Activation of the EBV/C3d receptor (CR2, CD21) on human B lymphocyte surface triggers tyrosine phosphorylation of the 95-kDa nucleolin and its interaction with phosphatidylinositol 3 kinase

Ubiquitination-dependent degradation of nucleolin mediated by porcine circovirus type 3 capsid protein

IMPORTANCE

Porcine circovirus type 3 (PCV3) is an emerging pathogen that causes multisystem disease in pigs and poses a severe threat to the swine industry. However, the mechanisms of how PCV3 uses host proteins to regulate its own life cycle are not well understood. In this study, we found that PCV3 capsid protein interacts with nucleolin and degrades it. Degradation of nucleolin by the PCV3 capsid protein requires recruitment of the enzyme RNF34, which is transported to the nucleolus from the cytoplasm in the presence of the PCV3 capsid protein. Nucleolin also decreases PCV3 replication by promoting the release of interferon β. These findings clarify the mechanism by which nucleolin modulates PCV3 replication in cells, thereby facilitating to provide an important strategy for preventing and controlling PCV3 infection.

New aspects in the regulation of human B cell functions by complement receptors CR1, CR2, CR3 and CR4

The involvement of complement in the regulation of antibody responses has been known for long. By now several additional B cell functions - including cytokine production and antigen presentation - have also been shown to be regulated by complement proteins. Most of these important activities are mediated by receptors interacting with activation fragments of the central component of the complement system C3, such as C3b, iC3b and C3d, which are covalently attached to antigens and immune complexes. This review summarizes the role of complement receptors interacting with these ligands, namely CR1 (CD35), CR2 (CD21), CR3 (CD11b/CD18) and CR4 (CD11c/CD18) expressed by B cells in health and disease. Although we focus on human B lymphocytes, we also aim to call the attention to important differences between human and mouse systems.

Myogenetic Oligodeoxynucleotide (myoDN) Recovers the Differentiation of Skeletal Muscle Myoblasts Deteriorated by Diabetes Mellitus

Skeletal muscle wasting in patients with diabetes mellitus (DM) is a complication of decreased muscle mass and strength, and is a serious risk factor that may result in mortality. Deteriorated differentiation of muscle precursor cells, called myoblasts, in DM patients is considered to be one of the causes of muscle wasting. We recently developed myogenetic oligodeoxynucleotides (myoDNs), which are 18-base single-strand DNAs that promote myoblast differentiation by targeting nucleolin. Herein, we report the applicability of a myoDN, iSN04, to myoblasts isolated from patients with type 1 and type 2 DM. Myogenesis of DM myoblasts was exacerbated concordantly with a delayed shift of myogenic transcription and induction of interleukins. Analogous phenotypes were reproduced in healthy myoblasts cultured with excessive glucose or palmitic acid, mimicking hyperglycemia or hyperlipidemia. iSN04 treatment recovered the deteriorated differentiation of plural DM myoblasts by downregulating myostatin and interleukin-8 (IL-8). iSN04 also ameliorated the impaired myogenic differentiation induced by glucose or palmitic acid. These results demonstrate that myoDNs can directly facilitate myoblast differentiation in DM patients, making them novel candidates for nucleic acid drugs to treat muscle wasting in patients with DM.

Identification of the Myogenetic Oligodeoxynucleotides (myoDNs) That Promote Differentiation of Skeletal Muscle Myoblasts by Targeting Nucleolin

Herein we report that the 18-base telomeric oligodeoxynucleotides (ODNs) designed from the Lactobacillus rhamnosus GG genome promote differentiation of skeletal muscle myoblasts which are myogenic precursor cells. We termed these myogenetic ODNs (myoDNs). The activity of one of the myoDNs, iSN04, was independent of Toll-like receptors, but dependent on its conformational state. Molecular simulation and iSN04 mutants revealed stacking of the 13-15th guanines as a core structure for iSN04. The alkaloid berberine bound to the guanine stack and enhanced iSN04 activity, probably by stabilizing and optimizing iSN04 conformation. We further identified nucleolin as an iSN04-binding protein. Results showed that iSN04 antagonizes nucleolin, increases the levels of p53 protein translationally suppressed by nucleolin, and eventually induces myotube formation by modulating the expression of genes involved in myogenic differentiation and cell cycle arrest. This study shows that bacterial-derived myoDNs serve as aptamers and are potential nucleic acid drugs directly targeting myoblasts.

