Quinotrierixin Inhibited ER Stress-Induced XBP1 mRNA Splicing through Inhibition of Protein Synthesis

2011 ◽  
Vol 75 (2) ◽  
pp. 284-288 ◽  
Author(s):  
Kohta YAMAMOTO ◽  
Etsu TASHIRO ◽  
Masaya IMOTO
Keyword(s):  
Protein Synthesis ◽  
Er Stress ◽  
Mrna Splicing ◽  
Xbp1 Mrna ◽  
Inhibition Of Protein Synthesis

scholarly journals AMP-Activated Protein Kinase Protects Cardiomyocytes against Hypoxic Injury through Attenuation of Endoplasmic Reticulum Stress

2005 ◽  
Vol 25 (21) ◽  
pp. 9554-9575 ◽  
Author(s):  
Kazuo Terai ◽  
Yoshimune Hiramoto ◽  
Mitsuru Masaki ◽  
Shoko Sugiyama ◽  
Tadashi Kuroda ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Protein Kinase ◽  
Er Stress ◽  
Misfolded Proteins ◽  
Hypoxic Injury ◽  
Caspase 12 ◽  
Inhibition Of Protein Synthesis ◽  
Cardioprotective Effects ◽  
Amp Activated Protein Kinase

ABSTRACT Oxygen deprivation leads to the accumulation of misfolded proteins in the endoplasmic reticulum (ER), causing ER stress. Under conditions of ER stress, inhibition of protein synthesis and up-regulation of ER chaperone expression reduce the misfolded proteins in the ER. AMP-activated protein kinase (AMPK) is a key regulatory enzyme involved in energy homeostasis during hypoxia. It has been shown that AMPK activation is associated with inhibition of protein synthesis via phosphorylation of elongation factor 2 (eEF2) in cardiomyocytes. We therefore examined whether AMPK attenuates hypoxia-induced ER stress in neonatal rat cardiomyocytes. We found that hypoxia induced ER stress, as assessed by the expression of CHOP and BiP and cleavage of caspase 12. Knockdown of CHOP or caspase 12 through small interfering RNA (siRNA) resulted in decreased expression of cleaved poly(ADP-ribose) polymerase following exposure to hypoxia. We also found that hypoxia-induced CHOP expression and cleavage of caspase 12 were significantly inhibited by pretreatment with 5-aminoimidazole-4-carboxyamide-1-β-d-ribofuranoside (AICAR), a pharmacological activator of AMPK. In parallel, adenovirus expressing dominant-negative AMPK significantly attenuated the cardioprotective effects of AICAR. Knockdown of eEF2 phosphorylation using eEF2 kinase siRNA abolished these cardioprotective effects of AICAR. Taken together, these findings demonstrate that activation of AMPK contributes to protection of the heart against hypoxic injury through attenuation of ER stress and that attenuation of protein synthesis via eEF2 inactivation may be the mechanism of cardioprotection by AMPK.

scholarly journals A Molecular Mechanism for Turning off IRE1α Signaling During Endoplasmic Reticulum Stress

2020 ◽  
Author(s):  
Xia Li ◽  
Sha Sun ◽  
Suhila Appathurai ◽  
Arunkumar Sundaram ◽  
Rachel Plumb ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Mammalian Cells ◽  
Mrna Splicing ◽  
Xbp1 Mrna ◽  
Long Time ◽  
A Subunit ◽  
Active Transcription ◽  
J Domain ◽  
Sustained Activation

SummaryMisfolded proteins in the endoplasmic reticulum (ER) activate IRE1α endoribonuclease in mammalian cells, which mediates XBP1 mRNA splicing to produce an active transcription factor. This promotes the expression of specific genes to alleviate ER stress and thereby attenuating IRE1α. Although sustained activation of IRE1α is linked to human diseases, it is not clear how IRE1α is attenuated during ER stress. Here, we identify that Sec63 is a subunit of the previously identified IRE1α/Sec61 translocon complex. We find that Sec63 recruits and activates BiP ATPase through its luminal J-domain to bind onto IRE1α. This leads to inhibition of higher-order oligomerization and attenuation of IRE1α RNase activity during prolonged ER stress. In Sec63 deficient cells, IRE1α remains activated for a long time despite the presence of excess BiP in the ER. Thus, our data suggest that the Sec61 translocon bridges IRE1α with Sec63/BiP to regulate the dynamics of IRE1α signaling in cells.

