bims-lypmec 2023-01-29 papers

bims-lypmec

Biomed News

on Lysosomal positioning and metabolism in cardiomyocytes

Issue of 2023–01–29
six papers selected by
Satoru Kobayashi, New York Institute of Technology

LYST deficiency impairs autophagic lysosome reformation in neurons and alters lysosome number and size.
Structure of the lysosomal mTORC1-TFEB-Rag-Ragulator megacomplex.
One Stone, Three Birds: A Smart Single Fluorescent Probe for Simultaneous and Discriminative Imaging of Lysosomes, Lipid Droplets, and Mitochondria.
The selective autophagy adaptor p62/SQSTM1 forms phase condensates regulated by HSP27 that facilitate the clearance of damaged lysosomes via lysophagy.
Tex2 is required for lysosomal functions at TMEM55-dependent ER membrane contact sites.
Mechanosensitive membrane proteins: Usual and unusual suspects in mediating mechanotransduction.

Cell Mol Life Sci. 2023 Jan 28. 80(2): 53

LYST deficiency impairs autophagic lysosome reformation in neurons and alters lysosome number and size.

Jenny Serra-Vinardell, Maxwell B Sandler, Raffaella De Pace, Javier Manzella-Lapeira, Antony Cougnoux, Keyvan Keyvanfar, Wendy J Introne, Joseph A Brzostowski, Michael E Ward, William A Gahl, Prashant Sharma, May Christine C Malicdan.

  Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive disorder caused by biallelic mutations in the lysosomal trafficking regulator (LYST) gene. Even though enlarged lysosomes and/or lysosome-related organelles (LROs) are the typical cellular hallmarks of CHS, they have not been investigated in human neuronal models. Moreover, how and why the loss of LYST function causes a lysosome phenotype in cells has not been elucidated. We report that the LYST-deficient human neuronal model exhibits lysosome depletion accompanied by hyperelongated tubules extruding from enlarged autolysosomes. These results have also been recapitulated in neurons differentiated from CHS patients' induced pluripotent stem cells (iPSCs), validating our model system. We propose that LYST ensures the correct fission/scission of the autolysosome tubules during autophagic lysosome reformation (ALR), a crucial process to restore the number of free lysosomes after autophagy. We further demonstrate that LYST is recruited to the lysosome membrane, likely to facilitate the fission of autolysosome tubules. Together, our results highlight the key role of LYST in maintaining lysosomal homeostasis following autophagy and suggest that ALR dysregulation is likely associated with the neurodegenerative CHS phenotype.

Keywords:  Autolysosome tubule; Autolysosomes; Chediak–Higashi syndrome; Lysosome fission; Protolysosomes; iPSC

DOI:  https://doi.org/10.1007/s00018-023-04695-x
Nature. 2023 Jan 25.

Structure of the lysosomal mTORC1-TFEB-Rag-Ragulator megacomplex.

Zhicheng Cui, Gennaro Napolitano, Mariana E G de Araujo, Alessandra Esposito, Jlenia Monfregola, Lukas A Huber, Andrea Ballabio, James H Hurley.

The transcription factor TFEB is a master regulator of lysosomal biogenesis and autophagy1. The phosphorylation of TFEB by the mechanistic target of rapamycin complex 1 (mTORC1)2-5 is unique in its mTORC1 substrate recruitment mechanism, which is strictly dependent on the amino acid-mediated activation of the RagC GTPase activating protein FLCN6,7. TFEB lacks the TOR signalling motif responsible for the recruitment of other mTORC1 substrates. We used cryogenic-electron microscopy to determine the structure of TFEB as presented to mTORC1 for phosphorylation, which we refer to as the 'megacomplex'. Two full Rag-Ragulator complexes present each molecule of TFEB to the mTOR active site. One Rag-Ragulator complex is bound to Raptor in the canonical mode seen previously in the absence of TFEB. A second Rag-Ragulator complex (non-canonical) docks onto the first through a RagC GDP-dependent contact with the second Ragulator complex. The non-canonical Rag dimer binds the first helix of TFEB with a RagCGDP-dependent aspartate clamp in the cleft between the Rag G domains. In cellulo mutation of the clamp drives TFEB constitutively into the nucleus while having no effect on mTORC1 localization. The remainder of the 108-amino acid TFEB docking domain winds around Raptor and then back to RagA. The double use of RagC GDP contacts in both Rag dimers explains the strong dependence of TFEB phosphorylation on FLCN and the RagC GDP state.

DOI: https://doi.org/10.1038/s41586-022-05652-7
Anal Chem. 2023 Jan 24.

One Stone, Three Birds: A Smart Single Fluorescent Probe for Simultaneous and Discriminative Imaging of Lysosomes, Lipid Droplets, and Mitochondria.

Jiaxin Hong, Jinzheng Zhang, Qianhua Li, Guoqiang Feng.

