Abstract
GA binding protein (GABP) consists of GABPalpha and GABPbeta subunits. GABPalpha is a member of Ets family transcription factors and binds DNA via its conserved Ets domain, whereas GABPbeta 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-7Ralpha) and postulated to be critical in T cell development. To directly investigate its function in early thymocyte development, we used GABPalpha conditional knock-out mice where the exons encoding the Ets DNA-binding domain are flanked with LoxP sites. Ablation of GABPalpha 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 GABPalpha is associated with transcription initiation sites of genes encoding key molecules in TCR rearrangements. Among these GABP-associated genes, knockdown of GABPalpha 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-7Ralpha can alleviate the DN3 block in GABPalpha-targeted mice. Our observations collectively indicate that in addition to regulating IL-7Ralpha expression, GABP is critically required for TCR rearrangements and hence normal T cell development.
Highlights
T cells are derived from multipotent lymphoid progenitors in the bone marrow and differentiate into mature T cells as a result of a series of lineage commitment steps occurring in the thymus and periphery [1, 2]
Because IL-7-derived signals are critical for T cell receptor (TCR)␥ but not TCR rearrangements [34, 35], our findings suggest that GA binding protein (GABP) regulates at least two independent pathways, IL-7R␣ and TCR, during the early thymocyte developmental stages
We found that ablation of GABP␣ in developing T cells by Lck-Cre transgene resulted in severe reduction of thymic cellularity, a substantial block at the double negative 3 (DN3) stage, and diminished intracellular expression of TCR in DN4 thymocytes
Summary
T cells are derived from multipotent lymphoid progenitors in the bone marrow and differentiate into mature T cells as a result of a series of lineage commitment steps occurring in the thymus and periphery [1, 2]. The direct binding of GABP␣ was confirmed in the TISs of Atm Prkdc, Xrcc5, Dclre1c, and Lig4 genes (Fig. 3C), supporting a potential role for GABP in regulating key factors involved in the rearrangements of TCR loci.
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