Microtubule capture by mitotic kinesin centromere protein E (CENP-E)

Kinesin-7 CENP-E in tumorigenesis: Chromosome instability, spindle assembly checkpoint, and applications

Kinesin motors are a large family of molecular motors that walk along microtubules to fulfill many roles in intracellular transport, microtubule organization, and chromosome alignment. Kinesin-7 CENP-E (Centromere protein E) is a chromosome scaffold-associated protein that is located in the corona layer of centromeres, which participates in kinetochore-microtubule attachment, chromosome alignment, and spindle assembly checkpoint. Over the past 3 decades, CENP-E has attracted great interest as a promising new mitotic target for cancer therapy and drug development. In this review, we describe expression patterns of CENP-E in multiple tumors and highlight the functions of CENP-E in cancer cell proliferation. We summarize recent advances in structural domains, roles, and functions of CENP-E in cell division. Notably, we describe the dual functions of CENP-E in inhibiting and promoting tumorigenesis. We summarize the mechanisms by which CENP-E affects tumorigenesis through chromosome instability and spindle assembly checkpoints. Finally, we overview and summarize the CENP-E-specific inhibitors, mechanisms of drug resistances and their applications.

Coordination between the Ndc80 complex and dynein is essential for microtubule plus-end capture by kinetochores during early mitosis

Mitotic kinetochores are initially captured by dynamic microtubules via a "search-and-capture" mechanism. The microtubule motor, dynein, is critical for kinetochore capture as it has been shown to transport microtubule-attached chromosomes toward the spindle pole during prometaphase. The microtubule-binding nuclear division cycle 80 (Ndc80) complex that is recruited to kinetochores in prophase is known to play a central role in forming kinetochore-microtubule (kMT) attachments in metaphase. It is not yet clear, however, how Ndc80 contributes to initial kMT capture during prometaphase. Here, by combining CRISPR/Cas9-mediated knockout and RNAi technology with assays specific to study kMT capture, we show that mitotic cells lacking Ndc80 exhibit substantial defects in this function during prometaphase. Rescue experiments show that Ndc80 mutants deficient in microtubule-binding are unable to execute proper kMT capture. While cells inhibited of dynein alone are predominantly able to make initial kMT attachments, cells co-depleted of Ndc80 and dynein show severe defects in kMT capture. Further, we use an in vitro total internal reflection fluorescence microscopy assay to reconstitute microtubule capture events, which suggest that Ndc80 and dynein coordinate with each other for microtubule plus-end capture and that the phosphorylation status of Ndc80 is critical for productive kMT capture. A novel interaction between Ndc80 and dynein that we identify in prometaphase extracts might be critical for efficient plus-end capture. Thus, our studies, for the first time, identify a distinct event in the formation of initial kMT attachments, which is directly mediated by Ndc80 and in coordination with dynein is required for efficient kMT capture and chromosome alignment.

Crystal structure of the motor domain of centromere-associated protein E in complex with a non-hydrolysable ATP analogue

Centromere-associated protein E (CENP-E) is a kinesin motor protein essential for mitosis and a new target for anticancer agents with less side effects. To rationally design anticancer drug candidates based on structure, it is important to determine the three-dimensional structure of the CENP-E motor domain bound to its inhibitor. Here, we report the first crystal structure of the CENP-E motor domain in complex with a non-hydrolysable ATP analogue, adenylyl-imidodiphosphate (AMPPNP). Furthermore, the structure is compared with the ADP-bound form of the CENP-E motor domain as well as the AMPPNP-bound forms of other kinesins. This study indicates that helix α4 of CENP-E participates in the slow binding of CENP-E to microtubules. These results will contribute to the development of anticancer drugs targeting CENP-E.

