Viruses that establish latent infection must maintain their DNA in the host nucleus through many cellular generations. Here we identify a novel mechanism by which the gammaherpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV) may achieve this persistence in latently infected body cavity-based lymphoma (BCBL) cells. We find that KSHV genomic DNA is associated with host chromosomes and colocalizes with the latency-associated nuclear antigen (LANA). Furthermore, a region at the left end of the KSHV genome binds strongly to LANA and can colocalize to the host chromosomes with LANA. Additionally, we found that LANA associates with histone H1 in KSHV-infected BCBL cells. We propose that this chromosomal association of the KSHV genome is mediated by LANA and involves a tethering mechanism by which viral episomes are linked to host chromatin through simultaneous interaction with host chromosomal proteins including histone H1 and cis-acting KSHV DNA elements. This strategy may be employed by other viruses in establishment of latency in the infected cells.

Like other herpesviruses, Kaposi's sarcoma-associated herpesvirus (KSHV, also designated human herpesvirus 8) can establish a latent infection in the infected host. During latency a small number of genes are expressed. One of those genes encodes latency-associated nuclear antigen (LANA), which is constitutively expressed in cells during latent as well as lytic infection. LANA has previously been shown to be important for the establishment of latent episome maintenance through tethering of the viral genome to the host chromosomes. Under specific conditions, KSHV can undergo lytic replication, with the production of viral progeny. The immediate-early Rta, encoded by open reading frame 50 of KSHV, has been shown to play a critical role in switching from viral latent replication to lytic replication. Overexpression of Rta from a heterologous promoter is sufficient for driving KSHV lytic replication and the production of viral progeny. In the present study, we show that LANA down-modulates Rta's promoter activity in transient reporter assays, thus repressing Rta-mediated transactivation. This results in a decrease in the production of KSHV progeny virions. We also found that LANA interacts physically with Rta both in vivo and in vitro. Taken together, our results demonstrate that LANA can inhibit viral lytic replication by inhibiting expression as well as antagonizing the function of Rta. This suggests that LANA may play a critical role in maintaining latency by controlling the switch between viral latency and lytic replication.

Cellular protein degradation pathways can be utilized by viruses to establish an environment that favors their propagation. Here we report that the Kaposi's sarcoma–associated herpesvirus (KSHV)-encoded latency-associated nuclear antigen (LANA) directly functions as a component of the EC5S ubiquitin complex targeting the tumor suppressors von Hippel-Lindau (VHL) and p53 for degradation. We have characterized a suppressor of cytokine signaling box-like motif within LANA composed of an Elongin B and C box and a Cullin box, which is spatially located at its amino and carboxyl termini. This motif is necessary for LANA interaction with the Cul5–Elongin BC complex, to promote polyubiquitylation of cellular substrates VHL and p53 in vitro via its amino- and carboxyl-terminal binding domain, respectively. In transfected cells as well as KSHV-infected B lymphoma cells, LANA expression stimulates degradation of VHL and p53. Additionally, specific RNA interference–mediated LANA knockdown stabilized VHL and p53 in primary effusion lymphoma cells. Thus, manipulation of tumor suppressors by LANA potentially provides a favorable environment for progression of KSHV-infected tumor cells.

A dysbiotic microbiome can potentially contribute to the pathogenesis of many different diseases including cancer. Breast cancer is the second leading cause of cancer death in women. Thus, we investigated the diversity of the microbiome in the four major types of breast cancer: endocrine receptor (ER) positive, triple positive, Her2 positive and triple negative breast cancers. Using a whole genome and transcriptome amplification and a pan-pathogen microarray (PathoChip) strategy, we detected unique and common viral, bacterial, fungal and parasitic signatures for each of the breast cancer types. These were validated by PCR and Sanger sequencing. Hierarchical cluster analysis of the breast cancer samples, based on their detected microbial signatures, showed distinct patterns for the triple negative and triple positive samples, while the ER positive and Her2 positive samples shared similar microbial signatures. These signatures, unique or common to the different breast cancer types, provide a new line of investigation to gain further insights into prognosis, treatment strategies and clinical outcome, as well as better understanding of the role of the micro-organisms in the development and progression of breast cancer.

