Differential binding, biological and biochemical actions of recombinant PDGF AA, AB, and BB molecules on connective tissue cells

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Abstract
We have compared the biological and biochemical properties of recombinant PDGF AA, AB, and BB using three types of fibroblastic cells: NIH/3T3, human skin fibroblast, and fetal bovine aortic smooth muscle. PDGF binding, receptor autophosphorylation, phosphatidyl inositol hydrolysis, as well as chemotactic and mitogenic responses of the cells were analyzed. PDGF‐AB and PDGF‐BB showed similar receptor binding, receptor autophosphorylation, and potent biological activity for all three of the cell types tested. In contrast, PDGF‐AA was biologically active only for the NIH/3T3 cells in which binding sites for PDGF‐AA were abundant, but was inactive for bovine aortic smooth muscle cells and human skin fibroblasts in which binding sites for PDGF‐AA were absent. PDGF‐AA could not induce any biochemical changes in the human skin fibroblasts or smooth muscle cells. Western blot studies with anti‐Type α and β PDGF receptor antibodies indicate that the NIH/3T3 cells contained both PDGF α and β receptors, whereas the human skin fibroblasts and bovine smooth muscle cells contained only detectable levels of β receptors. These results indicate that cells possessing high levels of PDGF β receptors only are capable of responding equally well to either PDGF AB or BB.