Global conformational changes in IgG-Fc upon mutation of the FcRn-binding site are not associated with altered antibody-dependent effector functions

2018 ◽  
Vol 475 (13) ◽  
pp. 2179-2190
Author(s):  
Ingrid J.G. Burvenich ◽  
William Farrugia ◽  
Zhanqi Liu ◽  
Dahna Makris ◽  
Dylan King ◽  
...  
Keyword(s):  
Binding Site ◽  
Conformational Changes ◽  
Solution Structure ◽  
Antibody Engineering ◽  
Target Cells ◽  
Wild Type ◽  
Gamma Receptor ◽  
Complement Dependent Cytotoxicity ◽  
Conformational Plasticity

Antibody engineering is important for many diagnostic and clinical applications of monoclonal antibodies. We recently reported a series of fragment crystallizable (Fc) mutations targeting the neonatal Fc receptor (FcRn) site on a Lewis Y (Ley) binding IgG1, hu3S193. The hu3S193 variants displayed shortened in vivo half-lives and may have potential for radioimaging or radiotherapy of Ley-positive tumors. Here, we report Fc crystal structures of wild-type hu3S193, seven FcRn-binding site variants, and a variant lacking C1q binding or complement-dependent cytotoxicity (CDC) activity. The Fc conformation of the FcRn-binding sites was similar for wild-type and all mutants of hu3S193 Fc, which suggests that FcRn interactions were directly affected by the amino acid substitutions. The C1q-binding site mutant Fc was nearly identical with the wild-type Fc. Surprisingly, several hu3S193 Fc variants showed large changes in global structure compared with wild-type Fc. All hu3S193 Fc mutants had similar antibody-dependent cellular cytotoxicity, despite some with conformations expected to diminish Fc gamma receptor binding. Several hu3S193 variants displayed altered CDC, but there was no correlation with the different Fc conformations. All versions of hu3S193, except the C1q-binding site mutant, bound C1q, suggesting that the altered CDC of some variants could result from different propensities to form IgG hexamers after engaging Ley on target cells. Overall, our findings support the concept that the antibody Fc is both flexible and mobile in solution. Structure-based design approaches should take into account the conformational plasticity of the Fc when engineering antibodies with optimal effector properties.

scholarly journals Glycoprotein D-Independent Infectivity of Pseudorabies Virus Results in an Alteration of In Vivo Host Range and Correlates with Mutations in Glycoproteins B and H

2001 ◽  
Vol 75 (21) ◽  
pp. 10054-10064 ◽  
Author(s):  
Jerg Schmidt ◽  
Volker Gerdts ◽  
Jörg Beyer ◽  
Barbara G. Klupp ◽  
Thomas C. Mettenleiter
Keyword(s):  
Host Range ◽  
Pseudorabies Virus ◽  
Natural Host ◽  
Target Cells ◽  
Glycoprotein D ◽  
Wild Type ◽  
Cellular Receptors ◽  
Receptor Usage

