Enhanced pro-apoptotic activity of rituximab through IBTK silencing in non-Hodgkin lymphoma B-cells

Rituximab is a commonly used chemotherapeutic drug for patients with aggressive lymphomas, such as non-Hodgkin's lymphoma (NHL). Currently, the combination of Rituximab and chemotherapy (R-CHOP) stands as the most prevalent first-line therapy for NHL. Nevertheless, the development of new therapeutic approaches remains imperative. An increasing body of evidence highlights a novel role for IBTK in tumorigenesis and cancer growth. In this study, we aim to broaden our understanding of IBTK's function in B-lymphoma, with a particular focus on its impact on the expression of the oncogene MYC. Here, we assessed the effects of combining Rituximab with IBTK silencing on cell viability through cell cycle analysis and Annexin V assays in vitro. Furthermore, we leveraged the transplantability of Eμ-myc lymphomas to investigate whether the inhibition of IBTK could elicit anti-tumor effects in the treatment of lymphomas in vivo. Our data suggests that IBTK silencing may serve as an effective anti-tumor agent for aggressive B-Lymphomas, underscoring its role in promoting apoptosis when used in combination with Rituximab, both in in vitro and in vivo settings.

SARS CoV-2 spike protein-guided exosome isolation facilitates detection of potential miRNA biomarkers in COVID-19 infections

OBJECTIVES

Nearly three years into the pandemic, SARS-CoV-2 infections are occurring in vaccinated and naturally infected populations. While humoral and cellular responses in COVID-19 are being characterized, novel immune biomarkers also being identified. Recently, an increase in angiotensin-converting enzyme 2 expressing (aka, ACE2 positive) circulating exosomes (ExoACE2) were identified in the plasma of COVID-19 patients (El-Shennawy et al.). In this pilot study, we describe a method to characterize the exosome-associated microRNA (exo-miRNA) signature in ACE2-positive and ACE2-negative exosomal populations (non-ExoACE2).

METHODS

We performed a sorting protocol using the recombinant biotin-conjugated SARS CoV-2 spike protein containing the receptor binding domain (RBD) on plasma samples from six patients. Following purification, exo-miRNA were characterized for ACE2-positive and ACE2-negative exosome subpopulations by RT-PCR.

RESULTS

We identified differential expression of several miRNA. Specifically let-7g-5p and hsa-miR-4454+miR-7975 were upregulated, while hsa-miR-208a-3p and has-miR-323-3p were downregulated in ExoACE2 vs. non-ExoACE2.

CONCLUSIONS

The SARS CoV-2 spike-protein guided exosome isolation permits isolation of ExoACE2 exosomes. Such purification facilitates detailed characterization of potential biomarkers (e.g. exo-miRNA) for COVID-19 patients. This method could be used for future studies to further the understanding mechanisms of host response against SARS CoV-2.

Development of Cyclic Peptides Targeting the Epidermal Growth Factor Receptor in Mesenchymal Triple-Negative Breast Cancer Subtype

Triple-negative breast cancer (TNBC) is an aggressive malignancy characterized by the lack of expression of estrogen and progesterone receptors and amplification of human epidermal growth factor receptor 2 (HER2). Being the Epidermal Growth Factor Receptor (EGFR) highly expressed in mesenchymal TNBC and correlated with aggressive growth behavior, it represents an ideal target for anticancer drugs. Here, we have applied the phage display for selecting two highly specific peptide ligands for targeting the EGFR overexpressed in MDA-MB-231 cells, a human TNBC cell line. Molecular docking predicted the peptide-binding affinities and sites in the extracellular domain of EGFR. The binding of the FITC-conjugated peptides to human and murine TNBC cells was validated by flow cytometry. Confocal microscopy confirmed the peptide binding specificity to EGFR-positive MDA-MB-231 tumor xenograft tissues and their co-localization with the membrane EGFR. Further, the peptide stimulation did not affect the cell cycle of TNBC cells, which is of interest for their utility for tumor targeting. Our data indicate that these novel peptides are highly specific ligands for the EGFR overexpressed in TNBC cells, and thus they could be used in conjugation with nanoparticles for tumor-targeted delivery of anticancer drugs.

Unmutated IGHV1-69 CLL Clone Displays a Distinct Gene Expression Profile by a Comparative qRT-PCR Assay

Chronic Lymphocytic Leukemia (CLL) is a heterogeneous disease characterized by variable clinical courses among different patients. This notion was supported by the possible coexistence of two or more independent CLL clones within the same patients, identified by the characterization of the B cell receptor immunoglobulin (BcR IG) idiotypic sequence. By using the antigen-binding site of the BcR IG as bait, the identification and isolation of aggressive and drug-resistance leukemic B-cell clones could allow a deeper biological and molecular investigation. Indeed, by the screening of phage display libraries, we previously selected a peptide binder of the idiotypic region of CLL BCR IGs expressing the unmutated rearrangement IGHV1-69 and used it as a probe to perform a peptide-based cell sorting by flow cytometry in peripheral blood samples from patients with CLL. Since the IGHV1-69 clones persisted during the follow-up time in both patients, we explored the possibility of these clones having acquired an evolutive advantage compared to the other coexisting clones in terms of a higher expression of genes involved in the survival and apoptosis escape processes. To this end, we studied the expression patterns of a panel of genes involved in apoptosis regulation and in NF-kB-dependent pro-survival signals by comparative qRT-PCR assays. According to the results, IGHV1-69 clones showed a higher expression of pro-survival and anti-apoptotic genes as compared to the other CLL clones with different immunogenetic characteristics. Moreover, these IGHV1-69 clones did not carry any characteristic genetic lesions, indicating the relevance of our approach in performing a comprehensive molecular characterization of single tumor clones, as well as for designing new personalized therapeutic approaches for the most aggressive and persistent tumor clones.

A novel phage display based platform for exosome diversity characterization

We present an innovative approach allowing the identification, isolation, and molecular characterization of disease-related exosomes based on their different antigenic reactivities. The designed strategy could be immediately translated into any disease in which exosomes are involved. The identification of specific markers and their subsequent association with exosome subtypes, together with the possibility to engineer target-guided exosome-like particles, could represent the key for the effective adoption of exosomes in clinical practice.

Metabolites Profiling of Melanoma Interstitial Fluids Reveals Uridine Diphosphate as Potent Immune Modulator Capable of Limiting Tumor Growth

Tumor interstitial fluid (TIF) surrounds and perfuses tumors and collects ions, metabolites, proteins, and extracellular vesicles secreted by tumor and stromal cells. Specific metabolites, accumulated within the TIF, could induce metabolic alterations of immune cells and shape the tumor microenvironment. We deployed a metabolomic approach to analyze the composition of melanoma TIF and compared it to the plasma of C57BL6 mice, engrafted or not with B16-melanoma cells. Among the classes of metabolites analyzed, monophosphate and diphosphate nucleotides resulted enriched in TIF compared to plasma samples. The analysis of the effects exerted by guanosine diphosphate (GDP) and uridine diphosphate (UDP) on immune response revealed that GDP and UDP increased the percentage of CD4+CD25+FoxP3- and, on isolated CD4+ T-cells, induced the phosphorylation of ERK, STAT1, and STAT3; increased the activity of NF-κB subunits p65, p50, RelB, and p52; increased the expression of Th1/Th17 markers including IFNγ, IL17, T-bet, and RORγt; and reduced the expression of IL13, a Th2 marker. Finally, we observed that local administrations of UDP in B16-engrafted C57BL6 mice reduced tumor growth and necrotic areas. In addition, UDP-treated tumors showed a higher presence of MHCIIhi tumor-associated macrophage (TAM) and of CD3+CD8+ and CD3+CD4+ tumor-infiltrating T-lymphocytes (TILs), both markers of anti-tumor immune response. Consistent with this, intra-tumoral gene expression analysis revealed in UDP-treated tumors an increase in the expression of genes functionally linked to anti-tumor immune response. Our analysis revealed an important metabolite acting as mediator of immune response, which could potentially represent an additional tool to be used as an adjuvant in cancer immunotherapy.

