The actin-capping protein CapG localizes to microtubule-dependent organelles during the cell cycle

Tumor vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA): Suppresses macrophage capping protein beyond STING activation

The vascular disrupting agent (VDA) 5,6-dimethylxanthenone-4-acetic acid (DMXAA) induces apoptosis in vascular endothelial cells and leads to tumor hemorrhagic necrosis. While DMXAA has been proven to be a potent agonist of murine stimulator of interferon genes (mSTING), it has little effect on human-STING (hSTING). This species selectivity of DMXAA may explain its effectiveness against solid tumors in mice and its failure in clinical trials. However, DMXAA did reduce tumor volume in some patients during clinical trials. These paradoxical results have prompted us to investigate the anti-tumor mechanism of DMXAA beyond STING in the destruction of tumor vasculature in humans. In this study, we demonstrated that DMXAA binds to both human and mouse macrophage capping protein (CapG), with a KD of 5.839 μM for hCapG and a KD of 2.867 μM for mCapG, as determined by surface plasmon resonance (SPR) analysis. Homology modeling and molecular docking analysis of hCapG indicated that the critical residues involved in the hydrogen bond interaction of DMXAA with hCapG were Arg153, Thr151, and GLN141, Asn234. In addition, electrostatic pi-cation interaction occurred between DMXAA and hCapG. Further functional studies revealed that CapG protein plays a crucial role in the effects of DMXAA on human umbilical endothelial vein cell (HUEVC) angiogenesis and migration, as well as the expression of cytoskeletal proteins actin and tubulin, and the invasion of A549 lung adenocarcinoma cells. Our study has originally uncovered a novel cross-species pathway underlying the antitumor vascular disruption of DMXAA extends beyond STING activation. This finding deepens our understanding of the multifaceted actions of flavonoid VDAs in animal models and in clinical settings, and may provide insights for the precise therapy of DMXAA based on the biomarker CapG protein.

The Endothelial Centrosome: Specific Features and Functional Significance for Endothelial Cell Activity and Barrier Maintenance

This review summarizes information about the specific features that are characteristic of the centrosome and its relationship with the cell function of highly specialized cells, such as endotheliocytes. It is based on data from other researchers and our own long-term experience. The participation of the centrosome in the functional activity of these cells, including its involvement in the performance of the main barrier function of the endothelium, is discussed. According to modern concepts, the centrosome is a multifunctional complex and an integral element of a living cell; the functions of which are not limited only to the ability to polymerize microtubules. The location of the centrosome near the center of the interphase cell, the concentration of various regulatory proteins in it, the organization of the centrosome radial system of microtubules through which intracellular transport is carried out by motor proteins and the involvement of the centrosome in the process of the perception of the external signals and their transmission make this cellular structure a universal regulatory and distribution center, controlling the entire dynamic morphology of an animal cell. Drawing from modern data on the tissue-specific features of the centrosome's structure, we discuss the direct involvement of the centrosome in the performance of functions by specialized cells.

Vincristine-Induced Peripheral Neuropathy in Childhood Acute Lymphoblastic Leukemia: Genetic Variation as a Potential Risk Factor

Vincristine (VCR) is the first-line chemotherapeutic medication often co-administered with other drugs to treat childhood acute lymphoblastic leukemia. Dose-dependent neurotoxicity is the main factor restricting VCR’s clinical application. VCR-induced peripheral neuropathy (VIPN) sometimes results in dose reduction or omission, leading to clinical complications or affecting the patient’s quality of life. With regard to the genetic basis of drug responses, preemptive pharmacogenomic testing and simultaneous blood level monitoring could be helpful for the transformation of various findings into individualized therapies. In this review, we discussed the potential associations between genetic variants in genes contributing to the pharmacokinetics/pharmacodynamics of VCR and VIPN incidence and severity in patients with acute lymphoblastic leukemia. Of note, genetic variants in the CEP72 gene have great potential to be translated into clinical practice. Such a genetic biomarker may help clinicians diagnose VIPN earlier. Besides, genetic variants in other genes, such as CYP3A5, ABCB1, ABCC1, ABCC2, TTPA, ACTG1, CAPG, SYNE2, SLC5A7, COCH, and MRPL47, have been reported to be associated with the VIPN, but more evidence is needed to validate the findings in the future. In fact, a variety of complex factors jointly determine the VIPN. In implementing precision medicine, the combination of genetic, environmental, and personal variables, along with therapeutic drug monitoring, will allow for a better understanding of the mechanisms of VIPN, improving the effectiveness of VCR treatment, reducing adverse reactions, and improving patients’ quality of life.