ABSTRACT Infection of cells by herpesviruses is initiated by the interaction of viral envelope glycoproteins with cellular receptors. In the alphaherpesvirus pseudorabies virus (PrV), the causative agent of Aujeszky's disease in pigs, the essential glycoprotein D (gD) mediates secondary attachment of virions to target cells by binding to newly identified cellular receptors (R. J. Geraghty, C. Krummenacher, G. H. Cohen, R. J. Eisenberg, and P. G. Spear, Science 280:1618–1620, 1998). However, in the presence of compensatory mutations, infection can also occur in the absence of gD, as evidenced by the isolation in cell culture of an infectious gD-negative PrV mutant (PrV-gD− Pass) (J. Schmidt, B. G. Klupp, A. Karger, and T. C. Mettenleiter, J. Virol. 71:17–24, 1997). PrV-gD− Pass is replication competent with an only moderate reduction in specific infectivity but appears to bind to receptors different from those recognized by wild-type PrV (A. Karger, J. Schmidt, and T. C. Mettenleiter, J. Virol. 72:7341–7348, 1998). To analyze whether this alteration in receptor usage in vitro influences infection in vivo, the model host mouse and the natural host pig were intranasally infected with PrV-gD− Pass and were compared to animals infected by wild-type PrV. For mice, a comparable progress of disease was observed, and all animals infected with mutant virus died, although they exhibited a slight delay in the onset of symptoms and, correspondingly, a longer time to death. In contrast, whereas wild-type PrV-infected pigs showed clinical signs and histological and histopathological findings typical of PrV infection, no signs of disease were observed after infection with PrV-gD− Pass. Moreover, in these animals, virus-infected cells were not detectable by immunohistochemical staining of different organ samples and no virus could be isolated from nasal swabs. Mutations in glycoproteins B and H were found to correlate with, and probably contribute to, gD-independent infectivity. In conclusion, although PrV-gD− Pass is virulent in mice, it is apparently unable to infect the natural host, the pig. This altered host range in vivo correlates with a difference of receptor usage in vitro and demonstrates for the first time the importance of gD receptors in alphaherpesvirus infection of an animal host.

scholarly journals Pseudorabies Virus Expressing Bovine Herpesvirus 1 Glycoprotein B Exhibits Altered Neurotropism and Increased Neurovirulence

2000 ◽  
Vol 74 (2) ◽  
pp. 817-827 ◽  
Author(s):  
Volker Gerdts ◽  
Jörg Beyer ◽  
Béla Lomniczi ◽  
Thomas C. Mettenleiter
Keyword(s):  
Respiratory Symptoms ◽  
Pseudorabies Virus ◽  
Bovine Herpesvirus ◽  
Glycoprotein B ◽  
Target Cells ◽  
Homologous Gene ◽  
Wild Type ◽  
Bovine Herpesvirus 1 ◽  
Herpesvirus 1

ABSTRACT Herpesvirus glycoproteins play dominant roles in the initiation of infection of target cells in culture and thus may also influence viral tropism in vivo. Whereas the relative contribution of several nonessential glycoproteins to neurovirulence and neurotropism ofPseudorabies virus (PrV), an alphaherpesvirus which causes Aujeszky's disease in pigs, has recently been uncovered in studies using viral deletion mutants, the importance of essential glycoproteins is more difficult to assess. We isolated an infectious PrV mutant, PrV-9112C2, which lacks the gene encoding the essential PrV glycoprotein B (gB) but stably carries in its genome and expresses the homologous gene of bovine herpesvirus 1 (BHV-1) (A. Kopp and T. C. Mettenleiter, J. Virol. 66:2754–2762, 1992). Apart from exhibiting a slight delay in penetration kinetics, PrV-9112C2 was similar in its growth characteristics in cell culture to wild-type PrV. To analyze the effect of the exchange of these homologous glycoproteins in PrV's natural host, swine, 4-week-old piglets were intranasally infected with 106 PFU of either wild-type PrV strain Kaplan (PrV-Ka), PrV-9112C2, or PrV-9112C2R, in which the PrV gB gene was reinserted instead of the BHV-1 gB gene. Animals infected with PrV-Ka and PrV-9112C2R showed a similar course of disease, i.e., high fever, marked respiratory symptoms but minimal neurological disorders, and excretion of high amounts of virus. All animals survived the infection. In contrast, animals infected with PrV-9112C2 showed no respiratory symptoms and developed only mild fever. However, on day 5 after infection, all piglets developed severe central nervous system (CNS) symptoms leading to death within 48 to 72 h. Detailed histological analyses showed that PrV-9112C2R infected all regions of the nasal mucosa and subsequently spread to the CNS preferentially by the trigeminal route. In contrast, PrV-9112C2 primarily infected the olfactory epithelium and spread via the olfactory route. In the CNS, more viral antigen and significantly more pronounced histological changes resulting in more severe encephalitis were found after PrV-9112C2 infection. Thus, our results demonstrate that replacement of PrV gB by the homologous BHV-1 glycoprotein resulted in a dramatic increase in neurovirulence combined with an alteration in the route of neuroinvasion, indicating that the essential gB is involved in determining neurotropism and neurovirulence of PrV.

