Role For Nek2 Research Articles

Bifunctional Inhibitor Reveals NEK2 as a Therapeutic Target and Regulator of Oncogenic Pathways in Lymphoma.

Expression of the serine/threonine kinase never in mitosis gene A (NIMA)-related kinase 2 (NEK2) is essential for entry into mitosis via its role in facilitating centrosome separation. Its overactivity can lead to tumorigenesis and drug resistance through the activation of several oncogenic pathways, including AKT. Although the cancer-enabling activities of NEK2 are documented in many malignancies, including correlations with poor survival in myeloma, breast, and non-small cell lung cancer, little is known about the role of NEK2 in lymphoma. Here, in tumors from patients with diffuse large B-cell lymphoma (DLBCL), the most common, aggressive non-Hodgkin lymphoma, we found a high abundance of NEK2 mRNA and protein associated with an inferior overall survival. Using our recently developed NEK2 inhibitor, NBI-961, we discovered that DLBCL cell lines and patient-derived cells exhibit a dependency on NEK2 for their viability. This compromised cell fitness was directly attributable to efficient NEK2 inhibition and proteasomal degradation by NBI-961. In a subset of particularly sensitive DLBCL cells, NBI-961 induced G2/mitosis arrest and apoptosis. In contrast, an existing indirect NEK2 inhibitor, INH154, did not prevent NEK2 autophosphorylation, induce NEK2 proteasomal degradation, or affect cell viability. Global proteomics and phospho-proteomics revealed that NEK2 orchestrates cell-cycle and apoptotic pathways through regulation of both known and new signaling molecules. We show the loss of NEK2-sensitized DLBCL to the chemotherapy agents, doxorubicin and vincristine, and effectively suppressed tumor growth in mice. These studies establish the oncogenic activity of NEK2 in DLBCL and set the foundation for development of anti-NEK2 therapeutic strategies in this frequently refractory and relapse-prone cancer.

Role of NIMA-related kinase 2 in lung cancer: Mechanisms and therapeutic prospects.

The second most common cancer in both males and females is lung cancer. Chemotherapeutic resistance is the main problem associated with the treatment of lung cancer. Radiation therapy and surgery also produce recurrence in lung cancer patients; this shows the need to develop novel agents acting on new targets. A never in mitosis (NIMA)-related kinase 2 (NEK2) is a serine/threonine kinase associated with the family of NIMA-related kinase (NEK). NEK2 plays an important role in the regulating mitotic processes, such as centrosome duplication and separation, kinetochore attachment, spindle assembly checkpoint, and microtubule stabilization. Several in vitro, in vivo, and clinical studies have confirmed the overexpression of NEK2 in various types of cancers including lung cancer. Overexpression of NEK2 in non-small cell lung cancer (NSCLC) cells increased cell proliferation and chromosomal instability. The overexpression of NEK2 results in the activation of its downstream proteins such as β-catenin, MAD2, Hec1, rootletin, C-Nap1, CDC20, Cep68, and Sgo1. Activation of the Akt, β-catenin, and Wnt pathways could promote growth and metastasis of lung cancer cells. Such confirmation suggests that NEK2 is a novel target for treating many cancers including lung cancer. The current review provides an idea about functions and regulation of NEK2 and emphasizes about the role of NEK2 in lung cancer by discussing in vitro, in vivo, and clinical studies pertaining to the same.

