Cellular adhesion mediated by factor J, a complement inhibitor. Evidence for nucleolin involvement

Japanese encephalitis virus NS5 protein interacts with nucleolin to enhance the virus replication

Japanese encephalitis virus (JEV) is an arthropod-borne, plus-strand flavivirus causing viral encephalitis in humans with a high case fatality rate. The JEV non-structural protein 5 (NS5) with the RNA-dependent RNA polymerase activity interacts with the viral and host proteins to constitute the replication complex. We have identified the multifunctional protein Nucleolin (NCL) as one of the several NS5-interacting host proteins. We demonstrate the interaction and colocalization of JEV NS5 with NCL in the virus-infected HeLa cells. The siRNA-mediated knockdown of NCL indicated that it was required for efficient viral replication. Importantly, JEV grew to higher titers in cells over-expressing exogenous NCL, demonstrating its pro-viral role. We demonstrated that NS5 interacted with the RRM and GAR domains of NCL. We show that the NCL-binding aptamer AS1411 containing the G-quadruplex (GQ) structure and the GQ ligand BRACO-19 caused significant inhibition of JEV replication. The antiviral effect of AS1411 and BRACO-19 could be overcome in HeLa cells by the overexpression of exogenous NCL. We demonstrated that the synthetic RNAs derived from the 3'-NCR of JEV genomic RNA containing the GQ sequence could bind NCL in vitro. The replication complex binding to the 3'-NCR is required for the viral RNA synthesis. It is likely that NCL present in the replication complex destabilizes the GQ structures in the genomic RNA, thus facilitating the movement of the replication complex resulting in efficient virus replication.IMPORTANCEJapanese encephalitis virus (JEV) is endemic in most parts of South-East Asia and the Western Pacific region, causing epidemics of encephalitis with a high case fatality rate. While a tissue culture-derived JEV vaccine is available, no antiviral therapy exists. The JEV NS5 protein has RNA-dependent RNA polymerase activity. Together with several host and viral proteins, it constitutes the replication complex necessary for virus replication. Understanding the interaction of NS5 with the host proteins could help design novel antivirals. We identified Nucleolin (NCL) as a crucial host protein interactor of JEV NS5 having a pro-viral role in virus replication. The NS5-interacting NCL binds to the G-quadruplex (GQ) structure sequence in the 3'-NCR of JEV RNA. This may smoothen the movement of the replication complex along the genomic RNA, thereby facilitating the virus replication. This study is the first report on how NCL, a host protein, helps in JEV replication through GQ-binding.

Tumor diagnosis using carbon-based quantum dots: Detection based on the hallmarks of cancer

Carbon-based quantum dots (CQDs) have been shown to have promising application value in tumor diagnosis. Their use, however, is severely hindered by the complicated nature of the nanostructures in the CQDs. Furthermore, it seems impossible to formulate the mechanisms involved using the inadequate theoretical frameworks that are currently available for CQDs. In this review, we re-consider the structure-property relationships of CQDs and summarize the current state of development of CQDs-based tumor diagnosis based on biological theories that are fully developed. The advantages and deficiencies of recent research on CQDs-based tumor diagnosis are thus explained in terms of the manifestation of nine essential changes in cell physiology. This review makes significant progress in addressing related problems encountered with other nanomaterials.

To Boost or to Reset: The Role of Lactoferrin in Energy Metabolism

Many pathological conditions, including obesity, diabetes, hypertension, heart disease, and cancer, are associated with abnormal metabolic states. The progressive loss of metabolic control is commonly characterized by insulin resistance, atherogenic dyslipidemia, inflammation, central obesity, and hypertension, a cluster of metabolic dysregulations usually referred to as the "metabolic syndrome". Recently, nutraceuticals have gained attention for the generalized perception that natural substances may be synonymous with health and balance, thus becoming favorable candidates for the adjuvant treatment of metabolic dysregulations. Among nutraceutical proteins, lactoferrin (Lf), an iron-binding glycoprotein of the innate immune system, has been widely recognized for its multifaceted activities and high tolerance. As this review shows, Lf can exert a dual role in human metabolism, either boosting or resetting it under physiological and pathological conditions, respectively. Lf consumption is safe and is associated with several benefits for human health, including the promotion of oral and gastrointestinal homeostasis, control of glucose and lipid metabolism, reduction of systemic inflammation, and regulation of iron absorption and balance. Overall, Lf can be recommended as a promising natural, completely non-toxic adjuvant for application as a long-term prophylaxis in the therapy for metabolic disorders, such as insulin resistance/type II diabetes and the metabolic syndrome.

Interaction of Nucleolin with the Fusion Protein of Avian Metapneumovirus Subgroup C Contributes to Viral Replication

Avian metapneumovirus subgroup C (aMPV/C) is highly pathogenic to various avian species with acute respiratory tract clinicopathology and/or drops in egg production. Nucleolin (NCL), an important nucleolar protein, has been shown to regulate multiple viral replication and serve as a functional receptor for viral entry and internalization. Whether NCL is involved in aMPV/C pathogenesis is not known. In this study, we found that aMPV/C infection altered the subcellular localization of NCL in cultured cells. siRNA-targeted NCL resulted in a remarkable decline in aMPV/C replication in Vero cells. DF-1 cells showed a similar response after CRISPR/Cas9-mediated knock out of NCL during aMPV/C infection. Conversely, NCL overexpression significantly increased aMPV/C replication. Pretreatment with AS1411-a aptamer, a guanine (G)-rich oligonucleotide that forms four-stranded structures and competitively binding to NCL, decreased aMPV/C replication and viral titers in cultured cells. Additionally, we found that the aMPV/C fusion (F) protein specifically interacts with NCL through its central domain and that AS1411 disrupts this interaction, thus inhibiting viral replication. Taken together, these results reveal that the aMPV/C F protein interacts with NCL, which is employed by aMPV/C for efficient replication, thereby highlighting the strategic potential for control and therapy of aMPV/C infection.

Fluorescent Polymer-AS1411-Aptamer Probe for dSTORM Super-Resolution Imaging of Endogenous Nucleolin

Nucleolin is a multifunctional protein involved in essential biological processes. To precisely localize it and unravel its different roles in cells, fluorescence imaging is a powerful tool, especially super-resolution techniques. Here, we developed polymer-aptamer probes, both small and bright, adapted to direct stochastic optical reconstruction microscopy (dSTORM). Well-defined fluorescent polymer chains bearing fluorophores (AlexaFluor647) and a reactive end group were prepared via RAFT polymerization. The reactive end-group was then used for the oriented conjugation with AS1411, a DNA aptamer that recognizes nucleolin with high affinity. Conjugation via strain-promoted alkyne/azide click chemistry (SPAAC) between dibenzylcyclooctyne-ended fluorescent polymer chains and 3'-azido-functionalized nucleic acids proved to be the most efficient approach. In vitro and in cellulo evaluations demonstrated that selective recognition for nucleolin was retained. Their brightness and small size make these polymer-aptamer probes an appealing alternative to immunofluorescence, especially for super-resolution (10-20 nm) nanoscopy. dSTORM imaging demonstrated the ability of our fluorescent polymer-aptamer probe to provide selective and super-resolved detection of cell surface nucleolin.

Nucleolin mediates the binding of cancer cells to L-selectin under conditions of lymphodynamic shear stress

Head and neck squamous cell carcinoma (HNSCC) cells bind to lymphocytes via L-selectin in a shear-dependent manner. This interaction takes place exclusively under low-shear stress conditions, such as those found within the lymph node parenchyma. This represents a novel functional role for L-selectin-selectin ligand interactions. Our previous work has characterized as-of-yet unidentified L-selectin ligands expressed by HNSCC cells that are specifically active under conditions of low shear stress consistent with lymph flow. Using an affinity purification approach, we now show that nucleolin expressed on the surface of HNSCC cells is an active ligand for L-selectin. Parallel plate chamber flow-based experiments and atomic force microscopy (AFM) experiments show that nucleolin is the main functional ligand under these low-force conditions. Furthermore, AFM shows a clear relationship between work of deadhesion and physiological loading rates. Our results reveal nucleolin as the first major ligand reported for L-selectin that operates under low-shear stress conditions.

