1. Nucleocytoplasmic shuttling of the splicing factor SIPP1.
- Author
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Llorian M, Beullens M, Lesage B, Nicolaescu E, Beke L, Landuyt W, Ortiz JM, and Bollen M
- Subjects
- Active Transport, Cell Nucleus, Alternative Splicing, Amino Acid Sequence, Animals, Carrier Proteins metabolism, Cell Line, Cytosol metabolism, DNA-Binding Proteins, Female, Green Fluorescent Proteins metabolism, HeLa Cells, Humans, Immunohistochemistry, Ligands, Luciferases metabolism, Mice, Microscopy, Confocal, Microscopy, Fluorescence, Molecular Sequence Data, NIH 3T3 Cells, Neurodegenerative Diseases metabolism, Nuclear Proteins metabolism, Peptides chemistry, Protein Binding, Protein Structure, Tertiary, Proteins chemistry, RNA Splicing, RNA Splicing Factors, RNA, Messenger metabolism, Recombinant Fusion Proteins chemistry, Time Factors, Ultraviolet Rays, beta-Galactosidase chemistry, Cell Nucleus metabolism, Cytoplasm metabolism, Proteins physiology
- Abstract
SIPP1 (splicing factor that interacts with PQBP1 and PP1) is a widely expressed protein of 70 kDa that has been implicated in pre-mRNA splicing. It interacts with protein Ser/Thr phosphatase-1 (PP1) and with the polyglutamine-tract-binding protein 1 (PQBP1), which contributes to the pathogenesis of X-linked mental retardation and neurodegenerative diseases caused by polyglutamine tract expansions. We show here that SIPP1 is a nucleocytoplasmic shuttling protein. Under basal circumstances SIPP1 was largely nuclear, but it accumulated in the cytoplasm following UV- or X-radiation. Nuclear import was mediated by two nuclear localization signals. In addition, SIPP1 could be piggy-back transported to the nucleus with its ligand PQBP1. In the nucleus SIPP1 and PQBP1 formed inclusion bodies similar to those detected in polyglutamine diseases. SIPP1 did not function as a nuclear targeting subunit of PP1 but re-localized nuclear PP1 to storage sites for splicing factors. The C-terminal residues of SIPP1, which do not conform to a classic nuclear export signal, were required for its nuclear export via the CMR-1 pathway. Finally, SIPP1 activated pre-mRNA splicing in intact cells, and the extent of splicing activation correlated with the nuclear concentration of SIPP1. We conclude that SIPP1 is a positive regulator of pre-mRNA splicing that is regulated by nucleocytoplasmic shuttling. These findings also have potential implications for a better understanding of the pathogenesis of X-linked mental retardation and polyglutamine-linked neurodegenerative disorders.
- Published
- 2005
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