IDENTIFICATION OF 2 JUXTAMEMBRANE AUTOPHOSPHORYLATION SITES IN THE PDGF BETA-RECEPTOR - INVOLVEMENT IN THE INTERACTION WITH SRC FAMILY TYROSINE KINASES

Two novel sites of autophosphorylation were localized to the juxtamemb rane segment of the human platelet-derived growth factor (PDGF) beta-r eceptor. To evaluate the importance of these phosphorylation sites, re ceptor mutants were made in which Tyr579, Tyr581 or both were replaced with phenylalanine residues; the receptor mutants were stably express ed in porcine aortic endothelial cells. Compared with the wild-type re ceptor, the Y579F and Y581F mutants were less able to mediate associat ion with and activation of the Src family tyrosine kinases. The abilit y of these phosphorylation sites to mediate directly the binding of th e Src family proteins was also demonstrated by using phosphotyrosine-c ontaining synthetic peptides representing the juxtamembrane sequence o f the receptor. Both the Y579F and Y581F mutants were similar to the w ild-type receptor with regard to their protein tyrosine kinase activit y and ability to induce mitogenicity in response to PDGF-BB. A conclus ive evaluation of the role of the Src family members in signal transdu ction could, however, not be made since our attempt to prevent complet ely the association by mutation of both Tyr579 and Tyr581, resulted in loss of kinase activity and was therefore not informative. The presen t data, together with previous observations, demonstrate a high degree of specificity in the interaction between different autophosphorylati on sites in the PDGF beta-receptor and downstream components in the si gnal transduction pathway.