Respiratory syncytial virus prolifically infects N2a neuronal cells, leading to TLR4 and nucleolin protein modulations and RSV F protein co-localization with TLR4 and nucleolin

BACKGROUND

Respiratory syncytial virus (RSV) infects the central nervous system, resulting in neurological symptoms. However, the precise underlying pathogenic mechanisms have not been elucidated. In the present study, the infectivity of RSV on N2a neuronal cells and the possible roles of Toll-like receptor 4 (TLR4) and nucleolin (C23) during RSV infection were investigated.

METHODS

We compared two experimental groups (infected and non-infected) and monitored the RSV viral titers in the culture supernatant by a viral plaque assay. We also inspected the morphology of the nucleus in infected N2a cells. We measured the level of RSV F protein and studied its co-localization with TLR4 and nucleolin using immunofluorescence assays and laser confocal microscopy. The potential interaction of RSV F protein with TLR4 and nucleolin was examined by coimmunoprecipitation. The expression changes of TLR4, nucleolin, TLR3 and TLR7 proteins in N2a cells and IL-6 and TNF-α in the culture supernatant were investigated by Western Blot analysis and ELISA assay. Changes in neuronal cell apoptosis status was examined by flow cytometry.

RESULTS

The results demonstrated prolific RSV infection of N2a cells, which triggered a decrease of NeuN protein expression, coinciding with an increase of nuclear lesions, F protein expression, RSV viral titers, and late apoptotic levels of N2a cells. RSV infection induced co-localization of RSV F protein with TLR4 and nucleolin, which could potentially lead to a direct interaction. Furthermore, it was found that TLR4 and nucleolin levels increased early after infection and decreased subsequently, whereas TLR3 and TLR7 expression increased throughout RSV infection.

CONCLUSION

The RSV Long strain can prolifically infect N2a neuronal cells, modulating the expression of TLR4 and nucleolin, as well as TLR3, TLR7 and their downstream inflammatory factors, and inducing the co-localization of the RSV F protein with TLR4 and nucleolin.

New perspectives of physiological and pathological functions of nucleolin (NCL)

Nucleolin (NCL) is a multifunctional protein that mainly localized in the nucleolus, it is also found in the nucleoplasm, cytoplasm and cell membrane. The three main structural domains allow the interaction of NCL with different proteins and RNA sequences. Moreover, specific post-translational modifications and its shuttling property also contribute to its multifunctionality. NCL has been demonstrated to be involved in a variety of aspects such as ribosome biogenesis, chromatin organization and stability, DNA and RNA metabolism, cytokinesis, cell proliferation, angiogenesis, apoptosis regulation, stress response and microRNA processing. NCL has been increasingly implicated in several pathological processes, especially in tumorigenesis and viral infection, which makes NCL a potential target for the development of anti-tumor and anti-viral strategies. In this review, we present an overview on the structure, localizations and various functions of NCL, and further describe how the multiple functions of NCL are correlated to its multiple cellular distributions.

Nuclear factor kappa-B- and activator protein-1-mediated immunostimulatory activity of compound K in monocytes and macrophages

Background

Compound K (CK) is a bioactive derivative of ginsenoside Rb1 in Panax ginseng (Korean ginseng). Its biological and pharmacological activities have been studied in various disease conditions, although its immunomodulatory role in innate immunity mediated by monocytes/macrophages has been poorly understood. In this study, we aimed to elucidate the regulatory role of CK on cellular events mediated by monocytes and macrophages in innate immune responses.

Methods

The immunomodulatory role of CK was explored by various immunoassays including cell-cell adhesion, fibronectin adhesion, cell migration, phagocytic uptake, costimulatory molecules, reactive oxygen species production, luciferase activity, and by the measurement of mRNA levels of proinflammatory genes.

Results

Compound K induced cell cluster formation through cell-cell adhesion, cell migration, and phagocytic activity, but it suppressed cell-tissue interactions in U937 and RAW264.7 cells. Compound K also upregulated the surface expression of the cell adhesion molecule cluster of differentiation (CD) 43 (CD43) and costimulatory molecules CD69, CD80, and CD86, but it downregulated the expression of monocyte differentiation marker CD82 in RAW264.7 cells. Moreover, CK induced the release of reactive oxygen species and induced messenger RNA expression of proinflammatory genes, inducible nitric oxide synthase, and tumor necrosis factor-alpha by enhancing the nuclear translocation and transcriptional activities of nuclear factor kappa-B and activator protein-1.

Conclusion

Our results suggest that CK has an immunomodulatory role in innate immune responses through regulating various cellular events mediated by monocytes and macrophages.

Expression of Nucleolin Affects Microtubule Dynamics

Nucleolin is present in diverse cellular compartments and is involved in a variety of cellular processes from nucleolar structure and function to intracellular trafficking, cell adhesion and migration. Recently, nucleolin has been localized at the mature centriole where it is involved in microtubule nucleation and anchoring. Although this new function of nucleolin linked to microtubule regulation has been identified, the global effects of nucleolin on microtubule dynamics have not been addressed yet. In the present study, we analyzed the roles of nucleolin protein levels on global microtubule dynamics by tracking the EB3 microtubule plus end binding protein in live cells. We have found that during microtubule growth phases, nucleolin affects both the speed and life time of polymerization and by analyzing catastrophe events, we showed that nucleolin reduces catastrophe frequency. This new property of nucleolin was then confirmed in a cold induced microtubule depolymerization experiment in which we have found that cold resistant microtubules were totally destabilized in nucleolin depleted cells. Altogether, our data demonstrate a new function of nucleolin on microtubule stabilization, thus bringing novel insights into understanding the multifunctional properties of nucleolin in healthy and cancer cells.

The roles of nucleolin subcellular localization in cancer

Nucleolin (NCL) is one of the most abundant non ribosomal protein of the nucleolus where it plays a central role in polymerase I transcription. NCL is also found outside of the nucleolus, in the nucleoplasm, cytoplasm as well as on the cell membrane. It acts in all cell compartments to control cellular homeostasis and therefore each cellular pool of NCL can play a different role in cancer development. NCL overexpression and its increased localization at the cell membrane is a common feature of several tumor cells. In cancer cells, NCL overexpression influences cell survival, proliferation and invasion through its action on different cellular pathways. In this review, we describe how the multiple functions of NCL that are associated to its multiple cellular localization can participate to the development of cancer.

The dietary flavonoid Kaempferol mediates anti-inflammatory responses via the Src, Syk, IRAK1, and IRAK4 molecular targets

Even though a lot of reports have suggested the anti-inflammatory activity of kaempferol (KF) in macrophages, little is known about its exact anti-inflammatory mode of action and its immunopharmacological target molecules. In this study, we explored anti-inflammatory activity of KF in LPS-treated macrophages. In particular, molecular targets for KF action were identified by using biochemical and molecular biological analyses. KF suppressed the release of nitric oxide (NO) and prostaglandin E2 (PGE2), downregulated the cellular adhesion of U937 cells to fibronectin (FN), neutralized the generation of radicals, and diminished mRNA expression levels of inflammatory genes encoding inducible NO synthase (iNOS), TNF-α, and cyclooxygenase- (COX-) 2 in lipopolysaccharide- (LPS-) and sodium nitroprusside- (SNP-) treated RAW264.7 cells and peritoneal macrophages. KF reduced NF-κB (p65 and p50) and AP-1 (c-Jun and c-Fos) levels in the nucleus and their transcriptional activity. Interestingly, it was found that Src, Syk, IRAK1, and IRAK4 responsible for NF-κB and AP-1 activation were identified as the direct molecular targets of KF by kinase enzyme assays and by measuring their phosphorylation patterns. KF was revealed to have in vitro and in vivo anti-inflammatory activity by the direct suppression of Src, Syk, IRAK1, and IRAK4, involved in the activation of NF-κB and AP-1.

Cell-surface nucleolin acts as a central mediator for carcinogenic, anti-carcinogenic, and disease-related ligands

PURPOSE

Cell-surface nucleolin in human gastric cancer cell lines is a receptor for TNF-α-inducing protein (Tipα) of Helicobacter pylori. The binding complex of nucleolin and Tipα is internalized into the cells and then induces tumor progression of human gastric cancer. Surface nucleolin is also a receptor of human immunodeficiency virus-1, and the anti-HIV pseudopeptide (HB-19) showed anti-carcinogenic activity in vivo. Surface nucleolin has dual functions depending on the ligands: In order to understand the mechanisms of surface nucleolin, it is necessary to review surface nucleolin and its relation to carcinogenic ligands and anti-carcinogenic ligands. Other ligands can be grouped among disease-related ligands, which is an important new topic for the prevention of various ailments.

