The protein phosphatase-1 regulator NIPP1 is also a splicing factor involved in a late step of spliceosome assembly.
NIPP1 is a ubiquitous regulator of protein phosphatase-1 (PP1) and is targeted to the splicing factor storage sites (speckles) in the nucleus by its forkhead-associated domain. We show here that NIPP1 is also a component of the spliceosomes in HeLa cell-splicing extracts and that the interaction with the spliceosomes requires a functional forkhead-associated domain. The in vitro splicing of beta-globin pre-mRNA was not affected by exogenous wild type NIPP1 but was blocked by mutants that lacked residues 225-329. The inhibition by these dominant negative mutants resulted from a block in a late phase of spliceosome assembly, i.e. at the transition between the B-complex and the C-complex. Site-directed mutagenesis furthermore showed that this spliceosomal function of NIPP1 was unrelated to its ability to bind PP1 or RNA. Our data suggest that NIPP1 can function independently as a splicing factor and a phosphatase regulator.
Beullens
Monique
M
Afdeling Biochemie, Faculteit Geneeskunde, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium.
Bollen
Mathieu
M
D017398:Alternative Splicing; D002352:Carrier Proteins; D002467:Cell Nucleus / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004722:Endoribonucleases; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005914:Globins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases; D011485:Protein Binding; D054645:Protein Phosphatase 1; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism* / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D017381:Spliceosomes / Q000502:physiology*; D013696:Temperature; D013997:Time Factors
D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; C021042:protein phosphatase inhibitor-1; D019319:Okadaic Acid; D005914:Globins; D004722:Endoribonucleases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; C097081:PPP1R8 protein, human