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.

Receptor protein tyrosine phosphatase beta/zeta is a functional binding partner for vascular endothelial growth factor

BACKGROUND

Receptor protein tyrosine phosphatase beta/zeta (RPTPβ/ζ) is a chondroitin sulphate (CS) transmembrane protein tyrosine phosphatase and is a receptor for pleiotrophin (PTN). RPTPβ/ζ interacts with ανβ₃ on the cell surface and upon binding of PTN leads to c-Src dephosphorylation at Tyr530, β₃ Tyr773 phosphorylation, cell surface nucleolin (NCL) localization and stimulation of cell migration. c-Src-mediated β₃ Tyr773 phosphorylation is also observed after vascular endothelial growth factor 165 (VEGF₁₆₅) stimulation of endothelial cells and is essential for VEGF receptor type 2 (VEGFR2) - ανβ₃ integrin association and subsequent signaling. In the present work, we studied whether RPTPβ/ζ mediates angiogenic actions of VEGF.

METHODS

Human umbilical vein endothelial, human glioma U87MG and stably transfected Chinese hamster ovary cells expressing different β₃ subunits were used. Protein-protein interactions were studied by a combination of immunoprecipitation/Western blot, immunofluorescence and proximity ligation assays, properly quantified as needed. RPTPβ/ζ expression was down-regulated using small interference RNA technology. Migration assays were performed in 24-well microchemotaxis chambers, using uncoated polycarbonate membranes with 8 μm pores.

RESULTS

RPTPβ/ζ mediates VEGF₁₆₅-induced c-Src-dependent β₃ Tyr773 phosphorylation, which is required for VEGFR2-ανβ₃ interaction and the downstream activation of phosphatidylinositol 3-kinase (PI3K) and cell surface NCL localization. RPTPβ/ζ directly interacts with VEGF165, and this interaction is not affected by bevacizumab, while it is interrupted by both CS-E and PTN. Down-regulation of RPTPβ/ζ by siRNA or administration of exogenous CS-E abolishes VEGF₁₆₅-induced endothelial cell migration, while PTN inhibits the migratory effect of VEGF₁₆₅ to the levels of its own effect.

CONCLUSIONS

These data identify RPTPβ/ζ as a cell membrane binding partner for VEGF that regulates angiogenic functions of endothelial cells and suggest that it warrants further validation as a potential target for development of additive or alternative anti-VEGF therapies.

Tyrosine phosphorylation of 3BP2 is indispensable for the interaction with VAV3 in chicken DT40 cells

Adaptor protein c-Abl SH3 domain-binding protein-2 (3BP2) is known to play regulatory roles in immunoreceptor-mediated signal transduction. We have previously demonstrated that Tyr(174), Tyr(183) and Tyr(446) in mouse 3BP2 are predominantly phosphorylated by Syk, and the phosphorylation of Tyr(183) and the Src homology 2 (SH2) domain of mouse 3BP2 are critical for B cell receptor (BCR)-induced activation of nuclear factor of activated T cells (NFAT) in human B cells. In this report, we have shown that Syk, but not Abl family protein-tyrosine kinases, is critical for BCR-mediated tyrosine phosphorylation of 3BP2 in chicken DT40 cells. Mutational analysis showed that Tyr(174), Tyr(183) and Tyr(426) of chicken 3BP2 are the major phosphorylation sites by Syk and the SH2 domain of 3BP2 is critical for tyrosine phosphorylation. In addition, phosphorylation of Tyr(426) is required for the inducible interaction with the SH2 domain of Vav3. Moreover, the expression of the mutant form of 3BP2 in which Tyr(426) was substituted to Phe resulted in the reduction in BCR-mediated Rac1 activation, when compared with the case of wild-type. Altogether, these data suggest that 3BP2 is involved in the activation of Rac1 through the regulation of Vav3 by Syk-dependent phosphorylation of Tyr(426) following BCR stimulation.

