Site-selective Dephosphorylation of the Platelet-derived Growth Factor β-Receptor by the Receptor-like Protein-tyrosine Phosphatase DEP-1

Ligand stimulation of PDGF β-receptors leads to autophosphorylation of the regulatory tyrosine 857 and of tyrosine residues that in their phosphorylated form serve as docking sites for Src homology 2 domain-containing proteins. Regulation of the PDGF β-receptor by protein-tyrosine phosphatases is poorly understood. We have investigated PDGF β-receptor dephosphorylation by receptor-like protein-tyrosine phosphatase DEP-1 using a cell line with inducible DEP-1 expression and by characterizing in vitro dephosphorylation of the PDGF β-receptor and of receptor-derived phosphopeptides by DEP-1. After DEP-1 induction PDGF β-receptor·DEP-1 complexes and reduced receptor tyrosine phosphorylation were observed. Phosphopeptide analysis of the PDGF β-receptors from DEP-1-expressing cells and of the receptors dephosphorylated in vitro by DEP-1 demonstrated that dephosphorylation of autophosphorylation sites of the receptor differed and revealed that the regulatory Tyr(P) 857 was not a preferred site for DEP-1 dephosphorylation. When dephosphorylation of synthetic receptor-derived peptides was analyzed, the selectivity was reproduced, indicating that amino acid sequence surrounding the phosphorylation sites is the major determinant of selectivity. This notion is supported by the observation that the poorly dephosphorylated Tyr(P) 562 and Tyr(P) 857 , in contrast to other analyzed phosphorylation sites, are surrounded by basic amino acid residues at positions −4 and +3 relative to the tyrosine residue. Our study demonstrates that DEP-1 dephosphorylation of the PDGF β-receptor is site-selective and may lead to modulation, rather than general attenuation, of signaling.