Glycogen synthase kinase 3beta interacts with and phosphorylates the spindle-associated protein astrin

Role of microRNA-363 during tumor progression and invasion

Recent progresses in diagnostic and therapeutic methods have significantly improved prognosis in cancer patients. However, cancer is still considered as one of the main causes of human deaths in the world. Late diagnosis in advanced tumor stages can reduce the effectiveness of treatment methods and increase mortality rate of cancer patients. Therefore, investigating the molecular mechanisms of tumor progression can help to introduce the early diagnostic markers in these patients. MicroRNA (miRNAs) has an important role in regulation of pathophysiological cellular processes. Due to their high stability in body fluids, they are always used as the non-invasive markers in cancer patients. Since, miR-363 deregulation has been reported in a wide range of cancers, we discussed the role of miR-363 during tumor progression and metastasis. It has been reported that miR-363 has mainly a tumor suppressor function through the regulation of transcription factors, apoptosis, cell cycle, and structural proteins. MiR-363 also affected the tumor progression via regulation of various signaling pathways such as WNT, MAPK, TGF-β, NOTCH, and PI3K/AKT. Therefore, miR-363 can be introduced as a probable therapeutic target as well as a non-invasive diagnostic marker in cancer patients.

CLUH controls astrin-1 expression to couple mitochondrial metabolism to cell cycle progression

Proliferating cells undergo metabolic changes in synchrony with cell cycle progression and cell division. Mitochondria provide fuel, metabolites, and ATP during different phases of the cell cycle, however it is not completely understood how mitochondrial function and the cell cycle are coordinated. CLUH (clustered mitochondria homolog) is a post-transcriptional regulator of mRNAs encoding mitochondrial proteins involved in oxidative phosphorylation and several metabolic pathways. Here, we show a role of CLUH in regulating the expression of astrin, which is involved in metaphase to anaphase progression, centrosome integrity, and mTORC1 inhibition. We find that CLUH binds both the SPAG5 mRNA and its product astrin, and controls the synthesis and the stability of the full-length astrin-1 isoform. We show that CLUH interacts with astrin-1 specifically during interphase. Astrin-depleted cells show mTORC1 hyperactivation and enhanced anabolism. On the other hand, cells lacking CLUH show decreased astrin levels and increased mTORC1 signaling, but cannot sustain anaplerotic and anabolic pathways. In absence of CLUH, cells fail to grow during G1, and progress faster through the cell cycle, indicating dysregulated matching of growth, metabolism, and cell cycling. Our data reveal a role of CLUH in coupling growth signaling pathways and mitochondrial metabolism with cell cycle progression.

GSK3 as a Regulator of Cytoskeleton Architecture: Consequences for Health and Disease

Glycogen synthase kinase 3 (GSK3) was initially isolated as a critical protein in energy metabolism. However, subsequent studies indicate that GSK-3 is a multi-tasking kinase that links numerous signaling pathways in a cell and plays a vital role in the regulation of many aspects of cellular physiology. As a regulator of actin and tubulin cytoskeleton, GSK3 influences processes of cell polarization, interaction with the extracellular matrix, and directional migration of cells and their organelles during the growth and development of an animal organism. In this review, the roles of GSK3–cytoskeleton interactions in brain development and pathology, migration of healthy and cancer cells, and in cellular trafficking of mitochondria will be discussed.

Casein kinase TbCK1.2 regulates division of kinetoplast DNA, and movement of basal bodies in the African trypanosome

