Purification and biochemical characterization of the Epstein-Barr virus-determined nuclear antigen and an associated protein with a 53,000-dalton subunit

TP53 gene mutations in Hodgkin lymphoma are infrequent and not associated with absence of Epstein-Barr virus

Reed-Sternberg (RS) cells, the neoplastic cells of Hodgkin lymphoma (HL) have clonal immunoglobulin gene rearrangements. The presence of somatic mutations suggests a germinal center origin, whereas the presence of crippling mutations suggests rescue of RS precursors from apoptosis by a transforming event. Epstein-Barr virus (EBV), which can be detected in 30-50% of HL cases, probably plays a role in this transforming event. The frequent presence of p53 protein expression in RS cells also suggests a role of the TP53 gene in this escape from apoptosis. Although mutations of the TP53 gene occur infrequently in RS cells, it has been suggested that in EBV-negative cases this gene mutation may be fundamental for the inhibition of apoptosis. In this study, we tested the hypothesis that there is an inverse correlation between the presence of TP53 gene mutations and the presence of EBV. In 21 of 67 cases EBV encoded small RNA (EBER)1-2 mRNAs were detected. Immunostaining for p53 protein revealed positivity in all 67 cases with variable percentages of positive cells and staining intensity. Screening for mutations in exons 5, 6, 7 and 8 of the TP53 gene in single RS cells obtained by laser microdissection from 26 HL specimens and 4 HL-derived cell lines revealed mutations in 2 of 15 EBV-positive cases and in 1 of 11 EBV-negative cases. Our results confirm the presence of infrequent (11.5%) TP53 gene mutations in HL and suggest that mutations of the TP53 gene are not correlated to the absence of EBV.

p53 protein expression in non-Hodgkin's lymphomas is infrequently related to p53 gene mutations

Accumulation of the p53 protein has been found in several types of lymphomas. However, p53 gene mutations have been infrequently demonstrated in some specific types of lymphomas. In the present study, a correlation between p53 immunoreactivity and p53 gene mutations in a large panel of non-Hodgkin's lymphoma (NHL) cases is attempted. A panel of 202 cases of NHL was evaluated by immunohistochemical staining for p53 protein. All cases that were immunohistochemically positive for p53 protein were analyzed by the polymerase chain reaction (PCR) single strand conformation polymorphism (SSCP) method to identify mutations within the p53 gene. In order to confirm the mutation, sequencing of PCR-amplified p53 gene segments was performed. Overexpression of p53 protein was found in 59 of the 202 cases of NHL, but only four of these 59 cases showed a shift on SSCP analysis, and point mutations were detected in three of them by the subsequent sequencing. p53 immunoreactivity was generally greater in high-grade lymphoma. The results of this study suggest that immunohistochemical reactivity for p53 protein is not a reliable indicator of the presence of their structural alterations of p53 gene exons 4-9 in NHL.

Pathophysiology of Hodgkin's disease: functional and molecular aspects

Hodgkin's disease (HD) is characterized by the presence of the typical, clonal malignant Hodgkin and Reed-Sternberg (H-RS) cells in a hyperplastic background of normal reactive lymphocytes, plasma cells, histiocytes, neutrophils, eosinophils and stromal cells. The neoplastic nature of HD is based on aggressive clinical progression, presence of the proliferating and atypical H-RS cells, aneuploidy and cellular clonality. Immunophenotypical studies have demonstrated frequent expression of lymphoid "activation markers' including CD15, CD25, CD30, CD40, CD54, CD70, CD71, CD80, CD86 and MHC class II and less frequent expression of T- or B-cell-associated antigens by the neoplastic H-RS cells. The clonality of H-RS cells is demonstrated by clonal EBV integration, clonal cytogenetic abnormalities including p53 mutations and clonal immunoglobulin rearrangements in some HD cases. There is involvement of diverse molecules with oncogenic potential, including presence of viruses (Epstein-Barr virus and human herpes virus-6) and/or oncogenes/tumour suppressor genes (bcl-2/bcl-x, p53/MDM-2, c-myc, c-fms, N-ras, lck). The histopathological presentation and characteristic clinical features of HD correlate with an unbalanced production of multiple cytokines and define HD as a tumour of cytokine-producing cells. The proportion of malignant H-RS cells to reactive cellular components and fibrosis is dependent on the production of particular cytokines and allows subtyping of HD cases. The combined use of immunohistochemical, biochemical and molecular techniques has thus allowed recognition that HD represents more than one clinico-pathological entity with different types of H-RS cells. The defined mechanism for the biological nature, origin and oncogenesis of H-RS cells remains not fully understood, but is susceptible to further analysis using modern technology.

p53 protein expression in cutaneous T-cell lymphomas

p53 is an oncosuppressor gene located on chromosome 17p. Point mutations of the p53 gene are seen frequently in human malignancies, and are closely associated with malignant transformation under in vitro conditions. Mutated p53 protein shows a slow cell turnover rate, and accumulates in cells at the nuclear and/or cytoplasmic level. As a result, mutated p53 protein can be detected more readily by immunohistology than the wild-type protein. In this study, we used a monoclonal anti-p53 antibody (clone DO7) to examine the expression of p53 protein in 25 cutaneous T-cell lymphomas (CTCL) of low- and high-grade malignancy, i.e. mycosis fungoides (n = 6), Sézary's syndrome (n = 2), and large cell lymphomas of pleomorphic (n = 14) or anaplastic (n = 3) subtype. The results showed that easily detectable p53 protein was present in many of the neoplastic cells in half of the high-grade lymphomas. In contrast, in the low-grade lymphomas no, or only very few, p53-positive neoplastic cells could be detected. These findings suggest that molecular and/or genetic alterations of p53 may be implicated in the pathogenesis of high-grade CTCL, but are unlikely to be of critical importance in low-grade CTCL.