NEK2 Inhibition Enhances the Efficacy of PD-1/PD-L1 Blockade in Multiple Myeloma

IntroductionThe development of new treatments for high-risk multiple myeloma (HRMM) are needed. The PD-1/PD-L1 axis is one of the chief inhibitory immune checkpoints in antitumor immunity. Despite the success of PD-1 (PDCD1) / PD-L1 (CD274) blockade in some neoplasms, use of it as a monotherapy has failed to improve outcome in RRMM. We have previously demonstrated that the cell-cycle-regulated serine-threonine kinase, NEK2 is elevated in HRMM and that inhibition of NEK2 can overcome drug-resistance and prolong survival of xenografted MM cells. Here, we aimed to investigate the possible role of NEK2 in regulating the immune checkpoint response in MM and development of possible anti-PD1/PDL1 combination therapies.MethodsGene expression profiles and pathway enrichment analyses were conducted on oligonucleotide microarray gene expression profiles from over 1000 primary MM samples to evaluate the correlation of NEK2 and immune checkpoint expression levels. To elucidate the underlying mechanism, we used Nek2 -/- mice crossed with EμMyc mice to generate B cell tumor mouse model with NEK2 deficiency. RNA-sequencing analyses of premalignant B cells was compared between EμMyc/Nek2 WT and EμMyc/Nek2 -/- mice. The hub molecular regulators in the NEK2 correlated pathways were further determined by western blot using NEK2 overexpressing and knockdown cell lines and then verified by co-immunoprecipitation with a NEK2 antibody. Lastly, to establish its clinic significance, the efficacy of INH1 (small compound NEK2 inhibitor), (D)-PPA 1 (peptide-based PD-1/PD-L1 interaction inhibitor) or a PD-L1 (monoclonal antibody) was tested in bone marrow BM mononuclear cells from primary MM patients in-vitro as well as in MM xenografts. Tumor burden and T cell immune responses were monitored by M-spike and mass cytometry.ResultsGene expression profiles demonstrated that CD274 expression was significantly higher in the non-proliferative hyperdiploid (HY) subtype of MM, representing between 25-35% of all MM. NEK2 was negatively correlated with CD274 gene expression across all 7 MM subtypes. Gene set enrichment analysis showed that the IFN-γ signaling pathway, which can induce CD274 expression, was significantly enriched in the HY subtype as well as premalignant B cells from EμMyc/Nek2 -/- mice. Elevated expression of EZH2, a histone methyltransferase gene, is also highly correlated wirth NEK2 levels in primary MM. We found that NEK2 inhibition increases CD274 expression as well as reduced EZH2 expression and H3K27me3 levels in MM cell lines. In contrarst, myeloma cells overexpressing NEK2 showed increased expression and activity of EZH2 and H3K27me3 levels. Thus, NEK2 appears to regulate CD274/PD-L1 expression through EZH2-mediated histone methylation. Next we demonstrated that NEK2 and EZH2 directly interact and that overexpression of NEK2 leads to increased methylation of the CD274/PD-L1 gene. We treated BM mononuclear cells from primary MM with PD-1/PD-L1 inhibitor with and without a NEK2 inhibitor. The combination was most effective at eliminating CD138 + myeloma cells while having no effects on T, B and myeloid cell populations.ConclusionOur study showed that expression of CD274/PD-L1 is suppressed in primary HRMM and that CD274/PD-L1 expression is negatively regulated by NEK2 via EZH2-mediated methylation. Inhibition of NEK2 sensitizes myeloma cells to PD-1/PD-L1 blockade, showing either a synergistic or an additive effect in MM cell cytotoxicity. DisclosuresNo relevant conflicts of interest to declare.

Abstract 2545: Nek2 and other mitotic kinases are downstream of the E2F activators, and may modulate the epithelial-to-mesenchymal transition in breast cancer

Abstract The E2F transcription factors have been extensively studied in cancer since they are known for their role in the regulation of cell cycle progression, centrosome duplication, cell survival, and other functions. We recently demonstrated that the E2F activators (E2F1, E2F2, and E2F3) regulate mitosis through the elevated expression of multiple mitotic proteins including Sgo1, Nek2, Hec1, BubR1, and Mps1. We have shown that Mps1 triggers EMT through multiple mechanisms. NIMA-related kinase 2 (Nek2) is a centrosome-associated protein kinase particularly abundant in cells during the G2-M phase, which primary function is to phosphorylate centrosome linker proteins to cause centrosome disjunction and the formation of the bipolar mitotic spindle. Previous results from our lab showed that overexpression of Nek2 in HCC1954 (Her2+ breast cancer cell line) with a knock down for E2F3 rescued a high centrosome amplification pattern and enhances the formation of invasive protrusions. cBioportal analysis using the TCGA database showed Nek2 mRNA alterations in 9.1% of breast cancer patients and is predominantly present in tumors that are ER-, PR-, and Her2- (25%). Similarly, analysis using the METABRIC database showed Nek2 mRNA alterations in 6.1% of breast cancer patients and is predominantly present in tumors from basal (24%), Her2+ (10%), and luminal B (13.9%) subtypes. Based on these results, we hypothesize that Nek2 overexpression has a role in the epithelial-to-mesenchymal (EMT) pathway leading to cell migration and invasion as prelude to metastasis in breast cancer. To address this, we used MCF10A non-tumorigenic mammary cells with or without the overexpression of Nek2 (MCF10A/GFP and MCF10A/GFP-Nek2). Our preliminary data indicates that overexpression of GFP-Nek2 in mammary epithelial cells enhances levels of vimentin, whereas decreased the levels of E-cadherin, suggesting a role of Nek2 in a mesenchymal state. Likewise, siRNA-mediated silencing of Nek2 in mesenchymal breast cancer cells modulates markers of EMT. Because inhibitors are available for Nek2, it would be feasible to target this kinase to combat metastatic HR- breast cancers. Our work will allow the identification of mechanistic molecular pathways influenced by Nek2 role in driving invasion and metastasis to highlight this mitotic kinase as a potential prognostic marker for high-risk breast tumors. Citation Format: Yainyrette Rivera-Rivera, Mihaela Marina, Harold I. Saavedra. Nek2 and other mitotic kinases are downstream of the E2F activators, and may modulate the epithelial-to-mesenchymal transition in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2545.

