Restoration of down‐regulated PDGF receptors by TGF‐β in human embryonic fibroblasts

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Abstract
The study of [125I]PDGF-BB binding to normal human embryonic lung fibroblasts, quiescent when cultured at sparsity in the presence of minute concentrations of homologous PDS, reveals approximately 2 × 105 binding sites for PDGF per cell; this number significantly increases during prolonged quiescence of the culture. As late as 48 h after down-regulation of PDGF receptors, the cells restore only partially their capacity to bind PDGF, with aged cells (above CPD 45) responding more rapidly and efficiently than younger ones. TGF-β significantly enhances restoration of PDGF receptors and, in aged cells in particular, its presence results in total receptor recovery within 24 h, suggesting a concerted action of PDGF and TGF-β regulating the proliferation of human fibroblasts in tissue regeneration.