Cyclin E-Cdk2 is a cell cycle regulator that promotes the G1-S transition by phosphorylating proteins involved in cell division and genome duplication. Cyclin E activity is frequently increased in many cancers, usually as a result of deregulation of mechanisms that control cyclin E protein levels and activity. Cyclin E T74A/T393A mice, in which cyclin E has been rendered resistant to degradation by the Fbw7 ubiquitin ligase by ablating two phosphorylation sites, exhibit enhanced epithelial proliferation and erythroid hyperplasia with inefficient erythropoiesis and macrocytic anemia. However, despite this widespread hyperproliferation, cyclin E T74A/T393A mice do not develop spontaneous tumors. To accelerate tumorigenesis and identify cooperating oncogenes in cyclin E T74A/T393A mice that complement the block in erythroid differentiation, we performed an insertional mutagenesis screen using the Sleeping Beauty (SB) transposon system.
Expression of SB by the inducible Mx-Cre caused rapid leukemiagenesis within 9–15 weeks post poly (I/C) injection in both control and cyclin E T74AT393A mice. The majority of tumors were T-cell lymphomas/leukemias and erythroid leukemias. Surprisingly, both wild type and cyclin E T74AT393A mice developed erythroid leukemias at similar frequencies. The erythroleukemia were composed of homogeneous populations of immature proerythroblasts akin to pure erythroleukemia in humans. Immunophenotypic profiling showed dim CD45 with variable CD117 (c-kit) and CD71 (transferrin receptor) expression. Preliminary sequencing of 29 erythroid leukemias identified 27 common insertion sites (CIS), including several genes associated with AML (Flt3, Erg and Ets1) as well as erythropoiesis (Fli-1 and Epo), highlighting the specificity of the SB-induced mutations for myeloid and erythroid leukemias. Preliminary analyses have also revealed preferential gCISs in erythroid leukemias isolated from cyclin E T74AT393A mice.
We conclude that the Mx-Cre SB mutagenesis system provides a unique and rapid murine model of pure erythroid leukemia. We have identified a set of genes that promote erythroleukemia in mice may represent potential therapeutic targets for human erythroid and myeloid leukemias.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.