Interaction between NF-κB- and serum response factor-binding elements activates an interleukin-2 receptor α-chain enhancer specifically in T lymphocytes

We find that a short enhancer element containing the NF-κB binding site from the interleukin-2 receptor α-chain gene (IL-2Rα) is preferentially activated in T cells. The IL-2Rα enhancer binds NF-κB poorly and is only weakly activated by the NF-κB site alone. Serum response factor (SRF) binds to a site adjacent to the NF-κB site in the IL-2R enhancer, and both sites together have strong transcriptional activity specifically in T cells. Surprisingly, the levels of SRF constitutively expressed in T cells are consistently higher than in other cell types. Overexpression of SRF in B cells causes the IL-2R enhancer to function as well as it does in T cells, suggesting that the high level of SRF binding in T cells is functionally important.