TTBK2 with EB1/3 regulates microtubule dynamics in migrating cells through KIF2A phosphorylation

Spinocerebellar ataxia type 11 (SCA11): TTBK2 variants, functions and associated disease mechanisms

Spinocerebellar ataxia type 11 (SCA11) is a rare type of autosomal dominant cerebellar ataxia, mainly characterized by progressive cerebellar ataxia, abnormal eye signs and dysarthria. SCA11 is caused by variants in TTBK2, which encodes tau tubulin kinase 2 (TTBK2) protein. Only a few families with SCA11 were described to date, all harbouring small deletions or insertions that result in frameshifts and truncated TTBK2 proteins. In addition, TTBK2 missense variants were also reported but they were either benign or still needed functional validation to ascertain their pathogenic potential in SCA11. The mechanisms behind cerebellar neurodegeneration mediated by TTBK2 pathogenic alleles are not clearly established. There is only one neuropathological report and a few functional studies in cell or animal models published to date. Moreover, it is still unclear whether the disease is caused by TTBK2 haploinsufficiency of by a dominant negative effect of TTBK2 truncated forms on the normal allele. Some studies point to a lack of kinase activity and mislocalization of mutated TTBK2, while others reported a disruption of normal TTBK2 function caused by SCA11 alleles, particularly during ciliogenesis. Although TTBK2 has a proven function in cilia formation, the phenotype caused by heterozygous TTBK2 truncating variants are not clearly typical of ciliopathies. Thus, other cellular mechanisms may explain the phenotype seen in SCA11. Neurotoxicity caused by impaired TTBK2 kinase activity against known neuronal targets, such as tau, TDP-43, neurotransmitter receptors or transporters, may contribute to neurodegeneration in SCA11.

Connecting neurodevelopment to neurodegeneration: a spotlight on the role of kinesin superfamily protein 2A (KIF2A)

Microtubules play a central role in cytoskeletal changes during neuronal development and maintenance. Microtubule dynamics is essential to polarity and shape transitions underlying neural cell division, differentiation, motility, and maturation. Kinesin superfamily protein 2A is a member of human kinesin 13 gene family of proteins that depolymerize and destabilize microtubules. In dividing cells, kinesin superfamily protein 2A is involved in mitotic progression, spindle assembly, and chromosome segregation. In postmitotic neurons, it is required for axon/dendrite specification and extension, neuronal migration, connectivity, and survival. Humans with kinesin superfamily protein 2A mutations suffer from a variety of malformations of cortical development, epilepsy, autism spectrum disorder, and neurodegeneration. In this review, we discuss how kinesin superfamily protein 2A regulates neuronal development and function, and how its deregulation causes neurodevelopmental and neurological disorders.

Identification of Novel Tau-Tubulin Kinase 2 Inhibitors Using Computational Approaches

Tau tubulin kinase 2 (TTBK2) associated with multiple diseases is one of the kinases which phosphorylates tau and tubulin. Numerous efforts have been made to understand the role of TTBK2 in protein folding mechanisms and misfolding behavior. The misfolded protein intermediates form polymers with unwanted aggregation properties that initiate several diseases, including Alzheimer's. The availability of TTBK2 inhibitors can enhance the understanding of the molecular mechanism of action of the kinase and assist in developing novel therapeutics. In the quest for TTBK2 inhibitors, this study focuses on screening two chemical libraries (ChEMBL and ZINC-FDA). The molecular docking, RO5/absorption, distribution, metabolism, and excretion/toxicity, density functional theory, molecular dynamics (MD) simulations, and molecular mechanics with generalized Born and surface area solvation techniques enabled shortlisting of the four most active compounds, namely, ChEMBL1236395, ChEMBL2104398, ChEMBL3427435, and ZINC000000509440. Moreover, 500 ns MD simulation was performed for each complex, which provided valuable insights into the structural changes in the complexes. The relative fluctuation, solvent accessible surface area, atomic gyration, compactness covariance, and free energy landscapes revealed that the compounds could stabilize the TTBK2 protein. Overall, this study would be valuable for the researchers targeting the development of novel TTBK2 inhibitors.

Dynamic Regulation Genes at Microtubule Plus Ends: A Novel Class of Glioma Biomarkers

Simple Summary

Microtubule plus-end-related genes (MPERGs) encode a group of proteins that specifically aggregate at the microtubule plus ends to play critical biological roles in the cell cycle, cell movement, ciliogenesis, and neuronal development by coordinating microtubule assembly and dynamics; however, the MPERG correlations and their clinical significance in glioma are not fully understood. This study is the first to systematically analyze and define a seven-gene signature (CTTNBP2, KIF18A, NAV1, SLAIN2, SRCIN1, TRIO, and TTBK2) and nomogram model closely associated with clinical factors and the tumor microenvironment as a reliable and independent prognostic biomarker to guide personalized choices of immunotherapy and chemotherapy for glioma patients.

Abstract

Glioma is the most prevalent and aggressive primary nervous system tumor with an unfavorable prognosis. Microtubule plus-end-related genes (MPERGs) play critical biological roles in the cell cycle, cell movement, ciliogenesis, and neuronal development by coordinating microtubule assembly and dynamics. This research seeks to systematically explore the oncological characteristics of these genes in microtubule-enriched glioma, focusing on developing a novel MPERG-based prognostic signature to improve the prognosis and provide more treatment options for glioma patients. First, we thoroughly analyzed and identified 45 differentially expressed MPERGs in glioma. Based on these genes, glioma patients were well distinguished into two subgroups with survival and tumor microenvironment infiltration differences. Next, we further screened the independent prognostic genes (CTTNBP2, KIF18A, NAV1, SLAIN2, SRCIN1, TRIO, and TTBK2) using 36 prognostic-related differentially expressed MPERGs to construct a signature with risk stratification and prognostic prediction ability. An increased risk score was related to the malignant progression of glioma. Therefore, we also designed a nomogram model containing clinical factors to facilitate the clinical use of the risk signature. The prediction accuracy of the signature and nomogram model was verified using The Cancer Genome Atlas and Chinese Glioma Genome Atlas datasets. Finally, we examined the connection between the signature and tumor microenvironment. The signature positively correlated with tumor microenvironment infiltration, especially immunoinhibitors and the tumor mutation load, and negatively correlated with microsatellite instability and cancer stemness. More importantly, immune checkpoint blockade treatment and drug sensitivity analyses confirmed that this prognostic signature was helpful in anticipating the effect of immunotherapy and chemotherapy. In conclusion, this research is the first study to define and validate an MPERG-based signature closely associated with the tumor microenvironment as a reliable and independent prognostic biomarker to guide personalized choices of immunotherapy and chemotherapy for glioma patients.

