Alternative Splicing Controls Nuclear Translocation of the Cell Cycle-regulated Nek2 Kinase

Abstract

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. 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. Cell division involves the replication and segregation of genetic material between daughter cells. During mitotic and the second meiotic division, duplicated sister chromatids are segregated, whereas during the first meiotic division homologous chromosomes are segregated. Mitosis and meiosis are both highly complex processes involving condensation of chromatin, breakdown of the nuclear envelope, and reorganization of the microtubule cytoskeleton into a spindle capable of bipolar segregation. These events are known to be regulated in large part by cell cycle-dependent protein kinases, most notably members of the Cdk (cyclin-dependent kinase), Plk (polo-like kinase), Aurora, and Nek (NIMA-related kinase) families (1Nigg E.A. Nat. Rev. Mol. Cell Biol. 2001; 2,: 21-32Crossref PubMed Scopus (1228) Google Scholar). The Neks represent a comparatively large family (11 members in humans) of serine/threonine kinases that are related to the NIMA kinase of Aspergillus nidulans (2O'Connell M.J. Krien M.J. Hunter T. Trends Cell Biol. 2003; 13,: 221-228Abstract Full Text Full Text PDF PubMed Scopus (181) Google Scholar). NIMA was first identified in a screen for conditional loss-of-function mutants that were unable to enter mitosis (3Oakley B.R. Morris N.R. J. Cell Biol. 1983; 96,: 1155-1158Crossref PubMed Scopus (92) Google Scholar). nimA mutants remain blocked in G2 despite activation of cyclin-dependent kinase 1 (4Osmani A.H. McGuire S.L. Osmani S.A. Cell. 1991; 67,: 283-291Abstract Full Text PDF PubMed Scopus (185) Google Scholar), whereas overexpression of wild-type NIMA drives cells into mitosis from any point in the cell cycle with premature condensation of chromosomes and spindle formation (5Osmani S.A. Pu R.T. Morris N.R. Cell. 1988; 53,: 237-244Abstract Full Text PDF PubMed Scopus (241) Google Scholar). Interestingly, overexpression of Aspergillus NIMA in fission yeast, Xenopus oocytes, and cultured human cells induces aspects of a premature mitosis, including condensation of chromosomes, suggesting that similar pathways may be conserved in higher eukaryotes (6Lu K.P. Hunter T. Cell. 1995; 81,: 413-424Abstract Full Text PDF PubMed Scopus (141) Google Scholar, 7O'Connell M.J. Norbury C. Nurse P. EMBO J. 1994; 13,: 4926-4937Crossref PubMed Scopus (100) Google Scholar). More recently, it has been reported that NIMA activity is essential for phosphorylation of histone H3 thereby promoting chromatin condensation in Aspergillus (8De Souza C.P. Osmani A.H. Wu L.P. Spotts J.L. Osmani S.A. Cell. 2000; 102,: 293-302Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar). So far it remains unclear which if any of the human Neks represents the closest functional homologue of NIMA. Mitotic functions have been proposed for Nek2, Nek6, Nek7, and Nek9 (also known as Nercc1) (9Roig J. Mikhailov A. Belham C. Avruch J. Genes Dev. 2002; 16,: 1640-1658Crossref PubMed Scopus (112) Google Scholar, 10Yin M.J. Shao L. Voehringer D. Smeal T. Jallal B. J. Biol. Chem. 2003; 278,: 52454-52460Abstract Full Text Full Text PDF PubMed Scopus (78) Google Scholar, 11Faragher A.J. Fry A.M. Mol. Biol. Cell. 2003; 14,: 2876-2889Crossref PubMed Scopus (199) Google Scholar, 12Belham C. Roig J. Caldwell J.A. Aoyama Y. Kemp B.E. Comb M. Avruch J. J. Biol. Chem. 2003; 278,: 34897-34909Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar). Nek2 is the most closely related of the human proteins to NIMA based on amino acid conservation within the N-terminal catalytic kinase domain (13Fry A.M. Oncogene. 