Structure of HTLV and its biological function in leukemogenesis of adult T-cell leukemia.

There is a high homology of nucleotide sequence between 3' two-thirds of the X (or pX) regions of human T-cell leukemia virus (HTLV)-I, and of HTLV-II. Monoclonal antibody against p41 coded from X-IV, an open reading frame of X region of HTLV-I, was established. Two proteins coded by Xb, one of the open reading frames in X region of HTLV-II, were newly identified as p24 and p26. The expression of X protein of HTLV-II in the reconstituted mouse embryonal carcinoma cell line, which shows myoblastic morphology, reverted the morphology to that of the original embryonal carcinoma cells. This suggests that the function of X protein is to disturb the regulation of cell lineage determination. Leukemogenesis of adult T-cell leukemia (ATL) is also considered to consist of multisteps, in which HTLV-I constitutes one step, other factors also being involved. Even the role of HTLV-I factor could be similarly played by other factor(s). In agreement with this hypothesis, there are patients with ATL without associated HTLV-I.