Signal transduction of chondroitin sulfate proteoglycans and neuronal network formation

PTPζ是一种受体型蛋白酪氨酸磷酸酶，以肝素结合生长因子多营养因子为配体，在小脑浦肯野细胞的形态发生中起重要作用。在这项研究中，我们研究了PTPζ和DNER之间的功能相互作用，DNER是浦肯野细胞中高度表达的Delta/ notch样受体。PTPζ和DNER在浦肯野细胞的树突轴和表达这两种蛋白的COS-7转染物中表现出斑片状共定位。免疫沉淀实验表明，PTPζ与DNER在体内外均形成复合物。DNER细胞内区域的几个酪氨酸残基，包括酪氨酸分类基序内和邻近的残基被磷酸化，并且很容易被PTPζ催化结构域去磷酸化。基于酪氨酸的分类基序在DNER的内吞作用和细胞内运输中起着关键作用，酪氨酸磷酸化和该基序的破坏导致DNER在表达ptpζ细胞的质膜上积累。DNER在神经- 2a细胞质膜上的积累导致了包括突起延长在内的形态学改变。多养蛋白抑制DNER的内吞作用和DNER诱导的对神经2a细胞突起生长的抑制。这些观察结果表明，多营养蛋白- ptpζ信号通过改变DNER的细胞内转运来调节浦肯野细胞的形态发生。

PTPζ, a receptor-type protein tyrosine phosphatase, uses a heparin-binding growth factor pleiotrophin as a ligand and play important roles in the morphogenesis of cerebellar Purkinje cells. In this study, we studied functional interaction between PTPζ and DNER, a Delta/Notch-like receptor highly expressed in Purkinje cells. PTPζ and DNER displayed patchy co-localization in the dendritic shafts of Purkinje cells and in the COS-7 transfectants expressing both proteins. Immunoprecipitation experiments indicated that PTPζ and DNER formed complex both in vivo and in vitro. Several tyrosine residues in the intracellular region of DNER including the ones in and adjacent to the tyrosine-based sorting motif were phosphorylated, and were easily dephosphorylated by the PTPζ catalytic domain. The tyrosine-based sorting motif played critical roles in the endocytosis and intracellular transport of DNER, and tyrosine phosphorylation and destruction of this motif resulted in the accumulation of DNER on the plasma membrane of the PTPζ-expressing cells. Accumulation of DNER on the plasma membrane of Neuro-2A cells led to the morphological changes including extension of processes. Pleiotrophin suppressed the endocytosis of DNER and DNER-induced inhibition of neurite outgrowth of Neuro-2A cells. These observations suggests that pleiotrophin-PTPζ signaling regulates the morphogenesis of Purkinje cells by modifying the intracellular transport of DNER.