Rab11 endosomes contribute to mitotic spindle organization and orientation

Mitotic spindle membranes

The mitotic spindle, which uses microtubules (MTs) and MT-based motor proteins to separate sister chromosomes prior to cell division, contains abundant membranes, organelles, and protein assemblies derived from the familiar interphase intracellular membrane network. In this essay, mainly with reference to selected animal and fungal cells, I summarize current ideas about the reciprocal functional relationship between these mitotic spindle-associated membranes and the spindle MT cytoskeleton, in which; 1) spindle membranes control the composition, Ca++ ion concentration and mechanical performance of the spindle MT cytoskeleton; and conversely 2) the spindle MT cytoskeleton contributes to membrane/organelle partitioning and inheritance during cell division and serves as a reservoir of membranes, organelles, and vesicles for delivery to the interphase cytoplasm, plasma membrane, and cleavage furrow.

Tight Junction Component Occludin Binds to FIP5 to Regulate Endosome Trafficking and Mitotic Spindle Function

The genetic basis of vertebrate emergence during metazoan evolution has remained largely unknown. Understanding vertebrate-specific genes, such as the tight junction protein Occludin (Ocln), may help answer this question. Here, it is shown that mammary glands lacking Ocln exhibit retarded epithelial branching, owing to reduced cell proliferation and surface expansion. Interestingly, Ocln regulates mitotic spindle orientation and function, and its loss leads to a range of defects, including prolonged prophase and failed nuclear and/or cytoplasmic division. Mechanistically, Ocln binds to the RabGTPase-11 adaptor FIP5 and recruits recycling endosomes to the centrosome to participate in spindle assembly and function. FIP5 loss recapitulates Ocln null, leading to prolonged prophase, reduced cell proliferation, and retarded epithelial branching. These results identify a novel role in OCLN-mediated endosomal trafficking and potentially highlight its involvement in mediating membranous vesicle trafficking and function, which is evolutionarily conserved and essential.

From dusk till dawn: cell cycle progression in the red seaweed Gracilariopsis chorda (Rhodophyta)

The conserved eukaryotic functions of cell cycle genes have primarily been studied using animal/plant models and unicellular algae. Cell cycle progression and its regulatory components in red (Rhodophyta) seaweeds are poorly understood. We analyzed diurnal gene expression data to investigate the cell cycle in the red seaweed Gracilariopsis chorda. We identified cell cycle progression and transitions in G. chorda which are induced by interactions of key regulators such as E2F/DP, RBR, cyclin-dependent kinases, and cyclins from dusk to dawn. However, several typical CDK inhibitor proteins are absent in red seaweeds. Interestingly, the G1-S transition in G. chorda is controlled by delayed transcription of GINS subunit 3. We propose that the delayed S phase entry in this seaweed may have evolved to minimize DNA damage (e.g., due to UV radiation) during replication. Our results provide important insights into cell cycle-associated physiology and its molecular mechanisms in red seaweeds.

Rab11 maintains the undifferentiated state of adult midgut precursors via DPP pathway

Asymmetric stem cell divisions play instrumental roles in the maintenance, growth and differentiation of organs. Failure of asymmetric stem cell divisions may result in an array of developmental disorders, including cancer. It is well established that the gene, inscuteable, acts as the upstream component of asymmetric cell divisions. In Drosophila larval midgut, a founder adult midgut precursor (AMP) experiences an asymmetric division to instruct its first daughter to become a peripheral cell that serves as a niche where the AMP and its future daughters can remain undifferentiated. The present study demonstrates that inscuteable expressing stem cells require Rab11, a conserved small Ras-like GTPase, for proper proliferation and differentiation. As insc-GAL4 mediated Rab11RNAi in Drosophila larval and adult midguts show the disruption of the niche microenvironment of adult midgut precursors as well as elevated DPP signalling at the larval stage, which is associated with aberrant over-proliferation and early differentiation of larval AMPs and adult intestinal stem cells. The observed connections between Rab11, larval AMP proliferation, niche establishment, and DPP signalling highlight the potential for Rab11 to serve as a key regulatory factor in maintaining tissue homeostasis and balanced cellular growth.

Dysregulation of the endoplasmic reticulum blocks recruitment of centrosome-associated proteins resulting in mitotic failure

The endoplasmic reticulum (ER) undergoes a remarkable transition in morphology during cell division to aid in the proper portioning of the ER. However, whether changes in ER behaviors modulate mitotic events is less clear. Like many animal embryos, the early Drosophila embryo undergoes rapid cleavage cycles in a lipid-rich environment. Here, we show that mitotic spindle formation, centrosomal maturation, and ER condensation occur with similar time frames in the early syncytium. In a screen for Rab family GTPases that display dynamic function at these stages, we identified Rab1. Rab1 disruption led to an enhanced buildup of ER at the spindle poles and produced an intriguing 'mini-spindle' phenotype. ER accumulation around the mitotic space negatively correlates with spindle length/intensity. Importantly, centrosomal maturation is defective in these embryos, as mitotic recruitment of key centrosomal proteins is weakened after Rab1 disruption. Finally, division failures and ER overaccumulation is rescued by Dynein inhibition, demonstrating that Dynein is essential for ER spindle recruitment. These results reveal that ER levels must be carefully tuned during mitotic processes to ensure proper assembly of the division machinery.

Multiple functions and dual characteristics of RAB11A in cancers

Vesicle trafficking is an unceasing and elaborate cellular process that functions in material transport and information delivery. Recent studies have identified the small GTPase, Ras-related protein in brain 11A (RAB11A), as a key regulator in this process. Aberrant RAB11A expression has been reported in several types of cancers, suggesting the important functions and characteristics of RAB11A in cancer. These discoveries are of great significance because therapeutic strategies based on the physiological and pathological status of RAB11A might make cancer treatment more effective, as the molecular mechanisms of cancer development have not been completely revealed. However, these studies on RAB11A have not been reviewed and discussed specifically. Therefore, we summarize and discuss the recent findings of RAB11A involvement in different biological processes, including endocytic recycling regulation, receptors and adhesion molecules recycling, exosome secretion, phagophore formation and cytokinesis, as well as regulatory mechanisms in several tumor types. Moreover, contradictory effects of RAB11A have also been observed in different types of cancers, implying the dual characteristics of RAB11A in cancer, which are either oncogenic or tumor-suppressive. This review on the functions and characteristics of RAB11A highlights the value of RAB11A in inducing multiple important phenotypes based on vesicle trafficking and therefore will offer insights for future studies to reveal the molecular mechanisms, clinical significance, and therapeutic targeting of RAB11A in different cancers.