TTBK2 controls cilium stability by regulating distinct modules of centrosomal proteins

The serine-threonine kinase tau tubulin kinase 2 (TTBK2) is a key regulator of the assembly of primary cilia, which are vital signaling organelles. TTBK2 is also implicated in the stability of the assembled cilium through mechanisms that remain to be defined. Here we use mouse embryonic fibroblasts derived from Ttbk2^fl/fl, UBC-CreERT+ embryos (hereafter Ttbk2^cmut) to dissect the role of TTBK2 in cilium stability. This system depletes TTBK2 levels after cilia formation, allowing us to assess the molecular changes to the assembled cilium over time. As a consequence of Ttbk2 deletion, the ciliary axoneme is destabilized and primary cilia are lost within 48-72 h following recombination. Axoneme destabilization involves an increased frequency of cilia breaks and a reduction in axonemal microtubule modifications. Cilia loss was delayed by using inhibitors that affect actin-based trafficking. At the same time, we find that TTBK2 is required to regulate the composition of the centriolar satellites and to maintain the basal body pools of intraflagellar transport proteins. Altogether, our results reveal parallel pathways by which TTBK2 maintains cilium stability.

Spatial models of pattern formation during phagocytosis

Phagocytosis, the biological process in which cells ingest large particles such as bacteria, is a key component of the innate immune response. Fcγ receptor (FcγR)-mediated phagocytosis is initiated when these receptors are activated after binding immunoglobulin G (IgG). Receptor activation initiates a signaling cascade that leads to the formation of the phagocytic cup and culminates with ingestion of the foreign particle. In the experimental system termed "frustrated phagocytosis", cells attempt to internalize micropatterned disks of IgG. Cells that engage in frustrated phagocytosis form "rosettes" of actin-enriched structures called podosomes around the IgG disk. The mechanism that generates the rosette pattern is unknown. We present data that supports the involvement of Cdc42, a member of the Rho family of GTPases, in pattern formation. Cdc42 acts downstream of receptor activation, upstream of actin polymerization, and is known to play a role in polarity establishment. Reaction-diffusion models for GTPase spatiotemporal dynamics exist. We demonstrate how the addition of negative feedback and minor changes to these models can generate the experimentally observed rosette pattern of podosomes. We show that this pattern formation can occur through two general mechanisms. In the first mechanism, an intermediate species forms a ring of high activity around the IgG disk, which then promotes rosette organization. The second mechanism does not require initial ring formation but relies on spatial gradients of intermediate chemical species that are selectively activated over the IgG patch. Finally, we analyze the models to suggest experiments to test their validity.

Actin nano-architecture of phagocytic podosomes

Podosomes are actin-enriched adhesion structures important for multiple cellular processes, including migration, bone remodeling, and phagocytosis. Here, we characterize the structure and organization of phagocytic podosomes using interferometric photoactivated localization microscopy, a super-resolution microscopy technique capable of 15-20 nm resolution, together with structured illumination microscopy and localization-based super-resolution microscopy. Phagocytic podosomes are observed during frustrated phagocytosis, a model in which cells attempt to engulf micropatterned IgG antibodies. For circular patterns, this results in regular arrays of podosomes with well-defined geometry. Using persistent homology, we develop a pipeline for semi-automatic identification and measurement of podosome features. These studies reveal an hourglass shape of the podosome actin core, a protruding knob at the bottom of the core, and two actin networks extending from the core. Additionally, the distributions of paxillin, talin, myosin II, α-actinin, cortactin, and microtubules relative to actin are characterized.

Molecular mechanisms underlying the role of the centriolar CEP164-TTBK2 complex in ciliopathies

Cilia formation is essential for human life. One of the earliest events in the ciliogenesis program is the recruitment of tau-tubulin kinase 2 (TTBK2) by the centriole distal appendage component CEP164. Due to the lack of high-resolution structural information on this complex, it is unclear how it is affected in human ciliopathies such as nephronophthisis. Furthermore, it is poorly understood if binding to CEP164 influences TTBK2 activities. Here, we present a detailed biochemical, structural, and functional analysis of the CEP164-TTBK2 complex and demonstrate how it is compromised by two ciliopathic mutations in CEP164. Moreover, we also provide insights into how binding to CEP164 is coordinated with TTBK2 activities. Together, our data deepen our understanding of a crucial step in cilia formation and will inform future studies aimed at restoring CEP164 functionality in a debilitating human ciliopathy.

Spinocerebellar ataxias (SCAs) caused by common mutations

The term SCA refers to a phenotypically and genetically heterogeneous group of autosomal dominant spinocerebellar ataxias. Phenotypically they present as gait ataxia frequently in combination with dysarthria and oculomotor problems. Additional signs and symptoms are common and can include various pyramidal and extrapyramidal signs and intellectual impairment. Genetic causes of SCAs are either repeat expansions within disease genes or common mutations (point mutations, deletions, insertions etc.). Frequently the two types of mutations cause indistinguishable phenotypes (locus heterogeneity). This article focuses on SCAs caused by common mutations. It describes phenotype and genotype of the presently 27 types known and discusses the molecular pathogenesis in those 21 types where the disease gene has been identified. Apart from the dominant types, the article also summarizes findings in a variant caused by mutations in a mitochondrial gene. Possible common disease mechanisms are considered based on findings in the various SCAs described.

