Clues to CD2-associated protein involvement in cytokinesis

Hepatitis C virus alters the morphology and function of peroxisomes

Despite the introduction of effective treatments for hepatitis C in clinics, issues remain regarding the liver disease induced by chronic hepatitis C virus (HCV) infection. HCV is known to disturb the metabolism of infected cells, especially lipid metabolism and redox balance, but the mechanisms leading to HCV-induced pathogenesis are still poorly understood. In an APEX2-based proximity biotinylation screen, we identified ACBD5, a peroxisome membrane protein, as located in the vicinity of HCV replication complexes. Confocal microscopy confirmed the relocation of peroxisomes near HCV replication complexes and indicated that their morphology and number are altered in approximately 30% of infected Huh-7 cells. Peroxisomes are small versatile organelles involved among other functions in lipid metabolism and ROS regulation. To determine their importance in the HCV life cycle, we generated Huh-7 cells devoid of peroxisomes by inactivating the PEX5 and PEX3 genes using CRISPR/Cas9 and found that the absence of peroxisomes had no impact on replication kinetics or infectious titers of HCV strains JFH1 and DBN3a. The impact of HCV on peroxisomal functions was assessed using sub-genomic replicons. An increase of ROS was measured in peroxisomes of replicon-containing cells, correlated with a significant decrease of catalase activity with the DBN3a strain. In contrast, HCV replication had little to no impact on cytoplasmic and mitochondrial ROS, suggesting that the redox balance of peroxisomes is specifically impaired in cells replicating HCV. Our study provides evidence that peroxisome function and morphology are altered in HCV-infected cells.

In silico analysis revealed the potential circRNA-miRNA-mRNA regulative network of non-small cell lung cancer (NSCLC)

BACKGROUND

The primary source of death in the world is non-small cell lung cancer (NSCLC). However, NSCLCs pathophysiology is still not completely understood. The current work sought to study the differential expression of mRNAs involved in NSCLC and their interactions with miRNAs and circRNAs.

METHODS

We utilized three microarray datasets (GSE21933, GSE27262, and GSE33532) from the GEO NCBI database to identify the differentially expressed genes (DEGs) in NSCLC. We employed DAVID Functional annotation tool to investigate the underlying GO biological process, molecular functions, and KEGG pathways involved in NSCLC. We performed the Protein-protein interaction (PPI) network, MCODE, and CytoHubba analysis from Cytoscape software to identify the significant DEGs in NSCLC. We utilized miRnet to anticipate and build interaction between miRNAs and mRNAs in NSCLC and ENCORI to predict the miRNA-circRNA relationships and build the ceRNA regulatory network. Finally, we executed the gene expression and Kaplan-Meier survival analysis to validate the significant DEGs in the ceRNA network utilizing TCGA NSCLC and GEPIA data.

RESULTS

We revealed a total of 156 overlapped DEGs (47 upregulated and 109 downregulated genes) in NSCLC. The PPI network, MCODE, and CytoHubba analysis revealed 12 hub genes (cdkn3, rrm2, ccnb1, aurka, nuf2, tyms, kif11, hmmr, ccnb2, nek2, anln, and birc5) that are associated with NSCLC. We identified that these 12 genes encode 12 mRNAs that are strongly linked with 8 miRNAs, and further, we revealed that 1 circRNA was associated with this 5 miRNA. We constructed the ceRNAs network that contained 1circRNA-5miRNAs-7mRNAs. The expression of these seven significant genes in LUAD & LUSC (NSCLC) was considerably higher in the TCGA database than in normal tissues. Kaplan-Meier survival plot reveals that increased expression of these hub genes was related to a poor survival rate in LUAD.

CONCLUSION

Overall, we developed a circRNA-miRNA-mRNA regulation network to study the probable mechanism of NSCLC.

Lipid Polarization during Cytokinesis

The plasma membrane of eukaryotic cells is composed of a large number of lipid species that are laterally segregated into functional domains as well as asymmetrically distributed between the outer and inner leaflets. Additionally, the spatial distribution and organization of these lipids dramatically change in response to various cellular states, such as cell division, differentiation, and apoptosis. Division of one cell into two daughter cells is one of the most fundamental requirements for the sustenance of growth in all living organisms. The successful completion of cytokinesis, the final stage of cell division, is critically dependent on the spatial distribution and organization of specific lipids. In this review, we discuss the properties of various lipid species associated with cytokinesis and the mechanisms involved in their polarization, including forward trafficking, endocytic recycling, local synthesis, and cortical flow models. The differences in lipid species requirements and distribution in mitotic vs. male meiotic cells will be discussed. We will concentrate on sphingolipids and phosphatidylinositols because their transbilayer organization and movement may be linked via the cytoskeleton and thus critically regulate various steps of cytokinesis.

An anillin-CIN85-SEPT9 complex promotes intercellular bridge maturation required for successful cytokinesis

Cleavage of one cell into two is the most dramatic event in the life of a cell. Plasma membrane fission occurs within a narrow intercellular bridge (ICB) between the daughter cells, but the mechanisms underlying ICB formation and maturation are poorly understood. Here we identify CIN85 as an ICB assembly factor and demonstrate its requirement for robust and timely cytokinesis. CIN85 interacts directly with the N-terminal region of anillin and SEPT9 and thereby facilitates SEPT9-containing filament localization to the plasma membrane of the ICB. In contrast, the C-terminal pleckstrin homology (PH) domain of anillin binds to septin units lacking SEPT9 but enriched in SEPT11. Anillin's interactions with distinct septin units are required to promote ICB elongation and maturation that, we propose, generate the physical space into which the abscission machinery is recruited to drive the final membrane scission event releasing two independent daughter cells.

Revisiting the multisite phosphorylation that produces the M-phase supershift of key mitotic regulators

The term M-phase supershift denotes the phosphorylation-dependent substantial increase in the apparent molecular weight of numerous proteins of varied biological functions during M-phase induction. Although the M-phase supershift of multiple key mitotic regulators has been attributed to the multisite phosphorylation catalyzed by the Cdk1/cyclin B/Cks complex, this view is challenged by multiple lines of paradoxical observations. To solve this problem, we reconstituted the M-phase supershift of Xenopus Cdc25C, Myt1, Wee1A, APC3 and Greatwall in Xenopus egg extracts and characterized the supershift-producing phosphorylations. Our results demonstrate that their M-phase supershifts are each due to simultaneous phosphorylation of a considerable portion of S/T/Y residues in a long intrinsically disordered region that is enriched in both S/T residues and S/TP motifs. Although the major mitotic kinases in Xenopus egg extracts, Cdk1, MAPK, Plx1 and RSK2, are able to phosphorylate the five mitotic regulators, they are neither sufficient nor required to produce the M-phase supershift. Accordingly, inhibition of the four major mitotic kinase activities in Xenopus oocytes did not inhibit the M-phase supershift in okadaic acid-induced oocyte maturation. These findings indicate that the M-phase supershift is produced by a previously unrecognized category of mitotic phosphorylation that likely plays important roles in M-phase induction.

