[Nasopharyngeal carcinoma in sub-Saharan Africa: a tribute to Mr. Peter Clifford]

Poorly differentiated nasopharyngeal carcinoma (NPC) is a major malignancy in certain areas of Asia. It exists also in Africa, notably among largely Arab populations in North Africa, and in "hotspots" in East Africa among "native" Africans. This article deals with the latter, as studied and defined in depth during the 1960s and 70s by the Irish-born surgeon, Peter Clifford. Through his published works, he has influenced and helped define the field of head and neck cancer as it exists in Kenya. He also did pioneering work on the African childhood malignancy, Burkitt's lymphoma (BL). Both BL and NPC have been ultimately shown to be associated with the human herpes Epstein-Barr virus (EBV). This article is written as a tribute to Peter Clifford, focusing on his work on NPC, where he first defined the disease "hotspots" in the Kenyan Highlands, studied how best to treat the malignancy in the absence of radiotherapy, looked at possible NPC predisposing factors in the Kenyan setting, and ultimately addressed how the cancer cells interact with EBV. Peter Clifford's pioneering work was cut short by accident. Although outside East Africa he remains largely an 'unsung hero' in the field, his influence has been great. It begs to be re-addressed and reconsidered.

Pilot study of sodium phenylbutyrate as adjuvant in cyclophosphamide-resistant endemic Burkitt's lymphoma

Burkitt's lymphoma (BL) accounts for the majority of childhood malignancies seen in sub-Saharan Africa. In Malawi, cyclophosphamide (CPM), the mainstay of treatment for endemic BL, is effective in around 50% of cases. Evidence exists in support of an association between activation of replication of Epstein-Barr virus (EBV) in the tumour and response to this chemotheraupeutic agent. Phenylbutyrate (PB), approved for treatment of inborn errors of the urea cycle with minimal toxicity in children, induces EBV replication and cell lysis in BL-derived cell cultures. It has also shown some success as adjuvant in treatment of chronic leukaemia and lymphoma. We tested in African BL patients with CPM-resistant tumours, and thus unlikely to survive, the hypothesis that PB can reverse this resistance. A study of five patients showed PB before CPM to induce shrinkage of CPM-resistant tumours in two of them. Findings suggested that for this effect PB pre-treatment should be given for a week before CPM treatment. A larger study is indicated.

Complexities associated with expression of Epstein-Barr virus (EBV) lytic origins of DNA replication

EBV has two lytic origins (oriLyt) of DNA replication lying at divergent sites on the viral genome within a duplicated sequence (DS). The latter contains potential hairpin loops, ‘hinge’ elements and the promoters for transcripts from viral genes BHLF1 and LF3. These genes themselves consist largely of 125 and 102 bp repetitive sequences, respectively, and encode basic proteins. We have examined these genomic regions in detail in attempts to understand why lytic replication—necessary for virus survival—is so inefficient, and to identify controlling elements. Our studies uncovered a diverse family of promoters (P) for BHLF1 and LF3, only one pair of which (P1) proved sensitive to chemical inducing agents. The others (P2–P3/4), abutting the replication ‘core’ origin elements in DS and extending into 5′-unique sequences, may play roles in the maintenance of viral latency. We further identified a family of overlapping small complementary-strand RNAs that transverse the replication ‘core’ origin elements in a manner suggesting a role for them as ‘antisense’ species and/or DNA replication primers. Our data are discussed in terms of alternative lytic replication models. We suggest our findings might prove useful in seeking better control over viral lytic replication and devising strategies for therapy.

Virus-associated RNA I-deleted adenovirus, a potential oncolytic agent targeting EBV-associated tumors

Given the growing number of tumor types recognizably associated with EBV infection, it is critically important that therapeutic strategies are developed to treat such tumors. Replication-selective oncolytic adenoviruses represent a promising new platform for anticancer therapy. Virus-associated I (VAI) RNAs of adenoviruses are required for efficient translation of viral mRNAs. When the VAI gene is deleted, adenovirus replication is impeded in most cells (including HEK 293 cells). EBV-encoded small RNA1 is uniformly expressed in most EBV-associated human tumors and can functionally substitute for the VAI RNAs of adenovirus. It enables replication to proceed through complementation of VAI-deletion mutants. We hypothesized that VAI-deleted adenovirus would selectively replicate in EBV-positive tumor cells due to the presence of EBV-encoded small RNA1 with no (or poor) replication in normal or EBV-negative tumor cells. In this report, we show that high levels of replication occurred in the VAI-deleted mutant in the EBV-positive tumor cells compared with low (or negligible) levels in EBV-negative and normal human primary cells. Correspondingly, high toxicity levels were observed in EBV-positive tumor cells but not in EBV-negative tumor or normal human primary cells. In vivo, VAI-deleted adenovirus showed superior antitumoral efficacy to wild-type adenovirus in EBV-positive tumor xenografts, with lower hepatotoxicity than wild-type adenovirus. Our data suggest that VAI-deleted adenovirus is a promising replication-selective oncolytic virus with targeting specificity for EBV-associated tumors.

Effect of dose and long-term storage on the immunogenicity of murine polyomavirus VP1 virus-like particles

We have analysed the stability and immunogenicity of murine polyomavirus virus-like particles (VLPs) following intranasal administration without adjuvant. No morphological or immunological changes were observed in a preparation of these VLPs stored for 9 weeks at room temperature. Strong humoral and cellular (Th1) responses were obtained after a single 5.55 microg dose immunisation, which are efficiently boosted after a second dose. However, at dose concentrations above 0.22 microg/microl, these VLPs appear to aggregate and, when used for immunisations, they fail to induce a strong cellular response, even though the humoral response is unaffected. These results may reflect the differential processing of VLP aggregates by the immune system or, alternatively, VLP neutralisation by antibodies induced after a primary immunisation.

Epstein-Barr virus gene expression in human breast cancer: protagonist or passenger?

The presence and transcriptional expression of Epstein-Barr virus (EBV)-encoded genes, oestrogen receptor (ER) status and degree of lymphocyte infiltration were evaluated in 15 mastectomy-removed breast cancer samples, mostly of ductal origin. With regard to these parameters, the tumours were heterogeneous. Viral genes, including EBNA1 - a universal EBV marker - and others, selected in part on the basis of expression in other EBV-associated carcinomas and/or presence in an epithelial cell immortalising subfragment p31 of viral DNA, were detected in up to 40% of the breast malignancies. The small viral RNAs, EBERs, were not observed. In culture, p31 EBV DNA, alone among EBV fragments, stimulated the growth of human breast-milk epithelial cells. There was no correlation between viral and ER expression and tumours were heterogeneous with regard to their invasive lymphocytes: of three studied in detail, one contained none, another had (mainly) T-lymphocyte aggregates on the tumour periphery, and a third (BC 12) was infiltrated with both T- and B-lymphocytes. BC 12 differed in several aspects from other malignancies in expressing a transcriptional activator (BZLF1) associated with overcoming virus latency, and failing to express a viral oncogene, BARF1. Arguments are given for EBV as a protagonist cocarcinogen in some breast malignancies.