The single mitochondrial nucleoid (kinetoplast) of Trypanosoma brucei is found proximal to a basal body (mature (mBB)/probasal body (pBB) pair). Kinetoplast inheritance requires synthesis of, and scission of kinetoplast DNA (kDNA) generating two kinetoplasts that segregate with basal bodies into daughter cells. Molecular details of kinetoplast scission and the extent to which basal body separation influences the process are unavailable. To address this topic, we followed basal body movements in bloodstream trypanosomes following depletion of protein kinase TbCK1.2 which promotes kinetoplast division. In control cells we found that pBBs are positioned 0.4 um from mBBs in G1, and they mature after separating from mBBs by at least 0.8 um: mBB separation reaches ~2.2 um. These data indicate that current models of basal body biogenesis in which pBBs mature in close proximity to mBBs may need to be revisited. Knockdown of TbCK1.2 produced trypanosomes containing one kinetoplast and two nuclei (1K2N), increased the percentage of cells with uncleaved kDNA 400%, decreased mBB spacing by 15%, and inhibited cytokinesis 300%. We conclude that (a) separation of mBBs beyond a threshold of 1.8 um correlates with division of kDNA, and (b) TbCK1.2 regulates kDNA scission. We propose a Kinetoplast Division Factor hypothesis that integrates these data into a pathway for biogenesis of two daughter mitochondrial nucleoids.

Astrin: A Key Player in Mitosis and Cancer

Astrin, which is a spindle-associated protein, was found to be closely related to mitotic spindle formation and maintenance. It interacts with other spindle-related proteins to play a key role in maintaining the attachment of the kinetochore-microtubule and integrity of centrosomes and promoting the centriole duplication. In addition, Astrin was quite recently found to be abnormally highly expressed in a variety of cancers. Astrin promotes the development of cancer by participating in various molecular pathways and is considered as a potential prognostic and survival predictor.

p53 suppression is essential for oncogenic SPAG5 upregulation in lung adenocarcinoma

Aberrant expression of sperm-associated antigen 5 (SPAG5) is implicated to play oncogenic roles in several types of cancers. However, the functions of SPAG5 in lung adenocarcinoma remain unclear. In this study, we investigated the role of SPAG5 in lung adenocarcinoma. We found that SPAG5 was upregulated in most of the lung adenocarcinoma cell lines as compared to normal lung epithelial cells. SPAG5 knockdown suppressed proliferation, colony forming, and migration of lung adenocarcinoma A549 cells in vitro and inhibited tumor growth in vivo. These suggest that upregulated SPAG5 promotes lung tumor progression. Importantly, treatment with MDM2 inhibitor, Nutlin-3a, restored p53 and p21 expression and suppressed SPAG5 expression in wild-type p53 lung adenocarcinoma cells, A549 and H460, but not in p53-null lung cancer cells, H1299. This suggests that the p53 signal pathway is essential for SPAG5 suppression. In addition, knocking-down p53 or p21 in A549 and H460 cells attenuated Nutlin-3a-induced repression of SPAG5, which further supports that the p53-p21 axis is required for SPAG5 repression. Thus, SPAG5 can serve as a prognostic marker, and therapeutic strategy targeting the p53-p21-SPAG5 axis may have important clinical implications.

Emerging Roles of the TRIM E3 Ubiquitin Ligases MID1 and MID2 in Cytokinesis

Ubiquitination is a post-translational modification that consists of ubiquitin attachment to target proteins through sequential steps catalysed by activating (E1), conjugating (E2), and ligase (E3) enzymes. Protein ubiquitination is crucial for the regulation of many cellular processes not only by promoting proteasomal degradation of substrates but also re-localisation of cellular factors and modulation of protein activity. Great importance in orchestrating ubiquitination relies on E3 ligases as these proteins recognise the substrate that needs to be modified at the right time and place. Here we focus on two members of the TRIpartite Motif (TRIM) family of RING E3 ligases, MID1, and MID2. We discuss the recent findings on these developmental disease-related proteins analysing the link between their activity on essential factors and the regulation of cytokinesis highlighting the possible consequence of alteration of this process in pathological conditions.

SPAG5 interacts with CEP55 and exerts oncogenic activities via PI3K/AKT pathway in hepatocellular carcinoma

Background

Deregulation of microtubules and centrosome integrity is response for the initiation and progression of human cancers. Sperm-associated antigen 5 (SPAG5) is essential for the spindle apparatus organization and chromosome segregation, but its role in hepatocellular carcinoma (HCC) remains undefined.

Methods

The expression of SPAG5 in HCC were examined in a large cohort of patients by RT-PCR, western blot and IHC. The clinical significance of SPAG5 was next determined by statistical analyses. The biological function of SPAG5 in HCC and the underlying mechanisms were investigated, using in vitro and in vivo models.

