bims-lymeca Biomed News
on Lysosome metabolism in cancer
Issue of 2023‒03‒05
eight papers selected by
Harilaos Filippakis
University of New England

  1. Autophagy. 2023 Mar 01. 1-2
      Among the various signals governing autophagy, ubiquitination plays a critical role both by controlling the stability of upstream regulators or components of macroautophagy/autophagy pathways and by facilitating the recruitment of cargo to autophagy receptors. As such, modulators of ubiquitin signaling can influence autophagic substrate degradation. Recently, we identified a non-proteolytic ubiquitin signal at the Ragulator complex subunit LAMTOR1 that is reversed by the deubiquitinase USP32. Loss of USP32 promotes ubiquitination within the unstructured N-terminal region of LAMTOR1 and prevents its efficient interaction with the vacuolar-type H+-ATPase, a prerequisite for full activation of MTORC1 at lysosomes. Consequently, MTORC1 activity is decreased and autophagy is upregulated in USP32 knockout cells. This phenotype is conserved in Caenorhabditis elegans. Depletion of USP32 homolog CYK-3 in worms results in LET-363/MTOR inhibition and autophagy induction. Based on our data, we propose an additional control layer of the MTORC1 activation cascade at lysosomes via USP32-regulated LAMTOR1 ubiquitination.
    Keywords:  ATPase; LAMTOR1; USP32; V-MTORC1; autophagy; deubiquitinase (DUB); ragulator complex; ubiquitin
  2. Heliyon. 2023 Feb;9(2): e13691
      A new ent-abietane diterpenoid, named Euphejolkinolide A (1), was isolated from the whole plant of Euphorbia peplus L. Its structure, including absolute configurations, was determined by spectroscopic analyses and was corroborated by single-crystal X-ray diffraction analysis. This new compound was assessed for its activity to induce lysosome biogenesis through Lyso-Tracker Red staining, in which compound 1 could significantly induce lysosome biogenesis. In addition, quantitative real-time PCR (qRT-PCR) analysis demonstrated a direct correlation between the observed lysosome biogenesis and the transcriptional activation of the lysosomal genes after treatment with the compound 1. Moreover, compound 1 promoted autophagic flux by upregulating LC3-II and downregulating SQSTM1 in both human microglia cells and U251 cells, which is required for cellular homeostasis. Further results suggested 1 induced lysosome biogenesis and autophagy which was mediated by TFEB (transcription factor EB). The structure activity relationships (SAR) analysis suggested that the carbony1 at C-7 in 1 might be a key active group. Overall, the current data suggested that 1 could be a potential compound for lysosome disorder therapy by induction of autophagy.
    Keywords:  Autophagy-lysosomal pathway; Ent-abietane diterpenoid; Euphejolkinolide A; Euphorbia peplus L.; Euphorbiaceae
  3. Cell. 2023 Feb 22. pii: S0092-8674(23)00097-1. [Epub ahead of print]
      The uptake and metabolism of nutrients support fundamental cellular process from bioenergetics to biomass production and cell fate regulation. While many studies of cell metabolism focus on cancer cells, the principles of metabolism elucidated in cancer cells apply to a wide range of mammalian cells. The goal of this review is to discuss how the field of cancer metabolism provides a framework for revealing principles of cell metabolism and for dissecting the metabolic networks that allow cells to meet their specific demands. Understanding context-specific metabolic preferences and liabilities will unlock new approaches to target cancer cells to improve patient care.
  4. Nat Metab. 2023 Mar 02.
      Whereas cholesterol is vital for cell growth, proliferation, and remodeling, dysregulation of cholesterol metabolism is associated with multiple age-related pathologies. Here we show that senescent cells accumulate cholesterol in lysosomes to maintain the senescence-associated secretory phenotype (SASP). We find that induction of cellular senescence by diverse triggers enhances cellular cholesterol metabolism. Senescence is associated with the upregulation of the cholesterol exporter ABCA1, which is rerouted to the lysosome, where it moonlights as a cholesterol importer. Lysosomal cholesterol accumulation results in the formation of cholesterol-rich microdomains on the lysosomal limiting membrane enriched with the mammalian target of rapamycin complex 1 (mTORC1) scaffolding complex, thereby sustaining mTORC1 activity to support the SASP. We further show that pharmacological modulation of lysosomal cholesterol partitioning alters senescence-associated inflammation and in vivo senescence during osteoarthritis progression in male mice. Our study reveals a potential unifying theme for the role of cholesterol in the aging process through the regulation of senescence-associated inflammation.
