bims-mecosi 2022-04-17 papers

bims-mecosi

Biomed News

on Membrane contact sites

Issue of 2022‒04‒17
nine papers selected by
Verena Kohler

The Role of Impaired Mitochondrial Dynamics in MFN2-Mediated Pathology.
VAP-A and its binding partner CERT drive biogenesis of RNA-containing extracellular vesicles at ER membrane contact sites.
Entamoeba histolytica EHD1 Is Involved in Mitosome-Endosome Contact.
Hyperosmotic Stress Induces Phosphorylation of CERT and Enhances Its Tethering throughout the Endoplasmic Reticulum.
The ER Is a Common Mediator for the Behavior and Interactions of Other Organelles.
Endoplasmic reticulum-mitochondria coupling attenuates vanadium-induced apoptosis via IP3R in duck renal tubular epithelial cells.
CARD19 Interacts with Mitochondrial Contact Site and Cristae Organizing System Constituent Proteins and Regulates Cristae Morphology.
Targeting calcium-mediated inter-organellar crosstalk in cardiac diseases.
TRPC3 channel gating by lipids requires localization at the ER/PM junctions defined by STIM1.

Front Cell Dev Biol. 2022 ;10 858286

The Role of Impaired Mitochondrial Dynamics in MFN2-Mediated Pathology.

Mashiat Zaman, Timothy E Shutt.

  The Mitofusin 2 protein (MFN2), encoded by the MFN2 gene, was first described for its role in mediating mitochondrial fusion. However, MFN2 is now recognized to play additional roles in mitochondrial autophagy (mitophagy), mitochondrial motility, lipid transfer, and as a tether to other organelles including the endoplasmic reticulum (ER) and lipid droplets. The tethering role of MFN2 is an important mediator of mitochondrial-ER contact sites (MERCs), which themselves have many important functions that regulate mitochondria, including calcium homeostasis and lipid metabolism. Exemplifying the importance of MFN2, pathogenic variants in MFN2 are established to cause the peripheral neuropathy Charcot-Marie-Tooth Disease Subtype 2A (CMT2A). However, the mechanistic basis for disease is not clear. Moreover, additional pathogenic phenotypes such as lipomatosis, distal myopathy, optic atrophy, and hearing loss, can also sometimes be present in patients with CMT2A. Given these variable patient phenotypes, and the many cellular roles played by MFN2, the mechanistic underpinnings of the cellular impairments by which MFN2 dysfunction leads to disease are likely to be complex. Here, we will review what is known about the various functions of MFN2 that are impaired by pathogenic variants causing CMT2A, with a specific emphasis on the ties between MFN2 variants and MERCs.

Keywords:  CMT2A; MFN2; lipid homeostasis; mitochondria; mitochondrial dynamics; mitochondrial endoplasmic reticulum contact sites; mitophagy; mtDNA

DOI:  https://doi.org/10.3389/fcell.2022.858286
Dev Cell. 2022 Apr 07. pii: S1534-5807(22)00206-4. [Epub ahead of print]

VAP-A and its binding partner CERT drive biogenesis of RNA-containing extracellular vesicles at ER membrane contact sites.

Bahnisikha Barman, Bong Hwan Sung, Evan Krystofiak, Jie Ping, Marisol Ramirez, Bryan Millis, Ryan Allen, Nripesh Prasad, Sergei Chetyrkin, M Wade Calcutt, Kasey Vickers, James G Patton, Qi Liu, Alissa M Weaver.

  RNA transfer via extracellular vesicles (EVs) influences cell phenotypes; however, lack of information regarding biogenesis of RNA-containing EVs has limited progress in the field. Here, we identify endoplasmic reticulum membrane contact sites (ER MCSs) as platforms for the generation of RNA-containing EVs. We identify a subpopulation of small EVs that is highly enriched in RNA and regulated by the ER MCS linker protein VAP-A. Functionally, VAP-A-regulated EVs are critical for miR-100 transfer between cells and in vivo tumor formation. Lipid analysis of VAP-A-knockdown EVs revealed reductions in the EV biogenesis lipid ceramide. Knockdown of the VAP-A-binding ceramide transfer protein CERT led to similar defects in EV RNA content. Imaging experiments revealed that VAP-A promotes luminal filling of multivesicular bodies (MVBs), CERT localizes to MVBs, and the ceramide-generating enzyme neutral sphingomyelinase 2 colocalizes with VAP-A-positive ER. We propose that ceramide transfer via VAP-A-CERT linkages drives the biogenesis of a select RNA-containing EV population.

Keywords:  ER membrane contact sites; RNA-binding proteins; VAP-A; ceramide; colon cancer; exosomes; extracellular RNA; extracellular vesicles; miRNA

DOI:  https://doi.org/10.1016/j.devcel.2022.03.012
mBio. 2022 Apr 11. e0384921

Entamoeba histolytica EHD1 Is Involved in Mitosome-Endosome Contact.

