Cloning and expression of a cDNA coding for the human platelet-derived growth factor receptor: evidence for more than one receptor class

The complete nucleotide sequence of a cDNA encoding the human platelet-derived growth factor (PDGF) receptor is presented. The cDNA contains an open reading frame that codes for a protein of 1106 Amino acids. Comparison to the mouse PDGF receptor reveals an overall amino acid sequence identity of 86%. This sequence identity rises to 98% in the cytoplasmic split tyrosine kinase domain. RNA blot hybridization analysis of poly(A)+ RNA from human dermal fibroblasts detects a major (approximately 5.7 kb) and a minor (approximately 4.8 kb) transcript using the cDNA as a probe. Baby hamster kidney cells, transfected with an expression vector containing the receptor cDNA, express an approximately equal to 190-kDa cell surface protein that is recognized by an anti-human PDGF receptor antibody. The recombinant PDGF receptor is functional in the transfected baby hamster kidney cells as demonstrated by ligand-induced phosphorylation of the receptor. Binding properties of the recombinant PDGF receptor were also assessed with pure preparations of BB and AB isoforms of PDGF (i.e., PDGF dimers composed of two B chains or an A and a B chain). Unlike human dermal fibroblasts, which bind both isoforms with high affinity, the transfected baby hamster kidney cells bind only the BB isoform of PDGF with high affinity. This observation is consistent with the existence of more than one PDGF receptor class.