bims-mecosi Biomed News
on Membrane contact sites
Issue of 2022–12–04
eight papers selected by
Verena Kohler, University of Graz
  1. An ER phospholipid hydrolase drives ER-associated mitochondrial constriction for fission and fusion.
  2. The roles of a mitochondrial protein Miga in autophagy.
  3. Altered Lysosomal Function Manipulates Cellular Biosynthetic Capacity By Remodeling Intracellular Cholesterol Distribution.
  4. Mitochondria-associated niches in health and disease.
  5. Expression of Synj2bp in mouse liver regulates the extent of wrappER-mitochondria contact to maintain hepatic lipid homeostasis.
  6. The Tricalbin-Family Endoplasmic Reticulum-Plasma Membrane Tethering Proteins Attenuate ROS-Involved Caspofungin Sensitivity in Candida albicans.
  7. Distinct changes in endosomal composition promote NLRP3 inflammasome activation.
  8. Characterization of the Multiple Domains of Pex30 Involved in Subcellular Localization of the Protein and Regulation of Peroxisome Number.
  1. Elife. 2022 Nov 30. pii: e84279. [Epub ahead of print]11
    An ER phospholipid hydrolase drives ER-associated mitochondrial constriction for fission and fusion.
    Tricia T Nguyen, Gia K Voeltz.
      Mitochondria are dynamic organelles that undergo cycles of fission and fusion at a unified platform defined by endoplasmic reticulum (ER)-mitochondria membrane contact sites (MCSs). These MCSs or nodes co-localize fission and fusion machinery. We set out to identify how ER-associated mitochondrial nodes can regulate both fission and fusion machinery assembly. We have used a promiscuous biotin ligase linked to the fusion machinery, Mfn1, and proteomics to identify an ER membrane protein, ABHD16A, as a major regulator of node formation. In the absence of ABHD16A, fission and fusion machineries fail to recruit to ER-associated mitochondrial nodes and fission and fusion rates are significantly reduced. ABHD16A contains an acyltransferase motif and an α/β hydrolase domain and point mutations in critical residues of these regions fail to rescue the formation of ER-associated mitochondrial hot spots. These data suggest a mechanism whereby ABHD16A functions by altering phospholipid composition at ER-mitochondria MCSs. Our data present the first example of an ER membrane protein that regulates the recruitment of both fission and fusion machineries to mitochondria.
    Keywords:  cell biology; human
    DOI:  https://doi.org/10.7554/eLife.84279
  2. Autophagy. 2022 Nov 30.
    The roles of a mitochondrial protein Miga in autophagy.
    Lingna Xu, Liquan Wang, Chao Tong.
      Miga is an evolutionarily conserved protein that localizes to the outer membrane of mitochondria and mediates endoplasmic reticulum (ER)-mitochondrial contacts through interaction with VAP proteins in the ER. We recently reported that Miga is required for autophagosome-lysosome fusion during macroautophagy/autophagy. Miga binds to Atg14 and Uvrag, two alternative subunits of the class III phosphatidylinositol 3-kinase (PtdIns3K) complex. Miga regulates phosphatidylinositol-3-phosphate (PtdIns3P) levels through its interaction with Uvrag and its ER-mitochondrial contact site (ERMCS) tethering activity. Miga stabilizes Atg14, which maintains steady levels of the SNARE protein, Syx17. We propose that Miga establishes a direct link between mitochondria and autophagy to maintain cellular homeostasis.
    Keywords:  Drosophila; autophagy; endoplasmic reticulum-mitochondrial contacts; mitochondrion; phosphatidylinositol-3 kinase
    DOI:  https://doi.org/10.1080/15548627.2022.2153569
  3. Cell Biochem Biophys. 2022 Dec 02.
    Altered Lysosomal Function Manipulates Cellular Biosynthetic Capacity By Remodeling Intracellular Cholesterol Distribution.
