A novel calcium-dependent phosphorylation of a ribosome-associated protein.
The degree of phosphorylation of ribosome-associated proteins of intact GH3 pituitary tumor cells before and after Ca2+ depletion was examined. A 26-kDa ribosome-associated protein was found to dephosphorylate upon Ca2+ depletion of the cells and to re-phosphorylate upon restoration of the cation. This protein was distinct from eukaryotic initiation factor 4E on the basis of subcellular distribution, antigenicity, and susceptibility to dephosphorylation in Ca2+-depleted cells. Temporal correlation was observed between the phosphorylation/dephosphorylation state of the 26-kDa protein, and the stimulation/inhibition of protein synthesis by Ca2+ repletion/depletion. Phosphorylation of the 26-kDa protein was rapidly abolished in Ca2+-repleted cells by the ionophore, A23187, which elevates cytosolic Ca2+ while reducing sequestered cation. Dephosphorylation of the protein and inhibition of protein synthesis occurred at comparable times after addition of ionophore. The novelty of a Ca2+-dependent phosphorylation supported by sequestered rather than cytosolic free Ca2+ is discussed.
Fawell
E H
EH
Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854.
Boyer
I J
IJ
Brostrom
M A
MA
Brostrom
C O
CO
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D007526:Isoelectric Point; D008970:Molecular Weight; D010448:Peptide Initiation Factors / Q000378:metabolism; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism*
D039561:Eukaryotic Initiation Factor-4E; D039562:Eukaryotic Initiation Factor-4F; D010448:Peptide Initiation Factors; D012269:Ribosomal Proteins; D000001:Calcimycin; D002118:Calcium