Herbert J Santos, Yuki Hanadate, Kenichiro Imai, Haruo Watanabe, Tomoyoshi Nozaki.

  Interorganellar cross talk is often mediated by membrane contact sites (MCSs), which are zones where participating membranes come within 30 nm of one another. MCSs have been found in organelles, including the endoplasmic reticulum, Golgi bodies, endosomes, and mitochondria. Despite its seeming ubiquity, reports of MCS involving mitochondrion-related organelles (MROs) present in a few anaerobic parasitic protozoa remain lacking. Entamoeba histolytica, the etiological agent of amoebiasis, possesses an MRO called the mitosome. We previously discovered several Entamoeba-specific transmembrane mitosomal proteins (ETMPs) from in silico and cell-biological analyses. One of them, ETMP1 (EHI_175060), was predicted to have one transmembrane domain and two coiled-coil regions and was demonstrated to be mitosome membrane integrated based on carbonate fractionation and immunoelectron microscopy (IEM) data. Immunoprecipitation analysis detected a candidate interacting partner, EH domain-containing protein (EHD1; EHI_105270). We expressed hemagglutinin (HA)-tagged EHD1 in E. histolytica, and subsequent immunofluorescence and IEM data indicated an unprecedented MCS between the mitosome and the endosome. Live imaging of a green fluorescent protein (GFP)-EHD1-expressing strain demonstrated that EHD1 is involved in early endosome formation and is observed in MCS between endosomes of various sizes. In vitro assays using recombinant His-EHD1 demonstrated ATPase activity. MCSs are involved in lipid transfer, ion homeostasis, and organelle dynamics. The serendipitous discovery of the ETMP1-interacting partner EHD1 led to the observation of the mitosome-endosome contact site in E. histolytica. It opened a new view of how the relic mitochondria of Entamoeba may likewise be involved in organelle cross talk, a conserved feature of mitochondria and other organelles in general. IMPORTANCE Membrane contact sites (MCSs) are key regulators of interorganellar communication and have been widely demonstrated between various organelles. However, studies on MCSs involving mitochondrion-related organelles (MROs), present in some anaerobic parasitic protozoans, remain scarce. Entamoeba histolytica, the etiological agent of amoebiasis, possesses an MRO called the mitosome. This organelle is crucial for cellular differentiation and disease transmission, thereby significantly contributing to the amoeba's parasitic lifestyle. Our recent discovery of the interaction between the Entamoeba-specific transmembrane mitosomal protein (ETMP1) and EH domain-containing protein (EHD1) showcases a newly found mitosome-endosome contact site in E. histolytica. This finding reflects the idea that despite their substantially divergent and reduced nature, MROs like mitosomes conserve mechanisms for interorganellar cross talk. We posit lipid and ion transport, mitosome fission, and quality control as potential processes that are mediated by the ETMP1-EHD1-tethered mitosome-endosome contact site in E. histolytica.

Keywords:  EH domain; Entamoeba histolytica; endosome; membrane contact site; mitochondrion-related organelles; mitosome

DOI:  https://doi.org/10.1128/mbio.03849-21
Int J Mol Sci. 2022 Apr 05. pii: 4025. [Epub ahead of print]23(7):

Hyperosmotic Stress Induces Phosphorylation of CERT and Enhances Its Tethering throughout the Endoplasmic Reticulum.

Kentaro Shimasaki, Keigo Kumagai, Shota Sakai, Toshiyuki Yamaji, Kentaro Hanada.

  The ceramide transport protein (CERT) delivers ceramide from the endoplasmic reticulum (ER) to the Golgi apparatus, where ceramide is converted to sphingomyelin (SM). The function of CERT is regulated in two distinct phosphorylation-dependent events: multiple phosphorylations in a serine-repeat motif (SRM) and phosphorylation of serine 315 residue (S315). Pharmacological inhibition of SM biosynthesis results in an increase in SRM-dephosphorylated CERT, which serves as an activated form, and an enhanced phosphorylation of S315, which augments the binding of CERT to ER-resident VAMP-associated protein (VAP), inducing the full activation of CERT to operate at the ER-Golgi membrane contact sites (MCSs). However, it remains unclear whether the two phosphorylation-dependent regulatory events always occur coordinately. Here, we describe that hyperosmotic stress induces S315 phosphorylation without affecting the SRM-phosphorylation state. Under hyperosmotic conditions, the binding of CERT with VAP-A is enhanced in an S315 phosphorylation-dependent manner, and this increased binding occurs throughout the ER rather than restrictedly at the ER-Golgi MCSs. Moreover, we found that de novo synthesis of SM with very-long acyl chains preferentially increases via a CERT-independent mechanism under hyperosmotic-stressed cells, providing an insight into a CERT-independent ceramide transport pathway for de novo synthesis of SM.