Abstract 506: The role of Nek2 in hepatocellular carcinoma

Abstract Cancer is a disease of aging. Among different types of cancer, liver cancer is one of the most prevalent cancers over the world and particularly affects people in some East Asia countries such as Korea, Japan and China. The NIMA-related kinase 2 (Nek2), which regulates centrosome cohesion, is a potential player in carcinogenesis. Our evidence showed Nek2 mRNA and protein levels are overexpressed in liver cancer cells and promotes HCC cell growth. Since Nek2 is pertinent to centrosome, we speculated that it might take part in centrosome regulation. To study the effect of Nek2 in chromosomal instability, centrosome splitting and cell cycle, a stable isoform Nek2A overexpression inducible system was generated in different Hepatocellular Carcinoma cell lines for investigations through immunofluorescent staining and cell-cytometry. For the study of centrosome, we observed that higher proportion of cells with centrosome splitting occurred in the Nek2A overexpressing cells in both HepG2 and SMMC-7721 inducible cell lines. Moreover, cell cycle analysis showed an increased content of DNA when Nek2A is overexpressed, suggesting that Nek2A induces more aneuploidy cells. To conclude, overexpression of Nek2 exacerbates chromosomal instability. Dysregulation of centrosome may be the key for understanding of regulatory mechanism of chromosomal instability by Nek2. Citation Format: Chan Shing Ho Vincent. The role of Nek2 in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 506. doi:10.1158/1538-7445.AM2017-506

NEK2 serves as a prognostic biomarker for hepatocellular carcinoma.

Never in mitosis gene A (NIMA)-related kinase 2 (NEK2) is a microtubule-associated protein that regulates spindle assembly in human cells and is overexpressed in various malignancies. However, the role of NEK2 in hepatocellular carcinoma (HCC) remains undetermined. We performed RNA-seq of the HCC cell line SMMC-7721 and the normal liver cell line HL-7702 using the Ion Proton System. NEK2 expression was detected using quantitative reverse transcription polymerase chain reaction in two cell lines and 5 matched HCC and adjacent non-tumorous liver tissues. The correlation between survival and NEK2 expression was analyzed in 359 patients with HCC using RNASeqV2 data available from The Cancer Genome Atlas (TCGA) website (https://tcga-data.nci.nih.gov/tcga/). The expression of NEK2, phospho-AKT and MMP-2 was evaluated by immunohistochemistry in 63 cases of HCC and matched adjacent non-tumorous liver tissues. Relationships between protein expression and clinicopathological parameters were assessed, and the correlations between NEK2 with phospho-AKT and MMP-2 expressions were evaluated. A total of 610 differentially expressed genes (DEGs) were revealed in the transcriptome comparison, 297 of which were upregulated and 313 were downregulated in HCC. NEK2, as the most obviously different DEG in cells and tissues from the RNA-seq data, was listed as an HCC candidate biomarker for further verification. NEK2 was overexpressed in HCC cells and tissues (P=0.002, P=0.013) and HCC patients with a high expression of NEK2 had a poor prognosis (P=0.0145). Clinical analysis indicated that the overexpression of NEK2 in HCC was significantly correlated with diolame complete (P<0.001), tumor nodule number (P=0.012) and recurrence (P=0.004). NEK2 expression was positively correlated with the expression of phospho-AKT (r=0.883, P<0.01) and MMP-2 (r=0.781, P<0.01). Overexpression of NEK2 was associated with clinicopathological characteristics and poor patient outcomes, suggesting that NEK2 serves as a prognostic biomarker for HCC. Alteration of NEK2 protein levels may contribute to invasion and metastasis of HCC, which may occur through activation of AKT signaling and promotion of MMP-2 expression.

