bims-mecosi 2024-02-04 papers

bims-mecosi

Biomed News

on Membrane contact sites

Issue of 2024–02–04
seven papers selected by
Verena Kohler, Umeå University

Calcium Flow at ER-TGN Contact Sites Facilitates Secretory Cargo Export.
Cell biology of Parkinson's disease: Mechanisms of synaptic, lysosomal, and mitochondrial dysfunction.
Optineurin provides a mitophagy contact site for TBK1 activation.
IP3R1-mediated MAMs formation contributes to mechanical trauma-induced hepatic injury and the protective effect of melatonin.
Mitophagy in plants: Emerging regulators of mitochondrial targeting for selective autophagy.
Routing of Kv7.1 to endoplasmic reticulum plasma membrane junctions.
Mlg1, a yeast acyltransferase located in ER membranes associated with mitochondria (MAMs), is involved in de novo synthesis and remodelling of phospholipids.

Mol Biol Cell. 2024 Jan 31. mbcE23030099

Calcium Flow at ER-TGN Contact Sites Facilitates Secretory Cargo Export.

Bulat R Ramazanov, Anup Parchure, Rosaria Di Martino, Abhishek Kumar, Minhwan Chung, Yeongho Kim, Oliver Griesbeck, Martin A Schwartz, Alberto Luini, Julia von Blume.

Ca2+ influx into the trans-Golgi Network (TGN) promotes secretory cargo sorting by the Ca2+-ATPase SPCA1 and the luminal Ca2+ binding protein Cab45. Cab45 oligomerizes upon local Ca2+ influx, and Cab45 oligomers sequester and separate soluble secretory cargo from the bulk flow of proteins in the TGN. However, how this Ca2+ flux into the lumen of the TGN is achieved remains mysterious, as the cytosol has a nanomolar steady-state Ca2+ concentration. The TGN forms membrane contact sites (MCS) with the Endoplasmic Reticulum (ER), allowing protein-mediated exchange of molecular species such as lipids. Here, we show that the TGN export of secretory proteins requires the integrity of ER-TGN MCS and inositol 3 phosphate receptor (IP3R)-dependent Ca2+ fluxes in the MCS, suggesting Ca2+ transfer between these organelles. Using an MCS-targeted Ca2+ FRET sensor module, we measure the Ca2+ flow in these sites in real time. These data show that ER-TGN MCS facilitates the Ca2+ transfer required for Ca2+-dependent cargo sorting and export from the TGN, thus solving a fundamental question in cell biology.

DOI: https://doi.org/10.1091/mbc.E23-03-0099
Curr Opin Neurobiol. 2024 Feb 01. pii: S0959-4388(24)00003-5. [Epub ahead of print]85 102841

Cell biology of Parkinson's disease: Mechanisms of synaptic, lysosomal, and mitochondrial dysfunction.

Sarah M Brooker, Grace E Naylor, Dimitri Krainc.

Parkinson's disease (PD) is a growing cause of disability worldwide and there is a critical need for the development of disease-modifying therapies to slow or stop disease progression. Recent advances in characterizing the genetics of PD have expanded our understanding of the cell biology of this disorder. Mitochondrial oxidative stress, defects in synaptic function, and impaired lysosomal activity have been shown to be linked in PD, resulting in a pathogenic feedback cycle involving the accumulation of toxic oxidized dopamine and alpha-synuclein. In this review, we will highlight recent data on a subset of PD-linked genes which have key roles in these pathways and the pathogenic cycle. We will furthermore discuss findings highlighting the importance of dynamic mitochondria-lysosome contact sites that mediate direct inter-organelle cross-talk in the pathogenesis of PD and related disorders.

DOI: https://doi.org/10.1016/j.conb.2024.102841
EMBO J. 2024 Jan 29.

Optineurin provides a mitophagy contact site for TBK1 activation.

Koji Yamano, Momoha Sawada, Reika Kikuchi, Kafu Nagataki, Waka Kojima, Ryu Endo, Hiroki Kinefuchi, Atsushi Sugihara, Tomoshige Fujino, Aiko Watanabe, Keiji Tanaka, Gosuke Hayashi, Hiroshi Murakami, Noriyuki Matsuda.

