We report that the expression of murine or human mutant p53 proteins in cells with no endogenous p53 proteins confers new or additional phenotypes upon these cells. Mutant p53 proteins expressed in cell lines lacking p53 resulted in either enhanced tumorigenic potential in nude mice ((10)3 cells) or enhanced plating efficiency in agar cell culture (human SAOS-2 cells). Also, mutant human p53 alleles, unlike the wild-type p53 protein, could also enhance the expression of a test gene regulated by the multi-drug resistance enhancer-promoter element. These data demonstrate a gain of function associated with p53 mutations in addition to the loss of function shown previously to be associated with mutations in this tumour suppressor gene.

EBV-encoded microRNAs (miRNAs) have been identified and their functions are being studied. The expression pattern of these miRNAs in clinical samples of EBV-associated nonHodgkin's lymphomas is unknown. We analyzed five primary ''endemic'' pediatric Burkitt's lymphomas (BL), two acquired immunodeficiency syndrome (AIDS)-related type I latency BL lines, a type III latency line, three EBV + primary effusion lymphomas (PEL), and three AIDS-related diffuse large B-cell lymphomas (DLBCL) for expression of EBV-encoded miRNAs.

Transfection of a Kaposi's sarcoma (KS) herpesvirus (KSHV) Bacterial Artificial Chromosome (KSHVBac36) into mouse bone marrow endothelial-lineage cells generates a cell (mECK36) that forms KS-like tumors in mice. mECK36 expressed most KSHV genes and were angiogenic, but they didn't form colonies in soft agar. In nude mice, mECK36 formed KSHV-harboring vascularized spindle cell sarcomas that were LANA+/podoplanin+, overexpressed VEGF and Angiopoietin ligands and receptors, and displayed KSHV and host transcriptomes reminiscent of KS. mECK36 that lost the KSHV episome reverted to nontumorigenicity. siRNA suppression of KSHV vGPCR, an angiogenic gene upregulated in mECK36 tumors, inhibited angiogenicity and tumorigenicity. These results show that KSHV malignancy is in vivo growth restricted and reversible, defining mECK36 as a biologically sensitive animal model of KSHV-dependent KS.

Infection of cells with DNA viruses triggers innate immune responses mediated by DNA sensors. cGMP-AMP synthase (cGAS) is a key DNA sensor that produces the cyclic dinucleotide cGMP-AMP (cGAMP) upon activation, which binds to and activates stimulator of interferon genes (STING), leading to IFN production and an antiviral response. Kaposi's sarcoma-associated herpesvirus (KSHV) is a DNA virus that is linked to several human malignancies. We report that KSHV infection activates the cGAS-STING pathway, and that cGAS and STING also play an important role in regulating KSHV reactivation from latency. We screened KSHV proteins for their ability to inhibit this pathway and identified six viral proteins that block IFN-β activation through this pathway. This study is the first report identifying multiple viral proteins encoded by a human DNA virus that inhibit the cGAS-STING DNA sensing pathway. One such protein, viral interferon regulatory factor 1 (vIRF1), targets STING by preventing it from interacting with TANK binding kinase 1 (TBK1), thereby inhibiting STING's phosphorylation and concomitant activation, resulting in an inhibition of the DNA sensing pathway. Our data provide a unique mechanism for the negative regulation of STING-mediated DNA sensing. Moreover, the depletion of vIRF1 in the context of KSHV infection prevented efficient viral reactivation and replication, and increased the host IFN response to KSHV. The vIRF1-expressing cells also inhibited IFN-β production following infection with DNA pathogens. Collectively, our results demonstrate that gammaherpesviruses encode inhibitors that block cGAS-STING-mediated antiviral immunity, and that modulation of this pathway is important for viral transmission and the lifelong persistence of herpesviruses in the human population.aposi's sarcoma-associated herpesvirus (KSHV/HHV8) is the etiological agent of several human malignancies, including Kaposi's sarcoma (KS), multicentric Castleman's disease, and primary effusion lymphoma (1, 2). Evasion of the host innate immune response is essential for viral infection, replication, latency, transmission, and lifelong persistence.A member of the gammaherpesvirus subfamily, KSHV contains a large dsDNA genome that encodes for more than 80 ORFs. Different pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs), nucleotide-binding domain leucine-rich repeat-containing (NLR) proteins, and retinoic acid-inducible gene-I-like receptors (RLRs), are activated upon KSHV infection in different cell types (3-5). As is the case with many pathogens, multiple PRRs can detect an incoming pathogen in the cell. Depending on the cell type, detection of viral DNA may take place in the nucleus (6) or in the cytoplasm due to premature release of the herpesviral DNA into the cytoplasm (7). It is plausible that defective herpesvirus virions release their genomic contents into the cytoplasm rather than the nucleus and that this viral DNA triggers cytosolic DNA sensors to be activated. Additionally, HSV-1 infection induces mitochon...

The release of membrane-bound vesicles from cells has been increasingly recognized as a mechanism for intercellular communication. Extracellular vesicles (EVs) are also produced by virus-infected cells and are thought to be involved in intercellular communication between infected and uninfected cells. Viruses, in particular oncogenic viruses and viruses that establish chronic infections, have been shown to modulate the production and content of EVs. Viral microRNAs, protein and even entire virions can be incorporated into EVs, which can impact immune recognition of viruses or modulate neighboring cells. In this Review, we will discuss the roles that EVs have during virus infection to either promote or restrict viral infection in target cells. We will also discuss our current understanding of the molecular mechanisms that underlie these effects, the potential consequences for the infected host, and possible future diagnostic applications.