Early DNA-binding polypeptides of Epstein-Barr virus

Association of Epstein-Barr virus early antigen diffuse component and virus-specified DNA polymerase activity

The role of Epstein-Barr virus (EBV) early antigen diffuse component (EA-D) and its relationship with EBV DNA polymerase in EBV genome-carrying cells are unclear, EBV-specified DNA polymerase was purified in a sequential manner from Raji cells treated with phorbol-12,13-dibutyrate and n-butyrate by phosphocellulose, DEAE-cellulose, double-stranded DNA-cellulose, and blue Sepharose column chromatography. Four polypeptides with molecular masses of 110,000, 100,000, 55,000, and 49,000 daltons were found to be associated with EBV-specified DNA polymerase activity. A monoclonal antibody which could neutralize the EBV DNA polymerase activity was prepared and found to recognize 55,000- and 49,000-dalton polypeptides. An EA-D monoclonal antibody, R3 (G. R. Pearson, V. Vorman, B. Chase, T. Sculley, M. Hummel, and E. Kieff, J. Virol. 47:183-201, 1983), was also able to recognize these same two polypeptides associated with EBV DNA polymerase activity. It was concluded that EBV EA-D polypeptides, as identified by R3 monoclonal antibody, are critical components of EBV DNA polymerase.

Characterization of the Epstein-Barr virus-induced early polypeptide complex p50/58 EA-D using rabbit antisera, a monoclonal antibody, and human antibodies

A polypeptide complex (p52) belonging to the D-subspecificity of the EBV-induced early antigens (EA-D) was purified from chemically induced P3HR-1 cells. Rabbit antisera raised against the isolated polypeptides reacted with components of EA-D as could be shown by indirect immunofluorescence and immunoperoxidase staining of IdU-induced EA positive Raji cells, ELISA, and immunoblotting. In one-dimensional immunoblots the rabbit antisera detected a predominant polypeptide complex of 52 kDa. Two-dimensional immunoblots prepared with proteins from IdU-induced Raji cells showed that the rabbit sera detect three series of polypeptides of 52 kDa (pl 8.5-6.2), 55-58 kDa (pl 6.2-4.5), and 48-50 kDa (pl 6.0-4.5). These three groups of polypeptides could also be identified by 50 high titered anti-EA-D positive human sera and a specific monoclonal antibody (R3) as being the main components of EA-D in Raji and B95-8 cells. All polypeptides of the p50/58 complex showed DNA binding properties either by themselves or by an interaction with other proteins. When TPA or IdU-induced Raji cells were labeled with 2Pi, two phosphorylated polypeptides pp50 and pp58 could be immunoprecipitated with the rabbit sera and a high anti-EA titered human serum. The time course of the synthesis of polypeptides associated with the EA-D complex was studied by 2-D immunoblots: EA polypeptides of 52 kDa appeared as early as 6 hr after the addition of IdU to Raji cells in culture, polypeptides of 55-58 and 48-50 kDa after 18 and 25 hr, respectively. The coordinated appearance of these groups of polypeptides and their similar size and reactivity with human sera and rabbit antisera produced against the isolated p52 as well as with a monoclonal antibody (R3) suggested that most of these polypeptides are derived from post-translational modifications of one or a few initially synthesized polypeptides, possibly p52. Phosphorylation seems to be at least one possibility of post-translational modification.

Expression of the HSV specified major DNA-binding protein in virus infected RAJI and VERO cells

We studied the expression of the Herpes Simplex virus type-2 (HSV-2) specified major DNA-binding protein (ICSP 11/12) in virus infected RAJI and VERO cells. Immunofluorescence staining by a specific ICSP 11/12 antiserum distinguished between different cell-virus interactions. ICSP 11/12 synthesized in the HSV-2 infected VERO cells showed dense homogenous nuclear staining early in the infection. During virus replication the pattern changed into a less dense, somewhat marginating staining. The corresponding protein synthesized during persistent HSV-2 infection in the RAJI cells showed granular cytoplasmic staining. Late in the infection a whole cell fluorescence was noted. In the absence of virus DNA-synthesis (PFA treated VERO cells) ICSP 11/12 showed dense homogenous or speckled nuclear pattern. The ICSP 11/12 protein extracted from the different virus-cell interactions also showed different elution from double stranded DNA.