Truncated forms of the NOTCH1 transmembrane receptor engineered to resemble mutant forms of NOTCH1 found in certain cases of human T cell leukemia/lymphoma (T-ALL) efficiently induce T-ALL when expressed in the bone marrow of mice. Unlike full-sized NOTCH1, two such truncated forms of the protein either lacking a major portion of the extracellular domain (⌬E) or consisting only of the intracellular domain (ICN) were found to activate transcription in cultured cells, presumably through RBP-J response elements within DNA. Both truncated forms also bound to the transcription factor RBP-J in extracts prepared from human and murine T-ALL cell lines. Transcriptional activation required the presence of a weak RBP-J-binding site within the NOTCH1 ankyrin repeat region of the intracellular domain. Unexpectedly, a second, stronger RBP-J-binding site, which lies within the intracellular domain close to the transmembrane region and significantly augments association with RBP-J, was not needed for oncogenesis or for transcriptional activation. While ICN appeared primarily in the nucleus, ⌬E localized to cytoplasmic and nuclear membranes, suggesting that intranuclear localization is not essential for oncogenesis or transcriptional activation. In support of this interpretation, mutation of putative nuclear localization sequences decreased nuclear localization and increased transcriptional activation by membranebound ⌬E. Transcriptional activation by this mutant form of membrane-bound ⌬E was approximately equivalent to that produced by intranuclear ICN. These data are most consistent with NOTCH1 oncogenesis and transcriptional activation being independent of association with RBP-J at promoter sites.NOTCH1 (also referred to as TAN-1), a homolog of Drosophila NOTCH, was first identified at the breakpoint of a recurrent (7;9)(q34;q34.3) chromosomal translocation associated with a subset of human T cell acute lymphoblastic leukemia/ lymphoma (T-ALL) 1 (1-3). RNA transcribed from the normal NOTCH1 gene is found in most cells but is present at highest levels in developing thymus and brain (2, 4). The product of this gene is a 2555 amino acid type I transmembrane receptor protein of about 350 kDa (p350) containing a series of structural motifs originally described in other polypeptides (Fig. 1), including 36 epidermal growth factor-like repeats and three lin-12-like repeats in the extracellular domain and six ankyrinlike repeats in the intracellular domain. All chromosomal breakpoints in human T-ALLs occur within a single intron dividing the coding sequence for epidermal growth factor repeat 34 and result in overexpression of novel mRNAs containing sequences from the 3Ј end of NOTCH1 (5). These transcripts encode a series of truncated NOTCH1 polypeptides of ϳ100 -125 kDa lacking the epidermal growth factor-like and lin-12-like repeats (5). The oncogenicity of truncated NOTCH1 has been confirmed by inserting cDNAs encoding portions of the NOTCH1 gene into murine bone marrow progenitor cells which were then transplanted into syngeneic r...

