T. Ng et al., Ezrin is a downstream effector of trafficking PKC-integrin complexes involved in the control of cell motility, EMBO J, 20(11), 2001, pp. 2723-2741
Protein kinase C (PKC) a has been implicated in beta1 integrin-mediated cel
l migration. Stable expression of PKC alpha is shown here to enhance wound
closure. This PKC-driven migratory response directly correlates with increa
sed C-terminal threonine phosphorylation of ezrin/moesin/radixin (ERM) at t
he wound edge. Both the wound migratory response and ERM phosphorylation ar
e dependent upon the catalytic function of PKC and are susceptible to inhib
ition by phosphatidylinositol 3-kinase blockade. Upon phorbol 12,13-dibutyr
ate stimulation, green fluorescent protein-PKC alpha and beta1 integrins co
-sediment with ERM proteins in low-density sucrose gradient fractions that
are enriched in transferrin receptors, Using fluorescence lifetime imaging
microscopy, PKC alpha is shown to form a molecular complex with ezrin, and
the PKC-co-precipitated endogenous ERR I is hyperphosphorylated at the C-te
rminal threonine residue, i.e, activated. Electron microscopy showed an enr
ichment of both proteins in plasma membrane protrusions. Finally, overexpre
ssion of the C-terminal threonine phosphorylation site mutant of ezrin has
a dominant inhibitory effect on PKC alpha -induced cell migration. We provi
de the first evidence that PKC alpha or a PKC alpha -associated serine/thre
onine kinase can phosphorylate the ERM C-terminal threonine residue within
a kinase-ezrin molecular complex in vivo.