Abstract
The acquired activation of stem cell leukemia (SCL) during T-lymphopoiesis is a common event in T-cell acute lymphoblastic leukemia. Here, we generated a novel tamoxifen-inducible transgenic mouse model (lck-ERT2-SCL) to study the cellular targets of acquired SCL activation during T-cell development. Upon tamoxifen treatment we observed the thymic emergence of abnormal, non-cycling CD8+TCRβlow and immature CD4+CD8+ (double-positive, DP) cells displaying increased viability. Unexpectedly, fetal thymic organ culture analysis of lck-ERT2-SCL thymi revealed the development of DP cells before the emergence of CD8+TCRβlow cells, which implied the derivation of CD8+TCRβlow cells from DPs rather than immature CD8 single-positive (SP) thymocytes. Interestingly, histone deacetylase (HDAC) inhibition with trichostatin A (TSA) had a divergent effect on SCL perturbed thymopoiesis: TSA increased T-cell receptor surface expression within DP and CD8 SP cells however did not alter the CD8 shifted CD4/CD8-ratio. Furthermore, we studied the expression of NOTCH1 in SCL induced TCRβlow thymocytes. Strikingly, we found that SCL induced NOTCH1-upregulation in DP TCRβlow cells. We therefore conclude that SCL promotes the emergence of abnormal CD8+TCRβlow cells by an only partially HDAC dependent mechanism from DP TCRβlow cells. Moreover, SCL induced DP TCRβlow cells are characterized by upregulated NOTCH1, which in turn might promote the effect of acquired NOTCH1 mutations during T-leukemogenesis.
Tissue-specific expression of B-cell translocation gene 2 (BTG2) and its function in T-cell immune responses in a transgenic mouse model