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Structural basis for FLCN RagC GAP activation in MiT-TFE substrate-selective mTORC1 regulation

Rachel M Jansen1,2, Roberta Peruzzo1, Simon A Fromm1,2

  • 1Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.

Science Advances
|September 14, 2022
PubMed

Insights

The folliculin (FLCN) complex structure reveals how it activates mTORC1 signaling to control cell growth and autophagy by regulating MiT-TFE transcription factors. This finding offers a new strategy for developing targeted cancer therapies.

Area of Science:

  • Cellular biology
  • Molecular mechanisms
  • Biochemistry

Background:

  • The mechanistic target of rapamycin complex 1 (mTORC1) is a key regulator of cell growth and metabolism.
  • The tumor suppressor folliculin (FLCN) interacts with mTORC1, influencing lysosome biogenesis and autophagy.
  • FLCN's role as a GTPase-activating protein (GAP) for RagC/D GTPases is crucial for mTORC1 regulation.

Purpose of the Study:

  • To determine the cryo-electron microscopy structure of the active FLCN complex (AFC).
  • To elucidate the structural basis for FLCN's GAP activity towards Rag GTPases.
  • To understand how FLCN regulates mTORC1 signaling specifically for MiT-TFE transcription factors.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) to resolve the AFC structure.
  • Biochemical assays to assess GAP activity.
  • Mutagenesis studies to investigate protein-protein interactions.

Main Results:

  • The AFC structure reveals a 90° reorientation of FLCN, with new contacts with RagC essential for catalysis.
  • Disruption of FLCN and FNIP2 interfaces with RagC abolished GAP activity.
  • Inhibition of FLCN's GAP activity led to TFE3 nuclear retention, without affecting other mTORC1 substrates like S6K or 4E-BP1.

Conclusions:

  • The determined AFC structure provides critical insights into the regulation of mTORC1 substrate-specific pathways.
  • This structural understanding paves the way for developing selective mTORC1 antagonists targeting the MiT-TFE pathway.
  • FLCN's unique mechanism of action offers a potential therapeutic target for diseases involving dysregulated cell growth and autophagy.

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