Predominant VH1-69 IgBCR Clones Show Higher Expression of CD5 in Heterogeneous Chronic Lymphocytic Leukemia Populations

The immunoglobulin B cell receptor (IgBCR) expressed by chronic lymphocytic leukemia (CLL) B cells plays a pivotal role in tumorigenesis, supporting neoplastic transformation, survival, and expansion of tumor clones. We demonstrated that in the same patient, two or more CLL clones could coexist, recognized by the expression of different variable regions of the heavy chain of IgBCR, composing the antigen-binding site. In this regard, phage display screening could be considered the easier and most advantageous methodology for the identification of small peptide molecules able to mimic the natural antigen of the tumor IgBCRs. These molecules, properly functionalized, could be used as a probe to specifically identify and isolate single CLL subpopulations, for a deeper analysis in terms of drug resistance, phenotype, and gene expression. Furthermore, CLL cells express another surface membrane receptor, the CD5, which is commonly expressed by normal T cells. Piece of evidence supports a possible contribution of CD5 to the selection and maintenance of autoreactivity in B cells and the constitutive expression of CD5 on CLL cells could induce pro-survival stimuli. In this brief research report, we describe a peptide-based single-cell sorting using as bait the IgBCR of tumor cells; in the next step, we performed a quantitative analysis of CD5 expression by qRT-PCR related to the expressed IgBCR. Our approach could open a new perspective for the identification, isolation, and investigation of all subsets of IgBCR-related CLL clones, with particular attention to the more aggressive clones.

Phage-Displayed Peptides for Targeting Tyrosine Kinase Membrane Receptors in Cancer Therapy

Receptor tyrosine kinases (RTKs) regulate critical physiological processes, such as cell growth, survival, motility, and metabolism. Abnormal activation of RTKs and relative downstream signaling is implicated in cancer pathogenesis. Phage display allows the rapid selection of peptide ligands of membrane receptors. These peptides can target in vitro and in vivo tumor cells and represent a novel therapeutic approach for cancer therapy. Further, they are more convenient compared to antibodies, being less expensive and non-immunogenic. In this review, we describe the state-of-the-art of phage display for development of peptide ligands of tyrosine kinase membrane receptors and discuss their potential applications for tumor-targeted therapy.

Role of Chronic Lymphocytic Leukemia (CLL)-Derived Exosomes in Tumor Progression and Survival

Chronic lymphocytic leukemia (CLL) is a B-lymphoproliferative disease, which consists of the abnormal proliferation of CD19/CD5/CD20/CD23 positive lymphocytes in blood and lymphoid organs, such as bone marrow, lymph nodes and spleen. The neoplastic transformation and expansion of tumor B cells are commonly recognized as antigen-driven processes, mediated by the interaction of antigens with the B cell receptor (BCR) expressed on the surface of B-lymphocytes. The survival and progression of CLL cells largely depend on the direct interaction of CLL cells with receptors of accessory cells of tumor microenvironment. Recently, much interest has been focused on the role of tumor release of small extracellular vesicles (EVs), named exosomes, which incorporate a wide range of biologically active molecules, particularly microRNAs and proteins, which sustain the tumor growth. Here, we will review the role of CLL-derived exosomes as diagnostic and prognostic biomarkers of the disease.

Uncovering the Exosomes Diversity: A Window of Opportunity for Tumor Progression Monitoring

Cells can communicate through special “messages in the bottle”, which are recorded in the bloodstream inside vesicles, namely exosomes. The exosomes are nanovesicles of 30–100 nm in diameter that carry functionally active biological material, such as proteins, messanger RNA (mRNAs), and micro RNA (miRNAs). Therefore, they are able to transfer specific signals from a parental cell of origin to the surrounding cells in the microenvironment and to distant organs through the circulatory and lymphatic stream. More and more interest is rising for the pathological role of exosomes produced by cancer cells and for their potential use in tumor monitoring and patient follow up. In particular, the exosomes could be an appropriate index of proliferation and cancer cell communication for monitoring the minimal residual disease, which cannot be easily detectable by common diagnostic and monitoring techniques. The lack of unequivocal markers for tumor-derived exosomes calls for new strategies for exosomes profile characterization aimed at the adoption of exosomes as an official tumor biomarker for tumor progression monitoring.

Insights about MYC and Apoptosis in B-Lymphomagenesis: An Update from Murine Models

The balance between cell survival and cell death represents an essential part of human tissue homeostasis, while altered apoptosis contributes to several pathologies and can affect the treatment efficacy. Impaired apoptosis is one of the main cancer hallmarks and some types of lymphomas harbor mutations that directly affect key regulators of cell death (such as BCL-2 family members). The development of novel techniques in the field of immunology and new animal models has greatly accelerated our understanding of oncogenic mechanisms in MYC-associated lymphomas. Mouse models are a powerful tool to reveal multiple genes implicated in the genesis of lymphoma and are extensively used to clarify the molecular mechanism of lymphoma, validating the gene function. Key features of MYC-induced apoptosis will be discussed here along with more recent studies on MYC direct and indirect interactors, including their cooperative action in lymphomagenesis. We review our current knowledge about the role of MYC-induced apoptosis in B-cell malignancies, discussing the transcriptional regulation network of MYC and regulatory feedback action of miRs during MYC-driven lymphomagenesis. More importantly, the finding of new modulators of apoptosis now enabling researchers to translate the discoveries that have been made in the laboratory into clinical practice to positively impact human health.

IBTK contributes to B-cell lymphomagenesis in Eμ-myc transgenic mice conferring resistance to apoptosis

Increasing evidence supports the involvement of IBTK in cell survival and tumor growth. Previously, we have shown that IBTK RNA interference affects the wide genome expression and RNA splicing in cell-type specific manner. Further, the expression of IBTK gene progressively increases from indolent to aggressive stage of chronic lymphocytic leukemia and decreases in disease remission after therapy. However, the role of IBTK in tumorigenesis has not been elucidated. Here, we report that loss of the murine Ibtk gene raises survival and delays tumor onset in Eμ-myc transgenic mice, a preclinical model of Myc-driven lymphoma. In particular, we found that the number of pre-cancerous B cells of bone marrow and spleen is reduced in Ibtk^-/-Eμ-myc mice owing to impaired viability and increased apoptosis, as measured by Annexin V binding, Caspase 3/7 cleavage assays and cell cycle profile analysis. Instead, the proliferation rate of pre-cancerous B cells is unaffected by the loss of Ibtk. We observed a direct correlation between Ibtk and myc expression and demonstrated a Myc-dependent regulation of Ibtk expression in murine B cells, human hematopoietic and nonhematopoietic cell lines by analysis of ChIP-seq data. By tet-repressible Myc system, we confirmed a Myc-dependent expression of IBTK in human B cells. Further, we showed that Ibtk loss affected the main apoptotic pathways dependent on Myc overexpression in pre-cancerous Eμ-myc mice, in particular, MCL-1 and p53. Of note, we found that loss of IBTK impaired cell cycle and increased apoptosis also in a human epithelial cell line, HeLa cells, in Myc-independent manner. Taken together, these results suggest that Ibtk sustains the oncogenic activity of Myc by inhibiting apoptosis of murine pre-cancerous B cells, as a cell-specific mechanism. Our findings could be relevant for the development of IBTK inhibitors sensitizing tumor cells to apoptosis.

