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Abstract
Phosphorylation is a reversible, enzyme-controlled posttranslational process affecting approximately one-third of all proteins in eukaryotic cells at any given time. Any deviation in the degree and/or site of phosphorylation leads to an abnormal conformation of proteins, resulting in a decline or loss of their function. Knowledge of phosphorylation-related pathways is essential for understanding the understanding of the disease pathogenesis and for the design of new therapeutic strategies. Recent availability of various kinases at an affordable price differs in activity, specificity, and stability and provides the opportunity of studying and modulating this reaction in vitro. We can exploit this knowledge for other applications. There is an enormous potential to produce fully decorated and active recombinant proteins, either for biomedical or cosmetic applications. Closely related is the possibility to exploit current achievements and develop new safe and efficacious vaccines, drugs, and immunomodulators. In this review, we outlined the current enzyme-based possibilities for in vitro phosphorylation of peptides and recombinant proteins and the added value that immobilized kinases provide.
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Donnarumma D, Faleri A, Costantino P, Rappuoli R, Norais N. The role of structural proteomics in vaccine development: recent advances and future prospects. Expert Rev Proteomics 2016; 13:55-68. [PMID: 26714563 DOI: 10.1586/14789450.2016.1121113] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Vaccines are the most effective way to fight infectious diseases saving countless lives since their introduction. Their evolution during the last century made use of the best technologies available to continuously increase their efficacy and safety. Mass spectrometry (MS) and proteomics are already playing a central role in the identification and characterization of novel antigens. Over the last years, we have been witnessing the emergence of structural proteomics in vaccinology, as a major tool for vaccine candidate discovery, antigen design and life cycle management of existing products. In this review, we describe the MS techniques associated to structural proteomics and we illustrate the contribution of structural proteomics to vaccinology discussing potential applications.
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Manghera A, McLean GR. Human cytomegalovirus vaccination: progress and perspectives of recombinant gB. Future Virol 2016. [DOI: 10.2217/fvl-2016-0039] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
A vaccine for Human cytomegalovirus (HCMV) remains a high priority as complications following infection are observed in immunocompromised individuals and in congenitally infected neonates. Numerous preclinical and clinical studies have investigated vaccine strategies ranging from live attenuated preparations, nucleic acid-based approaches and recombinant delivery systems to subunit vaccines. These have defined the importance of both cell-mediated and humoral immunity to viral gB in the control of HCMV infection. This review will cover clinical trials investigating vaccine approaches that have incorporated gB and discuss the future perspectives of the recombinant gB subunit vaccine for HCMV.
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Affiliation(s)
- Avneet Manghera
- National Heart & Lung Institute, Imperial College London, London, UK
| | - Gary R McLean
- National Heart & Lung Institute, Imperial College London, London, UK
- Cellular & Molecular Immunology Research Centre, London Metropolitan University, London, UK
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Lilja AE, Mason PW. The next generation recombinant human cytomegalovirus vaccine candidates—Beyond gB. Vaccine 2012; 30:6980-90. [DOI: 10.1016/j.vaccine.2012.09.056] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Revised: 09/07/2012] [Accepted: 09/22/2012] [Indexed: 11/16/2022]
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Spaderna S, Kropff B, Ködel Y, Shen S, Coley S, Lu S, Britt W, Mach M. Deletion of gpUL132, a structural component of human cytomegalovirus, results in impaired virus replication in fibroblasts. J Virol 2005; 79:11837-47. [PMID: 16140760 PMCID: PMC1212622 DOI: 10.1128/jvi.79.18.11837-11847.2005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The coding capacity of human cytomegalovirus (HCMV) for glycoproteins by far exceeds that of other herpesviruses. Few of these proteins have been characterized so far. We have investigated the gene product of reading frame UL132. The putative protein product of UL132 is a glycoprotein with a theoretical mass of 29.8 kDa. Transcription analysis revealed that the gene is transcribed with a true late kinetics from the laboratory-adapted strain AD169 and the low-passage isolate TB40E. Two proteins of 22 to 28 kDa and 45 to 60 kDa were detected in virus-infected cells as well as in extracellular virions. The larger protein carried N-linked carbohydrates. Both protein forms were present in laboratory-adapted strains as well as in low-passage isolates of HCMV. Recombinant viruses with the UL132 gene deleted were constructed in the low-passage HCMV isolate PAN as well as the high-passage isolate AD169. Deletion of UL132 from either genome resulted in a pronounced replication deficit with a reduction of approximately 100-fold for HCMV strain AD169. Thus, the protein product of the UL132 reading frame represents a structural viral glycoprotein of HCMV that has an important function for viral replication in tissue culture.
