Receptor binding of PDGF‐AA and PDGF‐BB, and the modulation of PDGF receptors by TGF‐β, in human periodontal ligament cells

The growth factors PDGF‐AA and PDGF‐BB have previously been shown to be potent mitogens for human periodontal ligament (hPDL) cells in vitro. Additionally, the mitogenic response to PDGF‐AA has been shown to be specifically inhibited by TGF‐β. The purpose of the present investigation was to examine the binding of PDGF‐AA and PDGF‐BB, and the modulation of PDGF binding by TGF‐β, in hPDL cells. Scatchard analysis identified an average of 32,000 PDGF‐AA high‐affinity binding sites per cell with a dissociation constant (K_d) of 0.66 nM and an average of 36,000 PDGF‐BB binding sites per cell with a dissociation constant (k_d) of 0.44 nM. After treatment with TGF‐β, the receptor number for PDGF‐AA was found to specifically decrease by approximately 50%, with no change in binding affinity. This reduced number of binding sites was shown to correlate with both a decrease in levels of receptor tyrosine phosphorylation and a decreased number of α receptor subunits. Northern blot analysis identified the TGF‐β‐mediated decrease in PDGF α receptor subunit mRNA levels. PDGF‐BB showed little change in the number of binding sites or in the binding affinity with TGF‐β treatment, and the data were consistent with an increase in the number of β receptor subunits. These results demonstrate nearly equivalent numbers of receptors for both PDGF‐AA and PDGF‐BB in hPDL cells. Also, modulation of PDGF binding, by TFG‐β, was shown to result in a reduced number of α receptor subunits with an increase in the number of β receptor subunits. © 1995 Wiley‐Liss, Inc.