title: Okadaic acid activates the PKR pathway and induces apoptosis through PKR stimulation in MG63 osteoblast-like cells.
abstract: Double-stranded RNA-dependent protein kinase (PKR) is one of the players in the cellular antiviral responses and is involved in transcriptional stimulation through activation of NF-κB. Treatment of the human osteosarcoma cell line MG63 with the protein phosphatase inhibitor okadaic acid stimulated the expression and phosphorylation of IκBα, as judged from the results of real-time PCR and western blot analysis. We investigated the functional relationship between PKR and signal transduction of NF-κB by establishing PKR-K/R cells that produced a catalytically inactive mutant of PKR. Phosphorylation of eIF-2α, a substrate of PKR, was not stimulated by okadaic acid in the PKR-K/R cells, whereas okadaic acid induced phosphorylation of eIF-2α in MG63 cells. Phosphorylation of NF-κB in MG63 cells was stimulated by okadaic acid; however, okadaic acid did not induce phosphorylation of NF-κB in the PKR-K/R cells. Finally, okadaic acid-induced apoptosis was inhibited in the PKR-K/R cells. Our results suggest that okadaic acid-induced phosphorylation of IκBα was mediated by PKR kinase activity, thus, indicating the involvement of this kinase in the control mechanism governing the activation of NF-κB and induction of apoptosis.
authors.affiliation: Department of Histology and Oral Histology, Institute of Health Biosciences, The University of Tokushima Graduate School, Kuramoto, Tokushima 770-8504, Japan. tat-hane@tokushima-u.ac.jp
authors.forename: Tatsuji
authors.initials: T
authors.lastname: Haneji
authors.forename: Kanji
authors.initials: K
authors.lastname: Hirashima
authors.forename: Jumpei
authors.initials: J
authors.lastname: Teramachi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Morimoto
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001859:Bone Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D006801:Humans; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology*; D010006:Osteoblasts / Q000378:metabolism; D012516:Osteosarcoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D015398:Signal Transduction / Q000187:drug effects; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism*
chemical_list: D015852:Eukaryotic Initiation Factor-2; D020672:I-kappa B Proteins; D016328:NF-kappa B; D019319:Okadaic Acid; D019892:eIF-2 Kinase