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Affiliation(s)
- Simone Spaderna
- Institut für Klinische und Molekulare Virologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Schlossgarten 4, 91054 Erlangen, Germany
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Scott GK, Gu F, Crump CM, Thomas L, Wan L, Xiang Y, Thomas G. The phosphorylation state of an autoregulatory domain controls PACS-1-directed protein traffic. EMBO J 2004; 22:6234-44. [PMID: 14633983 PMCID: PMC291837 DOI: 10.1093/emboj/cdg596] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
PACS-1 is a cytosolic sorting protein that directs the localization of membrane proteins in the trans-Golgi network (TGN)/endosomal system. PACS-1 connects the clathrin adaptor AP-1 to acidic cluster sorting motifs contained in the cytoplasmic domain of cargo proteins such as furin, the cation-independent mannose-6-phosphate receptor and in viral proteins such as human immunodeficiency virus type 1 Nef. Here we show that an acidic cluster on PACS-1, which is highly similar to acidic cluster sorting motifs on cargo molecules, acts as an autoregulatory domain that controls PACS-1-directed sorting. Biochemical studies show that Ser278 adjacent to the acidic cluster is phosphorylated by CK2 and dephosphorylated by PP2A. Phosphorylation of Ser278 by CK2 or a Ser278-->Asp mutation increased the interaction between PACS-1 and cargo, whereas a Ser278-->Ala substitution decreased this interaction. Moreover, the Ser278-->Ala mutation yields a dominant-negative PACS-1 molecule that selectively blocks retrieval of PACS-1-regulated cargo molecules to the TGN. These results suggest that coordinated signaling events regulate transport within the TGN/endosomal system through the phosphorylation state of both cargo and the sorting machinery.
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Affiliation(s)
- Gregory K Scott
- Vollum Institute, L-474, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA
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Crump CM, Hung CH, Thomas L, Wan L, Thomas G. Role of PACS-1 in trafficking of human cytomegalovirus glycoprotein B and virus production. J Virol 2003; 77:11105-13. [PMID: 14512558 PMCID: PMC224974 DOI: 10.1128/jvi.77.20.11105-11113.2003] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2003] [Accepted: 07/18/2003] [Indexed: 12/19/2022] Open
Abstract
The final envelopment of herpesviruses during assembly of new virions is thought to occur by the budding of core viral particles into a late secretory pathway organelle, the trans-Golgi network (TGN), or an associated endosomal compartment. Several herpesvirus envelope glycoproteins have been previously shown to localize to the TGN when expressed independently from other viral proteins. In at least some cases this TGN localization has been shown to be dependent on clusters of acidic residues within their cytoplasmic domains. Similar acidic cluster motifs are found in endogenous membrane proteins that also localize to the TGN. These acidic cluster motifs interact with PACS-1, a connector protein that is required for the trafficking of proteins containing such motifs from endosomes to the TGN. We show here that PACS-1 interacts with the cytoplasmic domain of the HCMV envelope glycoprotein B (gB) and that PACS-1 function is required for normal TGN localization of HCMV gB. Furthermore, inhibition of PACS-1 activity in infected cells leads to a decrease in HCMV titer, whereas an increase in expression of functional PACS-1 leads to an increase in HCMV titer, suggesting that PACS-1 is required for efficient production of HCMV.