RAB11A and RAB11B control mitotic spindle function in intestinal epithelial progenitor cells

RAB11 small GTPases and associated recycling endosome have been localized to mitotic spindles and implicated in regulating mitosis. However, the physiological significance of such regulation has not been observed in mammalian tissues. We have used newly engineered mouse models to investigate intestinal epithelial renewal in the absence of single or double isoforms of RAB11 family members: Rab11a and Rab11b. Comparing with single knockouts, mice with compound ablation demonstrate a defective cell cycle entry and robust mitotic arrest followed by apoptosis, leading to a total penetrance of lethality within 3 days of gene ablation. Upon Rab11 deletion ex vivo, enteroids show abnormal mitotic spindle formation and cell death. Untargeted proteomic profiling of Rab11a and Rab11b immunoprecipitates has uncovered a shared interactome containing mitotic spindle microtubule regulators. Disrupting Rab11 alters kinesin motor KIF11 function and impairs bipolar spindle formation and cell division. These data demonstrate that RAB11A and RAB11B redundantly control mitotic spindle function and intestinal progenitor cell division, a mechanism that may be utilized to govern the homeostasis and renewal of other mammalian tissues.

Centrosome Movements Are TUBG1-Dependent

The centrosome of mammalian cells is in constant movement and its motion plays a part in cell differentiation and cell division. The purpose of this study was to establish the involvement of the TUBG meshwork in centrosomal motility. In live cells, we used a monomeric red-fluorescence-protein-tagged centrin 2 gene and a green-fluorescence-protein-tagged TUBG1 gene for labeling the centrosome and the TUBG1 meshwork, respectively. We found that centrosome movements occurred in cellular sites rich in GTPase TUBG1 and single-guide RNA mediated a reduction in the expression of TUBG1, altering the motility pattern of centrosomes. We propose that the TUBG1 meshwork enables the centrosomes to move by providing them with an interacting platform that mediates positional changes. These findings uncover a novel regulatory mechanism that controls the behavior of centrosomes.

Using Optogenetics to Investigate the Shared Mechanisms of Apical-Basal Polarity and Mitosis

The initiation of apical-basal (AB) polarity and the process of mitotic cell division are both characterised by the generation of specialised plasma membrane and cortical domains. These are generated using shared mechanisms, such as asymmetric protein accumulation, Rho GTPase signalling, cytoskeletal reorganisation, vesicle trafficking, and asymmetric phosphoinositide distribution. In epithelial tissue, the coordination of AB polarity and mitosis in space and time is important both during initial epithelial development and to maintain tissue integrity and ensure appropriate cell differentiation at later stages. Whilst significant progress has been made in understanding the mechanisms underlying cell division and AB polarity, it has so far been challenging to fully unpick the complex interrelationship between polarity, signalling, morphogenesis, and cell division. However, the recent emergence of optogenetic protein localisation techniques is now allowing researchers to reversibly control protein activation, localisation, and signalling with high spatiotemporal resolution. This has the potential to revolutionise our understanding of how subcellular processes such as AB polarity are integrated with cell behaviours such as mitosis and how these processes impact whole tissue morphogenesis. So far, these techniques have been used to investigate processes such as cleavage furrow ingression, mitotic spindle positioning, and in vivo epithelial morphogenesis. This review describes some of the key shared mechanisms of cell division and AB polarity establishment, how they are coordinated during development and how the advance of optogenetic techniques is furthering this research field.

Rab11 endosomes and Pericentrin coordinate centrosome movement during pre-abscission in vivo

The last stage of cell division involves two daughter cells remaining interconnected by a cytokinetic bridge that is cleaved during abscission. Conserved between the zebrafish embryo and human cells, we found that the oldest centrosome moves in a Rab11-dependent manner towards the cytokinetic bridge sometimes followed by the youngest. Rab11-endosomes are organized in a Rab11-GTP dependent manner at the mother centriole during pre-abscission, with Rab11 endosomes at the oldest centrosome being more mobile compared with the youngest. The GTPase activity of Rab11 is necessary for the centrosome protein, Pericentrin, to be enriched at the centrosome. Reduction in Pericentrin expression or optogenetic disruption of Rab11-endosome function inhibited both centrosome movement towards the cytokinetic bridge and abscission, resulting in daughter cells prone to being binucleated and/or having supernumerary centrosomes. These studies suggest that Rab11-endosomes contribute to centrosome function during pre-abscission by regulating Pericentrin organization resulting in appropriate centrosome movement towards the cytokinetic bridge and subsequent abscission.

Fine-tuning cell organelle dynamics during mitosis by small GTPases

During mitosis, the allocation of genetic material concurs with organelle transformation and distribution. The coordination of genetic material inheritance with organelle dynamics directs accurate mitotic progression, cell fate determination, and organismal homeostasis. Small GTPases belonging to the Ras superfamily regulate various cell organelles during division. Being the key regulators of membrane dynamics, the dysregulation of small GTPases is widely associated with cell organelle disruption in neoplastic and non-neoplastic diseases, such as cancer and Alzheimer's disease. Recent discoveries shed light on the molecular properties of small GTPases as sophisticated modulators of a remarkably complex and perfect adaptors for rapid structure reformation. This review collects current knowledge on small GTPases in the regulation of cell organelles during mitosis and highlights the mediator role of small GTPase in transducing cell cycle signaling to organelle dynamics during mitosis.

Mechanisms of microtubule organization in differentiated animal cells

Microtubules are polarized cytoskeletal filaments that serve as tracks for intracellular transport and form a scaffold that positions organelles and other cellular components and modulates cell shape and mechanics. In animal cells, the geometry, density and directionality of microtubule networks are major determinants of cellular architecture, polarity and proliferation. In dividing cells, microtubules form bipolar spindles that pull chromosomes apart, whereas in interphase cells, microtubules are organized in a cell type-specific fashion, which strongly correlates with cell physiology. In motile cells, such as fibroblasts and immune cells, microtubules are organized as radial asters, whereas in immotile epithelial and neuronal cells and in muscles, microtubules form parallel or antiparallel arrays and cortical meshworks. Here, we review recent work addressing how the formation of such microtubule networks is driven by the plethora of microtubule regulatory proteins. These include proteins that nucleate or anchor microtubule ends at different cellular structures and those that sever or move microtubules, as well as regulators of microtubule elongation, stability, bundling or modifications. The emerging picture, although still very incomplete, shows a remarkable diversity of cell-specific mechanisms that employ conserved building blocks to adjust microtubule organization in order to facilitate different cellular functions.