Results

Here, we demonstrated that SPAG5 exhibited pro-HCC activities via the activation of PI3K/AKT signaling pathway. SPAG5 expression was increased in HCC and correlated with poor outcomes in two independent cohorts containing 670 patients. High SPAG5 expression was associated with poor tumor differentiation, larger tumor size, advanced TNM stage, tumor vascular invasion and lymph node metastasis. In vitro and in vivo data showed that SPAG5 overexpression promoted tumor growth and metastasis, whereas SPAG5 knockdown led to the opposite phenotypes. SPAG5 interacted with centrosomal protein CEP55 to trigger the phosphorylation of AKT at Ser473. Inhibition of PI3K/AKT signaling markedly attenuated SPAG5-mediated cell growth. Furthermore, SPAG5 expression was suppressed by miR-363-3p which inhibited the activity of SPAG5 mRNA 3’UTR. Ectopic expression of SPAG5 partly abolished the miR-363-3p-caused cell cycle arrest and suppression of cell proliferation and migration.

Conclusions

Collectively, these findings indicate that SPAG5 serves a promising prognostic factor in HCC and functions as an oncogene via CEP55-mediated PI3K/AKT pathway. The newly identified miR-363-3p/SPAG5/CEP55 axis may represent a potential therapeutic target for the clinical intervention of HCC.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0872-3) contains supplementary material, which is available to authorized users.

Potential Role of Microtubule Stabilizing Agents in Neurodevelopmental Disorders

Neurodevelopmental disorders (NDDs) are characterized by neuroanatomical abnormalities indicative of corticogenesis disturbances. At the basis of NDDs cortical abnormalities, the principal developmental processes involved are cellular proliferation, migration and differentiation. NDDs are also considered “synaptic disorders” since accumulating evidence suggests that NDDs are developmental brain misconnection syndromes characterized by altered connectivity in local circuits and between brain regions. Microtubules and microtubule-associated proteins play a fundamental role in the regulation of basic neurodevelopmental processes, such as neuronal polarization and migration, neuronal branching and synaptogenesis. Here, the role of microtubule dynamics will be elucidated in regulating several neurodevelopmental steps. Furthermore, the correlation between abnormalities in microtubule dynamics and some NDDs will be described. Finally, we will discuss the potential use of microtubule stabilizing agents as a new pharmacological intervention for NDDs treatment.

Phosphorylation of Astrin Regulates Its Kinetochore Function

The error-free segregation of chromosomes, which requires the precisely timed search and capture of chromosomes by spindles during early mitotic and meiotic cell division, is responsible for genomic stability and is achieved by the spindle assembly checkpoint in the metaphase-anaphase transition. Mitotic kinases orchestrate M phase events, such as the reorganization of cell architecture and kinetochore (KT) composition with the exquisite phosphorylation of mitotic regulators, to ensure timely and temporal progression. However, the molecular mechanisms underlying the changes of KT composition for stable spindle attachment during mitosis are poorly understood. Here, we show that the sequential action of the kinase Cdk1 and the phosphatase Cdc14A control spindle attachment to KTs. During prophase, the mitotic spindle protein Spag5/Astrin is transported into centrosomes by Kinastrin and phosphorylated at Ser-135 and Ser-249 by Cdk1, which, in prometaphase, is loaded onto the spindle and targeted to KTs. We also demonstrate that Cdc14A dephosphorylates Astrin, and therefore the overexpression of Cdc14A sequesters Astrin in the centrosome and results in aberrant chromosome alignment. Mechanistically, Plk1 acts as an upstream kinase for Astrin phosphorylation by Cdk1 and targeting phospho-Astrin to KTs, leading to the recruitment of outer KT components, such as Cenp-E, and the stable attachment of spindles to KTs. These comprehensive findings reveal a regulatory circuit for protein targeting to KTs that controls the KT composition change of stable spindle attachment and chromosome integrity.

