How kinesin motor proteins drive mitotic spindle function: Lessons from molecular assays

Prognostic value of Kinesin-4 family genes mRNA expression in early-stage pancreatic ductal adenocarcinoma patients after pancreaticoduodenectomy

BACKGROUND

The aim of this study was to investigate the potential prognostic value of Kinesin-4 family genes mRNA expression in early-stage pancreatic ductal adenocarcinoma (PDAC) patients after pancreaticoduodenectomy.

METHODS

Kaplan-Meier survival analysis method with log-rank test and Cox proportional hazards regression analysis were performed to figure out the association between Kinesin-4 family genes expression and PDAC patients overall survival time. Joint-effect survival analysis and stratified survival analysis were carried out to assess the prognosis prediction value of prognosis-related gene. Nomogram was constructed for the individualized prognosis prediction. In addition, we had used the gene set enrichment analysis and genome-wide co-expression analysis to further explore the potential mechanism.

RESULTS

KIF21A expression level was significantly associated with PDAC patient clinical prognosis outcome and patient with a high expression of KIF21A would have a shorter overall survival time. The prognosis prediction significance of KIF21A was well validated by the joint-effect survival analysis, stratified survival analysis, and nomogram. Meanwhile, the gene set enrichment analysis and genome-wide co-expression analysis revealed that KIF21A might involve in DNA damage and repair, transcription and translation process, post-translation protein modification, cell cycle, carcinogensis genes and pathways.

CONCLUSIONS

Our current research demonstrated that KIF21A could serve as a potential prognostic biomarker for patient with early-stage PDAC after pancreaticoduodenectomy.

Mapping the kinetochore MAP functions required for stabilizing microtubule attachments to chromosomes during metaphase

In mitosis, faithful chromosome segregation is orchestrated by the dynamic interactions between the spindle microtubules (MTs) emanating from the opposite poles and the kinetochores of the chromosomes. However, the precise mechanism that coordinates the coupling of the kinetochore components to dynamic MTs has been a long-standing question. Microtubule-associated proteins (MAPs) regulate MT nucleation and dynamics, MT-mediated transport and MT cross-linking in cells. During mitosis, MAPs play an essential role not only in determining spindle length, position, and orientation but also in facilitating robust kinetochore-microtubule (kMT) attachments by linking the kinetochores to spindle MTs efficiently. The stability of MTs imparted by the MAPs is critical to ensure accurate chromosome segregation. This review primarily focuses on the specific function of nonmotor kinetochore MAPs, their recruitment to kinetochores and their MT-binding properties. We also attempt to synthesize and strengthen our understanding of how these MAPs work in coordination with the kinetochore-bound Ndc80 complex (the key component at the MT-binding interface in metaphase and anaphase) to establish stable kMT attachments and control accurate chromosome segregation during mitosis.

Growth arrest and apoptosis induced by kinesin Eg5 inhibitor K858 and by its 1,3,4-thiadiazoline analogue in tumor cells

Tumors are complex and heterogeneous but, despite this, they share the ability to proliferate continuously, irrespective of the presence of growth signals, leading to a higher fraction of actively growing and dividing cells compared with normal tissues. For this reason, the cytotoxic antimitotic treatments remain an important clinical tool for tumors. Among these drugs, antitubulin compounds constitute one of the most effective anticancer chemotherapies; however, they cause dose-limiting side effects. Therefore, it is still necessary to develop compounds with new targets and new mechanisms of action to reduce side effects or chemoresistance. Mitosis-specific kinesin Eg5 can represent an attractive target for discovering such new anticancer agents because its role is fundamental in mitotic progression. Therefore, we analyzed the effects induced by an inhibitor of kinesin Eg5, K858, and by its 1,3,4-thiadiazoline analogue on human melanoma and prostate cancer cell lines. We found that both compounds have an antiproliferative effect, induce apoptosis, and can determine a downmodulation of survivin.

FOXM1 promotes hepatocellular carcinoma progression by regulating KIF4A expression

BACKGROUND

Forkhead box M1 (FOXM1) is a proliferation-associated transcription factor of the forkhead box proteins superfamily, which includes four isoforms FOXM1a, b, c, and d. FOXM1 has been implicated in hepatocellular carcinoma (HCC) progression, but the underlying molecular mechanism remains elusive. In this study, we aim to clarify the molecular basis for FOXM1-mediated HCC progression.

METHODS

Bioinformatic analysis was used to explore the differentially expressed genes predicting HCC proliferation. The expression of FOXM1 and kinesin family member (KIF)4A was confirmed by western blotting and immunohistochemistry in HCC tissues. Kaplan-Meier survival analysis was conducted to analyze the clinical impact of FOXM1 and KIF4A on HCC. The effect of FOXM1 on the regulation of KIF4A expression was studied in cell biology experiments. The interaction between KIF4A and FOXM1 was analyzed by chromatin immunoprecipitation and luciferase experiments. A series of experiments was performed to explore the functions of FOXM1/KIF4A in HCC progression, such as cell proliferation, cell growth, cell viability, and cell cycle. A xenograft mouse model was used to explore the regulatory effect of FOXM1-KIF4A axis on HCC tumor growth.

RESULTS

FOXM1 and KIF4A were overexpressed in human primary HCC tissues compared to that in matched adjacent normal liver tissue and are significant risk factors for HCC recurrence and shorter survival. We found that KIF4A was dominantly regulated by FOXM1c among the four isoforms, and further identified KIF4A as a direct downstream target of FOXM1c. Inhibiting FOXM1 decreased KIF4A expression in HCC cells, whereas its overexpression had the opposite effect. FOXM1-induced HCC cell proliferation was dependent on elevated KIF4A expression as KIF4A knockdown abolished FOXM1-induced proliferation of HCC cells both in vitro and in vivo.

CONCLUSION

The FOXM1-KIF4A axis mediates human HCC progression and is a potential therapeutic target for HCC treatment.

Chromokinesin Kif4 promotes proper anaphase in mouse oocyte meiosis

Oocytes of many species lack centrioles and therefore form acentriolar spindles. Despite the necessity of oocyte meiosis for successful reproduction, how these spindles mediate accurate chromosome segregation is poorly understood. We have gained insight into this process through studies of the kinesin-4 family member Kif4 in mouse oocytes. We found that Kif4 localizes to chromosomes through metaphase and then largely redistributes to the spindle midzone during anaphase, transitioning from stretches along microtubules to distinct ring-like structures; these structures then appear to fuse together by telophase. Kif4’s binding partner PRC1 and MgcRacGAP, a component of the centralspindlin complex, have a similar localization pattern, demonstrating dynamic spindle midzone organization in oocytes. Kif4 knockdown results in defective midzone formation and longer spindles, revealing new anaphase roles for Kif4 in mouse oocytes. Moreover, inhibition of Aurora B/C kinases results in Kif4 mislocalization and causes anaphase defects. Taken together, our work reveals essential roles for Kif4 during the meiotic divisions, furthering our understanding of mechanisms promoting accurate chromosome segregation in acentriolar oocytes.

