Ileana Quinto

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

Brutons 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-κB–driven transcription. These results define a potential mechanism for the regulation of Btk function in B cells.

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.

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-κB-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-κB-activating stimuli, such as DNA alkylating agents, phorbol 12-myristate 13-acetate, and tumor necrosis factor-α. The TAR NF-κB site GGGAGCTCTC spans from positions +31 to +40 and cooperates with the NF-κB enhancer upstream of the TATA box in the NF-κB-mediated induction of HIV-1 LTR. The conclusion stems from the following observations: (i) deletion of the two NF-κB sites upstream of the TATA box reduces, but does not abolish, the HIV-1 LTR activation by NF-κB inducers; (ii) deletion or base pair substitutions of the TAR NF-κB site significantly reduce the HIV-1 LTR activation by NF-κB inducers; (iii) deletions of both the NF-κB sites upstream of the TATA box and the TAR NF-κB site abolish the activation of HIV-1 LTR in response to NF-κB inducers. Moreover, the p50·p65 NF-κB complex binds to the TAR NF-κB sequence and trans-activates the TAR NF-κB-directed expression. The identification of an additional NF-κB site in the HIV-1 LTR points to the relevance of NF-κB factors in the HIV-1 life cycle.

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.

Aberrant Glycosylation as Biomarker for Cancer: Focus on CD43

Glycosylation is a posttranslational modification of proteins playing a major role in cell signalling, immune recognition, and cell-cell interaction because of their glycan branches conferring structure variability and binding specificity to lectin ligands. Aberrant expression of glycan structures as well as occurrence of truncated structures, precursors, or novel structures of glycan may affect ligand-receptor interactions and thus interfere with regulation of cell adhesion, migration, and proliferation. Indeed, aberrant glycosylation represents a hallmark of cancer, reflecting cancer-specific changes in glycan biosynthesis pathways such as the altered expression of glycosyltransferases and glycosidases. Most studies have been carried out to identify changes in serum glycan structures. In most cancers, fucosylation and sialylation are significantly modified. Thus, aberrations in glycan structures can be used as targets to improve existing serum cancer biomarkers. The ability to distinguish differences in the glycosylation of proteins between cancer and control patients emphasizes glycobiology as a promising field for potential biomarker identification. In this review, we discuss the aberrant protein glycosylation associated with human cancer and the identification of protein glycoforms as cancer biomarkers. In particular, we will focus on the aberrant CD43 glycosylation as cancer biomarker and the potential to exploit the UN1 monoclonal antibody (UN1 mAb) to identify aberrant CD43 glycoforms.

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

Brutons 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.

Evolutionary screening and adsorption behavior of engineered M13 bacteriophage and derived dodecapeptide for selective decoration of gold interfaces.

There is a growing interest in identifying biomacromolecules such as proteins and peptides to functionalize metallic surfaces through noncovalent binding. One method for functionalizing materials without fundamentally changing their inherent structure is using biorecognition moieties. Here, we proved a general route to select a biomolecule adhesive motif for surface functionalization by comprehensively screening phage displayed peptides. In particular, we selected a genetically engineered M13 bacteriophage and a linear dodecapeptide derived from its pIII domain for recognizing gold surfaces in a specific and selective manner. In the phage context, we demonstrated the adhesive motif was capable to adsorb on gold in a preferential way with a morphological and viscoelastic signature of the adsorbed layer as evidenced by QCM-D and AFM investigations. Out of the phage context, the linear dodecapeptide is reproducibly found to adhere to the gold surface, and by quantitative SPR measurements, high affinity constants (K(eq)~10(6)M(-1), binding energy ~-8 kcal/mol) were determined. We proved that the interactions occurring at gold interface were mainly hydrophobic as a consequence of high frequency of hydrophobic residues in the peptide sequence. Moreover, by CD, molecular dynamics and steered molecular dynamics, we demonstrated that the molecular flexibility only played a minor role in the peptide adsorption. Such noncovalent but specific modification of inorganic surfaces through high affinity biomolecule adsorption represents a general strategy to modulate the functionality of multipurpose metallic surfaces.

In vivo targeting and growth inhibition of the A20 murine B-cell lymphoma by an idiotype-specific peptide binder.

B-cell lymphoma is a clonal expansion of neoplastic cells that may result in fatal outcomes. Here, we report the in vivo targeting and growth inhibition of aggressive A20 murine B-cell lymphoma by idiotype-specific peptide pA20-36. pA20-36 was selected from random peptide libraries and bound specifically to the B-cell receptor (BCR) of A20 cells in mice engrafted with A20 lymphoma, as shown by histology and positron emission tomographic analysis. BCR cross-linking of A20 cells with pA20-36 resulted in massive apoptosis of targeted tumor cells and in an increased survival of the diseased animals without any detectable evidence of toxicity. The pA20-36 treatment reverted the immune suppression of the tumor microenvironment as shown by reduced expression of vascular endothelial growth factor, interleukin-10, and transforming growth factor-beta cytokines together with a lower number of CD11b+Gr-1+ inhibitor myeloid-derived suppressor cells and Foxp3+CD4+ Treg cells. Furthermore, pA20-36 treatment was associated with an increased number of tumor-infiltrating, activated CD8+ T cells that exerted a tumor-specific cytolytic activity. These findings show that a short peptide that binds specifically to the complementarity-determining regions of the A20 BCR allows in vivo detection of neoplastic cells together with significant inhibition of tumor growth in vivo.

IκB-α Represses the Transcriptional Activity of the HIV-1 Tat Transactivator by Promoting Its Nuclear Export

The long terminal repeat of human immunodeficiency virus, type 1 (HIV-1) contains an NF-κB enhancer and is potently inhibited by IκB-αS32/36A, a proteolysis-resistant inhibitor of NF-κB transacting factors. The evidence that NF-κB is dispensable for HIV-1 expression raises the question of whether IκB-α represses the HIV-1 transcription by mechanisms distinct from NF-κB inhibition. Here, we report that IκB-α negatively regulates the HIV-1 expression and replication in an NF-κB-independent manner by directly binding to Tat, which results in the nuclear export and cytoplasmic sequestration of the viral transactivator. The sequence of IκB-α required for Tat inhibition spans from amino acids 72 to 287 and includes the nuclear localization signal, the carboxyl-terminal nuclear export signal, and the binding site for the arginine-rich domain of Tat. This novel mechanism of cross-talk between Tat and IκB-α provides further insights into the mechanisms of HIV-1 regulation and could assist in the development of novel strategies for AIDS 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 Kaposis Sarcoma and non-Hodgkins 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 vivobinding 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·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.