RT Journal Article
SR Electronic
T1 Phosphorylation of Homer3 by Calcium/Calmodulin-Dependent Kinase II Regulates a Coupling State of Its Target Molecules in Purkinje Cells
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 5369
OP 5382
DO 10.1523/JNEUROSCI.4738-07.2008
VO 28
IS 20
A1 Akihiro Mizutani
A1 Yukiko Kuroda
A1 Akira Futatsugi
A1 Teiichi Furuichi
A1 Katsuhiko Mikoshiba
YR 2008
UL http://www.jneurosci.org/content/28/20/5369.abstract
AB Homer proteins are components of postsynaptic density (PSD) and play a crucial role in coupling diverse target molecules. However, the regulatory aspect of Homer-mediated coupling has been addressed only about a dominant-negative effect of Homer1a, which requires de novo gene expression. Here, we present evidence that Homer-mediated coupling is regulated by its phosphorylation state. We found that Homer3, the predominant isoform in Purkinje cells, is phosphorylated by calcium/calmodulin-dependent protein kinase II (CaMKII) both in vitro and in vivo. Biochemical fractionation with phosphor-specific antibodies revealed the presence of phosphorylated Homer3 in the cytosolic fraction in contrast to high levels of nonphosphorylated Homer3 in PSD. In P/Q-type voltage-gated-Ca2+ channel knock-out mice, in which CaMKII activation was reduced, the levels of Homer3 phosphorylation and the soluble form of Homer 3 were markedly lower. Furthermore, both robust phosphorylation of Homer3 and its dissociation from metabotropic glutamate receptor 1α (mGluR1α) were triggered by depolarization in primary cultured Purkinje cells, and these events were inhibited by CaMKII inhibitor. An in vitro binding kinetic analysis revealed that these phosphorylation-dependent events were attributable to a decrease in the affinity of phosphorylated Homer3 for its ligand. In a heterologous system, the Ca2+ signaling pattern induced by mGluR1α activation was modulated by the Homer3 phosphorylation state. Together, these findings suggested that Homer3 in Purkinje cells might function as a reversible coupler regulated by CaMKII phosphorylation and that the phosphorylation is capable of regulating the postsynaptic molecular architecture in response to synaptic activity.