Ligand stimulation reduces platelet-derived growth factor beta-receptor susceptibility to tyrosine dephosphorylation

Ligand binding to the platelet-derived growth factor (PDGF) beta -receptor leads to increased receptor tyrosine phosphorylation as a consequence of di merization-induced activation of the intrinsic receptor tyrosine kinase act ivity. In this study we asked whether ligand-stimulated PDGF -receptor tyro sine phosphorylation, to some extent, also involved reduced susceptibility to tyrosine dephosphorylation. To investigate this possibility we compared the sensitivity of ligand-stimulated and nonstimulated forms of tyrosine-ph osphorylated PDGF beta -receptors to dephosphorylation using various prepar ations containing protein-tyrosine phosphatase activity. Ligand-stimulated or unstimulated tyrosine-phosphorylated receptors were obtained after incub ation of cells with pervanadate only or pervanadate, together with PDGF-BB, respectively. Dephosphorylation of receptors immobilized on wheat germ agg lutinin-Sepharose, as well as of receptors in intact cell membranes, was in vestigated under conditions when rephosphorylation did not occur. As compar ed with unstimulated receptors the ligand-stimulated PDGF beta -receptors s howed about 10-fold reduced sensitivity to dephosphorylation by cell membra nes, a recombinant form of the catalytic domain of density-enhanced phospha tase-1, or recombinant protein-tyrosine phosphatase 1B. We conclude that li gand-stimulated forms of the PDGF beta -receptor display a reduced suscepti bility to dephosphorylation. Our findings suggest a novel mechanism whereby ligand stimulation of PDGF beta -receptor, and possibly other tyrosine kin ase receptors, leads to a net increase in receptor tyrosine phosphorylation .