Insights into the Molecular Mechanisms of Eg5 Inhibition by (+)-Morelloflavone

(+)-Morelloflavone (MF) is an antitumor biflavonoid that is found in the Garcinia species. Recently, we reported MF as a novel inhibitor of ATPase and microtubules-gliding activities of the kinesin spindle protein (Eg5) in vitro. Herein, we provide dynamical insights into the inhibitory mechanisms of MF against Eg5, which involves binding of the inhibitor to the loop5/α2/α3 allosteric pocket. Molecular dynamics simulations were carried out for 100 ns on eight complexes: Eg5-Adenosine diphosphate (Eg5-ADP), Eg5-ADP-S-trityl-l-cysteine (Eg5-ADP-STLC), Eg5-ADP-ispinesib, Eg5-ADP-MF, Eg5-Adenosine triphosphate (Eg5-ATP), Eg5-ATP-STLC, Eg5-ATP-ispinesib, and Eg5-ATP-MF complexes. Structural and energetic analyses were done using Umbrella sampling, Molecular Mechanics Poisson–Boltzmann Surface Area (MM/PBSA) method, GROMACS analysis toolkit, and virtual molecular dynamics (VMD) utilities. The results were compared with those of the known Eg5 inhibitors; ispinesib, and STLC. Our data strongly support a stable Eg5-MF complex, with significantly low binding energy and reduced flexibility of Eg5 in some regions, including loop5 and switch I. Furthermore, the loop5 Trp127 was trapped in a downward position to keep the allosteric pocket of Eg5 in the so-called “closed conformation”, comparable to observations for STLC. Altered structural conformations were also visible within various regions of Eg5, including switch I, switch II, α2/α3 helices, and the tubulin-binding region, indicating that MF might induce modifications in the Eg5 structure to compromise its ATP/ADP binding and conversion process as well as its interaction with microtubules. The described mechanisms are crucial for understanding Eg5 inhibition by MF.

Identification of KIF11 As a Novel Target in Meningioma

Kinesins play an important role in many physiological functions including intracellular vesicle transport and mitosis. The emerging role of kinesins in different cancers led us to investigate the expression and functional role of kinesins in meningioma. Therefore, we re-analyzed our previous microarray dataset of benign, atypical, and anaplastic meningiomas (n = 62) and got evidence for differential expression of five kinesins (KIFC1, KIF4A, KIF11, KIF14 and KIF20A). Further validation in an extended study sample (n = 208) revealed a significant upregulation of these genes in WHO°I to °III meningiomas (WHO°I n = 61, WHO°II n = 88, and WHO°III n = 59), which was most pronounced in clinically more aggressive tumors of the same WHO grade. Immunohistochemical staining confirmed a WHO grade-associated upregulated protein expression in meningioma tissues. Furthermore, high mRNA expression levels of KIFC1, KIF11, KIF14 and KIF20A were associated with shorter progression-free survival. On a functional level, knockdown of kinesins in Ben-Men-1 cells and in the newly established anaplastic meningioma cell line NCH93 resulted in a significantly inhibited tumor cell proliferation upon siRNA-mediated downregulation of KIF11 in both cell lines by up to 95% and 71%, respectively. Taken together, in this study we were able to identify the prognostic and functional role of several kinesin family members of which KIF11 exhibits the most promising properties as a novel prognostic marker and therapeutic target, which may offer new treatment options for aggressive meningiomas.

The Orphan Kinesin PAKRP2 Achieves Processive Motility via a Noncanonical Stepping Mechanism

Phragmoplast-associated kinesin-related protein 2 (PAKRP2) is an orphan kinesin in Arabidopsis thaliana that is thought to transport vesicles along phragmoplast microtubules for cell plate formation. Here, using single-molecule fluorescence microscopy, we show that PAKRP2 is the first orphan kinesin to exhibit processive plus-end-directed motility on single microtubules as individual homodimers. Our results show that PAKRP2 processivity is achieved despite having an exceptionally long (32 residues) neck linker. Furthermore, using high-resolution nanoparticle tracking, we find that PAKRP2 steps via a hand-over-hand mechanism that includes frequent side steps, a prolonged diffusional search of the tethered head, and tight coupling of the ATP hydrolysis cycle to the forward-stepping cycle. Interestingly, truncating the PAKRP2 neck linker to 14 residues decreases the run length of PAKRP2; thus, the long neck linker enhances the processive behavior. Based on the canonical model of kinesin stepping, such a long neck linker is expected to decrease the processivity and disrupt the coupling of ATP hydrolysis to forward stepping. Therefore, we conclude that PAKRP2 employs a noncanonical strategy for processive motility, wherein a long neck linker is coupled with a slow ATP hydrolysis rate to allow for an extended diffusional search during each step without sacrificing processivity or efficiency.

Distinct Diagnostic and Prognostic Values of Kinesin Family Member Genes Expression in Patients with Breast Cancer

BACKGROUND This study investigated the diagnostic and prognostic values of kinesin superfamily proteins (KIFs) in breast cancer (BC) patients. MATERIAL AND METHODS All data were obtained from the Cancer Genome Atlas. DESeq was run to test for differentially expressed KIF genes. Patients were divided into high- and low-expression groups according to the median expression values of each KIF genes. Survival data were calculated using the Cox proportional hazard model. Comprehensive survival analysis was performed to evaluate the prognostic value of the prognostic signature. Gene set enrichment analysis (GSEA) was conducted to identify associated gene ontology and KEGG pathways. RESULTS Bioinformatics analysis showed that all KIF genes were significantly enriched during DNA replication and the cell cycle, and co-expressed with each other. Thirteen KIF genes were differentially expressed in cancer and adjacent tissues, and high levels of KIF15, KIF20A, KIF23, KIF2C and KIF4A genes were significantly correlated with poor overall survival (OS). GSEA showed that BC patients with high expression of KIF15, KIF20A, KIF23, KIF2C and KIF4A were enriched in the cell cycle process, P53 regulation pathway and mismatch repair. Combinations of low expression of KIF15, KIF20A, KIF23, KIF2C and KIF4A were more highly correlated with favorable OS. Nomograms showed that the KIF4A risk score provided the maximum number of risk points (range 0-100), whereas other genes made a lower contribution. CONCLUSIONS We conclude that 13 KIF genes are differentially expressed in BC tumor tissues, and KIF15, KIF20A, KIF23, KIF2C and KIF4A are associated with prognostic factors in BC.