Plasma cell-free RNA profiling distinguishes cancers from pre-malignant conditions in solid and hematologic malignancies

Cell-free RNA (cfRNA) in plasma reflects phenotypic alterations of both localized sites of cancer and the systemic host response. Here we report that cfRNA sequencing enables the discovery of messenger RNA (mRNA) biomarkers in plasma with the tissue of origin-specific to cancer types and precancerous conditions in both solid and hematologic malignancies. To explore the diagnostic potential of total cfRNA from blood, we sequenced plasma samples of eight hepatocellular carcinoma (HCC) and ten multiple myeloma (MM) patients, 12 patients of their respective precancerous conditions, and 20 non-cancer (NC) donors. We identified distinct gene sets and built classification models using Random Forest and linear discriminant analysis algorithms that could distinguish cancer patients from premalignant conditions and NC individuals with high accuracy. Plasma cfRNA biomarkers of HCC are liver-specific genes and biomarkers of MM are highly expressed in the bone marrow compared to other tissues and are related to cell cycle processes. The cfRNA level of these biomarkers displayed a gradual transition from noncancerous states through precancerous conditions and cancer. Sequencing data were cross-validated by quantitative reverse transcription PCR and cfRNA biomarkers were validated in an independent sample set (20 HCC, 9 MM, and 10 NC) with AUC greater than 0.86. cfRNA results observed in precancerous conditions require further validation. This work demonstrates a proof of principle for using mRNA transcripts in plasma with a small panel of genes to distinguish between cancers, noncancerous states, and precancerous conditions.

Structure and comparison of the motor domain of centromere-associated protein E

Centromere-associated protein E (CENP-E) plays an essential role in mitosis and is a target candidate for anticancer drugs. However, it is difficult to design small-molecule inhibitors of CENP-E kinesin motor ATPase activity owing to a lack of structural information on the CENP-E motor domain in complex with its inhibitors. Here, the CENP-E motor domain was crystallized in the presence of an ATP-competitive inhibitor and the crystal structure was determined at 1.9 Å resolution. In the determined structure, ADP was observed instead of the inhibitor in the nucleotide-binding site, even though no ADP was added during protein preparation. Structural comparison with the structures of previously reported CENP-E and those of other kinesins indicates that the determined structure is nearly identical except for several loop regions. However, the retention of ADP in the nucleotide-binding site of the structure strengthens the biochemical view that the release of ADP is a rate-limiting step in the ATPase cycle of CENP-E. These results will contribute to the development of anticancer drugs targeting CENP-E and to understanding the function of kinesin motor domains.

Leaving no-one behind: how CENP-E facilitates chromosome alignment

Chromosome alignment and biorientation is essential for mitotic progression and genomic stability. Most chromosomes align at the spindle equator in a motor-independent manner. However, a subset of polar kinetochores fail to bi-orient and require a microtubule motor-based transport mechanism to move to the cell equator. Centromere Protein E (CENP-E/KIF10) is a kinesin motor from the Kinesin-7 family, which localizes to unattached kinetochores during mitosis and utilizes plus-end directed microtubule motility to slide mono-oriented chromosomes to the spindle equator. Recent work has revealed how CENP-E cooperates with chromokinesins and dynein to mediate chromosome congression and highlighted its role at aligned chromosomes. Additionally, we have gained new mechanistic insights into the targeting and regulation of CENP-E motor activity at the kinetochore. Here, we will review the function of CENP-E in chromosome congression, the pathways that contribute to CENP-E loading at the kinetochore, and how CENP-E activity is regulated during mitosis.

Kinesin-7 CENP-E regulates the formation and structural maintenance of the acrosome

The acrosome is a special organelle that develops from the Golgi apparatus and the endolysosomal compartment in the spermatids. Centromere protein E (CENP-E) is an essential kinesin motor in chromosome congression and alignment. This study is aimed at investigating the roles and mechanisms of kinesin-7 CENP-E in the formation of the acrosome during spermatogenesis. Male ICR mice are injected with GSK923295 for long-term inhibition of CENP-E. Chemical inhibition and siRNA-mediated knockdown of CENP-E are carried out in the GC-2 spd cells. The morphology of the acrosomes is determined by the HE staining, immunofluorescence, and transmission electron microscopy. We have identified CENP-E is a key factor in the formation and structural maintenance of the acrosome during acrosome biogenesis. Long-term inhibition of CENP-E by GSK923295 results in the asymmetric acrosome and the dispersed acrosome. CENP-E depletion leads to the malformation of the Golgi complex and abnormal targeting of the PICK1- and PIST-positive Golgi-associated vesicles. Our findings uncover an essential role of CENP-E in membrane trafficking and structural organization of the acrosome in the spermatids during spermatogenesis. Our results shed light on the molecular mechanisms involved in vesicle trafficking and architecture maintenance of the acrosome.

