INTERACTION BETWEEN NF-KAPPA-B AND SERUM RESPONSE FACTOR-BINDING ELEMENTS ACTIVATES AN INTERLEUKIN-2 RECEPTOR ALPHA-CHAIN ENHANCER SPECIFICALLY IN T-LYMPHOCYTES

We find that a short enhancer element containing the NF-kappaB binding site from the interleukin-2 receptor alpha-chain gene (IL-2Ralpha) is preferentially activated in T cells. The IL-2Ralpha enhancer binds NF-kappaB poorly and is only weakly activated by the NF-kappaB site alone. Serum response factor (SRF) binds to a site adjacent to the NF-kappaB site in the IL-2R enhancer, and both sites together have strong transcriptional activity specifically in T cells. Surprisingly, the levels of SPF 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.