Epstein-Barr virus (EBV) infection in immunocompetenthumans is predominantly latent and persists for the life of the individual (reviewed in reference 41). Recently, it has been shown that EBV is capable of adopting at least three distinct forms of latency (27). Type III latency is observed upon in vitro infection of B lymphocytes and results in immortalization and continuous proliferation of the infected B cells via the action of a subset of the six EBV nuclear antigens (EBNAs; EBNA1, EBNA2, EBNA3a, EBNA3b, EBNA3c, and EBNA4) and three membrane proteins (LMP1, LMP2a, and LMP2b) expressed in the type III (immortalizing) program. However, in vivo, the type III latency program is likely to be only transiently observed upon initial infection of a naive host, since several of the type III latent antigens elicit a potent cytotoxic T-lymphocyte response resulting in very effective elimination of type III latently infected B cells (reviewed in reference 33).EBV is also capable of entering programs of latency in which the expression of latent antigens is restricted with respect to the type III program. In type I latency, only the EBNA1 protein is expressed (64). It has recently been shown that EBNA1 peptides do not enter the major histocompatibility complex class I antigen processing and presentation pathway (29, 39, 52), and cells which express only EBNA1 are not detected by host cellular immune surveillance mechanisms (63). The type II latency program differs from type I latency only in the expression of variable combinations of LMP1, LMP2a, and LMP2b, in addition to EBNA1. Since the type I latency program was identified, there has been speculation that type I latently infected B lymphocytes represent the lifelong reservoir of virus in immunocompetent, seropositive individuals, and there have recently been several reports which provide evidence that a type I-like form of restricted viral latency does indeed exist in healthy carriers of EBV (6,51,60,85).Investigations into the molecular basis of type III and type I latency have demonstrated that distinct promoters are used to drive transcription of the EBNAs in each latent program. In type III latency, transcription of all six nuclear antigens is initiated from either Wp (during initial infection of resting B cells) or Cp (in cycling B cells), and the long primary transcripts are differentially spliced to generate the mature EBNA transcripts (75, 94; see Fig. 1A for a schematic representation of EBV latent transcription and locations of promoters). Recent investigations have shown that transcription of the EBNA1 gene in type I latency is driven by a promoter designated Qp, which is considerably downstream of the type III latency EBNA gene promoters (57,(70)(71)(72). Qp has an architecture with numerous similarities to eukaryotic housekeeping

Prion and other neurodegenerative diseases are associated with misfolded protein assemblies called amyloid. Research has begun to uncover common mechanisms underlying transmission of amyloids, yet how amyloids form in vivo is still unclear. Here, we take advantage of the yeast prion, [PSI +], to uncover the early steps of amyloid formation in vivo. [PSI +] is the prion form of the Sup35 protein. While [PSI +] formation is quite rare, the prion can be greatly induced by overexpression of the prion domain of the Sup35 protein. This de novo induction of [PSI +] shows the appearance of fluorescent cytoplasmic rings when the prion domain is fused with GFP. Our current work shows that de novo induction is more complex than previously thought. Using 4D live cell imaging, we observed that fluorescent structures are formed by four different pathways to yield [PSI +] cells. Biochemical analysis of de novo induced cultures indicates that newly formed SDS resistant oligomers change in size over time and lysates made from de novo induced cultures are able to convert [psi −] cells to [PSI +] cells. Taken together, our findings suggest that newly formed prion oligomers are infectious.

We conducted experiments to determine if p53 alterations, which are frequent in human breast cancers, were also common in murine mammary tumors. In 13 mammary tumors from 7,12-dimethylbenz[a]anthracene (DMBA)-treated BALB/c mice were immunohistochemically analyzed for overexpression of p53; p53 protein was not detectable. Three of the tumors were established as cell lines in vitro. p53 protein was rarely detected at passage 4 in these lines but was overexpressed by passage 8 in two of them. The p53 nucleotide sequence was shown to be wild type in one primary mammary tumor and in the two p53-overexpressing cell lines. One cell line that overexpressed p53 in vitro was implanted into BALB/c mice. The resulting tumors retained the wild-type p53 nucleotide sequence but no longer expressed detectable levels of p53 protein, suggesting that the overexpression of wild-type p53 was related to in vitro culture conditions. The effect of DMBA on mammary-tumor development was also tested in mice rendered hemizygous for p53. These mice and wild-type littermate controls had no differences in susceptibility to induction of mammary tumors by oral administration of DMBA. Furthermore, Southern blot hybridization detected no gross alterations in the wild-type p53 allele in mammary tumors from the p53-deficient mice. Point mutation of the wild-type p53 allele was also infrequent in the DMBA-induced mammary tumors from hemizygous p53 mice; it occurred in only one of seven tumors. Thus, the p53 gene is apparently not a primary target for genetic alterations in DMBA-induced mammary tumors. Next, we examined mammary tumors derived from D1 and D2 transplantable hyperplastic alveolar nodule (HAN) outgrowths, which rapidly form tumors containing Ha-ras mutations after DMBA treatment. As ras and p53 mutants can cooperate in transformation, we examined whether D1 and D2 HAN outgrowths have p53 mutations. Unlike in the DMBA-induced primary mammary tumors, nuclear p53 accumulation was observed frequently (10 of 14) in tumors that arose from D1 and D2 HAN outgrowths. Direct sequencing of the entire coding region of the p53 cDNA from six D1 and D2 tumors confirmed that the sequence was wild type. Although wild-type p53 was retained in both DMBA-induced mammary tumors and mammary tumors derived from D1 and D2 preneoplastic outgrowths, wild-type p53 overexpression was detected only in D1 and D2 tumors. Therefore, D1 and D2 tumors appear to arise by a pathway in which p53 expression is altered, whereas DMBA induction affects a different pathway that does not require such alteration.

The carboxy-terminal region of major histocompatibility complex class I (MHC I) molecules is required for the rapid internalization mediated by Kaposi's sarcoma-associated herpesvirus (KSHV) proteins K3 and K5. The cytoplasmic tail of MHC I contains highly conserved serine phosphorylation sites that have been implicated in intracellular trafficking. Indeed, in vivo labeling experiments reveal a lack of MHC I phosphorylation in K5-transfected HeLa cells. Phosphorylation of the MHC I tail was restored upon mutation of the PHD/LAP domain of K5. However, deletion and mutation studies of the MHC I tail show that both K3 and K5 are able to downregulate MHC I lacking the conserved phosphorylation site. This result suggests that inhibition of phosphorylation reflects, but does not cause, MHC I internalization. Interestingly, K3 and K5 differ from each other, as well as from human immunodeficiency virus nef, with respect to the minimal MHC I tail sequences required for MHC downregulation. These data support the notion that K3 and K5 downregulate MHC I molecules by a distinct molecular mechanism that is different from other viral immune evasion molecules.