IDENTIFICATION OF A DOMAIN WITHIN THE CARBOXYL-TERMINAL REGION OF THEBETA-PLATELET-DERIVED GROWTH-FACTOR (PDGF) RECEPTOR THAT MEDIATES THEHIGH TRANSFORMING ACTIVITY OF PDGF

We have reported previously that a chimeric platelet-derived growth fa ctor receptor (PDGFR) possessing the ligand binding domain of the alph a PDGFR and the intracellular domain of the beta PDGFR (alpha(340)beta (342)R) was markedly more efficient than the wild type alpha PDGFR (al pha RWT) in its ability to enhance PDGF-A transforming activity in NIH /3T3 fibroblasts. To determine the region within the cytoplasmic domai n of beta PDGFR that confers this higher transforming activity, we gen erated several additional alpha/beta PDGFR chimerae. When a chimeric P DGFR possessing the first 933 amino-terminal amino acids from the alph a PDGFR and the final 165 amino acids from the carboxyl-terminal of th e beta PDGFR (alpha(933)beta(942)R) was cotransfected with the PDGF-A gene into NIH/3T3 cells, it showed a similar high efficiency to enhanc e PDGF-A chain transforming activity as alpha(340)beta(342)R. However, when chimeric PDGFRs in which either the kinase insert domain (alpha beta RKI) or the last 79 amino acids from the carboxyl-terminal end of the beta PDGFR (alpha(1024)beta(1028)R) were substituted into alpha P DGFR sequences were cotransfected with PDGF-A, they showed similar low efficiencies in enhancing transforming activity as the alpha RWT. The se results predicted that the 86 amino acids following the tyrosine ki nase 2 domain of beta PDGFR (amino acid residues 942-1027) were respon sible for the higher transforming activity of beta PDGFR. To confirm t his finding, we next constructed a chimera in which amino acid residue s 942-1028 of the beta PDGFR (alpha beta(942-1028)R) were substituted for those in the alpha PDGFR. Cotransfection experiments indicated tha t alpha beta(942-1028)R increased transforming activity of PDGF-A to s imilar extent as the alpha(933)beta(942)R or alpha(340)beta(342)R. The refore, our findings define a critical domain within the noncatalytic region of beta PDGFR intracellular domain that confers the higher focu s forming activity mediated by the beta PDGFR.