Identification and Characterization of Control Elements within the Murine CD4 Gene

The control of CD4 gene expression is essential for T lymphocyte development. Since the molecular mechanism for the control of CD4 gene expression during T cell development had not been elucidated, a study of the factors that control CD4 gene expression may lead to further. Toward these goals, we have made a series of recombinant DNA constructs to define the cis-acting transcriptional control elements in the murine CD4 locus that control CD4 gene expression during T cell development. In this study, we have identified multiple cis-acting control elements, which are critical for regulating the expression of the murine CD4 gene. Two intronic enhancers, which are located in a 122 bp Alul-Alul fragment 5\u27 of the first intron and a 174 bp Pstl-SalI fragment 3\u27 of the first intron, act in an orientation- and position-independent manner in both CD4+ and CD4- T cells. DNase I footprint analyses revealed the location of potential transcription factor-binding sequences in the protected regions include GATA-1, Elf-1, and AP-1 for the 5\u27 intronic enhancer, and PU.1, IRF-1, and GATA-1 for the 3\u27 intronic enhancer. Among them, Elf-1 and PU.1, members of the Ets protein family, and AP-1 have been implicated in the regulation of T cell-specific gene expression. An intronic promoter is located in the 138 bp fragment within the first intron. This promoter is activated preferentially in the CD4+CD8- T cells. Primer extension analysis indicates that the transcription initiation is located 107 bp upstream from the ATG site. A silencer element is loctaed in a 250 bp fragment corresponding to DH8, has a negative effect on the CD4 promoter activation in an orientation- and position-independent way in T cells. In summary, the molecular mechanisms, which control CD4 gene expression during T cell development, are complex and the result of coordinate interplay of multiple transcriptional control elements