The pT alpha promoter and enhancer are direct targets for transactivation by E box-binding proteins

The pre-T alpha (pT alpha) gene encodes a protein that forms the pre-TCR together with the newly expressed TCR beta chain during a defined stage of early T cell development. The restricted expression of this gene has been suggested to depend on a promoter and an enhancer element containing E boxes, which are potential binding sites for basic helix-loop-helix (bHLH) proteins. We here report that increased expression of E47 and E12 mRNA in CD4(-)CD8(-)TCR(-) thymocytes correlates with the initiation of pT alpha transcription. Furthermore, electrophoretic mobility shift assays suggested that E47 binds directly to both the pT alpha promoter and enhancer in vitro. Ectopic expression of E47 in non-lymphoid HeLa cells resulted in a dose- and template-dependent activation of these control elements. In addition to this, ectopic expression of E47 in combination with the ets-protein Pu.1 and/or the Pu.1-interacting protein(Pip-1), resulted in a synergistic effect on the activity of the pT alpha control elements. Thus, we suggest that E47, Pu.1 and Pip-1 are directly involved in the regulation of pT alpha expression in early T cell development.