Maternal age affects equine day 8 embryo gene expression both in trophoblast and inner cell mass

BACKGROUND

Breeding a mare until she is not fertile or even until her death is common in equine industry but the fertility decreases as the mare age increases. Embryo loss due to reduced embryo quality is partly accountable for this observation. Here, the effect of mare's age on blastocysts' gene expression was explored. Day 8 post-ovulation embryos were collected from multiparous young (YM, 6-year-old, N = 5) and older (OM, > 10-year-old, N = 6) non-nursing Saddlebred mares, inseminated with the semen of one stallion. Pure or inner cell mass (ICM) enriched trophoblast, obtained by embryo bisection, were RNA sequenced. Deconvolution algorithm was used to discriminate gene expression in the ICM from that in the trophoblast. Differential expression was analyzed with embryo sex and diameter as cofactors. Functional annotation and classification of differentially expressed genes and gene set enrichment analysis were also performed.

RESULTS

Maternal aging did not affect embryo recovery rate, embryo diameter nor total RNA quantity. In both compartments, the expression of genes involved in mitochondria and protein metabolism were disturbed by maternal age, although more genes were affected in the ICM. Mitosis, signaling and adhesion pathways and embryo development were decreased in the ICM of embryos from old mares. In trophoblast, ion movement pathways were affected.

CONCLUSIONS

This is the first study showing that maternal age affects gene expression in the equine blastocyst, demonstrating significant effects as early as 10 years of age. These perturbations may affect further embryo development and contribute to decreased fertility due to aging.

Anillin is an emerging regulator of tumorigenesis, acting as a cortical cytoskeletal scaffold and a nuclear modulator of cancer cell differentiation

Remodeling of the intracellular cytoskeleton plays a key role in accelerating tumor growth and metastasis. Targeting different cytoskeletal elements is important for existing and future anticancer therapies. Anillin is a unique scaffolding protein that interacts with major cytoskeletal structures, e.g., actin filaments, microtubules and septin polymers. A well-studied function of this scaffolding protein is the regulation of cytokinesis at the completion of cell division. Emerging evidence suggest that anillin has other important activities in non-dividing cells, including control of intercellular adhesions and cell motility. Anillin is markedly overexpressed in different solid cancers and its high expression is commonly associated with poor prognosis of patient survival. This review article summarizes rapidly accumulating evidence that implicates anillin in the regulation of tumor growth and metastasis. We focus on molecular and cellular mechanisms of anillin-dependent tumorigenesis that include both canonical control of cytokinesis and novel poorly understood functions as a nuclear regulator of the transcriptional reprogramming and phenotypic plasticity of cancer cells.

CD2AP links actin to PI3 kinase activity to extend epithelial cell height and constrain cell area

Epithelial cells are categorized as cuboidal versus squamous based on the height of the lateral membrane. Wang and Brieher show that CD2AP links PI3K activity to actin assembly to extend the height of the lateral membrane.

Maintaining the correct ratio of apical, basal, and lateral membrane domains is important for epithelial physiology. Here, we show that CD2AP is a critical determinant of epithelial membrane proportions. Depletion of CD2AP or phosphoinositide 3-kinase (PI3K) inhibition results in loss of F-actin and expansion of apical–basal domains, which comes at the expense of lateral membrane height in MDCK cells. We demonstrate that the SH3 domains of CD2AP bind to PI3K and are necessary for PI3K activity along lateral membranes and constraining cell area. Tethering the SH3 domains of CD2AP or p110γ to the membrane is sufficient to rescue CD2AP-knockdown phenotypes. CD2AP and PI3K are both upstream and downstream of actin polymerization. Since CD2AP binds to both actin filaments and PI3K, CD2AP might bridge actin assembly to PI3K activation to form a positive feedback loop to support lateral membrane extension. Our results provide insight into the squamous to cuboidal to columnar epithelial transitions seen in complex epithelial tissues in vivo.

Role of Anillin in Tumour: From a Prognostic Biomarker to a Novel Target

Anillin (ANLN), an actin-binding protein, reportedly plays a vital role in cell proliferation and migration, particularly in cytokinesis. Although there have been findings pointing to a contribution of ANLN to the development of cancer, the association of ANLN to cancer remains not fully understood. Here, we gather evidence to determine the applicability of ANLN as a prognostic tool for some types of cancer, and the impact that ANLN has on the hallmarks of cancer. We searched academic repositories including PubMed and Google Scholar to find and review studies related to cancer and ANLN. The conclusion is that ANLN could be a potent target for cancer treatment, but the roles ANLN, other than in cytokinesis and its influence on tumour microenvironment remodeling in cancer development, must be further elucidated, and specific ANLN inhibitors should be found.

"Amyloid-beta accumulation cycle" as a prevention and/or therapy target for Alzheimer's disease

The cell cycle and its regulators are validated targets for cancer drugs. Reagents that target cells in a specific cell cycle phase (e.g., antimitotics or DNA synthesis inhibitors/replication stress inducers) have demonstrated success as broad-spectrum anticancer drugs. Cyclin-dependent kinases (CDKs) are drivers of cell cycle transitions. A CDK inhibitor, flavopiridol/alvocidib, is an FDA-approved drug for acute myeloid leukemia. Alzheimer's disease (AD) is another serious issue in contemporary medicine. The cause of AD remains elusive, although a critical role of latent amyloid-beta accumulation has emerged. Existing AD drug research and development targets include amyloid, amyloid metabolism/catabolism, tau, inflammation, cholesterol, the cholinergic system, and other neurotransmitters. However, none have been validated as therapeutically effective targets. Recent reports from AD-omics and preclinical animal models provided data supporting the long-standing notion that cell cycle progression and/or mitosis may be a valid target for AD prevention and/or therapy. This review will summarize the recent developments in AD research: (a) Mitotic re-entry, leading to the "amyloid-beta accumulation cycle," may be a prerequisite for amyloid-beta accumulation and AD pathology development; (b) AD-associated pathogens can cause cell cycle errors; (c) thirteen among 37 human AD genetic risk genes may be functionally involved in the cell cycle and/or mitosis; and (d) preclinical AD mouse models treated with CDK inhibitor showed improvements in cognitive/behavioral symptoms. If the "amyloid-beta accumulation cycle is an AD drug target" concept is proven, repurposing of cancer drugs may emerge as a new, fast-track approach for AD management in the clinic setting.

CD2AP inhibits metastasis in gastric cancer by promoting cellular adhesion and cytoskeleton assembly

Diffuse gastric cancer (DGC) is a lethal malignancy lacking effective systemic therapy. Among the most provocative recent results in DGC has been that the alter of the cellular cytoskeleton and intercellular adhesion. CD2‐associated protein (CD2AP) is one of the critical proteins regulating cytoskeleton assembly and intercellular adhesion. However, no study has investigated the expression and biological significance of CD2AP in gastric cancer (GC) to date. Therefore, the aim of our study was to explore if the expression of CD2AP is associated with any clinical features of GC and to elucidate the underlying mechanism. Immunohistochemistry of 620 patient tissue samples indicated that the expression of CD2AP is downregulated in DGC. Moreover, a low CD2AP level was indicative of poor patient prognosis. In vitro, forced expression of CD2AP caused a significant decrease in the migration and invasion of GC cells, whereas depletion of CD2AP had the opposite effect. Immunofluorescence analysis indicated that CD2AP promoted cellular adhesion and influenced cell cytoskeleton assembly via interaction with the F‐actin capping protein CAPZA1. Overall, the upregulation of CD2AP could attenuate GC metastasis, suggesting CD2AP as a novel biomarker for the prognosis and treatment of patients with GC.