Genetic diversity: frameshift mechanisms alter coding of a gene (Epstein-Barr virus LF3 gene) that contains multiple 102-base-pair direct sequence repeats

Frameshift mutations provide recognized mechanisms for changing the coding potential of an organism. Here, multiple frameshifts are identified in repetitive sequences within an Epstein-Barr virus unspliced early gene, LF3, which is associated with the viral replicative cycle and also transcriptionally expressed in many virally associated tumors. On the DNA strand encoding LF3, there are three open reading frames, only one of which contains an initiation codon. Most (>95%) of the gene consists of numerous (>20, varying with cell source) GC-rich copies of a 102-bp direct repeat (called IR 4) flanked by small unique sequences. LF3 may express a protein if its initiation and termination codons reside in the same reading frame, but this is not always the case. Frameshifting events, occurring in short runs of pyrimidines (mainly C residues) in the repeats, give rise to mutations which may provide a mechanism for escape of an LF3 function from host surveillance. Sequence studies link these frameshifts to DNA replication errors. Notably, the number of sites in LF3 at which such mutations can occur permits a very large amount of diversity in this gene. Our data also suggest a second degeneracy mechanism within the protein itself, which influences its stability and may reflect a host defense mechanism. LF3 thus provides a potentially important model for studying the quest for supremacy between a virus and its host.

Long term survival of children with Burkitt lymphoma in Malawi after cyclophosphamide monotherapy

BACKGROUND

Between 1991 and 1997, limited funding at times restricted available treatment for children with Burkitt lymphoma (BL) to cyclophosphamide (CPM) monotherapy at Lilongwe Central Hospital, Malawi. Our objective was to assess long-term survival in Malawian children with Burkitt lymphoma (BL) who had received one or more treatments with intravenous CPM at 40 mg/kg/dose at 14-day intervals.

PROCEDURE AND RESULTS

The study population consisted of 92 children in whom BL had been confirmed on fine needle aspirates (FNA), a home address had been documented on discharge from hospital, and the treatment records could be verified. Only the clinical site(s) of disease had been recorded. The M:F ratio was 1.4 and median age 8 years. A clinical officer on motorcycle attempted to locate the given addresses and interview parents or other sources. In 19 patients, the address was incorrect. Of 73 evaluable patients, 40 children are alive at a mean follow-up time of 59 (range: 29-104) months. The survival rate was 63.5% in 52 children with BL of the head only, and 33.3% in 21 children with primary disease involving the abdomen or other sites. Survivors had received a median number of 6 (range: 1-12), non-survivors 4 (range: 1-12), and untracable children 3 (range: 1-11) courses of CPM.

CONCLUSIONS

We confirmed that CPM could cure children with facial and abdominal BL. The unavoidable bias in the selection of patients and the variable amount of CPM given, precludes accurate survival estimates. A prospective study with proper staging, assessment of FNA, marrow and cerebrospinal fluid with modern techniques, a standard treatment protocol, and adequate follow-up will better define the current therapeutic value of CPM monotherapy. CPM can be purchased at about 3 US dollars per 500 mg.

Analysis of mouse polyomavirus mutants with lesions in the minor capsid proteins

Polyomavirus mutants E, Q and H, expressing non-myristylated VP2, were generated by replacing the N-terminal glycine residue with glutamic acid, glutamine or histidine, respectively. Viruses mutated in either VP2 or VP3 translation initiation codons were also prepared. All mutated genomes, when transfected into murine host cells, gave rise to viral particles. Infectivity of VP2- and VP3- viruses, as measured by the number of cells expressing viral antigens, was dramatically diminished, indicative of defects in the early stages of infection. In contrast, the absence of a myristyl moiety on VP2 did not substantially affect the early steps of virus infection. No differences in numbers of cells expressing early or late viral antigens were observed between wild-type (wt) and E or Q myr- viruses during the course of a life cycle. Furthermore, no delay in virus DNA replication was detected. However, when cells were left for longer in culture, the number of infected cells, measured by typical virus bursts, was much lower when mutant rather than wt genomes were used. In situ, cell fractionation studies revealed differences in the interaction of viral particles with host cell structures. The infectivity of mutants was affected not only by loss of the myristyl group on VP2, but also, and to a greater extent, by alterations of the N-terminal amino acid composition.

Promiscuous expression of Epstein-Barr virus genes in Burkitt's lymphoma from the central African country Malawi

Primary BL in Malawian children has a very high frequency association, approaching 100%, with the human herpesvirus EBV. A detailed study carried out on viral gene expression in these tumours, using both fresh material and methanol-fixed FNAs, showed, contrary to prediction, that most belong to a variant "class II" latency category, with lytic cycle-related genes also expressed. That is, in addition to EBNA1 expression, membrane proteins (LMP1/2A), immediate early (BZLF1) and early (IR2 and IR4) genes, a putative viral oncogene (BARF1), CST (BART) antisense transcripts and the viral bcl-2 homologue are expressed in a high proportion of the BLs. Most, but not all, express the small viral (EBER) RNAs. Two other significant observations were made: (i) in addition to expression of cellular cytokine (IL-10) transcripts in all tumours investigated, the normally silent viral IL-10 homologue was expressed in some tumours; (ii) whereas EBNA1 expression from its restricted Qp promoter was generally observed, the nonrestricted Cp/Wp promoter was also active in some tumours. Viral gene expression in the Malawian [endemic (e)] BLs appears to be more promiscuous than predicted from other studies, but expression accords with the cytopathologic picture of eBLs as a rapidly proliferating cell population accompanied by considerable necrosis, and a clinically diverse disease. A small-scale study of relapse Malawian BLs revealed a different picture of viral association, more akin to systemic BL than eBL, where EBV appears to be absent or present only at very low levels. The significance of these findings is considered.

Immunization of T-cell deficient mice against polyomavirus infection using viral pseudocapsids or temperature sensitive mutants

A murine experimental model system aimed at developing potential vaccines to papovavirus infection in immunosuppressed individuals was explored. A VP1-pseudocapsid based on the major capsid protein of the murine polyomavirus A2 strain and a mutant, M17-pseudocapsid as well as four temperature sensitive (ts)-mutants were used as immunogens. T-cells deficient CD4-/-8-/- mice were immunized four times with each immunogen and then together with non-immunized control mice challenged with polyomavirus. In contrast to all control mice, only half of the immunized mice exhibited presence of polyoma DNA when assayed by PCR. The results indicate that pseudocapsids and ts-mutant immunization may potentially protect mice with an impaired T-cell function from polyomavirus infection.

