ALV Integration-Associated Hypomethylation at the TERT Promoter Locus

Avian leukosis virus (ALV) is a simple retrovirus that can induce B-cell lymphoma in chicken(s) and other birds by insertional mutagenesis. The promoter region of telomerase reverse transcriptase (TERT) has been identified as an important integration site for tumorigenesis. Tumors with TERT promoter integrations are associated with increased TERT expression. The mechanism of this activation is still under investigation. We asked whether insertion of proviral DNA perturbs the epigenome of the integration site and, subsequently, impacts the regulation of neighboring genes. DNA cytosine methylation, which generally acts to suppress transcription, is one major form of epigenetic regulation. In this study, we examine allele-specific methylation patterns of genomic DNA from chicken tumors by bisulfite sequencing. We observed that alleles with TERT promoter integrations are associated with decreased methylation in the host genome near the site of integration. Our observations suggest that insertion of ALV in the TERT promoter region may induce expression of TERT through inhibition of maintenance methylation in the TERT promoter region.