Critical Requirement of GABP α for Normal T Cell Development

GA binding protein (GABP) consists of GABP alpha and GABP beta subunits. GABP alpha is a member of Ets family transcription factors and binds DNA via its conserved Ets domain, whereas GABP beta does not bind DNA but possesses transactivation activity. In T cells, GABP has been demonstrated to regulate the gene expression of interleukin-7 receptor alpha chain (IL-7R alpha) and postulated to be critical in T cell development. To directly investigate its function in early thymocyte development, we used GABP alpha conditional knock-out mice where the exons encoding the Ets DNA-binding domain are flanked with LoxP sites. Ablation of GABP alpha 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) beta chain in DN4 thymocytes. By chromatin immunoprecipitation, we demonstrated in DN thymocytes that GABP alpha is associated with transcription initiation sites of genes encoding key molecules in TCR rearrangements. Among these GABP-associated genes, knockdown of GABP alpha 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 alpha can alleviate the DN3 block in GABP alpha-targeted mice. Our observations collectively indicate that in addition to regulating IL-7R alpha expression, GABP is critically required for TCR rearrangements and hence normal T cell development.