A novel assay to screen siRNA libraries identifies protein kinases required for chromosome transmission

One of the hallmarks of cancer is chromosome instability (CIN), which leads to aneuploidy, translocations, and other chromosome aberrations. However, in the vast majority of human tumors the molecular basis of CIN remains unknown, partly because not all genes controlling chromosome transmission have yet been identified. To address this question, we developed an experimental high-throughput imaging (HTI) siRNA assay that allows the identification of novel CIN genes. Our method uses a human artificial chromosome (HAC) expressing the GFP transgene. When this assay was applied to screen an siRNA library of protein kinases, we identified PINK1, TRIO, IRAK1, PNCK, and TAOK1 as potential novel genes whose knockdown induces various mitotic abnormalities and results in chromosome loss. The HAC-based assay can be applied for screening different siRNA libraries (cell cycle regulation, DNA damage response, epigenetics, and transcription factors) to identify additional genes involved in CIN. Identification of the complete spectrum of CIN genes will reveal new insights into mechanisms of chromosome segregation and may expedite the development of novel therapeutic strategies to target the CIN phenotype in cancer cells.

Biomolecular interfaces based on self-assembly and self-recognition form biosensors capable of recording molecular binding and release

This research proposed to create the next generation of versatile electrochemical-based biosensors capable of monitoring target capture and release as dictated by molecular binding or unbinding. The biosensor integrates cellular machines (i.e., microtubules, structural elements of cells and kinesin molecular motors involved in cellular transport) as functional units; its assembly is based on molecular self-assembly and self-recognition. Our results demonstrate that the designed biosensor was capable of allowing detection of binding and unbinding events based on redox reactions at user-controlled electrode interfaces. The analysis also showed that the sensitivity of the designed biosensor or its ability to record such events could be user-controlled at any given time by adjusting the energy source that "fuels" the system.

Mechanisms of kinesin-7 CENP-E in kinetochore-microtubule capture and chromosome alignment during cell division

Chromosome congression is essential for faithful chromosome segregation and genomic stability in cell division. Centromere-associated protein E (CENP-E), a plus-end-directed kinesin motor, is required for congression of pole-proximal chromosomes in metaphase. CENP-E accumulates at the outer plate of kinetochores and mediates the kinetochore-microtubule capture. CENP-E also transports the chromosomes along spindle microtubules towards the equatorial plate. CENP-E interacts with Bub1-related kinase, Aurora B and core kinetochore components during kinetochore-microtubule attachment. In this review, we introduce the structures and mechanochemistry of kinesin-7 CENP-E. We highlight the complicated interactions between CENP-E and partner proteins during chromosome congression. We summarise the detailed roles and mechanisms of CENP-E in mitosis and meiosis, including the kinetochore-microtubule capture, chromosome congression/alignment in metaphase and the regulation of spindle assembly checkpoint. We also shed a light on the roles of CENP-E in tumourigenesis and CENP-E's specific inhibitors.

Altered chemomechanical coupling causes impaired motility of the kinesin-4 motors KIF27 and KIF7

Despite their shared ability to regulate microtubule polymerization dynamics, kinesin-4 motors display dramatically different motility properties ranging from fast processive motility to no movement. Yue et al. demonstrate that for KIF7 and KIF27, altered chemomechanical coupling results in immotile behavior and slow processive movement, respectively.

Kinesin-4 motors play important roles in cell division, microtubule organization, and signaling. Understanding how motors perform their functions requires an understanding of their mechanochemical and motility properties. We demonstrate that KIF27 can influence microtubule dynamics, suggesting a conserved function in microtubule organization across the kinesin-4 family. However, kinesin-4 motors display dramatically different motility characteristics: KIF4 and KIF21 motors are fast and processive, KIF7 and its Drosophila melanogaster homologue Costal2 (Cos2) are immotile, and KIF27 is slow and processive. Neither KIF7 nor KIF27 can cooperate for fast processive transport when working in teams. The mechanistic basis of immotile KIF7 behavior arises from an inability to release adenosine diphosphate in response to microtubule binding, whereas slow processive KIF27 behavior arises from a slow adenosine triphosphatase rate and a high affinity for both adenosine triphosphate and microtubules. We suggest that evolutionarily selected sequence differences enable immotile KIF7 and Cos2 motors to function not as transporters but as microtubule-based tethers of signaling complexes.