Biopathologic features of Hodgkin's disease

The neoplastic nature of Hodgkin's disease (HD) is suggested by several lines of evidence, including aggressive clinical course, presence of proliferating atypical cells morphologically recognized as Hodgkin's and Reed-Sternberg cells (H-RS), aneuploidy, and, in the minority of cases, clonality. Nevertheless, the etiopathogenesis of HD still remains elusive, and probably diverse. This uncertainty is partly due to the peculiar histology of HD lesions, characterised by the paucity of the putative neoplastic cell component, i.e. H-RS cells, admixed to a variety of reactive cells which prevent an exhaustive investigation at molecular level. Nevertheless, the possible involvement of different molecules with oncogenic potential has been recently suggested on the basis of immunohistological and molecular biology studies. These include oncogenes such as bcl-2 and MDM2 and anti-oncogenes such as p53. In addition, a large amount of data has accumulated on the possible role of EBV infection in HD. The colonization of lymphoid tissues by immortalized H-RS cells can account for the derangement of cytokine networks leading to microenvironmental and systemic abnormalities. In addition, a variety of soluble receptors (sIL-2R, sCD30, sTNF-R), and adhesion molecules (sICAM-1) are abnormally produced at sites of disease involvement. Some of these molecules still retain the ability to bind their ligands and can potentially contribute to the derangement of immune mechanisms observed in HD. Many of these soluble molecules can also be found in the patient's sera providing new potential prognostic and follow-up parameters in HD patients. The comparative analysis of the same molecules within the tissue, using immunohistochemistry, and in the blood, using immunochemical assays, appears as a promising informative approach.

Post-thymic T cell lymphomas frequently overexpress p53 protein but infrequently exhibit p53 gene mutations

We recently demonstrated that only one of 36 T-cell neoplasms contained p53 gene mutations. Although p53 gene mutations are known to result in overexpression of the p53 gene product, we also recently discovered that p53 protein overexpression does not correlate with p53 gene mutations, but does correlate with proliferation (r = 0.92), in anaplastic large cell lymphoma. In view of these findings, we investigated 34 non-human T-cell lymphotropic virus type I (HTLV-I) related postthymic T-cell lymphomas immunohistochemically for p53 protein, using monoclonal antibody 1801, and for proliferation, using monoclonal antibody Ki-67, and quantitated the results with the CAS-200 computerized image analysis system. We evaluated the presence of mutations in conserved exons 5 to 9 of the p53 gene using single-strand conformation polymorphism analysis and DNA sequencing. p53 mutations were detected in three of 34 cases, including two that contained deletions. p53 protein overexpression was detected in 17 of 34 cases, including the three mutated cases, with reactivities ranging from 10% to 48%. However, many cases in which a structural alteration could not be detected demonstrated levels of p53 protein expression comparable to those cases that were mutated. Correlation of p53 protein expression and proliferation, as assessed by Ki-67 expression, in this group of lymphomas was poor (r = 0.34). Whether alternative mechanisms of p53 protein inactivation are causing phenotypic overexpression of the p53 protein in these malignant lymphomas is unknown, although preliminary studies do not support a major role for such mechanisms. Therefore, the etiology and the significance of p53 protein overexpression in the cases that lack a demonstrable mutation is unclear. Nevertheless, as in anaplastic large cell lymphoma, overexpression of the p53 gene product is not a reliable predictor of the presence of mutations in conserved portions of the p53 gene in non-HTLV-I associated post-thymic T-cell lymphoma.

High levels of p53 protein expression do not correlate with p53 gene mutations in anaplastic large cell lymphoma

Strong immunohistochemical reactivity for p53 tumor suppressor gene product has been reported in a variety of different human malignancies including CD30- (Ki-1) positive anaplastic large cell lymphoma (ALCL). Although high levels of p53 protein have been interpreted as abnormal, rapidly proliferating benign and neoplastic lymphoid cells may have increased p53 expression in the absence of structural alterations. On the other hand, mutations in the p53 gene can lead to a lack of p53 protein production. Structural alterations of the p53 gene have not been documented in cases of ALCL and the mechanism for an abnormal pattern of p53 expression in these lymphomas has not been elucidated. Therefore, to determine whether an altered pattern of p53 expression correlates with mutations in the p53 locus in ALCL, we analyzed the expression of p53 protein immunohistochemically, compared it with the proliferation index using monoclonal antibody Ki-67, and assessed the presence of mutations in exons 5 though 9 of the p53 gene using a single-strand conformation polymorphism assay in a panel of 17 ALCLs. Furthermore, we studied the presence of allelic deletions of chromosome 17p by restriction fragment length polymorphism analysis. We found significant levels of p53 protein expression in 12 of the 15 cases studied, but identified mutations in only one of 17 cases. An allelic deletion in chromosome 17p was identified only in the one case containing a mutated p53 gene. Whereas the case containing structural alterations in the p53 gene did have strong p53 immunoreactivity, 11 cases that lacked p53 mutations in the regions examined also had significant levels of p53. Thus, our studies indicate that strong immunohistochemical reactivity for p53 is not a reliable indicator of the presence of structural alterations of p53 gene exons 5 through 9 in ALCL.