RESULTS AND DISCUSSION

This paper mainly deals with two ligands of surface nucleolin, Tipα and pseudopeptide HB-19. The binding complex of nucleolin and Tipα induces expression of TNF-α and chemokine genes and activates NF-κB in gastric cancer cells of humans and mice. However, when human gastric cancer cell line MKN-1 was transfected with nucleolin-targeted siRNA, the result was inhibition of cell migration and elongation induced by Tipα. The amount of surface nucleolin was reduced in membrane fraction of the nucleolin knockdown MKN-1 cells, but the amount of nucleolin in the cytosol or nuclear fractions of the cells did not change. The results indicate that surface nucleolin acts as a carcinogenic mediator for Tipα of H. pylori. In contrast, both the viral external envelop glycoprotein gp120 of HIV and the anti-HIV pseudopeptide HB-19 bind to surface nucleolin. Through this binding, treatment with HB-19 inhibited tumor development in human breast cancer cell line MDA-MB-231 and rhabdoid tumor cell line derived from Wilms's tumor in xenograft nude mouse models. The results show that surface nucleolin acts as an anti-carcinogenic mediator for HB-19.

CONCLUSION

Based on these discrete functions of surface nucleolin, the binding complex of carcinogenic ligands and surface nucleolin seems to be competing with that of anti-carcinogenic ligands and surface nucleolin. Moreover, carcinogenic ligands derived from endogenous sources play a significant role in human cancer development, and the interaction of surface nucleolin with disease-related ligands will be a new research subject for the prevention and treatment of various ailments.

Lancemaside A from Codonopsis lanceolata modulates the inflammatory responses mediated by monocytes and macrophages

In this study, we aimed to examine the cellular and molecular mechanisms of lancemaside A from Codonopsis lanceolata (Campanulaceae) in the inflammatory responses of monocytes (U937 cells) and macrophages (RAW264.7 cells). Lancemaside A significantly suppressed the inflammatory functions of lipopolysaccharide- (LPS-) treated RAW264.7 cells by suppressing the production of nitric oxide (NO), the expression of the NO-producing enzyme inducible NO synthase (iNOS), the upregulation of the costimulatory molecule CD80, and the morphological changes induced by LPS exposure. In addition, lancemaside A diminished the phagocytic activity of RAW264.7 cells and boosted the neutralizing capacity of these cells when treated with the radical generator sodium nitroprusside (SNP). Interestingly, lancemaside A strongly blocked the adhesion activity of RAW264.7 cells to plastic culture plates, inhibited the cell-cell and cell-fibronectin (FN) adhesion of U937 cells that was triggered by treatment with an anti-β1-integrin (CD29) antibody and immobilized FN, respectively. By evaluating the activation of various intracellular signaling pathways and the levels of related nuclear transcription factors, lancemaside A was found to block the activation of inhibitor of κB kinase (IKK) and p65/nuclear factor- (NF-) κB. Taken together, our findings strongly suggest that the anti-inflammatory function of lancemaside A is the result of its strong antioxidative and IKK/NF-κB inhibitory activities.

20S-dihydroprotopanaxadiol, a ginsenoside derivative, boosts innate immune responses of monocytes and macrophages

20S-dihydroprotopanaxadiol (2H-PPD) is a derivative of protopanaxadiol, a glycone of ginsenosides prepared from Panax ginseng. Although ginsenosides and acidic polysaccharides are known to be major active ingredients in ginseng, the immunopharmacological activities of their metabolites and derivatives have not been fully explored. In this study, we aimed to elucidate the regulatory action of 2H-PPD on the function of monocytes and macrophages in innate immune responses. 2H-PPD was able to boost the phagocytic uptake of fluorescein isothiocyanate-dextran in macrophages and enhance the generation of radicals (reactive oxygen species) in sodium nitroprusside-treated RAW264.7 cells. The surface levels of the costimulatory molecules such as CD80 and CD86 were also increased during 2H-PPD treatment. In addition, this compound boosted U937 cellcell aggregation induced by CD29 and CD43 antibodies, but not by cell-extracellular matrix (fibronectin) adhesion. Similarly, the surface levels of CD29 and CD43 were increased by 2H-PPD exposure. Therefore, our results strongly suggest that 2H-PPD has the pharmacological capability to upregulate the functional role of macrophages/monocytes in innate immunity.

20S-dihydroprotopanaxatriol modulates functional activation of monocytes and macrophages

20S-dihydroprotopanaxatriol (2H-PPT) is a derivative of protopanaxatrol from ginseng. Unlike other components from Panax ginseng, the pharmacological activity of this compound has not been fully elucidated. In this study, we investigated the modulatory activity of 2H-PPT on the cellular responses of monocytes and macrophages to understand its immunoregulatory actions. 2H-PPT strongly upregulated the release of radicals in sodium nitroprusside-treated RAW264.7 cells and the surface levels of costimulatory molecule CD86. More importantly, this compound remarkably suppressed nitric oxide production, morphological changes, phagocytic uptake, cell-cell aggregation, and cell-matrix adhesion in RAW264.7 and U937 cells in the presence or absence of lipopolysaccharide, anti-CD43 antibody, fibronectin, and phorbal 12-myristate 13-acetate. Therefore, our results suggest that 2H-PPT can be applied as a novel functional immunoregulator of macrophages and monocytes.

Prognostic significance of the combined score of endothelial expression of nucleolin and CD31 in surgically resected non-small cell lung cancer

Nucleolin is implicated to play a role in angiogenesis, a vital process in tumor growth and metastasis. However, the presence and clinical relevance of nucleolin in human non small cell lung cancer (NSCLC) remains largely unknown. In this study, we explored the expression and prognostic implication of nucleolin in surgically resected NSCLC patients. A cohort of 146 NSCLC patients who underwent surgical resection was selected for tissue microarray. In this tissue microarray, nucleolin expression was measured by immunofluorescence. Staining for CD31, a marker of endothelial cells, was performed to mark blood vessels. A Cox proportional hazards model was used to assess the prognostic significance of nucleolin. Nucleolin expression was observed in 34.2% of all patients, and 64.1% in high CD31 expression patients. The disease-free survival (DFS) was significantly shorter in patients with high nucleolin (CD31(hi)NCL(hi)) compared to patients with low tumor blood vessels (CD31(lo)NCL(lo)) (5 ys of DFS 24% vs 64%, p = 0.002). Such a difference was demonstrated in the following stratified analyses: stage I (p<0.001), squamous cell carcinoma and adenosquamous cell carcinoma (p = 0.028), small tumor (<5 cm, p = 0.008), and surgery alone (p = 0.015). Multivariate analysis further revealed that nucleolin expression independently predicted for worse survival (p = 0.003). This study demonstrates that nucleolin is associated with the clinical outcomes in postoperative NSCLC patients. Thus, the expression levels of nucleolin may provide a new prognostic marker to identify patients at higher risk for treatment failure, especially in some subgroups.

The pseudopeptide HB-19 binds to cell surface nucleolin and inhibits angiogenesis

Background

Nucleolin is a protein over-expressed on the surface of tumor and endothelial cells. Recent studies have underlined the involvement of cell surface nucleolin in tumor growth and angiogenesis. This cell surface molecule serves as a receptor for various ligands implicated in pathophysiological processes such as growth factors, cell adhesion molecules like integrins, selectins or laminin-1, lipoproteins and viruses (HIV and coxsackie B). HB-19 is a synthetic multimeric pseudopeptide that binds cell surface expressed nucleolin and inhibits both tumor growth and angiogenesis.

