Mitsui Akira

Role of ATL-derived factor (ADF) in the normal and abnormal cellular activation: Involvement of dithiol related reduction

Abstract HTLV-I transformed T cells not only express a large number of interleukin-2 receptors (IL-2R/p55(Tac)), but also produce an IL-2R/Tac inducer named ATL-derived factor (ADF). We have cloned the ADF cDNA and found that ADF production in human lymphocytes can be enhanced by cellular activators such as mitogens or phorbol esters. Recombinant ADF produced by E. coli was shown to have growth-promoting activity in combination with interleukin-2 or suboptimal mitogenic stimuli on several lymphoid cells including human PBMCs, besides the originally reported IL-2R/Tac inducing activity. Homology analysis revealed an unexpected structural relationship between ADF and dithiol-reducing enzyme, thioredoxin, which had been characterized originally in prokaryotic system. Recombinant ADF also has a reducing activity, suggesting the presence of still unknown features of ADF action in vivo . The requirement of dithiol reduction in the biological activities of ADF, together with the possible involvement of ADF production in the normal and abnormal activation of human cells are discussed.

Lymphocyte transformation and thiol compounds; the role of ADF/thioredoxin as an endogenous reducing agent.

Abstract ADF (adult T-cell leukemia-derived factor), an inducer of IL-2R with growth promoting activity, is a homologue of thioredoxin which is involved in many thiol-dependent reducing reactions. ADF is constitutively produced and released by human lymphoid cell lines transformed by lymphocyte-tropic viruses, such as human T-lymphotropic virus type I (HTLV-I) and Epstein-Barr virus (EBV). We found that the viability and growth of these ADF high-producer cell lines (ATL-2, HUT102, MT-2, 3B6 and RPMI8866) were highly dependent on l -cystine in the culture. In contrast to the relative cystine independency of ADF low-producer cells (Jurkat, Jijoye, U937 and K562), the growth of ADF high-producer cells was almost completely suppressed in l -cystine-free condition. Their viability and growth in l -cystine-free medium were markedly improved by 5 × 10 −5 M l -cysteine, 5 × 10 −5 M 2-ME or 10 −3 M GSH and partially by 10 −3 M DTT. The results demonstrate the requirement of reducing condition involving thiol compounds for the optimal growth of the virally transformed lymphoid cells. Furthermore, recombinant ADF (rADF) and suboptimal dose of 2-ME additively enhanced the growth of ATL-2 cells in l -cystine-free medium, implying the possible involvement of endogenous reducing agents such as ADF/thioredoxin homologue in the process of lymphocyte transformation/activation.