Nucleocytoplasmic shuttling of the splicing factor SIPP1.
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.
Llorian
Miriam
M
Afdelingen Biochemie, Faculteit Geneeskunde, KULeuven, B-3000 Leuven, Belgium.
Beullens
Monique
M
Lesage
Bart
B
Nicolaescu
Emilia
E
Beke
Lijs
L
Landuyt
Willy
W
Ortiz
José-Miguel
JM
Bollen
Mathieu
M
D021581:Active Transport, Cell Nucleus; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004268:DNA-Binding Proteins; D005260:Female; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D008024:Ligands; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D019636:Neurodegenerative Diseases / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry / Q000502:physiology*; D012326:RNA Splicing; D000072260:RNA Splicing Factors; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D013997:Time Factors; D014466:Ultraviolet Rays; D001616:beta-Galactosidase / Q000737:chemistry
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D008024:Ligands; D009687:Nuclear Proteins; C119246:PQBP1 protein, human; D010455:Peptides; C492272:Pqbp1 protein, mouse; D011506:Proteins; D000072260:RNA Splicing Factors; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C483880:Wbp11 protein, mouse; D049452:Green Fluorescent Proteins; C097188:polyglutamine; D008156:Luciferases; D001616:beta-Galactosidase