In vitro methylation of bovine papillomavirus alters its ability to transform mouse cells

Evasion of host immune defenses by human papillomavirus

A majority of human papillomavirus (HPV) infections are asymptomatic and self-resolving in the absence of medical interventions. Various innate and adaptive immune responses, as well as physical barriers, have been implicated in controlling early HPV infections. However, if HPV overcomes these host immune defenses and establishes persistence in basal keratinocytes, it becomes very difficult for the host to eliminate the infection. The HPV oncoproteins E5, E6, and E7 are important in regulating host immune responses. These oncoproteins dysregulate gene expression, protein-protein interactions, posttranslational modifications, and cellular trafficking of critical host immune modulators. In addition to the HPV oncoproteins, sequence variation and dinucleotide depletion in papillomavirus genomes has been suggested as an alternative strategy for evasion of host immune defenses. Since anti-HPV host immune responses are also considered to be important for antitumor immunity, immune dysregulation by HPV during virus persistence may contribute to immune suppression essential for HPV-associated cancer progression. Here, we discuss cellular pathways dysregulated by HPV that allow the virus to evade various host immune defenses.

Differences in methylation patterns of the alpha-fetoprotein and albumin genes in hepatic and non hepatic developing rat tissues

By use of different restriction enzymes sensitive to internal cytosine methylation (HpaII, AvaI, HhaI) we have analysed the methylation patterns of albumin and AFP genes in tissues and cell lines with high (liver, yolk sac, hepatoma cell lines), low (fetal and neonatal kidney) or undetectable (spleen, JF1 fibroblasts) expression of either gene. We show that expression of the AFP gene is associated to the demethylation of a whole region or domain extending from -4 to +3 Kb. Moreover, demethylation of a site located at the upstream limit of this domain appears to be correlated with the commitment of the cell type to synthesize AFP. As concerns the albumin gene, we show that the domain in which demethylation is correlated with active gene transcription in hepatoma cell lines has different borders than in tissue. This difference might be related to the different amounts of mRNA synthesized or to an alteration in gene regulation in tumor cells. Finally, we show that low expression of albumin and AFP genes in fetal and neonatal kidney is not correlated with domain demethylation, suggesting that the regulatory mechanisms of expression of these genes are different in kidney as compared with liver.

Effects of S-adenosylhomocysteine and analogs on Epstein-Barr virus-induced transformation, expression of the Epstein-Barr virus capsid antigen, and methylation of Epstein-Barr virus DNA

S-Adenosylhomocysteine was found to have no effect on Epstein-Barr virus-induced transformation of B-lymphocytes and to stimulate viral capsid antigen expression only slightly in the FF41-1 cell line. In contrast, the S-adenosylhomocysteine analogs sinefungin and S-isobutyladenosine inhibited Epstein-Barr virus transformation and induced a significant increase in the numbers of cells expressing the viral capsid antigen. An inverse relationship between levels of viral DNA methylation and gene expression was demonstrated.