C53 Interacting with UFM1-Protein Ligase 1 Regulates Microtubule Nucleation in Response to ER Stress

ER distribution depends on microtubules, and ER homeostasis disturbance activates the unfolded protein response resulting in ER remodeling. CDK5RAP3 (C53) implicated in various signaling pathways interacts with UFM1-protein ligase 1 (UFL1), which mediates the ufmylation of proteins in response to ER stress. Here we find that UFL1 and C53 associate with γ-tubulin ring complex proteins. Knockout of UFL1 or C53 in human osteosarcoma cells induces ER stress and boosts centrosomal microtubule nucleation accompanied by γ-tubulin accumulation, microtubule formation, and ER expansion. C53, which is stabilized by UFL1, associates with the centrosome and rescues microtubule nucleation in cells lacking UFL1. Pharmacological induction of ER stress by tunicamycin also leads to increased microtubule nucleation and ER expansion. Furthermore, tunicamycin suppresses the association of C53 with the centrosome. These findings point to a novel mechanism for the relief of ER stress by stimulation of centrosomal microtubule nucleation.

Endolysosomal Mesoporous Silica Nanoparticle Trafficking along Microtubular Highways

This study examines intra- and intercellular trafficking of mesoporous silica nanoparticles along microtubular highways, with an emphasis on intercellular bridges connecting interphase and telophase cells. The study of nanoparticle trafficking within and between cells during all phases of the cell cycle is relevant to payload destination and dilution, and impacts delivery of therapeutic or diagnostic agents. Super-resolution stochastic optical reconstruction and sub-airy unit image acquisition, the latter combined with Huygens deconvolution microscopy, enable single nanoparticle and microtubule resolution. Combined structural and functional data provide enhanced details on biological processes, with an example of mitotic inheritance during cancer cell trivision.

Dysregulation of Microtubule Nucleating Proteins in Cancer Cells

Simple Summary

The dysfunction of microtubule nucleation in cancer cells changes the overall cytoskeleton organization and cellular physiology. This review focuses on the dysregulation of the γ-tubulin ring complex (γ-TuRC) proteins that are essential for microtubule nucleation. Recent research on the high-resolution structure of γ-TuRC has brought new insight into the microtubule nucleation mechanism. We discuss the effect of γ-TuRC protein overexpression on cancer cell behavior and new drugs directed to γ-tubulin that may offer a viable alternative to microtubule-targeting agents currently used in cancer chemotherapy.

Abstract

In cells, microtubules typically nucleate from microtubule organizing centers, such as centrosomes. γ-Tubulin, which forms multiprotein complexes, is essential for nucleation. The γ-tubulin ring complex (γ-TuRC) is an efficient microtubule nucleator that requires additional centrosomal proteins for its activation and targeting. Evidence suggests that there is a dysfunction of centrosomal microtubule nucleation in cancer cells. Despite decades of molecular analysis of γ-TuRC and its interacting factors, the mechanisms of microtubule nucleation in normal and cancer cells remains obscure. Here, we review recent work on the high-resolution structure of γ-TuRC, which brings new insight into the mechanism of microtubule nucleation. We discuss the effects of γ-TuRC protein dysregulation on cancer cell behavior and new compounds targeting γ-tubulin. Drugs inhibiting γ-TuRC functions could represent an alternative to microtubule targeting agents in cancer chemotherapy.

Proximity labeling reveals non-centrosomal microtubule-organizing center components required for microtubule growth and localization

Microtubules are polarized intracellular polymers that play key roles in the cell, including in transport, polarity, and cell division. Across eukaryotic cell types, microtubules adopt diverse intracellular organization to accommodate these distinct functions coordinated by specific cellular sites called microtubule-organizing centers (MTOCs). Over 50 years of research on MTOC biology has focused mainly on the centrosome; however, most differentiated cells employ non-centrosomal MTOCs (ncMTOCs) to organize their microtubules into diverse arrays, which are critical to cell function. To identify essential ncMTOC components, we developed the biotin ligase-based, proximity-labeling approach TurboID for use in C. elegans. We identified proteins proximal to the microtubule minus end protein PTRN-1/Patronin at the apical ncMTOC of intestinal epithelial cells, focusing on two conserved proteins: spectraplakin protein VAB-10B/MACF1 and WDR-62, a protein we identify as homologous to vertebrate primary microcephaly disease protein WDR62. VAB-10B and WDR-62 do not associate with the centrosome and instead specifically regulate non-centrosomal microtubules and the apical targeting of microtubule minus-end proteins. Depletion of VAB-10B resulted in microtubule mislocalization and delayed localization of a microtubule nucleation complex ɣ-tubulin ring complex (γ-TuRC), while loss of WDR-62 decreased the number of dynamic microtubules and abolished γ-TuRC localization. This regulation occurs downstream of cell polarity and in conjunction with actin. As this is the first report for non-centrosomal roles of WDR62 family proteins, we expand the basic cell biological roles of this important disease protein. Our studies identify essential ncMTOC components and suggest a division of labor where microtubule growth and localization are distinctly regulated.

CD13 orients the apical-basal polarity axis necessary for lumen formation

Polarized epithelial cells can organize into complex structures with a characteristic central lumen. Lumen formation requires that cells coordinately orient their polarity axis so that the basolateral domain is on the outside and apical domain inside epithelial structures. Here we show that the transmembrane aminopeptidase, CD13, is a key determinant of epithelial polarity orientation. CD13 localizes to the apical membrane and associates with an apical complex with Par6. CD13-deficient cells display inverted polarity in which apical proteins are retained on the outer cell periphery and fail to accumulate at an intercellular apical initiation site. Here we show that CD13 is required to couple apical protein cargo to Rab11-endosomes and for capture of endosomes at the apical initiation site. This role in polarity utilizes the short intracellular domain but is independent of CD13 peptidase activity.

The γ-tubulin meshwork assists in the recruitment of PCNA to chromatin in mammalian cells

Changes in the location of γ-tubulin ensure cell survival and preserve genome integrity. We investigated whether the nuclear accumulation of γ-tubulin facilitates the transport of proliferating cell nuclear antigen (PCNA) between the cytosolic and the nuclear compartment in mammalian cells. We found that the γ-tubulin meshwork assists in the recruitment of PCNA to chromatin. Also, decreased levels of γ-tubulin reduce the nuclear pool of PCNA. In addition, the γ-tubulin C terminus encodes a PCNA-interacting peptide (PIP) motif, and a γ-tubulin–PIP-mutant affects the nuclear accumulation of PCNA. In a cell-free system, PCNA and γ-tubulin formed a complex. In tumors, there is a significant positive correlation between TUBG1 and PCNA expression. Thus, we report a novel mechanism that constitutes the basis for tumor growth by which the γ-tubulin meshwork maintains indefinite proliferation by acting as an opportune scaffold for the transport of PCNA from the cytosol to the chromatin.

