title: Nuclear import of RNA polymerase II is coupled with nucleocytoplasmic shuttling of the RNA polymerase II-associated protein 2.
abstract: The RNA polymerase II (RNAP II)-associated protein (RPAP) 2 has been discovered through its association with various subunits of RNAP II in affinity purification coupled with mass spectrometry experiments. Here, we show that RPAP2 is a mainly cytoplasmic protein that shuttles between the cytoplasm and the nucleus. RPAP2 shuttling is tightly coupled with nuclear import of RNAP II, as RPAP2 silencing provokes abnormal accumulation of RNAP II in the cytoplasmic space. Most notably, RPAP4/GPN1 silencing provokes the retention of RPAP2 in the nucleus. Our results support a model in which RPAP2 enters the nucleus in association with RNAP II and returns to the cytoplasm in association with the GTPase GPN1/RPAP4. Although binding of RNAP II to RPAP2 is mediated by an N-terminal domain (amino acids 1-170) that contains a nuclear retention domain, and binding of RPAP4/GPN1 to RPAP2 occurs through a C-terminal domain (amino acids 156-612) that has a dominant cytoplasmic localization domain. In conjunction with previously published data, our results have important implications, as they indicate that RPAP2 controls gene expression by two distinct mechanisms, one that targets RNAP II activity during transcription and the other that controls availability of RNAP II in the nucleus.
authors.affiliation: Institut de Recherches Cliniques de Montréal (IRCM), Montréal, Québec, Canada H2W 1R7, McGill Centre for Bioinformatics and School of Computer Science, McGill University, Montréal, Québec, Canada H3A 2B4.
authors.forename: Diane
authors.initials: D
authors.lastname: Forget
authors.forename: Andrée-Anne
authors.initials: AA
authors.lastname: Lacombe
authors.forename: Philippe
authors.initials: P
authors.lastname: Cloutier
authors.forename: Mathieu
authors.initials: M
authors.lastname: Lavallée-Adam
authors.forename: Mathieu
authors.initials: M
authors.lastname: Blanchette
authors.forename: Benoit
authors.initials: B
authors.lastname: Coulombe
mesh_terms: D021581:Active Transport, Cell Nucleus; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism*; D003593:Cytoplasm / Q000201:enzymology; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D019913:Nuclear Localization Signals; D054730:Protein Interaction Domains and Motifs; D021382:Protein Sorting Signals; D034622:RNA Interference; D012319:RNA Polymerase II / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D019913:Nuclear Localization Signals; D021382:Protein Sorting Signals; C571028:RPAP2 protein, human; D012319:RNA Polymerase II; C472669:GPN1 protein, human; D019204:GTP-Binding Proteins