M phase phosphoprotein 1 is a human plus-end-directed kinesin-related protein required for cytokinesis

Anti-KIF20B autoantibodies are associated with cranial neuropathy in systemic lupus erythematosus

BACKGROUND

Cranial neuropathies (CN) are a rare neuropsychiatric SLE (NPSLE) manifestation. Previous studies reported that antibodies to the kinesin family member 20B (KIF20B) (anti-KIF20B) protein were associated with idiopathic ataxia and CN. We assessed anti-KIF20B as a potential biomarker for NPSLE in an international SLE inception cohort.

METHODS

Individuals fulfilling the revised 1997 American College of Rheumatology (ACR) SLE classification criteria were enrolled from 31 centres from 1999 to 2011 and followed annually in the Systemic Lupus Erythematosus International Collaborating Clinics inception cohort. Anti-KIF20B testing was performed on baseline (within 15 months of diagnosis or first annual visit) samples using an addressable laser bead immunoassay. Logistic regression (penalised maximum likelihood and adjusting for confounding variables) examined the association between anti-KIF20B and NPSLE manifestations (1999 ACR case definitions), including CN, occurring over the first 5 years of follow-up.

RESULTS

Of the 1827 enrolled cohort members, baseline serum and 5 years of follow-up data were available on 795 patients who were included in this study: 29.8% were anti-KIF20B-positive, 88.7% female, and 52.1% White. The frequency of anti-KIF20B positivity differed only for those with CN (n=10) versus without CN (n=785) (70.0% vs 29.3%; OR 5.2, 95% CI 1.4, 18.5). Compared with patients without CN, patients with CN were more likely to fulfil the ACR haematological (90.0% vs 66.1%; difference 23.9%, 95% CI 5.0%, 42.8%) and ANA (100% vs 95.7%; difference 4.3%, 95% CI 2.9%, 5.8%) criteria. In the multivariate analysis adjusting for age at baseline, female, White race and ethnicity, and ACR haematological and ANA criteria, anti-KIF20B positivity remained associated with CN (OR 5.2, 95% CI 1.4, 19.1).

CONCLUSION

Anti-KIF20B is a potential biomarker for SLE-related CN. Further studies are needed to examine how autoantibodies against KIF20B, which is variably expressed in a variety of neurological cells, contribute to disease pathogenesis.

Anti-KIF20B autoantibodies in systemic autoimmune rheumatic diseases: Their high prevalence in systemic lupus erythematosus

The kinesin superfamily protein 20B (KIF20B), also known as M-phase phosphoprotein-1, is a plus-end-directed motor enzyme for cytokinesis. Anti-KIF20B antibodies have been reported in idiopathic ataxia, but no previous studies have examined anti-KIF20B antibodies in systemic autoimmune rheumatic diseases (SARDs). We aimed to establish methods for detecting anti-KIF20B antibodies and to investigate the clinical significance of these antibodies in SARDs. Serum samples from 597 patients with various SARDs and 46 healthy controls (HCs) were included. Fifty-nine samples that had been examined by immunoprecipitation using the recombinant KIF20B protein produced by in vitro transcription/translation were used for establishing the ELISA cutoff with the same recombinant protein for measuring the anti-KIF20B antibodies. The ELISA performed well, showing close agreement with the immunoprecipitation results (Cohen's κ >0.8). The ELISA results for 643 samples showed the prevalence of anti-KIF20B to be higher in the systemic lupus erythematosus (SLE) patients than in the HCs (18/89 vs. 3/46, P = 0.045). Since no SARD other than SLE had higher frequencies of anti-KIF20B antibodies than those of the HCs, we investigated the clinical characteristics of anti-KIF20B antibody-positive cases in SLE. The score on the SLE Disease Activity Index-2000 (SLEDAI-2K) was significantly higher for the anti-KIF20B-positive SLE patients than for the anti-KIF20B-negative SLE patients (P = 0.013). In a multivariate regression analysis of the anti-single-stranded deoxyribonucleic acid, anti-double-stranded deoxyribonucleic acid, and anti-KIF20B antibodies, the presence of anti-KIF20B antibody was significantly associated with high SLEDAI-2K scores (P = 0.003). Anti-KIF20B antibodies were found in ~20% of patients with SLE and were associated with high SLEDAI-2K scores. Much larger cohort and longitudinal studies are needed to confirm the association between anti-KIF20B antibodies and SLE.

Proteomic signature for detection of high-grade ovarian cancer in germline BRCA mutation carriers

No current screening methods for high-grade ovarian cancer (HGOC) guarantee effective early detection for high-risk women such as germline BRCA mutation carriers. Therefore, the standard-of-care remains risk-reducing salpingo-oophorectomy (RRSO) around age 40. Proximal liquid biopsy is a promising source of biomarkers, but sensitivity has not yet qualified for clinical implementation. We aimed to develop a proteomic assay based on proximal liquid biopsy, as a decision support tool for monitoring high-risk population. Ninety Israeli BRCA1 or BRCA2 mutation carriers were included in the training set (17 HGOC patients and 73 asymptomatic women), (BEDOCA trial; ClinicalTrials.gov Identifier: NCT03150121). The proteome of the microvesicle fraction of the samples was profiled by mass spectrometry and a classifier was developed using logistic regression. An independent cohort of 98 BRCA mutation carriers was used for validation. Safety information was collected for all women who opted for uterine lavage in a clinic setting. We present a 7-protein diagnostic signature, with AUC >0.97 and a negative predictive value (NPV) of 100% for detecting HGOC. The AUC of the biomarker in the independent validation set was >0.94 and the NPV >99%. The sampling procedure was clinically acceptable, with favorable pain scores and safety. We conclude that the acquisition of Müllerian tract proximal liquid biopsies in women at high-risk for HGOC and the application of the BRCA-specific diagnostic assay demonstrates high sensitivity, specificity, technical feasibility and safety. Similar classifier for an average-risk population is warranted.

Single-motor and multi-motor motility properties of kinesin-6 family members

Kinesin motor proteins are responsible for orchestrating a variety of microtubule-based processes including intracellular transport, cell division, cytoskeletal organization, and cilium function. Members of the kinesin-6 family play critical roles in anaphase and cytokinesis during cell division as well as in cargo transport and microtubule organization during interphase, however little is known about their motility properties. We find that truncated versions of MKLP1 (HsKIF23), MKLP2 (HsKIF20A), and HsKIF20B largely interact statically with microtubules as single molecules but can also undergo slow, processive motility, most prominently for MKLP2. In multi-motor assays, all kinesin-6 proteins were able to drive microtubule gliding and MKLP1 and KIF20B were also able to drive robust transport of both peroxisomes, a low-load cargo, and Golgi, a high-load cargo, in cells. In contrast, MKLP2 showed minimal transport of peroxisomes and was unable to drive Golgi dispersion. These results indicate that the three mammalian kinesin-6 motor proteins can undergo processive motility but differ in their ability to generate forces needed to drive cargo transport and microtubule organization in cells.