    Sudarshana Rajasekaran, Anand Ramaian Santhaseela, Shamila Ragunathan, Sangita Venkataraman, Tamilselvan Jayavelu.
      Lysosomes are known to influence cholesterol trafficking into endoplasmic reticulum (ER) membranes. Though intracellular cholesterol levels are known to influence the lipid biosynthetic responses in ER, the specific effects of lysosomal modulation on these outcomes is not known. To demonstrate this, C2C12 cells were treated with chloroquine, a lysosomotropic agent, and its effects on cellular biosynthetic capacity, structural and functional status of ER was determined. In addition to its known effects on autophagy reduction, chloroquine treatment induced accumulation of total cellular lipid and ER-specific cholesterol content. It was also observed that chloroquine caused an increase in smooth-ER content with defects in overall protein turnover. Further, since ER and mitochondria function in close association through ER membrane contact sites, it is likely that lysosomal modulation also brings about associated changes in mitochondria. In this regard, we found that chloroquine reduces mitochondrial membrane potential and mitochondrial dynamics. Collectively, the differential biosynthetic response of rise in lipid content, but not protein content, cannot be accounted by merely considering that chloroquine induced suppression of autophagy causes defects in organelle function. In this defective autophagy scenario, both biosynthetic responses such as lipid and protein synthesis are expected to be reduced rather than only the latter, as observed with chloroquine. These findings suggest that cholesterol trafficking/distribution within cellular organelles could act as an intracellular mediator of differential biosynthetic remodelling in interconnected organelles.
    Keywords:  Chloroquine; Cholesterol; Endoplasmic reticulum; Lysosome; Mitochondria
    DOI:  https://doi.org/10.1007/s12013-022-01123-y
  4. J Cell Sci. 2022 Dec 01. pii: jcs259634. [Epub ahead of print]135(23):
    Mitochondria-associated niches in health and disease.
    Mateus Milani, Philippe Pihán, Claudio Hetz.
      The appreciation of the importance of interorganelle contacts has steadily increased over the past decades. Advances in imaging, molecular biology and bioinformatic techniques allowed the discovery of new mechanisms involved in the interaction and communication between organelles, providing novel insights into the inner works of a cell. In this Review, with the mitochondria under the spotlight, we discuss the most recent findings on the mechanisms mediating the communication between organelles, focusing on Ca2+ signaling, lipid exchange, cell death and stress responses. Notably, we introduce a new integrative perspective to signaling networks that is regulated by interorganelle interactions - the mitochondria-associated niches - focusing on the link between the molecular determinants of contact sites and their functional outputs, rather than simply physical and structural communication. In addition, we highlight the neuropathological and metabolic implications of alterations in mitochondria-associated niches and outline how this concept might improve our understanding of multi-organelle interactions.
    Keywords:  Apoptosis; Bioenergetics; MAMs; Mitochondria; Mitochondria-associated membranes; Stress responses
    DOI:  https://doi.org/10.1242/jcs.259634
  5. Biol Direct. 2022 Dec 01. 17(1): 37
    Expression of Synj2bp in mouse liver regulates the extent of wrappER-mitochondria contact to maintain hepatic lipid homeostasis.
    Nicolò Ilacqua, Irene Anastasia, Danylo Aloshyn, Rana Ghandehari-Alavijeh, Emily Ann Peluso, Madelaine C Brearley-Sholto, Leonardo V Pellegrini, Andrea Raimondi, Thomas Q de Aguiar Vallim, Luca Pellegrini.
       BACKGROUND: In mouse liver hepatocytes, nearly half of the surface area of every mitochondrion is covered by wrappER, a wrapping-type of ER that is rich in fatty acids and synthesizes lipoproteins (VLDL) (Anastasia et al. in Cell Rep 34:108873, 2021; Hurtley in Science (80- ) 372:142-143, 2021; Ilacqua et al. in J Cell Sci 135:1-11, 2021). A disruption of the ultrastructure of the wrappER-mitochondria contact results in altered fatty acid flux, leading to hepatic dyslipidemia (Anastasia et al. 2021). The molecular mechanism that regulates the extent of wrappER-mitochondria contacts is unknown.