The migration behavior of human glioblastoma cells is influenced by the redox-sensitive human macrophage capping protein CAPG

The macrophage capping protein CAPG belongs to the gelsolin superfamily which modulates actin dynamics by capping the growing end of actin filaments in a Ca²⁺- and PIP₂-dependent manner resulting in polymerization inhibition of actin filaments. In the last years, additional functions for CAPG in transcription regulation were described and higher CAPG amounts have been linked to increased invasiveness and migration behavior in different human tumor entities like e.g. glioblastoma. Nevertheless, there is a lack of knowledge how additional functions of CAPG are regulated. As CAPG contains several cysteine residues which may be accessible to oxidation we were especially interested to investigate how alterations in the cysteine oxidation state may influence the function, localization, and regulation of CAPG. In the present study, we provide strong evidence that CAPG is a redox-sensitive protein and identified two cysteines: C282 and C290 as reversibly oxidized in glioblastoma cell lines. Whereas no evidence could be found that the canonical actin capping function of CAPG is redox-regulated, our results point to a novel role of the identified cysteines in the regulation of cell migration. Along with this, we found a localization shift out of the nucleus of CAPG and RAVER1, a potential interaction partner identified in our study which might explain the observed altered cell migration properties. The newly identified redox sensitive cysteines of CAPG could perspectively be considered as new targets for controlling tumor invasive properties.

Genetic factors influencing the development of vincristine-induced neurotoxicity

Introduction: One of the most common side effects during vincristine (VCR) use is the establishment of VCR-induced peripheral neuropathy (VIPN). Among several risk factors that can influence the development of VIPN, such as cumulative dose and patient's age, sex, ethnicity, and genetic variants, this review is focused on the genetic variability. Areas covered: A literature research was performed firstly using the following PubMed search string ((((CIPN OR (vincristine AND neurotoxicity OR (vincristine AND neuropathy))) AND (polymorphisms OR (genetic variants OR (genetic factors OR (genetic profile OR (pharmacogenetics OR (genome-wide OR (genetic risk OR (expression genotype))))))))))) but also other relevant papers cited by the selected articles were included. Based on the obtained results, we identified two main categories of genes: genes involved in pharmacokinetics (genes related to metabolism and transport) or pharmacodynamics (genes related to mechanism of action) of VCR. Expert opinion: Despite several clinical retrospective studies investigating the possible correlations between patient genotype and VIPN onset, contrasting and inconsistent results are reported. In conclusion, given the clinical relevance of VIPN, further and more focused research would be fundamental in order to identify genetic variants able to predict its development and to allow a safer management of treated patients.

Identification of HeLa cell proteins that interact with Chlamydia trachomatis glycogen synthase using yeast two‑hybrid assays

Chlamydia trachomatis (C. trachomatis) is the leading cause of bacterial sexually transmitted diseases and infectious diseases that cause blindness. The pathophysiology of chlamydial infections is poorly understood, but secreted proteins have emerged as key virulence factors. C. trachomatis glycogen synthase (GlgA) is a chlamydial secretory protein, which localizes in the lumen of chlamydial inclusion bodies and the cytosol of host cells. In order to improve understanding of the roles of GlgA in chlamydial pathogenesis, four proteins that interact with GlgA, Homo sapiens CXXC finger protein 1, prohibitin (PHB), gelsolin-like actin-capping protein and apolipoprotein A-I binding protein were identified using yeast two-hybrid assays. The functions of these proteins are complex, and preliminary results suggested that PHB interacts with GlgA. However, further studies are required to determine the specific interactions of these proteins with GlgA. The findings of the present study may provide a direction and foundation for future studies focusing on the mechanism of GlgA in C. trachomatis infection.