P53 protein expression in Hodgkin's disease

P53 is an oncosuppressor gene which is located on chromosome 17. Mutations of the p53 gene are closely associated with malignant transformation under in vitro conditions and are the most common genetic alteration in human malignancy. Unlike normal p53 protein which is unstable and usually cannot be detected by immunohistology, mutated p53 shows a decreased cell turnover rate and overexpression as compared with the wild-type protein. In this study a panel of four anti-p53 antibodies (PAb240, PAb421, PAb1801 and DO7) was applied to 52 cases of Hodgkin's disease: three cases of nodular lymphocytic predominance (LP), 33 cases of nodular sclerosis (NS), and 16 cases of mixed cellularity (MC). The results show that 53 protein is present in the Hodgkin's- and Reed-Sternberg cells in 82% of NS and 94% of MC, but not in nodular LP. It is suggested that mutations of the p53 gene and loss of normal p53 function are frequent in Hodgkin's disease and may be implicated in the pathogenesis of this disease.

Pancreatic adenocarcinomas frequently show p53 gene mutations

Thirty-four pancreatic adenocarcinomas were studied for the presence of p53 gene mutations by the single-strand conformation polymorphism method and by direct sequencing of PCR-amplified fragments. p53 protein expression was immunohistochemically evaluated using monoclonal PAb1801 and polyclonal CM1 antibodies. Mutations were detected in 14 cases. The transitions were six G to A and two A to G; the transversions were one C to G and two A to C; the remaining three were frameshift mutations. Immunostaining results were identical with both antibodies. Nuclear immunohistochemical p53-positive cells were found in nine p53 mutated cases and in 12 cases in which no mutation was detected. In most of these latter cases only a minority of cancer cells showed immunohistochemical positivity. Twenty-nine cases, including all p53 mutated cancers, were known to contain codon 12 Ki-ras gene mutations. Also in the light of the demonstrated cooperation of ras and p53 gene alterations in the transformation of cultured cells, our data suggest that p53 mutation is one of the genetic defects that may have a role in the pathogenesis of a proportion of pancreatic cancers.

The pathogenesis of AIDS lymphomas: a foundation for addressing the challenges of therapy and prevention

The association between AIDS and a spectrum of malignancies relates to chronic, profound defects in both cellular and humoral mechanisms of immune surveillance. Ironically, as AIDS patients live longer in response to increasingly effective antiretroviral therapies, the incidence of AIDS-related malignancies will continue to rise. The emergence of non-Hodgkin's lymphomas (NHL) as a major sequela of HIV infection bears a striking relationship to depletion of CD4 lymphocytes, particularly below 50/mm3. The ability to interfere early in the course of active HIV infection with additional mechanisms that may promulgate transformed cell hyperproliferation and clonal expansion--growth factors, HIV itself or other viruses (Epstein-Barr, in particular), aberrant oncogene or tumor suppressor genes expression, factors that induce genetic instability or DNA damage or alter host or viral genome repair--might decrease the occurrence or prolong the time to development of AIDS-related malignancies. The development of antiretroviral strategies that confer long-term suppression of HIV activity and relative preservation of immune function are essential to the ultimate prevention of malignancies that arise as a consequence of HIV-induced immunosuppression.

Overexpression of p53 in Hodgkin's disease: lack of correlation with Epstein-Barr virus infection

Recent work has shown that p53 gene mutations are frequently found in Epstein-Barr virus (EBV)-positive and EBV-negative cases of Burkitt's lymphoma but not in EBV-associated undifferentiated nasopharyngeal carcinomas (NPCs). Similar viral gene expression patterns are observed in undifferentiated NPCs and in EBV-positive cases of Hodgkin's disease (HD), suggesting that the contribution of the virus to the pathogenesis of these malignancies may also be similar. We have analysed 116 cases of HD for EBV association and for immunohistologically detectable overexpression of p53. p53 overexpression was detected in the tumour cell population of 37 (32 per cent) of the cases. Fifteen cases showed p53-specific labelling of more than 40 per cent of tumour cells; in six of these, virtually all tumour cells were stained. In eight cases, between 5 and 40 per cent of tumour cells were labelled, and in another 14 cases, less than 5 per cent of tumour cells expressed detectable amounts of p53. EBV-positive HD cases were found in all groups with different levels of p53 overexpression as well as amongst p53-negative cases. While a more detailed analysis of the p53 gene in HD is required, these data show that overexpression of p53 in HD is heterogeneous and that there is no simple correlation between EBV infection and p53 overexpression.

