IN-VIVO REGULATION OF INTERLEUKIN-2 RECEPTOR-ALPHA GENE-TRANSCRIPTIONBY THE COORDINATED BINDING OF CONSTITUTIVE AND INDUCIBLE FACTORS IN HUMAN PRIMARY T-CELLS

IL-2R alpha transcription is developmentally restricted to T cells and physiologically dependent on specific stimuli such as antigen recogni tion. To analyse the mechanisms used to activate IL-2R alpha transcrip tion as well as those used to block it in non-expressing cells, we det ermined the protein-DNA interactions at the IL-2R alpha locus in three different cell types using the DMS/LMPCR genomic footprinting method. CD25/IL-2R alpha can be efficiently induced in primary human T cells since similar to 100% express this gene when receiving an appropriate combination of mitogenic stimuli. To understand why IL-2R alpha is not expressed in other haematopoietic cell types, we analysed BJAB B lymp homa cells which do not express the IL-2R alpha gene and contain const itutively active nuclear NF-kappa B. Primary fibroblasts from embryo a nd adult skin were selected to examine the mechanisms that may be used to keep the IL-2R alpha gene inactive in non-haematopoietic cells. Th e three main results are: (i) the stable in vivo occupancy of IL-2R al pha kappa B element in resting T cells, most probably by constitutive NF kappa B p50 homodimer that could impair SRF binding to the flanking SRE/CArG box; (ii) its inducible occupancy by NF-kappa B p50-p65 asso ciated with the binding of an SRE/CArG box DNA-binding factor upon mit ogenic stimulation; and (iii) a correlation between the precommitment of T cells to activation and the presence of stable preassembled prote in-DNA complexes in contrast with the bare IL-2R alpha locus in non-T cells.