2002; 21,: 6184-6194Crossref PubMed Scopus (170) Google Scholar). However, depletion studies in human cells do not support an essential role for Nek2 in mitotic entry (14Fletcher L. Cerniglia G.J. Yen T.J. Muschel R.J. Biochim. Biophys. Acta. 2005; 1744,: 89-92Crossref PubMed Scopus (34) Google Scholar). Rather there is strong evidence that in mitotic cells Nek2 contributes to centrosome separation and perhaps reorganization of the microtubule network at the G2/M transition (11Faragher A.J. Fry A.M. Mol. Biol. Cell. 2003; 14,: 2876-2889Crossref PubMed Scopus (199) Google Scholar, 15Fry A.M. Meraldi P. Nigg E.A. EMBO J. 1998; 17,: 470-481Crossref PubMed Scopus (335) Google Scholar, 16Rapley J. Baxter J.E. Blot J. Wattam S.L. Casenghi M. Meraldi P. Nigg E.A. Fry A.M. Mol. Cell. Biol. 2005; 25,: 1309-1324Crossref PubMed Scopus (73) Google Scholar). Nek2 may have additional roles in chromatin condensation, at least in meiotic cell division, as it has been shown to phosphorylate the chromatin-associated protein, high mobility protein A2, and be activated during the extracellular signal-regulated kinase 1/p90Rsk2-stimulated condensation of chromatin in mouse pachytene spermatocytes (17Di Agostino S. Rossi P. Geremia R. Sette C. Development. 2002; 129,: 1715-1727Crossref PubMed Google Scholar, 18Di Agostino S. Fedele M. Chieffi P. Fusco A. Rossi P. Geremia R. Sette C. Mol. Biol. Cell. 2004; 15,: 1224-1232Crossref PubMed Scopus (75) Google Scholar). In human cultured cells, Nek2 is predominantly expressed as two alternative splice variants, Nek2A and Nek2B (19Hames R.S. Fry A.M. Biochem. J. 2002; 361,: 77-85Crossref PubMed Scopus (68) Google Scholar). These differ at their non-catalytic C termini as a result of an alternative polyadenylation signal within intron 7 that prevents splicing to the terminal exon 8 in Nek2B. Nek2A, therefore, encodes a protein of 445 amino acids (48 kDa), whereas Nek2B encodes a protein of 384 amino acids (44 kDa) with the sequence diverging after amino acid 370. Downstream of the kinase domain, both Nek2A and Nek2B share a leucine acids that dimerization, and activation of the kinase A.M. L. Nigg E.A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus (73) Google Scholar, P. Baxter J.E. A. T.J. S. S. Fry A.M. S. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). This is by a acids shown to be for centrosome and microtubule R.S. A. M.J. A.J. Fry A.M. Mol. Biol. Cell. 2005; 16,: PubMed Scopus Google Scholar). However, the position of splicing that a site for protein phosphatase 1 phosphatase localization substrate and complex phosphatase localization substrate and complex amino acids and two a acids and an acids are in Nek2A from Nek2B N.R. Biochem. J. 2000; PubMed Scopus Google Scholar, R.S. Wattam S.L. R. Fry A.M. EMBO J. 2001; PubMed Scopus (170) Google Scholar, M.J. Y. Wattam S.L. C. Fry A.M. Nat. Cell Biol. PubMed Scopus Google Scholar). This in with that Nek2A is mitotic whereas Nek2B remains that Nek2B may not be to by is by the that Nek2A and Nek2B their leucine at least in (19Hames R.S. Fry A.M. Biochem. J. 2002; 361,: 77-85Crossref PubMed Scopus (68) Google Scholar). protein phosphatase 1 nuclear localization sequence C-terminal domain in kinase substrate and human cells nuclear signal complex protein phosphatase 1 nuclear localization sequence C-terminal domain in kinase substrate and human cells nuclear signal complex Recently, a third splice of Nek2 was identified during a screen and as M. Wu R. S. C. C. Y. 2004; PubMed Scopus (34) Google Scholar). This is to Nek2A that it lacks amino acids This eight-amino acid at the splice position of the splice site a splice sequence within exon This was as it was from However, we to it Nek2C Nek2A is expressed in the M. Wu R. S. C. C. Y. 2004; PubMed Scopus (34) Google Scholar, Development. PubMed Google Scholar, M. Nigg E.A. Cell PubMed Scopus (34) Google Scholar, A. A. B. Oncogene. 