Kinesin Family of Proteins Kif11 and Kif21B Act as Inhibitory Constraints of Excitatory Synaptic Transmission Through Distinct Mechanisms

Despite our understanding of the functions of the kinesin family of motor proteins (Kifs) in neurons, their specific roles in neuronal communication are less understood. To address this, by carrying out RNAi-mediated loss of function studies, we assessed the necessity of 18 Kifs in excitatory synaptic transmission in mouse primary hippocampal neurons prepared from both sexes. Our measurements of excitatory post-synaptic currents (EPSCs) have identified 7 Kifs that were found to be not critical and 11 Kifs that are essential for synaptic transmission by impacting either frequency or amplitude or both components of EPSCs. Intriguingly we found that knockdown of mitotic Kif4A and Kif11 and post-mitotic Kif21B resulted in an increase in EPSCs suggesting that they function as inhibitory constraints on synaptic transmission. Furthermore, Kifs (11, 21B, 13B) with distinct effects on synaptic transmission are expressed in the same hippocampal neuron. Mechanistically, unlike Kif21B, Kif11 requires the activity of pre-synaptic NMDARs. In addition, we find that Kif11 knockdown enhanced dendritic arborization, synapse number, expression of synaptic vesicle proteins synaptophysin and active zone protein Piccolo. Moreover, expression of Piccolo constrained Kif11 function in synaptic transmission. Together these results suggest that neurons are able to utilize specific Kifs as tools for calibrating synaptic function. These studies bring novel insights into the biology of Kifs and functioning of neural circuits.

A dynamic transcriptomic atlas of cytokine-induced killer cells

Several clinical immunotherapy trials with cytokine-induced killer (CIK) cells have been reported. However, molecular evidence of cell expansion, acquisition of tumor cytotoxicity, and safety of CIK cells is required before putting them to clinical use. Here, we performed dynamic transcriptomic analyses of CIKs generated from primary peripheral blood mononuclear cells exposed to interferon-γ, OKT3, and interleukin-2. CIK mRNAs were extracted and sequenced at days 0, 1, 7, and 14 and subjected to bioinformatics analyses. Using weighted correlation network analysis (WGCNA), we identified two major gene modules that mediate immune cell activation and mitosis. We found that activation and cytotoxicity of CIK cells likely rely on cluster of differentiation 8 (CD8) and its protein partner LCK proto-oncogene, Src family tyrosine kinase (LCK). A time-course series analysis revealed that CIK cells have relatively low immunogenicity because of decreased expression of some self-antigens. Importantly, we identified several crucial activating receptors and auxiliary adhesion receptors expressed on CIK cells that may function as tumor sensors. Interestingly, cytotoxicity-associated genes, including those encoding PRF1, GZMB, FASL, and several cytokines, were up-regulated in mature CIK cells. Most immune-checkpoint molecules and inflammatory tumor-promoting factors were down-regulated in the CIK cells, suggesting efficacy and safety in future clinical trials. Notably, insulin-like growth factor 1 (IGF-1) was highly expressed in CIK cells and may promote cytotoxicity, although it also could facilitate tumorigenesis. The transcriptomic atlas of CIK cells presented here may inform efforts to improve CIK-associated tumor cytotoxicity and safety in clinical trials.

The Central Stalk Determines the Motility of Mitotic Kinesin-14 Homodimers

Mitotic kinesin-14 homodimers that contain an N-terminal nonmotor microtubule-binding tail contribute to spindle organization by preferentially crosslinking two different spindle microtubules rather than interacting with a single microtubule to generate processive motility. However, the mechanism underlying such selective motility behavior remains poorly understood. Here, we show that when a flexible polypeptide linker is inserted into the coiled-coil central stalk, two homodimeric mitotic kinesin-14s of distinct motility-the processive plus-end-directed KlpA from Aspergillus nidulans [1] and the nonprocessive minus-end-directed Ncd from Drosophila melanogaster [2]-both switch to become processive minus-end-directed motors. Our results demonstrate that the polypeptide linker introduces greater conformational flexibility into the central stalk. Importantly, we find that the linker insertion significantly weakens the ability of Ncd to preferentially localize between and interact with two microtubules. Collectively, our results reveal that besides the canonical role of enabling dimerization, the central stalk also functions as a mechanical component to determine the motility of homodimeric mitotic kinesin-14 motors. We suggest that the central stalk is an evolutionary design that primes these kinesin-14 motors for nontransport roles within the mitotic spindle.

KIF4A facilitates cell proliferation via induction of p21-mediated cell cycle progression and promotes metastasis in colorectal cancer

Kinesin family member 4A (KIF4A) was found to be implicated in the regulation of chromosome condensation and segregation during mitotic cell division, which is essential for eukaryotic cell proliferation. However, little is known about the role of KIF4A in colorectal carcinoma (CRC). This study explored the biological function of KIF4A in CRC progression and investigated the potential molecular mechanisms involved. Here, we found that KIF4A was remarkably upregulated in primary CRC tissues and cell lines compared with paired non-cancerous tissues and normal colorectal epithelium. Elevated expression of KIF4A in CRC tissues was significantly correlated with clinicopathological characteristics in patients as well as with shorter overall and disease-free cumulative survival. Multivariate Cox regression analysis revealed that KIF4A was an independent prognostic factor for poor survival in human CRC patients. Functional assays, including a CCK-8 cell proliferation assay, colony formation analysis, cancer xenografts in nude mice, cell cycle and apoptosis analysis, indicated that KIF4A obviously enhanced cell proliferation by promoting cell cycle progression in vitro and in vivo. Furthermore, gene set enrichment analysis, Luciferase reporter assays, and ChIP assays revealed that KIF4A facilitates cell proliferation via regulating the p21 promoter, whereas KIF4A had no effect on cell apoptosis. In addition, Transwell analysis indicated that KIF4A promotes migration and invasion in CRC. Taken together, these findings not only demonstrate that KIF4A contributes to CRC proliferation via modulation of p21-mediated cell cycle progression but also suggest the potential value of KIF4A as a clinical prognostic marker and target for molecular treatments.