Corvaisier et al discover that γ-tubulin and replication protein PCNA forms a complex and that this facilitates recruitment of PCNA to chromatin both during cell division and during the DSB repair response. They identify a PCNA binding motif in γ-tubulin, which when mutated affects replication fork progression, providing insights into the role of the nuclear γ-tubulin meshwork.

Mauve/LYST limits fusion of lysosome-related organelles and promotes centrosomal recruitment of microtubule nucleating proteins

Lysosome-related organelles (LROs) are endosomal compartments carrying tissue-specific proteins, which become enlarged in Chediak-Higashi syndrome (CHS) due to mutations in LYST. Here, we show that Drosophila Mauve, a counterpart of LYST, suppresses vesicle fusion events with lipid droplets (LDs) during the formation of yolk granules (YGs), the LROs of the syncytial embryo, and opposes Rab5, which promotes fusion. Mauve localizes on YGs and at spindle poles, and it co-immunoprecipitates with the LDs' component and microtubule-associated protein Minispindles/Ch-TOG. Minispindles levels are increased at the enlarged YGs and diminished around centrosomes in mauve-derived mutant embryos. This leads to decreased microtubule nucleation from centrosomes, a defect that can be rescued by dominant-negative Rab5. Together, this reveals an unanticipated link between endosomal vesicles and centrosomes. These findings establish Mauve/LYST's role in regulating LRO formation and centrosome behavior, a role that could account for the enlarged LROs and centrosome positioning defects at the immune synapse of CHS patients.

The recycling endosome protein Rab25 coordinates collective cell movements in the zebrafish surface epithelium

In emerging epithelial tissues, cells undergo dramatic rearrangements to promote tissue shape changes. Dividing cells remain interconnected via transient cytokinetic bridges. Bridges are cleaved during abscission and currently, the consequences of disrupting abscission in developing epithelia are not well understood. We show that the Rab GTPase Rab25 localizes near cytokinetic midbodies and likely coordinates abscission through endomembrane trafficking in the epithelium of the zebrafish gastrula during epiboly. In maternal-zygotic Rab25a and Rab25b mutant embryos, morphogenic activity tears open persistent apical cytokinetic bridges that failed to undergo timely abscission. Cytokinesis defects result in anisotropic cell morphologies that are associated with a reduction of contractile actomyosin networks. This slows cell rearrangements and alters the viscoelastic responses of the tissue, all of which likely contribute to delayed epiboly. We present a model in which Rab25 trafficking coordinates cytokinetic bridge abscission and cortical actin density, impacting local cell shape changes and tissue-scale forces.

To nucleate or not, that is the question in neurons

Microtubules are the structural center of neurons, stretching in overlapping arrays from the cell body to the far reaches of axons and dendrites. They also act as the tracks for long-range transport mediated by dynein and kinesin motors. Transcription and most translation take place in the cell body, and newly made cargoes must be shipped from this site of synthesis to sites of function in axons and dendrites. This constant demand for transport means that the microtubule array must be present without gaps throughout the cell over the lifetime of the animal. This task is made slightly easier in many animals by the relatively long, stable microtubules present in neurons. However, even stable neuronal microtubules have ends that are dynamic, and individual microtubules typically last on the order of hours, while the neurons around them last a lifetime. "Birth" of new microtubules is therefore required to maintain the neuronal microtubule array. In this review we discuss the nucleation of new microtubules in axons and dendrites, including how and where they are nucleated. In addition, it is becoming clear that neuronal microtubule nucleation is highly regulated, with unexpected machinery impinging on the decision of whether nucleation sites are active or inactive through space and time.

Importin α phosphorylation promotes TPX2 activation by GM130 to control astral microtubules and spindle orientation

Spindle orientation is important in multiple developmental processes as it determines cell fate and function. The orientation of the spindle depends on the assembly of a proper astral microtubule network. Here, we report that the spindle assembly factor TPX2 regulates astral microtubules. TPX2 in the spindle pole area is activated by GM130 (GOLGA2) on Golgi membranes to promote astral microtubule growth. GM130 relieves TPX2 inhibition by competing for importin α1 (KPNA2) binding. Mitotic phosphorylation of importin α at serine 62 (S62) by CDK1 switches its substrate preference from TPX2 to GM130, thereby enabling competition-based activation. Importin α S62A mutation impedes local TPX2 activation and compromises astral microtubule formation, ultimately resulting in misoriented spindles. Blocking the GM130-importin α-TPX2 pathway impairs astral microtubule growth. Our results reveal a novel role for TPX2 in the organization of astral microtubules. Furthermore, we show that the substrate preference of the important mitotic modulator importin α is regulated by CDK1-mediated phosphorylation.

A centriole's subdistal appendages: contributions to cell division, ciliogenesis and differentiation

The centrosome is a highly conserved structure composed of two centrioles surrounded by pericentriolar material. The mother, and inherently older, centriole has distal and subdistal appendages, whereas the daughter centriole is devoid of these appendage structures. Both appendages have been primarily linked to functions in cilia formation. However, subdistal appendages present with a variety of potential functions that include spindle placement, chromosome alignment, the final stage of cell division (abscission) and potentially cell differentiation. Subdistal appendages are particularly interesting in that they do not always display a conserved ninefold symmetry in appendage organization on the mother centriole across eukaryotic species, unlike distal appendages. In this review, we aim to differentiate both the morphology and role of the distal and subdistal appendages, with a particular focus on subdistal appendages.

Promotion of cancer cell stemness by Ras

Cancer stem cells (CSC) may be the most relevant and elusive cancer cell population, as they have the exquisite ability to seed new tumors. It is plausible, that highly mutated cancer genes, such as KRAS, are functionally associated with processes contributing to the emergence of stemness traits. In this review, we will summarize the evidence for a stemness driving activity of oncogenic Ras. This activity appears to differ by Ras isoform, with the highly mutated KRAS having a particularly profound impact. Next to established stemness pathways such as Wnt and Hedgehog (Hh), the precise, cell cycle dependent orchestration of the MAPK-pathway appears to relay Ras activation in this context. We will examine how non-canonical activities of K-Ras4B (hereafter K-Ras) could be enabled by its trafficking chaperones calmodulin and PDE6D/PDEδ. Both dynamically localize to the cellular machinery that is intimately linked to cell fate decisions, such as the primary cilium and the centrosome. Thus, it can be speculated that oncogenic K-Ras disrupts fundamental polarized signaling and asymmetric apportioning processes that are necessary during cell differentiation.

