Co-ordinated activation of classical and novel PKC isoforms is required for PMA-induced mTORC1 activation
Mengling Liu1,2, Christopher J Clarke1,2, Mohamed F Salama1,3
1Department of Medicine, Stony Brook University, Stony Brook, NY, United States of America.
Abstract:
Protein kinase C (PKC) has been shown to activate the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway, a central hub in the regulation of cell metabolism, growth and proliferation. However, the mechanisms by which PKCs activate mTORC1 are still ambiguous. Our previous study revealed that activation of classical PKCs (cPKC) results in the perinuclear accumulation of cPKC and phospholipase D2 (PLD2) in recycling endosomes in a PLD2-dependent manner. Here, we report that mTORC1 activation by phorbol 12,13-myristate acetate (PMA) requires both classic, cPKC, and novel PKC (nPKC) isoforms, specifically PKCη, acting through distinct pathways. The translocation of mTOR to perinuclear lysosomes was detected after treatment of PKC activators, which was not colocalized with PKCα- or RAB11-positive endosomes and was not inhibited by PLD inhibitors. We found that PKCη inhibition by siRNA or bisindolylmaleimide I effectively decreased mTOR accumulation in lysosomes and its activity. Also, we identified that PKCη plays a role upstream of the v-ATPase/Ragulator/Rag pathway in response to PMA. These data provides a spatial aspect to the regulation of mTORC1 by sustained activation of PKC, requiring co-ordinated activation of two distinct elements, the perinuclear accumulation of cPKC- and PLD-containing endosomes and the nPKC-dependent translation of of mTOR in the perinuclear lysosomes. The close proximity of these two distinct compartments shown in this study suggests the possibility that transcompartment signaling may be a factor in the regulation of mTORC1 activity and also underscores the importance of PKCη as a potential therapeutic target of mTORC-related disorders.
Insights
Protein kinase C (PKC) activates the mTORC1 pathway through distinct mechanisms involving both classical and novel PKC isoforms. This study highlights PKCη
Area of Science:
- Cellular Biology
- Molecular Signaling
- Metabolism Regulation
Background:
- Protein kinase C (PKC) activates the mammalian target of rapamycin complex 1 (mTORC1) pathway, crucial for cell metabolism and growth.
- The precise mechanisms linking PKC activation to mTORC1 signaling remain unclear.
- Previous work showed classical PKC (cPKC) activation leads to perinuclear accumulation of cPKC and phospholipase D2 (PLD2) in recycling endosomes.
Purpose of the Study:
- To elucidate the distinct pathways through which classical and novel PKC isoforms activate mTORC1.
- To investigate the role of PKCη in mTORC1 activation and its spatial regulation.
- To identify potential therapeutic targets for mTORC1-related disorders.
Main Methods:
- Utilized phorbol 12,13-myristate acetate (PMA) to activate PKC isoforms.
- Investigated mTOR translocation to perinuclear lysosomes using microscopy.
- Employed siRNA and pharmacological inhibitors (bisindolylmaleimide I) to assess PKCη function.
- Examined the involvement of PKCη upstream of the v-ATPase/Ragulator/Rag pathway.
Main Results:
- Phorbol 12,13-myristate acetate (PMA)-induced mTORC1 activation requires both cPKC and novel PKC (nPKC) isoforms, notably PKCη.
- mTOR translocated to perinuclear lysosomes, independent of PKCα or RAB11-positive endosomes and unaffected by PLD inhibitors.
- PKCη inhibition reduced mTOR lysosomal accumulation and activity, indicating its crucial role.
- PKCη acts upstream of the v-ATPase/Ragulator/Rag pathway in response to PMA.
Conclusions:
- Sustained PKC activation regulates mTORC1 through coordinated signaling involving perinuclear cPKC/PLD endosomes and nPKC-dependent mTOR translocation to lysosomes.
- The spatial proximity of these compartments suggests transcompartment signaling in mTORC1 regulation.
- PKCη emerges as a significant regulator of mTORC1 and a potential therapeutic target for related disorders.
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