The Centrosome as the Main Integrator of Endothelial Cell Functional Activity

The centrosome is an intracellular structure of the animal cell responsible for organization of cytoplasmic microtubules. According to modern concepts, the centrosome is a very important integral element of the living cell whose functions are not limited to its ability to polymerize microtubules. The centrosome localization in the geometric center of the interphase cell, the high concentration of various regulatory proteins in this area, the centrosome-organized radial system of microtubules for intracellular transport by motor proteins, the centrosome involvement in the perception of external signals and their transmission - all these features make this cellular structure a unique regulation and distribution center managing dynamic morphology of the animal cell. In conjunction with the tissue-specific features of the centrosome structure, this suggests the direct involvement of the centrosome in execution of cell functions. This review discusses the involvement of the centrosome in the vital activity of endothelial cells, as well as its possible participation in the implementation of barrier function, the major function of endothelium.

Nup62, associated with spindle microtubule rather than spindle matrix, is involved in chromosome alignment and spindle assembly during mitosis

An increasing number of the active mitotic functions of nucleoporins in the distinct steps of mitosis have been assigned over the past few years. As one of FG-repeats containing nucleoporins, Nup62 has been found to be involved in nuclear transport, cell migration, virus infection, and cell cycle regulation. However, the role and mechanism of Nup62 in mitotic regulation have not been fully revealed. In this paper, it was revealed that a fraction of Nup62 was associated with mitotic spindle microtubule instead of spindle matrix, and the localization of Nup62 in the mitotic spindle depended on its three coiled-coil domains rather than Crm1, although Nup62 strongly interacted with Crm1 during mitosis. Moreover, depletion of Nup62 by small interference of RNA seriously induced the defects of chromosome alignment and spindle assembly although the bipolar spindle was observed in most of the Nup62 knock-down cells. Notably, congression of polar chromosome defect was observed in more than 30% of Nup62 knock-down cells. These findings revealed that Nup62 was a novel mitotic spindle associated nucleoporin and involved in chromosome alignment and spindle assembly.

Proteomic identification of predictive tissue biomarkers of sensitive to neoadjuvant chemotherapy in squamous cervical cancer

AIMS

The regimens of neoadjuvant chemotherapy (NAC) in squamous cervical cancer (SCC) frequently use cisplatin combined with paclitaxel. Unfortunately, some cervical cancers show resistance to the principal chemotherapeutic agents in the treatment, decreasing the effectiveness of this therapy. The objective of this study was to search for predictive markers of response to NAC in patients with SCC.

MAIN METHODS

Two-dimensional gel electrophoresis (2-DE) accompanied by matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF-MS) was used to analyze and identify differentially expressed proteins in ten cases of advanced cervical cancer patients receiving cisplatin-based NAC. Each of these patients received more than two cycles of NAC. Cell proliferation rate in cisplatin resistant human cervical cancer cell Hela/DDP and its parent cell Hela after treatment with Hsp70 inhibitor and/or cisplatin were tested by MTT assay.

KEY FINDINGS

Twelve protein spots changed in abundance, quantitative comparison of spot volumes showed that seven protein spots were up-regulated and five spots were down-regulated in the NAC non-responders compared to the NAC responders. These proteins are involved in various cellular processes essential for cell metabolism, migration and apoptotic signal transduction. The high-fold changes proteins of stathmin1, Hsp70 and pyruvate kinase isoform M2 were validated by Western blot analysis. Over-expression of Hsp70 inhibits the efficacy of cisplatin. Hsp70 inhibitor enhanced the sensitivity to cisplatin in both Hela and Hela/DDP cells.

SIGNIFICANCE

The study found many candidate proteins involved in chemotherapy resistance/sensitivity, among them Hsp70 might be potential biomarkers to predict the efficacy of chemotherapy for SCC patients.

The centrosome is an actin-organizing centre

Microtubules and actin filaments are the two main cytoskeleton networks supporting intracellular architecture and cell polarity. The centrosome nucleates and anchors microtubules and is therefore considered to be the main microtubule-organizing centre. However, recurring, yet unexplained, observations have pointed towards a connection between the centrosome and actin filaments. Here we have used isolated centrosomes to demonstrate that the centrosome can directly promote actin-filament assembly. A cloud of centrosome-associated actin filaments could be identified in living cells as well. Actin-filament nucleation at the centrosome was mediated by the nucleation-promoting factor WASH in combination with the Arp2/3 complex. Pericentriolar material 1 (PCM1) seemed to modulate the centrosomal actin network by regulating Arp2/3 complex and WASH recruitment to the centrosome. Hence, our results reveal an additional facet of the centrosome as an intracellular organizer and provide mechanistic insights into how the centrosome can function as an actin-filament-organizing centre.