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Affiliation(s)
- Colin M Crump
- Vollum Institute, Oregon Health and Science University, Portland, Oregon 97239, USA
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Halary F, Amara A, Lortat-Jacob H, Messerle M, Delaunay T, Houlès C, Fieschi F, Arenzana-Seisdedos F, Moreau JF, Déchanet-Merville J. Human cytomegalovirus binding to DC-SIGN is required for dendritic cell infection and target cell trans-infection. Immunity 2002; 17:653-64. [PMID: 12433371 DOI: 10.1016/s1074-7613(02)00447-8] [Citation(s) in RCA: 283] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Cytomegalovirus (CMV) infection is characterized by host immunosuppression and multiorganic involvement. CMV-infected dendritic cells (DC) were recently shown to display reduced immune functions, but their role in virus dissemination is not clear. In this report, we demonstrated that CMV could be captured by DC through binding on DC-SIGN and subsequently transmitted to permissive cells. Moreover, blocking DC-SIGN by specific antibodies inhibited DC infection by primary CMV isolates and expression of DC-SIGN or its homolog DC-SIGNR rendered susceptible cells permissive to CMV infection. We demonstrated that CMV envelope glycoprotein B is a viral ligand for DC-SIGN and DC-SIGNR. These results provide new insights into the molecular interactions contributing to cell infection by CMV and extend DC-SIGN implication in virus propagation.
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Affiliation(s)
- Franck Halary
- Laboratoire d'immunologie, CNRS UMR 5540, Université Bordeaux 2, France
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Mitchell DK, Holmes SJ, Burke RL, Duliege AM, Adler SP. Immunogenicity of a recombinant human cytomegalovirus gB vaccine in seronegative toddlers. Pediatr Infect Dis J 2002; 21:133-8. [PMID: 11840080 DOI: 10.1097/00006454-200202000-00009] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
BACKGROUND Immunization of young children against cytomegalovirus (CMV) might decrease child-to-child and child-to-adult transmission of CMV and thereby reduce maternal infection during pregnancy. We conducted a Phase I trial in CMV-seronegative toddlers to evaluate the reactogenicity and immunogenicity of a CMV gB vaccine administered with MF59, an oil and water adjuvant. METHODS Eighteen children between 12 and 35 months of age received either 20 microg of CMV gB/MF59 (n = 15) or a control hepatitis A vaccine (n = 3) at 0, 1 and 6 months. The study was open-label for the first six children and then observer-blinded and randomized. Children were monitored for local and systemic reactions and for the development of antibodies to the envelope protein gB and CMV-neutralizing antibodies. RESULTS Adverse reactions were uncommon and mild. Two children were excluded from the immunogenicity analysis because they had serologic evidence of CMV infection. Reciprocal geometric mean neutralizing titers were: 0 preimmunization (n = 18); 90 (range, 53 to 188) after Dose 2 (n = 6); and 638 (range, 210 to 1645) 1 month after Dose 3 (n = 13). The reciprocal geometric mean neutralizing titers of antibody to gB by EIA were: 0 preimmunization (n = 18); 857 (range, 307 to 2073) after Dose 1 (n = 12); 27 457 (range, 9312 to 55,080) after Dose 2 (n = 6); and 98,264 (range, 35,480 to 228,780) 1 month after Dose 3 (n = 5). After Dose 3 antibody responses of toddlers were greater than those of naturally infected adults and were notably higher than among 149 adults given 3 doses of the same vaccine in other trials. CONCLUSION The CMV gB vaccine is well-tolerated and highly immunogenic in toddlers.