Exosome-associated miRNA profile as a prognostic tool for therapy response monitoring in multiple sclerosis patients

Multiple sclerosis (MS) is an autoimmune pathology leading to neurodegeneration. Because of the complexity and heterogenic etiology of this disease, diagnosis and treatment for individual patients are challenging. Exosome-associated microRNAs (miRNAs) have recently emerged as a new class of diagnostic biomarkers involved in both autoimmune and neurologic disorders. Interesting new evidence has emerged showing that circulating miRNAs are dysregulated in MS body fluids, including serum, plasma, and cerebrospinal fluid. We hypothesized that exosome-associated miRNAs could present a readily accessible blood-based assay for MS disease. We detected expression of miRNAs by quantitative PCR on a small cohort of MS patients. We analyzed circulating exosome-associated miRNAs of MS patients before and after therapy and found that 14 exosome-associated miRNAs were significantly down-regulated, while 2 exosome-associated miRNAs were significantly up-regulated in IFN-β-treated relapsing-remitting MS patients with response to therapy compared to those without response. We identified a serum miRNA panel that could be used to monitor the response to IFN-β therapy. Overall, these data suggest that circulating exosome-associated miRNA profiling could represent an easily detectable biomarker of disease and treatment response.-Manna, I., Iaccino, E., Dattilo, V., Barone, S., Vecchio, E., Mimmi, S., Filippelli, E., Demonte, G., Polidoro, S., Granata, A., Scannapieco, S., Quinto, I., Valentino, P., Quattrone, A. Exosome-associated miRNA profile as a prognostic tool for therapy response monitoring in multiple sclerosis patients.

Peptide-guided targeting of GPR55 for anti-cancer therapy

Expression of the lysophosphatidylinositol receptor GPR55 correlates with invasive potential of metastatic cells and bone metastasis formation of different types of tumors. These findings suggest a role for GPR55 signaling in cancer progression, including in lymphoproliferative diseases. Here, we screened a M13-phage-displayed random library using the bait of HEK293 cells that heterologously expressed full-length HA-GPR55. We selected a set of phagotopes that carried 7-mer insert peptides flanked by a pair of cysteine residues, which resulted in cyclized peptides. Sequencing of selected phagotopes dictated the primary structure for the synthetic FITC-labeled peptide P1, which was analyzed for binding specificity to immunoprecipitated HA-GPR55, and to endogenously expressed GPR55, using cells interfered or not for GPR55, as well as for co-localization imaging with HA-GPR55 at the membrane level. The peptide P1 stimulated GPR55 endocytosis and inhibited GPR55-dependent proliferation of EHEB and DeFew cells, two human B-lymphoblastoid cell lines. Our data support the potential therapeutic application of peptide ligands of GPR55 for targeting and inhibiting growth of neoplastic cells, which overexpress GPR55 and are dependent on GPR55 signaling for their proliferation.

The expression of inhibitor of bruton's tyrosine kinase gene is progressively up regulated in the clinical course of chronic lymphocytic leukaemia conferring resistance to apoptosis

Chronic lymphocytic leukaemia (CLL) is the most common B-cell malignancy with a variable clinical outcome. Biomarkers of CLL progression are required for optimising prognosis and therapy. The Inhibitor of Bruton’s tyrosine kinase—isoform α (IBTKα) gene encodes a substrate receptor of Cullin 3-dependent E3 ubiquitin ligase, and promotes cell survival in response to the reticulum stress. Searching for novel markers of CLL progression, we analysed the expression of IBTKα in the peripheral blood B-cells of CLL patients, before and after first line therapy causing remission. The expression of IBTKα was significantly increased in disease progression, and decreased in remission after chemotherapy. Consistently with a pro-survival action, RNA interference of IBTKα increased the spontaneous and Fludarabine-induced apoptosis of MEC-1 CLL cells, and impaired the cell cycle of DeFew B-lymphoma cells by promoting the arrest in G0/G1 phase and apoptosis. Consistently, RNA interference of IBTKα up regulated the expression of pro-apoptotic genes, including TNF, CRADD, CASP7, BNIP3 and BIRC3. Our results indicate that IBTKα is a novel marker of CLL progression promoting cell growth and resistance to apoptosis. In this view, IBTKα may represent an attractive cancer drug target for counteracting the therapy-resistance of tumour cells.

Monitoring multiple myeloma by idiotype-specific peptide binders of tumor-derived exosomes

Tumor-derived exosomes (TDEs) play a pivotal role in tumor establishment and progression, and are emerging biomarkers for tumor diagnosis in personalized medicine. To date, there is a lack of efficient technology platforms for exosome isolation and characterization. Multiple myeloma (MM) is an incurable B-cell malignancy due to the rapid development of drug-resistance. MM-released exosomes express the immunoglobulin B-cell receptor (Ig-BCR) of the tumor B-cells, which can be targeted by Idiotype-binding peptides (Id-peptides). In this study, we analyzed the production of MM-released exosomes in the murine 5T33MM multiple myeloma model as biomarkers of tumor growth. To this end, we selected Id-peptides by screening a phage display library using as bait the Ig-BCR expressed by 5T33MM cells. By FACS, the FITC-conjugated Id-peptides detected the MM-released exosomes in the serum of 5T33MM-engrafted mice, levels of which are correlated with tumor progression at an earlier time point compared to serum paraprotein. These results indicate that Id-peptide-based recognition of MM-released exosomes may represent a very sensitive diagnostic approach for clinical evaluation of disease progression.

IBTK Differently Modulates Gene Expression and RNA Splicing in HeLa and K562 Cells

The IBTK gene encodes the major protein isoform IBTKα that was recently characterized as substrate receptor of Cul3-dependent E3 ligase, regulating ubiquitination coupled to proteasomal degradation of Pdcd4, an inhibitor of translation. Due to the presence of Ankyrin-BTB-RCC1 domains that mediate several protein-protein interactions, IBTKα could exert expanded regulatory roles, including interaction with transcription regulators. To verify the effects of IBTKα on gene expression, we analyzed HeLa and K562 cell transcriptomes by RNA-Sequencing before and after IBTK knock-down by shRNA transduction. In HeLa cells, 1285 (2.03%) of 63,128 mapped transcripts were differentially expressed in IBTK-shRNA-transduced cells, as compared to cells treated with control-shRNA, with 587 upregulated (45.7%) and 698 downregulated (54.3%) RNAs. In K562 cells, 1959 (3.1%) of 63128 mapped RNAs were differentially expressed in IBTK-shRNA-transduced cells, including 1053 upregulated (53.7%) and 906 downregulated (46.3%). Only 137 transcripts (0.22%) were commonly deregulated by IBTK silencing in both HeLa and K562 cells, indicating that most IBTKα effects on gene expression are cell type-specific. Based on gene ontology classification, the genes responsive to IBTK are involved in different biological processes, including in particular chromatin and nucleosomal organization, gene expression regulation, and cellular traffic and migration. In addition, IBTK RNA interference affected RNA maturation in both cell lines, as shown by the evidence of alternative 3′- and 5′-splicing, mutually exclusive exons, retained introns, and skipped exons. Altogether, these results indicate that IBTK differently modulates gene expression and RNA splicing in HeLa and K562 cells, demonstrating a novel biological role of this protein.

