Summary
Contactin-associated protein 2 (Caspr2) is a neuronal membrane protein that is mutated in autism and related disorders. Although it is highly enriched at juxtaparanodes of Ranvier where it is essential for Shaker-type K+ channel clustering, little is known about its function and regulation. In the present study, we examined the polarized expression of Caspr2 in hippocampal neurons using extracellular hemagglutinin (HA)-tagged Caspr2 constructs. We found that Caspr2 was targeted to the axonal surface, but colocalized with early endosomes in the somatodendritic compartment. The inhibition of endocytosis using a Dynamin-1 mutant or treatment with Dynasore prevented Caspr2 internalization from the dendrites and cell body. We identified a short sequence included into the 4.1B-binding domain that is required for the endocytosis of Caspr2. This sequence contains a protein kinase C (PKC) substrate motif on Thr1292, and point mutation of this residue or treatment with a PKC inhibitor prevented the somatodendritic internalization of Caspr2. Thus, the PKC-dependent trafficking of Caspr2 underlies its polarized expression in hippocampal neurons.
Footnotes
Supplementary material available online at http://jcs.biologists.org/cgi/content/full/122/18/3403/DC1
We wish to thank Marion Benoist, Bénédicte Dargent, Christophe Leterrier and Jérôme Devaux for helpful discussions, Marie-Pierre Blanchard and Christophe Leterrier for help with videomicroscopy. This work was supported by the Agence Nationale de la Recherche (C.F.-S. and L.G.), Association pour la Recherche sur la Sclérose en Plaques (fellowship to C.B.), and the National Multiple Sclerosis Society (C.F.-S. and L.G.).
- Accepted July 13, 2009.
- © The Company of Biologists Limited 2009
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