bims-lymeca Biomed News
on Lysosome metabolism in cancer
Issue of 2023–01–29
two papers selected by
Harilaos Filippakis, University of New England
  1. Structure of the lysosomal mTORC1-TFEB-Rag-Ragulator megacomplex.
  2. Stonin 2 activates lysosomal-mTOR axis for cell survival in oral cancer.
  1. 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
  2. Toxicol In Vitro. 2023 Jan 23. pii: S0887-2333(23)00010-3. [Epub ahead of print] 105561
    Stonin 2 activates lysosomal-mTOR axis for cell survival in oral cancer.
    Kewal Kumar Mahapatra, Soumya Ranjan Mishra, Rohan Dhiman, Sujit Kumar Bhutia.
      Aberrant expression of various genes is associated with the progression of oral squamous cell carcinoma. Stonin 2, an endocytic protein, has a prominent role in clathrin-associated endocytosis. Its position in oral cancer is still unknown. Here, we report that STON2 expression increases with an increase in the grade of the oral cancer tissue. Further, STON2 overexpressed cells possess a higher rate of proliferation than normal cells. STON2 helps maintain lysosomal functions by preserving the lysosomal membrane integrity. It activates the Akt-mTOR axis and retains the mTOR on the membrane of the lysosomes. Further, we have identified an inhibitor of STON2, i.e., Trifluoperazine dihydrochloride (TFP), which targets the lysosomal axis by disrupting the Akt-mTOR pathway and causes lysosomal membrane permeabilization. TFP also shows anti-cancer effects on the oral cancer CAL33 and FaDu cells. Moreover, the lysosomal activity and the Akt-mTOR expression were restored in STON2 overexpressed cells co-treated with TFP. In addition, cell viability is also restored in TFP-treated STON2 overexpressed cells. Hence, TFP targets STON2 to showcase its anti-cancer effects in oral cancer. In addition, STON2 might serve as a potential biomarker in oral cancer therapeutics, and TFP may act as an anti-cancer drug against oral cancer.
    Keywords:  Lysosome; Oral cancer; STON2; Trifluoperazine dihydrochloride; mTOR
    DOI:  https://doi.org/10.1016/j.tiv.2023.105561
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