title: The distribution of phosphorylated SR proteins and alternative splicing are regulated by RANBP2.
abstract: The mammalian cell nucleus is functionally compartmentalized into various substructures. Nuclear speckles, also known as interchromatin granule clusters, are enriched with SR splicing factors and are implicated in gene expression. Here we report that nuclear speckle formation is developmentally regulated; in certain cases phosphorylated SR proteins are absent from the nucleus and are instead localized at granular structures in the cytoplasm. To investigate how the nuclear architecture is formed, we performed a phenotypic screen of HeLa cells treated with a series of small interfering RNAs. Depletion of Ran-binding protein 2 induced cytoplasmic intermediates of nuclear speckles in G1 phase. Detailed analyses of these structures suggested that a late step in the sequential nuclear entry of mitotic interchromatin granule components was disrupted and that phosphorylated SR proteins were sequestered in an SR protein kinase-dependent manner. As a result, the cells had an imbalanced subcellular distribution of phosphorylated and hypophosphorylated SR proteins, which affected alternative splicing patterns. This study demonstrates that the speckled distribution of phosphorylated pre-mRNA processing factors is regulated by the nucleocytoplasmic transport system in mammalian cells and that it is important for alternative splicing.
authors.affiliation: Department of Medical Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, 2-2-1 Honjo, Kumamoto 860-0811, Japan. norikos@kumamoto-u.ac.jp
authors.forename: Noriko
authors.initials: N
authors.lastname: Saitoh
authors.forename: Chiyomi
authors.initials: C
authors.lastname: Sakamoto
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Hagiwara
authors.forename: Lourdes T
authors.initials: LT
authors.lastname: Agredano-Moreno
authors.forename: Luis Felipe
authors.initials: LF
authors.lastname: Jiménez-García
authors.forename: Mitsuyoshi
authors.initials: M
authors.lastname: Nakao
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D002467:Cell Nucleus / Q000737:chemistry* / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism; D016193:G1 Phase; D006801:Humans; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism*; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000032:analysis / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins / Q000378:metabolism; D010766:Phosphorylation; D016601:RNA-Binding Proteins / Q000032:analysis / Q000378:metabolism*; D000068103:Serine-Arginine Splicing Factors
chemical_list: D018832:Molecular Chaperones; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D029543:Nucleocytoplasmic Transport Proteins; D016601:RNA-Binding Proteins; C094493:ran-binding protein 2; D000068103:Serine-Arginine Splicing Factors