PDGF-induced glycosaminoglycan synthesis is mediated via phosphatidylinositol 3-kinase

• Published in: American journal of physiology. Lung cellular and molecular physiology 1998-05, Vol.274 (5), p.702-L713
• Main Authors: Liu, Jason, Fitzli, Dora, Liu, Mingyao, Tseu, Irene, Caniggia, Isabella, Rotin, Daniela, Post, Martin
• Format: Article
• Language: English
• ISSN: 1040-0605; 1522-1504
• DOI: 10.1152/ajplung.1998.274.5.L702

Medical Research Council Group in Lung Development and Lung Biology Program, Department of Pediatrics, Hospital for Sick Children Research Institute, University of Toronto, Toronto, Ontario, Canada M5G 1X8 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 35 SO 4 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 -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)- 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- 1 and RasGAP followed by their tyrosine phosphorylation failed, however, to activate PLC- 1, protein kinase C (PKC), and Ras. Neither a PLC- 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. platelet-derived growth factor; deoxyribonucleic acid synthesis; fetal lung fibroblasts