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J. Biol. Chem., Vol. 282, Issue 18, 13875-13883, May 4, 2007

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The Nuclear Import of the Human T Lymphotropic Virus Type I (HTLV-1) Tax Protein Is Carrier- and Energy-independent^*

Takahiro Tsuji, Noreen Sheehy, Virginie W. Gautier, Hitoshi Hayakawa, Hirofumi Sawa, and William W. Hall¹

From the Centre for Research in Infectious Disease, School of Medicine & Medical Science, University College Dublin, Belfield, Dublin 4, Ireland and the Department of Molecular Pathobiology and 21st Century COE Program for Zoonosis Control, Hokkaido University Research Center for Zoonosis Control, N18, W9, Kita-ku, Sapporo, 060-0818, Japan

HTLV-1 is the etiologic agent of the adult T cell leukemialymphoma (ATLL). The viral regulatory protein Tax plays a central role in leukemogenesis as a transcriptional transactivator of both viral and cellular gene expression, and this requires Tax activity in both the cytoplasm and the nucleus. In the present study, we have investigated the mechanisms involved in the nuclear localization of Tax. Employing a GFP fusion expression system and a range of Tax mutants, we could confirm that the N-terminal 60 amino acids, and specifically residues within the zinc finger motif in this region, are important for nuclear localization. Using an in vitro nuclear import assay, it could be demonstrated that the transportation of Tax to the nucleus required neither energy nor carrier proteins. Specific and direct binding between Tax and p62, a nucleoporin with which the importin beta family of proteins have been known to interact was also observed. The nuclear import activity of wild type Tax and its mutants and their binding affinity for p62 were also clearly correlated, suggesting that the entry of Tax into the nucleus involves a direct interaction with nucleoporins within the nuclear pore complex (NPC). The nuclear export of Tax was also shown to be carrier independent. It could be also demonstrated that Tax it self may have a carrier function and that the NF-B subunit p65 could be imported into the nucleus by Tax. These studies suggest that Tax could alter the nucleocytoplasmic distribution of cellular proteins, and this could contribute to the deregulation of cellular processes observed in HTLV-1 infection.

Received for publication, December 19, 2006 , and in revised form, March 6, 2007.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 353-1-716-1229; Fax: 353-1-716-1239; E-mail: william.hall{at}ucd.ie.

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