Protein tyrosine phosphatase (PTP) is a receptor type protein tyrosine phosphatase that uses pleiotrophin as a ligand. Pleiotrophin inactivates the phosphatase activity of PTP, resulting in the increase of tyrosine phosphorylation levels of its substrates. We studied the functional interaction between PTP and DNER, a Notch-related transmembrane protein highly expressed in cerebellar Purkinje cells. PTP and DNER displayed patchy colocalization in the dendrites of Purkinje cells, and immunoprecipitation experiments indicated that these proteins formed complexes. Several tyrosine residues in and adjacent to the tyrosine-based and the second C-terminal sorting motifs of DNER were phosphorylated and were dephosphorylated by PTP, and phosphorylation of these tyrosine residues resulted in the accumulation of DNER on the plasma membrane. DNER mutants lacking sorting motifs accumulated on the plasma membrane of Purkinje cells and Neuro-2A cells and induced their process extension. While normal DNER was actively endocytosed and inhibited the retinoic-acid-induced neurite outgrowth of Neuro-2A cells, pleiotrophin stimulation increased the tyrosine phosphorylation level of DNER and suppressed the endocytosis of this protein, which led to the reversal of this inhibition, thus allowing neurite extension. These observations suggest that pleiotrophin-PTP signaling controls subcellular localization of DNER and thereby regulates neuritogenesis.Protein tyrosine phosphatase (PTP), also known as RPTP/␤, is a receptor type protein tyrosine phosphatase that is synthesized as a chondroitin sulfate proteoglycan (12,16,17,21,28,32). There are three major splice variants of this molecule, the full-length form (PTP-A), the short receptor form (PTP-B), and the secreted form (phosphacan) (Fig.

J. Neurochem. (2010) 113, 1598–1610. Abstract The targeting of membrane proteins into axons and dendrites is of critical importance for directional signal transmission within specific neural circuits. Many dendritic proteins have been shown to reach the somatodendritic membrane based on selective sorting and transport of carrier vesicles. Using rat hippocampal neurons in culture, we investigated the trafficking pathways of Delta/Notch‐like EGF‐related receptor (DNER), a transmembrane Notch ligand which is specifically expressed in CNS dendrites. Mutations in the cytoplasmic domain of DNER that abolished somatodendritic localization also increased its surface expression. Furthermore, inhibition of endocytosis resulted in disruption of the somatodendritic localization of DNER, indicating that the somatodendritic targeting of DNER is dependent on endocytosis. The DNER cytoplasmic domain binds to a clathrin adaptor protein complex‐2 via a proximal tyrosine motif and a 40 amino acid stretch in the mid‐domain, but not by the C‐terminal tail. Molecular and pharmacological inhibition revealed that the surface expression of DNER is regulated by clathrin‐dependent and ‐independent endocytosis. In contrast, the somatodendritic targeting of DNER is predominantly regulated by clathrin‐ and adaptor protein complex‐2‐independent endocytosis via the C‐terminal tail of DNER. Our data suggest that clathrin‐independent endocytosis is critical for the polarized targeting of somatodendritic proteins.

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