The NIMA-like kinase Nek2 is a key switch balancing cilia biogenesis and resorption in the development of left-right asymmetry

Vertebrate left-right (LR) asymmetry originates at a transient left-right organizer (LRO), a ciliated structure where cilia play a crucial role in breaking symmetry. However, much remains unknown about the choreography of cilia biogenesis and resorption at this organ. We recently identified a mutation affecting NEK2, a member of the NIMA-like serine-threonine kinase family, in a patient with congenital heart disease associated with abnormal LR development. Here, we report how Nek2 acts through cilia to influence LR patterning. Both overexpression and knockdown of nek2 in Xenopus result in abnormal LR development and reduction of LRO cilia count and motility, phenotypes that are modified by interaction with the Hippo signaling pathway. nek2 knockdown leads to a centriole defect at the LRO, consistent with the known role of Nek2 in centriole separation. Nek2 overexpression results in premature ciliary resorption in cultured cells dependent on function of the tubulin deacetylase Hdac6. Finally, we provide evidence that the known interaction between Nek2 and Nup98, a nucleoporin that localizes to the ciliary base, is important for regulating cilium resorption. Together, these data show that Nek2 is a switch balancing ciliogenesis and resorption in the development of LR asymmetry.

The NIMA-like kinase Nek2 is a key switch balancing cilia biogenesis and resorption in the development of left-right asymmetry.

Vertebrate left-right (LR) asymmetry originates at a transient left-right organizer (LRO), a ciliated structure where cilia play a crucial role in breaking symmetry. However, much remains unknown about the choreography of cilia biogenesis and resorption at this organ. We recently identified a mutation affecting NEK2, a member of the NIMA-like serine-threonine kinase family, in a patient with congenital heart disease associated with abnormal LR development. Here, we report how Nek2 acts through cilia to influence LR patterning. Both overexpression and knockdown of nek2 in Xenopus result in abnormal LR development and reduction of LRO cilia count and motility, phenotypes that are modified by interaction with the Hippo signaling pathway. nek2 knockdown leads to a centriole defect at the LRO, consistent with the known role of Nek2 in centriole separation. Nek2 overexpression results in premature ciliary resorption in cultured cells dependent on function of the tubulin deacetylase Hdac6. Finally, we provide evidence that the known interaction between Nek2 and Nup98, a nucleoporin that localizes to the ciliary base, is important for regulating cilium resorption. Together, these data show that Nek2 is a switch balancing ciliogenesis and resorption in the development of LR asymmetry.

Nek2 is a novel regulator of B cell development and immunological response.

The serine/threonine kinase Nek2 is commonly found upregulated in a wide variety of neoplasms including diffuse large B cell lymphoma and multiple myeloma. High expression of Nek2 is implicated in the induction of chromosomal instability, promotion of cell proliferation, and drug resistance in tumor cells as well as a marker for poor clinical outcomes. Despite its well recorded involvement in chromosomal instability and neoplastic growth, little is known about the involvement of Nek2 in B cell development. Here we report the development of a transgenic mouse line with conditional expression of Nek2 in the B cell lineage and the effects it has on the development of B cells. Interestingly, we found that the overexpression of Nek2 does not induce spontaneous tumor formation within the transgenic mice up to 24 months after induction. Instead, overexpression of Nek2 in the B cell lineage affects the development of B cells by increasing the proportion of immature B cells in the bone marrow and decreasing B-1 B cells in peritoneal cavity. Furthermore, Nek2 transgenic mice develop spontaneous germinal centers and exhibit an enhanced T cell dependent immune response. Altogether, our data demonstrates a novel role for Nek2 in regulating B cell development and the immune response.

