CXCR4 deregulated expression in Notch3-induced T cell leukemia

Background: Constitutive activation of Notch signaling is one of the major causes of acute T cell lymphoblastic-leukemia (T-ALL). The oncogenic function of Notch3 in T-ALL was demonstrated by a murine model in our laboratory, characterized by enforced expression of the Notch3 active form (N3-IC) in immature thymocytes (N3-ICtg). Deregulated proliferation and maturation at the preT/T transition phase and constitutive activation of preTCR were observed in N3-ICtg mice. Cooperative signaling among the preTCR, CXC chemokine receptor (CXCR) 4 and Notch are required for double-negative (DN) to double-positive (DP) T cell differentiation (β- selection). CXCR4 and its ligand (SDF-1) promote DN thymocytes survival, regulate the migration during the DN/DP transition and have been recently suggested to play a role in the pathogenesis of T-ALL. Methods: Freshly isolated thymocytes were analysed by FACS and RTPCR was performed in sorted DN T cells. Results: FACS experiments demonstrated a decrease of CXCR4+ cells in DN-gated thymocytes of N3-ICtg mice with respect to wt, not attributable to any reduction of DN cell numbers in N3-ICtg mice.Furthermore, reduced CXCR4 gene transcription was observed in selected DN thymocytes of N3-ICtg with respect to wt mice. Notch3 may disrupt early events in preT-cell progressive maturation accompanied by altered migration through the thymus, as further supported by reduced EpCAM expression, a homotypic adhesion molecule. In contrast, CXCR4 expression per cell was increased in DP-gated cells of N3-ICtg. Conclusions: We hypothesize that Notch3 may deregulate positioning and degrees of immature thymocytes in early steps of T-ALL development.