Mechanisms of Regulation and Diverse Activities of Tau-Tubulin Kinase (TTBK) Isoforms

Tau-tubulin kinase 1 (TTBK1) is a CNS-specific, kinase that has been implicated in the pathological phosphorylation of tau in Alzheimer's Disease (AD) and Frontotemporal Dementia (FTD). TTBK1 is a challenging therapeutic target because it shares a highly conserved catalytic domain with its homolog, TTBK2, a ubiquitously expressed kinase genetically linked to the disease spinocerebellar ataxia type 11. The present study attempts to elucidate the functional distinctions between the TTBK isoforms and increase our understanding of them as distinct targets for the treatment of neurodegenerative disease. We demonstrate that in cortical neurons, TTBK1, not TTBK2, is the isoform responsible for tau phosphorylation at epitopes enriched in tauopathies such as Serine 422. In addition, although our elucidation of the crystal structure of the TTBK2 kinase domain indicates almost identical structural similarity with TTBK1, biochemical and cellular assays demonstrate that the enzymatic activity of these two proteins is regulated by a combination of unique extra-catalytic sequences and autophosphorylation events. Finally, we have identified an unbiased list of neuronal interactors and phosphorylation substrates for TTBK1 and TTBK2 that highlight the unique cellular pathways and functional networks that each isoform is involved in. This data address an important gap in knowledge regarding the implications of targeting TTBK kinases and may prove valuable in the development of potential therapies for disease.

Pathogenic LRRK2 regulates ciliation probability upstream of tau tubulin kinase 2 via Rab10 and RILPL1 proteins

Mutations that activate LRRK2 protein kinase cause Parkinson's disease. We showed previously that Rab10 phosphorylation by LRRK2 enhances its binding to RILPL1, and together, these proteins block cilia formation in a variety of cell types, including patient derived iPS cells. We have used live-cell fluorescence microscopy to identify, more precisely, the effect of LRRK2 kinase activity on both the formation of cilia triggered by serum starvation and the loss of cilia seen upon serum readdition. LRRK2 activity decreases the overall probability of ciliation without changing the rates of cilia formation in R1441C LRRK2 MEF cells. Cilia loss in these cells is accompanied by ciliary decapitation, and kinase activity does not change the timing or frequency of decapitation or the rate of cilia loss but increases the percent of cilia that are lost upon serum addition. LRRK2 activity, or overexpression of RILPL1 protein, blocks release of CP110 from the mother centriole, a step normally required for early ciliogenesis; LRRK2 blockade of CP110 uncapping requires Rab10 and RILPL1 proteins and is due to failure to recruit TTBK2, a kinase needed for CP110 release. In contrast, deciliation probability does not change in cells lacking Rab10 or RILPL1 and relies on a distinct LRRK2 pathway. These experiments provide critical detail to our understanding of the cellular consequences of pathogenic LRRK2 mutation and indicate that LRRK2 blocks ciliogenesis upstream of TTBK2 and enhances the deciliation process in response to serum addition.

An Asymmetric Genetic Signal Associated with Mechanosensory Expansion in Cave-Adapted Fish

A key challenge in contemporary biology is connecting genotypic variation to phenotypic diversity. Quantitative genetics provides a powerful technique for identifying regions of the genome that covary with phenotypic variation. Here, we present a quantitative trait loci (QTL) analysis of a natural freshwater fish system, Astyanax mexicanus, that harbors two morphs corresponding to a cave and surface fish. Following their divergence ~500 Kya, cavefish have adapted to the extreme pressures of the subterranean biome. As a consequence, cavefish have lost numerous features, but evolved gains for a variety of constructive features including behavior. Prior work found that sensory tissues (neuromasts) present in the "eye orbit" region of the skull associate with sensitivity to vibrations in water. This augmented sensation is believed to facilitate foraging behavior in the complete darkness of a cave, and may impact on evolved lateral swimming preference. To this point, however, it has remained unclear how morphological variation integrates with behavioral variation through heritable factors. Using a QTL approach, we discovered the genetic architecture of neuromasts present in the eye orbit region, demonstrating that this feature is under genetic control. Interestingly, linked loci were asymmetric-signals were detected using only data collected from the right, but not left, side of the face. This finding may explain enhanced sensitivity and/or feedback of water movements mediating a lateral swimming preference. The locus we discovered based on neuromast position maps near established QTL for eye size and a facial bone morphology, raising the intriguing possibility that eye loss, sensory expansion, and the cranial skeleton may be integrated for evolving adaptive behaviors. Thus, this work will further our understanding of the functional consequence of key loci that influence the evolutionary origin of changes impacting morphology, behavior, and adaptation.

In vitro Time-lapse Imaging of Primary Cilium in Migrating Neuroblasts

Neuronal migration is a critical step for the development of neuronal circuits in the brain. Immature new neurons (neuroblasts) generated in the postnatal ventricular-subventricular zone (V-SVZ) show a remarkable potential to migrate for a long distance at a high speed in the postnatal mammalian brain, and are thus a powerful model to analyze the molecular and cellular mechanisms of neuronal migration. Here we describe a methodology for in vitro time-lapse imaging of the primary cilium and its related structures in migrating V-SVZ-derived neuroblasts using confocal or superresolution laser-scanning microscopy. The V-SVZ tissues are dissected from postnatal day 0-1 (P0-1) mouse brains and dissociated into single cells by trypsinization and gentle pipetting. These cells are then transduced with a plasmid(s) encoding a gene(s) of interest, aggregated by centrifugation, and cultured for 2 days in Matrigel. Time-lapse images of migratory behaviors of cultured neuroblasts and their ciliary structures, including the ciliary membrane and basal body, are acquired by confocal or superresolution laser-scanning microscopy. This method provides information about the spatiotemporal dynamics of neuroblasts' morphology and ciliary structures, and is widely applicable to various types of migrating neuronal and nonneuronal cells in various species.