Cyclin-dependent Kinase 1 and Aurora Kinase choreograph mitotic storage and redistribution of a growth factor receptor

Endosomal trafficking of receptors and associated proteins plays a critical role in signal processing. Until recently, it was thought that trafficking was shut down during cell division. Thus, remarkably, the regulation of trafficking during division remains poorly characterized. Here we delineate the role of mitotic kinases in receptor trafficking during asymmetric division. Targeted perturbations reveal that Cyclin-dependent Kinase 1 (CDK1) and Aurora Kinase promote storage of Fibroblast Growth Factor Receptors (FGFRs) by suppressing endosomal degradation and recycling pathways. As cells progress through metaphase, loss of CDK1 activity permits differential degradation and targeted recycling of stored receptors, leading to asymmetric induction. Mitotic receptor storage, as delineated in this study, may facilitate rapid reestablishment of signaling competence in nascent daughter cells. However, mutations that limit or enhance the release of stored signaling components could alter daughter cell fate or behavior thereby promoting oncogenesis.

This study provides fundamental insights into the crosstalk between cell division and signaling, with implications for cancer. High-resolution in vivo analysis reveals that dividing cells sequester signal receptor proteins into internal compartments; stored receptors are then redistributed as cells complete division.

Rab11a Is Overexpressed in Gastric Cancer and Regulates FAK/AKT Signaling

Dysregulation of Rab11a has been implicated in the progression of several cancers. However, there have been no such studies for human gastric cancers. In the current study, we examined Rab11a protein expression and found it was upregulated in 49 of 108 gastric cancer tissues and correlated with local invasion, nodal metastasis, and advanced stage. Rab11a protein was higher in gastric cancer cell lines than normal gastric cell line. We transfected Rab11a plasmid and siRNA in both MGC803 and AGS cell lines. Rab11a overexpression increased the cell growth rate, colony numbers, and invasion ability in both MGC803 and AGS cell lines. Downregulation of Rab11a using siRNA decreased the cell proliferation rate, colony numbers, and inhibited invasion. Rab11a overexpression also conferred cisplatin resistance. Annexin V/PI staining showed that Rab11a overexpression suppressed cisplatin-induced apoptosis, while Rab11a depletion promoted cell apoptosis. We also showed that Rab11a overexpression maintained mitochondrial membrane potential. Western blot analysis revealed that Rab11a increased protein expression of MMP2, cyclin D1, Bcl-2, p-FAK, and p-AKT, while Rab11a depletion showed the opposite effects. Blockage of FAK using inhibitor downregulated Bcl-2, cyclin D1, MMP2, and p-AKT expression and abolished the effects of Rab11a on these proteins. In summary, our data demonstrated that Rab11a is upregulated in human gastric cancers. Rab11a facilitated cell proliferation and invasion, as well as cisplatin sensitivity and mitochondrial membrane potential, possibly via the FAK/AKT signaling pathway.

Non-Canonical Functions of the Gamma-Tubulin Meshwork in the Regulation of the Nuclear Architecture

Simple Summary

The appearance of a cell is connected to its function. For example, the fusiform of smooth muscle cells is adapted to facilitate muscle contraction, the lobed nucleus in white blood cells assists with the migratory behavior of these immune cells, and the condensed nucleus in sperm aids in their swimming efficiency. Thus, changes in appearance have been used for decades by doctors as a diagnostic method for human cancers. Here, we summarize our knowledge of how a cell maintains the shape of the nuclear compartment. Specifically, we discuss the role of a novel protein meshwork, the gamma-tubulin meshwork, in the regulation of nuclear morphology and as a therapeutic target against cancer.

Abstract

The nuclear architecture describes the organization of the various compartments in the nucleus of eukaryotic cells, where a plethora of processes such as nucleocytoplasmic transport, gene expression, and assembly of ribosomal subunits occur in a dynamic manner. During the different phases of the cell cycle, in post-mitotic cells and after oncogenic transformation, rearrangements of the nuclear architecture take place, and, among other things, these alterations result in reorganization of the chromatin and changes in gene expression. A member of the tubulin family, γtubulin, was first identified as part of a multiprotein complex that allows nucleation of microtubules. However, more than a decade ago, γtubulin was also characterized as a nuclear protein that modulates several crucial processes that affect the architecture of the nucleus. This review presents the latest knowledge regarding changes that arise in the nuclear architecture of healthy cells and under pathological conditions and, more specifically, considers the particular involvement of γtubulin in the modulation of the biology of the nuclear compartment.

Growth cone-localized microtubule organizing center establishes microtubule orientation in dendrites

A polarized arrangement of neuronal microtubule arrays is the foundation of membrane trafficking and subcellular compartmentalization. Conserved among both invertebrates and vertebrates, axons contain exclusively 'plus-end-out' microtubules while dendrites contain a high percentage of 'minus-end-out' microtubules, the origins of which have been a mystery. Here we show that in Caenorhabditis elegans the dendritic growth cone contains a non-centrosomal microtubule organizing center (MTOC), which generates minus-end-out microtubules along outgrowing dendrites and plus-end-out microtubules in the growth cone. RAB-11-positive endosomes accumulate in this region and co-migrate with the microtubule nucleation complex γ-TuRC. The MTOC tracks the extending growth cone by kinesin-1/UNC-116-mediated endosome movements on distal plus-end-out microtubules and dynein clusters this advancing MTOC. Critically, perturbation of the function or localization of the MTOC causes reversed microtubule polarity in dendrites. These findings unveil the endosome-localized dendritic MTOC as a critical organelle for establishing axon-dendrite polarity.

Crumbs, Galla and Xpd are required for Kinesin-5 regulation in mitosis and organ growth in Drosophila

Xeroderma Pigmentosum D (XPD, also known as ERCC2) is a multi-functional protein involved in transcription, DNA repair and chromosome segregation. In Drosophila, Xpd interacts with Crumbs (Crb) and Galla to regulate mitosis during embryogenesis. It is unknown how these proteins are linked to mitosis. Here, we show that Crb, Galla-2 and Xpd regulate nuclear division in the syncytial embryo by interacting with Klp61F, the Drosophila mitotic Kinesin-5 associated with bipolar spindles. Crb, Galla-2 and Xpd physically interact with Klp61F and colocalize to mitotic spindles. Knockdown of any of these proteins results in similar mitotic defects. These phenotypes are restored by overexpression of Klp61F, suggesting that Klp61F is a major effector. Mitotic defects of galla-2 RNAi are suppressed by Xpd overexpression but not vice versa. Depletion of Crb, Galla-2 or Xpd results in a reduction of Klp61F levels. Reducing proteasome function restores Klp61F levels and suppresses mitotic defects caused by knockdown of Crb, Galla-2 or Xpd. Furthermore, eye growth is regulated by Xpd and Klp61F. Hence, we propose that Crb, Galla-2 and Xpd interact to maintain the level of Klp61F during mitosis and organ growth.