1998; 16,: PubMed Scopus Google Scholar), whereas Nek2C is not expressed in In we the properties of Nek2C in to of Nek2A and Nek2B. As from the position of the described Nek2C is an kinase that to the and be in However, there is a in of Nek2C in the as with Nek2A Nek2B, and we show that is the result of the eight-amino acid a strong nuclear localization sequence (NLS) in Nek2C that is in Nek2A and in Nek2B. that the nuclear of Nek2C may be essential to the phosphorylation of nuclear that mitotic meiotic and have been described A.M. Meraldi P. Nigg E.A. EMBO J. 1998; 17,: 470-481Crossref PubMed Scopus (335) Google Scholar, R.S. Fry A.M. Biochem. J. 2002; 361,: 77-85Crossref PubMed Scopus (68) Google Scholar). a C-terminal was from with and and with the from M. Wu R. S. C. C. Y. 2004; PubMed Scopus (34) Google Scholar). is blocked by were for were the The and were by human from into the and amino acids of Nek2A into the were by by Cell and and were from cells were cultured in essential with amino and cells and human cells, were cultured in with and were cultured at in a were to the Cell extracts were as described A.M. Nigg E.A. PubMed Scopus Google Scholar). was from cultured cells to was for first and at for of and of and was in a of first as and the were a into a with and In and proteins were by from the to of were in the of by and to of proteins by of protein were to of A.M. Nigg E.A. PubMed Scopus Google of and on a for at at for The was to a and 1 of mouse was and on for of protein were blocked with of in of on a for The blocked were at for the was and the were with of The blocked were in of and to the This was on a for at for at The was and the were with of and in of was to a for of the of the The was and the was for kinase of cell the same was that to the of protein were to cell in of and of protein were to the by were three with kinase A.M. Nigg E.A. PubMed Scopus Google Scholar). The were in a of of kinase and and at for The was by the of of separation by the was with and to and and were expressed in and from on to proteins were for at proteins were to for by with 1 The were blocked by first with in and with for in were with for in proteins were by and with proteins by were as described R.S. A. M.J. A.J. Fry A.M. Mol. Biol. Cell. 2005; 16,: PubMed Scopus Google Scholar). of Xenopus in and the of were as described R.S. Wattam S.L. R. Fry A.M. EMBO J. 2001; PubMed Scopus (170) Google Scholar). of and cells was as described R.S. Wattam S.L. R. Fry A.M. EMBO J. 2001; PubMed Scopus (170) Google Scholar). on were at for at and was as described (11Faragher A.J. Fry A.M. Mol. Biol. Cell. 2003; 14,: 2876-2889Crossref PubMed Scopus (199) Google Scholar, R.S. A. M.J. A.J. Fry A.M. Mol. Biol. Cell. 2005; 16,: PubMed Scopus Google Scholar). were mouse Cell 2004; PubMed Scopus Google Scholar), mouse Cell and mouse Fry A.M. B. A.J. A. S. P. A. R. A. Mol. 2005; 14,: PubMed Scopus Google were and was with 1 with the were on in a of were on cells predominantly nuclear of protein, cytoplasmic were in of the and were the cell was to have the protein predominantly in the and cytoplasmic of cells with Nek2 was the to were as described (11Faragher A.J. Fry A.M. Mol. Biol. Cell. 2003; 14,: 2876-2889Crossref PubMed Scopus (199) Google Cell and and cells were in 1 1 1 and the nuclear was by for at The nuclear was for with and protein was by material by for at The was on and on of the extracts and were in 1 1 These were for with in the of Nek2, Nek6, Nek7, Nek9 kinases and by to and of Nek2C in Cell splice variants of the cell cycle-regulated Nek2 protein kinase have been Nek2A, Nek2B, and Nek2C the of Nek2C, were for in that the splice site on Nek2A and Nek2C of and a major of Nek2A, was from and human cell However, a at the of Nek2C was was and the of it was from the the same and into a that the the predicted sequence of Nek2C and lacks the in Nek2A Nek2C is a splice be Nek2A, in human cell Nek2C an and the catalytic kinase domain the leucine that is for and and the site A.M. L. Nigg E.A. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus (73) Google Scholar, N.R. Biochem. J. 2000; PubMed Scopus Google Scholar). However, the acid two and in Nek2A that as for M. Wu R. S. C. C. Y. 2004; PubMed Scopus (34) Google Scholar). to Nek2A and Nek2C kinase activity, Nek2C, Nek2A, and proteins were in not expressed in cells by Nek2 proteins were with and protein was by with an on the revealed that was as whereas Nek2A and Nek2C were both capable of the control substrate to a similar and not of of Nek2A and Nek2C were to binding, a protein was expressed in and to in proteins Nek2A and Nek2C proteins not In Nek2B, which lacks the which has a in the and not to dimerization, in Nek2A, Nek2B, Nek2C, and the control protein were with a Nek2A C-terminal domain protein that the non-catalytic domain including the leucine As Nek not were by the eight-amino acid in the non-catalytic domain not with the kinase activity, binding, of the Nek2C Nek2C in Mitotic and Nek2 exhibits cell cycle-dependent and protein with in and in and G2 A.J. Fry A.M. 2004; PubMed Scopus Google Scholar, A.M. J. Nigg E.A. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar). mitotic Nek2A is for as a result of whereas Nek2B remains as it lacks the in the C of Nek2A R.S. Wattam S.L. R. Fry A.M. EMBO J. 2001; PubMed Scopus (170) Google Scholar, M.J. Y. Wattam S.L. C. Fry A.M. Nat. Cell Biol. PubMed Scopus Google Scholar). These a and the C-terminal are in Nek2C, and we predicted that be in we first Nek2A and Nek2C proteins by and to mitotic extracts from Xenopus These extracts the for and Cell Biol. 1991; PubMed Scopus Google Scholar). In which represent of both proteins were whereas the of which the extracts into both proteins were and This was as it was by both Nek2A and Nek2C were in cells with in of mitosis not in cells Nek2C to Nek2A both in and in and is most an Nek2C and to C-terminal domain of Nek2 and the amino acids is essential for the protein to with and to the centrosome R.S. A. M.J. A.J. Fry A.M. Mol. Biol. Cell. 2005; 16,: PubMed Scopus Google Scholar). This is in Nek2C as as Nek2A and Nek2B. that Nek2C to in whereas revealed of Nek2C with at the centrosome As has been Nek2 with proteins at the of whereas is distributed the the two at high localization of shown that and are at the centrosome in mitotic cells J. Cell Biol. 1998; PubMed Scopus Google Scholar). Nek2C been in a screen with as and Nek2C the site we cells with Nek2C with we of the at These centrosome were to of Nek2A and Thus, as predicted from the known Nek2C with and to the centrosome in a complex with Nek2C in the cells with Nek2C, we that in most cells the non-centrosomal protein was predominantly in the and This was in to cells with Nek2A in which the protein a localization, mainly nuclear mainly cytoplasmic and distributed evenly the cell were in cells and we to the distribution of the third splice variant, Nek2B. Nek2B was predominantly in the with the of cells having the protein predominantly in the cells were to and by Nek2C was predominantly in the nuclear whereas Nek2A was in in the nuclear and cytoplasmic Nek2B to be distributed between nuclear and cytoplasmic This with the for Nek2B is most to the a of cells, whereas the is a of was from the that the most cells were the that to show the cell However, cells, of in the there were cells with protein in the we that there is a of Nek2C into the whereas Nek2A to be evenly and Nek2B remains in the at least in the cells. Thus, nuclear of Nek2 is regulated by alternative of Nek2C an the the nuclear of Nek2C, not Nek2A Nek2B, we the Nek2 protein sequence for potential and nuclear D. Rev. Cell Dev. Biol. 15,: PubMed Scopus Google Scholar, L. Rev. Biochem. 