Accumulation of p53 protein correlates with tumour proliferative activity in EBV positive Burkitt's lymphoma

p53 tumour suppressor gene is often found mutated in Burkitt's lymphoma (BL) cell lines and tumours. We analysed 35 BL tumours for the accumulation of p53 protein, and correlated the results with DNA flow cytometric data on the proliferative activity (SPF), and data on the presence or absence of Epstein-Barr virus (EBV) DNA. More than one-third (37 per cent) of the tumours showed accumulation of p53, which was considered to be consistent with mutation of the p53 gene. Tumours that were positive both for EBV DNA and p53 had significantly higher mean SPF than corresponding EBV DNA negative and/or p53 negative tumours. The proportions of tumour cells with accumulation of p53 appeared to correlate with tumour SPF only in EBV DNA positive BLs. However, there was no apparent association between accumulation of p53 and the presence or absence of EBV DNA. These findings are suggestive of multiple pathways in BL tumour progression.

Epstein-Barr virus/complement fragment C3d receptor (CR2) reacts with p53, a cellular antioncogene-encoded membrane phosphoprotein: detection by polyclonal anti-idiotypic anti-CR2 antibodies

Epstein-Barr virus and the C3d fragment of the third component of complement are specific extracellular ligands for complement receptor type 2 (CR2). However, intracellular proteins that react specifically with CR2 and are involved in post-membrane signals remain unknown. We recently prepared polyclonal anti-idiotypic anti-CR2 antibodies (Ab2) by using the highly purified CR2 molecule as original immunogen. We showed that Ab2 contained anti-idiotypic specificities that mimicked extracellular domains of CR2 and detected two distinct binding sites on CR2 for its specific extracellular ligands, Epstein-Barr virus and C3d. We postulated that Ab2 might also contain specificities that could mimic intracellular domains of CR2. Here we report that Ab2, which did not react with Raji B-lymphoma cell surface components, detected specifically, among all components solubilized from Raji cell membranes, a single intracellular membrane protein of apparent molecular mass of 53 kDa. This protein was identified as the p53 cellular antioncogene-encoded membrane phosphoprotein by analyzing its antigenic properties with Pab1801, a monoclonal anti-p53 antibody, and by comparing its biochemical properties with those of p53. Additionally, solubilized and purified CR2 bound to solubilized p53 immobilized on Pab1801-Sepharose. p53, like CR2, was localized only in purified plasma membranes and nuclei of Raji cells. These data suggest strongly that p53, a cellular antioncogene-encoded phosphoprotein, reacted specifically with CR2 in Raji membranes. This interaction may represent one of the important steps through which CR2 could be involved in human B-lymphocyte proliferation and transformation.

Quantitation of a 55K cellular protein: similar amount and instability in normal and malignant mouse cells

Quantitative expression of a specific 55,000 (55K)-molecular-weight cellular protein was studied in two groups of mouse embryo fibroblast (clonal) cells originating from two parent clones, one of which possessed high tumorigenicity and the other of which possessed very low tumorigenicity. From the clone with low tumorigenicity, tumor lines and clones were obtained by selecting rare spontaneously transformed highly tumorigenic (mutant) cells. Cells were labeled during exponential growth for 3 h at 37 degrees C, with [35S]methionine, and the cellular 55K protein was immunoprecipitated with a monoclonal antibody and quantitated. There were low and approximately equal amounts of 55K protein in cells (clones) with both low and high tumorigenicity from both groups of cells, and there was no correlation at all between quantitative expression of 55K protein and of cellular tumorigenicity. There was approximately 10- to 20-fold more 55K protein in all simian virus 40-transformed T antigen-positive derivative clones, as shown previously. The T antigen-negative revertant tumor lines and clones obtained by an immunological in vivo selection method had low amounts of 55K protein, similar to the parent cell before simian virus 40 transformation. In all of the T antigen-negative cells, including the highly tumorigenic cells, degradation (turnover?) of the 55K protein was rapid, and a half-life of 15 to 60 min was estimated from pulse-chase experiments. In all of the T antigen-positive cells the 55K protein was stable (half-life greater than 10 h). In primary cells established from the tumors induced by highly tumorigenic cells there was a very low or no detectable amount of the 55K protein. This is in contrast to the primary cells obtained from early murine embryos in which we have reported high amounts of (stable) 55K proteins.

Epstein-Barr virus (EBV) antigen-specific leukocyte migration inhibition (LMI) in infectious mononucleosis (IM). I. Kinetics and response to a membrane protein on EBV-transformed cells

Cell-mediated immune response of mononucleosis (IM) patients to Epstein-Barr virus (EBV)-determined antigens was measured by the leukocyte migration inhibition (LMI) assay. Patients in the acute phase of the disease failed to respond to partially purified nuclear antigen, EBNA, or to cell extracts that contained EBNA as the predominant EBV antigen. They showed a strong specific response to cell extracts enriched in early antigen (EA) and virus capsid antigen (VCA). The LMI response to EBNA appeared in convalescence in parallel with EBNA-specific antibodies, slightly later in children than in adults. Membrane fractions of EBV-carrying, virus nonproducer Raji cells induced an EBV-specific LMI at approximately the same time. A bacterial fusion protein containing the hydrophilic part of the virus-coded membrane antigen of latently EBV-infected cells also induced an EBV-specific response that parallelled the LMI reaction elicited by the Raji membrane fraction. This is in line with our previous finding (D. Sulitzeanu et al., J. Virol. 58, 230, 1986) that this fusion protein shares an epitope with Raji cell membranes.