Nuclear Mitotic Apparatus (NuMA) Interacts with and Regulates Astrin at the Mitotic Spindle

The large nuclear mitotic apparatus (NuMA) protein is an essential player in mitotic spindle assembly and maintenance. We report here the identification of Astrin, a spindle- and kinetochore-associated protein, as a novel interactor of NuMA. We show that the C-terminal tail of NuMA can directly bind to the C terminus of Astrin and that this interaction helps to recruit Astrin to microtubules. Knockdown of NuMA by RNA interference dramatically impaired Astrin recruitment to the mitotic spindle. Overexpression of the N terminus of mammalian homologue of Drosophila Pins (LGN), which blocks the microtubule binding of NuMA and competes with Astrin for NuMA binding, also led to similar results. Furthermore, we found that cytoplasmic dynein is required for the spindle pole accumulation of Astrin, and dynein-mediated transport is important for balanced distribution of Astrin between spindle poles and kinetochores. On the other hand, if Astrin levels are reduced, then NuMA could not efficiently concentrate at the spindle poles. Our findings reveal a direct physical link between two important regulators of mitotic progression and demonstrate the critical role of the NuMA-Astrin interaction for accurate cell division.

Hepatoma-derived growth factor/nucleolin axis as a novel oncogenic pathway in liver carcinogenesis

Hepatoma-derived growth factor (HDGF) overexpression is involved in liver fibrosis and carcinogenesis. However, the receptor(s) and signaling for HDGF remain unclear. By using affinity chromatography and proteomic techniques, nucleolin (NCL) was identified and validated as a HDGF-interacting membrane protein in hepatoma cells. Exogenous HDGF elicited the membrane NCL accumulation within 0.5 hour by protein stabilization and transcriptional NCL upregulation within 24 hours. Blockade of surface NCL by antibodies neutralization potently suppressed HDGF uptake and HDGF-stimulated phosphatidylinositol 3-kinase (PI3K)/Akt signaling in hepatoma cells. By using rescectd hepatocellular carcinoma (HCC) tissues, immunohistochemical analysis revealed NCL overexpression was correlated with tumour grades, vascular invasion, serum alpha-fetoprotein levels and the poor survival in HCC patients. Multivariate analysis showed NCL was an independent prognostic factor for survival outcome of HCC patients after surgery. To delineate the role of NCL in liver carcinogenesis, ectopic NCL overexpression promoted the oncogenic behaviours and induced PI3K/Akt activation in hepatoma cells. Conversely, NCL knockdown by RNA interference attenuated the oncogenic behaviours and PI3K/Akt signaling, which could be partially rescued by exogenous HDGF supply. In summary, this study provides the first evidence that surface NCL transmits the oncogenic signaling of HDGF and facilitates a novel diagnostic and therapeutic target for HCC.

Microtubule plus-end tracking proteins and their roles in cell division

Microtubules are cellular components that are required for a variety of essential processes such as cell motility, mitosis, and intracellular transport. This is possible because of the inherent dynamic properties of microtubules. Many of these properties are tightly regulated by a number of microtubule plus-end-binding proteins or +TIPs. These proteins recognize the distal end of microtubules and are thus in the right context to control microtubule dynamics. In this review, we address how microtubule dynamics are regulated by different +TIP families, focusing on how functionally diverse +TIPs spatially and temporally regulate microtubule dynamics during animal cell division.

MACF1 regulates the migration of pyramidal neurons via microtubule dynamics and GSK-3 signaling

Neuronal migration and subsequent differentiation play critical roles for establishing functional neural circuitry in the developing brain. However, the molecular mechanisms that regulate these processes are poorly understood. Here, we show that microtubule actin crosslinking factor 1 (MACF1) determines neuronal positioning by regulating microtubule dynamics and mediating GSK-3 signaling during brain development. First, using MACF1 floxed allele mice and in utero gene manipulation, we find that MACF1 deletion suppresses migration of cortical pyramidal neurons and results in aberrant neuronal positioning in the developing brain. The cell autonomous deficit in migration is associated with abnormal dynamics of leading processes and centrosomes. Furthermore, microtubule stability is severely damaged in neurons lacking MACF1, resulting in abnormal microtubule dynamics. Finally, MACF1 interacts with and mediates GSK-3 signaling in developing neurons. Our findings establish a cellular mechanism underlying neuronal migration and provide insights into the regulation of cytoskeleton dynamics in developing neurons.

