bims-unfpre 2019-02-03 papers

Issue of 2019–02–03
five papers selected by
Susan Logue, Apoptosis Research Centre

Front Immunol. 2018 ;9 3050

IRE1α Activation in Bone Marrow-Derived Dendritic Cells Modulates Innate Recognition of Melanoma Cells and Favors CD8+ T Cell Priming.

Bernardita Medel, Cristobal Costoya, Dominique Fernandez, Cristian Pereda, Alvaro Lladser, Daniela Sauma, Rodrigo Pacheco, Takao Iwawaki, Flavio Salazar-Onfray, Fabiola Osorio.

The IRE1α/XBP1s signaling pathway is an arm of the unfolded protein response (UPR) that safeguards the fidelity of the cellular proteome during endoplasmic reticulum (ER) stress, and that has also emerged as a key regulator of dendritic cell (DC) homeostasis. However, in the context of DC activation, the regulation of the IRE1α/XBP1s axis is not fully understood. In this work, we report that cell lysates generated from melanoma cell lines markedly induce XBP1s and certain members of the UPR such as the chaperone BiP in bone marrow derived DCs (BMDCs). Activation of IRE1α endonuclease upon innate recognition of melanoma cell lysates was required for amplification of proinflammatory cytokine production and was necessary for efficient cross-presentation of melanoma-associated antigens without modulating the MHC-II antigen presentation machinery. Altogether, this work provides evidence indicating that ex-vivo activation of the IRE1α/XBP1 pathway in BMDCs enhances CD8+ T cell specific responses against tumor antigens.

Keywords: IRE1α; UPR; XBP1s; cross-presentation; dendritic cell; melanoma

DOI: https://doi.org/10.3389/fimmu.2018.03050

Cancers (Basel). 2019 Jan 25. pii: E142. [Epub ahead of print]11(2):

The PERK Branch of the Unfolded Protein Response Promotes DLL4 Expression by Activating an Alternative Translation Mechanism.

Manon Jaud, Céline Philippe, Loic Van Den Berghe, Christèle Ségura, Laurent Mazzolini, Stéphane Pyronnet, Henrik Laurell, Christian Touriol.

Delta-like 4 (DLL4) is a pivotal endothelium specific Notch ligand that has been shown to function as a regulating factor during physiological and pathological angiogenesis. DLL4 functions as a negative regulator of angiogenic branching and sprouting. Interestingly, Dll4 is with Vegf-a one of the few examples of haplo-insufficiency, resulting in obvious vascular abnormalities and in embryonic lethality. These striking phenotypes are a proof of concept of the crucial role played by the bioavailability of VEGF and DLL4 during vessel patterning and that there must be a very fine-tuning of DLL4 expression level. However, to date the expression regulation of this factor was poorly studied. In this study, we showed that the DLL4 5'-UTR harbors an Internal Ribosomal Entry Site (IRES) that, in contrast to cap-dependent translation, was efficiently utilized in cells subjected to several stresses including hypoxia and endoplasmic reticulum stress (ER stress). We identified PERK, a kinase activated by ER stress, as the driver of DLL4 IRES-mediated translation, and hnRNP-A1 as an IRES-Trans-Acting Factor (ITAF) participating in the IRES-dependent translation of DLL4 during endoplasmic reticulum stress. The presence of a stress responsive internal ribosome entry site in the DLL4 msRNA suggests that the process of alternative translation initiation, by controlling the expression of this factor, could have a crucial role in the control of endothelial tip cell function.

Keywords: DLL4 (delta like ligand 4); IRES (internal ribosome entry site); PERK (PKR-Like endoplasmic reticulum kinase); UPR (unfolded protein response); angiogenesis; endoplasmic reticulum stress; hypoxia

DOI: https://doi.org/10.3390/cancers11020142

Cancers (Basel). 2019 Jan 31. pii: E159. [Epub ahead of print]11(2):

Targeting Glioblastoma Stem Cells with 2-Deoxy-D-Glucose (2-DG) Potentiates Radiation-Induced Unfolded Protein Response (UPR).

Sumedh S Shah, Gregor A Rodriguez, Alexis Musick, Winston M Walters, Nicolas de Cordoba, Eric Barbarite, Megan M Marlow, Brian Marples, Jeffrey S Prince, Ricardo J Komotar, Steven Vanni, Regina M Graham.

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, and despite optimized treatment options, median survival remains dismal. Contemporary evidence suggests disease recurrence results from expansion of a robustly radioresistant subset of GBM progenitor cells, termed GBM stem cells (GSCs). In this study, we utilized transmission electron microscopy to uncover ultrastructural effects on patient-derived GSC lines exposed to supratherapeutic radiotherapy levels. Elevated autophagosome formation and increased endoplasmic reticulum (ER) internal diameter, a surrogate for ER stress and activation of unfolded protein response (UPR), was uncovered. These observations were confirmed via protein expression through Western blot. Upon interrogating genomic data from an open-access GBM patient database, overexpression of UPR-related chaperone protein genes was inversely correlated with patient survival. This indicated controlled UPR may play a role in promoting radioresistance. To determine if potentiating UPR further can induce apoptosis, we exposed GSCs to radiation with an ER stress-inducing drug, 2-deoxy-D-glucose (2-DG), and found dose-dependent decreases in viability and increased apoptotic marker expression. Taken together, our results indicate GSC radioresistance is, in part, achieved by overexpression and overactivation of ER stress-related pathways, and this effect can be overcome via potentiation of UPR, leading to loss of GSC viability.