scholarly journals Identification of Toyocamycin, an agent cytotoxic for multiple myeloma cells, as a potent inhibitor of ER stress-induced XBP1 mRNA splicing

2012 ◽  
Vol 2 (7) ◽  
pp. e79-e79 ◽  
Author(s):  
M Ri ◽  
E Tashiro ◽  
D Oikawa ◽  
S Shinjo ◽  
M Tokuda ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Er Stress ◽  
Potent Inhibitor ◽  
Mrna Splicing ◽  
Myeloma Cells ◽  
Xbp1 Mrna

Identification of Toyocamycin, an Agent Cytotoxic for Multiple Myeloma Cells, As a Potent Inhibitor of ER Stress-Induced XBP1 mRNA Splicing

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 5034-5034
Author(s):  
Masaki Ri ◽  
Etsu Tashiro ◽  
Daisuke Oikawa ◽  
Satoko Shinjo ◽  
Mio Tokuda ◽  
...  
Keyword(s):  
Er Stress ◽  
Cell Lines ◽  
Inhibitory Effect ◽  
Mrna Splicing ◽  
Cellular Viability ◽  
Unfolded Protein ◽  
Xbp1 Mrna ◽  
Dose Dependent ◽  
Adenosine Analog

Abstract Abstract 5034 Introduction: The IRE1α-XBP1 pathway, a key component of the endoplasmic reticulum (ER) stress response, is considered to be a critical regulator for survival of multiple myeloma (MM) cells. Because of the production of abundant immunoglobulins and cytokines, MM cells need to survive under chronic ER stress. In addition, MM cells are located in the bone marrow milieu, which is usually considered hypoxic compared to other organs. Therefore, MM cells need to possess mechanisms to protect against ER stress. Among the unfolded protein responses in MM cells, the IRE1α-XBP1 pathway has been implicated in the proliferation and survival of MM cells to a greater extent than in those of monoclonal gammopathy of undetermined significance or normal plasma cells. It has been reported to be a prognostic factor and could be a target for immunotherapy or chemotherapy. Based on previous reports, it is proposed that an inhibitor of IRE1α-XBP1 activation should be a potent therapeutic agent for MM. Therefore, the availability of small molecule inhibitors targeting this pathway would offer a new therapeutic strategy for MM. Here, we screened small molecule inhibitors of ER stress-induced XBP1 activation, and identified toyocamycin from a culture broth of an Actinomycete strain. Materials & Methods: First, we evaluated the mechanism of toyocamycin-induced inhibition of IREα activity, with focused on its kinase activity, endonuclease activity, and other unfolded protein responses. Next, the activity of toyocamycin was evaluated on MM cell lines and other tumor cells about IRE1α activity and cytotoxicity. Similarly, 9 primary MM cells were tested. Finally, the in vivo efficacy of toyocamycin was evaluated in a human MM xenograft model. Results & Discussion: Toyocamycin was shown to suppress thapsigargin-, tunicamycin- and 2-deoxyglucose-induced XBP1 mRNA splicing in HeLa cells without affecting ATF6 and PERK activation. Furthermore, although toyocamycin was unable to inhibit IRE1 a phosphorylation, it prevented IRE1α-induced XBP1 mRNA cleavage in vitro. Thus, toyocamycin is an inhibitor of IRE1α-induced XBP1 mRNA cleavage. Next, we examined the effect of toyocamycin on MM cells. Most MM cell lines have activated XBP1 protein expression, represented as the overexpression of spliced XBP1 isoform, whereas non-MM cells including other hematological and solid tumor cells have little activation of XBP1. Toyocamycin inhibited constitutive activation of XBP1 in MM cell lines without affecting IRE1α phosphorylation. This inhibition occurred within 6 hours after exposure to 30 nM toyocamycin. We then evaluated the growth inhibitory effect of toyocamycin on 7 MM cell lines with high spliced-XBP1 expression, 3 MM cell lines with low spliced-XBP1 expression, and 4 non-MM cell lines as assessed by MTS assay. All MM cells with high spliced-XBP1 expression showed remarkable decline in cellular viability at 30 nM or higher concentrations of toyocamycin than other MM cells with low spliced-XBP1 expression, and non-MM cell lines showed little reduction in cellular viability. MM cell lines expressing high spliced-XBP1 showed robust dose-dependent apoptosis after exposure to various concentrations of toyocamycin for 24 hours, as assessed by the number of Annexin V-positive cells. Toyocamycin also induces marked apoptosis on two bortezomib (BTZ)-resistant MM cells at nM concentration. It also inhibited constitutive activation of XBP1 expression in primary MM cells derived from patients, showing dose-dependent reduced viability without any cytotoxicity to PBMCs from healthy donors. Toyocamycin also showed synergistic effects with bortezomib, and induced apoptosis of primary MM cells from patients including bortezomib-resistant cases at nano-molar levels in a dose-dependent manner. It also inhibited growth of xenografts in an in vivo model of human MM, and showed enhanced growth inhibition when combined with bortezomib. Taken together, we found that adenosine analog toyocamycin has a potent IRE1α-XBP1 inhibitory effect on MM cells with excessive ER-stress. It triggers dose-dependent apoptosis in MM cells. These results suggest toyocamycin can be a lead compound for developing novel anti-MM therapy, and also provide a preclinical rationale for conducting clinical trials using toyocamycin or other adenosine analog alone or in combination with BTZ for treating MM. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Stress-induced tyrosine phosphorylation of RtcB modulates IRE1 activity and signaling outputs

