Characterization of the δ2 Glutamate Receptor-binding Protein Delphilin: SPLICING VARIANTS WITH DIFFERENTIAL PALMITOYLATION AND AN ADDITIONAL PDZ DOMAIN

Keiko Matsuda,Shinji Matsuda,Clare M Gladding,Michisuke Yuzaki

doi:10.1074/jbc.m602044200

Abstract

The glutamate receptor delta2 (GluRdelta2) is predominantly expressed at parallel fiber-Purkinje cell postsynapses and plays crucial roles in synaptogenesis and synaptic plasticity. Although the mechanism by which GluRdelta2 functions remains unclear, its lack of channel activity and its role in controlling the endocytosis of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors have suggested that GluRdelta2 may convey signals by interacting with intracellular signaling molecules. Among several proteins that interact with GluRdelta2, delphilin is unique in that it is selectively expressed at parallel fiber-Purkinje cell synapses and that, in addition to a single PDZ domain, it contains a formin homology domain that is thought to regulate actin dynamics. Here, we report a new isoform of delphilin, designated as L-delphilin, that has alternatively spliced N-terminal exons encoding an additional PDZ domain. Although original delphilin, designated S-delphilin, was palmitoylated at the N terminus, this region was spliced out in L-delphilin. As a result, S-delphilin was associated with plasma membranes in COS cells and dendritic spines in hippocampal neurons, whereas L-delphilin formed clusters in soma and dendritic shafts. In addition, S-delphilin, but not L-delphilin, facilitated the expression of GluRdelta2 on the cell surface. These results indicate that, like PSD-95 and GRIP/ABP, delphilin isoforms with differential palmitoylation and clustering capabilities may provide two separate intracellular and surface GluRdelta2 pools and may control GluRdelta2 signaling in Purkinje cells.

Highlights

Numerous spontaneous ataxic mutant mice occur as a result of null mutations in the gene encoding glutamate receptor ␦2 (GluR␦2),2 a member of the ionotropic glutamate receptor family that is predominantly expressed at parallel fiber (PF)-Pur
S-delphilin, but not L-delphilin, facilitated the expression of GluR␦2 on the cell surface. These results indicate that, like postsynaptic density (PSD)-95 and GRIP/ABP, delphilin isoforms with differential palmitoylation and clustering capabilities may provide two separate intracellular and surface GluR␦2 pools and may control GluR␦2 signaling in Purkinje cells
The presence of isoforms with differential palmitoylation and clustering capabilities is analogous to other important PDZ proteins, such as ABP/ GRIP for AMPA receptors [14] and PSD-95 [15], and may point to the central role of delphilin in modulating GluR␦2 signaling in Purkinje cells

Summary

SPLICING VARIANTS WITH DIFFERENTIAL PALMITOYLATION AND AN ADDITIONAL PDZ DOMAIN*

The analysis of PDZ proteins that interact with GluR␦2, such as PSD-93 [10], PTPMEG [11], shank [12], and delphilin [13], is expected to provide clues to the function of GluR␦2 Of these PDZ proteins, delphilin is unique in that it is selectively expressed at PF-Purkinje cells [13] and that in addition to a PDZ domain it contains a formin homology domain, which is thought to control actin dynamics with profilin, and a tyrosine kinase Src. Here, we report a new isoform of delphilin, designated as L-delphilin, which we found while analyzing delphilin signaling. L-delphilin has alternatively spliced N-terminal exons encoding an additional PDZ domain but lacking the kidney 293 cells; PSD, postsynaptic density; LTD, long-term depression; GST, glutathione S-transferase; PF, parallel fiber

Identification of Alternatively Spliced Delphilin

EXPERIMENTAL PROCEDURES

RESULTS