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Affiliation(s)
- Douglas K Mitchell
- Center for Pediatric Research, Children's Hospital of The King's Daughters, Eastern Virginia Medical School, Norfolk, VA, USA
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Marshall BC, McPherson RA, Greidinger E, Hoffman R, Adler SP. Lack of autoantibody production associated with cytomegalovirus infection. ARTHRITIS RESEARCH 2002; 4:R6. [PMID: 12223109 PMCID: PMC125300 DOI: 10.1186/ar429] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 03/21/2002] [Revised: 05/02/2002] [Accepted: 05/20/2002] [Indexed: 11/10/2022]
Abstract
To confirm an association between cytomegalovirus (CMV) infection and the presence of antibodies to Smith (Sm), to ribonucleoprotein (RNP), and to a component of the U1 ribonucleoproteins (U1-70 kD), we measured antibodies to these protein antigens using an enzyme immunoassay and an immunoblot. The antibodies were measured in the sera of 80 healthy subjects, one-half of whom were naturally CMV seropositive and one-half were CMV seronegative, and in eight subjects immunized with a live attenuated strain of CMV. None of the vaccinees developed antibodies to Sm, to RNP, or to U1-70 kD at either 4 or 12 months after immunization. Additionally, there was no statistically significant association between levels of antibodies to Sm or to RNP and between sera obtained from vaccinees, natural CMV seropositive individuals, and CMV seronegative individuals. One CMV seropositive serum and one CMV seronegative serum tested positive for antibodies to U1-70 kD. These data indicate that neither wild-type infection nor the live-attenuated Towne vaccine frequently induce autoantibody production.
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Affiliation(s)
- Beth C Marshall
- Department of Pediatrics, Virginia Commonwealth University/Medical College of Virginia, Richmond, Virginia, USA
| | - Richard A McPherson
- Department of Pathology, Virginia Commonwealth University/Medical College of Virginia, Richmond, Virginia, USA
| | - Eric Greidinger
- Department of Internal Medicine, University of Missouri, Columbia, Missouri, USA
| | - Robert Hoffman
- Department of Internal Medicine, University of Missouri, Columbia, Missouri, USA
| | - Stuart P Adler
- Department of Pediatrics, Virginia Commonwealth University/Medical College of Virginia, Richmond, Virginia, USA
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Marshall GS, Li M, Stout GG, Louthan MV, Duliège AM, Burke RL, Hunt LA. Antibodies to the major linear neutralizing domains of cytomegalovirus glycoprotein B among natural seropositives and CMV subunit vaccine recipients. Viral Immunol 2001; 13:329-41. [PMID: 11016597 DOI: 10.1089/08828240050144653] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The gB protein (gpUL55) of human cytomegalovirus (CMV) contains C-terminal (AD-1) and N-terminal (AD-2) linear immunodominant neutralizing domains. To measure antibodies to these epitopes, a modified protein (delta-gB) lacking heavily glycosylated intervening regions, the transmembrane domain, and the cytoplasmic domain, was expressed in recombinant baculovirus-infected cells. Eighty-six percent of 600 naturally CMV-seropositive individuals and 93% of 121 gB vaccine recipients had antibodies to delta-gB as detected by enzyme-linked immunosorbent assay (ELISA). The antibody level in vaccinees (median optical density [OD] = 1.73) exceeded that in natural seropositives (median OD = 0.94; p < .0001). Eleven percent of 95 natural seropositives and 7% of 120 gB vaccinees lacked A-gB antibodies but had neutralizing activity. Among subjects with delta-gB antibody, there were weak correlations between antibody level and neutralizing titer. These data suggest that antibodies to linear neutralizing gB domains are highly prevalent in naturally-infected individuals and regularly develop in gB vaccinees. However, for some individuals, discontinuous and/or linear epitopes not represented on delta-gB may be more important in the generation of neutralizing responses.
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Affiliation(s)
- G S Marshall
- Department of Pediatrics, University of Louisville School of Medicine, Kentucky 40202, USA.
