A cytomegalovirus-encoded mitochondria-localized inhibitor of apoptosis structurally unrelated to Bcl-2.

Human cytomegalovirus (CMV), a herpesvirus that causes congenital disease and opportunistic infections in immunocompromised individuals, encodes functions that facilitate efficient viral propagation by altering host cell behavior. Here we show that CMV blocks apoptosis mediated by death receptors and encodes a mitochondria-localized inhibitor of apoptosis, denoted vMIA, capable of suppressing apoptosis induced by diverse stimuli. vMIA, a product of the viral UL37 gene, inhibits Fas-mediated apoptosis at a point downstream of caspase-8 activation and Bid cleavage but upstream of cytochrome c release, while residing in mitochondria and associating with adenine nucleotide translocator. These functional properties resemble those ascribed to Bcl-2; however, the absence of sequence similarity to Bcl-2 or any other known cell death suppressors suggests that vMIA defines a previously undescribed class of anti-apoptotic proteins.

The Epstein-Barr virus oncoprotein latent membrane protein 1 engages the tumor necrosis factor receptor-associated proteins TRADD and receptor-interacting protein (RIP) but does not induce apoptosis or require RIP for NF-kappaB activation.

A site in the Epstein-Barr virus (EBV) transforming protein LMP1 that constitutively associates with the tumor necrosis factor receptor 1 (TNFR1)-associated death domain protein TRADD to mediate NF-kappaB and c-Jun N-terminal kinase activation is critical for long-term lymphoblastoid cell proliferation. We now find that LMP1 signaling through TRADD differs from TNFR1 signaling through TRADD. LMP1 needs only 11 amino acids to activate NF-kappaB or synergize with TRADD in NF-kappaB activation, while TNFR1 requires approximately 70 residues. Further, LMP1 does not require TRADD residues 294 to 312 for NF-kappaB activation, while TNFR1 requires TRADD residues 296 to 302. LMP1 is partially blocked for NF-kappaB activation by a TRADD mutant consisting of residues 122 to 293. Unlike TNFR1, LMP1 can interact directly with receptor-interacting protein (RIP) and stably associates with RIP in EBV-transformed lymphoblastoid cell lines. Surprisingly, LMP1 does not require RIP for NF-kappaB activation. Despite constitutive association with TRADD or RIP, LMP1 does not induce apoptosis in EBV-negative Burkitt lymphoma or human embryonic kidney 293 cells. These results add a different perspective to the molecular interactions through which LMP1, TRADD, and RIP participate in B-lymphocyte activation and growth.

The Epstein-Barr virus oncogene product latent membrane protein 1 engages the tumor necrosis factor receptor-associated death domain protein to mediate B lymphocyte growth transformation and activate NF-kappaB.

The Epstein-Barr virus latent membrane protein 1 (LMP1) is essential for the transformation of B lymphocytes into lymphoblastoid cell lines. Previous data are consistent with a model that LMP1 is a constitutively activated receptor that transduces signals for transformation through its carboxyl-terminal cytoplasmic tail. One transformation effector site (TES1), located within the membrane proximal 45 residues of the cytoplasmic tail, constitutively engages tumor necrosis factor receptor-associated factors. Signals from TES1 are sufficient to drive initial proliferation of infected resting B lymphocytes, but most lymphoblastoid cells infected with a virus that does not express the 155 residues beyond TES1 fail to grow as long-term cell lines. We now find that mutating two tyrosines to an isoleucine at the carboxyl end of the cytoplasmic tail cripples the ability of EBV to cause lymphoblastoid cell outgrowth, thereby marking a second transformation effector site, TES2. A yeast two-hybrid screen identified TES2 interacting proteins, including the tumor necrosis factor receptor-associated death domain protein (TRADD). TRADD was the only protein that interacted with wild-type TES2 and not with isoleucine-mutated TES2. TRADD associated with wild-type LMP1 but not with isoleucine-mutated LMP1 in mammalian cells, and TRADD constitutively associated with LMP1 in EBV-transformed cells. In transfection assays, TRADD and TES2 synergistically mediated high-level NF-kappaB activation. These results indicate that LMP1 appropriates TRADD to enable efficient long-term lymphoblastoid cell outgrowth. High-level NF-kappaB activation also appears to be a critical component of long-term outgrowth.