Centrosomal kinase Nek2 cooperates with oncogenic pathways to promote metastasis

Centrosomal kinase Nek2 is overexpressed in different cancers, yet how it contributes toward tumorigenesis remains poorly understood. dNek2 overexpression in a Drosophila melanogaster model led to upregulation of Drosophila Wnt ortholog wingless (Wg), and alteration of cell migration markers—Rho1, Rac1 and E-cadherin (Ecad)—resulting in changes in cell shape and tissue morphogenesis. dNek2 overexpression cooperated with receptor tyrosine kinase and mitogen-activated protein kinase signaling to upregulate activated Akt, Diap1, Mmp1 and Wg protein to promote local invasion, distant seeding and metastasis. In tumor cell injection assays, dNek2 cooperated with Ras and Src signaling to promote aggressive colonization of tumors into different adult fly tissues. Inhibition of the PI3K pathway suppressed the cooperation of dNek2 with other growth pathways. Consistent with our fly studies, overexpression of human Nek2 in A549 lung adenocarcinoma and HEK293T cells led to activation of the Akt pathway and increase in β-catenin protein levels. Our computational approach identified a class of Nek2-inhibitory compounds and a novel drug-like pharmacophore that reversed the Nek2 overexpression phenotypes in flies and human cells. Our finding posits a novel role for Nek2 in promoting metastasis in addition to its currently defined role in promoting chromosomal instability. It provides a rationale for the selective advantage of centrosome amplification in cancer.

Role of Nek2 on centrosome duplication and aneuploidy in breast cancer cells

Breast cancer is the most common solid tumor and the second most common cause of death in women. Despite a large body of literature and progress in breast cancer research, many molecular aspects of this complex disease are still poorly understood, hindering the design of specific and effective therapeutic strategies. To identify the molecules important in breast cancer progression and metastasis, we tested the in vivo effects of inhibiting the functions of various kinases and genes involved in the regulation/modulation of the cytoskeleton by downregulating them in mouse PyMT mammary tumor cells and human breast cancer cell lines. These kinases and cytoskeletal regulators were selected based on their prognostic values for breast cancer patient survival. PyMT tumor cells, in which a selected gene was stably knocked down were injected into the tail veins of mice, and the formation of tumors in the lungs was monitored. One of the several genes found to be important for tumor growth in the lungs was NIMA-related kinases 2 (Nek2), a cell cycle-related protein kinase. Furthermore, Nek2 was also important for tumor growth in the mammary fat pad. In various human breast cancer cell lines, Nek2 knockdown induced aneuploidy and cell cycle arrest that led to cell death. Significantly, the breast cancer cell line most sensitive to Nek2 depletion was of the triple negative breast cancer subtype. Our data indicate that Nek2 has a pivotal role in breast cancer growth at primary and secondary sites, and thus may be an attractive and novel therapeutic target for this disease.

Abstract 3391: Overexpression of Nek2 promotes bortezomib resistance in multiple myeloma cells.

Abstract Drug resistance is a major complication in cancer therapy but the molecular mechanisms driving both innate and acquired drug resistance still remain largely unknown for many anti-cancer agents. Microarray analyses on paired primary multiple myeloma samples at baseline and after therapy or at relapse showed that the mitotic kinase NEK2 was one of the most up-regulated genes in myeloma cells after high-dose chemotherapy or at relapse. Nek2 is a Serine/Threonine kinase that is activated during mitosis and is associated centrosome function and structure at the G2/M transition. A role for Nek2 has been suggested in the separation of centrosomes as well as promoting cell cycle from G2 phase to M phase but no role for Nek2 in mediating drug resistance has been described. By analyzing the published (&amp;gt; 2,500) microarrays and clinical datasets, we found that NEK2 expression is increased in many malignancies, and that high expression of NEK2 was associated with a shorter event-free and overall survival. Moreover, NEK2 expression was typically increased in tumors with aggressive subtype and advanced stage. Our studies in myeloma cells indicate that over-expressing NEK2 results in enhanced cell proliferation and drug resistance, whereas knockdown of NEK2 induced significant cancer cell death and growth inhibition. Nek2 transfected myeloma cell lines ARP1, H929 and KMS28PE were used to investigate Nek2’s function relative to bortezomib resistance. We found that Nek2 over-expression significantly elevated the proteasome activity of transfected cells leading to decreased activity of Bortezomib in these cells. Using novel small molecule Nek2 inhibitors developed in our lab, we demonstrated efficient inhibition of proteasome activity in Nek2 over-expressing cancer cell lines. The treatment of cell with our lead compounds significantly inhibited the degradation of some proteasome targeted cell cycle regulators. Further, the combinations of these Nek2 inhibitors and bortezomib, greatly elevated the efficiency of bortezomib in decreasing the proteasome activity in vitro. The treatment with these novel Nek2 inhibitors successfully rescued the drug resistance in Nek2 over-expressed cells, indicating a potential therapy for bortezomib resistant myeloma patients. We conclude that NEK2 represents a predictor for drug resistance and poor prognosis in cancers and could be a potential target for cancer therapy. Citation Format: Jessica Flory, Rachel Brog, Ling Yao Meng, Lee Call, Hariprasad Vankayalapati, Guido Tricot, Fenghuang Zhan, David J. Bearss. Overexpression of Nek2 promotes bortezomib resistance in multiple myeloma cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3391. doi:10.1158/1538-7445.AM2013-3391