Distinct Roles of NANOS1 and NANOS3 in the Cell Cycle and NANOS3-PUM1-FOXM1 Axis to Control G2/M Phase in a Human Primordial Germ Cell Model

Nanos RNA-binding proteins are critical factors of germline development throughout the animal kingdom and their dysfunction causes infertility. During evolution, mammalian Nanos paralogues adopted divergent roles in germ cell biology. However, the molecular basis behind this divergence, such as their target mRNAs, remains poorly understood. Our RNA-sequencing analysis in a human primordial germ cell model-TCam-2 cell line revealed distinct pools of genes involved in the cell cycle process downregulated upon NANOS1 and NANOS3 overexpression. We show that NANOS1 and NANOS3 proteins influence different stages of the cell cycle. Namely, NANOS1 is involved in the G1/S and NANOS3 in the G2/M phase transition. Many of their cell cycle targets are known infertility and cancer-germ cell genes. Moreover, NANOS3 in complex with RNA-binding protein PUM1 causes 3′UTR-mediated repression of FOXM1 mRNA encoding a transcription factor crucial for G2/M phase transition. Interestingly, while NANOS3 and PUM1 act as post-transcriptional repressors of FOXM1, FOXM1 potentially acts as a transcriptional activator of NANOS3, PUM1, and itself. Finally, by utilizing publicly available RNA-sequencing datasets, we show that the balance between FOXM1-NANOS3 and FOXM1-PUM1 expression levels is disrupted in testis cancer, suggesting a potential role in this disease.

Curcumin induced the cell death of immortalized human keratinocytes (HaCaT) through caspase-independent and caspase-dependent pathways

Curcumin is a diketone compound found in turmeric. It is used as food additives and spices, and has anti-proliferation and anti-cancer properties. However, the effect of curcumin on human keratinocytes (KCs) is still unclear. In this study, curcumin dramatically inhibited the cell growth of immortalized human KCs (HaCaT) and arrested the cells at the G2/M phase, with an apoptosis rate of 33.95% after 24 μM curcumin treatment. HaCaT cells showed changes in typical apoptotic morphology and the configuration of nuclear matrix-intermediate filaments (NM-IFs) after treatment with curcumin. We identified 16 differentially expressed nuclear matrix (NM) proteins, including apoptosis inducing factor (AIF) and caspase 3, by 2-DE and MALDI-TOF/TOF mass spectrometry. The expression of AIF decreased in the mitochondria and increased in the nucleus. Immunofluorescence assays showed that AIF was released from the mitochondria to the nucleus. AIF silencing and caspase inhibitor (z-vad-fmk) both lead to HaCaT cells being insensitive to apoptosis induced by curcumin. Meanwhile, after curcumin treatment, mitochondrial membrane depolarization led to cytochrome c release from the mitochondria to the cytoplasm, and the ratio of Bax to Bcl-2 in HaCaT cells was also increased, which subsequently initiated the activation of caspase-3. These results suggest that curcumin-induced apoptosis of HaCaT cells occurs not only through the caspase-dependent pathway but also through the caspase-independent pathway. This discovery enhances the development and utilization of curcumin and provides possible evidence for the treatment of proliferative skin diseases, including skin cancer.

A Ran-binding protein facilitates nuclear import of human papillomavirus type 16

Human papillomaviruses (HPVs) utilize an atypical mode of nuclear import during cell entry. Residing in the Golgi apparatus until mitosis onset, a subviral complex composed of the minor capsid protein L2 and viral DNA (L2/vDNA) is imported into the nucleus after nuclear envelope breakdown by associating with mitotic chromatin. In this complex, L2 plays a crucial role in the interactions with cellular factors that enable delivery and ultimately tethering of the viral genome to mitotic chromatin. To date, the cellular proteins facilitating these steps remain unknown. Here, we addressed which cellular proteins may be required for this process. Using label-free mass spectrometry, biochemical assays, microscopy, and functional virological assays, we discovered that L2 engages a hitherto unknown protein complex of Ran-binding protein 10 (RanBP10), karyopherin alpha2 (KPNA2), and dynein light chain DYNLT3 to facilitate transport towards mitotic chromatin. Thus, our study not only identifies novel cellular interactors and mechanism that facilitate a poorly understood step in HPV entry, but also a novel cellular transport complex.

Human papillomaviruses (HPVs) cause proliferative lesions such as benign warts or malignant invasive cancers. Like other DNA viruses, HPV has to deliver its genome to the nucleus for viral genome transcription and replication. After initial attachment, HPVs are endocytosed to be eventually directed to the trans-Golgi-network (TGN) by intracellular trafficking, where they reside until cell division. Mitosis onset enables access of the virus to cellular chromatin after nuclear envelope breakdown. Tethering of the virus to mitotic chromatin ensures nuclear delivery upon reformation of the nuclear envelope after mitosis. Our previous work showed that the minor capsid protein L2 facilitates nuclear delivery. However, the detailed mechanism, namely, how HPV trafficks from cytosol to the nuclear space, is barely understood. Here, we identified for the first time cellular proteins that interacted with L2 for nuclear import. Mechanistically, the proteins formed a hitherto unknown cellular transport complex that interacted with L2 to direct the virus to mitotic chromosomes by microtubular transport. Our findings provided not only evidence for a transport mechanism of a poorly understood step of HPV entry, but also discovered a novel cellular transport complex.

Double Duty: Mitotic Kinesins and Their Post-Mitotic Functions in Neurons

Neurons, regarded as post-mitotic cells, are characterized by their extensive dendritic and axonal arborization. This unique architecture imposes challenges to how to supply materials required at distal neuronal components. Kinesins are molecular motor proteins that mediate the active delivery of cellular materials along the microtubule cytoskeleton for facilitating the local biochemical and structural changes at the synapse. Recent studies have made intriguing observations that some kinesins that function during neuronal mitosis also have a critical role in post-mitotic neurons. However, we know very little about the function and regulation of such kinesins. Here, we summarize the known cellular and biochemical functions of mitotic kinesins in post-mitotic neurons.

KIF20B Promotes Cell Proliferation and May Be a Potential Therapeutic Target in Pancreatic Cancer

KIFs have been reported to play a critical role in a variety of tumors, and KIF20B is a protein in KFIs. In this research, KIF20B was highly expressed in the GEO database and our hospital's data, and high expression of KIF20B suggested poor prognosis. We detect the expression of KIF20B in pancreatic cancer and adjacent normal tissues using immunohistochemistry. Knockdown of KIF20B in pancreatic cancer cell lines, PANC-1 and BxPC-3 cells, inhibited cell proliferation which are detected by colony formation assays, CCK8, and western bolt of Ki-67 and PCNA. Xenograft assay showed a similar result in vivo. KIF20B is a potential therapeutic target in pancreatic cancer.

Cytokinesis and postabscission midbody remnants are regulated during mammalian brain development

Building a brain of the proper size and structure requires neural stem cells (NSCs) to divide with tight temporal and spatial control to produce different daughter cell types in proper numbers and sequence. Mammalian NSCs in the embryonic cortex must maintain their polarized epithelial structure as they undergo both early proliferative divisions and later neurogenic divisions. To do this, they undergo a polarized form of cytokinesis at the apical membrane that is not well understood. Here, we investigate whether polarized furrowing and abscission in mouse NSCs are regulated differently at earlier and later stages and in a cytokinesis mutant, Kif20b This mutant was previously shown to have microcephaly and elevated apoptosis of NSCs. We developed methods to live image furrow ingression and midbody abscission in NSCs within cortical explants. We find that polarized furrow ingression occurs at a steady rate and completes in ∼15 min at two different ages. However, ingression is slower in a subset of Kif20b mutant NSCs. Abscission is usually observed on both sides of the midbody and takes 65 to 75 min to complete. Surprisingly, abscission is accelerated in the Kif20b mutant NSCs. Postabscission midbody remnants are observed at the apical membranes of daughter cells and are much more abundant in early-stage cortices. After NSC divisions in vitro, midbody remnants are more often retained on the daughter cells of early proliferative divisions. Altogether, these results suggest that regulation of abscission timing and midbody remnants in embryonic NSCs may influence proper brain growth and structure.