Hypothesis: a novel route for immortalization of epithelial cells by Epstein-Barr virus

Transfection of primate tissue explants with a specific sub-fragment (p31) of EBV DNA results in epithelial (but no other) cells proliferating indefinitely (becoming 'immortalized') without evidence of a 'growth crisis'. Molecular evidence supports integration of viral information into the host chromosome, and an early genotypic alteration involving specific amplification of a sub-component (IR1) of p31 DNA, followed by apparent loss of viral DNA from chromosomes, consistent with a 'hit and run' mechanism. However, analysis at the individual cell level during long-term culture, by FISH techniques, reveals chromosomal alterations, and viral sequences surviving within double minute (DM) bodies. Changing growth patterns occurring at different stages during propagation (>a year in culture) may be explained by sporadic reintegration of surviving viral DNA into the host chromosome. Notably, throughout culture, telomere lengths in chromosomal DNAs do not alter but rather retain the length observed in the primary cell populations. Introduction of a growth stimulating function of EBV, BARF1, into the immortalized, non-clonable epithelial cells under conditions which permit overexpression, allows clonal populations to be derived. Based on the data, mechanisms of immortalization, in the absence of a proven viral oncogene in p31 DNA, and possible genes involved, are considered.

Immunity against both polyomavirus VP1 and a transgene product induced following intranasal delivery of VP1 pseudocapsid-DNA complexes

Murine polyomavirus VP1 virus-like particles (VLPs) can bind plasmid DNA and transport it into cells both in vitro and in vivo. Long-term expression of the transgene can be observed, suggesting that VP1 VLPs may be used as DNA delivery vehicles for gene therapy. In this study we have analysed the in vitro efficiency of transfection using different DNA/VLP molar ratios and the immune response induced following intranasal administration of these complexes to mice. Our results indicate that in short-term in vitro culture VP1 VLP-DNA complexes appear to be as efficient as DNA alone at transfecting cell monolayers. They also show that VP1 VLPs are very immunogenic, inducing high proliferative cell responses and both serum and mucosal antibodies. Moreover, VP1 VLP-DNA complexes appear to be capable of inducing a stronger immune response to the transgene product (beta-galactosidase) than immunization with DNA only. The results suggest that polyomavirus VP1 VLPs derived from the wild-type sequence may be too immunogenic for repeated use as gene delivery vehicles in gene therapy. However, due to their high immunogenicity and apparent adjuvant properties, they could be modified and used as vaccines either on their own or complexed with DNA.

African Burkitt's lymphoma: a new perspective

High titres of antibody to Epstein-Barr virus (EBV) late genes identify individuals at risk of developing endemic Burkitt's lymphoma (eBL). Viral lytic cycle early and intermediate-early gene expression in BL is associated with a favourable tumour response to chemotherapy. Our study investigated whether serological data identifying antibody expression to zta, a viral function that activates lytic-cycle gene expression, correlate with expression of its gene in tumours, and could have prognostic value. Studies on 10 Malawian patients, with presumed BL on clinical grounds, showed good correlations, suggesting that serum antibody responses might predict treatment responsiveness. The results with 1 patient were particularly striking. When admitted in January 1998, prognosis was poor as he was unable to walk, and had tumour cells, characteristic of stage IV disease, in his bone marrow. Laboratory investigations showed particularly high levels both of serum zta antibodies and of gene expression in his tumour. Follow-up confirmed him alive 6 months after hospital discharge. Among the EBV-positive cases, 2 were ultimately diagnosed as rhabdomyosarcoma, a tumour not previously associated with this virus. The findings from this small study, if confirmed, should have value for future BL management in resource-poor parts of the world.

Virus-like gene transfer into cells mediated by polyoma virus pseudocapsids

Mouse polyoma virus-like particles (or pseudocapsids) are composed solely of recombinant viral coat protein. They can interact with DNA and transport it to cells, resulting in gene expression both in tissue culture and in mice. We demonstrate that DNA transfer in vitro depends on partial packaging of DNA within the virus-like capsid. Cell surface sialic acid residues and an intact microtubule network, required for viral infectivity, are also necessary for pseudocapsid-mediated gene expression from heterologous DNA. Thus, gene delivery in this system requires pathways utilised by polyoma virions, rather than proceeding via the 'nonspecific' endosomal route typical of nonviral systems such as liposomes or calcium phosphate precipitates. Despite the fact that all cells appear to internalise pseudocapsid/DNA complexes, only a proportion show productive gene delivery. Bulk internalisation of complexes is dependent on actin fibres, but not cell surface sialic acid or microtubules, indicating that a second transport pathway exists for pseudocapsids which is nonproductive for gene transfer. The model suggested by these data demonstrates the virus-like properties of the pseudocapsid system, and provides a basis for further development to produce a highly effective gene delivery vehicle. Gene Therapy (2000) 7, 2122-2131.

Persistence and tissue distribution of DNA in normal and immunodeficient mice inoculated with polyomavirus VP1 pseudocapsid complexes or polyomavirus

Introduction of DNA into normal and immunodeficient mice, alone or in complex with VP1 pseudocapsids, has been compared to DNA transfer by viral infection. Similar to natural infection and in contrast to plasmid alone, VP1 pseudocapsids efficiently introduced DNA, which remained for months in normal mice and possibly longer in B- and T-cell-deficient mice.

Pulse oximetry: what's normal in the newborn nursery?

The objective of this study was to establish normal values for pulse oximetry saturation (POS) in healthy newborn infants in the nursery. POS values were obtained from the right (R) hand and R foot at admission, 24 hr, and at discharge. The following information was recorded: postnatal age, activity state, gender, gestational age (GA), birth weight (BW), mode of delivery (MOD), and Apgar scores. Charts were reviewed and follow-up information was obtained for newborns with measurements < or =92%. The study group consisted of a convenience sample of newborn infants, excluding those on supplemental oxygen. Seven hundred eighteen patients were studied: 51% males, 28% cesarean sections, gestational age 39.3+/-1.6 weeks (mean +/- SD), birth weight 3370+/-550 g, and median Apgar scores 8 and 9. The mean POS was 97.2 +/-1.6%, and the median value was 97%. Only postnatal age and activity state affected POS significantly. POS increased 0.17% per 24 hr in the nursery (P = 0. 0001). POS values obtained while the infants were fussy and crying were lower compared to measurements obtained while sleeping [mean decreases: 0.44% while fussy (P = 0.001), 0.98% while crying (P = 0.0001)]. We conclude that newborns in the nursery have an overall mean POS of 97.2% (+/-2 SD: 94-100%). Mean POS values increase to a small degree with increasing postnatal age. Fussy and crying newborns have lower POS values compared to quiet and sleeping newborns. These reference data can be used in the evaluation of POS measurements in symptomatic newborn infants.

Sustained ex vivo and in vivo transfer of a reporter gene using polyoma virus pseudocapsids

Properties of a virus-like artificial gene delivery vehicle, synthesised from recombinant major coat protein of mouse polyoma virus, have been explored. The protein, VP1, self assembles into protein spheres, or 'pseudocapsids, which can bind and transfer DNA into cells in vitro and in vivo. Here, the ability of pseudocapsids to carry DNA into a complex cell system (ex vivo organ cultures of rabbit cornea) or whole animals (mice) has been assessed. Evidence from histochemical and PCR experiments indicate that pseudocapsids stimulate uptake and stable maintenance of marker DNA in nondividing corneal cells as efficiently as a recombinant adenovirus. In athymic and immunocompetent mice, gene transmission occurs with no apparent adverse effects on the animals. In the presence of pseudocapsids, the marker gene was transferred to a range of organs, including the brains of animals, following peripheral or intranasal administration. In immunocompetent mice, significant long-term transcriptional expression (at least 22 weeks) was observed with pseudocapsids, a period significantly longer than observed with DNA alone (several weeks only), again with no obvious adverse effects. This study demonstrates that pseudocapsids from the murine virus, polyoma, constitute a novel transfer agent for long-term gene therapeutic applications in tissues or whole animals.