Polymorphisms of the vincristine pathway and response to treatment in children with childhood acute lymphoblastic leukemia

BACKGROUND

Vincristine (VCR) is a standard component in the treatment of childhood acute lymphoblastic leukemia (ALL). VCR cytotoxicity is primarily due to its ability to disrupt the formation of microtubules of the mitotic spindle.

PATIENTS & METHODS

Seventeen polymorphisms in regulatory and coding regions of genes controlling VCR targets (TUBB1, MAP4, ACTG1 and CAPG) or potentially influencing VCR levels (ABCB1 and CYP3A5) were investigated for an association with peripheral neuropathy and outcome in childhood ALL patients.

RESULTS

High-grade neurotoxicity was more frequent in carriers of the A allele of synonymous (Ala310) G to A (rs1135989) variation in the ACTG1 gene. Substitution (rs4728709) in the promoter of the ABCB1 gene had a protective effect against lower grade neurotoxicity and C to A variation (rs3770102) located 17 nucleotides upstream from the transcription start site had a protective effect against high-grade neurotoxicity. Patients with the ABCB1 3435TT genotype had lower event-free survival; the association with event-free survival was not supported by the analysis in the replication patient set.

CONCLUSION

The polymorphisms in the ACTG1, CAPG and ABCB1 genes may modulate VCR-related neurotoxicity, whereas the risk of relapse seems not to be affected by the genes of the VCR pathway.

Toward a consensus on the mechanism of nuclear pore complex inheritance

Nuclear compartmentalization is achieved through the enclosure of the genome by the nuclear envelope; the nuclear envelope is perforated by nuclear pore complexes (NPCs), which form portals that control molecular exchange between the nucleus and cytoplasm. The number of NPCs per nucleus establishes a limit to the flux of molecules across the nuclear envelope and might directly impact genome organization and gene expression in a cell type specific manner. Mechanisms that control NPC number remain ill defined. Our recent study implicates a cytoplasmic pool of the nucleoporin Nsp1 as a factor that controls NPC number during the asymmetric division of budding yeast; Nsp1 acts to ensure that daughters inherit NPCs. We place our data within an emerging model of NPC inheritance in yeast and consider potential analogous mechanisms in multicellular eukaryotes, including the functional conservation of a cytoplasmic pool of Nsp1.

Differential proteomic analysis of synovial fluid from rheumatoid arthritis and osteoarthritis patients

Background

Rheumatoid arthritis and osteoarthritis are two common musculoskeletal disorders that affect the joints. Despite high prevalence rates, etiological factors involved in these disorders remain largely unknown. Dissecting the molecular aspects of these disorders will significantly contribute to improving their diagnosis and clinical management. In order to identify proteins that are differentially expressed between these two conditions, a quantitative proteomic profiling of synovial fluid obtained from rheumatoid arthritis and osteoarthritis patients was carried out by using iTRAQ labeling followed by high resolution mass spectrometry analysis.

Results

We have identified 575 proteins out of which 135 proteins were found to be differentially expressed by ≥3-fold in the synovial fluid of rheumatoid arthritis and osteoarthritis patients. Proteins not previously reported to be associated with rheumatoid arthritis including, coronin-1A (CORO1A), fibrinogen like-2 (FGL2), and macrophage capping protein (CAPG) were found to be upregulated in rheumatoid arthritis. Proteins such as CD5 molecule-like protein (CD5L), soluble scavenger receptor cysteine-rich domain-containing protein (SSC5D), and TTK protein kinase (TTK) were found to be upregulated in the synovial fluid of osteoarthritis patients. We confirmed the upregulation of CAPG in rheumatoid arthritis synovial fluid by multiple reaction monitoring assay as well as by Western blot. Pathway analysis of differentially expressed proteins revealed a significant enrichment of genes involved in glycolytic pathway in rheumatoid arthritis.

Conclusions

We report here the largest identification of proteins from the synovial fluid of rheumatoid arthritis and osteoarthritis patients using a quantitative proteomics approach. The novel proteins identified from our study needs to be explored further for their role in the disease pathogenesis of rheumatoid arthritis and osteoarthritis.

