Jun family members are controlled by a calcium-regulated, cyclosporin A-sensitive signaling pathway in activated T lymphocytes.

The octamer-binding transcription factor Oct-1 is involved in a wide variety of cellular processes but appears to lack a strong transcriptional activation domain, suggesting that it functions in the context of other proteins. We demonstrated previously that Oct-1, in association with a 40-kD protein, OAP40, contributes to the induction of interleukin-2 (IL-2), an early activation gene and major growth factor for T lymphocytes. Here we report that amino acid sequences obtained from purified OAP40 are identical to regions within JunD and c-Jun. We demonstrate that each of these Jun family members can participate in a complex that includes Oct-1 and a regulatory element in the IL-2 enhancer. In transient transfections, both JunD and c-Jun can contribute to activation-specific transcription mediated by this antigen receptor response element. These studies reveal a role, distinct from AP-1 activity, for Jun family members that is controlled by a calcium-triggered, cyclosporin A-sensitive mechanism.