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Plafker SM, Woods AS, Gibson W. Phosphorylation of simian cytomegalovirus assembly protein precursor (pAPNG.5) and proteinase precursor (pAPNG1): multiple attachment sites identified, including two adjacent serines in a casein kinase II consensus sequence. J Virol 1999; 73:9053-62. [PMID: 10516011 PMCID: PMC112937 DOI: 10.1128/jvi.73.11.9053-9062.1999] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The assembly protein precursor (pAP) of cytomegalovirus (CMV), and its homologs in other herpesviruses, functions at several key steps during the process of capsid formation. This protein, and the genetically related maturational proteinase, is distinguished from the other capsid proteins by posttranslational modifications, including phosphorylation. The objective of this study was to identify sites at which pAP is phosphorylated so that the functional significance of this modification and the enzyme(s) responsible for it can be determined. In the work reported here, we used peptide mapping, mass spectrometry, and site-directed mutagenesis to identify two sets of pAP phosphorylation sites. One is a casein kinase II (CKII) consensus sequence that contains two adjacent serines, both of which are phosphorylated. The other site(s) is in a different domain of the protein, is phosphorylated less frequently than the CKII site, does not require preceding CKII-site phosphorylation, and causes an electrophoretic mobility shift when phosphorylated. Transfection/expression assays for proteolytic activity showed no gross effect of CKII-site phosphorylation on the enzymatic activity of the proteinase or on the substrate behavior of pAP. Evidence is presented that both the CKII sites and the secondary sites are phosphorylated in virus-infected cells and plasmid-transfected cells, indicating that these modifications can be made by a cellular enzyme(s). Apparent compartmental differences in phosphorylation of the CKII-site (cytoplasmic) and secondary-site (nuclear) serines suggest the involvement of more that one enzyme in these modifications.
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Affiliation(s)
- S M Plafker
- Virology Laboratories, Department of Pharmacology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Tugizov S, Maidji E, Xiao J, Pereira L. An acidic cluster in the cytosolic domain of human cytomegalovirus glycoprotein B is a signal for endocytosis from the plasma membrane. J Virol 1999; 73:8677-88. [PMID: 10482621 PMCID: PMC112888 DOI: 10.1128/jvi.73.10.8677-8688.1999] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We previously reported that human cytomegalovirus (CMV) glycoprotein B (gB) is transported to apical membranes in CMV-infected polarized retinal pigment epithelial (ARPE-19) cells and in Madin-Darby canine kidney (MDCK) epithelial cells constitutively expressing gB. The cytosolic domain of gB contains a cluster of acidic amino acids, a motif that plays a pivotal role in vectorial trafficking in polarized epithelial cells and may also function as a signal for entry into the endocytic pathway. Here we compared gB internalization and recycling to the plasma membrane in CMV-infected human fibroblasts (HF) and ARPE-19 cells by using antibody-internalization experiments. Immunofluorescence and quantitative assays showed that gB was internalized from the cell surface into clathrin-coated transport vesicles and then recycled to the plasma membrane. gB colocalized with clathrin-coated vesicles containing the transferrin receptor in the early endocytic/recycling pathway, indicating that gB traffics in this pathway. The specific role of the acidic cluster in regulating the sorting of gB-containing vesicles in the early endocytic/recycling pathway was examined in MDCK cells expressing mutated gB derivatives. Immunofluorescence assays showed that derivatives lacking the acidic cluster were impaired in internalization and failed to recycle. These findings, together with our earlier observation that the acidic cluster is a key determinant for targeting gB molecules to apical membranes in epithelial cells, establish that this signal is recognized by cellular proteins that participate in polarized sorting and transport in the early endocytic/recycling pathway.