The mitosis-regulating and protein-protein interaction activities of astrin are controlled by aurora-A-induced phosphorylation

Cells display dramatic morphological changes in mitosis, where numerous factors form regulatory networks to orchestrate the complicated process, resulting in extreme fidelity of the segregation of duplicated chromosomes into two daughter cells. Astrin regulates several aspects of mitosis, such as maintaining the cohesion of sister chromatids by inactivating Separase and stabilizing spindle, aligning and segregating chromosomes, and silencing spindle assembly checkpoint by interacting with Src kinase-associated phosphoprotein (SKAP) and cytoplasmic linker-associated protein-1α (CLASP-1α). To understand how Astrin is regulated in mitosis, we report here that Astrin acts as a mitotic phosphoprotein, and Aurora-A phosphorylates Astrin at Ser(115). The phosphorylation-deficient mutant Astrin S115A abnormally activates spindle assembly checkpoint and delays mitosis progression, decreases spindle stability, and induces chromosome misalignment. Mechanistic analyses reveal that Astrin phosphorylation mimicking mutant S115D, instead of S115A, binds and induces ubiquitination and degradation of securin, which sequentially activates Separase, an enzyme required for the separation of sister chromatids. Moreover, S115A fails to bind mitosis regulators, including SKAP and CLASP-1α, which results in the mitotic defects observed in Astrin S115A-transfected cells. In conclusion, Aurora-A phosphorylates Astrin and guides the binding of Astrin to its cellular partners, which ensures proper progression of mitosis.

SPAG5 upregulation predicts poor prognosis in cervical cancer patients and alters sensitivity to taxol treatment via the mTOR signaling pathway

Previously, we found that sperm-associated antigen 5 (SPAG5) was upregulated in pelvic lymph node metastasis–positive cervical cancer. The aim of this study is to examine the role of SPAG5 in the proliferation and tumorigenicity of cervical cancer and its clinical significance in tumor progression. In our study, SPAG5 expression in cervical cancer patients was detected using quantitative real-time polymerase chain reaction, western blotting, and immunohistochemistry; cervical cancer cell function with downregulated SPAG5 in vitro was explored using tetrazolium assay, flow cytometry, and colony formation and Transwell assays. SPAG5 was upregulated in tumor tissue compared with paired adjacent noncancerous tissues; SPAG5 upregulation in tumor tissues indicated poor disease-free survival, which was also an independent prognostic indicator for cervical cancer patients. In vitro study demonstrated that SPAG5 downregulation inhibited cell proliferation and growth significantly by G2/M arrest and induction of apoptosis, and hindered cell migration and invasion. Under SPAG5 downregulation, the sensitivity of cervical cancer cells differed according to taxol dose, which correlated with mammalian target of rapamycin (mTOR) signaling pathway activity. In general, SPAG5 upregulation relates to poor prognosis in cervical cancer patients, and SPAG5 is a regulator of mTOR activity during taxol treatment in cervical cancer.

OSBP-related protein 8 (ORP8) interacts with Homo sapiens sperm associated antigen 5 (SPAG5) and mediates oxysterol interference of HepG2 cell cycle

We earlier identified OSBP-related protein 8 (ORP8) as an endoplasmic reticulum/nuclear envelope oxysterol-binding protein implicated in cellular lipid homeostasis, migration, and organization of the microtubule cytoskeleton. Here, a yeast two-hybrid screen identified Homo sapiens sperm associated antigen 5 (SPAG5)/Astrin as interaction partner of ORP8. The putative interaction was further confirmed by pull-down and co-immunoprecipitation assays. ORP8 did not colocalize with kinetochore-associated SPAG5 in mitotic HepG2 or HuH7 cells, but overexpressed ORP8 was capable of recruiting SPAG5 onto endoplasmic reticulum membranes in interphase cells. In our experiments, 25-hydroxycholesterol (25OHC) retarded the HepG2 cell cycle, causing accumulation in G2/M phase; ORP8 overexpression resulted in the same phenotype. Importantly, ORP8 knock-down dramatically inhibited the oxysterol effect on HepG2 cell cycle, suggesting a mediating role of ORP8. Furthermore, knock-down of SPAG5 significantly reduced the effects of both ORP8 overexpression and 25OHC on the cell cycle, placing SPAG5 downstream of the two cell-cycle interfering factors. Taken together, the present results suggest that ORP8 may via SPAG5 mediate oxysterol interference of the HepG2 cell cycle.

