Moroianu J, Riordan J F
Center for Biochemical and Biophysical Sciences and Medicine, Harvard Medical School, Boston, MA 02115.
Proc Natl Acad Sci U S A. 1994 Mar 1;91(5):1677-81. doi: 10.1073/pnas.91.5.1677.
The intracellular pathway of human angiogenin in calf pulmonary artery endothelial (CPAE) cells has been studied by immunofluorescence microscopy. Proliferating CPAE cells specifically endocytose native angiogenin and translocate it to the nucleus, where it accumulates in the nucleoli. Nuclear translocation of angiogenin does not occur in nonproliferative, confluent CPAE cells. These cells were previously found to express an angiogenin-binding protein (AngBP) that was identified as smooth muscle alpha-actin. Exogenous actin, an anti-actin antibody, heparin, and heparinase treatment all inhibit the internalization of angiogenin, suggesting the involvement of cell surface AngBP/actin and heparan sulfate proteoglycans in this process. It has been established that two regions of angiogenin are essential for its angiogenic activity, one is its endothelial cell binding site and the other its catalytic site capable of cleaving RNA. CPAE cells do not internalize four enzymatically active angiogenin derivatives whose cell binding site is modified, but they do internalize two enzymatically inactive mutants whose cell binding site is intact. Thus, the putative cell binding site of angiogenin is necessary for both endocytosis and nuclear translocation, but the catalytic site is not. Three other angiogenic molecules are also translocated to the nucleus of growing CPAE cells. Overall, the results suggest that nuclear translocation of angiogenin and other angiogenic molecules is a critical step in the process of angiogenesis.
通过免疫荧光显微镜研究了人血管生成素在小牛肺动脉内皮（CPAE）细胞中的细胞内途径。增殖的CPAE细胞特异性地内吞天然血管生成素，并将其转运至细胞核，在核仁中积累。血管生成素的核转位在非增殖性、汇合的CPAE细胞中不发生。这些细胞先前被发现表达一种血管生成素结合蛋白（AngBP），该蛋白被鉴定为平滑肌α-肌动蛋白。外源性肌动蛋白、抗肌动蛋白抗体、肝素和肝素酶处理均抑制血管生成素的内化，表明细胞表面的AngBP/肌动蛋白和硫酸乙酰肝素蛋白聚糖参与了这一过程。已经确定血管生成素的两个区域对其血管生成活性至关重要，一个是其内皮细胞结合位点，另一个是能够切割RNA的催化位点。CPAE细胞不内化细胞结合位点被修饰的四种具有酶活性的血管生成素衍生物，但它们内化细胞结合位点完整的两种无酶活性的突变体。因此，血管生成素假定的细胞结合位点对于内吞作用和核转位都是必需的，但催化位点不是。另外三种血管生成分子也被转运至生长中的CPAE细胞的细胞核。总体而言，结果表明血管生成素和其他血管生成分子的核转位是血管生成过程中的关键步骤。
