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Blood, 1 August 2005, Vol. 106, No. 3, pp. 1048-1053. Prepublished online as a Blood First Edition Paper on April 19, 2005; DOI 10.1182/blood-2004-11-4350.
NEOPLASIA Preferential selection of human T-cell leukemia virus type I provirus integration sites in leukemic versus carrier statesFrom the Laboratory of Virus Immunology, Institute for Virus Research, Kyoto University, Kyoto, Japan; Laboratory of Molecular Technology, National Cancer Institute-Frederick, Frederick, MD; and the Department of Laboratory Medicine, Faculty of Medicine, University of Miyazaki, Miyazaki, Japan.
Human T-cell leukemia virus type I (HTLV-I) is a causative agent of neoplastic disease, adult T-cell leukemia (ATL). Although the encoding viral proteins play an important role in oncogenesis, the role of the HTLV-I proviral integration site remains unsolved. We determined the integration sites of HTLV-I proviruses in ATL cells and HTLV-Iinfected cells in asymptomatic carriers. In carrier and ATL cells, HTLV-I provirus was integrated into the transcriptional unit at frequencies of 26.8% (15/56) and 33.9% (20/59), respectively, which were equivalent to the frequency calculated based on random integration (33.2%). In addition, HTLV-I provirus was prone to integration near the transcriptional start sites in leukemic cells (P = .006), and the transcriptional direction of the provirus was in accordance with that of integrated cellular genes in 70% of cases. More importantly, the integration sites in the carrier cells favored the alphoid repetitive sequences (11/56; 20%) whereas in leukemic cells they disfavored these sequences (2/59; 3.4%). Taken together, during natural course from carrier to onset of ATL, HTLV-Iinfected cells with integration sites favorable for viral gene transcription are susceptible to malignant transformation due to increased viral gene expression.
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