Transcriptional regulation alone does not explain the constitutive expression of the interleukin 2 receptor (Tac/L-chain) in HTLV-1 infected cells.

We have identified a suppressive element in the upstream region of the interleukin 2 (IL-2) receptor L chain (Tac) promoter. The inhibitory activity of this element was retained in human T cell leukemia virus type-1 (HTLV-1)-infected T cell lines which express constitutively a large number of IL-2 receptors on the cell surface. The promoter activities of the IL-2 receptor gene did not always correlate with the strong expression of the receptor and its mRNA in the HTLV-1-infected T cell lines we analysed. The results indicate that the constitutive up-regulation of the IL-2 receptor in HTLV-1-infected T cells may be ascribed to not only the transcriptional but also post-transcriptional regulation.