    METHODS: We evaluated the expression level of the mitochondrial protein Synj2bp in the liver of normal and obese (ob/ob) mice. In addition, we silenced its expression in the liver using an AAV8 vector. We coupled quantitative EM morphometric analysis to proteomics and lipid analyses on these livers.
    RESULTS: The expression level of Synj2bp in the liver positively correlates with the extent of wrappER-mitochondria contacts. A 50% reduction in wrappER-mitochondria contacts causes hepatic dyslipidemia, characterized by a gross accumulation of lipid droplets in the liver, an increased hepatic secretion of VLDL and triglycerides, a curtailed ApoE expression, and an increased capacity of mitochondrial fatty acid respiration.
    CONCLUSION: Synj2bp regulates the extent of wrappER-mitochondria contacts in the liver, thus contributing to the control of hepatic lipid flux.
    Keywords:  ApoE; Electron microscopy; Fatty acid; Inter-organelle contact; Lipoparticles; MAM; MERC; Mitochondria; NAFLD; Rrbp1; Synj2bp; VLDL; WrappER
    DOI:  https://doi.org/10.1186/s13062-022-00344-8
  6. Microbiol Spectr. 2022 Nov 29. e0207922
    The Tricalbin-Family Endoplasmic Reticulum-Plasma Membrane Tethering Proteins Attenuate ROS-Involved Caspofungin Sensitivity in Candida albicans.
    Li Yang, Hangqi Zhu, Mingchun Li, Qilin Yu.
      The endoplasmic reticulum-plasma membrane (ER-PM) contacts are one kind of important membrane contact structures in eukaryotic cells, which mediate material and message exchange between the ER and the PM. However, the specific types and functions of ER-PM tethering proteins are poorly understood in the human fungal pathogen Candida albicans. In this study, we observed that the two tricalbin-family proteins, i.e., Tcb1 and Tcb3, were colocalized with the ER-PM contacts in C. albicans. Deletion of the tricalbin-encoding genes TCB1 and TCB3 remarkably reduced ER-PM contacts, suggesting that tricalbins are ER-PM tethering proteins of C. albicans. Stress sensitivity assays showed that the TCB-deleted strains, including tcb1Δ/Δ, tcb3Δ/Δ, and tcb1Δ/Δ tcb3Δ/Δ, exhibited hypersensitivity to cell wall stress induced by caspofungin. Further investigation revealed that caspofungin induced drastic reactive oxygen species (ROS) accumulation in the mutants, which was attributed to enhanced oxidation of Ero1 in the ER lumen. Removal of intracellular ROS by the ROS scavenger vitamin C rescued the growth of the mutants under caspofungin treatment, indicating that Ero1 oxidation-related ROS accumulation was involved in caspofungin hypersensitivity of the mutants. Moreover, deletion of the TCB genes decreased secretion of extracellular aspartyl proteinases, reduced transport of the cell wall protein Hwp1 from the cytoplasm to the cell wall, and attenuated virulence of the fungal pathogen. This study sheds a light on the role of ER-PM tethering proteins in maintenance of cell wall integrity and virulence in fungal pathogens. IMPORTANCE The endoplasmic reticulum-plasma membrane contacts are important membrane contact structures in eukaryotic cells, functioning in material and message exchange between the ER and the PM. We observed that the two tricalbin-family endoplasmic reticulum-plasma membrane contact proteins are required for tolerance to caspofungin-induced cell wall stress in the pathogenic fungus Candida albicans. The tricalbin mutants exhibited hypersensitivity to cell wall stress induced by caspofungin. Further investigation revealed that Ero1 oxidation-related reactive species oxygen accumulation was involved in caspofungin hypersensitivity of the tricalbin mutants. Moreover, loss of tricalbins reduced secretion of extracellular aspartyl proteinases, decreased transport of the cell wall proteins from the cytoplasm to the cell wall, and attenuated virulence of the fungal pathogen. This study uncovers the role of ER-PM tethering proteins in sustaining protein secretion, maintenance of cell wall integrity and virulence in fungal pathogens.
