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This article is part of the supplement: 15th International Conference on Human Retroviruses: HTLV and Related Viruses

Open Access Open Badges Meeting abstract

MHC class II transactivator CIITA inhibits Tax-2-mediated HTLV-2 LTR transactivation and viral replication by binding to, and affecting Tax-2 intracellular localization

Chiara Orlandi, Greta Forlani, Giovanna Tosi and Roberto S Accolla*

Author Affiliations

Department of Experimental Medicine, University of Insubria, Varese, 21100, Italy

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Retrovirology 2011, 8(Suppl 1):A172  doi:10.1186/1742-4690-8-S1-A172

The electronic version of this article is the complete one and can be found online at:

Published:6 June 2011

© 2011 Orlandi et al; licensee BioMed Central Ltd.

This is an open access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Meeting abstract

CIITA, the MHC class II transactivator, inhibits the transcriptional function of HTLV-2 (Human T cell Lymphotropic Virus 2) Tax-2 viral transactivator and, consequently, the replication of the virus in human target cells. Here we demonstrate that CIITA and Tax-2 interact in vivo and we identified at least two independent regions, at the 1-252 N-term and at the 410-1130 C-term, respectively, necessary for this interaction, although only the N-term region mediates Tax-2 functional inhibition. Intracellular localization experiments in 293T cells demonstrate that CIITA and Tax-2, when expressed alone, are present both in the cytoplasm and in the nucleus; when co-expressed, however, Tax-2 mostly co-localize with CIITA in the cytoplasm and around the nuclear membrane. The remaining nuclear Tax-2, also co-localize with CIITA. Interestingly, when CIITA nucleus-cytoplasm shuttling is blocked by leptomycin B treatment, most of the Tax-2 molecules are also blocked and co-localize with CIITA in the nucleus, suggesting that direct CIITA-Tax-2 binding does not preclude Tax-2 entry into the nucleus.

Finally, the nuclear factor NF-YB, a CIITA-binding nuclear protein necessary for the MHC class II gene promoter activation, whose overexpression inhibits Tax-2-mediated HTLV-2 LTR transactivation, also strongly binds to Tax-2 in absence of CIITA. Notably, although endogenous NF-YB does not inhibit Tax-2-dependent HTLV-2 LTR transactivation, it still binds to Tax-2, and in presence of CIITA, this binding seems to increase. Taken together these results strongly suggest that that CIITA could inhibit Tax-2 by binding the viral transactivator both directly in the cytoplasm or through a tripartite interaction with NF-YB in the nucleus.