Receptor-Like Protein Tyrosine Phosphatase γ (RPTPγ), But Not PTPζ/RPTPβ, Inhibits Nerve-Growth-Factor-Induced Neurite Outgrowth in PC12D Cells

Abstract

Receptor-like protein tyrosine phosphatase γ (RPTPγ) and PTPζ/RPTPβ are RPTPs which structurally resemble each other and form a distinct RPTP family. Both molecules are highly expressed in the central nervous system (CNS), though RPTPγ is distributed also in several peripheral tissues. To date, the functional differences between RPTPγ and PTPζ in neuronal cells have not been made clear because their substrate and ligand molecules have not been fully elucidated. To address this issue, we established PC12D cell transfectants stably expressing rat RPTPγ or PTPζ and analyzed the effects on cellular response to nerve growth factor (NGF). Compared with the parent PC12D cells which extend neurites vigorously in response to NGF, the transfectants expressing RPTPγ showed almost no neurite outgrowth. In contrast, neurite extension in PTPζ-expressing clones on NGF treatment was the same as in parent cells. We investigated differences in tyrosine phosphorylation levels in the cellular proteins in these cells after the NGF treatment before morphological charges appeared. Despite the lack of a response, major proteins and MAP kinase in RPTPγ-expressing PC12D cells displayed normal tyrosine phosphorylation changes on NGF treatment. However, tyrosine phosphorylation levels in the protein components purified with p13^suc1 agarose (p13^suc1 complex) from RPTPγ-expressing cells were different from those of the control cells. (1) Tyrosine-phosphorylation levels of 140- and 117-kD proteins were significantly reduced. (2) Rapid tyrosine phosphorylation of 58-kD protein induced by NGF was absent. (3) Activities of tyrosine kinases and protein kinase C in the p13^suc1 complex were markedly reduced. We found that the p13^suc1 complex also contained cytoskeletal proteins such as MAP2 and neurofilaments, but their phosphorylation levels were not different. These results indicate that RPTPγ and PTPζ have different substrate specificities, and RPTPγ inhibits NGF-induced neurite outgrowth of PC12D cells through modulation of the p13^suc1 complex.