Mechanisms of Chromosome Congression during Mitosis

Chromosome congression during prometaphase culminates with the establishment of a metaphase plate, a hallmark of mitosis in metazoans. Classical views resulting from more than 100 years of research on this topic have attempted to explain chromosome congression based on the balance between opposing pulling and/or pushing forces that reach an equilibrium near the spindle equator. However, in mammalian cells, chromosome bi-orientation and force balance at kinetochores are not required for chromosome congression, whereas the mechanisms of chromosome congression are not necessarily involved in the maintenance of chromosome alignment after congression. Thus, chromosome congression and maintenance of alignment are determined by different principles. Moreover, it is now clear that not all chromosomes use the same mechanism for congressing to the spindle equator. Those chromosomes that are favorably positioned between both poles when the nuclear envelope breaks down use the so-called "direct congression" pathway in which chromosomes align after bi-orientation and the establishment of end-on kinetochore-microtubule attachments. This favors the balanced action of kinetochore pulling forces and polar ejection forces along chromosome arms that drive chromosome oscillatory movements during and after congression. The other pathway, which we call "peripheral congression", is independent of end-on kinetochore microtubule-attachments and relies on the dominant and coordinated action of the kinetochore motors Dynein and Centromere Protein E (CENP-E) that mediate the lateral transport of peripheral chromosomes along microtubules, first towards the poles and subsequently towards the equator. How the opposite polarities of kinetochore motors are regulated in space and time to drive congression of peripheral chromosomes only now starts to be understood. This appears to be regulated by position-dependent phosphorylation of both Dynein and CENP-E and by spindle microtubule diversity by means of tubulin post-translational modifications. This so-called "tubulin code" might work as a navigation system that selectively guides kinetochore motors with opposite polarities along specific spindle microtubule populations, ultimately leading to the congression of peripheral chromosomes. We propose an integrated model of chromosome congression in mammalian cells that depends essentially on the following parameters: (1) chromosome position relative to the spindle poles after nuclear envelope breakdown; (2) establishment of stable end-on kinetochore-microtubule attachments and bi-orientation; (3) coordination between kinetochore- and arm-associated motors; and (4) spatial signatures associated with post-translational modifications of specific spindle microtubule populations. The physiological consequences of abnormal chromosome congression, as well as the therapeutic potential of inhibiting chromosome congression are also discussed.

Heterodimerization of Kinesin-2 KIF3AB Modulates Entry into the Processive Run

Mammalian KIF3AB is an N-terminal processive kinesin-2 that is best known for its roles in intracellular transport. There has been significant interest in KIF3AB to define the key principles that underlie its processivity but also to define the mechanistic basis of its sensitivity to force. In this study, the kinetics for entry into the processive run were quantified. The results show for KIF3AB that the kinetics of microtubule association at 7 μm^-1 s^-1 is less than the rates observed for KIF3AA at 13 μm^-1 s^-1 or KIF3BB at 11.9 μm^-1 s^-1 ADP release after microtubule association for KIF3AB is 33 s^-1 and is significantly slower than ADP release from homodimeric KIF3AA and KIF3BB, which reach 80-90 s^-1 To explore the interhead communication implied by the rate differences at these first steps, we compared the kinetics of KIF3AB microtubule association followed by ADP release with the kinetics for mixtures of KIF3AA plus KIF3BB. Surprisingly, the kinetics of KIF3AB are not equivalent to any of the mixtures of KIF3AA + KIF3BB. In fact, the transients for each of the mixtures overlay the transients for KIF3AA and KIF3BB. These results reveal that intermolecular communication within the KIF3AB heterodimer modulates entry into the processive run, and the results suggest that it is the high rate of microtubule association that drives rebinding to the microtubule after force-dependent motor detachment.

Kinesin Motor Enzymology: Chemistry, Structure, and Physics of Nanoscale Molecular Machines

Molecular motors are enzymes that convert chemical potential energy into controlled kinetic energy for mechanical work inside cells. Understanding the biophysics of these motors is essential for appreciating life as well as apprehending diseases that arise from motor malfunction. This review focuses on kinesin motor enzymology with special emphasis on the literature that reports the chemistry, structure and physics of several different kinesin superfamily members.

