PDGF-induced glycosaminoglycan synthesis is mediated via phosphatidylinositol 3-kinase.
Platelet-derived growth factor (PDGF)-BB has been shown previously to increase glycosaminoglycan (GAG) synthesis but not DNA synthesis in freshly isolated fetal lung fibroblasts. In the present study, we found that PDGF-BB also enhanced 35SO4 incorporation into the small, soluble proteoglycan biglycan without affecting biglycan's core protein mRNA expression, suggesting that PDGF-BB mainly affects GAG chain elongation and/or sulfation. PDGF-BB-stimulated GAG synthesis was abrogated by tyrphostin 9, a PDGF receptor-associated tyrosine kinase inhibitor, implying that the stimulatory effect is mediated via the PDGF beta-receptor (PDGFR). The intracellular signal transduction pathways that mediate PDGF-BB-stimulated GAG synthesis in fetal lung fibroblasts were investigated. On ligand-induced tyrosine phosphorylation, PDGFR associated with phospholipase C (PLC)-gamma 1, Ras GTPase activating protein (RasGAP), and phosphatidylinositol 3-kinase (PI3K) but not with the Syp-growth factor receptor-bound protein 2-Son of Sevenless complex. Association of PDGFR with PLC-gamma 1 and RasGAP followed by their tyrosine phosphorylation failed, however, to activate PLC-gamma 1, protein kinase C (PKC), and Ras. Neither a PLC-gamma inhibitor, U-73122; a PKC inhibitor, calphostin C; nor a mitogen-activated protein kinase kinase inhibitor, PD-98059, inhibited PDGF-BB-induced GAG synthesis. In contrast, PDGF-BB stimulation triggered PDGFR-associated PI3K activity. Both PDGF-BB-induced PI3K activation and GAG synthesis were abolished by the PI3K inhibitors wortmannin and LY-294002. The results suggest that PI3K is a downstream mediator of PDGF-BB-stimulated GAG synthesis in fetal rat lung fibroblasts.
Liu
J
J
Department of Pediatrics, Hospital for Sick Children Research Institute, University of Toronto, Ontario, Canada.
Fitzli
D
D
Liu
M
M
Tseu
I
I
Caniggia
I
I
Rotin
D
D
Post
M
M
D000818:Animals; D000077214:Becaplermin; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006025:Glycosaminoglycans / Q000096:biosynthesis*; D007527:Isoenzymes / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D051966:Phospholipase C gamma; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011509:Proteoglycans / Q000096:biosynthesis; D020574:Proto-Oncogene Proteins c-sis; D051381:Rats; D017208:Rats, Wistar; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D011994:Recombinant Proteins; D010738:Type C Phospholipases / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
D006025:Glycosaminoglycans; D007527:Isoenzymes; D010982:Platelet-Derived Growth Factor; D011509:Proteoglycans; D020574:Proto-Oncogene Proteins c-sis; D011994:Recombinant Proteins; D000077214:Becaplermin; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D017479:Receptors, Platelet-Derived Growth Factor; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D018631:ras Proteins