The multifunctional nuclear protein p54nrb is multiphosphorylated in mitosis and interacts with the mitotic regulator Pin1.
The human protein p54nrb and its mouse homolog NonO have been implicated in a variety of nuclear processes including transcription, pre-mRNA processing, nuclear retention of edited RNA and DNA relaxation. We have identified p54nrb as an antigen of the phosphodependent monoclonal antibodies CC-3 and MPM-2 and shown that this protein is phosphorylated on multiple sites during mitosis. The use of the cyclin-dependent protein kinase inhibitor roscovitine and immunodepletion studies with an anti-cyclin B1 antibody established that Cdk1 was responsible for the phosphorylation of the carboxy-terminal extremity of p54nrb whereas a different kinase appeared to be involved in the generation of CC-3 epitope(s) in the amino-terminal moiety of the protein. Like many CC-3 and MPM-2 antigens, we show that p54nrb is a target of the peptidylprolyl isomerase Pin1, suggesting that it may be regulated by phosphorylation-dependent conformational changes as many other nuclear proteins upon entry into mitosis. In addition, site-directed mutagenesis indicated that the interaction of Pin1 with p54nrb was mediated by three threonine residues located in the proline-rich carboxy-terminal extremity of the protein. Our results also showed that Pin1 binding was favored when at least two of the three threonine residues were phosphorylated, suggesting a regulation mechanism based on multisite phosphorylation.
Proteau
Ariane
A
CREFSIP and Département de Médecine, Laval University, Pavillon C.-E.-Marchand, Room 4263 Laval University, Que., Canada, G1K 7P4.
Blier
Stéphanie
S
Albert
Alexandra L
AL
Lavoie
Sébastien B
SB
Traish
Abdulmaged M
AM
Vincent
Michel
M
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008938:Mitosis; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D034521:Nuclear Matrix-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D019696:Peptidylprolyl Isomerase / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000276:immunology / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D004268:DNA-Binding Proteins
D016203:CDC2 Protein Kinase; D000939:Epitopes; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins; D019696:Peptidylprolyl Isomerase; D017346:Protein Serine-Threonine Kinases; D016601:RNA-Binding Proteins; C000606846:PIN1 protein, human; C000606850:Pin1 protein, mouse; C500331:Nono protein, mouse; D004268:DNA-Binding Proteins