Structure and coding content of CST (BART) family RNAs of Epstein-Barr virus

CST (BART BARF0) family viral RNAs are expressed in several types of Epstein-Barr virus (EBV) infection, including EBV-associated cancers. Many different spliced forms of these RNAs have been described; here we have clarified the structures of some of the more abundant splicing patterns. We report the first cDNAs representing a full-length CST mRNA from a clone library and further characterize the transcription start. The relative abundance of splicing patterns and genomic analysis of the open reading frames (ORFs) suggest that, in addition to the much studied BARF0 ORF, there may be important products made from some of the upstream ORFs in the CST RNAs. Potential biological functions are identified for two of these. The product of the RPMS1 ORF is shown to be a nuclear protein that can bind to the CBF1 component of Notch signal transduction. RPMS1 can inhibit the transcription activation induced through CBF1 by NotchIC or EBNA-2. The protein product of another CST ORF, A73, is shown to be a cytoplasmic protein which can interact with the cell RACK1 protein. Since RACK1 modulates signaling from protein kinase C and Src tyrosine kinases, the results suggest a possible role for CST products in growth control, perhaps consistent with the abundant transcription of CST RNAs in cancers such as nasopharyngeal carcinoma.

Epstein-Barr virus (EBV) and human disease: facts, opinions and problems

The human herpesvirus, Epstein-Barr virus (EBV), has classically been associated with two pathologies with frequencies approaching 100%. One of these, Burkitt's lymphoma (BL), is of B-cell origin and the other, nasopharyngeal carcinoma (NPC), is a tumour of poorly differentiated epithelial cells. More recently, EBV had been identified with frequencies from a few percent to 100% (in one case) with a variety of other malignancies. These include Hodgkin's disease (HD; where in the west, the frequency of association is about 50%), sino-nasal T-cell lymphomas, lymphoepitheliomas, some sarcomas and breast cancers, other cancers from the head and neck, and lymphomas arising in patients with immune dysfunctions. Since EBV is ubiquitous, with the vast majority of the world's population having met and seroconverted to the virus, the diversity of tumours with which it has now been associated represents a substantial health burden. In a recent IARC monograph, EBV was classified as a group 1 carcinogen. Here, the data on BL and NPC, as they relate to geographical restrictions, viral strain variation, co-factors in disease, and genetic components are reexamined. We raise the question whether in their origins, these tumours genuinely reflect distinct and independent events, as deemed at present, or may represent a response by different cell types to common extracellular factors. For example, a situation in Kenya apparently existed in the past, where both BL and NPC were observed in ethnic Africans with roughly equal frequencies; more recently, in Kenya, EBV has been identified in nearly 100% of the tumours in children with HD. We also consider tumours where the viral association is reportedly of low frequency, and offer explanations for these data, including the possibility of loss of the viral genome once malignancy has been initiated. If this phenomenon occurs as a frequent secondary event, EBV could be an even greater health risk than presently believed.

Expression of two related viral early genes in Epstein-Barr virus-associated tumors

The transcription of two early "leftwardly" expressed genes carrying repetitive sequences, IR2 and IR4, has been studied for Epstein-Barr virus-associated tumors, and for established B-cell lines, using sequence-specific probes generated for this purpose. Whereas the IR4 transcript was identified in every tumor and cell line assessed (except B95-8, with a deletion that removes the gene), expression of the IR2 gene was restricted to B lymphocytes. Though the promoters for both transcripts lie within homologous regions (D(L) and D(R)) in the viral genome, the IR2 promoter appears more tightly regulated. Detailed characterization of the IR4 transcript from a nasopharyngeal carcinoma tumor, C15, identifies a sequence variant of this gene that differs from those reported for B cells; in situ hybridization methods show transcription to be restricted to a subset of cells, with the strongest signals seen adjacent to host stroma. As with B cells in culture (Y. Gao, P. R. Smith, L. Karran, Q. L. Lu, and B. E. Griffin, J. Virol. 71:84-94, 1997), chemical induction enhanced transcriptional expression of the IR4 gene in the C15 tumor, although staining for both the IR4 antigen and that of the virus lytic switch, Zta, gave negative results. In a Burkitt's lymphoma biopsy specimen, however, both proteins were found expressed, notably in the same subset of cells. The data here and elsewhere (Gao et al., J. Virol., 1997) are consistent with a block to intracellular transport of the transcript(s) and suggest nuclear roles for it in tumors, possibly in RNA processing and viral lytic replication. Both roles could be fulfilled in the absence of translation.

Sensitivity of an epstein-barr virus-positive tumor line, Daudi, to alpha interferon correlates with expression of a GC-rich viral transcript

The exquisite sensitivity of the Burkitt's lymphoma (BL)-derived cell line Daudi to type I interferons has not previously been explained. Here we show that expression of an Epstein-Barr virus (EBV) transcript, designated D-HIT (Y. Gao et al., J. Virol. 71:84-94, 1997), correlates with the sensitivity of different Daudi cell isolates (or that of other EBV-carrying cells, where known) to alpha interferon (IFN-alpha). D-HIT, transcribed from a GC-rich repetitive region (IR4) of the viral genome, is highly structured, responding to RNase digestion in a manner akin to double-stranded RNA. Comparing EBV-carrying BL cell lines with differing responses to IFN-alpha, we found the protein levels of the dsRNA-activated kinase, PKR, to be similar, whereas the levels of the autophosphorylated active form of PKR varied in a manner that correlated with endogenous levels of D-HIT expression. In a classical in vitro kinase assay, addition of either poly(I)-poly(C) or an in vitro-transcribed D-HIT homolog stimulated the autophosphorylation activity of PKR from IFN-alpha-treated cells in both EBV-positive and EBV-negative B lymphocytes. By transfection experiments, these RNAs were shown to reduce cell proliferation and to sensitize otherwise relatively insensitive Raji cells to IFN-alpha. The data lead to a model wherein the D-HIT viral RNA also serves as a possible transcriptional activator of IFN-alpha or cellular genes regulated by this cytokine.