Detection of the interaction between host and bacterial proteins: eukaryotic nucleolin interacts with Francisella elongation factor Tu

Dissecting the interaction between bacterial and host proteins is fundamental in understanding pathogenesis. It is also very helpful for exploring new therapeutic approaches, either preventive or curative. Here, we describe different techniques, which allowed us to detect new molecules involved in the binding and infection of the bacterium Francisella tularensis, on human cells. This facultative intracellular pathogen is the causative agent of tularemia and is considered as a bio-threatening agent. The privileged host cells are monocytes and macrophages. We used both "in vitro" and "in vivo" experiments to explore the modulation of F. tularensis infection and thereafter determine a bacterial ligand and its host receptor molecule.

AU-rich RNA binding proteins in hematopoiesis and leukemogenesis

Posttranscriptional mechanisms are now widely acknowledged to play a central role in orchestrating gene-regulatory networks in hematopoietic cell growth, differentiation, and tumorigenesis. Although much attention has focused on microRNAs as regulators of mRNA stability/translation, recent data have highlighted the role of several diverse classes of AU-rich RNA-binding protein in the regulation of mRNA decay/stabilization. AU-rich elements are found in the 3'-untranslated region of many mRNAs that encode regulators of cell growth and survival, such as cytokines and onco/tumor-suppressor proteins. These are targeted by a burgeoning number of different RNA-binding proteins. Three distinct types of AU-rich RNA binding protein (ARE poly-U-binding degradation factor-1/AUF1, Hu antigen/HuR/HuA/ELAVL1, and the tristetraprolin/ZFP36 family of proteins) are essential for normal hematopoiesis. Together with 2 further AU-rich RNA-binding proteins, nucleolin and KHSRP/KSRP, the functions of these proteins are intimately associated with pathways that are dysregulated in various hematopoietic malignancies. Significantly, all of these AU-rich RNA-binding proteins function via an interconnected network that is integrated with microRNA functions. Studies of these diverse types of RNA binding protein are providing novel insight into gene-regulatory mechanisms in hematopoiesis in addition to offering new opportunities for developing mechanism-based targeted therapeutics in leukemia and lymphoma.

Epstein-Barr virus infection of polarized epithelial cells via the basolateral surface by memory B cell-mediated transfer infection

Epstein Barr virus (EBV) exhibits a distinct tropism for both B cells and epithelial cells. The virus persists as a latent infection of memory B cells in healthy individuals, but a role for infection of normal epithelial is also likely. Infection of B cells is initiated by the interaction of the major EBV glycoprotein gp350 with CD21 on the B cell surface. Fusion is triggered by the interaction of the EBV glycoprotein, gp42 with HLA class II, and is thereafter mediated by the core fusion complex, gH/gL/gp42. In contrast, direct infection of CD21-negative epithelial cells is inefficient, but efficient infection can be achieved by a process called transfer infection. In this study, we characterise the molecular interactions involved in the three stages of transfer infection of epithelial cells: (i) CD21-mediated co-capping of EBV and integrins on B cells, and activation of the adhesion molecules, (ii) conjugate formation between EBV-loaded B cells and epithelial cells via the capped adhesion molecules, and (iii) interaction of EBV glycoproteins with epithelial cells, with subsequent fusion and uptake of virions. Infection of epithelial cells required the EBV gH and gL glycoproteins, but not gp42. Using an in vitro model of normal polarized epithelia, we demonstrated that polarization of the EBV receptor(s) and adhesion molecules restricted transfer infection to the basolateral surface. Furthermore, the adhesions between EBV-loaded B cells and the basolateral surface of epithelial cells included CD11b on the B cell interacting with heparan sulphate moieties of CD44v3 and LEEP-CAM on epithelial cells. Consequently, transfer infection was efficiently mediated via CD11b-positive memory B cells but not by CD11b-negative naïve B cells. Together, these findings have important implications for understanding the mechanisms of EBV infection of normal and pre-malignant epithelial cells in vivo.

