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Phospholipase D1 is an effector of Rheb in the mTOR pathway

Y Sun1, Y Fang, M-S Yoon

  • 1Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

Proceedings of the National Academy of Sciences of the United States of America
|June 14, 2008
PubMed

Insights

This study reveals Phospholipase D1 (PLD1) is essential for Rheb-mediated activation of the mTOR pathway, a key target in cancer therapy. Findings uncover a novel TSC-Rheb-PLD signaling cascade, offering new therapeutic strategies.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The mammalian target of rapamycin (mTOR) pathway regulates cell growth and is a critical target for anticancer therapies.
  • Upstream regulators of mTOR include the tuberous sclerosis complex (TSC1/2) proteins, the small GTPase Rheb, and Phospholipase D (PLD).
  • The integration of TSC/Rheb and PLD signaling pathways within the mTOR network remains largely unexplored.

Purpose of the Study:

  • To investigate the interaction and integration between the TSC/Rheb and PLD pathways in the context of mTOR signaling.
  • To determine the specific role of PLD isoforms (PLD1 and PLD2) in Rheb-mediated mTOR activation.
  • To elucidate the upstream regulators and downstream effectors within this newly proposed signaling cascade.

Main Methods:

  • RNA interference (RNAi) to assess the requirement of PLD1 and PLD2 in Rheb-mTOR signaling.
  • Overexpression and knockdown studies of Rheb and TSC2 to evaluate their impact on PLD1 activity.
  • Pharmacological inhibition of AMPK and PI3K to identify upstream regulators of the TSC-Rheb-PLD pathway.
  • In vitro binding assays to confirm the direct interaction between Rheb and PLD1.

Main Results:

  • PLD1, but not PLD2, is required for Rheb to activate the mTOR pathway.
  • Rheb overexpression activates PLD1, while Rheb knockdown impairs serum-stimulated PLD activation.
  • TSC2 overexpression suppresses PLD1 activation; TSC2 loss increases basal PLD activity, supporting a TSC-Rheb-PLD cascade.
  • AMPK, PI3K, and amino acid sufficiency are upstream regulators of PLD activation.
  • Rheb directly binds and activates PLD1 in a GTP-dependent manner, identifying PLD1 as a Rheb effector.

Conclusions:

  • Phospholipase D1 (PLD1) is a direct effector of Rheb and a crucial component of the mTOR signaling pathway.
  • A novel TSC-Rheb-PLD signaling cascade is identified, integrating previously separate regulatory pathways upstream of mTOR.
  • These findings provide new insights into mTOR regulation and suggest potential therapeutic targets for anticancer drug development.

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