Systematic construction and validation of an immune prognostic model for lung adenocarcinoma

Lung adenocarcinoma (LUAD), the most common non‐small‐cell lung cancer, is characterized by a dense lymphocytic infiltrate, which indicates that the immune system plays an active role in the development and growth of this cancer. However, no investigations to date have proposed robust models for predicting survival outcome for patients with LUAD in terms of tumour immunology. A total of 761 LUAD patients were included in this study, in which the database of The Cancer Genome Atlas (TCGA) was utilized for discovery, and the Gene Expression Omnibus (GEO) database was utilized for validation. Bioinformatics analysis and R language tools were utilized to construct an immune prognostic model and annotate biological functions. Lung adenocarcinoma showed a weakened immune phenotype compared with adjacent normal tissues. Immune‐related gene sets were profiled, an immune prognostic model based on 2 immune genes (ANLN and F2) was developed with the TCGA database to distinguish cases as having a low or high risk of unfavourable prognosis, and the model was verified with the GEO database. The model was prognostically significant in stratified cohorts, including stage I‐II, stage III‐IV and epidermal growth factor receptor (EGFR) mutant subsets, and was considered to be an independent prognostic factor for LUAD. Furthermore, the low‐ and high‐risk groups showed marked differences in tumour‐infiltrating leucocytes, tumour mutation burden, aneuploidy and PD‐L1 expression. In conclusion, an immune prognostic model was proposed for LUAD that is capable of independently identifying patients at high risk for poor survival, suggesting a relationship between local immune status and prognosis.

Endo-lysosomal dysregulations and late-onset Alzheimer's disease: impact of genetic risk factors

Increasing evidence supports that cellular dysregulations in the degradative routes contribute to the initiation and progression of neurodegenerative diseases, including Alzheimer's disease. Autophagy and endolysosomal homeostasis need to be maintained throughout life as they are major cellular mechanisms involved in both the production of toxic amyloid peptides and the clearance of misfolded or aggregated proteins. As such, alterations in endolysosomal and autophagic flux, as a measure of degradation activity in these routes or compartments, may directly impact as well on disease-related mechanisms such as amyloid-β clearance through the blood-brain-barrier and the interneuronal spreading of amyloid-β and/or Tau seeds, affecting synaptic function, plasticity and metabolism. The emerging of several genetic risk factors for late-onset Alzheimer's disease that are functionally related to endocytic transport regulation, including cholesterol metabolism and clearance, supports the notion that in particular the autophagy/lysosomal flux might become more vulnerable during ageing thereby contributing to disease onset. In this review we discuss our current knowledge of the risk genes APOE4, BIN1, CD2AP, PICALM, PLD3 and TREM2 and their impact on endolysosomal (dys)regulations in the light of late-onset Alzheimer's disease pathology.

Identification of ANLN as a new likely pathogenic gene of branchio-otic syndrome in a three-generation Chinese family

BACKGROUND

Branchio-oto-renal (BOR) syndrome is one of the most common autosomal dominant hearing loss syndromes and features clinical and genetic heterogeneity. When there is no renal deformity, this disease can also be called branchio-otic (BO) syndrome. Though many genes have been reported, there are still many BO syndrome-related genes to be identified. To identify a hitherto unknown candidate gene causing BO syndrome in a three-generation Chinese family, clinical, genetic, and functional analyses were employed.

METHODS

Whole-exome sequencing (WES) was conducted in three affected family members and two unaffected family members. PCR-Sanger sequencing was performed in all of the family members for segregation analysis and verification of the candidate variants. PCR-Sanger sequencing was also employed in 150 healthy people to examine the variants. In silico analysis was used to predict possible changes in the protein structure that may affect the phenotype.

RESULTS

We identified a heterozygous missense variant in ANLN: NM_018685.4: c.G1105A; NP_061155.2: p.G369R that segregated in the pedigree with an autosomal dominant pattern. No variant was found in the 150 controls and normal family members at this site. The variant c.G1105A was located in a highly conserved F-actin binding site. The amino acid residue at position 369 in the ANLN protein was highly conserved across different species.

CONCLUSION

In this study, we identified, for the first time, a heterozygous missense variant in ANLN (NM_018685.4: c.G1105A; NP_061155.2: p.G369R) that is likely to be a candidate causative gene of BO syndrome in a specific Chinese family.

Stem Cells as Potential Targets of Polyphenols in Multiple Sclerosis and Alzheimer's Disease

Alzheimer's disease (AD) and multiple sclerosis are major neurodegenerative diseases, which are characterized by the accumulation of abnormal pathogenic proteins due to oxidative stress, mitochondrial dysfunction, impaired autophagy, and pathogens, leading to neurodegeneration and behavioral deficits. Herein, we reviewed the utility of plant polyphenols in regulating proliferation and differentiation of stem cells for inducing brain self-repair in AD and multiple sclerosis. Firstly, we discussed the genetic, physiological, and environmental factors involved in the pathophysiology of both the disorders. Next, we reviewed various stem cell therapies available and how they have proved useful in animal models of AD and multiple sclerosis. Lastly, we discussed how polyphenols utilize the potential of stem cells, either complementing their therapeutic effects or stimulating endogenous and exogenous neurogenesis, against these diseases. We suggest that polyphenols could be a potential candidate for stem cell therapy against neurodegenerative disorders.

Identification and characterisation of a Theileria annulata proline-rich microtubule and SH3 domain-interacting protein (TaMISHIP) that forms a complex with CLASP1, EB1, and CD2AP at the schizont surface

Theileria annulata is an apicomplexan parasite that modifies the phenotype of its host cell completely, inducing uncontrolled proliferation, resistance to apoptosis, and increased invasiveness. The infected cell thus resembles a cancer cell, and changes to various host cell signalling pathways accompany transformation. Most of the molecular mechanisms leading to Theileria-induced immortalization of leukocytes remain unknown. The parasite dissolves the surrounding host cell membrane soon after invasion and starts interacting with host proteins, ensuring its propagation by stably associating with the host cell microtubule network. By using BioID technology together with fluorescence microscopy and co-immunoprecipitation, we identified a CLASP1/CD2AP/EB1-containing protein complex that surrounds the schizont throughout the host cell cycle and integrates bovine adaptor proteins (CIN85, 14-3-3 epsilon, and ASAP1). This complex also includes the schizont membrane protein Ta-p104 together with a novel secreted T. annulata protein (encoded by TA20980), which we term microtubule and SH3 domain-interacting protein (TaMISHIP). TaMISHIP localises to the schizont surface and contains a functional EB1-binding SxIP motif, as well as functional SH3 domain-binding Px(P/A)xPR motifs that mediate its interaction with CD2AP. Upon overexpression in non-infected bovine macrophages, TaMISHIP causes binucleation, potentially indicative of a role in cytokinesis.

Prognostic significance of ANLN in lung adenocarcinoma

Anillin actin binding protein (ANLN) is a biomarker of cancer progression and is overexpressed in lung adenocarcinoma. The aim of the present study was to investigate the role of ANLN protein and RNA in the development of lung adenocarcinoma. The ANLN protein sequence was downloaded from The National Centre for Biotechnology information, RNA sequencing (RNA-seq) data was obtained from The Cancer Genome Atlas database. All immunohistochemical staining pictures were adapted from the Human Protein Atlas. PyMOL software was employed to predict protein functional changes in response to mutations. Gene Set Enrichments Analysis was employed for pathway analysis. The results indicated that ANLN experiences genetic change and overexpression at the RNA and protein levels in patients with lung adenocarcinoma. Kaplan-Meier survival curve analysis revealed significant differences between high and low RNA-seq expression levels in ANLN, and patients exhibiting higher expression of ANLN had a relatively poor prognosis. Pathway analysis demonstrated that ANLN was involved in developmental processes via the regulation of nuclear division' pathway. In conclusion, ANLN has potential for use as a diagnostic and prognostic biomarker to diagnoseand predict the outcome of lung adenocarcinoma.