Virulence-related Mycobacterium avium subsp hominissuis MAV_2928 gene is associated with vacuole remodeling in macrophages

Background

Mycobacterium avium subsp hominissuis (previously Mycobacterium avium subsp avium) is an environmental organism associated with opportunistic infections in humans. Mycobacterium hominissuis infects and replicates within mononuclear phagocytes. Previous study characterized an attenuated mutant in which the PPE gene (MAV_2928) homologous to Rv1787 was inactivated. This mutant, in contrast to the wild-type bacterium, was shown both to have impaired the ability to replicate within macrophages and to have prevented phagosome/lysosome fusion.

Results

MAV_2928 gene is primarily upregulated upon phagocytosis. The transcriptional profile of macrophages infected with the wild-type bacterium and the mutant were examined using DNA microarray, which showed that the two bacteria interact uniquely with mononuclear phagocytes. Based on the results, it was hypothesized that the phagosome environment and vacuole membrane of the wild-type bacterium might differ from the mutant. Wild-type bacterium phagosomes expressed a number of proteins different from those infected with the mutant. Proteins on the phagosomes were confirmed by fluorescence microscopy and Western blot. The environment in the phagosome of macrophages infected with the mutant differed from the environment of vacuoles with M. hominissuis wild-type in the concentration of zinc, manganese, calcium and potassium.

Conclusion

The results suggest that the MAV_2928 gene/operon might participate in the establishment of bacterial intracellular environment in macrophages.

A novel receptor - ligand pathway for entry of Francisella tularensis in monocyte-like THP-1 cells: interaction between surface nucleolin and bacterial elongation factor Tu

BACKGROUND

Francisella tularensis, the causative agent of tularemia, is one of the most infectious human bacterial pathogens. It is phagocytosed by immune cells, such as monocytes and macrophages. The precise mechanisms that initiate bacterial uptake have not yet been elucidated. Participation of C3, CR3, class A scavenger receptors and mannose receptor in bacterial uptake have been already reported. However, contribution of an additional, as-yet-unidentified receptor for F. tularensis internalization has been suggested.

RESULTS

We show here that cell-surface expressed nucleolin is a receptor for Francisella tularensis Live Vaccine Strain (LVS) and promotes LVS binding and infection of human monocyte-like THP-1 cells. The HB-19 pseudopeptide that binds specifically carboxy-terminal RGG domain of nucleolin inhibits LVS binding and infection of monocyte-like THP-1 cells. In a pull-down assay, elongation factor Tu (EF-Tu), a GTP-binding protein involved in protein translation, usually found in cytoplasm, was recovered among LVS bacterial membrane proteins bound on RGG domain of nucleolin. A specific polyclonal murine antibody was raised against recombinant LVS EF-Tu. By fluorescence and electron microscopy experiments, we found that a fraction of EF-Tu could be detected at the bacterial surface. Anti-EF-Tu antibodies reduced LVS binding to monocyte-like THP-1 cells and impaired infection, even in absence of complement and complement receptors. Interaction between EF-Tu and nucleolin was illustrated by two different pull-down assays using recombinant EF-Tu proteins and either RGG domain of nucleolin or cell solubilized nucleolin.

DISCUSSION

Altogether, our results demonstrate that the interaction between surface nucleolin and its bacterial ligand EF-Tu plays an important role in Francisella tularensis adhesion and entry process and may therefore facilitate invasion of host tissues. Since phagosomal escape and intra-cytosolic multiplication of LVS in infected monocytes are very similar to those of human pathogenic F. tularensis ssp tularensis, the mechanism of entry into monocyte-like THP-1 cells, involving interaction between EF-Tu and nucleolin, might be similar in the two subspecies. Thus, the use of either nucleolin-specific pseudopeptide HB-19 or recombinant EF-Tu could provide attractive therapeutic approaches for modulating F. tularensis infection.

