Abstract
Ligand binding to the platelet-derived growth factor (PDGF) beta-receptor leads to increased receptor tyrosine phosphorylation as a consequence of dimerization-induced activation of the intrinsic receptor tyrosine kinase activity. In this study we asked whether ligand-stimulated PDGF beta-receptor tyrosine phosphorylation, to some extent, also involved reduced susceptibility to tyrosine dephosphorylation. To investigate this possibility we compared the sensitivity of ligand-stimulated and non-stimulated forms of tyrosine-phosphorylated PDGF beta-receptors to dephosphorylation using various preparations containing protein-tyrosine phosphatase activity. Ligand-stimulated or unstimulated tyrosine-phosphorylated receptors were obtained after incubation of cells with pervanadate only or pervanadate, together with PDGF-BB, respectively. Dephosphorylation of receptors immobilized on wheat germ agglutinin-Sepharose, as well as of receptors in intact cell membranes, was investigated under conditions when rephosphorylation did not occur. As compared with unstimulated receptors the ligand-stimulated PDGF beta-receptors showed about 10-fold reduced sensitivity to dephosphorylation by cell membranes, a recombinant form of the catalytic domain of density-enhanced phosphatase-1, or recombinant protein-tyrosine phosphatase 1B. We conclude that ligand-stimulated forms of the PDGF beta-receptor display a reduced susceptibility to dephosphorylation. Our findings suggest a novel mechanism whereby ligand stimulation of PDGF beta-receptor, and possibly other tyrosine kinase receptors, leads to a net increase in receptor tyrosine phosphorylation.
Highlights
Ligand binding to the platelet-derived growth factor (PDGF) -receptor leads to increased receptor tyrosine phosphorylation as a consequence of dimerizationinduced activation of the intrinsic receptor tyrosine kinase activity
Antisense studies have demonstrated increased signaling via receptors for insulin, epidermal growth factor (EGF), and hepatocyte growth factor after attenuation of expression of the receptor-like protein-tyrosine phosphatases (PTPs) LAR [5,6,7], and disruption of PTP1B in mice results in enhanced insulin sensitivity [8, 9]
To investigate whether receptors occurred as monomers or dimers after stimulation with PDGF-BB alone, pervanadate alone, or pervanadate, together with PDGF-BB, cross-linking of cell-surface proteins was performed, and WGASepharose fractions were isolated
Summary
Ligand binding to the platelet-derived growth factor (PDGF) -receptor leads to increased receptor tyrosine phosphorylation as a consequence of dimerizationinduced activation of the intrinsic receptor tyrosine kinase activity. To investigate this possibility we compared the sensitivity of ligand-stimulated and nonstimulated forms of tyrosine-phosphorylated PDGF -receptors to dephosphorylation using various preparations containing protein-tyrosine phosphatase activity. Ligand-stimulated or unstimulated tyrosine-phosphorylated receptors were obtained after incubation of cells with pervanadate only or pervanadate, together with PDGF-BB, respectively.
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