title: TGF-beta regulates differentially the proliferation of fetal and adult human skin fibroblasts via the activation of PKA and the autocrine action of FGF-2.
abstract: Transforming growth factor-beta (TGF-beta) is a potent regulator of cell proliferation; interestingly its action is clearly cell type-dependent. In particular, it inhibits epithelial and endothelial cells' proliferation, while its action on many mesenchymal cells has been reported to be stimulatory. In this direction, we have recently shown that TGF-beta regulates the proliferation of normal human skin fibroblasts according to their developmental origin: i.e. it inhibits fetal fibroblasts, while it stimulates the proliferation of adult ones. Here, we present evidence on the mechanisms underlying this differential action. Concerning fetal fibroblasts, we have found that TGF-beta activates Protein Kinase A (PKA) and induces the expression of the cyclin-dependent kinase inhibitors (CKIs) p21(CIP1/WAF1) and p15(INK4B). Moreover, the specific PKA inhibitor H-89 blocks the induction of both CKIs and annuls the TGF-beta-mediated inhibitory effect, indicating the central role of PKA in this process. In contrast, in adult cells no PKA activation is observed. Moreover, TGF-beta stimulates cell proliferation by activating the MEK-ERK pathway, as the MEK inhibitor PD98059 blocks this effect. A specific neutralizing antibody against Fibroblast Growth Factor-2 (FGF-2) inhibits both ERK activation and the mitogenic activity of TGF-beta, indicating that the latter establishes an autocrine loop, via FGF-2, leading to cell proliferation. This loop requires FGF receptor-1 (FGFR-1), as its down-regulation by siRNA approach prevents TGF-beta from stimulating ERK-1/2 activation and DNA synthesis. In conclusion, the differential proliferative response of fetal and adult normal human skin fibroblasts to TGF-beta is regulated by distinct signaling pathways and furthermore it may provide information on the bimodal effect of this factor on cell proliferation, in general.
authors.affiliation: Laboratory of Cell Proliferation and Ageing, Institute of Biology, National Centre for Scientific Research Demokritos, 153 10 Athens, Greece.
authors.forename: Christina C
authors.initials: CC
authors.lastname: Giannouli
authors.forename: Dimitris
authors.initials: D
authors.lastname: Kletsas
mesh_terms: D000328:Adult; D000818:Animals; D019898:Autocrine Communication / Q000502:physiology*; D049109:Cell Proliferation; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D050762:Cyclin-Dependent Kinase Inhibitor p15 / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D051496:Receptor, Fibroblast Growth Factor, Type 1 / Q000378:metabolism; D012867:Skin / Q000166:cytology*; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D050762:Cyclin-Dependent Kinase Inhibitor p15; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004791:Enzyme Inhibitors; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D016222:Fibroblast Growth Factor 2; D004247:DNA; D051496:Receptor, Fibroblast Growth Factor, Type 1; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases