Abstract
Disturbance to endoplasmic reticulum (ER) homeostasis that cannot be rescued by the unfolded protein response (UPR) results in autophagy and cell death, but the precise mechanism was largely unknown. Here we demonstrated that ER stress-induced cell death was mediated by autophagy which was partly attributed to the inactivation of the mammalian target of rapamycin (mTOR). Three widely used ER stress inducers including tunicamycin, DTT and MG132 led to the conversion of LC3-I to LC3-II , a commonly used marker of autophagy, as well as the downregulation of mTOR concurrently. TSC -deficient cells with constitutive activation of mTOR exhibited more resistance to ER stress-induced autophagy, compared with their wild-type counterparts. Furthermore, our studies showed that ER stress-induced deactivation of mTOR was attributed to the downregulation of AKT/TSC /mTOR pathway. Phosphatase and tensin homolog (PTEN) and AMP-activated protein kinase (AMPK) as two regulators in this pathway seemed to be absent in this regulation. As a chemical chaperone helping the correct folding of proteins, 4-phenylbutyric acid (4-PBA) partly rescued the AKT/TSC/mTOR pathway in drug-induced acute ER stress. Moreover, constitutively-activated mTOR-induced long-term ER stress attenuated the RTK/PI3K/AKT signaling pathway in response to the stimulation by various growth factors, which could also be partly restored by 4-PBA.
MeSH terms
-
Animals
-
Antineoplastic Agents / pharmacology
-
Autophagy / physiology*
-
Cells, Cultured
-
Cysteine Proteinase Inhibitors / pharmacology
-
Endoplasmic Reticulum / drug effects
-
Endoplasmic Reticulum / metabolism*
-
Fibroblasts / cytology
-
Fibroblasts / drug effects
-
Fibroblasts / physiology
-
Humans
-
Insulin Receptor Substrate Proteins / metabolism
-
Intracellular Signaling Peptides and Proteins / genetics
-
Intracellular Signaling Peptides and Proteins / metabolism*
-
Leupeptins / pharmacology
-
Mice
-
Mice, Knockout
-
Phenylbutyrates / pharmacology
-
Phosphatidylinositol 3-Kinases / metabolism
-
Protein Serine-Threonine Kinases / genetics
-
Protein Serine-Threonine Kinases / metabolism*
-
Proto-Oncogene Proteins c-akt / genetics
-
Proto-Oncogene Proteins c-akt / metabolism*
-
Receptors, Platelet-Derived Growth Factor / metabolism
-
Signal Transduction / physiology*
-
Stress, Physiological
-
TOR Serine-Threonine Kinases
-
Tuberous Sclerosis Complex 1 Protein
-
Tuberous Sclerosis Complex 2 Protein
-
Tumor Suppressor Proteins / genetics
-
Tumor Suppressor Proteins / metabolism*
Substances
-
Antineoplastic Agents
-
Cysteine Proteinase Inhibitors
-
IRS1 protein, human
-
Insulin Receptor Substrate Proteins
-
Intracellular Signaling Peptides and Proteins
-
Leupeptins
-
Phenylbutyrates
-
Tuberous Sclerosis Complex 1 Protein
-
Tuberous Sclerosis Complex 2 Protein
-
Tumor Suppressor Proteins
-
4-phenylbutyric acid
-
MTOR protein, human
-
mTOR protein, mouse
-
Receptors, Platelet-Derived Growth Factor
-
Protein Serine-Threonine Kinases
-
Proto-Oncogene Proteins c-akt
-
TOR Serine-Threonine Kinases
-
benzyloxycarbonylleucyl-leucyl-leucine aldehyde