bims-ershed 2023-01-08 papers

Issue of 2023‒01‒08
six papers selected by
Matías Eduardo González Quiroz
Worker’s Hospital

BMC Biol. 2023 Jan 04. 21(1): 1

Increased interaction between endoplasmic reticulum and mitochondria following sleep deprivation.

Amina Aboufares El Alaoui, Edgar Buhl, Sabrina Galizia, James J L Hodge, Luisa de Vivo, Michele Bellesi.

BACKGROUND: Prolonged cellular activity may overload cell function, leading to high rates of protein synthesis and accumulation of misfolded or unassembled proteins, which cause endoplasmic reticulum (ER) stress and activate the unfolded protein response (UPR) to re-establish normal protein homeostasis. Previous molecular work has demonstrated that sleep deprivation (SD) leads to ER stress in neurons, with a number of ER-specific proteins being upregulated to maintain optimal cellular proteostasis. It is still not clear which cellular processes activated by sleep deprivation lead to ER- stress, but increased cellular metabolism, higher request for protein synthesis, and over production of oxygen radicals have been proposed as potential contributing factors. Here, we investigate the transcriptional and ultrastructural ER and mitochondrial modifications induced by sleep loss.RESULTS: We used gene expression analysis in mouse forebrains to show that SD was associated with significant transcriptional modifications of genes involved in ER stress but also in ER-mitochondria interaction, calcium homeostasis, and mitochondrial respiratory activity. Using electron microscopy, we also showed that SD was associated with a general increase in the density of ER cisternae in pyramidal neurons of the motor cortex. Moreover, ER cisternae established new contact sites with mitochondria, the so-called mitochondria associated membranes (MAMs), important hubs for molecule shuttling, such as calcium and lipids, and for the modulation of ATP production and redox state. Finally, we demonstrated that Drosophila male mutant flies (elav > linker), in which the number of MAMs had been genetically increased, showed a reduction in the amount and consolidation of sleep without alterations in the homeostatic sleep response to SD.
CONCLUSIONS: We provide evidence that sleep loss induces ER stress characterized by increased crosstalk between ER and mitochondria. MAMs formation associated with SD could represent a key phenomenon for the modulation of multiple cellular processes that ensure appropriate responses to increased cell metabolism. In addition, MAMs establishment may play a role in the regulation of sleep under baseline conditions.

Keywords: Brain; Drosophila; Electron microscopy; Mouse; Neuron; Sleep deprivation

DOI: https://doi.org/10.1186/s12915-022-01498-7

FASEB J. 2023 Feb;37(2): e22758

The functional implication of ATF6α in castration-resistant prostate cancer cells.

Hongqing Zhou, Tingting Zhang, Liang Chen, Fengzhen Cui, Chenxiang Xu, Jiaxi Peng, Weixiang Ma, Jirong Huang, Xia Sheng, Mingsheng Liu, Faming Zhao.

Stress in the endoplasmic reticulum (ER) may perturb proteostasis and activates the unfolded protein response (UPR). UPR activation is frequently observed in cancer cells and is believed to fuel cancer progression. Here, we report that one of the three UPR sensors, ATF6α, was associated with prostate cancer (PCa) development, while both genetic and pharmacological inhibition of ATF6α impaired the survival of castration-resistance PCa (CRPC) cells. Transcriptomic analyses identified the molecular pathways deregulated upon ATF6α depletion, and also discovered considerable disparity in global gene expression between ATF6α knockdown and Ceapin-A7 treatment. In addition, combined analyses of human CRPC bulk RNA-seq and single-cell RNA-seq (scRNA-seq) public datasets confirmed that CRPC tumors with higher ATF6α activity displayed higher androgen receptor (AR) activity, proliferative and neuroendocrine (NE) like phenotypes, as well as immunosuppressive features. Lastly, we identified a 14-gene set as ATF6α NE gene signature with encouraging prognostic power. In conclusion, our results indicate that ATF6α is correlated with PCa progression and is functionally relevant to CRPC cell survival. Both specificity and efficacy of ATF6α inhibitors require further refinement and evaluation.

Keywords: ATF6α; CRPC; ER stress; UPR; prostate cancer

DOI: https://doi.org/10.1096/fj.202201347R

J Biol Chem. 2023 Jan 02. pii: S0021-9258(22)01306-0. [Epub ahead of print] 102863

Endoplasmic reticulum protein BIK binds to and inhibits mitochondria-localized anti-apoptotic proteins.

Elizabeth J Osterlund, Nehad Hirmiz, Dang Nguyen, James M Pemberton, Qiyin Fang, David W Andrews.

The pro-apoptotic BH3-only endoplasmic reticulum (ER) resident protein BIK, positively regulates mitochondrial outer membrane permeabilization (MOMP), the point-of-no-return in apoptosis. It is generally accepted that BIK functions at a distance from mitochondria by binding and sequestering anti-apoptotic proteins at the ER thereby promoting ER calcium release. Although BIK is predominantly localized to the ER, we detect by FLIM-FRET microscopy, BH3 region-dependent direct binding between BIK and mitochondria-localized chimeric mutants of the anti-apoptotic proteins BCL-XL and BCL-2 in both BMK and MCF-7 cells. Direct binding was accompanied by cell-type specific differential relocalization in response to co-expression of either BIK or one of its target binding partners, BCL-XL, when co-expressed in cells. In BMK cells with genetic deletion of both BAX and BAK (BMK-DKO) our data suggest a fraction of BIK protein moves towards mitochondria in response to the expression of a mitochondria-localized BCL-XL mutant. In contrast, in MCF-7 cells our data suggest BIK is localized at both ER and mitochondria-associated endoplasmic reticulum membranes (MAMs) and binds to the mitochondria-localized BCL-XL mutant via relocalization of BCL-XL to ER and MAMs. Rather than functioning at a distance, our data suggest BIK initiates MOMP via direct interactions with ER and mitochondria-localized anti-apoptotic proteins, that occur via ER-mitochondria contact sites, and/or by relocalization of either BIK or anti-apoptotic proteins in cells.