scholarly journals Estrogen and testosterone in concert with EFNB3 regulate vascular smooth muscle cell contractility and blood pressure

2016 ◽  
Vol 310 (7) ◽  
pp. H861-H872 ◽  
Author(s):  
Yujia Wang ◽  
Zenghui Wu ◽  
Eric Thorin ◽  
Johanne Tremblay ◽  
Julie L. Lavoie ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Gene Knockout ◽  
Target Cells ◽  
Wild Type ◽  
Cell Contractility ◽  
Risk Gene ◽  
Kinase Phosphorylation

EPH kinases and their ligands, ephrins (EFNs), have vital and diverse biological functions, although their function in blood pressure (BP) control has not been studied in detail. In the present study, we report that Efnb3 gene knockout (KO) led to increased BP in female but not male mice. Vascular smooth muscle cells (VSMCs) were target cells for EFNB3 function in BP regulation. The deletion of EFNB3 augmented contractility of VSMCs from female but not male KO mice, compared with their wild-type (WT) counterparts. Estrogen augmented VSMC contractility while testosterone reduced it in the absence of EFNB3, although these sex hormones had no effect on the contractility of VSMCs from WT mice. The effect of estrogen on KO VSMC contractility was via a nongenomic pathway involving GPER, while that of testosterone was likely via a genomic pathway, according to VSMC contractility assays and GPER knockdown assays. The sex hormone-dependent contraction phenotypes in KO VSMCs were reflected in BP in vivo. Ovariectomy rendered female KO mice normotensive. At the molecular level, EFNB3 KO in VSMCs resulted in reduced myosin light chain kinase phosphorylation, an event enhancing sensitivity to Ca2+ flux in VSMCs. Our investigation has revealed previously unknown EFNB3 functions in BP regulation and show that EFNB3 might be a hypertension risk gene in certain individuals.

Conformational changes in the third PDZ domain of the neuronal postsynaptic density protein 95

2019 ◽  
Vol 75 (4) ◽  
pp. 381-391 ◽  
Author(s):  
Ana Camara-Artigas ◽  
Javier Murciano-Calles ◽  
Jose C. Martínez
Keyword(s):  
Binding Site ◽  
Conformational Changes ◽  
Pdz Domain ◽  
Postsynaptic Density ◽  
Crystal Form ◽  
Space Groups ◽  
The Third ◽  
Conformational Plasticity ◽  
Α Helix ◽  
Postsynaptic Density Protein

PDZ domains are protein–protein recognition modules that interact with other proteins through short sequences at the carboxyl terminus. These domains are structurally characterized by a conserved fold composed of six β-strands and two α-helices. The third PDZ domain of the neuronal postsynaptic density protein 95 has an additional α-helix (α3), the role of which is not well known. In previous structures, a succinimide was identified in the β2–β3 loop instead of Asp332. The presence of this modified residue results in conformational changes in α3. In this work, crystallographic structures of the following have been solved: a truncated form of the third PDZ domain of the neuronal postsynaptic density protein 95 from which α3 has been removed, D332P and D332G variants of the protein, and a new crystal form of this domain showing the binding of Asp332 to the carboxylate-binding site of a symmetry-related molecule. Crystals of the wild type and variants were obtained in different space groups, which reflects the conformational plasticity of the domain. Indeed, the overall analysis of these structures suggests that the conformation of the β2–β3 loop is correlated with the fold acquired by α3. The alternate conformation of the β2–β3 loop affects the electrostatics of the carboxylate-binding site and might modulate the binding of different PDZ-binding motifs.

Phase I trial of a human-mouse chimeric anti-disialoganglioside monoclonal antibody ch14.18 in patients with refractory neuroblastoma and osteosarcoma.