Transgelin-2 and phosphoregulation of the LIC2 subunit of dynein govern mitotic spindle orientation

The molecular motor dynein is essential for mitotic spindle orientation, which defines the axis of cell division. The light intermediate chain subunits, LIC1 and LIC2, define biochemically and functionally distinct vertebrate dynein complexes, with LIC2-dynein playing a crucial role in ensuring spindle orientation. We reveal a novel, mitosis-specific interaction of LIC2-dynein with the cortical actin-bundling protein transgelin-2. Transgelin-2 is required for maintaining proper spindle length, equatorial metaphase chromosome alignment, spindle orientation and timely anaphase onset. We show that transgelin-2 stabilizes the cortical recruitment of LGN-NuMA, which together with dynein is required for spindle orientation. The opposing actions of transgelin-2 and LIC2-dynein maintain optimal cortical levels of LGN-NuMA. In addition, we show that the highly conserved serine 194 phosphorylation of LIC2 is required for proper spindle orientation, by maintaining mitotic centrosome integrity to ensure optimal astral microtubule nucleation. The work reveals two specific mechanisms through which LIC2-dynein regulates mitotic spindle orientation; namely, through a new interactor transgelin-2, which is required for engagement of LGN-NuMA with the actin cortex, and through mitotic phosphoregulation of LIC2 to control microtubule nucleation from the poles.This article has an associated First Person interview with the first author of the paper.

Rab11a regulates MMP2 expression by activating the PI3K/AKT pathway in human hepatocellular carcinoma cells

As a member of the Rab GTPase family, Rab11a plays an important role in vesicle transport and tumor progression. However, it is not clear whether it can also be used as an oncoprotein in hepatocellular carcinoma (HCC). In this study, database and immunohistochemical analyses showed that Rab11a was highly expressed in HCC tissues, and associated with poor clinical prognosis. Rab11a overexpression promoted the proliferation, migration, invasion, and anti-apoptosis of human HCC cell lines, MHCC-97H and HCC-LM3, whereas the downregulation of Rab11a inhibited these biological tumor activities. Nude mice xenograft demonstrated that Rab11a had a positive effect on the growth of hepatocellular carcinoma cells in vivo. Further studies found that the PI3K/AKT pathway and matrix metalloproteinase 2 (MMP2) upregulation can be activated by over-expression of Rab11a. However, MMP2 upregulation induced by Rab11a can be inhibited by the PI3K/AKT pathway inhibitor, LY294002. Altogether, our study established for the first time that Rab11a can play a pro-cancer role in HCC, as a novel oncoprotein, by activating the PI3K/AKT pathway to regulate MMP2 expression.

Rab25-Mediated EGFR Recycling Causes Tumor Acquired Radioresistance

Tumor acquired radioresistance remains as the major limit in cancer radiotherapy (RT). Rab25, a receptor recycling protein, has been reported to be enhanced in tumors with aggressive phenotype and chemotherapy resistance. In this study, elevated Rab25 expression was identified in an array of radioresistant human cancer cell lines, in vivo radioresistant xenograft tumors. Clinical investigation confirmed that Rab25 expression was also associated with a worse prognosis in patients with lung adenocarcinoma (LUAD) and nasopharyngeal carcinoma (NPC). Enhanced activities of EGFR were observed in both NPC and LUAD radioresistant cells. Rab25 interacts with EGFR to enhance EGFR recycling to cell surface and to decrease degradation in cytoplasm. Inhibition of Rab25 showed synergized radiosensitivity with reduced aggressive phenotype. This study provides the clinical and experimental evidence that Rab25 is a potential therapeutic target to alleviate the hyperactive EGFR signaling and to prevent RT-acquired tumor resistance in patients with LUAD and NPC.

Endocytic membrane trafficking in the control of centrosome function

Until recently, endocytic trafficking and its regulators were thought to function almost exclusively on membrane-bound organelles and/or vesicles containing a lipid bilayer. Recent studies have demonstrated that endocytic regulatory proteins play much wider roles in trafficking regulation and influence a variety of nonendocytic pathways, including trafficking to/from mitochondria and peroxisomes. Moreover, new studies also suggest that endocytic regulators also control trafficking to and from cellular organelles that lack membranes, such as the centrosome. Although endocytic membrane trafficking (EMT) clearly impacts pathways downstream of the centrosome, such as ciliogenesis (including transport to and from cilia), mitotic spindle formation, and cytokinesis, relatively few studies have focused on the growing role for EMT more directly on centrosome biogenesis, maintenance and control throughout cell cycle, and centrosome duplication. Indeed, a growing number of endocytic regulatory proteins have been implicated in centrosome regulation, including various Rab proteins (among them Rab11) and the leucine-rich repeat kinase 2. In this review, we will examine the relationship between centrosomes and EMT, focusing primarily on how EMT directly influences the centrosome.

Loss of MYO5B expression deregulates late endosome size which hinders mitotic spindle orientation

Recycling endosomes regulate plasma membrane recycling. Recently, recycling endosome–associated proteins have been implicated in the positioning and orientation of the mitotic spindle and cytokinesis. Loss of MYO5B, encoding the recycling endosome–associated myosin Vb, is associated with tumor development and tissue architecture defects in the gastrointestinal tract. Whether loss of MYO5B expression affects mitosis is not known. Here, we demonstrate that loss of MYO5B expression delayed cytokinesis, perturbed mitotic spindle orientation, led to the misorientation of the plane of cell division during the course of mitosis, and resulted in the delamination of epithelial cells. Remarkably, the effects on spindle orientation, but not cytokinesis, were a direct consequence of physical hindrance by giant late endosomes, which were formed in a chloride channel–sensitive manner concomitant with a redistribution of chloride channels from the cell periphery to late endosomes upon loss of MYO5B. Rab7 availability was identified as a limiting factor for the development of giant late endosomes. In accordance, increasing rab7 availability corrected mitotic spindle misorientation and cell delamination in cells lacking MYO5B expression. In conclusion, we identified a novel role for MYO5B in the regulation of late endosome size control and identify the inability to control late endosome size as an unexpected novel mechanism underlying defects in cell division orientation and epithelial architecture.

Loss of the recycling endosome-associated motor protein myosin Vb causes the formation of giant late endo-lysosomes; these in turn hinder the orientation of the mitotic spindle and chromosome segregation. Deregulated endosome size thus hampers faithful cell division.