HSV infected RAJI-cells specify HSV specific immediate early and/or early DNA-binding proteins

Herpes Simplex Virus specified DNA-binding proteins were purified from virus infected VERO and RAJI cells. The expression of the proteins differed depending on the type of the host cell. Polypeptides corresponding to HSV-1 specific ICP 8 and HSV-2 specific ICSP 11/12 were the major products of HSV-infected VERO cells. In RAJI cells polypeptides with a corresponding molecular weight, together with a cellular protein having almost similar mobility on SDS gels could be detected. Using immuno-blotting technique the HSV origin of these 135K molecular weight proteins synthesized in the HSV-1 and HSV-2-infected RAJI cells could be confirmed.

Expression of the Epstein-Barr virus 138-kDa early protein in Escherichia coli for the use as antigen in diagnostic tests

We have attempted to produce the 138-kDa early protein (ep 138) of Epstein-Barr virus (EBV) in Escherichia coli. This protein was found, by immunoprecipitation, to be a clinically relevant antigen, especially for the determination of the IgA-titer in patients with nasopharyngeal carcinoma (NPC). Since the expression of the entire ep 138 coding region was unsuccessful, we synthesized only the antigenic parts of this protein. Potential antigenic sites were predicted from the amino acid sequence by combining values for hydrophilicity with calculated estimates of the secondary structure. The two predicted fragments were found to be antigenic, but only one of them was stably expressed in E. coli as a non-fusion protein. This stable protein fragment was, in turn, able to stabilize the second antigenic fragment forming an autologous fusion protein, consisting exclusively of EBV-derived sequences. The resulting product reacts particularly well with IgA antibodies of NPC patients indicating its diagnostic value for NPC.

Biochemical characterization of two Epstein-Barr virus early antigen-associated phosphopolypeptides

Epstein-Barr virus (EBV) nonproducer cells NC37 induced to viral early antigen (EA) synthesis by the tumor promotor 12-O-tetradecanoylphorbol-13-acetate (TPA) were labeled at Day 4 after induction with 32P, and were analyzed by immunoprecipitation with human EA-positive sera. By employing this method the appearance of two phosphopolypeptides of 50 and 58K (pp50 and pp58) was well correlated with EA complex. Partial V8 protease digestion and two-dimensional peptide analysis revealed that the polypeptides pp50 and pp58 are related. The analysis of phosphoamino acids indicated that pp58 contains phosphoserine and phosphothreonine to the same percentage, whereas in pp50 only phosphoserine was found. The analysis of the subcellular distribution revealed that pp50 and pp58 are located in the chromatin. Both phosphopolypeptides exhibit DNA-binding activity, and are recognized by two monoclonal antibodies described recently (R3 and 1108-1).

Purification of Epstein-Barr virus DNA polymerase from P3HR-1 cells

The Epstein-Barr virus DNA polymerase was purified from extracts of P3HR-1 cells treated with n-butyrate for induction of the viral cycle. Sequential chromatography on DNA cellulose, phosphocellulose, and blue Sepharose yielded an enzyme preparation purified more than 1,300-fold. The purified enzyme was distinct from cellular enzymes but resembled the viral DNA polymerase in cells infected with herpes simplex virus type 1 or 2. The active enzyme had an apparent molecular weight of 185,000 as estimated by gel filtration on Sephacryl S-300. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a major polypeptide corresponding to a molecular weight of ca. 110,000. This polypeptide correlated with the catalytic function of the purified enzyme, whereas the other, less abundant polypeptides did not. By immunoblotting, the 110,000-molecular-weight polypeptide could be identified as a viral polypeptide. It could not be determined whether the native enzyme was composed of more than one polypeptide.