1998; 67,: PubMed Scopus Google Scholar). identified in Nek2A a bipartite at and a weak at The two of and two the 8 amino acids from Nek2C, in a of amino acids in Nek2A a of amino acids in most bipartite have a of amino acids J. C. Cell. 1991; Full Text PDF PubMed Scopus Google Scholar), we as a result of the amino acid the may be by the nuclear in Nek2C in Nek2A. Nek2B lacks the second not a bipartite NLS. the sequence within the eight-amino acid from Nek2C and as a functional in Nek2A. of was we a of mutants in the predicted and mutants at the suggesting that protein in the C-terminal domain was not to the in the Nek2A protein no with the protein a of In in the Nek2C protein of the first the second to proteins that were predominantly nuclear and with was at the protein from in the Thus, of the not to an of Nek2A in the of the of Nek2C into the that a functional bipartite is in Nek2C, is in Nek2A, and is in Nek2B. as a result of the the splice the cell the and the distribution of Nek2 in the and of a Nek2 NIMA chromatin condensation phosphorylation of histone H3 (8De Souza C.P. Osmani A.H. Wu L.P. Spotts J.L. Osmani S.A. Cell. 2000; 102,: 293-302Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar). therefore, nuclear of Nek2C However, cells chromatin that with cells with strong nuclear of Nek2C chromatin Nek2A has been reported to with in and to with the protein, Y. Y. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, J. C. A. Y. J. 2004; PubMed Scopus Google Scholar). therefore, Nek2C was in and with As the of cells in the there was from the no with a nuclear for Nek2C therefore, to an for nuclear of Nek2 the for substrate P. A. Biochem. J. PubMed Scopus Google Scholar). This has been for of kinases by of high of and high of with extracts that have been to kinases from their and the and nuclear extracts were from cells and by These were for with the substrate of Nek2 A.M. J. Nigg E.A. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google Scholar), and no kinase Nek2A, Nek6, Nek7, Nek9 separation by and 28-kDa protein in of the nuclear was by the Nek2 kinase not the closely related Nek6, Nek7, and Nek9 This protein was not in of the cytoplasmic be to the of the phosphorylation and the of the to that 28-kDa protein is to represent a novel nuclear substrate of Nek2. Nek2A was in a screen for human kinases related to Aspergillus NIMA Fry A.M. C. T. Nigg E.A. Cell 1994; Google Scholar). The first alternative splice variant, Nek2B, was identified in Xenopus Dev. Biol. PubMed Scopus Google and in cultured human cells (19Hames R.S. Fry A.M. Biochem. J. 2002; 361,: 77-85Crossref PubMed Scopus (68) Google Scholar). recently, Nek2C was described after a screen with a and and as M. Wu R. S. C. C. Y. 2004; PubMed Scopus (34) Google Scholar). These three splice variants differ in their non-catalytic C-terminal and not protein Nek2C from Nek2A in as it lacks amino acids in the of the non-catalytic that has on localization, which in may the splice variants to functions during cell Nek2C were identified in the screen with a the of in that were Nek2A M. Wu R. S. C. C. Y. 2004; PubMed Scopus (34) Google Scholar). Nek2A were from mouse in three Development. PubMed Google Scholar, M. Nigg E.A. Cell PubMed Scopus (34) Google Scholar, A. A. B. Oncogene. 