Stable induction of a 51K cellular protein in neuronal cells surviving herpes simplex virus type 1 infection

A series of survivor cell lines derived by infection of B103 rat neuroma cells with active wild-type herpes simplex virus type 1 (HSV-1) (M. Levine, A. L. Goldin, and J. C. Glorioso, J. Virol. 35, 203-210 (1980)) has been isolated. The survivor cells produced no infectious virus, yet they continued to react with HSV-1 antiserum for over 100 cell generations following the initial infection. The reactivity of the survivor cells with HSV-1 antiserum is characterized as being due to expression of a 51K protein. The 51K protein reacted with antiserum prepared against HSV-1 virions and was not detectable in the parental B103 cells. A protein of the same molecular weight was seen in productively infected B103 and HEL cells. The protein detected in the survivor cells comigrated with that seen in the infected cells on two-dimensional gel electrophoresis, indicating that they represent similar proteins. Despite the presence of the 51K protein reactive with HSV-1 antiserum, the survivor cells contain no detectable HSV-1 DNA sequences. They do contain DNA sequences which cross-hybridize with HSV-1 DNA, but similar cross-hybridizing sequences were also present in the parental B103 cells. No hybridizing polysomal, polyadenylated RNA species were present in the survivor cells that were not present in the parental B103 cells when probed with the cross-hybridizing HSV-1 restriction fragments. Therefore, the 51K protein evidently represents a cellular protein induced by the HSV-1 infection.

Leukocyte migration inhibitory factor production by activated lymphocytes representing immunological memory or virus-receptor interaction: response of T cell subsets to Epstein-Barr virus nuclear antigen, response of B cells to UV inactivated Epstein-Barr virus

Both T and B lymphocytes are known to produce leukocyte migration inhibitory factor (LIF) after appropriate activation. We showed that EBV nuclear antigen (EBNA) triggered T cells for LIF production in an immunologically specific way: only T cells of seropositive individuals responded. Both Fc receptor positive and negative T cells produced LIF, and the presence of macrophages was necessary. The virus itself activated B cells independently of the serological status of the donors, thus the function was not based on immunological memory. This phenomenon was independent of the transforming capacity of the virus, because UV-inactivated virus also elicited LIF production by B lymphocytes. This triggering seems to be the consequence of the virus-receptor interaction on the cell surface.

Cloning and expression analysis of full length mouse cDNA sequences encoding the transformation associated protein p53

We have cloned and sequenced overlapping cDNA fragments which together encode the entire mouse protein p53. Using these cDNA's we have reconstructed the full length coding region for the protein, and have analysed its coding potential by expression in vitro, both as a full length sequence and as a subfragment contained in a fusion protein. The predicted amino acid sequence contains no obvious homologies to any known oncogenes but includes a possible tyrosine kinase acceptor site.

Large-T-antigen-p53 complex formation is not cold sensitive in a cold-sensitive transformant induced by simian virus 40 mutant tsA1499

F111 rat cells transformed by simian virus 40 mutant tsA1499 are cold sensitive for the expression of transformation. Yet, unlike F111 cells transformed by tsA58, they do not lose the ability to stabilize the transformation-associated host cell protein p53 at the temperature at which transformation is extinguished.

Transformation by human adenoviruses

When, approximately 10 years ago, it was shown that the functions essential for cell transformation were localized in a small region of the adenovirus genome, a DNA segment which at that time was thought to be capable of encoding two or three average-sized proteins at most, it seemed reasonable to hope that an understanding of the mechanisms by which adenoviruses transform cells might be quickly achieved. While such optimism might be forgiven, it was quite clearly naive in the extreme. As a consequence of mRNA splicing and the use of overlapping reading frames the number of proteins encoded within E1 is 2-3-times greater than would have been predicted a decade ago, and post-translational modifications may add another dimension of complexity. In fact it has taken nearly all of the past decade just to identify the proteins encoded in E1 and to characterize them in the most rudimentary way. However, we have now entered a period in which new information is accumulating at an extremely rapid rate as a result of several major technical and fundamental advances. Chief among these are the use of recombinant DNA techniques, particularly site-directed mutagenesis, which combined with methods for introducing mutations made in cloned sequences back into infectious virus, clearly represents a powerful approach to studying the functions of transforming proteins. In addition, the ability to express transforming proteins in bacteria and to produce large amounts of highly purified proteins which previously were only just detectable in infected and transformed cells is a major breakthrough. Advances in immunological techniques, particularly the development of monoclonal antibodies and antisera against synthetic peptides, have enormously simplified the task of detecting and characterizing E1 proteins. Finally, recent results suggesting that adenovirus transforming proteins may be functionally and structurally similar to other oncogenes brings a new perspective to the study of oncogenic transformation. Have all the proteins involved in transformation by adenoviruses been identified? It seems probable that all those virally coded proteins which play a major role are now known but of course minor players in the cast could still be waiting in the wings. We have pointed out that viral functions encoded outside region E1 may have some importance at least in initiation of transformation by virions and have speculated on the possibility that one or more of these may be involved in the integration of viral DNA into the host cell chromosome.(ABSTRACT TRUNCATED AT 400 WORDS)

EGNA-specific LIF production of human lymphocyte subsets

Using the indirect leukocyte migration inhibition technique T cells have been identified as being responsible for Epstein-Barr virus nuclear antigen-induced specific leukocyte migration inhibitory factor production. The response was dependent on the presence of macrophages or their product, T-lymphocyte activating factor.