Long Non-Coding RNA Paternally Expressed Imprinted Gene 10 (PEG10) Elevates Diffuse Large B-Cell Lymphoma Progression by Regulating Kinesin Family Member 2A (KIF2A) via Targeting MiR-101-3p

Background

Diffuse large B-cell lymphoma (DLBCL) is a common malignant tumor in the immune system with high mortality. We investigated the functional effects of long non-coding RNA paternally expressed imprinted gene 10 (PEG10) on DLBCL progression.

Material/Methods

Real-time quantitative polymerase chain reaction was used to measure the level of PEG10, kinesin family member 2A (KIF2A) and microRNA-101-3p (miR-101-3p) in DLBCL tissues and cell lines. The relative protein level was detected by western blot analysis. The biological behaviors including cell proliferation, apoptosis, migration, and invasion were determined by MTT assay, flow cytometry analysis, and Transwell assays, respectively. Bioinformatics analysis and dual-luciferase reporter assay were performed to evaluate the interaction among PEG10, miR-101-3p, and KIF2A.

Results

PEG10 and KIF2A level were significantly upregulated, while miR-101-3p was downregulated in DLBCL tissues and cells. PEG10 positively regulated KIF2A level in DLBCL. PEG10, or KIF2A deletion significantly inhibited the proliferative, migratory, and invasive abilities of DLBCL cells and elevated cell apoptosis in DLBCL cells. KIF2A upregulation partially reversed the effects of PEG10 downregulation on cell growth, metastasis, and apoptosis in DLBCL. Moreover, PEG10 negatively regulated miR-101-3p level and miR-101-3p upregulation exerted inhibition effects on the progression of DLBCL. Besides, miR-101-3p was a target of PEG10 and miR-101-3p could directly target KIF2A. PEG10 promoted KIF2A level by sponging miR-101-3p.

Conclusions

Our findings revealed that PEG10 played an oncogenic role in DLBCL progression, which might be a potential target for the treatment of DLBCL.

High neuropilin and tolloid-like 1 expression associated with metastasis and poor survival in epithelial ovarian cancer via regulation of actin cytoskeleton

Abnormal expression of neuropilin and tolloid‐like 1 (NETO1) has been detected in some human carcinomas. However, the expression of NETO1 and the underlying mechanism in epithelial ovarian cancer (EOC) remain unknown. In this study, we found that a higher NETO1 expression in EOC tissue samples compared to normal ovarian tissue samples was significantly correlated with worse overall survival. Additionally, Cox regression analysis suggested that NETO 1 was independently associated with overall survival. NETO1 overexpression enhanced the EOC cells’ migration and invasion capability in vitro via regulation of actin cytoskeleton. Mechanistically, silencing NETO1 reduced the expression of β‐tubulin, F‐actin and KIF2A. In conclusion, our results demonstrated the critical role of NETO1 in EOC invasion, and therapies aimed at inhibiting its expression or activity might significantly control EOC growth, invasion and metastatic dissemination.

Ciliary proteins specify the cell inflammatory response by tuning NFκB signalling, independently of primary cilia

Complex inflammatory signalling cascades define the response to tissue injury but also control development and homeostasis, limiting the potential for these pathways to be targeted therapeutically. Primary cilia are subcellular regulators of cellular signalling, controlling how signalling is organized, encoded and, in some instances, driving or influencing pathogenesis. Our previous research revealed that disruption of ciliary intraflagellar transport (IFT), altered the cell response to IL-1β, supporting a putative link emerging between cilia and inflammation. Here, we show that IFT88 depletion affects specific cytokine-regulated behaviours, changing cytosolic NFκB translocation dynamics but leaving MAPK signalling unaffected. RNA-seq analysis indicates that IFT88 regulates one third of the genome-wide targets, including the pro-inflammatory genes Nos2, Il6 and Tnf. Through microscopy, we find altered NFκB dynamics are independent of assembly of a ciliary axoneme. Indeed, depletion of IFT88 inhibits inflammatory responses in the non-ciliated macrophage. We propose that ciliary proteins, including IFT88, KIF3A, TTBK2 and NPHP4, act outside of the ciliary axoneme to tune cytoplasmic NFκB signalling and specify the downstream cell response. This is thus a non-canonical function for ciliary proteins in shaping cellular inflammation.

This article has an associated First Person interview with the first author of the paper.

Summary: Ciliary proteins, acting independently of the ciliary axoneme, regulate the dynamics of cytosolic NFκB, but not other signalling pathways, defining an important subset of the inflammatory response.

Phosphorylation of multiple proteins involved in ciliogenesis by Tau Tubulin kinase 2

Primary cilia are organelles necessary for proper implementation of developmental and homeostasis processes. To initiate their assembly, coordinated actions of multiple proteins are needed. Tau tubulin kinase 2 (TTBK2) is a key player in the cilium assembly pathway, controlling the final step of cilia initiation. The function of TTBK2 in ciliogenesis is critically dependent on its kinase activity; however, the precise mechanism of TTBK2 action has so far not been fully understood due to the very limited information about its relevant substrates. In this study, we demonstrate that CEP83, CEP89, CCDC92, Rabin8, and DVL3 are substrates of TTBK2 kinase activity. Further, we characterize a set of phosphosites of those substrates and CEP164 induced by TTBK2 in vitro and in vivo. Intriguingly, we further show that identified TTBK2 phosphosites and consensus sequence delineated from those are distinct from motifs previously assigned to TTBK2. Finally, we show that TTBK2 is also required for efficient phosphorylation of many S/T sites in CEP164 and provide evidence that TTBK2-induced phosphorylations of CEP164 modulate its function, which in turn seems relevant for the process of cilia formation. In summary, our work provides important insight into the substrates-TTBK2 kinase relationship and suggests that phosphorylation of substrates on multiple sites by TTBK2 is probably involved in the control of ciliogenesis in human cells.