1998 ◽  
Vol 16 (6) ◽  
pp. 2169-2180 ◽  
Author(s):  
A L Yu ◽  
M M Uttenreuther-Fischer ◽  
C S Huang ◽  
C C Tsui ◽  
S D Gillies ◽  
...  
Keyword(s):  
Monoclonal Antibody ◽  
Phase I ◽  
Dose Escalation ◽  
Phase I Trial ◽  
Dose Schedule ◽  
Maximum Tolerated Dose ◽  
Target Cells ◽  
Complement Dependent Cytotoxicity ◽  
Clinical Responses

PURPOSE To evaluate the toxicity, immunogenicity, and pharmacokinetics of a human-mouse chimeric monoclonal antibody (mAb) ch 14.18 directed against disialoganglioside (GD2) and to obtain preliminary information on its clinical efficacy, we conducted a phase I trial in 10 patients with refractory neuroblastoma and one patient with osteosarcoma. PATIENTS AND METHODS Eleven patients were entered onto this phase I trial. They received 20 courses of mAb ch 14.18 at dose levels of 10, 20, 50, 100, and 200 mg/m2. Dose escalation was performed in cohorts of three patients; intrapatient dose escalation was also permitted. RESULTS The most prevalent toxicities were pain, tachycardia, hypertension, fever, and urticaria. Most of these toxicities were dose-dependent and rarely noted at dosages of 20 mg/m2 and less. Although the maximum-tolerated dose was not reached in this study, clinical responses were observed. These included one partial (PR) and four mixed responses (MRs) and one stable disease (SD) among 10 assessable patients. Biologic activity of ch 14.18 in vivo was shown by binding of ch 14.18 to tumor cells and complement-dependent cytotoxicity of posttreatment sera against tumor target cells. An anti-ch 14.18 immune response was detectable in seven of 10 patients studied. CONCLUSION In summary, with the dose schedule used, ch 14.18 appears to be clinically safe and effective, and repeated mAb administration was not associated with increased toxicities. Further clinical trials of mAb ch 14.18 in patients with neuroblastoma are warranted.

scholarly journals Marinobufagenin enhances cardiac contractility in mice with ouabain-sensitive α1 Na+-K+-ATPase

2009 ◽  
Vol 296 (6) ◽  
pp. H1833-H1839 ◽  
Author(s):  
Arshani N. Wansapura ◽  
Valerie Lasko ◽  
Zijian Xie ◽  
Olga V. Fedorova ◽  
Alexei Y. Bagrov ◽  
...  
Keyword(s):  
Binding Site ◽  
Functional Role ◽  
Cardiac Contractility ◽  
Cardiac Performance ◽  
Wild Type ◽  
Ouabain Binding ◽  
Atpase Subunit ◽  
Cardiac Inotropy ◽  
Rats And Mice

Endogenous Na+ pump inhibitors are thought to play important (patho)physiological roles and occur in two different chemical forms in the mammalian circulation: cardenolides, such as ouabain, and bufadienolides, such as marinobufagenin (MBG). Although all α Na+-K+-ATPase isoforms (α1-4) are sensitive to ouabain in most species, in rats and mice the ubiquitously expressed α1 Na+-K+-ATPase is resistant to ouabain. We have previously shown that selective modification of the putative ouabain binding site of either the α1 or α2 Na+-K+-ATPase subunit in mice substantially alters the cardiotonic influence of exogenously applied cardenolides. To determine whether the ouabain binding site also interacts with MBG and if this interaction plays a functional role, we evaluated cardiovascular function in α1-resistant/α2-resistant (α1R/Rα2R/R), α1-sensitive/α2-resistant (α1S/Sα2R/R), and α1-resistant/α2-sensitive mice (α1R/Rα2S/S, wild type). Cardiovascular indexes were evaluated in vivo by cardiac catheterization at baseline and during graded infusions of MBG. There were no differences in baseline measurements of targeted mice, indicating normal hemodynamics and cardiac function. MBG at 0.025, 0.05, and 0.1 nmol·min−1·g body wt−1 significantly increased cardiac performance to a greater extent in α1S/Sα2R/R compared with α1R/Rα2R/R and wild-type mice. The increase in LVdP/d tmax in α1S/Sα2R/R mice was greater at higher concentrations of MBG compared with both α1R/Rα2R/R and α1R/Rα2S/S mice ( P < 0.05). These results suggest that MBG interacts with the ouabain binding site of the α1 Na+-K+-ATPase subunit and can thereby influence cardiac inotropy.

