14-3-3 proteins are required for maintenance of Raf-1 phosphorylation and kinase activity

JA Thorson, LWK Yu, AL Hsu, NY Shih… - … and cellular biology, 1998 - Taylor & Francis
JA Thorson, LWK Yu, AL Hsu, NY Shih, PR Graves, JW Tanner, PM Allen, H Piwnica-Worms
Molecular and cellular biology, 1998Taylor & Francis
By binding to serine-phosphorylated proteins, 14-3-3 proteins function as effectors of serine
phosphorylation. The exact mechanism of their action is, however, still largely unknown.
Here we demonstrate a requirement for 14-3-3 for Raf-1 kinase activity and phosphorylation.
Expression of dominant negative forms of 14-3-3 resulted in the loss of a critical Raf-1
phosphorylation, while overexpression of 14-3-3 resulted in enhanced phosphorylation of
this site. 14-3-3 levels, therefore, regulate the stoichiometry of Raf-1 phosphorylation and its …
Abstract
By binding to serine-phosphorylated proteins, 14-3-3 proteins function as effectors of serine phosphorylation. The exact mechanism of their action is, however, still largely unknown. Here we demonstrate a requirement for 14-3-3 for Raf-1 kinase activity and phosphorylation. Expression of dominant negative forms of 14-3-3 resulted in the loss of a critical Raf-1 phosphorylation, while overexpression of 14-3-3 resulted in enhanced phosphorylation of this site. 14-3-3 levels, therefore, regulate the stoichiometry of Raf-1 phosphorylation and its potential activity in the cell. Phosphorylation of Raf-1, however, was insufficient by itself for kinase activity. Removal of 14-3-3 from phosphorylated Raf abrogated kinase activity, whereas addition of 14-3-3 restored it. This supports a paradigm in which the effects of phosphorylation on serine as well as tyrosine residues are mediated by inducible protein-protein interactions.
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