X-box Binding Protein (x-box + binding_protein)

Distribution by Scientific Domains

Selected Abstracts

Endoplasmic reticulum stress and the unfolded protein response are linked to synergistic IFN-, induction via X-box binding protein 1

Judith A. Smith Dr.
Abstract Type,I IFN are strongly induced upon engagement of certain pattern recognition receptors by microbial products, and play key roles in regulating innate and adaptive immunity. It has become apparent that the endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR), in addition to restoring ER homeostasis, also influences the expression of certain inflammatory cytokines. However, the extent to which UPR signaling regulates type,I IFN remains unclear. Here we show that cells undergoing a UPR respond to TLR4 and TLR3 ligands, and intracellular dsRNA, with log-fold greater IFN-, induction. This synergy is not dependent on autocrine type,I IFN signaling, but unexpectedly requires the UPR transcription factor X-box binding protein,1 (XBP-1). Synergistic IFN-, induction also occurs in HLA-B27/human ,2m-transgenic rat macrophages exhibiting a UPR as a consequence of HLA-B27 up-regulation, where it correlates with activation of XBP-1 splicing. Together these findings indicate that the cellular response to endogenous ,danger' that disrupts ER homeostasis is coupled to IFN-, induction by XBP-1, which has implications for the immune response and the pathogenesis of diseases involving the UPR. [source]

The flavonoid tangeretin activates the unfolded protein response and synergizes with imatinib in the erythroleukemia cell line K562

Sofie Lust
Abstract We explored the mechanism of cell death of the polymethoxyflavone tangeretin (TAN) in K562 breakpoint cluster region-abelson murine leukemia (Bcr-Abl+) cells. Flow cytometric analysis showed that TAN arrested the cells in the G2/M phase and stimulated an accumulation of the cells in the sub-G0 phase. TAN-induced cell death was evidenced by poly(ADP)-ribose polymerase cleavage, DNA laddering fragmentation, activation of the caspase cascade and downregulation of the antiapoptotic proteins Mcl-1 and Bcl-xL. Pretreatment with the pancaspase inhibitor Z-VAD-FMK_blocked caspase activation and cell cycle arrest but did not inhibit apoptosis which suggest that other cell killing mechanisms like endoplasmic reticulum (ER)-associated cell death pathways could be involved. We demonstrated that TAN-induced apoptosis was preceded by a rapid activation of the proapoptotic arm of the unfolded protein response, namely PKR-like ER kinase. This was accompanied by enhanced levels of glucose-regulated protein of 78,kDa and of spliced X-box binding protein 1. Furthermore, TAN sensitized K562 cells to the cell killing effects of imatinib via an apoptotic mechanism. In conclusion, our results suggest that TAN is able to induce apoptosis in Bcr-Abl+ cells via cell cycle arrest and the induction of the unfolded protein response, and has synergistic cytotoxicity with imatinib. [source]

HLA,B27 up-regulation causes accumulation of misfolded heavy chains and correlates with the magnitude of the unfolded protein response in transgenic rats: Implications for the pathogenesis of spondylarthritis-like disease

Matthew J. Turner
Objective HLA,B27 is implicated in the pathogenesis of spondylarthritis (SpA), yet the molecular mechanisms are incompletely defined. HLA,B27 misfolding has been associated with endoplasmic reticulum stress and activation of the unfolded protein response (UPR) in macrophages from HLA,B27/human ,2 -microglobulin,transgenic (B27-transgenic) rats. This study was performed to assess the mechanisms that drive activation of the HLA,B27,induced UPR and to determine whether splenocytes respond in a similar manner. Methods Splenocytes were isolated and bone marrow macrophages were derived from B27-transgenic and wild-type rats. Cells were treated for up to 24 hours with cytokines that induce class I major histocompatibility complex expression. HLA,B27 expression and misfolding were assessed by real-time reverse transcription,polymerase chain reaction, flow cytometry, and immunoblotting. Activation of the UPR was measured by quantifying UPR target gene expression and X-box binding protein 1 messenger RNA (mRNA) splicing. Results HLA,B27 mRNA up-regulation was accompanied by a dramatic increase in the accumulation of misfolded heavy chains and preceded robust activation of the UPR in macrophages. When macrophages were treated with various cytokines, the magnitude of the UPR correlated strongly with the degree of HLA,B27 up-regulation. In contrast, B27-transgenic splenocytes exhibited only low-level differences in the expression of UPR target genes after exposure to interferon-, or concanavalin A, which resulted in minimal HLA,B27 up-regulation. Conclusion These results suggest that HLA,B27,associated activation of the UPR in macrophages is attributable to the accumulation of misfolded heavy chains, and that certain cell types may be more susceptible to the effects of HLA,B27 misfolding. Strategies that eliminate HLA,B27 up-regulation and/or the accumulation of misfolded heavy chains may be useful in evaluating the role of these events in the pathogenesis of SpA. [source]