Qualitative and quantitative analyses of Epstein-Barr virus early antigen diffuse component by western blotting enzyme-linked immunosorbent assay with a monoclonal antibody

We report the use of monoclonal antibody against the early antigen diffuse component (anti-EA-D) of Epstein-Barr virus (EBV) to analyze, both qualitatively and quantitatively, the expression of EA-D in various human lymphoblastoid cell lines activated by chemical inducers. The kinetics of synthesis of EA-D in P3HR-1, B95-8, and Ramos/AW cells were similar in that they all reached the peak of synthesis on day 5 after induction. Surprisingly, no expression of EA-D was found in induced BJAB/GC, an EBV-genome-containing cell line. EBV-negative cell lines, BJAB and Ramos, were negative for EA-D. Raji cells had no detectable EA-D but responded rapidly to induction, reaching a peak on day 3. Superinfection of Raji cells also resulted in marked induction of EA-D, which reached a plateau between 8 to 12 h postinfection. Western blotting coupled with the enzyme-linked immunosorbent assay was employed to identify polypeptides representing EA-D. A family of four polypeptides with molecular weights of 46,000 (46K protein), 49,000, 52,000, and 55,000 were identified to be reactive with monoclonal anti-EA-D antiserum. The pattern of EA-D polypeptides expressed in each cell line was different. Of particular interest was the expression of a large quantity of 46K protein both in induced Raji and P3HR-1 cells, but not in superinfected Raji cells. A 49K doublet was expressed in activated p3HR-1, B95-8, and Ramos/AW cells and in superinfected Raji cells. In addition, two distinct 52K and 55K polypeptides were expressed in induced Ramos/AW and superinfected Raji cells. However, none of these EA-D polypeptides was detectable in BJAB/GC, BJAB, Ramos, and mock-infected Raji cells. To approximate relative concentrations of EA-D in cell extracts, we employed the enzyme-linked immunosorbent assay and immunoblot dot methods by using one of the purified EA-D components to construct a standard curve. Depending upon the cell lines, it was estimated that ca. 1 to 3% (determined by the enzyme-linked immunosorbent assay) and 0.8 to 1.6% (determined by immunoblot dot) of total proteins from maximally induced cells were EA-D. These results suggest that differential expression of EA-D polypeptides could be of importance in the diagnosis of state of EBV infection.

Characterization of a major protein with a molecular weight of 160,000 associated with the viral capsid of Epstein-Barr virus

A monoclonal antibody designated V3 was produced against a late protein associated with the Epstein-Barr virus-induced viral capsid antigen complex. The antibody reacted with discrete patches in the nuclei of infected cells as well as with virus particles, as shown by immunofluorescence and ultrastructural immunoperoxidase staining. The molecular weight of the protein precipitated by this monoclonal antibody was ca. 160,000. All anti-viral capsid antigen antibody-positive sera tested in an enzyme-linked immunosorbent assay reacted with this purified protein. The synthesis of the antigen was inhibited by phosphonoacetic acid but was not affected by tunicamycin, indicating that this was a late nonglycosylated viral protein. No differences were noted between the protein isolated from the P3HR-1 and B-95-8 cell lines as determined by immunoprecipitation and peptide mapping. By isoelectric focusing, this protein had a pI on the basic side ranging from 7.5 to 9.0.

Identification and mapping of polypeptides encoded by the P3HR-1 strain of Epstein-Barr virus

The Epstein-Barr virus (EBV)-specified polypeptides induced upon viral replication in the P3HR-1 cell line have been examined by immunoprecipitation with a high-titer human anti-EBV serum. Twenty-five predominant polypeptides were identified in cell extracts, whereas 18 polypeptides were precipitated from cell-free translation reactions directed by total mRNA. Hybrid selection of mRNA to the BamHI DNA clones of the EBV genome and immunoprecipitation of the corresponding cell-free translation products revealed 98 EBV-specified polypeptides and their coding location along the viral genome. In addition, the viral polypeptides that bind reversibly to DNA-cellulose have been characterized and the deduced map locations of this functional group of EBV-specified polypeptides is presented.

Immunobiochemical characterization with monoclonal antibodies of Epstein-Barr virus-associated early antigens in chemically induced cells