Methodology/principal findings

In the present work, we further investigated the biological actions of pseudopeptide HB-19 on HUVECs. In a previous work, we have shown that HB-19 inhibits the in vivo angiogenesis on the chicken embryo CAM assay. We now provide evidence that HB-19 inhibits the in vitro adhesion, migration and proliferation of HUVECs without inducing their apoptosis. The above biological actions seem to be regulated by SRC, ERK1/2, AKT and FAK kinases as we found that HB-19 inhibits their activation in HUVECs. Matrix metalloproteinases (MMPs) play crucial roles in tumor growth and angiogenesis, so we investigated the effect of HB-19 on the expression of MMP-2 and we found that HB-19 downregulates MMP-2 in HUVECs. Finally, down regulation of nucleolin using siRNA confirmed the implication of nucleolin in the biological actions of these peptides.

Conclusions/significance

Taken together, these results indicate that HB-19 could constitute an interesting tool for tumor therapy strategy, targeting cell surface nucleolin.

Nucleolin mediates the antiangiogenesis effect of the pseudopeptide N6L

BACKGROUND

Nucleolin is a protein over-expressed on the surface of activated cells. Recent studies have underlined the involvement of cell surface nucleolin in angiogenesis processes. This cell surface molecule serves as a receptor for various ligands implicated in pathophysiological processes such as growth factors, cell adhesion molecules like integrins, selectins or laminin-1, lipoproteins and viruses. N6L is a synthetic multimeric pseudopeptide that binds cell surface expressed nucleolin and inhibits cell proliferation.

RESULTS

In the present work, we further investigated the mechanisms of action of pseudopeptide N6L on angiogenesis using HUVECs. We provide evidence that N6L inhibits the in vitro adhesion, proliferation and migration of HUVECs without inducing their apoptosis. In addition, we found that N6L downregulates MMP-2 in HUVECs. The above biological actions are regulated by SRC, ERK1/2, AKT and FAK kinases as we found that N6L inhibits their activation in HUVECs. Finally, down regulation of nucleolin using siRNA demonstrated the implication of nucleolin in the biological actions of these peptides.

CONCLUSIONS

Taken together, these results indicate that N6L could constitute an interesting therapeutic tool for treating diseases associated with excessive angiogenesis.

Targeting surface nucleolin with multivalent HB-19 and related Nucant pseudopeptides results in distinct inhibitory mechanisms depending on the malignant tumor cell type

BACKGROUND

Nucleolin expressed at the cell surface is a binding protein for a variety of ligands implicated in tumorigenesis and angiogenesis. By using a specific antagonist that binds the C-terminal RGG domain of nucleolin, the HB-19 pseudopeptide, we recently reported that targeting surface nucleolin with HB-19 suppresses progression of established human breast tumor cells in the athymic nude mice, and delays development of spontaneous melanoma in the RET transgenic mice.

METHODS

By the capacity of HB-19 to bind stably surface nucleolin, we purified and identified nucleolin partners at the cell surface. HB-19 and related multivalent Nucant pseudopeptides, that present pentavalently or hexavalently the tripeptide Lysψ(CH2N)-Pro-Arg, were then used to show that targeting surface nucleolin results in distinct inhibitory mechanisms on breast, prostate, colon carcinoma and leukemia cells.

RESULTS

Surface nucleolin exists in a 500-kDa protein complex including several other proteins, which we identified by microsequencing as two Wnt related proteins, Ku86 autoantigen, signal recognition particle subunits SRP68/72, the receptor for complement component gC1q-R, and ribosomal proteins S4/S6. Interestingly, some of the surface-nucleolin associated proteins are implicated in cell signaling, tumor cell adhesion, migration, invasion, cell death, autoimmunity, and bacterial infections. Surface nucleolin in the 500-kDa complex is highly stable. Surface nucleolin antagonists, HB-19 and related multivalent Nucant pseudopeptides, exert distinct inhibitory mechanisms depending on the malignant tumor cell type. For example, in epithelial tumor cells they inhibit cell adhesion or spreading and induce reversion of the malignant phenotype (BMC cancer 2010, 10:325) while in leukemia cells they trigger a rapid cell death associated with DNA fragmentation. The fact that these pseudopeptides do not cause cell death in epithelial tumor cells indicates that cell death in leukemia cells is triggered by a specific signaling mechanism, rather than nonspecific cellular injury.

CONCLUSIONS

Our results suggest that targeting surface nucleolin could change the organization of the 500-kDa complex to interfere with the proper functioning of surface nucleolin and the associated proteins, and thus lead to distinct inhibitory mechanisms. Consequently, HB-19 and related Nucant pseudopeptides provide novel therapeutic opportunities in treatment of a wide variety of cancers and related malignancies.

N-Glycosylation influences the structure and self-association abilities of recombinant nucleolin

Nucleolin is a major nucleolar protein involved in fundamental processes of ribosome biogenesis, regulation of cell proliferation and growth. Nucleolin is known to shuttle between nucleus, cytoplasm and cell surface. We have previously found that nucleolin undergoes complex N- and O-glycosylations in extra-nuclear isoforms. We found that surface nucleolin is exclusively glycosylated and that N-glycosylation is required for its expression on the cells. Interestingly, the two N-glycans are located in the RNA-binding domains (RBDs) which participate in the self-association properties of nucleolin. We hypothesized that the occupancy of RBDs by N-glycans plays a role in these self-association properties. Here, owing to the inability to quantitatively produce full-size nucleolin, we expressed four N-glycosylation nucleolin variants lacking the N-terminal acidic domain in a baculovirus/insect cell system. As assessed by heptafluorobutyrate derivatization and mass spectrometry, this strategy allowed the production of proteins bearing or not paucimannosidic-type glycans on either one or two of the potential N-glycosylation sites. Their structure was investigated by circular dichroism and fluorimetry, and their ability to self-interact was analyzed by electrophoresis and surface plasmon resonance. Our results demonstrate that all nucleolin-derived variants are able to self-interact and that N-glycosylation on both RBD1 and RBD3, or RBD3 alone, but not RBD1 alone, modifies the structure of the N-terminally truncated nucleolin and enhances its self-association properties. In contrast, N-glycosylation does not modify interaction with lactoferrin, a ligand of cell surface nucleolin. Our results suggest that the occupancy of the N-glycosylation sites may contribute to expression and functions of surface nucleolin.

A simple approach to cancer therapy afforded by multivalent pseudopeptides that target cell-surface nucleoproteins

Recent studies have implicated the involvement of cell surface forms of nucleolin in tumor growth. In this study, we investigated whether a synthetic ligand of cell-surface nucleolin known as N6L could exert antitumor activity. We found that N6L inhibits the anchorage-dependent and independent growth of tumor cell lines and that it also hampers angiogenesis. Additionally, we found that N6L is a proapoptotic molecule that increases Annexin V staining and caspase-3/7 activity in vitro and DNA fragmentation in vivo. Through affinity isolation experiments and mass-spectrometry analysis, we also identified nucleophosmin as a new N6L target. Notably, in mouse xenograft models, N6L administration inhibited human tumor growth. Biodistribution studies carried out in tumor-bearing mice indicated that following administration N6L rapidly localizes to tumor tissue, consistent with its observed antitumor effects. Our findings define N6L as a novel anticancer drug candidate warranting further investigation.

Suppression of tumorigenicity of rhabdoid tumor derived G401 cells by the multivalent HB-19 pseudopeptide that targets surface nucleolin

Several studies have indicated that the cell-surface expressed nucleolin is implicated in tumorigenesis and angiogenesis, and represents an important target for cancer therapy. Here we show that treatment of rhabdoid tumor derived G401 cells with a nucleolin antagonist, the HB-19 pseudopeptide, could restore contact inhibition, impair anchorage-independent growth, and suppress tumor development in nude mice. G401 cells grow without contact inhibition, which is an in vitro characteristic property of malignant tumor cells. At concentrations of HB-19 that does not affect cell viability and multiplication index, there is restoration of contact inhibition thus suggesting that HB-19 treatment causes reversion of the malignant phenotype. Accordingly, HB-19 pretreated G401 cells lose the capacity to form colonies in soft agar. When assayed for tumorigenicity in nude mice, only 50% of mice injected with HB-19 pretreated G401 cells developed tumors with the mean tumor weight of 0.32 g, compared to 100% of mice injected with control G401 cells with the mean tumor weight of 2.36 g. Interestingly, the restoration of contact inhibition in HB-19 treated G401 cells is concomitant with marked reduction of transcripts coding the Wilms' tumor 1 gene, matrix metalloproteinase-2, epithelial isoform of CD44, and vascular endothelial growth factor, whereas no apparent modification is detected for transcripts coding the proto-oncogene c-Myc, anti-apoptotic Bcl-2, pro-apoptotic Bax, tissue inhibitor of metalloproteinase TIMP-1, angiogenesis inhibitor TSP-1, and growth factor Midkine. These findings indicate that the molecular mechanism of action of HB-19 on such highly malignant rhabdoid tumor cells is associated with a selective inhibitory effect on the expression of genes implicated in tumorigenesis and angiogenesis.