Keywords:  VAP; lipid transfer protein; membrane contact sites; regulation; sphingomyelin; very-long-chain

DOI:  https://doi.org/10.3390/ijms23074025
Front Plant Sci. 2022 ;13 846970

The ER Is a Common Mediator for the Behavior and Interactions of Other Organelles.

Jaideep Mathur, Olivia Friesen Kroeker, Mariann Lobbezoo, Neeta Mathur.

  Optimal functioning of a plant cell depends upon the efficient exchange of genetic information, ions, proteins and metabolites between the different organelles. Intuitively, increased proximity between organelles would be expected to play an important role in facilitating exchanges between them. However, it remains to be seen whether under normal, relatively non-stressed conditions organelles maintain close proximity at all. Moreover, does interactivity involve direct and frequent physical contact between the different organelles? Further, many organelles transition between spherical and tubular forms or sporadically produce thin tubular extensions, but it remains unclear whether changes in organelle morphology play a role in increasing their interactivity. Here, using targeted multicolored fluorescent fusion proteins, we report observations on the spatiotemporal relationship between plastids, mitochondria, peroxisomes and the endoplasmic reticulum in living plant cells. Under normal conditions of growth, we observe that the smaller organelles do not establish direct, physical contacts with each other but, irrespective of their individual form they all maintain intimate connectivity with the ER. Proximity between organelles does increase in response to stress through concomitant alterations in ER dynamics. Significantly, even under increased proximity the ER still remains sandwiched between the different organelles. Our observations provide strong live-imaging-based evidence for the ER acting as a common mediator in interactions between other organelles.

Keywords:  ER; chloroplasts; fluorescent proteins (FPs); mitochondria; organelle extensions; peroxisomes

DOI:  https://doi.org/10.3389/fpls.2022.846970
J Inorg Biochem. 2022 Apr 04. pii: S0162-0134(22)00098-8. [Epub ahead of print]232 111809

Endoplasmic reticulum-mitochondria coupling attenuates vanadium-induced apoptosis via IP3R in duck renal tubular epithelial cells.

Junjun Peng, Chengcheng Peng, Li Wang, Huabin Cao, Chenghong Xing, Guyue Li, Guoliang Hu, Fan Yang.

  Vanadium (V) is necessary for the health and growth of animals, but excessive V has harmful effects on the ecosystem health. Endoplasmic reticulum (ER)-mitochondria coupling as a membrane structure connects the mitochondrial outer membrane with the ER. The mitochondria-associated ER membrane (MAM) is a region of the ER-mitochondria coupling and is essential for normal cell function. Currently, the crosstalk between ER-mitochondrial coupling and apoptosis in the toxic mechanism of V on duck kidney is still unclear. In this study, duck renal tubular epithelial cells were incubated with different concentrations of sodium metavanadate (NaVO3) and/or inositol triphosphate receptor (IP3R) inhibitor 2-aminoethyl diphenyl borate (2-APB) for 24 h. The results showed that V could significantly increase lactate dehydrogenase (LDH) release, the mitochondrial calcium level and the numbers of the fluorescent signal points of IP3R; shortened the length ER-mitochondria coupling and reduced its formation; markedly upregulate the mRNA levels of MAM-related genes and protein levels, causing MAM dysfunction. Additionally, V treatment appeared to upregulate pro-apoptotic genes and downregulate anti-apoptotic genes, followed by cell apoptosis. The V-induced changes were alleviated by treatment with IP3R inhibitor. In summary, V could induce the dysfunction of ER-mitochondrial coupling and apoptosis, and inhibition of ER-mitochondrial coupling could attenuate V-induced apoptosis in duck renal tubular epithelial cells.

Keywords:  Apoptosis; Duck; Endoplasmic reticulum-mitochondria coupling; Inositol triphosphate receptor; Renal tubular epithelial cell; Vanadium

DOI:  https://doi.org/10.1016/j.jinorgbio.2022.111809
Cells. 2022 Mar 31. pii: 1175. [Epub ahead of print]11(7):

CARD19 Interacts with Mitochondrial Contact Site and Cristae Organizing System Constituent Proteins and Regulates Cristae Morphology.

Kariana E Rios, Ming Zhou, Nathaniel M Lott, Chelsi R Beauregard, Dennis P McDaniel, Thomas P Conrads, Brian C Schaefer.