    Keywords:  Candida albicans; drug sensitivity; drug tolerance; endoplasmic reticulum-plasma membrane contact; fungal pathogen; oxidative stress; reactive oxygen species; tricalbin
    DOI:  https://doi.org/10.1128/spectrum.02079-22
  7. Nat Immunol. 2022 Nov 28.
    Distinct changes in endosomal composition promote NLRP3 inflammasome activation.
    Zhirong Zhang, Rossella Venditti, Li Ran, Zengzhen Liu, Karl Vivot, Annette Schürmann, Juan S Bonifacino, Maria Antonietta De Matteis, Romeo Ricci.
      Inflammasome complexes are pivotal in the innate immune response. The NLR family pyrin domain containing protein 3 (NLRP3) inflammasome is activated in response to a broad variety of cellular stressors. However, a primary and converging sensing mechanism by the NLRP3 receptor initiating inflammasome assembly remains ill defined. Here, we demonstrate that NLRP3 inflammasome activators primarily converge on disruption of endoplasmic reticulum-endosome membrane contact sites (EECS). This defect causes endosomal accumulation of phosphatidylinositol 4-phosphate (PI4P) and a consequent impairment of endosome-to-trans-Golgi network trafficking (ETT), necessary steps for endosomal recruitment of NLRP3 and subsequent inflammasome activation. Lowering endosomal PI4P levels prevents endosomal association of NLRP3 and inhibits inflammasome activation. Disruption of EECS or ETT is sufficient to enhance endosomal PI4P levels, to recruit NLRP3 to endosomes and to potentiate NLRP3 inflammasome activation. Mice with defects in ETT in the myeloid compartment are more susceptible to lipopolysaccharide-induced sepsis. Our study thus identifies a distinct cellular mechanism leading to endosomal NLRP3 recruitment and inflammasome activation.
    DOI:  https://doi.org/10.1038/s41590-022-01355-3
  8. Cell Biochem Biophys. 2022 Dec 03.
    Characterization of the Multiple Domains of Pex30 Involved in Subcellular Localization of the Protein and Regulation of Peroxisome Number.
    Nayan Moni Deori, Terence Infant, Rajkumar P Thummer, Shirisha Nagotu.
      Pex30 is a peroxisomal protein whose role in peroxisome biogenesis via the endoplasmic reticulum has been established. It is a 58 KDa multi-domain protein that facilitates contact site formation between various organelles. The present study aimed to investigate the role of various domains of the protein in its sub-cellular localization and regulation of peroxisome number. For this, we created six truncations of the protein (1-87, 1-250, 1-352, 88-523, 251-523 and 353-523) and tagged GFP at the C-terminus. Biochemical methods and fluorescence microscopy were used to characterize the effect of truncation on expression and localization of the protein. Quantitative analysis was performed to determine the effect of truncation on peroxisome number in these cells. Expression of the truncated variants in cells lacking PEX30 did not cause any effect on cell growth. Interestingly, variable expression and localization of the truncated variants in both peroxisome-inducing and non-inducing medium was observed. Truncated variants depicted different distribution patterns such as punctate, reticulate and cytosolic fluorescence. Interestingly, lack of the complete dysferlin domain or C-Dysf resulted in increased peroxisome number similar to as reported for cells lacking Pex30. No contribution of this domain in the reticulate distribution of the proteins was also observed. Our results show an interesting role for the various domains of Pex30 in localization and regulation of peroxisome number.
    Keywords:  Domain; Dysferlin; ER; Peroxisomes; Pex30; Yeast
    DOI:  https://doi.org/10.1007/s12013-022-01122-z
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