Recombinant Epstein-Barr viruses (EBV) with a translation termination codon mutation inserted into the nuclear protein 3A (EBNA-3A) or 3C (EBNA-3C) open reading frame were generated by second-site homologous recombination. These mutant viruses were used to infect primary B lymphocytes to assess the requirement of EBNA-3A or-3C for growth transformation. The frequency of obtaining transformants infected with a wild-type EBNA-3A recombinant EBV was 10 to 15%. In contrast, the frequency of obtaining transformants infected with a mutant EBNA-3A recombinant EBV was only 1.4% (9 mutants in 627 transformants analyzed). Transformants infected with mutant EBNA-3A recombinant virus could be obtained only by coinfection with another transformation-defective EBV which provided wild-type EBNA-3A in trans. Cells infected with mutant EBNA-3A recombinant virus lost the EBNA-3A mutation with expansion of the culture. The decreased frequency of recovery of the EBNA-3A mutation, the requirement for transformation-defective EBV coinfection, and the inability to maintain the EBNA-3A mutation indicate that EBNA-3A is essential or critical for lymphocyte growth transformation and that the EBNA-3A mutation has a partial dominant negative effect. Five transformants infected with mutant EBNA-3C recombinant virus EBV were also identified and expanded. All five also required wild-type EBNA-3C in trans. Serial passage of the mutant recombinant virus into primary B lymphocytes resulted in transformants only when wild-type EBNA-3C was provided in trans by coinfection with a transformationdefective EBV carrying a wild-type EBNA-3C gene. A secondary recombinant virus in which the mutated EBNA-3C gene was replaced by wild-type EBNA-3C was able to transform B lymphocytes. Thus, EBNA-3C is also essential or critical for primary B-lymphocyte growth transformation. Epstein-Barr virus (EBV) is the etiological agent of infectious mononucleosis and is associated with several malignancies, including lymphomas in immunocompromised hosts (9, 70), Burkitt lymphoma (19, 35, 49, 71), nasopharyngeal carcinoma (14, 20, 71), and Hodgkin's disease (4, 62). EBV infects B lymphocytes and certain epithelial cells (27, 33, 59). EBV infection of B lymphocytes causes cell activation (7, 16, 38, 64, 68), continuous cell proliferation, and cell growth transformation as assayed in marmosets or SCID mice (43, 44, 55, 61, 67). Two EBV types, 1 and 2, coexist in most human populations. The two types have distinctive nuclear protein EBNA-LP,-2,-3A,-3B, and-3C genes (1, 13, 54, 56). Type 1 EBV is very efficient at transforming B lymphocytes, while type 2 EBV is very inefficient (52). This type-specific difference in transformation efficiency is primarily due to type-specific differences in the EBNA-2 gene (11, 52). Although EBV can potentially code for 80 to 100 genes (5), only a restricted set of 10 genes are expressed during B-lymphocyte latent infection (reviewed in references 29 and 30). Six genes encode EBNA-LP,-1,-2,-3A,-3B, and-3C. Two genes encode latent infection memb...

Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) is one of the essential latent antigens for primary B-cell transformation. Previous studies established that EBNA3C facilitates degradation of several vital cell cycle regulators, including the retinoblastoma (pRb) and p27KIP proteins, by recruitment of the SCF Skp2 E3 ubiquitin ligase complex. EBNA3C was also shown to be ubiquitinated at its N-terminal residues. Furthermore, EBNA3C can bind to and be degraded in vitro by purified 20S proteasomes. Surprisingly, in lymphoblastoid cell lines, EBNA3C is extremely stable, and the mechanism for this stability is unknown. In this report we show that EBNA3C can function as a deubiquitination enzyme capable of deubiquitinating itself in vitro as well as in vivo. Functional mapping using deletion and point mutational analysis showed that both the N-and C-terminal domains of EBNA3C contribute to the deubiquitination activity. We also show that EBNA3C efficiently deubiquitinates Mdm2, an important cellular proto-oncogene, which is known to be overexpressed in several human cancers. The data presented here further demonstrate that the N-terminal domain of EBNA3C can bind to the acidic domain of Mdm2. Additionally, the N-terminal domain of EBNA3C strongly stabilizes Mdm2. Importantly, EBNA3C simultaneously binds to both Mdm2 and p53 and can form a stable ternary complex; however, in the presence of p53 the binding affinity of Mdm2 toward EBNA3C was significantly reduced, suggesting that p53 and Mdm2 might share a common overlapping domain of EBNA3C. We also showed that EBNA3C enhances the intrinsic ubiquitin ligase activity of Mdm2 toward p53, which in turn facilitated p53 ubiquitination and degradation. Thus, manipulation of the oncoprotein Mdm2 by EBNA3C potentially provides a favorable environment for transformation and proliferation of EBV-infected cells.

Infectious agents are the third highest human cancer risk factor and may have a greater role in the origin and/or progression of cancers, and related pathogenesis. Thus, knowing the specific viruses and microbial agents associated with a cancer type may provide insights into cause, diagnosis and treatment. We utilized a pan-pathogen array technology to identify the microbial signatures associated with triple negative breast cancer (TNBC). This technology detects low copy number and fragmented genomes extracted from formalin-fixed paraffin embedded archival tissues. The results, validated by PCR and sequencing, define a microbial signature present in TNBC tissue which was underrepresented in normal tissue. Hierarchical clustering analysis displayed two broad microbial signatures, one prevalent in bacteria and parasites and one prevalent in viruses. These signatures demonstrate a new paradigm in our understanding of the link between microorganisms and cancer, as causative or commensal in the tumor microenvironment and provide new diagnostic potential.