Cell-surface nucleolin is a signal transducing P-selectin binding protein for human colon carcinoma cells

We have previously shown that P-selectin binding to Colo-320 human colon carcinoma cells induces specific activation of the alpha(5)beta(1) integrin with a concomitant increase of cell adhesion and spreading on fibronectin substrates in a phosphatidylinositol 3-kinase (PI3-K) and p38 MAPK-dependent manner. Here, we identified by affinity chromatography and characterized nucleolin as a P-selectin receptor on Colo-320 cells. Nucleolin mAb D3 significantly decreases the Colo-320 cell adhesion to immobilized P-selectin-IgG-Fc. Moreover, nucleolin becomes clustered at the external side of the plasma membrane of living, intact cells when bound to cross-linked P-selectin-IgG-Fc chimeric protein. We have also found P-selectin binding to Colo-320 cells induces tyrosine phosphorylation specifically of cell-surface nucleolin and formation of a signaling complex containing cell-surface nucleolin, PI3-K and p38 MAPK. Using siRNA approaches, we have found that both P-selectin binding to Colo-320 cells and formation of the P-selectin-mediated p38 MAPK/PI3-K signaling complex require nucleolin expression. These results show that nucleolin (or a nucleolin-like protein) is a signaling receptor for P-selectin on Colo-320 cells and suggest a mechanism for linkage of nucleolin to P-selectin-induced signal transduction pathways that regulate the adhesion and the spreading of Colo-320 on fibronectin substrates.

Novel roles for murine complement receptors type 1 and 2 I. Regulation of B cell survival and proliferation by CR1/2

Innate components of the immune system, such as complement are known to have a modulatory effect on adaptive immune responses. Complement receptors are expressed by both B and T lymphocytes and play part in antigen presentation and cellular activation and adhesion events. On murine B cells type 1 and 2 complement receptors (CR1/2) are expressed and form a co-receptor complex together with CD19 and CD81. We used CR1/2 specific antibodies to assess the role these receptors might play in regulating cell cycling events of B cells. We show that a CR1/2 specific antibody fragment, 7G6 scFv can induce the proliferation of mature B cells. This effect is countermodulated by FcR crosslinkage and enhanced by BCR engagement. The proliferative effect is severely impaired in Cr2-/- animals, strengthening the involvement of CR1/2. Transitional B cells are prone to apoptotic death by selection events, yet they are rescued from apoptosis by CR1/2 crosslinkage. CR1/2 ligation by 7G6 scFv alone can induce nuclear translocation of NF-kappaB, supporting the above observations. We conclude that engagement of complement receptor 2 of B cells promotes the survival of both mature and transitional B cells. This activity supplements the previously described adjuvant effects of complement.

AGRO100 inhibits activation of nuclear factor-kappaB (NF-kappaB) by forming a complex with NF-kappaB essential modulator (NEMO) and nucleolin

AGRO100, also known as AS1411, is an experimental anticancer drug that recently entered human clinical trials. It is a member of a novel class of antiproliferative agents known as G-rich oligonucleotides (GRO), which are non-antisense, guanosine-rich phosphodiester oligodeoxynucleotides that form stable G-quadruplex structures. The biological activity of GROs results from their binding to specific cellular proteins as aptamers. One important target protein of GROs has been previously identified as nucleolin, a multifunctional protein expressed at high levels by cancer cells. Here, we report that AGRO100 also associates with nuclear factor-kappaB (NF-kappaB) essential modulator (NEMO), which is a regulatory subunit of the inhibitor of kappaB (IkappaB) kinase (IKK) complex, and also called IKKgamma. In the classic NF-kappaB pathway, the IKK complex is required for phosphorylation of IkappaBalpha and subsequent activation of the transcription factor NF-kappaB. We found that treatment of cancer cells with AGRO100 inhibits IKK activity and reduces phosphorylation of IkappaBalpha in response to tumor necrosis factor-alpha stimulation. Using a reporter gene assay, we showed that AGRO100 blocks both tumor necrosis factor-alpha-induced and constitutive NF-kappaB activity in human cancer cell lines derived from cervical, prostate, breast, and lung carcinomas. In addition, we showed that, in AGRO100-treated cancer cells, NEMO is coprecipitated by nucleolin, indicating that both proteins are present in the same complex. Our studies suggest that abrogation of NF-kappaB activity may contribute to the anticancer effects of AGRO100 and that nucleolin may play a previously unknown role in regulating the NF-kappaB pathway.