Arachidonic acid stimulates formation of a novel complex containing nucleolin and RhoA

Arachidonic acid (AA) stimulates cell adhesion through a p38 mitogen activated protein kinase-mediated RhoA signaling pathway. Here we report that a proteomic screen following AA-treatment identified nucleolin, a multifunctional nucleolar protein, in a complex with the GTPase, RhoA, that also included the Rho kinase, ROCK. AA-stimulated cell adhesion was inhibited by expression of nucleolin-targeted shRNA and formation of the multiprotein complex was blocked by expression of dominant-negative RhoA. AA-treatment also induced ROCK-dependent serine phosphorylation of nucleolin and translocation of nucleolin from the nucleus to the cytoplasm, where it appeared to co-localize with RhoA. These data suggest the existence of a new signaling pathway through which the location and post-translational state of nucleolin are modulated.

Surface expressed nucleolin is constantly induced in tumor cells to mediate calcium-dependent ligand internalization

BACKGROUND

Nucleolin is one of the major proteins of the nucleolus, but it is also expressed on the cell surface where is serves as a binding protein for variety of ligands implicated in tumorigenesis and angiogenesis. Emerging evidence suggests that the cell-surface expressed nucleolin is a strategic target for an effective and nontoxic cancer therapy.

METHODOLOGY/PRINCIPAL FINDINGS

By monitoring the expression of nucleolin mRNA, and by measuring the level of nucleolin protein recovered from the surface and nucleus of cells, here we show that the presence of nucleolin at the cell surface is dependent on the constant induction of nucleolin mRNA. Indeed, inhibitors of RNA transcription or translation block expression of surface nucleolin while no apparent effect is observed on the level of nucleolin in the nucleus. The estimated half-life of surface nucleolin is less than one hour, whereas that of nuclear nucleolin is more than 8 hours. Nucleolin mRNA induction is reduced markedly in normal fibroblasts that reach confluence, while it occurs continuously even in post-confluent epithelial tumor cells consistent with their capacity to proliferate without contact inhibition. Interestingly, cold and heat shock induce nucleolin mRNA concomitantly to enhanced mRNA expression of the heat shock protein 70, thus suggesting that surface nucleolin induction also occurs in response to an environmental insult. At the cell surface, one of the main functions of nucleolin is to shuttle specific extracellular ligands by an active transport mechanism, which we show here to be calcium dependent.

CONCLUSION/SIGNIFICANCE

Our results demonstrate that the expression of surface nucleolin is an early metabolic event coupled with tumor cell proliferation and stress response. The fact that surface nucleolin is constantly and abundantly expressed on the surface of tumor cells, makes them a preferential target for the inhibitory action of anticancer agents that target surface nucleolin.

Targeting surface nucleolin with a multivalent pseudopeptide delays development of spontaneous melanoma in RET transgenic mice

BACKGROUND

The importance of cell-surface nucleolin in cancer biology was recently highlighted by studies showing that ligands of nucleolin play critical role in tumorigenesis and angiogenesis. By using a specific antagonist that binds the C-terminal tail of nucleolin, the HB-19 pseudopeptide, we recently reported that HB-19 treatment markedly suppressed the progression of established human breast tumor cell xenografts in the athymic nude mice without apparent toxicity.

METHODS

The in vivo antitumoral action of HB-19 treatment was assessed on the spontaneous development of melanoma in the RET transgenic mouse model. Ten days old RET mice were treated with HB-19 in a prophylactic setting that extended 300 days. In parallel, the molecular basis for the action of HB-19 was investigated on a melanoma cell line (called TIII) derived from a cutaneous nodule of a RET mouse.

RESULTS

HB-19 treatment of RET mice caused a significant delay in the onset of cutaneous tumors, several-months delay in the incidence of large tumors, a lower frequency of cutaneous nodules, and a reduction of visceral metastatic nodules while displaying no toxicity to normal tissue. Moreover, microvessel density was significantly reduced in tumors recovered from HB-19 treated mice compared to corresponding controls. Studies on the melanoma-derived tumor cells demonstrated that HB-19 treatment of TIII cells could restore contact inhibition, impair anchorage-independent growth, and reduce their tumorigenic potential in mice. Moreover, HB-19 treatment caused selective down regulation of transcripts coding matrix metalloproteinase 2 and 9, and tumor necrosis factor-alpha in the TIII cells and in melanoma tumors of RET mice.

CONCLUSIONS

Although HB-19 treatment failed to prevent the development of spontaneous melanoma in the RET mice, it delayed for several months the onset and frequency of cutaneous tumors, and exerted a significant inhibitory effect on visceral metastasis. Consequently, HB-19 could provide a novel therapeutic agent by itself or as an adjuvant therapy in association with current therapeutic interventions on a virulent cancer like melanoma.

Regulatory effect of cinnamaldehyde on monocyte/macrophage-mediated inflammatory responses

Cinnamaldehyde (CA) has been known to exhibit anti-inflammatory and anticancer effects. Although numerous pharmacological effects have been demonstrated, regulatory effect of CA on the functional activation of monocytes and macrophages has not been fully elucidated yet. To evaluate its monocyte/macrophage-mediated immune responses, macrophages activated by lipopolysaccharide (LPS), and monocytes treated with proaggregative antibodies, and extracellular matrix protein fibronectin were employed. CA was able to suppress both the production of nitric oxide (NO) and upregulation of surface levels of costimulatory molecules (CD80 and CD69) and pattern recognition receptors (toll-like receptor 2 (TLR2) and complement receptor (CR3)). In addition, CA also blocked cell-cell adhesion induced by the activation of CD29 and CD43 but not cell-fibronectin adhesion. Immunoblotting analysis suggested that CA inhibition was due to the inhibition of phosphoinositide-3-kinase (PI3K) and phosphoinositide-dependent kinase (PDK)1 as well as nuclear factor-(NF-) kappaB activation. In particular, thiol compounds with sulphydryl group, L-cysteine and dithiothreitol (DTT), strongly abrogated CA-mediated NO production and NF-kappaB activation. Therefore, our results suggest that CA can act as a strong regulator of monocyte/macrophage-mediated immune responses by thiolation of target cysteine residues in PI3K or PDK1.

Inhibitory effect of saponin fraction from Codonopsis lanceolata on immune cell-mediated inflammatory responses

Saponin components are known to be pharmaceutically, cosmetically and nutraceutically valuable principles found in various herbal medicine. In this study, we evaluated the inhibitory role of saponin fraction (SF), prepared from C. lanceolata, an ethnopharmacologically famous plant, on various inflammatory responses managed by monocytes, macrophages, lymphocytes and mast cells. SF clearly suppressed the release of nitric oxide (NO) and tumor necrosis factor (TNF)-alpha, but not prostaglandin E(2) (PGE(2)). While this fraction did not scavenge the reactivity of SNP-induced radicals in RAW264. 7 cells, it negatively modulated the phagocytic uptake of macrophages treated with FITC-dextran. Interestingly, SF completely diminished cell-cell adhesion events induced by both CD29 and CD43, but not cell-fibronectin adhesion. Concanavalin (Con) A [as well phytohemaglutinin A (PHA)]-induced proliferation of splenic lymphocytes as well as interferon (IFN)-gamma production were also clearly suppressed by SF treatment. Finally, SF also significantly blocked the degranulation process of mast cell line RBL-2H3 cell as assessed by DNP-BSA-induced beta-hexosaminidase activity. The anti-inflammatory activities of SF on NO production seemed to be due to inhibition of nuclear factor (NF)-kappaB activation signaling, since it blocked the phosphorylation of inhibitor of kappaB (IkappaB)alpha as well as inducible NO synthase (iNOS) expression. Therefore, these results suggest that SF may be considered as a promising herbal medicine with potent anti-inflammatory actions.