Regulation of XBP-1 signaling during transient and stable recombinant protein production in CHO cells

Sebastian C. Y. Ku
Abstract X-box binding protein 1 (XBP-1) is a key regulator of cellular unfolded protein response (UPR). The spliced isoform of XBP-1, XBP-1S, is a transcription activator, which is expressed only when UPR is induced. However, the impact of recombinant protein production on the regulation of XBP-1 signaling in CHO cells is not well understood. In this report, we cloned the Chinese hamster XBP-1 homolog to aid the investigation of the interplay between protein productivity, culture conditions, and endogenous XBP-1 signaling in CHO cells. Interestingly, expression of XBP-1S is detected in the non-producing and unstressed CHO-K1 cells. Transient expression of recombinant erythropoietin reveals a positive correlation between XBP-1 mRNA abundance and protein production level. However, such a correlation is not observed in batch cultivation of stable producing cell lines. The increased XBP-1 splicing is detected in late-phase cultures, suggesting that induction of XBP-1S may be a result of nutrient limitations or other environmental stresses rather than that of increased intracellular accumulation of recombinant proteins. Our data suggest that XBP-1 is a key determinant for the secretory capacity of CHO cells. Understanding its dynamic regulation hence provides a rational basis for cellular engineering strategies to improve recombinant protein secretion. 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source]

Nitric oxide selectively depletes macrophages in atherosclerotic plaques via induction of endoplasmic reticulum stress

W Martinet
Background and purpose: Macrophages in atherosclerotic plaques have a tremendous impact on atherogenesis and plaque destabilization. We previously demonstrated that treatment of plaques in cholesterol-fed rabbits with the nitric oxide (NO) donor molsidomine preferentially eliminates macrophages, thereby favouring features of plaque stability. In this study, we investigated the underlying mechanism. Experimental approach: Macrophages and smooth muscle cells (SMCs) were treated in vitro with the NO donors, spermine NONOate or S -nitroso- N -acetylpenicillamine (SNAP) as well as with the well-known endoplasmic reticulum (ER) stress inducers thapsigargin, tunicamycin, dithiothreitol or brefeldin A. Cell viability was analysed by Neutral Red viability assays. Cleavage of caspase-3, DNA fragmentation and ultrastructural changes were examined to characterize the type of macrophage death. Induction of ER stress was evaluated by measuring C/EBP homologous protein (CHOP) expression, phosphorylation of eukaryotic initiation factor 2, (eIF2a), splicing of X-box binding protein 1 (XBP1) and inhibition of protein synthesis. Key results: Macrophages and SMCs treated with spermine NONOate or SNAP showed several signs of ER stress, including upregulation of CHOP expression, hyperphosphorylation of eIF2,, inhibition of de novo protein synthesis and splicing of XBP1 mRNA. These effects were similar in macrophages and SMCs, yet only macrophages underwent apoptosis. Plaques from molsidomine-treated atherosclerotic rabbits showed a 2.7-fold increase in CHOP expression as compared to placebo. Beside NO, selective induction of macrophage death could be initiated with thapsigargin and tunicamycin. Conclusions and implications: Induction of ER stress explains selective depletion of macrophages in atherosclerotic plaques by a NO donor, probably via inhibition of protein synthesis. British Journal of Pharmacology (2007) 152, 493,500; doi:10.1038/sj.bjp.0707426; published online 13 August 2007 [source]