Plasmodium NEK1 coordinates MTOC organisation and kinetochore attachment during rapid mitosis in male gamete formation.

Mitosis is an important process in the cell cycle required for cells to divide. Never in mitosis (NIMA)-like kinases (NEKs) are regulators of mitotic functions in diverse organisms. Plasmodium spp., the causative agent of malaria is a divergent unicellular haploid eukaryote with some unusual features in terms of its mitotic and nuclear division cycle that presumably facilitate proliferation in varied environments. For example, during the sexual stage of male gametogenesis that occurs within the mosquito host, an atypical rapid closed endomitosis is observed. Three rounds of genome replication from 1N to 8N and successive cycles of multiple spindle formation and chromosome segregation occur within 8 min followed by karyokinesis to generate haploid gametes. Our previous Plasmodium berghei kinome screen identified 4 Nek genes, of which 2, NEK2 and NEK4, are required for meiosis. NEK1 is likely to be essential for mitosis in asexual blood stage schizogony in the vertebrate host, but its function during male gametogenesis is unknown. Here, we study NEK1 location and function, using live cell imaging, ultrastructure expansion microscopy (U-ExM), and electron microscopy, together with conditional gene knockdown and proteomic approaches. We report spatiotemporal NEK1 location in real-time, coordinated with microtubule organising centre (MTOC) dynamics during the unusual mitoses at various stages of the Plasmodium spp. life cycle. Knockdown studies reveal NEK1 to be an essential component of the MTOC in male cell differentiation, associated with rapid mitosis, spindle formation, and kinetochore attachment. These data suggest that P. berghei NEK1 kinase is an important component of MTOC organisation and essential regulator of chromosome segregation during male gamete formation.

ALS-associated C21ORF2 variant disrupts DNA damage repair, mitochondrial metabolism, neuronal excitability and NEK1 levels in human motor neurons.

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease leading to motor neuron loss. Currently mutations in > 40 genes have been linked to ALS, but the contribution of many genes and genetic mutations to the ALS pathogenic process remains poorly understood. Therefore, we first performed comparative interactome analyses of five recently discovered ALS-associated proteins (C21ORF2, KIF5A, NEK1, TBK1, and TUBA4A) which highlighted many novel binding partners, and both unique and shared interactors. The analysis further identified C21ORF2 as a strongly connected protein. The role of C21ORF2 in neurons and in the nervous system, and of ALS-associated C21ORF2 variants is largely unknown. Therefore, we combined human iPSC-derived motor neurons with other models and different molecular cell biological approaches to characterize the potential pathogenic effects of C21ORF2 mutations in ALS. First, our data show C21ORF2 expression in ALS-relevant mouse and human neurons, such as spinal and cortical motor neurons. Further, the prominent ALS-associated variant C21ORF2-V58L caused increased apoptosis in mouse neurons and movement defects in zebrafish embryos. iPSC-derived motor neurons from C21ORF2-V58L-ALS patients, but not isogenic controls, show increased apoptosis, and changes in DNA damage response, mitochondria and neuronal excitability. In addition, C21ORF2-V58L induced post-transcriptional downregulation of NEK1, an ALS-associated protein implicated in apoptosis and DDR. In all, our study defines the pathogenic molecular and cellular effects of ALS-associated C21ORF2 mutations and implicates impaired post-transcriptional regulation of NEK1 downstream of mutant C21ORF72 in ALS.

NEK1 and STMN2 short tandem repeat lengths are not associated with Australian amyotrophic lateral sclerosis risk.

Sporadic amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with a complex genetic architecture. The lengths of two short tandem repeats (STRs), at the NEK1 and STMN2 loci, were recently associated with ALS risk in cohorts of European descent. The STMN2 STR was proposed to be predictive of clinical features including the age of onset and disease duration in bulbar onset cases. We sought to investigate NEK1 and STMN2 STR lengths in a cohort of Australian sporadic ALS cases (n = 608) and neurologically healthy controls (n = 4689) of European ancestry. ExpansionHunter was used to determine NEK1 and STMN2 STR length genotypes from whole-genome sequencing data followed by PCR validation of predicted lengths. No significant association was identified between sporadic ALS risk and the length of either STR. Further, neither NEK1 nor STMN2 STR lengths were indicative of the age of onset or disease duration. We report that the NEK1 and STMN2 STRs were not associated with ALS risk or clinical features in this Australian sporadic ALS cohort.

Design, synthesis and biological evaluation of novel aminopyrazole- and 7-azaindole-based Nek1 inhibitors and their effects on zebrafish kidney development.