Discovery and development of the G-rich oligonucleotide AS1411 as a novel treatment for cancer

Certain guanine-rich (G-rich) DNA and RNA molecules can associate intermolecularly or intramolecularly to form four stranded or "quadruplex" structures, which have unusual biophysical and biological properties. Several synthetic G-rich quadruplex-forming oligodeoxynucleotides have recently been investigated as therapeutic agents for various human diseases. We refer to these biologically active G-rich oligonucleotides as aptamers because their activities arise from binding to protein targets via shape-specific recognition (analogous to antibody-antigen binding). As therapeutic agents, the G-rich aptamers may have some advantages over monoclonal antibodies and other oligonucleotide-based approaches. For example, quadruplex oligonucleotides are non-immunogenic, heat stable and they have increased resistance to serum nucleases and enhanced cellular uptake compared to unstructured sequences. In this review, we describe the characteristics and activities of G-rich oligonucleotides. We also give a personal perspective on the discovery and development of AS1411, an antiproliferative G-rich phosphodiester oligonucleotide that is currently being tested as an anticancer agent in Phase II clinical trials. This molecule functions as an aptamer to nucleolin, a multifunctional protein that is highly expressed by cancer cells, both intracellularly and on the cell surface. Thus, the serendipitous discovery of the G-rich oligonucleotides also led to the identification of nucleolin as a new molecular target for cancer therapy.

The cell surface expressed nucleolin is a glycoprotein that triggers calcium entry into mammalian cells

Nucleolin is an ubiquitous nucleolar phosphoprotein involved in fundamental aspects of transcription regulation, cell proliferation and growth. It has also been described as a shuttling molecule between nucleus, cytosol and the cell surface. Several studies have demonstrated that surface nucleolin serves as a receptor for various extracellular ligands implicated in cell proliferation, differentiation, adhesion, mitogenesis and angiogenesis. Previously, we reported that nucleolin in the extranuclear cell compartment is a glycoprotein containing N- and O-glycans. In the present study, we show that glycosylation is an essential requirement for surface nucleolin expression, since it is prevented when cells are cultured in the presence of tunicamycin, an inhibitor of N-glycosylation. Accordingly, surface but not nuclear nucleolin is radioactively labeled upon metabolic labeling of cells with [(3)H]glucosamine. Besides its well-demonstrated role in the internalization of specific ligands, here we show that ligand binding to surface nucleolin could also induce Ca(2+) entry into cells. Indeed, by flow cytometry, microscopy and patch-clamp experiments, we show that the HB-19 pseudopeptide, which binds specifically surface nucleolin, triggers rapid and intense membrane Ca(2+) fluxes in various types of cells. The use of several drugs then indicated that Store-Operated Ca(2+) Entry (SOCE)-like channels are involved in the generation of these fluxes. Taken together, our findings suggest that binding of an extracellular ligand to surface nucleolin could be involved in the activation of signaling pathways by promoting Ca(2+) entry into cells.

Suppressive effect of hydroquinone, a benzene metabolite, on in vitro inflammatory responses mediated by macrophages, monocytes, and lymphocytes

We investigated the inhibitory effects of hydroquinone on cytokine release, phagocytosis, NO production, ROS generation, cell-cell/cell fibronectin adhesion, and lymphocyte proliferation. We found that hydroquinone suppressed the production of proinflammatory cytokines [tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6], secretion of toxic molecules [nitric oxide (NO) and reactive oxygen species (ROS)], phagocytic uptake of FITC-labeled dextran, upregulation of costimulatory molecules, U937 cell-cell adhesion induced by CD18 and CD29, and the proliferation of lymphocytes from the bone marrow and spleen. Considering that (1) environmental chemical stressors reduce the immune response of chronic cigarette smokers and children against bacterial and viral infections and that (2) workers in petroleum factories are at higher risk for cancer, our data suggest that hydroquinone might pathologically inhibit inflammatory responses mediated by monocytes, macrophages, and lymphocytes.

G-rich oligonucleotides alter cell cycle progression and induce apoptosis specifically in OE19 esophageal tumor cells

Short synthetic oligonucleotides (ODNs) can be used to block cellular processes involved in cell growth and proliferation. Often acting as aptamers, these molecules interact with critical proteins that regulate the induction of apoptosis or necrosis. We have used a specialized class of ODNs that contain a monomeric sequence of guanosine to induce apoptosis specifically in the malignant esophageal cell line, OE19, in cell culture, and in a NODscid mouse model. OE19 cells were grown in culture and treated with a stable G-rich oligonucleotide (GRO). Cells were processed and apoptosis was measured by FACS analyses, caspase activity, and Hoescht staining. Circular dichroism (CD) was used to define the structure and stability of various GROs. The GRO works by first inducing retardation in the progression of the cell cycle and then by creating a sub-G1 population of apoptotic cells. The reaction is dose dependent, and appears to rely on the capacity of the G-rich ODN to adopt a G-quartet conformation. Apoptosis was measured by determining caspase 3/7 levels and by staining for nuclear fragmentation using the Hoechst dye. Importantly, nonmalignant esophageal cells or normal human lung fibroblasts are not impeded in their cell cycle progression when incubated with the G-rich ODNs. These results suggest that a selective killing of esophageal tumor cells is directed by G-rich ODNs. Selective killing was demonstrated in the unique activity of the GRO compared to other ODNs of different sequences as well as the response of oncogenic cells compared to nononcogenic cells.

Anti-inflammatory effect of honokiol is mediated by PI3K/Akt pathway suppression

AIM

In this study, we investigated the regulatory effects of honokiol on various inflammatory events mediated by monocytes/macrophages (U937/RAW264.7 cells) and lymphocytes (splenic lymphocytes and CTLL-2 cells) and their putative action mechanism.

METHODS

In order to investigate the regulatory effects, various cell lines and primary cells (U937, RAW264.7, CTLL-2 cells, and splenic lymphocytes) were employed and various inflammatory events, such as the production of inflammatory mediators, cell adhesion, cell proliferation, and the early signaling cascade, were chosen.

RESULTS

Honokiol strongly inhibited various inflammatory responses, such as: (i) the upregulation of nitric oxide (NO), prostaglandin E2 and TNF-alpha production and costimulatory molecule CD80 induced by lipopolysaccharide (LPS); (ii) the functional activation of beta1-integrin (CD29) assessed by U937 cell-cell and cell-fibronectin adhesions; (iii) the enhancement of lymphocytes and CD8+CTLL-2 cell proliferation stimulated by LPS, phytohemaglutinin A (PHA), and concanavalin A or interleukin (IL)-2; and (iv) the transcriptional upregulation of inducible NO synthase, TNF-alpha, cyclooxygenase-2, IL-12, and monocyte chemoattractant protein (MCP)-1. These anti-inflammatory effects of honokiol seem to be mediated by interrupting the early activated intracellular signaling molecule phosphoinositide 3-kinase (PI3K)/Akt, but not Src, the extracellular signal-regulated kinase, and p38, according to pharmacological, biochemical, and functional analyses.

CONCLUSION

These results suggest that honokiol may act as a potent anti-inflammatory agent with multipotential activities due to an inhibitory effect on the PI3K/Akt pathway.

In vitro immunoregulatory effects of Korean mistletoe lectin on functional activation of monocytic and macrophage-like cells

Korean mistletoe lectin (KML) is one of the major active components in Viscum album var. (coloratum), displaying various biological effects such as anti-tumor and anti-metastatic activities. Even though it has been shown to boost host immune defense mechanisms, the immunomodulatory effects of KML on specific immune responses mediated by macrophages have not been fully elucidated. Therefore, in this study, we aimed to demonstrate KML's regulatory roles on macrophage-mediated immune responses. KML clearly blocked lipopolysaccharide (LPS)-induced events [expression of interleukin (IL)-10, nitric oxide (NO) production and phagocytic uptake], and suppressed the normal expression levels of IL-10 (at 2 ng/ml) and tumor necrosis factor (TNF)-alpha (at 10 ng/ml). In contrast, (1) the expression of cytokine (TNF-alpha) and (2) the generation of reactive oxygen species (ROS) induced by LPS were significantly up-regulated with KML co-treatment. In addition, KML itself increased the mRNA levels of IL-3 and IL-23; phagocytic uptake; the surface levels of co-stimulatory molecules (CD80 and CD86), pattern recognition receptors (PRRs) [such as dectin-1 and toll like receptor (TLR)-2] and adhesion molecules [beta1-integrins (CD29) and CD43]; and CD29-mediated cell adhesion events. Finally, according to co-treatment of D-galactose with KML under LPS-induced NO production conditions, KML inhibition seems to be mediated by binding to proteins with D-galactose. Therefore, these data suggest that KML may participate in regulating various macrophage-mediated innate and adaptive responses via binding to surface protein with D-galactose and that some of these may deserve in KML's therapeutic activities such as anti-tumor and anti-microbial effects.

