FUNCTIONAL CHARACTERIZATION OF SECRETED FORM OF A VEGF RECEPTOR

一种内皮细胞特异性有丝分裂原，称为血管内皮细胞 从牛的条件培养液中纯化出一种生长因子（VEGF）， 垂体滤泡星状细胞。 VEGF可能由两个分子组成， 相同的链通过二硫键连接在一起。 的氨基酸 VEGF的序列与VEGF基因的序列有较远的相关性（18%的总体同一性）。 血小板衍生生长因子（PDGF）的序列，其也是 二硫键连接的二聚体。 八个半胱氨酸参与的内部和 PDGF中的链间二硫键与VEGF中的相同。 最近， 在COS细胞中表达fms样酪氨酸激酶（flt）cDNA， 显示赋予与VEGF的特异性、高亲和力结合。 表达 flt在非洲爪蟾卵母细胞中引起卵母细胞释放钙， 对VEGF的反应 这些发现表明，flt编码一种受体， VEGF。 Flt是一种受体型酪氨酸激酶，具有7个免疫球蛋白- 类似于其细胞外结构域中的区域。 然而，一个北方的污点 用FLT的胞外结构域作为探针的分析表明， 大多数flt信息由大小为2.2kb的mRNA组成， 3.0 kb的人内皮细胞。 PCR和序列分析表明， 这些短形式的flt mRNA编码前六种免疫球蛋白， Like结构域后紧跟着终止密码子。 因此， 分泌形式的FLT，因为它们不含跨膜 域. 该分泌形式的3'非翻译区的序列是 FLT表明它们通过选择性剪接合成。 这是否 分泌形式的flt在调节VEGF与 内皮细胞仍有待阐明。

A mitogen specific for endothelial cells, termed vascular endothelial growth factor (VEGF), was purified from the conditioned medium of bovine pituitary folliculo stellate cells. VEGF is composed of two presumably identical chains held together by disulfide bonds. The amino acid sequence of VEGF is distantly related (18% overall identity) to the sequence of platelet-derived growth factor (PDGF), which is also a disulfide-linked dimer. The eight cysteines involved in intra- and interchain disulfide bridges in PDGF are identical in VEGF. Recently, expression of the fms-like tyrosine kinase (flt) cDNA in COS cells was shown to confer specific, high-affinity binding to VEGF. Expression of flt in Xenopus laevis oocytes caused the oocytes to release calcium in response to VEGF. These findings show that flt encodes a receptor for VEGF. Flt is a receptor-type tyrosine kinase with seven immunoglobulin- like regions in its extracellular domain. However, a Northern blot analysis using extracellular domain of flt as probe reveals that the majority of flt messages are comprised of mRNAs with size of 2.2 kb and 3.0 kb in human endothelial cells. PCR and sequence analysis indicates that these short forms of flt mRNA code for the first six immunoglobulin- like domains followed shortly by the termination codon. Thus, these are the secreted forms of flt since they do not contain transmembrane domains. The sequence of 3' untranslated region of this secreted form of flt suggests they are synthesized by alternative splicing. Whether this secreted form of flt plays a role in regulating binding of VEGF to endothelial cells remains to be elucidated.