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Affiliation(s)
- S Tugizov
- Department of Stomatology, School of Dentistry, University of California San Francisco, San Francisco, California 94143-0512, USA
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Tackaberry ES, Dudani AK, Prior F, Tocchi M, Sardana R, Altosaar I, Ganz PR. Development of biopharmaceuticals in plant expression systems: cloning, expression and immunological reactivity of human cytomegalovirus glycoprotein B (UL55) in seeds of transgenic tobacco. Vaccine 1999; 17:3020-9. [PMID: 10462237 DOI: 10.1016/s0264-410x(99)00150-4] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Plant seeds offer unique opportunities for the production and delivery of oral subunit vaccines. We have used the immunodominant glycoprotein B complex of human cytomegalovirus (HCMV), introduced into tobacco plants, as a model system for studying the merit of this promising approach. Given the advantages of expressing proteins in seeds, a novel expression vector was developed incorporating regulatory sequences of glutelin, the major rice seed storage protein, to direct synthesis of recombinant glycoprotein B. Analysis of genomic DNA of 28 selected tobacco transformants by PCR amplification showed that 71% harboured the gB cDNA, a finding further documented by Southern blotting. Specific immunoassays of protein extracts from seeds of positive plants showed that all were producing antigenic glycoprotein B at levels ranging from 70-146 ng/mg extracted protein. In addition, similarity with native glycoprotein B produced in HCMV-infected cells was also demonstrated by inhibition of immunofluorescence on HCMV-infected human fibroblasts. These data are the first to report the expression of an immunodominant antigen of HCMV in plant tissues, indicating the fidelity with which this very large heterologous viral glycoprotein can be synthesized in this model system.
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Affiliation(s)
- E S Tackaberry
- Bureau of Biologics and Radiopharmaceuticals, Therapeutic Products Programme, Health Canada, Ottawa, Ont.
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Huber MT, Compton T. Intracellular formation and processing of the heterotrimeric gH-gL-gO (gCIII) glycoprotein envelope complex of human cytomegalovirus. J Virol 1999; 73:3886-92. [PMID: 10196283 PMCID: PMC104166 DOI: 10.1128/jvi.73.5.3886-3892.1999] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human cytomegalovirus (HCMV) gCIII complex contains glycoprotein H (gH; gpUL75), glycoprotein L (gL; gpUL115), and glycoprotein O (gO; gpUL74). To examine how gH, gL, and gO interact within HCMV-infected cells to assemble the tripartite complex, pulse-chase experiments were performed. These analyses demonstrated that gH and gL associate by the end of the pulse period to form a disulfide dependent gH-gL complex. Subsequently, the gH-gL complex interacts with a 100-kDa precursor form of gO to form a 220-kDa precursor of the mature gH-gL-gO complex that contains a 125-kDa form of gO. The 220-kDa precursor complex (pgCIII) was sensitive to treatment with endoglycosidase H (endo H), while the mature gCIII complex was essentially resistant to digestion with this enzyme, suggesting that formation of pgCIII complex occurs in the endoplasmic reticulum (ER) and is processed to mature gH-gL-gO (gCIII) in a post-ER compartment. While the N-linked glycans on the 100-kDa form of gO were modified to endo H-resistant states as the 125-kDa gO formed, additional posttranslational modifications were detected on gO. These processing alterations were non-N-linked oligosaccharide modifications that could not be accounted for by phosphorylation or by O-glycosylation of the type sensitive to O-glycanase. Of gH, gL, gO, and the various complexes that they form, only the mature form of the complex was detectable at the infected cell membrane, as judged by surface biotinylation studies.