Five monoclonal antibodies which are reactive to early antigens of Epstein-Barr virus have been produced by using somatic cell hybridization techniques. The specificity of the monoclonal antibodies to early antigens was demonstrated by indirect immunofluorescence, which showed that the antigens were localized to the nucleus of early antigen-induced Raji cells. Additional indirect immunofluorescence studies showed that like patient antisera to diffuse-staining early antigen, the monoclonal antibodies gave positive staining reactions after methanol fixation. One of the antibodies, 1150-4, was positive by the anti-complement immunofluorescence technique but differed with Epstein-Barr virus-associated nuclear antigen-positive patient sera in that it only stained induced cells. Different fixation methods were found to alter dramatically the appearance of the nuclear staining reactions produced by the monoclonal antibodies. Immunoprecipitation and immunoblot experiments revealed that monoclonal antibodies 1108-1 and 1129-1 recognized two polypeptides of 55,000 and 50,000 daltons (p55;50), 1173-6 and 1180-2 recognized just p50, and 1150-4 identified a 65,000-dalton nuclear protein. Immunobiochemical characterization of these viral antigens showed that p55 is a phosphoprotein, and p55;50 has strong DNA-binding activity preferentially to single-stranded DNA. Elucidation of the role of these nuclear proteins in Epstein-Barr virus infection and the events associated with Epstein-Barr virus-directed lymphocyte transformation may provide significant information on the pathogenicity of this important human virus.

Identification of polypeptide components of the Epstein-Barr virus early antigen complex with monoclonal antibodies

Three monoclonal antibodies were produced against the Epstein-Barr virus-induced early antigen complex. These antibodies were shown to be specific for the early antigen complex by the fact that they only reacted with cells supporting a permissive or abortive Epstein-Barr virus infection and their synthesis was not affected by inhibitors of viral DNA synthesis. One monoclonal antibody, designated R3, was directed against a diffuse component of the early antigen complex since it reacted by immunofluorescence with cells fixed in acetone or methanol. The other two monoclonal antibodies, designated K8 and K9, reacted with a methanol-sensitive restricted component of this complex. The appearance of the R3 antigen in P3HR-1 superinfected Raji cells occurred approximately 4 h earlier than the antigen detected by K8. By both sodium dodecyl sulfate-polyacrylamide gel electrophoresis and radioimmunoelectrophoresis, it was determined that the R3 monoclonal antibody recognized two major polypeptides with molecular weights of approximately 50,000 to 52,000, whereas K8 and K9 precipitated a protein of approximately 85,000. The R3 monoclonal antibody also immunoprecipitated an in vitro primary translation product. It was, therefore, possible to map this product to the Epstein-Barr virus DNA BamH1 M fragment. These in vitro products were slightly smaller than the in vivo proteins, suggesting that these proteins probably undergo posttranslational modification during the virus replication cycle.

Activation of latent Epstein-Barr virus genomes: selective stimulation of synthesis of chromosomal proteins by a tumor promoter

The tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) is a potent inducer of Epstein-Barr virus (EBV) gene expression. The optimal conditions for maximum activation of latent EBV genomes by TPA were determined. Although TPA is able to induce replication of EBV genomes in P3HR-1 cells in all phases of growth, the greatest increase in viral genome copies per cell (15-fold above the control level) occurred in nonproliferating cells as opposed to cells growing exponentially (6-fold above the control level). The synthesis of chromosomal proteins in nonproliferating cells under the conditions that induce maximum activation of latent virus genomes by TPA was studied. Selective stimulation in chromosomal protein synthesis accompanied the increase in EBV genomes in P3HR-1 cells despite an overall reduction in total cellular protein synthesis. Comparison of the chromosomal proteins from TPA-induced P3HR-1 cells and from superinfected Raji cells revealed comigrating chromosomal polypeptides of 145K, 140K, 135K, 110K, 85K, and 55K that are presumably EBV associated. The selective stimulation of synthesis of these chromosomal proteins in TPA-treated P3HR-1 cells was closely associated with the activation of latent EBV genomes.

Detection and characterization of EBV antigens by micro-ELISA and chromatofocusing

A micro-ELISA technique was developed for the detection of Epstein-Barr virus (EBV)-determined antigens. The enzyme-linked immunosorbent assay (ELISA) was applied with peroxidase-protein A to detect the antigens adsorbed to micro-ELISA plates. Human and rabbit antisera containing antibodies to known EBV components were used as reagents. The early antigen (EA) complex, associated with the viral cycle, was readily detected in extracts of n-butyrate- or n-butyrate + TPA-induced cells. The nuclear antigen, EBNA, could be unequivocally detected only after the partial purification of the antigen by DNA cellulose chromatography. EA (and VCA) could be separated by chromatofocusing of induced cell extracts into several fractions detected by the micro-ELISA technique. This indicates that the purification of individual antigens of the EA complex can be monitored by ELISA.