Transforming growth factor beta 1 downregulates the platelet-derived growth factor alpha-receptor subtype on human lung fibroblasts in vitro.
Fibroblasts are the central target cell in pulmonary fibrotic diseases, and their proliferation is mediated largely by platelet-derived growth factor (PDGF) isoforms secreted by activated lung macrophages. Several other macrophage-derived cytokines that are increased during fibrogenesis, including interleukin-1 beta and transforming growth factor-beta 1 (TGF-beta 1), could potentially modulate the mitogenic and chemotactic activity of PDGF by altering the expression of cell-surface PDGF receptors on fibroblasts. The PDGF receptor system on fibroblasts from a variety of tissues shows heterogeneous responses to TGF-beta 1. Lung fibroblasts have not been investigated in this regard. TGF-beta 1 downregulated the gene expression of the 6.5 kb PDGF-alpha receptor (PDGF-R alpha) transcript in normal human lung fibroblasts in a concentration-dependent fashion that was maximal at 3 ng/ml TGF-beta 1; this corresponded with a decrease in cell-surface PDGF-R alpha as measured by radioligand binding assays using [125I]PDGF-AA. The TGF-beta 1-induced down-regulation of the PDGF-R alpha gene was rapid (maximal suppression by 2 h post-treatment) and preceded the decrease in cell-surface alpha-receptor (maximal reduction by 6 h post-treatment). TGF-beta 1 treatment did not alter the rate of PDGF-R alpha mRNA degradation following the inhibition of transcription using actinomycin D, indicating that TGF-beta 1 increases PDGF-R alpha transcription. Scatchard analysis of saturation binding data showed that TGF-beta 1 decreased the number of [125I]PDGF-AA binding sites 5-fold without affecting receptor affinity. [125I]PDGF-AB binding sites were downregulated approximately 25%, and the number of [125I]PDGF-BB binding sites was not changed by TGF-beta 1 treatment, indicating that the PDGF-beta receptor was not affected. TGF-beta 1 reduced the mitogenic and chemotactic response to PDGF-AA by > 90%, whereas these biologic response to PDGF-AB and PDGF-BB were inhibited 50% to 80%. The proliferative and chemotactic responses of fibroblasts during tissue remodeling or during lung fibrosis are likely controlled by a complex network involving PDGF isoforms and cytokines that modify the PDGF receptor system.
Bonner
J C
JC
Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Badgett
A
A
Lindroos
P M
PM
Osornio-Vargas
A R
AR
D000077214:Becaplermin; D002478:Cells, Cultured; D002633:Chemotaxis / Q000187:drug effects; D004247:DNA / Q000096:biosynthesis; D003609:Dactinomycin / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects*; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008168:Lung; D008934:Mitogens / Q000494:pharmacology; D010982:Platelet-Derived Growth Factor / Q000378:metabolism / Q000494:pharmacology; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism; D020796:Receptor, Platelet-Derived Growth Factor alpha; D017479:Receptors, Platelet-Derived Growth Factor / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D008934:Mitogens; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; C075278:platelet-derived growth factor A; C095477:platelet-derived growth factor AB; D000077214:Becaplermin; D003609:Dactinomycin; D004815:Epidermal Growth Factor; D004247:DNA; D020796:Receptor, Platelet-Derived Growth Factor alpha; D017479:Receptors, Platelet-Derived Growth Factor