Expression of Epstein-Barr virus lytically related genes in African Burkitt's lymphoma: correlation with patient response to therapy

A study on the Epstein-Barr virus (EBV)-associated malignancy (endemic) Burkitt's lymphoma (BL) was initiated on fine-needle-aspiration biopsies from 46 proven BL cases in Malawi. Gene expression that might correlate with patient serology (where high levels of antibodies to lytically related genes are commonly observed) was explored. In two-thirds of the cases, we identified the EBV BZLF1 replication activator intermediate early protein ZEBRA in varying quantities and to varying extents in cells by immuno-cytochemistry. The early lytic-cycle gene transcript BHLF1 was assessed positively by solid-phase hybridisation in over half of the same tumours. Evidence of transcription of these genes was confirmed on a smaller number of surgically removed fresh biopsies by RT-PCR. We asked whether our findings, which are generally counter to the established notion that EBV gene expression in BLs is restricted to the latent function, EBNA1, might offer some explanation for the differential responses to chemotherapy observed among African patients. Where the duration of follow-up was sufficient to assign the cases (37 in number) to one of 3 categories, namely, complete, partial or no response, a significant correlation between expression of the viral function ZEBRA and a positive patient response to treatment was found. Lack of this was associated with poor prognosis. Clinical data and EBV gene expression results support the postulate of subgroups of African BLs, the intermediate early antigen providing a marker of potential use in patient management.

Interactions of heterologous DNA with polyomavirus major structural protein, VP1

'Empty' polyomavirus pseudocapsids, self-assembled from the major structural protein VP1, bind DNA non-specifically and can deliver it into the nuclei of mammalian cells for expression [Forstová et al. (1995) Hum. Gene Ther. 6, 297-3061. Formation of suitable VP1-DNA complexes appears to be the limiting step in this route of gene delivery. Here, the character of VP1-DNA interactions has been studied in detail. Electron microscopy revealed that VP1 pseudocapsids can create in vitro at least two types of interactions with double-stranded DNA: (i) highly stable complexes, requiring free DNA ends, where the DNA is partially encapsidated; and, (ii) weaker interactions of pseudocapsids with internal parts of the DNA chain.

Regulation of cytoskeletal association by a basic amino acid motif in polyoma virus middle T antigen

The subcellular localization of many oncogenic proteins is thought to be important for their function. In the case of the middle T antigen of the DNA tumour virus, polyoma, localization to membranes in a specific manner is essential for its cellular transforming activity. To investigate factors that influence this localization, heterologous membrane targetting sequences were substituted for the middle T antigen transmembrane domain and the properties of the resulting proteins studied. Whereas C-terminal lipid modification derived from the H-ras CaaX box restored oncogenic activity to non-transforming truncated middle T antigen species, N-terminal myristylation from pp60c-src did not. Furthermore, a region, rich in basic amino acids and adjacent to the middle T transmembrane domain, was found to mediate association with detergent-insoluble cytoskeleton. Co-operation between the basic motif and neighbouring membrane binding domains resulted in specific localization of proteins to particular membrane sites, characterized by the association with subcellular structures, likely to be cytoskeletal in nature. These results demonstrate that the cellular localization of MT is regulated by at least two determinants, a transmembrane sequence which confers membrane binding and a basic motif which specifies a particular site within the membrane.

Enhancement by polylysine of transient, but not stable, expression of genes carried into cells by polyoma VP1 pseudocapsids

Gene transfer to provide long-term expression of a therapeutic product, without introducing unwelcome genetic information, is a goal being sought for therapy of both hereditary and acquired diseases. Polyoma virus pseudocapsids, generated from a VP1-expressing recombinant baculovirus, lack viral DNA and have been successfully used to introduce small exogenous genes stably into cells in vitro by a process designated 'pseudofection'; although pseudocapsids protect only about 3 kbp of exogenous DNA, low efficiency transfer of a larger fragment (6.2 kbp) has been observed. Here, expression of a 7.2 kbp plasmid (pCMV beta) encoding the beta-galactosidase gene was assessed to monitor not only efficiency, but the ability of pseudocapsids to transfer larger-sized DNA on their own, or in the presence of the polycation, poly-L-lysine, added to protect nonencapsidated DNA. When complexed to pseudocapsids only, the efficiency of expression of the transferred beta-galactosidase gene (in human or rodent cells), although low, appeared to stabilise with time. In the presence of polylysine, unencapsidated DNA was shown to be protected against DNase activity, but electron microscopy (EM) revealed the formation of large mixed aggregates. The addition of pseudocapsids to these aggregates, and measurement of mobilities of the complexes in CsCl equilibrum centrifugation, indicated that they contained negligible amounts of VP1. For subsequent pseudofection experiments, DNA was complexed first with pseudocapsids, then polylysine was added. The latter did not appear to displace pseudocapsids from DNA, and was found to increase the efficiency of short-term expression both in in vitro and in vivo experiments. Gene expression, analysed histochemically or by the polymerase chain reaction, revealed transcriptional activity of the input gene, with expression first diminishing, then stabilising over time. The presence of pseudocapsids, in complexes with DNA with or without polylysine, allowed for stable and persistent gene expression.

Immunization of common marmosets with Epstein-Barr virus (EBV) envelope glycoprotein gp340: effect on viral shedding following EBV challenge

Epstein-Barr virus (EBV), the cause of infectious mononucleosis, is involved in the pathogenesis of several human cancers, the highest frequency of association being found in undifferentiated nasopharyngeal carcinoma and endemic Burkitt's lymphoma. The development of animal models in which potential vaccines can be tested is important. EBV infection of the common marmoset, using the M81 strain originally derived from a patient with nasopharyngeal carcinoma, induces a carrier state in this animal. Persistent infection is characterized by the production of antibodies to viral antigens, and the secretion of EBV DNA into buccal fluids. Following immunization with envelope glycoprotein gp340 derived from a bovine papilloma virus expression vector, prior to EBV infection, viral DNA was detected significantly less frequently in the buccal fluids of immunized, than of nonimmunized, infected animals, indicating that although the carrier state had not been abolished, it had been altered. A reduction in virus load was also observed when offspring of seronegative, and on occasion seropositive, parents were immunized neonatally, before EBV challenge.

Epstein-Barr virus expression within keratinizing nasopharyngeal carcinoma

Three stages of maturation can be seen in keratinizing nasopharyngeal carcinomas. These stages are similar morphologically to basal cells, intermediate and superficial squamous cells seen in normal squamous epithelium. Taking advantage of such a diverse tumour cell population, 10 keratinizing nasopharyngeal carcinoma (NPC) were examined by in situ hybridization for the presence of latent Epstein-Barr Virus (EBV) using EBV encoded RNAs (EBERs) and by immunohistology for the presence of EBV early antigen-diffuse (EA-D) and the 350/220 kd membrane glycoprotein of the EBV. The basal cell-like tumour cells are mainly infected latently with the virus; viral replication was found in isolated intermediate squamous cells, whilst superficial squamous cells are largely depleted of all the viral markers. We used a control series of nonkeratinizing nasopharyngeal carcinomas composed of undifferentiated and poorly differentiated tumour cells and EBV latency was present in these tumours. Viral replication was detected by RT-PCR, in the undifferentiated tumours but viral replication was not seen by immunohistology. The possible relationship between EBV life cycle in these tumours and tumour cell differentiation is discussed in the light of these findings.