Cytokinesis requires localized β-actin filament production by an actin isoform specific nucleator

Cytokinesis is initiated by the localized assembly of the contractile ring, a dynamic actomyosin structure that generates a membrane furrow between the segregating chromosomal masses to divide a cell into two. Here we show that the stabilization and organization of the cytokinetic furrow is specifically dependent on localized β-actin filament assembly at the site of cytokinesis. β-actin filaments are assembled directly at the furrow by an anillin-dependent pathway that enhances RhoA-dependent activation of the formin DIAPH3, an actin nucleator. DIAPH3 specifically generates homopolymeric filaments of β-actin in vitro. By employing enhancers and activators, cells can achieve acute spatio-temporal control over isoform-specific actin arrays that are required for distinct cellular functions.

Cytokinesis is initiated by the localized assembly of the contractile ring. Here the authors show that the stabilization and organization of the cytokinetic furrow requires localized β-actin filament assembly at the site of cytokinesis by an actin isoform specific nucleator.

Genetics of Alzheimer's disease: From pathogenesis to clinical usage

Alzheimer's disease (AD) is the most common type of dementia and has caused a major global health concern. Understanding the etiology of AD can be beneficial for the diagnosis and intervention of this disease. Genetics plays a vital role in the pathogenesis of AD. Research methods in genetics such as the linkage analysis, study of candidate genes, genome-wide association study (GWAS), and next-generation sequencing (NGS) technology help us map the genetic information in AD, which can not only provide a new insight into the pathogenesis of AD but also be beneficial for early targeted intervention of AD. This review summarizes the pathogenesis as well as the diagnostic and therapeutic value of genetics in AD.

Tumor susceptibility gene 101 regulates predisposition to apoptosis via ESCRT machinery accessory proteins

ESCRT proteins are implicated in myriad cellular processes, including endosome formation, fusion of autophagosomes/amphisomes with lysosomes, and apoptosis. The role played by these proteins in either facilitating or protecting against apoptosis is unclear. In this study, while trying to understand how deficiency of Mahogunin RING finger 1 (MGRN1) affects cell viability, we uncovered a novel role for its interactor, the ESCRT-I protein TSG101: it directly participates in mitigating ER stress-mediated apoptosis. The association of TSG101 with ALIX prevents predisposition to apoptosis, whereas ALIX-ALG-2 interaction favors a death phenotype. Altered Ca2+ homeostasis in cells and a simultaneous increase in the protein levels of ALIX and ALG-2 are required to elicit apoptosis by activating ER stress-associated caspase 4/12. We further demonstrate that in the presence of membrane-associated, disease-causing prion protein CtmPrP, increased ALIX and ALG-2 levels are detected along with ER stress markers and associated caspases in transgenic brain lysates and cells. These effects were rescued by overexpression of TSG101. This is significant because MGRN1 deficiency is closely associated with neurodegeneration and prenatal and neonatal mortality, which could be due to excess cell death in selected brain regions or myocardial apoptosis during embryonic development.

Endothelial CD2AP Binds the Receptor ICAM-1 To Control Mechanosignaling, Leukocyte Adhesion, and the Route of Leukocyte Diapedesis In Vitro

Inflammation is driven by excessive transmigration (diapedesis) of leukocytes from the blood to the tissue across the endothelial cell monolayer that lines blood vessels. Leukocyte adhesion, crawling, and transmigration are regulated by clustering of the endothelial mechanosensitive receptor intercellular adhesion molecule-1 (ICAM-1). Whereas several proteins are known to promote ICAM-1 function, the molecular mechanisms that limit ICAM-1-mediated adhesion to prevent excessive leukocyte transmigration remain unknown. We identify the endothelial actin-binding protein CD2-associated protein (CD2AP) as a novel interaction partner of ICAM-1. Loss of CD2AP stimulates the dynamics of ICAM-1 clustering, which facilitates the formation of ICAM-1 complexes on the endothelial cell surface. Consequently, neutrophil adhesion is increased, but crawling is decreased. In turn, this promotes the neutrophil preference for the transcellular over the paracellular transmigration route. Mechanistically, CD2AP is required for mechanosensitive ICAM-1 downstream signaling toward activation of the PI3K, and recruitment of F-actin and of the actin-branching protein cortactin. Moreover, CD2AP is necessary for ICAM-1-induced Rac1 recruitment and activation. Mechanical force applied on ICAM-1 impairs CD2AP binding to ICAM-1, suggesting that a tension-induced negative feedback loop promotes ICAM-1-mediated neutrophil crawling and paracellular transmigration. To our knowledge, these data show for the first time that the mechanoreceptor ICAM-1 is negatively regulated by an actin-binding adaptor protein, i.e., CD2AP, to allow a balanced and spatiotemporal control of its adhesive function. CD2AP is important in kidney dysfunction that is accompanied by inflammation. Our findings provide a mechanistic basis for the role of CD2AP in inflamed vessels, identifying this adaptor protein as a potential therapeutic target.

Anillin Phosphorylation Controls Timely Membrane Association and Successful Cytokinesis

During cytokinesis, a contractile ring generates the constricting force to divide a cell into two daughters. This ring is composed of filamentous actin and the motor protein myosin, along with additional structural and regulatory proteins, including anillin. Anillin is a required scaffold protein that links the actomyosin ring to membrane and its organizer, RhoA. However, the molecular basis for timely action of anillin at cytokinesis remains obscure. Here, we find that phosphorylation regulates efficient recruitment of human anillin to the equatorial membrane. Anillin is highly phosphorylated in mitosis, and is a substrate for mitotic kinases. We surveyed function of 46 residues on anillin previously found to be phosphorylated in human cells to identify those required for cytokinesis. Among these sites, we identified S635 as a key site mediating cytokinesis. Preventing S635 phosphorylation adjacent to the AH domain disrupts anillin concentration at the equatorial cortex at anaphase, whereas a phosphomimetic mutant, S635D, partially restores this localization. Time-lapse videomicroscopy reveals impaired recruitment of S635A anillin to equatorial membrane and a transient unstable furrow followed by ultimate failure in cytokinesis. A phosphospecific antibody confirms phosphorylation at S635 in late cytokinesis, although it does not detect phosphorylation in early cytokinesis, possibly due to adjacent Y634 phosphorylation. Together, these findings reveal that anillin recruitment to the equatorial cortex at anaphase onset is enhanced by phosphorylation and promotes successful cytokinesis.

The effect of the top 20 Alzheimer disease risk genes on gray-matter density and FDG PET brain metabolism

INTRODUCTION

We analyzed the effects of the top 20 Alzheimer disease (AD) risk genes on gray-matter density (GMD) and metabolism.

METHODS

We ran stepwise linear regression analysis using posterior cingulate hypometabolism and medial temporal GMD as outcomes and all risk variants as predictors while controlling for age, gender, and APOE ε4 genotype. We explored the results in 3D using Statistical Parametric Mapping 8.

