The role of cytoplasmic intermediates in IL 2-induced T cell growth.

In previous studies we showed that PHA-stimulated human peripheral blood lymphocytes contain an extractable cytoplasmic protein that is capable of inducing DNA synthesis in isolated quiescent nuclei. This factor, which we have called ADR (for activator of DNA replication), appears to represent an endogenous intracellular mitogen, or cytoplasmic transducer of extracellular mitogenic signals. In light of the known role of IL 2 in PHA-induced T cell mitogenesis, we continued these studies to investigate whether ADR may be involved in the mechanism of action of IL 2. Results from both dose-response and time-response studies strongly suggest a functional role for ADR in IL 2 mediated T cell growth. Furthermore, the absence of ADR in dexamethasone-treated, PHA-stimulated cells suggests that the induction of ADR is not an early event in T cell activation associated with the expression of IL 2 receptors; rather, the induction of ADR appears to be a later event resulting directly or indirectly from the binding of IL 2 to IL 2-responsive cells. In sum, our findings suggest a pathway for T cell growth in which extracellular exogenous mitogenic signals are transmitted to the nucleus first through an extracellular endogenous growth factor (IL 2) and finally through an intracellular, endogenous molecule (ADR) that acts at the level of the nucleus itself.