NIMA-related protein kinase Nek1 is crucially involved in cell cycle regulation, DNA repair and microtubule regulation and dysfunctions of Nek1 play key roles in amyotrophic lateral sclerosis (ALS), polycystic kidney disease (PKD) and several types of radiotherapy resistant cancer. Targeting of Nek1 could reveal a new class of radiosensitizing substances and provide useful tools to better understand the aforementioned diseases. In this report we explore substituted aminopyrazoles and 7-azaindoles as potent inhibitors for the Nek1 kinase domain and examine their effect on kidney organogenesis in Danio rerio.

NEK1-mediated retromer trafficking promotes blood-brain barrier integrity by regulating glucose metabolism and RIPK1 activation.

Loss-of-function mutations in NEK1 gene, which encodes a serine/threonine kinase, are involved in human developmental disorders and ALS. Here we show that NEK1 regulates retromer-mediated endosomal trafficking by phosphorylating VPS26B. NEK1 deficiency disrupts endosomal trafficking of plasma membrane proteins and cerebral proteome homeostasis to promote mitochondrial and lysosomal dysfunction and aggregation of α-synuclein. The metabolic and proteomic defects of NEK1 deficiency disrupts the integrity of blood-brain barrier (BBB) by promoting lysosomal degradation of A20, a key modulator of RIPK1, thus sensitizing cerebrovascular endothelial cells to RIPK1-dependent apoptosis and necroptosis. Genetic inactivation of RIPK1 or metabolic rescue with ketogenic diet can prevent postnatal lethality and BBB damage in NEK1 deficient mice. Inhibition of RIPK1 reduces neuroinflammation and aggregation of α-synuclein in the brains of NEK1 deficient mice. Our study identifies a molecular mechanism by which retromer trafficking and metabolism regulates cerebrovascular integrity, cerebral proteome homeostasis and RIPK1-mediated neuroinflammation.

Human Aurora kinase inhibitor Hesperadin reveals epistatic interaction between Plasmodium falciparum PfArk1 and PfNek1 kinases.

Mitosis has been validated by numerous anti-cancer drugs as being a druggable process, and selective inhibition of parasite proliferation provides an obvious opportunity for therapeutic intervention against malaria. Mitosis is controlled through the interplay between several protein kinases and phosphatases. We show here that inhibitors of human mitotic kinases belonging to the Aurora family inhibit P. falciparum proliferation in vitro with various potencies, and that a genetic selection for mutant parasites resistant to one of the drugs, Hesperadin, identifies a resistance mechanism mediated by a member of a different kinase family, PfNek1 (PF3D7_1228300). Intriguingly, loss of PfNek1 catalytic activity provides protection against drug action. This points to an undescribed functional interaction between Ark and Nek kinases and shows that existing inhibitors can be used to validate additional essential and druggable kinase functions in the parasite.

Protein-Bound Polysaccharides from Coriolus Versicolor Induce RIPK1/RIPK3/MLKL-Mediated Necroptosis in ER-Positive Breast Cancer and Amelanotic Melanoma Cells.

BACKGROUND/AIMS: The induction of necroptosis, a form of caspase-independent cell death, represents one of the most promising anticancer therapeutic modalities, as necroptosis serves as an alternative way to eliminate apoptosis-resistant tumor cells. Here, we investigated whether protein-bound polysaccharides (PBPs) derived from the fungus Coriolus versicolor (CV) induce the necroptotic death pathway in breast cancer and melanoma cells. METHODS: MCF-7 and SKMel-188 cells were exposed to PBPs either alone or in combination with necrostatin-1 (Nec-1), GSK'872 or necrosulfonamide (NSA), pharmacological inhibitors of the kinases receptor-interacting protein 1 kinase (RIPK1), receptor interacting protein kinase 3 (RIPK3) and mixed lineage kinase domain-like protein (MLKL), respectively, which are involved in necroptotic processes. The effects of cellular treatment with these inhibitors were quantified by measuring cell viability and reactive oxygen species (ROS) generation via 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and 2',7'-dichlorofluorescein diacetate (DCF-DA) assays, respectively. The morphological changes induced in these cells were detected using holotomographic (HT) microscopy. Activation of the TNF-α/TNFR1 pathway in the PBP-stimulated cells was evaluated using TNF-α-neutralizing antibody, qRT-PCR and immunofluorescence-based assays. RESULTS: PBPs showed effective antitumor activity against MCF-7 and SKMel-188 cells. Cotreatment of the cells with Nec-1, GSK'872 or NSA abrogated PBP-induced cell death, and the cells were protected against membrane rupture. Moreover, breast cancer cell death caused by PBPs was mediated by induced activation of the TNF-α/TNFR1 pathway. Interestingly, the melanoma cells did not express TNF-α or TNFR1 after PBP stimulation; instead, PBPs triggered intracellular ROS generation, which was partially diminished by the inhibitors Nec-1, GSK'872 and NSA. CONCLUSION: These results suggest that PBPs from the fungus CV induce RIPK1/RIPK3/MLKL-mediated necroptosis in breast cancer and melanoma cells, providing novel insights into the molecular effects of PBPs on cancer cells.