A Novel T-Cell Redirecting Anti-CD19-F(ab)2/CD3scFv Bispecific Antibody Exhibits Potent Lymphoma Cytotoxicity.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2762-2762
Author(s):  
Diane L Rossi ◽  
Edmund A Rossi ◽  
Thomas M Cardillo ◽  
David M Goldenberg ◽  
Chien-Hsing Chang
Keyword(s):  
T Cells ◽  
T Cell ◽  
Tumor Cells ◽  
Elimination Rate ◽  
Cell Killing ◽  
Antibody Engineering ◽  
In Vivo Studies ◽  
Target Cells ◽  
Daudi Cells

Abstract Abstract 2762 Background: The use of bispecific antibodies (bsAbs) to redirect effector T cells for the targeted killing of tumor cells is a very active area of antibody engineering. Various formats of such agents made recombinantly have shown considerable promise both pre-clinically and clinically. For example, one design termed Bispecific T-cell engager (BiTE) employs a single polypeptide containing 2 antigen-binding specificities (each contributed by a cognate VH and VL) linked in tandem via a flexible linker, and another design termed DART (Dual-Affinity Re-Targeting) utilizes a disulfide-stabilized diabody. Both BiTE and DART, however, exhibit fast blood clearance due to their small size (∼55 kDa). Herein, we describe, for the first time, the generation of a novel T-cell redirecting bsAb, (19)-3s, comprising an anti-CD3 scFv covalently conjugated to a stabilized anti-CD19 F(ab)2. The potential advantages of (19)-3s include bivalent binding to tumor cells, a larger size (∼130 kDa) to preclude rapid renal clearance, and potent T-cell mediated cytotoxicity. Methods and Results: The Dock-and-Lock (DNL) method was used to generate (19)-3s by combining a stabilized anti-CD19 F(ab)2 with an anti-CD3-scFv, resulting in a homogeneous covalent structure of the designed composition, as shown by SE-HPLC, ELISA, SDS-PAGE, and immunoblot analyses. Functionally, (19)-3s induced synapse formation between effector and target cells using freshly isolated human T cells mixed with Daudi Burkitt lymphoma cells. Using an E:T ratio of 2.5:1 and 1 μg/mL of (19)-3s, the cell mixture was stained with anti-CD20-APC (for Daudi) and anti-CD7-FITC (for T cells), and cobinding was measured by flow cytometry as the % of CD20+/CD7+ events. After treatment with (19)-3s, 45.5% of events were found to be CD20/CD7 dual-positive, indicating synapsed Daudi and T cells, compared with 2% measured for untreated cells. Gating of the Daudi cell population showed that >90% of Daudi cells were associated with T cells. To access the targeted T-cell killing of Daudi, isolated T cells and Daudi were mixed at an E:T ratio of 12.5:1 and treated with serial dilutions of (19)-3s. After 18-h incubation at 37°C, cytotoxicity was measured using a LDH-release assay. Potent (19)-3s-mediated T-cell killing of Daudi cells was observed at <1 pM, with maximal activity at 10 pM. Similar results were seen with both Ramos and Raji NHL cell lines. In vivo studies to determine Pk and efficacy are underway. Based on DNL constructs of similar design, we expect (19)-3s to have an elimination rate longer than that of MT103, a BiTE comprising scFvs derived from anti-CD19 and anti-CD3, thus perhaps avoiding continuous infusions with this new construct. Conclusions: (19)-3s can bind T cells and NHL cells simultaneously and induce T-cell-mediated killing at pM concentrations in an ex vivo setting. The modular nature of the DNL method will allow the rapid production of a large number of related conjugates for redirected T-cell killing of various malignancies, without the need for additional recombinant engineering and protein production. We are currently evaluating the in vivo activity of (19)-3s, as a prototype, to determine if this novel bsAb format offers additional advantages. Disclosures: Rossi: Immunomedics, Inc.: Employment. Rossi:Immunomedics, Inc.: Employment; IBC Pharmaceuticals Inc.: Employment. Cardillo:Immunomedics, Inc: Employment. Goldenberg:Immunomedics: Employment, Equity Ownership. Chang:Immunomedics, Inc.: Employment.