Dynamic Changes in Ultrastructure of the Primary Cilium in Migrating Neuroblasts in the Postnatal Brain

New neurons, referred to as neuroblasts, are continuously generated in the ventricular-subventricular zone of the brain throughout an animal's life. These neuroblasts are characterized by their unique potential for proliferation, formation of chain-like cell aggregates, and long-distance and high-speed migration through the rostral migratory stream (RMS) toward the olfactory bulb (OB), where they decelerate and differentiate into mature interneurons. The dynamic changes of ultrastructural features in postnatal-born neuroblasts during migration are not yet fully understood. Here we report the presence of a primary cilium, and its ultrastructural morphology and spatiotemporal dynamics, in migrating neuroblasts in the postnatal RMS and OB. The primary cilium was observed in migrating neuroblasts in the postnatal RMS and OB in male and female mice and zebrafish, and a male rhesus monkey. Inhibition of intraflagellar transport molecules in migrating neuroblasts impaired their ciliogenesis and rostral migration toward the OB. Serial section transmission electron microscopy revealed that each migrating neuroblast possesses either a pair of centrioles or a basal body with an immature or mature primary cilium. Using immunohistochemistry, live imaging, and serial block-face scanning electron microscopy, we demonstrate that the localization and orientation of the primary cilium are altered depending on the mitotic state, saltatory migration, and deceleration of neuroblasts. Together, our results highlight a close mutual relationship between spatiotemporal regulation of the primary cilium and efficient chain migration of neuroblasts in the postnatal brain.SIGNIFICANCE STATEMENT Immature neurons (neuroblasts) generated in the postnatal brain have a mitotic potential and migrate in chain-like cell aggregates toward the olfactory bulb. Here we report that migrating neuroblasts possess a tiny cellular protrusion called a primary cilium. Immunohistochemical studies with zebrafish, mouse, and monkey brains suggest that the presence of the primary cilium in migrating neuroblasts is evolutionarily conserved. Ciliogenesis in migrating neuroblasts in the rostral migratory stream is suppressed during mitosis and promoted after cell cycle exit. Moreover, live imaging and 3D electron microscopy revealed that ciliary localization and orientation change during saltatory movement of neuroblasts. Our results reveal highly organized dynamics in maturation and positioning of the primary cilium during neuroblast migration that underlie saltatory movement of postnatal-born neuroblasts.

Effects of KIF2A on the prognosis of nasopharyngeal carcinoma and nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is a common tumor in south China. Kinesin family member 2A (KIF2A) belongs to the kinesin-13 family and is associated with the growth and invasion of a number of different types of human cancer, including ovarian, breast and prostate cancer. The aim of the present study was to evaluate the expression of KIF2A in NPC and explore the relationship between KIF2A and the basic characteristics of 5-8F cells. Immunohistochemistry was performed on tissues from 97 patients with NPC to assess KIF2A protein expression. KIF2A was knocked down by a specific short interfering (si)RNA in 5-8F cell lines. Cell proliferation, apoptosis and cycle were analyzed by MTT assay and flow cytometry. The invasive ability and angiogenesis were evaluated by Matrigel assay and reverse transcription-quantitative PCR. The level of KIF2A was associated with the growth and migration of primary tumor, nodal status and tumor stage. The viability of KIF2A-knockdown cells was decreased compared with that of the control cells. The number of apoptotic cells, as well as the percentage of cells in the G0/G1 phase, was higher in the KIF2A siRNA group compared with the control group. The invasive and angiogenetic ability of 5-8F cells in the KIF2A siRNA group was decreased compared with the control group. In conclusion, the expression of KIF2A correlated with the poor clinicopathological features in NPC. Therefore, KIF2A may serve an important role in the progression of NPC and proliferation of 5-8F cells, which might present a potential therapeutic target for patients with NPC.

Memo1-Mediated Tiling of Radial Glial Cells Facilitates Cerebral Cortical Development

Polarized, non-overlapping, regularly spaced, tiled organization of radial glial cells (RGCs) serves as a framework to generate and organize cortical neuronal columns, layers, and circuitry. Here, we show that mediator of cell motility 1 (Memo1) is a critical determinant of radial glial tiling during neocortical development. Memo1 deletion or knockdown leads to hyperbranching of RGC basal processes and disrupted RGC tiling, resulting in aberrant radial unit assembly and neuronal layering. Memo1 regulates microtubule (MT) stability necessary for RGC tiling. Memo1 deficiency leads to disrupted MT minus-end CAMSAP2 distribution, initiation of aberrant MT branching, and altered polarized trafficking of key basal domain proteins such as GPR56, and thus aberrant RGC tiling. These findings identify Memo1 as a mediator of RGC scaffold tiling, necessary to generate and organize neurons into functional ensembles in the developing cerebral cortex.

Tau tubulin kinases in proteinopathy

A number of neurodegenerative diseases are characterized by deposition of abnormally phosphorylated tau or TDP-43 in disease-affected neurons. These diseases include Alzheimer's disease, frontotemporal lobar degeneration, and amyotrophic lateral sclerosis. No disease-modifying therapeutics is available to treat these disorders, and we have a limited understanding of the cellular and molecular factors integral to disease initiation or progression. Phosphorylated tau and TDP-43 are important markers of pathology in dementia disorders and directly contribute to tau- and TDP-43-related neurotoxicity and neurodegeneration. Here, we review the scope of tau and TDP-43 phosphorylation in neurodegenerative disease and discuss recent work demonstrating the kinases TTBK1 and TTBK2 phosphorylate both tau and TDP-43, promoting neurodegeneration.

Mechanism and Regulation of Centriole and Cilium Biogenesis

The centriole is an ancient microtubule-based organelle with a conserved nine-fold symmetry. Centrioles form the core of centrosomes, which organize the interphase microtubule cytoskeleton of most animal cells and form the poles of the mitotic spindle. Centrioles can also be modified to form basal bodies, which template the formation of cilia and play central roles in cellular signaling, fluid movement, and locomotion. In this review, we discuss developments in our understanding of the biogenesis of centrioles and cilia and the regulatory controls that govern their structure and number. We also discuss how defects in these processes contribute to a spectrum of human diseases and how new technologies have expanded our understanding of centriole and cilium biology, revealing exciting avenues for future exploration.