Recent advances in understanding oogenesis: interactions with the cytoskeleton, microtubule organization, and meiotic spindle assembly in oocytes

Maternal control of development begins with production of the oocyte during oogenesis. All of the factors necessary to complete oocyte maturation, meiosis, fertilization, and early development are produced in the transcriptionally active early oocyte. Active transcription of the maternal genome is a mechanism to ensure that the oocyte and development of the early embryo begin with all of the factors needed for successful embryonic development. To achieve the maximum maternal store, only one functional cell is produced from the meiotic divisions that produce the oocyte. The oocyte receives the bulk of the maternal cytoplasm and thus is significantly larger than its sister cells, the tiny polar bodies, which receive a copy of the maternal genome but essentially none of the maternal cytoplasm. This asymmetric division is accomplished by an enormous cell that is depleted of centrosomes in early oogenesis; thus, meiotic divisions in oocytes are distinct from those of mitotic cells. Therefore, these cells must partition the chromosomes faithfully to ensure euploidy by using mechanisms that do not rely on a conventional centrosome-based mitotic spindle. Several mechanisms that contribute to assembly and maintenance of the meiotic spindle in oocytes have been identified; however, none is fully understood. In recent years, there have been many exciting and significant advances in oogenesis, contributed by studies using a myriad of systems. Regrettably, I cannot adequately cover all of the important advances here and so I apologize to those whose beautiful work has not been included. This review focuses on a few of the most recent studies, conducted by several groups, using invertebrate and vertebrate systems, that have provided mechanistic insight into how microtubule assembly and meiotic spindle morphogenesis are controlled in the absence of centrosomes.

Increased KIF4A expression is a potential prognostic factor in prostate cancer

The kinesin super-family protein (KIF) 4A gene is reported to be overexpressed and associated with poor clinical prognosis in human cancers; however, its clinical significance in prostate cancer (PCa) has not been well studied. The present study performed dataset analyses and revealed that KIF4A expression was significantly increased in castration-resistant PCa patients. Additionally, KIF4A expression was significantly highly expressed in PCa tissues compared with non-cancerous tissues, particularly in advanced PCa pathological stages. Upregulated KIF4A mRNA expression in PCa tissues was significantly correlated with shorter overall survival and prostate-specific antigen failure. Furthermore, both univariate and multivariate analyses revealed that upregulated KIF4A may predict poor biochemical recurrence (BCR)-free survival. The data suggested that KIF4A may play a key role in PCa progression. Notably, increased KIF4A expression may potentially predict poor BCR-free survival in PCa patients.

Aberrantly activated Gli2-KIF20A axis is crucial for growth of hepatocellular carcinoma and predicts poor prognosis

Glioma-associated oncogene 2 (Gli2), a primary transcriptional regulator of Hedgehog (Hh) signaling, is essential for hepatocellular carcinoma (HCC) growth and survival. However, the underlying molecular mechanism and crucial downstream targets of Gli2 in human HCC are not fully understood. Here, we report the identification of kinesin family member 20A (KIF20A) as a novel downstream target of Gli2, which is important for HCC proliferation and tumor growth. Inhibition of Hh signaling leads to a remarkable decrease of KIF20A expression in HCC cells, whereas overexpression of Gli2 elevates KIF20A expression by activating Forkhead Box M1 (FoxM1)-MMB complex-mediated transcription of this kinesin gene. Gli2-induced HCC cell growth requires enhanced expression of KIF20A, and knockdown of Gli2 or KIF20A represses the proliferation of HCC cells in vitro and in vivo. Correlated with these results, analyses of clinical HCC samples show that Gli2, FoxM1 and KIF20A are highly elevated in primary HCC samples and represent significant risk factors for HCC recurrence and survival. Conclusion: KIF20A is an important downstream target gene of Hh signaling. And, the Gli2-KIF20A axis is essential for the proliferation and growth of human HCC cells. Our study also suggests Gli2-KIF20A axis as a potential target for future therapeutic intervention and as an independent prognostic biomarker for HCC.

Culture degeneration in conidia of Beauveria bassiana and virulence determinants by proteomics

The quality of Beauveria bassiana conidia directly affects the virulence against insects. In this study, continuous subculturing of B. bassiana on both rice grains and potato dextrose agar (PDA) resulted in 55 and 49 % conidial yield reduction after 12 passages and 68 and 60 % virulence reduction after 20 and 12 passages at four d post-inoculation, respectively. The passage through Tenebrio molitor and Spodoptera exigua restored the virulence of rice and PDA subcultures, respectively. To explore the molecular mechanisms underlying the conidial quality and the decline of virulence after multiple subculturing, we investigated the conidial proteomic changes. Successive subculturing markedly increased the protein levels in oxidative stress response, autophagy, amino acid homeostasis, and apoptosis, but decreased the protein levels in DNA repair, ribosome biogenesis, energy metabolism, and virulence. The nitro blue tetrazolium assay verified that the late subculture's colony and conidia had a higher oxidative stress level than the early subculture. A 2A-type protein phosphatase and a Pleckstrin homology domain protein Slm1, effector proteins of the target of rapamycin (TOR) complex 1 and 2, respectively, were dramatically increased in the late subculture. These results suggest that TOR signalling might be associated with ageing in B. bassiana late subculture, in turn affecting its physiological characteristics and virulence.

Immune microenvironment of experimental rat C6 gliomas resembles human glioblastomas

Glioblastoma (GBM) is the most aggressive primary brain tumor, with ineffective anti-tumor responses and a poor prognosis despite aggressive treatments. GBM immune microenvironment is heterogenous  and activation of specific immune populations in GBM is not fully characterized. Reliable animal models are critical for defining mechanisms of anti-tumor immunity. First we analyzed the immune subpopulations present in rat C6 gliomas. Using flow cytometry we determined kinetics of infiltration of myeloid cells and T lymphocytes into glioma-bearing brains. We found significant increases of the amoeboid, pro-tumorigenic microglia/macrophages, T helper (Th) and T regulatory (Treg) cells in tumor-bearing brains, and rare infiltrating T cytotoxic (Tc) cells. Transcriptomic analyses of glioma-bearing hemispheres revealed overexpression of invasion and immunosuppression-related genes, reflecting the immunosuppressive microenvironment. Microglia, sorted as CD11b⁺CD45^low cells from gliomas, displayed the pro-invasive and immunosuppressive type of activation. Accumulation of Th and Treg cells combined with the reduced presence of Tc lymphocytes in rat gliomas may result in the lack of effective anti–tumor responses. Transcriptional profiles of CD11b⁺ cells and composition of immune infiltrates in C6 gliomas indicate that rat C6 gliomas employ similar immune system evasion strategies as human GBMs.

