title: Human melanoma cells under endoplasmic reticulum stress are more susceptible to apoptosis induced by the BH3 mimetic obatoclax.
abstract: Past studies have shown that melanoma cells have largely adapted to endoplasmic reticulum (ER) stress, and this is associated with up-regulation of the antiapoptotic proteins Bcl-2 and Mcl-1. In this report, we show that the BH3 mimetic obatoclax potently overcomes resistance of melanoma cells to apoptosis induced by ER stress. Obatoclax, as a single agent at nanomolar concentrations, was relatively ineffective in the induction of apoptosis in melanoma cells, but treatment with obatoclax at these concentrations in combination with the ER stress inducer tunicamycin (TM) or thapsigargin markedly enhanced apoptotic cell death. This was primarily because of the inhibition of Mcl-1 by obatoclax, in that cotreatment with TM and another BH3 mimetic ABT737, which does not antagonize Mcl-1, caused only minimal increases in apoptosis. Moreover, overexpression of Mcl-1 inhibited apoptosis to greater degrees than overexpression of Bcl-2. In addition to direct inhibition of Mcl-1 by obatoclax, the combination of obatoclax and TM caused strong up-regulation of the BH3-only protein Noxa. Small RNA interference knockdown of Noxa partially inhibited apoptosis induced by cotreatment with obatoclax and TM. Similarly, knockdown of Bak also blocked induction of apoptosis by the compounds. The Mcl-1/Bak interaction seemed to be disrupted more efficiently in melanoma cells cotreated with obatoclax and TM. Taken together, these results identify obatoclax as a potent agent that overcomes resistance of melanoma cells to ER stress-induced apoptosis and seem to have important implications in the use of BH3 mimetics in the treatment of melanoma.
authors.affiliation: Immunology and Oncology Unit, Room 443, Calvary Mater Newcastle Hospital, NSW, Australia.
authors.forename: Chen Chen
authors.initials: CC
authors.lastname: Jiang
authors.forename: David
authors.initials: D
authors.lastname: Wroblewski
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
authors.forename: Peter
authors.initials: P
authors.lastname: Hersey
authors.forename: Xu Dong
authors.initials: XD
authors.lastname: Zhang
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D004721:Endoplasmic Reticulum / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D047468:Immunoprecipitation; D007211:Indoles; D008545:Melanoma / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D018384:Oxidative Stress; D010446:Peptide Fragments / Q000737:chemistry; D011518:Proto-Oncogene Proteins / Q000737:chemistry; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014415:Tunicamycin / Q000494:pharmacology; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D000998:Antiviral Agents; C494772:BAK1 protein, human; C474007:Bax protein (53-86); D004791:Enzyme Inhibitors; D007211:Indoles; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C498702:PMAIP1 protein, human; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011758:Pyrroles; D034741:RNA, Small Interfering; D050998:bcl-2 Homologous Antagonist-Killer Protein; D014415:Tunicamycin; D019284:Thapsigargin; C520962:obatoclax