Spinocerebellar ataxia type 11-associated alleles of Ttbk2 dominantly interfere with ciliogenesis and cilium stability

Spinocerebellar ataxia type 11 (SCA11) is a rare, dominantly inherited human ataxia characterized by atrophy of Purkinje neurons in the cerebellum. SCA11 is caused by mutations in the gene encoding the Serine/Threonine kinase Tau tubulin kinase 2 (TTBK2) that result in premature truncations of the protein. We previously showed that TTBK2 is a key regulator of the assembly of primary cilia in vivo. However, the mechanisms by which the SCA11-associated mutations disrupt TTBK2 function, and whether they interfere with ciliogenesis were unknown. In this work, we present evidence that SCA11-associated mutations are dominant negative alleles and that the resulting truncated protein (TTBK2^SCA11) interferes with the function of full length TTBK2 in mediating ciliogenesis. A Ttbk2 allelic series revealed that upon partial reduction of full length TTBK2 function, TTBK2^SCA11 can interfere with the activity of the residual wild-type protein to decrease cilia number and interrupt cilia-dependent Sonic hedgehog (SHH) signaling. Our studies have also revealed new functions for TTBK2 after cilia initiation in the control of cilia length, trafficking of a subset of SHH pathway components, including Smoothened (SMO), and cilia stability. These studies provide a molecular foundation to understand the cellular and molecular pathogenesis of human SCA11, and help account for the link between ciliary dysfunction and neurodegenerative diseases.

Defects in primary cilia structure and function are linked to a number of recessive genetic disorders, now collectively referred to as ciliopathies. Most of the characteristics of these disorders arise from disruptions to embryonic development, with the requirements for primary cilia in adult tissues being less well-defined. We previously showed that a kinase associated with an adult-onset neurodegenerative condition is required for cilium assembly and ciliary signaling during development. Here, we show that the human disease-associated mutations act as mild dominant negatives, interfering with the function of the full-length protein in cilia formation and ciliary signaling.

Syntaphilin Ubiquitination Regulates Mitochondrial Dynamics and Tumor Cell Movements

Syntaphilin (SNPH) inhibits the movement of mitochondria in tumor cells, preventing their accumulation at the cortical cytoskeleton and limiting the bioenergetics of cell motility and invasion. Although this may suppress metastasis, the regulation of the SNPH pathway is not well understood. Using a global proteomics screen, we show that SNPH associates with multiple regulators of ubiquitin-dependent responses and is ubiquitinated by the E3 ligase CHIP (or STUB1) on Lys111 and Lys153 in the microtubule-binding domain. SNPH ubiquitination did not result in protein degradation, but instead anchored SNPH on tubulin to inhibit mitochondrial motility and cycles of organelle fusion and fission, that is dynamics. Expression of ubiquitination-defective SNPH mutant Lys111→Arg or Lys153→Arg increased the speed and distance traveled by mitochondria, repositioned mitochondria to the cortical cytoskeleton, and supported heightened tumor chemotaxis, invasion, and metastasis in vivo Interference with SNPH ubiquitination activated mitochondrial dynamics, resulting in increased recruitment of the fission regulator dynamin-related protein-1 (Drp1) to mitochondria and Drp1-dependent tumor cell motility. These data uncover nondegradative ubiquitination of SNPH as a key regulator of mitochondrial trafficking and tumor cell motility and invasion. In this way, SNPH may function as a unique, ubiquitination-regulated suppressor of metastasis.Significance: These findings reveal a new mechanism of metastasis suppression by establishing the role of SNPH ubiquitination in inhibiting mitochondrial dynamics, chemotaxis, and metastasis. Cancer Res; 78(15); 4215-28. ©2018 AACR.

Phosphorylation of EB1 regulates the recruitment of CLIP-170 and p150glued to the plus ends of astral microtubules

Phosphorylation of end-binding protein 1 (EB1), a key member of microtubule plus end-tracking proteins (+TIPs), by apoptosis signal-regulating kinase 1 (ASK1) has been demonstrated to promote the stability of astral microtubules during mitosis by stimulating the binding of EB1 to microtubule plus ends. However, the roles of other members of the +TIPs family in ASK1/EB1-mediated regulation of astral microtubules are unknown. Herein, we show that ASK1-mediated phosphorylation of EB1 enhances the localization of cytoplasmic linker protein 170 (CLIP-170) and p150^glued to the plus ends of astral microtubules. Depletion of ASK1 or expression of phospho-deficient or phospho-mimetic EB1 mutants results in changes in the levels of plus-end localized CLIP-170 or p150^glued. Mechanistic studies reveal that EB1 phosphorylation promotes its interactions with CLIP-170 and p150^glued, thereby recruiting these +TIPs to microtubules. Structural analysis suggests that serine-40 is the primary phosphorylation site on EB1 that exerts these effects. Together, these findings provide novel insight into the molecular mechanisms that regulate the interactions of EB1 with other +TIPs.

Pathological phosphorylation of tau and TDP-43 by TTBK1 and TTBK2 drives neurodegeneration

BACKGROUND

Progressive neuron loss in the frontal and temporal lobes of the cerebral cortex typifies frontotemporal lobar degeneration (FTLD). FTLD sub types are classified on the basis of neuronal aggregated protein deposits, typically containing either aberrantly phosphorylated TDP-43 or tau. Our recent work demonstrated that tau tubulin kinases 1 and 2 (TTBK1/2) robustly phosphorylate TDP-43 and co-localize with phosphorylated TDP-43 in human postmortem neurons from FTLD patients. Both TTBK1 and TTBK2 were initially identified as tau kinases and TTBK1 has been shown to phosphorylate tau epitopes commonly observed in Alzheimer's disease and other tauopathies.