Motoring through: the role of kinesin superfamily proteins in female meiosis

BACKGROUND

The kinesin motor protein family consists of 14 distinct subclasses and 45 kinesin proteins in humans. A large number of these proteins, or their orthologues, have been shown to possess essential function(s) in both the mitotic and the meiotic cell cycle. Kinesins have important roles in chromosome separation, microtubule dynamics, spindle formation, cytokinesis and cell cycle progression. This article contains a review of the literature with respect to the role of kinesin motor proteins in female meiosis in model species. Throughout, we discuss the function of each class of kinesin proteins during oocyte meiosis, and where such data are not available their role in mitosis is considered. Finally, the review highlights the potential clinical importance of this family of proteins for human oocyte quality.

OBJECTIVE AND RATIONALE

To examine the role of kinesin motor proteins in oocyte meiosis.

SEARCH METHODS

A search was performed on the Pubmed database for journal articles published between January 1970 and February 2017. Search terms included 'oocyte kinesin' and 'meiosis kinesin' in addition to individual kinesin names with the terms oocyte or meiosis.

OUTCOMES

Within human cells 45 kinesin motor proteins have been discovered, with the role of only 13 of these proteins, or their orthologues, investigated in female meiosis. Furthermore, of these kinesins only half have been examined in mammalian oocytes, despite alterations occurring in gene transcripts or protein expression with maternal ageing, cryopreservation or behavioral conditions, such as binge drinking, for many of them.

WIDER IMPLICATIONS

Kinesin motor proteins have distinct and important roles throughout oocyte meiosis in many non-mammalian model species. However, the functions these proteins have in mammalian meiosis, particularly in humans, are less clear owing to lack of research. This review brings to light the need for more experimental investigation of kinesin motor proteins, particularly those associated with maternal ageing, cryopreservation or exposure to environmental toxicants.

Structural basis of human kinesin-8 function and inhibition

Kinesins are a superfamily of ATP-dependent motors important for many microtubule-based functions, including multiple roles in mitosis. Small-molecule inhibitors of mitotic kinesins disrupt cell division and are being developed as antimitotic therapies. We investigated the molecular mechanism of the multitasking human mitotic kinesin Kif18A and its inhibition by the small molecule BTB-1. We used cryo-electron microscopy to visualize nucleotide-dependent conformational changes in microtubule-bound Kif18A, and the conformation of microtubule-bound, BTB-1-bound Kif18A. We calculated a putative BTB-1–binding site and validated this site experimentally to reveal the BTB-1 inhibition mechanism. Our work points to a general mechanism of kinesin inhibition, with wide implications for a targeted blockade of these motors in both dividing and interphase cells.

Kinesin motors play diverse roles in mitosis and are targets for antimitotic drugs. The clinical significance of these motors emphasizes the importance of understanding the molecular basis of their function. Equally important, investigations into the modes of inhibition of these motors provide crucial information about their molecular mechanisms. Kif18A regulates spindle microtubules through its dual functionality, with microtubule-based stepping and regulation of microtubule dynamics. We investigated the mechanism of Kif18A and its inhibition by the small molecule BTB-1. The Kif18A motor domain drives ATP-dependent plus-end microtubule gliding, and undergoes conformational changes consistent with canonical mechanisms of plus-end–directed motility. The Kif18A motor domain also depolymerizes microtubule plus and minus ends. BTB-1 inhibits both of these microtubule-based Kif18A activities. A reconstruction of BTB-1–bound, microtubule-bound Kif18A, in combination with computational modeling, identified an allosteric BTB-1–binding site near loop5, where it blocks the ATP-dependent conformational changes that we characterized. Strikingly, BTB-1 binding is close to that of well-characterized Kif11 inhibitors that block tight microtubule binding, whereas BTB-1 traps Kif18A on the microtubule. Our work highlights a general mechanism of kinesin inhibition in which small-molecule binding near loop5 prevents a range of conformational changes, blocking motor function.

Kinesin superfamily: roles in breast cancer, patient prognosis and therapeutics

Breast cancer pathobiology is known to be influenced by the differential expression of a group of proteins called the kinesin superfamily (KIFs), which is instrumental in the intracellular transport of chromosomes along microtubules during mitosis. During cellular division, kinesins are strictly regulated through temporal synthesis so that they are present only when needed. However, their misregulation may contribute to uncontrolled cell growth owing to premature sister chromatid separation, highlighting their importance in cancer. This review covers the functions of kinesins in normal and breast cancer cells, the use of kinesins for breast cancer patient prognosis, and the targeting of these molecules for therapeutics. A better understanding of KIF proteins may be pivotal to improved disease outcomes for breast cancer patients.

Molecular mechanisms of kinesin-14 motors in spindle assembly and chromosome segregation

During eukaryote cell division, molecular motors are crucial regulators of microtubule organization, spindle assembly, chromosome segregation and intracellular transport. The kinesin-14 motors are evolutionarily conserved minus-end-directed kinesin motors that occur in diverse organisms from simple yeasts to higher eukaryotes. Members of the kinesin-14 motor family can bind to, crosslink or slide microtubules and, thus, regulate microtubule organization and spindle assembly. In this Commentary, we present the common subthemes that have emerged from studies of the molecular kinetics and mechanics of kinesin-14 motors, particularly with regard to their non-processive movement, their ability to crosslink microtubules and interact with the minus- and plus-ends of microtubules, and with microtubule-organizing center proteins. In particular, counteracting forces between minus-end-directed kinesin-14 and plus-end-directed kinesin-5 motors have recently been implicated in the regulation of microtubule nucleation. We also discuss recent progress in our current understanding of the multiple and fundamental functions that kinesin-14 motors family members have in important aspects of cell division, including the spindle pole, spindle organization and chromosome segregation.

The mitotic kinesin-14 KlpA contains a context-dependent directionality switch

Kinesin-14s are commonly known as nonprocessive minus end-directed microtubule motors that function mainly for mitotic spindle assembly. Here we show using total internal reflection fluorescence microscopy that KlpA—a kinesin-14 from Aspergillus nidulans—is a context-dependent bidirectional motor. KlpA exhibits plus end-directed processive motility on single microtubules, but reverts to canonical minus end-directed motility when anchored on the surface in microtubule-gliding experiments or interacting with a pair of microtubules in microtubule-sliding experiments. Plus end-directed processive motility of KlpA on single microtubules depends on its N-terminal nonmotor microtubule-binding tail, as KlpA without the tail is nonprocessive and minus end-directed. We suggest that the tail is a de facto directionality switch for KlpA motility: when the tail binds to the same microtubule as the motor domain, KlpA is a plus end-directed processive motor; in contrast, when the tail detaches from the microtubule to which the motor domain binds, KlpA becomes minus end-directed.

Kinesin-14s are commonly considered to be minus end-directed microtubule motor proteins. Here the authors show that KlpA, a fungal kinesin-14 orthologue, relies on its N-terminal nonmotor microtubule-binding tail to achieve context-dependent bidirectional motility.

