An Antibody Reactive with Domain 4 of the Platelet-derived Growth Factor β Receptor Allows BB Binding while Inhibiting Proliferation by Impairing Receptor Dimerization

A panel of murine monoclonal antibodies was generated against the extracellular domain of the human platelet-derived growth factor (PDGF) β receptor (PDGFRβ). These antibodies were assayed for both the ability to inhibit binding of PDGF BB to PDGFRβ+ cells as well as the capacity to inhibit PDGF BB-mediated mitogenesis. As expected, all antibodies that could prevent PDGF BB binding also inhibited mitogenesis. However one antibody (M4TS.11), with no detectable ability to inhibit PDGF BB binding, was a potent inhibitor of proliferation induced by PDGF BB. Further characterization indicated that M4TS.11 impaired PDGFRβ dimerization, revealing the mechanism by which it prevented PDGF BB-mediated mitogenesis. Using domain deletion mutants of the extracellular portion of PDGFRβ, the determinant recognized by this antibody was localized to the fourth extracellular domain of PDGFRβ, indicating that this domain, which is not involved in ligand binding, actively participates in receptor dimerization and signal transduction. The M4TS.11 antibody could also inhibit PDGF BB-mediated proliferation of responsive cells from both the baboon and the rabbit, indicating the determinant recognized by the antibody is not limited to humans and making it possible to use this antibody to evaluate the therapeutic benefit of interfering with PDGF in animal models of human disease.