Impairment of T cell development and acute inflammatory response in HIV-1 Tat transgenic mice

Immune activation and chronic inflammation are hallmark features of HIV infection causing T-cell depletion and cellular immune dysfunction in AIDS. Here, we addressed the issue whether HIV-1 Tat could affect T cell development and acute inflammatory response by generating a transgenic mouse expressing Tat in lymphoid tissue. Tat-Tg mice showed thymus atrophy and the maturation block from DN4 to DP thymic subpopulations, resulting in CD4⁺ and CD8⁺ T cells depletion in peripheral blood. In Tat-positive thymus, we observed the increased p65/NF-κB activity and deregulated expression of cytokines/chemokines and microRNA-181a-1, which are involved in T-lymphopoiesis. Upon LPS intraperitoneal injection, Tat-Tg mice developed an abnormal acute inflammatory response, which was characterized by enhanced lethality and production of inflammatory cytokines. Based on these findings, Tat-Tg mouse could represent an animal model for testing adjunctive therapies of HIV-1-associated inflammation and immune deregulation.

B-cell receptor-guided delivery of peptide-siRNA complex for B-cell lymphoma therapy

Background

Despite the clinical response of conventional anticancer therapy, including chemotherapeutic treatments, radiation therapy and corticosteroids, tumorigenic B-cell lymphomas show an incomplete response to clinical practices that result in a minimal residual disease (MRD) where few residual neoplastic cells undetected in vivo, replenish the cancer cell reservoir. This scenario, which is also shared with other cancer diseases, requires the development of strategies to advance in novel, selective targeting toward the tumorigenic cells that survive to the anticancer agents.

Methods

Here, we have taken advantage of the therapeutic properties of an idiotype specific peptide (pA20-36) that bind specifically to murine B-lymphoma cells in the setting of an anti cancer strategy, based on the selected delivery of electrostatic-based complex, peptide-siRNA. To this end, two engineered, arginine rich, peptides that included the pA20-36 targeting sequence were designed to bind fluorescent-labelled siRNA. One peptide presented 9 Arg at the C-terminal of pA20-36 whereas the other included 5 Arg at the N- and C-terminus, respectively.

Results

Compared to the control and random peptide-siRNA complexes, both pA20-36-siRNA complexes were endowed with the selective delivering of fluorescent-labelled siRNA toward the A20 murine B-cell lymphoma, as evaluated by cytofluorimetry and confocal microscopy, whereas fluorescent-labelled siRNA alone was not internalized in the selected cells. Compared to peptide controls, the use of the modified pA20-36 peptides complexed with siRNA anti-GAPDH and anti-Bcl2 showed a down-regulation in the expression levels of the corresponding genes.

Conclusions

Peptide-siRNA complex can be suitable tool for both selective peptide-driven cell targeting and gene silencing. In this setting, the improvement of this strategy is expected to provide a safe and non-invasive approach for the delivery of therapeutic molecules.

CRL3IBTK Regulates the Tumor Suppressor Pdcd4 through Ubiquitylation Coupled to Proteasomal Degradation

The human inhibitor of Bruton's tyrosine kinase isoform α (IBtkα) is a BTB protein encoded by the IBTK gene, which maps to chromosomal locus 6q14.1, a mutational hot spot in lymphoproliferative disorders. Here, we demonstrate that IBtkα forms a CRL3^IBTK complex promoting its self-ubiquitylation. We identified the tumor suppressor Pdcd4 as IBtkα interactor and ubiquitylation substrate of CRL3^IBTK for proteasomal degradation. Serum-induced degradation of Pdcd4 required both IBtkα and Cul3, indicating that CRL3^IBTK regulated the Pdcd4 stability in serum signaling. By promoting Pdcd4 degradation, IBtkα counteracted the suppressive effect of Pdcd4 on translation of reporter luciferase mRNAs with stem-loop structured or unstructured 5′-UTR. IBtkα depletion by RNAi caused Pdcd4 accumulation and decreased the translation of Bcl-xL mRNA, a well known target of Pdcd4 repression. By characterizing CRL3^IBTK as a novel ubiquitin ligase, this study provides new insights into regulatory mechanisms of cellular pathways, such as the Pdcd4-dependent translation of mRNAs.

Cancer-associated CD43 glycoforms as target of immunotherapy

CD43 is a sialoglycosylated membrane protein that is involved in cell proliferation and differentiation. CD43 glycoforms that are recognized by the UN1 monoclonal antibody (mAb) were expressed in lymphoblastoid T-cell lines and solid tumors, such as breast, colon, gastric, and squamous cell lung carcinomas, while unexpressed in the normal counterparts. The cancer association of UN1/CD43 epitope suggested the possibility to use the UN1 mAb for tumor diagnosis and therapy. In this study, we show that the UN1 mAb was endowed with antitumor activity in vivo because its passive transfer inhibited the growth of UN1-positive HPB-ALL lymphoblastoid T cells in mice. Furthermore, we demonstrate that tumor inhibition was due to UN1 mAb-dependent natural killer-mediated cytotoxicity. By screening a phage-displayed random peptide library, we identified the phagotope 2/165 as a mimotope of the UN1 antigen, as it harbored a peptide sequence that was specifically recognized by the UN1 mAb and inhibited the binding of the UN1 mAb to UN1-positive tumor cells. On the basis of sequence homology with the extracellular region of CD43 (amino acids 64 to 83), the 2/165 peptide sequence was likely mimicking the protein core of the UN1/CD43 epitope. When used as vaccine in mice, the 2/165 phagotope raised antibodies against the UN1/CD43 antigen, indicating that the 2/165 phagotope mimicked the UN1 antigen structure, and could represent a novel immunogen for cancer immunotherapy. These findings support the feasibility of using monoclonal antibodies to identify cancer-associated mimotopes for immunotherapy.

Eukaryotic Initiation Factor 4H Is under Transcriptional Control of p65/NF-κB

Protein synthesis is mainly regulated at the initiation step, allowing the fast, reversible and spatial control of gene expression. Initiation of protein synthesis requires at least 13 translation initiation factors to assemble the 80S ribosomal initiation complex. Loss of translation control may result in cell malignant transformation. Here, we asked whether translational initiation factors could be regulated by NF-κB transcription factor, a major regulator of genes involved in cell proliferation, survival, and inflammatory response. We show that the p65 subunit of NF-κB activates the transcription of eIF4H gene, which is the regulatory subunit of eIF4A, the most relevant RNA helicase in translation initiation. The p65-dependent transcriptional activation of eIF4H increased the eIF4H protein content augmenting the rate of global protein synthesis. In this context, our results provide novel insights into protein synthesis regulation in response to NF-κB activation signalling, suggesting a transcription-translation coupled mechanism of control.

