Alternative splicing controls nuclear translocation of the cell cycle-regulated Nek2 kinase.
Nek2 is a cell cycle-regulated serine/threonine protein kinase that is up-regulated in human cancers. Functionally, it is implicated in control of centrosome separation and bipolar spindle formation in mitotic cells and chromatin condensation in meiotic cells. Two major splice variants have been described in vertebrates, Nek2A and Nek2B, that differ in their non-catalytic C termini. Recently, a third splice variant, Nek2C, was identified that lacks an eight-amino acid internal sequence within the C-terminal domain of Nek2A. This excision occurs at the same position as the Nek2A/Nek2B splice point. As predicted from their high degree of similarity, we show here that Nek2C shares many properties with Nek2A including kinase activity, dimerization, protein phosphatase 1 interaction, mitotic degradation, microtubule binding, and centrosome localization. Unexpectedly, though, the non-centrosomal pool of protein exhibits a marked difference in distribution for the three splice variants. Nek2C is mainly nuclear, Nek2B is mainly cytoplasmic, and Nek2A is evenly distributed within nuclei and cytoplasm. Mutagenesis experiments revealed a functional bipartite nuclear localization sequence (NLS) that spans the splice site leading to Nek2C having a strong NLS, Nek2A having a weak NLS, and Nek2B having no NLS. Finally, we identified a 28-kDa protein in nuclear extracts as a potential novel substrate of Nek2. Thus, alternative splicing provides an unusual mechanism for modulating Nek2 localization, enabling it to have both nuclear and cytoplasmic functions.
Wu
Wenjuan
W
Laboratório de Transdução de Sinais, Centro de Biologia Celular, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
Baxter
Joanne E
JE
Wattam
Samantha L
SL
Hayward
Daniel G
DG
Fardilha
Margarida
M
Knebel
Axel
A
Ford
Eleanor M
EM
da Cruz e Silva
Edgar F
EF
Fry
Andrew M
AM
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D017398:Alternative Splicing / Q000235:genetics; D002467:Cell Nucleus / Q000378:metabolism* / Q000473:pathology; D018385:Centrosome / Q000378:metabolism* / Q000473:pathology; D042002:Chromatin Assembly and Disassembly / Q000235:genetics; D019281:Dimerization; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis / Q000235:genetics; D009154:Mutation; D000072379:NIMA-Related Kinases; D009369:Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D019913:Nuclear Localization Signals / Q000235:genetics; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D054645:Protein Phosphatase 1; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D022821:RNA Splice Sites / Q000235:genetics; D008941:Spindle Apparatus / Q000378:metabolism* / Q000473:pathology; D015854:Up-Regulation / Q000235:genetics
D019913:Nuclear Localization Signals; D022821:RNA Splice Sites; C089441:NEK2 protein, human; D000072379:NIMA-Related Kinases; D017346:Protein Serine-Threonine Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1