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The garlic compound ajoene targets protein folding in the endoplasmic reticulum of cancer cells
Author(s) -
Kaschula Catherine H.,
Hunter Roger,
Cotton Jonathan,
Tuveri Rossana,
Ngarande Ellen,
Dzobo Kevin,
Schäfer Georgia,
Siyo Vuyolwethu,
Lang Dirk,
Kusza Daniel A.,
Davies Bronwen,
Katz Arieh A.,
Parker M. Iqbal
Publication year - 2016
Publication title -
molecular carcinogenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.254
H-Index - 97
eISSN - 1098-2744
pISSN - 0899-1987
DOI - 10.1002/mc.22364
Subject(s) - endoplasmic reticulum , biology , microbiology and biotechnology , cancer cell , intracellular , apoptosis , protein folding , proteasome , unfolded protein response , green fluorescent protein , yellow fluorescent protein , biochemistry , cancer , gene , genetics
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.