Immunomodulatory effect of Hibiscus cannabinus extract on macrophage functions

Hibiscus cannabinus L. (Malvaceae) (known as Kenaf) has long been used as a folk medicine in India and Africa for the treatment of blood and throat disorders, bilious conditions, fever and puerperium. In this study, therefore, we aimed either to demonstrate its ethnopharmacological activity by examining its macrophage function-regulating effects or to expand its therapeutic efficacy into other macrophage-mediated diseases. The total crude extract (EtOH extract) of Hibiscus cannabinus fresh leaves, prepared with 80% ethanol, significantly suppressed TNF-alpha production and the mRNA expression of interleukin (IL)-3 and IL-12 in the RAW264.7 cells, stimulated by lipopolysaccharide (LPS, 2.5 microg/ml). The secretion of inflammatory mediators (i.e., nitric oxide [NO], reactive oxygen species [ROS] and prostaglandin E(2) [PGE(2)]) was diminished by the EtOH extract. The extract induced the expression of heme oxygenase-1 (HO-1) mRNA, a potent cytoprotective molecule. The Kenaf extract suppressed both the phagocytic uptake and the expression of costimulatory molecules (CD80 and CD86) of LPS-activated RAW264.7 cells. It is interesting that Kenaf also down-regulated both the functional activation of beta1-integrin (CD29) and the LPS-induced up-regulation of the surface CD29 level. Taken together, these data suggest that Kenaf may be able to modulate macrophage-mediated responses and that some of the activities may contribute to expand its therapeutic usage.

Regulatory effects of Codonopsis lanceolata on macrophage-mediated immune responses

Codonopsis lanceolata L. has long been used as a folk medicine in Korea, Japan and China for the treatment of lung inflammatory diseases. In this study, therefore, we aimed to demonstrate its ethnopharmacological activity by examining macrophage-function regulating effects. The total methanol extracts of fresh leaves (l-TME) or roots (r-TME) of Codonopsis lanceolata L. significantly suppressed the production of pro-inflammatory mediators (nitric oxide [NO] and tumor necrosis factor [TNF-alpha]) without altering mRNA levels. The expression of interleukin (IL)-3 and IL-6, however, was strongly diminished. According to the analysis of signaling enzyme activation by immunoblotting, phospho-IkappaB levels, a representative pro-inflammatory gene activation pathway, were not affected by the TMEs. By contrast, the Raf-ERK signaling pathway, which was involved in regulation of post-translational modification of pro-inflammatory gene products, was strongly blocked after 6-h of exposure. Moreover, l-TME down-regulated LPS-mediated phagocytic uptake and CD29-mediated cell-cell adhesion, while r-TME strongly up-regulated these two cellular events as well as fibronectin-cell adhesion. The surface levels of the costimulatory molecules (CD80 and CD86) of RAW264.7 cells were also enhanced by these extracts. l-TME also diminished functional activation (assessed by NO production) and the surface level of dectin-1, but not toll-like receptor (TLR)-2. Taken together, these data suggest that Codonopsis lanceolata may have the ability to modulate macrophage-mediated immune responses, thus contributing to its anti-inflammatory activity.

Dual localization: proteins in extracellular and intracellular compartments

The goal of this article is to provide a comprehensive catalog of those proteins documented to exhibit dual localization, being found in both the extracellular compartment (cell surface and extracellular medium) as well as the intracellular compartment (cytosol and nucleus). A large subset of these proteins that show dual localization is found both in the nucleus and outside of cells. Proteins destined to be secreted out of the cell or to be expressed at the cell surface usually enter the endomembrane pathway on the basis of a signal sequence that targets them into the endoplasmic reticulum. Proteins destined for import into the nucleus, on the other hand, usually carry a nuclear localization signal. We have organized our catalog in terms of the presence and absence of these trafficking signals: (a) proteins that contain a signal sequence but no nuclear localization signal; (b) proteins that contain both a signal sequence as well as a nuclear localization signal; (c) proteins that contain a nuclear localization signal but lack a signal sequence; and (d) proteins containing neither a signal sequence nor a nuclear localization signal. Novel insights regarding the activities of several classes of proteins exhibiting dual localization can be derived when one targeting signal is experimentally abrogated. For example, the mitogenic activity of both fibroblasts growth factor-1 and schwannoma-derived growth factor clearly requires nuclear localization, independent of the activation of the receptor tyrosine kinase signaling pathway. In addition, there is a growing list of integral membrane receptors that undergo translocation to the nucleus, with bona fide nuclear localization signals and transcription activation activity. The information provided in this descriptive catalog will, hopefully, stimulate investigations into the pathways and mechanisms of transport between these compartments and the physiological significance of dual localization.

Interactions of lactoferrin with cells involved in immune function

The antimicrobial activities of lactoferrin (Lf) depend on its capacity to bind iron and on its direct interaction with the surface of microorganisms. Its protective effect also extends to the regulation of the host response to infections. Depending on the immune status of an individual, Lf can have anti-inflammatory properties that downregulate the immune response and prevent septic shock and damage to tissues. It also acts as a promoter of the activation, differentiation, and (or) proliferation of immune cells. Although most of the anti-inflammatory activities are correlated with the neutralization of proinflammatory molecules by Lf, the promoting activity seems to be related to a direct effect of Lf on immune cells. Although the mechanisms that govern these activities are not clearly defined, and probably differ from cell to cell, several cellular targets and possible mechanisms of action are highlighted. The majority of the molecular targets at the surface of cells are multiligand receptors but, interestingly, most of them have been reported as signaling, endocytosis, and nuclear-targeting molecules. This review focuses on the known and putative mechanisms that allow the immunoregulating effect of Lf in its interactions with immune cells.

Cell surface nucleolin on developing muscle is a potential ligand for the axonal receptor protein tyrosine phosphatase-sigma

Reversible tyrosine phosphorylation, catalyzed by receptor tyrosine kinases and receptor tyrosine phosphatases, plays an essential part in cell signaling during axonal development. Receptor protein tyrosine phosphatase-sigma has been implicated in the growth, guidance and repair of retinal axons. This phosphatase has also been implicated in motor axon growth and innervation. Insect orthologs of receptor protein tyrosine phosphatase-sigma are also implicated in the recognition of muscle target cells. A potential extracellular ligand for vertebrate receptor protein tyrosine phosphatase-sigma has been previously localized in developing skeletal muscle. The identity of this muscle ligand is currently unknown, but it appears to be unrelated to the heparan sulfate ligands of receptor protein tyrosine phosphatase-sigma. In this study, we have used affinity chromatography and tandem MS to identify nucleolin as a binding partner for receptor protein tyrosine phosphatase-sigma in skeletal muscle tissue. Nucleolin, both from tissue lysates and in purified form, binds to receptor protein tyrosine phosphatase-sigma ectodomains. Its expression pattern also overlaps with that of the receptor protein tyrosine phosphatase-sigma-binding partner previously localized in muscle, and nucleolin can also be found in retinal basement membranes. We demonstrate that a significant amount of muscle-associated nucleolin is present on the cell surface of developing myotubes, and that two nucleolin-binding components, lactoferrin and the HB-19 peptide, can block the interaction of receptor protein tyrosine phosphatase-sigma ectodomains with muscle and retinal basement membranes in tissue sections. These data suggest that muscle cell surface-associated nucleolin represents at least part of the muscle binding site for axonal receptor protein tyrosine phosphatase-sigma and that nucleolin may also be a necessary component of basement membrane binding sites of receptor protein tyrosine phosphatase-sigma.