Recent findings and future directions for interpolar mitotic kinesin inhibitors in cancer therapy

The kinesin class of microtubule-associated motor proteins present attractive anti-cancer targets owing to their roles in key functions in dividing cells. Two interpolar mitotic kinesins Eg5 and HSET have opposing motor functions in mitotic spindle assembly with respect to microtubule movement, but both offer opportunities to develop cancer selective therapeutic agents. Here, we summarize the progress to date in developing inhibitors of Eg5 and HSET, with an emphasis on structural biology insights into the binding modes of allosteric inhibitors, compound selectivity and mechanisms of action of different chemical scaffolds. We discuss translation of preclinical studies to clinical experience with Eg5 inhibitors, recent findings on potential resistance mechanisms, and explore the implications for future anticancer drug development against these targets.

Erythroblast enucleation is a dynein-dependent process

Mammalian erythroblasts undergo enucleation through a process thought to be similar to cytokinesis. Microtubule-organizing centers (MTOCs) mediate organization of the mitotic spindle apparatus that separates the chromosomes during mitosis and are known to be crucial for proper cytokinesis. However, the role of MTOCs in erythroblast enucleation remains unknown. We therefore investigated the effect of various MTOC inhibitors on cytokinesis and enucleation using human colony-forming units-erythroid (CFU-Es) and mature erythroblasts generated from purified CD34(+) cells. We found that erythro-9-[3-(2-hydroxynonyl)]adenine (EHNA), a dynein inhibitor, and monastrol, a kinesin Eg5 inhibitor, as well as various inhibitors of MTOC regulators, including ON-01910 (Plk-1), MLN8237 (aurora A), hesperadin (aurora B), and LY294002 (PI3K), all inhibited CFU-E cytokinesis. Among these inhibitors, however, only EHNA blocked enucleation. Moreover, terminally differentiated erythroblasts expressed only dynein; little or none of the other tested proteins was detected. Over the course of the terminal differentiation of human erythroblasts, the fraction of cells with nuclei at the cell center declined, whereas the fraction of polarized cells, with nuclei shifted to a position near the plasma membrane, increased. Dynein inhibition impaired nuclear polarization, thereby blocking enucleation. These data indicate that dynein plays an essential role not only in cytokinesis but also in enucleation. We therefore conclude that human erythroblast enucleation is a process largely independent of MTOCs, but dependent on dynein.

Active contraction of microtubule networks

Many cellular processes are driven by cytoskeletal assemblies. It remains unclear how cytoskeletal filaments and motor proteins organize into cellular scale structures and how molecular properties of cytoskeletal components affect the large-scale behaviors of these systems. Here, we investigate the self-organization of stabilized microtubules in Xenopus oocyte extracts and find that they can form macroscopic networks that spontaneously contract. We propose that these contractions are driven by the clustering of microtubule minus ends by dynein. Based on this idea, we construct an active fluid theory of network contractions, which predicts a dependence of the timescale of contraction on initial network geometry, a development of density inhomogeneities during contraction, a constant final network density, and a strong influence of dynein inhibition on the rate of contraction, all in quantitative agreement with experiments. These results demonstrate that the motor-driven clustering of filament ends is a generic mechanism leading to contraction.

Bmk-1 regulates lifespan in Caenorhabditis elegans by activating hsp-16

The genetics of aging is typically concerned with lifespan determination that is associated with alterations in expression levels or mutations of particular genes. Previous reports in C. elegans have shown that the bmk-1 gene has important functions in chromosome segregation, and this has been confirmed with its mammalian homolog, KIF11. However, this gene has never been implicated in aging or lifespan regulation. Here we show that the bmk-1 gene is an important lifespan regulator in worms. We show that reducing bmk-1 expression using RNAi shortens worm lifespan by 32%, while over-expression of bmk-1 extends worm lifespan by 25%, and enhances heat-shock stress resistance. Moreover, bmk-1 over-expression increases the level of hsp-16 and decreases ced-3 in C. elegans. Genetic epistasis analysis reveals that hsp-16 is essential for the lifespan extension by bmk-1. These findings suggest that bmk-1 may act through enhanced hsp-16 function to protect cells from stress and inhibit the apoptosis pathway, thereby conferring worm longevity. Though it remains unclear whether this is a distinct function from chromosomal segregation, bmk-1 is a potential new target for extension of lifespan and enhancement of healthspan.

Loss of kinesin-14 results in aneuploidy via kinesin-5-dependent microtubule protrusions leading to chromosome cut

Aneuploidy – chromosome instability leading to incorrect chromosome number in dividing cells – can arise from defects in centrosome duplication, bipolar spindle formation, kinetochore-microtubule attachment, chromatid cohesion, mitotic checkpoint monitoring, or cytokinesis. As most tumors show some degree of aneuploidy, mechanistic understanding of these pathways has been an intense area of research to provide potential therapeutics. Here, we present a mechanism for aneuploidy in fission yeast based on spindle pole microtubule defocusing by loss of kinesin-14 Pkl1, leading to kinesin-5 Cut7-dependent aberrant long spindle microtubule minus end protrusions that push the properly segregated chromosomes to the site of cell division, resulting in chromosome cut at cytokinesis. Pkl1 localization and function at the spindle pole is mutually dependent on spindle pole-associated protein Msd1. This mechanism of aneuploidy bypasses the known spindle assembly checkpoint that monitors chromosome segregation.

Metabolic control of oocyte development: linking maternal nutrition and reproductive outcomes

Obesity, diabetes, and related metabolic disorders are major health issues worldwide. As the epidemic of metabolic disorders continues, the associated medical co-morbidities, including the detrimental impact on reproduction, increase as well. Emerging evidence suggests that the effects of maternal nutrition on reproductive outcomes are likely to be mediated, at least in part, by oocyte metabolism. Well-balanced and timed energy metabolism is critical for optimal development of oocytes. To date, much of our understanding of oocyte metabolism comes from the effects of extrinsic nutrients on oocyte maturation. In contrast, intrinsic regulation of oocyte development by metabolic enzymes, intracellular mediators, and transport systems is less characterized. Specifically, decreased acid transport proteins levels, increased glucose/lipid content and elevated reactive oxygen species in oocytes have been implicated in meiotic defects, organelle dysfunction and epigenetic alteration. Therefore, metabolic disturbances in oocytes may contribute to the diminished reproductive potential experienced by women with metabolic disorders. In-depth research is needed to further explore the underlying mechanisms. This review also discusses several approaches for metabolic analysis. Metabolomic profiling of oocytes, the surrounding granulosa cells, and follicular fluid will uncover the metabolic networks regulating oocyte development, potentially leading to the identification of oocyte quality markers and prevention of reproductive disease and poor outcomes in offspring.