Centrosomal and ciliary targeting of CCDC66 requires cooperative action of centriolar satellites, microtubules and molecular motors

Mammalian centrosomes and cilia play key roles in many cellular processes and their deregulation is linked to cancer and ciliopathies. Spatiotemporal regulation of their biogenesis and function in response to physiological stimuli requires timely protein targeting. This can occur by different pathways, including microtubule-dependent active transport and via centriolar satellites, which are key regulators of cilia assembly and signaling. How satellites mediate their functions and their relationship with other targeting pathways is currently unclear. To address this, we studied retinal degeneration gene product CCDC66, which localizes to centrosomes, cilia, satellites and microtubules and functions in ciliogenesis. FRAP experiments showed that its centrosomal pool was dynamic and the ciliary pool associated with the ciliary axoneme and was stable. Centrosomal CCDC66 abundance and dynamics required microtubule-dependent active transport and tethering, and was inhibited by sequestration at satellites. Systematic quantitation of satellite dynamics identified only a small fraction to display microtubule-based bimodal motility, consistent with trafficking function. Majority displayed diffusive motility with unimodal persistence, supporting sequestration function. Together, our findings reveal new mechanisms of communication between membrane-less compartments.

A novel, dynein-independent mechanism focuses the endoplasmic reticulum around spindle poles in dividing Drosophila spermatocytes

In dividing animal cells the endoplasmic reticulum (ER) concentrates around the poles of the spindle apparatus by associating with astral microtubules (MTs), and this association is essential for proper ER partitioning to progeny cells. The mechanisms that associate the ER with astral MTs are unknown. Because astral MT minus-ends are anchored by centrosomes at spindle poles, we hypothesized that the MT minus-end motor dynein mediates ER concentration around spindle poles. Live in vivo imaging of Drosophila spermatocytes revealed that dynein is required for ER concentration around centrosomes during late interphase. In marked contrast, however, dynein suppression had no effect on ER association with astral MTs and concentration around spindle poles in early M-phase. In fact, there was a sudden onset of ER association with astral MTs in dynein RNAi cells, revealing activation of an M-phase specific mechanism of ER-MT association. ER redistribution to spindle poles also did not require non-claret disjunctional (ncd), the other known Drosophila MT minus-end motor, nor Klp61F, a MT plus-end motor that generates spindle poleward forces. Collectively, our results suggest that a novel, M-phase specific mechanism of ER-MT association that is independent of MT minus-end motors is required for proper ER partitioning in dividing cells.

A New Look at the Functional Organization of the Golgi Ribbon

A characteristic feature of vertebrate cells is a Golgi ribbon consisting of multiple cisternal stacks connected into a single-copy organelle next to the centrosome. Despite numerous studies, the mechanisms that link the stacks together and the functional significance of ribbon formation remain poorly understood. Nevertheless, these questions are of considerable interest, since there is increasing evidence that Golgi fragmentation – the unlinking of the stacks in the ribbon – is intimately connected not only to normal physiological processes, such as cell division and migration, but also to pathological states, including neurodegeneration and cancer. Challenging a commonly held view that ribbon architecture involves the formation of homotypic tubular bridges between the Golgi stacks, we present an alternative model, based on direct interaction between the biosynthetic (pre-Golgi) and endocytic (post-Golgi) membrane networks and their connection with the centrosome. We propose that the central domains of these permanent pre- and post-Golgi networks function together in the biogenesis and maintenance of the more transient Golgi stacks, and thereby establish “linker compartments” that dynamically join the stacks together. This model provides insight into the reversible fragmentation of the Golgi ribbon that takes place in dividing and migrating cells and its regulation along a cell surface – Golgi – centrosome axis. Moreover, it helps to understand transport pathways that either traverse or bypass the Golgi stacks and the positioning of the Golgi apparatus in differentiated neuronal, epithelial, and muscle cells.

Organelle Inheritance Control of Mitotic Entry and Progression: Implications for Tissue Homeostasis and Disease

The Golgi complex (GC), in addition to its well-known role in membrane traffic, is also actively involved in the regulation of mitotic entry and progression. In particular, during the G2 phase of the cell cycle, the Golgi ribbon is unlinked into isolated stacks. Importantly, this ribbon cleavage is required for G2/M transition, indicating that a "Golgi mitotic checkpoint" controls the correct segregation of this organelle. Then, during mitosis, the isolated Golgi stacks are disassembled, and this process is required for spindle formation. Moreover, recent evidence indicates that also proper mitotic segregation of other organelles, such as mitochondria, endosomes, and peroxisomes, is required for correct mitotic progression and/or spindle formation. Collectively, these observations imply that in addition to the control of chromosomes segregation, which is required to preserve the genetic information, the cells actively monitor the disassembly and redistribution of subcellular organelles in mitosis. Here, we provide an overview of the major structural reorganization of the GC and other organelles during G2/M transition and of their regulatory mechanisms, focusing on novel findings that have shed light on the basic processes that link organelle inheritance to mitotic progression and spindle formation, and discussing their implications for tissue homeostasis and diseases.

NDR2 kinase contributes to cell invasion and cytokinesis defects induced by the inactivation of RASSF1A tumor-suppressor gene in lung cancer cells

Background

RASSF1A, a tumor suppressor gene, is frequently inactivated in lung cancer leading to a YAP-dependent epithelial-mesenchymal transition (EMT). Such effects are partly due to the inactivation of the anti-migratory RhoB GTPase via the inhibitory phosphorylation of GEF-H1, the GDP/GTP exchange factor for RhoB. However, the kinase responsible for RhoB/GEF-H1 inactivation in RASSF1A-depleted cells remained unknown.

Methods

NDR1/2 inactivation by siRNA or shRNA effects on epithelial-mesenchymal transition, invasion, xenograft formation and growth in SCID−/− Beige mice, apoptosis, proliferation, cytokinesis, YAP/TAZ activation were investigated upon RASSF1A loss in human bronchial epithelial cells (HBEC).

Results

We demonstrate here that depletion of the YAP-kinases NDR1/2 reverts migration and metastatic properties upon RASSF1A loss in HBEC. We show that NDR2 interacts directly with GEF-H1 (which contains the NDR phosphorylation consensus motif HXRXXS/T), leading to GEF-H1 phosphorylation. We further report that the RASSF1A/NDR2/GEF-H1/RhoB/YAP axis is involved in proper cytokinesis in human bronchial cells, since chromosome proper segregation are NDR-dependent upon RASSF1A or GEF-H1 loss in HBEC.

Conclusion

To summarize, our data support a model in which, upon RASSF1A silencing, NDR2 gets activated, phosphorylates and inactivates GEF-H1, leading to RhoB inactivation. This cascade induced by RASSF1A loss in bronchial cells is responsible for metastasis properties, YAP activation and cytokinesis defects.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1145-8) contains supplementary material, which is available to authorized users.

Microtubular and Nuclear Functions of γ-Tubulin: Are They LINCed?