METHODS

To further elucidate how TTBK1/2 activity contributes to both TDP-43 and tau phosphorylation in the context of the neurodegeneration seen in FTLD, we examined the consequences of elevated human TTBK1/2 kinase expression in transgenic animal models of disease.

RESULTS

We show that C. elegans co-expressing tau/TTBK1 tau/TTBK2, or TDP-43/TTBK1 transgenes in combination exhibit synergistic exacerbation of behavioral abnormalities and increased pathological protein phosphorylation. We also show that C. elegans co-expressing tau/TTBK1 or tau/TTBK2 transgenes in combination exhibit aberrant neuronal architecture and neuron loss. Surprisingly, the TTBK2/TDP-43 transgenic combination showed no exacerbation of TDP-43 proteinopathy related phenotypes. Additionally, we observed elevated TTBK1/2 protein expression in cortical and hippocampal neurons of FTLD-tau and FTLD-TDP cases relative to normal controls.

CONCLUSIONS

Our findings suggest a possible etiology for the two most common FTLD subtypes through a kinase activation driven mechanism of neurodegeneration.

PlexinD1 signaling controls morphological changes and migration termination in newborn neurons

Newborn neurons maintain a very simple, bipolar shape, while they migrate from their birthplace toward their destinations in the brain, where they differentiate into mature neurons with complex dendritic morphologies. Here, we report a mechanism by which the termination of neuronal migration is maintained in the postnatal olfactory bulb (OB). During neuronal deceleration in the OB, newborn neurons transiently extend a protrusion from the proximal part of their leading process in the resting phase, which we refer to as a filopodium-like lateral protrusion (FLP). The FLP formation is induced by PlexinD1 downregulation and local Rac1 activation, which coincide with microtubule reorganization and the pausing of somal translocation. The somal translocation of resting neurons is suppressed by microtubule polymerization within the FLP The timing of neuronal migration termination, controlled by Sema3E-PlexinD1-Rac1 signaling, influences the final positioning, dendritic patterns, and functions of the neurons in the OB These results suggest that PlexinD1 signaling controls FLP formation and the termination of neuronal migration through a precise control of microtubule dynamics.

Export of membrane proteins from the Golgi complex to the primary cilium requires the kinesin motor, KIFC1

Microtubule-based motors contribute to the efficiency and selectivity of Golgi exit and post-Golgi transport of membrane proteins that are targeted to distinct compartments. Cytoplasmic dynein moves post-Golgi vesicles that carry rhodopsin toward the base of the connecting cilium in photoreceptor cells; however, the identity of the motors that are involved in the vesicular trafficking of ciliary membrane proteins in nonphotoreceptor cells remains unclear. Here, we demonstrate that the minus end-directed kinesin KIFC1 (kinesin family member C1) is required for both ciliary membrane protein transport and serum starvation-induced ciliogenesis in retinal pigmented epithelial 1 cells. Although KIFC1 is known as a mitotic motor that is sequestered in the nucleus during interphase, KIFC1 immunoreactivity appeared in the Golgi region after serum starvation. Knockdown of KIFC1 inhibited the export of ciliary receptors from the Golgi complex. KIFC1 overexpression affected the Golgi localization of GMAP210 (Golgi microtubule-associated protein 210) and IFT20 (intraflagellar transport 20), which are involved in membrane protein transport to cilia. Moreover, KIFC1 physically interacted with ASAP1 (ADP-ribosylation factor GTPase-activating protein with SH3 domain, ankyrin repeat and PH domain 1), which regulates the budding of rhodopsin transport carriers from the Golgi complex, and KIFC1 depletion caused Golgi accumulation of ASAP1. A decrease in the centrosomal levels of IFT20 and TTBK2 (τ-tubulin kinase 2) was associated with ciliogenesis defects in KIFC1-depleted cells. Our results suggest that KIFC1 plays roles in the Golgi exit of ciliary receptors and in the recruitment of ciliogenesis regulators.-Lee, S.-H., Joo, K., Jung, E. J., Hong, H., Seo, J., Kim, J. Export of membrane proteins from the Golgi complex to the primary cilium requires the kinesin motor, KIFC1.

The MLL recombinome of acute leukemias in 2017

Chromosomal rearrangements of the human MLL/KMT2A gene are associated with infant, pediatric, adult and therapy-induced acute leukemias. Here we present the data obtained from 2345 acute leukemia patients. Genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) were determined and 11 novel TPGs were identified. Thus, a total of 135 different MLL rearrangements have been identified so far, of which 94 TPGs are now characterized at the molecular level. In all, 35 out of these 94 TPGs occur recurrently, but only 9 specific gene fusions account for more than 90% of all illegitimate recombinations of the MLL gene. We observed an age-dependent breakpoint shift with breakpoints localizing within MLL intron 11 associated with acute lymphoblastic leukemia and younger patients, while breakpoints in MLL intron 9 predominate in AML or older patients. The molecular characterization of MLL breakpoints suggests different etiologies in the different age groups and allows the correlation of functional domains of the MLL gene with clinical outcome. This study provides a comprehensive analysis of the MLL recombinome in acute leukemia and demonstrates that the establishment of patient-specific chromosomal fusion sites allows the design of specific PCR primers for minimal residual disease analyses for all patients.

Regulation of end-binding protein EB1 in the control of microtubule dynamics

The regulation of microtubule dynamics is critical to ensure essential cell functions, such as proper segregation of chromosomes during mitosis or cell polarity and migration. End-binding protein 1 (EB1) is a plus-end-tracking protein (+TIP) that accumulates at growing microtubule ends and plays a pivotal role in the regulation of microtubule dynamics. EB1 autonomously binds an extended tubulin-GTP/GDP-Pi structure at growing microtubule ends and acts as a molecular scaffold that recruits a large number of regulatory +TIPs through interaction with CAP-Gly or SxIP motifs. While extensive studies have focused on the structure of EB1-interacting site at microtubule ends and its role as a molecular platform, the mechanisms involved in the negative regulation of EB1 have only started to emerge and remain poorly understood. In this review, we summarize recent studies showing that EB1 association with MT ends is regulated by post-translational modifications and affected by microtubule-targeting agents. We also present recent findings that structural MAPs, that have no tip-tracking activity, physically interact with EB1 to prevent its accumulation at microtubule plus ends. These observations point out a novel concept of "endogenous EB1 antagonists" and emphasize the importance of finely regulating EB1 function at growing microtubule ends.