The Epstein-Barr virus LMP1 amino acid sequence that engages tumor necrosis factor receptor associated factors is critical for primary B lymphocyte growth transformation.

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) is essential for transforming primary B lymphocytes into lymphoblastoid cell lines. EBV recombinants with LMP1 genes truncated after the proximal 45 codons of the LMP1 carboxyl terminus are adequate for transformation. The proximal 45 residues include a domain that engages the tumor necrosis factor receptor associated factors (TRAFs). We investigated the importance of the TRAF binding domain by assaying the transforming ability of recombinant EBV genomes with a deletion of LMP1 codons 185-211. This mutation eliminates TRAF association in yeast and in lymphoblasts but does not affect LMP1 stability or localization. Specifically mutated recombinant EBV genomes were generated by transfecting P3HR-1 cells with overlapping EBV cosmids. Infection of primary B lymphocytes resulted in cell lines that were coinfected with an LMP1 delta185-211 EBV recombinant and P3HR-1 EBV, which has a wild-type LMP1 gene but is transformation defective due to another deletion. Despite the equimolar mixture of wild-type and mutated LMP1 genes in virus preparations from five coinfected cell lines, only the wild-type LMP1 gene was found in 412 cell lines obtained after transformation of primary B lymphocytes. No transformed cell line had only the LMP1 delta185-211 gene. An EBV recombinant with a Flag-tagged LMP1 gene passaged in parallel segregated from the coinfecting P3HR-1. These data indicate that the LMP1 TRAF binding domain is critical for primary B lymphocyte growth transformation.

Epstein-Barr virus vectors for gene delivery to B lymphocytes.

Basic research in Epstein-Barr virus (EBV) molecular genetics has provided means to maintain episomes in human cells, to efficiently deliver episomes with up to 150 kbp of heterologous DNA to human B lymphocytes, and to immortalize human B lymphocytes with EBV recombinants that can maintain up to 120 kbp of heterologous DNA. Episome maintenance requires an EBV nuclear protein, EBNA1, whereas immortalization of cells with EBV recombinants requires EBNA1, EBNA2, EBNA3A, EBNA3C, EBNALP, and LMP1. EBV-derived vectors are useful for experimental genetic reconstitution in B lymphocytes, a cell type frequently used in establishing repositories of human genetic deficiencies. The ability of EBV-infected cells to establish a balanced state of persistence in normal humans raises the possibility that cells infected with EBV recombinants could be useful for genetic reconstitution, in vivo.

Epstein-Barr virus types 1 and 2 have nearly identical LMP-1 transforming genes.

Although variation in the gene encoding the Epstein-Barr virus (EBV) nuclear protein 2 accounts for much of the difference in the transforming activities of the two EBV strain types, divergence in the principal lymphocyte growth-altering gene, LMP-1, has not been previously evaluated. We have now determined the nucleotide sequence of the LMP-1 gene of a type 2 isolate of EBV, AG876. Surprisingly, the AG876 LMP-1 protein is 93% identical to the prototype type 1 EBV strain B95-8, and this is well within the range of variability previously noted among type 1 EBV LMP-1 genes.

Epstein-Barr virus recombinant molecular genetic analysis of the LMP1 amino-terminal cytoplasmic domain reveals a probable structural role, with no component essential for primary B-lymphocyte growth transformation.

