Nucleo-cytoplasmic redistribution of the HTLV-I rex protein: Alterations by coexpression of the HTLV-I p21^x protein

The function of the Rex protein of human T-cell leukemia virus type I (HTLV-I) has been demonstrated to be very similar to the Rev protein of human immunodeficiency virus type 1 (HIV-1). Both of these retroviral regulatory proteins rescue unspliced viral RNAs from the nuclei of infected cells. The Rev protein of HIV-1 has been reported to shuttle between the nucleus/nucleolus and the cytoplasm. Here, we have found that Rex also relocated out of the nucleus in the presence of actinomycin D. This effect was demonstrated in dose- and time-course-dependent manners. In comparison with previous reports on HIV-1 Rev, these effects with Rex seemed to be similar, but less distinct, which may reflect precise differences in the subcellular localization and/or shuttling pathways of Rev and Rex. Interestingly, the endogenous truncated form of the Rex protein, p21^x, significantly interfered with the intracellular translocation of Rex, when coexpressed in trans. As expression of p21^x occurs in various HTLV-I-infected cells, p21^x may play a role in the life-cycle of HTLV-I, through regulating the dynamic subcellular distribution of the viral trans-activator, Rex.