Sartaj Ahmad and Raja Sekhar Nirujogi contributed equally to this article.

A nanobody targeting the F-actin capping protein CapG restrains breast cancer metastasis

Introduction

Aberrant turnover of the actin cytoskeleton is intimately associated with cancer cell migration and invasion. Frequently however, evidence is circumstantial, and a reliable assessment of the therapeutic significance of a gene product is offset by lack of inhibitors that target biologic properties of a protein, as most conventional drugs do, instead of the corresponding gene. Proteomic studies have demonstrated overexpression of CapG, a constituent of the actin cytoskeleton, in breast cancer. Indirect evidence suggests that CapG is involved in tumor cell dissemination and metastasis. In this study, we used llama-derived CapG single-domain antibodies or nanobodies in a breast cancer metastasis model to address whether inhibition of CapG activity holds therapeutic merit.

Methods

We raised single-domain antibodies (nanobodies) against human CapG and used these as intrabodies (immunomodulation) after lentiviral transduction of breast cancer cells. Functional characterization of nanobodies was performed to identify which biochemical properties of CapG are perturbed. Orthotopic and tail vein in vivo models of metastasis in nude mice were used to assess cancer cell spreading.

Results

With G-actin and F-actin binding assays, we identified a CapG nanobody that binds with nanomolar affinity to the first CapG domain. Consequently, CapG interaction with actin monomers or actin filaments is blocked. Intracellular delocalization experiments demonstrated that the nanobody interacts with CapG in the cytoplasmic environment. Expression of the nanobody in breast cancer cells restrained cell migration and Matrigel invasion. Notably, the nanobody prevented formation of lung metastatic lesions in orthotopic xenograft and tail-vein models of metastasis in immunodeficient mice. We showed that CapG nanobodies can be delivered into cancer cells by using bacteria harboring a type III protein secretion system (T3SS).

Conclusions

CapG inhibition strongly reduces breast cancer metastasis. A nanobody-based approach offers a fast track for gauging the therapeutic merit of drug targets. Mapping of the nanobody-CapG interface may provide a platform for rational design of pharmacologic compounds.

Biomarker analysis of neoadjuvant doxorubicin/cyclophosphamide followed by ixabepilone or Paclitaxel in early-stage breast cancer

PURPOSE

Predictive biomarkers offer the potential to improve the benefit:risk ratio of a therapeutic agent. Ixabepilone achieves comparable pathologic complete response (pCR) rates to other active drugs in the neoadjuvant setting. This phase II trial was designed to investigate potential biomarkers that differentiate response to this agent.

EXPERIMENTAL DESIGN

Women with untreated, histologically confirmed primary invasive breast adenocarcinoma received neoadjuvant doxorubicin/cyclophosphamide, followed by 1:1 randomization to ixabepilone (n = 148) or paclitaxel (n = 147). Rates of pCR were compared between treatment arms based on predefined biomarker sets: TUBB3, TACC3, and CAPG gene expression, a 20- and 26-gene expression model, MDR1 protein expression, and other potential markers of sensitivity. βIII-tubulin protein expression is reported separately but is referred to here for completeness. All patients underwent a core needle biopsy of the primary cancer for molecular marker analysis before chemotherapy. Gene expression profiling data were used for molecular subtyping.

RESULTS

There was no significant difference in the rate of pCR in both treatment arms in βIII-tubulin-positive patients. Higher pCR rates were observed among βIII-tubulin-positive patients than in βIII-tubulin-negative patients. Furthermore, no correlation was evident between TUBB3, TACC3, and CAPG gene expression, MDR1 protein expression, multi-gene expression models, and the efficacy of ixabepilone or paclitaxel, even within the estrogen receptor-negative subset.

CONCLUSION

These results indicate that βIII-tubulin protein and mRNA expression, MDR1 protein expression, TACC3 and CAPG gene expression, and multigene expression models (20- and 26-gene) are not predictive markers for differentiating treatment benefit between ixabepilone and paclitaxel in early-stage breast cancer.