Epstein-Barr virus infections and their association with human malignancies: some key questions

Epstein-Barr virus (EBV) expresses genes that stimulate cells to divide in culture. This property, coupled with the close association of the virus with numerous malignancies, has prompted its designation as a human DNA tumour virus. Before human herpesvirus 8 (HHV-8, alternatively KS virus) was discovered, EBV was unique in this property among the human herpesviruses. EBV infection has been best characterised in terms of gene expression in B lymphocytes and epithelium, which represent cells found in the best known of the associated malignancies, Burkitt's lymphoma and poorly differentiated nasopharyngeal carcinoma. The bulk of evidence supports B cells as the primary EBV reservoir with the viral route into other cell types remaining ill-defined. Molecular studies on gene expression in the associated tumours suggest that EBV encodes a number of functions associated with cell growth; whether they are expressed or silent may largely be under control of the host cell. Many questions partly addressed here remain with regard to this virus, two critical ones relating to the mechanisms by which viral gene products escape T-cell recognition - relevant from the fact that gene expression is not tightly restricted to nonimmunogenic functions in tumours - and whether EBV can invoke cell growth in a manner not requiring its continued presence. The latter seems a plausible hypothesis and is of particular importance with regard to identifying and understanding pathologies associated with EBV, as viral transcriptional transactivators may on initial infection permanently perturb cell regulation.

Serological diagnosis of nasopharyngeal carcinoma by enzyme linked immunosorbent assay: optimization, standardization and diagnostic criteria

OBJECTIVES

To produce an enzyme linked immunosorbent assay (ELISA) to detect antibodies against Epstein Barr virus (EBV) specified nuclear antigen 1 (EBNA 1) and the 18 kD EBV matrix protein, and to determine and optimize its sensitivity and specificity for the diagnosis of nasopharyngeal carcinoma (NPC).

METHODS

We used a combination of highly purified glutathione transferase fusion proteins of the 40 kD carboxy domain of EBNA1 and the 18 kD EBV matrix protein for coating ELISA plates. In three separate studies, we tested for IgA antibodies in serum specimens from 28 EBV seronegative donors, 284 EBV seropositive donors and 160 newly diagnosed NPC patients. By comparing the sensitivity and specificity of diagnosis obtained for different cutoff values, we derived several quantitative parameters to evaluate assay performance, establish objective diagnostic criteria which optimize the intrinsic diagnostic capability of the assay and assess the significance of individual test results, respectively. Optimum cutoff optical density (OD) is defined as the cutoff OD where sensitivity of the assay equals its specificity, and resolution of the assay is indicated by the value of sensitivity (or specificity) determined at the optimum cutoff OD. Diagnosis of NPC was achieved by setting a cutoff zone at +/- 20% of this value.

RESULTS

All the EBV seronegative donors tested were not reactive, and most of the EBV seropositive donors were weakly reactive, while the majority of NPC patients were moderately or strongly reactive. While the assay was thus shown to be specific for EBV, there was an overlap in the level of these serum antibodies between few individuals of the two latter groups. It was shown that the assay performed equally well in two separate studies conducted under different testing conditions and using different collections of sera in that assay resolution determined on these occasions were 86% and 87% respectively. Diagnosis of NPC can be achieved at the same expected sensitivity of 89% and 83% determined at the lower and upper limits of the cutoff zones, with the corresponding values of specificity being 78% and 91%. It was further shown in the third study that resolution of the assay can be increased to 90% using an assay produced with a higher concentration of the same antigens, and that diagnosis of NPC can be achieved at a higher sensitivity ranging between 86% and 95% at a corresponding specificity of 93% and 86%.

CONCLUSIONS

After optimization and standardization, the ELISA can achieve a sensitivity ranging from 86% to 95%, with corresponding specificities of 93% and 86% respectively for the diagnosis of NPC.

Induction of an exceptionally high-level, nontranslated, Epstein-Barr virus-encoded polyadenylated transcript in the Burkitt's lymphoma line Daudi

An Epstein-Barr virus transcript (designated D-HIT [Daudi high-level-inducible transcript]), constitutively expressed at low levels in the Burkitt's lymphoma (BL)-derived cell line Daudi, can be induced with tetradecanoylphorbol acetate or n-butyrate or, in combination, to about 1% of the levels of high-molecular-weight RNAs in cells. The transcript can also be induced in some other EBV-positive BL-derived cells but to a much lesser extent, particularly in lines that can give rise to productive infection. D-HIT is viral in origin and is composed largely of repetitive sequence. It is polyadenylated but mainly nuclear in location and is highly structured, sensitive only to double-strand-specific RNase. It is endogenously expressed in interferon-sensitive Daudi strains but not in an insensitive strain, Daudi 100K. D-HIT contains a part of a viral open reading frame (designated LF3, and deleted in the prototype B95-8 strain), using an internal polyadenylation (AAUAAA) sequence as a signal to specify processing of its 3' end. In Daudi cells, the promoter contains a putative hinge structure, as found in some interferon-inducible genes and c-myc. Since D-HIT lies adjacent to, probably even encompassing, one of the two viral lytic origins (D(R)) of replication, it may have a role in the regulation of DNA replication. Alternatively, or in addition via its double-stranded structure, D-HIT may play a regulatory role in interferon pathways. Its promoter could be of value for studying expression in constructions containing heterologous genes.

Tissue distribution of Epstein-Barr virus genotypes

The genome of naturally occurring Epstein-Barr virus contains either two or three copies of a 29-bp tandem repeat sequence in the first intron of the BZLF gene. These genotypes differ markedly in their distribution between blood and epithelial tissues, presumably because they have adapted to separate life cycles in these sites. The genotype prevalent in the blood also appears to be better able to transform B lymphocytes.

A cluster of atypical skin lesions in well-baby nurseries and a neonatal intensive care unit

We describe an epidemiologic investigation that elucidated the cause of vesicular and bullous skin lesions of the hands and feet that occurred in three otherwise well neonates during a 24-hour period. The investigation encompassed two well-baby nurseries of 28 and 17 beds and one level III neonatal intensive care unit (NICU) of 31 beds located in a 440-bed university-affiliated community hospital. Work-up for infectious causes of the skin lesions in the initial three cases had negative results. Expanded case surveillance disclosed seven additional cases that had occurred within the previous 2 weeks in the NICU. Analysis of risk factors focused attention on the insertion technique for peripheral intravenous catheters. This led to the discovery of a defective transillumination device, the tip of which reached a temperature of 88 degrees C within 20 seconds, causing thermal burns. The cause of the malfunction was the failure to install an infrared filter during the manufacture of the device. No additional cases were observed after the defective unit was removed from service. In summary, a defective transilluminating device caused a cluster of thermal burns in a newborn nursery and NICU. Epidemiologic investigation of the cluster allowed the investigators to focus on techniques of intravenous catheter insertion, which thus led to the identification of the cause of the injuries. With the increasing emphasis on health outcomes measurement, hospital epidemiologists will likely have an expanding role in investigating clusters of noninfectious adverse events.