Fractionation-Dependent Radiosensitization by Molecular Targeting of Nek1.

NIMA (never-in-mitosis gene A)-related kinase 1 (Nek1) is shown to impact on different cellular pathways such as DNA repair, checkpoint activation, and apoptosis. Its role as a molecular target for radiation sensitization of malignant cells, however, remains elusive. Stably transduced doxycycline (Dox)-inducible Nek1 shRNA HeLa cervix and siRNA-transfected HCT-15 colorectal carcinoma cells were irradiated in vitro and 3D clonogenic radiation survival, residual DNA damage, cell cycle distribution, and apoptosis were analyzed. Nek1 knockdown (KD) sensitized both cell lines to ionizing radiation following a single dose irradiation and more pronounced in combination with a 6 h fractionation (3 × 2 Gy) regime. For preclinical analyses we focused on cervical cancer. Nek1 shRNA HeLa cells were grafted into NOD/SCID/IL-2Rγc-/- (NSG) mice and Nek1 KD was induced by Dox-infused drinking water resulting in a significant cytostatic effect if combined with a 6 h fractionation (3 x 2 Gy) regime. In addition, we correlated Nek1 expression in biopsies of patients with cervical cancer with histopathological parameters and clinical follow-up. Our results indicate that elevated levels of Nek1 were associated with an increased rate of local or distant failure, as well as with impaired cancer-specific and overall survival in univariate analyses and for most endpoints in multivariable analyses. Finally, findings from The Cancer Genome Atlas (TCGA) validation cohort confirmed a significant association of high Nek1 expression with a reduced disease-free survival. In conclusion, we consider Nek1 to represent a novel biomarker and potential therapeutic target for drug development in the context of optimized fractionation intervals.

Expression of the NEK family in normal and cancer tissue: an immunohistochemical study.

BACKGROUND: The NEK serine/threonine protein kinases are involved in cell cycle checkpoints, DNA damage repair, and apoptosis. Alterations in these pathways are frequently associated with cell malignant cellular transformations. Thyroid cancer is the most common malignant tumour in the endocrine system. Despite good treatment methods, the number of cases has increased significantly in recent years. Here, we studied the expression of NEK1, NEK2, NEK3, and NEK5 in different types of normal and malignant tissues, using tissue microarray analysis, and identified NEKs as potential markers in thyroid malignancy. METHODS: The studied cases comprised multiple cancer tissue microarrays, including breast, colon, esophagus, kidney, lung, pancreas, prostate, stomach, thyroid and uterine cervix, as well as 281 patients who underwent thyroid resection for thyroid cancer or thyroid nodules. The expression of NEK1, NEK2, NEK3, and NEK5 was analyzed by immunohistochemistry. The expression pattern was evaluated in terms of intensity by two methods, semiquantitative and quantitative, and was compared between normal and cancer tissue. RESULTS: We analysed the expression of each member of the NEK family in a tissue-dependent manner. Compared to normal tissue, most of the evaluated proteins showed lower expression in lung tumour. However, in the thyroid, the expression was higher in malignant tissue, especially for NEK 1, NEK3 and NEK5. Concerning characteristics of the thyroid tumour, such as aggressiveness, NEK1 expression was higher in tumours with multifocality and in patients with lymph node metastasis. NEK3 expression was stronger in patients with stage II, that involved metastasis. NEK5, on the other hand, showed high expression in patients with invasion and metastasis and in patients with tumour size > 4 cm. Furthermore, this work, demonstrated for the first time a high specificity and sensitivity of over-expression of NEK1 in classical and follicular variants of papillary thyroid cancer and NEK3 in tall-cell papillary thyroid cancer. CONCLUSION: Taken together, the NEK protein kinases emerge as important proteins in thyroid cancer development and may help to identify malignancy and aggressiveness features during diagnosis. TRIAL REGISTRATION: This study was retrospectively registered.  www.accamargo.org.br/cientistas-pesquisadores/comite-de-etica-em-pequisa-cep.