Human immunodeficiency virus-1 Tat activates NF-κB via physical interaction with IκB-α and p65

Nuclear factor (NF)-κB is a master regulator of pro-inflammatory genes and is upregulated in human immunodeficiency virus 1 (HIV-1) infection. Mechanisms underlying the NF-κB deregulation by HIV-1 are relevant for immune dysfunction in AIDS. We report that in single round HIV-1 infection, or single-pulse PMA stimulation, the HIV-1 Tat transactivator activated NF-κB by hijacking the inhibitor IκB-α and by preventing the repressor binding to the NF-κB complex. Moreover, Tat associated with the p65 subunit of NF-κB and increased the p65 DNA-binding affinity and transcriptional activity. The arginine- and cysteine-rich domains of Tat were required for IκB-α and p65 association, respectively, and for sustaining the NF-κB activity. Among an array of NF-κB-responsive genes, Tat mostly activated the MIP-1α expression in a p65-dependent manner, and bound to the MIP-1α NF-κB enhancer thus promoting the recruitment of p65 with displacement of IκB-α; similar findings were obtained for the NF-κB-responsive genes CSF3, LTA, NFKBIA and TLR2. Our results support a novel mechanism of NF-κB activation via physical interaction of Tat with IκB-α and p65, and may contribute to further insights into the deregulation of the inflammatory response by HIV-1.

Structural and functional insights into IκB-α/HIV-1 Tat interaction

Protein-protein interactions play fundamental roles in physiological and pathological biological processes. The characterization of the structural determinants of protein-protein recognition represents an important step for the development of molecular entities able to modulate these interactions. We have recently found that IκB-α (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha) blocks the HIV-1 expression and replication in a NF-κB-independent manner by directly binding to the virus-encoded Tat transactivator. Here, we report the evaluation of the entity of binding of IκB-α to Tat through in vitro Surface Plasmon Resonance assay. Moreover, by designing and characterizing a set of peptides of the C-terminus region of IκB-α, we show that the peptide corresponding to the IκB-α sequence 262-287 was able to bind to Tat with high affinity (300 nM). The characterization of a number of IκB-α-based peptides also provided insights into their intrinsic folding properties. These findings have been corroborated by mutagenesis studies on the full-length IκB-α, which unveil that different IκB-α residues are involved in NF-κB or Tat recognition.

Mass spectrometry-based identification of the tumor antigen UN1 as the transmembrane CD43 sialoglycoprotein

The UN1 monoclonal antibody recognized the UN1 antigen as a heavily sialylated and O-glycosylated protein with the apparent molecular weight of 100-120 kDa; this antigen was peculiarly expressed in fetal tissues and several cancer tissues, including leukemic T cells, breast, and colon carcinomas. However, the lack of primary structure information has limited further investigation on the role of the UN1 antigen in neoplastic transformation. In this study, we have identified the UN1 antigen as CD43, a transmembrane sialoglycoprotein involved in cell adhesion, differentiation, and apoptosis. Indeed, mass spectrometry detected two tryptic peptides of the membrane-purified UN1 antigen that matched the amino acidic sequence of the CD43 intracellular domain. Immunological cross-reactivity, migration pattern in mono- and bi-dimensional electrophoresis, and CD43 gene-dependent expression proved the CD43 identity of the UN1 antigen. Moreover, the monosaccharide GalNAc-O-linked to the CD43 peptide core was identified as an essential component of the UN1 epitope by glycosidase digestion of specific glycan branches. UN1-type CD43 glycoforms were detected in colon, sigmoid colon, and breast carcinomas, whereas undetected in normal tissues from the same patients, confirming the cancer-association of the UN1 epitope. Our results highlight UN1 monoclonal antibody as a suitable tool for cancer immunophenotyping and analysis of CD43 glycosylation in tumorigenesis.

Computational analysis and in vivo validation of a microRNA encoded by the IBTK gene, a regulator of B-lymphocytes differentiation and survival

MicroRNAs (miRNAs) are small single-stranded RNA molecules that play an essential role in the regulation of gene expression and cell physiology. Gene rearrangements occurring in the miRNA sequence are associated with cancer. The IBTK genetic locus is located in the genomic sequence 6q14.1 that undergoes chromosomal aberration in lymphoproliferative disorders. The IBTK gene encodes the proteins IBtk-alpha, beta and gamma that regulate the B cell receptor signalling through Bruton's tyrosine kinase, which promotes B cell survival and differentiation. Pro-MirII-based analysis predicted four precursors of microRNAs (pre-miR) encoded by introns 17, 21, 26 and the 3' un-translated region of the IBTK gene. Pre-miR-IBTK3, which was encoded by intron 26, was the effective substrate of RNase III Dicer in vitro as well as the precursor of an IBtk miRNA generated in vivo. By CLUSTALW-based analysis, pre-miR-IBTK3 homologues were found in Pan troglodytes, Pongo pygmaeus and Macaca mulatta, suggesting an evolutionary conserved function in primates.

The aftermath of the Merck's HIV vaccine trial

The recently released results of the Merck's Phase IIb "test-of concept" vaccine trials have shown no protection from HIV-1 infection in the vaccinated group compared with a control group vaccinated with placebo. The study was designed to test the Merck's MRKAd5 trivalent candidate vaccine. The vaccine formulation was expected to stimulate a HIV-specific T cell immune response and to either prevent infection, or to reduce the levels of the viral load in vaccinated subjects. Upon the first evaluation of the interim data, the independent Data and Safety Monitoring Board (DSMB) underscored no protection from HIV-1 infection in the vaccine-inoculated volunteers compared with the control group; accordingly, the vaccine trial was stopped. This disappointing outcome warrants a critical analysis of the current vaccine studies and calls for a renewed effort toward a rational design of novel immunogens to be tested in large primate trials.

Physical and functional characterization of the genetic locus of IBtk, an inhibitor of Bruton's tyrosine kinase: evidence for three protein isoforms of IBtk

Bruton's tyrosine kinase (Btk) is required for B-cell development. Btk deficiency causes X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (Xid) in mice. Btk lacks a negative regulatory domain and may rely on cytoplasmic proteins to regulate its activity. Consistently, we identified an inhibitor of Btk, IBtk, which binds to the PH domain of Btk and down-regulates the Btk kinase activity. IBtk is an evolutionary conserved protein encoded by a single genomic sequence at 6q14.1 cytogenetic location, a region of recurrent chromosomal aberrations in lymphoproliferative disorders; however, the physical and functional organization of IBTK is unknown. Here, we report that the human IBTK locus includes three distinct mRNAs arising from complete intron splicing, an additional polyadenylation signal and a second transcription start site that utilizes a specific ATG for protein translation. By northern blot, 5′RACE and 3′RACE we identified three IBTKα, IBTKβ and IBTKγ mRNAs, whose transcription is driven by two distinct promoter regions; the corresponding IBtk proteins were detected in human cells and mouse tissues by specific antibodies. These results provide the first characterization of the human IBTK locus and may assist in understanding the in vivo function of IBtk.

Regulation of the HIV promoter/enhancer

This unit describes adaptations of two molecular techniques that can be used to study the regulation of HIV expression. The first two protocols describe the chloramphenicol acetyltransferase (CAT) assay, in which the CAT reporter gene is attached to an HIV-1 promoter and CAT activity is measured as an indication of the promoter's activity. The basic protocol is rapid, simple, and suited to analyzing multiple samples. An alternate protocol describes an assay for CAT function that involves separating the reaction products by thin-layer chromatography (TLC). The second basic protocol describes an electrophoretic mobility shift assay for detecting proteins present in cell extracts that can bind to the HIV-1 LTR (long terminal repeat). Such studies are central to current HIV research because it is important to know what agents induce and inhibit (or "down-regulate") HIV transcription.