γ-Tubulin is a conserved member of the tubulin superfamily with a function in microtubule nucleation. Proteins of γ-tubulin complexes serve as nucleation templates as well as a majority of other proteins contributing to centrosomal and non-centrosomal nucleation, conserved across eukaryotes. There is a growing amount of evidence of γ-tubulin functions besides microtubule nucleation in transcription, DNA damage response, chromatin remodeling, and on its interactions with tumor suppressors. However, the molecular mechanisms are not well understood. Furthermore, interactions with lamin and SUN proteins of the LINC complex suggest the role of γ-tubulin in the coupling of nuclear organization with cytoskeletons. γ-Tubulin that belongs to the clade of eukaryotic tubulins shows characteristics of both prokaryotic and eukaryotic tubulins. Both human and plant γ-tubulins preserve the ability of prokaryotic tubulins to assemble filaments and higher-order fibrillar networks. γ-Tubulin filaments, with bundling and aggregating capacity, are suggested to perform complex scaffolding and sequestration functions. In this review, we discuss a plethora of γ-tubulin molecular interactions and cellular functions, as well as recent advances in understanding the molecular mechanisms behind them.

γ-Tubulin⁻γ-Tubulin Interactions as the Basis for the Formation of a Meshwork

In cytoplasm, protein γ-tubulin joins with various γ-tubulin complex proteins (GCPs) to form a heterotetramer γ-tubulin small complex (γ-TuSC) that can grow into a ring-shaped structure called the γ-tubulin ring complex (γ-TuRC). Both γ-TuSC and γ-TuRC are required for microtubule nucleation. Recent knowledge on γ-tubulin with regard to its cellular functions beyond participation in its creation of microtubules suggests that this protein forms a cellular meshwork. The present review summarizes the recognized functions of γ-tubulin and aims to unite the current views on this protein.

γ-tubulin as a signal-transducing molecule and meshwork with therapeutic potential

Knowledge of γ-tubulin is increasing with regard to the cellular functions of this protein beyond its participation in microtubule nucleation. γ-Tubulin expression is altered in various malignancies, and changes in the TUBG1 gene have been found in patients suffering from brain malformations. This review recapitulates the known functions of γ-tubulin in cellular homeostasis and discusses the possible influence of the protein on disease development and cancer.

Vesicular trafficking plays a role in centriole disengagement and duplication

Centrosomes are the major microtubule-nucleating and microtubule-organizing centers of cells and play crucial roles in microtubule anchoring, organelle positioning, and ciliogenesis. At the centrosome core lies a tightly associated or “engaged” mother–daughter centriole pair.  During mitotic exit, removal of centrosomal proteins pericentrin and Cep215 promotes “disengagement” by the dissolution of intercentriolar linkers, ensuring a single centriole duplication event per cell cycle.  Herein, we explore a new mechanism involving vesicular trafficking for the removal of centrosomal Cep215. Using small interfering RNA and CRISPR/Cas9 gene-edited cells, we show that the endocytic protein EHD1 regulates Cep215 transport from centrosomes to the spindle midbody, thus facilitating disengagement and duplication. We demonstrate that EHD1 and Cep215 interact and show that Cep215 displays increased localization to vesicles containing EHD1 during mitosis. Moreover, Cep215-containing vesicles are positive for internalized transferrin, demonstrating their endocytic origin. Thus, we describe a novel relationship between endocytic trafficking and the centrosome cycle, whereby vesicles of endocytic origin are used to remove key regulatory proteins from centrosomes to control centriole duplication.

Kinesin-2 Controls the Motility of RAB5 Endosomes and Their Association with the Spindle in Mitosis

RAB5 is a small GTPase that belongs to the wide family of Rab proteins and localizes on early endosomes. In its active GTP-bound form, RAB5 recruits downstream effectors that, in turn, are responsible for distinct aspects of early endosome function, including their movement along microtubules. We previously reported that, at the onset of mitosis, RAB5positive vesicles cluster around the spindle poles and, during metaphase, move along spindle microtubules. RNAi-mediated depletion of the three RAB5 isoforms delays nuclear envelope breakdown at prophase and severely affects chromosome alignment and segregation. Here we show that depletion of the Kinesin-2 motor complex impairs long-range movement of RAB5 endosomes in interphase cells and prevents localization of these vesicles at the spindle during metaphase. Similarly to the effect caused by RAB5 depletion, functional ablation of Kinesin-2 delays nuclear envelope breakdown resulting in prolonged prophase. Altogether these findings suggest that endosomal transport at the onset of mitosis is required to control timing of nuclear envelope breakdown.

Primary Cilia Reconsidered in the Context of Ciliopathies: Extraciliary and Ciliary Functions of Cilia Proteins Converge on a Polarity theme?

Once dismissed as vestigial organelles, primary cilia have garnered the interest of scientists, given their importance in development/signaling, and for their implication in a new disease category known as ciliopathies. However, many, if not all, "cilia" proteins also have locations/functions outside of the primary cilium. These extraciliary functions can complicate the interpretation of a particular ciliopathy phenotype: it may be a result of defects at the cilium and/or at extraciliary locations, and it could be broadly related to a unifying cellular process for these proteins, such as polarity. Assembly of a cilium has many similarities to the development of other polarized structures. This evolutionarily preserved process for the assembly of polarized cell structures offers a perspective on how the cilium may have evolved. We hypothesize that cilia proteins are critical for cell polarity, and that core polarity proteins may have been specialized to form various cellular protrusions, including primary cilia.

Rab11 Functions as an Oncoprotein via Nuclear Factor kappa B (NF-κB) Signaling Pathway in Human Bladder Carcinoma

Background

Elevated expression of Rab11 has been reported in different human cancers, including human bladder carcinoma. This study, we investigated the biological effects and mechanism of Rab11 overexpression in human bladder carcinoma for the first time.

Material/Methods

Rab11 expression in bladder cancer tissues was detected using immunohistochemistry and Western blot analysis. Then, Rab11 expression was inhibited in T24 cells and it was overexpressed in BIU-87 cells. The effects of Rab11 perturbations on cell growth rate and invasion were analyzed by CCK8, cell cycle assay, and matrix gel invasion assay. MMP-9, cyclin E, and cyclin D1 levels were studied using Western blot and qPCR. NF-κB activity was studied by luciferase assay.

Results

High expression of Rab11 was detected in 41.5% (66/159) of tumor specimens. We found a significant correlation between high Rab11 expression and depth of tumor invasion (P=0.004). Rab11 overexpression was observed to promote the growth rate and invasiveness of cancer cells through upregulation of MMP9, cyclin E, and cyclin D1 levels. Rab11 overexpression further elevated NF-κB reporter activity and enhanced p-IκB expression. Use of BAY 11-7082, a noted NF-κB inhibitor, partially abolished overexpression of MMP9 and cyclin D1 by Rab11.

Conclusions

Our research proved that high Rab11 expression enhances cellular multiplication and invasiveness of bladder cancer, possibly by regulating the NF-κB signaling pathway.