Alterations in the structure of the EBV nuclear antigen, EBNA1, in epithelial cell tumours

The EBV nuclear antigen, EBNA1, is the only viral protein consistently expressed in all virus-infected cells. It is required in trans for viral replication, maintenance of EBV extrachromosomal episomes, and transcriptional transactivation in latently-infected B-cells. It binds RNA suggestive of a regulatory role in post-transcriptional events and in transgenic mice, it is tumorigenic. In RNase protection studies relating to the EBV-associated tumour, nasopharyngeal carcinoma (NPC), we show that a C-terminal EBNA1 RNA probe from the prototype B95-8 marmoset strain can protect its own mRNA from enzymatic digestion, but does not fully protect EBNA1 mRNA from NPC cells. This finding is consistent with changes in the coding region for the antigen. We thus determined the sequences of EBNA1 genes derived from an NPC xenograft and numerous patient biopsies and identified a number of mutations in the gene in these human cells, relative to B95-8. Many of the nucleotide changes would lead to non-conservative amino acid alterations in apparently functionally significant regions of the protein. We show that although some of the mutations lie in regions designated as critical to DNA binding, they have negligible effect on this property of EBNA1. The basic regions in EBNA1 that may bind to RNA, at least in vitro, are exempt from mutation. Thus, unless the alterations are 'silent', which for such a critical viral function seems unlikely, they may relate to as yet unmapped viral activities, such as a role in tumorigenesis and the ability of EBNA1 to evade the cellular immune system, or be associated with the ability of the antigen to regulate gene transcription.

Polyoma virus pseudocapsids as efficient carriers of heterologous DNA into mammalian cells

Polyoma virus VP1 pseudocapsids, generated from a recombinant baculovirus, have been successfully used to transfer exogenous DNA stably into rodent (rat-2) cells. To evaluate the efficiency and biological usefulness of this route for introducing heterologous DNA into cells, the gene for a transforming deletion mutant of the middle T antigen of polyoma virus, dl8 MT, was used initially. Whereas the amount of DNA packaged together with pseudocapsids was found to be variable (2-30%), even at low efficiency its transfer as biologically functional information was high. The dl8 MT gene was stably transferred and integrated in low copy numbers into the host chromosome. Transformed cell lines (derived from single foci) were shown to produce high levels of the corresponding mutant protein, which was active in an in vitro protein kinase assay. In comparisons with the calcium phosphate DNA coprecipitation procedure (or lipofectin route), the VP1 pseudocapsid approach was shown to have many advantages in terms of maintenance of DNA fidelity and increased efficiency of gene expression. This system was also assessed for its ability to transfer into and express the chloramphenicol acetyl transferase (CAT) gene in a human liver cell line. Here again, the assay for functional CAT expression showed the pseudocapsid transfer procedure to compare favorably with lipofectin transfer. In another transient assay, a low-level endogenously expressed gene, p43, was complexed with pseudocapsids and transferred into human embryo lung fibroblasts, thereby increasing the expression levels. The ease of production of VP1 pseudocapsids, coupled with their efficient transfer of biologically useful information, should make this route of gene delivery an attractive proposition for further exploration with regard to gene therapy.

Expression of a B-cell marker, CD24, on nasopharyngeal carcinoma cells

Random sequencing of clones from a lambda gt10 cDNA library, made from mRNA expressed in an Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) has revealed the gene transcript of human CD24. The CD24 antigen, a glycosylphosphatidylinositol-anchored cell surface molecule, has been identified as a B-cell marker that is lost during cell maturation. We show here that it is expressed on 3 NPC xenografts, previously defined as consisting of poorly differentiated epithelial cells, and on an NPC biopsy. In the case of the former, the level of expression of CD24 corresponds to the EBV load. A B-lymphoblastoid cell line carrying the same EBV genome as one of the tumours, C15, and an EBV-negative Burkitt's lymphoma cell line do not display the antigen, but epithelial-like cells of a laryngeal tumour cell line (Hep2) do express it. Our data suggest that CD24 may be a marker of cell differentiation not only for B cells but also for epithelial cells and may have an indirect association with EBV gene expression.

Epstein-Barr virus in epithelial cell tumors: a breast cancer study

The human herpes virus Epstein-Barr (EBV) is clearly associated with African Burkitt's lymphoma and the undifferentiated from of nasopharyngeal carcinoma, although its role in oncogenesis is still poorly defined. Recently EBV has been implicated in other types of lymphomas, as well as in some nonlymphomatous neoplastic processes. Its possible association with human breast cancer has been investigated here. DNA from 91 cases of breast carcinoma and blood samples from the same patients were amplified with the PCR over a region in the EBV BamHIW major repeat sequence following a single-step amplification protocol. Nineteen samples (21%) were found to be positive; 10 samples of blood (only 3 of them from patients with EBV-positive tumors) were found by the adopted protocol to contain EBV DNA. Another series of PCR amplifications using primers covering a unique (nonreiterated) fragment in BamHIC encoding the EBERs (two short nonpolyadenylated RNAs generally highly expressed in cells latently infected with EBV) confirmed these findings. A good correlation between the two sets of experiments was observed, and only five differences in results were obtained on samples tested. In situ hybridization was carried out using BamHIW biotinylated DNA probes or EBER-1 digoxigenin-labeled riboprobes with the aim of confirming as well as localizing the signal to the epithelial cell. Twelve sections (63%) among the PCR-positive samples were found positive by in situ hybridization with the DNA probe, and six (31.5%) sections were found with the RNA probe. Twenty-one samples from benign breast tumors or normal breast tissue were used as controls for PCR amplification in this study, none of which was found positive. This is the first known report showing positive results for EBV in breast cancer. No statistical association was found in these studies between the presence of EBV and the histological type of the tumor, however. Its role therefore remains for the moment unknown, as well as does the significance of the association of EBV with only a subset of the cases.

Correlation between cytopathological results and in situ hybridisation on needle aspiration biopsies of suspected African Burkitt's lymphomas

Burkitt's lymphoma (BL) is a very high-incidence malignancy in sub-Saharan Africa, where it targets mainly young children. This lymphoma is closely associated with Epstein-Barr virus (EBV). Diagnosis of BL relies on clinical presentation as well as histological results obtained from biopsies. In this report, 66 new patients from Malawi (one of the southernmost African countries with high-incidence BL), suspected on clinical grounds to present with BL, had fine needle aspiration biopsies taken, smeared on slides and used for May-Grünwald Giemsa staining. Duplicate slides were independently assessed for EBV presence and expression by DNA-DNA and/or RNA-RNA in situ hybridisation (ISH), using respectively the repetitive viral BamHIW DNA fragment in a biotinylated probe and the small EBV-encoded RNA EBER I in a digoxigenin-labelled riboprobe. There was very good correlation between the various techniques in the diagnosis of the lymphomas, showing 67% of clinically suspect cases to be BL. Our report, presenting data on BL in Malawi, illustrates the usefulness of a simple aspiration biopsy in the diagnosis of this malignancy by Giemsa staining and also in both types of ISH.