scholarly journals Characterization of the DNA-binding activity of GCR1: in vivo evidence for two GCR1-binding sites in the upstream activating sequence of TPI of Saccharomyces cerevisiae.

1992 ◽  
Vol 12 (6) ◽  
pp. 2690-2700 ◽  
Author(s):  
M A Huie ◽  
E W Scott ◽  
C M Drazinic ◽  
M C Lopez ◽  
I K Hornstra ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Fusion Protein ◽  
Binding Site ◽  
Gene Function ◽  
Binding Sites ◽  
Sequence Motif ◽  
Wild Type ◽  
Upstream Activating Sequence ◽  
Sequence Elements

GCR1 gene function is required for high-level glycolytic gene expression in Saccharomyces cerevisiae. Recently, we suggested that the CTTCC sequence motif found in front of many genes encoding glycolytic enzymes lay at the core of the GCR1-binding site. Here we mapped the DNA-binding domain of GCR1 to the carboxy-terminal 154 amino acids of the polypeptide. DNase I protection studies showed that a hybrid MBP-GCR1 fusion protein protected a region of the upstream activating sequence of TPI (UASTPI), which harbored the CTTCC sequence motif, and suggested that the fusion protein might also interact with a region of the UAS that contained the related sequence CATCC. A series of in vivo G methylation protection experiments of the native TPI promoter were carried out with wild-type and gcr1 deletion mutant strains. The G doublets that correspond to the C doublets in each site were protected in the wild-type strain but not in the gcr1 mutant strain. These data demonstrate that the UAS of TPI contains two GCR1-binding sites which are occupied in vivo. Furthermore, adjacent RAP1/GRF1/TUF- and REB1/GRF2/QBP/Y-binding sites in UASTPI were occupied in the backgrounds of both strains. In addition, DNA band-shift assays were used to show that the MBP-GCR1 fusion protein was able to form nucleoprotein complexes with oligonucleotides that contained CTTCC sequence elements found in front of other glycolytic genes, namely, PGK, ENO1, PYK, and ADH1, all of which are dependent on GCR1 gene function for full expression. However, we were unable to detect specific interactions with CTTCC sequence elements found in front of the translational component genes TEF1, TEF2, and CRY1. Taken together, these experiments have allowed us to propose a consensus GCR1-binding site which is 5'-(T/A)N(T/C)N(G/A)NC(T/A)TCC(T/A)N(T/A)(T/A)(T/G)-3'.

scholarly journals Discordance between Bovine Leukemia Virus Tax Immortalization In Vitro and Oncogenicity In Vivo

2000 ◽  
Vol 74 (21) ◽  
pp. 9895-9902 ◽  
Author(s):  
Jean-Claude Twizere ◽  
Pierre Kerkhofs ◽  
Arsène Burny ◽  
Daniel Portetelle ◽  
Richard Kettmann ◽  
...  
Keyword(s):  
Viral Replication ◽  
Bovine Leukemia Virus ◽  
Leukemia Virus ◽  
Wild Type Virus ◽  
Target Cells ◽  
Phosphorylation Sites ◽  
Primary Cells ◽  
Wild Type