Keywords: ER stress; autophagy; cancer stem cells; glioblastoma multiforme; radiation; unfolded protein response

DOI: https://doi.org/10.3390/cancers11020159

Cell Signal. 2019 Jan 28. pii: S0898-6568(19)30017-8. [Epub ahead of print]

ER stress activation impairs the expression of circadian clock and clock-controlled genes in NIH3T3 cells via an ATF4-dependent mechanism.

Lei Gao, Huatao Chen, Cuimei Li, Yaoyao Xiao, Dan Yang, Manhui Zhang, Dong Zhou, Wei Liu, Aihua Wang, Yaping Jin.

Endoplasmic reticulum (ER) stress and circadian clockwork signaling pathways mutually regulate various cellular functions, but the details regarding the cross-talk between these pathways in mammalian cells are unclear. In this study, whether perturbation of ER stress signaling affects the cellular circadian clockwork and transcription of clock-controlled genes was investigated in NIH3T3 mouse fibroblasts. An NIH3T3 cell model stably expressing luciferase (Luc) under the control of the Bmal1 clock gene promoter was established using a lentiviral system. Then, Luc activity was monitored in real-time to detect Bmal1-Luc oscillations. The ER stress activators thapsigargin (Tg) and tunicamycin (Tm) markedly reduced Bmal1-Luc oscillation amplitudes and induced phase delay shifts in NIH3T3 cells. Treatment with Tg/Tm activated ER stress signaling by upregulating GRP78, CHOP, ATF6, and ATF4 and simultaneously significantly decreased BMAL1 protein levels and inhibited the transcription of circadian clock (Bmal1, Per2, Nr1d1, and Dbp) and clock-controlled (Scad1, Fgf7, and Arnt) genes. 4-Phenylbutyric acid, an ER stress inhibitor, alleviated the transcriptional repression of the circadian clock genes and partially restored Bmal1-Luc oscillation amplitudes in Tg- or Tm-treated NIH3T3 cells. More importantly, knock-down of ATF4, but not ATF6, in Tg-treated NIH3T3 cells partially rescued Bmal1-Luc oscillation amplitudes and mRNA expression of the four circadian clock genes. Taken together, our study demonstrates that ER stress activation inhibits the transcription of circadian clock and clock-controlled genes via an ATF4-dependent mechanism.

Keywords: 4-Phenylbutyric acid; Circadian clock; Thapsigargin; Tunicamycin; Unfolded protein response

DOI: https://doi.org/10.1016/j.cellsig.2019.01.008

J Neuroinflammation. 2019 Feb 01. 16(1): 23

Oligodendrocyte-specific ATF4 inactivation does not influence the development of EAE.

Yuan Yue, Milos Stanojlovic, Yifeng Lin, Gerard Karsenty, Wensheng Lin.

BACKGROUND: Multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), are inflammatory demyelinating and neurodegenerative diseases of the CNS. Although recent studies suggest the neuroprotective effects of oligodendrocytes in neurodegenerative diseases, it remains unknown whether oligodendrocyte death induced by inflammatory attacks contributes to neurodegeneration in MS and EAE. Upon endoplasmic reticulum (ER) stress, activation of pancreatic ER kinase (PERK) promotes cell survival through induction of activating transcription factor 4 (ATF4) by phosphorylating eukaryotic translation initiation factor 2α (eIF2α). We have generated a mouse model that allows for temporally controlled activation of PERK specifically in oligodendrocytes. Our previous study has demonstrated that PERK activation specifically in oligodendrocytes attenuates EAE disease severity and ameliorates EAE-induced oligodendrocyte apoptosis, demyelination, and axon degeneration, without altering inflammation.
METHODS: We determined whether oligodendrocyte-specific PERK activation reduced neuron loss in the CNS of EAE mice using the mouse model that allows for temporally controlled activation of PERK specifically in oligodendrocytes. We further generated a mouse model that allows for inactivation of ATF4 specifically in oligodendrocytes, and determined the effects of ATF4 inactivation in oligodendrocytes on mice undergoing EAE.
RESULTS: We showed that protection of oligodendrocytes resulting from PERK activation led to attenuation of neuron loss in the CNS gray matter of EAE mice. Surprisingly, we found that ATF4 inactivation specifically in oligodendrocytes did not alter EAE disease severity and had no effect on oligodendrocyte loss, demyelination, axon degeneration, neuron loss, and inflammation in EAE mice.
CONCLUSIONS: These findings suggest the neuroprotective effects of PERK activation in oligodendrocytes in EAE, and rule out the involvement of ATF4 in oligodendrocytes in the development of EAE. These results imply that the protective effects of PERK activation in oligodendrocytes in MS and EAE are not mediated by ATF4.

Keywords: ATF4; EAE; Multiple sclerosis; Neurodegeneration; Oligodendrocyte; PERK

DOI: https://doi.org/10.1186/s12974-019-1415-6