Research Paper Volume 10, Issue 11 pp 3574—3589
Suppression of mTORC1 activity in senescent Ras-transformed cells neither restores autophagy nor abrogates apoptotic death caused by inhibition of MEK/ERK kinases
- 1 Institute of Cytology, Russian Academy of Sciences, St-Petersburg 194064, Russia
received: October 9, 2018 ; accepted: November 21, 2018 ; published: November 27, 2018 ;https://doi.org/10.18632/aging.101686
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Copyright: Kochetkova et al. This is an open‐access article distributed under the terms of the Creative Commons Attribution License (CC BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Autophagy is conservative catabolic process that degrades organelles, in particular, mitochondria, and misfolded proteins within the lysosomes, thus maintaining cellular viability. Despite the close relationship between mitochondrial dysfunction and cellular senescence, it is unclear how mitochondria damage can induce autophagy in senescent cells. We show that MEK/ERK suppression induces mitochondria damage followed by apoptosis of senescent Ras-expressing cells. To understand the role of persistent mTORC1 signaling in breaking the cAMPK-induced autophagy caused by mitochondrial damage, we inhibited mTORС1 with low concentrations of pp242. mTORC1 suppression neither restores the AMPK-induced autophagy nor decreases the level of apoptosis upon MEK/ERK inhibition. We discovered the existence of an alternative autophagy-like way that partially increases the viability of senescent cells under suppressed mTORC1. The pp242-treated cells survive due to formation of the non-autophagous LC3-negative vacuoles, which contain the damaged mitochondria and lysosomes with the following excretion the content from the cell. MEK/ERK activity is required to implement this process in senescent cells. Senescent cells exhibit distinctive spatial distribution of organelles and proteins that provides uncoupling of final participants of autophagy. We show that this feature stops the process of cytoprotective autophagy in response to MEK/ERK suppression, thus allowing selective elimination of senescent Ras-expressing cells.
NaBut: sodium butyrate; TEM: transmission electron microscopy; mTOR: mammalian Target of Rapamycin; mTORC1: mammalian Target of Rapamycin Complex 1; ERK: extracellular signal-regulated kinase; MEK: mitogen-activated protein kinase; LC3: microtubule-associated protein light chain 3; MTT: (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; SDS: sodium dodecyl sulphate; DMSO: dimethyl sulfoxide; DAPI: 4,6-diamidino-2-phenylindole; TBS: Tris-buffered solution.