Receptor-Type Protein Tyrosine Phosphatase -Pleiotrophin Signaling Controls Endocytic Trafficking of DNER that Regulates Neuritogenesis

Department of Developmental Neuroscience, Tokyo Metropolitan Institute for Neuroscience, Tokyo 183-8526, Japan; Laboratory for Neural Cell Polarity, RIKEN Brain Science Institute, Saitama 351-0198, Japan

^* To whom correspondence should be addressed. Email: maedan{at}tmin.ac.jp.

	Abstract

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 co-localization 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 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.