The TLK1/Nek1 axis contributes to mitochondrial integrity and apoptosis prevention via phosphorylation of VDAC1.

The TLK1/Nek1 axis contributes to cell cycle arrest and implementation of the DDR to mediate survival upon DNA damage. However, when the damage is too severe, the cells typically are forced into apoptosis, and the contribution of TLKs in this process has not been investigated. In contrast, it is known that Nek1 may play a role by phosphorylating VDAC1 maintaining proper opening and closure of the channel and thus mitochondrial integrity. We now show that the activating phosphorylation of Nek1-T141 by TLK1 contributes to the phosphorylation and stability of VDAC1 and thereby to mitochondrial permeability and integrity. Treatment of three different cell lines model that overexpress Nek1-T141A mutant with doxorubicin showed exquisite sensitivity to the drug, with implementation of rapid accumulation of cells with subG1 DNA content (apoptotic) and other alterations in the cell cycle. In addition, these cells displayed reduced oxygen consumption under normal conditions and less reliance on mitochondria and more dependence on glycolysis for energy production. Consistent with greater apoptosis, upon treatment with low doses of doxorubicin, cells overexpressing Nek1-T141A displayed leakage of Cyt-C into the cytoplasmic fraction. This suggests that inhibiting the TLK1/Nek1/VDAC1 nexus could sensitize cancer cells to apoptotic killing in combination with an appropriate DNA damaging agent. We in fact have previously reported that Nek1 expression is elevated in advanced Prostate Cancer (PCa) and we now report that VDAC1 expression is elevated and correlated with disease stage, thereby making the TLK1/Nek1/VDAC1 nexus a very attractive target for PCa.

The TLK1-Nek1 axis promotes prostate cancer progression.

We recently uncovered the critical TLK1>NEK1>ATR > Chk1 axis in mediating the DDR and cell cycle checkpoint while transiting from Androgen Sensitive to Insensitive growth for LNCaP and TRAMP-C2 cells. However, we did not know the generality of this pathway in PCa progression since there are few cell lines where the transition has been studied. Furthermore, the identification of Nek1, and more importantly the TLK-mediated phosphorylation of T141, has never been studied in PCa biopsies. We now report the first study of a PCa TMA of p-Nek1-T141 and correlation to the Gleason score. In addition we found that TRAMP mice treated with the TLK inhibitor, thioridazine (THD), following castration did not recover cancerous growth of their prostates. Moreover, we recapitulated the process of translational increase in TLK1B expression in a naïve PDX model that was established from an AR + adenocarcinoma. Therefore, we believe that this TLK1-Nek1 mediated DDR axis is likely to be a common adaptive response during the transition of PCa cells toward androgen-insensitive growth, and hence CRPC progression, which has the potential to be targeted with THD and other TLK or Nek1 inhibitors.

TgCep250 is dynamically processed through the division cycle and is essential for structural integrity of the Toxoplasma centrosome.

The apicomplexan centrosome has a unique bipartite structure comprising an inner and outer core responsible for the nuclear cycle (mitosis) and budding cycles (cytokinesis), respectively. Although these two cores are always associated, they function independently to facilitate polyploid intermediates in the production of many progeny per replication round. Here, we describe the function of a large coiled-coil protein in Toxoplasma gondii, TgCep250, in connecting the two centrosomal cores and promoting their structural integrity. Throughout the cell cycle, TgCep250 localizes to the inner core but, associated with proteolytic processing, is also present on the outer core during the onset of cell division. In the absence of TgCep250, stray centrosome inner and outer core foci were observed. The detachment between centrosomal inner and outer cores was found in only one of the centrosomes during cell division, indicating distinct states of mother and daughter centrosomes. In mammals, Cep250 processing is required for centrosomal splitting and is mediated by Nek phopsphorylation. However, we show that neither the nonoverlapping spatiotemporal localization of TgNek1 and TgCep250 nor the distinct phenotypes upon their respective depletion support conservation of this mechanism in Toxoplasma. In conclusion, TgCep250 has a tethering function tailored to the unique bipartite centrosome in the Apicomplexa.

VHL regulates NEK1 via both HIF-2α pathway and ubiquitin-proteasome pathway in renal cancer cell.