Partial purification and MALDI-TOF MS analysis of UN1, a tumor antigen membrane glycoprotein

UN1 is a membrane glycoprotein that is expressed in immature human thymocytes, a subpopulation of peripheral T lymphocytes, the HPB acute lymphoblastic leukemia (ALL) T-cell line and fetal thymus. We previously reported the isolation of a monoclonal antibody (UN1 mAb) recognizing the UN1 protein that was classified as "unclustered" at the 5th and 6th International Workshop and Conference on Human Leukocyte Differentiation Antigens. UN1 was highly expressed in breast cancer tissues and was undetected in non-proliferative lesions and in normal breast tissues, indicating a role for UN1 in the development of a tumorigenic phenotype of breast cancer cells. In this study, we report a partial purification of the UN1 protein from HPB-ALL T cells by anion-exchange chromatography followed by immunoprecipitation with the UN1 mAb and MALDI-TOF MS analysis. This analysis should assist in identifying the amino acid sequence of UN1.

Inhibition of HIV-1 replication in primary human monocytes by the IkappaB-alphaS32/36A repressor of NF-kappaB

Background

The identification of the molecular mechanisms of human immunodeficiency virus type 1, HIV-1, transcriptional regulation is required to develop novel inhibitors of viral replication. NF-κB transacting factors strongly enhance the HIV/SIV expression in both epithelial and lymphoid cells. Controversial results have been reported on the requirement of NF-κB factors in distinct cell reservoirs, such as CD4-positive T lymphocytes and monocytes. We have previously shown that IκB-αS32/36A, a proteolysis-resistant inhibitor of NF-κB, potently inhibits the growth of HIV-1 and SIVmac239 in cell cultures and in the SIV macaque model of AIDS. To further extend these observations, we have generated NL(AD8)IκB-αS32/36A, a macrophage-tropic HIV-1 recombinant strain endowed to express IκB-αS32/36A.

Results

In this work, we show that infection with NL(AD8)IκB-αS32/36A down-regulated the NF-κB DNA binding activity in cells. NL(AD8)IκB-αS32/36A was also highly attenuated for replication in cultures of human primary monocytes.

Conclusions

These results point to a major requirement of NF-κB activation for the optimal replication of HIV-1 in monocytes and suggest that agents which interfere with NF-κB activity could counteract HIV-1 infection of monocytes-macrophages in vivo.

High Attenuation and Immunogenicity of a Simian Immunodeficiency Virus Expressing a Proteolysis-resistant Inhibitor of NF-κB

NF-kappaB/IkappaB proteins play a major role in the transcriptional regulation of human immunodeficiency virus, type-1 (HIV-1). In the case of simian immunodeficiency virus (SIV) the cellular factors required for the viral transcriptional activation and replication in vivo remain undefined. Here, we demonstrate that the p50/p65 NF-kappaB transcription factors enhanced the Tat-mediated transcriptional activation of SIVmac239. In addition, IkappaB-alpha S32/36A, a proteolysis-resistant inhibitor of NF-kappaB, strongly inhibited the Tat-mediated transactivation of SIVmac239. Based on this evidence, we have generated a self-regulatory virus by endowing the genome of SIV-mac239 with IkappaB-alpha S32/36A; the resulting virus, SIVIkappaB-alpha S32/36A, was nef-deleted and expressed the NF-kappaB inhibitor. We show that SIVIkappaB-alpha S32/36A was highly and stably attenuated both in cell cultures and in vivo in rhesus macaque as compared with a nef-deleted control virus. Moreover, the high attenuation was associated with a robust immune response as measured by SIV-specific antibody production, tetramer, and intracellular IFN-gamma staining of SIV gag-specific T cells. These results underscore the crucial role of NF-kappaB/IkappaB proteins in the regulation of SIV replication both in cell cultures and in monkeys. Thus, inhibitors of NF-kappaB could efficiently counteract the SIV/HIV replication in vivo and may assist in developing novel approaches for AIDS vaccine and therapy.

Physical and functional interaction of HIV-1 Tat with E2F-4, a transcriptional regulator of mammalian cell cycle

Tat protein of the human immunodeficiency virus type-1 (HIV-1) plays a critical role in the regulation of viral transcription and replication. In addition, Tat regulates the expression of a variety of cellular genes and could account for AIDS-associated diseases including Kaposi's Sarcoma and non-Hodgkin's lymphoma by interfering with cellular processes such as proliferation, differentiation, and apoptosis. The molecular mechanisms underlying the pleiotropic activities of Tat may include the generation of functional heterodimers of Tat with cellular proteins. By screening a human B-lymphoblastoid cDNA library in the yeast two-hybrid system, we identified E2F-4, a member of E2F family of transcription factors, as a Tat-binding protein. The interaction between Tat and E2F-4 was confirmed by GST pull-down experiments performed with cellular extracts as well as with in vitro translated E2F-4. The physical association of Tat and E2F-4 was confirmed by in vivo binding experiments where Tat.E2F-4 heterodimers were recovered from Jurkat cells by immunoprecipitation and immunoblotting. By using plasmids expressing mutant forms of Tat and E2F-4, the domains involved in Tat.E2F-4 interaction were identified as the regions encompassing amino acids 1-49 of Tat and amino acids 1-184 of E2F-4. Tat x E2F-4 complexes were shown to bind to E2F cis-regions with increased efficiency compared with E2F-4 alone and to mediate the activity of E2F-dependent promoters including HIV-1 long terminal repeat and cyclin A. The data point to Tat as an adaptor protein that recruits cellular factors such as E2F-4 to exert its multiple biological activities.

Protection of rhesus macaques against disease progression from pathogenic SHIV-89.6PD by vaccination with phage-displayed HIV-1 epitopes

The antigenic polymorphism of HIV-1 is a major obstacle in developing an effective vaccine. Accordingly, we screened random peptide libraries (RPLs) displayed on phage with antibodies from HIV-infected individuals and identified an array of HIV-specific epitopes that behave as antigenic mimics of conformational epitopes of gp120 and gp41 proteins. We report that the selected epitopes are shared by a collection of HIV-1 isolates of clades A-F. The phage-borne epitopes are immunogenic in rhesus macaques, where they elicit envelope-specific antibody responses. Upon intravenous challenge with 60 MID50 of pathogenic SHIV-89.6PD, all monkeys became infected; however, in contrast to the naive and mock-immunized monkeys, four of five mimotope-immunized monkeys experienced lower levels of peak viremia, followed by viral set points of undetectable or transient levels of viremia and a mild decline of CD4+ T cells, and were protected from progression to AIDS-like illness. These results provide a new approach to the design of broadly protective HIV-1 vaccines.

Direct inhibition of Bruton's tyrosine kinase by IBtk, a Btk-binding protein

Bruton's tyrosine kinase (Btk) is required for human and mouse B cell development. Btk deficiency causes X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency in mice. Unlike Src proteins, Btk lacks a negative regulatory domain at the COOH terminus and may rely on cytoplasmic Btk-binding proteins to regulates its kinase activity by trans-inhibitor mechanisms. Consistent with this possibility, IBtk, which we identified as an inhibitor of Btk, bound to the PH domain of Btk. IBtk downregulated Btk kinase activity, Btk-mediated calcium mobilization and nuclear factor-kappaB-driven transcription. These results define a potential mechanism for the regulation of Btk function in B cells.

