title: mTOR signaling pathway is inhibited downstream of the cyclophilin D-mediated mitochondrial permeability transition in honokiol-triggered regulated necrosis.
abstract: Honokiol (HNK) is a pharmacologically active small molecule that is isolated from the traditional Chinese medicinal herb, houpu. It may induce diversified types of regulated cell death, which are dependent on different cell types and varying concentrations of therapeutic agent. We previously reported that HNK triggers a cyclophilin D (CypD)-mediated regulated necrosis in various cell lines at certain concentrations (two‑fold higher than its half maximal inhibitory concentration). Subsequent study revealed that HNK induced cell death transition from early apoptosis to regulated necrosis in parallel with the increase of HNK dose. In the current study, a lower concentration of HNK (30 µg/ml) than previously reported also induced simplex CypD‑mediated mitochondrial permeability transition (MPT)‑associated regulated necrosis in the HEK‑293 human embryonic kidney cell line. HNK, at concentration of 30 µg/ml, induced necrotic cell death in HEK‑293 cells, which was demonstrated by positive staining for propidium iodide. No DNA ladder patterns or apoptotic bodies were detected in cells that underwent this type of necrotic cell death. Caspase‑8 and ‑3 were not activated during the process of HNK‑induced necrosis. In addition, pan‑caspase inhibitor, z‑VAD‑fmk and receptor‑interacting protein 1 inhibitor, necrostatin‑1 did not inhibit HNK‑induced necrosis. However, CypD inhibitor, cyclosporin A (CsA), blocked HNK‑induced necrosis. These findings indicate that 30 µg/ml HNK induced simplex CypD-mediated MPT‑associated regulated necrosis in HEK‑293 cells. Furthermore, the findings demonstrated that during HNK-triggered regulated necrosis the mammalian target of rapamycin (mTOR) signaling pathway is also inhibited. Pretreatment with CsA, therefore, inhibits HNK‑triggered regulated necrosis and reverses dephosphorylation of Akt, eIF4E‑binding protein 1 and S6 kinase. This indicated that the mTOR signaling pathway is effective downstream of the CypD‑mediated MPT and before the onset of plasma membrane breakdown during the regulated necrosis process. Therefore, it has been demonstrated for the first time, to the best of our knowledge, that the mTOR signaling pathway was inhibited downstream of the CypD-mediated MPT in the process of HNK-induced regulated necrosis.
authors.affiliation: Department of Surgical Oncology, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang 310009, P.R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Tian
authors.affiliation: Department of Surgical Oncology, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang 310009, P.R. China.
authors.forename: Jieni
authors.initials: J
authors.lastname: Xiong
authors.affiliation: Department of Surgical Oncology, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang 310009, P.R. China.
authors.forename: Saisa
authors.initials: S
authors.lastname: Zhu
authors.affiliation: Department of Surgical Oncology, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang 310009, P.R. China.
authors.forename: Dong
authors.initials: D
authors.lastname: Xu
authors.affiliation: Department of Medical Oncology, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang 310009, P.R. China.
authors.forename: Hong
authors.initials: H
authors.lastname: Shen
authors.affiliation: Department of Surgical Oncology, The Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang 310009, P.R. China.
authors.forename: Yongchuan
authors.initials: Y
authors.lastname: Deng
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001713:Biphenyl Compounds / Q000633:toxicity*; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins / Q000494:pharmacology*; D016572:Cyclosporine / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D017705:Lignans / Q000633:toxicity*; D008928:Mitochondria / Q000378:metabolism*; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism; D010539:Permeability / Q000187:drug effects; D016601:RNA-Binding Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D000498:Allyl Compounds; D010636:Phenols
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D001713:Biphenyl Compounds; D053148:Caspase 3; D053181:Caspase 8; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins; D016572:Cyclosporine; D007093:Imidazoles; D007211:Indoles; D017705:Lignans; D028861:Nuclear Pore Complex Proteins; D016601:RNA-Binding Proteins; D058570:TOR Serine-Threonine Kinases; C119724:AGFG1 protein, human; C484771:benzyloxycarbonyl-valyl-aspartic acid fluoromethyl ketone; C507699:necrostatin-1; C005499:honokiol; D000498:Allyl Compounds; D010636:Phenols