Previous recombinant Epstein-Barr virus molecular genetic experiments with specifically mutated LMP1 genes indicate that LMP1 is essential for primary B-lymphocyte growth transformation and that the amino-terminal cytoplasmic and first transmembrane domains are together an important mediator of transformation. EBV recombinants with specific deletions in the amino-terminal cytoplasmic domain have now been constructed and tested for the ability to growth transform primary B lymphocytes into lymphoblastoid cell lines. Surprisingly, deletion of DNA encoding EHDLER or GPPLSSS from the full LMP1 amino-terminal cytoplasmic domain (MEHDLERGPPGPRRPPRGPPLSSS) had no discernible effect on primary B-lymphocyte transformation. These two motifs distinguish the LMP1 amino-terminal cytoplasmic domain from other arginine-rich membrane proximal sequences that anchor hydrophobic transmembrane domains. Two deletions which included the ERGPPGPRRPPR motif adversely affected but did not prevent transformation. This arginine- and proline-rich sequence is probably important in anchoring the first transmembrane domain in the plasma membrane, since these mutated LMP1s had altered stability and cell membrane localization. The finding that overlapping deletions of the entire amino-terminal cytoplasmic domain do not ablate transformation is most consistent with a model postulating that the transmembrane and carboxyl-terminal cytoplasmic domains are the likely biochemical effectors of transformation.

Antigens and DNA of a chimpanzee agent related to Epstein-Barr virus.

Biological and biochemical studies of the herpesvirus of chimpanzees previously demonstrated to be antigenically related to human Epstein-Barr virus (EBV) indicated that the agent is similar to EBV in that: (i) leukocyte culture of chimpanzees whose sera contained antibody against EBV capsid antigen could yield long-term lymphoblastoid cell lines (Ch-LCL) with B-cell characteristics; (ii) the DNA of Ch-LCL contained sequences homologous to approximately 35 to 45% of human EBV; (iii) Ch-LCL contained an intranuclear antigen, Ch-NA, that could be identified with some chimpanzee or orangutan serum in anticomplimentary immunofluorescence assays; and (iv) treatment of Ch-LCL with iododeoxyuridine resulted in expression of new antigenic activity that reacted with EA+ but not EA- human sera. Two lines of evidence indicate that the chimpanzee agent, although related to human EBV, is a distinct agent: (i) Ch-NA was antigenically distinct from EBV-rebv infection although it cross-reacts of a limited extent with a minor component of EBNA; and (ii) Ch-LCL are missing 55 to 65% of the DNA sequences of human EBV.

Epstein-Barr virus-specific RNA. I. Analysis of viral RNA in cellular extracts and in the polyribosomal fraction of permissive and nonpermissive lymphoblastoid cell lines.

We analyzed the viral RNA in permissive and nonpermissive Epstein-Barr virus (EBV) Pinfected lymphoblastoid cell lines by observing the kinetics of hybridization of labeled EBV HR-1 DNA with unalabeled RNA extracted from whole cells or from the polyribosomal fraction. The data indicate the following. (i) RNA, homologous to only 3% of the EBV HR-1 DNA, is present in the polyribosomal fraction of the nonpermissive Namalwa and Kurgans cells, suggesting that the function of only a small fraction of the EBV genome is required for the expression of the EBV-related intranuclear antigen and to maintain lymphoblastoid cells in a transformed state. (ii) In general, the extent of the viral DNA sequences transcribed into stable RNA correlates with the extent of phenotypic expression of the EBV geonome. RNA extracted from virus-producing HR-1 cells contains RNA sequences transcribed from at least 45% of the viral DNA, whereas the nonpermissive cell lines contain transcripts homologous to a much smaller proportion of the EBV DNA. (iii) Viral RNA sequences found in the polyribosomal fraction of HR-1 cells arise from almost the same template as the viral RNA sequences in extracts of infractionated HR-1 cells. In contrast, in nonpermissive lymphoblastoid cells, less than 30% of the viral RNA species found in whole-cell extracts can be identified in the polyribosomal fraction. We interpret these observations to indicate that the expression of EBV genetic information is regulated in at least two ways: first, by some mechanism that regulates which DNA sequences give rise to stable RNA; second, through a mechanism whereby certain viral RBA transcripts are selectively excluded from stable association with the polyribosomes.

DNA of Epstein-Barr virus. I. Comparative studies of the DNA of Epstein-Barr virus from HR-1 and B95-8 cells: size, structure, and relatedness.