Predictive value of Epstein-Barr virus genome copy number and BZLF1 expression in blood lymphocytes of transplant recipients at risk for lymphoproliferative disease

Epstein-Barr virus (EBV) genome numbers and RNA transcripts from the immediate-early EBV gene BZLF1 were monitored by means of polymerase chain reaction in peripheral blood lymphocytes (PBLs) of 44 children who received liver transplants. The 2 tests were compared, using several parameters to assess their value as predictors of posttransplantation lymphoproliferative disease (PTLD). All patients were infected with EBV. BZLF1 mRNA was positive in 70% of patients, with highest expression in those with largest virus load. Four patients developed PTLD that could not be unequivocally diagnosed by any of the parameters considered alone. Sensitivity of EBV genome number (>/=40,000 EBV copies/10(5) PBLs) and BZLF1 mRNA (BZLF1:glyceraldehyde-3-phosphate-dehydrogenase ratio >/=0.5) was 100%. Specificity of each of the 2 tests alone (98% and 58%, respectively) improved (to 100% and 83%, respectively) when measurement of serum IgG level was included. Because decreased virus load, but not BZLF1 mRNA expression, accurately predicted favorable responses of PTLD to therapy, monitoring of EBV genome numbers alone appears sufficient in children with liver transplants.

Potent and stable attenuation of live-HIV-1 by gain of a proteolysis-resistant inhibitor of NF-kappaB (IkappaB-alphaS32/36A) and the implications for vaccine development

Live-attenuated human immunodeficiency viruses (HIVs) are candidates for Acquired Immunodeficiency Syndrome (AIDS) vaccine. Based on the simian immunodeficiency virus (SIV) model for AIDS, loss-of-function (e.g. deletion of accessory genes such as nef) has been forwarded as a primary approach for creating enfeebled, but replication-competent, HIV-1/SIV. Regrettably, recent evidence suggests that loss-of-function alone is not always sufficient to prevent the emergence of virulent mutants. New strategies that attenuate via mechanisms distinct from loss-of-function are needed for enhancing the safety phenotype of viral genome. Here, we propose gain-of-function to be used simultaneously with loss-of-function as a novel approach for attenuating HIV-1. We have constructed an HIV-1 genome carrying the cDNA of a proteolysis-resistant nuclear factor-kappaB inhibitor (IkappaB-alphaS32/36A) in the nef region. HIV-1 expressing IkappaB-alphaS32/36A down-regulates viral expression and is highly attenuated in both Jurkat and peripheral blood mononuclear cells. We provide formal proof that the phenotypic and attenuating characteristics of IkappaB-alphaS32/36A permit its stable maintenance in a live, replicating HIV-1 despite 180 days of forced ex vivo passaging in tissue culture. As compared with other open-reading frames embedded into HIV/SIV genome, this degree of stability is unprecedented. Thus, IkappaB-alphaS32/36A offers proof-of-principle that artifactually gained functions, when used to attenuate the replication of live HIV-1, can be stable. These findings illustrate gain-of-function as a feasible strategy for developing safer live-attenuated HIVs to be tested as candidates for AIDS vaccine.

Impaired generation of bone marrow B lymphocytes in mice deficient in C/EBPbeta

CAAT/enhancer binding proteins (C/EBP) are a family of transcription factors that mediates adipocyte differentiation and the regulation of genes expressed in immune responses and inflammation, such as interleukin-6 (IL-6), IL-8, and granulocyte colony-stimulating factor (G-CSF). We investigated the role of C/EBPbeta (NF-IL6) in the generation of bone marrow B lymphocytes by taking advantage of C/EBPbeta-/- mice. We found that the expansion of bone marrow (BM) B lymphocytes was impaired in long-term lymphoid cultures from C/EBPbeta-/- mice. Consistent with this finding, the number of BM B cells was decreased in C/EBPbeta-/- mice. Both the levels of IL-7 gene expression and bioactive IL-7 from BM stromal cells were decreased in C/EBPbeta-/- mice. Furthermore, the proliferative responsiveness of BM B-cell precursors to IL-7 was also reduced as compared to wild-type mice, indicating that C/EBPbeta is required for the generation of BM B cells induced by IL-7. Accordingly, IL-7 stimulates the C/EBPbeta DNA-binding activity of normal BM pre-B lymphocytes as well as of 70Z/3 pre-B cells. These results point to C/EBPbeta as a critical signaling molecule in BM B lymphopoiesis.

HIV-1 Tat induces the expression of the interleukin-6 (IL6) gene by binding to the IL6 leader RNA and by interacting with CAAT enhancer-binding protein beta (NF-IL6) transcription factors

Human immunodeficiency virus type 1 (HIV-1) infection is associated with severe psoriasis, B cell lymphoma, and Kaposi's sarcoma. A deregulated production of interleukin-6 (IL6) has been implicated in the pathogenesis of these diseases. The molecular mechanisms underlying the abnormal IL6 secretion of HIV-1-infected cells may include transactivation of the IL6 gene by HIV-1. Here we report the molecular mechanisms of Tat activity on the expression of the IL6 gene. By using 5' deletion mutants of pIL6Pr-CAT and using IL6:HIV-1-LTR hybrid constructs where discrete regions of the IL6 promoter replaced the TAR sequence in HIV-1 LTR, we identified a short sequence of the 5'-untranslated region of the IL6 mRNA that is required for Tat to trans-activate the IL6 promoter. This sequence acquires a stem-loop structure and includes a UCU sequence that binds to Tat and is necessary for full trans-activation. In addition, we provide the evidence that Tat can function by enhancing the CAAT enhancer-binding protein (C/EBP) DNA binding activity and is able to complex with in vitro translated C/EBPbeta, which is a major mediator of IL6 promoter function. By using the yeast two-hybrid system and immunoprecipitation, we observed that the interaction of Tat with C/EBP proteins also occurred in vivo. The data are consistent with the possibility that Tat may function on heterologous genes by interacting with RNA structures possibly present in a large number of cellular and viral genes. In addition, Tat may function by protein-protein interactions, leading to the generation of heterodimers with specific transcription factors.

Shc mediates IL-6 signaling by interacting with gp130 and Jak2 kinase

IL-6 is a multifunctional cytokine involved in hemopoiesis, immune regulation, inflammation, neural development, and infection. IL-6 belongs to a family of related cytokines that includes leukemia inhibitory factor, oncostatin M, IL-11, ciliary neurotropic factor, and cardiotropin-1, all of which initiate signaling through a receptor-associated gp130. IL-6 induces homodimerization of gp130 and activates the Jak/STAT pathway of signal transduction. In addition, IL-6 stimulates the mitogen-activated protein kinases designated ERK (extracellular signal-regulated kinase)-1 and -2. Activation of ERK-1 and -2 may involve the Src homology-2 containing proteins Shc and Grb2. Here we provide evidence that Shc could function as signaling molecules for IL-6 in DeFew-IL-6R/gp130 cells, a human B lymphoma cell line engineered to express high levels of both the IL-6R (p80) and the gp130 subunit. IL-6 was shown to promote the rapid tyrosine phosphorylation of gp130, Jak2, and Shc proteins. Moreover, Shc associated both in vivo and in vitro with phosphorylated gp130 through the Shc-Src homology-2 domain. We also report that Shc bound to activated Jak2 by using the Shc amino terminal phosphotyrosine interaction domain. Following IL-6 stimulation, Shc physically associated with Grb2. Thus, the data point to Shc proteins as a functional link between the Jak2 and Ras pathways of IL-6 signal transduction.

