FUNCTIONAL GATA-3 BINDING-SITES WITHIN MURINE CD8-ALPHA UPSTREAM REGULATORY SEQUENCES

Genes encoding the accessory molecules CD8 and CD4 are activated early in thymocyte development, generating CD4+8+ double positive intermedi ates, which give rise to two functionally distinct mature T cell subse ts that express either CD4 or CD8. The mechanisms that govern the acti vation 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 m urine CD8alpha gene. We have identified three CD8+ cell-specific DNase I hypersensitive sites (HSS) located upstream of the murine CD8alpha gene. In vitro mobility shift analysis of the -4.0-kb HSS region has r evealed multiple binding sites for the T cell-restricted transcription factor GATA-3. In vitro translated murine GATA-3 binds specifically t o both CD8 GATA sites, and coexpression of this factor in transient tr ansfection 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 .