KIF20B promotes the progression of clear cell renal cell carcinoma by stimulating cell proliferation

Renal cell carcinoma (RCC) is a common urinary system cancer with high morbidity and mortality rate. Clear cell renal cell carcinoma (ccRCC) is a highly aggressive and common type of RCC. More and effective therapeutic targets are badly needed for the treatment of ccRCC. Kinesin family protein (KIF)20B, also named M-phase phosphoprotein 1, was reported as a microtubule-associated, plus-end-directed kinesin. KIF20B was involved in multiple cellular processes such as cytokinesis. Multiple studies indicated the oncogenic role for KIF20B in several types of tumors, including breast cancer and bladder cancer. However, the possible role of KIF20B in the progression of renal carcinoma is still unknown. Herein, our study demonstrated that KIF20B was relatively highly expressed in ccRCC tissues. In addition, KIF20B was inversely related to the clinical features including tumor size and T stage. We further found that inhibition of the KIF20B expression by a specific short hairpin RNA obviously reduces proliferation of ccRCC cells both in vitro and in vivo. Our study reveals the involvement of KIF20B in ccRCC progression. Generally, KIF20B is a promising novel therapeutic for the treatment of clear cell RCC.

p53 deletion rescues lethal microcephaly in a mouse model with neural stem cell abscission defects

Building a cerebral cortex of the proper size involves balancing rates and timing of neural stem cell (NSC) proliferation, neurogenesis and cell death. The cellular mechanisms connecting genetic mutations to brain malformation phenotypes are still poorly understood. Microcephaly may result when NSC divisions are too slow, produce neurons too early or undergo apoptosis but the relative contributions of these cellular mechanisms to various types of microcephaly are not understood. We previously showed that mouse mutants in Kif20b (formerly called Mphosph1, Mpp1 or KRMP1) have small cortices that show elevated apoptosis and defects in maturation of NSC midbodies, which mediate cytokinetic abscission. Here we test the contribution of intrinsic NSC apoptosis to brain size reduction in this lethal microcephaly model. By making double mutants with the pro-apoptotic genes Bax and Trp53 (p53), we find that p53-dependent apoptosis of cortical NSCs accounts for most of the microcephaly, but that there is a significant apoptosis-independent contribution as well. Remarkably, heterozygous p53 deletion is sufficient to fully rescue survival of the Kif20b mutant into adulthood. In addition, the NSC midbody maturation defects are not rescued by p53 deletion, showing that they are either upstream of p53 activation, or in a parallel pathway. Accumulation of p53 in the nucleus of mutant NSCs at midbody stage suggests the possibility of a novel midbody-mediated pathway for p53 activation. This work elucidates both NSC apoptosis and abscission mechanisms that could underlie human microcephaly or other brain malformations.

A Monoclonal Antibody to M-Phase Phosphoprotein 1/Kinesin-Like Protein KIF20B

Kinesin-like protein KIF20B, originally named M-phase phosphoprotein 1 (MPP1), is a plus-end-directed kinesin-related protein that exhibits in vitro microtubule-binding and -bundling properties as well as microtubule-stimulated ATPase activity. It has been characterized as a slow molecular motor that moves toward the plus-end of microtubules. Human autoantibodies directed against KIF20B have been described in up to 25% of patients with idiopathic ataxia and less commonly in other neuropathies and autoinflammatory conditions. One of the limitations of research into the structure and function of KIF20B has been a reliable monoclonal antibody that can be used in a variety of applications. To establish a reference standard for anti-KIF20B immunoassays and facilitate studies on the role of KIF20B in developmental cell biology, we developed an IgG1 monoclonal antibody, 10C7, which reacts with the cognate KIF20B protein in Western immunoblots and in addressable laser bead immunoassays. In HEp2 cells, leptomeningeal pericytes, and transfected HEK293T cells, indirect immunofluorescence studies showed that reactivity was mainly localized to a proportion of interphase nuclei, but during metaphase, it was redistributed throughout the cytoplasm and perichromatin mass. Later in telophase/anaphase, KIF20B was localized to the stem body and midzone of the midbody. 10C7 also showed remarkable staining of a subset of cells in the cerebellum, ovary, and testis tissues. KIF20B was shown to have extensive coiled-coil domains. The monoclonal antibody, 10C7, will be of value to diagnostic laboratory scientists interested in having a reliable reference standard for anti-KIF20B immunoassays as well as cell, molecular, and developmental biology researchers.

Kinesin-6 Klp9 plays motor-dependent and -independent roles in collaboration with Kinesin-5 Cut7 and the microtubule crosslinker Ase1 in fission yeast

Bipolar mitotic spindles play a critical part in accurate chromosome segregation. During late mitosis, spindle microtubules undergo drastic elongation in a process called anaphase B. Two kinesin motors, Kinesin-5 and Kinesin-6, are thought to generate outward forces to drive spindle elongation, and the microtubule crosslinker Ase1/PRC1 maintains structural integrity of antiparallel microtubules. However, how these three proteins orchestrate this process remains unknown. Here we explore the functional interplay among fission yeast Kinesin-5/Cut7, Kinesin-6/Klp9 and Ase1. Using total internal reflection fluorescence microscopy, we show that Klp9 forms homotetramers and that Klp9 is a processive plus end-directed motor. klp9Δase1Δ is synthetically lethal. Surprisingly, this lethality is not ascribable to the defective motor activity of Klp9; instead, it is dependent upon a nuclear localisation signal and coiled coil domains within the non-motor region. We isolated a cut7 mutant (cut7-122) that displays temperature sensitivity only in the absence of Klp9. Interestingly, cut7-122 alone is impaired in spindle elongation during anaphase B, and furthermore, cut7-122klp9Δ double mutants exhibit additive defects. We propose that Klp9 plays dual roles during anaphase B; one is motor-dependent that collaborates with Cut7 in force generation, while the other is motor-independent that ensures structural integrity of spindle microtubules together with Ase1.

USP7 Regulates Cytokinesis through FBXO38 and KIF20B

The ubiquitin specific protease 7 (USP7 or HAUSP) is known to regulate a variety of cellular processes by binding and deubiquitylating specific target proteins. To gain a more comprehensive understanding of its interactions and functions, we used affinity purification coupled to mass spectrometry to profile USP7 interactions. This revealed a novel interaction with FBXO38, a poorly characterized F-box protein. We showed that USP7 stabilizes FBXO38 dependent on its catalytic activity by protecting FBXO38 from proteasomal degradation. We used a BioID approach to profile the protein interactions (and putative functions) of FBXO38, revealing an interaction with KIF20B, a Kinesin-6 protein required for efficient cytokinesis. FBXO38 was shown to function independently from an SCF complex to stabilize KIF20B. Consequently, depletion of either FBXO38 or USP7 led to dramatic decreases in KIF20B levels and KIF20B at the midbody, which were manifested in cytokinetic defects. Furthermore, cytokinetic defects associated with USP7 silencing were rescued by restoring FBXO38 or KIF20B. The results indicate a novel mechanism of regulating cytokinesis through USP7 and FBXO38.