Noncanonical SMC protein in Mycobacterium smegmatis restricts maintenance of Mycobacterium fortuitum plasmids

Research on tuberculosis and leprosy was revolutionized by the development of a plasmid transformation system in the fast-growing surrogate, Mycobacterium smegmatis. This transformation system was made possible by the successful isolation of a M. smegmatis mutant strain mc(2)155, whose efficient plasmid transformation (ept) phenotype supported the replication of Mycobacterium fortuitum pAL5000 plasmids. In this report, we identified the EptC gene, the loss of which confers the ept phenotype. EptC shares significant amino acid sequence homology and domain structure with the MukB protein of Escherichia coli, a structural maintenance of chromosomes (SMC) protein. Surprisingly, M. smegmatis has three paralogs of SMC proteins: EptC and MSMEG_0370 both share homology with Gram-negative bacterial MukB; and MSMEG_2423 shares homology with Gram-positive bacterial SMCs, including the single SMC protein predicted for Mycobacterium tuberculosis and Mycobacterium leprae. Purified EptC was shown to bind ssDNA and stabilize negative supercoils in plasmid DNA. Moreover, an EptC-mCherry fusion protein was constructed and shown to bind to DNA in live mycobacteria, and to prevent segregation of plasmid DNA to daughter cells. To our knowledge, this is the first report of impaired plasmid maintenance caused by a SMC homolog, which has been canonically known to assist the segregation of genetic materials.

The crystal structure and biochemical characterization of Kif15: a bifunctional molecular motor involved in bipolar spindle formation and neuronal development

Kinesins constitute a superfamily of microtubule-based motor proteins with important cellular functions ranging from intracellular transport to cell division. Some kinesin family members function during the mitotic phase of the eukaryotic cell cycle and are crucial for the successful progression of cell division. In the early stages of mitosis, during prometaphase, certain kinesins are required for the formation of the bipolar spindle, such as Eg5 and Kif15, which seem to possess partially overlapping functions. Because kinesins transform the chemical energy from ATP hydrolysis into mechanical work, inhibition of their function is a tractable approach for drug development. Drugs targeting Eg5 have shown promise as anticancer agents. Kif15 has recently come to the fore because it can substitute the functions of Eg5, and may itself have potential as a prospective drug target. Here, the initial biochemical, kinetic and structural characterization of Kif15 is reported and it is compared with the functionally related motor Eg5. Although Kif15 contains ADP in the catalytic site, its motor-domain structure was captured in the `ATP-like' configuration, with the neck linker docked to the catalytic core. The interaction of Kif15 with microtubules was also investigated and structural differences between these two motors were elucidated which indicate profound differences in their mode of action, in agreement with current models of microtubule cross-linking and sliding.

Kinesin family member 4A: a potential predictor for progression of human oral cancer

BACKGROUND

Kinesin family member 4A (KIF4A), a microtubule-based motor protein, was implicated in regulation of chromosomal structure and kinetochore microtubule dynamics. Considering the functions of KIF4A, we assumed that KIF4A is involved in progression of oral squamous cell carcinomas (OSCCs) via activation of the spindle assembly checkpoint (SAC). However, little is known about the relevance of KIF4A in the behavior of OSCC. We investigated the KIF4A expression status and its functional mechanisms in OSCC.

METHODS

The KIF4A expression levels in seven OSCC-derived cells were analyzed by quantitative reverse transcriptase-polymerase chain reaction and immunoblotting analyses. Using a KIF4A knockdown model, we assessed the expression of (SAC)-related molecules (BUB1, MAD2, CDC20, and cyclin B1), cell-cycle, and cellular proliferation. In addition to in vitro data, the clinical correlation between the KIF4A expression levels in primary OSCCs (n = 106 patients) and the clinicopathologic status by immunohistochemistry (IHC) also were evaluated.

RESULTS

KIF4A mRNA and protein were up-regulated significantly (P < 0.05) in seven OSCC-derived cells compared with human normal oral keratinocytes. In the KIF4A knockdown cells, SAC activation was observed via increased BUB1 expression on the kinetochores, appropriate kinetochore localization of MAD2, down-regulation of CDC20, up-regulation of cyclin B1, and cell-cycle arrested at G2/M phase. The results showed that cellular proliferation of KIF4A knockdown cells decreased significantly (P < 0.05) compared with control cells. IHC showed that KIF4A expression in primary OSCCs was significantly (P < 0.05) greater than in the normal oral counterparts and that KIF4A-positive OSCCs were correlated closely (P < 0.05) with tumoral size.

CONCLUSIONS

Our results proposed for the first time that KIF4A controls cellular proliferation via SAC activation. Therefore, KIF4A might be a key regulator for tumoral progression in OSCCs.

Cell cycle regulation of microtubule interactomes: multi-layered regulation is critical for the interphase/mitosis transition

Microtubules dramatically change their dynamics and organization at the entry into mitosis. Although this change is mediated by microtubule-associated proteins (MAPs), how MAPs themselves are regulated is not well understood. Here we used an integrated multi-level approach to establish the framework and biological significance of MAP regulation critical for the interphase/mitosis transition. Firstly, we applied quantitative proteomics to determine global cell cycle changes in the profiles of MAPs in human and Drosophila cells. This uncovered a wide range of cell cycle regulations of MAPs previously unidentified. Secondly, systematic studies of human kinesins highlighted an overlooked aspect of kinesins: most mitotic kinesins suppress their affinity to microtubules or reduce their protein levels in interphase in combination with nuclear localization. Thirdly, in-depth analysis of a novel Drosophila MAP (Mink) revealed that the suppression of the microtubule affinity of this mitotic MAP in combination with nuclear localization is essential for microtubule organization in interphase, and phosphorylation of Mink is needed for kinetochore-microtubule attachment in mitosis. Thus, this first comprehensive analysis of MAP regulation for the interphase/mitosis transition advances our understanding of kinesin biology and reveals the prevalence and importance of multi-layered MAP regulation.

