Identification of nucleolin as a glucocorticoid receptor interacting protein

The glucocorticoid receptor (GR) is a ligand-induced transcription factor which modulates the transcriptional activity of target genes. Full transcriptional activity of GR is achieved with the help of accessory proteins that are able to interact with GR. We have identified a 95-kDa protein by a blotting technique which utilizes a radioactively labeled DNA-bound GR to detect proteins that bind to this complex. Biochemical purification of this protein followed by protein microsequencing resulted in the identification of human nucleolin. In addition we could show that a GR-deletion mutant localizes to the nucleolus, where nucleolin is one of the most abundant proteins. The binding of nucleolin to this deletion mutant was demonstrated by GST-pull-down experiments. We suggest a biological role of nucleolin in binding of GR in the nucleolus.