Pece N, Vera S, Cymerman U, White R I, Wrana J L, Letarte M
Division of Immunology and Cancer Research, Hospital for Sick Children, Toronto, Canada.
J Clin Invest. 1997 Nov 15;100(10):2568-79. doi: 10.1172/JCI119800.
Endoglin (CD105), a component of the TGF-beta 1 receptor complex, is the target gene for the dominantly inherited vascular disorder hereditary hemorrhagic telangiectasia type 1 (HHT1). We have identified a novel endoglin splice site mutation, leading to an in-frame deletion of exon 3, in a new-born from a family with HHT. Expression of normal and mutant endoglin proteins was analyzed in umbilical vein endothelial cells from this baby and in activated monocytes from the affected father. In both samples, only normal dimeric endoglin (160 kD) was observed at the cell surface, at 50% of control levels. Despite an intact transmembrane region, mutant protein was only detectable by metabolic labeling, as an intracellular homodimer of 130 kD. In monocytes from three clinically affected HHT1 patients, with known mutations creating premature stop codons in exons 8 and 10, surface endoglin was also reduced by half and no mutant was detected. Overexpression into COS-1 cells of endoglin cDNA truncated in exons 7 and 11, revealed their intracellular expression, inability to be secreted and to form heterodimers at the cell surface. These results indicate that mutated forms of endoglin are transiently expressed intracellularly and not likely to act as dominant negative proteins, as proposed previously. A reduction in the level of functional endoglin is thus involved in the generation of HHT1, and associated arteriovenous malformations.
内皮糖蛋白（CD105）是转化生长因子β1受体复合物的一个组成部分，是常染色体显性遗传血管疾病1型遗传性出血性毛细血管扩张症（HHT1）的靶基因。我们在一个患有HHT的家庭的新生儿中鉴定出一种新的内皮糖蛋白剪接位点突变，该突变导致外显子3的框内缺失。我们分析了这个婴儿的脐静脉内皮细胞以及患病父亲的活化单核细胞中正常和突变内皮糖蛋白的表达情况。在这两个样本中，仅在细胞表面观察到正常的二聚体内皮糖蛋白（160kD），其水平为对照水平的50%。尽管跨膜区域完整，但突变蛋白只能通过代谢标记检测到，表现为一种130kD的细胞内同型二聚体。在三名临床诊断为HHT1的患者的单核细胞中，已知其外显子8和10中的突变产生了过早的终止密码子，表面内皮糖蛋白也减少了一半，且未检测到突变体。将外显子7和11截短的内皮糖蛋白cDNA过表达至COS-1细胞中，结果显示它们在细胞内表达，无法分泌，也不能在细胞表面形成异二聚体。这些结果表明，内皮糖蛋白的突变形式在细胞内短暂表达，不太可能像之前所提出的那样作为显性负性蛋白发挥作用。因此，功能性内皮糖蛋白水平的降低与HHT1的发生以及相关的动静脉畸形有关。