  Tank-binding kinase 1 (TBK1) is a Ser/Thr kinase that is involved in many intracellular processes, such as innate immunity, cell cycle, and apoptosis. TBK1 is also important for phosphorylating the autophagy adaptors that mediate the selective autophagic removal of damaged mitochondria. However, the mechanism by which PINK1-Parkin-mediated mitophagy activates TBK1 remains largely unknown. Here, we show that the autophagy adaptor optineurin (OPTN) provides a unique platform for TBK1 activation. Both the OPTN-ubiquitin and the OPTN-pre-autophagosomal structure (PAS) interaction axes facilitate assembly of the OPTN-TBK1 complex at a contact sites between damaged mitochondria and the autophagosome formation sites. At this assembly point, a positive feedback loop for TBK1 activation is initiated that accelerates hetero-autophosphorylation of the protein. Expression of monobodies engineered here to bind OPTN impaired OPTN accumulation at contact sites, as well as the subsequent activation of TBK1, thereby inhibiting mitochondrial degradation. Taken together, these data show that a positive and reciprocal relationship between OPTN and TBK1 initiates autophagosome biogenesis on damaged mitochondria.

Keywords:  Autophagy; Mitochondria; PINK1; Parkin; Ubiquitin

DOI:  https://doi.org/10.1038/s44318-024-00036-1
Cell Mol Biol Lett. 2024 Feb 02. 29(1): 22

IP3R1-mediated MAMs formation contributes to mechanical trauma-induced hepatic injury and the protective effect of melatonin.

Rui Shi, Zhenhua Liu, Huan Yue, Man Li, Simin Liu, Dema De, Runjing Li, Yunan Chen, Shuli Cheng, Xiaoming Gu, Min Jia, Jun Li, Juan Li, Shumiao Zhang, Na Feng, Rong Fan, Feng Fu, Yali Liu, Mingge Ding, Jianming Pei.

   INTRODUCTION: There is a high morbidity and mortality rate in mechanical trauma (MT)-induced hepatic injury. Currently, the molecular mechanisms underlying liver MT are largely unclear. Exploring the underlying mechanisms and developing safe and effective medicines to alleviate MT-induced hepatic injury is an urgent requirement. The aim of this study was to reveal the role of mitochondria-associated ER membranes (MAMs) in post-traumatic liver injury, and ascertain whether melatonin protects against MT-induced hepatic injury by regulating MAMs.
METHODS: Hepatic mechanical injury was established in Sprague-Dawley rats and primary hepatocytes. A variety of experimental methods were employed to assess the effects of melatonin on hepatic injury, apoptosis, MAMs formation, mitochondrial function and signaling pathways.
RESULTS: Significant increase of IP3R1 expression and MAMs formation were observed in MT-induced hepatic injury. Melatonin treatment at the dose of 30 mg/kg inhibited IP3R1-mediated MAMs and attenuated MT-induced liver injury in vivo. In vitro, primary hepatocytes cultured in 20% trauma serum (TS) for 12 h showed upregulated IP3R1 expression, increased MAMs formation and cell injury, which were suppressed by melatonin (100 μmol/L) treatment. Consequently, melatonin suppressed mitochondrial calcium overload, increased mitochondrial membrane potential and improved mitochondrial function under traumatic condition. Melatonin's inhibitory effects on MAMs formation and mitochondrial calcium overload were blunted when IP3R1 was overexpressed. Mechanistically, melatonin bound to its receptor (MR) and increased the expression of phosphorylated ERK1/2, which interacted with FoxO1 and inhibited the activation of FoxO1 that bound to the IP3R1 promoter to inhibit MAMs formation.
CONCLUSION: Melatonin prevents the formation of MAMs via the MR-ERK1/2-FoxO1-IP3R1 pathway, thereby alleviating the development of MT-induced liver injury. Melatonin-modulated MAMs may be a promising therapeutic therapy for traumatic hepatic injury.

Keywords:  ERK1/2; FoxO1; IP3R1; MAMs; Mechanical trauma; Melatonin

DOI:  https://doi.org/10.1186/s11658-023-00509-x
J Microsc. 2024 Jan 31.

Mitophagy in plants: Emerging regulators of mitochondrial targeting for selective autophagy.

Patrick J Duckney, Pengwei Wang, Patrick J Hussey.

  The degradation and turnover of mitochondria is fundamental to Eukaryotes and is a key homeostatic mechanism for maintaining functional mitochondrial populations. Autophagy is an important pathway by which mitochondria are degraded, involving their sequestration into membrane-bound autophagosomes and targeting to lytic endosomal compartments (the lysosome in animals, the vacuole in plants and yeast). Selective targeting of mitochondria for autophagy, also known as mitophagy, distinguishes mitochondria from other cell components for degradation and is necessary for the regulation of mitochondria-specific cell processes. In mammals and yeast, mitophagy has been well characterised and is regulated by numerous pathways with diverse and important functions in the regulation of cell homeostasis, metabolism and responses to specific stresses. In contrast, we are only just beginning to understand the importance and functions of mitophagy in plants, chiefly as the proteins that target mitochondria for autophagy in plants are only recently emerging. Here, we discuss the current progress of our understanding of mitophagy in plants, the importance of mitophagy for plant life and the regulatory autophagy proteins involved in mitochondrial degradation. In particular, we will discuss the recent emergence of mitophagy receptor proteins that selectively target mitochondria for autophagy, and discuss the missing links in our knowledge of mitophagy-regulatory proteins in plants compared to animals and yeast.