Met-Independent Hepatocyte Growth Factor-mediated regulation of cell adhesion in human prostate cancer cells

BACKGROUND

Prostate cancer cells communicate reciprocally with the stromal cells surrounding them, inside the prostate, and after metastasis, within the bone. Each tissue secretes factors for interpretation by the other. One stromally-derived factor, Hepatocyte Growth Factor (HGF), was found twenty years ago to regulate invasion and growth of carcinoma cells. Working with the LNCaP prostate cancer progression model, we found that these cells could respond to HGF stimulation, even in the absence of Met, the only known HGF receptor. The new HGF binding partner we find on the cell surface may help to clarify conflicts in the past literature about Met expression and HGF response in cancer cells.

METHODS

We searched for Met or any HGF binding partner on the cells of the PC3 and LNCaP prostate cancer cell models, using HGF immobilized on agarose beads. By using mass spectrometry analyses and sequencing we have identified nucleolin protein as a novel HGF binding partner. Antibodies against nucleolin (or HGF) were able to ameliorate the stimulatory effects of HGF on met-negative prostate cancer cells. Western blots, RT-PCR, and immunohistochemistry were used to assess nucleolin levels during prostate cancer progression in both LNCaP and PC3 models.

RESULTS

We have identified HGF as a major signaling component of prostate stromal-conditioned media (SCM) and have implicated the protein nucleolin in HGF signal reception by the LNCaP model prostate cancer cells. Antibodies that silence either HGF (in SCM) or nucleolin (on the cell surfaces) eliminate the adhesion-stimulatory effects of the SCM. Likewise, addition of purified HGF to control media mimics the action of SCM. C4-2, an LNCaP lineage-derived, androgen-independent human prostate cancer cell line, responds to HGF in a concentration-dependent manner by increasing its adhesion and reducing its migration on laminin substratum. These HGF effects are not due to shifts in the expression levels of laminin-binding integrins, nor can they be linked to expression of the known HGF receptor Met, as neither LNCaP nor clonally-derived C4-2 sub-line contain any detectable Met protein. Even in the absence of Met, small GTPases are activated, linking HGF stimulation to membrane protrusion and integrin activation. Membrane-localized nucelolin levels increase during cancer progression, as modeled by both the PC3 and LNCaP prostate cancer progression cell lines.

CONCLUSION

We propose that cell surface localized nucleolin protein may function in these cells as a novel HGF receptor. Membrane localized nucleolin binds heparin-bound growth factors (including HGF) and appears upregulated during prostate cancer progression. Antibodies against nucleolin are able to ameliorate the stimulatory effects of HGF on met-negative prostate cancer cells. HGF-nucleolin interactions could be partially responsible for the complexity of HGF responses and met expression reported in the literature.

Pleiotrophin inhibits HIV infection by binding the cell surface-expressed nucleolin

The growth factor pleiotrophin (PTN) has been reported to bind heparan sulfate and nucleolin, two components of the cell surface implicated in the attachment of HIV-1 particles to cells. Here we show that PTN inhibits HIV-1 infection by its capacity to inhibit HIV-1 particle attachment to the surface of permissive cells. The beta-sheet domains of PTN appear to be implicated in this inhibitory effect on the HIV infection, in particular the domain containing amino acids 60-110. PTN binding to the cell surface is mediated by high and low affinity binding sites. Other inhibitors of HIV attachment known to bind specifically surface expressed nucleolin, such as the pseudopeptide HB-19 and the cytokine midkine prevent the binding of PTN to its low affinity-binding site. Confocal immunofluorescence laser microscopy revealed that the cross-linking of surface-bound PTN with a specific antibody results in the clustering of cell surface-expressed nucleolin and the colocalization of both PTN and nucleolin signals. Following its binding to surface-nucleolin, PTN is internalized by a temperature sensitive mechanism, a process which is inhibited by HB-19 and is independent of heparan and chondroitin sulfate proteoglycans. Nevertheless, proteoglycans might play a role in the concentration of PTN on the cell surface for a more efficient interaction with nucleolin. Our results demonstrate for the first time that PTN inhibits HIV infection and suggest that the cell surface-expressed nucleolin is a low affinity receptor for PTN binding to cells and it is also implicated in PTN entry into cells by an active process.

Surface nucleolin participates in both the binding and endocytosis of lactoferrin in target cells

Lactoferrin (Lf), a multifunctional molecule present in mammalian secretions and blood, plays important roles in host defense and cancer. Indeed, Lf has been reported to inhibit the proliferation of cancerous mammary gland epithelial cells and manifest a potent antiviral activity against human immunodeficiency virus and human cytomegalovirus. The Lf-binding sites on the cell surface appear to be proteoglycans and other as yet undefined protein(s). Here, we isolated a Lf-binding 105 kDa molecular mass protein from cell extracts and identified it as human nucleolin. Medium-affinity interactions ( approximately 240 nm) between Lf and purified nucleolin were further illustrated by surface plasmon resonance assays. The interaction of Lf with the cell surface-expressed nucleolin was then demonstrated through competitive binding studies between Lf and the anti-human immunodeficiency virus pseudopeptide, HB-19, which binds specifically surface-expressed nucleolin independently of proteoglycans. Interestingly, binding competition studies between HB-19 and various Lf derivatives in proteoglycan-deficient hamster cells suggested that the nucleolin-binding site is located in both the N- and C-terminal lobes of Lf, whereas the basic N-terminal region is dispensable. On intact cells, Lf co-localizes with surface nucleolin and together they become internalized through vesicles of the recycling/degradation pathway by an active process. Morever, a small proportion of Lf appears to translocate in the nucleus of cells. Finally, the observations that endocytosis of Lf is inhibited by the HB-19 pseudopeptide, and the lack of Lf endocytosis in proteoglycan-deficient cells despite Lf binding, point out that both nucleolin and proteoglycans are implicated in the mechanism of Lf endocytosis.

Nucleolin expressed at the cell surface is a marker of endothelial cells in angiogenic blood vessels

A tumor-homing peptide, F3, selectively binds to endothelial cells in tumor blood vessels and to tumor cells. Here, we show that the cell surface molecule recognized by F3 is nucleolin. Nucleolin specifically bound to an F3 peptide affinity matrix from extracts of cultured breast carcinoma cells. Antibodies and cell surface biotin labeling revealed nucleolin at the surface of actively growing cells, and these cells bound and internalized fluorescein-conjugated F3 peptide, transporting it into the nucleus. In contrast, nucleolin was exclusively nuclear in serum-starved cells, and F3 did not bind to these cells. The binding and subsequent internalization of F3 were blocked by an antinucleolin antibody. Like the F3 peptide, intravenously injected antinucleolin antibodies selectively accumulated in tumor vessels and in angiogenic vessels of implanted "matrigel" plugs. These results show that cell surface nucleolin is a specific marker of angiogenic endothelial cells within the vasculature. It may be a useful target molecule for diagnostic tests and drug delivery applications.

Nuclear targeting by the growth factor midkine

Ligand-receptor internalization has been traditionally regarded as part of the cellular desensitization system. Low-density lipoprotein receptor-related protein (LRP) is a large endocytosis receptor with a diverse array of ligands. We recently showed that LRP binds heparin-binding growth factor midkine. Here we demonstrate that LRP mediates nuclear targeting by midkine and that the nuclear targeting is biologically important. Exogenous midkine reached the nucleus, where intact midkine was detected, within 20 min. Midkine was not internalized in LRP-deficient cells, whereas transfection of an LRP expression vector restored midkine internalization and subsequent nuclear translocation. Internalized midkine in the cytoplasm bound to nucleolin, a nucleocytoplasmic shuttle protein. The midkine-binding sites were mapped to acidic stretches in the N-terminal domain of nucleolin. When the nuclear localization signal located next to the acidic stretches was deleted, we found that the mutant nucleolin not only accumulated in the cytoplasm but also suppressed the nuclear translocation of midkine. By using cells that overexpressed the mutant nucleolin, we further demonstrated that the nuclear targeting was necessary for the full activity of midkine in the promotion of cell survival. This study therefore reveals a novel role of LRP in intracellular signaling by its ligand and the importance of nucleolin in this process.