Shc mediates IL-6 signaling by interacting with gp130 and Jak2 kinase

IL-6 is a multifunctional cytokine involved in hemopoiesis, immune regulation, inflammation, neural development, and infection. IL-6 belongs to a family of related cytokines that includes leukemia inhibitory factor, oncostatin M, IL-11, ciliary neurotropic factor, and cardiotropin-1, all of which initiate signaling through a receptor-associated gp130. IL-6 induces homodimerization of gp130 and activates the Jak/STAT pathway of signal transduction. In addition, IL-6 stimulates the mitogen-activated protein kinases designated ERK (extracellular signal-regulated kinase)-1 and -2. Activation of ERK-1 and -2 may involve the Src homology-2 containing proteins Shc and Grb2. Here we provide evidence that Shc could function as signaling molecules for IL-6 in DeFew-IL-6R/gp130 cells, a human B lymphoma cell line engineered to express high levels of both the IL-6R (p80) and the gp130 subunit. IL-6 was shown to promote the rapid tyrosine phosphorylation of gp130, Jak2, and Shc proteins. Moreover, Shc associated both in vivo and in vitro with phosphorylated gp130 through the Shc-Src homology-2 domain. We also report that Shc bound to activated Jak2 by using the Shc amino terminal phosphotyrosine interaction domain. Following IL-6 stimulation, Shc physically associated with Grb2. Thus, the data point to Shc proteins as a functional link between the Jak2 and Ras pathways of IL-6 signal transduction.

High efficiency of site-directed mutagenesis mediated by a single PCR product

We describe a highly efficient procedure for site-specific mutagenesis of double-stranded plasmids. The method relies on a single PCR primer which incorporates both the mutations at the selection site and the desired single base substitutions at the mutant site. This primer is annealed to the denatured plasmid and directs the synthesis of the mutant strand. After digestion with selection enzyme, the plasmid DNA is amplified into Escherichia coli strain BMH71-18 and subjected to a second digestion and amplification into the bacterial strain DH5alpha. A mutagenesis efficiency >80% was consistently achieved in the case of two unrelated plasmids.

Regulation of HIV-1 long terminal repeats by interaction of C/EBP(NF-IL6) and NF-kappaB/Rel transcription factors

We report the characterization of a CAAT enhancer-binding protein (C/EBP) (NF-IL6) element encompassing the region from -174 to -166 of the U3 long terminal repeat (LTR) region of HIV-1. This C/EBP cis sequence was found to bind to C/EBPbeta and C/EBPdelta factors in DNA band shift assay. Transfection of NTera-2 cells with a HIV-1-LTR CAT construct (pC15CAT), together with C/EBPbeta or C/EBPdelta expression plasmids showed that C/EBP proteins strongly activated the HIV-1 promoter. Deletions encompassing the C/EBP-binding site resulted in the enhancement of the LTR activation mediated by C/EBP proteins, suggesting that other sequences located 3' to -170 were indeed the target for C/EBP factors. This possibility was confirmed by using the pCD54E9CAT plasmid, in which the NF-kappaB enhancer was inserted 5' to the HIV-1 LTR TATA box. A NF-kappaB1(p50) expression plasmid was also utilized to test for functional co-operation between NF-kappaB and C/EBP factors. We observed that p50 middle dotC/EBPbeta and p50 middle dotC/EBPdelta complexes were generated in tested cells and strongly activated the HIV-1 LTR by binding to the NF-kappaB sequences. The physical association of NF-kappaB1(p50) with C/EBP factors was assayed by direct interaction of in vitro translated p50 proteins with C/EBPbeta or C/EBPdelta produced as glutathione S-transferase fusion proteins. Moreover, p50 middle dotC/EBPbeta complexes were observed in vivo by using DNA affinity studies with biotinylated NF-kappaB oligonucleotides. By using mutant forms of p50 or C/EBPbeta proteins we found that the transactivation of HIV-1 LTR by p50 middle dotC/EBPbeta complexes required the DNA-binding domain of p50 and the transcription activation domain of C/EBPbeta.

An NF-kappaB site in the 5'-untranslated leader region of the human immunodeficiency virus type 1 enhances the viral expression in response to NF-kappaB-activating stimuli

The 5'-untranslated leader region of human immunodeficiency virus, type 1 (HIV-1), includes a complex array of putative regulatory elements whose role in the viral expression is not completely understood. Here we demonstrate the presence of an NF-kappaB-responsive element in the trans-activation response (TAR) region of HIV-1 that confers the full induction of HIV-1 long terminal repeat (LTR) in response to NF-kappaB-activating stimuli, such as DNA alkylating agents, phorbol 12-myristate 13-acetate, and tumor necrosis factor-alpha. The TAR NF-kappaB site GGGAGCTCTC spans from positions +31 to +40 and cooperates with the NF-kappaB enhancer upstream of the TATA box in the NF-kappaB-mediated induction of HIV-1 LTR. The conclusion stems from the following observations: (i) deletion of the two NF-kappaB sites upstream of the TATA box reduces, but does not abolish, the HIV-1 LTR activation by NF-kappaB inducers; (ii) deletion or base pair substitutions of the TAR NF-kappaB site significantly reduce the HIV-1 LTR activation by NF-kappaB inducers; (iii) deletions of both the NF-kappaB sites upstream of the TATA box and the TAR NF-kappaB site abolish the activation of HIV-1 LTR in response to NF-kappaB inducers. Moreover, the p50 p65 NF-kappaB complex binds to the TAR NF-kappaB sequence and trans-activates the TAR NF-kappaB-directed expression. The identification of an additional NF-kappaB site in the HIV-1 LTR points to the relevance of NF-kappaB factors in the HIV-1 life cycle.

Regulation of NF-kappa B through the nuclear processing of p105 (NF-kappa B1) in Epstein-Barr virus-immortalized B cell lines

Transcription factors of the NF-kappa B/Rel family are retained in the cytoplasm as inactive complexes through association with I kappa B inhibitory proteins. Several NF-kappa B activators induce the proteolysis of I kappa B proteins, which results in the nuclear translocation and DNA binding of NF-kappa B complexes. Here, we report a novel mechanism of NF-kappa B regulation mediated by p105 (NF-kappa B1) precursor of p50 directly at the nuclear level. In Epstein-Barr virus-immortalized B cells, p105 was found in the nucleus, where it was complexed with p65. In concomitance with NF-kappa B activation, mitomycin C induced the processing of p105 to p50 in the nucleus, while it did not affect the steady-state protein levels of I kappa B alpha and p105 in the cytoplasm. Differently, phorbol 12-myristate 13-acetate induced a significant proteolysis of both I kappa B alpha and p105 in the cytoplasm, while it did not affect the protein level of p105 in the nucleus. These results suggest that in Epstein-Barr virus-positive B cell lines the nuclear processing of p105 can contribute to NF-kappa B activation in response to specific signaling molecules, such as DNA-damaging agents.