Site-selective dephosphorylation of the platelet-derived growth factor beta-receptor by the receptor-like protein-tyrosine phosphatase DEP-1

Ligand stimulation of PDGF P-receptors leads to autophosphorylation of the regulatory tyrosine 857 and of tyrosine residues that in their phosphorylat ed form serve as docking sites for Src homology 2 domain-containing protein s. Regulation of the PDGF beta-receptor by protein-tyrosine phosphatases is poorly understood. We have investigated PDGF beta-receptor dephosphorylati on by receptor-like protein-tyrosine phosphatase DEP-1 using a cell line wi th inducible DEP-1 expression and by characterizing in vitro dephosphorylat ion of the PDGF beta-receptor and of receptor-derived phosphopeptides by DE P-1. After DEP-1 induction PDGF beta-receptor DEP-1 complexes and reduced r eceptor tyrosine phosphorylation were observed. Phosphopeptide analysis of the PDGF P-receptors from DEP-1-expressing cells and of the receptors depho sphorylated in vitro by DEP-1 demonstrated that dephosphorylation of autoph osphorylation sites of the receptor differed and revealed that the regulato ry Tyr(p)(857) was not a preferred site for DEP-1 dephosphorylation, When d ephosphorylation of synthetic receptor-derived peptides was analyzed, the s electivity was reproduced, indicating that amino acid sequence surrounding the phosphorylation sites is the major determinant of selectivity. This not ion 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 relativ e to the tyrosine residue. Our study demonstrates that DEP-1 dephosphorylat ion of the PDGF beta-receptor is site-selective and may lead to modulation, rather than general attenuation, of signaling.