Virus Research
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    • "Similarly, ER stress has been demonstrated to synergize with both dsRNA and LPS to induce much higher levels of IFNb [50]. This synergy is mediated by binding of the transcription factor XBP-1, which is associated with the ER stress-induced UPR, to an enhancer element upstream of the IFNb promoter [51]. "
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    ABSTRACT: The prototypic response to viral infection involves the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), leading to the activation of transcription factors such as IRF3 and NFkB and production of type 1 IFN. While this response can lead to the induction of hundreds of IFN-stimulated genes (ISGs) and recruitment and activation of immune cells, such a comprehensive response is likely inappropriate for routine low level virus exposure. Moreover, viruses have evolved a plethora of immune evasion strategies to subvert antiviral signalling. There is emerging evidence that cells have developed very sensitive methods of detecting not only specific viral PAMPS, but also more general danger or stress signals associated with viral entry and replication. Such stress-induced cellular responses likely serve to prime cells to respond to further PAMP stimulation or allow for a rapid and localized intracellular response independent of IFN production and its potential immune sequelae. This review discusses diversity in innate antiviral players and pathways, the role of “danger” sensing, and how alternative pathways, such as the IFN-independent pathway, may serve to prime cells for further pathogen attack.
    Full-text · Article · Oct 2014 · Cytokine & Growth Factor Reviews
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    • "XBP1 belongs to the CREB family of transcription factors and thus may directly interact with CBP/p300 as suggested by overexpression studies with tagged constructs. Interactions between XBP1 and CBP might strengthen factor recruitment to the ifnb1 regulatory elements (Zeng et al., 2010). However, the precise relationship between XBP1 and increased IRF3 remained unclear. "
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    ABSTRACT: THE IMMUNE SYSTEM DEPENDS UPON COMBINATIONS OF SIGNALS TO MOUNT APPROPRIATE RESPONSES: pathogen specific signals in the context of co-stimulatory "danger" signals drive immune strength and accuracy. Viral infections trigger anti-viral type I interferon (IFN) responses by stimulating endosomal and cytosolic pattern recognition receptors (PRRs). However, viruses have also evolved many strategies to counteract IFN responses. Are there intracellular danger signals that enhance immune responses to viruses? During infection, viruses place a heavy demand on the protein folding machinery of the host endoplasmic reticulum (ER). To survive ER stress, host cells mount an unfolded protein response (UPR) to decrease ER protein load and enhance protein-folding capacity. Viruses also directly elicit the UPR to enhance their replication. Increasing evidence supports an intersection between the host UPR and inflammation, in particular the production of pro-inflammatory cytokines and type I IFN. The UPR directly activates pro-inflammatory cytokine transcription factors and dramatically enhances cytokine production in response to viral PRR engagement. Additionally, viral PRR engagement may stimulate specific pathways within the UPR to enhance cytokine production. Through these mechanisms, viral detection via the UPR and inflammatory cytokine production are intertwined. Consequently, the UPR response is perfectly poised to act as an infection-triggered "danger" signal. The UPR may serve as an internal "co-stimulatory" signal that (1) provides specificity and (2) critically augments responses to overcome viral subterfuge. Further work is needed to test this hypothesis during viral infections.
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