Phosphorylated tubulin adaptor protein CRMP-2 as prognostic marker and candidate therapeutic target for NSCLC

Collapsin response mediator protein-2 (CRMP-2) is the first described and most studied member of a family of proteins that mediate the addition of tubulin dimers to the growing microtubule. CRMPs have mainly been studied in the nervous system, but recently, they have been described in other tissues where they participate in vesicle transport, migration and mitosis. In this work, we aimed at studying the role of CRMP-2 in lung cancer cell division. We first explored the expression of CRMP-2 and phosphorylated (Thr 514) CRMP-2 in 91 samples obtained from patients with localized nonsmall cell lung cancer. We observed a significant correlation between high levels of nuclear phosphorylated CRMP-2 and poor prognosis in those patients. Interestingly, this association was only positive for untreated patients. To provide a mechanistic explanation to these findings, we used in vitro models to analyze the role of CRMP-2 and its phosphorylated forms in cell division. Thus, we observed by confocal microscopy and immunoprecipitation assays that CRMP-2 differentially colocalizes with the mitotic spindle during cell division. The use of phosphodefective or phosphomimetic mutants of CRMP-2 allowed us to prove that anomalies in the phosphorylation status of CRMP-2 result in changes in the mitotic tempo, and increments in the number of multinucleated cells. Finally, here we demonstrate that CRMP-2 phosphorylation impairment, or silencing induces p53 expression and promotes apoptosis through caspase 3 activation. These results pointed to CRMP-2 phosphorylation as a prognostic marker and potential new target to be explored in cancer therapy.

Silencing of OSBP-related protein 8 (ORP8) modifies the macrophage transcriptome, nucleoporin p62 distribution, and migration capacity

ORP8 is an oxysterol/cholesterol binding protein anchored to the endoplasmic reticulum and the nuclear envelope, and is abundantly expressed in the macrophage. We created and characterized mouse RAW264.7 macrophages with ORP8 stably silenced using shRNA lentiviruses. A microarray transcriptome and gene ontology pathway analysis revealed significant alterations in several nuclear pathways and ones associated with centrosome and microtubule organization. ORP8 knockdown resulted in increased expression and altered subcellular distribution of an interaction partner of ORP8, nucleoporin NUP62, with an intranuclear localization aspect and association with cytoplasmic vesicular structures and lamellipodial edges of the cells. Moreover, ORP8 silenced cells displayed enhanced migration, and a more pronounced microtubule cytoskeleton than controls expressing a non-targeting shRNA. ORP8 was shown to compete with Exo70 for interaction with NUP62, and NUP62 knockdown abolished the migration enhancement of ORP8-silenced cells, suggesting that the endogenous ORP8 suppresses migration via binding to NUP62. As a conclusion, the present study reveals new, unexpected aspects of ORP8 function in macrophages not directly involving lipid metabolism, but rather associated with nuclear functions, microtubule organization, and migration capacity.

Dynamics and diverse functions of nuclear pore complex proteins

Nuclear pore complexes (NPCs) are best known for their central role in controlling the molecular trafficking between the cytoplasm and the nucleus. NPCs are assembled from about 30 different proteins and a growing body of evidence suggests that these nucleoporins are not only acting in the context of NPCs, but also in the nucleoplasm and cytoplasm. In this context it is well accepted that a set of nucleoporins are important regulators of a variety of mitotic processes, including kinetochore assembly, spindle checkpoint control and cytokinesis, whereas others associate with chromatin and administer gene expression. However, the functional importance of nucleoporins go far beyond these roles and this review will provide an overview of the latest insights into the versatility of metazoan nucleoporins with an emphasis on their roles in cell migration, cellular signaling and tissue-specific activities.

Nucleoporins: leaving the nuclear pore complex for a successful mitosis

The nuclear envelope (NE) separates the cytoplasm and the cell nucleus of interphase eukaryotic cells and nuclear pore complexes (NPCs) mediate the macromolecular exchange between these two compartments. The NE and the NPCs of vertebrate cells disassemble during prophase and the nuclear pore proteins (nucleoporins) are distributed within the mitotic cytoplasm. For an increasing number of them active mitotic functions have been assigned over the past few years. Nucleoporins are participating in spindle assembly, kinetochore organisation, and the spindle assembly checkpoint, all processes that control chromosome segregation and are important for maintenance of genome integrity. But nucleoporins are also engaged in early and late mitotic events, such as centrosome positioning and cytokinesis. Here we will highlight recent progress in deciphering the roles for nucleoporins in the distinct steps of mitosis.

