Journal of Neuroscience, Vol 7, 3976-3983, Copyright © 1987 by Society for Neuroscience
Calcium-promoted translocation of protein kinase C to synaptic membranes: relation to the phosphorylation of an endogenous substrate (protein F1) involved in synaptic plasticity
RF Akers and A Routtenberg
Cresap Neuroscience Laboratory, Northwestern University, Evanston, Illinois 60201.
The translocation of protein kinase C between membrane and cytosol has been
implicated in several cellular processes (Kraft and Anderson, 1983; Wooten
and Wrenn, 1984; Akers et al., 1985, 1986; Hirota et al., 1985; Wolf et
al., 1986). We desired to identify potential trigger mechanisms underlying
the translocation of protein kinase C activity to neural membranes
following the synaptic plasticity observed after long- term potentiation
(LTP; Akers et al., 1986). Takai et al. (1979) have suggested an important
role for calcium in protein kinase C translocation; we have therefore
studied the effects of Ca2+ on both the translocation of protein kinase C
activity and the in vitro phosphorylation of its endogenous substrate,
protein F1, in rat hippocampal synaptosomes. Since identical free Ca2+
levels were maintained in subsequent assays of synaptosomal membranes (SPM)
and cytosol preparations, alterations in endogenous enzyme activity and in
vitro phosphorylation were due to the Ca2+ present during treatment of
synaptosomes, and not to the Ca2+ present during assays of enzymatic
activity. This afforded the opportunity to relate directly such enzyme
translocation to endogenous substrate phosphorylation. The major findings
were as follows: 1. Following treatment of synaptosomes with Ca2+, protein
kinase C activity in synaptic membrane and protein F1 in vitro
phosphorylation were elevated in a dose-dependent manner. 2. The greatest
increment in membrane protein kinase C activity and protein F1 in vitro
phosphorylation occurred when Ca2+ was increased from 0.1 to 1.0 microM.
Maximal levels of enzyme activity were seen following treatment with 10
microM Ca2+, and minimum levels were observed following treatment with
EGTA.(ABSTRACT TRUNCATED AT 250 WORDS)