RESULTS

Significant predictors of brain GMD were SLC24A4/RIN3 in the pooled and mild cognitive impairment (MCI); ZCWPW1 in the MCI; and ABCA7, EPHA1, and INPP5D in the AD groups. Significant predictors of hypometabolism were EPHA1 in the pooled, and SLC24A4/RIN3, NME8, and CD2AP in the normal control group.

DISCUSSION

Multiple variants showed associations with GMD and brain metabolism. For most genes, the effects were limited to specific stages of the cognitive continuum, indicating that the genetic influences on brain metabolism and GMD in AD are complex and stage dependent.

Bin1 and CD2AP polarise the endocytic generation of beta-amyloid

The mechanisms driving pathological beta-amyloid (Aβ) generation in late-onset Alzheimer's disease (AD) are unclear. Two late-onset AD risk factors, Bin1 and CD2AP, are regulators of endocytic trafficking, but it is unclear how their endocytic function regulates Aβ generation in neurons. We identify a novel neuron-specific polarisation of Aβ generation controlled by Bin1 and CD2AP We discover that Bin1 and CD2AP control Aβ generation in axonal and dendritic early endosomes, respectively. Both Bin1 loss of function and CD2AP loss of function raise Aβ generation by increasing APP and BACE1 convergence in early endosomes, however via distinct sorting events. When Bin1 levels are reduced, BACE1 is trapped in tubules of early endosomes and fails to recycle in axons. When CD2AP levels are reduced, APP is trapped at the limiting membrane of early endosomes and fails to be sorted for degradation in dendrites. Hence, Bin1 and CD2AP keep APP and BACE1 apart in early endosomes by distinct mechanisms in axon and dendrites. Individuals carrying variants of either factor would slowly accumulate Aβ in neurons increasing the risk for late-onset AD.

Genes associated with Alzheimer's disease: an overview and current status

Alzheimer's disease (AD) is a progressive, neurodegenerative disease and the most common form of dementia in elderly people. It is an emerging public health problem that poses a huge societal burden. Linkage analysis was the first milestone in unraveling the mutations in APP, PSEN1, and PSEN2 that cause early-onset AD, followed by the discovery of apolipoprotein E-ε4 allele as the only one genetic risk factor for late-onset AD. Genome-wide association studies have revolutionized genetic research and have identified over 20 genetic loci associated with late-onset AD. Recently, next-generation sequencing technologies have enabled the identification of rare disease variants, including unmasking small mutations with intermediate risk of AD in PLD3, TREM2, UNC5C, AKAP9, and ADAM10. This review provides an overview of the genetic basis of AD and the relationship between these risk genes and the neuropathologic features of AD. An understanding of genetic mechanisms underlying AD pathogenesis and the potentially implicated pathways will lead to the development of novel treatment for this devastating disease.

Importin β2 Mediates the Spatio-temporal Regulation of Anillin through a Noncanonical Nuclear Localization Signal

The compartmentalization of cell cycle regulators is a common mechanism to ensure the precise temporal control of key cell cycle events. For instance, many mitotic spindle assembly factors are known to be sequestered in the nucleus prior to mitotic onset. Similarly, the essential cytokinetic factor anillin, which functions at the cell membrane to promote the physical separation of daughter cells at the end of mitosis, is sequestered in the nucleus during interphase. To address the mechanism and role of anillin targeting to the nucleus in interphase, we identified the nuclear targeting motif. Here, we show that anillin is targeted to the nucleus by importin β2 in a Ran-dependent manner through an atypical basic patch PY nuclear localization signal motif. We show that although importin β2 binding does not regulate anillin's function in mitosis, it is required to prevent the cytosolic accumulation of anillin, which disrupts cellular architecture during interphase. The nuclear sequestration of anillin during interphase serves to restrict anillin's function at the cell membrane to mitosis and allows anillin to be rapidly available when the nuclear envelope breaks down to remodel the cellular architecture necessary for successful cell division.

Sep(t)arate or not – how some cells take septin-independent routes through cytokinesis

Cytokinesis is the final step of cell division, and is a process that requires a precisely coordinated molecular machinery to fully separate the cytoplasm of the parent cell and to establish the intact outer cell barrier of the daughter cells. Among various cytoskeletal proteins involved, septins are known to be essential mediators of cytokinesis. In this Commentary, we present recent observations that specific cell divisions can proceed in the absence of the core mammalian septin SEPT7 and its Drosophila homolog Peanut (Pnut) and that thus challenge the view that septins have an essential role in cytokinesis. In the pnut mutant neuroepithelium, orthogonal cell divisions are successfully completed. Similarly, in the mouse, Sept7-null mutant early embryonic cells and, more importantly, planktonically growing adult hematopoietic cells undergo productive proliferation. Hence, as discussed here, mechanisms must exist that compensate for the lack of SEPT7 and the other core septins in a cell-type-specific manner. Despite there being crucial non-canonical immune-relevant functions of septins, septin depletion is well tolerated by the hematopoietic system. Thus differential targeting of cytokinesis could form the basis for more specific anti-proliferative therapies to combat malignancies arising from cell types that require septins for cytokinesis, such as carcinomas and sarcomas, without impairing hematopoiesis that is less dependent on septin.

Mutations in the gene that encodes the F-actin binding protein anillin cause FSGS

FSGS is characterized by segmental scarring of the glomerulus and is a leading cause of kidney failure. Identification of genes causing FSGS has improved our understanding of disease mechanisms and points to defects in the glomerular epithelial cell, the podocyte, as a major factor in disease pathogenesis. Using a combination of genome-wide linkage studies and whole-exome sequencing in a kindred with familial FSGS, we identified a missense mutation R431C in anillin (ANLN), an F-actin binding cell cycle gene, as a cause of FSGS. We screened 250 additional families with FSGS and found another variant, G618C, that segregates with disease in a second family with FSGS. We demonstrate upregulation of anillin in podocytes in kidney biopsy specimens from individuals with FSGS and kidney samples from a murine model of HIV-1-associated nephropathy. Overexpression of R431C mutant ANLN in immortalized human podocytes results in enhanced podocyte motility. The mutant anillin displays reduced binding to the slit diaphragm-associated scaffold protein CD2AP. Knockdown of the ANLN gene in zebrafish morphants caused a loss of glomerular filtration barrier integrity, podocyte foot process effacement, and an edematous phenotype. Collectively, these findings suggest that anillin is important in maintaining the integrity of the podocyte actin cytoskeleton.

Supervillin binding to myosin II and synergism with anillin are required for cytokinesis

Cytokinesis, the process by which cytoplasm is apportioned between dividing daughter cells, requires coordination of myosin II function, membrane trafficking, and central spindle organization. Most known regulators act during late cytokinesis; a few, including the myosin II-binding proteins anillin and supervillin, act earlier. Anillin's role in scaffolding the membrane cortex with the central spindle is well established, but the mechanism of supervillin action is relatively uncharacterized. We show here that two regions within supervillin affect cell division: residues 831-1281, which bind central spindle proteins, and residues 1-170, which bind the myosin II heavy chain (MHC) and the long form of myosin light-chain kinase. MHC binding is required to rescue supervillin deficiency, and mutagenesis of this site creates a dominant-negative phenotype. Supervillin concentrates activated and total myosin II at the furrow, and simultaneous knockdown of supervillin and anillin additively increases cell division failure. Knockdown of either protein causes mislocalization of the other, and endogenous anillin increases upon supervillin knockdown. Proteomic identification of interaction partners recovered using a high-affinity green fluorescent protein nanobody suggests that supervillin and anillin regulate the myosin II and actin cortical cytoskeletons through separate pathways. We conclude that supervillin and anillin play complementary roles during vertebrate cytokinesis.