EBNA-1, the major nuclear antigen of Epstein-Barr virus, resembles ‘RGG’ RNA binding proteins

Nuclear antigen 1 (EBNA-1) is one of the key functions of the oncogenic DNA virus, Epstein-Barr virus (EBV), and is the only viral protein consistently expressed in EBV-associated malignancies. EBNA-1 binds in a site-specific manner to the viral DNA and is essential for viral replication, as well as for maintaining the genome as an extrachromosomal episome within infected cells. EBNA-1 is not recognized by the cellular immune system. Here we demonstrate that, in addition to its known DNA binding properties, EBNA-1 can also act as a strong RNA binding protein, interacting with diverse substrates in vitro, including the EBV-encoded RNA polymerase III transcript EBER1 and the HIV-encoded transactivation response (TAR) element. We also show that EBNA-1 can bind exon sequences derived from its own RNA expressed from the Fp promoter, as found in Burkitt's lymphoma-related cells and in nasopharyngeal carcinomas. EBNA-1 has been identified as a component in an RNA complex; moreover, an anti-EBNA-1 antibody 1H4-1, that does not inhibit DNA binding, blocks binding to RNA. Arginine/glycine-containing (so-called 'RGG') motifs have been found in an increasing number of proteins that interact with RNA. The EBV antigen contains three potential 'RGG' motifs located around an internal glycine/alanine-rich repetitive sequence in the protein, and outside the region of EBNA-1 mapped previously as essential for viral DNA replication and other functionally defined properties. These motifs could be involved in the observed binding between EBNA-1 and RNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell fractionation in non-ionic detergent distinguishes sub-populations of polyoma virus middle T antigen and reveals a novel form

The transforming function of polyoma virus, middle T antigen (MT), interacts with several cellular enzymes, essential to its oncogenic activity. We have used cell fractionation to study the various MT/cellular protein complexes. We demonstrate that MT can be separated into three sub-species, dependent upon extraction in two buffers that we designate A and B: Antigen extracted from whole cells by both buffers (called MT1) is associated with most of the phosphorylated phosphatidyl-inositol kinase 85 kD subunit, pp85, and protein phosphatase 2A. Antigen (MT2), associated with the greater portion of pp60c-src, is extracted by buffer B, but not buffer A. A third population (MT3), resistant to extraction by either buffer, is not detectably associated with protein phosphatase 2A or pp85. It is, however, associated with a low level kinase activity. The interaction between pp60c-src and MT appears to influence the formation of both MT2 and MT3. MT2 fractionates with the cellular microtubule network, but does not appear to be directly associated with it. MT3, a previously undescribed population, comprises about one third of MT in wild type antigen-containing cells. It is missing in mutants incapable of interacting with pp60c-src, but exists in the absence of an interaction with pp85. We suggest that MT3 may be an intermediate in, or product of, one of the MT/pp60c-src signalling pathways, distinct from that involving pp85.

Are plant factors a missing link in the evolution of endemic Burkitt's lymphoma?

Burkitt's lymphoma, an Epstein-Barr virus (EBV)-associated non-Hodgkin's malignant lymphoma is endemic in an area of Africa known as the Lymphoma Belt. This zone is demarcated by climatic requirements of temperature and rainfall. EBV-activating plant factors are among several co-factors which have been proposed for the development of epidemic Burkitt's Lymphoma (eBL). The distribution of Euphorbia tirucalli, a plant which possesses EBV-activating substances and can induce the characteristic 8:14 translocation of eBL in EBV-infected lymphoblastic cell lines in vitro, conforms closely to the climatic requirements of the Lymphoma. This plant, other EBV-activating plants and plants of unknown EBV-activating status with medicinal uses, are found significantly more often at the homes of eBL patients in Malawi than in those of controls. The possible role of these plant factors in the pathogenesis of eBL and their routes of bodily access are discussed. It is postulated that the associations described in this paper provide support for the theory that EBV-activating plants are co-factors involved in the pathogenesis of some cases of eBL.

Complex nature of the major viral polyadenylated transcripts in Epstein-Barr virus-associated tumors

The most abundant polyadenylated viral transcripts in the Epstein-Barr virus (EBV)-associated tumor nasopharyngeal carcinoma are a family (apparent sizes, 4.8, 5.2, 6.2, and 7.0 kb) of highly spliced cytoplasmic RNAs expressed from the BamHI-I and -A regions of the viral genome in an antisense direction with respect to several viral lytic functions encoded within the same region and concerned with the lytic cycle of the virus. We have called these complementary-strand transcripts. They are also expressed in B cells, including Burkitt's lymphoma and EBV-immortalized marmoset cell lines, and tumors generated in cottontop tamarins in response to EBV infection, but at a lower level. The complete structure of the major 4.8-kb RNAs (seven or eight exons) was determined in this study; the larger, but related, transcripts appear to be produced by differential splicing. The transcriptional promoter for the major complementary-strand transcripts, located in BamHI-I, contains several well-characterized transcriptional control elements (E2A, SP1, and AP1) and is functionally active in both B lymphocytes and epithelial cells. It appears to be a bifunctional viral promoter, as it also contains the initiation codon for a gene (BILF2) that encodes a glycoprotein that is expressed off the other strand. Splicing events create a number of small AUG-initiated open reading frames, one of which has homology to functionally significant regions of the EBV-encoded nuclear antigen 2 and to E2 (in papillomavirus). The complex nature of these transcripts and their potential role in the virus association with malignancy are considered.

Cooperation of structural proteins during late events in the life cycle of polyomavirus

The polyomavirus minor late capsid antigen, VP2, is myristylated on its N-terminal glycine, this modification being required for efficient infection of mouse cells. To study further the functions of this antigen, as well as those of the other minor late antigen, VP3, recombinant baculoviruses carrying genes for VP1, VP2, and VP3 have been constructed and the corresponding proteins have been synthesized in insect cells. A monoclonal antibody recognizing VP1, alpha-PyVP1-A, and two monoclonal antibodies against the common region of VP2 and VP3, alpha-PyVP2/3-A and alpha-PyVP2/3-B, have been generated. Reactions of antibodies with antigens were characterized by indirect immunofluorescence, immunoprecipitation, and immunoblot analysis. Immunofluorescent staining of mouse cells infected with polyomavirus showed all antigens to be localized in nuclei. When the late polyomavirus proteins were expressed separately in insect cells, however, only VP1 was efficiently transported into the nucleus; VP2 was localized discretely around the outside of the nucleus, and VP3 exhibited a diffused staining pattern in the cytoplasm. Coexpression of VP2, or VP3, with VP1 restored nuclear localization. Immunoprecipitation of infected mouse cells with either anti-VP1 or anti-VP2/3 antibodies precipitated complexes containing all three species, consistent with the notion that VP1 is necessary for efficient transport of VP2 and VP3 into the nucleus. Purified empty capsid-like particles, formed in nuclei of insect cells coinfected with all three baculoviruses, contained VP2 and VP3 proteins in amounts comparable to those found in empty capsids purified from mouse cells infected with wild-type polyomavirus. Two-dimensional gel analysis of VP1 species revealed that coexpression with VP2 affects posttranslational modification of VP1.