Critical Requirement of GABP for Normal T Cell Development

GA binding protein (GABP) consists of GABP and GABP subunits. GABP is amember of Ets family transcription factors and binds DNA via its conserved Ets domain, whereas GABP does not bind DNA but possesses transactivation activity. In T cells, GABP has been demonstrated to regulate the gene expression of interleukin-7 receptor chain (IL-7R ) and postulated to be critical in T cell development. To directly investigate its function in early thymocyte development, we used GABP conditional knock-out mice where the exons encoding the Ets DNA-binding domain are flanked with LoxP sites. Ablation of GABP with the Lck-Cre transgene greatly diminished thymic cellularity, blocked thymocyte development at the double negative 3 (DN3) stage, and resulted in reduced expression of T cell receptor (TCR) chain in DN4 thymocytes. By chromatin immunoprecipitation, we demonstrated in DN thymocytes that GABP is associated with transcription initiation sites of genes encoding key molecules in TCR rearrangements. Among these GABP-associated genes, knockdown of GABP expression by RNA interference diminished expression of DNA ligase IV, Artemis, and Ku80 components in DNA-dependent protein kinase complex. Interestingly, forced expression of prearranged TCR but not IL-7R can alleviate the DN3 block in GABP targeted mice. Our observations collectively indicate that in addition to regulating IL-7R expression, GABP is critically required for TCR rearrangements and hence normal T cell development.