Impact of foreign DNA integration on tumor biology and on evolution via epigenetic alterations

The insertion of foreign DNA into mammalian genomes can alter their methylation and transcription patterns at remote sites from the locus of foreign DNA integration. The mechanisms leading to these fundamental changes and their frequencies are unknown. Sites and extent of changes in the recipient cells might depend on the location of foreign DNA integration. In the second part of this review, it will be hypothesized that the insertion event itself, for example, of tumor viral DNA via its epigenetic genome-wide consequences, plays an important role in oncogenesis. During evolution, the impact of ancient retrotransposon or retroviral genomes and the ensuing epigenetic alterations in the recipient genomes might have generated cells with completely different transcriptional profiles. Due to the continued presence of the transgenomes these alterations were genetically stable and were selected for or against by the environmental conditions prevalent at the time. These evolutionary effects are very different from those postulated for insertional mutagenesis, added genetic information or regulatory elements placed into the vicinity of cellular functions.