Mutation of tyrosine residue 857 in the PDGF beta-receptor affects cell proliferation but not migration

Activation of platelet-derived growth factor (PDGF) receptors occurs through ligand-induced dimerization and autophosphorylation. In this study, we investigated the effects of mutation of tyrosine residue 857 (Y857) in the activation loop of the PDGF beta-receptor (PDGFRbeta) to phenylalanine (Y857F). In agreement with previous observations, we found that PDGFRbeta(Y857F) had a severely diminished in vitro kinase activity. However, in vivo the overall amount of tyrosine phosphorylation of PDGFRbeta(Y857F) was similar to that of the wild-type receptor, except for the tyrosine residue 771 (Y771) which displayed a stronger phosphorylation in the mutant receptor. Analysis of the ability to induce signal transduction revealed that the PDGFRbeta(Y857F) mutant had an attenuated activation of Akt and Erk1/2 MAP kinase. In contrast, the mutant receptor efficiently mediated phosphorylation of the ubiquitin-ligase c-Cbl that participates in receptor internalization and degradation, and PLCgamma which has previously been shown to be connected with various cellular responses, including migration. However, the protein tyrosine phosphatase SHP-2, implicated in the PDGF-induced mitogenic response, together with the adaptor proteins Alix and Stam, involved in intracellular sorting of receptor, was not phosphorylated in cells expressing PDGFRbeta(Y857F). We found that both receptor variants were internalized from the cell surface and degraded at a comparable rate. Interestingly, PDGFRbeta(Y857F) was unable to mediate PDGF-BB-induced mitogenic signaling, whereas it could elicit a chemotactic response.