Association of platelet-derived growth factor-induced protein with nuclear material

Platelet-derived growth factor (PDGF) has been proposed to initiate the cell-cycle traverse of density-arrested BALB/c-3T3 cells by rendering quiescent cells 'competent' to respond to 'progression' factors contained in platelet-poor plasma (PPP). PDGF-treated cells remain competent for many hours following PDGF removal; subsequent addition of PPP triggers G0-G1 traversal and entry into S phase. Numerous observations suggest that the competent state reflects the existence of a stable PDGF-induced 'second signal' as opposed to a persistent association of PDGF with cells. Several unique proteins have been shown to be synthesized in response to PDGF; of these, the dose-dependent production of 'pI' (molecular weight 29,000) was found to correlate closely with the induction of competence. We report here the further characterization of pI in terms of its time-dependent synthesis, intracellular location and stability. Electrophoretic analysis of nuclear and non-nuclear extracts of PDGF-treated BALB/c-3T3 cells demonstrated that pI is synthesized during the first 6 h of G0-G1, is associated with nuclear material and is stable for 9-12 h. These findings are consistent with the proposed role of pI as the cellular mediator of PDGF.

Pre-crisis mouse cells show strain-specific covariation in the amount of 54-kilodalton phosphoprotein and in susceptibility to transformation by simian virus 40

We have used several inbred mouse strains to examine the role of the 54-kilodalton (kDa) cellular phosphoprotein in transformation by the papovavirus simian virus 40. We have measured the endogenous 54-kDa phosphoprotein in cells obtained from these inbred mouse strains. To study the effect of passage, cell cultures were measured for amount of the 54-kDa phosphoprotein at the 2nd and 12th passages. In the absence of any transforming agent, the amount of endogenous 54-kDa phosphoprotein in early pre-crisis mouse cells varied in a strain-specific way. Transformation frequency varied coordinately with endogenous 54-kDa expression. Mouse strains whose cells produced a high level of endogenous 54-kDa phosphoprotein on passage did not further increase its expression after simian virus 40 transformation.

p53, a transformation-related cellular-encoded protein, can be used as a biochemical marker for the detection of primary mouse tumor cells

p53, a transformation-related cellular-encoded protein, was found to accumulate at high concentration in transformed cell lines. The results presented here show that p53 biosynthesis is also increased in most induced and spontaneous mouse tumors. Judged by the identity in antigenic determinants (estimated by binding to monoclonal antibodies), size, and partial peptide mapping, I conclude that the p53 molecule found in primary tumors is indistinguishable from that in established cell lines. The fact that p53 is found in heterogeneous populations of primary tumors makes it a convenient biochemical diagnostic marker for the detection of primary tumors in mice. It is found in primary tumors as a phosphoprotein, just as it was found previously in established cell lines. On the other hand, the p53 found at low concentration in normal thymocytes is labeled with [35S]methionine but cannot be found in its phosphorylated form.

Antibodies of predetermined specificity for the NH2 terminus of a cellular protein p53 react with the native molecule: evidence for the presence of different p53s

Two synthetic peptides corresponding to residues 1-20 and 10-20, respectively, of one type of a cellular protein called "p53" have been linked to a carrier protein and injected into rabbits to raise antibodies. The antibodies obtained were capable of reacting with the native protein, as judged by an enzyme-linked immunosorbent assay, protein A-linked staining of immunoblots after NaDodSO4 gel electrophoresis, and immunoprecipitation. The immunoassay titers against the protein were lower for these antibodies than for antisera derived from immunization with purified p53. However, staining with the immunoblot method showed that the antipeptide antibodies against p53 were uniquely specific. The data suggest that at least two different types of p53 molecules occur. The cellular protein previously isolated from human cells transformed by Epstein-Barr virus and from murine tumors induced by methylcholanthrene appears to be larger than the p53 reported in relation to simian virus 40- or adenovirus-transformed cells and to some other tumors. Some interrelationships have not been excluded, but it is clear that the two protein molecules do not behave identically. The reactions of the antipeptide antibodies with the intact protein have implications in regard to protein conformations. The strict specificities of such antibodies allow the generation of distinct sets of reagents useful for quantitation, purification, and cloning.

