bims-ershed 2022-08-07 papers

Cell Calcium. 2022 Jul 20. pii: S0143-4160(22)00095-1. [Epub ahead of print]106 102622

Ca2+ signalling system initiated by endoplasmic reticulum stress stimulates PERK activation.

Constanza Feliziani, Macarena Fernandez, Gonzalo Quassollo, Deborah Holstein, Sebastián M Bairo, James C Paton, Adrienne W Paton, Juan de Batista, James D Lechleiter, Mariana Bollo.

The accumulation of unfolded proteins within the Endoplasmic Reticulum (ER) activates a signal transduction pathway termed the unfolded protein response (UPR), which attempts to restore ER homoeostasis. If this cannot be done, UPR signalling ultimately induces apoptosis. Ca2+ depletion in the ER is a potent inducer of ER stress. Despite the ubiquity of Ca2+ as an intracellular messenger, the precise mechanism(s) by which Ca2+ release affects the UPR remains unknown. Tethering a genetically encoded Ca2+ indicator (GCamP6) to the ER membrane revealed novel Ca2+ signalling events initiated by Ca2+ microdomains in human astrocytes under ER stress, induced by tunicamycin (Tm), an N-glycosylation inhibitor, as well as in a cell model deficient in all three inositol triphosphate receptor isoforms. Pharmacological and molecular studies indicate that these local events are mediated by translocons and that the Ca2+ microdomains impact (PKR)-like-ER kinase (PERK), an UPR sensor, activation. These findings reveal the existence of a Ca2+ signal mechanism by which stressor-mediated Ca2+ release regulates ER stress.

Keywords: (PKR)-like-ER kinase (PERK); Calcium signalling; Inositol triphosphate receptor; Translocon; Unfolded protein response

DOI: https://doi.org/10.1016/j.ceca.2022.102622

Biochim Biophys Acta Gen Subj. 2022 Aug 01. pii: S0304-4165(22)00137-4. [Epub ahead of print] 130219

Inhibiting IRE-1 RNase signaling decreases HIV-1 tat-induced inflammatory M1 state in microglial cells.

Aguinaldo Roberto Pinto, Monique Ferrary Américo, Hernán Terenzi, Douglas Bardini Silveira.

HIV-1 transactivator (Tat) protein plays a critical role in neurological disorders resulting from viral infection, commonly known as HIV-1-associated neurocognitive disorders (HAND). Previous studies have shown that circulant Tat induces M1 microglial activation, one of the hallmark features of HAND, and this is coupled with ER stress and subsequent Unfolded Protein Response (UPR) triggering. Here, we demonstrate that bystander stimuli of Tat in microglial cells result in the simultaneous overexpression of IRE1-related markers and production of M1-typed proinflammatory mediators. We also show that blocking IRE1/XBP-1 signaling using 4μ8C diminishes such inflammatory response. These findings reinforce a role for the IRE1/XBP-1 pathway in HIV-1 Tat neuropathology and suggest that targeting IRE1 RNase activity using 4μ8C or analogue compounds may provide a therapeutic intervention to mitigate against neuroinflammation in HAND.

Keywords: ER stress; HAND; HIV-1 tat; IRE1; Microglia; XBP-1

DOI: https://doi.org/10.1016/j.bbagen.2022.130219

J Cell Biochem. 2022 Jul 31.

Identification of an ERN1 target site within EGFP mRNA.

Marius W Baeken, Yohei Yokobayashi.

EGFP (enhanced green fluorescent protein) is one of the most common tools used in life sciences, including research focusing on proteostasis. Here we report that ERN1 (endoplasmic reticulum to nucleus signaling 1), which is upregulated by UPR (unfolded protein response), targets an RNA hairpin loop motif in EGFP mRNA. A silent mutation introduced into EGFP mRNA abolished the ERN1-dependent mRNA decay. Therefore, experiments that employ EGFP as a reporter gene in studies that involve upregulation of the UPR pathway should be interpreted carefully, and a mutant devoid of the ERN1 target motif may be more suitable for such studies.

Keywords: EGFP; ERN1; IRE1; proteostasis; unfolded protein response

DOI: https://doi.org/10.1002/jcb.30314

Theranostics. 2022 ;12(12): 5337-5349

XBP1 is required in Th2 polarization induction in airway allergy.

Xianhai Zeng, Xiaojun Xiao, Suqin Hu, Weiyi He, Gaohui Wu, Xiaorui Geng, Jialiang Fan, Longpeng Ma, Jiangqi Liu, Zhiqiang Liu, Pingchang Yang.

Rationale: Th2 polarization plays a central role in the pathogenesis of allergic diseases such as airway allergy. The underlying mechanism is not fully understood yet. X-box-binding protein-1 (XBP1) can regulate immune cell activities upon exposing stressful events. The role of XBP1 in the development of Th2 polarization has not yet been explored. Methods: Mice carrying Xbp1-deficient CD4+ T cells were employed to observe the role of XBP1 in the induction of airway allergy. A cell culture model was established to evaluate the role of XBP1 in facilitating the Th2 lineage commitment. Results: We found that Xbp1 ablation in CD4+ T cells prevented induction of Th2 polarization in the mouse airway tract. XBP1 was indispensable in the Th2 lineage commitment. XBP1 mediated the effects of 3-methyl-4-nitrophenol (MNP) on facilitating inducing antigen-specific Th2 response in the airways. Exposure to MNP induced expression of XBP1 in CD4+ T cells. RhoA facilitated the binding between XBP1 and GATA3 in CD4+ T cells. XBP1 induced GATA3 phosphorylation to promote the Il4 gene transcription. Modulation of the RhoA/XBP1 axis mitigated experimental allergic response in the mouse airways. Conclusions: A potential therapeutic target, XBP1, was identified in this study. XBP1 was required in the development of skewed Th2 response in the airways. Inhibiting XBP1 alleviated Th2 polarization-related immune inflammation in the airways. The data suggest that inhibiting XBP1 has the translation potential for the treatment of airway allergy.

Keywords: Airway allergy; CD4+ T cells; Th2 polarization; XBP1.; air pollution

DOI: https://doi.org/10.7150/thno.75100