REGULATION OF THE T-CELL RECEPTOR-DELTA ENHANCER BY FUNCTIONAL COOPERATION BETWEEN C-MYB AND CORE-BINDING FACTORS

A T-cell-specific transcriptional enhancer lies within the J(delta)3-C(delta) intron of the human T-cell receptor (TCR) delta gene. The 30-bp minimal enhancer element denoted deltaE3 carries a core sequence (TGTGGTTT) that binds a T-cell-specific factor, and that is necessary but not sufficient for transcriptional activation. Here we demonstrate that the transcription factor c-Myb regulates TCR delta enhancer activity through a binding site in deltaE3 that is adjacent to the core site. Both v-Myb and c-Myb bind specifically to deltaE3. The Myb site is necessary for enhancer activity, because a mutation that eliminates Myb binding abolishes transcriptional activation by the deltaE3 element and by the 370-bp TCR delta enhancer. Transfection of cells with a c-Myb expression construct upregulates deltaE3 enhancer activity, whereas treatment of cells with an antisense c-myb oligonucleotide inhibits deltaE3 enhancer activity. Since intact Myb and core sites are both required for deltaE3 function, our data argue that c-Myb and core binding factors must cooperate to mediate transcriptional activation through deltaE3. Efficient cooperation depends on the relative positioning of the Myb and core sites, since only one of two overlapping Myb sites within deltaE3 is functional and alterations of the distance between this site and the core site disrupt enhancer activity. Cooperative regulation by c-Myb and core-binding factors is likely to play an important role in the control of gene expression during T-cell development.