Human angiogenin is rapidly translocated to the nucleus of human umbilicalvein endothelial cells and binds to DNA

Human angiogenin is translocated to the nucleus of human umbilical vein end othelial cells in a time-dependent manner. Exogenous angiogenin appears in the nucleus in 2 min, reaches saturation in 15 min when 85% of the internal ized angiogenin is in the nuclei, and remains associated with the nucleus f or at least 4 h. Endothelial cells cultured at low density have a much high er capacity to translocate angiogenin to the nucleus than do those cultured at high density. This observation is consistent with previous findings tha t both the ability of endothelial cells to proliferate in response to angio genin and the expression of an angiogenin receptor on the cell surface depe nd on cell density. Nuclear I-125-angiogenin is not degraded and is neither spontaneously dissociated nor replaced by unlabeled angiogenin. It is, how ever, released by deoxyribonuclease I, but not by ribonuclease A, suggestin g that angiogenin binds to DNA in the nucleus. These results suggest that i n addition to acting as a ribonuclease, angiogenin may play a role in regul ating gene expression by direct binding to DNA. (C) 2000 Wiley-Liss, Inc.