Both Von Hippel-Lindau tumor suppressor (VHL) and Never-in-mitosis A (NIMA)-related kinase 1 (NEK1) are involved in primary cilium formation, but whether VHL could regulate NEK1 is unknown. Here, we demonstrated that renal cancer cells Caki-1 and ACHN with wild-type VHL expressed lower level of NEK1 than that of VHL-defective cells including 786-O, 769-P and A498 cells. VHL-overexpression down-regulated NEK1 in 769-P cells, while VHL-knockdown up-regulated NEK1 in Caki-1 cells. In addition, we found the hypoxia response element (HRE) in the promoter sequence of NEK1 and hypoxia induced NEK1 expression both in vitro and in vivo. HIF-2α knockdown blocked hypoxia induced NEK1 upregulation instead of HIF-1α, which indicates that NEK1 may be a new target of HIF-2α. Moreover, we confirmed the association between VHL and NEK1 in Caki-1 cell, then showed VHL promoted NEK1 protein degradation and ubiquitination. In conclusion, our findings showed VHL regulates NEK1 via both HIF-2α pathway and ubiquitin-proteasome pathway in renal cancer cells.

Dialogue between centrosomal entrance and exit scaffold pathways regulates mitotic commitment.

The fission yeast scaffold molecule Sid4 anchors the septum initiation network to the spindle pole body (SPB, centrosome equivalent) to control mitotic exit events. A second SPB-associated scaffold, Cut12, promotes SPB-associated Cdk1-cyclin B to drive mitotic commitment. Signals emanating from each scaffold have been assumed to operate independently to promote two distinct outcomes. We now find that signals from Sid4 contribute to the Cut12 mitotic commitment switch. Specifically, phosphorylation of Sid4 by NIMAFin1 reduces Sid4 affinity for its SPB anchor, Ppc89, while also enhancing Sid4's affinity for casein kinase 1δ (CK1δ). The resulting phosphorylation of Sid4 by the newly docked CK1δ recruits Chk2Cds1 to Sid4. Chk2Cds1 then expels the Cdk1-cyclin B antagonistic phosphatase Flp1/Clp1 from the SPB. Flp1/Clp1 departure can then support mitotic commitment when Cdk1-cyclin B activation at the SPB is compromised by reduction of Cut12 function. Such integration of signals emanating from neighboring scaffolds shows how centrosomes/SPBs can integrate inputs from multiple pathways to control cell fate.

NEK1 kinase domain structure and its dynamic protein interactome after exposure to Cisplatin.

NEK family kinases are serine/threonine kinases that have been functionally implicated in the regulation of the disjunction of the centrosome, the assembly of the mitotic spindle, the function of the primary cilium and the DNA damage response. NEK1 shows pleiotropic functions and has been found to be mutated in cancer cells, ciliopathies such as the polycystic kidney disease, as well as in the genetic diseases short-rib thoracic dysplasia, Mohr-syndrome and amyotrophic lateral sclerosis. NEK1 is essential for the ionizing radiation DNA damage response and priming of the ATR kinase and of Rad54 through phosphorylation. Here we report on the structure of the kinase domain of human NEK1 in its apo- and ATP-mimetic inhibitor bound forms. The inhibitor bound structure may allow the design of NEK specific chemo-sensitizing agents to act in conjunction with chemo- or radiation therapy of cancer cells. Furthermore, we characterized the dynamic protein interactome of NEK1 after DNA damage challenge with cisplatin. Our data suggest that NEK1 and its interaction partners trigger the DNA damage pathways responsible for correcting DNA crosslinks.

Identification of the proteome complement of humanTLK1 reveals it binds and phosphorylates NEK1 regulating its activity.

The Tousled Like kinases (TLKs) are involved in numerous cellular functions, including the DNA Damage Response (DDR), but only a handful of substrates have been identified thus far. Through a novel proteomic screen, we have now identified 165 human proteins interacting with TLK1, and we have focused this work on NEK1 because of its known role in the DDR, upstream of ATR and Chk1. TLK1 and NEK1 were found to interact by coIP, and their binding is strengthened following exposure of cells to H2O2. Following incubation with doxorubicin, TLK1 and NEK1 relocalize with nuclear repair foci along with γH2AX. TLK1 phosphorylated NEK1 at T141, which lies in the kinase domain, and caused an increase in its activity. Following DNA damage, addition of the TLK1 inhibitor, THD, or overexpression of NEK1-T141A mutant impaired ATR and Chk1 activation, indicating the existence of a TLK1>NEK1>ATR>Chk1 pathway. Indeed, overexpression of the NEK1-T141A mutant resulted in an altered cell cycle response after exposure of cells to oxidative stress, including bypass of G1 arrest and implementation of an intra S-phase checkpoint.

