HIGH-AFFINITY BINDING OF PDGF-AA AND PDGF-BB TO NORMAL HUMAN OSTEOBLASTIC CELLS AND MODULATION BY INTERLEUKIN-1

Bone has the capacity for repair and regeneration. The repair process is thought to be locally regulated by growth factors. One of the growth factors that potentially plays a significant role in these processes is platelet-derived growth factor (PDGF). Two different PDGF genes have been identified, PDGF-A and PDGF-B, whose gene products give rise to biologically active dimers. We now report that PDGF-AA and PDGF-BB exhibit saturable binding to normal human osteoblastic cells. By Scatchard analysis we estimate that there are approximately 43,000 PDGF-AA binding sites per cell, with a dissociation constant (K(d)) of 2.2 x 10(-10) M, and 55,000 high-affinity PDGF-BB binding sites per cell, with a K(d) of 1.2 x 10(-10) M. The functional consequence of PDGF binding was also assessed. PDGF-AA and PDGF-BB both stimulated migration of normal human osteoblastic cells and stimulated thymidine incorporation. To gain insight into potential transmodulation of the PDGF response, we investigated the capacity of interleukin-1-beta (IL-1-beta), a cytokine that induces bone resorption, to modulate PDGF binding and PDGF-induced biological activity. IL-1-beta significantly reduced PDGF-AA binding and significantly decreased both PDGF-AA-mediated cell migration and thymidine incorporation. In contrast, IL-1-beta had only a small effect of PDGF-BB binding and PDGF-BB-induced biological activity in normal human osteoblastic cells.