ABSTRACT Bovine leukemia virus (BLV) Tax protein, a transcriptional activator of viral expression, is essential for viral replication in vivo. Tax is believed to be involved in leukemogenesis because of its second function, immortalization of primary cells in vitro. These activities of Tax can be dissociated on the basis of point mutations within specific regions of the protein. For example, mutation of the phosphorylation sites at serines 106 and 293 abrogates immortalization potential in vitro but maintains transcriptional activity. This type of mutant is thus particularly useful for unraveling the role of Tax immortalization activity during leukemogenesis independently of viral replication. In this report, we describe the biological properties of BLV recombinant proviruses mutated in the Tax phosphorylation sites (BLVTax106+293). Titration of the proviral loads by semiquantitative PCR revealed that the BLV mutants propagated at wild-type levels in vivo. Furthermore, two animals (sheep 480 and 296) infected with BLVTax106+293 developed leukemia or lymphosarcoma after 16 and 36 months, respectively. These periods of time are within the normal range of latencies preceding the onset of pathogenesis induced by wild-type viruses. The phenotype of the mutant-infected cells was characteristic of a B lymphocyte (immunoglobulin M positive) expressing CD11b and CD5 (except at the final stage for the latter marker), a pattern that is typical of wild-type virus-infected target cells. Interestingly, the transformed B lymphocytes from sheep 480 also coexpressed the CD8 marker, a phenotype rarely observed in tumor biopsies from chronic lymphocytic leukemia patients. Finally, direct sequencing of the tax gene demonstrated that the leukemic cells did not harbor revertant proviruses. We conclude that viruses expressing a Tax mutant unable to transform primary cells in culture are still pathogenic in the sheep animal model. Our data thus provide a clear example of the discordant conclusions that can be drawn from in vitro immortalization assays and in vivo experiments. These observations could be of interest for other systems, such as the related human T-cell leukemia virus type 1, which currently lack animal models allowing the study of the leukemogenic process.

scholarly journals Functional Analysis of the CAAT Box in the Major Late Promoter of the Subgroup C Human Adenoviruses

1998 ◽  
Vol 72 (4) ◽  
pp. 3213-3220 ◽  
Author(s):  
Byeongwoon Song ◽  
C. S. H. Young
Keyword(s):  
Binding Site ◽  
Transcription Initiation ◽  
Mutational Analysis ◽  
Wild Type ◽  
Late Promoter ◽  
Phenotypic Effect ◽  
Partial Restoration ◽  
Wild Type Phenotype ◽  
Major Late Promoter

ABSTRACT Comparisons among sequences predicted to encode the major late promoter (MLP) of adenoviruses from a wide variety of host species show that an inverted CAAT box is among the most highly conserved transcription elements found in the putative MLPs. The high degree of conservation suggests that the CAAT box plays an important role in the function of the MLP in vivo, an idea supported by a previous mutational analysis of the core CCAAT sequence. To address the importance of the CAAT box, in terms both of quantitative levels of transcription and of specificity, a further set of mutations was created and examined in the context of the viral genome. One mutation, CAAT5, contains individual changes at five positions, four of which correspond to invariant residues in a CAAT box consensus derived either by computer analysis or empirically. The CAAT5 mutation had no discernible phenotype by itself but when coupled with the previously described USF0 mutation, which disrupts binding of the upstream stimulating factor (USF) but is otherwise phenotypically silent, gave rise to virus with a severe replication deficiency. Nuclear run-on assays showed that transcription initiation at the mutant MLP was significantly reduced compared with that of the wild type or the virus containing CAAT5 alone. Replication of the double mutant was lower than that of the previously described USF0::CCCAT virus, suggesting that the additional mutations in the CAAT box had further lowered the binding of transcription factor CP1 (also called CBF, NF-Y). Replacement of the CAAT box by an ATF binding site or an OCT1 binding site had no phenotypic effect in an otherwise wild-type background, but replacement in a USF0::CCCAT background led to only partial restoration of the wild-type phenotype. The failure to restore the functional redundancy normally exhibited by the CAAT box and the proximal upstream activating element is consistent with the idea that in the adenovirus MLP the CAAT box is preferred over others as the distal transcriptional element.

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