Kinases and kinase signaling pathways: potential therapeutic targets in Parkinson's disease

Complex molecular mechanisms underlying the pathogenesis of Parkinson's disease (PD) are gradually being elucidated. Accumulating genetic evidence implicates dysfunction of kinase activities and phosphorylation pathways in the pathogenesis of PD. Causative and risk gene products associated with PD include protein kinases (such as PINK1, LRRK2 and GAK) and proteins related phosphorylation signaling pathways (such as SNCA, DJ-1). PINK1, LRRK2 and several PD gene products have been associated with mitogen-activated protein (MAP) and protein kinase B (AKT) kinase signaling pathways. C-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases (ERK) and p38, signaling pathways downstream of MAP, are particularly important in PD. JNK and p38 play an integral role in neuronal death. Targeting JNK or p38 signaling may offer an effective therapy for PD. Inhibitors of the ERK signaling pathway, which plays an important role in the development of l-DOPA-induced dyskinesia (LID), have been shown to attenuate this condition in animal models. In this review, we summarize experimental evidence gathered over the last decade on the role of PINK1, LRRK2 and GAK and their related phosphorylation signaling pathways (JNK, ERK, p38 and PI3K/AKT) in PD. It is speculated that improvement or modulation of these signaling pathways will reveal potential therapeutic targets for attenuation of the cardinal symptoms and motor complications in patients with PD in the future.

The role of GSK3beta in the development of the central nervous system

Glycogen synthase kinase 3β (GSK3β) is a multifunctional serine/threonine kinase. It is particularly abundant in the developing central nervous system (CNS). Since GSK3β has diverse substrates ranging from metabolic/signaling proteins and structural proteins to transcription factors, it is involved in many developmental events in the immature brain, such as neurogenesis, neuronal migration, differentiation and survival. The activity of GSK3β is developmentally regulated and is affected by various environmental/cellular insults, such as deprivation of nutrients/trophic factors, oxidative stress and endoplasmic reticulum stress. Abnormalities in GSK3β activity may disrupt CNS development. Therefore, GSK3β is a critical signaling protein that regulates brain development. It may also determine neuronal susceptibility to damages caused by various environmental insults.

Functions of GSK-3 Signaling in Development of the Nervous System

Glycogen synthase kinase-3 (GSK-3) is central to multiple intracellular pathways including those activated by Wnt/β-catenin, Sonic Hedgehog, Notch, growth factor/RTK, and G protein-coupled receptor signals. All of these signals importantly contribute to neural development. Early attention on GSK-3 signaling in neural development centered on the regulation of neuronal polarity using in vitro paradigms. However, recent creation of appropriate genetic models has demonstrated the importance of GSK-3 to multiple aspects of neural development including neural progenitor self-renewal, neurogenesis, neuronal migration, neural differentiation, and synaptic development.

Issues associated with the use of phosphospecific antibodies to localise active and inactive pools of GSK-3 in cells

Abstract

Background

Glycogen synthase kinase-3 (GSK-3) is a ubiquitously expressed serine/threonine (Ser/Thr) kinase comprising two isoforms, GSK-3α and GSK-3β. Both enzymes are similarly inactivated by serine phosphorylation (GSK-3α at Ser21 and GSK-3β at Ser9) and activated by tyrosine phosphorylation (GSK-3α at Tyr279 and GSK-3β at Tyr216). Antibodies raised to phosphopeptides containing the sequences around these phosphorylation sites are frequently used to provide an indication of the activation state of GSK-3 in cell and tissue extracts. These antibodies have further been used to determine the subcellular localisation of active and inactive forms of GSK-3, and the results of those studies support roles for GSK-3 phosphorylation in diverse cellular processes. However, the specificity of these antibodies in immunocytochemistry has not been addressed in any detail.

