Prothymosin alpha stimulates Ca2+-dependent phosphorylation of elongation factor 2 in cellular extracts.

The Journal of Biological Chemistry
F V VegaF Dominguez

Abstract

Prothymosin alpha (PTA) stimulates in a dose-dependent manner the phosphorylation of a 105-kDa protein (p105) in cell extracts from different cell types. Protein sequencing and immunological analysis indicated that this protein is elongation factor 2 (EF-2). We propose that calcium/calmodulin-dependent protein kinase III is responsible for the PTA-dependent EF-2 phosphorylation based on the following lines of evidence: (a) Ca2+ is required for the effect; (b) calmodulin enhances the reaction, and calmodulin inhibitors block the phosphorylation; and (c) no phosphorylation is seen in cell extracts depleted of calmodulin-binding proteins. To obtain a strong phosphorylated EF-2 band, we found it necessary to add PTA to cytosolic extracts from synchronized dividing cells in various phases of the cell cycle except in mitosis. Since PTA is a nuclear protein everywhere in the cell cycle except in mitosis, when it is found in the cytoplasm, we hypothesize that, if PTA activates EF-2 phosphorylation in vivo, as present data suggest, its presence in the cytoplasm during mitosis could explain why EF-2 phosphorylation is mainly restricted to that phase of the cell cycle. Moreover, other bands in addition to EF-2 were phosphorylated in a cal...Continue Reading

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Citations

Jul 14, 2011·Cellular and Molecular Neurobiology·Sebok Kumar Halder, Hiroshi Ueda
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Apr 17, 2004·The Journal of Biological Chemistry·Miguel G BlancoJaime Gómez-Márquez
Jun 22, 1999·The Journal of Biological Chemistry·S A EnkemannS L Berger
Nov 23, 2000·Protein Expression and Purification·M W Trumbore, S L Berger

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