Keywords: BCL-2 family; BCL-2 interacting killer; BIK; FLIM-FRET; apoptosis; subcellular localization fluorescence lifetime imaging microscopy

DOI: https://doi.org/10.1016/j.jbc.2022.102863

Cell Rep. 2022 Dec 23. pii: S2211-1247(22)01798-3. [Epub ahead of print] 111899

The endoplasmic reticulum kinase PERK interacts with the oxidoreductase ERO1 to metabolically adapt mitochondria.

Endoplasmic reticulum (ER) homeostasis requires molecular regulators that tailor mitochondrial bioenergetics to the needs of protein folding. For instance, calnexin maintains mitochondria metabolism and mitochondria-ER contacts (MERCs) through reactive oxygen species (ROS) from NADPH oxidase 4 (NOX4). However, induction of ER stress requires a quick molecular rewiring of mitochondria to adapt to new energy needs. This machinery is not characterized. We now show that the oxidoreductase ERO1⍺ covalently interacts with protein kinase RNA-like ER kinase (PERK) upon treatment with tunicamycin. The PERK-ERO1⍺ interaction requires the C-terminal active site of ERO1⍺ and cysteine 216 of PERK. Moreover, we show that the PERK-ERO1⍺ complex promotes oxidization of MERC proteins and controls mitochondrial dynamics. Using proteinaceous probes, we determined that these functions improve ER-mitochondria Ca2+ flux to maintain bioenergetics in both organelles, while limiting oxidative stress. Therefore, the PERK-ERO1⍺ complex is a key molecular machinery that allows quick metabolic adaptation to ER stress.

Keywords: CP: Metabolism; CP: Molecular biology; ER; ER stress; ERO1; MAMs; MERCs; PERK; bioenergetics; endoplasmic reticulum; mitochondria; mitochondria-associated membranes; mitochondria-endoplasmic reticulum contacts; oxidoreductase

DOI: https://doi.org/10.1016/j.celrep.2022.111899

Sci Rep. 2022 Dec 31. 12(1): 22624

Evaluation of age-specific causes of death in the context of the Italian longevity transition.

Andrea Nigri, José Manuel Aburto, Ugofilippo Basellini, Marco Bonetti.

In many low-mortality countries, life expectancy at birth increased steadily over the last century. In particular, both Italian females and males benefited from faster improvements in mortality compared to other high-income countries, especially from the 1960s, leading to an exceptional increase in life expectancy. However, Italy has not become the leader in longevity. Here, we investigate life expectancy trends in Italy during the period 1960-2015 for both sexes. Additionally, we contribute to the existing literature by complementing life expectancy with an indicator of dispersion in ages at death, also known as lifespan inequality. Lifespan inequality underlies heterogeneity over age in populating health improvements and is a marker of uncertainty in the timing of death. We further quantify the contributions of different age groups and causes of death to recent trends in life expectancy and lifespan inequality. Our findings highlight the contributions of cardiovascular diseases and neoplasms to the recent increase in life expectancy but not necessarily to the decrease in lifespan inequality. Our results also uncover a more recent challenge across Italy: worsening mortality from infectious diseases and mortality at older age.

DOI: https://doi.org/10.1038/s41598-022-26907-3

J Exp Med. 2023 Mar 06. pii: e20221676. [Epub ahead of print]220(3):

Regulatory T cells suppress CD4+ effector T cell activation by controlling protein synthesis.

Lomon So, Kazushige Obata-Ninomiya, Alex Hu, Virginia S Muir, Ayako Takamori, Jing Song, Jane H Buckner, Ram Savan, Steven F Ziegler.

Regulatory T cells (Tregs) suppress the activation and subsequent effector functions of CD4 effector T cells (Teffs). However, molecular mechanisms that enforce Treg-mediated suppression in CD4 Teff are unclear. We found that Tregs suppressed activation-induced global protein synthesis in CD4 Teffs prior to cell division. We analyzed genome-wide changes in the transcriptome and translatome of activated CD4 Teffs. We show that mRNAs encoding for the protein synthesis machinery are regulated at the level of translation in activated CD4 Teffs by Tregs. Tregs suppressed global protein synthesis of CD4 Teffs by specifically inhibiting mRNAs of the translation machinery at the level of mTORC1-mediated translation control through concerted action of immunosuppressive cytokines IL-10 and TGFβ. Lastly, we found that the therapeutic targeting of protein synthesis with the RNA helicase eIF4A inhibitor rocaglamide A can alleviate inflammatory CD4 Teff activation caused by acute Treg depletion in vivo. These data show that peripheral tolerance is enforced by Tregs through mRNA translational control in CD4 Teffs.

DOI: https://doi.org/10.1084/jem.20221676