ZEB2 and LMO2 Drive Immature T-Cell Lymphoblastic Leukemia Via Distinct Oncogenic Mechanisms

ZEB2, a E-box binding homeobox transcription factor, is able to induce epithelial-to-mesenchymal transition in the context of solid tumors. As such, its expression is correlated with cancer cell invasion, dissemination and metastasis, but also with the acquisition of cancer stem cell properties and therapy resistance.

Using conditional knockout mice, we previously have shown that ZEB2 is an essential hematopoietic transcription factors, indispensable for normal embryonic⁽¹⁾ and adult⁽²⁾ hematopoiesis. In addition, using conditional overexpressing mice we have demonstrated that ZEB2 is a bona fide driver of an immature subtype of T-ALL with increased leukemia-initiating potential⁽³⁾.

Here, we investigated the effects of ZEB2 overexpression on normal T-cell differentiation. Already from young age, ZEB2-overexpressing mice have a smaller thymus, with increased percentages of early T-cell precursors. Detailed flow cytometric analysis indicate a T-cell differentiation delay at the beta-selection checkpoint, with accumulation of DN3 (CD4^- CD8^- CD44^- CD25⁺) cells. Using in vitro differentiation assays on OP9-DL1 stromal cells, we demonstrate that the perturbed T-cell differentiation is independent of the thymic micro-environment. Lowering the dose of exogenous interleukin-7 levels in the culture media can partially rescue this phenotype, which suggests that ZEB2-overexpressing thymocytes are delayed in T-cell differentiation due to their inability to downregulate the interleukin-7 receptor (IL7R) levels.

Both the perturbed T-cell differentiation, and the latency/penetrance of immature subtype of the T-ALL formed in ZEB2-overexpressing mice is similar to what has been described for LMO2-overexpressing mice. Based on this phenocopy, we hypothesized that ZEB2 and LMO2 induce immature T-ALL via converging oncogenic pathway and/or via regulating similar crucial genes for the T-cell differentiation program. However, in contrast to LMO2, ZEB2-overexpresssing pre-leukemic thymocytes do not display aberrant self-renewal potential as demonstrated by transplantation experiments in sublethal irradiated syngeneic hosts. In addition, by using multiple Cre-transgenic lines, allowing the expression of ZEB2 at different stages of T-cell differentiation, we demonstrate that the oncogenic potential of ZEB2 is independent of the perturbed T-cell differentiation observed during the early stage of the disease.

Based on these results we conclude that ZEB2 and LMO2 both drive the development of an immature subtype of T-ALL, but via distinct oncogenic mechanisms.

(1) Goossens S. et al., Blood 2011 May 26; 117(21):5620-30.

(2) Li J. et al., Blood 2017 Jan 26; 129(4):460-472.

(3) Goossens S. et al., Nat Commun. 2015 Jan 7;6:5794.