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Affiliation(s)
- M T Huber
- Program in Cellular and Molecular Biology and Department of Medical Microbiology and Immunology, University of Wisconsin, Madison, Wisconsin 53706, USA
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Molloy SS, Thomas L, Kamibayashi C, Mumby MC, Thomas G. Regulation of endosome sorting by a specific PP2A isoform. J Cell Biol 1998; 142:1399-411. [PMID: 9744873 PMCID: PMC1424221 DOI: 10.1083/jcb.142.6.1399] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
The regulated sorting of proteins within the trans-Golgi network (TGN)/endosomal system is a key determinant of their biological activity in vivo. For example, the endoprotease furin activates of a wide range of proproteins in multiple compartments within the TGN/endosomal system. Phosphorylation of its cytosolic domain by casein kinase II (CKII) promotes the localization of furin to the TGN and early endosomes whereas dephosphorylation is required for efficient transport between these compartments (Jones, B.G., L. Thomas, S.S. Molloy, C.D. Thulin, M.D. Fry, K.A. Walsh, and G. Thomas. 1995. EMBO [Eur. Mol. Biol. Organ.] J. 14:5869-5883). Here we show that phosphorylated furin molecules internalized from the cell surface are retained in a local cycling loop between early endosomes and the plasma membrane. This cycling loop requires the phosphorylation state-dependent furin-sorting protein PACS-1, and mirrors the trafficking pathway described recently for the TGN localization of furin (Wan, L., S.S. Molloy, L. Thomas, G. Liu, Y. Xiang, S.L. Ryback, and G. Thomas. 1998. Cell. 94:205-216). We also demonstrate a novel role for protein phosphatase 2A (PP2A) in regulating protein localization in the TGN/endosomal system. Using baculovirus recombinants expressing individual PP2A subunits, we show that the dephosphorylation of furin in vitro requires heterotrimeric phosphatase containing B family regulatory subunits. The importance of this PP2A isoform in directing the routing of furin from early endosomes to the TGN was established using SV-40 small t antigen as a diagnostic tool in vivo. The role of both CKII and PP2A in controlling multiple sorting steps in the TGN/endosomal system indicates that the distribution of itinerant membrane proteins may be acutely regulated via signal transduction pathways.
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Affiliation(s)
- S S Molloy
- Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201, USA
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Tugizov S, Maidji E, Xiao J, Zheng Z, Pereira L. Human cytomegalovirus glycoprotein B contains autonomous determinants for vectorial targeting to apical membranes of polarized epithelial cells. J Virol 1998; 72:7374-86. [PMID: 9696834 PMCID: PMC109962 DOI: 10.1128/jvi.72.9.7374-7386.1998] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
We previously reported that human cytomegalovirus (CMV) glycoprotein B (gB) is vectorially transported to apical membranes of CMV-infected polarized human retinal pigment epithelial cells propagated on permeable filter supports and that virions egress predominantly from the apical membrane domain. In the present study, we investigated whether gB itself contains autonomous information for apical transport by expressing the molecule in stably transfected Madine-Darby canine kidney (MDCK) cells grown on permeable filter supports. Laser scanning confocal immunofluorescence microscopy and domain-selective biotinylation of surface membrane domains showed that CMV gB was transported to apical membranes independently of other envelope glycoproteins and that it colocalized with proteins in transport vesicles of the biosynthetic and endocytic pathways. Determinants for trafficking to apical membranes were located by evaluating the targeting of gB derivatives with deletions in the lumen, transmembrane (TM) anchor, and carboxyl terminus. Derivative gB(Delta717-747), with an internal deletion in the luminal juxtamembrane sequence that preserved the N- and O-glycosylation sites, retained vectorial transport to apical membranes. In contrast, derivatives that lacked the TM anchor and cytosolic domain (gBDelta646-906) or the TM anchor alone (gBDelta751-771) underwent considerable basolateral targeting. Likewise, derivatives lacking the entire cytosolic domain (gBDelta772-906) or the last 73 amino acids (gBDelta834-906) showed disrupted apical transport. Site-specific mutations that deleted or altered the cluster of acidic residues with a casein kinase II phosphorylation site at the extreme carboxyl terminus, which can serve as an internalization signal, caused partial missorting of gB to basolateral membranes. Our studies indicate that CMV gB contains autonomous information for apical targeting in luminal, TM anchor, and cytosolic domain sequences, forming distinct structural elements that cooperate in vectorial transport in polarized epithelial cells.
