bims-apauto Biomed News
on Apoptosis and autophagy
Issue of 2022‒10‒23
five papers selected by
Su Hyun Lee
Seoul National University

  1. Autophagy. 2022 Oct 17. 1-20
      ABBREVIATIONS: A:C autophagic membrane:cytosol; ALS amyotrophic lateral sclerosis; ATG4 autophagy related 4; Atg8 autophagy related 8; BafA1 bafilomycin A1; BNIP3L/Nix BCL2 interacting protein 3 like; CALCOCO2/NDP52 calcium binding and coiled-coil domain 2; EBSS Earle's balanced salt solution; GABARAP GABA type A receptor-associated protein; GST glutathione S transferase; HKO hexa knockout; Kd dissociation constant; LIR LC3-interacting region; MAP1LC3/LC3 microtubule associated protein 1 light chain 3; NLS nuclear localization signal/sequence; PE phosphatidylethanolamine; SpHfl1 Schizosaccharomyces pombeorganic solute transmembrane transporter; SQSTM1/p62 SQSTM1/p62; TARDBP/TDP-43 TAR DNA binding protein; TKO triple knockout.
    Keywords:  Autophagy; GABARAP; LIR motif; RavZ protein; mammalian ATG8; selective mATG8–PE delipidation
  2. Nature. 2022 Oct 19.
      The ubiquitin E3 ligase substrate adapter cereblon (CRBN) is a target of thalidomide and lenalidomide1, therapeutic agents used in the treatment of haematopoietic malignancies2-4 and as ligands for targeted protein degradation5-7. These agents are proposed to mimic a naturally occurring degron; however, the structural motif recognized by the thalidomide-binding domain of CRBN remains unknown. Here we report that C-terminal cyclic imides, post-translational modifications that arise from intramolecular cyclization of glutamine or asparagine residues, are physiological degrons on substrates for CRBN. Dipeptides bearing the C-terminal cyclic imide degron substitute for thalidomide when embedded within bifunctional chemical degraders. Addition of the degron to the C terminus of proteins induces CRBN-dependent ubiquitination and degradation in vitro and in cells. C-terminal cyclic imides form adventitiously on physiologically relevant timescales throughout the human proteome to afford a degron that is endogenously recognized and removed by CRBN. The discovery of the C-terminal cyclic imide degron defines a regulatory process that may affect the physiological function and therapeutic engagement of CRBN.
  3. Autophagy. 2022 Oct 20.
      Macroautophagy/autophagy is a catabolic recycling pathway and is tightly regulated by upstream signals. Autophagy genes are quickly upregulated upon stimuli such as nutrition limitation in response to the external environment. However, how the transcriptional activation of autophagy genes occurs is not well understood. We recently found that in yeast, the RNA polymerase II subunit Rpb9 specifically and efficiently upregulates the transcription of the autophagy gene ATG1 with the mediation of Gcn4. Such regulation was shown to be essential for autophagic activities induced by starvation. Furthermore, the function of Rpb9 in autophagy and the activation of ATG1 transcription is conserved in mammalian cells. In conclusion, Rpb9 specifically and positively regulates ATG1 transcription as a key regulator of autophagy.
    Keywords:  ATG1 gene; Gcn4; Rpb9; autophagy; starvation; transcription; yeast
  4. Proc Natl Acad Sci U S A. 2022 Oct 25. 119(43): e2200085119
      Autophagy is a multiple fusion event, initiating with autophagosome formation and culminating with fusion with endo-lysosomes in a Ca2+-dependent manner. The source of Ca2+ and the molecular mechanism by which Ca2+ is provided for this process are not known. The intracellular Ca2+ permeable channel transient receptor potential mucolipin 3 (TRPML3) localizes in the autophagosome and interacts with the mammalian autophagy-related protein 8 (ATG8) homolog GATE16. Here, we show that lipid-regulated TRPML3 is the Ca2+ release channel in the phagophore that provides the Ca2+ necessary for autophagy progress. We generated a TRPML3-GCaMP6 fusion protein as a targeted reporter of TRPML3 compartment localization and channel function. Notably, TRPML3-GCaMP6 localized in the phagophores, the level of which increased in response to nutrient starvation. Importantly, phosphatidylinositol-3-phosphate (PI3P), an essential lipid for autophagosome formation, is a selective regulator of TRPML3. TRPML3 interacted with PI3P, which is a direct activator of TRPML3 current and Ca2+ release from the phagophore, to promote and increase autophagy. Inhibition of TRPML3 suppressed autophagy even in the presence of excess PI3P, while activation of TRPML3 reversed the autophagy inhibition caused by blocking PI3P. Moreover, disruption of the TRPML3-PI3P interaction abolished both TRPML3 activation by PI3P and the increase in autophagy. Taken together, these results reveal that TRPML3 is a downstream effector of PI3P and a key regulator of autophagy. Activation of TRPML3 by PI3P is the critical step providing Ca2+ from the phagophore for the fusion process, which is essential for autophagosome biogenesis.
    Keywords:  Ca2+ channel; GCaMP6; PI3P; TRPML3; autophagy
  5. Nat Commun. 2022 Oct 20. 13(1): 6212
      Lysosomes are well-established as the main cellular organelles for the degradation of macromolecules and emerging as regulatory centers of metabolism. They are of crucial importance for cellular homeostasis, which is exemplified by a plethora of disorders related to alterations in lysosomal function. In this context, protein complexes play a decisive role, regulating not only metabolic lysosomal processes but also lysosome biogenesis, transport, and interaction with other organelles. Using cross-linking mass spectrometry, we analyze lysosomes and early endosomes. Based on the identification of 5376 cross-links, we investigate protein-protein interactions and structures of lysosome- and endosome-related proteins. In particular, we present evidence for a tetrameric assembly of the lysosomal hydrolase PPT1 and a heterodimeric structure of FLOT1/FLOT2 at lysosomes and early endosomes. For FLOT1-/FLOT2-positive early endosomes, we identify >300 putative cargo proteins and confirm eleven substrates for flotillin-dependent endocytosis, including the latrophilin family of adhesion G protein-coupled receptors.