Molecular cloning of a cDNA specific for the murine p53 cellular tumor antigen

A cDNA library was constructed from sucrose-gradient-fractionated mRNA from SVT2, a mouse cell line transformed by simian virus 40. Polysomes containing the p53 messenger were specifically immunoprecipitated with monoclonal antibodies against the protein and used to prepare mRNA. This immunoselected mRNA, enriched 1,000-to 2,000-fold for p53-specific sequences, was used to make a cDNA probe and to screen the cDNA library. When approximately 10,000 colonies were screened by differential hybridization with probes made from immunoselected vs. nonenriched mRNA, a single clone was found that contained p53-specific sequences. The identity of this clone, termed pp53-208, was confirmed by the ability of its DNA to hybridize the mRNA coding for p53 (hybrid selection assay). When hybridized to a blot of EcoRI digested mouse DNA, the pp53-208 insert reacted with a single 3.3-kilobase band, suggesting that it is complementary to a single gene.

Discordant Epstein-Barr virus nuclear antigen (EBNA) antibody patterns in nasopharyngeal carcinoma

Epstein-Barr virus nuclear antigen (EBNA) preparations from three sources were tested with sera from normal individuals and patients with Hodgkin's disease, breast carcinoma, Burkitt's lymphoma, and American and Chinese nasopharyngeal carcinoma. Individual sera with discordant antibody patterns were noted in all groups. Sera from both NPC groups gave significantly higher anti-EBNA titers on cell lines converted with P3HR-1 or B95-8 virus compared with anti-EBNA titers on Raji cells. Anti-EBNA titers of Chinese NPC sera showed no correlation among the three EBNA sources, while all other groups had highly correlated titers. Cross-absorption experiments present evidence for more than one antigenic determinant on EBNA. These results suggest an additional parameter for distinguishing Chinese NPC from other EBV-related disorders.

Regulation of the cellular p53 tumor antigen in teratocarcinoma cells and their differentiated progeny

F9 embryonal carcinoma cells express high levels of a 53,000-molecular-weight cellular tumor antigen called p53. When F9 cell cultures are treated with retinoic acid and dibutyryl adenosine 3',5'-phosphate, they differentiate, predominantly into endoderm-like cells. This differentiation is accompanied by a marked decrease in the levels of p53. The mechanism(s) responsible for this decline in the level of p53 in differentiated cells was investigated. The results demonstrate that the high levels of p53 in F9 cells relative to their differentiated progeny were not due to alterations in the stability or turnover of this protein. Rather, the regulation during differentiation involved a marked decrease in the amount of in vitro translatable p53 mRNA detected in the differentiated cell cultures. This mechanism is unlike the one operating during the simian virus 40 infection or transformation, where the increased levels of p53 are largely due to the increased stability of the p53 protein.

Microinjection of monoclonal antibody to protein p53 inhibits serum-induced DNA synthesis in 3T3 cells

Monoclonal antibody directed against the transformation-related protein p53 was microinjected manually into the nuclei of quiescent Swiss 3T3 mouse cells. The cells were subsequently stimulated with 10% fetal calf serum. Microinjection of p53 antibody at or around the time of serum stimulation clearly inhibited the subsequent entry of Swiss 3T3 cells into the S phase of the cell cycle. p53 antibody had no effect on serum-stimulated DNA synthesis when it was microinjected 4 hr or later after serum stimulation. Monoclonal antibody to an unrelated antigen, Lyt-2.2, had no effect on serum-stimulated DNA synthesis regardless of the time it was microinjected. Under similar experimental conditions, p53 antibody had no effect on simian virus 40- or adenovirus 2-induced DNA synthesis. These experiments add strength to the suggestion that p53 is involved in the regulation of cell proliferation.

The alpha 2 HS glycoprotein receptor on lymphocytes transformed by Epstein--Barr virus

The alpha 2HS glycoprotein receptor from lymphocytes transformed by Epstein--Barr Virus was isolated by affinity chromatography. The protein receptor has a monomer Mr of 48 000, which is similar to the Epstein--Barr virus-determined nuclear antigen (EBNA), and pI = 7.2. Like EBNA the 48 000 Mr component in unfractionated labelled detergent solubilised cell supernatants also binds DNA. These results may suggest some similarity between the alpha 2HS receptor and EBNA.

Quantitation of a 55K cellular protein: similar amount and instability in normal and malignant mouse cells

Quantitative expression of a specific 55,000 (55K)-molecular-weight cellular protein was studied in two groups of mouse embryo fibroblast (clonal) cells originating from two parent clones, one of which possessed high tumorigenicity and the other of which possessed very low tumorigenicity. From the clone with low tumorigenicity, tumor lines and clones were obtained by selecting rare spontaneously transformed highly tumorigenic (mutant) cells. Cells were labeled during exponential growth for 3 h at 37 degrees C, with [35S]methionine, and the cellular 55K protein was immunoprecipitated with a monoclonal antibody and quantitated. There were low and approximately equal amounts of 55K protein in cells (clones) with both low and high tumorigenicity from both groups of cells, and there was no correlation at all between quantitative expression of 55K protein and of cellular tumorigenicity. There was approximately 10- to 20-fold more 55K protein in all simian virus 40-transformed T antigen-positive derivative clones, as shown previously. The T antigen-negative revertant tumor lines and clones obtained by an immunological in vivo selection method had low amounts of 55K protein, similar to the parent cell before simian virus 40 transformation. In all of the T antigen-negative cells, including the highly tumorigenic cells, degradation (turnover?) of the 55K protein was rapid, and a half-life of 15 to 60 min was estimated from pulse-chase experiments. In all of the T antigen-positive cells the 55K protein was stable (half-life greater than 10 h). In primary cells established from the tumors induced by highly tumorigenic cells there was a very low or no detectable amount of the 55K protein. This is in contrast to the primary cells obtained from early murine embryos in which we have reported high amounts of (stable) 55K proteins.

