Rapid isolation of viral integration site reveals frequent integration of HTLV-1 into expressed loci

Although there is tight association of the human T-cell leukemia virus type-1 (HTLV-1) with adult T-cell leukemia/lymphoma (ATLL), it has remained unresolved whether the HTLV-1 integration into the host genome has any role in the development of this disease. We isolated a total of 58 HTLV-1 integration sites using newly developed, adaptor-ligated PCR from 33 ATLL patients and five ATLL cell lines. We compared our data as well as the previously reported ones with the complete human genomic sequence for the location of its placement, structure, and expression of genes nearby the integration site. The chromosomal target for integration was selected at random, but the integration favorably occurred within the transcription units; more than 59.5% of total integration was observed within the transcriptional unit. All inserted genes by HTLV-1 integration were expressed in normal T cells. Upregulation of genes due to viral integration was found in two out of nine ATLL cases; about 4.4- and 102-fold elevated ankyrin-1 (ANK-1) and gephyrin (GPHN) gene expressions were observed, respectively. These data suggest that the preferential integration of HTLV-1 into an expressed locus occasionally causes deregulation of corresponding gene, which may lead to leukemogenesis of a fraction of ATLL.