Identification and characterization of an angiogenin-binding DNA sequence that stimulates luciferase reporter gene expression

Angiogenin undergoes nuclear translocation in endothelial and smooth muscle cells where it accumulates in the nucleolus and binds to DNA. Nuclear translocation of angiogenin is necessary for its biological activity and is mediated by an endocytotic pathway that is independent of the microtubule system and lysosomal processing. Because the nucleolus is a subnuclear organelle containing clusters of transcriptionally active ribosomal RNA genes, we studied the binding of angiogenin to the intergenic spacer of the ribosomal RNA gene where many of the transcription regulatory elements are located. Here we report that angiogenin binds to CT repeats that are abundant in the nontranscribed region of the ribosomal RNA gene. An angiogenin-binding DNA sequence (CTCTCTCTCTCTCTCTCCCTC) has been identified and designated angiogenin-binding element (ABE). ABE binds angiogenin specifically and exhibits angiogenin-dependent promoter activity in a luciferase reporter system. CT repeats, or inverted GA box, which are abundantly distributed in the eukaryotic genome and are often located in the 5'-flanking region, have been implicated in regulating gene expression. We have previously shown that angiogenin stimulates rRNA synthesis. The present results suggest that the nuclear function of angiogenin may not only be related to rRNA production but also play a role in regulating expression of genes containing CT repeats.