Rab4b controls an early endosome sorting event by interacting with the γ-subunit of the clathrin adaptor complex 1

The endocytic pathway is essential for cell homeostasis and numerous small Rab GTPases are involved in its control. The endocytic trafficking step controlled by Rab4b has not been elucidated, although recent data suggested it could be important for glucose homeostasis, synaptic homeostasis or adaptive immunity. Here, we show that Rab4b is required for early endosome sorting of transferrin receptors (TfRs) to the recycling endosomes, and we identified the AP1γ subunit of the clathrin adaptor AP-1 as a Rab4b effector and key component of the machinery of early endosome sorting. We show that internalised transferrin (Tf) does not reach Vamp3/Rab11 recycling endosomes in the absence of Rab4b, whereas it is rapidly recycled back to the plasma membrane. By contrast, overexpression of Rab4b leads to the accumulation of internalised Tf within AP-1- and clathrin-coated vesicles. These vesicles are poor in early and recycling endocytic markers except for TfR and require AP1γ for their formation. Furthermore, the targeted overexpression of the Rab4b-binding domain of AP1γ to early endosome upon its fusion with FYVE domains inhibited the interaction between Rab4b and endogenous AP1γ, and perturbed Tf traffic. We thus proposed that the interaction between early endocytic Rab4b and AP1γ could allow the budding of clathrin-coated vesicles for subsequent traffic to recycling endosomes. The data also uncover a novel type of endosomes, characterised by low abundance of either early or recycling endocytic markers, which could potentially be generated in cell types that naturally express high level of Rab4b.

Spatiotemporal control of Cindr at ring canals during incomplete cytokinesis in the Drosophila male germline

During male and female gametogenesis in species ranging from insects to mammals, germ cell cyst formation by incomplete cytokinesis involves the stabilization of cleavage furrows and the formation of stable intercellular bridges called ring canals. Accurate regulation of incomplete cytokinesis is required for both female and male fertility in Drosophila melanogaster. Nevertheless, the molecular mechanisms controlling complete versus incomplete cytokinesis are largely unknown. Here, we show that the scaffold protein Cindr is a novel component of both mitotic and meiotic ring canals during Drosophila spermatogenesis. Strikingly, unlike other male germline ring canal components, including Anillin and Pavarotti, Cindr and contractile ring F-actin dissociate from mitotic ring canals and translocate to the fusome upon completion of the mitotic germ cell divisions. We provide evidence that the loss of Cindr from mitotic ring canals is coordinated by signals that mediate the transition from germ cell mitosis to differentiation. Interestingly, Cindr loss from ring canals coincides with completion of the mitotic germ cell divisions in both Drosophila females and males, thus marking a common step of gametogenesis. We also show that Cindr co-localizes with Anillin at mitotic and meiotic ring canals and is recruited to the contractile ring by Anillin during male germ cell meiotic cytokinesis. Taken together, our analyses reveal a key step of incomplete cytokinesis at the endpoint of the mitotic germ cell divisions in D. melanogaster.

George-Hyslop P, Seaman MN, Farrer LA. Identification of Alzheimer disease-associated variants in genes that regulate retromer function

The proteolytic processing of amyloid precursor protein (APP) to generate the neurotoxic amyloid β (Aβ) peptide is central to the pathogenesis of Alzheimer disease (AD). The endocytic system mediates the processing of APP by controlling its access to secretases that cleave APP. A key mediator of APP localization is SorL1-a membrane protein that has been genetically linked to AD. The retromer complex is a conserved protein complex required for endosome-to-Golgi retrieval of a number of physiologically important membrane proteins including SorL1. Based on the prior suggestion that endocytosis and retromer sorting pathways might be involved, we hypothesized that variants in other genes in this pathway might also modulate AD risk. Genetic association of AD with 451 polymorphisms in 15 genes encoding retromer or retromer-associated proteins was tested in a Caucasian sample of 8309 AD cases and 7366 cognitively normal elders using individual single nucleotide polymorphism (SNP)- and gene-based tests. We obtained significant evidence of association with KIAA1033 (VEGAS p = 0.025), SNX1 (VEGAS p = 0.035), SNX3 (p = 0.0057), and RAB7A (VEGAS p = 0.018). Ten KIAA1033 SNPs were also significantly associated with AD in a group of African Americans (513 AD cases, 504 control subjects). Findings with four significant SNX3 SNPs in the discovery sample were replicated in a community-based sample of Israeli-Arabs (124 AD cases, 142 control subjects). We show that Snx3 and Rab7A proteins interact with the cargo-selective retromer complex through independent mechanisms to regulate the membrane association of retromer and thereby are key mediators of retromer function. These data implicate additional AD risk genes in the retromer pathway and formally demonstrate a direct link between the activity of the retromer complex and the pathogenesis of AD.

Septin 7 forms a complex with CD2AP and nephrin and regulates glucose transporter trafficking

Podocytes are insulin-sensitive and take up glucose in response to insulin. This requires nephrin, which interacts with vesicle-associated membrane protein 2 (VAMP2) on GLUT4 storage vesicles (GSVs) and facilitates their fusion with the plasma membrane. In this paper, we show that the filament-forming GTPase septin 7 is expressed in podocytes and associates with CD2-associated protein (CD2AP) and nephrin, both essential for glomerular ultrafiltration. In addition, septin 7 coimmunoprecipitates with VAMP2. Subcellular fractionation of cultured podocytes revealed that septin 7 is found in both cytoplasmic and membrane fractions, and immunofluorescence microscopy showed that septin 7 is expressed in a filamentous pattern and is also found on vesicles and the plasma membrane. The filamentous localization of septin 7 depends on CD2AP and intact actin organization. A 2-deoxy-d-glucose uptake assay indicates that depletion of septin 7 by small interfering RNA or alteration of septin assembly by forchlorfenuron facilitates glucose uptake into cells and further, knockdown of septin 7 increased the interaction of VAMP2 with nephrin and syntaxin 4. The data indicate that septin 7 hinders GSV trafficking and further, the interaction of septin 7 with nephrin in glomeruli suggests that septin 7 may participate in the regulation of glucose transport in podocytes.

Identification of phosphoproteins associated with human neutrophil granules following chemotactic peptide stimulation

Regulated exocytosis of neutrophil intracellular storage granules is necessary for neutrophil participation in the inflammatory response. The signal transduction pathways that participate in neutrophil exocytosis are complex and poorly defined. Several protein kinases, including p38 MAPK and the nonreceptor tyrosine kinases, Hck and Fgr, participate in this response. However, the downstream targets of these kinases that regulate exocytosis are unknown. The present study combined a novel inhibitor of neutrophil exocytosis with proteomic techniques to identify phosphopeptides and phosphoproteins from a population of gelatinase and specific granules isolated from unstimulated and fMLF-stimulated neutrophils. To prevent loss of granule-associated phosphoproteins upon exocytosis, neutrophils were pretreated with a TAT-fusion protein containing a SNARE domain from SNAP-23 (TAT-SNAP-23), which inhibited fMLF-stimulated CD66b-containing granule exocytosis by 100±10%. Following TAT-SNAP-23 pretreatment, neutrophils were stimulated with the chemotactic peptide fMLF for 0 min, 1 min, and 2 min. Granules were isolated by gradient centrifugation and subjected to proteolytic digestion with trypsin or chymotrypsin to obtain peptides from the outer surface of the granule. Phosphopeptides were enriched by gallium or TiO2 affinity chromatography, and phosphopeptides and phosphorylation sites were identified by reversed phase high performance liquid chromatography-electrospray ionization-tandem MS. This resulted in the identification of 243 unique phosphopeptides corresponding to 235 proteins, including known regulators of vesicle trafficking. The analysis identified 79 phosphoproteins from resting neutrophils, 81 following 1 min of fMLF stimulation, and 118 following 2 min of stimulation. Bioinformatic analysis identified a potential Src tyrosine kinase motif from a phosphopeptide corresponding to G protein coupled receptor kinase 5 (GRK5). Phosphorylation of GRK5 by Src was confirmed by an in vitro kinase reaction and by precursor ion scanning for phospho-tyrosine specific immonium ions containing Tyr251 and Tyr253. Immunoprecipitation of phosphorylated GRK5 from intact cells was reduced by a Src inhibitor. In conclusion, targets of signal transduction pathways were identified that are candidates to regulate neutrophil granule exocytosis.