Up-regulation of the KLF2 transcription factor by fluid shear stress requires nucleolin

We have previously characterized the regulation of the KLF2 transcription factor gene by describing an induction complex that binds to and regulates its promoter. In the present study, by using DNA affinity chromatography and mass spectrometry, we have identified nucleolin as an additional protein that binds to a palindromic response region in the KLF2 promoter. The presence of nucleolin on the KLF2 promoter in macrophages was verified by electrophoretic mobility shift assays. Interestingly, in mouse and human endothelial cell lines, electrophoretic mobility shift assays and chromatin immunoprecipitation analyses indicated that nucleolin binds the KLF2 promoter only upon application of fluid shear stress. Pretreatment of the endothelial cells with LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), blocked the shear stress-induced binding of nucleolin to the promoter, demonstrating its PI3K-dependent regulation. Additionally, nucleolin exhibited dynamic flow-specific, PI3K-dependent alterations in size. Anti-nucleolin antibodies interacted with a 110-kDa form in static endothelial cells and with several catalytic forms that changed in abundance after the application of shear stress. Immunoprecipitation experiments demonstrated that fluid flow induced the interaction of nucleolin with the p85 regulatory subunit of PI3K. Finally, introduction of small interfering RNAs targeting the nucleolin genetic sequence selectively reduced nucleolin expression and was sufficient to block the induction of KLF2 by shear stress. These data support a general role for nucleolin in gene regulation and identify it as a novel factor involved in regulation of KLF2 expression.

Activation of Epstein-Barr virus/C3d receptor (gp140, CR2, CD21) on human B lymphoma cell surface triggers Cbl tyrosine phosphorylation, its association with p85 subunit, Crk-L and Syk and its dissociation with Vav

It is well established that CD21 activation on human B cell surface triggers B cell proliferation. We previously demonstrated that CD21 activation also triggers tyrosine phosphorylation of two components, p95 and p120, both interacting with SH2 domains of the p85 subunit of PI 3-kinase. We successively identified p95 as the nucleolin and the first signal transduction pathway specifically triggered by CD21 activation, i.e.: pp60Src activation, tyrosine phosphorylation of p95 nucleolin, its interaction with SH2 domains of p85 subunit and PI 3-kinase activation, followed by AKT-GSK-3 activations. We herein identified the p120 component as the protooncoprotein Cbl and the first steps associated to its activation. First, CD21 activation triggered Cbl tyrosine phosphorylation, which required c-Src kinase but not PI 3-kinase or Syk kinase activities. Involvement of Src kinase in this step was supported by inhibition of Cbl phosphorylation and its interactions with other components when cells were either preincubated with specific Src inhibitor or transfected with dominant-negative c-Src form. Second, once tyrosine phosphorylated, Cbl interacts with SH2 domains of p85 subunit, SH2 domains of Crk-L and with tyrosine phosphorylated Syk kinase. The third and unexpected feature was to found that, at the contrary of BCR or of CD19 (herein also analyzed for the first time), CD21 activation triggers dissociation of Cbl-Vav complex. Thus, these results provide the first molecular basis of a new signal transduction pathway specifically triggered by CD21 activation.

Role of CD21 antigen in diffuse large B-cell lymphoma and its clinical significance

Recent advances in immunological and molecular technology have prompted proposals to change tumour classification and treatment strategies. Cell surface antigens are now easy to access, and tumour origins and clinical characteristics are now readily identifiable. However, in diffuse large B-cell lymphoma (DLBCL), one of the heterogeneous forms of haematological malignancy, the clinical significance of tumour surface antigens has not been well documented. We analysed the tumour surface antigens of 50 tumours from newly diagnosed DLBCL patients by flow cytometry in accordance with their clinical characteristics and followed the patients for a median 3.7 years. Statistical analysis showed that CD21 expression was significantly negatively associated with mortality in DLBCL (CD21 negative versus positive; relative risk = 2.36, P < 0.05). As a result of these clinical observations, we generated CD21-overexpressed (CD21(+)) lymphoma cell lines after gene transfection and analysed tumour cell growth in vivo in immunocompromised mice. Mice challenged with vector-only transfectants and parental cells as controls died within 50 d. In contrast, mice injected with CD21(+) transfectants exhibited significantly reduced tumour growth and 83% survived long term (versus control groups; P < 0.05). Interestingly, all established CD21(+) transfectants (six clones from different bulks) showed homotypic aggregation during in vitro cell culture, and anti-CD21 antibodies did not block this aggregation. Expression of CD21 is strongly associated with increased survival in DLBCL in vivo. CD21 expression may be indirectly concerned with the expression of additional cell adhesion molecules.