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Affiliation(s)
- S Tugizov
- Department of Stomatology, School of Dentistry, University of California-San Francisco, San Francisco, California 94143-0512, USA
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18
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Fish KN, Soderberg-Naucler C, Nelson JA. Steady-state plasma membrane expression of human cytomegalovirus gB is determined by the phosphorylation state of Ser900. J Virol 1998; 72:6657-64. [PMID: 9658112 PMCID: PMC109858 DOI: 10.1128/jvi.72.8.6657-6664.1998] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/1998] [Accepted: 04/23/1998] [Indexed: 02/08/2023] Open
Abstract
Human cytomegalovirus (HCMV) infection of an astrocytoma cell line (U373) or human fibroblast (HF) cells results in a differential cell distribution of the major envelope glycoprotein gB (UL55). This 906-amino-acid type I glycoprotein contains an extracellular domain with a signal sequence, a transmembrane domain, and a 135-amino-acid cytoplasmic tail with a consensus casein kinase II (CKII) site located at Ser900. Since phosphorylation of proteins in the secretory pathway is an important determinant of intracellular trafficking, the state of gB phosphorylation in U373 and HF cells was examined. Analysis of cells expressing wild-type gB and gB with site-specific mutations indicated that the glycoprotein was equally phosphorylated at a single site, Ser900, in both U373 and HF cells. To assess the effect of charge on gB surface expression in U373 cells, Ser900 was replaced with an aspartate (Asp) or alanine (Ala) residue to mimic the phosphorylated and nonphosphorylated states, respectively. Expression of the Asp but not the Ala gB mutation resulted in an increase in the steady-state expression of gB at the plasma membrane (PM) in U373 cells. In addition, treatment of U373 cells with the phosphatase inhibitor tautomycin resulted in the accumulation of gB at the PM. Interestingly, the addition of a charge at Ser900 trapped gB in a low-level cycling pathway at the PM, preventing trafficking of the protein to the trans-Golgi network or other intracellular compartments. Therefore, these results suggest that a tautomycin-sensitive phosphatase regulates cell-specific PM retrieval of gB to intracellular compartments.
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Affiliation(s)
- K N Fish
- Department of Molecular Microbiology and Immunology, Oregon Health Sciences University, Portland, Oregon 97201, USA
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19
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Wan L, Molloy SS, Thomas L, Liu G, Xiang Y, Rybak SL, Thomas G. PACS-1 defines a novel gene family of cytosolic sorting proteins required for trans-Golgi network localization. Cell 1998; 94:205-16. [PMID: 9695949 DOI: 10.1016/s0092-8674(00)81420-8] [Citation(s) in RCA: 301] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We report the role of one member of a novel gene family, PACS-1, in the localization of trans-Golgi network (TGN) membrane proteins. PACS-1 directs the TGN localization of furin by binding to the protease's phosphorylated cytosolic domain. Antisense studies show TGN localization of furin and mannose-6-phosphate receptor, but not TGN46, is strictly dependent on PACS-1. Analyses in vitro and in vivo show PACS-1 has properties of a coat protein and connects furin to components of the clathrin-sorting machinery. Cell-free assays indicate TGN localization of furin is directed by a PACS-1-mediated retrieval step. Together, these findings explain a mechanism by which membrane proteins in mammalian cells are localized to the TGN.
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Affiliation(s)
- L Wan
- Vollum Institute, The Oregon Health Sciences University, Portland 97201, USA
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20
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Pinna LA, Meggio F. Protein kinase CK2 ("casein kinase-2") and its implication in cell division and proliferation. PROGRESS IN CELL CYCLE RESEARCH 1998; 3:77-97. [PMID: 9552408 DOI: 10.1007/978-1-4615-5371-7_7] [Citation(s) in RCA: 242] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Protein kinase CK2 (also termed casein kinase-2 or -II) is a ubiquitous Ser/Thr-specific protein kinase required for viability and for cell cycle progression. CK2 is especially elevated in proliferating tissues, either normal or transformed, and the expression of its catalytic subunit in transgenic mice is causative of lymphomas. CK2 is highly pleiotropic: more than 160 proteins phosphorylated by it at sites specified by multiple acidic residues are known. Despite its heterotetrameric structure generally composed by two catalytic (alpha and/or alpha') and two non catalytic beta-subunits, the regulation of CK2 is still enigmatic. A number of functional features of the beta-subunit which could cooperate to the modulation of CK2 targeting/activity will be discussed.
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Affiliation(s)
- L A Pinna
- Dipartimento di Chimica Biologica, Università di Padova, Italy
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