HTLV-1 and HTLV-2 Tax, HBZ and APH-2 interaction with host factors: their involvement in cellular pathways regulation.

Background: HTLV-1 and HTLV-2 encode several genes which play a pivotal role in viral replication and proliferation of infected cells. Among them, Tax and the antisense strand genes HBZ and APH-2 are the most investigated. HBZ is directly involved in HTLV-1 infection and persistence. Tax-1 and HBZ expression causes an opposite effect on NF-ĸB activation and exerts a central role in transforming and immortalizing T lymphocytes. Unlike HBZ, APH-2 binds Tax-2, but both repress Tax LTR transactivation interacting with CREB. In previous study, we have compared the effect of Tax-1 and Tax-2 interaction with cellular factors that act on NF-ĸB and IFN-I cell signaling pathways regulation. Based on the differences between HBZ and APH-2 interaction with Tax-1 and Tax-2 proteins, we aimed to investigate whether HBZ and APH-2 differ in the interactions with cellular factors, and how these interactions modulate cellular pathways regulation. Methods: The study is based on cell culture models transiently transfected with vectors expressing viral proteins. Protein interactions were demonstrated by complexes immunoprecipitations performed using Dynabeads® Protein G with specific antibodies and western blot analyses. NF-ĸB promoter activation was quantified by luciferase reporter assay in co-transfected HEK293T cells. Tax, HBZ, APH-2 and host factors intracellular distribution was analyzed by confocal microscopy. Results: In our comparative studies, we observed that APH-2 shares with HBZ the ability to suppress the Tax-mediated NF-ĸB activation. Both proteins form complexes with p65. APH-2, like HBZ, inhibits the p65-induced NF-ĸB activation. Consistent with the differences in binding properties, we observed, by confocal microscopy, a different intracellular redistribution of APH-2 compared to HBZ when Tax proteins are expressed. Moreover, by immunoprecipitation and intracellular co-localization analyses, we have identified cellular factors involved in cell signaling pathways that form complexes with APH-2 when Tax-2 is expressed. Conclusions: These results contribute to understand the different involvement of the antisense proteins in the regulation of the NF-κB pathway. Our results demonstrate that APH-2, unlike HBZ, is present in Tax-2 complexes in the cytoplasm and interacts with factors that crosstalk between cellular pathways affecting cell growth and survival.