Functional GATA-3 binding sites within murine CD8α upstream regulatory sequences

Genes encoding the accessory molecules CD8 and CD4 are activated early in thymocyte development, generating CD4⁺8⁺ double positive intermediates, which give rise to two functionally distinct mature T cell subsets that express either CD4 or CD8. The mechanisms that govern the activation or suppression of the CD8 gene are likely to be central to the T cell development program. To identify the key regulatory factors, we have initiated an analysis of the transcriptional regulation of the murine CD8α gene. We have identified three CD8⁺ cell-specific DNase I hypersensitive sites (HSS) located upstream of the murine CD8α gene. In vitro mobility shift analysis of the -4.0-kb HSS region has revealed multiple binding sites for the T cell-restricted transcription factor GATA-3. In vitro translated murine GATA-3 binds specifically to both CD8 GATA sites, and coexpression of this factor in transient transfection assays transactivates a reporter construct containing these sequences. These results provide the first evidence for the role of a T cell-restricted factor in the regulation of either CD8 or CD4 genes.