Aurora B kinase controls the targeting of the Astrin-SKAP complex to bioriented kinetochores

Localization of the spindle and kinetochore proteins Astrin, SKAP, and LC8 is antagonized by Aurora B so that they target exclusively to bioriented kinetochores.

During mitosis, kinetochores play multiple roles to generate interactions with microtubules, and direct chromosome congression, biorientation, error correction, and anaphase segregation. However, it is unclear what changes at the kinetochore facilitate these distinct activities. Here, we describe a complex of the spindle- and kinetochore-associated protein Astrin, the small kinetochore-associated protein (SKAP), and the dynein light chain LC8. Although most dynein-associated proteins localize to unaligned kinetochores in an Aurora B–dependent manner, Astrin, SKAP, and LC8 localization is antagonized by Aurora B such that they target exclusively to bioriented kinetochores. Astrin–SKAP-depleted cells fail to maintain proper chromosome alignment, resulting in a spindle assembly checkpoint–dependent mitotic delay. Consistent with a role in stabilizing bioriented attachments, Astrin and SKAP bind directly to microtubules and are required for CLASP localization to kinetochores. In total, our results suggest that tension-dependent Aurora B phosphorylation can act to control outer kinetochore composition to provide distinct activities to prometaphase and metaphase kinetochores.

GSK3beta in ethanol neurotoxicity

Alcohol consumption during pregnancy is a significant public health problem and may result in a wide range of adverse outcomes for the child. The developing central nervous system (CNS) is particularly susceptible to ethanol toxicity. Children with fetal alcohol spectrum disorders (FASD) have a variety of cognitive, behavioral, and neurological impairments. FASD currently represents the leading cause of mental retardation in North America ahead of Down syndrome and cerebral palsy. Ethanol exposure during development causes multiple abnormalities in the brain such as permanent loss of neurons, ectopic neurons, and alterations in synaptogenesis and myelinogenesis. These alcohol-induced structural alterations in the developing brain underlie many of the behavioral deficits observed in FASD. The cellular and molecular mechanisms of ethanol neurotoxicity, however, remain unclear. Ethanol elicits cellular stresses, including oxidative stress and endoplasmic reticulum stress. Glycogen synthase kinase 3beta (GSK3beta), a multifunctional serine/threonine kinase, responds to various cellular stresses. GSK3beta is particularly abundant in the developing CNS, and regulates diverse developmental events in the immature brain, such as neurogenesis and neuronal differentiation, migration, and survival. Available evidence indicates that the activity of GSK3beta in the CNS is affected by ethanol. GSK3beta inhibition provides protection against ethanol neurotoxicity, whereas high GSK3beta activity/expression sensitizes neuronal cells to ethanol-induced damages. It appears that GSK3beta is a converging signaling point that mediates some of ethanol's neurotoxic effects.

Astrin regulates Aurora-A localization

Alterations in the expression and activity of the centrosomal kinase, Aurora-A/STK15, affect genomic stability, disrupt the fidelity of centrosome duplication, and induce cellular transformation. A mitotic spindle-associated protein, astrin/DEEPEST, was identified as an Aurora-A interacting protein by a two-hybrid screen. Astrin and Aurora-A co-express at mitosis and co-localize to mitotic spindles. RNAi-mediated depletion of astrin abolishes the localization of Aurora-A on mitotic spindles and leads to a moderate mitotic cell cycle delay, which resembles the mitotic arrest phenotypes in siAurora-A treated cells. However, depletion of Aurora-A does not affect astrin localization, and co-depletion of both astrin and Aurora-A causes a mitotic arrest phenotype similar to depletion of siAurora-A alone. These results suggest that astrin acts upstream of Aurora-A to regulate its mitotic spindle localization.