title: Spatiotemporal behavior of nuclear cyclophilin B indicates a role in             RNA transcription.
abstract: Cyclophilin B (CypB) is an ubiquitously expressed protein, which performs several intra- and extracellular functions. Despite its abundant use as a household protein, little is known about its exact cellular localization and dynamics. In the present study we show that endogenous CypB localizes in one of two distinct compartments, either within the endoplasmic reticulum (ER) or inside the nucleus, accumulating in the fibrillar centers of the nucleoli. By means of a genetic deletion screen, we identified a minimal nucleolar localization signal for efficient relocation to the nucleoli. Within the fibrillar centers, CypB colocalized with RNA polymerase, upstream binding factor-1 (UBF), fibrillarin and dyskerin (DCK1). Even after chemical disruption of the nucleoli, a strong interaction with these proteins remained. Using live cell imaging, we showed a persistent colocalization of CypB with proteins involved in the ribosome biogenesis during the transcriptionally more active phases of the cell cycle. Supported by in silico data, our observations suggest that CypB interacts with these proteins and is involved in ribosome biogenesis and RNA transcription.
authors.affiliation: Department of Molecular Biotechnology, Ghent University, Ghent, Belgium. birger.dieriks@gmail.com
authors.forename: Birger
authors.initials: B
authors.lastname: Dieriks
authors.forename: Patrick
authors.initials: P
authors.lastname: Van Oostveldt
mesh_terms: D002466:Cell Nucleolus / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects / Q000235:genetics*; D020541:Coiled Bodies / Q000187:drug effects / Q000378:metabolism; D019295:Computational Biology; D021983:Cyclophilins / Q000378:metabolism*; D016572:Cyclosporine / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008297:Male; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D012313:RNA / Q000235:genetics* / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D011993:Recombinant Fusion Proteins; C081786:cyclophilin B; D049452:Green Fluorescent Proteins; D012313:RNA; D016572:Cyclosporine; D021983:Cyclophilins