The cooperative roles of two kinetoplastid-specific kinesins in cytokinesis and in maintaining cell morphology in bloodstream trypanosomes

The cytoskeleton of Trypanosoma brucei, a unicellular eukaryote and a parasitic protozoan, is defined by the subpellicular microtubule corset that is arranged underneath the plasma membrane. We recently identified two orphan kinesins, TbKIN-C and TbKIN-D, that cooperate to regulate the organization of the subpellicular microtubule corset and thereby maintain cell morphology in the procyclic form of T. brucei. In this report, we characterize the function of TbKIN-C and TbKIN-D in the bloodstream form of T. brucei and investigate their functional cooperation in both the bloodstream and procyclic forms. TbKIN-C and TbKIN-D form a tight complex in vivo in the bloodstream form. TbKIN-C is strongly enriched at the posterior tip of the cell, whereas TbKIN-D is distributed throughout the cell body at all cell cycle stages. RNAi of TbKIN-C or TbKIN-D in the bloodstream form inhibits cell proliferation and leads to cell death, due to cytokinesis defects. RNAi of TbKIN-C and TbKIN-D also results in defects in basal body segregation, but does not affect the synthesis and segregation of the flagellum and the flagellum attachment zone (FAZ) filament. Knockdown of TbKIN-C and TbKIN-D does not disrupt the organization of the subpellicular microtubule corset, but produces multinucleated cells with an enlarged flagellar pocket and misplaced flagella. Interestingly, depletion of TbKIN-C results in rapid degradation of TbKIN-D and, similarly, knockdown of TbKIN-C destabilizes TbKIN-D, suggesting that formation of TbKIN-C/TbKIN-D complex stabilizes both kinesins and is required for the two kinesins to execute their essential cellular functions. Altogether, our results demonstrate the essential role of the two kinesins in cell morphogenesis and cytokinesis in the bloodstream form and the requirement of heteromeric complex formation for maintaining the stability of the two kinesins.

Mitochondria localize to the cleavage furrow in mammalian cytokinesis

Mitochondria are dynamic organelles with multiple cellular functions, including ATP production, calcium buffering, and lipid biosynthesis. Several studies have shown that mitochondrial positioning is regulated by the cytoskeleton during cell division in several eukaryotic systems. However, the distribution of mitochondria during mammalian cytokinesis and whether the distribution is regulated by the cytoskeleton has not been examined. Using live spinning disk confocal microscopy and quantitative analysis of mitochondrial fluorescence intensity, we demonstrate that mitochondria are recruited to the cleavage furrow during cytokinesis in HeLa cells. After anaphase onset, the mitochondria are recruited towards the site of cleavage furrow formation, where they remain enriched as the furrow ingresses and until cytokinesis completion. Furthermore, we show that recruitment of mitochondria to the furrow occurs in multiple mammalian cells lines as well as in monopolar, bipolar, and multipolar divisions, suggesting that the mechanism of recruitment is conserved and robust. Using inhibitors of cytoskeleton dynamics, we show that the microtubule cytoskeleton, but not actin, is required to transport mitochondria to the cleavage furrow. Thus, mitochondria are specifically recruited to the cleavage furrow in a microtubule-dependent manner during mammalian cytokinesis. Two possible reasons for this could be to localize mitochondrial function to the furrow to facilitate cytokinesis and / or ensure accurate mitochondrial inheritance.

Kinesin spindle protein (KSP) inhibitors in combination with chemotherapeutic agents for cancer therapy

A diverse group of proteins, the activities of which are precisely orchestrated during mitosis, have emerged as targets for cancer therapeutics; these include the Aurora kinases (AKs), Polo-like kinases (PLKs), and the kinesin spindle protein (KSP). KSP is essential for the proper separation of spindle poles during mitosis. Agents that target KSP selectively act on cells undergoing cell division, which means that KSP inhibitors are mitosis-specific drugs, and have demonstrated remarkable activities in vitro. However, a significant obstacle to the success of KSP inhibitors is that these compounds, with tremendous efficacy in vitro, have demonstrated little or even no antitumor activity in vivo. Accumulated data suggest that a combination of KSP inhibitors with various cytostatic drugs will result in a more powerful tumor-killing effect than monotherapy. Combination therapies might predominate and represent the next frontier in the discovery research of KSP inhibitors as potential anticancer drugs. Few published studies have reviewed combination therapy using KSP inhibitors. Herein we provide a comprehensive review of the literature on KSP inhibitor monotherapy and therapeutic combinations. The current state and problems are also discussed.

Structure of a kinesin-tubulin complex and implications for kinesin motility

The typical function of kinesins is to transport cargo along microtubules. Binding of ATP to microtubule-attached motile kinesins leads to cargo displacement. To better understand the nature of the conformational changes that lead to the power stroke that moves a kinesin's load along a microtubule, we determined the X-ray structure of human kinesin-1 bound to αβ-tubulin. The structure defines the mechanism of microtubule-stimulated ATP hydrolysis, which releases the kinesin motor domain from microtubules. It also reveals the structural linkages that connect the ATP nucleotide to the kinesin neck linker, a 15-amino acid segment C terminal to the catalytic core of the motor domain, to result in the power stroke. ATP binding to the microtubule-bound kinesin favors neck-linker docking. This biases the attachment of kinesin's second head in the direction of the movement, thus initiating each of the steps taken.

Targeted deletion of Kif18a protects from colitis-associated colorectal (CAC) tumors in mice through impairing Akt phosphorylation

Kinesins are a superfamily of molecular motors involved in cell division or intracellular transport. They are becoming important targets for chemotherapeutic intervention of cancer due to their crucial role in mitosis. Here, we demonstrate that the kinesin-8 Kif18a is overexpressed in murine CAC and is a crucial promoter during early CAC carcinogenesis. Kif18a-deficient mice are evidently protected from AOM-DSS-induced colon carcinogenesis. Kif18A is responsible for proliferation of colonic tumor cells, while Kif18a ablation in mice promotes cell apoptosis. Mechanistically, Kif18a is responsible for induction of Akt phosphorylation, which is known to be associated with cell survival regulation. In conclusion, Kif18a is critical for colorectal carcinogenesis in the setting of inflammation by mechanisms of increased PI3K-AKT signaling. Inhibition of Kif18A activity may be useful in the prevention or chemotherapeutic intervention of CAC.

Oncogenic role of kinesin proteins and targeting kinesin therapy

The kinesin superfamily (KIF) is a group of proteins that share a highly conserved motor domain. Except for some members, many KIF proteins have adenosine triphosphatase activity and microtubule-dependent plus-end motion ability. Kinesins participate in several essential cellular functions, including mitosis, meiosis and the transport of macromolecules. Increasing evidence indicates kinesin proteins play critical roles in the genesis and development of human cancers. Some kinesin proteins are associated with maligancy as well as drug resistance of solid tumor. Thus, targeting KIF therapy seems to be a promising anticancer strategy. Inhibitors of KIF such as kinesin spindle protein (KSP/Eg5) have entered clinical trials for monotherapy or in combination with other drugs, and kinesins other than Eg5 with various potential anticancer target characteristics are also constantly being discovered and studied. Here, we summarize the oncogenic roles of kinesin proteins and potential cancer therapy strategies that target KIF.