Identification of a domain within the carboxyl-terminal region of the beta platelet-derived growth factor (PDGF) receptor that mediates the high transforming activity of PDGF

We have reported previously that a chimeric platelet-derived growth factor receptor (PDGFR) possessing the ligand binding domain of the alpha PDGFR and the intracellular domain of the beta PDGFR (alpha(340)beta(342)R) was markedly more efficient than the wild type alpha PDGFR (alpha RWT) in its ability to enhance PDGF-A transforming activity in NIH/3T3 fibroblasts. To determine the region within the cytoplasmic domain of beta PDGFR that confers this higher transforming activity, we generated several additional alpha/beta PDGFR chimerae. When a chimeric PDGFR possessing the first 933 amino-terminal amino acids from the alpha PDGFR and the final 165 amino acids from the carboxyl-terminal of the 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 enhance 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 PDGFR sequences were cotransfected with PDGF-A, they showed similar low efficiencies in enhancing transforming activity as the alpha RWT. These results predicted that the 86 amino acids following the tyrosine kinase 2 domain of beta PDGFR (amino acid residues 942-1027) were responsible for the higher transforming activity of beta PDGFR. To confirm this finding, we next constructed a chimera in which amino acid residues 942-1028 of the beta PDGFR (alpha beta(942-1028)R) were substituted for those in the alpha PDGFR. Cotransfection experiments indicated that alpha beta(942-1028)R increased transforming activity of PDGF-A to similar extent as the alpha(933)beta(942)R or alpha(340)beta(342)R. Therefore, our findings define a critical domain within the noncatalytic region of beta PDGFR intracellular domain that confers the higher focus forming activity mediated by the beta PDGFR.