bims-mecosi 2021-11-07 papers

Issue of 2021–11–07
four papers selected by
Verena Kohler, Stockholm University

Sci Rep. 2021 Nov 02. 11(1): 21477

β2-adrenergic receptor regulates ER-mitochondria contacts.

Youngshin Lim, Il-Taeg Cho, Helmut G Rennke, Ginam Cho.

Interactions between the endoplasmic reticulum (ER) and mitochondria (Mito) are crucial for many cellular functions, and their interaction levels change dynamically depending on the cellular environment. Little is known about how the interactions between these organelles are regulated within the cell. Here we screened a compound library to identify chemical modulators for ER-Mito contacts in HEK293T cells. Multiple agonists of G-protein coupled receptors (GPCRs), beta-adrenergic receptors (β-ARs) in particular, scored in this screen. Analyses in multiple orthogonal assays validated that β2-AR activation promotes physical and functional interactions between the two organelles. Furthermore, we have elucidated potential downstream effectors mediating β2-AR-induced ER-Mito contacts. Together our study identifies β2-AR signaling as an important regulatory pathway for ER-Mito coupling and highlights the role of these contacts in responding to physiological demands or stresses.

DOI: https://doi.org/10.1038/s41598-021-00801-w

Autophagy. 2021 Oct 31. 1-16

SHISA5/SCOTIN restrains spontaneous autophagy induction by blocking contact between the ERES and phagophores.

Jee-Eun Lee, Nari Kim, Minkyo Jung, Ji-Young Mun, Joo-Yeon Yoo.

The phagophore expands into autophagosomes in close proximity to endoplasmic reticulum (ER) exit sites (ERESs). Here, we propose that a single-pass ER transmembrane protein, SHISA5/SCOTIN, acts as an autophagy suppressor under basal condition by blocking the contact between the phagophore and ERES. HeLa cells lacking SHISA5 displayed higher levels of macroautophagy/autophagy. The enhanced autophagy in SHISA5 KO cells requires class III phosphatidylinositol 3-kinase complex I (PtdIns3K-C1) activity and functional assembly of ERES, but not ULK1 activity. A proximity ligation assay (PLA) of SEC16A (Sec16 homolog A, endoplasmic reticulum export factor)-WIPI2 (WD repeat domain, phosphoinositide interacting 2) and SEC31A (Sec31 homolog A, COPII coat complex component)-MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3 beta) demonstrated that contact between the ERES and phagophore increased in SHISA5 KO cells, and the cytosolic domain of SHISA5 was sufficient to rescue this phenotype. Close proximity between ERES and phagophore in SHISA5 KO cells was also visualized by performing an ultrastructure correlative image analysis of SEC31A associated with LC3-positive membranes. Furthermore, we observed that SHISA5 was located near ERES under basal conditions, but displaced away from ERES under autophagy-inducing conditions. These data suggest that SHISA5 functions to block spontaneous contact between ERES and phagophore, and the blockage effect of SHISA5 should be relieved for the proper induction of autophagy.

Keywords: Constitutive autophagy; SHISA5/SCOTIN; endoplasmic reticulum exit sites; membrane contact; phagophore

DOI: https://doi.org/10.1080/15548627.2021.1994297

Mol Cancer Res. 2021 Nov 02. pii: molcanres.0702.2021. [Epub ahead of print]

PERK, Beyond an Unfolded Protein Response Sensor in Estrogen-induced Apoptosis in Endocrine-Resistant Breast Cancer.

Ping Fan, V Craig Jordan.

The discovery of 17β-estradiol (E2)-induced apoptosis has clinical relevance. Mechanistically, E2 over activates nuclear estrogen receptor α (ERα) that results in stress responses. The unfolded protein response (UPR) is initiated by E2 in the endoplasmic reticulum after hours of treatment in endocrine-resistant breast cancer cells, thereby activating three UPR sensors-PRK-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6) with different functions. Specifically, PERK plays a critical role in induction of apoptosis while IRE1α and ATF6 are involved in the endoplasmic reticulum stress-associated degradation (ERAD) of PI3K/Akt/mTOR pathways. In addition to attenuating protein translation, PERK increases the DNA-binding activity of nuclear factor-κB (NF-κB) and subsequent tumor necrosis factor α (TNFα) expression. Additionally, PERK communicates with the mitochondria to regulate oxidative stress at mitochondria-associated endoplasmic reticulum membranes (MAMs). Furthermore, PERK is a component enriched in MAMs that interacts with multifunctional MAM-tethering proteins and integrally modulates the exchange of metabolites such as lipids, reactive oxygen species (ROS), and Ca2+ at contact sites. MAMs are also critical sites for the initiation of autophagy to remove defective organelles and misfolded proteins through specific regulatory proteins. Thus, PERK conveys signals from nucleus to these membrane-structured organelles that form an interconnected network to regulate E2-induced apoptosis. Herein, we address the mechanistic progress on how PERK acts as a multifunctional molecule to commit E2 to inducing apoptosis in endocrine-resistant breast cancer.

DOI: https://doi.org/10.1158/1541-7786.MCR-21-0702

Proc Natl Acad Sci U S A. 2021 Nov 09. pii: e2110996118. [Epub ahead of print]118(45):

In-cell structures of conserved supramolecular protein arrays at the mitochondria-cytoskeleton interface in mammalian sperm.

Miguel Ricardo Leung, Riccardo Zenezini Chiozzi, Marc C Roelofs, Johannes F Hevler, Ravi Teja Ravi, Paula Maitan, Min Zhang, Heiko Henning, Elizabeth G Bromfield, Stuart C Howes, Bart M Gadella, Albert J R Heck, Tzviya Zeev-Ben-Mordehai.

Mitochondria-cytoskeleton interactions modulate cellular physiology by regulating mitochondrial transport, positioning, and immobilization. However, there is very little structural information defining mitochondria-cytoskeleton interfaces in any cell type. Here, we use cryofocused ion beam milling-enabled cryoelectron tomography to image mammalian sperm, where mitochondria wrap around the flagellar cytoskeleton. We find that mitochondria are tethered to their neighbors through intermitochondrial linkers and are anchored to the cytoskeleton through ordered arrays on the outer mitochondrial membrane. We use subtomogram averaging to resolve in-cell structures of these arrays from three mammalian species, revealing they are conserved across species despite variations in mitochondrial dimensions and cristae organization. We find that the arrays consist of boat-shaped particles anchored on a network of membrane pores whose arrangement and dimensions are consistent with voltage-dependent anion channels. Proteomics and in-cell cross-linking mass spectrometry suggest that the conserved arrays are composed of glycerol kinase-like proteins. Ordered supramolecular assemblies may serve to stabilize similar contact sites in other cell types in which mitochondria need to be immobilized in specific subcellular environments, such as in muscles and neurons.

Keywords: cross-linking mass spectrometry; cryo-FIB milling; cryoelectron tomography; mitochondria–cytoskeleton contacts; subtomogram averaging

DOI: https://doi.org/10.1073/pnas.2110996118