title: Nuclear functions of the Arf guanine nucleotide exchange factor BRAG2.
abstract: BRAG2 is a guanine nucleotide exchange factor for the GTPase Arf6 that cycles between the cytoplasm and nucleus in a CRM1/exportin1-dependent manner. Despite its presence in the nucleus, nuclear functions have not previously been described. Here, we show that depletion of endogenous BRAG2 by RNAi leads to an increased number of Cajal bodies (CBs), and altered structure of nucleoli, as indicated by less focal fibrillarin staining. This result was surprising given that nuclear BRAG2 is diffusely distributed throughout the nucleoplasm and is not concentrated within nucleoli at steady state. However, we found that ectopic expression of the nuclear GTPase PIKE/AGAP2 causes both BRAG2 and the CB marker coilin to accumulate in nucleoli. Neither the GTPase activity of PIKE nor the nucleotide exchange activity of BRAG2 is required for this nucleolar concentration. Increased levels of exogenous BRAG2 in nucleoli result in a redistribution of fibrillarin to the nucleolar periphery, supporting a role for BRAG2 in regulating nucleolar architecture. These observations suggest that, in addition to its role in endocytic regulation at the plasma membrane, BRAG2 also functions within the nucleus.
authors.affiliation: Department of Cell Biology, University of Virginia Health Sciences Center, Box 800732, Charlottesville, VA 22908, USA.
authors.forename: Jillian L
authors.initials: JL
authors.lastname: Dunphy
authors.forename: Keqiang
authors.initials: K
authors.lastname: Ye
authors.forename: James E
authors.initials: JE
authors.lastname: Casanova
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D000818:Animals; D002466:Cell Nucleolus / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D020541:Coiled Bodies / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D016716:PC12 Cells; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D051381:Rats; D014162:Transfection
chemical_list: D000089982:ADP-Ribosylation Factor 6; D002868:Chromosomal Proteins, Non-Histone; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; D020033:Protein Isoforms; C047458:fibrillarin; C068921:p80-coilin; C485997:AGAP2 protein, human; D019204:GTP-Binding Proteins; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human; C000715349:Arf6 protein, rat