Expression of three recombinant homodimeric isoforms of PDGF in saccharomyces cerevisiae: Evidence for difference in receptor binding and functional activities

Three recombinant homodimeric isoforms of platelet-derived growth factor (PDGF) were produced and purified in milligram quantities by expression of PDGF A-and B-chains in yeast cells. Structural analysis of the purified short and long variants of PDGF-AA (PDGF-AA_S and PDGF-AA_L) and PDGF-BB showed that they had been properly processed and assembled into dimers. PDGF-AA_s and PDGF-AA_L were found to bind only to the PDGF A-type receptor on human fibroblasts, with affinities of 0.1 and 0.2 uM, respectively. PDGF-BB bound to cells with A-and B-type receptors and to cells with B-type receptor only with affinities of 0.6 nM in both cases. Each fibroblast appeared to express about 4-5 times more B-type receptors than A-type receptors. The maximal mitogenic response to PDGF-BB of human fibroblasts was almost 2-fold higher than that induced by either of the two PDGF-AA forms. The three isoforms of PDGF also stimulated growth in soft agar of human fibroblasts with PDGF-BB inducing a higher maximal response.