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Phosphatidic acid drives mTORC1 lysosomal translocation in the absence of amino acids
Maria A Frias1, Suman Mukhopadhyay2, Elyssa Lehman2
1Department of Biological Sciences, Hunter College of the City University of New York, New York, New York 10021; Clinical and Translational Master's Program, Clinical and Translational Science Center, Weill Cornell Medicine, New York, New York 10065.
Abstract:
Mammalian target of rapamycin complex 1 (mTORC1) promotes cell growth and proliferation in response to nutrients and growth factors. Amino acids induce lysosomal translocation of mTORC1 via the Rag GTPases. Growth factors activate Ras homolog enriched in brain (Rheb), which in turn activates mTORC1 at the lysosome. Amino acids and growth factors also induce the phospholipase D (PLD)-phosphatidic acid (PA) pathway, required for mTORC1 signaling through mechanisms that are not fully understood. Here, using human and murine cell lines, along with immunofluorescence, confocal microscopy, endocytosis, PLD activity, and cell viability assays, we show that exogenously supplied PA vesicles deliver mTORC1 to the lysosome in the absence of amino acids, Rag GTPases, growth factors, and Rheb. Of note, pharmacological or genetic inhibition of endogenous PLD prevented mTORC1 lysosomal translocation. We observed that precancerous cells with constitutive Rheb activation through loss of tuberous sclerosis complex subunit 2 (TSC2) exploit the PLD-PA pathway and thereby sustain mTORC1 activation at the lysosome in the absence of amino acids. Our findings indicate that sequential inputs from amino acids and growth factors trigger PA production required for mTORC1 translocation and activation at the lysosome.
Insights
Phosphatidic acid (PA) delivers mammalian target of rapamycin complex 1 (mTORC1) to lysosomes, independent of nutrients or growth factors. This phospholipase D (PLD)-dependent pathway is crucial for mTORC1 signaling and activation.
Area of Science:
- Cellular signaling
- Molecular biology
- Biochemistry
Background:
- Mammalian target of rapamycin complex 1 (mTORC1) regulates cell growth and proliferation.
- mTORC1 signaling is activated by nutrients (amino acids) and growth factors.
- The phospholipase D (PLD)-phosphatidic acid (PA) pathway is involved in mTORC1 activation, but its precise role is unclear.
Purpose of the Study:
- To investigate the role of the PLD-PA pathway in mTORC1 lysosomal translocation and activation.
- To determine if PA can induce mTORC1 translocation independently of canonical signaling pathways.
- To examine the PLD-PA pathway's involvement in cancer cell metabolism.
Main Methods:
- Utilized human and murine cell lines.
- Employed immunofluorescence and confocal microscopy.
- Performed endocytosis, PLD activity, and cell viability assays.
Main Results:
- Exogenous PA vesicles delivered mTORC1 to lysosomes without amino acids, growth factors, Rag GTPases, or Rheb.
- Inhibiting endogenous PLD blocked mTORC1 lysosomal translocation.
- Precancerous cells with TSC2 loss exploited the PLD-PA pathway for sustained mTORC1 activation.
Conclusions:
- The PLD-PA pathway is essential for mTORC1 translocation and activation at the lysosome.
- PA delivery of mTORC1 to lysosomes can occur independently of canonical nutrient and growth factor inputs.
- The PLD-PA pathway is a potential target for therapeutic intervention in cancers with dysregulated mTORC1 signaling.
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