Kinesin family member 20B regulates tongue cancer progression by promoting cell proliferation

Oral cancer refers to the malignant tumors that occur in the oral cavity, of which 80% are squamous cell carcinomas. The incidence of oral cancer accounts for ~5% of the incidence of systemic malignancies, with rapid progression, extensive infiltration and poor prognosis. In the present study, Kinesin family member (KIF)20B, a member of Kinesin-6 family, was identified as a potential biomarker which could promote cancer progression. A total of 82 patients were recruited and KIF20B expression levels were investigated by immunohistochemistry, and were divided into high and low groups based on the median of KIF20B expression levels. The clinicopathological features and survival-associated data of the two groups were analyzed and the results were provided as a table and by a Kaplan-Meier plot, respectively. Additionally, KIF20B was successfully silenced in two tongue cancer cell lines, CAL-27 and TCA-8113. MTT and colony formation assay were performed to determine the changes of cell proliferation in knocked down-KIF20B cell lines. In addition, proliferation-associated proteins Ki67 and PCNA were investigated, by western blotting. In animal experiments, subcutaneous tumor formation was performed with control cells and cells with knocked down KIF20B, to determine the inhibitory effect of KIF20B in vivo. Firstly, it was found that there was significantly high expression levels of KIF20B in tongue cancer patients (P<0.05). Patients with high expression of KIF20B had poorer clinicopathological results including tumor differentiation level, lymph node metastasis and clinical stages. The overall survival and relapse-free survival of high-expression group were also poor. Secondly, after successful establishment of cells with knocked down KIF20B, this resulted in a notable reduction in cell proliferation in vitro. Subsequent western blotting further confirmed that Ki67 and PCNA expression levels had a significant decline. Finally, it was demonstrated that knocking down KIF20B could inhibit tumor volume growth in vivo. In conclusion, the high level of KIF20B in oral squamous cell carcinoma was significantly associated with poor clinicopathological features and survival. KIF20B might promote cancer development through enhancing cell proliferation in vitro, and might be a potential biomarker of oral squamous cell carcinoma.

Targeting mitosis exit: A brake for cancer cell proliferation

The transition from mitosis to interphase, referred to as mitotic exit, is a critical mitotic process which involves activation and inactivation of multiple mitotic kinases and counteracting protein phosphatases. Loss of mitotic exit checkpoints is a common feature of cancer cells, leading to mitotic dysregulation and confers cancer cells with oncogenic characteristics, such as aberrant proliferation and microtubule-targeting agent (MTA) resistance. Since MTA resistance results from cancer cells prematurely exiting mitosis (mitotic slippage), blocking mitotic exit is believed to be a promising anticancer strategy. Moreover, based on this theory, simultaneous inhibition of mitotic exit and additional cell cycle phases would likely achieve synergistic antitumor effects. In this review, we divide the molecular regulators of mitotic exit into four categories based on their different regulatory functions: 1) the anaphase-promoting complex/cyclosome (APC/C, a ubiquitin ligase), 2) cyclin B, 3) mitotic kinases and phosphatases, 4) kinesins and microtubule-binding proteins. We also review the regulators of mitotic exit and propose prospective anticancer strategies targeting mitotic exit, including their strengths and possible challenges to their use.

Clinicopathological Significance and Antitumor Effect of MPHOSPH1 in Testicular Germ Cell Tumor

MPHOSPH1, which is one of the kinesin superfamily proteins, has been reported to play an essential role in the carcinogenesis and progression of several kinds of cancers. MPHOSPH1 has also been suggested to be involved in STAT3 phosphorylation in hepatocellular carcinoma. However, the biological behavior of MPHOSPH1 in testicular germ cell tumors (TGCTs) is unclear at present. The purposes of this study were to investigate the correlation between the expression of MPHOSPH1 and clinicopathological factors and to examine the efficacy of MPHOSPH1 target therapy in TGCTs. We investigated 75 formalin-fixed paraffin-embedded TGCT samples, containing a total of 86 germ cell tumor components, by immunohistochemistry and 12 frozen samples by Western blotting. Moreover, we carried out in vitro studies to clarify the antitumor effect of MPHOSPH1 knockdown in embryonal carcinoma cell lines, NEC8 and NEC14, using small interference RNA (siRNA). A significantly high expression of MPHOSPH1 was recognized in embryonal carcinoma and yolk sac tumor components compared to the seminoma component (p<0.001, respectively). Clinically, non-seminoma cases are known to have worse prognosis than pure-seminoma cases. Interestingly, high MPHOSPH1 expression was associated with distant metastasis (p=0.001), and thus with advanced-stage disease in this study. High expression of MPHOSPH1 interacted with high expression of phosphorylated STAT3 (p=0.01). The in vitro experiments demonstrated that MPHOSPH1 interruption by siRNA resulted in a significant reduction of cell migration, invasion, proliferation and colony formation in both embryonal carcinoma cell lines (p<0.001, respectively). In conclusion, MPHOSPH1 may be a potential treatment option for TGCTs, and its expression may be a novel biomarker of poor prognosis.

Quantitative proteomic and phosphoproteomic comparison of human colon cancer DLD-1 cells differing in ploidy and chromosome stability

Although aneuploidy is poorly tolerated during embryogenesis, aneuploidy and whole chromosomal instability (CIN) are common hallmarks of cancer, raising the question of how cancer cells can thrive in spite of chromosome aberrations. Here we present a comprehensive and quantitative proteomics analysis of isogenic DLD-1 colorectal adenocarcinoma cells lines, aimed at identifying cellular responses to changes in ploidy and/or CIN. Specifically, we compared diploid (2N) and tetraploid (4N) cells with posttetraploid aneuploid (PTA) clones and engineered trisomic clones. Our study provides a comparative data set on the proteomes and phosphoproteomes of the above cell lines, comprising several thousand proteins and phosphopeptides. In comparison to the parental 2N line, we observed changes in proteins associated with stress responses and with interferon signaling. Although we did not detect a conspicuous protein signature associated with CIN, we observed many changes in phosphopeptides that relate to fundamental cellular processes, including mitotic progression and spindle function. Most importantly, we found that most changes detectable in PTA cells were already present in the 4N progenitor line. This suggests that activation of mitotic pathways through hyper-phosphorylation likely constitutes an important response to chromosomal burden. In line with this conclusion, cells with extensive chromosome gains showed differential sensitivity toward a number of inhibitors targeting cell cycle kinases, suggesting that the efficacy of anti-mitotic drugs may depend on the karyotype of cancer cells.

Pseudopod-associated protein KIF20B promotes Gli1-induced epithelial-mesenchymal transition modulated by pseudopodial actin dynamic in human colorectal cancer

Kinesin family member 20B (KIF20B) has been reported to have an oncogenic role in bladder and hepatocellular cancer cells, but its role in colorectal cancer (CRC) progression remains unclear. In this study, we assessed the mRNA and protein levels of KIF20B in CRC tissues using qRT-PCR and immunohistochemistry, respectively. KIF20B was overexpressed in CRC tissues and was associated with cancer invasion and metastasis. Mechanistically, KIF20B overexpression promoted the epithelial-mesenchymal transition (EMT) process mediated by glioma-associated oncogene 1 (Gli1) as well as CRC cell migration and invasion. Interestingly, KIF20B was localized in pseudopod protrusions of CRC cells and influenced the formation of cell protrusions, especially the EMT-related invadopodia. Moreover, intracellular actin dynamic participated in the modulation of the Gli1-mediated EMT and EMT-related cell pseudopod protrusion formation induced by KIF20B. We identified a role for KIF20B in CRC progression and revealed a correlation between KIF20B expression in CRC tissues and patient prognosis. The underlying mechanism was associated with the Gli1-mediated EMT and EMT-related cell protrusion formation modulated by intracellular actin dynamic. Thus, KIF20B may be a potential biomarker and promising treatment target for CRC.