Complex intracellular life processes are usually completed through the cooperation of multiple organelles. Real-time tracking of the interplays between multiple organelles with a single fluorescent probe (SFP) is very helpful to deepen our understanding of complex biological processes. So far, SFP for simultaneously differentiating and visualizing of more than two different organelles has not been reported. Herein, we report an SFP (named ICM) that can be used for simultaneously differentiating and visualizing three important organelles: mitochondria, lysosomes, and lipid droplets (LDs). The probe can simultaneously light up mitochondria/lysosomes (∼700 nm) and LDs (∼480 nm) at significantly different emission wavelengths with high fidelity, and mitochondria and lysosomes can be effectively distinguished by their different shapes and fluorescence intensities. With this smart probe, real-time and simultaneous tracking of the interplays of these three organelles was successfully achieved for the first time.

DOI: https://doi.org/10.1021/acs.analchem.2c03073
Cell Rep. 2023 Jan 25. pii: S2211-1247(23)00048-7. [Epub ahead of print]42(2): 112037

The selective autophagy adaptor p62/SQSTM1 forms phase condensates regulated by HSP27 that facilitate the clearance of damaged lysosomes via lysophagy.

Elizabeth R Gallagher, Erika L F Holzbaur.

  In response to lysosomal damage, cells engage several quality-control mechanisms, including the selective isolation and degradation of damaged lysosomes by lysophagy. Here, we report that the selective autophagy adaptor SQSTM1/p62 is recruited to damaged lysosomes in both HeLa cells and neurons and is required for lysophagic flux. The Phox and Bem1p (PB1) domain of p62 mediates oligomerization and is specifically required for lysophagy. Consistent with this observation, we find that p62 forms condensates on damaged lysosomes. These condensates are precisely tuned by the small heat shock protein HSP27, which is phosphorylated in response to lysosomal injury and maintains the liquidity of p62 condensates, facilitating autophagosome formation. Mutations in p62 have been identified in patients with amyotrophic lateral sclerosis (ALS); ALS-associated mutations in p62 impair lysophagy, suggesting that deficits in this pathway may contribute to neurodegeneration. Thus, p62 condensates regulated by HSP27 promote lysophagy by forming platforms for autophagosome biogenesis at damaged lysosomes.

Keywords:  ALS; CP: Cell biology; CP: Neuroscience; HSP27; autophagy; condensates; lysophagy; lysosome; neurodegeneration; neurons; p62/SQSTM1; phase separation

DOI:  https://doi.org/10.1016/j.celrep.2023.112037
J Cell Biol. 2023 Apr 03. pii: e202205133. [Epub ahead of print]222(4):

Tex2 is required for lysosomal functions at TMEM55-dependent ER membrane contact sites.

Yuanjiao Du, Weiping Chang, Lei Gao, Lin Deng, Wei-Ke Ji.

ER tubules form and maintain membrane contact sites (MCSs) with late endosomes/lysosomes (LE/lys). The molecular composition and cellular functions of these MCSs are poorly understood. Here, we find that Tex2, an SMP domain-containing lipid transfer protein conserved in metazoan and yeast, is a tubular ER protein and is recruited to ER-LE/lys MCSs by TMEM55, phosphatases that convert PI(4,5)P2 to PI5P on LE/lys. We show that the Tex2-TMEM55 interaction occurs between an N-terminal region of Tex2 and a catalytic motif in the PTase domain of TMEM55. The Tex2-TMEM55 interaction can be regulated by endosome-resident type 2 PI4K activities. Functionally, Tex2 knockout results in defects in lysosomal trafficking, digestive capacity, and lipid composition of LE/lys membranes. Together, our data identify Tex2 as a tubular ER protein that resides at TMEM55-dependent ER-LE/lys MCSs required for lysosomal functions.

DOI: https://doi.org/10.1083/jcb.202205133
J Gen Physiol. 2023 Mar 06. pii: e202213248. [Epub ahead of print]155(3):

Mechanosensitive membrane proteins: Usual and unusual suspects in mediating mechanotransduction.

Miriam B Goodman, Elizabeth S Haswell, Valeria Vásquez.

This Viewpoint, which accompanies a Special Issue focusing on membrane mechanosensors, discusses unifying and unique features of both established and emerging mechanosensitive (MS) membrane proteins, their distribution across protein families and phyla, and current and future challenges in the study of these important proteins and their partners. MS membrane proteins are essential for tissue development, cellular motion, osmotic homeostasis, and sensing external and self-generated mechanical cues like those responsible for touch and proprioception. Though researchers' attention and this Viewpoint focus on a few famous ion channels that are considered the usual suspects as MS mechanosensors, we also discuss some of the more unusual suspects, such as G-protein coupled receptors. As the field continues to grow, so too will the list of proteins suspected to function as mechanosensors and the diversity of known MS membrane proteins.

DOI: https://doi.org/10.1085/jgp.202213248