Mandriota S J, Menoud P A, Pepper M S
Department of Morphology, University Medical Center, Geneva, Switzerland.
J Biol Chem. 1996 May 10;271(19):11500-5. doi: 10.1074/jbc.271.19.11500.
Although the importance of the vascular endothelial growth factor (VEGF)/VEGF tyrosine kinase receptor (VEGFR) system in angiogenesis is well established, very little is known about the regulation of VEGFR expression in vascular endothelial cells. We have cloned partial cDNAs encoding bovine VEGFR-1 (flt) and -2 (flk-1) and used them to study VEGFR expression by bovine microvascular- and large vessel-derived endothelial cells. Both cell lines express flk-1, but not flt. Transforming growth factor beta 1 (TGF-beta 1) reduced the high affinity 125I-VEGF binding capacity of both cell types in a dose-dependent manner, with a 2.0-2.7-fold decrease at 1-10 ng/ml. Cross-linking experiments revealed a decrease in 125I-VEGF binding to a cell surface monomeric protein corresponding to Flk-1 on the basis of its affinity for VEGF, molecular mass (185-190 kDa), and apparent internalization after VEGF binding. Immunoprecipitation and Western blot experiments demonstrated a decrease in Flk-1 protein expression, and TGF-beta 1 reduced flk-1 mRNA levels in a dose-dependent manner. These results imply that TGF-beta 1 is a major regulator of the VEGF/Flk-1 signal transduction pathway in endothelial cells.
尽管血管内皮生长因子（VEGF）/VEGF酪氨酸激酶受体（VEGFR）系统在血管生成中的重要性已得到充分证实，但对于血管内皮细胞中VEGFR表达的调控却知之甚少。我们克隆了编码牛VEGFR-1（flt）和-2（flk-1）的部分cDNA，并利用它们研究牛微血管和大血管来源的内皮细胞中VEGFR的表达。两种细胞系均表达flk-1，但不表达flt。转化生长因子β1（TGF-β1）以剂量依赖的方式降低了两种细胞类型的高亲和力125I-VEGF结合能力，在1-10 ng/ml时下降了2.0-2.7倍。交联实验显示，基于其对VEGF的亲和力、分子量（185-190 kDa）以及VEGF结合后的明显内化作用，125I-VEGF与细胞表面对应于Flk-1的单体蛋白的结合减少。免疫沉淀和蛋白质印迹实验表明Flk-1蛋白表达减少，并且TGF-β1以剂量依赖的方式降低flk-1 mRNA水平。这些结果表明TGF-β1是内皮细胞中VEGF/Flk-1信号转导途径的主要调节因子。