2020 ◽  
Author(s):  
Alexandra Papaioannou ◽  
Alice Metais ◽  
Marion Maurel ◽  
Luc Negroni ◽  
Matías González-Quiroz ◽  
...  
Keyword(s):  
Er Stress ◽  
Tyrosine Kinases ◽  
Regulatory Network ◽  
Initial Step ◽  
Mrna Splicing ◽  
Rnase Activity ◽  
Unfolded Protein ◽  
Xbp1 Mrna ◽  
The Unfolded Protein Response ◽  
Protein Response

AbstractEndoplasmic Reticulum (ER) stress is a hallmark of various diseases. Cells cope with ER stress through the activation of an adaptive signaling pathway named the Unfolded Protein Response (UPR) which is mediated by three ER-resident sensors. The most evolutionary conserved of the UPR sensors is IRE1α that elicits diverse downstream effects through its kinase and endoribonuclease (RNase) activities. IRE1α RNase activity can either catalyze the initial step of XBP1 mRNA unconventional splicing or degrade a number of RNAs through Regulated IRE1-Dependent Decay (RIDD). The degree of exertion of these two activities plays an instrumental role in cells’ life and death decisions upon ER stress. Until now, the biochemical and biological outputs of IRE1α RNase activity have been well documented, however, the precise mechanisms controlling whether IRE1 signaling is adaptive or pro-death (terminal) remain unclear. This prompted us to further investigate those mechanisms and we hypothesized that XBP1 mRNA splicing and RIDD activity could be co-regulated within the context of the IRE1α RNase regulatory network. We showed that a key nexus in this pathway is the tRNA ligase RtcB which, together with IRE1α, is responsible for XBP1 mRNA splicing. We demonstrated that RtcB is tyrosine phosphorylated by c-Abl and dephosphorylated by PTP1B. Moreover, we identified RtcB Y306 as a key residue which, when phosphorylated, perturbs RtcB interaction with IRE1α, thereby attenuating XBP1 mRNA splicing and favoring RIDD. Our results demonstrate that the IRE1α RNase regulatory network is dynamically fine-tuned by tyrosine kinases and phosphatases upon various stresses and depending on the nature of the stress determines cell adaptive or death outputs.

Abstract B150: Toyocamycin inhibits ER stress‐induced XBP1 mRNA splicing through IRE1α activation

2009 ◽  
Author(s):  
Etsu Tashiro ◽  
Yumi Yokouchi ◽  
Kohta Yamamoto ◽  
Masaya Imoto
Keyword(s):  
Er Stress ◽  
Mrna Splicing ◽  
Xbp1 Mrna

scholarly journals Palmitate-induced ER stress and inhibition of protein synthesis in cultured myotubes does not require Toll-like receptor 4

PLoS ONE ◽  
2018 ◽  
Vol 13 (1) ◽  
pp. e0191313 ◽  
Author(s):  
Ben D. Perry ◽  
Jill A. Rahnert ◽  
Yang Xie ◽  
Bin Zheng ◽  
Myra E. Woodworth-Hobbs ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Er Stress ◽  
Toll Like Receptor ◽  
Toll Like Receptor 4 ◽  
Inhibition Of Protein Synthesis ◽  
Cultured Myotubes
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