Identification of a novel, developmental-stage-specific enhancer in the Cd4 gene (P4442)

Abstract

Abstract CD4 helper T cells coordinate the immune response and are highly dependent on the expression of the Cd4 gene for proper development and function. The function of a promoter, proximal enhancer, and a silencer have been well documented and together explain how the Cd4 gene gets turned on in CD4 T cells and off in CD8 T cells. However once turned on, the amount and timing of Cd4 expression varies during T cell development and activation. This modulation of CD4 surface levels is essential for proper lineage specification and T cell function. Yet, how subtle changes of CD4 expression are regulated remains unclear. We have recently identified a novel positive cis-acting transcriptional regulatory element (NCE) in the Cd4 locus. Here we demonstrate that NCE enhances Cd4 promoter function in position and orientation independent manner using a transient transfection assay with an eGFP reporter construct in RLM11 murine thymoma cell line. Using cell lines at different developmental stages, we determined that NCE functions well at the intermediate, but not the DP stage of development. This formally demonstrates that NCE functions as an enhancer and may have developmental specificity. We are in the process of confirming these findings in vivo by generating BAC transgenic mice that lack the NCE in the Cd4 locus.