Elongation Factor 2-Specific Calcium- and Calmodulin-Dependent Protein Kinase III Activity in Rat Livers Varies with Age and Calorie Restriction

Riis, Bent; Rattan, Suresh I. S.; Palmquist, Kim; Nilsson, Anders; Nygård, Odd; Clark, Brian F. C.

doi:10.1006/bbrc.1993.1545

Cited by 12 publications

(3 citation statements)

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“…Possible candidates are the R subunit of eukaryotic initiation factor 2 (eIF-2R) that is phosphorylated and inhibited by several eIF-2R protein kinases, and eukaryotic elongation factor 2 (eEF2) that is phosphorylated and inhibited by eEF2 kinase (previously called CaM kinase III) (32)(33)(34). There is good evidence that eIF-2R is dephosphorylated by PP1 (20)(21)(22)(26)(27)(28), while various studies show that eEF2 is dephosphorylated with considerable specificity by PP2A (23)(24)(25)(32)(33)(34). We found here that transient overexpression of FLAG-R4 produced a significant and selective decrease in the level of phospho-eEF2.…”

Section: Discussionmentioning

confidence: 99%

“…Possible candidates are the α subunit of eukaryotic initiation factor-2 (eIF-2α) or eukaryotic elongation factor-2 (eEF2). There is good evidence that eIF-2α is dephosphorylated by PP1 ( − ), while eEF2 is dephosphorylated by PP2A ( − ). In the present study, we found that overexpression of FLAG-α4 resulted in a selective decrease in phospho-eEF2.…”

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confidence: 99%

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Mutation of Tyr307 and Leu309 in the Protein Phosphatase 2A Catalytic Subunit Favors Association with the α4 Subunit Which Promotes Dephosphorylation of Elongation Factor-2

et al. 1999

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The cellular location and substrate specificity of the catalytic subunit (C) of protein phosphatase 2A (PP2A) depend on its interaction with A and B subunits. The distribution of epitope-tagged wild-type or mutated C subunits was studied by transient expression in COS-7 cells. Wild-type tagged C expressed at low levels formed ABC trimer and AC dimer like the endogenous C. Single mutations of C at the site of phosphorylation (Y307F) or carboxymethylation (L309Q) resulted in recovery of only AC dimer. Double mutation of both residues resulted in association of C with alpha 4 protein (alpha 4), a novel subunit of PP2A, instead of with A and B subunits. Thus, the distribution of C between ABC trimer, AC dimer, and alpha 4C complexes can be affected by modifications of the C-terminal residues. The alpha 4 protein is a homologue of the yeast Tap42 protein that functions downstream of the TOR protein to regulate protein synthesis. Transient overexpression of FLAG-alpha 4 resulted in increased dephosphorylation of elongation factor 2, but had no effect on phosphorylation of either p70S6 kinase or PHAS-I (eIF4E-BP). Signals that affect phosphorylation or methylation of the C subunit of PP2A may promote subunit exchange and direct phosphatase activity to specific intracellular substrates.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Mutation of Tyr307 and Leu309 in the Protein Phosphatase 2A Catalytic Subunit Favors Association with the α4 Subunit Which Promotes Dephosphorylation of Elongation Factor-2

et al. 1999

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“…At the level of protein elongation, there is indirect evidence that alterations in the phosphorylation and dephosphorylation of EF-2 caused by changes in the activities of an EF-Zspecific protein kinase I11 [29] and protein phosphatase 2A [30] may affect the rates of protein synthesis during aging. Furthermore, since the phosphorylation of the S6 ribosomal protein correlates with the activation of protein synthesis, failure to phosphorylate S6 protein in senescent human fibroblasts in response to serum [31] can be one of the reasons for the decline in the rate of protein synthesis observed during aging.…”

Section: Phosphorylationmentioning

confidence: 99%