We have compared the properties of the DNA of Epstein-Barr virus (EBV) purified from HR-1 (EBV HR-1 DNA) and B95-8 (EBV B95-8 DNA) continuous lymphoblast cultures. Our data indicate that (i) the S suc of native EBV DNA relative to T4D DNA is 55S. Using the modified Burgi-Hershey relationship (5), we estimate the molecular weight of native EBV DNA is 101 (plus or minus the molecular weight of native FBV DNA by measurement of the length of 3) times 106. Estimation of the molecule relative to form II PM2 DNA yields a value of 105 (plus or minus 3) times 106. (ii) After alkali denaturation, less than 50% of EBV DNA sediments as a single band in alkaline sucrose gradients in the region expected for DNA of 50 times 406 daltons. (iii) Intact EBV HR-1 and EBV B 95-8 DNAs band at 1.718 g/cm3 and a smaller band (approximately 25% of the DNA) AT 1.720 G/CM3. (IV) EBV HR-1 DNA possesses greater than 97% of the sequences of EBV B95-8 DNA. Hybrid DNA molecules formed between (3H)EBV HR-1 DNA and EBV HR-1 DNA or EBV B95-8 DNA had identical thermal stability. EBV B95-8 DNA lacks approximately 15% of the DNA sequences of EBV HR-1 DNA. We interpret these data to mean that EBV B95-8 is derived from a parental EBV through loss of genetic complexity. This defect may be linked to the ability of EBV B95-8 to "transform" lymphocytes invitro.

Size, composition, and structure of the deoxyribonucleic acid of herpes simplex virus subtypes 1 and 2.

Studies of the size, composition, and structure of the deoxyribonucleic acid (DNA) of the F and G prototypes of herpes simplex virus (HSV) subtypes 1 and 2 (HSV-1 and HSV-2) showed the following. (i) As previously reported by Good-heart et al. HSV-1 and HSV-2 DNA have a buoyant density of 1.726 and 1.728 g/cm(3), corresponding to 67 and 69 guanine +/- cytosine moles per cent, respectively. The difference in guanine plus cytosine content of the DNA species was confirmed by the finding of a 1 C difference in T(m). (ii) The DNA from purified virus on cocentrifugation with T4 DNA in neutral sucrose density gradients sedimented at 55S, corresponding to 99 +/- 5 million daltons in molecular weight. HSV-1 and HSV-2 DNA could not be differentiated with respect to size. (iii) Cosedimentation of alkali-denatured DNA from purified virus with T4 DNA on alkaline sucrose density gradients consistently yielded several bands of single-stranded HSV DNA ranging from fragments 7 x 10(6) daltons to intact strands 48 x 10(6) daltons in molecular weight.

Size and composition of Marek's disease virus deoxyribonucleic acid.

Deoxyribonucleic acid (DNA) extracted from purified nucleocapsids of Marek's disease herpesvirus (MDV) was cosedimented with T4 and with herpes simplex virus (HSV) DNA in neutral sucrose density gradients and with T4 DNA in alkaline sucrose density gradients. These experiments indicated that the intact MDV DNA had a sedimentation constant of 56S corresponding to a molecular weight of 1.2 x 10(8) daltons. In the alkaline gradients, the largest and most prominent band contains a DNA sedimenting at 70S corresponding to 6.0 x 10(7) daltons in molecular weight. The DNA is therefore double-stranded and not cross-linked. Isopycnic sedimentation of the MDV DNA molecules with SPO1, Micrococcus lysodeikticus, and HSV DNA gave a density of 1.705 g/cm(3) corresponding to 46 guanine plus cytosine moles per cent. Lastly, in hybridization tests the DNA hybridized with RNA of infected cells but not with that of uninfected cells supporting the conclusion that it is viral.

Marek's disease herpes virus: a cytomegalovirus.

The DNA of herpes viruses associated with Marek's disease of fowl contains 56-57 moles of guanine and cytosine per 100. The composition of its DNA and lack of infectiousness of cell-free preparations suggest that the herpes virus associated with Marek's disease belongs to the herpes virus group B which contains predominantly cytomegaloviruses.