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.

Migration inhibition caused by EBV-specific 48K subcomponent of EBNA and the associated 53K cellular protein

Leukocytes from EBV-seropositive but not seronegative healthy donors responded with significant migration inhibition to the 48K subcomponent of the Epstein-Barr virus determined nuclear antigen (EBNA), known to carry the virally determined antigenic specificity. A concentration of 10 micrograms/ml was still effective while 5 micrograms/ml had no detectable effect. EBNA-associated cellular 53K protein had no effect by itself, but it potentiated the effect of 48K, even if the latter was added at the subliminal concentration of 5 micrograms/ml. The related 53K protein, isolated from EBV-negative human lymphoma cells, was also effective, whereas the corresponding murine-tumor-associated 53K had no potentiating effect. Immunization of mice with an extract of DNA-binding proteins from EBV-carrying Raji cells, known to contain both 48K and 53K, induced a significant macrophage migration inhibition response, to both human 48K and 53K. Murine 53K was ineffective, however. Human but not murine 53K increased the migration inhibitory activity of subliminal concentrations of 48K in the murine macrophage system as well. These findings suggest that human but not murine 53K may reconstitute with 48K (EBNA) to form a highly immunogenic complex.

Regulation of the cellular p53 tumor antigen in teratocarcinoma cells and their differentiated progeny

F9 embryonal carcinoma cells express high levels of a 53,000-molecular-weight cellular tumor antigen called p53. When F9 cell cultures are treated with retinoic acid and dibutyryl adenosine 3',5'-phosphate, they differentiate, predominantly into endoderm-like cells. This differentiation is accompanied by a marked decrease in the levels of p53. The mechanism(s) responsible for this decline in the level of p53 in differentiated cells was investigated. The results demonstrate that the high levels of p53 in F9 cells relative to their differentiated progeny were not due to alterations in the stability or turnover of this protein. Rather, the regulation during differentiation involved a marked decrease in the amount of in vitro translatable p53 mRNA detected in the differentiated cell cultures. This mechanism is unlike the one operating during the simian virus 40 infection or transformation, where the increased levels of p53 are largely due to the increased stability of the p53 protein.

Adenovirus E1b-58kd tumor antigen and SV40 large tumor antigen are physically associated with the same 54 kd cellular protein in transformed cells

The adenovirus E1b-58kd tumor antigen has been detected in a physical association with a 54 kilodalton cellular protein in adenovirus-transformed mouse cells. Antibody specific for the E1b-58kd protein coimmunoprecipitates a 54 kd protein from transformed, but not from productively infected, cells. Monoclonal antibody specific for the cellular 54 kd protein coimmunoprecipitates the adenovirus E1b-58kd protein from transformed cell extracts. The same or closely related cellular 54 kd protein, associated with the adenovirus E1b-58kd protein, was present in the SV40 large T antigen-54 kd complex previously detected in SV40-transformed mouse cells. The identity of the 54 kd protein is based on the immunological specificities of the anti-54 kd monoclonal antibodies and partial peptide maps of the 54 kd protein associated with the adenovirus and SV40 tumor antigens. The adenovirus E1b-58kd-54 kd complex, like the SV40 large T antigen-54 kd complex, is heterogeneous in size or mass. While all of the cellular 54 kd protein in the adenovirus-transformed cell extract is found in a complex with the E1b-58kd protein, some of the viral 58 kd antigen is detected in a form not associated with the 54 kd protein. The fact that the adenovirus and Sv40 tumor antigens, both required for transformation, can be found in physical association with the same cellular protein in a transformed cell is a good indication that these two diverse viral proteins share some common mechanisms or functions.

A 53-kilodalton protein common to chemically and virally transformed cells shows extensive sequence similarities between species

A heat-stable DNA-binding protein with subunits of about 53 kilodaltons (kDal) was purified from two virally transformed human cell lines (Epstein-Barr virus-positive Raji and Namalwa) and two mouse tumor cell lines (methylcholanthrene-induced Meth A sarcoma and TA3 mammary carcinoma). All four 53kDal proteins showed closely related total amino acid compositions, similar peptide maps, and identical NH2-terminal amino acid sequences for 20 residues. These 53-kDal proteins are therefore evolutionarily highly conserved, independent of whether they originate from virally or chemically transformed cells. The NH2-terminal sequence and the protein chain as a whole are not hydrophobic; however, some unexpected residue distributions were observed. Comparisons with other proteins reveal no clear sequence similarity with known tumor antigen structures, homologous immunoglobulins, or some other proteins of known sequence. Epstein-Barr virus-determined nuclear antigen also appears to have a different NH2-terminal sequence. Thus, the results show that the 53-kDal proteins represent a unique protein type with little species variation; this finding suggests that these proteins must perform an important common function in different transformation systems.