Spatial association of HIV-1tat protein and the nucleolar transport protein B23 in stably transfected Jurkat T-cells

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Abstract
The human immunodeficiency virus (HIV-1) encodes a transactivator protein, the product of the tat gene (tat), which is essential for virus replication. In this study, immunogold electron microscopy was used in a stably transfected Jurkat T-cell line that constitutively expresses HIV-1tat protein to determine the subcellular and intranuclear distribution oftat protein. Two nucleocytoplasmic shuttle proteins C23/nucleolin and B23 and a third nucleolar antigen that was detected by monoclonal antibody MAb 1277 were also examined. In addition, spatial association of C23 and B23 withtat protein at several subcellular locations was examined in dual-labeling experiments. The results showed thattat protein was found in both the cytoplasm and nucleus but was especially prominent within the dense fibrillar and granular components of the nucleolus. There was little labeling oftat protein in the fibrillar centers where MAb 1277 antigen was localized at a comparatively high level. The subcellular and intranucleolar distribution oftat protein was virtually identical to the pattern seen with C23 and B23. Although the intranuclear distributions of C23, B23 andtat protein were very similar, C23 andtat protein were seldom spatially associated. In contrast, B23 andtat protein were frequently spatially associated in the nucleolus and in several other subcellular locations including the cytoplasm, nucleoplasm, at the nuclear envelope and plasma membrane. While a physical association was not directly demonstrated in this study, the spatial association between B23 andtat protein strongly suggest that such an association may exist.