  5. Nat Rev Mol Cell Biol. 2023 Mar 02.
      Maintenance of protein homeostasis and organelle integrity and function is critical for cellular homeostasis and cell viability. Autophagy is the principal mechanism that mediates the delivery of various cellular cargoes to lysosomes for degradation and recycling. A myriad of studies demonstrate important protective roles for autophagy against disease. However, in cancer, seemingly opposing roles of autophagy are observed in the prevention of early tumour development versus the maintenance and metabolic adaptation of established and metastasizing tumours. Recent studies have addressed not only the tumour cell intrinsic functions of autophagy, but also the roles of autophagy in the tumour microenvironment and associated immune cells. In addition, various autophagy-related pathways have been described, which are distinct from classical autophagy, that utilize parts of the autophagic machinery and can potentially contribute to malignant disease. Growing evidence on how autophagy and related processes affect cancer development and progression has helped guide efforts to design anticancer treatments based on inhibition or promotion of autophagy. In this Review, we discuss and dissect these different functions of autophagy and autophagy-related processes during tumour development, maintenance and progression. We outline recent findings regarding the role of these processes in both the tumour cells and the tumour microenvironment and describe advances in therapy aimed at autophagy processes in cancer.
  6. Proc Natl Acad Sci U S A. 2023 Mar 07. 120(10): e2215290120
      Major Facilitator Superfamily Domain containing 2a (Mfsd2a) is a sodium-dependent lysophosphatidylcholine (LPC) transporter expressed at the blood-brain barrier that constitutes the main pathway by which the brain obtains omega-3 fatty acids, such as docosahexanoic acid. Mfsd2a deficiency in humans results in severe microcephaly, underscoring the importance of LPC transport by Mfsd2a for brain development. Biochemical studies and recent cryo-electron microscopy (cryo-EM) structures of Mfsd2a bound to LPC suggest that Mfsd2a transports LPC via an alternating access mechanism between outward-facing and inward-facing conformational states in which the LPC inverts during transport between the outer and inner leaflet of a membrane. However, direct biochemical evidence of flippase activity by Mfsd2a has not been demonstrated and it is not understood how Mfsd2a could invert LPC between the outer and inner leaflet of the membrane in a sodium-dependent manner. Here, we established a unique in vitro assay using recombinant Mfsd2a reconstituted in liposomes that exploits the ability of Mfsd2a to transport lysophosphatidylserine (LPS) coupled with a small molecule LPS binding fluorophore that allowed for monitoring of directional flipping of the LPS headgroup from the outer to the inner liposome membrane. Using this assay, we demonstrate that Mfsd2a flips LPS from the outer to the inner leaflet of a membrane bilayer in a sodium-dependent manner. Furthermore, using cryo-EM structures as guides together with mutagenesis and a cell-based transport assay, we identify amino acid residues important for Mfsd2a activity that likely constitute substrate interaction domains. These studies provide direct biochemical evidence that Mfsd2a functions as a lysolipid flippase.
    Keywords:  Mfsd2a; blood–brain barrier; flippase; membrane; transporter
  7. Nat Commun. 2023 Feb 28. 14(1): 947
      The ability of cells to manage consequences of exogenous proteotoxicity is key to cellular homeostasis. While a plethora of well-characterised machinery aids intracellular proteostasis, mechanisms involved in the response to denaturation of extracellular proteins remain elusive. Here we show that aggregation of protein ectodomains triggers their endocytosis via a macroendocytic route, and subsequent lysosomal degradation. Using ERBB2/HER2-specific antibodies we reveal that their cross-linking ability triggers specific and fast endocytosis of the receptor, independent of clathrin and dynamin. Upon aggregation, canonical clathrin-dependent cargoes are redirected into the aggregation-dependent endocytosis (ADE) pathway. ADE is an actin-driven process, which morphologically resembles macropinocytosis. Physical and chemical stress-induced aggregation of surface proteins also triggers ADE, facilitating their degradation in the lysosome. This study pinpoints aggregation of extracellular domains as a trigger for rapid uptake and lysosomal clearance which besides its proteostatic function has potential implications for the uptake of pathological protein aggregates and antibody-based therapies.