Plasmodium falciparum NIMA-related kinase Pfnek-1: sex specificity and assessment of essentiality for the erythrocytic asexual cycle

The Plasmodium falciparum kinome includes a family of four protein kinases (Pfnek-1 to -4) related to the NIMA (never-in-mitosis) family, members of which play important roles in mitosis and meiosis in eukaryotic cells. Only one of these, Pfnek-1, which we previously characterized at the biochemical level, is expressed in asexual parasites. The other three (Pfnek-2, -3 and -4) are expressed predominantly in gametocytes, and a role for nek-2 and nek-4 in meiosis has been documented. Here we show by reverse genetics that Pfnek-1 is required for completion of the asexual cycle in red blood cells and that its expression in gametocytes in detectable by immunofluorescence in male (but not in female) gametocytes, in contrast with Pfnek-2 and Pfnek-4. This indicates that the function of Pfnek-1 is non-redundant with those of the other members of the Pfnek family and identifies Pfnek-1 as a potential target for antimalarial chemotherapy. A medium-throughput screen of a small-molecule library provides proof of concept that recombinant Pfnek-1 can be used as a target in drug discovery.

Inhibition of centrosome separation after DNA damage: a role for Nek2.

DNA damage results in cell cycle arrest in G2. Centrosomes also separate in G2, raising the question of whether separation occurs during the DNA damage-induced G2 arrest. Nek2, the mammalian homologue of NIMA, is a cell cycle-regulated serine/threonine protein kinase that regulates centrosome separation during G2. Here we show that damaged cells fail to activate Nek2. Both Nek2 levels and activity are reduced after DNA damage. Radiation inhibits the premature centrosome splitting induced by overexpression of Nek2, indicating that Nek2 is involved in activation of the G2 checkpoint and is not secondary to cell cycle arrest. We confirm using siRNA that centrosome separation and cell growth are impaired in the absence of Nek2. These studies define a previously unreported DNA damage response of inhibition of centrosome separation mechanistically linked to Nek2.

Activity of the Human Centrosomal Kinase, Nek2, Depends on an Unusual Leucine Zipper Dimerization Motif

Nek2 is a human cell cycle-regulated kinase that is structurally related to the mitotic regulator, NIMA, of Aspergillus nidulans. Localization studies have shown that Nek2 is a core component of the centrosome, the microtubule organizing center of the cell, and functional approaches suggest a possible role for Nek2 in centrosome separation at the G2/M transition. Here, we have investigated the importance of an unusual leucine zipper coiled-coil motif present in the C-terminal noncatalytic domain of the Nek2 kinase. Glycerol gradient centrifugation indicated that endogenous Nek2 is present in HeLa cells as a salt-resistant 6 S complex, the predicted size of a Nek2 homodimer. Recombinant Nek2 overexpressed in insect cells also formed a 6 S complex, whereas a Nek2 mutant specifically lacking the leucine zipper motif was monomeric. Using yeast two-hybrid interaction analyses and coprecipitation assays, we found that Nek2 can indeed form homodimers both in vivo and in vitro and that this dimerization specifically required the leucine zipper motif. Moreover, deletion of the leucine zipper prevented a trans-autophosphorylation reaction on the C-terminal domain of Nek2 and strongly reduced Nek2 kinase activity on exogenous substrates. Finally, we emphasize that the Nek2 leucine zipper described here differs from classical leucine zippers in that it exhibits a radically different arrangement of hydrophobic and charged amino acids. Thus, this study reveals not only an important mechanism for the regulation of the Nek2 kinase but, furthermore, highlights an unusual organization of a leucine zipper dimerization motif.