Kinesin-6 KIF20B is required for efficient cytokinetic furrowing and timely abscission in human cells

KIF20B is in the Kinesin-6 family that includes KIF23/MKLP1 and KIF20A/MKLP2. Previously we showed that mouse Kif20b regulates cerebral cortex growth and neural stem cell midbodies. Now we show KIF20B has a cell-autonomous role in regulating cytokinetic furrowing and abscission. KIF20B may coordinate late midbody maturation before abscission.

Cytokinesis requires the cooperation of many cytoskeletal and membrane regulators. Most of the major players required for cytokinesis are known, but the temporal regulation and adaptations for different cell types are less understood. KIF20B (previously called MPHOSPH1 or MPP1) is a member of the Kinesin-6 family, which also includes the better-known members KIF23/MKLP1 and KIF20A/MKLP2. Previously, we showed that mouse Kif20b is involved in cerebral cortex growth and midbody organization of neural stem cells. Here, using siRNA-mediated knockdown of KIF20B in a human cell line and fixed and live imaging, we show that KIF20B has a cell-autonomous role in cytokinesis. KIF20B depletion affects the speed of both furrow ingression and abscission. It localizes to microtubules of the central spindle and midbody throughout cytokinesis, at sites distinct from the other Kinesin-6 family members. KIF20B is not required for midbody assembly, but may accelerate or coordinate midbody maturation. In particular, KIF20B appears to regulate late steps of maturation including anillin dispersal, ESCRT-III recruitment, and the formation of microtubule constriction sites.

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.

A microtubule polymerase cooperates with the kinesin-6 motor and a microtubule cross-linker to promote bipolar spindle assembly in the absence of kinesin-5 and kinesin-14 in fission yeast

Kinesin-5 is required for bipolar spindle assembly; yet in the absence of kinesins-5 and -14, cells can form spindles. In fission yeast, three distinct pathways compensate for their loss. Microtubule polymerase, kinesin-6, and microtubule cross-linker execute individual roles in concert at different mitotic stages in place of the two kinesins.

Accurate chromosome segregation relies on the bipolar mitotic spindle. In many eukaryotes, spindle formation is driven by the plus-end–directed motor kinesin-5 that generates outward force to establish spindle bipolarity. Its inhibition leads to the emergence of monopolar spindles with mitotic arrest. Intriguingly, simultaneous inactivation of the minus-end–directed motor kinesin-14 restores spindle bipolarity in many systems. Here we show that in fission yeast, three independent pathways contribute to spindle bipolarity in the absence of kinesin-5/Cut7 and kinesin-14/Pkl1. One is kinesin-6/Klp9 that engages with spindle elongation once short bipolar spindles assemble. Klp9 also ensures the medial positioning of anaphase spindles to prevent unequal chromosome segregation. Another is the Alp7/TACC-Alp14/TOG microtubule polymerase complex. Temperature-sensitive alp7cut7pkl1 mutants are arrested with either monopolar or very short spindles. Forced targeting of Alp14 to the spindle pole body is sufficient to render alp7cut7pkl1 triply deleted cells viable and promote spindle assembly, indicating that Alp14-mediated microtubule polymerization from the nuclear face of the spindle pole body could generate outward force in place of Cut7 during early mitosis. The third pathway involves the Ase1/PRC1 microtubule cross-linker that stabilizes antiparallel microtubules. Our study, therefore, unveils multifaceted interplay among kinesin-dependent and -independent pathways leading to mitotic bipolar spindle assembly.

Two mechanisms coordinate the recruitment of the chromosomal passenger complex to the plane of cell division

Proper positioning of the chromosomal passenger complex (CPC) at the cell division plane is required for cytokinesis. We show here that CPC targeting to the equatorial cortex depends on both the kinesin MKlp2 and a direct interaction with actin. These recruitment mechanisms converge to promote successful cleavage furrow ingression.

During cytokinesis, the chromosomal passenger complex (CPC) promotes midzone organization, specifies the cleavage plane, and regulates furrow contractility. The localizations of the CPC are coupled to its cytokinetic functions. At the metaphase-to-anaphase transition, the CPC dissociates from centromeres and localizes to midzone microtubules and the equatorial cortex. CPC relocalization to the cell middle is thought to depend on MKlp2-driven, plus end–directed transport. In support of this idea, MKlp2 depletion impairs cytokinesis; however, cytokinesis failure stems from furrow regression rather than failed initiation of furrowing. This suggests that an alternative mechanism(s) may concentrate the CPC at the division plane. We show here that direct actin binding, via the inner centromere protein (INCENP), enhances CPC enrichment at the equatorial cortex, thus acting in tandem with MKlp2. INCENP overexpression rescues furrowing in MKlp2-depleted cells in an INCENP-actin binding–dependent manner. Using live-cell imaging, we also find that MKlp2-dependent targeting of the CPC is biphasic. MKlp2 targets the CPC to the anti-parallel microtubule overlap of the midzone, after which the MKlp2-CPC complex moves in a nondirected manner. Collectively, our work suggests that both actin binding and MKlp2-dependent midzone targeting cooperate to precisely position the CPC during mitotic exit, and that these pathways converge to ensure successful cleavage furrow ingression.

The divergent mitotic kinesin MKLP2 exhibits atypical structure and mechanochemistry

MKLP2, a kinesin-6, has critical roles during the metaphase-anaphase transition and cytokinesis. Its motor domain contains conserved nucleotide binding motifs, but is divergent in sequence (~35% identity) and size (~40% larger) compared to other kinesins. Using cryo-electron microscopy and biophysical assays, we have undertaken a mechanochemical dissection of the microtubule-bound MKLP2 motor domain during its ATPase cycle, and show that many facets of its mechanism are distinct from other kinesins. While the MKLP2 neck-linker is directed towards the microtubule plus-end in an ATP-like state, it does not fully dock along the motor domain. Furthermore, the footprint of the MKLP2 motor domain on the MT surface is altered compared to motile kinesins, and enhanced by kinesin-6-specific sequences. The conformation of the highly extended loop6 insertion characteristic of kinesin-6s is nucleotide-independent and does not contact the MT surface. Our results emphasize the role of family-specific insertions in modulating kinesin motor function.

Cells constantly replicate to provide new cells for growing tissues, and to replace ageing or defective cells around the body. Each new cell needs a copy of the genetic material, and a cellular structure called the mitotic spindle makes sure that this material is shared correctly when a cell divides in two. The spindle is built from protein filaments called microtubules, and the protein filaments grow and shrink as the mitotic spindle carries out its role. Many of these changes in the spindle are driven by proteins called molecular motors, which break down energy-rich molecules of ATP to power them as they walk along the filaments.

Kinesins, for example, are molecular motors that can move along microtubules and there are over 40 different kinesins encoded in the human genome. More than half of the human kinesins are involved in cell division including one called MKLP2. Little is known about MKLP2 but some earlier findings had suggested that it would behave very differently compared to other kinesins.

Understanding how a kinesin motor works requires studying it in complex with its microtubule tracks. Atherton, Yu et al. have now used a technique called cryo-electron microscopy – which is uniquely suited to looking at large and complicated samples in three dimensions – to observe how the motor in MKLP2 changes shape as it works. This revealed that, while MKLP2 works in a fundamentally similar way to other kinesins, many aspects of its molecular mechanism are highly unusual. These include how it binds to the microtubule, how it interacts with ATP and how it generates force.

These findings show that there is much greater diversity in the molecular mechanisms of the kinesins involved in cell division than was previously thought. Several anticancer drugs target kinesins to stop cells dividing and so this diversity may make it easier to target only certain kinesins with drugs, which in turn would have fewer side effects. First, though, it will be important to find out how the unusual mechanism of MKLP2 coordinates and influences other components of the spindle to reveal a fuller picture of what happens when cells replicate.