Tetracycline-inducible protein expression in pancreatic cancer cells: Effects of CapG overexpression

AIM: To establish stable tetracycline-inducible pancreatic cancer cell lines.

METHODS: Suit-2, MiaPaca-2, and Panc-1 cells were transfected with a second generation reverse tetracycline-controlled transactivator protein (rtTA2S-M2), under the control of either a cytomegalovirus (CMV) or a chicken β-actin promoter, and the resulting clones were characterised.

RESULTS: Use of the chicken (β-actin) promoter proved superior for both the production and maintenance of doxycycline-inducible cell lines. The system proved versatile, enabling transient inducible expression of a variety of genes, including GST-P, CYP2E1, S100A6, and the actin capping protein, CapG. To determine the physiological utility of this system in pancreatic cancer cells, stable inducible CapG expressors were established. Overexpressed CapG was localised to the cytoplasm and the nuclear membrane, but was not observed in the nucleus. High CapG levels were associated with enhanced motility, but not with changes to the cell cycle, or cellular proliferation. In CapG-overexpressing cells, the levels and phosphorylation status of other actin-moduating proteins (Cofilin and Ezrin/Radixin) were not altered. However, preliminary analyses suggest that the levels of other cellular proteins, such as ornithine aminotransferase and enolase, are altered upon CapG induction.

CONCLUSION: We have generated pancreatic-cancer derived cell lines in which gene expression is fully controllable.

Actin and Arp2/3 localize at the centrosome of interphase cells

Although many actin binding proteins such as cortactin and the Arp2/3 activator WASH localize at the centrosome, the presence and conformation of actin at the centrosome has remained elusive. Here, we report the localization of actin at the centrosome in interphase but not in mitotic MDA-MB-231 cells. Centrosomal actin was detected with the anti-actin antibody 1C7 that recognizes antiparallel ("lower dimer") actin dimers. In addition, we report the transient presence of the Arp2/3 complex at the pericentriolar matrix but not at the centrioles of interphase HEK 293T cells. Overexpression of an Arp2/3 component resulted in expansion of the pericentriolar matrix and selective accumulation of the Arp2/3 component in the pericentriolar matrix. Altogether, we hypothesize that the centrosome transiently recruits Arp2/3 to perform processes such as centrosome separation prior to mitotic entry, whereas the observed constitutive centrosomal actin staining in interphase cells reinforces the current model of actin-based centrosome reorientation toward the leading edge in migrating cells.

Decoding pooled RNAi screens by means of barcode tiling arrays

Background

RNAi screens via pooled short hairpin RNAs (shRNAs) have recently become a powerful tool for the identification of essential genes in mammalian cells. In the past years, several pooled large-scale shRNA screens have identified a variety of genes involved in cancer cell proliferation. All of those studies employed microarray analysis, utilizing either the shRNA's half hairpin sequence or an additional shRNA-associated 60 nt barcode sequence as a molecular tag. Here we describe a novel method to decode pooled RNAi screens, namely barcode tiling array analysis, and demonstrate how this approach can be used to precisely quantify the abundance of individual shRNAs from a pool.

Results

We synthesized DNA microarrays with six overlapping 25 nt long tiling probes complementary to each unique 60 nt molecular barcode sequence associated with every shRNA expression construct. By analyzing dilution series of expression constructs we show how our approach allows quantification of shRNA abundance from a pool and how it clearly outperforms the commonly used analysis via the shRNA's half hairpin sequences. We further demonstrate how barcode tiling arrays can be used to predict anti-proliferative effects of individual shRNAs from pooled negative selection screens. Out of a pool of 305 shRNAs, we identified 28 candidate shRNAs to fully or partially impair the viability of the breast carcinoma cell line MDA-MB-231. Individual validation of a subset of eleven shRNA expression constructs with potential inhibitory, as well as non-inhibitory, effects on the cell line proliferation provides further evidence for the accuracy of the barcode tiling approach.

Conclusions

In summary, we present an improved method for the rapid, quantitative and statistically robust analysis of pooled RNAi screens. Our experimental approach, coupled with commercially available lentiviral vector shRNA libraries, has the potential to greatly facilitate the discovery of putative targets for cancer therapy as well as sensitizers of drug toxicity.