Inhibition of human angiogenin by DNA aptamers: nuclear colocalization of an angiogenin-inhibitor complex

Specific ligands (aptamers) for angiogenin were selected from a 72-mer oligodeoxynucleotide library consisting of 28 randomized positions flanked by two constant regions of 22 residues each. From a starting pool of approximately 10(14) molecules, 19 angiogenin-binding ligands were obtained. Among them, two oligonucleotides showed significant inhibition of the ribonucleolytic activity of angiogenin with apparent Kis of 0.65 and 0.60 micro M, respectively. One of them was shortened on the basis of its secondary structure to provide a 45-mer oligonucleotide that retained much of the inhibitory properties of the parent molecule. It inhibits both the angiogenic and cell proliferative activities of angiogenin but does not interfere with its nuclear translocation in human endothelial cells. Importantly, the inhibitor is cotranslocated to the nucleus with angiogenin in a approximately 1:1 stoichiometric ratio. These results demonstrate that the inhibition of angiogenin-induced cell proliferation and angiogenesis by the oligonucleotide is due to suppression of the ribonucleolytic activity of angiogenin, an event that occurs most likely within the cell nucleus.