title: Inhibition of endoplasmic reticulum stress-induced apoptosis of melanoma cells by the ARC protein.
abstract: We have shown previously that most melanoma cell lines are insensitive to endoplasmic reticulum (ER) stress-induced apoptosis, but resistance can be reversed through activation of caspase-4 by inhibition of the MEK/ERK pathway. We report in this study that apoptosis was induced by the ER stress inducer thapsigargin or tunicamycin via a caspase-8-mediated pathway in the melanoma cell line Me1007, although the MEK/ERK pathway was activated in this cell line. The high sensitivity of Me1007 to ER stress-induced apoptosis was associated with low expression levels of the apoptosis repressor with caspase recruitment domain (ARC) protein that was expressed at relatively high levels in the resistant melanoma cell lines. Transfection of cDNA encoding ARC into Me1007 cells inhibited both caspase-8 activation and apoptosis induced by thapsigargin or tunicamycin. In contrast, inhibition of ARC by small interfering RNA knockdown sensitized the resistant melanoma cell lines to ER stress-induced apoptosis, which was inhibitable by blockage of caspase-8 activation. Both exogenous and endogenous ARC seemed to predominantly locate to the cytoplasm and mitochondria and could be coimmunoprecipitated with caspase-8. Taken together, ER stress can potentially activate multiple apoptosis signaling pathways in melanoma cells in a context-dependent manner. Whereas the MEK/ERK signaling pathway plays an important role in inhibiting ER stress-induced caspase-4 activation, ARC seems to be critical in blocking activation of caspase-8 in melanoma cells subjected to ER stress.
authors.affiliation: Immunology and Oncology Unit, Calvary Mater Newcastle Hospital, Newcastle, New South Wales, Australia.
authors.forename: Li Hua
authors.initials: LH
authors.lastname: Chen
authors.forename: Chen Chen
authors.initials: CC
authors.lastname: Jiang
authors.forename: Ralph
authors.initials: R
authors.lastname: Watts
authors.forename: Rick F
authors.initials: RF
authors.lastname: Thorne
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 / Q000187:drug effects / Q000502:physiology*; D053181:Caspase 8 / Q000378:metabolism; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000096:biosynthesis* / Q000378:metabolism / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology; D008928:Mitochondria / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000096:biosynthesis* / Q000378:metabolism / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D061945:Caspase Inhibitors; D003598:Cytoskeletal Proteins; D009419:Nerve Tissue Proteins; C092069:activity regulated cytoskeletal-associated protein; D014415:Tunicamycin; D019284:Thapsigargin; D053181:Caspase 8