The myriad roles of Anillin during cytokinesis

Anillin is a highly conserved multidomain protein that interacts with cytoskeletal components as well as their regulators. Throughout phylogeny, Anillins contribute to cytokinesis, the cell shape change that occurs at the end of meiosis and mitosis to separate a cell into daughter cells. Failed cytokinesis results in binucleation, which can lead to genomic instability. Study of Anillin in several model organisms has provided us with insight into how the cytoskeleton is coordinated to ensure that cytokinesis occurs with high fidelity. Here we review Anillin's interacting partners and the relevance of these interactions in vivo. We also discuss questions of how these interactions are coordinated, and finally provide some perspective regarding Anillin's role in cancer.

Understanding cytokinesis failure

Cytokinesis is the final step in cell division. The process begins during chromosome segregation, when the ingressing cleavage furrow begins to partition the cytoplasm between the nascent daughter cells. The process is not completed until much later, however, when the final cytoplasmic bridge connecting the two daughter cells is severed. Cytokinesis is a highly ordered process, requiring an intricate interplay between cytoskeletal, chromosomal and cell cycle regulatory pathways. A surprisingly broad range of additional cellular processes are also important for cytokinesis, including protein and membrane trafficking, lipid metabolism, protein synthesis and signaling pathways. As a highly regulated, complex process, it is not surprising that cytokinesis can sometimes fail. Cytokinesis failure leads to both centrosome amplification and production of tetraploid cells, which may set the stage for the development of tumor cells. However, tetraploid cells are abundant components of some normal tissues including liver and heart, indicating that cytokinesis is physiologically regulated. In this chapter, we summarize our current understanding of the mechanisms of cytokinesis, emphasizing steps in the pathway that may be regulated or prone to failure. Our discussion emphasizes findings in vertebrate cells although we have attempted to highlight important contributions from other model systems.

CD2AP is indispensable to multistep cytotoxic process by NK cells

CD2-associated protein (CD2AP) is a cytoplasmic protein which localizes to membrane ruffles, lipid rafts and the leading edges of cells. It is implicated in podocyte homeostasis, signal transduction, dynamic actin remodeling and also membrane trafficking during endocytosis and cytokinesis. CD2AP was reported to orchestrate receptor patterning and cytoskeletal polarity in T cell contacts and it could also modulate TCR signaling. However, whether it plays a role in NK cell killing remains unknown. In this study, we discovered that interfering with CD2AP expression strongly reduced cytotoxicity of human NK92 cell line and this effect was independent of FasL sensitivity of target cells. Conjugate formation and degranulation were impeded in NK92 cells after CD2AP knockdown. Upon encountering target cells, CD2AP in NK92 is enriched near contact site and colocalizes with FasL-bearing granules. In contrast, FasL-bearing granules were found rarely polarized toward cell contact site after CD2AP knockdown. Furthermore, by immunoprecipitation from NK92 cell lysates and transient expression studies in 293T and Hela cells, we demonstrated that CD2AP associates with FasL. Thus, CD2AP, through facilitating conjugate formation and directed transport of lytic granules, plays an important role in NK cells killing.

Coordinating cellular events during spermatogenesis: a biochemical model

Throughout spermatogenesis, a select pool of germ cells, the leptotene spermatocytes, must traverse the blood-testis barrier (BTB) to enter the adluminal compartment of the seminiferous epithelium. This event requires extensive restructuring of cell junctions, and it must also coincide with germ cell cycle progression in preparation for primary spermatocyte meiosis. Recent findings show that cell-cycle-associated kinases and phosphatases, including mitogen-activated protein kinases (MAPKs), participate in the pathways that also direct germ cell adhesion and movement. Our new biochemical model explains, in part, how two distinct cellular events, BTB restructuring and spermiation, are coordinated to maintain spermatogenesis and fertility. In this way, MAPKs would synchronize cell cycle progression in primary spermatocytes with junction remodeling and cell migration across the BTB.

Proteins recruited by SH3 domains of Ruk/CIN85 adaptor identified by LC-MS/MS

Background

Ruk/CIN85 is a mammalian adaptor molecule with three SH3 domains. Using its SH3 domains Ruk/CIN85 can cluster multiple proteins and protein complexes, and, consequently, facilitates organisation of elaborate protein interaction networks with diverse regulatory roles. Previous research linked Ruk/CIN85 with the regulation of vesicle-mediated transport and cancer cell invasiveness. Despite the recent findings, precise molecular functions of Ruk/CIN85 in these processes remain largely elusive and further research is hampered by a lack of complete lists of its partner proteins.

Results

In the present study we employed a LC-MS/MS-based experimental pipeline to identify a considerable number (over 100) of proteins recruited by the SH3 domains of Ruk/CIN85 in vitro. Most of these identifications are novel Ruk/CIN85 interaction candidates. The identified proteins have diverse molecular architectures and can interact with other proteins, as well as with lipids and nucleic acids. Some of the identified proteins possess enzymatic activities. Functional profiling analyses and literature mining demonstrate that many of the proteins recruited by the SH3 domains of Ruk/CIN85 identified in this work were involved in the regulation of membranes and cytoskeletal structures necessary for vesicle-mediated transport and cancer cell invasiveness. Several groups of the proteins were also associated with few other cellular processes not previously related to Ruk/CIN85, most prominently with cell division.

Conclusion

Obtained data support the notion that Ruk/CIN85 regulates vesicle-mediated transport and cancer cell invasiveness through the assembly of multimeric protein complexes governing coordinated remodelling of membranes and underlying cytoskeletal structures, and imply its important roles in formation of coated vesicles and biogenesis of invadopodia. In addition, this study points to potential involvement of Ruk/CIN85 in other cellular processes, chiefly in cell division.

Functional involvement of human discs large tumor suppressor in cytokinesis

Cytokinesis is the final step of cell division that completes the separation of two daughter cells. We found that the human discs large (hDlg) tumor suppressor homologue is functionally involved in cytokinesis. The guanylate kinase (GUK) domain of hDlg mediates the localization of hDlg to the midbody during cytokinesis, and over-expression of the GUK domain in U2OS and HeLa cells impaired cytokinesis. Mouse embryonic fibroblasts (MEFs) derived from dlg mutant mice contained an increased number of multinucleated cells and showed reduced proliferation in culture. A kinesin-like motor protein, GAKIN, which binds directly to the GUK domain of hDlg, exhibited a similar intracellular distribution pattern with hDlg throughout mitosis and localized to the midbody during cytokinesis. However, the targeting of hDlg and GAKIN to the midbody appeared to be independent of each other. The midbody localization of GAKIN required its functional kinesin-motor domain. Treatment of cells with the siRNA specific for hDlg and GAKIN caused formation of multinucleated cells and delayed cytokinesis. Together, these results suggest that hDlg and GAKIN play functional roles in the maintenance of midbody architecture during cytokinesis.

