This paper presents evidence that a member of the L1 family of
ankyrin-binding
cell adhesion molecules is a substrate for
protein tyrosine kinase(s) and
phosphatase(s), identifies the highly conserved FIGQY
tyrosine in the cytoplasmic domain as the principal site of phosphorylation, and demonstrates that phosphorylation of the FIGQY
tyrosine abolishes
ankyrin-binding activity. Neurofascin expressed in
neuroblastoma cells is subject to
tyrosine phosphorylation after activation of
tyrosine kinases by
NGF or bFGF or inactivation of
tyrosine phosphatases with
vanadate or
dephostatin. Furthermore, both neurofascin and the related molecule Nr-CAM are
tyrosine phosphorylated in a developmentally regulated pattern in rat brain. The FIGQY sequence is present in the cytoplasmic domains of all members of the L1 family of
neural cell adhesion molecules. Phosphorylation of the FIGQY
tyrosine abolishes
ankyrin binding, as determined by coimmunoprecipitation of endogenous
ankyrin and in vitro
ankyrin-binding assays. Measurements of fluorescence recovery after photobleaching demonstrate that phosphorylation of the FIGQY
tyrosine also increases lateral mobility of neurofascin expressed in
neuroblastoma cells to the same extent as removal of the cytoplasmic domain.
Ankyrin binding, therefore, appears to regulate the dynamic behavior of neurofascin and is the target for regulation by
tyrosine phosphorylation in response to external signals. These findings suggest that
tyrosine phosphorylation at the FIGQY site represents a highly conserved mechanism, used by the entire class of L1-related
cell adhesion molecules, for regulation of
ankyrin-dependent connections to the
spectrin skeleton.