Neural Stem Cells to Cerebral Cortex: Emerging Mechanisms Regulating Progenitor Behavior and Productivity

This review accompanies a 2016 SFN mini-symposium presenting examples of current studies that address a central question: How do neural stem cells (NSCs) divide in different ways to produce heterogeneous daughter types at the right time and in proper numbers to build a cerebral cortex with the appropriate size and structure? We will focus on four aspects of corticogenesis: cytokinesis events that follow apical mitoses of NSCs; coordinating abscission with delamination from the apical membrane; timing of neurogenesis and its indirect regulation through emergence of intermediate progenitors; and capacity of single NSCs to generate the correct number and laminar fate of cortical neurons. Defects in these mechanisms can cause microcephaly and other brain malformations, and understanding them is critical to designing diagnostic tools and preventive and corrective therapies.

Mutation of Kinesin-6 Kif20b causes defects in cortical neuron polarization and morphogenesis

BACKGROUND

How neurons change their cytoskeleton to adopt their complex polarized morphology is still not understood. Growing evidence suggests that proteins that help build microtubule structures during cell division are also involved in building and remodeling the complex cytoskeletons of neurons. Kif20b (previously called MPP1 or Mphosph1) is the most divergent member of the Kinesin-6 family of "mitotic" kinesins that also includes Kif23/MKLP1 and Kif20a/MKLP2. We previously isolated a loss-of-function mouse mutant of Kif20b and showed that it had a thalamocortical axon guidance defect and microcephaly.

METHODS

We demonstrate here, using the mouse mutant, that Kif20b is required for neuron morphogenesis in the embryonic neocortex. In vivo and in vitro cortical neurons were labeled and imaged to analyze various aspects of morphogenesis.

RESULTS

Loss of Kif20b disrupts polarization as well as neurite outgrowth, branching and caliber. In vivo, mutant cortical neurons show defects in orientation, and have shorter thinner apical dendrites that branch closer to the cell body. In vitro, without external polarity cues, Kif20b mutant neurons show a strong polarization defect. This may be due in part to loss of the polarity protein Shootin1 from the axonal growth cone. Those mutant neurons that do succeed in polarizing have shorter axons with more branches, and longer minor neurites. These changes in shape are not due to alterations in cell fate or neuron layer type. Surprisingly, both axons and minor neurites of mutant neurons have increased widths and longer growth cone filopodia, which correlate with abnormal microtubule organization. Live analysis of axon extension shows that Kif20b mutant axons display more variable growth with increased retraction.

CONCLUSIONS

These results demonstrate that Kif20b is required cell-autonomously for proper morphogenesis of cortical pyramidal neurons. Kif20b regulates neuron polarization, and axon and dendrite branching, outgrowth, and caliber. Kif20b protein may act by bundling microtubules into tight arrays and by localizing effectors such as Shootin1. Thus it may help shape neurites, sustain consistent axon growth, and inhibit branching. This work advances our understanding of how neurons regulate their cytoskeleton to build their elaborate shapes. Finally, it suggests that neuronal connectivity defects may be present in some types of microcephaly.

Depsidones from Lichens as Natural Product Inhibitors of M-Phase Phosphoprotein 1, a Human Kinesin Required for Cytokinesis

M-Phase Phosphoprotein 1 (MPP1), a microtubule plus end directed kinesin, is required for the completion of cytokinesis. Previous studies have shown that MPP1 is upregulated in various types of bladder cancer. This article describes inhibitor screening leading to the identification of a new class of natural product inhibitors of MPP1. Two compounds with structural similarity, norlobaridone (1) and physodic acid (2), were found to inhibit MPP1. Physodic acid is not competitive with ATP, indicating the presence of an allosteric inhibitor-binding pocket. Initial drug-like property screening indicates that physodic acid is more soluble than norlobaridone and has more favorable lipophilicity. However, both suffer from high clearance in human microsomal stability assays mediated by the lability of the lactone ring as well as hydroxylation of the alkyl chains as shown by metabolite identification studies. In cell-based assays physodic acid is a weak inhibitor with EC50 values of about 30 μM in a range of tumor cell lines. The two depsidones identified and characterized here could be used for future improvement of their activity against MPP1 and will be useful chemical probes for studying this unique molecular motor in more depth.

Imaging and quantitative analysis of cytokinesis in developing brains of Kinesin-6 mutant mice

Cytokinesis in neural progenitors occurs with specialized constraints due to their highly polarized structure and the need for both symmetric and asymmetric divisions. They must produce proper numbers of progenitors, neurons, and glia in a precise order. Yet very few functional studies of cytokinesis have been done in the developing brain. To elucidate mechanisms of cytokinesis during brain development, we designed a novel method to study cytokinesis in whole mount "slabs" of embryonic mouse cerebral cortex. It takes advantage of cytokinesis occurring on the ventricular surface of the cortex and allows examination of cytokinesis across many cells in the context of an intact brain tissue. The cortical slabs can be fixed for immunohistochemistry or used in live imaging experiments. In particular, we investigated mutants of the Kinesin-6, Kif20b, which show defects in cytokinetic abscission and have small brains. Here, we describe how to dissect neocortex from embryonic cerebral hemispheres, immunostain the cortical slabs for cytokinetic midbodies and other structures, and image the apical surface. We show how to quantitatively analyze apical structures including midbody numbers, organization, and morphology. New images and analyses of Kif20b(magoo) loss of function mutants are shown. Applying and adapting these types of analyses to other cytoskeletal proteins and mouse mutants will help advance our understanding on how the embryonic neuroepithelium generates neurons and builds the brain.

Proteomic analyses uncover a new function and mode of action for mouse homolog of Diaphanous 2 (mDia2)

mDia2 is an auto-inhibited Formin influencing actin dynamics upon conversion to the active conformation. mDia2 regulates actin-based protrusions and cell invasion, cell differentiation, vesicle trafficking, and cytokinesis. However, whether mDia2 has additional functions and how its action is functionally specified remain unknown. Here we draw the interactome of auto-inhibited and constitutively active mDia2 to address these issues. We embed mDia2 in protein networks accounting for its attributed functions and unexpectedly link it to the Ubiquitin Proteasome System. Taking FBXO3 as a test case, we show that mDia2 binds FBXO3 and p53, and regulates p53 transcriptional activity in an actin-nucleation-independent and conformation-insensitive manner. Increased mDia2 and FBXO3 levels elevate p53 activity and expression thereby sensitizing cells to p53-dependent apoptosis, whereas their decrease produces opposite effects. Thus, we discover a new role of mDia2 in p53 regulation suggesting that the closed conformation is biologically active and an FBXO3-based mechanism to functionally specify mDia2's activity.

MPHOSPH1: a potential therapeutic target for hepatocellular carcinoma

MPHOSPH1 is a critical kinesin protein that functions in cytokinesis. Here, we show that MPHOSPH1 is overexpressed in hepatocellular carcinoma (HCC) cells, where it is essential for proliferation. Attenuating MPHOSPH1 expression with a tumor-selective shRNA-expressing adenovirus (Ad-shMPP1) was sufficient to arrest HCC cell proliferation in a manner associated with an accumulation of multinucleated polyploid cells, induction of postmitotic apoptosis, and increased sensitivity to taxol cytotoxicity. Mechanistic investigations showed that attenuation of MPHOSPH1 stabilized p53, blocked STAT3 phosphorylation, and prolonged mitotic arrest. In a mouse subcutaneous xenograft model of HCC, tumoral injection of Ad-shMPP1 inhibited MPHOSPH1 expression and tumor growth in a manner correlated with induction of apoptosis. Combining Ad-shMPP1 injection with taxol administration enhanced antitumor efficacy relative to taxol alone. Furthermore, Ad-shMPP1 tail vein injection suppressed formation of orthotopic liver nodules and prevented hepatic dysfunction. Taken together, our results identify MPHOSPH1 as an oncogenic driver and candidate therapeutic target in HCC.

