Nuclear factor of activated T cells contributes to the function of the CD28 response region of the granulocyte macrophage-colony stimulating factor promoter

The granulocyte macrophage colony stimulating factor (GM-CSF) promoter contains a 10 bp element known as CK-1 or CD28RE that specifically responds to the co-stimulatory signal delivered to T cells via the CD28 surface receptor. This element is a variant NF kappa B site that does not function alone but requires an adjacent promoter region that includes a classical NF kappa B element, an Sp-l site and a putative activator protein-1 (AP-l)-like binding site. The entire region is referred to as the CD28 response region (CD28RR), The GM-CSF CK-1 element has been shown to bind NF kappa B proteins, in particular c-Rel, whose binding and function is dependent on the architectural transcription factor HMGI(Y). It has been previously suggested that the nuclear factor of activated T cells (NFAT) family of proteins also plays a role in the activity of this region. We show here that recombinant NFATp but not AP-1 can bind to the GM-CSF CD28RR. NFATp present in activated Jurkat T cell extracts can also interact with the CD28RR, The binding of NFATp and Rel proteins requires the same core CK-1 sequences, and appears to be mutually exclusive. We investigated the functional significance of NFATp binding to CK-1 by overexpressing the protein in Jurkat T cells and found that NFATp cannot activate the CD28RR alone but can cooperate with signals generated by phorbol 12-myristate 13-acetate/calcium ionophore, The CD28RR is therefore a complex region that can bind and respond to a combination of transcription factors and signals.