  CARD19 is a mitochondrial protein of unknown function. While CARD19 was originally reported to regulate TCR-dependent NF-κB activation via interaction with BCL10, this function is not recapitulated ex vivo in primary murine CD8+ T cells. Here, we employ a combination of SIM, TEM, and confocal microscopy, along with proteinase K protection assays and proteomics approaches, to identify interacting partners of CARD19 in macrophages. Our data show that CARD19 is specifically localized to the outer mitochondrial membrane. Through deletion of functional domains, we demonstrate that both the distal C-terminus and transmembrane domain are required for mitochondrial targeting, whereas the CARD is not. Importantly, mass spectrometry analysis of 3×Myc-CARD19 immunoprecipitates reveals that CARD19 interacts with the components of the mitochondrial intermembrane bridge (MIB), consisting of mitochondrial contact site and cristae organizing system (MICOS) components MIC19, MIC25, and MIC60, and MICOS-interacting proteins SAMM50 and MTX2. These CARD19 interactions are in part dependent on a properly folded CARD. Consistent with previously reported phenotypes upon siRNA silencing of MICOS subunits, absence of CARD19 correlates with irregular cristae morphology. Based on these data, we propose that CARD19 is a previously unknown interacting partner of the MIB and the MIC19-MIC25-MIC60 MICOS subcomplex that regulates cristae morphology.

Keywords:  BinCARD; CARD proteins; CARD19; MIB; MICOS; cristae

DOI:  https://doi.org/10.3390/cells11071175
Expert Opin Ther Targets. 2022 Apr 15.

Targeting calcium-mediated inter-organellar crosstalk in cardiac diseases.

Mohit M Hulsurkar, Satadru K Lahiri, Jason Karch, Meng C Wang, Xander H T Wehrens.

IntroductionAbnormal calcium signaling between organelles such as the sarcoplasmic reticulum (SR), mitochondria and lysosomes is a key feature of various heart diseases. Calcium serves as a secondary messenger mediating inter-organellar crosstalk, which is essential for maintaining the overall cardiomyocyte function.Areas coveredThis article examines the available literature related to various calcium channels and transporters involved in inter-organellar calcium signaling. The SR calcium-release channels known as ryanodine receptor type-2 (RyR2) and inositol 1,4,5-trisphosphate receptor (IP3R), as well as calcium-transporter SR/ER-ATPase 2a (SERCA2a) are illuminated. The roles of mitochondrial voltage-dependent anion channels (VDAC), the mitochondria Ca2+ uniporter complex (MCUC), and the lysosomal H+/Ca2+ exchanger, two pore channels (TPC), and transient receptor potential mucolipin (TRPML) are discussed. Furthermore, recent studies showing calcium-mediated crosstalk between the SR, mitochondria, and lysosomes as well as how this crosstalk is dysregulated in cardiac diseases are placed under the spotlight.Expert opinionEnhanced SR calcium release via RyR2 and reduced SR reuptake via SERCA2a, increased VDAC and MCUC-mediated calcium-uptake into mitochondria, enhanced MPTP opening, and enhanced lysosomal calcium-release via lysosomal TPC and TRPML may all contribute to aberrant calcium homeostasis causing heart disease. While mechanisms of this crosstalk need to be studied further, interventions targeting these calcium channels or combinations thereof might represent a promising therapeutic strategy.

DOI: https://doi.org/10.1080/14728222.2022.2067479
J Cell Biol. 2022 May 02. pii: e202107120. [Epub ahead of print]221(5):

TRPC3 channel gating by lipids requires localization at the ER/PM junctions defined by STIM1.

Haiping Liu, Wei-Yin Lin, Spencer R Leibow, Alexander J Morateck, Malini Ahuja, Shmuel Muallem.

TRPC3, a member of the transient receptor potential (TRP) superfamily of cation channels, is a lipid-regulated, Ca2+-permeable channel that mediates essential components of the receptor evoked Ca2+ signal. The modes and mechanisms by which lipids regulate TRPC3 and other members of the TRPC channel family are not well understood. Here, we report that PI(4,5)P2 regulates TRPC3 in three independent modes. PLC-dependent hydrolysis generates diacylglycerol (DAG) that interacts with lipid-binding site 2 in the channel pore. PI(4,5)P2 interacts with lipid site 1 to inhibit TRPC3 opening and regulate access of DAG to the pore lipid site 2. PI(4,5)P2 is required for regulating pore ionic selectivity by receptor stimulation. Notably, the activation and regulation of TRPC3 by PI(4,5)P2 require recruitment of TRPC3 to the ER/PM junctions at a PI(4,5)P2-rich domain. Accordingly, we identified an FFAT site at the TRPC3 N-terminal loop within the linker helices that envelope the C-terminus pole helix. The FFAT site interacts with the ER-resident VAPB to recruit TRPC3 to the ER/PM junctions and control its receptor-mediated activation. The TRPC3's lipid interacting sites are fully conserved in TRPC6 and TRPC7 and in part in other TRPC channels. These findings inform on multiple modes of regulation of ion channels by lipids that may be relevant to diseases affected by aberrant TRPC channel functions.

DOI: https://doi.org/10.1083/jcb.202107120