Mitogenic effect of transforming growth factor β1 on human fibroblasts involves the induction of platelet‐derived growth factor α receptors

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Abstract
Platelet‐derived growth factor (PDGF) and transforming growth factor β (TGF‐β), potent modulators of mesenchymal cell growth and differentiation, are often colocalizable in vivo. Previous in vitro studies in fibroblastic cell lines have shown variable, even antagonistic effects of TGF‐β on the mitogenic action of PDGF. This study demonstrates that in diploid human dermal fibroblasts, TGF‐β1 is weakly mitogenic in the absence of serum or purified growth factors, and that TGF‐β1 potentiates DNA synthesis in PDGF‐stimulated fibroblasts with delayed kinetics when compared to stimulation with PDGF alone. TGF‐β enhances mitogenic potency of all three PDGF isoforms and increases receptor binding of both 125I PDGF‐AA and 125I PDGF‐BB, consistent with the increased expression of the α type PDGF receptor. The induction of PDGF α receptor subunits by TGF‐β may play a role in enhancing the proliferative potential of human fibroblasts in certain physiologic and pathologic conditions.