title: Inhibition of translational initiation in eukaryotic cells by calcium ionophore.
abstract: Ca2+ has been recently reported to be required for high rates of translational initiation in GH3 pituitary cells (Chin, K.-V., Cade, C., Brostrom, C.O., Galuska, E.M., and Brostrom, M.A. (1987) J. Biol. Chem. 262, 16509-16514). In the present investigation low concentrations of the Ca2+ ionophores, A23187 and ionomycin, were found to rapidly suppress the Ca2+-dependent component of protein synthesis in GH3 cells. More ionophore was required to inhibit amino acid incorporation into protein as extracellular Ca2+ was increased. Pre-existing inhibitions of protein synthesis produced by low concentrations of ionophore at low extracellular Ca2+ concentrations were reversed by adjustment to high extracellular Ca2+. Treatment with ionophore reduced the cellular contents of polysomes and 43 S preinitiation complex to values equivalent to those found for Ca2+-depleted cells. Average ribosomal transit times were unaffected by ionophore, and treated cells retained the ability to accumulate polysomes when incubated with cycloheximide. Cell types, such as HeLa and Chinese hamster ovary, that normally display only a modest Ca2+-dependent component of protein synthesis, manifested a strong underlying Ca2+ dependence in amino acid incorporation and polysome formation following treatment with low concentrations of ionophore. Protein synthesis in GH3 or HeLa cells during recovery from heat shock and arsenite treatment was not affected by cellular Ca2+ depletion or ionophore treatment. On the basis of these results, Ca2+ ionophore is proposed to inhibit Ca2+-dependent translational initiation through facilitating the mobilization of sequestered intracellular Ca2+.
authors.affiliation: Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854.
authors.forename: C O
authors.initials: CO
authors.lastname: Brostrom
authors.forename: K V
authors.initials: KV
authors.lastname: Chin
authors.forename: W L
authors.initials: WL
authors.lastname: Wong
authors.forename: C
authors.initials: C
authors.lastname: Cade
authors.forename: M A
authors.initials: MA
authors.lastname: Brostrom
mesh_terms: D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002477:Cells / Q000378:metabolism*; D004987:Ethers / Q000494:pharmacology; D005057:Eukaryotic Cells / Q000378:metabolism*; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015759:Ionomycin; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects
chemical_list: D004987:Ethers; D000001:Calcimycin; D015759:Ionomycin; D002118:Calcium