1998; 16,: PubMed Scopus Google Scholar). both Nek2A and Nek2C are in may have functions to during meiotic cell that the splice site and of we were to Nek2C in three human cell and at Nek2A. studies revealed of Nek2 in cell and between Nek2A and Nek2C Fry A.M. 2005; PubMed Scopus Google Scholar). be to there is of both splice variants. at the sequence there is difference between Nek2A and Nek2C, and that share many of the same to of kinase activity, we that Nek2A and Nek2C phosphorylate the substrate show similar of have the to dimerization, and both the C which two is in the two and we no difference in their in mitotic extracts cells. Finally, Nek2A and Nek2C both the amino acids for microtubule and centrosome localization, and we were to that Nek2C Thus, not that Nek2A and Nek2C are similar evidence for the of functional the high degree of sequence we were to an difference in the of the two variants. of it was that Nek2C was into the whereas Nek2A was evenly distributed the be by the of the amino acids from Nek2C that result from Nek2C an is an that to the bipartite J. C. Cell. 1991; Full Text PDF PubMed Scopus Google Scholar). of the to of nuclear Nek2C, whereas of a within the amino acids from Nek2C no Nek2B, which has the first and lacks a functional was within the Nek2A Nek2C in cell Nek2 proteins are are to the for proteins that into the This proteins were in both in the most cells. of the protein, which is at is to be of to the domain of show that there is to two in the and in the second are by a of M. L. J. Cell. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, J. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). on the sequence of revealed that amino acids are not whereas are have activity J. C. Cell. 1991; Full Text PDF PubMed Scopus Google Scholar). In Nek2A, the is to amino acids and additional and that the of the and with to as a bipartite NLS. there is support for of the with J. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). However, there are cells in which Nek2A is in the that the not activity A.M. Meraldi P. Nigg E.A. EMBO J. 1998; 17,: 470-481Crossref PubMed Scopus (335) Google Scholar). there may be an additional of at which the distribution of Nek2A is is that the second with the site the that nuclear and are the to and be for of Nek2. The of Nek2 in the remains to be on Nek2 is to chromatin in meiotic cells Development. PubMed Google Scholar, M. Nigg E.A. Cell PubMed Scopus (34) Google Scholar). However, studies on mouse spermatocytes that Nek2 an role in chromatin condensation during the first meiotic division phosphorylation of the chromatin-associated protein, high mobility protein (17Di Agostino S. Rossi P. Geremia R. Sette C. Development. 2002; 129,: 1715-1727Crossref PubMed Google Scholar, 18Di Agostino S. Fedele M. Chieffi P. Fusco A. Rossi P. Geremia R. Sette C. Mol. Biol. Cell. 2004; 15,: 1224-1232Crossref PubMed Scopus (75) Google Scholar). entry of Nek2C may be for not to as high mobility protein A2, to including activated extracellular signal-regulated kinase nuclear with the that NIMA chromatin condensation in Aspergillus (8De Souza C.P. Osmani A.H. Wu L.P. Spotts J.L. Osmani S.A. Cell. 2000; 102,: 293-302Abstract Full Text Full Text PDF PubMed Scopus (132) Google the most for nuclear Nek2. However, in to we that nuclear of Nek2C not phosphorylation of histone it is not to premature chromatin have been described for Nek2 with including (also known as Y. Y. J. Biol. Chem. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar, J. C. A. Y. J. 2004; PubMed Scopus Google Scholar). However, we that nuclear Nek2C was from and not with the of reported the nuclear of Nek2C remains we to a for novel nuclear of Nek2 the This to of a 28-kDa protein as a substrate of Nek2. be to to protein by In support for a nuclear role of Nek2, alternative splicing the and thereby of a bipartite are to Nigg for Cell for the S. of for the and J. for for the members of for