The Ciliopathy-Associated Cep104 Protein Interacts with Tubulin and Nek1 Kinase.

Cilia are thin cell projections with essential roles in cell motility, fluid movement, sensing, and signaling. They are templated from centrioles that dock against the plasma membrane and subsequently extend their peripheral microtubule array. The molecular mechanisms underpinning cilia assembly are incompletely understood. Cep104 is a key factor involved in cilia formation and length regulation that rides on the ends of elongating and shrinking cilia. It is mutated in Joubert syndrome, a genetically heterogeneous ciliopathy. Here we provide structural and biochemical data that Cep104 contains a tubulin-binding TOG (tumor overexpressed gene) domain and a novel C2HC zinc finger array. Furthermore, we identify the kinase Nek1, another ciliopathy-associated protein, as a potential binding partner of this array. Finally, we show that Nek1 competes for binding to Cep104 with the distal centriole-capping protein CP110. Our data suggest a model for Cep104 activity during ciliogenesis and provide a novel link between Cep104 and Nek1.

Cohesin Removal along the Chromosome Arms during the First Meiotic Division Depends on a NEK1-PP1γ-WAPL Axis in the Mouse.

Mammalian NIMA-like kinase-1 (NEK1) is a dual-specificity kinase highly expressed in mouse germ cells during prophase I of meiosis. Loss of NEK1 induces retention of cohesin on chromosomes at meiotic prophase I. Timely deposition and removal of cohesin is essential for accurate chromosome segregation. Two processes regulate cohesin removal: a non-proteolytic mechanism involving WAPL, sororin, and PDS5B and direct cleavage by separase. Here, we demonstrate a role for NEK1 in the regulation of WAPL loading during meiotic prophase I, via an interaction between NEK1 and PDS5B. This regulation of WAPL by NEK1-PDS5B is mediated by protein phosphatase 1 gamma (PP1γ), which both interacts with and is a phosphotarget of NEK1. Taken together, our results reveal that NEK1 phosphorylates PP1γ, leading to the dephosphorylation of WAPL, which, in turn, results in its retention on chromosome cores to promote loss of cohesion at the end of prophase I in mammals.

Frequent Nek1 overexpression in human gliomas.

Never in mitosis A (NIMA)-related kinase 1 (Nek1) regulates cell cycle progression to mitosis. Its expression and potential functions in human gliomas have not been studied. Here, our immunohistochemistry (IHC) assay and Western blot assay results showed that Nek1 expression was significantly upregulated in fresh and paraffin-embedded human glioma tissues. Its level in normal brain tissues was low. Nek1 overexpression in human gliomas was correlated with the proliferation marker (Ki-67), tumor grade, Karnofsky performance scale (KPS) and more importantly, patients' poor survival. Further studies showed that Nek1 expression level was also increased in multiple human glioma cell lines (U251-MG, U87-MG, U118, H4 and U373). Significantly, siRNA-mediated knockdown of Nek1 inhibited glioma cell (U87-MG/U251-MG) growth. Nek1 siRNA also sensitized U87-MG/U251-MG cells to temozolomide (TMZ), causing a profound apoptosis induction and growth inhibition. The current study indicates Nek1 might be a novel and valuable oncotarget of glioma, it is important for glioma cell growth and TMZ-resistance.

Nek1 Regulates Rad54 to Orchestrate Homologous Recombination and Replication Fork Stability.

Never-in-mitosis A-related kinase 1 (Nek1) has established roles in apoptosis and cell cycle regulation. We show that human Nek1 regulates homologous recombination (HR) by phosphorylating Rad54 at Ser572 in late G2 phase. Nek1 deficiency as well as expression of unphosphorylatable Rad54 (Rad54-S572A) cause unresolved Rad51 foci and confer a defect in HR. Phospho-mimic Rad54 (Rad54-S572E), in contrast, promotes HR and rescues the HR defect associated with Nek1 loss. Although expression of phospho-mimic Rad54 is beneficial for HR, it causes Rad51 removal from chromatin and degradation of stalled replication forks in S phase. Thus, G2-specific phosphorylation of Rad54 by Nek1 promotes Rad51 chromatin removal during HR in G2 phase, and its absence in S phase is required for replication fork stability. In summary, Nek1 regulates Rad51 removal to orchestrate HR and replication fork stability.