A regulatory subunit of protein phosphatase 2A, PPP2R5E, regulates the abundance of microtubule crosslinking factor 1

Dynamic changes in microtubule organization are regulated by numerous microtubule-associating proteins and their post-translational modification. Microtubule crosslinking factor 1 (MTCL1) is a recently identified protein that regulates microtubule organization. To obtain further insight into its functions, we searched for proteins that associate with it using mass spectrometry analysis. We found that PPP2R5E, a regulatory subunit of protein phosphatase 2A, interacted with MTCL1. Depletion of PPP2R5E reduced the abundance of MTCL1 abundance, whereas exogenous expression of PPP2R5E increased endogenous MTCL1. Furthermore, inhibition of phosphatase activity by okadaic acid reduced MTCL1, which was restored by the addition of the protease inhibitor MG132. Finally, we show that cells depleted of PPP2R5E and MTCL1 exhibited defects in microtubule organization. Our results suggest that the PPP2R5E phosphatase may contribute to microtubule organization by stabilizing MTCL1.

Regulation of neural stem cell proliferation and differentiation by Kinesin family member 2a

In the developing neocortex, cells in the ventricular/subventricular zone are largely multipotent neural stem cells and neural progenitor cells. These cells undergo self-renewal at the early stage of embryonic development to amplify the progenitor pool and subsequently differentiate into neurons. It is thus of considerable interest to investigate mechanisms controlling the switch from neural stem cells or neural progenitor cells to neurons. Here, we present evidence that Kif2a, a member of the Kinesin-13 family, plays a role in regulating the proliferation and differentiation of neural stem cells or neural progenitor cells at embryonic day 13.5. Silencing Kif2a by use of in utero electroporation of Kif2a shRNA reduced neural stem cells proliferation or self-renewal but increased neuronal differentiation. We further found that knockdown of Kif2a decreased the protein level of β-catenin, which is a critical molecule for neocortical neurogenesis. Together, these results reveal an important function of Kif2a in embryonic neocortical neurogenesis.

Pyk2 activates the NLRP3 inflammasome by directly phosphorylating ASC and contributes to inflammasome-dependent peritonitis

The inflammasome adaptor protein, ASC, contributes to both innate immune responses and inflammatory diseases via self-oligomerization, which leads to the activation of the protease, caspase-1. Here, we report that the cytosolic tyrosine kinases, FAK and Pyk2, are differentially involved in NLRP3 and AIM2 inflammasome activation. The inhibition of FAK and Pyk2 with RNA interference or chemical inhibitors dramatically abolished ASC oligomerization, caspase-1 activation, and IL-1β secretion in response to NLRP3 or AIM2 stimulation. Pyk2 is phosphorylated by the kinase Syk and relocalizes to the ASC specks upon NLRP3 inflammasome activation. Pyk2, but not FAK, could directly phosphorylate ASC at Tyr146, and only the phosphorylated ASC could participate in speck formation and trigger IL-1β secretion. Moreover, the clinical-trial-tested Pyk2/FAK dual inhibitor PF-562271 reduced monosodium urate-mediated peritonitis, a disease model used for studying the consequences of NLRP3 activation. Our results suggest that although Pyk2 and FAK are involved in inflammasome activation, only Pyk2 directly phosphorylates ASC and brings ASC into an oligomerization-competent state by allowing Tyr146 phosphorylation to participate ASC speck formation and subsequent NLRP3 inflammation.

KIF2A Overexpression and Its Association with Clinicopathologic Characteristics and Poor Prognoses in Patients with Gastric Cancer

Kinesin family protein 2A (KIF2A), an M-type nonmotile microtubule depolymerase, has attracted attention for its role in carcinogenesis and poor prognoses in various human cancers. In this study, we aimed to evaluate the expression of KIF2A and its robustness and potential to predict clinical outcomes in gastric cancer (GC) patients. The messenger RNA (mRNA) expression of KIF2A was determined in 24 pairs of cancerous and adjacent nontumor tissues by real-time polymerase chain reaction. Immunohistochemistry of KIF2A was performed on a tissue microarray composed of 461 GC and 65 matched adjacent nontumor tissues removed during surgeries and 18 chronic gastritis, 15 intestinal metaplasia, and 37 low-grade and 62 high-grade intraepithelial neoplasias acquired through gastric endoscopic biopsies. Univariate and multivariate Cox regression models were used to perform survival analyses. The high KIF2A expression was significantly correlated to histological type, TNM stage, and lymph node metastasis. A negative correlation was found between KIF2A expression and the 5-year survival rate of GC patients. In addition, multivariate analysis indicated that KIF2A is an independent prognostic factor in GC. This study demonstrated the high KIF2A expression might serve as an independent marker for poor prognoses in GC patients.

Microtubule plus-end tracking proteins in neuronal development

Regulation of the microtubule cytoskeleton is of pivotal importance for neuronal development and function. One such regulatory mechanism centers on microtubule plus-end tracking proteins (+TIPs): structurally and functionally diverse regulatory factors, which can form complex macromolecular assemblies at the growing microtubule plus-ends. +TIPs modulate important properties of microtubules including their dynamics and their ability to control cell polarity, membrane transport and signaling. Several neurodevelopmental and neurodegenerative diseases are associated with mutations in +TIPs or with misregulation of these proteins. In this review, we focus on the role and regulation of +TIPs in neuronal development and associated disorders.