MKlp2 inhibitor paprotrain affects polar body extrusion during mouse oocyte maturation

BACKGROUND

Mammalian oocyte meiotic maturation involves a number of important processes, including spindle assembly and migration, cortical reorganization and polar body extrusion. Numerous proteins contribute to these processes, but it is unknown whether MKlp2 (mitotic kinesin-like protein 2; also called KIF20A), a microtubule-associated protein that regulates cytokinesis during mitosis, is involved in oocyte maturation.

METHODS

Confocal microscopy, time lapse microscopy, inhibitor treatment were adopted to examine the roles of MKlp2 in mouse oocyte.

RESULTS

Immunostaining results showed that MKlp2 localized to oocyte microtubules. Time-lapse microscopy showed that disrupting MKlp2 expression with paprotrain, a specific inhibitor of MKlp2, resulted in polar body extrusion failure. This could be rescued after rescuing oocytes from paprotrain in fresh medium. Cell cycle analysis showed that most oocytes were arrested at metaphase I or telophase I. However, oocyte spindle structure and chromosome alignment were not disrupted after the inhibition of MKlp2 by paprotrain.

CONCLUSIONS

This study demonstrated that MKlp2 is crucial for oocyte maturation by regulating polar body extrusion.

The vertebrate-specific Kinesin-6, Kif20b, is required for normal cytokinesis of polarized cortical stem cells and cerebral cortex size

Mammalian neuroepithelial stem cells divide using a polarized form of cytokinesis, which is not well understood. The cytokinetic furrow cleaves the cell by ingressing from basal to apical, forming the midbody at the apical membrane. The midbody mediates abscission by recruiting many factors, including the Kinesin-6 family member Kif20b. In developing embryos, Kif20b mRNA is most highly expressed in neural stem/progenitor cells. A loss-of-function mutant in Kif20b, magoo, was found in a forward genetic screen. magoo has a small cerebral cortex, with reduced production of progenitors and neurons, but preserved layering. In contrast to other microcephalic mouse mutants, mitosis and cleavage furrows of cortical stem cells appear normal in magoo. However, apical midbodies show changes in number, shape and positioning relative to the apical membrane. Interestingly, the disruption of abscission does not appear to result in binucleate cells, but in apoptosis. Thus, Kif20b is required for proper midbody organization and abscission in polarized cortical stem cells and has a crucial role in the regulation of cerebral cortex growth.

Shootin1 acts in concert with KIF20B to promote polarization of migrating neurons

Shootin1 has been ascribed a role in regulating polarization of primary hippocampal neurons. To better understand the possible role of Shootin1 in the developing brain, we identified a member of the kinesin superfamily, KIF20B, as a novel Shootin1 interacting protein and a potential mediator of Shootin1 interaction with microtubules. KIF20B/Shootin1 binding was mapped to a 57 aa KIF20B sequence, which was used as a dominant-negative fragment. Direct interaction between that peptide (MBD) and Shootin1 was confirmed by surface plasmon resonance-based technology and the affinity was determined in the 10⁻⁷ m range. The proteins are expressed in the developing brain and formed a complex in vivo based on coimmunoprecipitation experiments and coimmunostaining in primary neurons. In primary hippocampal neurons Kif20b knockdown reduced Shootin1 mobilization to the developing axon, as evidenced by immunostaining and fluorescence recovery after photobleaching analysis, suggesting that Shootin1 is a novel KIF20B cargo. shRNA targeting of Shootin1 reduced PIP3 accumulation in the growth cone, as did Kif20b shRNA. In the developing mouse brain, Kif20b knockdown or expression of the KIF20B minimal binding domain inhibited neuronal migration, and in vivo migration assays suggested that Shootin1/Kif20b acts in the same genetic pathway. Time-lapse imaging of multipolar cells in the subventricular zone revealed that downregulating levels of either Shootin1 or Kif20b hindered the transition from multipolar to bipolar cells. Collectively, our data demonstrate the importance of the Shootin1/KIF20B interaction to the dynamic process of pyramidal neuronal polarization and migration.

Identification of HYPK-interacting proteins reveals involvement of HYPK in regulating cell growth, cell cycle, unfolded protein response and cell death

Huntingtin Yeast Two-Hybrid Protein K (HYPK) is an intrinsically unstructured huntingtin (HTT)-interacting protein with chaperone-like activity. To obtain more information about the function(s) of the protein, we identified 27 novel interacting partners of HYPK by pull-down assay coupled with mass spectrometry and, further, 9 proteins were identified by co-localization and co-immunoprecipitation (co-IP) assays. In neuronal cells, (EEF1A1 and HSPA1A), (HTT and LMNB2) and (TP53 and RELA) were identified in complex with HYPK in different experiments. Various Gene Ontology (GO) terms for biological processes, like protein folding (GO: 0006457), response to unfolded protein (GO: 0006986), cell cycle arrest (GO: 0007050), anti-apoptosis (GO: 0006916) and regulation of transcription (GO: 0006355) were significantly enriched with the HYPK-interacting proteins. Cell growth and the ability to refold heat-denatured reporter luciferase were decreased, but cytotoxicity was increased in neuronal cells where HYPK was knocked-down using HYPK antisense DNA construct. The proportion of cells in different phases of cell cycle was also altered in cells with reduced levels of HYPK. These results show that HYPK is involved in several biological processes, possibly through interaction with its partners.

A new oncolytic adenoviral vector carrying dual tumour suppressor genes shows potent anti-tumour effect

Cancer Targeting Gene-Viro-Therapy (CTGVT) is a promising cancer therapeutical strategy that strengthens the anti-tumour effect of oncolytic virus by expressing inserted foreign anti-tumour genes. In this work, we constructed a novel adenoviral vector controlled by the tumour-specific survivin promoter on the basis of the ZD55 vector, which is an E1B55KD gene deleted vector we previously constructed. Compared with the original ZD55 vector, this new adenoviral vector (ZD55SP/E1A) showed much better ability of replication and reporter gene expression. We then combined anti-tumour gene interleukine-24 (IL-24) with an RNA polymerase III-dependent U6 promoter driving short hairpin RNA (shRNA) that targets M-phase phosphoprotein 1 (MPHOSPH1, a newly identified oncogene) by inserting the IL-24 and the shRNA of MPHOSPH1 (shMPP1) expression cassettes into the new ZD55SP/E1A vector. Our results demonstrated excellent anti-tumour effect of ZD55SP/E1A-IL-24-shMPP1 in vitro on multiple cancer cell lines such as lung cancer, liver cancer and ovarian caner. At high multiplicity-of-infection (MOI), ZD55SP/E1A-IL-24-shMPP1 triggered post-mitotic apoptosis in cancer cells by inducing prolonged mitotic arrest; while at low MOI, senescence was induced. More importantly, ZD55SP/E1A-IL-24-shMPP1 also showed excellent anti-tumour effects in vivo on SW620 xenograft nude mice. In conclusion, our strategy of constructing an IL-24 and shMPP1 dual gene expressing oncolytic adenoviral vector, which is regulated by the survivin promoter and E1B55KD deletion, could be a promising method of cancer gene therapy.

