title: The garlic compound ajoene targets protein folding in the endoplasmic reticulum of cancer cells.
abstract: Ajoene is a natural allylsulfur compound found in crushed garlic that arrests growth and induces apoptosis in cancer cells. To gain mechanistic insights into the cytotoxicity of ajoene in cancer cells, two fluorescently labelled ajoene analogs with dansyl- (DP) and fluorescein- (FOX) tags were synthesized. The tagged ajoenes were found to retain their activity at inhibiting proliferation and inducing apoptosis in MDA-MB-231 human breast-cancer and WHCO1 human esophageal-cancer cells. Both tagged ajoenes localized to the endoplasmic reticulum (ER) in MDA-MB-231 cells as observed by live cell confocal laser scanning microscopy (CLSM) and confirmed by generating an MDA-MB-231 cell line expressing yellow fluorescent protein (YFP) in the ER. DP appears to S-thiolate multiple protein targets in MDA-MB-231 cells as observed by immunoblotting under non-reducing conditions only; and a competition assay demonstrated that DP and Z-ajoene in fact share the same target. Ajoene S-thiolation interfered with protein folding and led to an accumulation of misfolded protein aggregates and activated the unfolded protein response (UPR). Consistent with this mechanism, increased levels of GRP78 and total ubiquitinated proteins were observed; and an ER-folded protein, type-1 collagen, was tracked to the proteasome following ajoene treatment. The intracellular protein aggregates were observed by CLSM and transmission electron microscopy (TEM). This is the first time that ajoene has been shown to target protein folding in the ER of cancer cells. © 2015 Wiley Periodicals, Inc.
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Catherine H
authors.initials: CH
authors.lastname: Kaschula
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Roger
authors.initials: R
authors.lastname: Hunter
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Cotton
authors.affiliation: Department of Biomedical Science, University of Cagliari, Monserrato (CA), Italy.
authors.forename: Rossana
authors.initials: R
authors.lastname: Tuveri
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Cape Town, South Africa.
authors.forename: Ellen
authors.initials: E
authors.lastname: Ngarande
authors.affiliation: Division of Medical Biochemistry, University of Cape Town, Cape Town, South Africa.
authors.forename: Kevin
authors.initials: K
authors.lastname: Dzobo
authors.affiliation: Division of Medical Biochemistry, University of Cape Town, Cape Town, South Africa.|MRC/UCT Receptor Biology Unit, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: Georgia
authors.initials: G
authors.lastname: Schäfer
authors.affiliation: Division of Medical Biochemistry, University of Cape Town, Cape Town, South Africa.
authors.forename: Vuyolwethu
authors.initials: V
authors.lastname: Siyo
authors.affiliation: Department of Human Biology, Division of Physiology, University of Cape Town, Cape Town, South Africa.
authors.forename: Dirk
authors.initials: D
authors.lastname: Lang
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Kusza
authors.affiliation: Department of Chemistry, University of Cape Town, Rondebosch, Cape Town, South Africa.
authors.forename: Bronwen
authors.initials: B
authors.lastname: Davies
authors.affiliation: Division of Medical Biochemistry, University of Cape Town, Cape Town, South Africa.|MRC/UCT Receptor Biology Unit, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa.
authors.forename: Arieh A
authors.initials: AA
authors.lastname: Katz
authors.affiliation: International Centre for Genetic Engineering and Biotechnology, Cape Town, South Africa.|Division of Medical Biochemistry, University of Cape Town, Cape Town, South Africa.
authors.forename: M Iqbal
authors.initials: MI
authors.lastname: Parker
mesh_terms: D017209:Apoptosis; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004220:Disulfides / Q000737:chemistry / Q000494:pharmacology*; D004721:Endoplasmic Reticulum / Q000187:drug effects; D000091342:Endoplasmic Reticulum Chaperone BiP; D060746:Endoplasmic Reticulum-Associated Degradation / Q000187:drug effects; D019793:Fluorescein / Q000737:chemistry; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D046529:Microscopy, Electron, Transmission; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000737:chemistry; D010936:Plant Extracts / Q000494:pharmacology*; D017510:Protein Folding / Q000187:drug effects*; D013454:Sulfoxides; D054875:Ubiquitination; D056811:Unfolded Protein Response / Q000187:drug effects
chemical_list: C496906:1-myristoyl-2-(12-((5-dimethylamino-1-naphthalenesulfonyl)amino)dodecanoyl)-sn-glycero-3-phosphocholine; D004220:Disulfides; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D010713:Phosphatidylcholines; D010936:Plant Extracts; D013454:Sulfoxides; C048980:ajoene; D019793:Fluorescein
keywords: ajoene; cancer prevention; endoplasmic reticulum; garlic; protein folding