Journal of Neuroscience, Vol 9, 381-389, Copyright © 1989 by Society for Neuroscience
The two major phosphoproteins in growth cones are probably identical to two protein kinase C substrates correlated with persistence of long- term potentiation
RB Nelson, DJ Linden, C Hyman, KH Pfenninger and A Routtenberg
Cresap Neuroscience Laboratory, Northwestern University, Evanston, Illinois 60201.
Regulation of neural protein kinase C (PKC) activity appears to directly
affect the persistence of long-term potentiation (LTP; Akers and
Routtenberg, 1985; Lovinger et al., 1985, 1986, 1987; Routtenberg et al.,
1985, 1986; Akers et al., 1986; Linden et al., 1987), a model of neural
plasticity (Bliss and Lomo, 1973). In addition, the in vitro
phosphorylation of a brain-specific PKC substrate, protein F1 (Mr 47 kDa,
pl 4.5), has been directly correlated with persistence of LTP (Lovinger et
al., 1986). Because PKC has been implicated in neurite outgrowth and is
present at high levels in growth cone-rich areas of fetal brain, we
investigated and characterized PKC substrates in a preparation of isolated
nerve growth cone fragments from fetal rat brain and compared them with PKC
substrates found in adult rat hippocampus. Four major proteins in the
growth cone preparation showed endogenous phosphorylation levels at least
10-fold greater than any other phosphoproteins. Three of these 4
phosphoproteins, termed pp40, pp46, and pp80 (Katz et al., 1985), were
phosphorylated by exogenous PKC in a dose-dependent manner, indicating that
PKC activity might be of particular importance relative to other kinases in
growth cone function. The 2 most highly labeled PKC substrates, pp46 and
pp80, comigrated on 2-dimensional gels with the adult hippocampal proteins
F1 and "80k" (Mr 78-80 kDa, pl 4.0), respectively. In addition,
similarities in charge heterogeneity, 2-dimensional phosphopeptide maps,
and increased phosphorylation in the presence of exogenous PKC or PKC
stimulators suggest that protein F1 and 80k are highly homologous to, if
not identical to, pp46 and pp80, respectively.(ABSTRACT TRUNCATED AT 250
WORDS)