Intrinsic Disorder in the Kinesin Superfamily

Kinesin molecular motors perform a myriad of intracellular transport functions. While their mechanochemical mechanisms are well understood and well-conserved throughout the superfamily, the cargo-binding and regulatory mechanisms governing the activity of kinesins are highly diverse and in general, are incompletely characterized. Here we present evidence from bioinformatic predictions indicating that most kinesin superfamily members contain significant regions of intrinsically disordered (ID) residues. ID regions can bind to multiple partners with high specificity, and are highly labile to post-translational modification and degradation signals. In kinesins, the predicted ID regions are primarily found in areas outside the motor domains, where primary sequences diverge by family, suggesting that ID may be a critical structural element for determining the functional specificity of individual kinesins. To support this idea, we present a systematic analysis of the kinesin superfamily, family by family, for predicted regions of ID. We combine this analysis with a comprehensive review of kinesin binding partners and post-translational modifications. We find two key trends across the entire kinesin superfamily. First, ID residues tend to be in the tail regions of kinesins, opposite the superfamily-conserved motor domains. Second, predicted ID regions correlate to regions that are known to bind to cargoes and/or undergo post-translational modifications. We therefore propose that ID is a structural element utilized by the kinesin superfamily in order to impart functional specificity to individual kinesins.

Molecular cloning and mRNA expression of M-phase phosphoprotein 6 gene in black tiger shrimp (Penaeus monodon)

It is widely accepted that protein phosphorylation is a major control event in regulating cell cycle. In the present study, a novel M-phase phosphoprotein 6 (MPP6) was identified from black tiger shrimp Penaeus monodon (designated as PmMPP6) by cDNA library and RACE approaches. The full-length cDNA of PmMPP6 was of 690 bp, including a 5'-terminal un-translated region (5'UTR) of 68 bp, a 3'UTR of 172 bp with a poly (A) tail, and an open reading frame (ORF) of 450 bp encoding a polypeptide of 149 amino acids with a predicted molecular weight of 17.01 kDa. Blastx and phylogenetic analysis together supported that PmMPP6 was a novel member of shrimp MPP6. The mRNA expression of PmMPP6 in thirteen tissues was examined by real-time PCR, and mRNA transcript of PmMPP6 was predominantly detectable in tissues of lymphoid and muscle, to a lesser degree in the tissues of gill, ovary and hepatopancreas, and mainly detected in haemocytes, heart and gonad. The temporal expression of PmMPP6 in different developmental stages of ovary was investigated by real-time PCR. During the six stages of ovary development, two peaks expression of PmMPP6 was detected in stage II with 3.78-fold increase and stage V with 3.48-fold increase compared to that in stage I. All these results indicated that PmMPP6 might be involved in regulating shrimp cell cycle and ovary development.

Kinesins and cancer

Kinesins are a family of molecular motors that travel unidirectionally along microtubule tracks to fulfil their many roles in intracellular transport or cell division. Over the past few years kinesins that are involved in mitosis have emerged as potential targets for cancer drug development. Several compounds that inhibit two mitotic kinesins (EG5 (also known as KIF11) and centromere-associated protein E (CENPE)) have entered Phase I and II clinical trials either as monotherapies or in combination with other drugs. Additional mitotic kinesins are currently being validated as drug targets, raising the possibility that the range of kinesin-based drug targets may expand in the future.

Elucidating the functionality of kinesins: an overview of small molecule inhibitors

Kinesin motor proteins are ubiquitously involved in multiple fundamental cellular processes, coordinating transport and mediating changes to cellular architecture. Thus, specific small molecule kinesin inhibitors can shed new light on the functions of kinesins and the dynamic roles in which they participate. Here we review the range of known inhibitors, their key characteristics, and specificity, and discuss their potential suitability for chemical genetics as starting points to further investigate complex kinesin-mediated processes.

Still entangled: assembly of the central spindle by multiple microtubule modulators

The central spindle is a microtubule-based structure that assembles during anaphase of mitosis in animal cells and is essential for multiple steps of cytokinesis. Central spindle assembly occurs by the cooperative action of multiple microtubule motors and modulators. Here, we review the mechanism by which the central spindle is formed, the role of several key proteins in this process and how central spindle assembly is temporally and spatially coordinated with mitosis.

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

Kinesins are enzymes that use the energy of ATP to perform mechanical work. There are approximately 14 families of kinesins within the kinesin superfamily. Family classification is derived primarily from alignments of the sequences of the core motor domain. For this reason, the enzymatic behavior and motility of each motor generally reflects its family. At the cellular level, kinesin motors perform a variety of functions during cell division and within the mitotic spindle to ensure that chromosomes are segregated with the highest fidelity possible. The cellular functions of these motors are intimately related to their mechanical and enzymatic properties at the single molecule level. For this reason, motility studies designed to evaluate the activity of purified molecular motors are a requirement in order to understand, mechanistically, how these motors make the mitotic spindle work and what can cause the spindle to fail. This review will focus on a selection of illustrative kinesins, which have been studied at the molecular level in order to inform our understanding of their function in cells. In addition, the review will endeavor to point out some kinesins that have been studied extensively but which still lack sufficient molecular underpinnings to fully predict their contribution to spindle function.

Kinesins to the core: The role of microtubule-based motor proteins in building the mitotic spindle midzone

In mammalian cultured cells the initiation of cytokinesis is regulated - both temporally and spatially - by the overlapping, anti-parallel microtubules of the spindle midzone. This region recruits several key central spindle components: PRC-1, polo-like kinase 1 (Plk-1), the centralspindlin complex, and the chromosome passenger complex (CPC), which together serve to stabilize the microtubule overlap, and also to coordinate the assembly of the cortical actin/myosin cytoskeleton necessary to physically cleave the cell in two. The localization of these crucial elements to the spindle midzone requires members of the kinesin superfamily of microtubule-based motor proteins. Here we focus on reviewing the role played by a variety of kinesins in both building and operating the spindle midzone machinery during cytokinesis.

Cytokinesis and cancer

Cytokinesis is the final stage of cell division during which the two daughter cells separate completely. Although less well understood than some of the earlier phases of the cell cycle, recent discoveries have shed light on the mechanisms that orchestrate this process, including cleavage furrow formation, midbody maturation and abscission. One of the reasons why research on cytokinesis has been attracting increasing attention is the concept that failure of this process in mammals is associated with carcinogenesis. In this minireview, we will discuss the possible links between cytokinesis and cancer, and highlight key mechanisms that connect these processes.

Low-dose radiation-induced senescent stromal fibroblasts render nearby breast cancer cells radioresistant

In addition to cell cycle arrest, DNA repair or/and apoptosis, ionizing radiation can also induce premature senescence, which could lead to very different biological consequences depending on the cell type. We show in this report that low-dose radiation-induced senescent stromal fibroblasts stimulate proliferation of cocultured breast carcinoma cells. Such effects of senescent fibroblasts appear to result from their ability to induce the expression in carcinoma cells of mitotic genes and subsequent mitotic division. The elevated proliferation of breast carcinoma cells correlates with resistance to radiation as well as to adriamycin. Of interest is the observation that exposure to lower doses (<20 cGy) augments the ability of senescent fibroblasts to promote the survival of cocultured breast carcinoma cells. The resistance appears to be mediated partially by the Akt pathway, because expression of a dominant negative Akt mutant in breast carcinoma cells results in a partial reversal of the radioresistance. The ability of fibroblasts to modulate the radiosensitivity of nearby carcinoma cells implicates the importance of targeting the stroma during therapy.