Thr199 phosphorylation targets nucleophosmin to nuclear speckles and represses pre-mRNA processing.
Nucleophosmin (NPM) is a multifunctional phosphoprotein, being involved in ribosome assembly, pre-ribosomal RNA processing, DNA duplication, nucleocytoplasmic protein trafficking, and centrosome duplication. NPM is phosphorylated by several kinases, including nuclear kinase II, casein kinase 2, Polo-like kinase 1 and cyclin-dependent kinases (CDK1 and 2), and these phosphorylations modulate the activity and function of NPM. We have previously identified Thr(199) as the major phosphorylation site of NPM mediated by CDK2/cyclin E (and A), and this phosphorylation is involved in the regulation of centrosome duplication. In this study, we further examined the effect of CDK2-mediated phosphorylation of NPM by using the antibody that specifically recognizes NPM phosphorylated on Thr(199). We found that the phospho-Thr(199) NPM localized to dynamic sub-nuclear structures known as nuclear speckles, which are believed to be the sites of storage and/or assembly of pre-mRNA splicing factors. Phosphorylation on Thr(199) by CDK2/cyclin E (and A) targets NPM to nuclear speckles, and enhances the RNA-binding activity of NPM. Moreover, phospho-Thr(199) NPM, but not unphosphorylated NPM, effectively represses pre-mRNA splicing. These findings indicate the involvement of NPM in the regulation of pre-mRNA processing, and its activity is controlled by CDK2-mediated phosphorylation on Thr(199).
Tarapore
Pheruza
P
Department of Cell Biology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0521, USA.
Shinmura
Kazuya
K
Suzuki
Hitoshi
H
Tokuyama
Yukari
Y
Kim
Song-Hee
SH
Mayeda
Akila
A
Fukasawa
Kenji
K
D000818:Animals; D045163:Antibodies, Phospho-Specific / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D019925:Cyclin A / Q000378:metabolism; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D000090243:Nucleophosmin; D010766:Phosphorylation; D012322:RNA Precursors / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013912:Threonine / Q000378:metabolism*
D045163:Antibodies, Phospho-Specific; D019925:Cyclin A; D019927:Cyclin E; C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D012322:RNA Precursors; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D000090243:Nucleophosmin; D013912:Threonine; D051357:Cyclin-Dependent Kinase 2