Platelet-derived growth factor (PDGF) stimulates PDGF receptor subunit dimerization and intersubunit trans-phosphorylation.
High affinity binding of platelet-derived growth factor (PDGF) has been proposed to involve the interaction of the dimeric PDGF ligand with two receptor subunits, designated alpha and beta. We have cloned and expressed a human PDGF receptor cDNA which differs in sequence from the beta-subunit and which has the PDGF binding properties and monoclonal antibody recognition, predicted for the alpha-subunit. Scatchard analysis indicated that PDGF-AA and PDGF-AB bound to transfected alpha-subunits with affinities of Kd = 0.06 and 0.05 nM, respectively. PDGF-BB bound with a significantly lower affinity (Kd = 0.4 nM). Nevertheless, this affinity is still great enough to mediate substantial PDGF-BB binding at physiological concentrations and would be considered to be "high affinity." We have used wild-type and kinase-inactive human beta-subunits to show that PDGF binding promotes receptor subunit dimerization in intact cells. In addition, we found that PDGF stimulates tyrosine phosphorylation of the kinase-inactive beta-subunit when it is expressed with alpha-subunits. The kinase-inactive beta-subunits were phosphorylated at tyrosine 857 and 751, the major phosphorylation sites of the wild-type beta-subunit, indicating either that intra- and intermolecular phosphorylation occurs on the same sites, or that a significant fraction of receptor tyrosine phosphorylation is intermolecular.
Kelly
J D
JD
Department of Pathology, University of Washington, Seattle 98195.
Haldeman
B A
BA
Grant
F J
FJ
Murray
M J
MJ
Seifert
R A
RA
Bowen-Pope
D F
DF
Cooper
J A
JA
Kazlauskas
A
A
D000818:Animals; D003001:Cloning, Molecular; D006224:Cricetinae; D004247:DNA / Q000235:genetics; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D010766:Phosphorylation; D019000:Phosphotyrosine; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D011940:Receptor Aggregation; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017479:Receptors, Platelet-Derived Growth Factor; D011994:Recombinant Proteins / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D046911:Macromolecular Substances; D010982:Platelet-Derived Growth Factor; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; D019000:Phosphotyrosine; D014443:Tyrosine; D004247:DNA; D011505:Protein-Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor