Liu J, Fitzli D, Liu M, Tseu I, Caniggia I, Rotin D, Post M
Department of Pediatrics, Hospital for Sick Children Research Institute, University of Toronto, Ontario, Canada.
Am J Physiol. 1998 May;274(5):L702-13. doi: 10.1152/ajplung.1998.274.5.L702.
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.
血小板衍生生长因子（PDGF）-BB先前已被证明可增加新鲜分离的胎肺成纤维细胞中糖胺聚糖（GAG）的合成，但不影响DNA合成。在本研究中，我们发现PDGF-BB还可增强35SO4掺入小分子可溶性蛋白聚糖双糖链蛋白聚糖，而不影响双糖链蛋白聚糖核心蛋白的mRNA表达，这表明PDGF-BB主要影响GAG链的延长和/或硫酸化。酪氨酸磷酸化酶9（一种与PDGF受体相关的酪氨酸激酶抑制剂）可消除PDGF-BB刺激的GAG合成，这意味着这种刺激作用是通过PDGFβ受体（PDGFR）介导的。我们研究了介导胎肺成纤维细胞中PDGF-BB刺激的GAG合成的细胞内信号转导途径。在配体诱导的酪氨酸磷酸化过程中，PDGFR与磷脂酶C（PLC）-γ1、Ras GTP酶激活蛋白（RasGAP）和磷脂酰肌醇3激酶（PI3K）结合，但不与Syp-生长因子受体结合蛋白2-七号染色体失活蛋白复合体结合。然而，PDGFR与PLC-γ1和RasGAP结合并随后发生酪氨酸磷酸化，但未能激活PLC-γ1、蛋白激酶C（PKC）和Ras。PLC-γ抑制剂U-73122、PKC抑制剂钙泊三醇C或丝裂原活化蛋白激酶激酶抑制剂PD-98059均未抑制PDGF-BB诱导的GAG合成。相反，PDGF-BB刺激可触发与PDGFR相关的PI3K活性。PI3K抑制剂渥曼青霉素和LY-294002可消除PDGF-BB诱导的PI3K激活和GAG合成。结果表明，PI3K是胎鼠肺成纤维细胞中PDGF-BB刺激的GAG合成的下游介质。