Lytic viral replication as a contributor to the detection of Epstein-Barr virus in breast cancer

Epstein-Barr virus (EBV) has an accepted association with the epithelial malignancy nasopharyngeal carcinoma and has also been reported in other more controversial carcinoma settings. Evaluation of EBV association with epithelial carcinomas such as breast cancer would benefit from a better understanding of the outcome of EBV infection of these cells. Cell-free preparations of a green fluorescent protein-expressing virus, BX1, were used to infect breast cancer cell lines, which were then examined for EBV gene expression and viral genome copy number. Reverse transcription-PCR analyses revealed that the cells supported a mixture of latency II and lytic EBV gene expression. Lytic Zta and BMRF1 protein expression was detected by immunohistochemistry, and DNA PCR analyses estimated an EBV copy number of 300 to 600 genomes per infected cell. Evidence for lytic EBV expression was also found in breast tissue, where reverse transcription-PCR analyses detected lytic Zta transcripts in 7 of 10 breast carcinoma tissues and 4 of 10 normal tissues from the same patients. Scattered cells immunoreactive for Zta protein were also detectable in breast carcinoma. Quantitative real-time PCR analysis of EBV-positive breast carcinoma tissues suggested that less than 0.1% of the cells contained viral genomes. We suggest that sporadic lytic EBV infection may contribute to PCR-based detection of EBV in traditionally nonvirally associated epithelial malignancies.

Activation of Epstein-Barr virus/C3d receptor (gp140, CR2, CD21) on human cell surface triggers pp60src and Akt-GSK3 activities upstream and downstream to PI 3-kinase, respectively

We previously demonstrated that CR2 activation on human B lymphocyte surface specifically triggered tyrosine phosphorylation of the 95-kDa nucleolin, this leading to its binding on SH2 domains of p85 sub-unit of PI 3-kinase and to activation of this enzyme. The specificity of CR2 pathway was clearly demonstrated as neither CD19 nor BCR could induce tyrosine phosphorylation of nucleolin in normal B lymphocytes. These data led us to investigate herein additional molecular events, which were triggered by CR2 activation, upstream and downstream to PI 3-kinase activation. Upstream, we demonstrated that pp60src, a tyrosine kinase of the src family, was involved in tyrosine phosphorylation of nucleolin, while syk tyrosine kinase was not. We also demonstrated a direct protein-protein interaction of pp60src with nucleolin in a CR2-dependent and CD19-independent pathway. Downstream, we demonstrated that CR2 activation also triggered Akt and GSK3 enzyme activation, this pathway being under the control of pp60src tyrosine kinase activation. These regulatory functions of activated CR2 were specific as independent of syk tyrosine kinase and of CD19 and BCR activation. Thus, CR2 activation recruits a specific mechanism to activate PI 3-kinase and its subsequent pathways, this mechanism being different to those recruited by CD19 and BCR.

Antigen receptor triggered upregulation of CD86 and CD80 in human B cells: augmenting role of the CD21/CD19 co-stimulatory complex and IL-4

The impact of BCR:CD21 co-engagement on B cell expression of molecules critical for T cell activation was investigated with receptor-specific mAbs conjugated to high MW dextran as stimulatory ligands. In the absence of IL-4, BCR:CD21 co-ligation augmented BCR-triggered CD86 only under conditions of very low BCR ligand dose or affinity, and CD80 was minimally induced by BCR and/or CD21 crosslinking. In the presence of IL-4, BCR:CD21 co-ligation augmented CD86 and CD80 expression under conditions of greater BCR engagement. However, with very high level BCR engagement, no bonus effect of BCR:CD21 crosslinking was observed. Co-ligation-promoted CD86 and CD80 expression was associated with heightened B cell activation of resting allogeneic T cells. The data suggest that co-clustering of BCR and the CD21/CD19 co-stimulatory complex following B cell engagement with C3d-bound microbial or self-antigens will enhance B cell recruitment of T cell help only when IL-4 is present and/or BCR engagement is very limiting.