Expression of Spindle and Kinetochore-Associated Protein 1 Is Associated with Poor Prognosis in Papillary Thyroid Carcinoma

AIM

Spindle and kinetochore-associated protein 1 (SKA1) is one subtype of SKA, whose protein can make spindle microtubules attach steadily to the kinetochore in the middle of mitosis. At present, there are fewer researches on the relationship between SKA1 expression and tumor development.

METHODS

In this study, immunohistochemical analysis was used to determine the expression of SKA1 in papillary thyroid carcinoma (PTC) and adjacent tissues. We used quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis to further verify the results.

RESULTS

We found that SKA1 expression was significantly higher in PTC tissues than normal adjacent tissues (P < 0.05). There existed a significant correlation among a higher SKA1 expression, including lymphoid node (P = 0.005), clinical stage (P = 0.015), and extrathyroid invasion (P = 0.004). Survival analysis showed high SKA1 expression in PTC patients more likely to relapse after surgery.

CONCLUSION

High SKA1 expression is predictive of poor prognosis of PTC, implying that SKA1 may be a promising new target for targeted therapies for PTC.

Kinesin-2 KIF3AB exhibits novel ATPase characteristics

KIF3AB is an N-terminal processive kinesin-2 family member best known for its role in intraflagellar transport. There has been significant interest in KIF3AB in defining the key principles that underlie the processivity of KIF3AB in comparison with homodimeric processive kinesins. To define the ATPase mechanism and coordination of KIF3A and KIF3B stepping, a presteady-state kinetic analysis was pursued. For these studies, a truncated murine KIF3AB was generated. The results presented show that microtubule association was fast at 5.7 μm(-1) s(-1), followed by rate-limiting ADP release at 12.8 s(-1). ATP binding at 7.5 μm(-1) s(-1) was followed by an ATP-promoted isomerization at 84 s(-1) to form the intermediate poised for ATP hydrolysis, which then occurred at 33 s(-1). ATP hydrolysis was required for dissociation of the microtubule·KIF3AB complex, which was observed at 22 s(-1). The dissociation step showed an apparent affinity for ATP that was very weak (K½,ATP at 133 μm). Moreover, the linear fit of the initial ATP concentration dependence of the dissociation kinetics revealed an apparent second-order rate constant at 0.09 μm(-1) s(-1), which is inconsistent with fast ATP binding at 7.5 μm(-1) s(-1) and a Kd ,ATP at 6.1 μm. These results suggest that ATP binding per se cannot account for the apparent weak K½,ATP at 133 μm. The steady-state ATPase Km ,ATP, as well as the dissociation kinetics, reveal an unusual property of KIF3AB that is not yet well understood and also suggests that the mechanochemistry of KIF3AB is tuned somewhat differently from homodimeric processive kinesins.

Prime movers: the mechanochemistry of mitotic kinesins

Mitotic spindles are self-organizing protein machines that harness teams of multiple force generators to drive chromosome segregation. Kinesins are key members of these force-generating teams. Different kinesins walk directionally along dynamic microtubules, anchor, crosslink, align and sort microtubules into polarized bundles, and influence microtubule dynamics by interacting with microtubule tips. The mechanochemical mechanisms of these kinesins are specialized to enable each type to make a specific contribution to spindle self-organization and chromosome segregation.

Functional asymmetry in kinesin and dynein dimers

Active transport along the microtubule lattice is a complex process that involves both the Kinesin and Dynein superfamily of motors. Transportation requires sophisticated regulation much of which occurs through the motor's tail domain. However, a significant portion of this regulation also occurs through structural changes that arise in the motor and the microtubule upon binding. The most obvious structural change being the manifestation of asymmetry. To a first approximation in solution, kinesin dimers exhibit twofold symmetry, and microtubules exhibit helical symmetry. The higher symmetries of both the kinesin dimers and microtubule lattice are lost on formation of the kinesin-microtubule complex. Loss of symmetry has functional consequences such as an asymmetric hand-over-hand mechanism in plus-end-directed kinesins, asymmetric microtubule binding in the Kinesin-14 family, spatially biased stepping in dynein and cooperative binding of additional motors to the microtubule. This review focusses on how the consequences of asymmetry affect regulation of motor heads within a dimer, dimers within an ensemble of motors, and suggests how these asymmetries may affect regulation of active transport within the cell.