Keywords:  Arabidopsis; TRB1; TraB; autophagy; contact site; homeostasis; mitochondria; mitophagy; plant; stress

DOI:  https://doi.org/10.1111/jmi.13267
Acta Physiol (Oxf). 2024 Jan 29. e14106

Routing of Kv7.1 to endoplasmic reticulum plasma membrane junctions.

Clara Serrano-Novillo, Irene Estadella, María Navarro-Pérez, Anna Oliveras, Angela de Benito-Bueno, Paula G Socuéllamos, Manel Bosch, María José Coronado, Daniel Sastre, Carmen Valenzuela, Christian Soeller, Antonio Felipe.

   AIM: The voltage-gated Kv7.1 channel, in association with the regulatory subunit KCNE1, contributes to the IKs current in the heart. However, both proteins travel to the plasma membrane using different routes. While KCNE1 follows a classical Golgi-mediated anterograde pathway, Kv7.1 is located in endoplasmic reticulum-plasma membrane junctions (ER-PMjs), where it associates with KCNE1 before being delivered to the plasma membrane.
METHODS: To characterize the channel routing to these spots we used a wide repertoire of methodologies, such as protein expression analysis (i.e. protein association and biotin labeling), confocal (i.e. immunocytochemistry, FRET, and FRAP), and dSTORM microscopy, transmission electron microscopy, proteomics, and electrophysiology.
RESULTS: We demonstrated that Kv7.1 targeted ER-PMjs regardless of the origin or architecture of these structures. Kv2.1, a neuronal channel that also contributes to a cardiac action potential, and JPHs, involved in cardiac dyads, increased the number of ER-PMjs in nonexcitable cells, driving and increasing the level of Kv7.1 at the cell surface. Both ER-PMj inducers influenced channel function and dynamics, suggesting that different protein structures are formed. Although exhibiting no physical interaction, Kv7.1 resided in more condensed clusters (ring-shaped) with Kv2.1 than with JPH4. Moreover, we found that VAMPs and AMIGO, which are Kv2.1 ancillary proteins also associated with Kv7.1. Specially, VAP B, showed higher interaction with the channel when ER-PMjs were stimulated by Kv2.1.
CONCLUSION: Our results indicated that Kv7.1 may bind to different structures of ER-PMjs that are induced by different mechanisms. This variable architecture can differentially affect the fate of cardiac Kv7.1 channels.

Keywords:  ERPMj inducers; adaptors; cell surface targeting; potassium channels

DOI:  https://doi.org/10.1111/apha.14106
FEBS J. 2024 Jan 31.

Mlg1, a yeast acyltransferase located in ER membranes associated with mitochondria (MAMs), is involved in de novo synthesis and remodelling of phospholipids.

Patricia Laquel, Sophie Ayciriex, François Doignon, Nadine Camougrand, Louise Fougère, Christophe Rocher, Valérie Wattelet-Boyer, Jean-Jacques Bessoule, Eric Testet.

  In cells, phospholipids contain acyl chains of variable lengths and saturation, features that affect their functions. Their de novo synthesis in the endoplasmic reticulum takes place via the cytidine diphosphate diacylglycerol (CDP-DAG) and Kennedy pathways, which are conserved in eukaryotes. PA is a key intermediate for all phospholipids (PI, PIPs, PS, PE, PC, PG and CL). The de novo synthesis of PA occurs by acylation of glycerophosphate leading to the synthesis of 1-acyl lysoPA and subsequent acylation of 1-acyl lysoPA at the sn-2 position. Using membranes from Escherichia coli overexpressing MLG1, we showed that the yeast gene MLG1 encodes an acyltransferase, leading specifically to the synthesis of PA from 1-acyl lysoPA. Moreover, after their de novo synthesis, phospholipids can be remodelled by acyl exchange with one and/or two acyl chains exchanged at the sn-1 and/or sn-2 position. Based on shotgun lipidomics of the reference and mlg1Δ strains, as well as biochemical assays for acyltransferase activities, we identified an additional remodelling activity for Mlg1p, namely, incorporation of palmitic acid into the sn-1 position of PS and PE. By using confocal microscopy and subcellular fractionation, we also found that this acyltransferase is located in ER membranes associated with mitochondria, a finding that highlights the importance of these organelles in the global cellular metabolism of lipids.

Keywords:  ER Mitochondria-associated membranes (MAMs); MLG1: hoMoLoG to PSI1; Saccharomyces cerevisiae; glycerophospholipid remodelling; lysolipid acyltransferase

DOI:  https://doi.org/10.1111/febs.17068