PubMed Journals: J Biol Chem
Source: PMID: 8663493
⇦ ⇨ J Biol Chem. 1996 Jul 26;271(30):18217-23.
Involvement of p90rsk in neurite outgrowth
mediated by the cell adhesion molecule L1.
Wong EV(1), Schaefer AW, Landreth G, Lemmon
(1) Department of Neurosciences,
Case Western Reserve University, Cleveland,
Ohio 44106-4975, USA.
L1 is a neural cell adhesion molecule that
has been shown to help guide nascent axons
to their targets. This guidance is based
on specific interactions of L1 with its
binding partners and is likely to involve
signaling cascades that alter cytoskeletal
elements in response to these binding events.
We have examined the phosphorylation of
L1 and the role it may have in L1-directed
neurite outgrowth. Cytosolic extracts from
nerve growth factor-stimulated PC12 cells
were fractionated by anion-exchange chromatography,
and an activity was found that phosphorylated
the cytoplasmic domain of L1. This activity
was then assayed using a battery of L1-derived
synthetic peptides. Based on these peptide
assays and sequencing of radiolabeled L1
proteolytic fragments, the phosphorylation
site was determined to be Ser1152. Western
blot analysis demonstrated that the L1 kinase
activity from PC12 cells that phosphorylated
this site was co-eluted with the S6 kinase,
p90(rsk). Moreover, S6 kinase activity and
p90(rsk) immunoreactivity co-immunoprecipitate
with L1 from brain, and metabolic labeling
studies have demonstrated that Ser1152 is
phosphorylated in vivo in the developing
rat brain. The phosphorylation site is located
in a region of high conservation between
mammalian L1 sequences as well as L1-related
molecules in vertebrates from fish to birds.
We performed studies to investigate the
functional significance of this phosphorylation.
Neurons were loaded with peptides that encompass
the phosphorylation site, as well as the
flanking regions, and their effects on neurite
outgrowth were observed. The peptides, which
include Ser1152, inhibit neurite outgrowth
on L1 but not on a control substrate, laminin.
A nonphosphorylatable peptide carrying a
Ser to Ala mutation did not affect neurite
outgrowth on either substrate. These data
demonstrate that the membrane-proximal 15
amino acids of the cytoplasmic domain of
L1 are important for neurite outgrowth on
L1, and the interactions it mediates may
be regulated by phosphorylation of Ser1152.
PMID: 8663493 [Indexed for MEDLINE]