title: Tiron and trolox potentiate the autophagic cell death induced by magnolol analog Ery5 by activation of Bax in HL-60 cells.
abstract: This study describes the mechanism of trolox and tiron induced potentiation of cytotoxicity caused by Ery5, an analog of magnolol, in human myeloid leukemia HL-60 cells. Ery5 induced cytotoxicity in HL-60 cells by involving activation of bax and cleavage of caspase 3, which contributed towards activation of both apoptotic and autophagic pathways. Trolox and tiron, even at non-toxic concentrations, contributed to the cytotoxicity of Ery5 by activation of autophagic proteins like ATG7, ATG12 and LC3-II. Z-VAD-fmk mediated reduction in the cytotoxicity and expression of autophagic proteins, further suggested that autophagy induced by Ery5 is largely dependent upon caspases. Interestingly, Ery5 induced autophagy was accompanied by the downregulation of PI3K/AKT pathway whereas, trolox and tiron strongly enhanced this effect. In addition to that treatment of cells with Ery5, trolox and tiron individually, displayed a marked upregulation of Bax. The involvement of Bax in trolox and tiron induced enhancement of the cytotoxicity of Ery5 was confirmed, when siRNA induced silencing of Bax led to increased viability of the cells and exerted a strong inhibitory effect on LC3-II accumulation and p62 degradation in case of cells treated by the combination of Ery5 with trolox or tiron. Additionally, an important role of PARP in Ery5 mediated cell death has been suggested by PARP silencing experiments, however, potentiation of autophagic cytotoxicity by trolox and tiron did not seem to be dependent on PARP-1. Therefore, Bax seems to play a vital role in trolox and tiron mediated potentiation of autophagic cell death by Ery5 in HL-60 cells.
authors.affiliation: Department of Cancer Pharmacology, Indian Institute of Integrative Medicine CSIR, Canal Road, Jammu 180001, India.
authors.forename: Suresh
authors.initials: S
authors.lastname: Kumar
authors.forename: Ajay
authors.initials: A
authors.lastname: Kumar
authors.forename: Anup Singh
authors.initials: AS
authors.lastname: Pathania
authors.forename: Santosh Kumar
authors.initials: SK
authors.lastname: Guru
authors.forename: Srinivas
authors.initials: S
authors.lastname: Jada
authors.forename: Parduman Raj
authors.initials: PR
authors.lastname: Sharma
authors.forename: Shashi
authors.initials: S
authors.lastname: Bhushan
authors.forename: Ajit Kumar
authors.initials: AK
authors.lastname: Saxena
authors.forename: H M Sampath
authors.initials: HM
authors.lastname: Kumar
authors.forename: Fayaz
authors.initials: F
authors.lastname: Malik
mesh_terms: D014013:1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt / Q000494:pharmacology*; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000138:chemical synthesis / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001343:Autophagy / Q000187:drug effects* / Q000235:genetics; D000071192:Autophagy-Related Protein 12; D000071193:Autophagy-Related Protein 7; D001713:Biphenyl Compounds / Q000138:chemical synthesis / Q000494:pharmacology*; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D002839:Chromans / Q000494:pharmacology*; D004357:Drug Synergism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D018922:HL-60 Cells; D006801:Humans; D017705:Lignans / Q000138:chemical synthesis / Q000494:pharmacology*; D008869:Microtubule-Associated Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010636:Phenols / Q000138:chemical synthesis / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D025841:Small Ubiquitin-Related Modifier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics* / Q000378:metabolism
chemical_list: C466624:ATG12 protein, human; D000590:Amino Acid Chloromethyl Ketones; D000970:Antineoplastic Agents; D000071192:Autophagy-Related Protein 12; C494826:BAX protein, human; D001713:Biphenyl Compounds; D002839:Chromans; C584245:Ery5 compound; D017705:Lignans; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; D010636:Phenols; D025841:Small Ubiquitin-Related Modifier Proteins; D051028:bcl-2-Associated X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C005498:magnolol; D014013:1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt; D019869:Phosphatidylinositol 3-Kinases; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; D051057:Proto-Oncogene Proteins c-akt; D020169:Caspases; C509349:ATG7 protein, human; D000071193:Autophagy-Related Protein 7; D044764:Ubiquitin-Activating Enzymes; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid