title: Inhibition of MEK sensitizes human melanoma cells to endoplasmic reticulum stress-induced apoptosis.
abstract: Past studies have shown that activation of mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK is a common cause for resistance of melanoma cells to death receptor-mediated or mitochondria-mediated apoptosis. We report in this study that inhibition of the MEK/ERK pathway also sensitizes melanoma cells to endoplasmic reticulum (ER) stress-induced apoptosis, and this is mediated, at least in part, by caspase-4 activation and is associated with inhibition of the ER chaperon glucose-regulated protein 78 (GRP78) expression. Treatment with the ER stress inducer tunicamycin or thapsigargin did not induce significant apoptosis in the majority of melanoma cell lines, but resistance to these agents was reversed by the MEK inhibitor U0126 or MEK1 small interfering RNA (siRNA). Induction of apoptosis by ER stress when MEK was inhibited was caspase dependent with caspase-4, caspase-9, and caspase-3 being involved. Caspase-4 seemed to be the apical caspase in that caspase-4 activation occurred before activation of caspase-9 and caspase-3 and that inhibition of caspase-4 by a specific inhibitor or siRNA blocked activation of caspase-9 and caspase-3, whereas inhibition of caspase-9 or caspase-3 did not inhibit caspase-4 activation. Moreover, overexpression of Bcl-2 inhibited activation of caspase-9 and caspase-3 but had minimal effect on caspase-4 activation. Inhibition of MEK/ERK also resulted in down-regulation of GRP78, which was physically associated with caspase-4, before and after treatment with tunicamycin or thapsigargin. In addition, siRNA knockdown of GRP78 increased ER stress-induced caspase-4 activation and apoptosis. Taken together, these results seem to have important implications for new treatment strategies in melanoma by combinations of agents that induce ER stress and inhibitors of the MEK/ERK pathway.
authors.affiliation: Immunology and Oncology Unit, Newcastle Misericordiae Hospital, Newcastle, New South Wales, Australia.
authors.forename: Chen Chen
authors.initials: CC
authors.lastname: Jiang
authors.forename: Li Hua
authors.initials: LH
authors.lastname: Chen
authors.forename: Susan
authors.initials: S
authors.lastname: Gillespie
authors.forename: Yu Fang
authors.initials: YF
authors.lastname: Wang
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Kiejda
authors.forename: Xu Dong
authors.initials: XD
authors.lastname: Zhang
authors.forename: Peter
authors.initials: P
authors.lastname: Hersey
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D002070:Butadienes / Q000494:pharmacology; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004721:Endoplasmic Reticulum / Q000502:physiology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006360:Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D008545:Melanoma / Q000201:enzymology* / Q000473:pathology; D018832:Molecular Chaperones / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D002070:Butadienes; D061945:Caspase Inhibitors; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D007527:Isoenzymes; D018832:Molecular Chaperones; D009570:Nitriles; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; C113580:U 0126; D014415:Tunicamycin; D019284:Thapsigargin; D020930:MAP Kinase Kinase Kinases; D020169:Caspases