Differential requirements for Alix and ESCRT-III in cytokinesis and HIV-1 release

The ESCRT machinery functions in topologically equivalent membrane fission events, namely multivesicular body formation, the terminal stages of cytokinesis and HIV-1 release. Here, we show that the ESCRT-III-binding protein Alix is recruited to the midbody of dividing cells through binding Cep55 via an evolutionarily conserved peptide. Disruption of Cep55/Alix/ESCRT-III interactions causes formation of aberrant midbodies and cytokinetic failure, demonstrating an essential role for these proteins in midbody morphology and cell division. We also show that the C terminus of Alix encodes a multimerization activity that is essential for its function in Alix-dependent HIV-1 release and for interaction with Tsg101. Last, we demonstrate that overexpression of Chmp4b and Chmp4c differentially inhibits HIV-1 release and cytokinesis, suggesting possible reasons for gene expansion within the mammalian Class E VPS pathway.

The Drosophila CD2AP/CIN85 orthologue Cindr regulates junctions and cytoskeleton dynamics during tissue patterning

Developing tissues require cells to undergo intricate processes to shift into appropriate niches. This requires a functional connection between adhesion-mediating events at the cell surface and a cytoskeletal reorganization to permit directed movement. A small number of proteins are proposed to link these processes. Here, we identify one candidate, Cindr, the sole Drosophila melanogaster member of the CD2AP/CIN85 family (this family has been previously implicated in a variety of processes). Using D. melanogaster retina, we demonstrate that Cindr links cell surface junctions (E-cadherin) and adhesion (Roughest) with multiple components of the actin cytoskeleton. Reducing cindr activity leads to defects in local cell movement and, consequently, tissue patterning and cell death. Cindr activity is required for normal localization of Drosophila E-cadherin and Roughest, and we show additional physical and functional links to multiple components of the actin cytoskeleton, including the actin-capping proteins capping protein alpha and capping protein beta. Together, these data demonstrate that Cindr is involved in dynamic cell rearrangement in an emerging epithelium.

Rab proteins in endocytosis and Glut4 trafficking

The intracellular trafficking of numerous proteins requires a tight control to fulfil their physiological functions. It is the case of the adipocyte and muscle glucose transporter Glut4 that is retained intracellularly until insulin induces its recruitment to the plasma membrane. Rabs are evolutionarily conserved small GTPases that control intracellular traffic events from yeast to mammalian cells. In the past few decades, considerable progresses have been made in identifying the route of Glut4, the Rabs involved in controlling it, and more recently the connection between insulin signalling and Glut4 trafficking through Rab activity control.

Human ESCRT and ALIX proteins interact with proteins of the midbody and function in cytokinesis

TSG101 and ALIX both function in HIV budding and in vesicle formation at the multivesicular body (MVB), where they interact with other Endosomal Sorting Complex Required for Transport (ESCRT) pathway factors required for release of viruses and vesicles. Proteomic analyses revealed that ALIX and TSG101/ESCRT-I also bind a series of proteins involved in cytokinesis, including CEP55, CD2AP, ROCK1, and IQGAP1. ALIX and TSG101 concentrate at centrosomes and are then recruited to the midbodies of dividing cells through direct interactions between the central CEP55 'hinge' region and GPP-based motifs within TSG101 and ALIX. ESCRT-III and VPS4 proteins are also recruited, indicating that much of the ESCRT pathway localizes to the midbody. Depletion of ALIX and TSG101/ESCRT-I inhibits the abscission step of HeLa cell cytokinesis, as does VPS4 overexpression, confirming a requirement for these proteins in cell division. Furthermore, ALIX point mutants that block CEP55 and CHMP4/ESCRT-III binding also inhibit abscission, indicating that both interactions are essential. These experiments suggest that the ESCRT pathway may be recruited to facilitate analogous membrane fission events during HIV budding, MVB vesicle formation, and the abscission stage of cytokinesis.

Interphase nucleo-cytoplasmic shuttling and localization of SIRT2 during mitosis

The human NAD+-dependent protein deacetylase SIRT2 resides predominantly in the cytoplasm where it functions as a tubulin deacetylase. Here we report that SIRT2 maintains a largely cytoplasmic localization during interphase by active nuclear export in a Crm1-dependent manner. We identified a functional, leptomycin B-sensitive, nuclear export signal sequence within SIRT2. During the cell cycle, SIRT2 becomes enriched in the nucleus and is associated with mitotic structures, beginning with the centrosome during prophase, the mitotic spindle during metaphase, and the midbody during cytokinesis. Cells overexpressing wild-type or a catalytically inactive SIRT2 exhibit an increase in multinucleated cells. The findings suggest a novel mechanism of regulating SIRT2 function by nucleo-cytoplasmic shuttling, as well as a role for SIRT2 in the nucleus during interphase and throughout mitosis.

Focal segmental glomerulosclerosis in a patient homozygous for a CD2AP mutation

Focal segmental glomerulosclerosis (FSGS) is a histologic diagnosis in several kidney diseases characterized by proteinuria and a severe decrease in kidney function. Mutations in several genes were found in patients with primary FSGS, one of which is a CD2-associated protein CD2AP (originally referred to as CMS). This gene encodes an adaptor protein that plays a role in endocytosis, cell motility, and cell survival. Mice deficient in Cd2ap (the mouse homolog) die due to kidney failure, while heterozygous mice develop lesions similar to those of FSGS patients. In the kidney, CD2AP regulates the actin cytoskeleton. The only previously described patient with CD2AP mutation had a severely truncated protein. In this study, we describe a patient with a novel mutation resulting in a premature stop codon yielding a protein truncated by only 4%. This shortened CD2AP protein displays a significantly decreased F-actin binding efficiency in vitro with no expression of the mutated allele in the patient's lymphocytes. Heterozygous expression of the CD2AP mutation in both parents did not lead to any kidney pathology, as both have normal glomerular filtration rates and no proteinuria.

Structure and function analysis of the CMS/CIN85 protein family identifies actin-bundling properties and heterotypic-complex formation

Members of the CMS/CIN85 protein family participate in clathrin-mediated endocytosis and play a crucial role in maintaining the kidney filtration barrier. The CMS protein structure includes three Src homology 3 (SH3) domains and a proline-rich (PR) region that is connected by a `linker' sequence to a coiled-coil (CC) domain. We show that CMS is a component of special actin-rich adhesion structures – podosomes – and demonstrate specific actin-binding properties of CMS. We have found that the entire C-terminal half of CMS is necessary for efficient binding to filamentous actin (F-actin). CMS and CIN85 can crosslink F-actin into bundles, a function that depends on the PR region and the CC domain. Removal of these domains reduces migration. CMS can also form heterotypic complexes with CIN85. CIN85 is expressed as multiple isoforms that share the CC domain, suggesting that heterotypic interactions with CMS provides a mechanism to regulate CMS binding to F-actin and thus for modulating dynamic rearrangements of the cytoskeleton.